FR3039553A1 - METHOD AND DEVICE FOR THE PREPARATION OF LIQUID PHASE RUBBER MIXTURE - Google Patents

Abstract

A method and a device for continuously preparing a filled rubbery masterbatch, the method comprising contacting a first liquid phase flow and a second liquid phase flow in a mixing zone, the first flow being an emulsion of elastomer, the second flow being an aqueous suspension of charge particles, such that one of the two flows flows into the other flow and the two flows are conveyed at low pressure before they come into contact.

Description

METHOD AND DEVICE FOR THE PREPARATION OF LIQUID PHASE RUBBER MIXTURE

Field of the Invention [0001] The invention relates to the field of the preparation of rubber mixes, in particular the preparation of a diene elastomer masterbatch and filler.

STATE OF THE ART [0002] "Masterbatch" (commonly referred to by its English name as "masterbatch") means an elastomer-based composite in which an organic or inorganic filler and optionally other additives have been introduced.

[0003] The masterbatches are then used for the manufacture of reinforced diene rubber compositions, intended for example for the manufacture of tires or semi-finished products for tires, these semi-finished products being for example profiled products such as treads or reinforcing plies for these tires.

To obtain the optimal reinforcing properties conferred by a filler in a rubber composition, it is known that it is generally appropriate for this filler to be present in the elastomer matrix in a final form which is both the more finely divided possible and distributed in the most homogeneous way possible. However, such conditions can be achieved only to the extent that this charge has a very good ability, on the one hand to incorporate into the matrix during mixing with the elastomer and to deagglomerate, on the other hand to to disperse homogeneously in this matrix.

In known manner, the carbon black has such capabilities, which is generally not the case of inorganic fillers, especially silicas. Indeed, for reasons of mutual affinities, these inorganic filler particles have an unfortunate tendency in the elastomeric matrix to agglomerate together. These interactions have the detrimental consequence of limiting the dispersion of the charge and therefore the reinforcing properties to a level substantially lower than that which it would be theoretically possible to achieve if all the bonds (inorganic filler / elastomer) that can be created during the mixing operation, were actually obtained; these interactions tend on the other hand to increase the consistency in the green state of the rubber compositions and thus to make their implementation ("processability") more difficult than in the presence of carbon black.

US 6,048,923 discloses a process for the continuous preparation of a charged rubbery masterbatch consisting of bringing into contact in a mixing zone a first liquid phase flow and a second liquid phase flow, the first flow being an elastomer emulsion, the second flow being an aqueous suspension of charge particles, wherein the second flow is introduced under very high pressure into the mixing zone to form a sufficiently energetic current to cause the first flow and substantially completely coagulate the elastomer with the filler particles and wherein the fillers used are carbon black particles.

Brief Description of the Invention [0007] The applicants have discovered a simplified method for obtaining a masterbatch.

The method according to one of the objects of the invention consists, as indicated in the above document, of bringing into contact in a mixing zone a first flow in the liquid phase and a second flow in a liquid phase, the first flow. being an elastomer emulsion, the second flow being an aqueous suspension of filler particles. This process is characterized in that one of the two flows flows into the other flow and the two flows are conveyed at low pressure before they come into contact.

[0009] Very surprisingly, the fact of causing one of the flows to flow into the second and to convey them at low pressure makes it possible to obtain, downstream from the contacting zone, excellent dispersion of the charge particles in the atmosphere. elastomer emulsion.

By low pressure is meant the delivery pressures of the first and second flows in the zone upstream of the mixing zone less than 2 bar and preferably less than 1.5 bar.

This greatly simplifies the routing devices of the two flows.

Preferably, upstream of the mixing zone, the first flow having a first flow section, the second flow has a second flow section greater than the first flow section in a ratio between 5 and 8.

Alternatively or concomitantly, preferably, upstream of the mixing zone, the first flow having a first flow, the second flow has a second flow greater than the first flow in a ratio between 5 and 8.

When one or both ratios of the flow sections and flow rates are in this range, it is very surprisingly noted that the coagulation yield is maximum, of the order of 95 to 100 %.

When the two ratios are outside, there is a decrease of a few percent of this coagulation yield.

It is recalled that the coagulation yield corresponds to the ratio of the dry mass recovered from the mass initially targeted, multiplied by one hundred.

This ratio of the sections also allows a first adjustment of the respective concentrations of elastomer and filler in the masterbatch to achieve. A finer adjustment is related to the respective concentrations of elastomer and charge in the flows as well as the respective flow rates of the two flows.

According to a preferred embodiment, the first flow opens into the second flow.

As the flow section of the first flow is much smaller than that of the second, this embodiment is simpler to achieve.

[0020] Advantageously, the mixture of the two flows opens in the open air.

Advantageously, the method according to one of the objects of the invention further comprises a stirring step of the mixture resulting from the contacting with a minimum shear rate of the order of 10 s'1 to initiate coagulating the materials of said mixture and obtaining a coagulated mixture.

This stirring step can be performed by an oscillating table or an oscillating belt.

It can also be carried out by a rotary stirrer.

[0024] Advantageously, the coagulated mixture is then poured onto a conveyor.

Preferably, at the outlet of the conveyor the coagulated mixture is wrung out by pressing to obtain a wrung mixture.

This spin can be achieved by means of a device selected from the group consisting of the following devices: conical screw extruder, piston, twin-screw extruder with water evacuation systems.

The wrung mixture is then advantageously dried by bringing it to a temperature above the vaporization temperature of the water.

This gives a masterbatch of elastomer and charge particles ready to receive the additional additives such as the crosslinking system before being shaped and used in the manufacture in particular of a pneumatic tire. or any other rubbery object.

According to a preferred embodiment, the preparation of the second flow comprises a step of fragmenting the charge aggregates of the second flow.

The method according to one of the objects of the invention allows to use fillers selected from the group consisting of carbon blacks, silicas, kaolin, chalk, synthetic organic fillers, organic fillers. and their mixtures.

This method is therefore very wide use. In the case of fillers such as silicas, the first flow may advantageously comprise agents facilitating coagulation after bringing the two flows into contact, such as metal salts or coupling agents, as indicated in document FR 2 981 076.

The invention also relates to a device for continuously preparing a loaded rubbery masterbatch comprising a feed zone with conveying means in a first channel of a first flow of an emulsion. of elastomer and means for conveying in a second pipe of a second flow of an aqueous suspension of charge particles, a zone of parallel flows of the first and second flows in which the pipe of smaller section is arranged to the interior of the pipe of larger section and a mixing zone downstream of the parallel flow zone constituted by the internal cavity of the pipe of larger section downstream of the end of the pipe of smaller section.

Advantageously, the pipe of larger section is the second pipe.

According to an advantageous embodiment, the two pipes upstream of the mixing zone are coaxial.

Very advantageously, the two pipes each have a circular section.

Preferably, in the region of parallel flows, the first flow having a first flow section, the second flow has a second flow section greater than the first in a ratio between 5 and 8.

Preferably, D being the inner diameter of the larger diameter pipe and L being the length of the mixing zone, the L / D ratio is variable and preferably between 0.5 and 3.

Below 0.5, the homogeneity of the master mixture obtained may be insufficient and beyond 3, it is observed that the coagulation of the masterbatch becomes important in the mixing zone.

Very preferably, H being the length of the parallel flow zone and D the diameter of the pipe of the highest diameter, the H / D ratio is greater than 1. This allows to find laminar flows in the area. parallel flows.

DESCRIPTION OF THE FIGURES [0040] The various objects of the invention are now described with the aid of the appended drawing in which: FIG. 1 shows an overall diagram of an installation for the preparation of rubbery masterbatches; - Figure 2 shows a simplified sectional view of a mixing device according to one of the objects of the invention; - Figure 3 A and B show, in section, two embodiments of the device of Figure 2; - Figure 4 shows a perspective view of the mixing device of Figure 2; and FIGS. 5 and 6 show very schematically the types of flows as well as the evolution of the mass fraction of the two materials in contact in the mixing device obtained with a fluidics software.

DETAILED DESCRIPTION OF THE INVENTION [0041] FIG. 1 shows an embodiment of a plant 1 for preparing a loaded rubbery masterbatch.

The installation comprises a first reservoir 14 filled with an elastomer emulsion. The pipe 16 connects the reservoir 14 to a peristaltic pump 18 intended to measure very precisely the volume of elastomer emulsion introduced into the mixer 30 via the pipe 20.

The installation 1 also comprises a second tank 2 filled with charge particles pre-dispersed in water. Preferably, the dispersion of the charge particles is maintained by means of a rotary stirrer 3. An ultrasonic probe may also be used. Line 4 conveys the aqueous dispersion of charges to a Microfluidizer® 6 to break up the charge aggregates remaining in the dispersion. Line 12 connects the outlet of the Microfluidizer® 6 to a peristaltic pump 8 intended to accurately determine the volume of the aqueous dispersion of charges introduced into the mixer 30 via line 10.

At the output of the mixer 30 is a conveyor preferably a vibrating belt 40 for initiating or accelerating coagulation by stirring the loaded rubber mixture. Then a conical screw extruder 50 allows to wring and then dry the coagulated mixture. A twin-screw extruder 60 is then found to prolong the drying of the coagulated mixture 42 and to obtain a masterbatch 70 capable of receiving the additional additives such as the crosslinking system on a cylinder tool for example (not shown).

Figure 2 shows a sectional view of the mixer 30 according to an object of the invention.

The mixer 30 comprises a feed zone 33, a parallel flow zone 31 and a mixing zone 32.

The feed zone 33 comprises the two pipes 20 and 10 which respectively convey the flows of elastomer emulsion and slurry ("slurry") charges and the zone 22 where the pipe 20 enters the pipe 10 of larger diameter. Arrow A indicates the direction of flow of the elastomer emulsion in line 20 and arrow B the flow direction of the charge slurry in line 10.

The parallel flow zone 31 is downstream of the zone 22. The two pipes 10 and 20 are coaxial in this zone which ends at the end 24 of the pipe 20.

The mixing zone 32 is downstream of the zone of parallel flows 31. This zone starts at the end 24 of the pipe 20 and ends at the end 19 of the pipe 10. This zone is therefore constituted by the inner wall of the pipe of larger section 10 upstream of the zone of parallel flows 31. The mixing zone 32 opens at 19 in the open air.

In this embodiment, the pipe of greater section is the pipe 10 which conveys the aqueous suspension of charge particles and both pipes have both a circular section.

FIG. 4 shows a perspective view of a mixer 30 with the feed zone 33 comprising the pipes 10 and 20, the parallel flow zone 31 and the mixing zone 32 with its end 19. This FIG. illustrates that one can easily adjust the length of the mixing zone by more or less sliding the pipe 20 in the opening of the pipe 10 from a first position shown in phantom.

As in Figure 2, the two arrows A and B indicate the directions of the two flows.

Both flows are conveyed through peristaltic type pumps. These pumps make it possible to control their respective flow rates with great precision and have the advantage of avoiding any contamination of the flows.

Figures 2 and 4 show the introduction of the pipe 20 in the pipe 10, that is to say that one introduces the elastomer emulsion of 20 in the slurry of loads of 10. C is the preferred embodiment.

FIG. 3A is a section CC of the zone of parallel flows 31 of the device 30 as indicated in FIG. 2. Line 10 is the pipe of larger diameter and conducts the flow of the slurry of loads. Line 20 is the smaller diameter line that conducts the flow of the elastomeric emulsion. Line 20 of flow flow section S2 is disposed at the center of line 10. Flow flow of the charge slurry at a flow section S2. In the example presented, the diameter of the pipe 10 is 10 mm and that of the pipe 20 of 4 mm. The ratio S2 / S1 is here equal to 5.2.

It is also possible to invert the two pipes while respecting the desired ratios of 5 to 8 sections of the flows in the area of parallel flows 31. An example is shown in Figure 3B. In this case, it is the pipe 10 which enters the pipe 20 to form the parallel flow zone and the mixing zone. In the example presented, the diameter of the pipe 20 is 10 mm, that of the pipe 10 is 9.2 mm, the ratio of the flow flow sections is close to that of FIG. 3A and is equal to 5.5. It can be seen that the diameters of the two pipes are very close, which can be less easy to achieve in a robust manner, especially when the ratio of the sections of the flow flows increases.

The introduction into the zone 22 of the pipe 20 in the pipe 10 so that the two pipes are coaxial provides an area in which the two flows are parallel. After a disturbance zone associated with the introduction of the pipe 20, the two flows are preferably laminar.

At the end 24 of the pipe 20, the two flows are brought into contact and the mixing begins.

Table 1 shows the operating conditions of an exemplary embodiment of a masterbatch according to one of the objects of the invention.

Table 1 [0060] The slurry of the slurry of fillers has an internal diameter of 10 mm and that of the latex emulsion is 5 mm. The ratio S2 / S1 is thus 3.

The flow of the charge slurry is composed of 4% by weight of carbon black and 96% of water.

The flow of the latex emulsion is composed of 60% by weight of latex and 40% of water.

The flow pressure of the two flows was measured in the parallel flow zone in the immediate vicinity of the mixing zone. Both pressures are 1 bar.

It was found a clear difference in viscosity of the two flows and the flow ratio is 6.6.

It should be noted that the heating associated with mixing is very limited because of the very low energy nature of it: the temperature of the flows is 30 degrees Celsius.

FIG. 4 very schematically shows the flow modes of the two flows at the end of the parallel flow zone 31 and in the mixing zone 32.

There are four main areas: - a zone I of laminar flows of the two flows of elastomer emulsion and charge slurry in the parallel flow zone 31; a highly turbulent flow zone II in the central portion of the first portion of the mixing zone 32 adjacent to the parallel flow zone 31; a zone III of turbulent flow in the lateral parts of the first part of the mixing zone 32; and a laminar flow zone IV in the part of the mixing zone 32 on the end-end side of the pipe.

The length of the mixing zone is adjusted so that at the end 19 of the pipe 10 the mixture of the two flows is not coagulated but still liquid.

FIG. 6 shows the evolution of the mass fraction of the two flows obtained with the same fluidic software as FIG. 5.

There are three main areas: - zone 1: before the contacting zone, the two flows are "pure" and homogeneous; zone 2: zone of very rapid variation of the mass fraction of the two flows, it is noted that this zone 2 is relatively reduced; zone 3: the mass fraction is practically homogeneous throughout this third zone and the dispersion of the filler particles in the latex matrix is excellent.

It should be noted that the coagulation of the mixture obtained does not start or almost not in the mixing zone but only in the vibrating conveyor 40 which receives it. It can be seen that as soon as this liquid is deposited on this vibrating conveyor 40, the coagulation is immediate and in bulk.

The mixer 30 therefore has several very important advantages, a low energy requirement due to Γ flow flows at very low pressures, less than 2 bar and even close to atmospheric pressure and micro-turbulence very effective in the meeting area of the two streams.

This mixer also has the advantage of being able to achieve mixtures with loads of very varied natures: carbon black, silica, kaolin, synthetic organic fillers, natural organic fillers such as wood fibers, cellulose.

The concentrations of the filler slurry can reach 20% by weight depending on the type of filler.

The elastomer emulsions may also be natural rubber latices at different concentrations, for example 30, 60% by weight, SBR, BR, ERA type emulsions at concentrations which may also reach 30, 60% by weight. mass.

The resulting charge rates can be very wide. A masterbatch can be produced with rates of 15 to 120 phr of carbon black and for silica, rates of 15 to 150 phr.

Another advantage of this mixing device is its great ease of adjustment by varying the depth of penetration of the internal pipe in the other, it changes the length of the mixing zone which allows to adapt it finely depending on the master mixtures to be made.

Claims (24)

A process for the continuous preparation of a charged rubbery masterbatch, said method comprising contacting in a mixing zone a first liquid phase flow and a second liquid phase flow, the first flow being an emulsion of elastomer, the second flow being an aqueous suspension of charge particles, characterized in that one of the two flows flows into the other flow and the two flows are conveyed at low pressure before being brought into contact. The method of claim 1, wherein upstream of the mixing zone, the first flow having a first flow section, the second flow has a second flow section greater than the first flow in a ratio of between 5 and 8. 3. The method of claim 1, wherein upstream of the mixing zone, the first flow having a first flow, the second flow has a second flow greater than the first in a ratio between 5 and 8. 4. Method according to one of claims 1 to 3, wherein the first flow opens into the second flow. 5. Method according to any one of the preceding claims, wherein, upstream of the mixing zone, the first and second flows are conveyed at a pressure of less than 2 bar and preferably less than 1.5 bar. 6. Method according to one of the preceding claims, wherein the mixture of the two flows opens in the open air. 7. Method according to any one of the preceding claims, further comprising a step of stirring the mixture resulting from contacting with a minimum shear rate of about 10 s'1 to initiate coagulation of the materials of said mix and obtain a coagulated mixture. 8. The method of claim 7, wherein the stirring is performed by an oscillating table. 9. The method of claim 7, wherein the stirring is performed by a rotary stirrer. 10. Process according to any one of claims 7 to 9, wherein the coagulated mixture is poured onto a conveyor. 11. The method of claim 7, wherein the stirring step is performed by an oscillating belt. The process according to any one of the preceding claims, further comprising a subsequent step of wringing the coagulated mixture by pressing to obtain a wrung mixture. The method of claim 12, further comprising a subsequent step of drying the wrung mixture by raising it to a temperature above the vaporization temperature of the water. The method of any of the preceding claims, wherein the preparation of the second flow comprises a step of fragmenting the charge aggregates of said second flow. The process according to any one of the preceding claims, wherein the fillers are selected from the group consisting of carbon blacks, silicas, kaolin, chalk, synthetic organic fillers, natural organic fillers and mixtures thereof. . 16. A device for the continuous preparation of a charged rubber-mix masterbatch comprising: a feed zone with means for conveying in a first pipe a first flow of an elastomer emulsion and conveying means in a second channel of a second flow of an aqueous suspension of charge particles; a zone of parallel flows of the first and second flows in which the pipe of smaller section is disposed inside the pipe of larger section; and a mixing zone downstream from the parallel flow zone constituted by the internal cavity of the pipe of greater section downstream from the end of the pipe of smaller section. 17. Device according to claim 16, wherein the mixing zone opens in the open air. 18. Device according to one of claims 16 and 17, wherein the pipe of larger section is the second pipe. 19. Device according to one of claims 16 to 18, wherein the conveying means comprise peristaltic pumps. 20. Device according to one of claims 16 to 19, wherein the two pipes upstream of the mixing zone are coaxial. Apparatus according to any of claims 16 to 20, wherein upstream of the mixing zone, in the region of parallel flows, the first flow having a first flow section, the second flow having a second section. greater than the first flow section in a ratio between 5 and 8. 22. Device according to any one of claims 16 to 21, wherein the two pipes each have a circular section. 23. Device according to claim 22, wherein, D being the inside diameter of the larger diameter pipe and L being the length of the mixing zone, the L / D ratio is variable and preferably between 0.5 and 3. 24. Device according to one of claims 22 and 23, wherein, H being the length of the parallel flow zone and D being the inner diameter of the pipe of larger diameter, the ratio H / D is greater than 1. .