MFFT datasheet(3/4 Pages) ETC

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MINIMUM FILM-FORMING TEMPERATURE BAR

A nickel plated copper platen is electronically cooled

at one end and warmed at the other end. Air or ni-

trogen is caused to flow over the surface, from cool

end to warm end as a uniform blanket. To achieve

the required degree of uniformity the air or gas is

delivered via a 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 a transparent container. The com-

plete air conditioning system is readily accessible

at the side of the instrument.

Water at normal mains pressure removes the ex-

cess heat from the coolers. Quick release couplings

are provided. Water is normally drawn from a labo-

ratory tap and the outlet is run to drain by gravity.

Alarms, both audible and visual are actuated in the

event of cooling water supply failure.

PRINCIPLE OF OPERATION

The “minimum film-forming temperature” has been

described as “the minimum temperature at which a

water-borne synthetic latex or emulsion will coa-

lesce when laid on a substrate as a thin film. When

this process occurs, in the absence of pigmenta-

tion or other opacifying materials, a clear transpar-

ent film is formed. At lower temperatures than the

minimum, a white, powdery, cracked film will re-

sult”.

The minimum film-forming temperature is usually

closely related to the glass transition temperature

Tg but not synonymous with it; whilst the Tg may be

determined by predicted calculation, the minimum

film-forming temperature is best determined by the

use of a MFFT Bar; the basic principles of which

are described in ASTM D2354. Early instruments

were usually cumbersome, inaccurate and slow to

achieve equilibrium. I.C.I. plc devised a simple inte-

grated instrument which was able to achieve the de-

sired results quickly and efficiently. The initial de-

velopment was carried out in I.C.I. Paints’ laborato-

ries.

Temperature sensors are mounted at intervals under

the surface of the platen. These are used to control

the temperature of the platen in accordance with the

chosen programme. They are also used to indicate

the platen temperatures down the length of the bar, or

they can be switched to indicate differential tempera-

tures between adjacent sensing points, so providing

an instantaneous indication of temperature gradient.

A roving probe temperature sensor is provided to

facilitate temperature measurement at every point

on the platen, it also serves to check the static

sensors.

A hinged perspex cover over the platen provides

thermal insulation whilst allowing visual inspection

of the determination as it progresses. A transparent

cursor is mounted on the cover to simplify the iden-

tification of the exact minimum film-forming tempera-

ture.

Programmes

Standard model MFFT-60

Degrees C.

Cool end (Left)

-5

+15

+23

+33

Warm end (Right)

+13

+18

+23

+33

+50

+60

Extended range model MFFT 90

Additional programmes

Cool end

+43

+53

+63

Warm end

+70

+90

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