Potlife is a way of specifying a hard plastic’s reactivity. Normally, it indicates the time required for a resin-hardener mixture of 100 grams to increase the temperature from +20°C to +50°C. For slow systems, the time is indicated that is needed for the viscosity to double. If larger amounts are mixed, the potlife is shorter because of the heat released during the reaction.
Hardening time is the time that passes until no improvement in strength can be measured. This normally occurs after 7 days at room temperature. By raising the temperature to +30°C, the hardening time is halved.
Primer is the first layer that is applied to a surface. Another term used is priming.
A primer is intended to provide good wetting and adhesion for subsequent coats. On absorbent substrates, the primer also prevents the intake of succeeding coats.
During the time that an amine-epoxy mixture is hardening, the surface is exposed to the carbon dioxide that is present in air. The free amines then form a compound that is called amine carbonate. The thin film of amine carbonate is usually invisible to the naked eye, but if it is present, adhesion to the following coat is degraded.
For this reason, sanding between coats is recommended. Working “wet-on-wet” seldom entails any problems.
Air at a specific temperature can dissolve a certain amount of water vapour. This amount is called the air’s vapour concentration at saturation point. At +20°C, air can dissolve 17.28 grams of water vapour per m³. The relative atmospheric humidity is then equal to 100%. If the atmospheric humidity is 60%, it thus contains 10.37 grams of water per m³. The colder the air, the less water vapour can be retained. When warm air with a certain amount of water vapour is cooled, the air’s vapour concentration at saturation point will be reached and further reduction of the temperature leads to water being released from the air, i.e. dew.
When heat is released during a chemical reaction, the reaction is said to be exothermic. The opposite is when heat must be applied; this reaction is referred to as endothermic.
HDT is the abbreviation for Heat Deflection Temperature. HDT is the temperature at which a plastic’s physical properties are degraded. Used in older data sheets.
Tg is the abbreviation for Glass transition temperature. Mostly the same value as HDT, but measured in another way.
Thixotropic is an indication of a special consistency of a liquid. When not agitated, the consistency is nearly solid, but becomes liquid under agitation.