MXPA97009025A - Preparation of rubber composition with gruds that fluy libreme - Google Patents

Abstract

Using the process of the present invention can easily prepare a rubber composition in free flowing lumps on a commercial scale. This invention more specifically discloses a process for preparing a free flowing rubber composition comprising the steps of: (1) adding a wax emulsion to a latex of a rubber polymer to produce a latex containing the wax, wherein the wax has a degree of formation that is within the range of about 40 ° C to 175 ° C; (2) stir the latex containing the wax in such a way that the wax is distributed through the latex; (3) coagulate the latex which contains the wax to produce a rubber mortar in lump covered with wax in water; (4) recover the rubber in wax-covered lump water in the mortar and, (5) dry the rubber polymer covered in wax in a medium of air under forced movement to produce the rubber composition in free-flowing lump, where the hot air medium is at a temperature that is within the range of approximately 20øC to 90øC approximately

Description

PREPARATION OF RUBBER COMPOSITION WITH FREELY FREE FLOWS Background of the Invention It is often convenient for synthetic rubbers to be in the form of free flowing lumps. In the case of rubber with free flowing lumps, the rubber is in the form of discrete particles (rubber in lumps). These particles can flow freely allowing them to have an easy process and handling. However, synthetic rubbers that are made by means of emulsion, suspension or suspension polymerization techniques tend to be viscous. Accordingly, the particles of these synthetic elastomers generally agglomerate when stored. This in turn destroys the nature of the free flow of rubber lumps and makes it more difficult, if not impossible to manage and process.

The problem of agglomeration associated with the rubber polymer particles is sometimes overcome by coating the lumps with a molten resinous release agent, such as polystyrene, polymethyl ethacrylate, polyrilnitrile, polyvinylchloride (PVC) or polyethylene. For example, U.S. Patent No. 3,813,259 relates to the use of polymethylmethacrylate as a separation agent and U.S. Patent No. 4,271,213 discloses the use of a mixture of a styrenebutadene copolymer resin and a resin of polymethyl methacrylate as separation agent.

In some cases, inorganic separation agents, such as talc, are used as separation agents for the lumpy rubber. However, dry powders tend to settle during coating applications, causing undesirable inconsistency. Also, inorganic polymer separation agents can not be tolerated in some applications. For example, the presence of talc can not be tolerated in the nitrile rubber that is used to make electric cables because it can interfere with its useful and functional life.

At present, there is a need for an improved technique for making rubber compositions in highly consistent free-flowing lumps. It is also important that a technique of this type is commercially viable and can be easily implemented in industrial bases. There is also a need to eliminate the polymeric or inorganic separation agents from the rubber compositions with free flowing lumps.

In U.S. Patent Applications Serial No. 08 / 629,285, filed April 8, 1966, a process for preparing free flowing lump rubber compositions comprising the steps of: (1) extruding a rubber polymer into a wax emulsion; wherein the rubber polymer is extruded into particles having a diameter in the range of about 1 m to about 15 mm; wherein the wax emulsion comprises from about 35 weight percent to about 80 weight percent water; from about 10 weight percent to about 50 weight percent of a wax, and from about 1 weight percent to about 15 weight percent of an emulsifier; wherein the wax has a degree of melting that is within the range of about 40 ° C to about 175 ° C; and wherein the wax emulsion is at a temperature that is within the range of about 5 ° C to about 70 ° C, (2) stirring the wax emulsion containing the rubber polymer to produce a rubber polymer with wax coating; (3) separating the wax-coated rubber polymer from the water phase to thereby recover a rubber polymer with wet wax coating; and (4) drying the wax-coated rubber polymer in a medium of hot air under force movement to produce the rubber composition in free-flowing lumps, wherein the hot air medium is at a temperature ranging from 10 ° C approximately until 50 ° C approximately.

In the United States Patent Application Serial No. 08 / 629,285 there is also disclosed a free flowing lump rubber composition comprising rubber polymer particles having a diameter that is within the range of about 1. mm to about 15 mm, wherein the surface of the particles of the rubber polymer is covered with a wax having a degree of melting which is in the range of about 40 ° C to about 175 ° C, and wherein the composition Free flowing lump rubber contains from about 1 weight percent to about 10 weight percent wax.

SUMMARY OF THE INVENTION By using the technique of this invention, free-flowing lump compositions can be made on a commercial basis without having to use the polymeric or inorganic separation agents. This process offers the advantage of being highly energy efficient, because the extrusion step is not required. By eliminating the extrusion step, labor requirements are also reduced. Also the elimination of the extrusion equipment and of course the costs are reduced by reducing the requirements of the capital and excludes the possibility of a mechanical failure of the extruder.

The subject invention discloses more specifically a process for the preparation of a rubber composition with free flowing lumps comprising the steps of: (1) adding a wax emulsion to a latex of a rubber polymer to produce a latex containing the wax, wherein the wax has a degree of melting that is within the range of about 40 ° to about 175 ° C; (2) stir the latex containing the wax in such a way that the wax is distributed through the latex; (3) coagulate the latex that contains the wax to produce a rubber mortar in lumps covered with wax in water; (4) recover the rubber in lumps covered with water wax in the mortar, and; (5) drying the rubber polymer coated with wax in a hot air medium under forced movement to produce the rubber composition in free-flowing lumps, where the hot air medium is at a temperature ranging from 20 °. C approximately up to 99 ° C.

Detailed Description of the Invention The technique of this invention can virtually be used in the production of flow lumps of any type of rubber polymer. In most cases, the rubber polymer will be composed of repeating units that are derived from one or more conjugated diolefin monomers, such as 1,3-butadine or isoprene. It may also contain repeating units derived from one or more other monomers which are copolymerizable with the conjugated diolefin monomer, such as acrylonitrile, styrene, @ -methylstyrene or n-butylacrylate. Some representative examples of rubber polymers that may be included: polybutadene rubber, styrene rubber, butadene-styrene rubber (SBR), isoprene-styrene rubber (SIR) butadene-isoprene rubber (IBR), butadene rubber -isoprene-styrene (SIBR) nitrile rubber (NBR) or carboxylated nitrile rubber (XNBR).

In the first step of the process of this invention, a wax emulsion is added to a latex of a rubber polymer. This can be achieved by simply adding the wax emulsion to the latex. The amount of wax emulsion added will normally be sufficient to contain about 1 percent by weight to about 10 percent by weight of wax, based on the dry weight of the rubber polymer in the latex. The amount of wax emulsion added will preferably be sufficient to contain from about 2 weight percent to about 5 weight percent wax, based on the dry weight of the rubber polymer in the latex. The latex containing wax should be shaken so that it is thoroughly mixed in the wax emulsion within the latex. This mixing step is carried out normally at a temperature that is within the range of approximately 5 ° C to approximately 70 ° C. It is usually preferable that the mixing be carried out while the latex is at a temperature that is within the range of about 20 ° C to about 50 ° C. In any case, it is critical for the temperature of the latex to be kept at a temperature that is lower than the degree of fusion of the wax that is being used.

The wax emulsion comprises water, wax and an emulsifier. The wax will have a degree of fusion that is within the range of about 40 ° C to about 175 ° C. It will be preferable to have a melting degree that is within the range of about 50 ° C to about 150 ° C and more preferably having a melting degree ranging from the range of about 60 ° C to the 70 ° C approximately.

Wax is a high molecular weight fatty acid ester with a high molecular weight alcohol that is not glycerol. Typically it will be a mineral wax selected from the group consisting of paraffin waxes, microcrystalline waxes, microcrystalline waxes, xenon waxes, lignite montana waxes, hoeschst waxes and amorphous hydrocarbon waxes. Paraffin waxes are usually preferred.

The emulsifier can be virtually any type of anionic emulsifier or nonionic amulsifier. Some representative examples of the types of anionic surfactants that can be used include carboxylates, sulphonates of alkylbenzene, sulphonates of alkano, sulphonated @ -olefin, fatty alcohol sulfates and oxo-alxohol sulfates. Of the alkali benzene sulfonates of anionic emulsifiers, the fatty alcohol sulfates and the oxo-alcohol ether sulfates are preferred.

It is generally preferred that the emulsifier be a nonionic emulsifier. Some representative examples of the types of nonionic surfactants that can be used include alkylphenol ethocylates, polyethylene glycol fatty alcohol ethers, polyethylene glycol exo-alcohol ethers, polymers of ethylene oxide, polymers of propylene oxide and ethers of fatty alcohol polyglycol. Ethoxylated alcohols are a highly preferred class of nonionic emulsifiers.

After the wax emulsion has completely mixed through the latex, the latex containing the wax coagulates. The latex containing the wax can be coagulated using a conventional salt / acid coagulation process. In other words, a combination of a salt and an acid can be added to the latex to cause coagulation. This salt / acid coagulation is typically achieved by simply adding at least one strong inorganic acid and one salt to the latex. However, in some cases coagulation of the latex is preferable by the addition of only a highly effective salt such as aluminum sulfate. The coagulation aids can also be used in the coagulation of the rubber polymer containing the emulsion. Some representative examples of the strong inorganic acids that can be used in the coagulation of the latex include sulfuric acid, hydrochloride acid and nitric acid with sulfuric acid preferably. A wide variety of salts can be used. Some representative examples of those that can be used include sodium chloride, potassium chloride, calcium chloride, aluminum sulfate, magnesium sulfate and quaternary ammonium salts. The amount of salt and acid needed to cause coagulation will vary with the specific emulsion and the type of salt used. Calcium chloride is a highly preferred salt and will normally be added in an amount that is within the approximate range of 13 phr to about 40 phr.

After the latex has coagulated, a coagulated rubber mortar is formed. The rubber in the mortar is in the form of rubber in lumps covered with wax. The coagulated rubber mortar consists of serum and rubber crumbs covered in wax. The serum is essentially in aqueous phase with the rubber crumb that is in the solid phase. Of course, the serum is composed of water, emulsifiers, acids, salts and other water-soluble residual compounds.

The coagulated rubber mortar is typically transferred to a conversion tank in order to complete the coagulation process. The wax-coated rubber crumb is then filtered through an oscillating screen that collects wax-covered rubber lumps and deposits them into the re-mix tank. Washing is typically used to remove excess soap and / or electrolyte from the rubber with wax-covered lumps. In the re-mix tank, the wax-coated rubber crumb is washed and shaken in fresh washing water to produce a wax-coated rubber mortar.

The pH of the rubber remover can then be adjusted optionally, so that it can be within the range of about 5 to about 8. The neutralization step is achieved by the addition of a base. A number of bases known to those skilled in the art can be used, including calcium hydroxide, magnesium hydroxide, potassium hydroxide and sodium hydroxide. The pH of the wax-covered rubber remorter will preferably be adjusted within the range of about 5.5 to about 7.5 and more preferably will be adjusted within the range of about 6 to about 7.

The serum of the oscillating sieve is then typically recycled back into the coagulator, allowing efficient use of the coagulants. Then, the rubber crumb normally covered wax tank remortero a second oscillating sieve are passed and directed to an ejector where the polymer can be drained. The extruder consists typically of a screw that transports the rubber down an ejector rod under more stringent constriction conditions. The ejector barrel is coated along with narrow grooves, the width of which decreases when the rubber moves through the ejector.

Optionally water can be squeezed through the slots while the rubber advances to an open end cone located at the far end of the barrel. The cone provides a counter pressure for the drain screw. The drainage force can be controlled by adjusting the cone adjustment. This adjustment can vary with the different types of rubber and can be altered during the finishing run to achieve the desired moisture content. The moisture content of the rubber that exits the ejector is typically about 10 percent by weight.

The rubber covered in dewatered wax is then typically dried. It is highly preferred for this type of drying to carry it out under forced movement. The forced movement must be sufficient to prevent the rubber in wax-covered lumps from agglomerating before drying. Drying is typically achieved by passing hot air through a rubber bed in lumps covered with wax. In one embodiment of this invention, the forced movement is provided passing through hot air through a bed of polymer particles coated with wax rubber at a rate sufficient to fluidize the bed of polymer particles rubber covered wax. Higher drying temperatures favor faster drying, which of course reduces the time needed for drying. However, high temperatures can cause degradation and agglomeration of the polymer, which limits the drying temperature that can be used. The maximum drying temperature is limited to a maximum of 210 ° F (99 ° C) approximately, because the history of rubber heat significantly affects the ideal properties. Drying temperatures that are as low as room temperature (approximately 20 ° C) can be used. However, in order to obtain a satisfactory commercial drying average, the temperature will normally be at least 150 ° F (66 ° C) approximately. In this way the drying temperature will typically be within the range of 150 ° F (66 ° C) to approximately 210 ° F (99 ° C) approximately. It is usually preferred to use a drying temperature that is within the range of 165 ° F (74 ° C) to about 195 ° F (91 ° C) approximately.

In a typical drying step, the rubber covered lumps wax is air which becomes a cyclone, where subsequently falls on a metal screen and proceeds through a drying screen. The cyclone works like a beating vessel that separates the rubber from the air. Consequently, the rubber falls on a screen of a uniform and scattered way. Screen drying is typically a single drying step that contains a series of hot zones that can each be set at specific temperatures. The hot air is directed through each zone at the specified temperature and extracts the moisture from the wax-covered rubber. Both the zone temperatures and the speed of the screen can vary to adjust the drying conditions within the screen drying. The moisture content of the finished rubber is preferably less than about 1 percent, and more preferably below about 0.7 percent. When the rubber exits the screen drying, it is allowed to cool and packed for shipment.

The free flowing lump rubber composition that was made by this process has the surface covered with a wax having a degree of melting that is within the range of about 40 ° C to about 175 ° C, in wherein the free flowing lump rubber composition contains from about 1 weight percent to about 10 weight percent of the wax. This free flowing lump rubber composition does not contain inorganic materials or polymeric materials other than the rubber polymer itself. These rubber compositions in free-flowing lumps should be stored at a temperature below about 60 ° F (l ° C) to prevent agglomeration from occurring. It is desirable to store the rubber composition in free-flowing lumps at a temperature not greater than about 75 ° F (24 ° C). It is preferable to store the rubber in free-flowing lumps at a temperature that is less than about 40 ° F (4 ° C). However, it is possible to store the rubber in free-flowing lumps at a higher temperature for short periods without the agglomeration occurring.

This invention is illustrated by the following examples, which are for the purpose of illustration only and are not to be construed as limiting the scope of the invention or the manner in which they should be practiced. Unless specifically indicated otherwise, parts and percentages are given by weight.

Example 1 In this experiment, free-flowing nitrile rubber crumb was prepared using the technique of this invention. In the process that was used, 35 pounds (15.9 kg) of Chemigum® nitrile rubber latex was mixed by Good Year Tire & Rubber Company with approximately 1 pound (0.545 Kg) of Petrolite® 01 wax dispersion. This nitrile rubber contained approximately 33 percent acrylonitrile in combination.

The latex was then coagulated by the addition of 10 pounds (9.1 Kg.) Of coagulant which was composed of water and 240 grams of aluminum sulfate. The coagulation was carried out at a temperature of 160 ° F (71 ° C). After coagulation, the rubber was washed twice in lumps covered with wax with 20 gallons (76 liters) of cold running water. The lumpy rubber was then dried on a thin screen at a temperature of 120 ° F (49 ° C) which reduced the water content of the nitrile rubber lump to less than 0.5 percent. The crumb rubber composition caused the free flow to remain after several months of storage at room temperature (approximately 20 ° C) In light of the description provided herein, variations to the present invention are possible. While certain representative embodiments and details have been shown for purposes of illustration of the invention, it will be apparent to those skilled in the art that various changes and modifications may be made to the invention without having to depart from the scope of the invention.

Therefore, it is understood that the changes can be made in the particular embodiments described, which will be within the scope of the invention as defined by the following appended claims.

Claims (10)

1. A process for preparing a free flowing lump rubber composition characterized by the following steps: (1) adding a wax emulsion to a latex of a rubber polymer to produce a latex containing the wax, wherein the wax has a degree of formation that is within the range of about 40 ° C up to 175 ° C; (2) stirring the latex containing the wax in such a way that the wax emulsion is distributed through the latex; (3) coagulate the latex that contains the wax to produce a gum rubber mortar covered in wax in water; (4) recover the rubber in lump covered with wax the water in the mortar and, (5) drying the wax-coated rubber polymer in a hot air medium under forced motion to produce the free-flowing rubber composition; wherein the hot air medium is at a temperature that is within the range of about 20 ° C to about 99 ° C.

2. A process as specified in claim 1, characterized in that the amount of the wax emulsion added contains from about 1 weight percent to about 10 weight percent wax, based on the dry weight of the rubber polymer in Latex

3. A process as specified in claim 2, characterized in that the wax is a mineral wax having a degree of melting that is within the range of about 50 ° C to about 150 ° C.

4. A process as specified in claim 3, characterized in that the wax emulsion is composed of wax, water and an emulsifier, wherein the emulsifier is selected from a group consisting of anionic emulsifiers and nonionic emulsifiers.

5. A process as specified in claim 3, characterized in that the wax-coated rubber polymer is dried in step (5) at a temperature that is within the range of about 66 ° C to about 99 ° C. .

6. A process as specified in claim 4, characterized in that the emulsifier is an anionic emulsifier selected from the group consisting of carboxylates, alkylobenzone sulfonates, alkane sulfonates, @ -olefin sulfonates, fatty alcohol sulfates and sulfates of oxo-alcohol.

7. A process as specified in claim 4, characterized in that the emulsifier is a nonionic emulsifier selected from the group consisting of alkylphenol ethoxylates, fatty alcohol polyethylene glycol ethers, polyethylene glycol ethers of oxo-alcohol , polymers of ethylene oxide, polymers of propylene oxide and polyglycol fatty alcohol ethers.

8. A process as specified in claim 6, characterized in that the rubber polymer is a nitrile rubber.

A process as specified in claim 4, characterized in that the amount of the wax emulsion added contains about 2 weight percent up to about 5 weight percent wax, based on the dry weight of the wax polymer. rubber in the latex.

10. A process as specified in claim 9, characterized in that it further comprises the additional steps of (6) packing the wax-coated rubber polymer after the drying step; and (7) storing the rubber composition in free flowing lump at a temperature that is less than about 16 ° C. SUMMARY OF THE INVENTION Using the process of the present invention, a rubber composition in free flowing lumps can be easily prepared on a commercial scale. This invention more specifically discloses a process for preparing a rubber composition in free flowing lumps comprising the steps of: (1) adding a wax emulsion to a latex of a rubber polymer to produce a latex containing the wax, wherein the wax has a degree of formation that is within the range of about 40 ° C 175 ° C; (2) stirring the latex containing the wax in such a way that the wax is distributed through the latex; (3) coagulate the latex that contains the wax to produce a gum rubber mortar covered in wax in water; (4) recover the rubber in lump covered with wax the water in the mortar and, (5) drying the wax-coated rubber polymer in a hot air medium under forced motion to produce the free-flowing rubber composition; wherein the hot air medium is at a temperature that is within the range of about 20 ° C to about 99 ° C.