Minimum Temperature Film Forming Bar (MFFT)

The desired temperature program is selected and the instrument allowed to reach thermal equilibrium. Tracks of wet test material are applied using a cube applicator or spreader. Once the material has dried or cured the result is visually apparent. A dull, nickel-plated copper platen is cooled at one end electronically and warmed at the other end, while air or nitrogen is caused to flow over the surface as a uniform blanket. The air flow is from cold end to hot end.

In practice, the instrument is switched on and the program chosen. Air and water having been connected, an equilibrium condition is noted after about 20 minutes (the time may be less dependent on the program chosen). At equilibrium, the heating cooling lamps illuminate at very low frequency. Several tracks are laid down in quick succession using an applicator, normally a 75 micron (3 mil) one inch cube applicator. The tracks may be laid down left to right or right to left, but the most common form is a U horizontal, with the track starting and finishing at the right, warm end. Two tracks are normally laid down last as a control using an emulsion of known MFFT. A clearly defined limit of coalescence will show in about 90 minutes and the MFFT temperature can then be read using the cursor scale. Pigmented emulsions may be tested but the determination is more difficult to see. Most operators, however, find that they can readily ascertain the MFFT point. This can be proven using a wooden spatula or, more commonly, a finger nail to check the point at which the soft, uncoalesced coating commences. MFFT Determination, one continuous track displays the evenness of the heating,cooling and air flow. A photographic record of the performance of every instrument is made before dispatch.

To achieve the required uniformity, the air or gas is delivered via a very carefully designed sintered metal distribution block. The design is such that freezing does not take place at the inlet. For use with air, a drying system is incorporated into the housing together with a flow controller. The air dryer contains indicator crystals which are clearly visible in their transparent container. The complete air conditioning system is accessible at the side of the instrument.

Paints & Coatings - The minimum film-forming temperature (MFFT) of a paint or coating is the lowest temperature at which it will uniformly coalesce when applied on a substrate as a thin film. The standard test for determining this temperature involves using a MFFT-Bar, as specified by such standards as ASTM D 2354 and ISO 2115. The design of the instrument is based directly on these standards.

Adhesives - The MFFT of one-pack adhesives can be found in a similar way to paints and coatings. With two-pack adhesives, a strip of aluminum foil can be laid on the platen, to ease cleaning, before applying the adhesive. Two-pack adhesives do not show an MFFT, but the minimum cure temperature can be found by scraping the sample with a spatula.