JPS6134028A - Regeneration of vulcanized rubber - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for recycling used vulcanized rubber.

[Conventional technology]

It is known in the rubber industry to reuse vulcanized rubber in particulate form. Such particulate materials are usually prepared by milling in two roll mills and are generally
0 mesh (ie, approximately 388 microns in 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. .

[Problem that the invention seeks to solve]

The 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 problems]

The 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, the resulting fine-grain regenerated product, and a regenerated product in which the same is blended into a rubber composition. The present invention was completed after various studies on the physical properties of rubber compounded rubber compositions.

That is, the method of the present invention comprises: (a) contacting pulverized or shredded used vulcanized rubber with a fatty acid; (b) contacting the product of step (a) with a solid alkali;
(c) dispersing the product of step (b) in a liquid that dissolves the alkali but does not affect the rubber; (c) mechanical treatment of the rubber during or during contact with the alkali; This is a method for producing recycled fine-grained vulcanized rubber, characterized by forming a liquid and further pulverizing the rubber particles.

The inventors have discovered that used vulcanized rubber, such as vulcanized natural rubber, vulcanized synthetic rubber, and mixtures thereof, can generally be micronized to a fine powder size of less than 20 microns, and that such fine particles are that can be added to a rubber composition and form a vulcanized product as a whole, the physical properties of which are very slightly inferior compared to the product obtained by vulcanization of the rubber compound. I found out that it is only .

In the first step of the production method of the present invention, pulverized 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 include, for example, oleic acid, stearic acid,
Acids such as tall oil fatty acids or rosin acids are effective in plasticizing 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.

2 to 25 parts by weight, for example 1 per 100 parts by weight of rubber.
0 parts by weight of alkali are used.

The 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 is preferably as low as possible. must be retained. 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 crushing the rubber particles in the mixture. Appropriate methods of grinding include, for example, grinding an aqueous mixture with one of the disks fixed and the other rotating at a constant speed.

or both discs in opposite directions or in the same direction,
This is a method of passing it between two disks that are rotating at different speeds. In this manner, the rubber particles in the aqueous mixture are mechanically fractured and stabilized as an aqueous dispersion of rubber.

This aqueous dispersion of rubber becomes stable and becomes a creamy paste. To get dry powder from this.

Generally, after dilution with water, the paste is coagulated with an acid, such as hydrochloric acid, or another electrolyte, such as sodium chloride, or by some coagulation method, and the coagulum is then passed through a centrifugal dehydrator to remove the feed liquid. Wash the product with water until the effluent 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 above 100°C, the molecules of natural rubber are known to break, resulting in an inferior substance with a low molecular weight.In the case of synthetic rubber, this reaction becomes much more complicated. . 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 material.

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 preferred when at least 80% of the number of vulcanized rubber particles are smaller than 20 microns and the colloidal dimension, i.e. larger than 0.1 micron, if the particle size is larger than 20 microns.
The properties of the compound are close to those of conventional recycled rubber, and
If it is smaller than 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 (22X44
cm), 300 g of a commercially available tire (particle size: 4 o mesh, not including rubber scraps other than tires) and 9 g of primary/inic acid were ground for 10 minutes. At this stage, 30 g of powdered solid sodium hydroxide was added evenly to the rubber mixture and milling was continued for a further 10 minutes.

The mill temperature was 60°C.

The dry, brittle sheet-like product is removed from the mill and used for industrial purposes. , into the hopper of a 5c+a disc mill. That pi! Add enough water (500 ml) to the acid to moisten it.
). Grindstone (46 grit, carporundum) gap set to 0.5H, rotation speed 4QOOrpm
I started the disc mill. 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 dried in a dryer where the moisture retained in polyester fiber (750 denier) bags was removed by centrifugal force, 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 under reduced pressure <10 parts m*silver column) at SO°C.

In order to compare the fine powder thus produced with conventional recycled rubber, 100 parts by weight of each of these two materials were
It was formulated with 2 parts of zinc oxide, 1 part of stearic acid, 1 part of the anti-aging agent Frectol H, 0.27 parts of cyclohexylbenzthiadiylsulfenamide, 24 parts of diphenylguanidine O and 0.53 parts of sulfur. This mixture was compression molded at 150°C, which is the optimum temperature for curing, to form a flat plate with dimensions of 150 x 150 x 2 +u+. The following results were obtained when tested using standard methods.

Table 1 Tensile strength MN/l112) 7.4
10.4 Elongation at break (%) 380 30
0 modulus 100% 1.6 2.4
(MW/m modulus 300% 5.7 10.5
(MW/m') Hardness IRHD) 55
67 The above results demonstrate a good improvement in the tensile strength of compounds made from the particulate vulcanized rubber recycle of the present invention. Improvements were also observed in tipper wear and tear strength.

To further compare the aforementioned fine powder with 40 mesh type granules and conventional recycled rubber, 82 parts by weight of each of these three materials were combined with 100 parts of styrene-putadiene rubber (grade 1500), 3 parts of zinc oxide, and stearic acid. 3 parts, Frektor H1 part, ) IAF Black 43 parts,
It was formulated with Dutrex R Softener IHB, 0.8 parts of cyclohexylbenzthiadiylsulfenamide, 0.8 parts of diphenylguanidine and 1.75 parts of sulfur. The formulation was compression molded at a temperature of 150°C for 15 minutes into flat plates with dimensions of 150 x 150 x 2 rats. Similar slabs of the base compound (ie, without any recycled rubber) were also made.

The following results were obtained when tested using standard methods.

Table 2 Elongation at break (3c) 580 400 520
490 hard Saku IRHII) 83
63 62 61 The rubber in column 1 above did not contain recycled rubber. The rubbers in columns 2-4a all contain recycled rubber, and the rubber in column 4 was made according to the present invention. It can be seen that the tensile strength of the rubber in column 4 is lower than that of rubber in column 141I, but is superior to the tensile strength of the rubber in columns 2 and 3. The rubbers in column 4 also have satisfactory abrasion resistance.

The above test results show that the recycled rubber using the fine particles obtained by the method of the present invention is clearly superior to the conventional recycled rubber.

Example 2 Example 1 was repeated except that the product from the disc mill was diluted with water and neutralized by the addition of dilute hydrochloric acid (2N). The resulting vulcanizate had properties similar to those made in Example 1.

〔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 impart 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.

Patent Applicant: The Guttoire Tire and Rubber Company

Claims (1)

[Claims] 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. ,
Continue grinding 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.