Rubber products with low heat build up on mechanical stressing

Details Rubber products with low heat build up on mechanical stressing Rubber products with low heat build up on mechanical stressing

2001-05-22

2004-02-03

Short, Patricia A. (Department: 1712)

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

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S133000, C525S134000, C525S139000, C525S141000, C525S142000, C525S164000

Reexamination Certificate

active

06686418

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for reducing the heat build-up on dynamic stressing (energy dissipation) in vulcanised rubber products.
2. Description of the Related Art
It is known that phenol novolaks or modified phenol novolaks cured with hexamethylene tetramine (HMT) or certain melamine formaldehyde resins like the highly etherified compound hexamethoxymethyl melamine (HMMM) give good reinforcement in the vulcanisate. In particular, there is a marked increase in vulcanisate hardness and tensile strength (stress), in each case measured at a specified extension. For processing, the melamine resin derived curing agents (in particular HMMM) are used in liquid form or, as is preferred in the rubber industry, adsorbed on solid carrier materials (e.g. finely divided silica or diatomaceous earth) to become free-flowing powders with a mass fraction of from about 65 to 75% of active ingredient (in this case HMMM) (see, for example “Phenolic Resins for Rubber Reinforcement”; E. Leicht and R. Sattelmeyer; Kautschuk+Gummi Kunststoffe, Vol. 40, No. 2/87; page 126).
According to the prior art, however, reinforcing resins in the vulcanisate do not merely increase hardness and tensile strength, but also undesirably affect the viscoelastic performance of the vulcanisates by increasing the amount of mechanical energy converted into heat and dissipated within the rubber products. This property of heat evolution and the resultant temperature increase in the event of dynamic load (heat build-up) is significant for those rubber products which in service are exposed to severe dynamic loads, for example parts in automotive tires. Now, according to the prior art, this undesirable heat evolution becomes more pronounced in a given rubber composition as the resin becomes more effective in its reinforcing action.
EP-A 0 013 330 discloses that rubber mixtures can be vulcanised in the presence of novolak resins and of reactive melamine resins obtainable by reacting melamine with from 0.5 to 6 mol of aldehyde per mole of melamine. The methylol groups present in the melamine resins may be free or may be etherified. No study was made of the effect which the melamine-resin curing agent used has on heat evolution in dynamically stressed rubber products.
There is increasing demand by the industry for systems of reinforcing resins and curing agents therefor for use in rubber products which combine good reinforcing action with moderate heat build-up in the event of dynamic load.
SUMMARY OF THE INVENTION
Surprisingly, it has now been found that the use of a combination of novolaks with selected non-etherified or at least partially etherified reaction products of formaldehyde and triazines gives good vulcanisate reinforcement together with a heat build-up markedly lower than that obtained using the same reinforcing resin and using a prior-art highly etherified melamine resin, such as HMMM (hexamethoxymethyl melamine) or using another formaldehyde source as curing agent. It was not to be expected that this combination of reinforcing resins and curing agents can be used for the purpose of reducing heat evolution in dynamically stressed rubber products.
The invention therefore provides a process for reducing the heat build-up on dynamic stressing of vulcanised rubber products, which comprises admixing for this purpose, to vulcanisable rubber mixtures, as a combination of reinforcing resin and curing agent, mixtures made from non-selfcuring novolaks A as reinforcing resins and non-etherified or partially etherified triazine resins B as curing agents for these reinforcing resins. The triazine resins suitable for the invention are those with a molar ratio of formaldehyde to triazine (F/T) of from 0.5 to 5.5 mol/mol, preferably 0.75 to 5.25 mol/mol, and especially preferred 1.0 to 5.0 mol/mol, and which are non-etherified or at least partially etherified, with a degree of etherification of preferably from 0 to 80%, based on bonded formaldehyde. The alcohols used for etherification include linear and branched aliphatic alcohols having from 1 to 18 carbon atoms.
The invention also provides combinations of novolaks A and partially etherified triazine resins B as reinforcing resins in rubber mixtures and curing agents for these, the triazine resins being condensation products of formaldehyde and of triazines selected from melamine, acetoguanamine, benzoguanamine and caprinoguanamine, or else mixtures of these, preferably only melamine, with the ratio F/T of the amount of substance of formaldehyde to the amount of substance of triazine in the resins B of from 0.5 to 5.5 mol/mol, preferably 0.75 to 5.25 mol/mol, and especially preferred 1.0 to 5.0 mol/mol, and having an amount of substance of alkoxy groups per 1 mol of triazine of (F/T-1.75 mol/mol), but at least 0.5 mol/mol, preferably at least 0.75 mol/mol, and especially preferred at least 1 mol/mol, and having an amount of substance of alkoxy groups per 1 mol of triazine of not more than F/T, preferably not more than 90% of F/T, and especially preferred not more than 80% of F/T.
The invention also provides a method of use of these combinations of novolaks A and partially etherified triazine resins B for reducing heat build-up in dynamically stressed vulcanised rubber mixtures comprising admixing these combinations to the rubber formulation.
The process for reduction of the heat build-up according to the invention can be used in a very wide variety of vulcanisable rubber mixtures to give rubber products with low heat evolution. Suitable types of rubber which may be used are sulfur-vulcanisable rubbers, e.g. natural rubber NR), styrene-butadiene rubber (SBR), polyisoprene rubber (IR), polybutadiene rubber (BR), nitrile rubber (NBR), butyl rubber (IIR), ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM) and mixtures of these, as conventionally used in the tire industry or for industrial rubber products.
Examples of usual other additives are fillers, such as carbon black, silica, chalk, and kaolin. Other constituents which may be added to the mixtures are vulcanizing agents, accelerators, activators, processing aids, antioxidants and plasticisers, e.g. mineral oils.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Suitable reinforcing resins A are non-selfcuring phenolic resins, such as phenol novolaks, or polynuclear phenols. Examples of particularly suitable novolak resins are those made from phenol and/or from polyfunctional mono- or polynuclear phenols, such as resorcinol, or from bisphenols and/or in particular from mono- or polyhydric phenols substituted with a hydrocarbon radical, for example alkyl- or aralkylphenols whose substituent has from 1 to 20 carbon atoms, preferably from 4 to 18 carbon atoms, for example tert.-butylphenol, octylphenol, the phenols cardol and cardanol present as a mixture in the oil from cashew nut shells, and also those from styrenated phenols, or fatty-acid-modified, e.g. linseed-oil-fatty acid-modified, phenol or phenylphenol. Useful phenolic resins may also comprise mixtures of the individual resins and resins made from mixtures of these phenols.
These reinforcing resins are prepared by reacting the phenol or the mixture of phenols with aldehydes, such as acetaldehyde, but preferably formaldehyde, in an acid medium as in the prior art. The novolaks may also have some content of plasticizing materials, such as polyethylene glycols, tall oil, or other conventional plasticisers. The phenolic resins may also have been modified with natural resins, such as colophony or tall resin, or with terpenes, and in specific cases the natural resin content may even predominate.
Preferred are those novolaks A where the phenols comprise a mass fraction of at least 10% of alkylphenols having at least one alkyl group per phenol ring and having an alkyl radical of from 1 to 20 carbon atoms. Especially preferred are reaction products of mixtures of phenol and tert-butylphenol with formaldehyde as novolaks A.
The triazine resins B used according to the invention are non-etherifie

Affiliated with

Also associated with

Rating

Rubber products with low heat build up on mechanical stressing does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Rubber products with low heat build up on mechanical stressing, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Rubber products with low heat build up on mechanical stressing will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3342885