US 2238681 A
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G. L. BOROUGH 2,238,681
CONTAINER CLOSURE Filed March 16, 1939 g sh s 1 EIEE L. UP Ugh 1. e. L. BOROUGH 3 5 CONTAINER CLOSURE Filed March 16, 1839 2 Sheets-Sheet 2 \J L HHHIIIIII" Ring O/JOZZCZ EZhgZene. poly/718% GEL-EEG L.DI:JP 'I Lh Patented Apr. 35, Edi
CONTAINER CLOSURE George L. Borough, Holly Oak, DeL, assignor to E. I. du Pont de Nemours & Company, Wllmington, DeL, a corporation of Delaware Application March 16, 1939, Serial No. 262,323
This invention relates to container closures and more particularly to improved caps of the screw and crown types.
Container closures are commonly made by combining a shell with a liner of cork. The porosity of the thin cork layer. permits the liquid contents of the container to come in contact with the outer shell causing destruction of the shell and contamination of the contents. Unprotected cork also serves to contaminate many liquids with which it may be placed in contact due to the action of the liquid on the cork. It is also known to use a liner prepared from comminuted cork bound together with various resins. This construction renders the liner capable of preventing contact of the liquid contents of the container with the closure shell and provides a protective coating for the cork particles. Further, it is known to apply a surface coating or protective membrane or spot disc to the exposed face of the liner to prevent contact of liquids with the cushion material of the liner, and it is still further known to prepare cushion materials for closure liners from more or less complex mixtures containing various adhesives, solids, fillers, rubber, etc.
Container closures prepared using any of the above methods have in common such disadvantages as being resistant to only a small group of materials and being relatively complex and diflicult as well as expensive to prepare.
This invention has as its object to provide a container closure, the 'cushion liner of which comprises a relatively simple material. A further object is to provide a container closure the cushion of which combines the properties of resilience, toughness, etc., which make it suitable for a cushion liner together with the property of inertness, i. e. of being unafiected by diversified classes of materials. A still further object is to provide suitable means for perparing container closures of the type described above. Other objects will appear hereinafter.
These objects are accomplished by preparing a container closure by combining a metal or plastic shell with a cushion liner comprising a solid polymer of ethylene the physical properties and method of preparation of which are referred to in more detail below.
In the accompanying drawings Figs. 1 to 7 are sectional views of various forms of container closures and elements thereof embodying my invention.
In Fig. l, the numeral i indicates a beverage crown in which the sealing element 2 is a disc of solid polymer of ethylene,
Fig. 2 shows a screw cap closure consisting of a molded plastic shell 3 and a disc 8 of the ethylene polymer,
Fig. 3 shows sheet material, which consists of a metal sheet 5 having an adherent coating 6 of ethylene polymer, and from which is stamped the crown closure shown in Fig. 4 consisting of the outer metal shell 1 and cushion liner or sealing element 8 of the ethylene polymer.
In Fig. 5 the sealing element consists of a disc of spongy ethylene polymer i0 contained in the metal crown 9,
In Fig. 6 the sealing, element in the beverage crown ii consists of a disc i2 of spongy ethylene polymer faced with solid ethylene polymer i3, and
Fig. '7 shows a cross section of a screw-type closure consisting of a metal shell l4 and a ring gasket l5 of solid polymer of ethylene,
The process for preparing the solid polymers of ethylene used in the practice of this invention consists in subjecting ethylene to a pressur in excess of 500 atmospheres under controlled. elevated temperature conditions. This procedure results in polymers of ethylene, the molecular weight of which varies, depending particularly upon the pressure employed. By using pressures of more than 1000 atmospheres, solid polymers are formed and under these conditions the polymerization reaction takes place, requiring several hours for completion. These polymers may also be made by including in the ethylene a small quantity of oxygen which may be as little as 0.01 per cent but preferably 0.02 per cent to 0.10 per cent at 1500 atmospheres. The pressures are at least 500 atmospheres and preferably at least 1000 atmospheres and below 3000 atmospheres. The temperatures are between 100 C. and 400 C. and more desirably from 150 C. to 250 C. Thus, as a specific instance of obtaining the polymers, ethylene containing 0.05 per cent oxygen is compressed in a steel bomb to a total pressure of 1500 atmospheres and heated rapidly to 210 C., whereupon a very sudden rise in pressure, followed by a slow drop in pressure, is observed. After five hours heating at 210 C. the'pressure is released and the product cooled. Under these conditions an yield of the solid polymer based on the ethylene used is obtained. 7
The ethylene polymers obtained as outlined above melt at temperatures in excess of C.
and generally within the range of about 110 C. to about 200 C., have a molecular weight in exce s of 6000, are essentially saturated products corresponding in composition substantially to (CH2) a: and when subjected to X-ray diffraction analysis show. a crystalline structure. These polymers are insoluble in xylene at ordinary tem- -peratures but soluble in xylene at its boiling point, are unaffected by prolonged contact with A air at ordinary temperatures, and are characterized by the fact that they can be formed into films and filaments which yield oriented products on application of stress herein referred to as cold drawing. The oriented products furnish fiber diffraction patterns on examination with X-rays and exhibit birefringence and parallel extinction when observed under crossed Nicol prisms. Of these polymers, those having molecular weights in excess of 10,000 are the most useful in the practice of this invention.
The melting points referred to above are determined by a modification of the ball and ring method as follows: a film of the ethylene polymer 0.005" thick is clamped in a 1" diameter circular clamp and supports a 0.4" diameter steel ball. The whole is immersed in glycerin and the temperature raised at a rate of 5 C. per minute. The melting point is taken as the temperature at which the ball shows all the way 7 through the ring.
The improved closures of the present invention which contain cushion liners of the above described ethylene polymer may be made by casting or molding the ethylene polymer cushion liner disc or ring directly in the metal or plastic shell or by inserting a preformed disc or ring of ethylene polymer directly in the metal or plastic shell. Methods for forming the liner directly in the cap include stamping the cap from shell -material previously coated with ethylene polymer, casting the disc in the shell from molten ethylene polymer or from ethylene polymer in solution in a suitable organic solvent or by compressing the powdered ethylene polymer into the cap and fusing to form a coherent liner. Preformed discs for inserting in cap shells are prepared variously by compression molding, injection molding, or by stamping from sheeting of the ethylene polymer. To insure the attachment of the liner to the shell when a preformed disc is inserted in the shell, the size of the disc may be selected to be slightly larger than the space it is to fill, so that its own resiliency will allow it to be forced into position and maintain it there in a snug fit; ,or the assembly may be heated to fuse the ethylene polymer liner to the shell,' or the liner may be spot welded to the 'shell by local heating.
The practice of this invention may be further illustrated by means of the following examples:
Example I A sheet of the ethylene polymer is prepared -from a melt of ethylene polymer of average molecular weight about 16,000 maintained in a pressure chamber at a temperature of about 200 C., by extruding through a slit in the bottom of the chamber directly into cold water. The width of the slit and the rate of extrusion are adjusted to produce finished sheeting 0.0.50" thick. From this sheeting discs 1.050" in diameter are cut by stamping in a punch press. These discs are then inserted in beverage type crown shells prepared by stamping from tin plate (for example, 107 lb. tin plate) lacquered on both sides. The assembled caps are capable of forming a secure seal when applied to containers according to the usual technique well known in the art. The seal is resistant to gas pressures within the container such as those met in bottled soft drinks and beer. The cushion liners remain unaffected after long exposure to such materials as catsup and chili sauce for which caps containing cork liners are highly unsuitable. These caps impart no taste or odor to the contents of the container.
Example I! A container closure is assembled using a metal crown shell similar to that employed in Example I and a disc of the ethylene polymer 1.050" in diameter by 0.040" thick which is prepared by compression molding polymer of molecular weight around 24,000 in a suitable die at 130 C. followed by cooling and ejection from the die. The center" of the metal crown is then spot heated by pressing its outer surface against the end of a hot rod. The ethylene polymer cushion liner is then pressed against the shell and the assembly allowed to 'cool. This seals the liner firmly to the shell and provides a cap, the liner of which is unimpaired by the mechanical stress of the capping operation.
Example III A container closure is assembled, using a rigid molded plastic shell prepared from a phenolformaldehyde resin. The shell is threaded to engage with corresponding threads on the neck of the container. For a cushion liner, a disc of ethylene polymer of average molecular weight about 25,000 is prepared by injection molding. After the liner has been placed in the shell the assembly is placed open end up in a vacuum chamber and heated at 130 C. until the liner has fused firmly to the shell. Vacuum is used during this process to prevent the trapping of air bubbles between shell and liner. This procedure provides good adhesion of the liner to the shell in the finished closure and prevents the annoying situation of the liner remaining on the container when the cap is removed, which is so frequently the case with closures for toothpaste, shaving creams, inks and cosmetics.
Example IV A metal beverage crown shell is placed open side up and heated at 0. Into this cup is poured a predetermined amount of a 40% (by weight) solution of ethylene polymer of average molecular weight about 18,000 in xylene which is also at a temperature of 120 C. The assembly is kept at 120 C. until substantially all the xylene has evaporated (about 45 minutes) and there remains a shell lined with molten ethylene polymer. This assembly is then plunger at once into cold water to preserve the transparency of the polymer and enhance the toughness of the cushion liner.
' Example V The procedure of Example IV is repeated except that instead of the ethylene polymer being in solution it is cast into the shell directly from melt at 250 C. Due to the high viscosity of the molten polymer, it is usually necessary to place the hot assembly in an apparatus whereby centrifugal force is applied to spread the molten polymer in the cup and remove air bubbles, producing, on cooling, a cap with a strongly adherent cushion liner.
Example VI in the form of a compressed cake of the polymer.
To render this liner durable for use, the assembly is then heated at 120 C. until the polymer is fused into a coherent mass. The assembly is then rapidly cooled as in Example IV.
Example VII Sheeting of 107 lb. tin plate is lacquered on one side. The other side is coated in a suitable manner with a coating of the ethylene polymer of average molecular weight about 26,000 to a thickness of about 0.035". From this coated sheeting, discs are stamped and formed into crown caps in a suitable press. The cold drawing properties of the polymer render the coatings stable to this forming operation. The resultant inner coating not only provides a cushion liner for the cap but also provides a cushioning surface for the skirt of the shell and in turn protects the top of glass containers during the capping process. It further avoids the necessity of lacquering one side of the metal shell to prevent corrosion.
Example VIII A porous, spongy sheet of an ethylene polymer of average molecular weight about 22,000 is prepared by extruding a froth of the polymer at 130 C. through a slit 0.033" in thickness directly into cold water from a pressure chamber under 1500 lbs. per sq. in. pressure of nitrogen. The sheet thus obtained has a thickness of 0.050", is porous, highly flexible, resilient, has an apparent density of 0.288 (as compared to about 0.94 for solid ethylene polymer), and an average pore diameter of 0.003". A disc 1.050" in diameter is cut from this sheet and a container closure prepared as in Example I by mounting in a metal beverage crown shell.
Since the sheeting is not a sponge, in the sense of having interconnecting interstices, but rather a solidified froth in which the pores are discrete units entirely surrounded by ethylene polymer, the face of the disc is as impervious to liquids and offers as good protection of the shell from the container contents as the other forms of ethylene polymer mentioned in the foregoing examples. This type of closure is especially valuable for sealing containers in which considerable pressures are to be maintained.
In the above type of closure, if desired, the face of the disc adjacent to the contents and in direct contact with the lip of the container is heated to form a continuous film of the polymer.- In assemblies of this type the ethylene polymer disc has the face adjacent to the contents as a continuous film supported on a spongy resilient backing, thus providing an assembly which is exceptionally well suited to capping against high pressures.
In some cases it is desirable to incorporate in the liners such stiffening materials as cloth, glass fibers, paper, felt, mats and fabrics of regenerated cellulosic materials, wire mesh, etc. These materials are completely embedded beneath the sealing surface of the ethylene polymer, so that they in no wise may come in contact with the contents of the container.
The ethylene polymer compositions used in preparing cushion liners may also contain various fillers such as chalk or alpha fioc cellulose, pigments such as TiOz, ZnO, modifying agents such as paraffin wax, etc., which serve to reduce the cost of the liners and alter their appearance without impairing their cushioning or sealing properties as liners.
It is to be understood that although the container closures prepared according to the ex amples given above are all circular in shape and employ disc shaped cushion liners, the invention is applicable to the preparation of closures of any suitable shape such as square, oval, etc., employing liners of corresponding shapes. Or the closure may comprise a shell of any shape employing a ring or other shaped gasket of the ethylene polymer with the center portion removed, so that the liner serves only as a cushion material between the shell and container, leaving the center portions of the shell which are not adjacent to the container lip exposed to the contents of the container.
This invention is useful for preparing closures for containers for all sorts. It provides a new type of closure which is resistant to a wide variety of materials and may be adapted for use on bottles, beer cans, food and cosmetic jars, tooth paste and shaving cream tubes, containers for chemicals, etc.
A highly valuable advantage of this invention is that it provides a container closure which combines a metal or plastic shell, e. g. phenolformaldehyde, urea-formaldehyde, hard rubber, casein, polyvinyl resin, or similar shell, with a single material possessing the cushioning properties necessary for forming a tight, elastic seal along with the capacity for being unaffected by a wide variety of materials. It thus provides a simplified form of closure which may safely be exposed to the contents of the container without the use of a spot cover or coating and which will impart no odor or taste thereto. In addition to being inert to water, these closures are also unaffected by "canned food. and fruit Juices, catsup, vinegar, hydrogen peroxide, pharmaceutical materials, carbonated beverages, beer, mineral acids, alkalies, soaps, salts, organic solvents, cosmetics, shaving cream, tooth paste and other similar materials frequently packaged in containers on which closures of the type described in this invention may be used.
As many apparent widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claim.
A container closure comprising a shell having a, cushion liner comprising essentially solid ethylene polymer having a molecular weight of at least 6000, melting from about C. to about 200 C., and having a crystalline structure.
GEORGE L. DOROUGH.