EP1664439A1

EP1664439A1 - Dynamic road marking unit

Info

Publication number: EP1664439A1
Application number: EP04744808A
Authority: EP
Inventors: Antonius H. M. Raaijmakers; Peter J. Slikkerveer; Lucas L. D. Van Der Poel; Nicolaas P. Willard
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2003-09-04
Filing date: 2004-08-23
Publication date: 2006-06-07
Also published as: US20070041785A1; CN1846031A; WO2005024136A1; JP2007504378A

Abstract

A dynamic road marking unit is capable of switching between a first and a second display state. It has an electro-optical layer which is bistable. In principle the dynamic road marking unit only requires energy when switching between the states, i.e. when the visual properties of the dynamic road marking unit are changed.

Description

Dynamic road marking unit

TECHNICAL FIELD OF THE INVENTION The present invention relates to a dynamic road marking unit and a method of operating a dynamic road marking unit, which unit is capable of switching between a first and a second display state.

BACKGROUND ART During the last few years there has been an increasing interest from traffic authorities in traffic signs which can be altered to reflect the current traffic conditions. For instance, there might be a need to change the speed limit due to bad weather or to warn drivers that there is a traffic jam ahead on the road. Lately, experiments have been made where road marks are changed according to certain criteria, e.g. the white painted lines that mark the different lanes on a road can be changed so that two lanes are changed into three when the need for this arises in the morning rush hour. This is accomplished by applying three lines and turning these on and off, as desired, to achieve the envisaged result. US 6,092,909 discloses a dynamic road marking unit which uses an electro- optical switch to switch between an activated, light-reflecting state and a deactivated, light- absorbing state. In the activated state the road marking unit is clearly visible as a white line, and in the deactivated state it is practically invisible against the road surface. However, this dynamic road marking unit requires a constant supply of energy in the activated state, which may be a problem in cases of energy supply shortage. Therefore, there is a need for a dynamic road marking unit which requires a minimum of energy and still has the desired functionality of being able to be turned on and off.

SUMMARY OF THE INVENTION It is an object of the present invention to meet this need, which is achieved by a dynamic road marking unit having the characterizing features of claim 1 , with preferred embodiments indicated in the dependent claims 2-19. The invention further relates to a method of operating a dynamic road marking unit according to claim 20. The dynamic road marking unit according to claim 1 comprises a bistable electro-optical layer. This dynamic road marking unit has the advantage of being very energy-efficient since it requires energy only when the display properties are switched. The electro-optical layer may comprise a layer of electrophoretic material which contains a set of charged particles with predetermined visual properties, and at least a first electrically conductive layer arranged adjacent to one side of the layer of electrophoretic material. The conductive layer makes it possible to control the movements of the charged particles in the electrophoretic material. Depending on the charge of the conductive layer, the particles can be moved towards or away from the conductive layer, and the visual properties of the dynamic road marking unit can be changed in accordance with the visual properties of the charged particles. This dynamic road marking unit, as was noted above, has the advantage of being very energy-efficient since it requires energy only when the display properties are switched. This is because the charged particles are bistable and stay in the same place in the electrophoretic layer for months without any energy supply, i.e. the dynamic road marking unit is switchable from a first, inactivated state to a second, inactivated state and vice versa. This means that the visual properties of the dynamic road marking unit basically stay the same until a new voltage is applied to the conductive layer to change the charge thereof. A low voltage of lower than 20-30 V is enough to move the particles and change the visual properties of the dynamic road marking unit. This has the advantage that solar energy can be used to power the dynamic road marking unit. The dynamic road marking unit also has the advantages of being durable and easy to install. It can be applied to a road surface in much the same way as ordinary temporary thermoplastic roadmarks. Furthermore, the dynamic road marking unit can be easily folded or rolled up and thus be easily transported. It can also be made very thin and therefore it does not disturb traffic or cause any extra noise when vehicles drive over it. The dynamic road marking unit can be formed into any shape, which means that it can indicate not only lines, but also arrows and other signs. This can be used to improve traffic flow as well as traffic safety. The dynamic road marking unit may comprise a second conductive layer adjacent to the other side of the layer of electrophoretic material. This further improves the control of the charged particles in the electrophoretic layer and thereby the visual properties. According to one alternative, the charged particles can be surrounded by a colored fluid. In this case the particles are of one color, for instance white, and the fluid is of a contrasting color. In one state the particles are visible and the roadmark appears white, and in another state they are covered by the fluid and the roadmarks appear black. This is a simple and efficient way of providing the two states of the dynamic road marking unit. According to a second alternative, the set of charged particles may comprise a set of positively charged particles with first visual properties or a set of negatively charged particles with second visual properties, or it may comprise a set of positively charged particles with first visual properties and a set of negatively charged particles with second visual properties which are different from the first visual properties. This makes it possible to switch the visual properties of the dynamic road unit between two states. For instance, the positively charged particles may be white and the negatively charged particles black, which makes it possible to change the color of the dynamic road marking from black to white and vice versa by changing the charge of the conductive layer(s). According to a second embodiment of the invention, the electro-optical layer comprises at least two redox-active layers, of which at least one layer is of electrochromic material, and conductive layers are provided to generate a voltage difference between the two redox-active layers, and means are provided to prevent direct electrical contact between the at least two redox-active layers. This dynamic road marking unit, as was noted above, has the advantage of being very energy-efficient since it requires energy only when the display properties are switched. This is achieved by making the electrochromic effect bistable in that direct electrical contact between the two redox-active materials is prevented. The electrochromic material stays in the same state for about an hour without any energy supply. Then only a small "boost" is needed to retain the state. This means that the visual properties of the dynamic road marking unit basically stay the same until a new voltage is applied to the conductive layer to change the charge thereof. A low voltage of merely 5 V or less is enough to change the visual properties of the dynamic road marking unit. This has the advantage that solar energy can be used to power the dynamic road marking unit. The dynamic road marking unit also has the advantages of being durable and easy to install. It can be applied to a road surface in much the same way as ordinary temporary thermoplastic roadmarks. Furthermore, the dynamic road marking unit can be easily folded or rolled up and thus be easily transported. It can also be made very thin and therefore it does not disturb traffic or cause any extra noise when vehicles drive over it. The dynamic road marking unit can be formed into any shape, which means that it can indicate not only lines, but also arrows and other signs. This can be used to improve traffic flow as well as traffic safety. The electro-optical layer may further comprise an electrolyte layer, preferably a gel electrolyte layer. The gel electrolyte may function as an adhesive between the adjacent layers. The at least one layer of electrochromic material may comprise at least one conductive polymer, and the conductive polymer may be an organic conductive polymer. This is advantageous since these materials are flexible, which renders it easy to transport the dynamic road marking unit. The conductive layers may comprises indium-tin oxide or highly doped poly(ethylenedioxythiophene), which both have excellent conductive properties and are flexible. The electro-optical layer may comprise an electrochromic layer of polypyrrole and an electrochromic layer of a mixture of normally doped poly(ethylenedioxythiophene) and normally doped polyethylenedioxypyrrole and a gel electrolyte layer sandwiched between these two layers, two conductive layers being arranged, one on each side of the electro-optical layer i.e., adjacent to the side of the polypyrrole layer not facing the gel electrolyte and adjacent to the side of the layer of the mixture of normally doped poly(ethylenedioxythiophene) and normally doped polyethylenedioxypyrrole not facing the gel electrolyte, respectively. This provides an efficiently working electro-optical layer which is simple to switch between two states, one transparent and one black. A voltage of no more than approximately 2 V is enough to switch between the states. A white reflecting layer arranged adjacent to one of the conductive layers has the effect that the dynamic road marking unit appears white when the electro-optical layer is in the transparent state. According to a third embodiment of the invention, the electro-optical layer may be a bistable liquid crystal layer, which also gives the above advantages of being bistable and thus energy-efficient. A layer of visibility-enhancing optical structures may be arranged on the dynamic road marking unit according to any of the above embodiments. These structures may fulfil several functions. They may improve the reflection of the incident light from the headlights of a car towards the driver of the car and thus make it easier for the driver to see the roadmark. They may also focus light from headlamps in designated other directions, highlighting these structures for other road users, for example at road crossings. These structures are especially useful during the night or in situations with reduced visibility. The dynamic road marking unit may further comprise a coating of polyurethane. This protects the road marking unit and makes it very resistant to wear. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS In the following detailed description the invention will be further elucidated with reference to certain embodiments thereof shown in the accompanying drawings. Fig. 1 is a schematic cross-sectional view of part of a dynamic road marking unit according to a first embodiment of the invention, Fig. 2 is a schematic plan view of the part of the dynamic road marking unit shown in Fig 1, Fig. 3 schematically shows visibility-enhancing structures on a dynamic road marking unit according to the invention, Fig. 4 shows the first embodiment of the dynamic road marking unit from above, Fig. 5 is a cross-sectional view of the first embodiment of the dynamic road marking unit in less detail than Fig. 1, and Fig. 6. is a cross-sectional view of part of dynamic road marking unit according to a second embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Figs 1, 2, 4 and 5 show a first embodiment of the dynamic road marking unit according to the present invention. Fig. 1 is a schematic view of a cross-section of part of the dynamic road marking unit. The dynamic road marking unit comprises a first and a second electrically conductive layer, or electrode, 1 and 2. The first conductive layer 1 is transparent. An electro- optical layer in the form of an electrophoretic layer 3 is sandwiched between the conductive layers 1 and 2. The electrophoretic layer comprises microcapsules 4 which contain a clear fluid 5 and particles 6 and 7 coated with white and black pigments, respectively. Of course, the particles may have any suitable visual properties. For instance, they may be coated with different colors or have reflective and non-reflective surfaces, respectively. They may also include intermediate colors between two predetermined colors so as to provide gray scales. The particles have mutually opposed surface charges (e.g. negative for black and positive for white). Such a product is manufactured under the name Electronic Ink by E Ink Corporation. It has the advantage of scattering incident light in all directions, which in the present application means that the road mark is clearly visible not only to the driver in a car whose headlamps are lighting up the roadmark, but also to other road users. The conductive layers 1 and 2 make it possible to cause the white or the black particles 6, 7 to travel in the clear liquid to the surface of the electrophoretic layer 3, i.e. next to the transparent first electrode 1, thus changing the effective color of the dynamic road marking unit from white to black and vice versa. This is accomplished by a process known as electrophoresis, in which charged particles travel in a fluid under the influence of an electric field. The electric field in this case is provided by a voltage applied to the conductive layers 1 and 2. The voltage is supplied and controlled by a voltage supply and control means 9, which may be solar-powered and remote-controlled. Assuming that the black particles are negatively charged and the white particles are positively charged, and a positive voltage is applied to the first conductive layer and a negative voltage is applied to the second conductive layer, the negatively charged black particles 7 will travel to the first conductive layer 1 and the positively charged white particles

6 will travel to the second conductive layer 2. Then, since the first conductive layer is transparent and turned towards the viewer, the dynamic roadmark unit is perceived as black, i.e. the same color as the road, by a viewer. If on the other hand a negative voltage is applied to the first conductive layer and a positive voltage is applied to the second conductive layer, the positively charged white particles 6 will travel to the first conductive layer 1 and the negatively charged black particles

7 will travel to the second conductive layer 2. Then the dynamic roadmark unit is perceived by a viewer as white and clearly distinguishable from the road surface. Furthermore, as is shown in Fig. 1, the conductive layers may be divided into segments, each separately controllable, so that different two-dimensional black or white shapes against a white or black background can be formed by the dynamic road mark. This is useful for changing a line from a solid line to a dashed line to no line at all, or a left arrow to a right arrow to no arrow at all, or a max speed 50 indication to a max speed 80 indication to no max speed indication. This is shown in Figs. 1 and 2, where the right half of the visible surface is black and the right half is white. This is because a negative voltage is applied to the left half of the first conductive layer 1 and a positive voltage is applied to the left half of the second conductive layer 1. An application of this is shown in Fig. 4, where the number 25 is formed by a dynamic road marking unit. It may alternatively be useful to switch the electrophoretic layer incompletely, which will result in a display state where both the first and the second particles 6 and 7 are at the surface, i.e. the first conductive layer. This may be used to tune the dark state of the road marking unit to the true color of the surrounding road. Furthermore, it would also be possible to use a colored fluid 5 and have particles 6, 7 which all have the same charge, either positive or negative, and the same visual properties. For example, one could use a black fluid and white particles. With a colored fluid and two types of particles it is also possible to make three colors, e.g. the color of the ground and two further colors. The electro-optical layer, in this case the electrophoretic layer 3, is bistable. It retains its state for days up to months without any energy being supplied. In this case it means that the charged particles 6, 7 stays in the same place commonly for weeks to months when the power is switched off. This means that power is needed only when the pattern of the dynamic road marking unit is changed. The dynamic road marking unit is made by a process in which the electrophoretic layer 3 is coated in a roll-to-roll process on a flexible film, e.g. of plastic material, with the transparent conductive layer 1 thereon. The transparent conductive layer 1 may be non-patterned. On top of the electrophoretic layer a pressure-sensitive adhesive is provided by means of which it can be laminated onto a second film, e.g. of plastic material, with the second conductive layer 2 thereon, which preferably is crudely patterned and made of a material which adheres well to a road surface. The second conductive layer 2 does not have to be transparent. The second conductive layer 2 is the layer which is closest to the road surface when the dynamic road marking unit is applied to a road. The dynamic road marking unit may be applied to the road in the same way as ordinary temporary thermoplastic roadmarks. The dynamic roadmark can be rolled up with a small bending radius for easy transport and installation on a road surface. The first and/or the second film of plastic material may be made, for example, of a polymer with a rubber-like behavior at normal usage temperature such as polyurethane, which makes the dynamic road mark more durable. The contrasting pigments on the particles 6 and 7 are highly reflective and have a good contrast, e.g. 12:1. Fig. 6 shows a second embodiment of the dynamic road marking unit according to the present invention. The dynamic road marking unit in Fig. 6 has an electro-optical layer in the form of two redox-active layers 1 1 and 12, of which at least one is an electrochromic layer, and a gel electrolyte layer 13 which is sandwiched between the two redox-active or electrochromic layers 11, 12. Respective electrically conductive layers 14 and 15 are arranged on the sides of the electrochromic layers not facing the gel electrolyte. Two respective plastic foil layers 16 and 17 are arranged on the outside of the conductive layers 14, 15, and a white bottom reflector 18 is provided on the bottom. The conductive layers 14, 15 are connected to an external power source 19. The functions of some of the layers in Fig. 6 may be combined in a single layer. Thus the conductor function in layer 14 or 15 may be integrated in the electrochrome material 11 or 12 by using poly(ethylenedioxythiophene) (PEDOT). As an alternative, the conductor function 15 may be combined with the package layer 17 if a metal film is used instead of a plastic film. Moreover, the reflector function 18 may be integrated in the electrolyte 13, e.g. by incorporating white scattering particles (e.g. Ti0₂ particles) into the electrolyte. The latter has the advantage that it is easier to obtain a transparent state since the properties of the second electrochrome layer 12 has no influence on the optical effect. Electrochromic materials, such as conductive polymers, have different optical properties in dependence on their electrochemical potential. They can switch between a transparent and a colored state or between two or more different colored states under the influence of an electric field. The states of the electrochromic materials are bistable owing to the construction of the layers in the dynamic road marking unit device. Therefore, energy is in principle only needed when switching from one state to the other. However, a small "boost" is often needed after an hour or so to keep the electrochromic material in the desired state. A wide variety of colors can be obtained, including black, with the use of a combination of different electrochromic materials. A solution for road marking purposes comprises a combination of electrochromic materials that switch between transparent and colored. In their colored state, the combined colors will absorb all light and appear black. In their transparent state, a white bottom reflector can be seen. Possible electrochromic materials are organic conductive polymers such as: (poly(ethylenedioxythiophene) (PEDOT), which can be switched between a transparent state and a blue state, polypyrrole, which can be switched between a green state and a transparent state, polyethylenedioxypyrrole (PEDOP), which can be switched between a transparent state and a red state. However, there is a wide variety of different materials with different optical properties to choose from, for instance inorganic titanium oxide or other dyes may be used (cf B.C. Thompson, P. Schottland, K. Zong, J.R. Reynolds, Chem. Mater.2000, 12, 1563). The exemplifying embodiment according to Fig. 6 will be described below. A plastic foil 16 is coated with highly doped PEDOT or indium-tin oxide (ITO) 14, followed by polypyrrole 1 1. The highly doped PEDOT or ITO will act as a conductor 14 and will not take part in the electrochromic cell. A gel electrolyte 13 is applied on the polypyrrole layer 1 1. A possible polymeric gel electrolyte is described in H. W. Heurer, R. Wehrmann, S. Kirchmeyer, Adv. Funct. Mater. 2002, 12, 89. A second foil 17 is provided with a transparent conductor 15, such as ITO or highly doped PEDOT. On this transparent conductor 15, an electrochromic layer is deposited, which may be a mixture of at least two different electrochromic materials 12. Examples are normally doped PEDOT and PEDOP. The two foils 16 and 17 are sealed together, for which the polymeric electrolyte 13 may act as an adhesive between the two foils 16 and 17. The conductor layers 14 and 15 (ITO or highly doped PEDOT) are connected to an external power source 19. A voltage of 2 V is enough to dope or undope the conductive polymers in the layers 11 and 12 and to change their optical properties from fully transparent to fully colored. The combination of red, blue and green gives a black appearance. Gray scales can be achieved for the electrochrome embodiment either by voltage or current control. According to a third embodiment of the invention, the electro-optical layer may be a bistable liquid crystal layer. Examples of the effects that can be used for such layers are the cholesteric texture liquid crystal (CTLC) effect, the bistable nematic liquid crystal effect, and the ferro-electric liquid crystal effect. The dynamic road marking unit according to all of the above embodiments can be used in systems of large surface area and is viewable at an angle of 180° vertically and 360° horizontally, which is very effective during daytime. To enhance the visibility during the dark hours further, it is possible to apply an additional layer of optical, for instance prism-like structures on top of the dynamic road marking unit, e.g. on top of the transparent first conductive layer 1 according to the first embodiment of the invention, as is shown schematically in Fig. 3, to ensure that the light from the headlight of a passing car is deflected downwards towards the electro-optical layer, which then reflects it upwards via the optical structures 8 directly towards the driver of the car. Additional structures or layers may also be applied to remove the effect of specular reflection of, for example, the sun on top of the road marking unit. A further visibility-enhancing measure could be to apply the electro-optical layer of the first and the second embodiment of the invention directly on a retro-reflecting film. A retro-reflector is a reflector which reflects an incident light beam in a direction parallel to the direction in which it was incident. To make the dynamic road marking unit even more durable, a transparent polymeric coating 10, preferably of a polymer with a rubber-like behavior at normal usage temperature such as polyurethane, may be applied on top of the dynamic road marking unit 1. This enhances the scratch resistance against car tyres. The protective scope of the invention is not limited to the embodiments shown. The invention resides in each and every novel characteristic and each and every combination of characteristic features. Moreover, reference numerals in the claims are not to be construed as limiting their protective scope.

Claims

CLAIMS:

1. A dynamic road marking unit capable of switching between a first and a second display state and comprising an electro-optical layer (3; 11, 12), characterized in that the electro-optical layer (3; 11 , 12) is bistable.

2. A dynamic road marking unit according to claim 1, wherein the electro-optical layer is a layer of electrophoretic material (3) which contains a set of charged particles (6, 7) with predetermined visual properties, and wherein at least a first electrically conductive layer (1) is arranged adjacent to one side of the layer of electrophoretic material (3).

3. A dynamic road marking unit according to claim 2, further comprising a second conductive layer (2) arranged adjacent to the other side of the layer of electrophoretic material (3).

4. A dynamic road marking unit according to claim 2 or 3, wherein the charged particles (6, 7) are surrounded by a colored fluid (5).

5. A dynamic road marking unit according to claim 2 or 3, wherein the set of charged particles (6, 7) comprises a set of positively charged particles (6) with first visual properties.

6. A dynamic road marking unit according to claim 2 or 3, wherein the set of charged particles (6, 7) comprises a set of negatively charged particles (7) with second visual properties.

7. A dynamic road marking unit according to claim 2 or 3, wherein the set of charged particles (6, 7) comprises a set of positively charged particles (6) with first visual properties and a set of negatively charged particles (7) with second visual properties different from the first visual properties.

8. A dynamic road marking unit according to claim 1, wherein the electro-optical layer comprises at least two redox-active layers (11, 12) of which at least one layer is of electrochromic material, wherein conductive layers (14, 15) are provided to generate a voltage difference between the two redox-active layers (11, 12), and wherein means are provided to prevent direct electrical contact between the at least two redox-active layers (11, 12).

9. A dynamic road marking unit according to claim 8, wherein the electro-optical layer further comprises an electrolyte layer (13).

10. A dynamic road marking unit according to claim 9, wherein the electrolyte layer is a gel electrolyte layer (13).

11. A dynamic road marking unit according to claim 8, 9 or 10, wherein the at least one layer of electrochromic material (11, 12) comprises at least one conductive polymer.

12. A dynamic road marking unit according to claim 11, wherein the at least one layer of electrochromic material (11, 12) comprises at least one organic conductive polymer.

13. A dynamic road marking unit according to any of claims 8 to 12, wherein the conductive layers (14, 15) comprise indium-tin oxide.

14. A dynamic road marking unit according to any of claims 8 to 12, wherein the conductive layers (14, 15) comprise highly doped poly(ethylenedioxythiophene).

15. A dynamic road marking unit according to any of claims 8 to 14, wherein the electro-optical layer comprises an electrochromic layer (1 1) of polypyrrole and an electrochromic layer (12) of a mixture of normally doped poly(ethylenedioxythiophene) and normally doped polyethylenedioxypyrrole, with a gel electrolyte layer (13) sandwiched between these two layers, two conductive layers (14, 15) being arranged, one on each side of the electro-optical layer, adjacent to the side of the polypyrrole layer (1 1) not facing the gel electrolyte (13) and to the side of the layer (12) of the mixture of normally doped poly(ethylenedioxythiophene) and normally doped polyethylenedioxypyrrole not facing the gel electrolyte (13), respectively.

16. A dynamic road marking unit according to claims 8 to 15, wherein a white reflecting layer (18) is provided adjacent to one of the conductive layers (16).

17. A dynamic road marking unit according to claim 1, wherein the electro-optical layer is a bistable liquid crystal layer.

18. A dynamic road marking unit according to any of the preceding claims, wherein a layer of visibility-enhancing optical structures (8) is arranged on the dynamic road marking unit.

19. A dynamic road marking unit according to any of the preceding claims, further comprising a coating of polyurethane.

20. Method of operating a dynamic road marking unit, comprising the step of switching an electro-optical layer in a dynamic road marking unit to a desired state, characterized in that the dynamic road marking unit is designed in accordance with any of claims 1 to 19.