DE2905977C2 - Vulcanizable rubber compound with low sulfur excursion - Google Patents

Description

The invention relates to a vulcanizable rubber compound with low sulfur growth.

In the manufacture of rubber products, such as wheel tires, conveyor belts, etc., it is often necessary to mix rubber with rubber or rubber with other material, such as metal or organic fibers, to connect, it is well known that the Maintaining the adhesiveness of the rubber material is of considerable importance for the processability and Productivity is

One of the reasons by which the adhesiveness of the rubber material is lowered is that Occurrence of foreign substances, which have a lower bond strength than the self-adhesive strength of the rubber have, in part or in whole of the adhesive area of the rubber material as a result of a extended storage time etc, creating a wetting area between each sticky material is decreased, d. H. so-called blooming occurs or migrate back to the surface. In particular, it reduces back migration as a vulcanizing agent sulfur used to the surface considerably reduces the stickiness and tackiness of the Rubber, so that it appears to be absolutely necessary and indispensable for rubber mixtures, a to prevent such back migration of sulfur to the surface.

Investigations of the state of sulfur in rubber during an actual manufacturing process by means of an X-ray microanalyzer of an optical microscope, an electron microscope and a scanning electron microscope revealed a mechanism of appearance of the Sulfur excursion according to the individual processing steps listed in the table below:

Ambient
and treatment steps

29 (mechanism of appearance of
Sulfur rash)

Banibury mixer ,

calendering / temperature- \

extrude X elevation

What cooling,
Winding up

Shrink, Cut

Stationary
treatment

<C. Stationary>

(A)

Admixed sulfur (S)
becomes more ring-shaped than 8-membered in rubber
Dissolved sulfur (S “)

(B)

S _Q in supersaturated state]
in rubber

(C)

Accumulation of
oversaturated
Sg on the rubber surface
(Nucleation on
the surface)

collision

by

Braunsche
ί molecule cirjbewegung or
| collection

from übeγ-Ι saturated-. S.
'within
j (inner cladding)

in rubber]
diffuses to the
Surface core

—1Ώ 1
Crystal ^

growth
within
of rubber

As a result of intensive studies to control the sulfur rash on the basis of the above findings, it was found that the sulfur rash hitherto was achieved by using an insoluble sulfur (JP-PS 13 075/61) or by using a sulfur dispenser (JP-PS 6 096 / 72 and 6 498/72) so that the admixed sulfur is prevented as much as possible from being dissolved as 8-membered ring-shaped sulfur (Se) in the rubber when the temperature is increased or from being dissolved in the rubber when the Temperature is increased, or Se dissolved in the rubber is prevented from being over-saturated and precipitated when overcooling, if points (A) and (B) in the table above are observed. However, since the temperature at the transition of the insoluble sulfur in S ₈ is about 105-UO ⁰ C, the speed during calendering or extrusion must inevitably be reduced to such an extent that the temperature, especially during calendering or extrusion of highly elastic rubber, does not reach the Transition temperature exceeds As a result, not only productivity but also decreases Very fine distribution of the insoluble sulfur itself is disadvantageously destroyed. The other hand is the use of a sulfur dispenser posed a cost problem, so it has been extremely difficult to date to obtain that To effectively control the migration of sulfur back to the surface in practice.

Points (C) and (D) of the above list are accelerated by the strength and conditions of excitation and storage temperature, etc., and the formation of the sulfur nucleus and the growth of crystals on the rubber surface as sulfur rash are a diffusion process in which the oversaturated sulfur moves along the rubber surface or within the rubber compound migrates and collects and grows around the core.

It is also already known (Kautschuk-Lexikon, 1966, page 137/131 $), natural and / or synthetic Rubber diethylene glycol stearate as a plasticizer

to add. However, this has so far not brought the problems around the sulfur rash closer to a solution

The object of the invention is to restore the original adhesiveness of vulcanizable rubber mixtures to be preserved even after longer storage or over a subsequent processing time.

This object is achieved according to the invention in that the mixture consists of natural and / or synthetic rubber and as a vulcanizing agent, based on the rubber weight, 0.5 to 10 percent by weight Sulfur, 0.5 to 100 percent by weight based on the sulfur weight of at least one H LB value of 1 to 8, a supersaturated sulfur is finely distributed in the rubber mixture holding surfactant from the compound group sorbitanoleinic acid ester, Sorbitan stearic acid ester, sorbitan palmitic acid ester, sorbitan lauric acid ester and possibly usual additives.

The invention makes use of the knowledge that this is the best way to reduce the adhesiveness can prevent the sulfur from being retained in the mixture in a finely dispersed form, d. H. the Prevents sulfur from diffusing to the surface of the mixture. This behavior is surprisingly easy by adding the individually specified Surfactants can be achieved, but other properties of the rubber mixture are not impaired.

If the HLB of the surfactant is less than 1, the The affinity for rubber is so high that the surfactant is hardly at the interface between rubber and sulfur is adsorbed and is consequently dissolved in the rubber, while the affinity for rubber at a H LB value above 8 is so low that the adsorbed Small amount of surfactant due to partial adsorption at the interface between rubber and sulfur and a stable state cannot be obtained for a long period of time. With a surfactant addition of less than 0.1 Percentage by weight, the amount of surfactant is insufficient for monomolecular adsorption at the interface between all of the sulfur and the rubber, while with a surfactant addition of more than 150 weight percent adversely affect the physical properties of the rubber.

The invention is particularly suitable for all cases in which an excitation or stimulus time of Rubber surface on the cooling and the respective start times of the standstill steps as with the Extrusion and when serving the rubber is limited

In the case of the rubber mixture according to the invention, in addition to sulfur, another vulcanizing agent, a vulcanization accelerator, a vulcanization promoter, a plasticizer, an antioxidant reinforcing filler, etc. can be selected and mixed as desired. For the rubber compound all types of synthetic rubber, such as polyisoprene rubber, polybutadiene rubber, Styrene-butadiene copolymer rubber, acrylonitrile-butadiene copolymer rubber. Ethylene propylene copolymer rubber, Butyl rubber and all other types of rubber can be used.

That added to the rubber mixture according to the invention Surfactant has practically no influence on the physical properties of unvulcanized and vulcanized rubber.

The invention is explained in detail below with the aid of a few examples

Examples

Various rubber compounds according to the attached Table 1 were kneaded by a 6-inch, cold tube extruded, cooled with water, stimulated by a shrink tension and then 1 to 3 days left lying around for a long time. To check the state of the sulfur rash, the rubber surfaces were photographed through an optical microscope and the area of the sulfur rash through an image analyzer measured. The deflection ratio based on the rubber surface was then determined. The physical properties of various unvulcanized and vulcanized rubber compounds were measured in accordance with Japanese standards JIS K 6300 and JIS K 6301; the results are also given in Table 1.

As can be seen from Table 1, show the rubber mixtures according to the invention with a Surfactant is a significant improvement in terms of sulfur rash and physical properties of unvulcanized and vulcanized rubber practically does not change if you change them Compare values with the rubber mixture which did not contain any surfactant.

Table 1 No. 2 3 4th 5 6th 7th mixture 1 (Example) (Example) (Example) (Comparative (Example) (Example) (Comparative example) example) 100 100 100 100 100 100 100 50 so 50 50 50 50 Natural rubber 50 2 2 2 2 2 2 HAF carbon black 2 5 5 5 5 5 5 Stearic acid 5 1 l. _f 1 1 1 1 Zinc white 1 Antioxidant ¹ ) 4th 4th 4th Vulcanization accelerator ² ) 4th 7th 7th 7th sulfur 1.5 Insoluble sulfur Sorbitanoleinic acid triester

continuation

Mix no.

(Comparative (example) (example) (example) (comparative (example) (example) example) example)

Sorbitan anic acid ο η
O, V monoester 13.5 Sorbitan palmitic acid 83 monoester 18th HLB value of the various 63 Surfactants 52 Deflection ratio (%) 450 after 1 day of rest 30th after 3 days of rest 134 Mooney viscosity (ML _{1 + 4} ) 240 Mooney Burn Time (min) Hardness (degree) Elasticity (%) Stretching (4) 100% module (kg / cm ² ) 200% modulus (kg / cm ² ) Tensile strength (kg / cm ² )

1.5 1.5 ! 0.0 1.8 1.5 6.7 15.0 7.0 1.8 4.7 3.0 75 13.0 4.7 3.9 2.7 5.1 10 74 7.3 11.6 4.6 82 74 9 12.0 82 13th 48 74 75 17th 62 270 49 9 62 53 53 265 73 51 450 132 52 48 460 30th 200 130 270 29 132 205 54 130 240 132 250 202

') Ν, Ν'-diphenyl-p-phenylenediamine.

² ) N-oxydiethylen-2-benzothiazylsulphenamide.

230242/486

Claims (1)

Claim. Vulcanisable rubber mixture with low sulfur impact, thus identifiable draws that the mixture consists of natural and / or synthetic rubber and as a vulcanizing agent based on the rubber weight 0.5 up to 10 percent by weight sulfur, 0.5 to 100 percent by weight based on the sulfur weight ι ο at least one having an H LB value of 1 to 8, a supersaturated sulfur in the Rubber mixture containing finely divided surfactant from the group of compounds sorbitanic acid ester, sorbitan stearic acid ester, sorbitan palmitic acid ester, sorbitan lauric acid ester and possibly usual additives.