WO2022172137A1 - Wet method for producing pre-mixtures of particulate natural rubber - Google Patents

Abstract

The present invention relates to a method for preparing pre-mixtures of natural rubber comprising stabilising and concentrating field latex and subsequently mixing same with dispersions of strengthening loads and emulsions of oils of mineral or vegetable origin, and optionally other additives, to obtain a pre-mixture of rubber in the liquid phase, which is finally sprayed into a mixing, micronisation and drying system of the turbo-rotor type to obtain rubber pre-mixtures in a particulate form. The method developed allows pre-mixtures of natural rubber with better integration between the rubber and the strengthening loads to be obtained, thereby resulting in materials with enhanced mechanical properties and superior performances than the pre-mixtures obtained using conventional methods.

Description

METHOD FOR THE PRODUCTION OF PARTICULATE NATURAL RUBBER PREMIXES BY WET

FIELD OF THE INVENTION

The development belongs to the field of engineering processes, in particular, to processes for the production of rubber composite materials, and more particularly to a process to obtain natural rubber pre-blends in particulate form via the wet process using a mixing system, micronized and turbo-rotor type drying. The rubber premixes obtained through the process of this development provide improved mechanical properties and superior performance to the premixes obtained through conventional processes, and are also useful in a wide range of applications, because their presentation in particulate form facilitates their subsequent use. processing according to the particular needs of each type of product to be manufactured.

DESCRIPTION OF THE STATE OF THE ART

The modern challenges of natural rubber production are fundamentally oriented towards increasing the amount of production in plantations and improving the performance at the industrial level of the products obtained. Specifically, in the production of materials based on natural rubber, mixing it with reinforcing fillers and with plasticizing agents, requires processes that consume a lot of time, with high energy and labor inputs. This is mainly due to the fact that natural rubber has a high viscosity while the reinforcing fillers have high surface areas, which makes it difficult for the fillers to disperse in the natural rubber matrix. Consequently, conventional processes require a lot of energy and long processing times, and in most cases, high levels of contamination are produced in the work areas due to the presence of particulate matter in the environment from the reinforcing charges.

In conventional manufacturing processes, the rubber raw material comes from the processors, which transform the rubber from the plantations into raw material. standardized raw material in the form of a bullet, in such a way that in order to disperse the reinforcing fillers with natural rubber, the rubber bullet has to be crushed in roller mills or in internal mixers with two or more processing stages together with plasticizers such as oils mineral, vegetable and other processing aids with the purpose of improving the fluidity of the rubber, therefore, favoring its integration with the reinforcing fillers. However, the integration of the reinforcing fillers with the natural rubber matrix is not always homogeneous due to the formation of agglomerates, affecting the mechanical properties of the premixes obtained, as well as the products made from them.

In fact, the mixing of the reinforcing fillers with the natural rubber matrix has always been a problem, especially when open mixing mills (roller or dough) are used. Carbon black and silica dust can cause contamination and pollution, which is why the industry in general is avoiding carbon black blending, while other manufacturers spend considerable money on pollution control systems.

For example, in the past, the production of coatings or paints was considered to be a three-stage approach namely: i) pre-mix: dry and wet ingredients are mixed; ii) grinding: the fillers are mechanically broken down until the desired particle size is reached and iii) finishing: it includes the addition of various additives to keep the fillers or pigments in suspension.

Equipment with greater efficiency and with technologies that allow obtaining very stable and highly reproducible dispersions has now been developed, for example, through the use of disk-type bead mills with 2.0 mm diameter microspheres.

Therefore, in recent years there has been a growing interest in the development of alternative processes for the production of natural rubber premixes capable of improving the dispersion of reinforcing fillers in the polymeric matrix, reducing contamination levels and also facilitating their subsequent use. prosecution. The production of Rubber premixes in particulate or powder form is one of the available alternatives through which it is possible to improve the integration of the fillers with the rubber matrix and other formulation components, as well as to facilitate the processing of the premixes. in a simple and fast way by means of methods similar to those used with thermoplastic polymers whose commercial presentation is generally in particulate form.

In the state of the art, some processes have been proposed to produce natural rubber premixes in particulate form. Patent CN 102585309 discloses a process for obtaining rubber and silica nanocomposite materials, which consists of mixing a modified silica dispersion with a rubber emulsion to subsequently spray this mixture in a spray dryer-type spray drying system, where preferably During the spraying process, the flocculation of the latex is carried out by injecting a flocculant gas together with the drying air at high temperature. Additionally, the flocculation process can be done by adding a flocculating agent directly to the mixture before carrying out the spraying process or it is also possible to introduce the flocculating agent during the spraying process.

Patent US20170121511 discloses a process for preparing rubber premixes comprising highly dispersed silica nanoparticles through the use of a process where fine particles are first mixed with a bifunctional organosilane coupling agent and then reduced to nanometric sizes (silica nanoparticles). compatibilized silica) by means of an appropriate grinding device in aqueous solution. Finally, patent US20170260340 discloses a process for the preparation of butadiene-styrene rubber premixes using carbon nanotubes and nanofibers as reinforcing filler to obtain a rubber premix reinforced with carbon nanotubes and nanofibers.

However, these and similar processes do not always guarantee a good dispersion between the fillers and the rubber matrix. In addition, they generally require the use of acid coagulating agents or other substances for this purpose. They also require special fillers or the use of coupling agents to guarantee the integration of the premix components, which results in complex processes that are difficult to apply on a large scale.

Therefore, there is still a need to develop alternative processes for the efficient and low-polluting production of natural rubber premixes in particulate form with a high degree of dispersion of filler reinforcers and other formulation components so that improved mechanical properties are achieved. and superior performance to those of premixes obtained through conventional processes, guaranteeing the versatility of said premixes to be used in a wide variety of applications while maintaining the highest performance standards.

BRIEF DESCRIPTION OF THE INVENTION

The present development refers to a process for the preparation of natural rubber premixes that comprises the steps of: a) stabilizing the field latex; b) concentrating the latex content to 40% to 70% by weight (w/w) dry rubber content; c) mixing the concentrated latex with dispersions of reinforcing fillers and with emulsions of oils of mineral or vegetable origin, previously elaborated, to obtain a rubber premix in liquid phase; d) pulverizing the rubber premix in liquid phase using a turbo-rotor type mixing, micronizing and drying system until obtaining the rubber premix in particulate form; where the concentrated natural latex from step b) is optionally mixed with synthetic rubber and where additives are optionally added to the rubber premix in liquid phase from step c). This development also refers to the rubber premixes obtained through the developed process.

In a third aspect, the present development refers to the use of rubber premixes in the manufacture of a wide range of applications, mainly in the manufacture and retreading of tires, in the manufacture of engineering parts (for example, engine mounts, auto parts and seals), in the manufacture of shoe soles, products for the pharmaceutical sector, among others.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 Schematic representation of the process for obtaining natural rubber pre-blends in particulate form via the wet method using a turbo-rotor type mixing, micronizing and drying system.

FIG. 2 General scheme of the turbo-rotor type mixing, micronizing and drying system.

FIG. 3 Degree of dispersion of carbon black: (A) premix obtained through the wet process of development; (B) pre-mix obtained through a conventional method using a Banbury-type mixer.

DETAILED DESCRIPTION OF THE INVENTION

For purposes of interpreting the terms used throughout this document, their usual meaning in the technical field should be taken into account, unless a particular definition is incorporated or the context clearly indicates otherwise. Additionally, terms used in the singular form will also include the plural form.

Unless otherwise indicated, implied from the context or customary in the art, all parts and percentages in this Descriptive Chapter are based on weight.

The present development corresponds to a process for the preparation of natural rubber premixes in particulate form with improved mechanical and processability properties, as well as superior performance compared to the premixes obtained through conventional processes for the manufacture of a wide range of products based on rubber. in rubber. In particular, the developed process comprises stabilize and concentrate the field latex to subsequently mix it with dispersions of reinforcing fillers and with mineral or vegetable oil emulsions and optionally other additives, until obtaining a rubber premix in liquid phase, which is finally pulverized in a mixing system , micronized and turbo-rotor type dried to obtain rubber premixes in particulate form. A schematic representation of one of the modalities of the process can be seen in Figure 1.

According to the present development, rubber premix or masterbatch is understood as the mixture of reinforcing fillers, mineral and vegetable oils with other additives dispersed in a rubber matrix. The quality of a premix depends, among other things, on the quality of the rubber matrix and the degree of dispersion and compatibility between reinforcing fillers, mineral and vegetable oils and other additives with said matrix. Additionally, the properties, functionality, performance and quality of a premix largely depend on the degree of integration that can be achieved with other formulating agents during the manufacture of specialized products from said premixes.

For the purposes of this development, "field latex or natural latex" is understood as the colloidal aqueous suspension composed of gums, oils, sugars, mineral salts (magnesium, copper, calcium and manganese, among others), nucleic acids, proteins, terpenes, waxes, hydrocarbons, starch, gummy resins, tannins and balsams, obtained from the cytoplasm of the laticiferous cells present in some plants, mainly in the Hevea brasiliensis tree. In particular, field latex is a colloidal system formed by two immiscible phases, one in suspension (internal phase) containing solid particles mainly of cis-14-polyisoprene with a degree of polymerization between 2500 and 4500 known as natural rubber and an external phase (non-rubber components) that is composed of an aqueous whey containing other solids and other organic components.

For purposes of the present invention, field latex is obtained from the Hevea brasiliensis tree. The latex is a white colloidal suspension consisting mainly of rubbery hydrocarbon (between 28% and 38%), the components "not rubber” (between 3% and 5%) and the remaining amount is water. The “non-rubber” components are mainly made up of: proteins, amino acids, carbohydrates, lipids, amines, nucleic acids, as well as other inorganic and mineral components.

The set of the suspended phase and other solids can vary between 25% and 45% depending on the plant, the climate and the frequency of extraction or scratching. However, more than 90% of these solids correspond to cis-14-polyisoprene particles with diameters between 0.5 pm and 3 pm (rubber), while the remaining solids are particles known as lutoids (intracellular vesicles responsible for controlling pH and protection mechanisms against pathogens) and to a lesser extent oils, sugars, mineral salts, nucleic acids, proteins, terpenes, waxes, hydrocarbons, starch, gummy resins, tannins and balsams.

The conventional rubber production process uses natural rubber or synthetic rubbers in solid form as raw material and reinforcing fillers in powder form to be mixed in traditional Banbury-type equipment or open cylinder mixers. In other words, in the conventional process for the preparation of premixes, natural rubber must first be obtained in solid form, which normally involves a field latex coagulation stage by adding acids or salts, mainly acetic acid or formic acid, and subsequently carry out continuous granulating and washing processes and finally the drying process to obtain the solid rubber (generally in the form of solid blocks). Finally, the dry natural rubber is mixed with the reinforcing fillers and the other components.

On the other hand, in the conventional process of the production of the Technically Specified Rubbers -TSR, the latex is coagulated in the cup of the trees or when it arrives at the processing plant, but at no time during the process of elaboration of the TSR is it removal of inorganic minerals (magnesium, copper, calcium and manganese) or other non-rubber components present in the field latex has been carried out. However, these minerals are pro-oxidants of rubber and can generate oxidative decomposition, which in turn generates problems during processability and on the Final technical properties of premixes and products made from them.

Unlike the above, the process of this development is based on mixing the rubber with the reinforcing fillers in the liquid phase, that is, without the need to coagulate the field latex. Consequently, with the developed process, a substantial reduction in pollution levels and energy requirements is achieved; Elimination of natural rubber coagulum washing stages, eliminating water consumption and the need for oxidation ponds for subsequent treatment and better dispersion of reinforcing fillers in the rubber matrix. Additionally, the process of this development allows the elaboration of a wide range of ratios rubber: reinforcing fillers: mineral oils: other components, according to the different requirements of the transforming industry and the particular specifications for each application.

According to the present development, the extraction of the latex is carried out by "superficial cuts" in the trunk of the tree. The natural latex thus obtained generally has a practically neutral pH that ranges between 7.0 and 7.2, which when it comes into contact with air becomes acidic. Twelve to twenty-four hours after extraction, the pH drops to values between 5.0 and 4.2, resulting in coagulation of the latex and, therefore, the impossibility of making rubber premixes in the liquid phase (wet method), for what is required of field latex stabilization to prevent unwanted coagulation of the rubber.

Stabilize field latex

The process of the present development comprises a field latex stabilization stage by adding a stabilizing agent that includes, without limitation, ammonia, zinc oxide (ZnO), tetramethylthiuran disulfide (TMTD), sodium bisulfite, styrenated phenols, butyl alcohol or formaldehyde , sodium or potassium hydroxide, 1,3,5-tri-(hydroxyethyl)-hexahydrotriazine, potassium or ammonium laureate, octyl-phenol-ethoxylate, and mixtures thereof. More particularly, in one embodiment of the present development, the stabilizer is low in ammonia, which guarantees a stable process with low release of ammonia during storage and allows field latex to be kept stable for at least 90 days without the need for adjustments throughout the process. In a particular embodiment, the stabilizer comprises ammonia between 2.0% p/p and 4% p/p, between 3.5% p/p and 5.2% p/p or between 4.8% p/ p and 6.0% w/w; sodium or potassium hydroxide between 3.5% w/w and 5.5% w/w, between 3.8% w/w and 4.9% w/w or between 4.9% w/w and 6.7% w/w; l,3,5-tri-(hydroxyethyl)-hexahydrotriazine between 1.5% w/w and 3.5% w/w, between 1.5% w/w and 2.5% w/w or between 2.5% w/w and 3.5% w/w; potassium or ammonium laureate between 1.0% w/w and 3.0% w/w, between 1.5% w/w and 3.7% w/w or between 2.1% w/w and 3.0% w/w; octyl-phenol-ethoxylate between 0.2% w/w and 0.6% w/w, between 0.2% w/w and 0.4% w/w or between 0.4% w/w and 0.6% w/w and zinc oxide (in the form of a 50% dispersion) between 0.4% w/w and 3.2% w/w.

In a particular embodiment, the amount of stabilizer added to the field latex can vary between 6% p/p to 12% p/p, or between 6% p/p to 9% p/p, or between 9% p/p to 12%. w/w In addition, the amount of ammonia added can vary between 0.1% w/w to 0.4% w/w, or between 0.1% w/w to 0.2% w/w, or between 0.2% w/ wt to 0.4% w/w. In a particular embodiment, the amount of ammonia in the stabilizer is 2.5% w/w, which corresponds to a final amount of ammonia in the stabilized latex between 0.15% and 0.30%.

For purposes of the present invention, between 6 L to 12 L of stabilizer can be added for every 100 kg of field latex, or between 6 L to 9 L for every 100 kg of stabilizer, or between 9 L to 12 L of stabilizer. for every 100 kg of field latex.

In order to achieve greater stability of the latex and taking into account that the inorganic minerals (magnesium, copper, calcium and manganese) or the other non-rubber components can generate oxidative decomposition, the present development includes an optional stage of sludge precipitation and concentration. which are intended to remove non-rubber components, including inorganic minerals after stabilizing the field latex.

The stage of partial elimination of the non-rubber components and more specifically of the sludge precipitation of the present development comprises adding to the field latex stabilized a solution comprising ammonium acid phosphate (DAHP), EDTA (ethylenediaminetetraacetic acid) or mixtures thereof, which act as chelating agents. In a particular embodiment, DAHP is added between 15% p/p and 25% p/p, or between 15% p/p and 20% p/p, or between 20% p/p and 25% p/p, which corresponds to a final amount of DAHP in the stabilized field latex between 0.005% p/p 0.045% p/p, or between 0.005 p/p 0.015% p/p, or between 0.015 p/p % p/p 0.30% p/ p, or between 0.3% w/w to 0.45

% w/w.

With the sludge precipitation stage it is possible to eliminate between 15% and 35% of the non-rubber components of the field latex.

The process of the present development can include a filtering and homogenization stage that can be carried out by any technique known in the art, for example, at the time of filling the reception tanks with the field latex, a metal mesh is placed. For the purposes of this development, the filtering is carried out by passing the field latex through a No. 60 stainless steel mesh to a tank where it is stirred between 35 rpm and 60 rpm to achieve homogenization. In one embodiment the agitation is carried out between 40 rpm and 55 rpm. In a particular embodiment, the agitation is carried out at 45 rpm.

Concentrate latex content

The process for obtaining natural rubber premixes in particulate form by the wet method of the present development comprises concentrating the content of the stabilized latex up to 40% p/p to 70% p/p, or between 40% p/p to 60% p/p, or between 50% w/w to 70% w/w, or between 60% w/w to 70% w/w, or between 55% w/w to 65% w/w dry rubber content by centrifugation or creaming.

Cremation is accomplished by applying a product that partially absorbs water, commonly called a cremation agent, to the field latex. The most common are alginates, especially ammonium or cellulose alginate; the mixture obtained is stirred and stored in tanks for a time that can vary between 12 and 15 days; finally after this time the latex is divided into two phases, the upper phase made up of concentrated latex, with a concentration between 50% w/w and 70% w/w of rubber, and the lower phase which is made up of a serum that has between 4% w/w and 10% w/w of rubber .

In a particular embodiment, the cremation process is carried out using a cellulose (hydroxyethyl ether) as the cremation agent. Cellulose is added to the field latex in an aqueous solution with a concentration that varies between 0.6% p/p and 2.8% p/p or between 1.5% p/p and 3.5% p/p. The amount of this solution added to the field latex is between 10% w/w and 15% w/w or between 12.5% w/w and 17.5% w/w. Once the creaming process is finished and after eliminating the aqueous phase, cellulase is added in order to terminate the reaction, thus controlling the stabilization of the latex over time. Cellulase is added through an aqueous solution with a concentration between 0.1% p/p and 0.5% p/p or between 0.5% p/p and 1.5% p/p. The amount of this solution added to the creamed latex is between 0.75% w/w and 1.5% w/w or between 1.4% w/w and 2.5% w/w.

The centrifugation of the latex also has the objective of eliminating the water, for which, instead of using creaming agents, a mechanical separator or a centrifuge is used. The centrifugation speed to concentrate the latex can be from 4,000 rpm to 10,000 rpm or from 6,000 rpm to 8,000 rpm. In one mode the speed is 7000 rpm.

With the elimination of sludge and with the centrifugation or creaming process of the present development, it is possible to eliminate a large number of non-rubber components, which negatively affect the mechanical and dynamic properties of the natural rubber premixes obtained through the developed process, as well as well as the industrial rubber products produced with said premixes.

Stabilized and concentrated latex can be mixed with synthetic rubber. Synthetic rubber types are selected, not limited to styrene butadiene rubber (SBR) or polybutadiene (BR). The amount of synthetic rubber is added between 15 to 35 phr (parts per hundred of rubber) of SBR and between 12 and 32 phr of SBR. In addition, the premixes rubber of the present invention comprise different types of rubbers, including natural, synthetic rubbers and mixtures thereof.

Mixing the concentrated latex with dispersions of reinforcing careas In the context of the present invention, fillers are classified into three types: reinforcing, semi-reinforcing and inactive. For purposes of this development, the reinforcing fillers are used for the preparation of technical products and correspond to carbon blacks and silica including, but not limited to conventional carbon blacks, silicas obtained from, for example, rice husks and mixtures thereof. .

The amount of reinforcing fillers with respect to the amount of rubber contained in the concentrated latex varies between 25 phr and 70 phr, depending on the specifications and requirements of the premix. In a particular embodiment, the proportion of the reinforcing fillers with respect to the amount of rubber contained in the concentrated latex is from 15 phr to 70 phr in the case of carbon black; from 10 phr to 50 phr in the case of silica and from 25 phr to 65 phr in the case of mixtures between carbon black and silica.

For the preparation of the dispersions of the reinforcing fillers, any equipment traditionally used for this purpose can be used, for example, a ball mill type mixer, Attritor mill, a "rotor-stator" type mixer, a "Cowles" type mixer can be used. ” or pearl mills (both horizontal and vertical).

Mix the concentrated latex with emulsions of oils of mineral or vegetable origin

For purposes of the present invention, the concentrated latex is additionally mixed with aqueous emulsions of oils selected from minerals, vegetables and mixtures thereof. In particular, mineral oils are selected from, but are not limited to, aromatic, naphthenic, and paraffinic oils and mixtures thereof, while vegetable oils are selected from, but are not limited to, soybean oil, palm oil, castor oil, and mixtures. thereof. In a particular embodiment, aromatic oils are used for dispersions with carbon black, and for dispersions where only silica is used, paraffinic oils and "degummed" soybean oil are used. The aqueous emulsions of oils of the present development contain between 3% p/p and 40% p/p, or between 12% p/p and 37.5% p/p, or between 5% p/p and 30% p/p. of mineral or vegetable oil or mixtures thereof depending on the specifications of the premix and the percentage of concentrated dry rubber.

The amount of mineral or vegetable oils with respect to the premix varies between 5.0 phr (parts per hundred of dry rubber) to 12.0 phr or between 6.0 to 18.0 phr or between 12.0 to 38 phr, depending on the specifications and requirements of the premix.

In accordance with the present invention, the oil emulsions may additionally comprise dispersing, surface-active and wetting agents. The amount of these in an emulsion or dispersion varies according to the nature of the component to be emulsified or dispersed. There is a wide range of families that make up this type of material. For the purposes of the present invention, sodium salts from the condensation of naphthalene sulfonic acids, polyethylene glycol monolaurates, ethoxylated alcohols, polymeric dispersants, polyalkoxylated surfactants or ammonium soaps are used. .

In one embodiment of the invention, mixtures of polyethylene glycol monolaurates with ethoxylated alcohols or ammonium soaps can be used in the oil emulsions. In the first case, the concentration can vary between 3% w/w to 6.5% w/w or between 4.5% w/w to 8.5% w/w. In the second case, the concentration of the ammonium soaps can vary between 0.8% w/w to 2.5% w/w or between 1% w/w to 4.5% w/w.

For the preparation of the emulsions, any equipment traditionally used for this purpose can be used, for example, a "Cowles" type or "rotor-stator" type mixer can be used, operating under the conditions normally known in the art. For purposes of this development, a rotor-stator type mixer operating at 3600 rpm was used. The mixture of concentrated latex with the dispersions of reinforcing fillers and with the oil emulsions can be carried out by any technique known in the art. For example, tanks with agitation between 45 rpm to 55 rpm can be used.

For purposes of the present invention, the liquid phase rubber premix may be further blended with various additives well known in the art selected from, but not limited to, peptizing agents, pigments, protective agents, and mixtures thereof. The amount of each additive depends on the technical specifications required for each premix based on the expected performance of the final product to be manufactured. For example, the amount of peptizing agents added can vary between 0.05 phr to 1.8 phr, the amount of pigments added can vary between 10.0 phr to 25.0 phr, and the amount of protection agents can vary between 0.75 phr to 8.0 phr.

Spray the yre-mix

The process of the present development comprises a stage of pulverizing the rubber premix in liquid phase, to obtain the rubber premixes in particulate form. The rubber premix in liquid phase is pulverized using a turbo-rotor type mixing, micronizing and drying system until the rubber premix is obtained in particulate form according to the general scheme of Figure 2. This stage of the process comprises the following components :

® Premix dosing system, composed of a “buffer tank” with agitation, where the mixture previously defined is stored according to the specifications required based on the application and the desired performance, and a double diaphragm pump used to controlled feeding of the premix in liquid form to the mixing, micronizing and drying unit;

© heat exchanger, for heating the process air;

@ turbulence micronizer mill with load feed dosing and temperature controllers; © high performance cyclone with pre-separator;

© High performance high pressure fan;

© bag filter with low pressure pneumatic cleaning;

© transport screw of the obtained product;

® rotary screen for the separation of predefined granulometries;

@ transport screw for the final packaging of the product.

For the purposes of this development, the variables that are controlled during the micronizing, mixing and drying stage are the inlet air flow, heat generator, solids content of the liquid phase premix, liquid phase premix flow, density of the premix in liquid phase, speed and air inlet and outlet temperatures. The optimum conditions for each of these variables must be adjusted according to the characteristics of the premix in liquid phase and the desired characteristics of the premix in particulate form. For example, the micronizing, mixing and drying process can be carried out under the following conditions: density of the liquid premix in the feed between 0.89 g/mL and 1.25 g/mL; liquid premix feed flow between 20 kg/h to 100 kg/h; solids content of the premix between 40% and 70%;

- inlet air temperature between 80 °C 190 °C;

- outlet air temperature between 60 °C and 130 °C;

- air speed between 5 m/s and 14 m/s; amount of output particulate material between 40 kg/h and 350 kg/h.

Applications

The properties of the premixes obtained through the process of the present development depend on the components and their proportion. Natural rubber premixes in particulate form are useful in the manufacture of parts for a wide range of applications, for example, but not limited to the manufacture and retreading of tires, tires, engineering parts (for example, engine mounts, auto parts and stamps), shoe soles and products for the pharmaceutical sector, among others. The applications of the premixes obtained through this process can be classified as follows: high volume: Including high consumption products, but with very high specifications. For example, the manufacture of tires and retread bands. It is important to point out that almost 70% of the world's natural rubber production is intended for the production of this type of medium-volume product: This group includes the footwear industry, including its subsectors, such as sports footwear, work footwear and the casual footwear sector. In this aspect, it is important to highlight the possibility of manufacturing premixes with the concept of "green products", that is, premixes made from natural rubber, silica from rice husks and vegetable oils. Additionally, the manufacture of conveyor belts is included in this group.

- Special niches: This group includes items that require high performance during use. For example, auto parts, especially engine mounts; engineering products, pharmaceutical products and products for the mining sector.

The present invention will be presented in detail through the following examples, which are provided for illustrative purposes only and not for the purpose of limiting its scope.

EXAMPLES

Example 1. Field latex stabilization.

3545 kg of field latex were collected and mixed with a stabilizer solution with the composition shown in Table 1, in a proportion of 8 L of stabilizer per 100 kg of field latex.

Table 1: Composition of the stabilizer or preservative solution Component % Weight

Ammonia (25% ammonia solution) 5.5 Potassium or sodium hydroxide 4.5

1,3,5-tri(hydroxyethyl)hexahydrotriazine 2.6

Ammonium or potassium laureate 2.9

Octyl-phenol-ethoxylate 0.4

Zinc oxide (50% dispersion) 2.9

water csp

TOTAL 100 csp: Enough quantity to complete 100% by weight

The way and the moment in which the preservative should be applied to the field latex is very important. In the first place, apply between 1 and 2 cubic centimeters of preservative for each cup, in this way when the latex falls into the cup and comes into contact with the preservative, bacterial growth is inhibited by the action of the preservative. Subsequently, according to the amount of field latex collected, the preservative is added according to the previously defined percentage.

Example 2. Elimination of non-rubber components

The amount of DAHP needed to reduce the amount of metal ions, in particular Mg, was determined using the following formula:

where:

Wp = Weight of the DAHP solution, in grams; m = Magnesium content in field latex, in ppm;

W _L = Weight of the latex, in kg;

C = Concentration of DAHP solution as a percentage.

The formula used is adjusted to the results regarding the magnesium determined in the concentrated latex. However, from thermogravimetric measurements carried out during the development of the process, it was established that the best behavior of the rubber is achieved when the Mg content is below 25 ppm in the concentrated latex so it is sometimes necessary to add additional DAHP to keep the magnesium content below 25 ppm. Consequently, for the removal of the non-rubber components of the following examples, a 20% DAHP solution increased by 3% relative to the value calculated by Equation 1 was added to the latex under constant agitation to ensure proper mixing. . Subsequently, the above mixture was left to stand for a period between 12 h and 24 h before carrying out the dry rubber content concentration step in which a dry rubber content of 60.5% was obtained. This process was carried out using a Westfalia centrifuge operating at 7000 rpm.

Example 3. Obtaining particulate natural rubber pre-blends

The mixtures were made in three groups according to their components:

• Group 1: Comprised of natural latex, carbon black dispersions, oil emulsions. The carbon black dispersions involved can be mixtures of various types of carbon blacks depending on the final application of the premix. For example, it can be mixtures of carbon black 234 with a carbon black 330.

• Group 2: Comprised of natural latex, carbon black dispersions, silica dispersions and oil emulsions. In this group there is also the possibility of mixing various carbon black references with various silica references.

• Group 3: Comprised of natural latex, silica dispersions and oil emulsions. As in the previous cases, the silica dispersions can be composed of various silica references and the oil emulsions can be emulsions with different types of oils.

The mixtures defined in the previous groups were elaborated following the method of the present development (wet method) and a conventional method using a mixer type Banbury, with two different proportions of ingredients (A and B) according to the formulations in Tables 2 to 4.

Table 2. Mixtures of natural rubber, carbon black and oil

Formulations - Group 1

A B

Components - phr % w/w phr % w/w

Natural rubber 100 64.9 100 71.4

Carbon black 234 42 27.3 30 21.4

Naphthenic oil 12 7.8 10 7.2 phr: Parts per hundred dry rubber

Table 3. Mixtures of natural rubber, carbon black, silica and oil.

Formulations - Group 2

Components phr % w/w

Natural rubber loo 60.6 Carbon black 330 40 24.2 Silica 175 15 9.1 Naphthenic oil 10 6.1 phr: Parts per hundred dry rubber

Table 4. Mixtures of natural rubber, silica and oil

Formulations - Group 3

A B

Components - phr % w/w phr % w/w

Natural rubber 100 65.8 100 80

Silica 175 40 26.3 20 16

Paraffinic oil 12 7.9 5 4 phr: Parts per hundred dry rubber

The process conditions that were used for each group are defined in Table 5. However, according to the size of the micronized, mixed and dried system, the parameters corresponding to the feed flows may change. Table 5: Parameters used during the micronizing, mixing and drying process

density of

Content Flow Temperature Premix Temperature

Components air solids feed air liquid outlet

(kg/h) (%) input (°C) (°C)

(g/mL)

Group 1 L08 40 55 Ϊ48 86

Group 2 L05 37 53 146 85

Group 3 L04 35 50 Ϊ40 82

Example 4. Physical and mechanical properties of the pre-mixtures obtained

The results corresponding to the physical and mechanical properties of the premixes of the formulations of groups 1 to 3 obtained according to Example 3 are shown in Tables 6, 7 and 8, respectively.

Table 6: Results of mixtures corresponding to Group 1:

Group 1

Properties A B

Banbury Wet Route Banbury Wet Route

Tension (N/mm ² ) 32.4 26.1 29.0 26.5 Elongation (%) 541.8 387.6 668.9 534.6 Tear (N/mm) 73.5 53.0 67.7 56.8 Abrasion (mm ³ ) 104.7 130.2 137.6 148.5 Hardness (Shore A) 61.9 66.5 55.0 57.8 Table 7: Results of mixtures corresponding to Group 2.

Group 2

Properties A

Banbury wet method

Tension (N/mm ² ) 36.3 29.8

Elongation (%) 501.0 381.2

Tear (N/mm) 75.6 60.4

Abrasion (mm ³ ) 119.6 125.1

Hardness (Shore A) 64.1 65.7

Table 8: Results of mixtures corresponding to Group 3.

Group 3

Properties A B

Banbury Wet Route Banbury Wet Route

Tension (N/mm ² ) 27.1 24.3 19.9 18.0 Elongation (%) 677.0 598.5 721.4 615.8 Tear (N/mm) 80.2 49.6 35.9 30.8 Abrasion (mm ³ ) 212.0 259 .4 226.7 251.7 Hardness (Shore A) 62.5 63.8 53.7 55.3

As can be seen in the previous tables, in all cases the pre-mixes obtained through the method of the present development (wet method) presented better mechanical properties compared to the traditional Banbury-type method. In particular, a significant increase in tensile, elongation and tear properties is obtained, even more evident in the premixes prepared with a higher percentage of carbon black and/or silica (concentration level A), which demonstrates the surprising and the enormous versatility of the process to obtain pre-mixtures of natural rubber in particulate form by the wet method developed. In fact, the benefits of the process are also observed in Figure 3, in which a significant increase in the dispersion index of the pre-mix components can be seen, especially the reinforcing fillers (carbon black) obtained by the process. developed. In this case, the bright spots in the micrograph correspond to agglomerates of the reinforcing fillers, which, as shown in Figure 3, appear in greater quantities and larger in the premixes obtained through the traditional method using a Banbury-type mixer.

Claims

1. A process for the preparation of natural rubber premixes that includes the stages of:

(a) stabilizing the field latex;

(b) concentrating the latex content to 40% to 70% by weight (w/w) dry rubber content;

(c) mixing the concentrated latex with dispersions of reinforcing fillers and with emulsions of oils of mineral or vegetable origin to obtain a rubber premix in liquid phase;

(d) pulverizing the rubber premix in liquid phase using a turbo-rotor type mixing, micronizing and drying system until obtaining the rubber premix in particulate form; where the concentrated natural latex from step b) is optionally mixed with synthetic rubber and where additives are optionally added to the rubber premix in liquid phase from step c).

2. The process of Claim 1 wherein in step a) the field latex is stabilized by adding a stabilizing agent comprising ammonia, zinc oxide (ZnO), tetramethyltriuran disulfide (TMTD), sodium bisulfite, styrenated phenols, alcohol butyl, formaldehyde, sodium or potassium hydroxide, 1,3,5-tri-(hydroxyethyl)-hexahydrotriazine, potassium or ammonium laureate, octyl-phenol-ethoxylate and mixtures thereof.

3. The process of Claim 1 wherein in step a) the field latex is stabilized by adding between 6% p/p to 12% p/p of a stabilizer comprising between 0.1% p/p to 0.4% w/w of ammonia.

4. The process of Claim 1 further comprising removing between 15% to 35% w/w of the "non-rubber" components after stabilizing the field latex.

5. The process of Claim 4, wherein the elimination of non-rubber components is carried out by adding between 0.005% p/p to 0.030% p/p of a solution comprising between 15% p/p and 25% p/p of phosphate. ammonium acid.

6. The process of Claim 1 wherein in step b) the latex is concentrated by centrifugation or creaming.

7. The process of Claim 1 wherein the reinforcing fillers of step c) are selected from carbon black, silica and mixtures thereof.

8. The process of Claim 1 wherein mineral oils are selected from aromatic, naphthenic and paraffinic and mixtures thereof, vegetable oils are selected from soybean oil, palm oil and castor oil and mixtures thereof and where the amount of mineral or vegetable oils with respect to the premix varies between 5 to 38 parts per hundred of dry rubber.

9. The process of Claim 1 wherein the additives are selected from peptizing agents, fluidity improvers, pigments, protection agents, flame retardants and mixtures thereof.

10. The process of Claim 1 wherein step d) is carried out under the following conditions: density of the liquid premix in the feed between 0.89 g/mL and

1.25g/mL; liquid premix feed flow between 20 kg/h to 100 kg/h; the solids content of the premix between 40% and 70%; inlet air temperature between 80 °C and 190 °C; outlet air temperature between 60 °C and 130 °C; air speed between 5 m/s and 14 m/s; amount of output particulate material between 40 kg/h and 350 kg/h

11. A natural rubber premix obtained according to the process of Claim 1