BOTTLE CLOSURES 373 used in moulded caps. In addition a rubber latex or polyvinyl acetate base compound can be flowed into caps and set with heat treatment. A difference in the retention of liners is that the majority of metal cap liners are friction fitted into a recess, whereas the bulk of moulded cap liners are glued in. Some advantages and disadvantages of the use of metal caps are: 1. With correct dimensions of cap and container, suitable cap liner and good application, satisfactory use can always be expected. 2. They are virtually unbreakable. 3. There is a slight price advantage over moulded caps. 4. Metal screw caps do not have the same sales appeal as plastic caps. ' 5. Frequently they appear to be affixed to containers too tightly also, if dented when on bottles, caps can be extremely difficult to remove 6. To avoid corrosion of metal some care should be taken in storage. METAL SPRING OR CLIP-ON CAPS There are many types that come under this heading. Some that are widely used are: 1. Decmated tinplate lever caps that are used for gin and whisky bottling where a tin-wrapped composition cork liner is used. This type o! closure can be re-used with safety, and has had some popularity in the British spirit bottling trade for some years. 2. The aluminium cap or seal used for the bottling of preserves which have a liner ring of flowed-in rubber or polyvinyl based material. In many instances the caps are used for purposes where they are sterilised. These caps can be decorated by coating or printing to any requirement in all cases a sanitary lacquer is applied to inside surface. In use, the pre-formed caps are crimped on to jars or bottles in much the same manner as crowns. With sterilised containers a vacuum is invariably created which has to be broken by perforation or leverage before cap can be removed. This type of closure has had increasing popularity for the last ten years. No doubt this is because of its efficiency and the fact that it can be used on common jam jar finishes. 3. Phoenix Seal. This is the conventional simple tinplate cap with rubber ring liner and separate formed tinplate scaling ring that is generally used on meat or fish-paste spreads. Criticisms of this might be made on account of possible difficulty in removal of seal and cap it is also comparatively expen- sive. However, this type of cap has been used with apparent satisfaction for some time. 4. Metal Press-on Caps. Liners used in these are usually of the ceresine faced wood pulp or composition cork type. This closure is fairly economical

374 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS and has its place in industry for use on containers of certain types of heavy lubricating oils and like materials. An asset in its use is that it can be conveniently re-used, but in re-use, however, it would be unsuitable for journeys unless a fresh sealing ring is put on. ALUMINIUM FOIL SEAL WITH COMPOSITION CORK LINERS These are being used to some extent in the sterilised milk bottling trade and to a limited extent in the wine bottling trade, in the latter principally on miniature bottles. Foil caps are made in situ from strip aluminium, a composition cork disc being automatically inserted and the cap rolled on filled bottles. A tab is made on the cap for easy tear-off removal. The cork liner in this instance does play a very important part, and unless it is of good quality an effective seal for sterilisation purposes, in particular, will not be made. Although it is suitable for the bottling of sterilised milk, this type of closure is not used for any other large-scale bottling purpose in Britain, probably because of its fragility and because it will not withstand the internal pressures encountered in carbonated beverage bottling. PLASTICS FOR PACKAGING A Lecture delivered to the Society on Thursday, February 9th, 1956 L. F. BULL, M.I.E.I., A.M.I.E.E.* PLASTICS IN many different forms have very rapidly become established in the field of packaging because of properties which make them particularly valuable for such applications. The term "plastics," moreover, is a generic one like metals, which covers a very wide variety of dissimilar materials ranging from those for really solid containers to coating solutions, trans- parent film and expanded substances for the protective embedment of articles. Methods of producing completed packages with these materials are equally varied. They can be compression, transfer, or injection moulded, extruded, calendered, or cast into sheet, extrusion blown and used as a medium for dip coating. This range of techniques includes both those capable of producing to close tolerances the smallest mouldings such as a closure cap for a scent bottle to a very large container or housing. * British Resin Products, Ltd., Mayfair Place, London, W. 1.