JPS599341B2 - Processing method for cross-linked non-plastic rubber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for processing crosslinked non-plastic rubber, such as vulcanized rubber.

It is known to recycle crosslinked (eg vulcanized) non-plastic rubber for reuse.

Known methods for reusing vulcanized rubber mostly prepare vulcanized rubber scrap material in one of two forms.

On the one hand, the process is mechanical in nature, separating the vulcanized rubber from contaminants such as metal flakes or textile residues, and then crushing and classifying the rubber into a free-flowing material while still in a vulcanized and non-plastic state. Rubber scraps are obtained and used as rubber scraps, or alternatively, the rubber scraps are further processed by a combination of machining, the action of chemical additives, and heating to produce materials commonly referred to as "recycled rubber". form.

"Reclaimed rubber" is no longer in a vulcanized state and is again plastic and can be molded and then revulcanized.

"Recycled rubber" takes the form of a homogeneous mass and can be handled in the same way as ordinary unvulcanized rubber.

It is clear that it is significantly more expensive to produce "recycled rubber" than to produce vulcanized rubber scraps from scrap rubber material.

Vulcanized rubber crumbs are usually included in small proportions in unvulcanized rubber formulations and serve to facilitate processing during shaping, such as extrusion or calendering, prior to vulcanization.

It is also becoming increasingly important to include vulcanized rubber scraps to reduce the cost of the final rubber product.

The reason for the cost reduction is that scrap rubber is generally available at a lower price than unvulcanized rubber compounds.

However, the inclusion of vulcanized rubber scraps in an unvulcanized rubber compound has the disadvantage that the product obtained by vulcanizing this rubber compound becomes weak.

Such weakening becomes particularly noticeable when vulcanized rubber scraps are added to the unvulcanized rubber compound in an amount of about 25% by weight or more in terms of the final product.

Such mechanical weakness is believed to be due to the stress concentration at the interface between the particles of vulcanized rubber waste and the rubber compound into which they are introduced, resulting in distortion.

The interface exists because the surface of the vulcanized rubber crumb is non-plastic and therefore immiscible with the surrounding rubber compound before the rubber compound is vulcanized to form the final product.

As a result, there are many well-defined adhesive interfaces, which create stress concentrations and lead to mechanical weakness.

Therefore, reusing vulcanized rubber scraps in rubber compounds and then vulcanizing them rarely yields products that are comparable to articles made from freshly vulcanized rubber compounds.

On the other hand, fully plasticized "recycled rubber" obtained by destroying the vulcanization of rubber scraps is significantly weakened during the regeneration process, so the product obtained by subsequent revulcanization is
This "recycled rubber" has the disadvantage of exhibiting only a moderate relative strength, much less than the strength of the original vulcanized rubber from which it was made.

It is an object of the present invention to provide another method for processing crosslinked non-plastic rubber so that it can be reused.

According to the method of the present invention, in processing a crosslinked non-plastic rubber piece, the surface layer of the rubber piece is rendered plastic while the inner core of the rubber piece remains non-plastic.

For ease of handling, it is preferred to process the crosslinked non-plastic rubber in particulate form.

The surface layer of a crosslinked non-plastic rubber piece can be made plastic by treating it with chemicals, or the surface layer of a rubber piece can be made plastic by heating.

Alternatively, the plasticizing treatment can involve both the use of chemicals and heating.

According to a preferred method of the invention, the surface layer of the cross-linked non-plastic rubber piece is heated by direct application of a flame to the surface layer of the cross-linked non-plastic rubber piece, thereby making the surface layer of the cross-linked non-plastic rubber piece plastic.

In a preferred embodiment of the present invention, in treating the vulcanized rubber particles, the vulcanized rubber particles are desulfurized and/or
or through a region of flame that provides heat of sufficient intensity to cause partial depolymerization, rendering the surface layer plastic during the passage of the particle and leaving the inner core of the particle in a vulcanized and non-plastic state. to be maintained.

The particles are passed through single or multiple heating zones.

Processing using single or multiple heating zones can be either batchwise or continuous, and the movement of the particles can be either horizontal or vertical.

However, according to a preferred method of the invention, the particles are allowed to fall through the heated region under the action of gravity.

The pieces of rubber material obtained by the treatment according to the invention have an inner core made of crosslinked non-plastic rubber and a surface layer which is plastic and can be fused with other similar pieces of rubber material or with unvulcanized rubber. and has.

The vulcanized rubber piece treated by the method of the present invention is produced by heating the treated rubber piece and the unvulcanized rubber under pressure and heating to obtain a vulcanized rubber on the surface layer of the unvulcanized rubber and the treated rubber piece. It can be shaped with unvulcanized rubber by molding it in the presence of sufficient vulcanizing agent to vulcanize it.

The treated rubber pieces obtained from vulcanized rubber can be formed into molded articles without the addition of unvulcanized rubber, or alternatively under pressure and heat, the surface layer of the treated rubber pieces can be plasticized. It can be molded in the presence of sufficient vulcanizing agent to vulcanize the rubber.

Furthermore, it has been found that it is not necessary to introduce vulcanization additives into the treated rubber piece in order to obtain a vulcanized molded article by molding the treated piece under pressure and heat.

In a particularly preferred method of the invention, the vulcanized rubber piece is subjected to one or more flame zones of sufficient intensity to cause desulfurization and/or partial depolymerization of the surface layer of the rubber piece. Let it pass.

Examples of vulcanized rubbers suitable for the treatment of plasticizing the surface layer of vulcanized rubber pieces by applying heat include natural rubber, butadiene-styrene copolymers, isobutylene vulcanized copolymers, and ethylene-propylene vulcanized copolymers. There are copolymers.

The invention will now be explained in more detail with reference to preferred embodiments and with reference to the drawings.

Identical or similar parts in the drawings are designated by the same reference numerals.

The apparatus shown in FIG. 1 preferably has a reaction chamber 1 made of metal.
Equipped with.

A hopper 2 is provided at the upper end 3 of the reaction chamber 1.

A supply device having a supply control mechanism 4 and a droplet 5 is provided in the feeder 2.

A gas burner 6 is attached to the side of the reaction chamber 1 below the drop port 5.

The gas burner 6 is connected to a gas supply source through a connecting pipe 7, and a plurality of air holes 8 are provided to allow air to enter the gas burner 6 for burning gas from the gas source.

When the gas burner 6 is activated, this creates a region of hot gas consisting of a flame, hot air and gaseous combustion products, which hot gas flows across the chamber 1 from the side of the chamber 1 on which the gas burner 6 is installed and into the chamber 10 opposite. flowing towards the side.

The air inlet pipe 9 is connected to the top 3 of the reaction chamber 10 to the gas burner 6 of the chamber 1.
Attach it facing the opposite side.

Air inlet pipe 9 is connected to an air source to deliver a downward flow of cooling air to the side of reaction chamber 1 opposite gas burner 6 .

The bottom end 10 of the reaction chamber 1 is an opening. When operating the apparatus of FIG. 1, rubber scraps are loaded into the hopper 2 and fed into the reaction chamber 1 through the droplet 5 at a rate controlled by the feed control mechanism 4.

The rubber crumbs fall into the heating area formed by the gas burner 6 under the action of gravity.

The flow of flame, heated air and gaseous combustion products from the gas burner 6 burns the surface of the rubber waste particles, which are then carried across the reaction chamber 1 by the downward flow of cooling air from the air inlet pipe 9. transported inside.

The cooling air flow from the air inlet tube 9 quenches the heat-treated surface of the rubber crumb particles and facilitates the movement of the heat-treated rubber powder downward to the bottom end 10 of the reaction chamber 1.

Heat treated rubber crumb can be collected from the bottom end 10.

The downward flow of cooling air from the air inlet tube 9 maintains the airflow within the reaction chamber 1, in addition to quenching the heat-treated surface of the rubber scraps and promoting the downward movement of the heat-treated rubber scraps. to assist combustion of gas from the gas burner 6.

The treated rubber scraps emerging from the bottom end 10 of the reaction chamber 1 can be collected in a hopper or dropped onto a continuously moving conveyor belt.

The use of the apparatus shown in FIG. 1 is particularly suitable because it facilitates the treatment of rubber scraps obtained from tires.

Rubber waste obtained from tires usually contains textile residues.

It is extremely difficult to remove these textile residues;
This difficulty has made it impossible to reuse the rubber obtained from tires.

When rubber scraps obtained from tires are heat-treated using the apparatus shown in Figure 1 described above, it has been confirmed that the textile fibers in the scraps are carbonized or completely burned out, and that no residual mixed fibers are observed. Ta.

In the test apparatus having the configuration of the apparatus shown in FIG. 1, the height of the reaction chamber 1 is 82 CrfL, and the inner diameter is 15.5 CrfL.
And so.

The diameter of the droplet 5 was 2crfL, and the diameter of the air inlet pipe 9 was also 2cIrL.

The gas burner 6 had a rectangular cross section at the point where it was inserted into the reaction chamber 1, and had a width of 2 cIrL and a height of 15 cm.

The gas burner 6 is connected to the reaction chamber 1 through an orifice with a diameter of 3 mm.
penetrated the wall.

During operation, the supply control mechanism 4 is adjusted to allow rubber scraps to pass through the droplet 5 at 200? It was supplied at a rate of about 1/min.

Butane gas was supplied to the gas burner 6, and the flame was adjusted appropriately so that the length of the "blue region" of the flame was approximately 3.5 cfrL.

The droplet 5 was arranged so that the rubber crumb particles fell vertically into the "blue region" of the flame.

The air supply was adjusted such that a downward flow of cooling air flowed through the air inlet tube 9 at a rate of 250 tl.

Examples specifically illustrating the method of the present invention will be described below, which were carried out using the test apparatus described above in connection with FIG.

Example 1 Crushed whole tire vulcanized rubber crumbs passing through a 30 mesh/inch node were processed in a test apparatus.

Treated whole tire rubber waste was compared with untreated whole tire rubber waste in a comparative test.

100 parts by weight of treated whole tire rubber waste was blended with 100 parts by weight of unvulcanized rubber compound.

This unvulcanized rubber formulation contains 100 parts to 72 parts of a styrene-butadiene rubber compound and abrasion resistant furnace black.
2 to 3 parts of a vulcanizing agent and an antioxidant.

The blend of treated rubber scrap and unvulcanized rubber was formed into slabs 15% inch (7.4 mm) thick in a forming press.
Vulcanization treatment was performed at 5°C for 25 minutes.

Similar slabs were formed from a mixture of 100 parts by weight of untreated whole tire rubber waste and 100 parts by weight of unvulcanized rubber compound.

When tested according to British Standard Standard (BSS) A903, slabs containing treated rubber scraps had a tensile strength of 106.61 kg/crA (1523 ps).
i), the elongation at break is 410%, and these values are equal to the tensile strength of the slab containing untreated rubber crumb 8 1.7
6k9/cy7 (1 1 6 8 psi) and an elongation at break of 360%.

= parts of treated rubber waste were tumble mixed with powdered vulcanizate ingredients according to the following composition.

Total tire rubber treated by weight <-g- 1oo. o
o This mixture was fed to two rolls of a two roll rubber cross mill with a roll temperature of about 40°C and cut from the rolls to form a coarse but cohesive sheet.

This composition was then molded in a compression mold with a hemispherical recess 6 cm in diameter to produce a hollow hemisphere with a wall thickness of 0.5 crrL.

Before loading, this mold was preheated in an open type press with a heating plate heated to 170°C.

The mold was returned to the press and the composition was cured for 3 minutes.

Upon removal from the press, the product was immediately removed from the mold while still hot to ensure that the product was no longer plastic but had vulcanized rubber properties.

Example 2 Vulcanized natural rubber molding scraps were pulverized in a two-roll rubber mill to produce an unclassified but 0. Particles with a maximum dimension on the order of 5 varb were obtained.

The rubber particles were processed in a test device.

The treated product was a fluffy crumb with coarse clumps.

The treated rubber particles were mixed in a rubber mill with the vulcanizate components according to the following composition.

A portion of this composition was used to form vulcanized specimens, which were tested in accordance with British Standard A903.

The vulcanized test piece has a tensile strength of 1 2 7. 0 5 kg/
cat (1815 psi), elongation at break 470%, and these values correspond to the tensile strength of 59.5 to 63.0 kg/C for a vulcanized product made from first grade whole tire recycled rubber.
rA (850-900psi), elongation at break 300-3
It was confirmed that it was significantly superior even when compared with the typical value of 50%.

= parts of the above composition were loaded into a single recess conical Q-IJ mold, and the composition was placed in an open stepped molding press for 15 minutes.
Vulcanization treatment was performed at 0°C for 10 minutes.

The product was removed from the mold while hot and found to be non-plastic but vulcanized and to have very good elasticity.

Example 3 Vulcanized natural rubber molded scrap was crushed and processed in the apparatus of FIG. 1 as in Example 2.

The treated rubber scraps are directly loaded into a flat plunger mold without being mixed with a vulcanizing agent, placed in a vulcanizing press, and
Heated at 50°C for 30 minutes.

When the mold was opened, it was confirmed that the crushed scrap had solidified into a homogeneous sheet.

The sheet was removed from the mold hot and was non-plastic.

It is believed that vulcanization occurs as a result of residual vulcanizing agent migrating from within the core of the treated rubber particles to the plastic outer layer of the treated rubber particles.

In the apparatus shown in FIG. 2, the rubber scraps are passed through a plurality of heating zones.

Rubber scraps are put into a hopper 2, from which the rubber scraps are conveyed by a conveyor belt 19.

By adjusting the speed of the conveyor belt 19, the feeding speed of rubber scraps from the hopper 2 can be varied.

A conveyor belt 19 feeds the rubber waste into the reaction chamber 1 via the open upper end 3 of the reaction chamber 1 .

The conveyor belt 19 and the hopper 2 are protected by the heat shield plate 20.
shield from heat.

Three pairs of gas burners 6 facing each other are arranged downward along the length of the reaction chamber 1 at predetermined intervals.

These gas burners 6 have the same construction as ordinary burner members for household gas orbs.

The gas burner 6 is pivotally mounted in the reaction chamber 1, and the gas burner 6 is connected to the reaction chamber 9.
It can be rotated between 0° angles to adjust the angle of the flame coming out of the gas burner.

Connecting pipes T are connected to the gas burner 6, and each connecting pipe 7 is provided with a tap 21 for connecting to a gas supply source.

A pair of air inlet pipes 22 are installed below the lowest pair of gas burners in the reaction chamber 1.

Each air inlet tube 22 is provided with a longitudinal slit 23 or a plurality of longitudinally spaced openings to allow air to escape into the reaction chamber.

The air inlet pipe 22 is pivotally mounted in the reaction chamber 1 in the same manner as in the case of the gas burner 6, and the air inlet pipes are arranged appropriately to form the reaction chamber 1.
forming an air curtain that moves downward within the air.

The air inlet pipe 22 is connected to an air source by a connecting pipe 24.

Rubber waste particles fed by the conveyor belt 19 to the open upper end of the reaction chamber 1 fall within the reaction chamber 1 between successive pairs of gas burners 6 under the action of gravity.

The flame, heated air and gaseous combustion products formed by the gas burner 6 burn the surface of the rubber waste particles.

When the rubber crumb particles reach the downward moving air curtain formed by the air inlet pipe 22, the surface of the heat-treated rubber crumb particles is rapidly cooled.

The downward movement of air from the air inlet pipe 22, with the aid of gravity, moves the heat treated rubber crumb downwards into the bottom end 10 of the reaction chamber 1.
Transfer to.

The bottom end 10 is open so that heated rubber crumbs can fall and be collected, for example into a hopper or onto a conveyor belt.

In order to create an optimum temperature distribution within the reaction chamber 1, thermocouples can be inserted at various points within the reaction chamber 1 of the apparatus of FIG.

Rubber particles can be treated in the method of the invention by subjecting the rubber particles to the action of heat without allowing them to fall under the action of gravity.

An example of this is shown below.

Example 4 Approximately 5001 pieces of crushed whole tire vulcanized rubber (passing through a 30 mesh/inch node) was spread in a uniform thin layer on a metal plate.

The flame of a pressurized butane/air burner was applied to the exposed surface of the rubber scrap, and the burner was moved appropriately to ensure that the rubber scrap smoked but did not reach its ignition point.

After several passes of the flame across the exposed surface and cooling between passes, the rubber shavings were stirred to expose new surfaces and the flame treatment was repeated.

When this operation was repeated two more times, the treated rubber crumbs obtained at this stage tended to agglomerate into fluffy clumps.

The treated rubber scraps obtained as described above were mixed with vulcanized components in a two-roll mill at a roll temperature of 40° C. according to the following composition.

A rough band was formed in the mill during crosstalk.

A portion of the composition was transferred from the mill to a flat mold and heated to 150°C.
Vulcanization treatment was performed for 15 minutes between the hot plates of a press heated to .

The hot product was removed from the mold and it was confirmed that the product was not plastic and had been converted into a fairly homogeneous vulcanized product with good rubber properties.

A portion of the composition was used to make vulcanized specimens which were tested in accordance with British Standard A903.

The test piece has a tensile strength of 99.4 kg/c4 (14
20 psi) and an elongation at break of 250%, these values correspond to the tensile strength of the vulcanized product obtained from first grade whole tire recycled rubber of 59.5-63, Okg/cr/f. (
850-900psi), elongation at break 300-350
%.

The treatment of rubber particles according to the invention can therefore be carried out either by moving the particles or by moving the heating zone in a horizontal plane.

The appearance and texture of rubber scraps heat treated by the method of the invention will vary depending on the degree of treatment and the nature and composition of the vulcanized rubber scraps before treatment.

For example, the treated rubber crumb may be in the form of a coarsely cohesive material with a sticky surface, or may be in the form of a free-flowing material with a dusty surface appearance.

FIG. 3 diagrammatically shows a section cut from a rubber particle heat-treated according to the method of the invention.

The particles have a core portion 15 that remains non-plastic.

The core portion 15 is surrounded by a partially plasticized intermediate region 16 which is almost completely plasticized and contains an outer layer of other particles of treated rubber waste or an unvulcanized rubber compound. It is surrounded by an outer layer 17 that is compatible with objects.

The outer surface 18 of the outer layer 17 is optionally at least partially composed of free carbon residues resulting from the combustion of textile residues left on the rubber waste prior to treatment or from limited surface combustion during heat treatment. covered.

The boundaries between the core portion 15 and the intermediate region 16 and between the intermediate region 16 and the outer layer 17 are not sharply defined and the rubber is completely plasticized from the non-plastic core portion 15. The degree of plasticity changes gradually up to the outer surface 18, which has been softened.

No sharply defined boundaries between the particles are found when the treated rubber particles are consolidated or when the treated rubber particles are mixed with an unvulcanized rubber compound.

Crosslinking of the solidified particles or a mixture of particles and unvulcanized rubber compound forms a substantially homogeneous product with no apparent presence of separate rubber particles.

As is clear from the above example, significantly different mechanisms can be used to plasticize only the outer layer of crosslinked rubber material.

Pieces of rubber material according to the invention having a plastic surface layer and an inner core of non-plastic rubber are conventionally manufactured from vulcanized rubber scraps or so-called "recycled rubber", which are completely plasticized products made from vulcanized rubber. It can be used in almost any treatment process that has been used.

However, rubber pieces treated with the method of the invention are advantageous over untreated rubber scraps because they can be used to make crosslinked rubber products without the need for compounding with fresh unvulcanized rubber.

One of the advantages that pieces of rubber material treated according to the method of the invention have over "recycled rubber" is that the amount added is sufficient to crosslink only the plasticized or partially plasticized parts of the rubber pieces. vulcanizing agents or other crosslinking agents.

If the vulcanizing agent or other cross-linking agent in the untreated rubber material is completely consumed and the vulcanizing agent or other cross-linking agent remains in the inner core of the treated rubber piece, the vulcanizing agent or other cross-linking agent or other crosslinking agents.If sufficient, these migrate into the plasticized or partially plasticized portion of the treated rubber, eliminating the need for the inclusion of additional vulcanizing agents or other crosslinking agents. Can be completely or partially eliminated.

The above-described method of processing a rubber material to obtain a piece of rubber material having an inner core of non-plastic rubber and a surface layer of plasticity requires a given amount of energy input to produce a useful material from a given rubber material. The advantages are lower than in the case of known methods of producing "recycled rubber" from rubber materials.

This advantage is partly due to the fact that only the outer layer of the rubber piece is treated,
The core of the treated rubber piece remains unchanged;
This is due to the fact that the known method of producing "recycled rubber" combines the application of heat, the action of chemical additives and machining to plasticize the entire rubber mass.

In addition to the above-mentioned method of obtaining pieces of rubber material with an inner core of non-plastic rubber and a plastic surface layer using only heat treatment, unlike known methods of producing "recycled rubber", chemical additives are not added. There are advantages to not using

It is clear that significant cost advantages result from the savings in energy consumption and/or the use of chemical additives.

Furthermore, when producing "recycled rubber," rubber scraps containing textile residues cannot normally be used, whereas according to the method of the present invention, vulcanized rubber scraps containing textile residues can be easily used as described above. can be processed.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a particularly preferred embodiment of the apparatus for heat treating rubber scraps, FIG. 2 is a schematic sectional view showing a second embodiment of the apparatus for heat treating rubber scraps, and FIG. FIG. 2 is a perspective cross-sectional view showing a section of a piece of rubber crumb treated by the method of the invention. 15... Inner core portion, 16... Middle region, 17... Surface layer, 18... Outer surface.

Claims (1)

[Claims] 1. In a method for recycling vulcanized rubber in which the surface layer of vulcanized rubber is made plastic by devulcanization while the inner core of the vulcanized rubber remains non-plastic, the surface of the vulcanized rubber is A method characterized in that the surface of the vulcanized rubber is burned by direct application of at least one flame for a time insufficient to cause ignition.