COLOUR ELECTROCHROMIC DISPLAY

Abstract

There is provided an electrochromic fixed image display and a method for manufacturing the display. The electrochromic fixed image display for displaying a predetermined symbol comprising a stack of layers of: a colour layer which is configured to provide a resulting colour contrast to the display when comparing its on-state and off-state; a first electrochromic electrode layer arranged behind said colour layer in a viewing direction; an electronically and ionically insulating symbol defining layer, arranged behind the first electrode layer, which comprises at least one opening defining the shape the predetermined symbol; an electrolyte, arranged behind the symbol defining layer, which fills and covers the opening of said symbol defining layer; and a counter electrode layer, arranged behind the electrolyte layer, comprising an electronically conductive material, wherein the electrolyte layer is in ionic contact with the first electrode layer and the counter electrode layer.

Claims

1. An electrochromic fixed image display, comprising: at least one switchable segment which is repeatedly switchable between an on-state and an off-state, wherein each of said at least one switchable segment is configured to display at least one predetermined symbol in said on-state, further each switchable segment comprises a stack of layers, wherein the stack of layers comprises: a colour layer which is configured to provide a resulting colour contrast to said at least one switchable segment when comparing said on-state and off-state of the same at least one switchable segment; a first electrode layer comprising an electrically conducting electrochromic and electrochemically active organic polymer material which is electrochemically switchable between two different visually detectable colouring states respectively corresponding to said on-state and said off-state of said switchable segment, said first electrode layer being arranged behind said colour layer in the viewing direction of said display; a symbol defining layer which is electronically and ionically insulating and comprises at least one opening, wherein said at least one opening defines the shape of said at least one predetermined symbol, said symbol defining layer being arranged behind said first electrode layer in the viewing direction of said display; an electrolyte layer being arranged behind said first symbol defining layer in the viewing direction of said display, wherein said electrolyte layer fills and covers the at least one opening of said symbol defining layer; and a counter electrode layer comprising an electronically conductive material being arranged behind said electrolyte layer in the viewing direction of said display, wherein said electrolyte layer is in ionic contact with the first electrode layer and the counter electrode layer.

2. The electrochromic fixed image display according to claim 1, wherein said colour layer comprises colourants and/or opacifiers, preferably said colourants and/or opacifiers are selected from dyes and pigment particles.

3. The electrochromic fixed image display according to claim 1, wherein said resulting colour contrast (E) is at least 9.

4. The electrochromic fixed image display according to claim 1, wherein the thickness of said colour layer is in the range from 5 m to 50 m, preferably a thickness in the range from 10 m to 40 m, preferably a thickness in the range from 10 m to 20 m, preferably a thickness in the range from 11 m to 17 m.

5. The electrochromic fixed image display according to claim 1, wherein said first electrode layer comprises a homopolymer or copolymer of a 3,4-dialkoxythiophene.

6. The electrochromic fixed image display according to claim 1, wherein said electrolyte layer is transparent or comprises colourants and/or opacifiers.

7. The electrochromic fixed image display according to claim 1, further comprising a transparent plastic substrate arranged, in the viewing direction of the display, in front of said colour layer or between said colour layer and said first electrode layer.

8. The electrochromic fixed image display according to claim 7, wherein said transparent plastic substrate is arranged in front of said colour layer in the viewing direction of the display.

9. The electrochromic fixed image display according to claim 7, wherein said transparent plastic substrate is arranged between said colour layer and said first electrode layer in the viewing direction of the display.

10. The electrochromic fixed image display according to claim 7, wherein said transparent plastic substrate comprises a moisture protective layer.

11. A method of manufacturing an electrochromic fixed image display comprising at least one switchable segment which is repeatedly switchable between an on-state and an off-state, wherein each of said at least one switchable segment is configured to display at least one predetermined symbol in said on-state, said method comprising: providing a substrate comprising a colour layer; providing a continuous or discontinuous first electrode layer to said substrate comprising said colour layer, wherein said first electrode layer comprises an electrochromic and electrochemically active organic polymer material being electrochemically switchable between two different visually detectable colouring states; fully or partly covering said first electrode layer by a symbol defining layer, which symbol defining layer is electronically and ionically insulating and comprises at least one opening for each one of said at least one switchable segments, which at least one opening defines the shape of the at least one predetermined symbol of a respective one of said at least one switchable segment, and wherein each of said at least one opening exposes a respective surface portion of said first electrode layer; providing an electrolyte layer which comprises at least one electrolyte layer portion, wherein each one of said electrolyte layer portions are spatially separated from each other and each one of said electrolyte layer portions fully covers a respective one of said opening(s) in the symbol defining layer; providing a counter electrode layer which comprises at least one counter electrode layer portion, wherein each one of said counter electrode layer portions are spatially separated from each other, and each one of said counter electrode layer portions are in ionic contact with said electrolyte layer portions, wherein said colour layer comprises colourants and/or opacifiers and provides a resulting colour contrast to said at least one switchable segment when comparing said on-state and off-state of the same at least one switchable segment.

12. The method according to claim 11, wherein each of the layers are provided by printing or coating techniques comprising of screen printing, inkjet printing, aerosol-jet printing, flexographic printing, gravure printing, offset printing, digital printing, laser printing, LED printing or bar-coating.

13. The method according to claim 11, wherein said colour layer is provided to said substrate by printing or coating techniques comprising screen printing, inkjet printing, aerosol-jet printing, flexographic printing, gravure printing, offset printing, digital printing, laser printing, LED printing or bar-coating.

14. The method according to claim 11, wherein said colour layer is arranged on one side of said substrate and the continuous or discontinuous first electrode layer is provided to said substrate on the same side as said colour layer.

15. Use of an electrochromic fixed image display according to claim 1 in devices such as television screens, computer monitors, portable systems comprising smartphones, handheld game consoles and personal digital assistants (PDAs).

16. The electrochromic fixed image display according to claim 2, wherein said resulting colour contrast (E) is at least 9.

17. The method according to claim 12, wherein said colour layer is provided to said substrate by printing or coating techniques comprising screen printing, inkjet printing, aerosol-jet printing, flexographic printing, gravure printing, offset printing, digital printing, laser printing, LED printing or bar-coating.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0103] Embodiments of the invention is described, by way of example, with reference to the accompanying drawings (which are not drawn to scale), wherein:

[0104] FIG. 1a illustrates a schematic exploded perspective view of a part for a display according to the invention.

[0105] FIG. 1b shows a schematic illustration of a finalized or assembled display.

[0106] FIG. 1c illustrates schematic top views of each layer of part for a display according to the invention, arranged in the same order as they face the viewer from top to bottom.

[0107] FIGS. 2a, 3a and 3b illustrates photographs of a display falling outside the scope of the claims.

[0108] FIGS. 2b, 4a and 4b illustrates photographs of a display within the scope of the claims.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0109] Presented below are more details of how different embodiments of the colour electrochromic display may be arranged and manufactured.

[0110] FIG. 1 is a schematic drawing illustrating one example of a part for a directly addressed electrochromic fixed image display, wherein the figure illustrates the layers one by one.

[0111] In more detail, FIG. 1 illustrates a directly addressed electrochromic fixed image display comprising nine switchable segments, each switchable segment being arranged for displaying a symbol, which is switchable between an on-state and an off-state. The switchable segments are numbered 1 to 9, from left to right. The symbol PIN is displayed by switchable segment number 1, i.e. the leftmost switchable segment is PIN. A star-symbol, *, is displayed by each one of switchable segments number 2-7. A question mark-symbol, ?, is displayed by switchable segment number 8, and the symbol OK is displayed by switchable segment number 9. The symbol displayable by the respective switchable segment, may be turned on and off independently of the state of the other switchable segments. In operation, normally the symbol PIN is displayed as the display switches on, one star is lit for each character that the user enters/button that the user presses, and upon verification of the PIN-code an OK-symbol is displayed if a match is found, and a question mark if no match is found.

[0112] Moreover, the display device is connected to an addressing circuit 64, which in turn is connected to a power supply 66. Each counter electrode 140 of the switchable segments 1-9 is connected to a respective output of the addressing circuit 64 by electronic conductors 62 by means of a holder or clip 68. The power supply 66 may power the display device, optionally via the addressing circuit 64. The power supply and the optional addressing circuit thereby provides for individual control of the potential difference over each switchable segment 1-9 by the application of different potentials to the counter electrode layer 140 and the pixel electrode layer 150. In other words, one or more power supplies may be directly electronically connected to a respective one of said counter electrodes and the outer electrode 150. According to one example the holder 68 is a 1.25 mm FPC/FFC BackFlip Housing, part number 49597-2017 provided by Molex. However, there exists many different alternatives for connecting the counter electrodes to the electric conductors of a circuit board, which is well known to the person skilled in the art.

[0113] With reference to FIG. 1a, the directly addressable fixed image display is described layer by layer below. First a transparent substrate is provided, and a colour layer 170 arranged thereon. A continuous or discontinuous first electrode layer 110 is further arranged on said transparent substrate comprising said colour layer 170. The electrochromic first electrode layer is preferably continuous between different switchable segments, such that the electrochromic layers in different switchable segments each is a separate portion of the continuous electrochromic layer. Alternatively, the electrochromic first electrode layer may be discontinuous between different switchable segments. In this case, each of the isolated electrochromic electrode layer is provided with a separate electrode for application of a potential.

[0114] Secondly, a symbol defining layer 120 is printed on the electrochromic first electrode layer 110, which symbol defining layer 120 comprises openings or through holes 121-129, corresponding to the shape of the symbols that are to be displayed. References 121-129 are shown in FIG. 1c.

[0115] Thirdly, an electrolyte layer 130 is printed on top of the symbol defining layer 120. The electrolyte layer comprises nine portions 131-139 which are ionically isolated from each other such that the electric field in one electrolyte 131 does not influence the electric field in another electrolyte 132 in an adjacent switchable segment; one portion for each switchable segment. Each portion of electrolyte layer 131-139 is printed such that it covers the respective opening(s) 121-129 in the beneath symbol defining layer 120. The printed symbol defining layer may have any shape, as long as the electrolyte layer portions are ionically isolated from each other. Preferably the electrolyte layer is only in direct ionic contact with the electrochromic layer at portions where a colour switch of the electrochromic material is desired.

[0116] The symbol defining layer 120 is arranged of ion isolative/insulating material, and advantageously the adhesion between the symbol defining layer 120 and the electrochromic electrode layer 110 is verified, such that a migration and/or diffusion of electrolyte in between the symbol defining layer and the electrochromic layer is prevented or minimized. A migration of the electrolyte may deteriorate the contrast, or sharpness, of the displayed image.

[0117] Fourthly, a counter electrode layer 140 is printed on top of the electrolyte layer 130. The counter electrode layer comprises nine portions 141-149 which are electronically isolated from each other such that a potential applied to one electrode 141 do not influence the electric field in an electrolyte 132 belonging to an adjacent switchable segment. Each counter electrode portion 141-149 is printed such that it is in ionic contact with a respective one of the electrolyte layer portions 131-139. The counter electrode layer may have any shape, as long as suitable electric fields may be created in the electrolyte.

[0118] Optionally, a protective layer 160 (illustrated in FIG. 1a) is provided on top of the counter electrode layer to protect and/or encapsulate the display.

[0119] Experiments

[0120] Manufacturing Process

[0121] The Type I display is equal to the Type II display, except that the step of providing the colour layer is left out.

[0122] Type II Display

[0123] The below examples were all manufactured by means of screen printing, using a screen printing mesh having 120 threads/cm, and a thread diameter of 34 m, and in the below described order, unless stated otherwise. An insulating layer, comprising 125 m thick polyethylene terephthalate (called PET hereinafter) film (Polifoil Bias manufactured by Policrom Screen), was provided and served as the substrate, a colour layer 170 was screen printed on the substrate, and then a uniform first electrode layer 110 layer of PEDOT:PSS (Clevios SV3 screen printing paste provided by Heraeus) was screen printed on the same side, i.e. on top of the colour layer.

[0124] A symbol defining layer 120 (e.g. UV curable dielectric 5018A purchased from DuPont, Uviplast UV curing ink Omniplus UL-025 from Fujifilm Sericol, Ultragraph UVAR from Marabu Printing Inks) having holes defining the symbols was then printed on top of the electrochromic layer. Additionally, a portion of the electrochromic layer was left free of the symbol defining layer. The thickness of the layer was about 10-20 m. The symbol defining layer was cured upon exposure to UV light.

[0125] Each opening in the symbol defining layer was assigned to a respective pixel cell, and an electrolyte layer portion 131-139 was printed on top of all openings in the symbol defining layer belonging to the respective same pixel, ensuring that the openings in the symbol defining layer were filled with electrolyte, such that an electrolyte layer portion belonging to a first pixel cell was not in direct contact with an electrolyte layer portion belonging to a different pixel cell, and that no electrolyte was in ionic contact with the electrochromic layer outside the openings of the symbol defining layer. The thickness of the layer was about 5-10 m. Thereafter the electrolyte layer was UV-cured, whereupon another electrolyte layer was printed having the same thickness. This final layer was also UV-cured. The electrolyte layer comprises Luviquat Excellence, a copolymer of vinylpyrrolidone and quaternised vinylimidazole in aqueous solution manufactured by BASF, including 10 wt.-% of TiO.sub.2 powder (Kronos 2300 manufactured by KRONOS), in order to make the electrolyte white and opaque.

[0126] A counter electrode portions 141-149 (electrically conducting carbon paste 7102 purchased from DuPont) was then screen printed on top of each of the electrolyte layer portions, ensuring that a counter electrode portion belonging to a first pixel cell was not in direct contact with a counter electrode portion belonging to a different pixel cell, and that no portion of the counter electrode layer 140 is in direct electronic contact with the electrochromic layer outside the openings of the symbol defining layer. The thickness of the layer was about 5-20 m.

[0127] A pixel electrode 150 (electrically conducting carbon paste 7102 purchased from DuPont) was then screen printed on top of and in direct physical contact with a portion of the electrochromic layer not covered by the symbol defining layer. The portion of the electrochromic layer not covered by the symbol defining layer extends along the K of the pixel cell displaying OK. Further, the pixel electrode extends to the side of the leftmost and rightmost electrolyte portion 131, 139, and ends in alignment with the ends of the counter electrodes 141-149. Thereafter the counter electrode layer 140 and the pixel electrode 150 was dried at 120 C. for 3 minutes.

[0128] One conducting line was connected to each counter electrode, and one conducting line to each end of the pixel electrode. Finally, the conducting lines were connected to a voltage supply, capable of individually controlling the electric potential distributed to the pixel electrode and each counter electrode. The applied potential difference across the pixel cell was 3 V unless stated otherwise.

[0129] The symbol defining layer and the segmented electrolyte layer are discussed in more detail in WO 2013/068185. How these types of layers may be combined with a colour layer into a display according to the present invention is further described below.

[0130] Colour Layer Displays According to the Present Invention

[0131] FIG. 2a shows a display without a colour layer, whereas FIG. 2b shows an electrochromic fixed image display according to the present invention, wherein each display is in the off-state. The displays shown in FIG. 2b are manufactured as described in the section Manufacturing process above. The displays shown in FIG. 2a are manufactured in the exact same way as those in FIG. 2b, with the only difference that no colour layer is provided; i.e. the step of screen printing the colour layer was left out. A display manufactured as those shown in FIG. 2a is hereinafter referred to as a Type I display; while a display manufactured as those shown in FIG. 2b is hereinafter referred to as a Type II display. FIGS. 3a and 3b show the switching of a Type I display, where the display is in an off-state in FIG. 3a and in an on-state in FIG. 3b. FIGS. 4a and 4b show the switching of six Type II displays, where the displays are in an off-state in FIG. 4a and in an on-state in FIG. 4b.

[0132] Colour Contrast and Thickness Measurements

[0133] The definition of the colour contrast (E*) is copied from this article: P. Andersson, et al., Advanced Functional Materials, Volume17, Issue16, November 2007, p. 3074-3082.

[0134] The inventors of the present invention have chosen to measure the colour contrasts of the reflective display cells using the CIE L*a*b* colour system, where L* (lightness), a* (greenred) and b* (blueyellow) are used to parameterize the colour space. The motivation for using the CIE L*a*b* system is that this colour evaluation toolkit adapts well to the vision of the human eye and that it is commonly used in the graphic art industry. With CIE L*a*b*, the colour contrast (E*) is defined as the Euclidean distance between the colour coordinates of the different states of the pixel electrode:

E*={square root over (L*.sup.2+*.sup.2+b*.sup.2)}

The colour contrast, E*, obtained for a standard version of the electrochromic display printed at RISE, i.e. without the colour layer, is typically 30.

[0135] The colour contrast is in most cases reduced upon adding the colour layer, but the advantage is that other colours can be obtained when the colour layer is combined with the colours of the on- and off-states of the electrochromic display.

The colour contrast, E*, has also been measured for several electrochromic displays in which a colour layer has been included.

[0136] In all these examples, the display is observed through the plastic substrate.

Example 1

[0137] A Type II display was manufactured as described above, wherein a red colour layer was screen printed on the substrate. The thickness of the screen printed layer was ranging from 10 m to 17 m across the display area. These displays using a red colour layer are losing quite a lot of their initial contrast. Thus, this explains why the colour contrast was measured at different voltages. The colour contrasts obtained at 3V and 1.5V are both high, while the colour contrast obtained at 1.2 V is acceptable. The colour contrast obtained at 1.0V is definitely too low. Hence, a lower limit of the E*=9 is preferred for the colour contrast in these printed electrochromic displays.

TABLE-US-00001 Oxidation (reference Reduction Reduction Reduction Reduction Red value) 3 V 1.5 V 1.2 V 1.0 V L* 38.98 33.99 34.49 36.02 37.40 a* 40.13 27.16 28.16 32.53 36.11 b* 20.05 13.00 13.22 15.71 17.73 E* 15.58 14.49 9.24 4.89

Example 2

[0138] A Type II display was manufactured as described above, wherein a magenta colour layer and the display were printed on different sides of the substrate. The magenta colour layer was digital printed at a thickness of approximately 15 m. The colour contrast when using the magenta colour layer is higher as compared to when using the red colour layer; the colour contrast when using the red colour layer is therefore determining the preferred minimum colour contrast value. Therefore, the measurements were only performed at 3V as a lower voltage would have resulted in higher E as compared to the preferred minimum colour contrast value obtained for the red colour layer at the same lower voltage.

TABLE-US-00002 Oxidation (reference Reduction Magenta value) 3 V L* 41.76 34.81 a* 36.93 20.03 b* 9.82 14.78 E* 18.94

Example 3

[0139] A Type II display was manufactured as described above, wherein a brown colour layer and the display were printed on different sides of the substrate. The brown colour layer was digital printed at a thickness of approximately 13 m. The colour contrast when using the brown colour layer is higher as compared to when using the red colour layer; the colour contrast when using the red colour layer is therefore determining the preferred minimum colour contrast value.

TABLE-US-00003 Oxidation (reference Reduction Brown value) 3 V L* 53.41 41.25 a* 7.17 5.06 b* 31.46 13.39 E* 24.98

Example 4

[0140] A Type II display was manufactured as described above, wherein a green colour layer and the display were printed on different sides of the substrate. The green colour layer was digital printed at a thickness of approximately 13 m. The colour contrast when using the green colour layer is higher as compared to when using the red colour layer; the colour contrast when using the red colour layer is therefore determining the preferred minimum colour contrast value.

TABLE-US-00004 Oxidation (reference Reduction Green value) 3 V L* 64.41 46.86 a* 14.66 18.57 b* 44.72 19.50 E* 30.97

[0141] The use of a colour layer to improve the hidden message effect and/or the visual appearance is applicable not only to Type I displays but essentially to any electrochromic and electrochemically active display having an organic polymer material which is switchable between two colouring states, e.g. to matrix addressable displays and flexible fixed image displays. Exemplifying configurations of such displays may be found e.g. in WO 2008/062149, EP 2 607 950 WO 2011/042431, WO 2012/136738 and WO 2013/068185, and a self-contained and/or printed colour layer may be provided in front of the front electrode or first electrode of those displays, in the same or a similar way as has been described above.