WO2006067573A1

WO2006067573A1 - A process for obtaining a back-reflecting multi-layer film, with a microprism support and a film obtained using the process

Info

Publication number: WO2006067573A1
Application number: PCT/IB2005/003741
Authority: WO
Inventors: Giorgio Corradi; Paolo Corradi
Original assignee: Giorgio Corradi; Paolo Corradi
Priority date: 2004-12-22
Filing date: 2005-12-05
Publication date: 2006-06-29

Abstract

The process comprises stages of: preparing a transparent layer (32) obtained by spreading on a support (32a) made of a mixture of an acrylic base and a polycarbonate, a layer of acrylic resin (32b), heating the layer (32) and embossing a microprism structure (20) on the layer of resin (32b), cooling the transparent layer in order to stabilise the resin layer (32b); laying a reflective layer (3) made of a silver-containing material on the microprisms; realisation of a protection surface for the reflective layer. The back-reflecting film comprises a transparent layer (32) which in turn comprises a support (32a.) realised with a mixture of an acrylic base with a polycarbonate and a layer of an acrylic resin (32b) on which the microprisms (20) are impressed, a reflective layer (3) made of a material containing silver which covers the structured surface and a protection surface for the reflective layer.

Description

A Process for obtaining a back-reflecting multi-layer Film, with a Microprism Support and a Film obtained using the Process.

Technical Field

Specifically, though not exclusively, the back-reflecting film obtained using the process of the invention can be usefully applied for manufacturing road signals (horizontal, vertical and lateral), road signs, signs in general and so on. Background Art

Various types of back-reflecting tapes with microprisms are known, for example in patents US 5376431, US 5657162, US 6083607 and US 6139158, which are used when a much greater luminosity is required with respect what is obtained with back-reflectors using glass microspheres. The prior art back-reflecting tapes with microprisms are realised starting from a support sheet, on which the microprisms are afforded, which is then usually protected by a second sheet which is superposed on the support sheet and anchored thereto. The support sheets at present used are constituted by an extruded film of heat- formable plastic material, for example a metacrylic resin such as polymethylmetacrylate, on which the microprisms are formed by moulding; the second protective sheet is anchored to the support sheet by heat-welding, for example in a beehive lattice or another design. If the back-reflecting film is subjected to considerable heat variations, such as for example can happen when the films are used for products destined to be used outside, the thermoplastic nature of the support sheet is subject to deformation, with a possible loss of reflecting power or with a possible detachment of the reflecting surface or the protection sheet. The present invention provides a process for realising a film having high back-reflecting powers which enable all the drawbacks of films of known type to be overcome.

An advantage of the invention is that it provides a back-reflecting film for road use which has characteristics of luminosity, colorimetry and reflectiveness which satisfy the requisites of the existing standards and which maintain these characteristics unaltered over time.

A further advantage is that the invention provides a film which can be manufactured at low cost and at high production levels. A further advantage is to provide a multi-layer film having high coupling stability between the various layers, which can be 100% coupled over their surface, forming a single compact multilayer sheet, with a practically zero risk of the layers' coming away from each other.

A further advantage is represented by the fact that the film is resistant over time and has a long working life, even when used for horizontal road signals. These aims and advantages and more besides are all attained by the invention as it is characterised in the claims that follow. Disclosure of Invention

Further characteristics and advantages of the present invention will better emerge from the detailed description of the stages of the process of the invention that follows, and a preferred but non-exclusive embodiment of the film of the invention, illustrated purely by way of example in the appended figures of the drawings, in which: Figure 1 is a broken section, performed along a vertical plane, of a film made according to the invention;

Figure 2 is a small-scale drawing of a preferred embodiment of the film of figure 1, applied on a surface. With reference to the figures of the drawings, 1 denotes in its entirety a multilayer back-reflecting film used in particular, but not exclusively, to realise road signals. The film comprises a transparent layer 32 having, on a lower side opposite to the light source to be reflected, represented by the arrows L, a structured surface which has an embossed distribution of microprisms 20 of a predefined height; the height of the microprisms 20 is preferably comprised between about 60 and 180 micrometres. The structured surface which bears these microprisms 20 is covered by a reflective layer 3 made of a material containing silver. The material of the reflective layer 3 is 99.9 % silver - it is preferable that this material is at least 90% weight silver. The thickness of the reflective layer 3 is preferably at least 0.1 μm; in the preferred embodiment now described the thickness is about 0.8-1.2 μm. The reflective layer 3 is however relatively very thin in comparison to the height of the microprisms 20. The transparent layer 32, which can also be transparent-coloured, comprises a support 32a, realised using a mixture of known type of an acrylic base with a polycarbonate, and a layer of acrylic resin 32b, preferably heat-hardening, on which the microprisms 20 are impressed.

The transparent layer 32, which has an overall thickness comprised between 120 and 340 μm, is obtained by spreading, on the support 32a which has a thickness comprised between 20 and 40 μm, a layer of acrylic resin 32b, preferably heat-hardening, with a thickness comprised between 100 and 300 μm; the operation is particularly easy as these resins, of known type, are in A-

fact a watery spreadable emulsion paste. The transparent layer thus obtained is heated to a temperature comprised between 140 and 17O⁰C; a cylindrical embossing process is then generally used to impress the microprism structure 20, with the transparent layer heated. The transparent layer is then cooled to stabilise the transparent layer 32.

These operations can be performed on continuous machines which enable a transparent layer to be obtained which can be used later to obtain a multilayer back-reflecting film with a microprism support. Before spreading the layer of acrylic resin 32b on the support 32a, a word-, figure or other printing stage on the support surface 32a on which the resin will be spread 32b can be included in order to customise the film or make it suitable for special uses. This printing stage, conveniently and economically performed using a continuous process prior to the subsequent continuous spreading process of the resin layer 32b, is immediately protected by the layer of resin. The print thus obtained in covered between the acrylic resin layer 32b and the support 32a which protect it and prevent any subsequent deterioration thereof; the quality of the print obtained in this way is especially good. A description now follows of a film of a preferred type, although the transparent layer 32 can be used to obtain different films from those described.

The film further comprises a first anchoring layer 4, interpositioned between the transparent layer 32 and the reflective layer 3, which is solidly anchored to the transparent layer 32 and the reflective layer 3. The presence of the anchoring layer 4 means that the transparent layer 32 and the reflective layer 3 are solidly anchored to one another. The anchoring layer 4 is constituted by a metal primer layer of a thickness such that the overall thickness of the anchoring layer 4 and the reflective layer 3 is less than the height of the microprisms 20. The metal primer, preferably polyurethane based, has the task of improving the grip and strength of the bond between the transparent layer 32 and the reflective layer 3, and of protecting the reflective layer 3 from oxidation. Alternatively the anchoring layer 4 can be obtained with a "crown" treatment, specific for surfaces to be metalised. The microprisms 20 covered by the anchoring layer 4 and the reflective layer 3 define a succession of crests and valleys which are filled and covered at least up to the level of the crests by a first protective layer 5 which, in a first embodiment of the film, is distributed directly in contact with the reflective layer 3. The material the first protective layer 5 is made of is, for example, an aromatic or aliphatic polyurethane resin. Preferably however the protective layers superposed on the reflective layer, in particular the first protective layer 5, are realised in materials not containing solvent which might damage the microprisms. For example, polyoils or resins of the solventless type can be used, or with 100% dry residue.

The use of polyoils for the first protective layer 5 has an important advantage from the point of view of the film. As will be better described herein below, the film of the present invention can be produced in a continuous line in the form of a continuous strip unwound from a reel, which strip then passes through the various work stations. The first protective layer 5 can be laid on the continuous strip (on the microprisms 20 covered by the anchoring layer 4 and the reflective layer 3) at a production speed of 25-30 m/minute. Following the laying of the first protective layer 5 the film, in the form of a continuous strip, is coupled in-line with a polyethylene film of a thickness comprised between about 50 and 100 μm, and is therefore wound on itself in a reel, waiting for the next operations. The first protective layer is blocked and held in position by the polyethylene film and the trapping effect of the roll the strip is wound up into. The polyethylene film does not adhere to the first protective layer 5 and can easily be removed from the film for the following operations. The first protective layer 5 fills up the valleys of the structured surface with the aim of protecting the microprisms 20, and especially in order to prevent the risk of modifications in the conformation of the microprisms during any subsequent operations and during use. Once polymerised the first protective layer 5 exhibits very high resistance and stability. The first protective layer 5 also has the function of protecting the silver reflective layer 3 from oxidation. A second anchoring layer 7, obtained with a crown treatment or by spreading a primer similar to the one described above for the anchoring layer 4, can advantageously be interpositioned between the reflective layer 3 and the first protective layer 5. As with the first anchoring layer 4, the second anchoring layer 7 has the function of protecting the reflective layer 3 from oxidation and of increasing the solidity of the bond of the first protective layer 5. On the opposite side to the reflective layer 3, the first protective layer 5 can be coupled to a metal sheet 9, preferably made of soft aluminium having a thickness of about 100-200 μm and having a function of further increasing the resistance of the film, so that it can be fastened using screws, rivets and the like.

A layer of adhesive or self-adhesive material 8 can be applied on the first protective layer 5 (or on the metal sheet 9 if present), on the opposite side of the reflective layer 3, useful for the positioning of the film when being laid. Once obtained, with the above-described process, the transparent layer 32 comprising the support 32a and the layer 32b on which the microprisms 20 are impressed can be used for obtaining the back-reflecting film of the invention, using a continuous working process that, starting from a transparent layer 32 in the shape of a continuous strip unwound from a reel, passes through the various work stages.

A first anchoring layer 4 is laid on a side of the continuous strip of transparent layer 32, which first anchoring layer 4 is preferably constituted by a metal primer; alternatively for the first anchoring layer 4 a surface treatment of the layer 32 can be applied, for example a "crown" treatment which is a specific treatment for surfaces to be metalised. Preferably with a known high-vacuum metallization process but other processes can also be used, a layer of silver reflective material 3 is applied on the anchoring layer 4. A first protective layer 5 (for example an aromatic polyurethane or aliphatic resin with 100% dry residue without solvents, which polymerises at atmospheric temperature) is spread on the reflective layer 3 to smooth the bottom side of the film, filling the valleys of the microprisms 20 in relief on the resin layer 32b, so as to obtain total protection of the microprisms; before the final stage described above, a second thin anchoring layer 7 can be applied on the reflective layer 3, for protection and as an antioxidant; the second anchoring layer 7 is preferably constituted by a metal primer, for example a bicomponent polyurethane, which is interpositioned between the reflective layer 3 and the first protective layer 5; the first protective layer 5 can however be constituted by a metal primer and be directly applied on the reflective layer 3 with no interposition of other layers.

At this point, if so desired, the metal sheet 9 can be coupled to the first protective layer 5, and the layer of adhesive or self-adhesive material can be applied.

The above-described film 1, when destined to be used for horizontal road markers, can advantageously be shaped, in a known way, in order to form a distribution of macroscopic reliefs 30, projecting from an upper side of the film 1, to which correspond, on the opposite, lower side of the film 1, "negatives", i.e. cells. A filler layer 10 is predisposed on the lower side of the film 1, to fill these cells. The height of the macroscopic reliefs is about 2-5 mm, i.e. about at least one order greater than the dimensions of the microprisms, so that the lateral surface of each relief exhibits a multiplicity of microprisms. This is because the lateral surface of the reliefs is the most responsible for the back-reflecting effect when the laminate is used for horizontal road signalling. The reliefs (and respective cells on the lower side) preferably exhibit in plan view a hexagonal form and are distributed in and ordered and regular way. They can be, for example, truncopyramidal with a hexagonal base. Another particularly advantageous form of shaping of the film, especially is the film is in the embodiment with the metal sheet 9, exhibits macroscopic reliefs in parallel ribbings, either transversal or inclined. It is however possible to have other forms, even though it is preferable that the reliefs each exhibit a top surface which is substantially flat, horizontal and parallel to the film, and also exhibit an inclined lateral surface. At least a part of the microprisms is on the lateral surface (inclined) of the reliefs: the microprisms are protected against traffic wear and are also the most exposed to the beam of light coming from the headlights of a road vehicle, in order to optimize the back-reflection result and the visibility of the horizontal road signal, in all atmospheric conditions and no matter what the situation of the road surface, and also for any possible angle of incidence of the light beam emitted by a road vehicle. The filler layer 10 of the cells and for covering the lower shaped side has a thickness which is greater than the depth of the cells, so as to obtain a total cover and to form a continuous base surface over all of the lower side of the film 1, the surface opposite to the back-reflecting upper side. The material used for making the filler layer 10 is preferably a spreadable plastic substance, for example a polyurethane resin or a synthetic rubber. In a case in which the film is shaped in macroscopic reliefs, the layer of adhesive or self- adhesive material 8 for positioning the film in the work position is arranged below the cell filler layer 10.

The distribution of the macroscopic reliefs 30 to which the cells correspond is obtained by heat-forming the film; during this stage the first protective layer 5 has the task of protecting the microprisms so that their conformation and their optical properties are conserved. The film 1 is heat-formed by passing it through two oppositely-situated embossing cylinders (not illustrated), peripherally provided with two matrices (male-female) which cooperate and are predisposed to obtain reliefs on one side of the film 1 and the respective cells on the other side thereof. Preferably one of the two matrices (preferably the male matrix) is made of an elastically deformable material and more deformable with respect to the material of the other matrix; for example the male matrix could be made of silicone rubber and the female matrix of metal (for example steel, nickel etc.); alternatively two cooled metal matrix cylinders could be used, interpositioning two polyethylene or HDPE films or the like between the cylinders and the film 1, the two films being of a thickness comprised between 50 and 100 micron, and protecting the film from direct contact with the matrix cylinders. Before heat-forming the film 1 is preheated, for example by infrared batteries and/or heater rollers, and the heat-forming is then done by two embossing cylinders (cooled) which operate reciprocally staggered, so that in the heat forming zone each projection (male) of a matrix collaborates with a recess (female) of the other matrix. The heat- formable layer of material ensures an efficient heat-forming of the film 1. As mentioned herein above, a filler layer 10 is spread to fill up the cells and cover the lower side of the film I₅ on the side of the first protective layer 5. A layer of adhesive 8 or self-adhesive (either permanent or removable) is then spread on the filler layer 10, in order to fix the film 1 to an external surface (for example, the road surface) with paper or silicone film protection.

The film 1 with reliefs as described above is especially suited to realising a horizontal signal, and also a lateral signal such as on a guard rail, road sign etc), which will last over a long period of time and does not require special maintenance. The film is already in use as a back-reflecting film 1, and is provided with high back-reflecting properties and can maintain these properties over a long time, even if subjected to wear, such as for example by atmospheric agents or by passing vehicles. Signals obtained with the film of the invention are highly visible for drivers even where the atmospheric conditions are very unfavourable for driving, such as for example at night and in the presence of fog and/or rain, thus increasing road safety conditions. The film's light and colorimetry properties satisfy the requisites of the existing legal standards (especially for daytime vision), and offer excellent back-reflecting properties. Thanks to the special realisation of the transparent layer 32, the film is especially stable even in conditions of large temperature swings. The layer 32b on which the microprisms 20 are afforded is in fact not, as happens in prior art films, a laminar thermoplastic film with oriented fibres which are susceptible to dilation, but is instead obtained with a spreadable resin paste, in particular heat-hardening, which exhibit an amorphous structure that is not subject to heat dilation. The presence of the support 32a and the nature thereof give the film a special resistance to flexional deformation. Furthermore, the described process enables high quality and durable printed images to be obtained on the film.

Claims

Claims.

1). A process for obtaining a back-reflecting multi-layer film, with a microprism support, comprising stages of: preparation of a transparent layer (32) exhibiting a structured surface exhibiting a distribution of embossed microprisms (20); laying a reflective layer (3) on the structured surface; obtaining a protection surface for the reflective layer; wherein the stage of preparation of a transparent layer (32) comprises stages of: spreading, on a support (32a) constituted by an acrylic base made of a mixture of known type including a polycarbonate, a layer of acrylic resin (32b); heating the transparent layer thus obtained and impressing the microprism structure on the resin layer (32b); cooling the transparent layer in order to stabilise the resin layer (32b).

2). The process of claim 1, wherein: the support (32a) exhibits a thickness comprised between 20 and 40 μm; the layer of acrylic resin is obtained with a heat-hardening acrylic resin (32b) and has a thickness which is comprised between 100 and 300 μm.

3). The process of claim 1, wherein the stage of heating of the transparent layer (32) is performed at a temperature comprised between 140 and 17O⁰C. 4). The process of claim 1, wherein before the stage of laying the reflective layer (3) there is a stage of spreading a layer of metal primer on the transparent layer (32) in order to obtain a first anchoring layer (4) interpositioned between the transparent layer (32) and the reflective layer (3). 5). The process of claim 1, wherein before the stage of laying the reflective layer (3) there is a stage of treating the transparent layer (32), with a specific metal surface treatment in order to obtain a first anchoring layer (4) interpositioned between the transparent layer (32) and the reflective layer (3).

6). The process of claim I₅ wherein after the stage of laying of the reflective layer (3), it includes a stage of spreading a layer of polyoil or solvent-free resin on the reflective layer (3) in order to obtain a first protective layer (5) on the reflective layer (3).

7). The process of claim 6, wherein before the stage of spreading a layer of polyoil or solvent-free resin on the reflective layer (3), it includes a stage of spreading a layer of metal primer on the reflective layer (3) in order to obtain a second anchoring layer (7) interpositioned between the reflective layer (3) and the first protective layer (5).

8). The process of claim 6, wherein before the stage of spreading a layer of polyoil or solvent-free resin on the reflective layer (3), it includes a stage of a specific treatment for metal surfaces on the reflective layer (3) in order to obtain a second anchoring layer (7) interpositioned between the reflective layer (3) and the first protective layer (5).

9). The process of claim 1, wherein the stage of laying the reflective layer (3) includes a laying of a layer of at least 90% pure silver having a thickness of at least 0.1 μm.

10). The process of claim 1, wherein before the stage of spreading the layer of acrylic resin (32b) on the support (32a), it includes a stage of printing words, figures and the like on the surface of the support (32a) on which the layer of resin (32b) will be spread.

11). A multi-layer back-reflecting film with a microprism support, comprising: a transparent layer (32) which exhibits a structured surface with an embossed distribution of microprisms (20), a reflective layer (3) made of a material containing silver which covers the structured surface; a protective surface for the reflective layer; wherein the transparent layer (32) comprises a support (32a), made of a mixture of known type having an acrylic base with a polycarbonate, and a layer of acrylic resin (32b) on which the microprisms are embossed (20).

12). The film of claim 11, wherein the support (32a) exhibits a thickness comprised between 20 and 40 μm and the layer of acrylic resin (32b) is obtained using a heat-hardening acrylic resin spread with a thickness comprised between 100 and 300 μm.

13). The film of claim 11, wherein it comprises a first anchoring layer (4) interpositioned between the transparent layer (32) and the reflective layer (3) and having a thickness of such a size that the overall thickness of the anchoring layer (4) and the reflective layer (3) is lower than a height of the microprisms (20), which anchoring layer (4) is solidly anchored to the transparent layer (32) and the reflective layer (3) in such a way that the two layers (32, 3) are solidly constrained one to another.

14). The film of claim 12, wherein it comprises at least a first protective layer

(5), realised using a polyoil or a solvent-less resin having 100% dry residue, which covers the reflective layer (3) on an opposite side thereof from the first anchoring layer (4).

15). The film of claim 14, wherein the microprisms (20) covered by the anchoring layer (4) and the reflective layer (3) define a succession of crests and valleys which are filled and covered, at least to a height of the crests, by the first protective layer (5).

16). The film of claim 15, wherein a second anchoring layer (7) is interpositioned between the reflective layer (3) and the protective layer (5). 17). The film of claim 14, wherein it comprises a metal sheet (9) coupled to the first protective layer (5) on an opposite side thereof from the reflective layer (3).

18). The film of claim 17, wherein the metal sheet (9) is made of soft aluminium having a thickness of about 100-200 micron.

19). The film of any one of the preceding claims, wherein the film is shaped in order to form a distribution of macroscopic reliefs (30), projecting from an upper side of the film, to which cells correspond on an opposite, lower side; a layer of filler material (10) being included on the lower side of the film, to fill the cells.