The equipment used in the food processing industry varies by segment with the leading segments comprising meat and poultry, beverages, snack foods, vegetables, and dairy. While the equipment varies from segment to segment, the moving parts such as bearings, gears, and slide mechanisms are similar and often require lubrication. The lubricants most often used include hydraulic, refrigeration, compressor and gear oils, as well as all-purpose greases. These food industry oils must meet more stringent standards than other industry lubricants.
Due to the importance of ensuring and maintaining safeguards and standards of quality for food products, the food industry must comply with the rules and regulations set forth by the United States Department of Agriculture (USDA). The Food Safety inspection Service (FSIS) of the USDA is responsible for all programs involving the inspection, grading, and standardization of meat, poultry, eggs, dairy products, fruits, and vegetables. These programs are mandatory, and inspection of non-food compounds used in federally inspected plants is required.
The FSIS is custodian of the official list of authorized compounds for use in federally inspected plants. The official list (see page 11-1, List of Proprietary Substances and Non-food Compounds, Miscellaneous Publication Number 1419 (1989) by the Food Safety and Inspection Service, United States Department of Agriculture) states that lubricants and other substances that are susceptible to incidental food contact are considered indirect food additives under USDA regulations. Therefore, these lubricants, classified as either H-1 or H-2, are required to be approved by the USDA before being used in food processing plants. The most stringent classification, H-1, is for lubricants approved for incidental food contact. The H-2 classification, is for uses where there is no possibility of food contact, assures that no known poisons or carcinogens are used in the lubricant. One embodiment of the present invention pertains to an H-1 approved lubricating oil. The terms “H-1 approved oil” and “food grade” will be used interchangeably for the purpose of this application.
Although the USDA is no longer approving new ingredients and compositions, the H-1 classification is still recognized by the world food industry. NSF is now listing and approving the food grade classification.
In addition to meeting the requirements for safety set by federal regulatory agencies, the product must be an effective lubricant. Lubricating oils for food processing plants should lubricate machine parts, resist viscosity change, resist oxidation, protect against rusting and corrosion, provide wear protection, prevent foaming and resist the formation of sludge while in service. The product should also perform effectively at various lubrication regimes ranging from hydrodynamic thick film regimes to boundary thin film regimes.
The oxidation, thermal, and hydrolytic stability characteristics of a lubricating oil help predict how effectively an oil will maintain its lubricating properties over time and resist sludge formation. Hydrocarbon oils are partially oxidized when contacted with oxygen at elevated temperatures for prolonged periods of time. The oxidation process produces acidic bodies within the lubricating oil. These acidic bodies are corrosive to metals often present in food processing equipment, and, when in contact with both the oil and the air, are effective oxidation catalysts that further increase the rate of oxidation. Oxidation products contribute to the formation of sludges that can clog valves, plug filters, and result in overall breakdown of the viscosity characteristics of the lubricant. Under some circumstances, sludge formation can result in pluggage, complete loss of oil system flow, and failure or damage to machinery.
The thermal and hydrolytic stability characteristics of lubricating oil reflect primarily on the stability of the lubricating base oil properties and the oil additive package. The stability criteria monitor sludge formation, viscosity change, acidity change, and the corrosion tendencies of the oil. Hydrolytic stability assesses these characteristics in the presence of water. Inferior stability characteristics result in lubricating oil that loses lubricating properties over time and precipitates sludge.
Although such lubricants have been designed to be non-toxic as a food source contaminant, their lubricating properties are often less effective compared to conventional lubricants e.g., lubricants having ingredients not approved for direct food contact. The lubrication industry has, to some degree, overcome this problem by incorporating specialty additives into the lubricant compositions. For example, the inclusion of performance additives has been used to enhance antiwear properties, oxidation inhibition, rust/corrosion inhibition, metal passivation, extreme pressure, friction modification, foam inhibition, and lubricity. Such chemistries are described in the following patents: U.S. Pat. No. 5,538,654 (Lawate, et al.); U.S. Pat. No. 4,062,785 (Nibert); U.S. Pat. No. 4,828,727 (McAninch); U.S. Pat. Nos. 5,338,471 and 5,413,725 (Lai).
A drawback to the food-grade-lubricants described in the above patents relates to oxidation resistance, pour point characteristics, limited formulating capability for viscosity breadth, and limited viscosity protection. The lubricants often have poor rheology characteristics when subjected to prolonged heat and mechanical stress.
Therefore, there remains a need for a food-grade-lubricant that exhibits excellent hydrolytic stability, corrosion resistance, and anti-wear, with substantial improvements in oxidation resistance, pour point, viscosity index, viscosity breadth formulating capability, and viscosity stability when subjected to the thermal and mechanical stresses.