Bartoli, Cesare (Via Pederzola 1/3, Scanzorosciate, I-24020, IT)
The present invention refers to a method for producing printed retroreflective high-visibility products. It is verified that retroreflective products used for safety garments can reduce the risk of accidents, especially for people who live in an outdoor society, fireman, paramedics, police and every adult and child that is biking, hiking, running, playing or walking. Safety vests displaying a retroreflective strip often are worn by road construction workers to improve visibility to oncoming motorists. The technical characteristics of high visibility retro-reflective jackets and sashes which must be worn by the drivers of vehicles which are stationary on the roadway refer to unifying standard UNI EN 471:1994 on high visibility warning clothing. Technical requirements should be indicated on the label of the safety vest. To avoid imitations and forgery and to protect the producer of the retroreflective trim, the solution which is described in this invention refers to a printed brand which is visible upon the product, under the glass beads layer, washing resistant and, above all, the printed design does not modify the retroreflective characteristics required by the EN 471.The photometric and colorimetric characteristics of the material of the present invention comply with the provisions of the same international standard EN 471. No colored printing remains upon the glass beads . The commercial products suitable for reflective garments have generally been single colored. For example in US-A-4.763.985, US-A-5.283.101, US-A-5.738.746 launderable retroreflective gray metal colored structures are disclosed. A retroreflective structure described in US-A-5.962.121 is capable of exhibiting a decorative effect both daytime and night time and particularly a rainbow colored effect. In US-A-4.605.461 a method is described for transferring a retroreflective pattern onto a fabric. Retroreflective images formed on garments and other substrates are described in US-A-4.102.562. US-A- 5.508.105 discloses a thermal printing system and a resin- based colorant/binder for printing frangible, retro¬ reflective polymeric sheeting material. US-A-5.620.613 discloses retroreflective multi-colored designs or emblems on garments comprising a monolayer of transparent microspheres, a color layer with colorant in a transparent resin screen printed over the glass beads. When the prints of the first color are all dried, they may be printed and dried with subsequent colors until all the desired colored portions of the image are complete for decorating textile surfaces with a transfer. US-A-5.679.198 discloses a printing step on a support sheet that has a layer of microspheres embedded therein, one or more colored layers that are prepared from a polyester resin and an isocyanate hardener, drying each color layer separately before the next layer is printed. The process for decorating textile surfaces with images comprising light-reflecting areas is described in US-A-5.785.790. In this case, the layer of glass microspheres are printed by one or more coatings of two-component colors based on polyester resin and isocyanate hardener. A silk screen-printing machine is used for printing the layers in an image wise inverted fashion on the support sheet of the glass beads. Many other patents (US-A-3.689.346, US-A-5.643.400, US-A-4.082.426, US-A-2.231.139, US-A-2.422.256, US-A- 4.656.072, US-A-4.952.023) describe processes for producing retroreflective materials having printed patterns or graphics formed thereon. US-A-6.120.636 discloses a higher speed, low cost process for producing printed patterns for graphic, decorative and other retroreflective sheeting using partially cured pattern printed on ,a roll of film produced with a rotary screen printing station and UV curing. Insofar as known, no-one has previously found a practical and useful way to produce a printed retroreflective product which can maintain the homogenous gray color if desired and, consequently, maintain a high retroreflective value as required by EN 471 standard, with a continuous light visible pattern on the retroreflective surface. The printed effect should avoid imitations and forgery, protect the producer of the retroreflective trim and give a guarantee to the customer. Of course, in this invention, we can obtain a multicolored effect as desired, independently of an homogenous gray color. In this invention, a temporary support sheet is covered with a monolayer of transparent glass microspheres having an average diameter in the range of about 30 to 200 microns and a refractive index of about 1.5 to 2.0. The beads are partially embedded in a layer of self-adhesive or softened polymer adhesive to a depth averaging between 20% and about 50% of their diameters and coated with a reflecting aluminum layer covering the surface of the glass microspheres as described in US-A-3.700.305 and US- A-6.416.188 and the surface between the microspheres. On a realized paper, a transparent polyurethane two-component resin is coated dried and laminated with the printed fabric. The polyurethane coating is dried detached from the silicon paper and the two faces of the polymer are laminated with the temporary support sheet and with the printed textile base. Regarding the printing method of the textile base, the above-described state of the art discloses the screen- printing technology (US-A-5.620.630, US-A-5.785.790 and other) . Besides, the screen printing technology is generally used on textile products. The same considerations may be done with rotary screen-printing (US-A-6.120.636) . A sublimating pigments printed method from a paper base to the synthetic textile base can be used: then the support sheet of the beads is pulled off. The aluminum layer between the spheres remains on the support sheet. The base printed textile with the transferred glass beads should be cured. The above and other objects and advantages of the invention, as will appear from the following description, are obtained by a method as claimed in Claim 1. Preferred embodiments and non-trivial variations of the present invention are claimed in the dependent Claims. The present invention will be better described by some preferred embodiments thereof, provided as a non- limiting example, with reference to the enclosed drawings, in which : - Fig. 1 shows a schematic carrier web 9, which secures microspheres thereon in a desired temporary arrangement; - Fig. 2 is a view of the partially removed film 9 from the carrier printed web, which secures microspheres covered with a vapor coating of a metal such as aluminum light reflecting material 2 but without reflective aluminum between the spheres 1 after removing the self- adhesive paper 4; - Fig. 3 is a schematic plan view showing an article in accordance with the present invention having a fabric 8 printed with the pattern "i b r" with a retroreflective layer thereto; - Fig. 4 is a microscopic plan view showing the portion of letter "i" in fig. 3 of the retroreflective fabric 8. The black color of the letter "i" is visible around the glass microspheres; and - Fig. 5 shows an article of clothing, displaying a retroreflective trim in accordance with the present invention. The above figures, which' are idealized, are not to scale and are intended to be merely illustrative and non- limiting of the present invention. In the invention as described and shown, a specific terminology is used for better clarity. However, the invention is not constrained to the specific terms being chosen and it is obvious that every chosen term comprises every technical equivalent that generates a similar behavior. Fig. 1 is a cross sectional view of the carrier web, which secures glass microspheres 1 on a temporary transport support carrier sheet 9. The carrier sheet used as a sheet material is produced as described in US-A- 4.102.562 and in Example 2 of US-A-4.075.049. The microspheres used in the present invention typically have an average diameter in the range of about 30 to 150 microns and a refractive index of about 1.7 to 2.0. Preferably glass microspheres 1 are arranged substantially in a monolayer on the temporary carrier sheet 9, which comprises a polymeric coating 3 and a stiff backing 4. The polymeric coating 3 is a softenable material such as polyethylene or modified polyvinyl acetate - polyethylene, polypropylene • and the like, or a self-adhesive polyacrylate polymer. The stiff backing 4 could be kraft paper, polyester film and the like. The microspheres may be arranged upon the temporary carrier sheet 9 by printing, cascading, transferring, and screening or any convenient transfer process. The microspheres 1 are embedded in the carrier sheet 9 with a pressure roll or by heating the softened polymer, preferably to a depth between about 20 to 40 percent of their average diameter. With reference again to Fig. 1, the glass beads 1 are covered with a single layer of aluminum 2 as described in US-A-5.650.213. A retroreflective printed transfer material 10 as shown in Fig. 2 illustrates a idealized, not to scale sectional view of portion of an article of printed fabric at the final stage of production or use in accordance with the present invention. In the drawing, the end product 10 is partially delaminated from the carrier web 9 comprising the polymeric self-adhesive or softenable polyethylene- poly-vinyl-acetate adhesive coating 3 and the kraft paper or polyester film. Incidentally, the aluminum deposited on the resin layer 11 between the glass beads 1 is removed by the polymeric adhesive 3 of the temporary carrier sheet 9 as indicated with arrow 6 . The base fabric 8 is printed with the design 5. With reference again to Fig. 2, finally, a binder layer of two- component polyurethane adhesive 11 provides an adequate adhesion of the glass beads 1 to the fabric 8, for example a polyester/cotton fabric, a polyester nonwoven base, a nylon knitted fabric as Lycra© and other textile bases. Fig. 3 is a schematic plan view illustrating a trim material 10 in accordance with the present invention having a fabric printed with the design "i b r" with a retroreflective layer thereon. The color choice depends on the type of required contrast. For example, if a trim looking as an uniform gray color like the aluminum color is needed, a dark-gray design is printed upon the fabric. The contrast between printing and aluminum color will be soft, sufficient for reading the "i b r " writing but without influence on the plain gray color of the trim. Fig. 4 is an extension of the microscopic plan view of a portion of letter " i " shown in fig. 3 of the retroreflective product. The dark-gray color 5 of the letter λλi" is visible around the glass microspheres 1. Generally, the surface between the microspheres 1 is more than 60% of the total surface of the trim. Therefore, the printed color which is deposited between the beads seems as a continuous line and consequently the writing is visible in a non-interrupted form. Fig. 5 shows a safety jacket 12 displaying a retroreflective article 10. Safety vests often are worn by road workers and drivers out of vehicles which are stationary on the roadway. Although the safety jacket 12 has been chosen for illustration purposes, the article of clothing of the invention may come in a variety of forms. "Article of clothing" means an item including shirts, sweaters, coats, pants, gloves, bags, shoes, etc. The invention will be further explained by the following illustrative examples, whose purpose is showing the features and advantages of this invention. However, the ingredients and specific amounts recited therein, as well as other conditions and details, are not intended to be limiting the scope of this invention. Unless otherwise indicated, all amounts expressed in the examples are in parts by weight. EXAMPLE 1 In Example 1, glass spheres 1 with a refractive index of 1.93 and a diameter from 45 up to 100 micrometers were cascaded on a kraft paper covered with a self-adhesive film producing a densely monolayer of glass beads embedded in the binder layer. Suitable bonding adhesives include, for example, urethanes, rubbers, silicones and acrylics. Alternative suitable bonding adhesives will be apparent to those skilled of the art, given the benefit of this disclosure. Aluminum is then vapor-coated over the exposed surface of the beads until a specularly visually continuous coating is formed. The exposed beads as well as the exposed surface of the 'adhesive coating are thus reflectorized. Thereafter, over a release silicon paper, a binder 11 was applied consisting of the following composition :
Ingredients Parts by Weight Transparent Polyurethane resin 100
Melamine curing agent 3
Isocyanate curing agent 5 ("Icaplink X3" from leap) Methyl Ethyl Ketone 40
formulation 1
This composition was applied at a coating weight sufficient to give a dry film of about 20 to 50 g/sqm, after which solvent was evaporated from the coating by forced air drying at 110 0C. Then, the transparent polyurethane film 11 was detached from the release paper and laminated on one face with printed letters λλi b r " on the base textile 8 and on the other face with the metallized beads supported by the temporary sheet 9. After or before curing the resin at about 150°C. the sheet 9 was stripped. EXAMPLE 2 A comparative example was prepared using the same base textile without the printed design shown in Fig. 3 and the same conditions and formulation indicated in Example 1. Each of these examples 1 and 2 was laundered and tested simultaneously. The initial reflectivity of the two examples was the same, about 450 cd/(lux m) , and the final reflectivity after 50 laundering cycles at 600C was about 250 cd(lux m) , a value higher than required by UNI EN 471:1994 standard. EXAMPLE 3 The retroreflective product of this example was made as set forth above, except for the difference in the temporary carrier web 9 which was a temperature sensitive adhesive 3 supported by a polyester sheet 4. The adhesive used was a blend of polyethylene containing generally more than 8% of poly-vinyl-acetate . EXAMPLE 4 The monolayer of glass microspheres was embedded in a carrier sheet as described in Example 3. Then aluminum was vapor-coated over the exposed surface of the beads as described in Example 1. A transparent polyurethane binder solution indicated in formulation 1 was directly knife- coated upon the metallized beads after which solvent was evaporated from the coating by forced air drying at 110 0C. The polyurethane film 11 was laminated with the printed base textile and cured. The sheet 9 was then stripped. EXAMPLE 5 The monolayer of glass microspheres was embedded in a carrier sheet as described in Example 3. Then the beads were knife-coated with about a 10% solution of a transparent acrylic self-adhesive containing 2% of isocyanate curing agent. The dry resin was deposited mainly between the microspheres. Aluminum was then vapor- coated over the exposed surface of the beads and over the thin acrylic layer until a specularly visually continuous coating was formed. The subsequent operations were described in Example 1. EXAMPLE 6 The retroreflective product of this example was made as described in Example 1, except for- the difference in the printed textile. A nonwoven polyester base was printed with sublimate pigments supported by a release paper, at a temperature close to 1800C, because a maximum yield of the transferring but also a partial transferring of the design at lower temperatures may give a satisfactory aesthetic design on the final product. With this sublimate printing it was in fact possible to print a design containing many shapes and colors while maintaining the precision of the combination of the colors. The subsequent operations were described in Example 1. In this example, a multicolored effect is obtained without an homogenous gray color look.