CA1305541C

CA1305541C - White touch pads for capacitive touch control panels

Info

Publication number: CA1305541C
Application number: CA000586012A
Authority: CA
Inventors: John Schultz Jr.
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1988-01-04
Filing date: 1988-12-15
Publication date: 1992-07-21
Anticipated expiration: 2009-07-21
Also published as: IT1228600B; IT8919011A0; US4855550A; FR2625632A1; GB2213597B; GB8900021D0; GB2213597A; JPH01246736A; FR2625632B1; DE3844392A1

Abstract

WHITE TOUCH PADS FOR CAPACITIVE TOUCH CONTROL PANELS

ABSTRACT OF THE DISCLOSURE
A capacitive touch pad assembly which provides a touch control panel for an appliance with white touch pad appearance. A thin dielectric substrate has an outer touch electrode of a relatively dark-colored conductive material deposited on its outer surface and a pair of spatially separated inner electrodes formed on the inner surface of the dielectric layer for connecting to the control circuitry. To achieve a light-colored appearance for the touch pads, a layer of relatively light-colored non-conductive decorative material is applied to the outer surface overlaying the electrode to hide its dark color except for a small exposed area of the electrode which defines a symbol relating to the function of the pad. The exposed area may be covered by a second layer of dark conductive material or left exposed.
The symbol enables direct human body member contact with the outer electrode.

Description

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BACKGROUND OF THE INVENTION
.__ The present invention relates to capacit~ve touch pads and more particularly 'tQ novel touch pad construction enabling the ple3sing appearance of light-colored touch pids for an applianse control panel.
Use of glass capacitiYe touch control pane~s for appliance controls ls well known. However, such control panels typitally employ touch pads which are relatively dark in ~olor. Current trends ln kitchen design have created a need for a glass capacitance touch control panel with white touch pads with black lettering a11d/Or symbols. The control par,el touch pads must meet the normal standards Ç~ ~or such panels~fti~at the pad nmst be conductive, ~st be of at least a minimum size, and must be resistant to abrasion and to corrosive food stuffs. Such pads are normally applied by ;creen printing a ceramic enamel to which a metallic powder has been added.
The printed film is then fired to form a conductive glassy film. The conventional approach providss satisfactory results for relatively dark-colored pads. However, the necessary addition of commonly used conductive metallic components to a white enamel darkens the enamel resulting in an off-white or gray color. Use of almost pure silver as the metallic component results in 2 reasonably satisfactory white color; howe~er, it lacks other required properties and is subject to tarnishing on exposure to the air.
In view of the aforementioned shortcomings of the pr~or art, a reed exists for a means of providing capacitivE touch control panel havi ng whi te touch pads .
013JECT OF THE ~NVENTION
It is therefore a primary object of the present invention to provide a glass capacitance touch control panel for an appl~arce featuring white tollch pads with black lettering.

_l _ ~k PATENT 9D-MA-17064 - Schultz, Jr.
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SUMMARY ûF THE INVENTION
A capacitive touch pad Asse~ly in accordance tlrith the present invention has a thin dielectric layer or substrate having an outer touch electrode of a relatively dark-colored conductive material deposited on its outer surface and a pair of spatially separated inner electrodes for0ed on its inner surface for connecting to the control circuitry. To achie~le a light-colored appearance for the touch pads, a layer of relatively light-colored non-conductive decorative material ts applied to the outer surface overlaying the touch electrode to hide its dark color except for a small exposed area of the electrode whicll may define a symbol relating to ehe function nf the Pad. The exposed area provides the means for direct human body member contact with the outer touch electrode.
Preferably the outer electrode is formed by screen printing or otherwise depositing a screena91e paste comprising a mixture of finely ground black glass particles~,~ a conductive metallic powder, in an organic medium, ~hich is covered w;th a layer of non-conductive white ceramic enamel except for the small exposed area. The exposed area provides the black lettering or other synbol on the touch pad.
In accordance with another aspect of the invention, the layer of decorative l~laterial may be applied in ~ultiple coats to provide adequate coverage to hide the underlying dark electrode. Surh Inultiple eoats if not aligned precisely may result in an unsightly uneven border for the exposed area. To relieve the alignment ~roblem and enhance the appearance~ a second layer of dark conductive material covers the exposed area aad the immediately adjacent portions of the decorative layer thereby defining a slightly enlarged version of the sy~rbol deflned by the exposed area.

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In accordance with yet another aspect o~ the invention, the outer el.ctrode is formed of a gray or silver material to facilitate one coat coverage by the decorative layer. A layer of black conductive material covers the exposed area and the immediately adjacent portions of the decorative layer again defining a slightly enlarged version of the symbol defined by the exposed area.
BRIEF DESCRIPTION OF TXE DRAWIl!~GS
While the novel features of the invention are set forth with particularity in the appended claims, the invention, both as to organization and content, will be better understood and appreciated from the following detailed description taken in conjunction with the drawings in which:
FIGS. lA and lB are respectively top and side views of a portion of a touch conkrol panel illustrating a pr.ior art touch pad construction;
FIGS. 2A is a plan view of a capacitive touch control panel for a range surface unit;
FIG. 2B is a bottom view of a portion of the control panel of FIG. 2A showing one of the control panel touch pads;
FIG. 3A is a plan view of the touch pad of FIG. 2B;
FIG. 3B is a sectional view of the touch pad of FIG. 3A taken along section lines 3B-3B;
FIG. 4A is a plan view of an alternative touch pad construction for the touch pad of FIG. 2B; and FIG. 4B is a sectional view of a touch pad of FIG.
4A taken along section lines 4B-4B.
DETAILlE~D DESCRIPTION
Referring initially to FIGS. lA and lB, a prior art capacitive touch pad construction designated generally 10 includes a dielectric substrate 12; a touch electrode 14 of electrically conductive material, fabricated on the outer facing surface 12A of substrate 12, having a preselected boundary of generally rectangular shape; and pair of inner '~

PATENT - 9D-MA-17064 - Schultz, Jr.

electrodes 16 and 18 commonly referred to as a transmitting electrode and a receiving electrode respecSively, fabricated ~n the inner surface 12B of substrat~ 12 underlying and substantially ~ithin ~he boundary of electrode 14. The transmitting and receiving electrDdes are adavted for connection to ~e71-known electronic control circuitry /not shown for simplicity). Such circuitry typically is configured to dri~e the transmitting electrode with a scanning pulse and to recogni~e a change 1n the amplitude of that pulse at ~he receiving electrode as the effective series coupling impedance bet~een transmitting and receiving ~lectrodes varies when touch electrode 14 is contacted by a human body member.
As described in the Background discussion such prior art touch pdd assemblies feature dark-colored touch pads because the addition of metallic powder to the enamel which is deposited on the substrate to form the pad electrodes inherently darkens the enamel. Thus, there are no known conductive enamels which meet both the whiteness requ~rement and possess the aforementioned physical and electr;cal characteristics required for touch pads for an appllance control panel.
The present invention overcomes the aforementioned deficiences of the prior art in accordance with the present inYentiOn by pro~iding a capacitive touch pad assem~y for an appliance control Panel which is relatiYely light, preferably white, in color.
An illustrative appliance control panel 20 for a range cooktop is shown in Fig. 2A. Control panel 20 is a capacitive touch control panel with an ON/OFF touch pad 22, touch pads 24 for selecting low, medium and high ~ower settings for the surface unit, and slew touch pads 26A and 26B for slewing the power setting selection up and down resFecSively. Pads 22~ 24 and 26A ~ H ~are formed on a dielectric substrate 27 preferab~y of t~pered glass. Nsrmally in control panel PATENT - 9D-MA-17064 - Schultz, Jr.
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applications the inner surface of the glass is coated ~ith an opaque decorative film prior to ~pplication of the inner electrodes. This filw may be a ceramic enamel or an organic material. In ~he panel of the illustrative embodiment a rectangular port;on of the glass is not covered by ~he opaque film to provide a viewing window 28 for underlying display elements ~hich may be vacuum ~ uorescent devices or LEDs or other elements suitable for providing a Yisual indication of the selected power setting for the surface unit.
In control panel 20, each of the touch pads is a relatively light color, preferably ~hite. The triangular slew symbol on pads 26A
and 26B and the lettering on pads 22 and 24 is a relatively dark color, preferably black.
As w~ll be described hereinafter in greater detail with respect to pad 26B, the various function indicating sy~bols on the pads are defined by screen printing the white enamel decorative finish over the black electrode using a drop out lettering technique such that the exposed area of ~he electrode defines the symbols which may be letters or other indicia for identifying the function of the pad to the user.
Referring now to Figs. 2B~ 3A and 3B, the constructlon of slew touch pad 2fiB will be described in greater detail. It is to be understood that the other touch pads are similarly constructed varying only in ~he shape of the symbol defining exposed area. Fig. 2B shows a portion of the inner s~de of control panel 20 contdining touch Pad 26L. The inner electrodes 30 and 32 for touch pad 268 are fabricated on the inner surface of substrate 27 underlylng and within the boundary of outer electrode 34 in a conventional manner such as by by screen printing a cond~ctive metallic paste on ~he glass in the desir~d configuration. Leads 30A and 32A extend from electrodes 30 and 32 respectively for connection with external electronic control circuitry (not shown)~

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9D~MA-17064 FIG. 3A is a top view of touch pad 26B. FIG. 3B is a sectional view of the portion of control panel 20 shown in FIG. 3A taken alony lines 3B-3B, showing the electrodes 30, 32 and 34 together with the layer of re:Latively light-colored decorative material 36 which overlays electrode 34except for an exposed area 38 which def:ines the triangular "slew" symbol. In FIGS. 3A and 3B, the leads from electrodes 30 and 32 are not shown for simplicity and clarity; however, it will be appreciated that in practice leads would be employed as shown in FIG. 2B to connect the inner electrode pair to appropriate electronic circuitry for interfacing the key pad with the appliance control. In the illustrative embodiment the light-colored material is a white ceramic enamel. It will be appreciated that the thicknesses of electrodes 30, 32 and 34 and non-conductive decorative layer 36 have been grossly exaggerated for purposes of illustration and are not necessarily to scale relative to the thickness of the substrate or relative to each other. In addition in the interest of simplicity and since it is not a part of the present invention, the thin opaque decorative film on the inner surface of substrata 27 is not shown in FIG. 3B. In practice the inner electrodes 32 and 34 are applied over the opaque film.
The material for electrode 34 is a relatively dark-colored conductive material preferably comprising a mixture of finely ground black glass, a metallic component such as siIver, palladium, or other suitably conductive material alement in the form of a fine powder or metallo-organic compound such as a resinate, with an organic medium and other ingredients conventional in nature, in the form of a screenable paste. This paste is deposited on the outer surface of substrate 22 by screen printing. The print is dried then fired to 600-700C to remove organic components and fuse the paste resulting in a conductive ', '~

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film pad. A layer of light-rolored non-conductive preferably ~hite ceramic enamel is then applied, also by screen printing, to cover electrode 34 except for exposed area 38 fcrmed by a drop-out lettering technique to define the desired symbol which for pad ~6B is a triangle. The lettering on the other pads is similarly provided. This enamel layer is then dried and fired.
By this arrangement a light-colored pad area with black lettering is provided for a pleasing appearance. The black lettering also contributes functionally by enabling direct contact between a hum~n body part and the touch elec~rode via ~he exposed symbol area for 5Wi tch actuation.
In some instances a ~ingle coat of white enamel may not sufficiently hide the underlying black electrode causing the resulting touch pad to have a grayish appearance. A second coat of white enamel could be applied; however, precise alignment of it for sharp letterin~
would be diff;cult. The alternate embodiment illustrated in Flgs. 4A
and 4B overcomes this problem.
In the emhodim~nts to be described with reference to Figs. 4A
and 4B, the relatively dark outer electrode 34' and inner electrodes 30 and 32 are deposited on substrate 22 and a white enamel layer 36' is applied as hereinbefore described with reference to Figs. 3A and 3B, except that, for reasons ~hich ~ill be herein~fter apparent, the exposed area 38' left uncovered by the layer of white enamel 36' is preferably somewhat smaller than that desired for the symbol with respect to appearance cDnsiderations. The white layer 36' may be applied in multiple coats to provide the desired hiding of the black electrode. HoNever, it is very diff;cult to control alignmen~ with sufficient precision to retain sharp symbol definition with m~ltiple coats. To ccmpensate for such multiple co~t alignment problems, a sf~
PATENT- 9D-MA-17064 - Schultz, Jr.

~econd layer 40 of black conductive ~aterial is applied to the exposed area. Actually the pa~tern ~r screen printing of this second black layer is slightly larger than the exposed area to overlap adjacent portions of the white layer. This overlap provides alignment compensation for the sy~bol with the underlying s~nrbol and also covers the edges of the exposed area which may have been blurred by the application of 0ultiple coats. Touching the sy7bol deffned by layer 40 will actuate the touch pad just as in the en~odiment of Figs. 3A and 3B.
As yet another alternative using the basic fabrication technique just described with reference to Figs. 4A and 4B, electrode 34' may be formed using an electrode material having a lighter grayish color such as with greater silver content. Since the electrode is ultimately completely sealed by additionat layers, tarnishing is not a concern. This lighter color enables a sfngle coat of white enamel to more reliably hide the still relatively dark electrode. However, the resulting exposed area is gray rather than the desired black. This is remedied by again applying layer 40 of black conduc~fve naterial to the exposed pattern. The overlap of the enlarged pattern allows for some mi sal i gnment duri ng appl i cati on O
In both the black electrode and gray electrode embodiments just described, the enlarged black s~bol proYides electrical continuity from the point of contact with the human body n~ember to the underlying electrode serving as a capacitor plate, enabling touch pad actuation by touching the sy0bol.
While specific enbodi~llents of the inven~ion have been fllustrated and described herein, it ts realized that numerous modifications and chanses may occur to those skflled in the art. It is therefore to be understood that the appended claims are fntended ~o oover all such modifications arld chan~es which fall within the trl~e spirit and scope of the invention.

Claims

1. A capacitive touch pad assembly comprising:
a layer of dielectric material having an outer surface and an inner surface;
an outer electrode comprising a first thin layer of relatively dark-colored conductive material fabricated on said outer surface to be responsive to contact with a human body member;
a pair of spatially separated inner electrodes fabricated on said inner surface substantially within the boundaries of said outer electrode; said inner electrodes being adapted for electrical contact with external electronic control circuitry;
a layer of relatively light-colored non-conductive decorative material applied to said outer surface substantially overlaying said outer electrode, surrounding a small exposed area of said outer electrode, said exposed area defining a symbol to be touched;
whereby said pad provides a pleasing light-colored appearance with a contrasting dark symbol, said symbol providing the means for direct human body member contact with said outer electrode.

2. The touch pad assembly of claim 1 wherein said relatively dark conductive material is a screenable paste comprising a mixture of finely ground black glass, a conductive metallic component and an organic medium.

3. The touch pad assembly of claim 2 wherein said relatively light-colored non-conductive decorative material comprises a white ceramic enamel.

4. The touch pad assembly of claim 1 wherein said symbol identifies the function of said touch pad.

5. A capacitive touch pad assembly comprising:
a layer of dielectric material having an outer surface and an inner surface;
a first outer electrode comprising a thin layer of relatively dark-colored conductive material fabricated on said outer surface to be responsive to contact with a human body member;
a pair of spatially separated inner electrodes fabricated on said inner surface underlying said first electrode and adapted for electrical connection with external electronic circuitry;
a thin layer of relatively light-colored non-conductive decorative material deposited on said outer surface overlying said outer electrode defining an uncovered area of said outer electrode; and a second outer electrode comprising a second thin layer of relatively dark-colored conductive material deposited on said uncovered area and that portion of said thin decorative layer adjacent said uncovered area, said second layer defining a symbol to be touched;
whereby said pad provides a pleasing light-colored appearance with a contrasting dark symbol, said symbol being exposed for direct contact with a human body member and in good electrical contact with said outer electrode.

6. The touch pad assembly of claim 5 wherein said relatively dark conductive material is a screenable paste comprising a mixture of finely ground black glass, a conductive metallic component and an organic medium.

7. The touch pad assembly of claim 6 wherein said relatively light-colored non-conductive decorative material comprises a white ceramic enamel.