WO2005056275A1

WO2005056275A1 - System and method for the manufacture of a film comprising a retro reflective pattern

Info

Publication number: WO2005056275A1
Application number: PCT/DK2004/000864
Authority: WO
Inventors: Henrik Givskov Larson; Henning Schou
Original assignee: Multi Sign A/S
Priority date: 2003-12-15
Filing date: 2004-12-15
Publication date: 2005-06-23

Abstract

The present invention concerns a system and a method for the manufacture of a film comprising a retro reflective pattern (2). Features of the system according to the invention involve, that the system comprises: dispensing means (4) for dispensing a fluent material, said material being curable to form a transparent polymeric material, curing means (6) for at least partly curing said fluent material, molding means (7) comprising a molding surface (8) provided with a molding pattern, which is the reverse of a retro reflective pattern to be made, wherein said molding surface (8) is adapted for moving along at least one predetermined path passing the dispensing means (4) and the curing means (6), where the dispensing means (4) are adapted to apply an even layer (5) of fluent material on said molding surface (8), and where the curing means (6) are adapted to at least partly cure said layer of fluent material (5) to form a film (10) having said pattern (2) on one surface from said fluent material present on said molding surface (8). The curing means (6) comprises a rotatable transparent roll (13) applying force on said fluent material when said molding surface (8) comprising said fluent material passes said rotatable transparent roll (13), and where radiation means (14) are provided inside said transparent roll (13), said radiation means (14) being adapted for curing said material when said molding surface (8) comprising said fluent material passes said rotatable transparent roll (13).

Description

System and method for the manufacture of a film comprising a retro reflective pattern

FIELD OF THE INVENTION 5 The present invention concerns a system and a method for the manufacture of a film comprising a retro reflective pattern. The invention further relates to a film manufactured by the aforementioned method.

l o BACKGROUND OF THE INVENTION

Rowland, US 3,684,348, which is hereby incorporated for reference, discloses a method for making a retro reflective composite material, where a hardenable molding material is deposited on a mold surface having an array

15 of minute, contiguous cube corner recesses therein. A preformed body member of transparent resin is applied onto and pressed against the molding material while deposited on the mold surface. After solidification of the molding material and bonding of the body member to the molding material, the thus formed composite material is then removed from the molding surface.

20 The composite material is described as having retro reflective properties, when the surface having faced the mold surface is facing a source of light. US 3,684,348 further describes that a metallic layer may be deposited on the surface having faced the mold surface, whereby the composite material may have retro reflective properties when the body member is facing a source of

25 light. The metallic layer may be provided with an adhesive in order to bond the composite material onto a substrate. According to US 3,684,348 it is necessary to apply the body member onto the molding material in order to control the cube corner formation. It is described that efforts to mold the cube corner formations and the body portion simultaneously have proven not

30 to be satisfactory, however being silent about how and by what means the efforts were performed. The necessity of applying both a molding material and a preformed body member, however, involves a number of issues in case a retro reflective material is to be made in an automatic process. The body member must be handled, which is an extra task. And it must be applied while at least slightly stretched in order that folds are avoided. Also, it must be avoided that air is trapped between the body member and the molding material. Often it is desired to print or by other method form an image on the retro reflective material. This is very difficult, if not impossible, to do on the surface with the cube corners. In stead a flat surface must be provided. Such a surface is available on the body member. However, if the composite material disclosed in US 3,684,348 is provided with an image on the body member, which should represent the exposed and retro reflective side, such an arrangement would have very poor retro reflective properties due to the boundary, which is present between the body member and the molding material. Any boundary will disturb the retro reflection. In US 3,684,348 it is therefore suggested to provide the metallic layer on the cube corner formation to improve reflection when bonding that side to a substrate, cf. US 3,684,348 Fig. 3. Such an additional step of providing a metallic layer as well as the body member is of coarse adding cost as well as increasing the complexity of the manufacture.

Other efforts have been made in order to manufacture well functioning retro reflective devices. One example is Priscone et al., US 4,601 ,861 , which is hereby incorporated for reference. In US 4,601 ,861 a sheeting of thermoplastic material provided with a carrier film, said carrier film having a glass transition temperature, which is higher than that of the sheeting, is heated to a temperature above the glass transition temperature of the sheeting but be- low the glass transition temperature of the carrier film, and in that state brought in contact with an embossing tool to form a pattern of cube corner reflective elements on one surface of the sheeting, where after the sheeting and the film are cooled. Also, in this technique additional support means must be employed, which here is the carrier film, and in US 3,684,348 the body member. In case it should be desired to print an image on the non- embossed side of the sheeting, the carrier film must be removed first, and the flat surface then exposed be cleaned or the like in order to have a sufficiently smooth surface. OBJECT AND SUMMARY OF THE INVENTION

One object is to provide a system and a method for manufacturing retro re- flective film without using cost-increasing support means, such as a body member or a carrier film, as described above. Another object is to provide a system and a method for manufacturing retro reflective film, which comprise at least one printable surface.

Further objects appear from the description elsewhere.

Features of the system according to the invention involve that the system comprises: - dispensing means for dispensing a fluent material, said material being curable to form a transparent polymeric material,

- curing means for at least partly curing said fluent material, - molding means comprising a molding surface provided with a molding pattern, which is the reverse of a retro reflective pattern to be made,

wherein said molding surface is adapted for moving along at least one predetermined path passing the dispensing means and the curing means, where the dispensing means are adapted to apply an even layer of fluent material on said molding surface, and where the curing means are adapted to at least partly cure said layer of fluent material to form a film having said pattern on one surface from said fluent material present on said molding surface. The curing means comprises a rotatable transparent roll applying force on said fluent material when said molding surface comprising said fluent material passes said rotatable transparent roll, and where radiation means are provided inside said transparent roll, said radiation means being adapted for curing said material when said molding surface comprising said fluent material passes said rotatable transparent roll.

The radiation means could be chosen from a group comprising an ultraviolet light source, an infrared light source and a radiant heating source dependent on the fluent material used. The transparent roll such as e.g. a glass roll may be used to equalize the layer of fluent material on the surface opposite the side engaging the molding surface, which is the surface which is desired to be printable. By the use of a glass roll light and heat may be transmitted through the roll. By using a roll it is also obtained that a fluent material with high viscosity may be used, since the roll may apply force on the material, which may assist the distribution and equalization of the layer. Further it is a feature making a body member or carrier film redundant.

In an embodiment said system further comprises application means adapted for transferring a film formed of said fluent material from the molding surface as well as for applying the film on a substrate and where said film may be transferred from the molding surface and applied on said substrate, with the surface having the pattern oriented towards said substrate, with the applica- tion means. A film is hereby formed having a retro reflective pattern, where the film is molded and at least partly cured before being applied to a substrate. A device comprising the film and the substrate is hence manufactured without using cost-increasing support means, such as a body member or a carrier film, as known from the related art. Since the material is fluent when applied to the molding surface, only limited or no pressure at all is necessary to ensure that the material is making complete and perfect reverse replica of the molding surface. This fact is one important aspect, which makes a body member or carrier film redundant. Another aspect is that the material is at least partly cured while present on the molding surface, which is a fact also making additional support means redundant. As the surface of the formed film is oriented towards the substrate, the opposite surface, which is oriented away from the substrate, will provide a substantially even and smooth surface, which provides a printable surface. The retro reflective pattern may be oriented towards the substrate and having air enclosed in the pattern, whereby the retro reflective effect is enhanced.

A preferred embodiment of the system involves that the dispensing means may comprise one or more rotatable rolls, where at least one roll is partly submerged in the fluent material. The roll being at least partly submerged will provide a suitable thin layer of the fluent material, which may be spread and evened out to a specific thickness by being passed on between more rolls before the fluent material is applied in an even layer on the molding surface of the molding means.

Another preferred embodiment involves that the molding means may comprise a rotatable roll with a reverse retro reflective pattern provided by an outside and substantially cylindrical surface. The cylindrical surface may be manufactured with high precision at a relatively low cost. The cylindrical shape also enables simple adjustment of neighbouring equipment. Instead of a roll, an endless belt could also be used.

The system may in a further embodiment comprise means for providing a printed image on a surface of a formed film, said surface being oriented away from the substrate. The system may hereby both manufacture a device and furnish it with a printed image.

In a still further embodiment the system may comprise curing means adapted for curing at least a formed film in a position where said film is applied to the substrate. This feature may be used for adhering the film to the substrate.

Features of the method according to the invention involve that the method for the manufacture of a film with a retro reflective pattern comprises the steps of: - dispensing a layer of fluent material on a moulding surface of moulding means, said material being curable to form a transparent polymeric material, - at least partly curing said fluent material using curing means based on radiation to form a film having said pattern on one surface from said fluent material present on said molding surface.

The step of at least partly curing said fluent material using curing means also comprises applying force on said fluent material while at least partly curing said fluent material.

By this method a film for a retro reflective device may be obtained without using cost-increasing support means, such as a body member or a carrier film, as known from the related art.

The method may further comprise the step of transferring the formed film from the molding surface and applying it on a substrate, with the surface having the retro reflective pattern oriented towards said substrate.

Effects and advantages of the method are equivalent to the aforementioned regarding the system according to the invention.

The method may preferably comprise a step of additional curing of the formed film after it is applied on a surface of a substrate. In this way the film and the substrate may be fused or bonded together.

Another feature of the method may advantageously involve that the substrate is a metal plate.

A further feature of the method may advantageously involve that the substrate is chosen from a group comprising a road sign, a license plate and an outdoor sign. Such products may desirable have a retro reflective surface in order to enhance visibility of e.g. information displayed them.

The method may alternatively comprise the step that an adhesive layer is provided on the substrate, on which layer the film is applied. The film may hereby be applied in a completely cured state.

The method may further comprise that at least part of the substrate is treated in a process providing said part with a substantially white colour, before the film is applied at least on said part. Improved reflection from the device may hereby be obtained.

The method may advantageously comprise that the fluent material is chosen from a group comprising fluent materials curable with ultraviolet light, fluent materials curable with infrared light and fluent materials curable with heat. Such materials are well suited for providing very thin layers, which by use of the method according to the invention may still be furnished with a retro reflective surface.

The method may also advantageously comprise that the retro reflective pattern is adapted to provide a retro reflective effect in a plurality of angles of incidence. This is suited e.g. for road signs, which must be visible from a wide range of angles.

The method may preferably comprise that the printed image is provided by transferring process involving electrical charging of the image and/or the substrate. This may include the use of laser printing technique, where different images may be made without down time for resetting the system. The images may as well be controlled from an electronic device, such as a com- puter where the images are created or stored. After printing, a weatherproof layer may be added over the printed image. The invention further relates to a film with a retro reflective pattern manufactured by a method as described above. The film may e.g. be used on a road sign, a license plate or an outdoor sign.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention is described with reference to the drawings, which display examples of embodiments of the invention.

Fig. 1 shows a schematic view from one side of a system according to the invention,

Fig. 2 shows a section of a device according to the invention,

Fig. 3 shows a section of film with a retro reflective pattern, and

Fig. 4 shows a schematic view from one side of a system including means for providing a printed image on a device according to the invention

DESCRIPTION OF PREFERRED EMBODIMENTS

Fig. 1 displays a system for the manufacture of a device 1 comprising a substrate 3 and a surface comprising a retro reflective pattern 2. The system comprises dispensing means 4 for dispensing a fluent material, curing means 6 for at least partly curing said fluent material, molding means 7 comprising a molding surface 8 provided with a molding pattern, which is the reverse of a retro reflective pattern 2 to be made, said molding surface 8 being adapted for moving along at least one predetermined path passing the dis- pensing means 4 and the curing means 6. The system further comprises application means 9 adapted for transferring a film 10 formed of said fluent material from the molding surface 8 as well as for applying the film 10 on a substrate 3. The dispensing means 4 are adapted to apply an even layer 5 of fluent material on the molding surface 8. The curing means 6 are adapted to at least partly cure said layer 5 of fluent material to form a film 10 having a retro reflective pattern 2 on one surface. The formed film 10 may be transferred from the molding surface 8 and applied on a substrate 3, with the sur- face having the pattern 2 oriented towards said substrate 3, whereby a flat surface of the film 10 may face away from the substrate, and thus be exposed e.g. for application of a printed image. The dispensing means 4 may include a number of rolls 1 , where one roll is submerged in fluent material in a container 32. The curing means 6 may include a glass roll 13, a radiation source 14 and a focusing prism 31.

Fig. 2 displays a device 1 including a substrate 3 and a retro reflective pattern or surface 2 provided in a film 10 with a printable surface provided with an image 17. The image 17 may include several colours, which are e.g. printed individually. The pattern or surface 2 is oriented towards the substrate 3. Between the film 10 and the substrate are air-filled gaps 33. The gaps 33 may alternatively be filled with other substances.

Features of the device according to the invention involve, that the device comprises a substrate and a retro reflective layer, wherein the device comprises at least a film having an embedded retro reflective pattern oriented towards the substrate, said film being formed from a cured fluent material, said fluent material being chosen from a group comprising fluent materials curable with ultraviolet light, fluent materials curable with infrared light and fluent materials curable with heat. By using any of the listed materials, it is enabled that the device is manufacturable without use of cost-increasing supporting means, such as body members or carrier film, as known form the related art, and also that the device comprise a printable surface, since the retro reflective pattern is oriented towards the substrate. Fig. 3 displays the film 10 of Fig. 2 without the substrate and the image. The film 10 includes spacers 34 defining a surface, which controls the distance between the pattern 2 and the substrate.

Fig. 4 displays illustrates a system as described above relating to Fig. 1. The system comprises dispensing means 4 for dispensing a fluent material, curing means 6 for at least partly curing said fluent material and molding means 7 comprising a molding pattern, which is the reverse of a retro reflective pattern 2 The system further comprises application means 9 adapted for trans- ferring a non-displayed film formed of said fluent material from the molding means 7 as well as for applying the film on a substrate 3. The system comprises a transport surface 28 for placing e.g. a metal plate to be furnished with a retro reflective surface and printed on.

The substrate 3 is firstly provided with a partly cured non-displayed film having a retro reflective pattern, and then cured when passing curing means 16 in the direction indicated by the arrow. The substrate 3 and the film, i.e. device 1 , are then transferred to means 15 for providing a printed image on the device. The means 15 comprises a laser 20, a controllable mirror 19 and a drum 21 with photoconductive material placed next to a charging device 22. The laser 20 emits infra red light to parts of the surface of a negatively electrically charged metal drum 21 , charged by the charging device 22, by controlling the mirror 19. Thereby the parts of the surface of the drum being illuminated by the light are discharged resulting in a pattern on the drum of charged areas, the pattern corresponding to the print, which is to be made on the film. Further, the means 15 comprises a powder roller 23, where negatively charged powder is brought from a powder compartment 24 toward the drum 21 via the powder roller 23. The powder sticks to the parts of the drum that are exposed to light, whereby it is no longer negatively charged. The powder binds to the areas of the drum that have been exposed by light, and the process results in a pattern of powder being the inverse of the pattern of charged areas. A positive electrical field is generated on the surface of the device, here being a metal plate, by a charger 25, and when the de- vice passes the drum 21 , the negatively charged powder on the drum 21 is electrostatically attracted to the positively charged surface of the device. Now the pattern of powder has been removed from the surface of the drum 21 and lies on the surface of the substrate, and as the next step, the surface of the substrate with the powder is heated by a heating system, e.g. a heater drum 26 (or another heating system, using e.g. convection, radiant or IR- heating) until the film and the powder melt, whereby the powder is fused to the surface of the film. Finally, the device is discharged by a discharger 27. This is to ensure that the device can be removed by an operator without the operator getting an electric shock. The means for discharging the device could in one embodiment be means for establishing an electrical contact between the device and electrical ground.

In one embodiment the powder could be a special UV resistant colour pow- der with good surface properties, alternatively it could be standard toner powder similar to the powder used in the toner cartridge of a paper laser printer. Further, the colour of the print to be made can be changed by changing the colour of the powder, and further multicoloured print can be made by adding different powder colours e.g. by using colour specific drums.

The system comprises a table 18 comprising elevation means 30 and transport means 29 for transporting the transport surface 18.

By an alternative method, a layer 5 of fluent material may be formed with dispensing means 4 on a smooth and substantially planar holding surface, e.g. a metal plate, whereafter a retro reflective pattern 2 is pressed into the layer 5 with forming means, such as a roll or plate, having a surface comprising a molding pattern, which is the reverse of a retro reflective pattern to be made, wherein forming means comprise curing means 6 for curing the layer 5 while influenced by the forming means to form a film 10. In this way the retro reflective pattern 2 is formed and fixated in the film 10. Said film 10 may followingly in an at least partly cured state be transferred from the holding surface and applied to a substrate 3 thereby forming a device 1. Preferably the retro reflective pattern 2 is oriented towards the substrate. Also, by such a method the use of a carrier film or a body member can be avoided.

The molding surface 8 may e.g. be made or provided with at least a layer of nickel or a nickel alloy. Before applying the fluent material, a release agent may be applied to enhance release of a formed film 10.

The layer 5 may have a thickness in a range between 100 to 150 μm and the depth of the retro reflective pattern 2 be between 50 to 100 μm. The film 10 may be formed at a speed preferably up to approx. one meter per second.

The fluent material may be e.g.:

A UV-light curable lacquer such as UV 9206 supplied by Akzo™, which is an acrylic type of lacquer. Also NOA 71 supplied by Norland Products™, which is a urethane type of lacquer may be used. Also OG 603 supplied by Epo- Tek™, which is an epoxy type of lacquer may be used. Of course a range of other types of curable fluent materials may be used.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word 'comprising' does not exclude the presence of other elements or steps than those listed in a claim. In claims enumerating several means, several of these means can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. A system for the manufacture of a film with a retro reflective pattern, said system comprising: dispensing means for dispensing a fluent material, said material being curable to form a transparent polymeric material, curing means for at least partly curing said fluent material,0 molding means comprising a molding surface provided with a molding pattern, which is the reverse of a retro reflective pattern to be made, wherein said molding surface is adapted for moving along at least one pre-5 determined path passing the dispensing means and the curing means, where the dispensing means are adapted to apply an even layer of fluent material on said molding surface, and where the curing means are adapted to at least partly cure said layer of fluent material to form a film having said pattern on one surface from said fluent material present on said molding sur- o face characterised in, that said curing means comprise a rotatable transparent roll applying force on5 said fluent material when said molding surface comprising said fluent material passes said rotatable transparent roll, and where radiation means are provided inside said transparent roll, said radiation means being adapted for curing said material when said molding surface comprising said fluent material passes said rotatable transparent roll.0

2. A system according to claim 1 wherein said system further comprises application means adapted for transferring a film formed of said fluent material from the molding surface as well as for applying the film on a substrate and where said film may be transferred from the molding surface and applied on said substrate, with the surface having the pattern oriented towards said substrate, with the application means.

3. A system according to claim 1-2, where the dispensing means comprise one or more rotatable rolls, where at least one roll is partly submerged in the fluent material.

4. A system according to claim 1-3, where the molding means comprise a rotatable roll with a reverse retro reflective pattern provided by an outside and substantially cylindrical surface.

5. A system according to one or more of claims 1-4, where the system comprises means for providing a printed image on a surface of a formed film, said surface being oriented away from the substrate.

6. A system according to one or more of claims 1-5, where the system comprises curing means adapted for curing at least a formed film in a position where said film is applied to the substrate.

7. A method for the manufacture of a film with a retro reflective pattern, said method comprises the steps of: - dispensing a layer of fluent material on a moulding surface of moulding means, said material being curable to form a transparent polymeric material,

- at least partly curing said fluent material using curing means based on radiation to form a film having said pattern on one surface from said fluent material present on said molding surface characterised in, that

said step of at least partly curing said fluent material using curing means also comprises applying force on said fluent material while at least partly curing said fluent material.

8. A method according to claim 7, wherein the method further comprises the step of transferring the formed film from the molding surface and applying it on a substrate, with the surface having the retro reflective pattern oriented towards said substrate.

9. A method according to claim 8, where the method comprises a step of additional curing of the formed film after it is applied on a surface of a sub- strate.

10. A method according to claim 8 or 9, where the substrate is a metal plate.

11. A method according to one or more of claims 8-10, where the substrate is chosen from a group comprising a road sign, a license plate and an outdoor sign.

12. A method according to one or more of claims 8-11 , where an adhesive layer is provided on the substrate, on which layer the film is applied.

13. A method according to one or more of claims 8-12, where at least part of the substrate is treated in a process providing said part with a substantially white colour, before the film is applied at least on said part.

14. A method according to one or more of claims 7-13, where the fluent material is chosen from a group comprising fluent materials curable with ultraviolet light, fluent materials curable with infrared light and fluent materials curable with heat.

15. A method according to one or more of claims 7-14, where the retro reflective pattern is adapted to provide a retro reflective effect in a plurality of angles of incidence.

16. A method according to one or more of claims 7-15, where a printed image is provided on the film.

17. A method according to claim 16, where the printed image is provided by a transferring process involving electrical charging of the image.

18. A film with a retro reflective pattern, said film being manufactured by a method according to any of claims 7-17.