DE2145728A1 - Process for the cryogenic regeneration of waste rubber - Google Patents

Description

Process for the cryogenic regeneration of waste rubber

The invention is generally concerned with the recovery of Rubber and is particularly concerned with a method of producing a reusable rubber mixture from waste or waste material, fabric or fiber-reinforced rubber objects, for example rubber tires, hoses and like that.

In the manufacture of numerous rubber goods, for example automobile and truck tires, it is customary to add rubber or rubber obtained from old rubber goods, for example tires, to the fresh rubber. The amount of reclaimed rubber or rubber used annually in this way can amount to 20% of the total rubber processed compared to natural and synthetic rubber. During periods when natural and synthetic rubber are not or only with difficulty available, for example during part of the Second World War, almost 40 % of the total rubber used over the course of a year consisted of rubber recovered from scrap material.

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INSPECTED

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When using reclaimed rubber in conjunction with fresh natural or synthetic rubber for the use of rubber goods But it's not just availability and costs that play a role of fresh rubber and rubber substitutes play a role. Recovered Rubber has various advantages over fresh rubber. This includes that reclaimed rubber or rubber alone or in conjunction with fresh rubber accelerates the mixing process, since it can be broken up quickly, wets the pigments and contributes to the mixing of the mixture. The use Reclaimed rubber can be beneficial in a number of ways. In this way, energy can be saved; the splash and Calendering can be done at higher speeds; the strength is increased; shrinkage is reduced; the vulcanization speed is increased. The making available of scrap or reclaimed rubber is consequent of considerable importance for the rubber industry.

The one previously used for adding to fresh natural or synthetic rubber Old rubber used in the manufacture of new rubber goods was mainly recovered in such a way that the rubber waste in Lumps or pieces a total size of a few centimeters cut and torn. The pieces were then recirculated and sifted until all of the mass consisted of particles the total size of which was not significantly larger than 1 cm. Before recycling and screening, larger pieces of metal were used, using scrap material in the form of tires, for example the bead wires, eliminated. During the repatriation

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and sieving can magnetically separate out smaller metal particles will. After the metal had been deposited, the particles, no more than 1 cm in size, were treated with chemicals, heat and pressure, usually in an autoclave, kettle or digester, to dissolve the fibrous residue generally present in rubber scraps.

In some known rubber recovery processes, the Objects heated to the point where the fibers char. The charred Particles are then separated off with the help of aerocyclones. In addition to chemical processing and charring is It is also possible to bring the rubber-fiber mass into a cyclone separator, where the heavier rubber particles are removed by centrifugal force be separated. After the fibers are removed, the rubber is dried and passed through a series of mills or rolling mills and screened to mix the elastomers and remove major contaminants. Those emerging from the rolling mills Skins are balesed for shipping and storage before being used in conjunction with fresh rubber will.

Most of the old rubber used for mixing with fresh natural or synthetic rubber is devulcanized or depolymerized. Devulcanization leads to the breaking of the crosslinking sulfur bonds, while depolymerization leads to a shortening of the molecular chain length. A certain amount of this old rubber is used without devulcanization of fibers

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free and ground in crushing mills so far that it is through Mesh screen openings approximately 0.495 mm in size (U.S. standard screen number 35) goes through. This material, known as "ground scrap rubber", is used directly for tire compounds, which are used for the manufacture of tire sidewalls, but not for treads. The ground old rubber should ensure a roughened surface that releases the air from the molds during processing to prevent the molded sidewalls to ease the shape. The reclaimed rubber, if not devulcanized, is usually referred to as "scrap rubber" while for devulcanized or depolymerized rubber is called regenerated rubber or briefly regenerated material is used.

The known processing methods described above for the recovery of rubber from rubber waste material have numerous disadvantages. In such a known method, for example, an old tire is fed into a crushing mill which has heavy, water-cooled rollers. As these rollers cut and tear the tire into lumps or pieces of the size desired for further processing, the fabric is also cut and torn; in addition, the rollers try to break up the metallic beads. As a result, repeated processing and treatment are required to deposit the fibers and metal before a reusable rubber or rubber product can be obtained. Some of the

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dissolving the fibers serving processes lead to a degradation of the Rubbers · In addition, odor nuisance and air pollution are common.

The invention is intended to avoid many of the difficulties that has so far been used in the recovery of rubber or set rubber made of old rubber material. The difficulties that arise in separating the rubber from the normally related fibers and metal parts should be cleared out. A chemical treatment and a heating of the rubber with the aim of dissolving or charring the fibers should be avoided so that there is no degradation or a Deterioration of the rubber is coming. Air pollution and odor nuisance, normally with known rubber regeneration processes connected should be kept to a minimum. It is to be obtained a fine powdery old rubber that can be used without devulcanization or can be devulcanized and used as reclaimed rubber.

In the method according to the invention for producing reusable Rubber or caoutchouc from fabric or fiber-reinforced rubber objects obtained as waste or used material the objects as a whole or after previous subdivision cooled by contact with a cryogenic medium, the one for an embrittlement of the rubber component sufficient, under -40 C temperature, the cooled material is so claims that the rubber component is separated from the fiber component

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nente peeled off, the peeled-off rubber together with at least some of the fiber components are shredded and at least part of the fiber component of the comminuted mixture through mechanical separation eliminated.

The term "detachment" is to be understood here as meaning that the connection between the rubber and the fabric fibers or the metal is broken. With "Separate" the physical Separation of the rubber from the non-rubber substances referred to. Under the term "low temperature" (or cryogenic temperature) is to be understood here as a temperature which is so low that it embrittles the Gums effects, d. H. a temperature below -4O C. It will be understood that lower temperatures will be used can be used to prevent the rubber from heating up during shredding or cutting. An advantage that as a result of going well below the embrittlement temperature, is that compared to comminution near the embrittlement temperature a greater degree of comminution is achievable, d. H. an increased throughput rate and reduced particle size per unit of the for Shredding expended energy can be achieved. Any conventional inert cryogenic material can be used. Appropriate cryogenic Substances include liquid helium »liquid neon, liquid Nitrogen, liquid argon and solid carbon dioxide, preferably liquid nitrogen, which has a boiling point, is used

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of -196 ° C.

The inventive method allows practically the entire Remove tissue and all fibers, or all of them To leave fibers or a part of the fibers in the mixture and to comminute them together with the rubber. The wished The extent to which fibers are retained depends on what the waste or reclaimed rubber product is used for will.

In the method according to the invention, the rubber article, for example a tire, from which the rubber is to be recovered, is cooled with a cryogenic substance to which the rubber is inert. For reasons of economy and safety, it is preferred to work with liquid nitrogen, but other cryogenic media, for example liquid air or liquid argon, can also be used. In some cases, solid COp (dry ice) can also be used. The purpose of the cryogenic material is to cool the article to a temperature at which the rubber becomes brittle while the fibers and fabric remain essentially flexible. While the rubber is brittle, the object is subjected to mechanical stresses, that is, broken, rolled or otherwise subjected to bending stresses, so that the brittle rubber breaks loose and becomes detached from the cord layers and the metallic bead. For this purpose, for example, a relatively blunt impact tool can be used, which the tissue or the wire

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does not tear or tear. At the temperature of liquid nitrogen, which is sufficiently low to cool and embrittle the rubber, the cord _p, which in the case of tires is usually made of cotton, nylon, fiberglass, rayon or combinations of these materials, remains intact during the Gum breaks up in chunks or lumps. The embrittled chunks of rubber, which break off from the undamaged fabric and metal bead, can then be easily and simply deposited and separated from most of the unwanted cord and metal. After the cooled rubber chunks have been separated from the cord and the bead, they can be further processed in the same way as was previously the case with the recovery of used rubber or regenerated rubber.

The separated chunks can be made from essentially pure rubber Allow to reach room temperature and then crush to the desired particle size in the usual way. Preferably which the gum chunks, however, kept cold and brittle by means of an inert cryogenic substance while they were reduced to the desired powder particle size be crushed. With the help of this preferred method, a much finer powdered rubber can be produced can be obtained than is possible by crushing at room temperature. The chilled chunks of rubber can be put in a hammer mill or another comminution device, which is expediently but not necessarily with a medium such as liquid nitrogen, is frozen. It can also be a ball or another mill to reduce the particle size

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and forming a powder. As the chunks of rubber are brittle, they can be removed using the shredding device and easily pulverize by mutual contact.

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Instead the chunks of gum to a powder with the required

To comminute particle size in a single comminution stage or device, the size of the chunks can also be partially reduced by pre-grinding to a particle size that allows the material to be introduced into a jet mill. Before being introduced into the jet mill, the partially crushed chunks can be cooled by means of a cryogenic gas which is sufficiently cold to keep the rubber particles cooled and brittle. Instead, the partially crushed chunks of rubber can also be introduced into the jet mill without being cooled and cooled and embrittled by means of the cryogenic gas that is introduced into the mill as a propellant. In any case, the cooled brittle rubber particles are thrown against the walls of the mill and against each other by the rapidly flowing swirling gas, whereby a comminution takes place. If the particles are cooled before they are introduced into the mill, the gaseous cryogenic medium used to cool the particles can be used as a propellant for the jet mill. If a cryogenic liquid is provided as the coolant, the gas which is developed as a result of the heat exchange between the rubber particles and the liquid can be used for this purpose.

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The old rubber parts produced according to the invention have a fur particle size suitable for the manufacture of useful rubber articles. The scrap rubber powder can be used in the form in which it leaves the mill. The particle masters, but also conventionally devulcanized and used as reclaimed rubber. The particle size obtained from the comminution can within a large particle size'- !? ere iches lie.

When using waste rubber or reclaimed rubber, the case often occurs that a uniform particle size or a predetermined maximum particle size is often desired. However, because of the stickiness and resilience of rubber particles, it has heretofore not been practically possible to provide for the crushing, separation and classification of rubber particles which have a particle size such that they can be passed through a sieve with approximately 0.295 mm openings (U.S. Standard Sieve No. 5O) go through it. It has been found that by cooling and embrittling the rubber particles, either prior to or during screening, substantially all of the particles are separated or classified after a relatively short screening period using screens with openings down to 0.043 mm (US Standard 325 Screen) can. This can be done without brushing. Rubber particles are sieved at room temperature, a substantially longer sieving time is required and must be brushed to the is at room temperature particles themselves through a sieve O _t 147 mm apertures (U.S. standard 100 mesh) hindurchzutrei-

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ben. Another improvement in room temperature sieving or at low temperatures can be achieved by adding the rubber powder a dispersing agent such as carbon black or silica is added in an amount of about 1 to 5 percent by weight will,

Instead of the rubber waste, for example a tire, go first cool, the waste can even at room temperature with the help of conventional Devices, for example by means of a crushing mill, cut or torn into lumps or chunks will. The chunks can then be processed using the cryogenic process processed according to the invention. The fabric, the fiber components and the metal can during the low temperature processing to be deposited. It is also possible to keep all or part of the fibers and together with the Crush rubber.

The one suitable for carrying out the method according to the invention Apparatus is similar to a conventional apparatus except that measures are taken to make it work allow under cryogenic conditions.

The invention is described below on the basis of exemplary embodiments explained in more detail in connection with the drawings. It shows;

Figure 1 is a flow chart showing various modifications of a reveals the process according to the invention,

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FIG. 2 shows a comparison in the form of a graphic bottom image

/ ■ between the sieving of powdery rubber at ' Low temperature and sieving at room temperature, and

FIG. 3 is a flow diagram of a circulating screen arrangement for separation of rubber and fiber material according to the present invention.

In the flow diagram of Figure 1, the various units are shown in block form and labeled with the procedural steps, which are carried out in these units. It is understood, however, that more than one device unit within each block can be provided. For example, in the practical implementation of the method for the comminution, several comminution devices be connected in series, the size of the particles being progressively reduced while the particles from one shredding device to the next

fen or circulated within one and the same comminuting device will .

In accordance with one embodiment of the invention, all stages of the rubber recovery process are carried out under cryogenic conditions executed. According to FIG. 1, the rubber article 2 to be processed, for example a tire, is placed in a freezer 4 cooled by means of a cryogenic refrigerant 6, which has a temperature below -40 ° C, until the

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Rubber reaches a temperature, which is at least as low as the embrittlement temperature of the rubber. The brittle rubber counter-material is then fed to a pushing or striking device 8, within which the rubber is broken off from the cord fabric and the metallic wire bead. The brittle rubber is then separated from the fabric and the metal within the device 10. The tissue, which remains essentially undamaged, can be sieved out and the metal can be separated out magnetically in a known manner. The still brittle rubber sheets are then fed to a mechanical comminuting device -: Maintain ^{or achieve 4ο 0} C or less.

While the gum is being cooled and kept brittle, or by cooling the gum down, the chunks become in the grinder 12 crushed to a relatively coarse particle size. The device 12 can be a ball or hammer mill be. Because the rubber is brittle, the size of the pieces is not only under the influence of the balls or hammers and the walls of the mill reduced; rather, the chunks break open in the event of mutual collisions. The device 12 is represented in the block diagram of Figure 1 by a single block. It is understood, however, that several crushing devices the same or different types can be used. This depends in detail on the desired reduction

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the particle size and the required capacity.

Because the rubber particles cooled at low temperature are hard and are brittle, in addition to the mechanical crusher 12 a jet mill 16 may be provided, which allows further reduce the particle size and produce a fine powder. Depending on the type of fabric or Impact device 8 can in some cases the rubber particles be so small that the shredding device 12 can be bypassed via a bypass line 18 and the rubber can be bypassed directly the jet mill 16 can be fed. If the in the jet mill 16 injected rubber is still sufficiently cold and brittle, no further cooling is required. Otherwise can the rubber can be cooled with cryogenic coolant 20. the end Economics can be used as a propellant for the Jet mill 16 used the cold gases, which are recovered from the cryogenic refrigerant in an earlier Process stage was used to cool the rubber.

The one leaving the jet mill 16 or via the bypass line 22 deflected powdery old rubber is considered immediately at 24 Reusable end product released. Instead, it can also be processed in a reactor 26 in Reclaimed rubber can be converted. Devulcanization or depolymerization occurs within the reactor 26 using conventional method. The rubber generate 28 can Shaped into skins in a conventional mill or in powder form

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can be used directly for the production of rubber articles.

In the above method, the rubber is continuously processed under low temperatures, ie, the rubber _f is held in each of the processing steps at a temperature which does not exceed -40 ° C. In addition, the cord fabric and bead of wire are separated from the rubber immediately after being peeled off by impact or blow, so that the rubber leaving the comminuting device 12 is essentially free of metal and fibers.

According to the method according to the invention described above produced rubber or rubber has a particle size which is equal to or smaller than the particle size in known Procedure is achieved. By further cryogenic cooling and sieving the particles, the larger particles can be separated out and passed through the comminuting device 12 again while the smaller particles can be separated.

Rubber particles at room temperature are difficult to sieve, even with a brush. However, if such particles have a cryogenic medium, for example at -196 C liquid nitrogen, frozen, is the screening process Significantly improved and accelerated even without brushing. The particles can be frozen and brittle even before they are sieved be made. But it is also possible to apply the particles to the

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to apply top sieve of a sequence of sieves and the partial. to cool to the brittle while they are kept in motion and pass through the sieves. When carrying out such a sieving process, the sieves can be stacked one on top of the other in a conventional manner, the size of the sieve openings progressively decreasing from the top to the bottom sieve of the stack. For a movement is preferably caused by DA * that the stacked sieves are placed in, vibration "The screening device can be pre-cooled or cooled together with the rubber particles.

As can also be seen from FIG. 1, in the cryogenic process according to the present invention, via the line 13 running cooled, ground, fiber-free, brittle rubber are fed to a classifier 30. It can be, for example be a sieve device or a cyclone separator. The rubber particles in classifier 30 can, if they are not sufficiently cooled and are brittle, can be cooled with the help of an additional cryogenic coolant 32, which is through Fine rubber fraction passing through the classifier 30 exits via a line 34. You can either get there via the bypass line 22 or the jet mill 16 to the extraction point 24 or to the devulcanizing device 26 and the extraction point 28. The coarse rubber fraction leaving the classifier 30 exits via a line 36 and is via the shredding device 12 returned to classifier 30.

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Instead of performing all the procedural steps while the rubber - If it is deep-frozen and brittle, certain process steps can occur can also be carried out with rubber at room temperature * As can also be seen from FIG. 1, the rubber article 2 can be placed in a conventional rolling mill at room temperature or rolling mill 40 introduced, cut into pieces there or torn and then via a conduit 41 of the freezer 4 are fed. The cooled, brittle pieces of rubber can then be sent via a line 43 to a mechanical Comminution device 42 arrive. Instead, you can also go directly from the rolling mill 4O to the mechanical one Comminution device 42 introduced and cooled there by means of a cryogenic coolant 44. If the rubber object is cut and torn into pieces of a sufficiently small size, and if the fabric and the Fibers in the crushing mill 40 are detached sufficiently from the rubber at room temperature, they can leave the rolling mill 40 Pieces are fed to a cyclone separator 60 via a line 45. After leaving the crushing mill 4O or the mechanical shredding device 42 runs the material over magnetic separators 48 or 50, in which the from the tire bead if the rubber article being processed is a tire or another metal-reinforced object.

The rubber leaving the comminution device 42 is passed over a magnetic separator 47 and into the cyclone separator 46

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brought in. After the fibers have been detached, the rubber can be fed to the comminution device 12, frozen and processed further in the manner described above. It is also possible to let the rubber run over the bypass line 18 and to further process it cryogenically in the classifier 30 operating at low temperature or the jet mill 16 in the manner explained.

The one cut into pieces and torn in the crushing mill 40 Except when passed over cyclone separator 46, rubber contains fabric fibers. If the rubber and the fibers subsequently, for example in a crusher operating at low temperature, finely divided and then sieved, the fibers agglomerate on the sieves of the sieve device 52, so that they can be separated from the rubber in a simple manner.

In the conventional processing of fiber-reinforced objects with the help of a crushing mill and mechanical crushing devices the fibers tend to stick or stick together. In the low temperature process according to the invention, in which the rubber and the textile fibers are comminuted at low temperatures the fibers become detached not only from the rubber but also from each other. It turned out, however, that the individually detached fibers agglomerate during the subsequent sieving and are retained on the sieve while the Rubber particles pass through the sieve. Fibers spread out on a sieve

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don't bunch up, try to bunch up on the next sieve. While the rubber particles go down through the sieves run through, more and more fibers clump together so that they can be separated.

As can be seen from Figure 3, the fibers agglomerated and separated on a screen are preferably returned and screened again on a screen the openings of which are larger than the openings of the screen from which the agglomerated fibers were withdrawn. This will remove loose rubber particles or particles that have been partially trapped in the fiber ball. When the fibers are detached from the rubber particles according to the screening process according to the invention, less than about 5% by weight of the rubber fraction consists of fibers and less than about 5 % of the fiber fraction consists of rubber. The percentages given in the figure are typical values; however, they can of course change.

In Figure 2, curve A represents the results obtained when sieving of the rubber particles were obtained at room temperature. In contrast, curve B gives the results for the sieving of the particles again under the low temperature conditions explained above. As can be seen from the drawing, sieving yields at lower Temperature a much larger proportion of fine particles and a higher degree of fineness than that obtained by sieving at room temperature can be achieved.

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Claims (9)

Expectations 1J method of making reusable rubber or Rubber made from woven, fabric or fiber-reinforced rubber objects accumulating as waste or used material, characterized in that that the objects are wholly or after previous' subdivision cooled by contact with a cryogenic medium at a temperature below -40 C which is sufficient for embrittlement of the rubber component, that the cooled material is stressed so that the rubber component is detached from the fiber component that the peeled rubber together with at least part of the fiber component is comminuted and that at least part of the fiber component by mechanical separation from the comminuted Mixture is eliminated. 2. The method according to claim 1, characterized in that the cooled material is stressed by breaking or bending, 3. The method according to claim 1 or 2, characterized in that The detached rubber and fiber components are crushed while they are exposed to a cryogenic medium are in contact at a temperature below -40 C. 4. The method according to claim 3, characterized in that the rial at a ur
209812/1173 shredded material at a temperature below -4O ° C temperature is sifted. 5. The method according to claim 4, characterized in that the Comminuted material is sieved to such a particle size that the product only contains a predetermined proportion of the fiber material remains mixed. 6. The method according to any one of the preceding claims, characterized characterized in that liquid nitrogen is used as the cryogenic medium. 7. The method according to any one of claims 1 to 6, characterized in that that used tires are used as the starting material. ■■ * 8. Manufactured by means of the method according to one of claims 1 to 7 Rubber compound essentially consisting of separate rubber and fiber particles. 9. Manufactured by means of the method according to any one of claims 1 to 7 Rubber mass essentially consisting of rubber particles that pass through a mesh screen with 0.295 mm openings go through. 209812/1173 Blank page