Reagents for swelling rubber and method of using

Details Reagents for swelling rubber and method of using Reagents for swelling rubber and method of using

2000-04-04

2003-05-27

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S348200, C526S348500, C526S348600, C526S346000, C524S356000, C524S401000

Reexamination Certificate

active

06569977

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to reagents for causing rubber to swell in order to facilitate recycling of rubber.
BACKGROUND OF THE INVENTION
It is estimated that 15,000,000 tons or more of vulcanized rubber products are discarded annually. Approximately half this amount is in the form of rubber tires—upwards of 700 million tires are discarded per year worldwide. It is estimated that there are as many as three billion waste tires in the U.S. alone. The handling and disposal of this large volume of rubber products is a significant environmental problem, and the desirability of recycling waste rubber is evident. Unfortunately, the very properties which make vulcanized rubber so useful make it extremely difficult to recycle. Specifically, rubber does not melt, age or decompose and is designed to be used in extreme environmental conditions. Rubber used in tires is highly elastic and tenacious in a temperature range of −50°-+150° C., and is highly resistant to attack by most common chemical substances. While significant research has been devoted to investigating techniques for recycling rubber, to date only a small percentage of waste rubber is recycled.
One avenue of investigation has been directed to forming rubber powders from waste rubber by grinding the rubber. The rubber powders are then added to a raw rubber mix to form new rubber. This technique has important potential cost savings because the rubber powder reduces the energy and processing required to make new rubber. Currently, rubber powder is used in making many rubber products, including tires, hoses, rubber bands, etc. In addition, rubber powders can be added to other products, such as building materials, to improve their properties.
The amount of rubber powder that can be added to a raw rubber mix during rubber production is highly dependant on the size and shape of the rubber particles which comprise the powder. Specifically, it is known that superfine rubber particles (particles having a diameter of about 200 &mgr;m or less) may be added in significantly higher percentages than larger particles. However, traditional grinding techniques produce rubber particles having a diameter in excess of 600 &mgr;m. To date, addition of rubber powder having particles in excess of 600 &mgr;m has not been accepted by producers of rubber products, because rubber made with large particles has poor properties. Rubber powder consisting of particles in the range of 200-400 &mgr;m may be added in an amount of up to 10% without adversely affecting the quality of the rubber produced.
Finer grain rubber particles may be produced by grinding the rubber at extremely low temperatures (for example, using liquid nitrogen) such that the rubber loses its elasticity. However, due to the energy required to cool the rubber to a sufficiently low temperature, it is uneconomically expensive to form rubber powder in this way.
The inventor of the present invention has previously disclosed a technique for grinding rubber which employs a reagent to cause the rubber to swell. The swollen rubber is more rigid and, therefore, more easily ground into fine particles. The prior disclosure teaches soaking coarsely ground rubber in a non-polar reagent for 5-30 seconds, and then performing further grinding of the resulting swollen powder to achieve a rubber powder with particles having a mean diameter as low as 10 &mgr;m. This disclosure further teaches that such a rubber powder can be mixed with raw rubber in excess of 40% without impairing the physical properties of the rubber. The prior disclosure suggests the use of toluene, xylene, carbon tetrachloride, carbon trichloride, acetone, ethyl alcohol or mixtures thereof. Toluene and xylene were thought, at the time of the prior disclosure, to be particularly good. However, at the time of the prior disclosure the inventor had not arrived at an optimal reagent system for use in his invention, nor had he optimized the soaking process, nor had he investigated the optimal reagents to use with various types of vulcanized rubber.
Accordingly, one object of the present invention is to provide an optimized reagent system for soaking rubber particles to cause them to swell.
Another object of the present invention is to provide a method for soaking rubber particles in a reagent to cause them to swell.
Yet another object of the present invention is to provide reagent mixtures for causing rubber to swell which are optimized for different types of vulcanized rubber.
SUMMARY OF THE INVENTION
The foregoing objects of the invention, and others that will be apparent to those skilled in the art, are realized in the present method for causing rubber particles to swell. In its basic aspect, the present invention comprises a method for causing rubber particles to swell, comprising the steps of mixing coarsely ground rubber particles with a swelling reagent comprising an organic solvent, soaking the mixture for at least five minutes, or until the rubber particles have increased in size by at least 100%, and, if necessary, removing any excess swelling reagent from said mixture. At least two parts of the swelling reagent is used for each part of rubber powder. Preferably, the weight ratio of reagent to rubber is between 2.5-3.5 to 1, so that substantially all of the reagent is absorbed by the rubber. Preferably, the swelling reagent comprises a hydrocarbon, a ketone or a lactone, more specifically a member of the group consisting of benzene, cyclohexanone, cyclohexane, toluene, xylene, hexane, heptane, acetone, gasoline, paramethadione, ethyl acetate and amyl acetate. Most preferred are benzene, cyclohexanone or cyclohexane, and may comprise a mixture of reagents, preferably reagents having the same polarity.
For natural rubber, isoprene rubber, butadiene styrene rubber or 3-polybutadiene rubber, benzene is preferred; for chloroprene rubber or acrylonitrile rubber, cyclohexanone is preferred; and for butyl rubber or ethylene propylene rubber cyclohexane is preferred. When processing different types of rubbers, a mixture comprising at least two of these compounds is preferred.
In order to facilitate removal and recovery of the reagent from the mixture after grinding, the method is performed in an enclosed system and the mixture is heated while applying a vacuum to the enclosed system.
DETAILED DESCRIPTION
According to the present invention, a reagent is mixed with coarsely ground rubber particles in order to cause the rubber particles to swell. The swollen rubber particles are substantially less elastic than unswollen rubber and can be ground into a superfine powder which, is suitable for recycling, as by incorporating the superfine powder into new rubber being produced.
The present invention starts with coarsely ground rubber particles, i.e., particles having a mean diameter in the range of about 500 &mgr;m to 1,500 &mgr;m. Methods of grinding rubber to form rubber particles in this size range are well known in the art and need not be described in detail. For example, a conventional high speed shearing roller crusher may be used. While practical considerations make it desirable to start with particles in the range stated, there is no reason why the starting particles cannot fall outside of this range.
The coarsely ground particles are placed into a soaking vessel which is, preferably, part of an enclosed system which is configured to automate the entire process. As described in greater detail below, the system is enclosed to facilitate reagent recovery.
A swelling reagent is then mixed with the coarsely ground rubber particles in the soaking vessel. The swelling reagents that have been found to be effective are various organic solvents, including hydrocarbons, ketone and lactones. Specifically, benzene, cyclohexanone, cyclohexane, toluene, xylene, hexane, heptane, acetone, gasoline, paramethadione, ethyl acetate, methyl ethyl ketone and amyl acetate have been found to be effective. The reagent that is selected should be a compound which causes the rubber particles to swell, but which does not attack or re

Affiliated with

Also associated with

Rating

Reagents for swelling rubber and method of using does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Reagents for swelling rubber and method of using, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Reagents for swelling rubber and method of using will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3092948