GB2489955A - Retroreflective sheeting - Google Patents

Retroreflective sheeting Download PDF

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Publication number
GB2489955A
GB2489955A GB1106181.9A GB201106181A GB2489955A GB 2489955 A GB2489955 A GB 2489955A GB 201106181 A GB201106181 A GB 201106181A GB 2489955 A GB2489955 A GB 2489955A
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GB
United Kingdom
Prior art keywords
sheeting
layer
retroreflective
substrate
print reception
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
GB1106181.9A
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GB201106181D0 (en
Inventor
John C Wright
Matthew Scarsbrook
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3M Innovative Properties Co
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3M Innovative Properties Co
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Filing date
Publication date
Application filed by 3M Innovative Properties Co filed Critical 3M Innovative Properties Co
Priority to GB1106181.9A priority Critical patent/GB2489955A/en
Publication of GB201106181D0 publication Critical patent/GB201106181D0/en
Publication of GB2489955A publication Critical patent/GB2489955A/en
Pending legal-status Critical Current

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Classifications

    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00Optical elements other than lenses
    • G02B5/12Reflex reflectors
    • G02B5/122Reflex reflectors cube corner, trihedral or triple reflector type
    • G02B5/124Reflex reflectors cube corner, trihedral or triple reflector type plural reflecting elements forming part of a unitary plate or sheet
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B60VEHICLES IN GENERAL
    • B60RVEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR
    • B60R13/00Elements for body-finishing, identifying, or decorating; Arrangements or adaptations for advertising purposes
    • B60R13/10Registration, licensing, or like devices
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00Optical elements other than lenses
    • G02B5/12Reflex reflectors

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Laminated Bodies (AREA)

Abstract

Retroreflective sheeting comprises a substrate 2, a layer of prismatic retroreflective material 5 and a print reception layer 9 with a topcoat having an alkyd resin component. The top coat material may comprise an alkyd resin component present in the range of 1 â 10wt% and may be a blend of at least one alkyd resin and at least one vinyl polymer component, the latter being present in the range 10 to 30 wt%. The sheeting may be part of a vehicle licence plate.

Description

RETROREFLECTIVE SHEETING
The present invention relates to retroreflective sheeting, in particular a sheeting comprising a substrate and a layer of retroreflective material, suitable for use as a vehicle licence plate retroreflective sheeting and adapted to be laser printable.
Vehicle licence plates are used throughout the majority of countries in the world to identify a vehicle and/or owner, and although their format varies, indicate a state or country in which the vehicle carrying the plate is registered. Traditionally licence plates have been made of pressed metal or plastic, with raised and coloured numbers and letters. However, in more recent years there has been a move towards digitally produced licence plates, which typically comprise a printed plastic plate, with the print being provided either directly onto the plate or onto a film that is subsequently laminated or adhered to the plate. In some instances, the film is a retroreflective sheeting.
Two known types of retroreflective sheeting are cube corner sheeting and microsphere-based sheeting. Microsphere-based sheeting, sometimes referred to as "beaded" sheeting, employs a multitude of microspheres typically at least partially embedded in a binder layer and having associated specular or diffuse reflecting materials (e.g., pigment particles, metal flakes or vapour coats, etc.) to retroreflect incident light. Due to the symmetrical geometry of beaded retroreflectors, microsphere based sheeting exhibits the same total light return regardless of orientation, i.e. when rotated about an axis normal to the surface of the sheeting. Thus, such microsphere-based sheeting has a relatively low sensitivity to the orientation at which the sheeting is placed on a surface. In general, however, such sheeting has a lower retroreflective efficiency than cube corner sheeting. Cube corner retroreflective sheeting, sometimes referred to as "prismatic" sheeting, typically comprises a thin transparent layer having a substantially planar first surface and a second structured surface comprising a plurality of geometric structures, some or all of which include three reflective faces configured as a cube corner element, that enables incident light to be reflected back towards the light source but translated and parallel to the incident light, creating the retroreflective effect.
The use of retroreflective materials on vehicle licence plates is known, for example, from W02009/120398 (Buoni). This discloses a sheeting comprising a retroreflective material layer and a transparent roughened film layer, with the peaks in the roughened surface being located over and coupled to the microspheres forming the retroreflective material layer. Such sheeting is printable using thermal transfer printing methods due to the low surface roughness of the transparent layer. The sheeting itself is formed using an extrusion process. A second example of such sheeting used in vehicle licence plates is described in U520020006559 (Mehta). A transparent ink and toner receptive layer is formed on a retroreflective sheeting from a cross-linked acrylic acid resin. The coating may be mixed with a carrier material used to carry a dispersion of microspheres or provided separately. US 7,048,989 (Watkins) discloses a digitally printable water-bone acrylic topcoat that can be used with a retroreflective sheeting. Such topcoats are proposed as an alternative to urethane topcoats.
It is desirable however to be able to provide alternatives to such receptive materials, for example, to offer ease of manufacture or ease of laser printing.
The present invention aims to address this by providing a retroreflective sheeting, comprising: substrate, having a first surface and a second surface, a layer of prismatic retroreflective material, also having a first surface and a second surface, the first surface being attached to the first surface of the substrate, and a print reception layer, comprising a topcoat material, provided on the second surface of the layer of retroreflective material, wherein the topcoat material comprises an alkyd resin component.
An advantage of using a topcoat material comprising a an alkyd resin to form a print reception layer in conjunction with a prismatic retroreflective material is that the pigment material used in a laser printing process keys easily with the print reception layer, which in turn bonds well with the underlying retroreflective material layer. This also makes the retroreflective sheeting particularly suitable for use as a vehicle licence plate retroreflective sheeting.
Preferably, the topcoat material comprises an alkyd resin component present in the range of 1 -lOwt%.
More preferably, the topcoat material comprises a blend of at least one alkyd resin component and at least one vinyl polymer component. In this case the topcoat material preferably comprises a blend of at least one alkyd resin component present in the range of 1 -10 wt% and at least one vinyl polymer component present in the range of 10 to 30 wt%.
Preferably the print reception layer has a surface resistivity in the range of 1 X 106 to 1 xl o8 ohms/m2.
Preferably the print reception layer is laser printable.
Preferably, the print reception layer has an exposed surface, and the exposed surface is porous.
The layer of retroreflective material may be laminated to the first surface of the substrate by an adhesive layer. The substrate may be a polyester terephthalate (PET) film. Preferably, the substrate is a low-shrinkage polyester terephthalate (PET) film. Preferably the substrate has a thickness in the range of 75gm to l2Spm. The layer of retroreflective material may comprise a carrier material having a plurality of microspheres dispersed therein. Alternatively, the layer of retroreflective material may be a prismatic material.
The present invention also provides for the use of such sheeting as vehicle licence plate retroreflective sheeting.
The present invention also provides a vehicle licence plate product comprising a substrate having a vehicle-facing surface and a road facing surface and having a layer of adhesive provided on the vehicle-facing surface, and sheeting as described above.
The present invention also provides for the use of a topcoat material comprising an alkyd resin component to form a print reception layer on a layer of prismatic retroreflective material forming a licence plate retroreflective sheeting.
The present invention will now be described by way of example only, and with reference to the accompanying drawings, in which: Figure 1 is a schematic cross-section of a retroreflective sheeting in accordance with the present invention; and Figure 2 is a schematic cross-section of a vehicle licence plate product having the sheeting shown in Figure 1 laminated thereto.
The present invention takes the approach of using a print reception layer that can itself be printed onto a layer of retroreflective material to enable a simple digital print method to be used to create text on a retrorcflective sheeting, one which is particularly suitable for use as a vehicle licence plate retroreflective sheeting. This simplifies the manufacturing process and the invention utilises a layer of topcoat material comprising an alkyd resin component that is typically used in printing processes as a liquid toner carrier for digital printing methods. Topcoat material therefore, as used in the following description, describes such liquid toner vehicles, whereas the term pigment is used to distinguish the material used in a laser printing process, which is typically a powder that is fused thermally into the surface of the print reception layer.
Consequently, the invention provides for the use of a topcoat material comprising an alkyd resin component to form a print reception layer on a layer of retroreflective material forming a retroreflective sheeting.
Figure 1 is a schematic cross-section of a retroreflective sheeting in accordance with the present invention. The sheeting 1 comprises a substrate 2, having a first surface 3 and a second surface 4. A layer of retroreflective material 5 is also provided, also having a first surface 6 and a second surface 7, the first surface 6 being provided with a reflective metallic layer 8 and laminated via the reflective metallic layer 8 to the first surface 3 of the substrate 2. A print reception layer 9 is provided on the second surface 7 of the layer of retroreflective material 5.
The print reception layer 9 is formed from a topcoat material comprising an alkyd resin component, and has an exposed surface 10. The layer of retroreflective material 5 is attached to the first surface 3 of the substrate 2 by an adhesive layer 11 that contacts both the reflective metallic layer 8 and the substrate 2.
Figure 2 is a schematic cross-section of a vehicle licence plate product having the sheeting shown in Figure 1 attached thereto. The vehicle licence plate 12 typically comprises an acrylic plate 13 having a first surface 14 that faces towards the road and a second surface 15 that faces towards a vehicle. A layer of a pressure sensitive adhesive 16 is provided on the second surface to enable the retroreflective sheeting 1 (as shown in Figure 1 but with detail omitted in Figure 2 for clarity) to be adhered to the acrylic plate 13. Once the retroreflective sheeting 1 has been S printed, the layer of digital print 17 sits between the retroreflective sheeting 1 and the acrylic plate 13 at the interface with the pressure sensitive adhesive 16.
The print reception layer 9 functions as a laser printable print reception layer as it provides a surface to which the black or other pigment used in a laser printing process can bond to. When prismatic retroreflective sheeting is used, printing directly onto the layer of retroreflective material can be problematic, due to the nature of the resin forming the upper surface of a prismatic retroreflective material. Keying of the ink on such a surface is difficult, and consequently the resultant final print quality may not be durable or aesthetically acceptable. The reflective elements within a prismatic retroreflective material create an overall macroscopic roughness that can in itself also cause difficulties with ink adhesion. Using a topcoat material comprising an alkyd resin component to form the print reception layer 9 creates a surface to which the pigment used in the laser printing process can bond easily. This is partly due to the upper surface of the print reception layer 9 being porous, a feature that favourably enables the pigment used in the laser printing process to melt into and bond with the topcoat material forming the print reception layer 9. By "porous" it is intended that the surface of the print reception layer 9 is permeable to the pigment used in laser printing. The degree of porosity can be influenced by the coating and curing of the toner, and the ability of the laser pigment used in the laser printing process to melt into and bond with the toner forming the print reception layer 9.
The topcoat material may be diluted with a solvent for ease of coating, and the solvent driven off during a curing and/or drying process to create a chemical bond between the topcoat material and the layer of retroreflective material 5. This coating process may be achieved using any suitable method, for example, a contact printing method. The chemical bonding of the topcoat material to the layer of retroreflective material S is also influenced by the resin contained within the topcoat material chosen. For example, the polyester resins contained within the topcoat material bond to the resin material forming the surface of the prismatic retroreflective material, in which the microspheres are dispersed in the retroreflective material, via an OH-bridge with free-hydroxyl functional groups present at the surface of the resin. Alkyd resins are particularly suitable for performing this task. Other components of the topcoat material may aid this by creating additional cross-linking between other resin materials and the free-hydroxyl functional groups present at the surface of the resin material. The topcoat materials used in the present invention therefore comprise an alkyd resin component. Such suitable topcoat materials may also comprise a vinyl polymer component, as described in the example below. In particular, suitable topcoat materials may comprise a blend of at least one alkyd resin component and at least one vinyl polymer component. In addition, any solvent used to dilute the topcoat material, or present in the topcoat material in its off-the-shelf concentration, may partially melt the upper surface of the resin material, giving a degree of physical bonding.
To be able to function as a laser printable print reception layer 9, the exposed surface 10 of the print reception layer 9 ideally needs to be able to withstand temperatures of over 100°C, as typically found in commercially available laser printers suitable for printing retroreflective sheeting. Consequently, the print reception layer 9 should have a mehing point of greater than 100°C. This enables it to withstand the laser printing process. Furthermore, in choosing appropriate topcoat material to form the print reception layer 9 it has been determined that the surface resistivity of the exposed surface 10 of the print reception layer 9 should be in the range of 1x106 to lxl08ohms/m2.
In addition, the optical properties of the print reception layer 9 are also an important consideration when choosing a suitable topcoat material. The print reception layer 9 should ideally be transparent to ensure minimum impact on colour and retroreflective performance.
Transparent as used herein means that the print reception layer 9 is able to transmit at least about percent of the intensity of the light incident upon it at a given wavelength. In some embodiments, the print reception layer 9 is able to transmit more than 80 percent, and in other embodiments, the print reception layer 9 is able to transmit more than 90 percent of incident light. The opalescence of the print reception layer 9 should be low, to minimise any scattering of the incident and retroreflective illumination. The refractive index n of the print reception layer 9 should be similar to that of the retroreflective material to reduce refraction effects at the boundary between the two materials. Furthermore, the surface energy characteristics of the print reception layer 9 should be compatible with the wetting characteristics of the pigment used in the laser printing process.
Preferably, the substrate 2 is a polyester terephthalate (PET) film, preferably a low-shrinkage polyester terephthalate (PET) film. An untreated PET film, which is a film having an initial low surface roughness and having been exposed to no treatments that could alter this surface roughness, is particularly preferred. However, other PET films having surface treatments are also suitable. Films having a nominal thickness in the range 75 pm to 125 iim are also suitable.
The thickness of the film should be selected to ensure that the resulting sheeting passes easily though a laser printer (if too thin the risk of blockage within the printer or damage to the sheeting increases and if too thick the sheeting does not pass through the printer at all) and to ensure that the thermal diffusivity of the print reception layer 9 is compatible with the melt characteristics of the laser toner particles.
The thickness of the print reception layer 9 is preferably in the range of 0.Sjim to 2.0gm. Too thin a layer makes printing difficult, and too thick a layer gives no additional noticeable benefit to the appearance of the final licence plate product. Preferably a polymeric topcoat material comprising an alkyd resin component is used to form the print reception layer 9, such as 3MTM Process Color 990-00 Toner, available from 3M United Kingdom plc, 3M Centre, Cain Road, Bracknell, Berkshire RG12 8HT, UK. A contact printing method is preferred as the means by which the print reception layer 9 is applied to the layer of retroreflective material 5. Details of the composition of the 990-00 material are given in Table 1 below: Component C.A.S no. Wt% Propanol, 1(or 2)-(2-methoxymethylethoxy)-889 17-22-0 15 -40 acetate ________________ ___________ 1-Methoxy-2-propyl acetate 108-65-6 10 -30 Vinyl polymer (New Jersey Trade Secret Trade Secret 10 -30 Registry # 04499600-5238P) _____________ _________ Cyclohexanone 108-94-1 10 -30 Alkyd Resin 3261 (NJ TSR # 04499600-6267P) Trade Secret 1 -10 Xylene 1330-20-7 3 -7 2, 4-Dihydroxybenzophenone 131-56-6 0.5 -1.5 Ethylbenzene 100-41-4 0.1 -1.5 2-(5-Chloro-benzotriazol-2-yl)-4,6-3864-99-1 0.1 -1 bis(tertbutyl)phenol _____________ _________ Bis(2, 2, 6, 6-tetramethyl-4-piperidinyl) 52829-07-9 0.1 -1 sebacate _______________ ___________ Toluene 108-88-3 <0.4 Phenyl isodecyl phosphite 68311-09-1 <0.3 Stoddard solvent 8052-41-3 <0.2 2-Methoxy-1-propyl acetate 70657-70-4 <0.2 Calcium 2-ethylhexanoate 136-51-6 <0.2
Table 1
A suitable prismatic retroreflective material comprises a layer of cube-corner retroreflective elements. As an alternative to using a metallic layer 8, a seal film may be used with the layer of retroreflective material comprising cube-corner elements to provide an air interface. Suitable commercially available prismatic retroreflective materials include 3MTM Diamond GradeTM DG3 sheeting and 3MTM High Intensity Prismatic retroreflective sheeting, both available from 3M United Kingdom plc, as above.
In the above embodiment an acrylic plate is used to mount the retroreflective sheeting 1 to form a vehicle licence plate. However, as an alternative an aluminium plate may be used and the retroreflective sheeting 1 applied to a surface of such a plate to form a vehicle licence plate.
The quality of the resultant sheeting may be assessed using a number of different criteria. Some of these are in relation to the appearance of the sheeting 1 "as is", that is, after production and before lamination within a licence plate construction, and some in relation to the appearance of an overall laminated licence plate product.
L Showthrough Showthrough is related to the appearance of the printed region to the naked eye in terms of density of the black pigmented printed regions. Areas that appear to be feint to the naked eye represent areas where there is some showing through of the print reception layer 9. This can be an overall effect or present only in certain discrete areas. In samples made according to the above example the print density had a solid, uniform appearance to the naked eye on both the sheeting "as is" and following lamination. This is a critical factor as retroreflective sheeting often has a "sparkly" appearance before printing, and so a dense black print is necessary to prevent any of this "sparkly" appearance from showing through in the printed regions.
Dots/Dropout Dots or dropout are terminologies to describe areas where there is a complete absence of printing, as these typically resemble white dots within the black printed regions.
3. Abrasion Resistance Following printing the lettering created on the sheeting needs to be abrasion resistant to the extent that it can withstand rubbing with a finger or other light abrasion, for example, being dragged across a work surface, clothing or similar.
Banding Banding is an artefact caused by the passage of the sheeting through the printer, for example, the effect of static electricity created by the movement of the substrate across the rollers. This results in distinctive bands of denser ink being seen on the resuhing print. The ability of a sample to resist banding therefore is dependent on the choice of the PET film used as the substrate, as well as the coating and curing of the print reception layer 9.
Lamination Appearance Once laminated behind an acrylic plate as shown in Figure 2 to form a licence plate product it is vital that the ink density and therefore the overall black appearance of the printed letters obtained using laser printing is sufficient to meet the relevant safety standards, such as BSAU145d. The appearance is also affected by any texture or roughness effects produced by the printing process, as this can also detract from an overall impression of a uniform, dense black in colour.
Forming the print reception layer 9 from a topcoat material comprising an alkyd resin component produces a sheeting that is adaptable to be laser printed, and meets the criteria described above.
A further advantage of such an approach is that existing retroreflective sheeting materials may be treated to ensure laser printability by using a print reception layer 9 formed from a topcoat material.

Claims (14)

  1. CLAIMS1. Retroreflective sheeting, comprising: a substrate, having a first surface and a second surface, a layer of prismatic retroreflective material, also having a first surface and a second surface, the first surface being attached to the first surface of the substrate, and a print reception layer, comprising a topcoat material, provided on the second surface of the layer of retroreflective material, wherein the topcoat material comprises an alkyd resin component.
  2. 2. Sheeting according to claim 1, wherein the topcoat material comprises an alkyd resin component present in the range of 1 -lOwt%.
  3. 3. Sheeting according to claim 1 or 2, wherein the topcoat material comprises a blend of at least one alkyd resin component and at least one vinyl polymer component.
  4. 4. Sheeting according to claim 3, wherein the topcoat material comprises a blend of at least one alkyd resin component present in the range of 1 -10 wt% and at least one vinyl polymer component present in the range of 10 to 30 wt%.
  5. 5. Sheeting according to any preceding claim, wherein the print reception layer has a surface resistivity in the range of lx 106 to lx 108 ohms/m2.
  6. 6. Sheeting according to any preceding claim, wherein the print reception layer is laserprintable.
  7. 7. Sheeting according to any preceding claim, wherein the print reception layer has an exposed surface and the exposed surface is porous.
  8. 8. Sheeting according to any preceding claim, wherein the layer of retroreflective material is attached to the first surface of the substrate by an adhesive layer.
  9. 9. Sheeting according to any preceding claim, wherein the substrate is a polyester terephthalate (PET) film.
  10. 10. Sheeting according to claim 9, wherein the substrate is a low-shrinkage polyester terephthalate (PET) film.
  11. 11. Sheeting according to any of claims 9 or 10, wherein the substrate has a thickness in the range of 75gm to i25m.
  12. 12. Use of the sheeting according to any preceding claim as a vehicle licence plate retroreflective sheeting.
  13. 13. Vehicle licence plate product comprising a substrate having a vehicle-facing surface and a road facing surface and having a layer of adhesive provided on the vehicle-facing surface, and sheeting as claimed in any of claims 1 to 11.
  14. 14. Use of a topcoat material comprising an alkyd resin component to form a print reception layer on a layer of prismatic retroreflective material forming a licence plate retroreflective sheeting.
GB1106181.9A 2011-04-12 2011-04-12 Retroreflective sheeting Pending GB2489955A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB1106181.9A GB2489955A (en) 2011-04-12 2011-04-12 Retroreflective sheeting

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Application Number Priority Date Filing Date Title
GB1106181.9A GB2489955A (en) 2011-04-12 2011-04-12 Retroreflective sheeting

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GB201106181D0 GB201106181D0 (en) 2011-05-25
GB2489955A true GB2489955A (en) 2012-10-17

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1458253A (en) * 1973-06-28 1976-12-15 Yankee Artists Multicoloured reflective articles
EP0887665A1 (en) * 1996-10-18 1998-12-30 Nippon Carbide Kogyo Kabushiki Kaisha Triangular pyramidal cube corner type retroreflective sheet
WO2000068714A1 (en) * 1999-05-11 2000-11-16 The Standard Register Company Image bonding treatment for retroreflective surfaces
EP1424572A1 (en) * 2001-08-09 2004-06-02 Nippon Carbide Kogyo Kabushiki Kaisha Retroreflection device

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1458253A (en) * 1973-06-28 1976-12-15 Yankee Artists Multicoloured reflective articles
EP0887665A1 (en) * 1996-10-18 1998-12-30 Nippon Carbide Kogyo Kabushiki Kaisha Triangular pyramidal cube corner type retroreflective sheet
WO2000068714A1 (en) * 1999-05-11 2000-11-16 The Standard Register Company Image bonding treatment for retroreflective surfaces
EP1424572A1 (en) * 2001-08-09 2004-06-02 Nippon Carbide Kogyo Kabushiki Kaisha Retroreflection device

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Publication number Publication date
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