THREE PRIME FACTORS IN SUCCESSFUL PACKAGING 11 The resin is filled with wood flour as an extender, with pigments and lubricants added. The standard type of wood flour filled material is available in the solid colors, though pastel shades cannot be produced since the resin is inclined to. be dark in color. This type of compound has good resistance to atmospheric moisture and will withstand steam autoclaving, though with some loss of gloss and a tendency toward roughness in the finished piece. Mineral-filled compounds are avail- able at a considerable increase in cost, which will withstand steam sterilization. The urea formaldehyde resins lend themselves to the molding of caps in the white or pastel shades. Alpha cellulose is generally used as the filler with the urea formaldehyde resins. Such caps have adequate moisture resistance for general use, but tend to chalk or change color when immersed in water, and do not resist steam sterilization. Origi- nally the urea formaldehyde caps were inclined to be slightly trans- lucent, and when a liner with back- ing which was opaque or dark in color was applied in the cap, the top portion would appear to be darker in shade than the sidewall. This con- dition can be corrected by using a more nearly opaque molding ma- terial or, in some cases, a lighter colored backing material, if avail- able. Melamine resins are currently being placed on the market. These can be produced in pastel shades and have excellent water resistance--in fact, will stand steam sterilization. Currently, they are high in cost. The thermoplastic molding mate- rials are just what their name im- plies, that is they soften with heat, even after molding. The thermo- plastic materials which have been used are cellulose acetate, cellulose aceto-butyrate, methyl methacryl- ate, ¾inylite, and polystyrene. Polystyrene has been used for the production of closures due to its ex- cellent acid and alkali resistance. It is also quite resistant to moisture attack. Transparent closures may be produced, though, generally speaking, they are unsightly on the package, due to the fact that the bottle finish threads and liner are readily apparent through the trans- parent materials, which does not add attractiveness to the package. These materials are available for the production of opaque closures. The thermoplastic materials are all sol- uble in organic solvents conse- quently, they do not lend themselves too well to use with perfume or toilet waters containing essential oils. While the closure itself may not, during the shelf life, be exposed to the contents of the container, during first use some of the product will remain on the thread and may then soften the inner portion of the cap. In use with perframes, some of the product may remain on the finger, and when the cap is again applied to the container, the essential oil may remain on the outside, being less volatile than the solvents contained in the product, and cause a softening of the molded part.

19, JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Molded caps can be produced in very attractive styles and a wide variety of shapes, though tapers or shapes in which the diameter at the top of the c. losure is greater than the diameter at the base where the clo- sure is screwed into place on the bottle, should be avoided. To make reverse tapers, very complicated molds are required, which slows down production and increases the cost of the cap. The liner for the closure is equally as important as the closure itself, and is considerably more complex. The liner acts as a more or less re- silient gasket which the cap com- presses and holds against the bottle the liner must make an efficient mechanical seal and re-seal. It must be of such physical and chem- ical nature that it will not disinte- grate or lose its efficiency even when the packages remain on the retailers' shelves over considerable periods of time. The liners in metal caps are not adhered in the closure. They are made somewhat larger in diam- eter than the threads, and in lining the cap, they are forced in past the threads into a recess in the top of the cap. It is the general practice to adhere the liners in molded caps for here the liner is somewhat smaller than the thread diameter. Liners may be divided into two funda- mental classes: (a) homogeneous and (b) duplexed or faced. Homogeneous liners, such as natural cork, cork composition, rub- ber and the special solvent type materials used to retain organic solvents, are g•nerally used for special purposes. Natural cork and cork composition may be used as liners for oils in the medium or high viscosity range, and for products sold quickly, where the shelf life is not over six months. In the case of product• that contain organic sol- vents, natural cork and cork com- position are not generally recom- mended. Rubber liners find general uke for alkaline preparations, for the hypo- chlorites and certain acids. Solvent liners are indicated where organic solvents are to be retained, such as nail polish, corn cures, and collodion. These homogeneous linerg are the only type which should be employed with molded caps utilizing a post or a well, for a quill brush, glass rod or other type of applicator. Duplexed liners, that is, those with facings applied to a backing material, are not suited for post or well type caps since the efficiency of this type liner depends upon the facing material employed. In a post or well type cap, the liquid will contact the backing material, since a gasket liner is used for such caps, and the liquid can pass through the center hole in the liner at the junc- ture of the post or well. The liners most generally used in screw caps'are of the duplexed type. These comprise a facing material and a backing material. The back- ings consist of newsboard, pulp- board or various types of cork com- position. Years of experience have indicated that newsboard with proper facing will produce an effec- tive seal for products which are not