•42 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS manufacturing aerosol bottles coated with plastic, and also bottles with plastic coatings tempered in the same way as glass tumblers. Glass bottles are made at high speeds and tempering would make an article very much more expensive. But is it worthwhile for the price involved ? MR. C. BLOOM: Can you give us any information on lightweight bottles ? THE LECTURER: Provided the bottle is well designed and the glass is well distributed, the container will be quite satisfactory with a uniform wall thickness of 0.020". The strongest type of bottle is the round one, which is approximately as wide as it is high square and oval bottles are next in regard of strength, and the rectangular bottle is the weakest. The bottle must be strong enough to withstand contact with other bottles in production and handling. A "multi-point" contact bottle is a much better proposition than a "one-point" contact bottle. The weakest part of a jar or bottle is the bottom half inch. "In-sweeping" of a bottle helps in production. Sharp shoulders should be avoided. Properly designed lightweight containers can be as good as thicker walled bottles. In order to dispense with the re-use of bottles, lightweight containers have been introduced in the United States. As a result, sterilization, etc., is no longer necessary. MR. A. MARSH: Using a semi-automatic process for small runs, is it reasonable to expect and rely on a fully automatic process to produce bottles of the same specification, or are the limits widened on a semi- automatic line ? THE LECTURER: A high speed machine has to be set up with six sets of moulds, and usually a few sample bottles are run off which should be the same as eventual production, but it is very difficult to relate semi- and fully automatic. It depends on the individual factory set-up. Manufac- turers who set up for short production runs would probably use the same machines for bulk production. FLEXIBLE PACKS F. W. NOBLE* Presented at the Symposium on "Packaging in the Cosmetic Industry", organised by the Society at Harrogate, Yorks., on 5th July 1961. The application of flexible films, such as polythene, Pliofilm, etc., to cosmetics, with particular reference to unit packaging of liquid shampoo, and some of the mechanical problems involved are discussed. TH• USE of plastics in packaging has extended very rapidly during the last few years. It is necessary, therefore, to define what we mean by "flexible * Robinson Waxed Paper Co. Ltd., Bristol.

FLEXIBLE PACKS 4• packaging". It is not proposed to deal with moulded plastic containers, and only to a limited extent with single plies of plastic material, e.g., P.V.C. tubing. It is the purpose of this paper to deal mainly with packages which can be formed from webs of composite or laminated materials. FIELD OF APPLICATION The field of application of such packages is necessarily limited. Cosmetics, in general, are in the luxury class, and the container plays a very important part in the general sales appeal. Most cosmetic containers have also to be designed for re-closure as the contents are usually used over a period. Consequently, the present field for flexible containers is largely confined to "one shot" units, e.g., liquid shampoo, face packs, face tissues, etc. The basic requirements of these packs, however, are the same as for the re-use pack---they must be attractive and give the impression of quality they must afford reasonable protection against the passage of moisture, scent, and, in many cases, essential ingredients which are incorporated in the product must not migrate into the material. At the same time, the container must be sufficiently robust to contain the product and to stand up to reasonable handling in transit and subsequent distribution. EFFECT OF PRODUCT REQUIREMENTS ON CHOICE OF MATERIAL Each product has to be considered entirely on its merits. It does not follow that if a particular sachet material is suitable for a given product it will necessarily be entirely suitable for a similar product with a different formulation. There are, for instance, variations in viscosity, and as a result a material which is suitable for a cream or concentrated viscous shampoo would not necessarily be suitable for a more free-flowing product. Again, a transparent sachet may be perfectly suitable for a product of a certain colour, whereas a similar product in a different colour may be affected by light and consequently a transparent pack is undesirable. Certain products are affected by having access to oxygen, and chemical changes can take place over a period. On the other hand, it is not always necessary that the material used should be a complete barrier to the perfume used in its formulation as a detectable scented odour can be an asset to sales if the transmission of odour is not sufficient to lose strength over a period or to affect other goods with which the packs may come into contact. For this reason laminations play such a big part in this type of packaging as it is possible to obtain different characteristics by using a variety of materials. DEVELOPMENT OF UNIT LIQUID PACK The unit liquid pack, particularly for shampoo, was originally based on