U.S. patent application number 11/911818 was filed with the patent office on 2009-05-21 for method of forming mirrors on a conducting substrate.
Invention is credited to John R. Fyson, Christopher B. Rider.
Application Number | 20090127120 11/911818 |
Document ID | / |
Family ID | 34640007 |
Filed Date | 2009-05-21 |
United States Patent
Application |
20090127120 |
Kind Code |
A1 |
Fyson; John R. ; et
al. |
May 21, 2009 |
Method of Forming Mirrors on a Conducting Substrate
Abstract
The invention provides a method of producing a mirror under a
layer of hydrophilic colloid (8) onto a transparent conducting
layer (4) by coating the layer of hydrophilic colloid (8) onto the
conductive substrate (4), placing the coated substrate in a plating
solution (100), and passing current through the solution (100).
Inventors: |
Fyson; John R.; (Hackney,
GB) ; Rider; Christopher B.; (Hardwick, GB) |
Correspondence
Address: |
EASTMAN KODAK COMPANY;PATENT LEGAL STAFF
343 STATE STREET
ROCHESTER
NY
14650-2201
US
|
Family ID: |
34640007 |
Appl. No.: |
11/911818 |
Filed: |
March 13, 2006 |
PCT Filed: |
March 13, 2006 |
PCT NO: |
PCT/GB06/00883 |
371 Date: |
October 18, 2007 |
Current U.S.
Class: |
205/116 |
Current CPC
Class: |
C25D 5/54 20130101; G02B
5/0808 20130101; C25D 7/08 20130101 |
Class at
Publication: |
205/116 |
International
Class: |
C25D 7/08 20060101
C25D007/08 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 23, 2005 |
GB |
0508235.9 |
Claims
1. A method of forming at least one metal layer on a conductive
substrate comprising; coating a layer of hydrophilic colloid onto
the conductive substrate, placing the coated substrate in a plating
solution, and passing current through the solution, thereby forming
the metal layer underneath the layer of hydrophilic colloid.
2. A method as claimed in claim 1 wherein the conductive layer lies
on a flexible support.
3. A method as claimed in claim 1 wherein the conductive substrate
is patterned, all parts of the pattern being at least temporarily
connected.
4. A method as claimed in claim 1, wherein the conductive substrate
is formed of a transparent material.
5. A method as claimed in claim 1, wherein the conductive substrate
is formed of indium tin oxide.
6. A method as claimed in claim 1, wherein the coated substrate is
placed in a silver plating solution.
Description
FIELD OF THE INVENTION
[0001] This invention relates to the field of manufacturing mirrors
on conducting transparent substrates.
BACKGROUND OF THE INVENTION
[0002] Digital pixelated non-emissive displays require conductive
tracks running to the electrodes at every pixel to address the
display. The display can be transparent and lit from behind or rely
on a reflector on one side, using ambient light to view the device.
In the case of displays which are illuminated from behind, the
tracks carrying the current must be substantially transparent over
the viewing area and may be made of an organic conductor such as
polythiophene, a derivative of polythiophene which may be mixed
with other components or an inorganic conductor such as indium tin
oxide (ITO). The track and electrode pattern may be formed in any
suitable manner such as photolithography and then etched with a
suitable etchant. However, these `conductive` materials have a
relatively large resistance when used to form transparent
conductors and this resistance will impair the operation of a
display, especially if the display is large.
[0003] A means of overcoming this is to put a conducting metal over
part of these tracks to reduce the resistance. This reduces the
light passing through the pixels. The area covered by the metal is
kept to a minimum. If the display is backlit, the effect of the
metal conductors can be partially overcome by malting them
reflective. Any light hitting the metal conductor would then be
reflected back into the light box or light guide instead of being
absorbed.
[0004] In the case of a light box, it is necessary that the metal
conductor be highly reflective but not necessarily highly specular.
However, to reduce the thickness of the display, especially for
example in portable high resolution displays, it is common practice
to use edge lighting of a planar waveguide structure which is
designed to leak some of the light from one side of the light-guide
and uniformly illuminate the display. In this case, it is important
that the reflection from the metal conductor be specular to avoid
brealing the waveguiding conditions and causing light leakage that
would reduce both the efficiency and the uniformity of the
backlight. Therefore, a reflective metal conductor with a good
mirror finish on the light box (base/substrate) side would be
advantageous in both cases. This metal is often coated by vacuum
deposition or sputtering and then subsequently etched. This process
is slow and requires the formation of a good vacuum around the
material. This puts a limit on the practical size of rigid
transparent substrates such as glass or requires a rolled up
flexible substrate to be rolled and unrolled within the vacuum.
[0005] U.S. Pat. No. 4,586,988 discloses a means of depositing
metals onto ITO and semi conducting materials using an electrolytic
process. In this process the surface is dipped in a suitable
plating solution and connected to the negative of a DC supply. An
inert anode or one of the metals being plated is placed in the
plating solution. A current is passed through the solution and
metal is plated on the conducting surface. EP 0352721 teaches that
metal plated in this way may not adhere well to the surface. This
document teaches the use of a surfactant and air bubbling to create
a foam to alleviate the problem.
[0006] To make a flexible display or other optical device it would
be useful to use a photographic silver halide imaging system to
write features onto the device. To this end silver halide in a
binder, e.g. gelatin could be coated onto the conducting surface.
This could subsequently be imaged as required. It has been found
relatively easy to coat gelatin and emulsions onto a conducting ITO
layer on glass or flexible PET (Estar.TM.) but more difficult to
coat onto metal due to poor adhesion.
PROBLEM TO BE SOLVED BY THE INVENTION
[0007] The invention aims to provide a method of producing a mirror
under a layer of hydrophilic colloid onto a transparent conducting
layer. The invention further aims to improve the robustness of the
mirror and allow easy coating of a hydrophilic colloid layer on top
of this.
SUMMARY OF THE INVENTION
[0008] According to the present invention there is provided a
method of forming at least one metal layer on a conductive
substrate comprising;
[0009] coating a layer of hydrophilic colloid onto the conductive
substrate,
[0010] placing the coated substrate in a plating solution, and
passing current through the solution, thereby forming the metal
layer underneath the layer of hydrophilic colloid.
ADVANTAGEOUS EFFECT OF THE INVENTION
[0011] The invention has a number of advantages. No vacuum is
required to deposit the metal layer and no high voltages are
required in sputtering. There is no size restriction on the layers
formed. The method of the invention leaves a gelatin/hydrophilic
colloid onto which an emulsion can be coated easily. During
formation of the mirror under the layer of hydrophilic colloid the
conductance can be changed by changing the plating conditions, for
example, the time, voltage, agitation etc..
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The invention will now be described with reference to the
accompanying drawings in which:
[0013] FIG. 1 is a schematic view of the apparatus for performing
the method of the invention;
[0014] FIG. 2 illustrates the structure of the layers of a device
produced by the method according to the invention; and
[0015] FIG. 3 is a graph comparing the properties of a device
manufactured in accordance with the invention with a device
manufacture by conventional means.
DETAILED DESCRIPTION OF THE INVENTION
[0016] FIG. 1 shows the apparatus for performing the method of the
invention. A vessel 60 is partially filled with plating solution
100. The solution may be any suitable plating solution but for a
good silver mirror a solution of a silver complex would be used.
The vessel 60 is provided with a lid 110. This lid may be of
rubber. Three electrodes 20, 30 and 40 are supported by the lid 10
and extend down into the solution 100. Each electrode is connected
to potentiostat 10, by connecting wires.
[0017] Electrode 20 is the cathode. Electrode 20 is formed of a
layer of conductive material 4 coated onto a transparent substrate
2. The substrate 2 may be flexible. The layer of conductive
material may be indium tin oxide. However it will be understood by
those skilled in the art that any suitable material may be used as
the conductive layer, for example an organic conductor such as
polythiophene, a derivative of polythiophene which may be mixed
with other components. The transparent substrate may be, for
example, PET, cellulose triacetate, PEN or glass. These are
examples only. A layer of hydrophilic colloid or gel 8 is coated
above the conductive layer 4. This layer is allowed to dry before
the plating process takes place. Examples of the colloid are
gelatin, polyvinyl pyrolidone (PVP) and polyvinyl alcohol (PVA).
These are examples only and the invention is not limited to such
colloids. Electrode 20 is connected to the potentiostat 10 by a
connecting wire 70.
[0018] Electrode 30 forms a reference electrode. Electrode 30 is
connected to the potentiostat 10 by a connecting wire 80.
[0019] Electrode 40 is a silver foil electrode and forms the anode.
Electrode 40 is connected to the potentiostat 10 by a connecting
wire 90.
[0020] A stirring device 50 is provided within the vessel 60.
[0021] To produce a mirror on a conducting transparent layer
deposited on an insulating transparent support underneath a layer
of a hydrophilic colloid the conducting layer is connected as the
cathode in an electrolytic cell charged with an appropriate plating
solution. Current is passed for such time that a mirror forms
between the transparent conducting coating and the hydrophilic
colloid.
[0022] FIG. 2 illustrates the structure of the mirrored coating
after the method described above. As can be seen a layer of silver
6 has been formed between the transparent conductor 4 and the layer
of hydrophilic colloid 8. Suitable metals other than silver include
nickel, copper and gold. These are examples only.
[0023] An enabling embodiment of the invention is now described.
[0024] All examples used the same sample of indium tin oxide (ITO)
coated flexible polyethylene teraphthalate sheet of about 175
microns thickness. The resistivity was measured to be about 400
Ohms/square. [0025] Four samples of ITO coating were prepared:
[0026] i) no further treatment [0027] ii) 10% gelatin, with 0.1%
Triton X-100 as coating aid, blade coated onto the ITO layer to a
wet thickness of 80 microns giving a laydown of 8 g/m2 gelatin.
[0028] iii) 10% gelatin to which formaldehyde solution (formalin)
was added to give a solution concentration of 0.04% was blade
coated as in ii). This coating was allowed to stand at 20.degree.
C. overnight before use. This gives a hardened coating. [0029] iv)
as in iii) but with 0.4% formaldehyde added. This gave a `harder`
coating.
[0030] A standard 3-electrode electrochemical cell was set up as
shown in FIG. 1. A three-electrode arrangement was used to keep
track of the voltage on the working electrode, 20 and the current
flowing between the working electrode 20 and auxiliary electrode
40.
[0031] A 10.times.50 mm strip of ITO coating, supported by a rubber
lid, 110, was connected with a crocodile clip (not shown), squashed
together to ensure good contact with the ITO through any coating,
to a potentiostat (Bruker.TM.) via a wire, 70, as the working
electrode. A length of 20 mm of this coating was immersed in the
plating liquid, 100, in the beaker, 60. Similarly a calomel
reference (Corning.TM.) electrode, 30, supported by the rubber lid,
110, was connected directly via its connecting wire, 80, to the
potentiostat, 10, and was allowed to dip in the plating solution,
100, the depth being unimportant. A 20.times.100 mm silver foil
electrode was connected as the auxiliary electrode, again supported
by the rubber lid, 110, via a crocodile clip (not shown) and wire,
80, to the potentiostat, 10. The potentiostat, 10, was set up to
deliver constant voltage, but this was adjusted to maintain a
more-or-less constant desired current, where possible. The plating
solution, 100, was stirred by means of an external magnetic stirrer
coupled through a stirrer bar, 50. [0032] The plating solution was
as follows:
TABLE-US-00001 [0032] ammonium thiosulfate 0.02 molar sodium
sulfite 0.01 molar silver chloride 0.01 molar
[0033] The current was set as 1 mA (50 .mu.A/mm.sup.2). The average
voltage applied to the electrode was recorded. After 10 minutes the
current flowing through the cell was switched off, the now plated
ITO coating removed from the cell and washed under the tap with
water and then allowed to dry at room temperature. The mirror was
looked at through the transparent base and its quality determined
by visual observation. Its robustness was determined by rubbing
gently with a finger. [0034] The following table is a summary of
the results:
TABLE-US-00002 [0034] Exp ID ITO voltage Mirror quality Effect of
gentle rubbing i (comp) 1.09 good mirror rubbed off ii (inv.) 1.20
excellent mirror remained iii (inv.) 1.22 excellent mirror remained
iv (inv.) 1.24 excellent mirror remained
[0035] This experiment demonstrated that a mirror, a good
reflective surface when viewed through the base, could be made by
electrolysis through a gel layer that may or may not be hardened
onto a conductive layer on a transparent support. The mirror formed
in this way was as good if not better than one formed without the
gel. The mirror under the gel was also robust to abrasion.
[0036] To test to see if gel could be coated onto these samples a
layer of gel was coated on to these using the following
technique.
[0037] The samples obtained above were taped to a coating block
covering up the smallest area of the mirror possible. The tape was
80 micron thick. This was used as the edge rails for a coating
knife (glass slide). Onto the sample was coated the same gelatin
solution as used in sample ii) described above. The coatings were
allowed to dry. The gelatin peeled off the sample without gel cover
(sample i described above) but not from the other samples.
[0038] This demonstrates that further layers of gelatin can be
coated on top of mirrors grown under gelatin with no added
treatment.
[0039] The experiment was repeated with coatings i and ii using a
larger area of 30.times.30 mm in the plating solution and using the
same current density of 50 .mu.A/mm.sup.2. The specular
reflectivity at different wavelengths was measured at different
wave lengths. FIG. 3 shows the results. The reflectivity of the
mirror formed under gelatin is more colour neutral and has a larger
area under the curve indicating the overall specular reflectance is
greater.
[0040] The invention has been described in detail with reference to
preferred embodiments thereof. It will be understood by those
skilled in the art that variations and modifications can be
effected within the scope of the invention.
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