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SILICA GEL OR ACTIVATED CLAY?
Both are desiccants and will adsorb water vapour whilst remaining dry
to touch. The surface area and structure of the desiccant particles will
influence the rate of moisture adsorption. The amount of moisture adsorbed
will depend on the quality of desiccant employed. At 25° C and
above the critical humidity zone of 50% RH (i.e. for prevention of corrosion
or mould formation) silica gel will outperform typical desiccant clays
by 35% in moisture adsorbency.
MOISTURE INDICATOR
Colour is added to white silica gel to give a visual indicator that
the desiccant has adsorbed moisture and may have become inactive. If
the desiccant is dried out again the indicator will revert to its original
colour. Traditionally the indicator used was “blue” changing
to “pink”. On 1st January 2000 new UK CHIPS legislation made
special labeling necessary for all products containing more than 1 per
cent cobalt. Subsequently a new food-safe indicator was adopted –
Orange to Cream. One of the prime considerations in choosing this particular
indicator was that the colour changes at the same rate as the old cobalt
blue to pink thereby giving an equally effective indicator. In order
that the indicator can be easily observed, small SG indicator sachets
have a clear, polyester “window” on one side of the pack.
Bags are produced in perforated clear poly.
BRITISH STANDARDS
The Standard for silica gel is BS.2540. In addition, BS.1133 gives a
formula for calculating the amount of silica gel required. Full copies
are obtainable from BSI Sales, Milton Keynes, MK14 6LE, or contact us
for further information.
DESICCANT UNITS
(German Standard DIN 55473). This may be specified instead of “weight”
of desiccant. A desiccant unit is the quantity of desiccant which, in
equilibrium with air at 23°C ± 2°C adsorbs water vapour
as follows:
Minimum 3.0g at 20% RH
Minimum 6.0g at 40% RH
25grm of silica gel used in SG sachet production is
equal to 1 Desiccant Unit. Other desiccant materials, such as activated
clays, will need more than 25 grm
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