Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Organic compound containing silicon
Reexamination Certificate
2002-06-14
2004-10-19
McAvoy, Ellen M. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Organic compound containing silicon
C508S110000, C198S500000, C427S424000
Reexamination Certificate
active
06806240
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to conveyor lubricants and lubricant compositions, to methods of use, for example, to treat or lubricate a container(s) and conveyor surfaces or system for containers. The invention also relates to containers and conveyor surface or system treated with a lubricant or lubricant composition. The container is, for example, a food or beverage container.
The invention relates to maintaining the physical and structural integrity of shaped thermoplastic articles by inhibiting stress cracking. Many thermoplastic articles are formed using thermal methods at elevated temperatures. When formed into simple, regular or complex shapes and cooled, significant stress can remain in the thermoplastic material. The stress is undesirably relieved in the form of cracking. Such stress cracking can be substantially promoted if the stressed thermoplastic is contacted with a material that tends to promote stress cracking. The lubricating methods and compositions of the invention are intended to passivate, inhibit or prevent the undesirable interaction between the stressed thermoplastic and stress cracking promoters.
BACKGROUND OF THE INVENTION
In commercial container filling or packaging operations, the containers typically are moved by a conveying system at very high rates of speed. In current bottling operations, copious amounts of aqueous dilute lubricant solutions (usually based on ethoxylated amines or fatty acid amine) are typically applied to the conveyor or containers using spray or pumping equipment. These lubricant solutions permit high-speed operation (up to 1000 containers per minute or more) of the conveyor and limit marring of the containers or labels, but also have some disadvantages. For example, aqueous conveyor lubricants based on fatty amines typically contain ingredients that can react with spilled carbonated beverages or other food or liquid components to form solid deposits. Formation of such deposits on a conveyor can change the lubricity of the conveyor and require shutdown to permit cleanup. Some aqueous conveyor lubricants are incompatible with thermoplastic beverage containers made of polyethylene terephthalate (PET) and other plastics, and can cause stress cracking (crazing and cracking that occurs when the plastic polymer is under tension) in carbonated beverage filled plastic containers. Dilute aqueous lubricants typically require use of large amounts of water on the conveying line, which must then be disposed of or recycled, and which causes an unduly wet environment near the conveyor line. Moreover, some aqueous lubricants can promote the growth of microbes.
Thermoplastic materials have been used for many years for the formation of thermoplastic materials in the form of film, sheet, thermoformed and blow molded container materials. Such materials include polyethylene, polypropylene, polyvinylchloride, polycarbonate, polystyrene, nylon, acrylic, polyester polyethylene terephthalate, polyethylene naphthalate or co-polymers of these materials or alloys or blends thereof and other thermoplastic materials. Such materials have been developed for inexpensive packaging purposes. Thermoplastic materials are manufactured and formulated such that they can be used in thermoforming processes. Such thermal processing is used to form film, sheet, shapes or decorative or mechanical structures comprising the thermoplastic material. In such processes, the thermoplastic is heated to above the glass transition temperature (T
g
) or above the melting point (T
m
) and shaped into a desirable profile by a shaping die. After the shape is achieved, the material is cooled to retain the shape. The cooling of such materials after shaping can often lock-in stresses from the thermal processing Filling such a container with carbonated beverage can place large amounts of stress in the bottle structure. Most thermoplastic materials when stressed react undesirably to the stress and often relieve the stress through cracking. Such cracking often starts at a flaw in the thermoplastic and creeps through the thermoplastic until the stress is relieved to some degree.
Such stress cracking can be promoted by stress cracking promoter materials. Thermoplastics that are highly susceptible to stress cracking include polyethylene terephthalate, polystyrene, polycarbonate and other thermoplastics well known to the skilled materials scientist. The mechanism of stress crack promotion, initiation and propagation has been discussed and investigated but not clearly delineates Stress cracking can be explained by discussing interactions between stress cracking promoters and the polymeric chains that make up the thermoplastic material. The stress cracking promoters are believed to cause one or more chain to move relative to another chain, often initiated at a flaw in the plastic, resulting in cracking. Other theories include a consideration of the chemical decomposition of the thermoplastic material or (e.g.) a base catalyzed hydrolysis of the polyester bond resulting in weakened areas in the thermoplastic resulting in associated cracking. Lastly, the thermoplastic materials are believed to absorb more hydrophobic materials that soften the thermoplastic and, by reducing the strength of the thermoplastic, can promote the growth and propagation of stress cracking.
Regardless of the theory of the creation and propagation of stress cracks, thermoplastics manufacturers are well aware of stress cracking and have sought to develop thermoplastic materials that are more resistant to stress cracking. Stress cracking can be reduced by sulfonating the bulk thermoplastic after formation into a final article. Further, the manufacture of containers in two, three, four or other multilayer laminate structures is also believed to be helpful in reducing stress cracking. However, we have found that even the improved polymer materials can be susceptible to stress cracking, Further, certain commonly used container structures including polystyrene materials, polycarbonate materials, polyethylene terephthalate materials tend to be extremely sensitive to stress cracking promoters particularly when pressurized or used at high altitudes and can during manufacture, use or storage quickly acquire a degree of stress cracking that is highly undesirable.
One technology involving significant and expensive stress cracking involves the manufacture of polyethylene terephthalate (PET) beverage containers. Such beverage containers are commonly made in the form of a 20 oz, one, two or three liter container for carbonated beverages. Alternatively, a petaloid design can be formed into the polyester to establish a stable base portion for the bottle. In both formats, the polyester beverage container can have significant stress formed in the shaped bottom portion of the bottle. The stresses in the pentaloid structure tend to be greater because of the larger amorphous region and more complex profile of the container base.
Polyester beverage containers are made in a two step process. Melt thermoplastic is formed into a preform. Such preforms are relatively small (compared to the finished bottle) comprising the threaded closure portion and a “test tube” like shape that is blow molded into a final bottle conformation. In manufacturing the beverage containers, the preform is inserted into a blow molding apparatus that heats the preform and, under pressure, inflates the softened preform forcing the preform into a mold resulting in the final shape. The finished beverage containers are shipped to a filling location. The containers are filled with carbonated beverage in a filling apparatus that involves a moving conveyor surface that transports the container during filling. The conveyor structure comprises a filling station, a capping station ant ends at a packing station. While on the conveyor, the containers are exposed to an environment that contains residual cleaners and conveyor lubricants containing organic and inorganic stress cracking components that can interact with the polyester thermoplastic of the container. Stress cra
Besse Michael E.
Hei Kimberly L. P.
Herdt Joy G.
Li Minyu
Lokkesmoe Keith Darrell
Ecolab Inc.
McAvoy Ellen M.
Merchant & Gould P.C.
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