COOLID indicators, which have been worked out by the three R&D units, and which are protected by the three patents, work on the base of enabling certain reagents to join above the critical temperature (indication temperature). These reagents are absolutely harmless to the health (accepted to be used in the groceries industry), therefore the contact with the sensor- even damaged- does not lead to any danger. The essence of working is the fact that, the reaction – which gives the coloured product – may occur only in an aqueous solution. Both reagents are diluted and placed in two neighbouring beds, where the two solutions are immobilised, which makes impossible for them to mix and create a colour. After freezing, the structure that immobilises the solution is damaged (it should occur in 1 or 2 hours of freezing), but the solutions are still kept in solid state, which still makes the indication impossible.
It means that activation (transforming into the state of indication) of the COOLID indicators occurs by itself, which is one of their biggest advantages. After exceeding the critical temperature, e.g. defrosting, and exposure at the given temperature during suitable time, the solutions are no longer immobilised and they can mix causing reaction, which gives the colour (visible in the window). Both beds (in the form of spots, stripes etc.) are placed on the base enabling their fastening to the package material, and coverage is made of artificial material with a transparent window enabling the reading.

Life  phases  of COOLID indicator

1. NON-ACTIVE INDICATOR – after manufacturing of COOLID, the immobilized solutions are in the form of gel (solid state) and the indicator is not active.
2. ACTIVATION – during application (or adequately after) the indicator is frozen and the gel structure is being destroyed due to solid water expansion.
3. ACTIVE INDICATOR  – delivered water stays in the solid state (ice crystals) and the COOLID is able to monitor the temperature of the product.
4. INDICATION – after defrosting (at a given critical temperature) ice melts, water spreads resulting in joining the activating substance with the indicating substance, which produce a color spot or an expanding color zone.

Indicator structure

Figure 1 a) and b) show the scheme of the simplest system, in which the moment of time delay (indication delay) is controlled by a presence (short delay) or absence (longer delay) of a thermal insulation element in the indicator base. Fig. 1 c) shows the model of the indicator with the time scale. Sizes of the indicators shown (single sensor) are: length – 30mm, width – 20mm, thickness – up to 2mm (in the place of the window, in others the thickness is about 0,5mm). Sizes of the window: 12x7mm or less without the time scale, 25x3mm – with time scale. The element of the base enables the application of indicators on a mass scale (it is self-adhesive).




Fig.1 The general view of the indicator: a) model with the time delay - top view, 3 stages: from the left: before indication, directly (with the constant time delay after exceeding the critical temperature), after longer time above the critical temperature; b) cross-section. Self-sticking surface is placed on the top - in the place of indication of the distance between the beds of the two immobilized reagents d, on which the delay time depends as well. Reagents beds are placed in the bulges in the covering element visible on the bottom. c) model with the time scale – top view: from the left: before indication, directly after indication, after longer exceeding of critical temperature. The scheme and technical details are temporary examples only.