1. Field of the Invention
The present invention pertains generally to lubrication of substrates and, more particularly, to an improved two-component lubrication composition and method of application, and, further, to an improved, scratch-resistant, low friction lubricated substrates such as photographic film and recording elements.
2. Description of the Prior Art
Lubrication of various substrates, and particularly of substrates upon which information has been stored and from which the information can be recalled by dynamic means, has long been recognized as a most difficult problem. Examples of such substrates include computer recording disks, magnetic recording for sound and video production and photographic projection film such as moving picture film, slide film and microfilm. Previous attempts to provide such lubrication have met with varying success.
Lubrication of photographic film, and particularly lubrication of photographic film utilized either statically or dynamically, for projection of images by directing a light beam through transparent photographic film, presents one of the most difficult of lubrication problems. When photographic film is repeatedly positioned in a gate or holder, the mechanical interface tends to abrade the film and, in the instance of motion pictures, such abrasion or sticking causes an erratic presentation upon the screen as the photographic film binds and releases. Recently, an even more demanding application has appeared. This involves continuous roll film cartridges utilizing a continuous loop of photographic film which unwinds internally of the roll and rewinds on the periphery of the roll. Rather substantial friction occurs as the photographic film is pulled laterally, in a generally spiral configuration, from the center portion of the roll. Despite such greatly increased wear potential, continuous loop film cartridges are finding favor as convenience items for use in such as projection of feature films on aircraft, sales films, educational films, etc.
Photographic film, by its nature, is a difficult substrate with regard to lubrication and wear. Basically, photographic film comprises a relatively soft emulsion coated on a generally pliant support. The emulsion must be both protected from abrasion and provided with a low coefficient of friction. Merely providing a low coefficient of friction does not afford the necessary protection in that the soft emulsion does not have the strength to withstand substantial forces impinging thereon even if friction is low. However, a prime consideration of the prior art has been to lower the coefficient of friction often to the exclusion of providing a protective coating with regard to surface coating strength. Since the emulsion has little inherent strength and scratch resistance, the lubricous coating must provide these properties as well as low friction. In addition to the emulsion side, it is important to also protect and lubricate the "backside" of the film since scratches therein will also be visible in projections.
Another seemingly apparent attribute of a lubricous coating for photographic film, and particularly photographic film which is intended for projection, is transparency of the coating. However, many of the previous coatings avoid complete opacity only by utilizing quite thin coatings. Though essentially opaque, little lubricant is applied as to permit adequate, if not complete, light transmission. The problem of opacity is compounded when properties other than lubricity, i.e., strength, are provided through the use of more than one component.
While photographic film is particularly difficult to lubricate, magnetic recording elements present somewhat different but also demanding conditions. Coatings of lubricants must be quite thin to avoid degrading the interaction between the recording or pickup head and the magnetic particles. The lubricous coating must not accumulate on the head. In the case of disk and cylindrical rotors recording elements, "flying heads" used with such recording elements tend to "crash" on the element with tremendous localized forces being generated. Thus, protection must be afforded the disk to prevent damage thereto as a result of such crashes.
Magnetic tape is comprised of highly abrasive particles dispersed in a binder. Without protection, the recording head can be rapidly worn by the particles as the magnetic tape moves over the recording head.
Put succinctly, the operating environment and nature of magnetic recording elements require most demanding performance from lubricants used thereon.
Various waxes and other substances have been used to lubricate substrates. Also, fluorinated compositions, such as Vydax composition, have been used as lubricants in sundry applications. U.S. Pat. No. 3,490,946 discusses the use of such fluorinated polymers in conjunction with lubrication of magnetic tapes. Generally, this patent would appear to constitute a typical prior art approach to lubrication of magnetic recording elements.
The most pertinent prior art applicable to photographic films would again appear to be the use of Vydax, a proprietary tetrafluoroethylene telomer, as a photographic film lubricant. This specific lubricant was utilized as a performance reference with regard to testing the effectivenss of the method and composition of the instant invention.