Keyboard Switch Assembly With Multilayer, Coextensive Contactor Means

Abstract

A keyboard structure which includes a circuit board or the like having a plurality of contacts, an insulator layer having a plurality of holes therethrough, said holes positioned above said board to expose said contacts, composite means comprising an electrically non-conductive elastomeric layer having adhered thereto and covering a major portion of one side thereof, a thin flexible electrically conductive non-selfsupporting and non-elastomeric plastic layer having electrically conductive particles dispersed therethrough, and means for pushing the non-conductive layer and the conductive layer through said holes to make electrical contact with contacts.

Description

BACKGROUND OF THE DISCLOSURE

This invention is directed to a new and improved keyboard structure for converting key depression to a coded electrical output and is more particularly directed to a new and improved composite electrical contactor means.

The present invention differs from the keyboard structures of the prior art such as shown in U.S. Pat. Nos. 3,705,276, and 3,699,294 which discloses a single relatively thick layer contactor of elastomeric material filled with electrically conductive particles, e.g., carbon, silver, etc., by providing a composite contactor of a thicker layer elastomeric, i.e., unfilled and non-electrically conductive, supporting a much thinner layer or coating of an electrically conductive flexible non-elastomeric conductive plastic.

The present invention provides substantial cost savings in comparison with the aforementioned prior art keyboard contactors with cost savings running 50 percent and more, while at the same time providing a very useful contactor for a keyboard.

The present invention also differs from other prior art keyboards which uses a non-conductive layer of plastic or elastomer plated with a layer of metal. Again the present invention provides substantial cost savings over this prior art with material cost savings again estimated to run 50 percent and more.

While these cost savings may not seem impressive in themselves, when one considers of the entire keyboard, it must be remembered that the keyboards of this invention find substantial utility in the consumer calculator market in which prices at this time are dropping rapidly.

Accordingly, when calculator manufacturers are looking for cost reductions, a keyboard manufacturer to remain competitive must also constantly pursue developments which can keep it competitive.

This invention provides one such cost saving development and permits a keyboard manufacturer to remain competitive in a market in which end product retail prices are decreasing rapidly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a keyboard according to the invention;

FIG. 2 is a sectional view taken along line 2--2 of FIG. 1;

FIG. 3 is a sectional view taken along line 3--3 of FIG. 1;

FIG. 4 is a bottom view of the composite member;

FIG. 5 is an enlarged side view of the composite member; and

FIG. 6 illustrates in cross-section a button shown as a key.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference should now be had to FIGS. 1-5 for a description of the preferred embodiment of the disclosure. The keyboard comprises a frame 10 preferably of insulator material, more preferably of a plastic, e.g., A.B.S. (a high impact polystyrene) or polyethylene. The frame 10 is provided with a plurality of divider members 11 which form the walls of windows 12 extending through the frame 10.

The underside of the frame includes a plurality of rods 13 (preferably formed at the same time as the frame, i.e., by molding (see FIG. 2) which extend downwardly as shown in FIG. 3. Reference may also be hade to U.S. Pat. No. 3,721,778 for a further description of the frame, rods, the construction of a keyboard.

The rods 13 may be softened by heat to form heads 13a to hold the keyboard assembly together as shown in FIG. 3. Alternatively, the rods may be threaded and nuts may be used to hold the keyboard assembly together.

Positioned directly below the frame member 11 is a thin plastic insulator layer 14, e.g., of Mylar which has indicia applied thereto. Instead of the layer 14 with indicia which functions as keys of the keyboard, buttons having indicia thereon may also be used as keys such as shown in U.S. Pat. No. 3,721,778 or U.S. Pat. application Ser. No. 297,721 filed Oct. 16, 1972 now U.S. Pat. No. 3,780,237 and Ser. No. 297,636 filed Oct. 16, 1972 now U.S. Pat. No. 3,773,998 or as shown in FIG. 6.

Positioned below the layer 14 is a composite electrical contactor 15 which comprises a non-electrically conductive elastomeric layer 15a supporting and having coupled or adhered (by adhesion e.g., an adhesive) thereto a thin non-selfsupporting and non-elastomeric flexible electrically conductive plastic layer 15b.

The elastomeric layer 15a may comprise any of the well known elastomeric, resilient materials such as silicone rubber or fluoro silicone rubber, nitrile rubber, natural rubber etc.

The flexible non-elastomeric electrically conductive plastic layer 15b comprises non-elastomeric plastics such as polyamides (e.g., Versalon 1140, polyamide adhesion resin by General Mills), polycarbonates (e.g., Lexan by General Electric) polyester (e.g., Mylar), epoxy (CORVEL by Polymer Corp.), polyacetate, polysterene etc., unmodified or modified if needed by a plastisizer to obtain the desired flexibility to permit the layer 15 to flex with the layer 15a and not separate or break away therefrom after continuous prolonged use.

The layer 15b also contains electrically conductive particles dispersed therethrough such as silver particles, carbon particles or other well known conductive particles such as shown in U.S. Pat. No. 3,140,342 and No. 3,576,387.

The amount of electrical particles may vary with particles in the amount of 20 to 40 percent volume being preferred, although in this application the amount may vary over a wide range, e.g., 10 to 80 percent volume percent.

In the preferred embodiment the layer 15a is preferably of a thickness t.sub.a of between 5 to 200 mils with 5 to 100 mils being more preferred and 20 to 50 mils being most preferred. The layer 15b is preferably of thickness t.sub.b of between 5 microns (0.197 mil) to 2.0 mils with a thickness of 10 microns (0.394 mil) to 25 microns (0.984 mil) being more preferred and a thickness of 10 microns (0.394 mil) to 20 microns (0.788 mil) being most preferred (about 25.4 microns = 1 mil).

In the preferred embodiment the composite contactor is constructed using a nitrile rubber layer 15a made by combining Hycar 1042 (NBR) (B. F. Goodrich), 100 parts by weight with zinc oxide 1 part by weight, hydrated silica (HI-SIL215), 40 parts by weight, dicumyl peroxide 5 parts by weight and then curing.

The layer 15b was made by mixing about 63 percent by volume of Versalon 1140 with 37 percent by volume of silflake 135, and then coating it on the layer 15a after it is formed e.g., by using an artists air brush. Solvents such as toluene and 1-propanol as in Example 7 may be added to the Versalon 1140 and Silflake 135 such as shown in U.S. Pat. No. 3,576,387 may be added to permit easy spraying or coating e.g., by a knife. The solvents are then permitted to evaporate in air.

The composite contactor 15 is positioned over an insulator or separator plastic layer 16 e.g., of Mylar having a plurality of windows 16a extending therethrough in alignment with windows 12. with the layer 15b directly over the windows 16a. See U.S. Pat. Nos. 3,699,294 and 3,705,276 for a further description of the separator layer.

The rods 13a also extend through holes 16b in layer 16 to locate the layer 16 within the frame 10. Below the layer 16 is a typical circuit board 16 e.g., of Bakelite having a plurality of electrically conductive contacts, contact elements or pathways formed thereon. See U.S. Pat. Nos. 3,705,276 and No. 3,721,778 for an illustration of various possible pathways.

The circuit pattern may be formed conventionally from copper which is etched or by the spraying of conductive paint.

The electrical pathways are at least in part aligned with the windows 16a so that the application of pressure by a finger to the key or force applying layer 14 can push portions of the composite layer 15 through the windows 16a and particular layer 15b against the pathways. In this manner electrical contact is made between the layer 15b and the pathways 18.

Where the force is withdrawn, the resiliency of the elastomeric layer 15a causes it to withdraw pulling the flexible non-elastomeric layer 15b back with it and breaking electrical contact between layer 15b and the pathways. Most preferably the thickness of layer 15a is at least 5 times that of layer 15b.

In order to make electrical contact with the electrically conductive layer 15b as well as the pathways 18, there are provided pins 20a and 20b retained with connector supports 19a and 19b respectively with pin 20a in contact with layer 15b and pin 20b in contact with pathway 18.

It should be understood that while preferred dimensions are given for the layers 15a and 15b, functionally the thickness of the layer 15a should be sufficient to provide the elasticity to pull the layer 15b back with after being depressed while the layer 15b should be as thin as physically possible to save as much money as possible so long as it provides good electrical conductivity for use as a contactor.

The volume resistivity of the conductive layer is preferably less than 10 ohm cm., more preferably less than 1 ohm cm., and most preferably less than 0.5 ohm cm. As used herein the term non-selfsupporting means that the layer unless backed as shown would curl up and not be useful for its intended purpose i.e., as a keyboard contactor layer for covering a plurality of openings in the insulator therebelow.

In FIG. 6 there is shown a button 30 preferably of non-conductive plastic supported in a redesigned frame 31 and held in its undepressed condition by a spring 32. The remainder of the keyboard members are identical with that of FIGS. 1-5 and are so numbered. Upon depression of the key 30 by a finger, the conductive layer 15b is brought into contact with the pathway 18.

Claims

We claim:

1. A keyboard assembly including in combination an electrical circuit board having contact elements, a separator insulator layer positioned over said circuit board, said separator insulator layer having openings registerable with portions of said contact elements, the improvement being a composite contactor positioned over said separator layer for movement through each of said openings to contact said contact elements said contactor comprising a nonconductive resilient, flexible, elastomeric layer supporting an electrically conductive non-elastomeric and non-selfsupporting flexible plastic layer adhered thereto and coextensive therewith for movement therewith, said non-conductive layer being

greater in thickness than said conductive layer and said conductive layer having a volume resistivity of about or less than 10 ohm centimeters, and said conductive layer being positioned directly over said openings.

2. A keyboard assembly according to claim 1 in which the conductive layer is less than 1.969 mil in thickness and in which the elastomeric layer is between 5 to 200 mils in thickness.

3. A keyboard assembly according to claim 2 in which the conductive layer has silver particles dispersed therethrough.

4. In a keyboard according to claim 1 in which the conductive layer is 0.197 mil to 1.0 mils in thickness.

5. In a keyboard according to claim 4 in which the elastomeric layer is 5 to 200 mils in thickness.

6. In a keyboard according to claim 1 in which the conductive layer is of a lesser thickness than the non-conductive elastomeric layer with the elastomeric layer being of a thickness sufficient and at least about 5 times that of the conductive layer to provide the elasticity to pull the conductive layer back with it after being depressed and the conductive layer being thick enough to provide electrical conductivity.

7. In a keyboard according to claim 6 in which the volume resistivity is less than 10 ohm cm.

8. In a keyboard according to claim 7 in which the volume resistivity is less than 1 ohm cm.

9. In a keyboard according to claim 8 in which the volume resistivity is less than 0.5 ohm cm.

10. In a keyboard according to claim 1 said conductive plastic layer comprises a plastic binder and electrically conductive particles dispersed therethrough.

11. In a keyboard which includes an insulator board having circuit pathways thereon, insulator means having a plurality of windows therethrough in alignment with selected portions of the pathways, composite contactor means positioned on the insulator layer and covering said windows of said insulator layer, said contactor means comprising an elastomeric layer having a thinner, flexible non-elastomeric electrically conductive plastic layer physically adhered thereto and coextensive therewith, said conductive layer positioned over at least one of said windows, and pressure application means for forcing said composite contactor through said windows to cause said conductive layer to electrically contact portions of said pathways, said elastomeric layer being thick enough to keep said conductive layer away from said pathway portions in the absence of pressure applied to pressure application means and for pulling said conductive layer away with it from said pathways after application of pressure to said pressure application means, and said conductive layer being thick enough to provide electrical conductivity while not being so inflexible to separate from the elastomer upon being flexed in continuous use.

12. In a keyboard according to claim 11 in which the conductive layer is 5 to 100 microns in thickness.

13. In a keyboard according to claim 12 in which the elastomeric layer is 10 to 100 mils in thickness.

14. In a keyboard according to claim 11 in which the conductive layer is of a thickness less than 1 mil.

15. In a keyboard according to claim 14 in which the conductive layer is of a thickness less than 0.788 mil.

16. In a keyboard according to claim 4 in which the conductive layer comprises polyamide adhesive resin having silver particles dispersed therein.

17. In a keyboard according to claim 4 in which said conductive plastic layer comprises a plastic binder and electrically conductive particles dispersed therethrough.