WO2012118377A1

WO2012118377A1 - Electrically dimming mirror comprising a curved mirror surface and method of manufacturing such a mirror

Info

Publication number: WO2012118377A1
Application number: PCT/NL2012/050125
Authority: WO
Inventors: Hermanus Feil
Original assignee: Miortech Holding B.V.
Priority date: 2011-03-01
Filing date: 2012-03-01
Publication date: 2012-09-07
Also published as: WO2012118366A1

Abstract

The invention provides a mirror comprising a curved mirror surface, said mirror surface comprising a curved carrier layer having a specular reflective surface, and said mirror surface further comprising an optically transmissive cover layer, said cover layer being curved and placed in a corresponding manner to said carrier layer for forming a correspondingly curved intermediate space in between said carrier layer and said cover layer, wherein a plurality of electrowetting optical cells is formed in said intermediate space for electrically controlling said optical transmissivity of said mirror, wherein said plurality of electrowetting optical cells is defined by a plurality of pixel walls present in said intermediate space, and said pixel walls being attached to the cover layer and extending towards the carrier layer, the pixel walls not being attached to the carrier layer. It further provides a method of manufacturing such a mirror.

Description

Title

Electrically dimming mirror comprising a curved mirror surface

and method of manufacturing such a mirror Field of the invention

The present invention relates to a mirror comprising a curved mirror surface, said mirror surface comprising a curved carrier layer having a specular reflective surface, and said mirror surface further comprising an optically transmissive cover layer, said cover layer being curved and placed in a corresponding manner to said carrier layer for forming a correspondingly curved intermediate space in between said carrier layer and said cover layer.

The present invention further relates to a method of manufacturing a mirror as mentioned above. Background

The use of automatically dimming rear view mirrors in vehicles is more and more common in the automotive industry, in particular in cars from the upper segment of the market. Although the main field of application of automatically dimming rear view mirrors relates to interior rear view mirrors (commonly having a flat surface), automatically dimming exterior rear view mirrors having a curved or aspheric surface is also known in the art. An example of an automatically dimming rear view mirror having a curved surface may for example be found in European patent application EP 0791503. In the above- mentioned document, an exterior rear view mirror having a curved surface is described which is automatically electrically dimmable using an electrochrome layer between two electrodes. The electro chrome layer is sandwiched in between a carrier glass layer and a cover glass layer.

Due to the liquid nature of the electrochrome layer of the mirror, the glass surfaces which enclose the electrochrome layer must be sufficiently stiff and robust in order to prevent any variations in the thickness of the mirror cross-section, which would give rise to optical artifacts and unwanted distortions of the image. For mirrors of the type mentioned above, curved glass layers are used having a thickness of several millimeters (e.g. typically 2 mm). The problem is enhanced by the manufacturing method of the mirrors, which often consists of filling of the interspace between the glass surfaces of the carrier and cover layer with the electrochrome material (of liquid nature) by means of vacuum filling, i.e. a low pressure is established in the interspace between the two glass layers and the liquid filling is sucked in.

Importantly, and also to prevent optical artefacts, it is necessary to match the radius of curvature of the glass carrier layer exactly with the radius of curvature of the glass cover layer. Without accurate matching, the small variations between the curved surfaces of both layers would still cause unwanted disturbances such as double imaging. Therefore, in manufacturing aspheric automatically dimming rear view mirrors, the selection process between the curved glass layers of the carrier layer and the cover layer of each mirror is extremely critical. This part of the process is therefore commonly performed manually, making such mirrors cumbersome to manufacture and thereby expensive.

Moreover, due to the fact that the glass layers need to be sufficiently robust, this adds onto the total weight of the mirror. As a result, since aspheric mirrors are often used as outside mirrors on a vehicle, it becomes more difficult to fix the mirrors to the vehicle in such a way that vibration of the mirror during driving of the vehicle is prevented.

Summary of the invention

It is an object of the present invention to obviate the disadvantages of the prior art mirrors mentioned above, and to provide a dimmable mirror having a curved mirror surface which is low weight and easy to manufacture.

The object of the present invention is achieved by the invention which provides a mirror comprising a curved mirror surface, said mirror surface comprising a curved carrier layer having a specular reflective surface, and said mirror surface further comprising an optically transmissive cover layer, said cover layer being curved and placed in a corresponding manner to said carrier layer for forming a correspondingly curved intermediate space in between said carrier layer and said cover layer, wherein a plurality of electrowetting optical cells is formed in said intermediate space for electrically controlling said optical transmissivity of said mirror, wherein said plurality of electrowetting optical cells is defined by a plurality of pixel walls present in said intermediate space. The pixel walls are attached to the cover layer and extend towards the carrier layer, whereas the pixel walls are not being attached to the carrier layer. The cover layer is sufficiently flexible for bending said cover layer in a corresponding manner to said curved carrier layer during manufacturing of said mirror. The mirror of the present invention uses electrowetting optical cells in order to enable automatic dimming of the mirror surface to prevent glare of the mirror when radiated with high-intensity lights. Due to the fact that electrowetting techniques are used, a plurality of pixel walls in between the carrier layer and the cover layer additionally function as spacer between the two layers that prevent unwanted variations in the thickness of the cross-section of the mirror. The pixel walls being attached to the cover layer, but not to the carrier layer, enables the cover layer or the combination of cover layer and carrier layer being bent, since the end faces of the pixel walls can move, slide or be repositioned relative to the carrier layer.

As a result, this enables the use of a flexible cover layer which is sufficiently flexible for bending the cover layer in a corresponding manner to the curved surface of the carrier layer, with the pixel walls in between. This provides many advantages to the mirror of the present invention. From the point of view of manufacturing, the mirror can be manufactured easily by providing the carrier layer and installing the electrodes for enabling switching of the optical cells, and thereafter after provide the pixel walls on the cover layer. Once this is done, the pixel wall structure may be filled with the polar liquid of the electrowetting optical cells while non-polar liquid is added to the carrier layer and/or the cover layer. Then, the cover layer, being of a flexible nature, can be easily bent on top of the carrier layer with the pixel walls in between, providing the final structure of the mirror with the electrowetting optical cells in between. The method can easily be performed automatically in a manufacturing process and the risk of thickness variations is prevented by the use of pixel walls as spacers.

The cover layer may be made flexible in many ways. As a skilled person may appreciate, the cover layer may be made of a flexible material which is optically transparent. In this respect, the skilled person may think of the use of a suitable polymer having a low elastic modulus (e.g. smaller than 10 GPa). On the other hand, it is possible to use a cover layer which is made of a more solid and stiff material such as glass (having a typical elastic modulus of 70 GPa), provided that the material is sufficiently thin in order to provide the required flexibility. A glass layer having a thickness of for example 1 ,0 mm or smaller is sufficiently robust and flexible to be bend on top of an aspheric mirror of the present invention having pixel walls in between the cover layer and the carrier layer. Therefore, according to an embodiment of the present invention, the cover layer is made of glass having a thickness smaller than or equal to 1 ,0 mm. In this respect, although the mirror of the present invention may be used in other applications, a preferred embodiment of the present invention is the use of the mirror as an exterior or outside vehicle mirror. Such mirrors often have dimensions of approximately 10 cm by 20 cm or smaller. Therefore, according another embodiment of the present invention, the mirror surface have service dimensions of at least 0,005 m². As will be understood, the bending properties of the cover layer are not only dependent on the material properties of the cover layer and the thickness thereof, but also partly on the surface of the mirror.

According to another embodiment of the present invention, the cover layer is made of a material having a thickness and a corresponding elastic modulus such as to enable a radius of curvature of 0,4-2, 1 m. The elastic modulus may for example be smaller than 100 Gpa.

According to another preferred embodiment, the mirror further comprises a carrier frame which supports the carrier layer which is placed on top of the frame. In this embodiment, the carrier frame may be shaped such as to enable bending of the carrier layer onto the frame for providing the curved carrier layer, while the carrier layer is sufficiently flexible for bending the carrier layer onto the carrier frame during manufacturing of the mirror.

The skilled person will appreciate that using a frame and a flexible carrier layer, also the carrier structure may have a reduced weight when compared to a conventional carrier layer structure (having for example a carrier layer made up of 2 mm thick glass). According to another embodiment of the present invention, the carrier layer is made up of glass having a thickness smaller than or equal to 1 ,0 mm (a comparable thickness as the thickness of the cover layer mentioned in one of the embodiments above). Also, the carrier layer may be made of a material having a thickness and a corresponding elastic modulus such as to enable a radius of curvature of 0,4-2, 1 m. The elastic modulus of the carrier layer may be smaller than 100 GPa.

According to another preferred embodiment, the mirror of the present invention is an exterior or interior vehicle mirror. As explained above, for use as a vehicle mirror, the low weight and automatically dimmable properties of the mirror have specific benefits such as to provide a stably fixed vehicle mirror which prevents the driver of a vehicle from being blinded by glare of the mirror as a result of a high intensity light source behind the vehicle and visible in the mirror. In addition, the low weight mirror structure enables less stringent requirements with respect to fixing of the mirror to the vehicle structure, since a low weight structure fixed to the vehicle is less sensible to vibration during driving of the vehicle.

According to a second aspect of the present invention there is provided a method of manufacturing a mirror comprising a curved mirror surface, said method comprising the steps of: for manufacturing said mirror surface, providing a curved carrier layer having a specular reflective surface, and providing an optically transmissive cover layer; forming a plurality of pixel walls onto said cover layer for forming a plurality of electrowetting cells, and at least partially filling said electrowetting cells with a polar liquid; adding a non-polar liquid to at least one other of said carrier layer or said cover layer; and bending and placing said cover layer onto said carrier layer for forming a correspondingly curved intermediate space comprising said electrowetting cells in between said carrier layer and said cover layer such that the pixel walls are not attached to the opposing the carrier layer.

In an embodiment of the method, the step of providing a carrier layer comprises providing a curved carrier layer. The step of bending and combining comprises pressing the cover layer on top of the curved carrier layer in a mid portion of the cover layer and forcing the sides of the cover layer on the sides of the carrier layer. This allows the cover layer to be bent over a previously bent carrier layer.

In another embodiment of the method, the step of bending and combining comprises placing the carrier layer on top of the cover layer with the pixel walls, and bending the combined carrier layer and cover layer. This allows the carrier and cover layers to be combined and being bent after the layers are combined. This can be advantageous during production, where the steps of combining and bending are performed separately, and where mirror assemblies having the combined carrier and cover layers may be bent into different shapes or curves.

After being bent, the combined carrier and cover layers can be sealed to prevent the polar and/or the non-polar liquids to leak or evaporate from the electrowetting mirror.

Although the use of low weight automatically dimmable curved mirrors as provided by the present invention may have specific advantages for use as vehicle mirrors, the skilled person may appreciate that the mirror structure of the present invention may also be used for different applications. The concept of the invention will be explained here and below with reference to the enclosed drawings. Brief description of the drawings

The enclosed drawings provide an illustration of the principles of the invention, in order to elucidate these principles of the invention to the skilled reader. In these figures:

figure 1 illustrates an embodiment of the curved mirror according to an embodiment of the present invention;

figure 2 illustrates a method of manufacturing a curved mirror according to an embodiment of the present invention;

figure 3 illustrates another embodiment of a curved mirror according to the present invention;

figure 4a illustrates an electrowetting optical cell that may be applied in a curved mirror according to an embodiment of the present invention;

figure 4b illustrates another electrowetting optical cell that may be applied in a curved mirror according to an embodiment of the present invention;

figure 5 schematically illustrates a method of manufacturing a curved mirror in accordance with figure 2 according to an embodiment of the present invention;

figure 6a - 6c illustrate an alternative method of manufacturing a curved mirror according to an embodiment of the present invention;

figure 7 schematically illustrates a method of manufacturing a curved mirror in accordance with figures 6a - 6c;

Detailed description of the embodiment

Figure 1 illustrates a curved mirror arrangement 35 according to the present invention. A curved carrier layer 3 forms the basis of the mirror. The curved carrier layer 3 may be made of glass or another suitable material for creating mirrors, such as a suitable polymer. The curved carrier layer 3 comprises at least one specular reflective surface 38 for providing the mirror functionality to the mirror. In order to provide a sufficiently strong and robust carrier layer, the carrier layer 3 may be made of a glass layer having a thickness of at least 2 mm. This prevents undesired bending of the glass carrier layer.

Opposing the glass carrier layer 3 there is provided a cover layer 5 which is made of a transparent material. In between the carrier layer 3 and the cover layer 5, a plurality of pixel walls 19 is distributed over the full surface of the mirror in such an arrangement that a plurality of optical pixels is created between the cover layer 5 and the carrier layer 3. The layers 3 and 7 (and everything in between) are kept together using clamping means 47 and/or glue or a sealing composition 45.

As the skilled person may appreciate, the plurality of pixel walls 19 may be arranged in a gridlike pattern for defining a matrix arrangement of optical pixels having a square for (a conventional arrangement of pixels on a screen), or may be arranged in a different manner which is optically advantageous in view of the function of the optical pixels for dimming the mirror. For example, in order to prevent optical interference patterns, it is advised to prevent using a regular arrangement of pixel walls giving rise to a regular pattern of pixels, as such a regularity causes optical interference visible in the mirror image of, for example, lights. Therefore, in another embodiment of the present invention, the pixel walls in the mirror may define a plurality of pixels having a randomised form or randomised surface area for each pixel; i.e. a randomised pattern of pixels.

Each pixel 1 is formed by an electrowetting optical cell. As an example, a typical design of an electrowetting optical cell that may be applied in a curved mirror according to the present invention is illustrated in figure 4 and explained later. For the moment, it is noted that surface of the curved carrier layer 3 and surface of the curved cover layer 5 of the mirror of the present invention each comprise an electrode layer 13 and 6 respectively, which enables to optically switch the optical cells 'dark' and 'bright', i.e. in the 'dark' state the non-polar or oily liquid in each optical cell spreads across the surface of the optical cell such as to decrease the optical transmissivity of the cell (making the cell a dark or black), while in the 'bright' state the non polar liquid 30 or oily substance is present on the side of each optical cell (as for example illustrated in figure 4) such as to provide a relatively good optical transmissivity (the mirror is not dimmed in the 'bright' state).

According to the present invention, cover layer 5 is either sufficiently thin or made of a sufficiently flexible material (or both) such as to enable bending of the cover layer in a corresponding manner on top of the curved carrier layer 3 during the manufacturing process of the mirror. The cover layer 5 may for example be made of a 0,5 mm thick glass layer which is (in view of the elastic modulus of glass being normally around 70 Gpa) sufficiently flexible for bending the glass cover layer 5 on the curved carrier layer 3 having the pixel walls 19 in between. In this respect, it is noted that good results have been achieved with glass having thicknesses of 0,3 mm, 0,4 mm, 0,5 mm, 0,6 mm and 0,7 mm). The skilled person may appreciate that the lower limit of the thickness of the glass is mainly determined by the structural integrity of a thin glass layer. Making the glass layer too thin severely increases the risk of breaking the glass. On the other hand if the glass cover layer 5 is made too thick (thicker than 1 ,0 mm), the glass layer becomes too stiff and bending of the glass without breaking it becomes difficult. At the same time, a glass layer which is too thick and which is bended on top of the glass carrier layer 3 anyway, having the pixel walls 19 in between, may impose too much stress on the pixel walls 19 in the middle of the mirror surface, increasing the risk of damaging the pixel walls.

As suggested above, the cover layer 5 may also be made of a flexible material such as a transparent polymer surface. The advantage of using a polymer surface is that the weight of a polymer surface is often lower, and polymers are generally more flexible than glass. As a result of the polymer molecule strains, the structural integrity of polymer layers is good enough to create a strong cover layer which has a very small thickness. Some polymer layers may be prone to scratching, but it is considered to be within the normal skills of the skilled person to adapt the design for preventing this issue.

In figure 2 a method of creating a curved mirror according to the present invention is schematically illustrated. The curved mirror of the present invention may be created by providing a curved carrier surface 3 on top of which a thin layer of a non-polar liquid 30 (e.g. oil) is added. A thin cover layer 5 is also provided. The thin cover layer 5 is sufficiently flexible for enabling bending of the cover layer 5 on top of the curved carrier layer 3. On the cover layer 5, a plurality of pixel walls 19 is created, such that a plurality of pixels will be defined by the pixel walls 19. When the mirror is finished, these pixels will be closed by the carrier layer 3 and the cover layer 5. During the manufacturing process, the pixel walls 19 are filled with a polar liquid 29, such as glycol, water, or water with a salty solution of suitable kind. The plurality of pixels all have dimensions such that they are sufficiently small for adhering the polar liquid 29 to each pixel keeping the polar liquid 29 in place under influence of the surface tension in the arrangement illustrated in figure 2.

The skilled person will appreciate that the figures 1 through 4 referred to here are schematic figures. In reality, the pixels formed on the surface of the cover layer 5 are much smaller, and the pixel walls have a typical height of an number of tenths of micrometers (e.g. 50 μηι). The cross section of each pixel may be a fraction of a millimeter (0, 1 -0,5mm). These dimensions are mentioned for explanatory purposes only here, and are not meant to be limiting.

In the next step, a middle portion of the cover layer 5 is pressed on top of the curved carrier layer 3, and the sides of the cover layer 5 are forced on the sides of the carrier layer 3 with forces indicated schematically by arrows 52 and 51. As will be appreciated, in order to force the cover layer 5 and to bend it on top of the carrier layer 3, the forces 52 and 51 on the side of the cover layer 5 will be larger than the force 50 required in the middle of the cover layer 5 (if required at all) for suitable bending of the cover layer 5. In the end product, each of the optical cells will be filled with a fraction of a non-polar liquid 30 and a fraction of a polar liquid 29. The volumetric fraction ratio of the non polar liquid 30 to the polar liquid 29 will be (more or less) the same (ideally) for each pixel created this way.

Figure 3 shows another example of a curved mirror according to the present invention. In figure 3, the construction of the curved mirror is almost the same as in the embodiment illustrated in figure 1 , having a cover layer 5, pixel walls 19, electrode layers 6 and 13 and being kept together on the side of the mirror by means of a clamping means 47 and a seal (e.g. glue) 45.

A structural difference between the embodiment of figure 3 in comparison to the embodiment of figure 1 is the fact that the carrier layer is not formed by a thick glass layer such as layer 3, but is instead formed by another thin flexible layer 57 of a suitable material (the same choice of material, and the same choice of thickness, applies to layer 57 as applies to cover layer 5 in figure 1). Underneath the flexible carrier layer 3 there is provided a carrier frame 59. The carrier frame 59 may be made of a light material providing a sufficient structural integrity to the mirror arrangement formed. The advantage of the curved mirror created herewith is that it provides an automatically dimmable curved mirror which has a very low total weight. Keeping the total weight of the mirror low is important when the mirror is for example used in a vehicle (e.g. a car mirror), since this prevents that the mirror is prone to vibrations of the vehicle during driving thereof. Providing a very light mirror enables easy fixing of the mirror to the vehicle in such a manner that it does not vibrate under influence of vibrations caused by driving. Although this is a general advantage of the mirror arrangement according to the present invention, this is a particular advantage of the embodiment of figure 3 since due to the fact that both the cover layer 5 and the carrier layer 3 are made of a thin flexible material, the total weight of the mirror of the embodiment of figure 3 is very small as compared to a conventional dimmable curved mirror arrangement as known from the prior art (e.g. the electrochrome designs). In figure 4a, a typical electrowetting optical cell that may be used in the curved mirror of the present invention is generally indicated with reference numeral 1 , and is situated between adjacent electrowetting optical cells. The electrowetting optical cells formed between the carrier layer 3 and the cover layer 5 of the curved mirror of the present invention may be of a same or similar construction as the electrowetting optical cell illustrated in figure 4. In the electrowetting optical cell 1 , a containment space 25 is present between a carrier layer 3 (or first electrode layer 3) and a cover layer 5 (or second electrode layer 5). The carrier layer 3 is primarily formed of a substrate 1 1 , comprising multiple layers 12, 13 and 14 that will be described below, and a hydrophobic interface surface 10 forming the interface with the containment space 25. The cover layer 5 comprises a superstrate 7 having a hydrophilic interface surface 6. The interface surfaces 6 and 10 could be formed by a suitable coating or layer. In particular, the hydrophilic interface surface 6 may be formed by a coating or layer of indium tin oxide (ITO), because of the transparent optical nature and electric conductivity of ITO. The superstrate 7 and substrate 11 may be formed by any suitable substrate. The superstrate 7 will often be formed by a glass layer, and the substrate 11 may be formed by a glass layer as well.

The different layers of the carrier layer 3 each perform their own function. Carrier layer 3 is (as mentioned) formed by a substrate 1 1 (such as glass), a reflective layer 14, an electrode layer 13 (for example formed of ITO), an electrically isolating layer 12, and the hydrophobic surface layer 10. This hydrophobic surface layer may be formed by a suitable fluoropolymer, such as CYTOP^tm or AF1600^tm. Preferably, the hydrophobic surface layer 10 comprises a small contact angle hysteresis for improving the switchability of the optical cell, i.e. enabling smooth opening and closing of the cell upon switching in the powered up and powered off state. The reflective layer 14 may also act as electrode layer for example when aluminium is used.

Pixel walls 19 are fixedly mounted on the hydrophilic surface interface and electrode layer 6 of the cover layer 5. As a result of the mounting of the pixel walls on the hydrophilic cover layer 5, and due to the physical properties of the hydrophilic surface, a strong mechanical connection between the pixel walls 19 and the hydrophilic surface interface 6 is achieved. This results in a good structural integrity of the pixel walls as mounted on the cover layer 5.

The pixel walls 19, and the carrier and cover layer 3 and 5 respectively, define the containment space 25 of the electrowetting optical cell 1. The containment space 25 is filled with a polar liquid 29 and a non-polar liquid 30. The polar liquid 29 and non-polar liquid 30 are immiscible with each other. In addition, the polar liquid is formed of a substance having molecules with non-zero chemical polarity. The non-polar liquid is formed of a substance having molecules with negligible or very small chemical polarity. As a result, switching of the electrodes in the powered up and powered off state modifies the balance of forces between the non-polar liquid and the polar liquid and the hydrophobic surface, causing these liquids to rearrange suitably for opening and closing the electrowetting optical cell.

The pixel walls 19 are dimensioned such that they span the distance between the cover layer 5 and the carrier layer 3, but are not attached to the carrier layer 5. This way, the pixel walls functionality as spacers between the carrier layer 3 and the cover layer 5. In addition, the pixel walls 19 are also able to prevent spreading of the polar liquid 30 to adjacent pixels, which would be unwanted. The pixel wall not being attached to the carrier layer 3 allows repositioning of the pixel walls 19 with respect to the carrier layer 5. This way bending of the cover layer 3 and carrier layer 5 is enabled, without tension in the form of traction or pressure in the pixel walls 19 being built up.

Figure 4b shows a further embodiment of the electrowetting cell of figure 4a. The pixel walls 19 comprise end faces 34 opposite the hydrophobic surface 10 of the carrier layer 3. Although the embodiments of figure 4a, the pixel walls 19 run all the way through to the hydrophobic surface layer 10, being contiguous thereto, in the embodiment of figure 4b a small slit 32 is present in between the end faces 34 and the hydrophobic surface layer 10 of the carrier layer 3. This enables the non-polar liquid 30 to entrain the slit 32, and to form a small capillary interface (such as interface 33) on the other side of the slit near the edge of the pixel walls 19. The effect of the small capillary interface is that it greatly reduces the amount of light scattering caused by the pixel walls in the electrowetting optical cell. As will be appreciated by the skilled person, light scattering in the electrowetting optical cell 1 is to be prevented as much as possible. This can be achieved by making the surfaces 21 of the pixel wall 19 hydrophobic, although at the same time it is advisable to prevent the pixel walls from becoming too much hydrophobic as this hinders the switching of the electrowetting element/display (due to adhering of the non-polar oil to the pixel walls too strongly). The slit 32 further improves the repositioning of the pixel walls 19 relative to the carrier layer 5.

As shown in figure 4b, to further improve the entrainment of the non-polar liquid 30 into the slit 32, the end faces 34 of the pixel walls 19 may be provided with a hydrophobic surface 35 thus enabling the non-polar liquid 30 to more easily be entrained into slit 32 in the powered state of the electrowetting element 1 and easy return of the non-polar liquid 30 onto the hydrophobic interface surface 10 of the cover layer 3.

Figure 5 schematically illustrates a method of manufacturing a curved mirror arrangement according to the present invention. In figure 5, in step 60, a carrier layer is provided forming the base of the mirror. In step 63, a plurality of pixel walls is created on either a cover layer or the carrier layer. This may be done by means of lithography. Step 665, the spaces defined by the pixel walls 19 are filled with a polar liquid 29. Then in step 667, a non polar liquid 30 is added to the carrier layer and/or the cover layer. After this in step 70, the flexible cover layer is bent on top of the carrier layer 3 having the pixel walls 19 in between, and after bending, the cover layer 5 is fixed to the carrier layer e.g. by means of glue 45 or a mechanical structure 47 such as a frame or clamping means or the like. Then in step 672, the end product is finished such as to provide a curved mirror surface of the present invention which is comprised of two layers having plurality of electrowetting optical cells in between for enabling automatic dimming of the mirror e.g. in case of glare.

Figure 7 provides a schematic overview of an alternative method for manufacturing an mirror having electrowetting elements. In figures 6a - 6c the steps of the method are illustrated.

In step 665 of the method illustrated in figure 7 and 6a, manufacturing is started by providing a cover layer 5 comprised of a superstrate 7 and a second electrode layer 6 having a less hydrophobic surface. The second electrode layer 6 may be provided by a suitable coating, e.g. ITO in view of its optical and electrical properties, which can be made less hydrophobic or hydrophilic using a plasma processing technique with a oxygen (02) processing gas.

In step 667, pixel walls 19 are mounted on the less hydrophobic surface

6 of the cover layer 5 using a suitable technique such as dry film resist lithography (DFR) wherein a photoresist layer is deposited on the hydrophilic surface of layer 6 and which is etched leaving only the pixel walls 19. as a consequence. The pixel walls 19 are created such that they are fixedly mounted on the less hydrophobic surface of the second electrode layer 6. Additionally plasma processing of the cover layer 5 with the pixel walls 19 using a processing gas comprising CF4 can be performed. This renders the pixel walls 19 to be hydrophobic. This is preferably performed only to the end face 34 of the pixel wall 19, prior to etching of the pixel walls, enabling the non-polar liquid to be entrained into the slits 32 to be formed when completing the manufacturing of the electrowetting element. After the pixel walls 19 are formed in step 667, the containment spaces 25 formed on the cover layer 5 are filled in step 668 with a suitable polar liquid 29 and a non-polar liquid 30. Step 668 consists, in the present embodiment, of three separate steps 681 , 683 and 685. In step 681 , the containment spaces formed by means of the pixel walls 19 are filled with the polar liquid 29. Often, the polar liquid 29 will primarily comprise water and/or more soluble organic substances such as glycol and / or methanol.

In step 683, part of the polar liquid 29 is evaporated. Since evaporation takes place equally across the full surface of the polar liquid, after evaporation, the level at which the containment spaces between the pixel walls 19 on the second surface are filled is equal across the surface. Evaporation 683 can be improved by the addition of methanol in the polar liquid 29, which will evaporate more readily than other solvents in the mixture, such that the overall level of the polar liquid 29 will be reduced by a certain amount, for example approximately 25%, after evaporation (the methanol being no longer present in the polar liquid 29).

Figure 6a shows the cover layer 5 comprising the superstrate 7 and the second electrode layer 6 having the less hydrophobic surface. The step 681 of filling is performed by filling the containment spaces 25 completely and increasing the level of the polar liquid 29 to a level above the height of the pixel walls 19. Then, evaporation 683 takes place as schematically illustrated by the arrows 40 above the surface of the polar liquid 29. The level of the polar liquid 29 thereby decreases equally across the surface, to a predetermined level which is schematically illustrated by dotted lines 42. As can be seen, in each containment space 25 of the electrowetting element 1 the level of the polar liquid after evaporation is equal

Subsequently in step 685, the non-polar liquid 30 is added to the containment spaces of the second electrode surface 5. Alternatively, the non-polar liquid 30 may also be added to the surface of the first electrode layer 3, simply by allowing an amount of non-polar liquid 30 to spread across the surface 10 of the carrier layer 3.

After step 685 of filling step 668, the electrowetting element 1 is to be covered with the carrier layer 3 in step 669. Step 669 is illustrated in figure 6b. In the presently described method it is assumed that the non-polar liquid 30 is already filled to a level above the pixel walls of the cover layer 5, as illustrated in figure 6b. A frame 45 running across the sides of the cover layer 5, and comprising an amount of glue or an adhesive or sealing substance, allows the carrier layer 3 to be mounted firmly on top of the cover layer 5, closing the containment spaces. Step 669 of covering the cover layer 5 with the carrier layer 3, comprises the step of pressing the carrier layer 3 slowly on top of the cover layer 5 (step 691), and simultaneously allowing the excess non-polar liquid 30 to be removed from the containment spaces 25 in step 693. This is done by exerting a force primarily on to the mid portion of the carrier layer 3. The forces 51 and 52 on the sides of the carrier layer 3 may be smaller than the force 50 exerted on the mid portion of the carrier layer 3 such as to slightly deform the carrier layer 3 allowing the mid portion of the carrier layer 3 to touch the end faces 34 of the pixel walls 19 on the cover layer 5 earlier than the sides and edges of the carrier layer 3. The excess non-polar liquid 30 in the containment spaces 25 is thereby forced outward to the periphery of the cover layer 5 where it is removed by step 693.

In order to allow the excess non-polar liquid 30 to be removed from the cover layer 5, as illustrated in figure 6c, a frame 55 of the cover layer 5 surrounding the electrowetting elements 1 comprises outlets or channels 58, 59, 60 and 61 in the corners thereof. When the non-polar liquid 30 is pressed outwards towards the periphery of the cover layer 5, it will be pressed through the channels 58-61 formed in the frame 55 prior to fixing the carrier layer 3 to the cover layer 5.

In step 672, while the carrier layer 3 is placed on top of the cover layer 5 and the edges not yet sealed or fixed, i.e. mechanically closed. The electrowetting mirror assembly, the combined carrier layer and cover layer can now be be bent using the forces 50, 51 and 52, whereby the force 50 is opposed to forces 51 and 52. This may be achieved by appropriately supporting the electrowetting mirror at the edges or in a preshaped mould and pressing 50 either on the carrier layer side or on the cover layer side. When pressing, the layers can move relative to each other by virtue of the pixel walls 19 not being attached to the carrier layer 3.

Subsequently, in step 674, the outlets 58-61 in the frame of the electrowetting elements 1 formed are sealed by a suitable substance (reference numeral 45 in figure 1), such as a resin, or mechanically closed (reference numeral 47 in figure 1). In figure 6c the sealing is performed by closing the outlets or channels 58, 59, 60, 61. The electrowetting element 1 according to the present invention is then ready for further processing dependent on the application, and the manufacturing method ends.

As will be appreciated by the skilled person, the present invention may be practised otherwise than as specifically described herein. Obvious modifications to the embodiments disclosed, and specific design choices will be apparent to the skilled reader after reading of the present description. The mirror layer may for example also be provided on the cover layer as well, where the carrier layer is transparent. The scope of the invention is only defined by the appended claims.

Claims

1. Mirror comprising a curved mirror surface,

said mirror surface comprising a curved carrier layer having a specular reflective surface, and said mirror surface further comprising an optically transmissive cover layer, said cover layer being curved and placed in a corresponding manner to said carrier layer for forming a correspondingly curved intermediate space in between said carrier layer and said cover layer, wherein a plurality of electrowetting optical cells is formed in said intermediate space for electrically controlling said optical transmissivity of said mirror, wherein said plurality of electrowetting optical cells is defined by a plurality of pixel walls present in said intermediate space, said pixel walls being attached to the cover layer and extending towards the carrier layer, the pixel walls not being attached to the carrier layer.

2. Mirror according to claim 1 , wherein said cover layer is made of a flexible material.

3. Mirror according to claim 1 or 2, wherein said cover layer is made of glass having a thickness smaller than or equal to 1 ,0 mm.

4. Mirror according to claim 3, wherein said mirror surface has surface dimensions of at least 0.005 m².

5. Mirror according to any of the previous claims, wherein said cover layer is made of a material having a thickness and a corresponding elastic modulus such as to enable a radius of curvature of 0,4-2, 1 m.

6. Mirror according to claim 5, wherein said elastic modulus is smaller than 100 Gpa.

7. Mirror according to any of the previous claims, said mirror further comprising a carrier frame for supporting said carrier layer.

8. Mirror according to claim 7, wherein said carrier frame is shaped such as to enable bending of said carrier layer onto said frame for providing said curved carrier layer, wherein said carrier layer is sufficiently flexible for bending said cover layer onto a carrier frame during manufacturing of said mirror.

9. Mirror according to claim 8, wherein said carrier layer is made of glass having a thickness smaller than or equal to 1.0 mm.

10. Mirror according to any of the previous claims, wherein said carrier layer is made of a material having a thickness and a corresponding elastic modulus such as to enable a radius of curvature of 0,4-2, 1 m.

1 1. Mirror according to claim 10, wherein said elastic modulus is smaller than 100 Gpa.

12. Mirror according to any of the previous claims, wherein said mirror is an exterior or interior vehicle mirror.

13. Method of manufacturing a mirror comprising a curved mirror surface, said method comprising the steps of:

for manufacturing said mirror surface, providing a carrier layer, and providing an optically transmissive cover layer, wherein one of the carrier layer and cover layer is provided with a specular reflective surface;

forming a plurality of pixel walls onto said cover layer for forming a plurality of electrowetting cells, and at least partially filling said electrowetting cells with a polar liquid;

adding a non-polar liquid to said cover layer having the pixel walls formed thereon; and

bending and combining said cover layer with said carrier layer for forming an intermediate space comprising said electrowetting cells between said carrier layer and said cover layer such that the pixel walls are not attached to the opposing the carrier layer.

14. Method according to claim 13, wherein the step of providing a carrier layer comprises providing a curved carrier layer, and wherein the step of bending and combining comprises pressing the cover layer on top of the curved carrier layer in a mid portion of the cover layer and forcing the sides of the cover layer on the sides of the carrier layer.

15. Method according to claim 13, wherein the step of bending and combining comprises placing the carrier layer on top of the cover layer with the pixel walls, and bending the combined carrier layer and cover layer.