JPH026617B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for recycling used vulcanized rubber. BACKGROUND OF THE INVENTION It is known in the rubber industry to reuse vulcanized rubber in particulate form. Such particulate materials are usually prepared by milling on two roll mills and generally contain 40 mesh (i.e. approximately 388
It is of such a size that it passes through a micron diameter. It is well known that when recycled particulates of this order of magnitude are added to rubber compounds, the tensile strength and other important properties of the resulting recycled rubber compounded rubber composition are substantially reduced. . [Problems to be Solved by the Invention] An object of the present invention is to provide a method for producing recycled vulcanized rubber from used vulcanized rubber, which does not have the above-mentioned drawbacks. [Means for solving the problem] The present inventors have proposed a method for pulverizing used vulcanized rubber, such as vulcanized natural rubber, vulcanized synthetic rubber, or a mixture thereof, into fine powder, and the resulting fine particle regenerated product. The present invention was completed by various studies on the physical properties of a recycled rubber compounded rubber composition in which this compound is blended into a rubber composition. That is, the method of the present invention comprises: (a) contacting crushed or shredded used vulcanized rubber with a fatty acid; (b) contacting the product of step (a) with a solid alkali;
(c) continuing to grind the rubber by mechanical treatment of the rubber during or after contact with the alkali; (c) dispersing the product of step (b) with a liquid that dissolves the alkali but does not affect the rubber; This is a method for producing recycled fine-grained vulcanized rubber, which comprises forming the rubber particles, and then pulverizing the rubber particles. The inventors have discovered that used vulcanized rubber, such as vulcanized natural rubber, vulcanized synthetic rubber, and mixtures thereof, are generally
that they can be reduced to a fine powder size of less than 20 microns, that such fine particles can be added to rubber formulations or compositions, and that they form a vulcanized product as a whole and that the physical properties of said product was found to be only marginally inferior to the product obtained by vulcanization of the rubber compound. In the first step of the production method of the present invention, the crushed or shredded used vulcanized rubber coarse particles are brought into contact with fatty acids to absorb 15% by weight or less (for example, 3% by weight). The fatty acids used here are acids such as oleic acid, stearic acid, tall oil fatty acids or rosin acid, which are effective in plasticizing the vulcanized rubber. The plasticized vulcanized rubber is then passed through the narrow nip of a roll mill into a sheet. In the second step of the process, solid alkali is sprinkled onto the sheet. The solid alkali can be an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide. However, weak alkalis or bases such as sodium carbonate, mixtures of alkalis or bases such as sodium hydroxide/sodium tetraborate may also be used. of rubber
2 to 25 parts by weight, for example 10 parts by weight, of alkali are used per 100 parts by weight. Mechanical processing of the rubber is continued during or after the addition of the alkali, for example by extrusion of the rubber mixture, and the temperature of the rubber mixture in this stage may be higher than in the first step, but preferably must be kept low. Grinding of the rubber to which the solid alkali has been added is continued until the rubber mixture becomes brittle, at which time it has also become hydrophilic. In the third step, the brittle rubber mixture obtained in the second step is dispersed in a liquid that dissolves the alkali but does not affect the rubber, such as water, methyl alcohol, ethylene glycol, or a mixture thereof to form a rubber dispersion. Prepare the liquid. The rubber dispersion in the third step is produced by mixing the brittle rubber mixture obtained in the second step with water when water is used in the dispersion, and by a method effective to produce rubber particles of the desired size. It is obtained by further grinding the rubber particles in the mixture. Suitable grinding methods include, for example, grinding an aqueous mixture with one of the disks fixed and the other rotating at a constant speed;
Alternatively, the discs may be passed between two discs that are both rotating at different speeds, either in opposite directions or in the same direction. In this way, the rubber particles in the aqueous mixture are mechanically fractured and stabilized as an aqueous dispersion of rubber. This aqueous dispersion of rubber becomes a stable creamy paste. To obtain a dry powder from this, generally after dilution with water, this paste is prepared with an acid such as hydrochloric acid.
Or, it is coagulated with other electrolyte such as sodium chloride or by some coagulation method, and then the coagulated product is placed in a centrifugal dehydrator and the liquid is removed. The product is then washed with water until the effluent from the dehydrator is neutral on universal test paper. Alternatively, simply separate in a centrifugal dehydrator and then wash with water until the effluent is neutral. The product is preferably dried at a temperature low enough not to damage the structure of the rubber and is obtained as a fine powder. It is clear that the mechanical treatment in the above process serves to uniformly disperse the fatty acids throughout the powder mass. The alkali then reacts with the thin layer of dispersed fatty acids, resulting in the formation of fine particles.
The addition of water also facilitates the formation of suspensions if appropriate mechanical action is applied. Furthermore, it is a preferred feature of the present invention that the temperature is always kept as low as possible in each of the above-mentioned steps. The reason for this is that at temperatures of 100°C or higher, natural rubber molecules are broken and become an inferior substance with a low molecular weight. In the case of synthetic rubbers, this reaction becomes even more complex. In some cases, low molecular weight materials are formed; in other cases, initial rupture is followed by additional crosslinking, producing much higher molecular weight materials. In either case,
The product is inferior to the original substance. The finely divided vulcanized rubber obtained by the process of the present invention has fine particles generally smaller than 20 microns, and its formulation properties are significantly superior to conventional recycled rubber. It is particularly suitable when at least 90% of the number of vulcanized rubber particles are smaller than 20 microns and have a colloidal dimension, ie larger than 0.1 microns. If the particle size is larger than 20 microns, the properties of the compound will approach those of conventional recycled rubber, and if the particle size is smaller than 0.1 micron, it will be too fine and difficult to separate from the dispersion and dry. . Example 1 Two-roll mill with a gap of 0.12 mm (22 x 44
cm), 300 g of commercially available tire scraps (particle size: 40 mesh, not including rubber scraps other than tires)
and 9 g of oleic acid were ground for 10 minutes. At this stage add 30% solid sodium hydroxide powder to the rubber mixture.
g was added uniformly and the grinding was continued for an additional 10 minutes.
The temperature of the mill was 60°C. The dry, brittle sheet-like product was removed from the mill and placed in the hopper of an industrial 7.5 cm disc mill. The product was poured with enough water (500ml) to moisten it. Grinding wheel (46 grit, carborundum) gap was set to 0.5mm, rotation speed
The disc mill was started at 4000 rpm. The product coming out of the mill was a stable creamy paste. This was fed directly to an industrial centrifugal dryer. However, the creamy paste was kept in a polyester fiber (750 denier) bag in the dryer.
Water was centrifugally removed and water was continuously added to the rotary dryer to wash the product. Washing continued until the wash water was neutral to universal indicator paper. The finely powdered product was dried at 80° C. under reduced pressure (10 mm of mercury). To compare the fine powder made in this way with conventional recycled rubber, 100% of each of these two materials was
The weight parts are 2 parts of zinc oxide, 1 part of stearic acid, 1 part of anti-aging agent Flectol H, and cyclohexylbenzthiadiylsulfenamide.
0.27 parts, diphenylguanidine 0.24 parts and sulfur
0.53 parts. This formulation is perfect for curing
It was compression molded at 150°C to form a flat plate with dimensions of 150 x 150 x 2 mm. The following results were obtained when tested using standard methods.

[Table] The above results show a good improvement in the tensile strength of the compounds made from the particulate vulcanized rubber recycle of the present invention. Improvements are also observed in Taber wear and tear strength. To further compare the aforementioned fine powder with 40 mesh granules and conventional recycled rubber, 82 parts by weight of each of these three materials, 100 parts of styrene-butadiene rubber (grade 1500), 3 parts of zinc oxide,
3 parts stearic acid, 1 part Frectol H, 43 parts HAF Black, Dutrex R softener
10 parts, 0.9 parts of cyclohexylbenzthiadiylsulfenamide, 0.8 parts of cyphenylguanidine and 1.75 parts of sulfur. The formulation at a temperature of 150℃
Compression molding was performed for 15 minutes to form a flat plate with dimensions of 150 x 150 x 2 mm. Similar slabs of the base compound (ie, without any recycled rubber) were also made. The following results were obtained when tested using standard methods.

〔Effect of the invention〕

As described in detail above, the recycled fine particulate vulcanized rubber obtained from used vulcanized rubber obtained by the method of the present invention is only slightly inferior to virgin rubber compared to the recycled rubber compounded rubber composition produced using this as a raw material. It can provide excellent properties. Further, whereas recycled rubber materials normally obtained on the market are coarse, the recycled fine-grained vulcanized rubber of the present invention is obtained in powder form and can therefore be effectively applied to automatic processes such as automatic weighing.

Claims (1)

[Claims] 1. In a method for recycling used vulcanized rubber, (a) contacting crushed or shredded used vulcanized rubber with a fatty acid; (b) contacting the product of step (a) with a solid alkali. let me,
(c) continuing to grind the rubber by mechanical treatment of the rubber during or after contact with the alkali; (c) dispersing the product of step (b) with a liquid that dissolves the alkali but does not affect the rubber; 1. A method for producing recycled fine-grained vulcanized rubber, which comprises forming recycled fine-grained vulcanized rubber, and further pulverizing the rubber particles.