JPH10287765A - Process for reclaiming vulcanized rubber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a novel process for reclaiming a vulcanized rubber whereby fine crushing, high temps., high pressures, and chemical agents are not required by decrosslinking a vulcanized rubber by subjecting it to a mechanical force, such as tension or shearing force, at a low temp. in a nonoxygen atmosphere in the presence of a specified amt. of an unvulcanized rubber, or an uncured polymer. SOLUTION: A vulcanized rubber in the form of fragments with diameters of about several mm to several tens of mm is mixed with an unvulcanized rubber or an uncured polymer in an amt. of 10 wt.% or higher, pref. 15-30 wt.%, based on the total wt. The mixture is subjected to a mechanical force, such as tension or shearing force, at 40 deg.C or lower, pref. 35 deg.C or lower, in a nonoxygen or low-oxygen atmosphere kept by injecting an inert gas, such as nitrogen or carbon dioxide, into a treating apparatus. Thus, the vulcanized rubber is decrosslinked and reclaimed. The mechanical force can be applied by using an ordinary extruder. The resultant reclaimed rubber can be used similarly to a raw rubber and can be vulcanized again.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for decrosslinking and regenerating vulcanized rubber used for automobile tires and the like for reuse.

[0002]

Conventionally, there has been known a method of chemically decrosslinking to regenerate waste rubber. However, conventional methods require extremely fine crushing of rubber, or require high temperature and high pressure for regeneration, and use various chemical agents. In fact, it is not completely satisfactory.

Accordingly, the present invention has been made to provide a new regenerating method which does not require fine crushing, high temperature and high pressure, and further does not require a chemical agent or the like.

[0004]

The present invention relates to a vulcanized rubber,
De-crosslinking is performed by applying mechanical force such as tension and shearing force. Simply by applying mechanical force, rubber molecules are cut and the molecular weight is reduced, making it impossible to recycle.
Therefore, in the present invention, the free radicals generated by molecular cleavage are bonded to oxygen so as not to terminate the molecule, so that the temperature is low and oxygen-free, and further, the free radicals are easily bonded to other rubber molecules. And a small amount of unvulcanized rubber.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The vulcanized rubber used as a raw material in the present invention may be either synthetic rubber or natural rubber. Also,
Unvulcanized rubber may be mixed. Further, carbon black, oil and the like may be contained. The shape is arbitrary as long as the device that applies mechanical force such as tension, shearing force, or the like permits, and it is usually preferable to form a small piece having a diameter of about several to several tens of millimeters. Due to the mechanical treatment, it is inconvenient to be in an excessively small powder form, but there is no problem in including a part of the powder. Therefore, waste tires and the like cut with a simple cutting machine can be used as a raw material as it is without making the size uniform with a sieve or the like.

The process of applying mechanical stretching and shearing force can be carried out by using a usual extruder. Also, a special-purpose machine, for example, a disk or a cylinder is opposed with a slight gap therebetween. It is also possible to prepare a device that rotates the surface relatively.

This mechanical treatment is performed at a low temperature, that is, at 40 ° C. or less, preferably at 35 ° C. or less. Friction heat is generated by mechanical processing, and it tends to become high temperature, so it is necessary to operate the processing device while cooling it with cold water, etc.In addition, to suppress the generation of heat, the operating speed should not be too fast It is important to do it. Specifically, in an extruder, it is desirable to provide a water-flowing space behind an opposing surface in an apparatus using an extrusion shaft or a casing, a disk or a cylinder so that cold water always flows. This low temperature also has the effect of maintaining the high viscosity state of the rubber and effectively applying mechanical force such as tension and shearing force.

[0008] This mechanical treatment is carried out in a state of no or low oxygen. The oxygen concentration need not be strictly zero, but is desirably as small as possible, generally less than 10 percent. The molecular weight of the finished recycled rubber is
If a slight decrease from the beginning is allowed, the oxygen concentration may be relatively high. This absence or hypoxia
For example, it is realized by injecting an inert gas such as nitrogen or carbon dioxide into the processing apparatus. In particular, when operating continuously, it is preferable to continuously inject this inert gas.

Further, in this treatment, unvulcanized rubber is added to the vulcanized rubber as a raw material. An uncured raw rubber is suitable for the unvulcanized rubber, and another uncured polymer may be used. Further, the rubber may be recycled according to the present invention. This unvulcanized rubber requires at least 10% by weight of the whole. The unvulcanized rubber wraps free radicals generated by molecular cleavage, and the free radicals easily bind to the unvulcanized rubber or other free radicals.
If the amount is too small, this effect cannot be obtained sufficiently. When the amount of unvulcanized rubber is large, there is no inconvenience in the properties of the finished recycled rubber, but the working efficiency is reduced.
It is good to be about 30% by weight.

[0010] The rubber regenerated according to the present invention can be used in the same manner as fresh rubber and can be vulcanized again. It is considered that the sulfur content in the raw rubber is trapped in the recycled rubber in a chemically stable state and does not perform the curing action. Since the rubber regenerated according to the present invention naturally contains additives such as carbon black as a raw rubber, it is easier to use a mixture with a new rubber than to use it alone, And practical.

[0011]

Next, examples of the present invention will be described.

As a raw material, a used tread of a waste truck tire cut into a length of 20 to 40 mm, a width of 10 mm, and a thickness of 5 mm is used. In addition, uncured synthetic rubber (SB
Contains additives such as R30%, NR70%, carbon black and oil. ) And natural rubber are each mixed to a total of 15 weight percent. These were put into an extruder whose internal space was filled with nitrogen gas, and operated while continuously supplying nitrogen gas. This operation is performed by repeating the operation of closing the tip with a cap, rotating the extrusion shaft, performing the extrusion operation, and then reversing the extrusion shaft. At this time, cold water was passed through the outer periphery of the casing, and the inside was maintained at about 35 degrees Celsius. Driving speed is low enough 2 per minute
It was 6 revolutions and operated for 8 minutes. Finally, the cap was removed, and extruded to take out the recycled rubber.

This recycled rubber is converted into an uncured rubber by adding
It was mixed at 5% by weight and vulcanized to obtain a finished product. As a comparative example, one obtained by vulcanizing only the uncured rubber into which the recycled rubber was not mixed was prepared. The results of the comparison are as follows. Comparative Example Finished product Shore hardness A 64 60 Shore hardness A (after 700 hours at 72 hours) 70 65 Modulus Mpa 2.5 2 Modulus of elasticity Mpa (after 700 hours at 72 hours) 3.325 2.6 (+33) %) (+ 30%) Tensile strength Mpa 22 18 Tensile strength Mpa (at 70 ° C., after 72 hours) 23 19 Elongation 520% 480% Elongation (at 700 ° C., after 72 hours) 468% 423% Tear strength KNm 7.2 6.5 Tear strength KNm (after 70 hours at 70 ° C.) 7.56 7.15 Coefficient of restitution 38% 39% Compression set (70 ° C., 22 hours) 17% 21%

Summarizing the above, it is considered that the finished product is substantially the same in each physical property value, though slightly lower than the comparative example.

[0015]

As described above, the present invention does not require pretreatment such as fine crushing, does not require high temperature, high pressure, or a chemical agent, and can be implemented very easily and at low cost. Moreover, the finished recycled rubber has almost the same physical properties as the new rubber, and can be used for a wide range of applications similar to the new rubber.

Claims (5)

[Claims] 1. An uncured rubber or an uncured polymer is added to a vulcanized rubber in an amount of 10% by weight or more, preferably 1% by weight or less.
It is mixed in an amount of about 5 to 30% by weight, and this is subjected to decrosslinking by applying a mechanical force such as tension or shear force in a no-to-low oxygen state of 40 ° C. or less, preferably 35 ° C. or less. A method for reclaiming vulcanized rubber. 2. The method for reclaiming vulcanized rubber according to claim 1, wherein the rubber regenerated by this method is used as the uncured polymer. 3. The method for reclaiming vulcanized rubber according to claim 1, wherein a gas containing no oxygen, such as nitrogen or carbon dioxide, is supplied during the process to realize a zero to low oxygen state. 4. The vulcanized rubber according to claim 1, 2 or 3, wherein a mechanical force such as a tension or a shearing force is applied between the opposed and relatively rotating surfaces of the extruder or the like to decrosslink. How to play. 5. The method for reclaiming vulcanized rubber according to claim 4, wherein one or both of the resisting surfaces is cooled with water.