FR2574698A1 - Process for manufacturing a rubber powder or a powder of products made from the vulcanisation of rubber, and powder obtained by the said process - Google Patents

Abstract

The invention relates to the rubber industry. The process, which forms the subject of the invention, of the type consisting in subjecting the raw materials to a grinding operation and to the simultaneous action of a shear force, is characterised in that the raw material is precompressed to a pressure ranging from 0.2 to 0.7 MPa and then the material, thus precompressed, is ground by simultaneous action of a pressure ranging from 0.2 to 50 MPa and of a shear force corresponding to a shear stress ranging from 0.03 to 5 N/mm<2> with heating up to a temperature ranging from 80 to 250 DEG C, followed by cooling down to 15 to 60 DEG C. The invention enables, compared to the known processes, the fineness of the powder to be increased and the energy consumptions to be decreased.

Description

The present invention relates to the field of processing waste rubber and rubber vulcanization products, and in particular relates to a process for manufacturing rubber powders or rubber vulcanization product powders.

The great development of the production of technical rubber products, as well as of the tire and footwear industry, leads to the accumulation of large quantities of rubber waste (scraps and rejects), which find no use. In addition, tires and used technical rubber products are not used either and accumulate in large quantities, cluttering up useful surfaces and polluting the environment. This has created an urgent problem: that of their recovery or reuse.

Waste from the rubber industry and used tires and technical rubber products can be recovered, provided they are transformed into fine powder.

It is known that after being used, rubber, including vulcanized rubber containing cord fibers, can, after grinding, be substituted for unvulcanized rubber, in an amount of 20 to 308 by mass, in rubber mixtures for the manufacture of many products. Ground rubber (particle size <500 / Mm) does not alter the properties of the finished products, but, on the contrary, improves some of these properties, such as, for example, resistance to abrasion wear and abrasion. propagation of cracks. However, the manufacture of fine vulcanized rubber powders is associated with great expenditure of energy.

A process is known for manufacturing fine powders from spent rubber products by cryogenic spraying ("Chemical Technology '!," Cryopulverizinq1 ,, T. Nazy, R. Davis, 1976, 6, no 3, pp. 200 to 203). This process consists in cooling the starting product beforehand to low temperatures by means of liquid nitrogen or solid carbon dioxide, then in subjecting it to the action of percussive loads, or to 6 Ruqer by cutting. This process makes it possible to obtain fine powders, in particular less than 500m, but requires great equipment expenses linked to the need to include in the production line a high-power liquid nitrogen production facility. of nitrogen amounts to 5 kg per kilogram of product, and the energy expenditure amounts to 1500 kWh / t.

A process is known for degrinding materials, including rubber, exhibiting properties of elasticity, adhesiveness and tendency to agglomeration, by grinding in blade mills in the presence of anti-caking agents opposing the sticking of the material to be sprayed on the cutting parts (U.S. Patent No. 3,190,565). The anti-caking agents used are powdered polyethylene or polypropylene, with a particle size corresponding to standard sieves with a mesh size of at least 0.42 mm (at least 40 mesh), preferably from about 0.149 mm to about 0.074. mm (100 to 200 mesh). However, this process does not make it possible to obtain fine powders. It can only produce large granules of 0.6 to 0.9 cm.

A process is known for grinding rubbers by means of a system of crushing and grinding rolls, in which they are subjected to shearing forces. The particles of ground product thus obtained have dimensions greater than 1002 m (Rogov N.A., "Manufacture of regenerated", Moscow, 1957, pp. 57 to 62).

This process makes it possible to produce a finer powder, but it requires great capital expenditure. In addition, this process does not make it possible to manufacture unvulcanized natural or synthetic rubber powders.

A process for manufacturing rubber powders by mechanical grinding is also known, during which shearing forces are made to act on the product (Great Britain patent 1,424,768). This method is implemented in an apparatus of the plunger-piston type, inside which is mounted a rotating element having a cross section of oval shape.

The product is ground in the minimum gap between the rotating element and the inner wall of the body of the apparatus.

The disadvantages of this process are the discontinuity of grinding and the lack of temperature control during grinding, which causes the product to heat up excessively, destroy it and agglomerate the product. powder obtained.

In addition, in this process, when grinding fabric rubber products, or even tires, the fibers are reduced only to particles of length) 50 mm, while the rubber is reduced up to 200 au, c ' that is, the powder obtained is non-uniform and requires additional separation of the fibers and the rubber for the subsequent use of the powder in the rubber mixes.

The invention therefore relates to a method of manufacturing a rubber powder or a powder of rubber vulcanization products, which would make it possible to increase the fineness of the powder and to reduce the energy expenditure compared with the known methods.

This object is achieved by the fact that the method of manufacturing a rubber powder or a powder of rubber vulcanization products, of the type in which a shear force is made to act on these materials, is characterized, according to the invention, in that the material is precompressed to a pressure of 0.2 to 0.7 MPa, then the material thus precompressed is crushed by the simultaneous action of a pressure of 0.2 to 50 MPa and d 'a shear force corresponding to a stress
shear te of 0.03 to 5 N / mm2, with heating to 80-250 C, followed by cooling to 15-600C.

Depending on the nature and the physico-mechanical properties of the material to be ground, the heating-cooling cycle can be performed twice. This increases the fineness of the powder obtained.

Depending on the starting material used, the grinding is carried out in the presence of an additive such as polyethylene
The addition of polyethylene also results in an increase in the fineness of the powder.

The grinding can be carried out continuously in a single or multiple screw extruder.

The process forming the subject of the invention makes it possible to manufacture, from rubber or rubber vulcanization products, a powder of great fineness, the particle size of which does not exceed 500 Arn, for unvulcanized rubber, and 300ss6m, for rubber vulcanization products.

The invention makes it possible to recover products which have completed their service life, for example tires, as well as waste from the manufacture of tires, rubber shoes and technical rubber products, by grinding these products into fine powder, the latter then being used as a filler in the rubber mixes.

The invention will be better understood and other aims, details and advantages thereof will be better understood on reading the following description of various embodiments of the method of the invention.

The process is implemented in particular in an extruder with a single screw or with two screws, having at least two temperature zones, each of these zones being able to heat up or cool down according to the desired thermal regime. The extruder is fed with pieces of vulcanized or unvulcanized rubber, roughly chopped up to dimensions preferably not exceeding 100x50x30 mm.

First, the product is piecompressed under a pressure of 0.2 to 0.7 MPa, then the precompressed material is crushed by simultaneous action at a pressure of 0.2 to 50 MPa and a shear force corresponding to a stress. shear strength from 0.03 to 5 N / mm2, with heating to 80-2500C, followed by cooling to 15 - 60 C.

Grinding the material under these conditions makes it possible to obtain a powder of great fineness.

The starting material can be an unvulcanized natural or synthetic rubber, as well as vulcanization products thereof: products having completed their service life, waste (scraps, rejects). The powder made from these products can be used as a filler in rubber mixes.

To increase the fineness of the powder of a vulcanized or unvulcanized butyl rubber, it is advantageous to add polyethylene thereto. Polyethylene is introduced directly into the starting material in a proportion of 0.5 to 20% by mass. In the present grinding process, polyethylene acts as a synergistic agent, while in the known process (U.S. Patent No. 3,190,565) polyethylene is employed to dust the rubber powder particles and plays the role of an anti-caking agent.

The process which is the subject of the invention does not require any special equipment and can be carried out in a single screw or twin screw extruder. At the end of the grinding, a powder is obtained, the particle size of which does not exceed 500 µm m for unvulcanized rubber, and 3009 m, for vulcanized rubber.

Such a fineness of the powder is obtained if all the treatment parameters indicated above are respected. Lowering the lower limit of precompression of the material, as well as the pressure and the shear force, below the limit values recommended by the invention cause an increase in the size of the powder particles, while their raising above the maximum values proposed by the inventors has no additional favorable effect, while increasing the energy expenditure and lowering the efficiency of the process. The recommended temperatures must also be observed so as not to harm the quality of the powder obtained.

The action of a temperature above 2500C on the product to be ground would cause the destruction of the polymer, which would adversely affect the properties of the products made with the use of such a powder as a filler. After heating, the material is cooled to 15-600C.

The choice of these limits is explained by the fact that the increase in temperature above 600C causes plasticization of the particles and their agglomeration, while its lowering below 150C leads to additional energy expenditure.

The process according to the invention is continuous. It is carried out in a single stage and its use in industrial conditions is easy.

Another advantage of the process is that the energy expenditure for its implementation is low. So, for example, the production of one ton of powder requires 200 to 400 kWh, which is far less than the energy consumption in the case of spraying by the cryogenic process, in which the energy expenditure increases. at 1500 kWh / t.

Another important advantage of the proposed process is that it enables rubber products which have completed their expected service life, as well as rubber waste, to be converted into fine powder. The powder obtained can be used to prepare the rubber mixes. In this way, the invention solves the problem of recycling tires or other rubber products out of use, as well as waste from the manufacture of tires, technical rubber products, footwear, using rubber and rubber products. vulcanization of rubber. The invention thus contributes to reducing pollution of the environment.

Thanks to the fact that the process makes it possible to transform waste rubber obtaining a powder which is recycled in the main manufactures as a filler for the rubber mixtures, it constitutes a contribution to the creation of production methods without waste in the industry. rubber industry.

For a better understanding of the invention, several concrete but non-limiting examples of the implementation of the process of the invention are given below.

EXAMPLE 1.

A twin screw extruder, having two temperature zones, is fed with vulcanized polyisoprene rubber having completed its service life and present in pieces of dimensions not exceeding 100x50x30mm.

In the extruder, the product is precompressed to a pressure of 0.3 MPa, then it is subjected to the simultaneous action of a pressure of 25 MPa and a shear force corresponding to a shear stress of 2.5 N / mm2, at a temperature of 1600C in the first zone, and 300C, in the second.

The powder obtained has the following particle size composition: 30% by mass of particles of size less than 50 m, 50% by mass of particles of size ranging from 50 to 100 ssm, and 20% by mass of particles of size ranging from 100 to 200 ss m.

EXAMPLE 2.

The process is carried out as indicated in Example 1, except that the extruder is supplied with waste from the production of technical rubber products based on natural rubber.

The powder obtained has the following particle size composition: 27% by mass of particles of size less than 50 m, 45% by mass of particles of size ranging from 50 to 100 m, and 28% by mass of particles of 100 to 250} 6 m.

EXAMPLE 3.

The process is carried out as indicated in Example 1, except that the extruder is supplied with waste from the production of technical products made from stryrene-butadiene rubber.

The powder obtained has the following particle size composition: 23% by mass of particles smaller than 50 μm, 54% by mass of particles of 50 to 100 μm, and 23% by mass of particles of 100 to 200 μm.

EXAMPLE 4.

The twin-screw extruder indicated in Example 1 is supplied with polychloroprene rubber which has completed its intended service life and is presented in pieces of dimensions not exceeding 100x50x30 mm. In the extruder, the product is precompressed to a pressure of 0.4 MPa, then it is subjected to the simultaneous action of a pressure of 15 MPa and a shear force corresponding to a shear stress of 5.0 N / mm2, at a temperature of 2100C in the first zone, and 30 C, in the second.

The powder obtained has the following particle size composition: 20% by mass of particles of size less than 50 gm, 26% by mass of particles of size ranging from 50 to 100 m, and 45% by mass of particles of size ranging from 100 to 250 Am.

EXAMPLE 5.

The process is carried out as indicated in Example 1, except that the extruder is fed with a vulcanized mixture of natural rubber, styrene-butadiene rubber and polychloroprene rubber in any proportions.

The powder obtained has the following particle size composition: 20% by mass of particles of size less than 50 m, 70% by mass of particles of 50 to 100 μm, and 10% by mass of particles of 100 to 250 μm.

EXAMPLE 6.

The twin-screw extruder indicated in Example 1 is supplied with nitrile rubber having completed its intended service life and in pieces with dimensions not exceeding 100x50x30 mm. In the extruder, the product is precompressed to a pressure of 0.3 MPa, then it is subjected to the simultaneous action of a pressure of 1.5 MPa and a shear force corresponding to a stress of shear of 0.03 N / mm2, at a temperature of 1800C in the first zone and 400C in the second.

The powder obtained has the following particle size composition: 4% by mass of particles with a size of less than 50ss / m, 17% by mass of particles of 50 to 100 Xm, and 79% by mass of particles of 100 to 300 / m .

EXAMPLE 7.

A single screw extruder, having four temperature zones, is fed with styrene butadiene rubber which has completed its intended service life and is presented in pieces of dimensions not exceeding 100x50x30 mm. In the extruder, the product is precompressed to a pressure of 0.7 MPa, then it is subjected to the simultaneous action of a pressure of 25 MPa and a shear force corresponding to a shear stress of 3.2 N / mm2, at a temperature of 1800C in the first zone, 600C in the second, 1200C in the third, and 150C in the fourth.

The powder obtained has the following particle size composition: 24% by mass of particles with a size of less than 50Xlm, 14% by mass of particles of 50 to 100n, and 62% by mass of particles of 100 to 300m.

EXAMPLE 8.

The twin-screw extruder indicated in Example 1 is supplied with cloth rubber containing 15% by mass of fibers. In the extruder, the product is precompressed to a pressure of 0.5 MPa, then it is subjected to the simultaneous action of a pressure of 30 MPa and a shear force corresponding to a shear stress of 2.5 N / mm2, at a temperature of 800C in the first zone, and 200C, in the second.

The powder obtained has the following particle size composition: 20% by mass of rubber particles and 10% by mass of fiber particles of size less than 50 m, 30% by mass of rubber particles and 50% by mass of fiber particles. 50 to 100m, 50% by mass of rubber particles and 40% by mass of fiber particles of 100 to 200ssMm.

EXAMPLE 9.

The twin-screw extruder indicated in Example 1 is supplied with vulcanized butyl rubber in pieces of dimensions not exceeding 100 × 50 × 30 mm, and with polyethylene in a proportion by mass of 0.58.

In the extruder, the product is precompressed to a pressure of 0.5 MPa, then it is subjected to the simultaneous action of a pressure of 5 MPa and a shear force corresponding to a shear stress of 1 N / mm2, at a temperature of 1500C in the first zone, and 400C, in the second.

The powder obtained has the following particle size composition: 5% by mass of particles with a size of less than 50 μm, 152 by mass of particles of 50 to 100 μm, 188 by mass of particles of 100 to 200 μm, 20% by mass of particles of 200 to 300flm and 42% by mass of particles of 300 to 500Um.

EXAMPLE 10.

The twin-screw extruder indicated in Example 1 is supplied with pieces of unvulcanized rubber based on styrene-acrylonitrile copolymer (74: 26% by mass) and with polyethylene in a proportion of 20% by mass.

In the extruder, the product is precompressed to a pressure of 0.3 MPa, then it is subjected to the simultaneous action of a pressure of 10 MPa and a shear force corresponding to a shear stress of 1.3 N / mm2, at a temperature of 1200C in the first zone, and 30 C, in the second.

The powder obtained has the following particle size composition: 15% by mass of particles of size ranging from 50 to 100 m, 25% by mass of particles of 100 to 200 gm, 25% by mass of particles of 200 to 300 gm, and 35 % by mass of particles from 300 to 500 m.

EXAMPLE 11.

The twin-screw extruder indicated in Example 1 is supplied with butyl rubber having completed its service life and in pieces of dimensions not exceeding 100x50x30 mm, and with polyethylene at a mass content of 10%. In the extruder, the product is precompressed to a pressure of 0.7 MPa, then it is subjected to the simultaneous action of a pressure of 3.5 MPa and a shear force corresponding to a stress of shear of 1.5 N / mm2, at a temperature of 1600C in the first zone, and 300C, in the second.

The powder obtained has the following particle size composition: 6% by mass of particles of size less than 50 gm, 10% by mass of particles of 50 to 100 ssm, 13% by mass of particles of 100 to 200J2m, 36% by mass of particles of 200 to 300 m, and 35% by mass of particles of 300 to 500 m.

Claims (5)

R E V E N D I C A T I O N S 1. A method of manufacturing a rubber powder or a powder of rubber vulcanization products, by grinding and simultaneous action of a shear force on the starting materials, characterized in that the starting material is precompressed up to a pressure of 0.2 to 0.7 MPa, then the material thus precompressed is crushed by the simultaneous action of a pressure of 0.2 to 50 MPa and a shear force corresponding to a shear stress of 0.03 to 5 N / mm2, with heating to a temperature of 80 to 2500C, followed by cooling to 15 to 600C. 2. Method according to claim 1, characterized in that the heating-cooling cycle is performed twice. 3. Method according to one of claims 1 and 2, characterized in that the starting materials are added with polyethylene in a proportion of 0.5 to 20% by mass. 4. Method according to one of claims 1, 2 and 3, characterized in that it is carried out continuously in an extruder with one or more screws. .5. Powder of rubber or of rubber vulcanization products, characterized in that it is obtained by the process according to one of claims 1, 2g3 and 4.