GB2194166A - Continuous production of high- internal-phase-ratio emulsions - Google Patents

Abstract

The process comprises simultaneously and continuously introducing an internal phase material and an external phase material into a mixing chamber (12) of a mixing assembly, said mixing chamber including ports (32,36,38) adapted to allow simultaneous introduction of said internal and external phase materials thereinto and a port (30) adapted to allow a prepared emulsion to exit therefrom. The mixing assembly further includes a rotatable shaft (26) extending into said mixing chamber, drive means (28), and a plurality of structurizing elements (44) attached to said shaft, each of said elements having two substantially opposing surfaces (48,50) wherein at least the peripheral portions thereof are separated from one another to form a peripheral edge portion (52), said peripheral edge portion including spaced apart recesses (54) extending between said peripheral surface portions. <IMAGE>

Description

SPECIFICATION Continuous process for the production of high-internal-phase-ratio emulsions BACKGROUND OF THE INVENTION 1. Field of the invention This invention relates to a continuous process for the preparation of thixotropic high-internalphase-ratio emulsions (HIPREs) having non-Newtonian flow characteristics and, more particularly, relates to an improved apparatus for use in the production of HIPREs on a continuous basis and to methods of use thereof. More particularly, the present invention relates to improvements in structurizing elements, or blades, which are adapted to be utilized in such apparatus to provide sufficient mixing of phases to produce HIPREs on a continuous basis.

An emulsion is defined as a continuous liquid phase in which is dispersed a second, discontinuous phase. When one liquid phase is introduced with agitation into another liquid phase with which it is immiscible, the introduced liquid phase will disperse into discrete droplets. If the two liquid phases are pure, the droplets will begin to coalesce when agitation is stopped and two discrete layers will form. If, however, appropriate surface active materials, generally referred to as emulsifiers, are present in the system, coalescence will be prevented such that when agitation is stopped a layer of droplets of the dispersed phase will form.If the droplets of the dispersed phase, or internal phase, are small enough so that thermal and Brownian forces overcome the settling effect of the gravity field, then a stable emulsion results.- Emulsions comprising greater than 75% by volume internal phase (dispersed phase) are referred to as high-internal-phase-ratio emulsions (HIPREs). The droplets present in HIPREs are deformed from the usual spherical shape into polyhedral shapes and are locked in place. Thus, HIPREs are sometimes referred to as "structured" systems and display unusual rheological properties which are generally attributed to the existence of the polyhedral droplets. For example, when HIPREs are subjected to sufficiently low levels of shear stress, they behave like elastic solids.As the level of shear stress is increased, a point is reached where the polyhedral droplets begin to slide past one another whereby the HIPRE begins to flow. This point is referred to as the yield value. When such emulsions are subjected to increasingly-higher shear stress, they exhibit non-Newtonian behavior, and the effective viscosity decreases rapidly.

When the shear rate ranges between 3000-8000 sec-l, the effective viscosity approaches the viscosities of the external and internal phases. At increasingly higher rates of shear, a point is reached where the emulsifying agents can no longer maintain stable films, and at this point the emulsion breaks and cannot be reconstituted readily. The yield value and shear stability point, as well as the shape of the viscosity versus shear rate curve, will vary with each particular emulsion formulation.

The "structured" nature of HIPREs, in addition to providing an explanation for the unusual rheological properties displayed thereby, also provides an explanation for the fact that special mixing methods are required in order to prepare such emulsions. If an attempt is made to mix two liquid phases of highly disparate viscosity, one finds that the mixing process is difficult and inefficient. When a small amount of low-viscosity liquid is added to a mass of high-viscosity liquid, it is difficult to incorporate homogeneously with conventional mixing means. Without appropriate mixing, as more of the low-viscosity liquid is added, the highly viscous phase tends to break up and form a coarse dispersion in the thinner liquid.It is this fact which makes the preparation of high-internal-phase-ratio emulsions difficult and which has prevented development of successful continuous emulsification processes for materials of this type. With the correct type and degree of mixing, however, the low-viscosity liquid can be adequately dispersed within the high-viscosity liquid as it is added to form a stable emulsion.

One attempt at developing a continuous process for the production of HIPREs is disclosed in U. S. Patent No. 3,565,817 and is directed at achieving sufficient mixing by providing shear rates high enough to reduce the effective viscosity of the emulsified mass near to the viscosities of the less viscous external and internal phases.

However, for certain types of emulsions, it is not possible to apply enough shear thereto to effect an apparent viscosity near those of the external and internal phases without going above the shear stability point of the emulsion. Low-fat spread emulsions are examples of such emulsions. For example, the viscosities of the emulsions disclosed in U.S. Patent No. 3,565,817 display an effective viscosity of less than 300 cps in the mixing region which, according to the disclosure therein, is about 104sec-' (shear rate), while the viscosities of low-fat spreads, when extrapolating the shear rate plot thereof to the same mixing region, display viscosities of about 6000 cps.

Furthermore, although a variety of structurizing elements are capable of producing shear rates sufficient to reduce the effective viscosity of the emulsion phase to near the external and internal phase viscosities thereby allowing the phases to be mixed to a certain degree, such elements do not provide complete mixing of the phases as evidenced by the fact that there is always some nonemulsified liquid present in the prepared emulsion.

It has now been discovered that complete mixing can be effected without applying sufficient shear to reduce the effective viscosity of the emulsified mass to near the viscosities of the external and internal phases. Furthermore, it has now been discovered that by providing complete mixing, the presence of non-emulsified liquid in the prepared emulsion is significantly reduced or eliminated whereby improvements in the quality of emulsions, in terms of texture, is achieved. This is important in the cosmetics and food industries, as well as others, where product appearance is a major marketing factor.

Therefore, the present invention overcomes the shortcomings and disadvantages of prior art processes for the production of HIPREs on a continuous basis by providing an apparatus which includes a plurality of structurizing elements which are adapted to provide complete mixing of the phases.

2. Prior Art The aforementioned U.S. Patent No. 3,565,817 discloses an apparatus adapted to be utilized in a process for the continuous production of HIPREs including a mixing chamber equipped with mixing blades. The structure of such mixing blades is not disclosed.

U.S. Patent Nos. 2,673,077; 2,682,376; 3,166,303; 3,207,488; 3,565,817; 3,939,073; and 4,128,342 all disclose mixing blade structures. Also note, for example British 841,743; German Auslegeschrift 1001663; German Offenlegungschrift 2753153, JP55-134634 and Czech 71479.

None of the mixing blade structures disclosed in these patents are adapted to provide complete mixing of the phases to produce HIPREs on a continuous basis.

Most so-called continuous emulsification devices which have been employed for the production of low- and medium-internal-phase-ratio emulsions are not suitable for producing high-internalphase-ratio emulsions because they are not capable of providing sufficient deforming force to the structured systems to move the polyhedral droplets past one another and therefore do not accomplish the required mixing, or such devices produce shear rates in excess of the inherent shear stability point. Most importantly, such devices do not provide for adequate mixing of the phases particularly where there is a large disparity in the viscosities of the two phases to be utilized wherein the polyhedral droplets are locked into a structured system to a greater degree.

Thus, colloid mills and other high-shear devices cannot be used. Also, low-shear mixing devices, such as Hobart mixers or other equipment utilizing slow moving paddle-type stirrers do not provide sufficient deforming force and therefore do not provide complete mixing of the phases to produce HIPREs on a continuous basis.

SUMMARY OF THE INVENTION The present invention is concerned with providing a process for producing HIPREs on a continuous basis utilizing an apparatus which includes a plurality of novel structurizing elements each of which is particularly adapted to provide complete mixing of the phases. Each of the structurizing elements has two opposing surfaces wherein at least the peripheral portions of the surfaces are separated by a peripheral edge portion. Each of such elements is characterized by a plurality of recesses substantially uniformly spaced around the peripheral edge portion. Preferably, each of such structurizing elements extends to a position adjacent the walls of the mixing chamber such that the space between the edge portion of the structurizing element and the wall of the mixing chamber is less than about 20% of the diameter of the mixing chamber.Each of the present structurizing elements is fixedly attached to and extends outwardly from a rotatable shaft member which is adapted to be engaged at one end thereof by rotator means such as a motor.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side view of an apparatus adapted to be utilized for the production of HIPREs on a continuous basis, showing a mixing chamber in cross-section and showing a plurality of structurizing elements constructed according to the teachings of the present invention.

Figure 2 is a perspective view of one of the structurizing elements shown in Fig. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to the drawings in which like numerals designate like parts, there is shown in Fig. 1 an apparatus 10 adapted to produce HIPREs on a continuous basis. The apparatus 10 includes a substantially cylindrical mixing chamber 12 which is preferably constructed of a stainless stealtype material, but which can be constructed of other materials, such as glass for example.

The mixing chamber 12 includes upper plate member 14 and lower plate member 16. Each of the plate members 14 and 16 is attached to respective upper and lower ends 18 and 20 of the mixing chamber 12, such as by standard clamps and bolts (not shown), and each is sealed with a gasket (not shown).

The upper plate member 14 includes an aperture 22 extending substantially through the center thereof. The aperture 22 is fitted with a gland member 24 adapted to receive a stirring shaft 26 therethrough such that the stirring shaft 26 extends from a stirring motor 28 to which one end portion 27 thereof is attached by appropriate attaching means, to and through the gland member 24 and into the mixing chamber 12 to a position adjacent the lower plate member 16. The upper plate member 14 also includes an outlet port 30 through which prepared emulsion can flow as the HIPRE is produced on a continuous basis. Although the outlet port 30 is shown as a part of the gland member 24, it will be recognized by those skilled in the art that an outlet port can be located at any convenient position so long as prepared emulsion can flow therethrough on a continuous basis.

The lower plate member 16 includes an entry port 32 adapted to receive fluids therethrough.

The entry port 32 is in fluid communication with the mixing chamber 12 and is adapted to receive a fitting 34 which includes at least two phase introduction ports 36 and 38 through which liquids representing the external and internal phases of the desired HIPRE can be simultaneously and continually introduced into the mixing chamber 12, preferably by way of pumping means such as by pumps 40 and 42, each of which is controlled by controlling means 43.

Simultaneous introduction of the external and internal phases into the mixing chamber 12 can also be accomplished in other ways, such as by introducing the phases through opposite sides of the chamber 12 at the appropriate rates.

The apparatus 10 is provided with a plurality of structurizing elements 44 which are particularly adapted to provide complete mixing of the phases without ever producing a shear rate sufficient to reduce the effective viscosity of the emulsion. In the present embodiment, there are three of the structurizing elements 44 and each includes an aperture 46 (Fig. 2) extending substantially through the center thereof through which the stirring shaft 26 extends. The number of structurizing elements 44 can vary depending on the length of the column and the particular type of HIPRE that is desired. Each of the elements 44 is fixedly attached to the stirring shaft 26 by any one of a number of methods known in the art such as by force fitting over splined portions (not shown) of the shaft 26 or by utilizing mounting plates or by utilizing pin members.

Each of the structurizing elements 44 is substantially cylindrical and has a diameter which is preferably slightly less than the diameter of the mixing chamber 12 and can be as little as about 80% of the diameter of the mixing chamber 12, but preferably no less than about 90%. Each of the structurizing elements 44 includes opposing surfaces 48 and 50 (Fig. 1) which are separated by a circumferential edge portion 52. A plurality of recessed portions 54 (Fig. 2) are preferably substantially uniformly spaced around the circumferential edge portion 52 thereof thereby forming a plurality of short blade-like members 56 which are likewise preferably substantially uniformly spaced around the circumference of each of the elements 44.

It should be noted that the structurizing elements 44 can be of any shape so long as the peripheral surface portions thereof are spaced apart to form a peripheral edge portion. The peripheral edge portion of each of the elements 44 is necessary so that portions thereof can be recessed to form the blade-like members 56 which are important for complete mixing.

The number of blade-like members 56 can vary according to the particular HIPRE produced.

Generally, the more viscous the emulsion, the greater the number of blade-like members 56.

Preferably, the number of blade-like members 56 fits a relationship 0.75 n d/n (1.6 where d is the diameter of the structurizing element 44, n is the number of blade-like members and n d lies between about 0.5 and about 3, preferably between about 0.75 and about 1.6.

The minimum thickness of each of the structurizing elements 44 is primarily determined by the strength of the material utilized to construct such elements. Thicker elements, however, tend to heat the emulsion more than thinner elements which may be detrimental to certain emulsions. It is preferable that the thickness be at least about 0.25 inches and no thicker than the diameter of the structurizing elements 44, such as about 0.75 inches to about 1/3 the diameter of the elements 44.

Aithough the width of the individual blade-like members 56 is not critical, the percentage of the circumference occupied by the blade-like members 56, as opposed to recessed portions 54, should be between about 20 percent and about 75 percent, preferably between about 35 percent and about 55 percent.

The depth of each of the recessed portions 54 can be from about one-sixteenth of an inch to about one-half inch, preferably about one-eighth to about five-sixteenths of an inch.

The structurizing elements 44 can be constructed of any one of a variety of materials known in the art. Preferably, the elements 44 are constructed of a tetrafluoroethylene polymer material, such as Teflon, or of linear polymers containing a large number of formaldehyde units, such as the polymer Delrin.

The apparatus 10, and particularly any apparatus which utilizes the structurizing elements 44 in a similar manner to that of the apparatus 10, is particularly adapted to be utilized in a process for the production of HIPREs on a continuous basis wherein an external phase liquid and an internal phase liquid are simultaneously and continuously introduced into a mixing chamber comprising such structuring elements and such internal and external phases are mixed in the presence of an emulsifying agent at a rate sufficient to produce a desired HIPRE.

As the pumping means such as the pumps 40 and 42 simultaneously and continuously introduce the internal and external phase materials into the mixing chamber 12, the mixture of phase materials is forced from a point within the mixing zone of one of the structurizing elements 44 to a point within the mixing zone of another. Thus, in this particular embodiment, movement of the mixture of phase materials through the mixing chamber 12 is dependent upon the means utilized to continuously introduce the external and internal phases, namely, the pumping means. Movement of the mixture of phase materials can also be accomplished by other means such as, for example, reversing the direction of flow through the mixing chamber 12 by inverting the apparatus 10 and allowing the phase materials to move by force of gravity.

The following non-limiting examples are presented for illustrative purposes only and represent the best mode for producing HIPREs on a continuous basis.

General Procedure: A stainless steel column equipped with a plurality of the structurizing elements 44 was utilized in each case. The formulation of phases was as follows: Oil Phase Mineral oil-one part by weight; polyglycerol polyoleate-one part by weight.

Aqueous Phase Water-89.8 parts by weight; 70% sorbitol solution-10.0 parts by weight; CaCI2(anhy- drous)-O.2 parts by weight. As a start-up procedure, the oil phase liquid was utilized to fill one-third of the volume of the column. The mixing motor was then started and the rate was maintained in the range of 1,200 to 1,500 rpm. The water phase liquid was then continuously introduced simultaneously with additional oil phase liquid. After about three column volumes, a steady-state composition comprising about 80% water phase and about 20% oil phase was achieved and the HIPRE was collected at the flow rate shown.

Column Flow RPM (of motor t of struc- Length of Example Diameter Rate used to rotate turizing column S (milli- (liters/ shaft) elements (centi meters) meters) min.) ~~~~~~~~~~~~~~ ~~~~~~~~~~~ meters) 1 25.4 0.1 3300 4 30.48 2 ' 76.2 1.0 1750 6 60.96 3 152.4 9.5 1300 6 121.92 The products produced were smoother and creamier than similar products which were prepared utilizing the same apparatus having various conventional impellers.

Example 4 The same general procedure was utilized wherein the external phase material was changed from a mineral oil to a vegetable oil.

External Phase Partially hydrogenated corn oil66.5% by weight of external phase material; corn oil28.5% by weight of external phase material; polyglycerol polyoleate and phosphated mono- and diglycerides, respectively 3.3% and 1.7% by weight of external phase material.

Internal Phase Water and sodium chloride, respectively 97.0% and 3.0% by weight of internal phase material.

The flow rates were 200 ml/min of external phase material and 800 ml/min of internal phase material. The number of structurizing elements was six (6) and the speed of the motor utilized to rotate the stirring shaft was 1750 rpm.

The product was smooth and contained a very negligible amount of free water.

The same external and internal phase materials were introduced into the same column under the same conditions except that the structurizing elements were replaced with conventional metal turbines. The product was course in texture and contained a large amount of unmixed water.

While the illustrative embodiments of the invention have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the invention.

Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside in the present invention, including all features which would be treated as equivalents thereof by those skilled in the art to which this invention pertains.

Claims (5)

1. A process for the continuous production of a stable, highly viscous high-internal-phaseratio emulsion having an internal phase content of above about 75 percent by volume of said emulsion and an external phase with which the internal phase is immiscible, said process comprising (a) simultaneously and continuously introducing an internal phase material and an external phase material into a mixing chamber of a mixing assembly, said mixing chamber including means adapted to allow simultaneous introduction of said internal and external phase materials thereinto and means adapted to allow a prepared emulsion to exit therefrom, said mixing assembly further including a rotatable elongated shaft member extending into said mixing chamber, means adapted to provide rotation of said shaft member, and a plurality of structurizing elements attached to and extending outwardly from said shaft member, each of said elements having two substantially opposing surfaces wherein at least the peripheral portions thereof are separated from one another to form a peripheral edge portion, said peripheral edge portion including a plurality of spaced apart recesses extending between said peripheral surface portions; and (b) mixing said internal and external phase materials in the presence of an emulsifying agent at a rate sufficient to produce said emulsion.

2. In an apparatus adapted to be utilized in a continuous process for preparing high-internalphase-ratio emulsions, said apparatus including a mixing chamber having a phase introduction port which communicates with said mixing chamber and which is adapted to have internal phase material and external phase material substantially simultaneously and continuously introduced therethrough, at least one outlet port adapted to allow a high-internal-phase-ratio emulsion to pass therethrough, means adapted to substantially simultaneously and continuously introduce said internal and external phase materials through said phase introduction port and into the mixing chamber and a mixing assembly including an elongated rotatable shaft member, rotator means adapted to rotate said shaft member, and means for attaching the shaft to said rotator means, the present improvement comprising a plurality of structurizing elements each of which is fixedly attached to said shaft member and extends outwardly therefrom, each of said elements including two substantially opposing surfaces wherein at least a peripheral portion of one of said surfaces is spaced from a peripheral portion of the other of said surfaces to form a peripheral edge portion, said peripheral edge portion including a plurality of spaced recesses extending between said peripheral surface portions.

3. A method of preparing a HIPRE on a continuous basis utilizing the apparatus of claim 2 comprising the steps of (a) substantially simultaneously and continuously introducing an emulsifying agent, an external phase material and an internal phase material into said mixing chamber by way of said phase introduction port, said internal phase being introduced in an amount of at least about 75% of total volume of liquid; (b) rotating said structurizing elements at a rate sufficient to completely mix said internal phase liquid and said external phase liquid to thereby produce said HIPRE.

4. A process for the continuous production of a high-internal-phase-ratio emulsion, substantially as described herein with reference to the accompanying drawings.

5. An apparatus for utilizing in a continuous process for preparing high-internal-phase-ratio emulsions, substantially as described herein with reference to and as illustrated in the accompanying drawings.