Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-11-28
2002-11-19
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S192000, C525S194000, C525S208000, C525S217000, C525S221000, C525S222000, C525S232000, C428S500000, C427S386000, C524S515000, C524S521000, C524S525000
Reexamination Certificate
active
06482894
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a liquid ebonite coating. More particularly, it relates to a liquid ebonite coating containing two reactive components.
BACKGROUND ART
There is a pervasive and continuing need for protecting metals from corrosive chemical action, such as in metal pipes, stacks, chimneys, bridges, chemical plant constructions, ship hulls, and containers for aggressive chemicals, to name just a few applications. In addition to having a high resistance to chemical action, an ideal coating has certain other properties: the raw materials required to produce the coating are commercially available, inexpensive and non-hazardous; the coating has the ability to be easily applied to the metal, e.g. by spraying, spreading, or free casting; the coating has strong adhesion to many different metals; it is strong, hard, abrasion resistant and thermostable; and the hardening process of the coating can be performed in contact with moisture, does not require extreme or long heating, and does not release toxic fumes. An ideal metal coating may have many additional properties, depending on the particular application or purpose of the coating.
The most widespread anticorrosive coatings possessing many of the above properties are polyurethanes and epoxide resins (see for example,
Coating Systems: A guidance Manual For Field Surveyors,
American Bureau of Shipping and Affiliated Companies, 1995). These coatings have good chemical resistance to many substances, have adhesion to metals that is satisfactory for many purposes, and have good mechanical properties. Neither polyurethanes nor epoxide resins, however., satisfy all the criteria for an ideal coating for metal. In particular, although polyurethanes have outstanding oil-gasoline resistance, a unique combination of favorable physical-mechanical properties, and strong adhesion to some metals, they are not stable under elevated temperature, alkaline hydrolysis, and persistent tension. Epoxide resins, although they have outstanding adhesion to some metals, do not have a satisfactory resistance to acids, certain solvents, temperature changes, and vibration. One of the most significant problems associated with both epoxide resins and polyurethanes is their susceptibility to underfilm corrosion associated with defects in the coating surface. Because these coatings are bonded to the metal only by adhesive bonding, these bonds can be broken by the introduction of moisture, solvents or other substances.
As is known from rubber chemistry (
Encyclopedia of Polymer Science & Technology,
John Wiley & Sons, N.Y., vol 12, p.161, 1970), solid ebonite, commonly known as hard rubber, is a polymer material with sulfur content used for vulcanization. Ebonite, like elastomeric or flexible rubber, is made from a combination of sulfur with polydienes (unsaturated rubbers containing double bonds). The sulfur and polydienes are combined with some auxiliary additives and heated to produce vulcanization. Typical mass ratios of sulfur to rubber are 2:100 for elastomeric rubber and 40:100 for hard rubber. Due to the large degree of sulfide cross-linking formed in the vulcanization process, solid ebonite is a hard, non-flexible, plastic-like material possessed of unique chemical resistance to aggressive substances such as acids, alkalis, salt solutions, oil, and gasoline. In addition, solid ebonite has good mechanical properties. Consequently, these conventional rubbers are commonly used as materials for fuel tanks, containers for aggressive substances, and other applications. In spite of these advantages, however, solid rubbers can not be easily applied to metal surfaces, they release toxic fumes during vulcanization, and they require a long time to harden.
More than 30 years ago liquid rubbers were synthesized. (See Alan R. Luxton, “The Preparation, modification and application of non-functional liquid polybutadienes”,
Rubber Chemistry and Technology,
54 (1981) 3, 596-626.) Like earlier rubbers, liquid rubbers are formed from compounds such as polybutadiene, polyisoprene, butadiene-styrene, and butadiene-nitrile. In contrast to the hard rubbers, which are made from such compounds having molecular weights on the order of 100,000 to 500,000, the liquid rubbers are made from such compounds having molecular weights of only 2,000 to 4,000. Consequently, the low molecular rubbers permit castable processing by pouring, spreading, spraying, or rolling, while providing similar properties as the hard rubbers after curing. Liquid rubber, therefore, may be used to more easily coat metal surfaces.
However, all the prior art liquid ebonite coatings suffer from two major disadvantages. First, during the heating, especially on a vertical surface, the coating will have problems of sagging, flowing or dripping since the viscosity of the coating decreases as the temperature increases. Therefore, their viscosity must be increased to prevent sagging. The high viscosity makes spraying of the liquid ebonite mixture very difficult, and even impossible in some cases. Second, the coatings are gooey, which makes the handling or inspection of the coating before vulcanization impractical. The coating of large equipment, such as a precipitator, requires a tack free surface so that coated parts can be handled and assembled before the whole equipment is heated and vulcanized. Also, critical coatings such as tank linings must be inspected to ensure even coating thickness and holiday free coating. Inspection requires tack free surface so that an inspector can touch or walk (for a large structure) on the coated surface.
Liquid ebonite mixture (LEM) compositions are disclosed by Figovsky in WO 0,006,639 issued Feb. 10, 2000, which contains 10% of a high molecular weight rubber for increasing the viscosity of the liquid ebonite mixture for preventing the problems of sagging. Unfortunately, the high viscosity LEM of Figovsky is unsprayable. Furthermore, LEM of Figovsky is gooey, which makes the handling and inspection of the coating before vulcanization impractical.
A liquid rubber based ebonite coating has been disclosed by Rappoport in U.S. Pat. No. 5,766,687 issued Jun. 16, 1998 and U.S. Pat. No. 5,997,953 issued Dec. 7, 1999. In these prior art patents, to prevent sagging, the viscosity of the liquid ebonite mixture is increased by adding thixotropic fillers, such as bentonites and fume silica, or high structure carbon black. The ebonite coating in Rappoport's inventions includes a single component with the compositions shown in Table 1.
TABLE 1
Compound
Mass Parts
Epoxidized liquid rubber, coating building
100
block
Sulfur, vulcanization agent
30-35
Polyamine, hardener and solvent
2-6
Micronized aluminum oxide, heat conducting
5-10
agent
2-mercapto benzothiazole, accelerator
2-3
Diphenylguanidine, accelerator
2-3
Zinc Oxide, activator
5-6
Cab-O-Sil, thixotropic agent
2-10
Butadiene-nitrile rubber, elastifer
1-2
Calcium oxide, absorber
3-5
Unfortunately, the single component ebonite coating of Rappoport sags and is unsprayable.
There is a need, therefore, for a liquid ebonite mixture for coating, which will overcome the disadvantages of the prior art, but still maintain excellent properties, such as chemical resistance and tenacious bonding to metal.
SUMMARY
These objects and advantages are attained by a two-component reactive liquid ebonite mixture.
According to an exemplary embodiment of the present invention, a liquid ebonite mixture for coating contains first and second components. The first component contains first unsaturated polymers, which include first functional groups that are capable of reaction at ambient temperature either with or without a catalyst, a vulcanization activator, and a vulcanization agent. The second component includes second unsaturated polymers, which contain second functional groups that will react with the first functional groups of the first unsaturated polymers at ambient temperature. The first and second unsaturated polymers must contain sufficient unsaturation in the backbones for forming linkages with the vu
Betts, III William L.
Chang Rong Jong
Mazeika Linas
3L & T, Inc.
Lumen Intellectual Property Services Inc.
Nutter Nathan M.
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