HeatSeal® Reliability – Chemical Test
Test Purpose: To determine the effect of common household cleaners on the switch bodies of membrane switches constructed with a GGI HeatSeal® spacer and with a pressure sensitive acrylic spacer.
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) GGI 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.
Eight beakers are each filled 3/4 full with a cleaning solution and four drops of green dye. The cleaning solutions are:
C) Dow® Bathroom Cleaner®
D) Lysol® Tub and Tile Cleaner®
Samples of each switch type are immersed in each of the four solutions. Each group of parts is 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. The failure occurred on day 42 (see Figure 5).
3) Dow Bathroom Cleaner – ingression and dissolving occurred as above. A failure occurred on day 56 (Figure 5).
4) Lysol Tub and Tile Cleaner – ingression and dissolving occurred as above. A 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 the key area (PSA switch soaked in 409).
FIGURE 5: PSA construction switches soaked in other cleaners.
The ingression and dissolving of the PSA adhesive were 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.
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 GGI HeatSeal® switch construction.