Quality control checks for packaging materials

Biscuits are very susceptible to the pick up of strong odours and even small traces can spoil their flavour.

Subtle problems may arise from solvents used in inks to print the wrappers so it is as well to discuss these problems with the converters of wrapping materials to ensure that adequate removal of odours takes place before the printed matter is reeled up or wrapped for delivery.

Cardboard may give a musty flavour note if in contact with biscuits within a moistureproof barrier. Always use good quality cardboard manufactured from new fibres (not recycled paper) and check carefully for odours that may be transferred to the products. It is permissible to use cardboard made from recycled paper for outer boxes which do not come into contact with the biscuits. It should be remembered also that recycled paper cardboard may present a hygiene hazard if placed in contact with food.

Moistureproofness is measured by the rate that moisture vapour passes across the film barrier when it separates an atmosphere of given humidity from one of zero humidity at a given temperature.

There are two standard test conditions known as (a) temperate (relative humidity of 75% at 25°C) and (b) tropical (relative humidity of 90% at 38°C).

Specifications for films should give the water vapour permeability (wvp) or water vapour transmission rate (wvtr) as g/m2/24 hours at one of the two standards given above. The important point to remember is that the performance may be affected if the film is creased or printed and the specification relates to flat basic film. In terms of the overall pack the performance is also usually affected by the quality of the seals.

Gas permeability properties (for example for oxygen) are specified in cm3/m2/24 hours/atm at 23±1°C. Although the gas permeability may not be well related to the wvp and also varies considerably for different gases, it is not normally felt necessary to check this property of films for biscuit wrapping.

The films must have good heat sealing properties because the seals compliment the basic film properties in the performance of the pack.

Storage of packaging materials

Cellulose films require protection from ambient moisture. If they absorb moisture (at the cut edges) they will expand and curl, making them difficult to run on the wrapping machine. Reels of cellulose film should therefore be stored in sealed polythene bags. Rather less care is needed for storing plastics films. Cardboard, however, whether as cartons or cases, needs very careful storage. The main problem is moisture pick up. If the paper should become damp it loses its strength and may become loosened from the adhesives inherent in the case design. It is not normally possible to wrap stocks of cases for protection, so they should be stored off the floor (on pallets), flat, to prevent distortions and in a well ventilated area, with low relatively humidity. To ensure low humidities in damp climates it may be necessary to install space heaters or dehumidifying machinery. Recent developments in the latter have made them very effective and economical.

Particular care should be used in storing small cartons which are to be run on automatic cartoning machines. Dampness will render the card weak and this will bend and interfere with the erection functions within the machine.