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
THREE PRIME FACTORS IN SUCCESSFUL PACKAGING 13 highly wfiatile, and this type of liner is quite generally used f•,r jar covers. Pulpboard is light in color and has been used in the past for lining semi-translucent urea form- aldehyde caps in order not to cause two shades in the cap, as mentioned previously. Currently, pulpboard is very diflScult to obtain, stocks in this country being now practically non-existent. Should the facing material be broken due to a fin on the glass container or due to pene- tration or action by the product, and pulpboard or newsboard be used as a backing, loss of product will result. Cork composition is, in it- self, a satisfactory liner for many products where the shelf life is short. With ,added protection from the facing, cork composition, though , more expensive, produces the most efiScient seal. Should the facing be , ruFtured or impaired, the cork corn- .position then acts as a secondary seal. The usual cork compositions tare produced from granulated cork land a'protein binder. Where indi- leated, cork compositions can be i supplied with a resinous binder. The facing materials for liners are I the metallic foils, varnished papers i or synthetic films. Tinfoil, 99.7% I pure, 0.0015" thick, mounted on white sulphite paper, has been used If or organic solvents and alcohol- , containing preparations. Such a i liner is indicated for nail polish re- movers, perfumes, colognes, and i products which do not etch or attack the foil. If the finish and sealing surface of the glass container is in good condi.tion, newsboard may t)e used as a backing otherwise, cork composition is indicated. Cur- rently, Tinfoil is unobtainable for such products, and during the war a urea formaldehyde-alkyd coating on paper producing a varnished paper type of liner was used. This liner is definitely inferior to Tinfoil, but was used during the emergency. Dead soft Aluminum Foil, 0.001" thick, backed with cork composi- tion, has been tried as a substitute for Tinfoil with rather poor results, due to the fact that the Aluminum Foil is not as soft as Tin, and does not give intimate contact with the glass and prevent evaporation. The manufacturers are currently attempting to produce Aluminum Foil with an organic coating such as Vinylire applied to the face. Early tests have indicated that an eflScient liner will result if the product does not dissolve the organic coating which has been applied to the Aluminum Foil. The varnished papers--which are _}ust what their name implies, name- ly, a varnish applied to a supporting paper or several coats of varnish being built up to yield the necessary thickness--•have been used for many years as facings. There are many types, such as Pale Yellow Oil, Yellow Oil or Light Brown Oil, Black Alkali Paper, Harvel, Brown Acid Resisting Paper, 8018, etc. The varnished papers have fair moisture-vapor transmission char- acteristics and are satisfactory for aqueous products and cold creams. Black Alkali Paper will withstand 50% alcohol solutions, although the
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