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HeatSeal Data Sheet

HeatSeal Reliability - Chemical Test

Test Purpose: To determine the effect of common household cleaners on the switch bodies of membrane switches constructed with a Bergquist HeatSeal spacer and with a pressure sensitive acrylic spacer.

Set Up
Standard 3 x 4 matrix switches 2.6" x 3.0" with 3" tails are used for testing. All switches are constructed one month prior to any testing. Spacers tested are as follows:
1) Bergquist HeatSeal spacer – .008" total thickness (.005" base polyester with .0015" of HeatSeal adhesive on each side).
2) Pressure sensitive acrylic spacer – .009" total thickness (.005" base polyester with .002" of acrylic adhesive on each side).

Pre-testing of all switches is performed by following these steps:
1) 24-hour immersion in a solution of water with .2% by volume of soap added.
2) Insulation resistance readings are then taken on each switch at 100 VDC. A minimum of 1 m? insulation resistance is required for each switch to enter the testing phase.

Solutions
Eight beakers are each filled 3/4 full with a cleaning solution and four drops of green dye. The cleaning solutions are:
A) 409®
B) Fantastik®
C) Dow® Bathroom Cleaner®
D) Lysol® Tub and Tile Cleaner®

Parameters
Samples of each switch type are immersed in each of the four solutions. Each group of parts are then placed in an airtight container, to reduce evaporation, for a period of 180 days at room temperature.

Results (Refer to Figure 1)

• HeatSeal spacer – no visual degradation of the switch occurred in
  any of the switches. There were no measurable changes in the
  insulation resistance of any of the parts (see Figure 2).
• Pressure sensitive acrylic spacer – results varied with each solution:

1) 409 – ingression and dissolving of the PSA adhesive occurred uniformly
around the perimeter of the switch. 1st failure of insulation resistance
occurred on day 20 (Figures 3 and 4).
2) Fantastik – ingression and dissolving occurred as above. Failure
occurred on day 42 (see Figure 5).
3) Dow Bathroom Cleaner – ingression and dissolving occurred as above. Failure occurred on day 56 (Figure 5).
4) Lysol Tub and Tile Cleaner – ingression and dissolving occurred as above. Failure occurred on day 92 (see Figure 5).

FIGURE 2: HeatSeal construction
switch soaked in 409.

FIGURE 3: PSA construction
switch soaked in 409.

FIGURE 4: Close-up of fluid ingression into
key area (PSA switch soaked in 409).

FIGURE 5: PSA construction switches
soaked in other cleaners.

Observations
The ingression and dissolving of the PSA adhesive was consistent around the perimeter, however at various stages some smaller areas of increased ingression would appear. These inconsistencies in ingression advancement point to inconsistency in lamination caused by air voids between the adhesive and circuit layer. These voids enhance the cleaners' ability to ingress.

Summary
This simple test shows that 409, Fantastik, Dow Bathroom Cleaner and Lysol Tub and Tile Cleaner are aggressive towards pressure sensitive acrylic adhesive. These same cleaners have no effect on the Bergquist HeatSeal switch construction.