FLEXIBLE PACKS 51 DISCUSSION MR. R. F. L. THOMAS: You have covered the relationship of jaw or platen pressures and temperatures to material type. You have not men- tioned, however, the possibility of temperature effects on the laminant (rather than the bonding laminate) and I should like to know your comments on the temperature stabfiity of the types employed. THE LECTURER: This is an extremely difficult question. In use there is a tendency for the heat to affect the laminate. We can very satisfactorily anchor foil to paper, and subsequently anchor paper to plastic material. With two laminates, we can test these individually for strength, ageing, etc. If the wrong laminant is used it tends to embrittle after applying heat, and then delamination of the foil and paper occurs. When anchoring paper to plastic, heat tends to force a certain amount of the laminate into the paper and not leave sufficient behind to hold the film the characteristics of the laminant can also be altered by the effect of heat, thus weakening the bond. This is a very complicated matter and we are working on it at the moment. Nevertheless, the laminants used at present are much better than those used in previous years. This brings me to another point. Cellulose acetate is plasticised. In order to get flexibility and the characteristics one requires, certain plasti- cisers have to be used. Cellulose acetate is often used in food packing, and the question of toxicity then arises. At too high a temperature (10-20 ø) the plasticiser volatilises, and the character of the material changes, becoming embrittled. Heat, therefore, affects not only the laminant, but also other ingredients. In foil, if there is excess moisture, etc., in the laminate, the platens will turn it into steam and this will blow the laminate apart. Immediately the platens come apart the lamination tends to separate. This trouble is ex- tremely difficult to spot, but it does happen. DR. H. W. HIBBOT•: (1) Have you any views on maximum amounts of moisture, and methods of determining moisture in paper, for this purpose ? (2) Plioffim deteriorates in alkaline conditions, particularly in the presence of light, and I wonder if development of metalized sachets and opaque finish sachets is a rather elegant method of getting over the shortcomings of Pliofilm ? THE LECTURER (1): This is a matter of compromise. When moisture is reduced below the order of 4-5% the paper becomes embritt!ed and there is loss of strength. With more than 7-8% moisture within the paper, there, is a tendency towards "blowing".

512 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS With regard to determining moisture content, there are electrical instru- ments specifically for this purpose which give quick determinations, but I know nothing of them. (2) Is this problem as serious as one would think ? The users may know more about it than the suppliers. I have not come across examples of the use of these types of sachets which can be attributed to deterioration of the Pliofilm. When cream or liquid substances are used, it is known that over a period there is a tendency for embrittlement and deterioration to occur, and it is unwise to keep stocks longer than is necessary, before use. With reference to light, the normal life of these sachets is mainly spent in the dark, enclosed in outers, and very often the sachets themselves are more exposed to electric light than to direct sunlight. One could not recommend the use of such materials if they were in fact to be exposed to direct sunlight for any length of time. There is a tendency for materials to alter in dimension under these conditions. Accelerated evaporation in the case of transparent sachets tends to occur under these conditions, rendering them unsightly. MR. A. FosrEl•: Is there any degree of generalisation which can be applied to the melting point and temperature of the sealing process ? THE LECTURER: This depends mainly on the matehal to be used. A make up such as paper/foil/Pliofilm would need a much higher temperature, because of the heat resistance of paper, than one would use with two straight films. It is advisable to use the minimum temperature at which an adequate seal can be made, and in the case of acetate/Pliofilm, this should not exceed 275øF. On the question of heat sealing, a great deal of work is being done at the moment and more positive information will be made available in a short time. Now to the question of pressure, temperature and dwell. Once the conditions on a machine are determined, and it is normally running 40-50 per minute, it entirely changes the conditions if an engineer decides to speed up the machine to obtain another 10 per minute. There is a time barrier if you have approx. one second for a total operation, with approx. 0.4 second in which accurate sealing can be done. To speed the operation up by raising the temperature usually causes difficulties. There is therefore a minimum time in which work can be done, and any attempt to shorten this time by increased temperatures and pressures leads to trouble. Ml•. R. CLA•K: To evaluate suitability of a particular pack for a product, it is necessary to carry out storage tests over a considerable period of time. To what extent is it necessary to fill such experimental packs on full machine