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

FLEXIBLE PACKS 53 runs. Do laboratory filled sachets suffice rather than production line samples ? THE LECTURER: It is not necessary to fill production line samples. In a static condition in the laboratory, it is possible to carry out tests on three- sided sachets which are sealed off on top and then evaluated, but it is important to carry out transit tests before embarking on a commercial production. The suitability of the sachets can only be determined if they have been transported through the country or submitted to an organization like PATRA, for transit tests. Packs can be subjected to pressure tests, and in these a 2" x 4" sachet should satisfactorily stand up to a static pressure of 100 lb. To give an indication of whether a sachet will stand up to travel or misuse, an impact test can be applied. In the early days, it was assumed because sachets were flexible and not brittle, that they did not require the same amount of packing care as one would give to a glass bottle. If you were to drop a container holding these sachets 3-4 feet, they would burst, unless there is some cushioning. Sufficient packing is therefore quite an important aspect commercially. MR. D. N. DAVIES: Polyethylene has excellent sealing properties, but heat sealing is critical. Have you any experience of high density poly- ethylene, and has it any advantages over ordinary polyethylene ? THE LECTURER: This material is applied on an extruder and there is some variation of performance. Once a suitable sealing temperature for high density polyethylene has been arrived at, this material retains its strength to a greater extent than low density polyethylene, but I am afraid that I cannot comment more fully since we have no actual experience. Trials are in hand. MR. R. H. CocKs: Regarding static pressure tests for evaluating efficiency of sealing when sachets are fresh, is there any degree of correlation to be established between results from such a test, and from the much longer term shelf tests ? THE LECTURER: These tests are only of real value in determining quality control. If they are conducted at regular intervals, they should show any variation which is occurring in the performance of the machine. They cannot, however, be taken as an indication of subsequent performance. Any very small flaws in sachets would probably not show up for three or four days, so the above tests are merely for quality control and usually indicate whether a machine is performing to a reasonable standard. Any build-up on the platens can certainly give an insulating effect, and a local area of bad sealing would be shown up in static tests.