US 3047526 A
Description (OCR text may contain errors)
United States Patent Orifice a My 19.,
season 2 Claims. (Cl. zen-32.8
This invention relates to a novel composition of matter used to coat the leather element in shaft and rod seals. This application is a division of our application Serial No. 713,024, filed February 3, 1958, now U.S. Patent No. 2,983,131, which in turn is a division of our application Serial Number 540,104, filed October 12, 1955, now U.S. Patent No. 2,854,267, which was a continuation-in-part of our application Serial Number 519,862, filed July 5, 1955 now abandoned.
Leather has long been favored as far superior to most materials as a pliant sealing element for shafts, reciprocating rods and the like. Despite this, it is recognized that leather has certain disadvantages and fails to exhibit, to the degree desired, all the characteristics needed to meet the ever increasing requirements for a satisfactory seal. For example, leather varies Widely in density, resilience, porosity and flexibility, all of which affect performance and suitability for use as sealing elements. Accordingly, over the years much effort has been directed toward improved processing procedures in an endeavor to provide a product of more uniform properties and longer service life. In addition, these attempts have included the augmentation of existing properties as well as the inclusion of new ones.
Another facet of the problem derives from the fact that certain desired properties of leather are customarily found only in combination with undesirable ones. For example, a leather having the desired flexibility is too soft to maintain good sealing contact with an eccentrically rotating shaft, or one which vibrates or whips as it rotates. Also, a flexible leather usually is quite porous. In consequence, it has a high reservoir capacity for lubricantan advantageous quality. But this porosity is also attended by seepage of lubricant through the side Walls of 'the leathera highly undesirable quality. Previous efforts to seal the pores have destroyed the leathers capacity for storing lubricant and have stiffened the leather vobjectionably.
of novel coating compositions suitable for sealing the surface of leather, textiles and the like and of imparting new and unique properties thereto in a simple, inexpensive and highly eflicient manner.
Numerous other objects and. advantages of the invention will become readily apparent from the following detailed specification.
The invention provides a thin film or veneer of a special elastomer bonded to one or more surfaces of the leather. If. only one surface of the leather member is to be coated, it is preferable to coat the hair side rather than the opposite flesh side and, in a shaft seal, to so mount the seal in the housing bore that the elastomeric veneer is in contact with the shaft and is remote from the interior of the housing.
The principal functional ingredients of the veneer are a synthetic oil-resistant elastomer such as neoprene, a polyacrylic, a nitrile, or a chlorosulfonated polyethylene rubber having a suitable dry lubricant dispersed therein, such as graphite, molybdenum disulfide, mica or talc. These substances, compounded along with a suitable solvent vehicle in a manner to be disclosed below, are applied in liquid form to the surface of the leather sealing member and then vulcanized.
The elastomer does not penetrate beyond the base of the hair pore openings or of the surface crevices and other imperfections of the leather. This confinement of the veneer to the immediate surface area of the leather and its absence from the many voids in the body of the leather is highly important and has several advantages. Thus, the absence of elastomer from the interior body of the leather permits of a free and natural capillary flow of lubricant within the leather in a path generally parallel to the inner and outer surfaces. Secondly, the many voids naturally present in the leather are available as lubricant storage reservoirs. And, thirdly, the inherent flexibility of the body of the leather is not adversely affected by the presence of incompressible particles filling the voids. And, of special significance, the exterior surface of the leather or the one in contact with the rotating shaft is sealed by a thin film of resilient material which is highly resistant to attack by lubricants, relatively impervious to both liquids and gases, and has a coefficient of friction at least 50% lower than the identical leather sealing element without the surface coating of this invention.
In practice, a film thickness of 2 to 5 mils has been found most effective. Greater thicknesses can be employed but have a tendency to stiffen the leather objectionably and are not found to add to the service life of the sealing element to any material extent.
Coating both sides of the sealing element has certain advantages. It stiflens each side of the leather in equal degree; it provides a smooth finished surface on both sides of the sealing element; and it provides a substantially 'sealed reservoir for lubricant within the body of leatherproper. The outer rim of this reservoir is sealed by the surrounding housing for the sealing element, leaving only the inner peripheral edge exposed to the interior of the appliance housing and the supply of oil therein. If the seal is to be used in a location not exposed to lubricating mediums, then the sealing element can be saturated with lubricant before installation. Thus, in either mode of use, the sealing edge of the lip has a continuous supply of oil available at all As soon as a film of oil between the shaft and the contacting edge of the seal tends to disappear, it is immediately replenished from the supply stored by capillary action in the body of the seal. Furthermore, the low friction coating in direct contact with the shaft contains a dry lubricant locked within the coating. This dry lubricant supplements the liquid lubricant within the body of the sealing element.
The coating compositions which we have found to be so satisfactory for surface films or coatings are elastomers or rubber-like synthetics incorporating one or more dry lubricants that are dispersed therein to impart lubricity and other related properties important to a properly functioning seal. For example, the coating elastomer may be Neoprene GN .(trade name for neoprene with an antioxidant stabilizer), or Neoprene, GRT (trade name for neoprene with low temperature crystallization inhibitor), standard elastomen'c polymers of chloroprene commeroially available from E. I. du 'POl'llt dc Nemburs & 00. One hundred parts of this material should be compounded for rapid curing and mixed with between and 60 parts by volume of a filling agent having lubricating properties such as graphite, molybdenum disulfide, mica or talc. F or graphite, the range by weight is between and 120 parts per 100 parts elastomer.) This mixture is dissolved in a suitable solvent to provide a low viscosity solution of 5-20% solids. If a lower solids content is employed, the film does not distribute uniformly to provide a reliably continuous veneer, while a solution of higher solids content is too viscous for satisfactory results. It will, of course, be understood by those skilled in the handling of elastomeric compositions that suitable curing agents, anti-oxidants and accelerators are required as usual.
Suitable solvents include a mixture of one or more aromatics (toluene, benzene, or xylene and homologues of them) with paraffin hydrocarbons (e.g., gasoline or kerosene) or ketones (acetone, methyl-ethyl-ketone, and other liquids of the group) or naphthas. Wide variations of quantities can be used, and which solvent mixture is selected will depend on factors such as evaporation rate desired, cost, toxicity, etc.
The following specific examples sufiice to illustrate the relative proportions of constituents which have been found particularly suitable in actual practice:
EXAMPLE I Neoprene rubber Another composition giving excellent results employs copolymers of butyl acrylate and acrylonitrile or ethyl acrylate and chloroethyl-vinyl ether in lieu of neoprene. Such a composition may be compounded as follows:
EXAMPLE II Polyacrylic elastomer Constituents: Parts by weight Lactoprene BA 12.5 (An acrylonitrile (87.5 )-butyl acrylate (12.5% copolymer) 100 Stearic acid 1 Sulfur 1 Triethylene tetramine 4 Graphite 80 Total solids 186 Methyl-ethyl-ketone 1,504 Toluene 170 Total liquids 1,674
Grand total 1,860
Still another composition which we have found to provide an excellent adherent veneer for leather employs chlorosulphonated polyethylene as a principal elastomeric component. This coating composition is made from the Kenflex BKenrich Corp. trademark for a non-volatile synthetic polymer of aromatic hydrocarbons which has a melting point of 80 F In any of these examples, mica, talc, and molybdenum disulfide may be substituted for graphite, in equal volumes.
Graphite is, however, preferred.
Any of the foregoing compositions may be applied to the leather by dipping, dripping, spraying or other common coating techniques. Curing or molding may be for one minute at a temperature of approximately 275 F. It will, of course, be appreciated that the pressure, molding period and temperature may be varied over a considerable range as found to give the best results for the particular leather and coating composition being used. Molding may be carried out for longer periods (up to 90 seconds) at lower temperatures, and shorter periods (down to 10 seconds) at higher temperatures, but temperatures higher than 325 F. should be avoided, else damage to the leather may result.
1. A coating composition for leather liquid-lubricantsealing members, consisting essentially of a solvent-elastomer dispersion of (1) 8095% by weight of a solvent mixture consisting (A) an aromatic solvent selected from the group consisting of benzene, toluene and xylene, and (B) an aliphatic solvent selected from the group consisting of acetone, methyl ethyl ketone, gasoline, kerosene and naphtha, and
(2) 520% by weight of a solids mixture consisting essentially of '(C) liquid-lubricant-resistant flexible elastomer selected from the group consisting of polychloroprene, copolymers of ethyl acrylate and chloroethyl vinyl ether, copolymers of butyl acrylate and acrylonitrile, and chlorosulfonated polyethylene, and (D) 10-60 parts by volume per 100 parts by volume of (C) of a dry lubricant selected from the group consisting of graphite, molybdenum disulfide, talc, and mica.
2. A coating composition for leather liquid-lubricantsealing members, consisting essentially of a solvent-elastomer dispersion of (1) -95% by weight of a solvent mixture consisting (A) about by weight of (1) of methyl ethyl ketone 75 (B) about 10% by weight of 1) of toluene 5 (2) 5-20% by weight of a solids mixture consisting essentially of (C) a liquid-lubricant-resistant flexible elastomer selected from the group consisting of polychloroprene, copolymers of ethyl acrylate and ohloroethyl vinyl ether, copolymers of butyl acrylate and acrylonitrile, and chlorosulfonated polyethylene, and (B) 10-60 parts by volume per 100 parts by volume of (C) of a dry lubricant selected from the group consisting of graphite, molybdenum disulfide, talc, and mica.
References Cited in the file of this patent UNITED STATES PATENTS Stewart Nov. 16, 1937 Dombnow et a1 Mar. 22, 1949 Pyle June 10, 1952 Cheronis Apr. 14, 1953 Wilson Sept. 30, 1958 Crissey et a1 Apr. 216, 1960 Morris May 31, 1960