IE42494B1 - Vulcanised elastomers - Google Patents

Abstract

1526482 Vulcanizing liquid diene polymers MICHELIN ET CIE 29 Jan 1976 [30 Jan 1975] 03578/76 Heading C3P Liquid diene prepolymers having a degree of functionality of 1À8-2À0 are vulcanized by (1) forming a mixture thereof with reinforcing filler, a sulphur vulcanization agent and a difunctional chain extender compound in amount such that the ratio of functional groups on the polymer to those on the chain extender is 1, (2) subjecting the mixture to a temperature at which chain extension occurs exclusively, e.g. 20-125‹ C., and (3) subjecting the product to a higher temperature, e.g. above 140‹ C., to effect vulcanization. In Examples, hydroxyfunctional liquid butadiene/styrene copolymers are mixed with carbon black, a conventional sulphur-curing system and methylene diphenyl diisocyanate, and heated first to 110‹ C. and then to 155‹ C. or 160‹ C.

Description

This invention relates to the preparation of vulcanisates derived from functional liquid copolymers and/or homopolymers, and to new or retreaded pneumatic tyres which include such vulcanisates.

Research has been carried out with a view to producing pneumatic tyres having a tread and/or side wall constituted by vulcanisates developed from liquid homopolymers or copolymers of low molecular weight which carry reactive functions such as hydroxyl or carboxyl functions, currently referred to by the term functional liquid polymers. In the Products Data Bulletin Nos. 505,506, 508 of the Sinclair Petrochemicals Company,the possibility is pointed out by using vulcanisates having a base of polyurea and polyurea-urethane, prepared by reaction of polymers and/or polyhydroxyl diene copolymers, that is to say carriers of more than two reactive functions, with diisocyanates in the production of private and agricultural vehicle tyres.

However, the properties which can be obtained with these vulcanisates are not sufficient for such use, as indicated in particular by the researchers of the Rubber and Plastics Research Association (R.A.P.R.A.) more especially in the bulletin No. 6, Vol. 25 of November - December , 1971 and in a study entitled Liquid rubber for reinforced rubber products. A technical and economic assessment published by the Rubber and Plastics Research Association of Great Britain, where Messrs. Daniel, Needham and Pyne indicate that experience suggests that the chances of -success with obtaining separately a lengthening of the chain and a cross-linkage with existing commercial functional liquid polymers · - 3 carrying carboxyl or hydroxyl functions at the end of the chain, are slight. These authors Indicate also that to obtain from such commercial liquid polymers vulcanisates with a Shore hardness sufficient for permitting the use thereof in tyres, it is necessary to use very large proportions of fillers and vulcanisations agents, resulting in vulcanisates with inadequate mechanical properties (see Table VII, page 17 of the study) for allowing them to be used in tyres.

At the conference organised by the I.U.P.A.C. (International Union 10 of Pure and Applied Chemistry) in September, 1973 at Aberdeen, in Great Britain, it was'mentioned by one of the lecturers of the R.A.P.R.A. that the reaction of polyfunctional liquid diene polymers with a hydrocarbon chain lengthener poly-functional compound results in elastomers which in the vulcanised or non-vulcanised state do in fact have a Shore hardness level near to that of conventional diene elastomers, that is to say non-functional elastomers, but whose mechanical properties in general are not sufficient to permit use in the production of tyres.

Finally, in the French Patent Specification Nos. 2,187,805 20 2,187,806, 2,187,807, 2,187,808, 2,187,809 and 2,187,842, it has been proposed to use, for the production of the tread portions of pneumatic tyres, vulcanisates obtained by reaction of polyfunctional (that is to say: carrying more than two functions) - 4 liquid homopolymers and/or copolymers with polyisocyanates which are also polyfunctional, the reagents being present in such quantity that in one and the same phase there is both chain lengthening and cross-linking or vulcanisation. A study of the examples in these Specifications using tests carried out with tyres,including a tread region constituted by such vulcanisates,shows that the vulcanisates have the same disadvantages as those mentioned previously.

The Applicants have found a means Of obviating the aforesaid disad10 vantages in the production of elastomers derived from functional liquid diene so giving polymers having properties sufficiently good to allow them to be used as the main component in mixtures used for the manufacture of pneumatic tyres.

According to the invention there is provided a process for the 15 production of vulcanised elastomers, in which one or more functional liquid diene prepolymers having a degree of functionality of from 1.8 to 2.0, either alone or in combination with one or more compounds chosen from difunctional non-diene polymers, non-functional liquid polymers, difunctional molecules of low molecular weight and containing, intimately mixed, reinforcing fillers and a sulphur vulcanisation agent, is/are mixed with a difunctional hydrocarbon chain lengthener compound in a quantity such that.in the mixture formed the ratio of the number of reactive group* of the hydrocarbon chain lengthener to the number of reactive groups of the functional liquid prepolymer is equal to 1, and in which the mixture is subjected in a first step to a temperature sufficient to obtain exclusively a lengthening reaction of the hydrocarbon chain of the prepolymer and, in a second step, to a higher temperature for carrying out the cross-linking or vulcanisation of the reaction product formed at the end of the first step.

Preferably the first step is carried out at a temperature of from 20 to 125°C and the second step at a temperature of above 140°C. jo allow them to be used in the treads or side walls of pneumatic tyres, vulcanisates have to achieve a compromise between properties which are often in-conflict with one another. Thus it is conventionally considered that to allow use as main component mixtures for the production of treads and/or side walls, a mixture having a base of elastomers containing no oil and loaded with parts of carbon black (control or reference mixture) should have the following properties: - a Shore hardness below 70; a 100%elongation modulus 2 measured after the third traction of 12.0 to 25.0 kg/cm ; a rebound rate at 60°C of at least 55 for a butadiene-styrene copolymer containing 25%styrene, of at least 60 for a copolymer of butadiene and styrene containing 12% styrene, or at least 65 for a cis-1,4poly-butadiene; a rate of breaking elongation and breaking strength 2 respectively of at least 370% and 120 kg/cm for a polybutadiene, of o at least 400% and 160 kg/cm for a copolymer of butadiene and styrene containing 12% styrene, of at least 420% and 180 kg/cm - 6 for a copolymer of butadiene and styrene containing 25% styrene, and SRT coefficient of friction at 20°C greater than 19 for a polybutadiene, 35 for a copolymer of butadiene and styrene containing 12% styrene,and 40 for a copolymer of butadiene and styrene containing 25% styrene.

Suitable prepolymers for use in the invention are liquid diene prepolymers of a molecular weight less than 50,000, and preferably from 1,000 20,000, whose hydrocarbon chain is composed of a homopolymer of conjugate dienes or a copolymer of conjugate dienes, either with one another or with vinylaromatic compounds-such as for example polybutadiene, polyisoprene, polypiperylene, polychloroprene, polypentadiene, copolymers of butadiene and styrene, of butadiene and isoprene, of styrene and isoprene, of butadiene or isoprene and vinyl naphthalene, and if appropriate the chains may be substituted by alkyl, alkoxyl radicals and halogen atoms; by a copolymer of a conjugate diene and a compound of the class of the vinyl nitriles such as for example a copolymer of butadiene or isoprene and acrylonitrile or methacrylonitrile; or by a terpolymer of conjugate dienes either with themselves or with vinyl20 aromatic compounds and/or with vinyl nitriles. The monomer units are incorporated in the chain either statistically or en bloc and also the proportions of the monomers are variable.

The liquid prepolymers are functional, i.e. they carry on their - 7 hydrocarbon chain, and preferably at the ends thereof, reactive groupings such as for example carboxyl, amino, hydroxyl, thiol, or halogen substituents, and have a degree of functionality of 1.8 to 2.

The functionality of the prepolymer is determined by suitable dosaging of the functions which are carried, by determination of the molecular weight of the prepolymer, and by a coupling reaction with the aid of a dlfunctional reagent appropriate to the function carried by the prepolymer, that is to say a polyaddition reagent or a polycondensation reagent. The coupling reaction results in a gelified product, substantially insoluble if the number of functions carried per hydrocarbon chain is greater than 2, or, if the functionality Is equal to or less than 2, a soluble product whose molecular weight can be determined by conventional techniques.

The functionality can easily be determined in accordance with the known relationship which appears in page 438 of Burnetts' manual entitled Mechanism of polymer reactions edited by Interscience Publishers.

These functional prepolymers can be used alone or in combination with one or more difunctional non-diene polymers, such as for example, polyethers, polyesters, polyisobutylene, with dlfunctional compounds of low molecular weight such as saturated dialcohols, or with non-functional homopolymers or copolymers, of low molecular weight, such as polybutadiene, polyisoprene, or a copolymer of butadiene and styrene.

By difunctional compounds which are hydrocarbon chain lengtheners we mean organic compounds which are carriers of reactive groups capable of reacting with the reactive groups of the prepolymer to give polyaddition or polycondensation products. Thus suitable compounds include compounds carrying epoxy functions, for example bisphenol-A glycidyl ether, imine functions for example phenyl bis £l-(2-methy1) aziridinylj phosphine oxide, phenyl-bis 0-(2-ethyl aziridinyl] -benzene-l-3-dicarboxamide, isocyanate functions such as for example tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate and hexa-methylene di isocyanate and amine functions. The reinforcing fillers used can be products at present employed in the field of tyre production, such as carbon black, silica, metal reinforcement elements and glass, plasticizers and/or extender oils. These fillers should be dispersed in a very uniform manner with the functional prepolymer.

Vulcanisation accelerators may also be used together with the sulphur vulcanising agent. Such vulcanisation accelerators include those compounds which are inactive with regard to the chain-lengthening difunctional Compound as well as compounds which are normally reactive relatively to the chain-lengthening compound at the polyaddition or polycondensation temperature but are rendered inactive relatively thereto by a suitable means, for example by encapsulation. Therefore, it is possible to use all the usual agents such as primary and secondary amines, sulphenamides of mercapto benzothiazole and more particularly N-diisopropyl mercapto benzothiazole sulphenamide, N-dicyclohexyl-mercapto benzothiazyl sulphenamide, sulphenamides of thiocarbonic acid such as the Nmorpholino-sulphenamide of N-morpholino-thiocarbonic acid, phosphorus compounds such as for example bis(diisopropyl-thiophosphoryl) disulphide, bis-(diethyl-thiosphosphoryl)trisulphide, zinc dibutyl di thiophosphate, the guanidines, and mercapto-triazines, such as for example bis^2-Nethylamine 6-N-diethyl-amine-1,3,5rtriazinej 4,4'-disulphide. It is also possible to add the appropriate polyaddition catalysts when carrying out the process of the invention.

The invention will now be illustrated by the following Examples in which Examples 1 and 2 are for comparative purposes.

Example 1 In this example two tests are carried out, A1 and Bp in order to compare the properties of the reaction product of a hydroxyl polybutadiene which is commercially obtainable and a diisocyanate with those of a non-functional poly-butadiene (test A)^and also the properties of the reaction product of a hydroxyl compolymer of butadiene and styrene (the latter being present in the proportion of 25% weight) and of a diiocyanate with those of a non-functional styrene and butadiene copolymer (the styrene being present in the proportion of 22%) (Test B(). In the two tests, the ratio of the 43484 - 10 number of NCO reactive groups of the hydrocarbon chain lengthener to the number of OH reactive groups of the prepolymer is equal to 1 when the mixture is completed.

The operating conditions and the results are indicated in the 10 following Table I.

TABLE 43494 - 12 TABLE I S is sulphur; R- 15- M is a liquid hydroxyl polybutadiene marketed by Arco; f is the degree of functionality of the prepolymer; Solprene 200 is a pol'ybutadiene marketed by Phillips; Santocure is a Trade Hark filed for N-cyclohexyl-2-benzothiazole sulphenamide, marketed by Monsanto; SBR CS 15 is a liqqid hydroxyl butadiene-styrene copolymer containing 25$ by weight of styrene, marketed by Arco, SBR 1500 is a copolymer of butadiene and styrene containing 25$ by weight of styrene- marketed by Shell; Sundex 8125 is a 70%‘aromatic oil of 380 molecular weight, 0.996 density, marketed by Sun Oil; 4010 NA is a N-isopropyl-N'-phenyl-para-phenylene diamine.

It will at once be noted how unsuitable sulphur vulcanisation of the elastomers obtained would be, since the moduli and the hardness are already too high to allow their use in pneumatic tyres, whilst on the other hand the breaking elongation is much too poor to allow such use. Consequently, the properties of polymers obtained from prepolymers of a functionality greater than 2, even 20 if the NCO/OH ratio is equal to 1, are insufficient to allow their use in the production of pneumatic tyres.

Example 2.

In this Example a test A,fwas conducted in which a hydroxyl - 13 precopolymer of butadiene and styrene (the latter being present in the proportion of 25% by weight) having a functionality f of 1.97 and a molecular weight of 6000, was reacted with methylenediphenyl diisocyanate. The ratio of the number of NCO reactive groups of the hydrocarbon chain lengthener to the number of the reactive OH groups of the precopolymer is 1 when the mixture is completed. Simultaneously with the polyaddition reagent the vulcanisation agents were introduced. When the mixing was completed, it was heated for an hour at 140°C to effect the polyaddition and vulcanisation reactions in a single step. The test was made with the following formulation: precopolymer 100 parts, HAF black 50 parts, dicyclohexylamine benzothiazyl sulphenamide 1.7 parts, sulphur 1.5 parts, ZnO 4 parts, iron -3 acetyl acetonate 9,10 * g per 100 g of precopolymer.

The properties were indicated in the following Table II and compared with those of a reference non-functional copolymer (SBR 1500). 3 484 - 14 TABLE II Properties Test A2 Control: SBR 1500 Modulus of elongation (100%), kg/cm2 20.1 19.0 Rebound rate at 60°C 50.3 67.0 Scott breaking number -breaking elongation, % 503 590 o -breaking strength, kg/cm 135 270 Shore hardness 68 68 It will be noted that it was not possible to obtain a copolymer having the same properties as those of the reference compound, and it will be seen that in particular the breaking strength and the rebound rate are mediocre. This is due to the fact that the elongation and vulcanisation steps cannot be controlled.

Example 3 Example 2 was repeated except that the mixture was heated for 20 minutes at 110°C and then 20 minutes at 160°C so as to separate clearly the elongation and vulcanisation phases. The properties of the two elastomers obtained are indicated in the following Table III. 43494 - 15 TABLE III Properties Test Ag Control: SBR 1500 Modulus of elongation (100%), kg/cm2 20.9 19.0 Rebound rate at 60°C 60.7 67,0 Scott breaking number 580 -breaking elongation, % 540 2 -breaking strength, kg/cm 256 270 Shore hardness 68 68 If the properties of copolymer Ag are compared with those of copolymers Ag of Example 2, it will be found that copolymer Ag has a distinctly improved breaking strength (about 100 kg/cm better) and a rebound rate at 50°C 20% approximately higher. It will also be noted that copolymer Ag has properties substantially equal to those of a conventional copolymer.

Rolling tests have been carried out with tyres including a tread containing as main component in some cases copolymer Ag proposed by the present invention and in others the conventional copolymer used for reference or control purposes, so as to compare the coefficients of friction and wear, that is to say the rate of weight loss by wear.

The coefficient of wear is expressed by the ratio: 43494 - 16 I loss of weight of the test tyre cover x 100 loss of weight of reference tyre cover The coefficient Of friction was measured at 20°C with the skid resistance tester apparatus (SRT apparatus) marketed by Messrs.

Stanley.

The losses of weight were determined after running a vehicle on a specific track and the value 100 is allotted to the reference tyre cover.

The results obtained are indicated in the following Table III bis.

TABLE III bis Properties Copolymer A3 (according to the invention) Control: SBR 1500 Friction coefficient number 65 45 Loss of weight, % 125 100 It will be noted that although the friction coefficient number of the tyre comprising a tread constituted by copolymer Ag is about 43494 - 17 40% better than that of the control tyre, the wear-grip compromise is distinctly better than that of the control.

Examples 4 to 9 In this series of Examples, copolymers were made by using as 5 precopolymer 100 parts of a hydroxyl copolymer of butadiene and styrene (this containing 12% by weight of styrene) of 1.97 functionality and a molecular weight of 6000. The tests were carried out with the following formulation :HAF black 50 parts, methylene diphenyl diisocyanate in quantity such that NCO/OH = 1.0 is obtained in the mixture formed, sulphur 1.5 parts, dicyclohexyl amine benzothiazyl sulphenamide 1.7 parts, ZnO 4 parts, iron acetyl acetonate 9.10 g per 100 g of precopolymer. After homogenisation, heating was carried out for 20 minutes at 110°C then for 20 minutes at 160°c.

The results obtained are indicated in Table IV hereinafter, and the properties of the products obtained are compared with those of a reference copolymer of butadiene and styrene called Stereon 700 in which the styrene is present to the amount of 12% by weight. 43494 - is - υ £ c φ «Ρ C <0 Ό Φ C S 4-> XI Sφ ε >ϊ ο Ο. Ο Ρ ί» Φ ΟΟ i~ CX φ .c Ρ •Ρ (0 χζ •Ρ Ό Φ Ρ ο C 3: •Ρ ►—ι Ο ί~ •Ρ φ -C Ρ ο U Οφ -C •Ρ φ φ χ: •Ρ •Ρ <0 -C «Ρ Ό C φ Running tests were carried out with tyres having as the main component of the tread in the - 19 to compare the coefficient of friction and the rate at which weight was lost by wear. The results are indicated 1n the following Table IV bis.

TABLE IV bis Properties SBR obtained with Example 4 Control: SBR 1500 Friction coefficient number 45 45 Loss of weight by wear, % 80 100 The better wear-grip compromise of the tyre including a tread which comprises an elastomer prepared according to the invention as the main component can be seen.

Example 10 An elastomer extended with oil was produced by starting, by way of precopolymer, with a hydroxyl copolymer of butadiene and IQ sytrene containing 12% by weight of styrene, of 1.97 functionality and a molecular weight of 6000, and methylene diphenyl diisocyanate as hydrocarbon chain lengthener, in quantity such that there the ratio NCO/OH was 1.0 in the completed mixture.

The test was carried out with the following formulation: precopolymer: 100 parts, naphthenic oil of 390 molecular weight, of a density of 0.946 (Circosol 2 x H marketed by Sun Oil): 30 parts, ISAF black: 65 parts, _3 ZnO: 5 parts, iron acetyl acetonate: 45.10 g per 100 g of precopolymer, sulphur 1.17 parts, bis(di-isopropyl-thiophosphoryl) disulphide: 1.56 parts, mercapto benziothiazole monosulphide: 0.482 part. The mixture was heated for 20 minutes at 110°C and then o for 22 minutes at 155 C.

The properties of the product obtained are compared with those of a reference copolymer of butadiene and styrene loaded with aromatic oil at the rate of 37.5 parts and called Solprene 384 marketed by Phillips Petroleum, and vulcanised for 60 minutes at 140°C with the following formulation: Solprene 384: 100 parts, ISAF black: 50 parts, stearic acid: 2 parts, ZnO: 1 part, 4010 NA: 1 part, Santocure: 1 part, sulphur: 1.8 parts.

The properties of the vulcanisates obtained are indicated on the following Table V.

Claims (9)

CLAIMS:

1. A process for the production of vulcanised elastomers in which one or more functional liquid diene prepolymers having a degree of functionality of from 1.8 to 2.0, either alone or in 5 combination with one or more compounds chosen from difunctional non-diene polymers, non-functional liquid polymers, difunctional molecules of low molecular weight and containing, intimately mixed, reinforcing fillers and a sulphur vulcanisation agent, 1s/are mixed with a difunctional hydrocarbon chain lengthened 10 compound in a quantity such that in the mixture formed the ratio of the number of reactive groups of the hydrocarbon chain lengthener compound to the number of reactive groups of the functional liquid prepolymer is equal to 1, and in which the mixture is subjected in a first step to a temperature sufficient 15 to obtain exclusively a lengthening reaction of the hydrocarbon chain of the prepolymer, and in a second step, to a higher temperature for carrying out the vulcanisation of the reaction product formed at the end of the first step.

2. A process as claimed in Claim 1 in which the functional 20 liquid diene prepolymer has a molecular weight of from 1000 to 20,000.

3. A process as claimed in Claim 1 or Claim 2 in which the reactive function of the prepolymer is a carboxyl, amino, hydroxyl, halogen or thiol function. 25

4. A process as claimed in any preceding claim in which the reactive group of the difunctional hydrocarbon chain lengthener 43484 - 23 compound is an epoxy, imine, amine or isocyanate function.

5. A process as claimed in any preceding claim in which the temperature of the first step is from 20 to 125°C and of the second step is above 140°C. 5

6. A process as claimed in any preceding claim in which the functional liquid diene prepolymer is a hydroxyl copolymer of butadiene and styrene and the chain lengthener is a dissocyanate.

7. A process for the production of vulcanised elastomers 10 substantially as herein described with reference to Test A 3 of Example 3, any of Examples 4 to 9, or Example 10.

8. A vulcanised elastomer which has been prepared by a process as claimed in any preceding claim.

9. A new or retreaded pneumatic tyre whose tread and/or 15 side wall includes an elastomer as claimed in Claim 8.