Bottle caps are a type of closure used to seal the openings of bottles of many types. They can be small circular pieces of metal, usually steel,[citation needed] with plastic backings, and for plastic bottles a plastic cap is used instead. A bottle cap is typically colorfully decorated with the logo of the brand of beverage. Caps can also be plastic, sometimes with a pour spout. Flip-Top caps like Flapper closures provide controlled dispensing of dry products. Bottle caps for plastic bottles are often made of a different type of plastic than the bottle.
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Types
Bottle caps were originally designed to be pressed over and around the top of a glass bottle to grab a small flange on the bottleneck.
Crown cork
The crown cork was patented by William Painter (inventor) on 2 February 1892 (U.S. Patent 468,258). It originally had 24 teeth[citation needed] and a cork seal with a paper backing to prevent contact between the contents and the metal cap. The current version has 21 teeth. To open these bottles, a bottle opener is generally advised.
The height of the crown cap was reduced and specified in the German standard DIN 6099 in the 1960s. This also defined the "twist-off" crown cap, now widely used in the United States, Canada, and Australia. This bottle cap is pressed around screw threads instead of a flange. Such a bottle cap can be taken off merely by twisting the cap, eliminating the need for the opener.
Other types
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Screw Caps
Screw on closures are the most common form of bottle caps. They are easy to apply by a wide variety of automated equipment, or they can be applied by hand. The application torque of closures however must be controlled in order for the closures to perform properly in the field. Closures must be applied tight enough to maintain a seal and to resist closure back-off, but must be not be applied so tightly that the end user cannot remove the closure. A general guide is that the application torque in inches per pound should equal approximately half of the closure millimeter size. As application torque cannot be measured directly on an automatic capper, removal torque measurements are used as an indication of application torque. Since each package will have its own relationship of application to removal torque, the packager should determine this relationship for each of his packages. By applying caps by hand with a torque meter and immediately measuring the removal torque, a correlation between application and removal torque can be determined. This correlation can then be used as an indicator of the actual application torque generated by the capper. By checking removal torque regularly after capping, one can determine if there is a need for adjustment.
Closure Lining Materials
Foamed Polyethylene (F217) Commonly used with plastic screw caps. F-217 is a soft polyethylene foam core covered on top and bottom with solid, clear polyethylene supplied in .050” thickness. F217 has become the industry standard due to its all purpose compatibility, resilient, compressible seal, cleanliness (no pulp dust) and economy. F217 liners have excellent chemical resistance and a low moisture transmission rate. F217 also has good taste and odor resistance.
Plastisol Plastisol is the standard lining material used in metal closures for vacuum packing glass bottles and jars. Plastisol is a flowed-in compound, usually a dispersion of pvc resins in plasticizers. It forms a solid, self-bonding, sealing gasket in the closures. Plastisol liners are used in metal twist-off and metal continuous thread screw caps for use on hot-pack food products where the preservation of a vacuum is essential.
Pressure Sensitive Liners (PS 22): Styrene foam material coated on the down facing side with torque activated adhesive. Pressure-sensitive inner seals adhere to plastic or glass bottles with normal application torque. Pressures sensitive liners are supplied pressed into closures and adhere to the bottle finish when the closure is applied. Pressure sensitive liners stick to the container because one side is coated with pockets of adhesive. When the closure is applied to the container, the pockets of adhesive rupture between the closure and finish of bottle or jar. The pressure sensitive liners then stick to the bottle or jar and remain in place when the closure is removed. No extra equipment is required. The closures are supplied with a standard liner as a backing. This material needs a dry land area on the bottle and therefore is suitable only for use with dry products such as vitamins, foods and pharmaceuticals.
Polyseal Cone Liners: Molded in Low Density Polyethylene, Polyseal cone liners form to the inside of the bottle neck providing a leak-proof seal which guards against back-off and product evaporation. Excellent for use with acid products and essential oils, these closures are recommended for use on glass bottles only and are sold in conjunction with our line of glass vials.
Linerless Designs: Land Seal (Crab’s Claw): A popular general purpose linerless sealing mechanism which can be used on most all bottles. The design typically features a .045” molded inner flange which when applied with normal application torque compresses to approximately one-half of its thickness while sealing against the bottle lip. The liner creates a water tight seal with a bottle having a minimum .065” wide sealing surface which is free of nicks, burrs or irregularities. This style linerless mechanism is available in popular dispensing caps.
Promotional use
Bottle caps are also a way for bottlers to hold promotions, especially for soda companies. A message is printed on the inside of the cap and people with the right message may win a prize. Since the bottle must be purchased to determine the message and win, people usually purchase more of the drink to increase their chances of winning. The most common prize is a free soda from that company.
Some companies, such as Snapple, also print interesting facts on the inside of their caps. Mickey's Malt Liquor as well, prints riddles underneath the 24 and 40 oz. bottle caps. Usually this is done on wide-mouthed bottles that have large caps with enough printing area to put a short sentence.
Collectibles
Bottle caps are, by some, considered a collectible item and some communities like Colnect provide collectors a database to manage their personal collections.
Further reading
- * Yam, K. L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, ISBN 978-0-470-08704-6
- U.S. Patent 468,258 -- Bottle sealing device
- U.S. Patent 314,358 -- Combined metallic cap and fastener