Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2002-03-22
2003-10-14
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C521S041000, C521S040500, C521S045500, C521S046500, C521S048000, C523S307000, C523S343000, C523S344000, C523S348000, C528S480000
Reexamination Certificate
active
06632918
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of reclaiming various kinds of crosslinked rubbers such as non-sulfur crosslinked rubber, sponge rubber, silicone rubber and diene-type rubber.
BACKGROUND ART
Heretofore, a reclaiming method wherein crosslinked rubber is converted into reclaimed rubber by applying heat and shear stress thereto has been known as a method of reutilizing wastes of rubber moldings such as tire wastes, or scrap, defective moldings etc. occurring in a process for producing rubber moldings.
According to the above reclaiming method, cross-linkages among rubber molecules constituting crosslinked rubber are cleaved by heat and shear stress, thus making the rubber molecules in a state similar to non-crosslinked molecules.
By re-crosslinking such reclaimed rubber singly or after being blended with new non-crosslinked rubber, the reclaimed rubber can form moldings.
The crosslinked rubber can thereby be recycled.
However, there are some kinds of crosslinked rubbers whose reclamation is difficult or not feasible by the prior art techniques described above.
For example, even if rubber such as non-sulfur crosslinked rubber (peroxide-crosslinked rubber) is heated and subjected to shear stress, the rubber is merely pulverized by the shear stress, resulting in little cleavage of the cross-linkages. Pulverization of rubber into fine powder is estimated to cause the rubber molecules to be hardly subjected to shear stress.
Further, when sponge rubber having a foamed phase, or a rubber blend prepared by blending such sponge rubber with normal crosslinked rubber (solid rubber), is reclaimed according to the prior art techniques, there arose the following problems.
Also, because of the gaseous components such as entrained air, the sponge rubber is poor in heat conductivity, requires longer preheating, and is slow in the progress of plasticization. Further, the sponge rubber is hardly sheared due to low bulk density, thus making the progress of plasticization slow. Accordingly, reclamation treatment thereof requires a longer time.
Further, due to entrained gaseous components, the pressure during reclamation treatment may be varied, and there may arise troubles such as pulsation, abnormal blowing or blowing back of rubber, so that stable reclamation treatment thereof was difficult.
For example, rubber such as silicone rubber or a rubber blend containing silicone rubber could not be reclaimed by the conventional method.
This is because main chains or cross-linkages of silicone rubber are stable to heat and difficult to be cleaved. Further, in an oxygen atmosphere, its molecules are recombined due to oxide deterioration.
During reclamation, a rubber blend, e.g., consisting of natural rubber and butadiene-type rubber used in automobile tires is deteriorated due to oxidation with air, thus rendering rubber molecules low-molecular by cleavage of their main chains or causing the molecules to be crosslinked with one another. Accordingly, reclamation that is excellent in qualities was difficult in the conventional method.
The present invention was made in view of these problems in the prior art, and the object of the present invention is to provide a method of reclaiming crosslinked rubber, which is capable of reclaiming various kinds of crosslinked rubbers whose reclamation is difficult.
DISCLOSURE OF INVENTION
The present invention relates to a method of reclaiming crosslinked rubber including a step of reclaiming crosslinked rubber by applying shear stress to the crosslinked rubber, wherein the maximum pressure in the reclaiming step is 1.5 MPa or more.
The most remarkable feature of the present invention is that the maximum pressure in the reclaiming step is 1.5 MPa or more.
When the maximum pressure is less than 5 MPa, crosslinked rubber may not be reclaimed.
The upper limit of the maximum pressure is preferably 100 MPa. Since a device capable of realizing the maximum pressure of higher than 100 MPa is very large-scale, realization may be difficult.
The lower limit of the maximum pressure is preferably 2 MPa, and the lower limit of the maximum pressure is more preferably 3 MPa.
By increasing the pressure in the reclaiming step as described above, rubber molecules in crosslinked rubber, whose reclamation is difficult in the conventional method because of failure in sufficiently subjecting them to shear stress, can be sufficiently subjected to shear stress, thus efficiently cleaving the cross-linkages therein to reclaim the crosslinked rubber whose reclamation is difficult.
According to the present invention as described above, a method of reclaiming crosslinked rubber can be provided, which is capable of reclaiming various kinds of crosslinked rubbers whose reclamation is difficult.
The reclaiming step in the present invention preferably includes a preheating step and a plasticizing step. In this plasticizing step, shear stress is applied while the maximum pressure is made preferably 1.5 Pa or more.
In the reclaiming method of the present invention, the temperature of crosslinked rubber to be reclaimed is increased due to evolution of heat by shear stress and/or heating from the outside. This is the preheating step.
When the crosslinked rubber attains a predetermined temperature in the preheating step and is further subjected to shear stress, cleavage of cross-linkages and/or some main chains in the crosslinked rubber is initiated, thus softening the crosslinked rubber. This is the plasticizing step.
These steps in the reclaiming method of the present invention can be independently conducted, but from the viewpoint of efficiency of production, it is preferable that the respective steps are conducted successively in one vessel. In this case, the process may proceed successively or simultaneously because the boundary between the respective steps is indefinite.
The two steps described above may be followed by a step of further applying shear stress to the softened crosslinked rubber in order to cleave cross-linkages sufficiently and to disperse and mix rubber molecules. This step is the kneading step. By this step, reclaimed rubber of uniform quality can be obtained.
In addition to the steps described above, there may be further steps such as a step of blending with other materials, a step of re-crosslinking by adding a vulcanizing agent, a step of deodorization, degasification and exhaust, and a step of denaturation-and modification by adding an additive and a reacting agent.
In the reclaiming method of the present invention, the crosslinked rubber is sheared preferably at such a temperature that the cross-linkages in the crosslinked rubber are cleaved and simultaneously cleavage of main chains of rubber molecules constituting the crosslinked rubber does not extremely proceed.
As the shear stress applied is increased, cross-linkages are cleaved more easily, and thus as the shear stress is increased, the temperature during reclamation (temperature of the crosslinked rubber and/or reclaimed rubber) can be lowered.
Specifically, the reclaiming step is conducted preferably at the temperature of 100 to 520° C. When the reclaiming step is conducted at a temperature of less than 100° C., the cleavage of cross-linkages etc. may not sufficiently proceed. Also, when the temperature is higher than 520° C., cleavage of main chains may extremely proceed to deteriorate the physical properties of reclaimed rubber. The upper limit of the above temperature range is more preferably 450° C.
In the reclaiming step, the crosslinked rubber is heated or cooled as required so as to be in the above temperature range. When the heat evolved by the crosslinked rubber upon shearing is too low, the rubber is heated, and when the heat evolved is too high, the rubber is cooled down. When the above temperature range is attained by the heat evolved by the crosslinked rubber upon shearing, heat transfer (heating or cooling) from the outside is not necessary.
The optimum temperature range is varied depending on the type of the crosslinked rubber. For example, when automobile tires etc. are to be reclaime
Fukumori Kenzo
Fukuta Masahito
Honda Hidenobu
Matsushita Mitsumasa
Mouri Makoto
Boykin Terressa M.
Kabushiki Kaisha Toyota Chuo Kenkyusho
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