Compositions: coating or plastic – Coating or plastic compositions – Bituminous material or tarry residue
Reexamination Certificate
2003-02-13
2004-08-17
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Bituminous material or tarry residue
Reexamination Certificate
active
06776833
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of sealants, coatings and mastics, and, more particularly to the use of emulsions as sealants, coatings and mastics for cold applications.
BACKGROUND OF THE INVENTION
The use of bitumens and/or blends thereof for sealant, coating and mastic applications is well known. Bitumens are mixtures of heavy hydrocarbons, essentially naphthenic and paraffinic, originating from the distillation of crude oils. These products are distillation residues and are classified by their physical properties, their chemical properties varying very widely as a function of the origins of the crude. Generally speaking, conventional crudes contain up to 30% bitumen, and heavy crudes up to 50%. As bitumen requirements of the majority of countries represent 2 to 4% of their crude oil consumption, this means that bitumen is available in very plentiful supply. Bitumens contain such a diversity of constituents that it is impossible to define their exact composition; nevertheless, it is possible to classify these constituents into major chemical families:
saturated compounds, essentially paraffinic;
aromatic compounds, in which 30% of the carbon atoms are included in aromatic cycles, with a sulphur content of around 2 to 3%;
asphaltenes, which are insoluble in hydrocarbons, are aromatic and rich in sulphur, nitrogen, and oxygen; they take the form of black brittle solids practically incapable of being melted.
For given bitumens, the percentage of these various families depends heavily on the extraction method used. Thus, products of this type are essentially classified by the following physical properties: penetrability (NFT 66-004), softening point (NFT 66-008), density (NFT 66-007), flashpoint (NFT 60-118), solubility (NFT 66-012) ductility (NFT 66-006), brittleness point. Commercially available bitumens, classified by penetrability index, are generally situated between 10 and 200.
Such bitumens and/or blends can be applied to surfaces using “hot application” or “cold application” methods. In hot applications, the composition is heated, typically to temperatures well over 100° F., in order to decrease viscosity of the composition to facilitate application to the intended surface. Such heating requires special equipment and experienced personnel. Obviously, it is desirable to avoid working with a hot material at a job site, which may be a roof top, roadway, or similar surface, thus there has been a trend toward cold application compositions.
Various technologies have been developed to provide for cold application. They involve placing the bitumen in a fluid media, or vehicle, allowing for application without requiring heating. After application, the bitumen solidifies or cures through the elimination, in most cases by evaporation, of the vehicle. The two most common vehicles are solvents and water.
When using a solvent as the vehicle, the bitumen must be soluble in the solvent. Most often, the solvent is a petroleum distillate. Petroleum distillates produce blends that are commonly referred to as cutbacks or road oils. They vary in viscosity and cure rate depending on the type of base bitumen, type of solvent, and composition.
In such cutbacks, bitumens of differing physical characteristics may be blended to offer improved performance characteristics, e.g., elongation, recovery, and weatherability. Organic and inorganic fillers may be utilized to provide reinforcement and resistance to flow. The introduction of elastomers may be accomplished via solvation in aromatic and aliphatic hydrocarbon solvents, or combinations thereof. In such cases large amounts of various solvents are typically necessary to decrease the viscosity of the composition to facilitate spreading on the intended surface at ambient temperature. Cutbacks have been used successfully in products for use as sealants, roof coatings and roof patches, mastics including plastic cements and the like. However, while these solvent-based compositions have great long term durability including a high degree of water resistance, the required use of large volumes of solvents results in the release of high levels of volatile organic compounds (“VOCs”) when the solvents evaporate as the compositions dries.
Many VOCs are known to be highly toxic and present health dangers. Others harm air quality, contribute to the creation of smog and are suspected to escalate global warming. Due to increasing concern over the effects of VOCs on humans and the environment, the need for compositions having lower levels of VOCs has become a high priority in the fields of sealants, coatings and mastics.
The use of water as the fluid media requires the action of surface active agents (emulsifiers). A mixture of water and bitumen produces a dispersion commonly called an emulsion. Bitumen emulsions consist of two types, those in which the bitumen is dispersed in an external or continuous phase of water, and those in which the water is dispersed in the external phase of bitumen.
The use of emulsions as compared to bitumen cutbacks is becoming increasingly popular as the product of choice for the non-heated applications. This is because of the dangers and hazards of solvent-containing compositions to the environment and hazards with employee exposure to solvents in manufacturing and application as discussed above. Storage stability, freeze thaw stability, limited compatibility with auxiliary additives, and low binder (bitumen solids) contents are deficiencies in current bitumen emulsions which hinder and often restrict their use.
For many years various clays have been used in combination with both petroleum- and coal tar-derived bitumens to form aqueous emulsions. These so-called “colloidal clays” have many of the chemical and physical properties necessary to suspend the bitumen in the aqueous phase, providing the emulsion the consistency and stability desired. However, colloidal clay emulsions have a tendency to phase-separate: the bitumen and clay particles (when in the discontinuous phase) settle over time, becoming a dense mass. Reblending into a homogeneous colloidal emulsion is often difficult and time-consuming. Phase-separation is especially troublesome and costly when extensive reblending is required just prior to application. The consequences of applying a phase-separated emulsion are even more undesirable and include: inadequate coverage rates, disabled spray equipment, non-uniform curing rates, varying cured-coating performance properties, and discolored and unsightly coating appearances, to mention but a few.
In order to reduce phase separation, manufacturers have attempted to achieve sufficient dispersion by extensive mixing of the water and colloidal clay slurry, typically for over 8 hours and often for much longer. However, such extensive mixing has still not led to a sufficiently stable bitumen emulsion nor sufficient hydration of the clay.
Concern over phase separation and the problems associated with it fostered the use of water-soluble gums, including cellulose ethers, which retard phase separation by absorbing water from the aqueous phase and increasing emulsion viscosity. While this approach is relatively inexpensive and alleviates many of the aforementioned concerns, it has associated with it a number of significant problems and deficiencies. Most are related to inadequate emulsion performance and phase-separation.
Another significant problem with the use of water-soluble gums is the required addition of biocides. Cellulose thickeners are, for the most part, vegetable matter. For example, cellulose gums are derived from various sources, including wood pulp and cotton. These materials support fungal and bacterial life, the bi-products of which are weakly acidic and may later “sour” the emulsion causing phase separation. As a preventative measure, synthetic biocides must be added during emulsion formulation and represent an extra production cost.
In summary, a considerable number of drawbacks and problems exist in the art relating to bituminous emulsions. There is a need for an improved emulsi
Hyer Raymont T.
Malina Barton J.
Yap Michael L.
Brunsman David
Gardner Asphalt Corporation
Jansson & Shupe & Munger Ltd.
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