Testing Methods- Weather Resistance

The water or water vapour transmission rate is an important property when the tape is to be used to seal against water or moisture. The test involves filling an aluminium cup with calcium chloride, which is very hygroscopic (absorbs water), and then applying the tape to be tested at the opening of the cup, completely sealing it. The specimen is weighed and then put either in a humid atmosphere or submerged in water for a specified time. Afterwards, the specimen is again weighed, and the difference in weight before and after exposure is calculated as water or water vapour transmission rate in grams/sq centimetre. 

  

Exposure Conditions-

 

The tape in use is, depending on the application and situation, exposed to a number of different conditions that may influence the bond and its performance. Some examples are heat, cold, humidity, water, UV-light and chemicals. By simulating these conditions, a good picture how the tape will perform over the time in the application is formed. Many tests can be conducted both after the normal dwell time and after exposure to different conditions, giving valuable information of the performance. Ocular inspection could also gives valuable information.

 

The TTC has different equipment at its disposal to simulate the conditions mentioned above.

  

 

In the QUV, the tape/application is exposed to a UV-light source at a specified wavelength with or without moisture, simulating the influence of sunshine and moisture on the tape and application. UV-light causes discoloration, deterioration, brittleness and even the total drying out of the adhesive. The test can be done with two types of UV-lamps; either UVA-light at a wavelength of 340 nm or UVB-light at 313 nm. The differences are the amount of UV energy emitted in the wavelength spectrum.

 

Some facts and differences between the lamps and light:

 

- UVA-340 is best for simulating the sunlight in the critical, short wave-

lengths between the solar cut-off of at 295 nm and 365 nm. The test gives resonably fast results in correlation with outdoor weathering.

 

- UVB-313 produces the shortest wavelength found in sunlight that causes most polymer damage and provide the fastest ageing and damage to materials caused by outdoor sunlight. This is a tough test that provides fast results.

 

Climate Chamber -Heat, Cold and Moisture-

 

The climate chamber is used for exposure of the tape/application to heat, cold and

humidity, either separatly or combined in a climate cycle, and is sometimes called a climate ageing. Especially warm and humid conditions may be harsh on some dispersion adhesives. In other cases, it have been seen that the performance of the bond has increased during such exposure.

Hot water - Hot water bath-

 

In a hot water bath, the water

resistance of the tape/application is tested in temperatures of up to 95°C. This can be a very harsh test, especially for some dispersion adhesives at higher temperatures. This test is a good choice for certian outdoor applications, or if the tape/application is to be exposed to hot water.

 

Heat - Heat chamber-

 

The heat chamber, or oven, is used to determine the heat resistance of the tape/application in temperatures up to 25°C. It is very useful for the plasticizer resistance of a tape laminated to rubber or plastics. In temperatures around 70°C, the plasticizers contained in some materials migrate, (”sweat out”), and always affect the adhesive in some way. This migration may make the adhesive soft and cause decreased cohesion and adhesion. In worst case the bond is totally destroyed.

 

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