Lubricant Properties          Relative Wear at Various Temperatures       Automotive Applications

"BONDED" SOLID FILM LUBRICANT

The simplest definition of a solid film lubricant is a system of solid materials used to separate two moving surfaces to reduce friction and wear. There is a mulititude of materials from which the solid lubricant can be formulated and also a variety of methods for adhering the lubricant to the substrate. The lubricants that NPI formulates and processes are composed of two or more lubricating pigments dispersed in a binder, diluted with a solvent, and sprayed or dipped onto the substrate, and cured to form a "bonded" solid film lubricant. The common constituent in NPI lubricants, as well as the majority of lubricants made by other companies, is molybdenum disulfide (MoS2). This material has a laminar structure composed of two layers of sulfur atoms separated by a layer of molybdenum atoms providing a layer lattice structure, much like a deck of cards. The generally accepted theory is that there is a strong bond between the sulfur to molybdenum atoms and weak bonds between the sulfur to sulfur atoms, thus creating low friction due to movement between the low shear strength sulfur to sulfur surfaces.

Commerically available bonded solid film lubricants came about in the late 1940's and early 1950's. Almost all of these were composed of MoS2, graphite, phenolic resin (binder), a suitable solvent, and a cure temperature of + 300 degrees F at a thickness of 0.0002 to 0.0005 inches. The ratio of MoS2 to graphite generally ranged from 90/10 to 70/30 and in some cases, powdered metals were also included in the mixture. In many respects a "bonded" solid film lubricants is like a paint except the pigment content (MoS2, graphite, materials, etc.) is much higher and the thickness is greatly reduced and more closely controlled.

The majority of R&D work on bonded solid film lubricants occured during the 1950's and 1960's by the government, government contractors, and dry film companies. Since 1950, there have been many changes or revisions to the original products.

The binders have been expanded to include such things as sodium silicates, phosphates and ceramics. The lubricating pigments have been expanded to include antimony trioxide (Sb2O3), silver, gold, and PTFE. Cure temperatures have also been changed to reflect the nature of the binder system to +1000 degrees F or higher. However, the performance of "bonded" solid film lubricants is still not only a function of the specific ingredients but also the care that is taken to insure that all products are as consistent as possible, given the inherent problems associated with this type of material. NPI feels very strongly that their emphasis on only a limited number of quality bonded solid film lubricants allows us to provide our customers the quality control that is necessary.