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Silicon Rubber Keypads

Introduction

Silicone Rubber Keypads:

Silicone Rubber Keypads are manufactured from elastic, nontoxic silicone rubber compounds and are processed from compression or injection molding. The result is an economical and reliable keypad for small, medium and large production runs. Silicone keypads can be integrated with printed circuit boards or flexible circuits and have excellent resistance to temperature and aging.


Uniontech can also integrate your rubber keypad solution with a graphic overlay, printed circuit board (PCB), membrane ½ switch to allow additional flexibility in your design.


BASE MATERIAL:

The natural color of raw silicone rubber material is translucent white. Raw materials are blended with silicone-based color pigments to obtain the color required. Phosphorescent materials can be blended with the base rubber to create a “glow-in-the-dark” effect.

Durometer is one of several ways to indicate the hardness of a material. It defines the material’s resistance to permanent indentation. It is named for instrument maker AlbertF.Shore, who developed a measurement device called a durometer in the 1920s. The term durometer is often used to refer to the measurement, as well as the instrument itself. Durometer is typically used as a measure of hardness in polymers, elastomers and rubbers.


Suggested hardness for silicone rubber keypads is 40 to 60 Shore A depending on your requirements for actuation force, tactile response and life. Higher hardness rubber keypads offer higher actuation force and snap ratio but shorter life. Lower hardness rubber keypads have lower actuation force and snap ratio but longer life. Silicone rubber is available in flame classifications of UL94HB and UL94V0. The flame classification of most silicone rubber used for keypads is UL94HB.


COMPARISON OF SHORE A DUROMETERS:

25 Shore A

Rubber band


40 Shore A

Pencil eraser


55 Shore A

Door Seal


65 Shore A

Tire Tread


100 Shore A

Hard skateboard wheel



Dual Durometer solutions are also available. In this construction, a higher (harder) durometer rubber is used for the key top and a lower (softer) durometer rubber is used for the base.


PRINTING, MOLDING AND HARDCOATING:

Silkscreen printing

Graphics can be applied directly to the keytops of the rubber keypad by screen printing. Multiple colors may be printed, with each color requiring an additional process. The optimum keytop for printing is a flat keytop. However, some curved keytops can also be printed.

Spray paint and laser etch

After the translucent rubber is molded into the keypad shape, the entire top surface of the keypad is spray-painted with one or more colors. A laser is used to etch graphics on the keytops to expose either an underlying layer of paint or the raw rubber. When backlit, light will pass through the translucent rubber and be visible in the etched areas.

Two-shot molding

Similar to Dual Durometer, a keypad can be produced using one color of rubber for the key top and a separate color for the base.

Flow molding

This process allows specific areas of a keypad to be molded with different colored rubber. This provides different base colors without requiring complicated spray-paint techniques. Silk screening is typically done on top of these base colors to provide additional graphics.

Key caps

Premolded hard plastic keytops can be applied to the molded rubber keypad. This provides a hard key feel with the economies and efficiencies of a rubber keypad.

PU coating

Silicone rubber keypads can also be spray-coated with PU resin to provide absolute lifetime abrasion resistance and oil resistance. This important technique has already been successfuly developed.

Hard coating

A screen-printing or spray-painting process is used to apply an additional protective clear silicone ink on the keytops. This increases the abrasion resistance of the printed graphics.

Epoxy coating

Silicone rubber keypads can be coated with a layer of epoxy resin to form a hard top and feel like plastic. The epoxy coating also provides additional abrasion resistance for the printed graphics.

Conductive contacts

Silicone rubber keypads can be co-molded with carbon impregnated silicone pills (carbon pills), gold -plated pills and metal pills according to the application requirements. Due to the low cost of production and acceptable resistance (less than 100 ohms), most rubber keypads are co-molded with carbon pills.


GENERAL SPECIFICATIONS:

Contact resistance

200 ohm maximum with 150 ohm typical


Life

1 million actuations per key


Contact bounce

10 Msec. maximum


Insulation resistance

100 Mohm at 250v DC


Maximum contact rating

24v DC 100mA


Dielectric strength

15 kv/mm


Operation temperature

40 to 150°C


Storage temperature

-50 to 175°C


Travel

0.8mm to 1.2mm typical


Material hardness

50±5 Shore A typical


FEATURES:

• Light pipes

• Abrasion-resistant coating

• Epoxy capped

• Laser etching

• Positive or negative printing

• Fluorosilicone

• Glow-in-the-dark

• Variety of colors

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