Colloid systems and wetting agents; subcombinations thereof; pro – Continuous liquid or supercritical phase: colloid systems;... – Aqueous continuous liquid phase and discontinuous phase...
Reexamination Certificate
2000-01-28
2003-08-05
Lovering, Richard D. (Department: 1712)
Colloid systems and wetting agents; subcombinations thereof; pro
Continuous liquid or supercritical phase: colloid systems;...
Aqueous continuous liquid phase and discontinuous phase...
C106S277000, C516S038000, C516S928000
Reexamination Certificate
active
06602917
ABSTRACT:
This application is a 371 of PCT/FR 98/01674 filed Jul. 28, 1998.
The present invention relates to a process for emulsifying a viscous hydrophobic or hydrophilic phase, which is useful in particular for preparing concentrated and calibrated bitumen emulsions, and also relates to the emulsions thus obtained.
Emulsions concentrated in highly viscous hydrophobic compound(s) are used in particular in the surfacings sector, such as, for example, in the road industry. The reason for this is that emulsions represent an attractive alternative to the problem of spreading bitumen on road surfaces. In the traditional technique, the pure bitumen is used hot, which works out to be expensive and can be hazardous for the worksite personnel. When the bitumen is emulsified in water, the material obtained is entirely fluid at room temperature, thus allowing it to be used without difficulty. Under the effect of the evaporation and drainage of the water, a homogenous bitumen film is obtained after a few hours. Emulsions concentrated in highly viscous hydrophobic compounds are also used in the adhesives industry via bonding agents made with emulsion based on colophony esters. For their part, emulsions concentrated in viscous hydrophilic compound(s) are more particularly used in the pharmaceutical and food industries.
However, the techniques available at the present time for preparing emulsions of this type in most cases require high temperatures, high pressures and/or high shear rates.
Thus, if we consider the specific case of bitumen, the corresponding emulsions are currently prepared by hot injection. In general, the bitumen is heated to a temperature above 120° C. and the continuous phase, generally water, is heated to about 60° C. The mixture of bitumen and the aqueous phase is injected into a turbomixer with a very high stirring speed, of about 5000 rpm, and under a pressure which can be up to 3 atmospheres. After such a treatment, bitumen emulsions having a bitumen concentration not exceeding 70% by weight of bitumen, a large average droplet size (typically greater than 5 microns) and a polydispersity which is also large are generally obtained.
This type of process thus has several drawbacks.
In particular, conventional processes do not make it possible to prepare emulsions with a bitumen concentration of more than 70%. However, certain specific applications require, as regards the handling of the emulsions, emulsions with bitumen concentrations of more than 90%. This is the case, for example, for the mastics used for leakproofing work (protection of buildings, pipelines and the undercarriage of cars).
Finally, the bitumen emulsions currently available are not satisfactory in terms of monodispersity. The size of the bitumen droplets present in these emulsions is generally greater than 5 microns and very heterogeneous. The stability on storage and the breaking of this type of emulsion are found to be difficult to control and the surfacings resulting therefrom are not sufficiently homogeneous. It is clear that this can be detrimental as regards the use of the emulsions and the final mechanical quality of the corresponding surfacings.
One subject of the present invention (is, specifically, to propose a process for preparing emulsions which are concentrated in a highly viscous phase such as bitumen and are also calibrated.
In particular, the invention is based on the demonstration that the direct mixing of a highly viscous phase, i.e. a phase which has a viscosity of between 1 and 5000 Pa.s at the time of emulsification, with a phase which is immiscible therewith, in the presence of a surfactant, leads, under low shear and in a very short space of time, to a viscoelastic paste which is advantageously found to have the specificities of an emulsion.
More specifically, the emulsification method according to the invention is novel in that it makes it possible to manufacture highly concentrated emulsions of “water-in-oil” or “oil-in-water” type by directly mixing together the two phases in a laminar shear regime. It thus differs clearly from conventional emulsification processes, such as the one mentioned above, which operate in a turbulent regime. It also differs from the conventional techniques of emulsification in a laminar regime which proceed by gradual incorporation of a first phase to be emulsified into a second phase, or vice versa.
A first subject of the present invention is thus a process which is useful for emulsifying a first hydrophobic or hydrophilic phase with a viscosity of between 1 and 5000 Pa.s or more with a second phase which is immiscible with the said first phase, characterized in that it involves:
where necessary, a pretreatment of the said first phase to be emulsified so as to adjust its viscosity to a value of less than 5000 Pa.s,
the addition, in a single portion, of the said phase to a second phase which is immiscible with the said first phase, in the presence of at least one surfactant, and
mixing them together under a laminar shear regime until a stable emulsion is obtained in which the said first phase is present in a proportion of from 75 to 95% by weight.
The emulsion obtained after the process claimed has the appearance of a viscoelastic paste. Advantageously, it is found to be redispersible despite a high concentration of one of its phases. It can thus be diluted so as to adapt the concentration of the final emulsion to the requirements of the application envisaged.
Besides a high concentration of one of its phases, the emulsion obtained according to the invention has a very narrow particle-size distribution and the average diameter of its droplets can be readily controlled by means of the shear rate or by means of the formulation parameters and more particularly the concentration of the second phase, also known as the diluent phase.
In this regard, a subject of the present invention is also a process which is useful for preparing an emulsion with a concentrated and calibrated hydrophobic or hydrophilic phase and with a viscosity of between 1 and 5000 Pa.s or more, comprising
where necessary, a pretreatment of the said phase to be emulsified so as to adjust its viscosity to a value of less than 5000 Pa.s,
the addition, in a single portion, of the said phase to a second phase, which is immiscible with the said first phase, in the presence of at least one surfactant, and
mixing them together under a laminar shear regime until a stable emulsion is obtained in which the said first phase is present in a proportion of from 75 to 95% by weight, characterized in that the size of the droplets in the said first phase is controlled in the said emulsion by adjusting the concentration in the second phase for a given shear rate and a given surfactant concentration.
As a general rule, the size of the droplets in the first phase decreases when the shear rate and/or the concentration of surfactant increase. The inventors have thus demonstrated, unexpectedly, that it is possible to adjust the size of the droplets in the first phase by controlling the amount of the second phase introduced to prepare the emulsion. The size of the droplets does not change monotonically with the amount of the second phase: the size first decreases and then increases when the amount of the second phase increases.
According to this specific mode of the invention, it is thus found to be possible to obtain an emulsion with a minimum average droplet diameter, i.e. about 2 microns or even less, for an optimum amount of this second phase. The assessment of this critical volume of the second phase in fact depends on the chemical nature of the said first viscous phase to be emulsified. For a given amount of the first phase to be emulsified, the change (for a fixed stirring speed) of the average diameter of the droplets, obtained during its emulsification, is established for variable amounts of second phase. The critical volume is the volume for which the diameter of the droplets is a minimum. Needless to say, this assessment of the critical volume is made for a given shear rate and a given surfactant concentrati
Bibette Jerome
Guimberteau Florence
Leal Calderon Fernando
Centre National de la Recherche Scientifique (C.N.R.S.)
Jacobson & Holman PLLC
Lovering Richard D.
LandOfFree
Method for preparing concentrated and emulsions calibrated... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for preparing concentrated and emulsions calibrated..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for preparing concentrated and emulsions calibrated... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3091338