AU1778492A

AU1778492A - Rubber compounds

Info

Publication number: AU1778492A
Application number: AU17784/92A
Authority: AU
Inventors: Ernest Gordon Hallsworth; Michael H.B. Hayes; Reginald Morton Taylor
Original assignee: Unilever Australia Ltd
Current assignee: Unilever Australia Ltd
Priority date: 1991-05-27
Filing date: 1992-05-27
Publication date: 1993-01-08

Description

RUBBER COMPOUNDS

This invention relates to formulations of rubbers and more particularly arises from a surprising finding of the effects of addition of compounds of the sort disclosed in the Patent Specification WO89/09758 to rubber or rubber-like compounds, and more specifically to a method of modifying the friction coefficient of rubber and to the rubber so modified.

Patent specification WO89/09758 discloses compounds formed by the reaction between certain oxygen-containing metal compounds and polyhydric alcohols which contain terminal -CH2OH group or groups connected to an adjacent -COH group. The metallo-polyhydroxyorganic compounds disclosed had a metal atom bonded via an oxygen residue of these hydroxyl groups.

It was anticipated that the addition of the metallo-polyhydroxyorganic compounds embraced by the disclosure in Patent specification WO89/09758 could be used as a replacement of zinc oxide as an additive in rubber and to achieve changes in physical properties such as for example a change in heat conductivity. Because of the more disperse nature of the zinc atoms in the compounds disclosed in Patent specification WO89/09758 than in fine grained zinc oxide, the advantages achieved by the addition of zinc oxide should be increased when these new metallo- polyhydroxyorganic compounds are added instead.

The present invention relates to a further and unexpected property of such compounds when added to rubber. It is found that with the addition of at least some of these compounds that the frictional coefficient of rubber is modified. This modification in the friction coefficient is more marked where the carbon chain length associated with the compound is longer. However, in some circumstances the friction coefficient decreases.

This invention embraces the use of such compounds as additives to achieve a modification in the frictional properties in the formulation of rubber, and the rubber compounds thus formed.

An object of this invention is to provide an additive to rubber compounds which confers a modification of the friction coefficient.

In one form therefore the invention is said to reside in a method of modifying the friction coefficient of rubbers including the steps of admixing said rubbers with compounds formed between a oxygen-containing metal compound of a polyvalent metal and a polyhydroxy organic material where the polyhydroxy organic material contains at least one terminal -CH2OH group connected to an adjacent -COH group with a bonding of the metal to adjacent carbon atoms of the polyhydroxy organic material via the residual oxygen atoms of the reacting hydroxyl groups of the said polyhydroxy organic material.

In an preferred form of the invention the method relates to an increase in the friction coefficient of rubber.

Examples of polyhydric alcohols that might be used to form the compounds are, for example, the hexahydric alcohols such as mannitol, the pentahydric alcohols such as xylitol , the tetrahydric alcohols such as erythritol and isomers, other lower polyhydric alcohols such as for example ethanediol or a propanediol or propanetriol or 1 ,2 butanediol or 1 ,2,3, butanetriol and poly-vinyl alcohols and similar compounds or substituted compounds such as 2-acyl-1 ,3-propanediol and similar compounds. Other such compounds and alcohols where the steric arrangement of the associated hydroxyl groups permit the metal to be bonded through the oxygen atoms of these hydroxyl groups with the elimination of the hydrogen of these involved hydroxyl groups as water are also included.

Metals which may be combined or bonded as described with the hydroxyl groups of suitable poly-hydroxy organic compounds are for example, cobalt, iron, zinc, calcium, magnesium, bismuth, nickel or chromium. The metal oxygen-containing compounds may comprise oxides, hydroxides, organo- metallic compounds such as acylates such as stearates or the oxy-salts of these metals, for example carbonates.

In some cases the compound may be formed very readily from a particular metal compound, for example the acetate salt, whereas preparation from the oxide may require high temperatures, or extended microwave heating or the addition of a catalyst. In an alternative form the invention may be said to reside in a rubber compound with a modified friction coefficient including a compound formed between a polyvalent metal and a polyhydroxy organic material where such compound is formed by a reaction between an oxygen-containing metal compound of the polyvalent metal and a polyhydroxy organic compound which contains at least one terminal -CH2OH group connected to an adjacent -COH group with a bonding of the metal to adjacent carbon atoms of the polyhydroxy organic material via the residual oxygen atoms of the reacting hydroxyl groups of the said polyhydroxy organic material.

The modification of the friction coefficient may be an increase or a decrease depending upon the desired properties of the compound.

In another form the invention relates to a method of decreasing the temperature build up of rubber due to friction and a means of modifying the friction coefficient of rubbers for this purpose by means of adding the formulations discussed above to the rubber.

The preferred amount of the additive may be at the rate of 1 to 15 units per hundred units of rubber (phr) by weight but departures from this are within the scope of the invention and depending upon the type of metal and the desired modification in the physical properties.

EXAMPLE 1

The effect of addition of some of the metallo-polyhydroxy organic compounds of the present invention on the properties of natural rubber have been examined using standard tests. Incorporation of the compounds was at the rate of 5% by weight of the mix, and the compound were added by standard admixture methods. The properties of the resulting rubbers were compared with those of rubbers containing 5% zinc oxide.

A natural rubber formulation having the following composition by weight was used:

phr Oil extended Natural Rubber 107

Poly-butadiene 20 Carbon Black 70

Stearic Acid 2.00

Poly-2,2,4-trimethyl-1 ,2 dihydroquinone (TMQ) 2.00

Wax 1.00 Sulphur 1.50

N-cyciohexyl-2-benzothiazo sulphanial (CBS) 1.50

(phr = parts per hundred rubber by weight)

Properties measured, using standard procedures, were tensile strength, extension at break, heat build up, hardness, abrasion, compression set and friction against steel.

The compounds were mixed initially on an internal mixer (B. R. Banbury: Trade Mark) and mixing was completed on a two roll mill. The mixing cycle for the two sets of compounds were:

Banbury start temperature 70°C Banbury ram pressure 50 psi

After adding all the constituents except sulphur and CBS, separately over a

15 minute period, the rubber mixture was taken off the mixer and put onto a cool clean two roll mill and the sulphur and CBS were added, distributed with three three-quarter cross cuts from each side, and refined six times by passing the compound through the mill with the mill set with a tight nip.

The compound was then sheeted off and allowed to stand for a minimum of

16 hours before any further work. Test buttons were moulded and the following physical properties were measured using the test methods indicated:

1. Hardness (BS 903 : Part A 26 : Method B)

2. Tensile Strength (BS 903 : Part A 2)

3. Elongation at Break (BS 903 : Part A 2)

4. Compression Set after constant strain (BS 903 : Part A6) 24 hours at 70°C (C.7) 5. Abrasion Resistance (BS 903 : Part A 9)

6. Heat Build-up (ASTM D623) Non-standard comparative test Repeat of tests 1 to 3 after aging.

Natural rubber compounds 70°C for 70 hours Nitrite rubber compounds 100°C for 70 hours

8. Friction testing

The friction tests were conducted on a Rapra/Daventest apparatus, at two different speeds (50 mm/minute and 500 mm/minute)

TABLE 1 EFFECTS OF FRICTION (figures are Friction coefficients)

It will be noted from Table 1 that the coefficient of friction in the dry condition increases with the increase in the chain length of the additive. It is expected that the compounds formed with carbon chain lengths equal to or greater than four will show the greatest friction coefficients. TABLE 2 COMPARISON OF ZINC ETHYLENE GLYCOLATE AND ZINC OXIDE AS AN ADDITIVE

It can be seen from Table 2 that heat build up is greatly reduced by the addition of zinc ethylene glycolate, and this property has desirable effects under particular circumstances.

Zinc oxide is one of a number of agents that are used for the reinforcement of light-coloured end products. The incorporation of zinc oxide enables the resulting product to withstand extended exposure at high temperatures, and it also functions as an activator during the vulcanization process. The addition of the metallo-polyhydroxyorganic compounds of the present invention will provide the advantages of friction coefficient and heat build up as discussed above while still providing the properties which are given by the use of zinc oxide.

Various features of the invention have been particularly shown and described in connection with the illustrated embodiments of the invention, however, it must be understood that these particular arrangements merely Illustrate and it is to be realised that the invention is not to be limited thereto but can include various modifications falling within the spirit and scope of the invention.

Claims

Claims:

1. A method of modifying the friction coefficient of rubbers including the steps of admixing with said rubbers compounds formed between a oxygen-containing metal compound of a polyvalent metal and a polyhydroxy organic material where the polyhydroxy organic material contains at least one terminal -CH2OH group connected to an adjacent -COH group with a bonding of the metal to adjacent carbon atoms of the polyhydroxy organic material via the residual oxygen atoms of the reacting hydroxyl groups of the said polyhydroxy organic material.

2. A method as in claim 1 wherein the polyhydroxy organic material is selected from a group comprising the hexahydric alcohols such as mannitol, the pentahydric alcohols such as xylitol , the tetrahydric alcohols such as erythritol and Isomers, other lower polyhydric alcohols such as for example ethanediol or a propanediol or propanetriol or 1 ,2 butane diol or 1 ,2,3, butane triol and poly-vinyl alcohols and similar compounds or substituted compounds such as 2-acyl-1 ,3-propanediol.

3. A method as in claim 1 wherein the metal of the oxygen-containing metal compound is selected from the group comprising cobalt, iron, zinc, calcium, magnesium, bismuth, nickel or chromium.

4. A method as in claim 1 wherein the oxygen-containing metal compound is selected from the group consisting of oxides, hydroxides, organo-metal compounds and/or the oxy-salts of metals.

5. A method as in claim 1 wherein the amount of the compounds formed between a oxygen-containing metal compound of a polyvalent metal and a polyhydroxy organic material added is in the range of from 1 to 10 units per hundred units of rubber by weight.

6. A method of increasing the friction coefficient of rubber comprising admixing therewith compounds formed between a oxygen-containing metal compound of a polyvalent metal and a polyhydroxy organic material where the polyhydroxy organic material contains at least one terminal -CH2OH group connected to an adjacent -COH group with a bonding of the metal to adjacent carbon atoms of the polyhydroxy organic material via the residual oxygen atoms of the reacting hydroxyl groups of the said polyhydroxy organic material.

7. A method as in claim 6 wherein the amount of the compounds formed between a oxygen-containing metal compound of a polyvalent metal and a polyhydroxy organic material added is in the range of from 1 to 15 units per hundred units of rubber by weight.

8. A rubber having its friction coefficient modified by the method of claim 1.

9. A rubber having its friction coefficient increased by the method of claim 6.

10. A rubber compound with a modified friction coefficient including a compound formed between a polyvalent metal and a polyhydroxy organic material where such compound is formed by a reaction between an oxygen- containing metal compound of the polyvalent metal and a polyhydroxy organic compound which contains at least one terminal -CH2OH group connected to an adjacent -COH group with a bonding of the metal to adjacent carbon atoms of the polyhydroxy organic material via the residual oxygen atoms of the reacting hydroxyl groups of the said polyhydroxy organic material.

11. A rubber compound with a modified friction coefficient as in claim 10 wherein the polyhydroxy organic material is selected from a group comprising the hexahydric alcohols such as mannitol, the pentahydric alcohols such as xylitol , the tetrahydric alcohols such as erythritol and isomers, other lower polyhydric alcohols such as for example ethanediol or a propanediol or propanetriol or 1 ,2 butane dioi or 1 ,2,3, butane triol and poiy-vinyl alcohols and similar compounds or substituted compounds such as 2-acyl-1 ,3-propanediol.

12. A rubber compound with a modified friction coefficient as in claim 10 wherein the metal of the oxygen-containing metal compound is selected from the group comprising cobalt, iron, zinc, calcium, magnesium, bismuth, nickel or chromium.

13. A rubber compound with a modified friction coefficient as in claim 10 wherein the oxygen-containing metal compound is selected from the group consisting of oxides, hydroxides, organo-metal compounds and/or the oxy-salts of metals.

14. A rubber compound with a modified friction coefficient as in claim 10 wherein the amount of the compounds formed between a oxygen- containing metal compound of a polyvalent metal and a polyhydroxy organic material added is in the range of from 1 to 15 units per hundred units of rubber by weight.

15. A rubber compound with a modified friction coefficient as in claim 10 wherein the modification in friction coefficient is an increase.

16. A method of modifying the friction coefficient of rubber substantially as herein before described with reference to and as illustrated by the non-comparative examples.

17. A rubber compound having modified friction characteristics substantially as hereinbefore described with reference to the non- comparative examples.