Compositions: coating or plastic – Coating or plastic compositions – Bituminous material or tarry residue
Reexamination Certificate
2000-01-07
2003-06-10
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Bituminous material or tarry residue
Reexamination Certificate
active
06576050
ABSTRACT:
DESCRIPTION OF THE INVENTION
This is a 371 of PCT/FR99/01093 filed May 7, 1999.
The invention relates to a process for preparing emulsions of bituminous binder which can be used in all the applications of bitumen emulsions, including the construction and maintenance of the road surfaces as well as the construction and building industry.
The invention also relates to the emulsions prepared according to the process of the invention.
Emulsions of bituminous binder are conventionally prepared by mixing a dispersed phase and a dispersing phase in a suitable mixer. The dispersed phase can consist either of pure bitumen or of a bitumen mixed with a flux, a fluidizing agent and/or an elastomer, i.e. a modified bitumen. The dispersing phase comprises, in particular, water and various emulsifiers or surfactants. Examples of mixers which may be mentioned are colloidal mills and static mixers.
More generally, mixers which are suitable produce a shear of phases present during mixing.
As a variant, it is also known practice to add the surfactant or an additional surfactant to the dispersed phase.
When the surfactant used for manufacturing the emulsion is cationic or nonionic, the emulsion generally contains from 50 to 70% by weight of bituminous binder. When the surfactant used is anionic, the concentration of binder in the emulsion is typically from 50 to 65% by weight. The emulsions obtained from anionic surfactants are usually finer and more viscous than those comprising cationic surfactants.
According to the process of the prior art, it is possible, by varying the nature and amount of surfactant used, to control the stability of the emulsion, i.e. both its stability on storage and its stability with respect to breaking.
More specifically, it is known in the art that by increasing the amount of emulsifier, it is possible to slow down the breaking of the emulsion and to increase its stability on storage.
However, the amount of emulsifier added also has an influence on the particle size of the resulting emulsion and on its viscosity, such that, according to the prior art, a compromise must be accepted in order to optimize the rate of breaking of the emulsion, its viscosity and the properties associated with the fineness of the emulsion.
The process of the invention allows better control of the rate of breaking almost independently of the viscosity and the particle size distribution of the emulsion.
SUMMARY OF THE INVENTION
The emulsions of the invention have a higher viscosity than the emulsions of the same formulation obtained according to the processes of the prior art. Viscous emulsions are particularly desirable for certain applications, such as the preparation of surface dressings (chipseals) which need to be applied to roads with a high slope or a high crossfall (superelevation).
Unexpectedly, the inventors have realized that the process of the invention results in the preparation of emulsions which have a narrower size distribution of the droplets in the dispersed phase (referred to as the granulometric distribution hereinbelow) and thus a higher viscosity. The other advantages of the process of the invention will readily become apparent to a person skilled in the art on reading the present description.
More specifically, the process of the invention comprises:
a) the preparation of a concentrated primary emulsion containing a surfactant and at least 65% by weight in the case of an anionic emulsion, or at least 70% by weight in the case of the other emulsions, of bituminous binder, by mixing an initial aqueous phase and a liquid bituminous phase under the effect of a mechanical shear energy and in the presence of the said surfactant; and
b) the addition of an aqueous dilution phase to the said primary emulsion.
The emulsions prepared according to the process of the invention have a higher viscosity than that of a corresponding emulsion of the same formulation, obtained by mixing an aqueous phase and a bituminous phase under the effect of the same mechanical shear energy as used for the preparation of the primary emulsion. Generally, the viscosity is at least 20% higher than that of the corresponding emulsion.
According to the invention, the expression “bituminous binder” means direct distillation, de-asphalting or oxidized bitumens, in pure, fluidized or fluxed form. As is known, hydrocarbon-based binders can be fluidized with light petroleum solvents such as kerosene, and fluxed with oils from coal or from petroleum. Other examples of bituminous binders which may also be mentioned are acidic bitumens such as naphthenic acid derivatives. These same binders can be used in a form modified by adding one or more polymers, organic resins or recycled rubber crumbs.
The primary emulsion is prepared in a manner which is known per se by mixing, under shear, an initial aqueous phase with a liquid bituminous phase containing the bituminous binder, in the presence of a surfactant.
DETAILED DESCRIPTION OF THE INVENTION
The mixing under shear can be performed in the conventional mixers used in the art for the preparation of bitumen emulsions. This type of mixture can be prepared using colloidal mills, turbomixers, pumps or the like or alternatively using static mixers.
When the mixing is carried out continuously, the aqueous phase and the liquid bituminous phase are introduced in proportions which allow direct production of the desired concentration for the primary emulsion.
The mixing can also be performed in a batchwise manner by gradual enrichment of the initial aqueous phase, maintained under mechanical stirring in a suitable mixer, with liquid bituminous phase until the desired concentration for the primary emulsion is obtained.
The primary emulsion can be a direct emulsion (oil-in-water emulsion) or a reverse emulsion (water-in-oil emulsion).
The temperature at which the bituminous phase is introduced into the mixer is sufficient to maintain the bituminous binder in the liquid state. A temperature above 100° C. is generally necessary.
A person skilled in the art will take care to ensure that the primary emulsion does not start boiling when it leaves the mixer.
To this end, it is convenient to adjust the respective temperatures of the aqueous phase and the bituminous phase which have to be introduced into the mixer and, if need be, to carry out the mixing under pressure.
As a guide, a temperature between room temperature and 70° C. is generally suitable for the initial aqueous phase.
The primary emulsion is either anionic (and in this case it is prepared in the presence of an anionic surfactant) or cationic (in which case the surfactant is cationic), or alternatively nonionic (when the surfactant is nonionic). Cationic emulsions are preferred in the context of the invention.
According to the invention, it is possible to envisage the preparation of any other type of primary emulsion, for example a primary emulsion prepared using a zwitterionic surfactant.
The surfactants which can be used according to the invention are those generally used in the art for the preparation of a bitumen emulsion and can be cationic, anionic, nonionic or zwitterionic.
The surfactant can be added to the initial aqueous phase, to the bituminous phase or partly to each of these two phases.
As a general rule, all of the surfactant is added to the initial aqueous phase. However, addition of all or some of the said surfactant to the bituminous phase during the preparation of the primary emulsion leads to a finer particle size of the primary emulsion, i.e. the average diameter of the droplets of the primary emulsion is smaller than when all of the surfactant is present in the aqueous phase.
The amount of surfactant which needs to be used during the preparation of the primary emulsion will readily be determined by a person skilled in the art depending on the final use for which the bituminous binder emulsion is intended.
However, as a guide, it may be noted that an amount of surfactant of less than 20 kg per tonne of primary emulsion is generally sufficient.
When the surfactant is cationic, an amount of surfactant of fro
Brunsman David
Colas
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