Mixing aspects of Duralink HTS in steel cord adhesion compounds

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1 Gummi Fasern Kunstoffe, No. 7, 00, pp Mixing aspects of in steel cord adhesion compounds R.N. Datta Market Development Manager, Flexsys BV, Technology Centre in Deventer in the Netherlands Selected from International Polymer Science and Technology, 9, No. 10, 00, reference GK 0/07/439; transl. serial no Translation submitted by C. Hinchliffe Studies were carried out with the aim of finding the temperature-dependence of in typical steel cord skim compounds. It has been found that the mixing temperature plays a key role in compounding. Mixing at C has a negative impact, while mixing at temperatures above 10 C has a positive impact on the retention of adhesion especially after ageing in various conditions. This phenomenon was elucidated using thermal gravimetric analysis (TGA). Also investigated was the impact of zinc on the reaction kinetics of. It was demonstrated that the presence of zinc is necessary to activate. Finally, we also studied the effect of concomitant materials, such as sodium sulfate and sodium thiosulfate, which are formed from. No deleterious impacts were identified when sodium salts were incorporated into standard steel cord skim compounds. INTRODUCTION The bonding of the natural rubber compounds to brasscoated steel cord is of great significance in radial tyres with steel cord belts. It is generally assumed that good initial adhesion may be achieved if high volumes of sulfur and high sulfur/accelerator ratios are used [1-6]. Organic metal salts or binders such as cobalt naphthenate or HR additives (for example, hexamethoxymethyl melamine, HMMM, a resorcinol formaldehyde resin) are widely used to promote adhesion between rubber and brass-coated steel cord [7]. It has also been reported [9] that small quantities of cobalt salts greatly improve the stripping force after ageing in steam, humidity or salt. Even if cobalt salts to a certain extent also inhibit certain corrosion reactions, which still occur even under optimum cord and compound conditions, promoters of this type do not offer complete protection against corrosion [7]. It is therefore desirable that a compound be developed to counteract the reduction in adhesion following ageing in steam, humidity and salt. A recent publication covers the use of the disodium salt dihydrate of hexamethylene-1,6-bis-(thiosulfate) ( ) in steel cord bonding compounds []. Certain results have already been described by earlier authors [10-13]. However, so far, no-one has dealt with questions concerning the impact of the mixing temperature and the role of activators (for example zinc ) in mixtures with. The fate and impact of inorganic salts, such as, for example, sodium sulfate or thiosulfate which form during the reaction of the are also still unknown. This study had three objectives: to investigate the impact of varying the mixing temperature and its influence on adhesion to elucidate the role of zinc during the reaction of to investigate the impact of concomitant materials (such as, for example, sodium salts) formed from on adhesion.. EXPERIMENTAL The ingredients zinc, stearic, carbon black N336, the tackifier 1068 were used as supplied. The cobalt naphthenate (NAPCO10) contains 1 % cobalt., and S are polymerised,,4-trimethyl- International Polymer Science and Technology, Vol. 30, No. 3, 003 T/1

2 1,-dihyroquinoline, N-1,3-dimethylbutyl-N -phenyl-pphenylene diamine or N,N-dicyclohexyl--benzothiaozole sulfenamide. OT 0 and PVI-0 are polymeric sulfur (0 % oil-treated) or N- (cyclohexylthio)phthalimide (0 % active). The formulations in the test mixtures are shown in s 1-4. Here, it is important to point out that when is used, it is possible to reduce the amount of sulfur without this having any negative impacts on the adhesion properties [10]. Advantage was taken of this for this investigations described here. The production of the compounds was performed in two stages in a Banbury laboratory kneader with a capacity of 0 l. Three different mixing sequences were used which differed in the time at which the zinc was added and in the output temperature. Mixing sequence 1 All ingredients with the exception of the vulcanising agent were incorporated in the pre-mixing stage in accordance with the following mixing regulation: 0 min add rubber 1 min add 1 carbon black + zinc + stearic 1 min add 1 carbon black + + the remaining ingredients 4 min raise and lower punch min output Formulations (influence of mixing temperature, mixing sequences 1A and B) Compound ingredients 01 0A 0B NAPCO PVI-0 OT A = masterbatch temperature C ; B = masterbatch temperature 10-1 C. Formulation - mixing sequence 1 Compound ingredients NAPCO 10 PVI-0 OT Formulation - mixing sequence Compound ingredients NAPCO 10 PVI-0 OT T/ International Polymer Science and Technology, Vol. 30, No. 3, 003

3 4. Impact of sodium salts Compound ingredients NAPCO 10 PVI-0 OT 0 4 Sodium thiosulfate Sodium sulfate The output temperature was varied. In case A, the output temperature was kept at C and in case B the output temperature was 10-1 C. The vulcanisation ingredients were incorporated in the final stage on a roll mill with two roll faces. Mixing sequence This mixing sequence is similar to mixing sequence 1, case B, except that the zinc is incorporated together with the vulcanising agents in the final stage. Mixing sequence 3 This mixing sequence is similar to mixing sequence 1, case B, except that the zinc is divided into two halves and the following mixing regulation observed: 0 min add rubber 1 min add 1 carbon black + zinc ( phr) + stearic 1 min add 1 carbon black + + the remaining ingredients 4 min raise and lower punch min output at 10-1 C Accelerator, sulfur and the remaining zinc (6 phr) were added on a roll mill with two roll faces. The vulcanisation properties of the mixtures were determined by means of a MDR 000E Monsanto rheometer. Test pieces were vulcanised in an electrically heated hydraulic press at 10 C corresponding to the t times. The brass-coated steel coated used involved the construction 3+9x+1 with a Cu content of 63 %. The rubber-metal adhesion was determined according to ASTM D9-8. The steel cord bonding values are mean values from ten individual tests. Steel cord adhesion samples were aged under the following conditions Heat ageing 3 d at 10 C in air Steam ageing d at 11 C Salt ageing 14 d at C in 10 % aqueous NaCl solution Humidity ageing d at 80 C at 9 % rel. atmospheric humidity 3. RESULTS AND DISCUSSION 3.1 Impact of the mixing temperature behaves like an inorganic salt which is insoluble and not readily dispersed in rubber. The best way to achieve optimum dispersion is to add early in the mixing cycle. The mixing sequence used is described in the section Experimental part under mixing sequence 1 A and B. In one case (mixture 0A), the output temperature was C, in the other (mixture 0B), it was 10-1 C. The vulcanisation characteristics are shown in. These values clearly show that the mixing output at 1 C resulted in a specific advantage with regard to resistance to reversion, as confirmed by the numerical values for tr. The mixture is slightly more susceptible to scorching, while International Polymer Science and Technology, Vol. 30, No. 3, 003 T/3

4 . Vulcanisation characteristics of the mixtures at 10 C B Extent of crosslinking Scorch time ts, m in Optimum vulcanisation time t min Reversion time, tr, min Adhesion values (vulcanisation: 10 C/t) Properties Non-aged, N A ged in hot air, 3 d/10 C A ged in steam, d/11 C Aged in salt (solution), 14 d/rt A ged in humidity, 9 % RH d/80 C 01 0A 0B Values in brackets indicate the degree of cover; (W) = repetition 04 (W) (W) (W) () () (80) (60) ( 0) ( 0) ( 0) (60) t is longer. It is expected that a longer value for t will have certain advantages with regard to adhesion in nonaged condition [14, 1]. The adhesion values are shown in 6. The values shown in brackets are the degrees of cover. While no differences were observed for the values in non-aged condition, there were clear differences in the values after ageing. The output of the mixture at C had negative impacts on adhesion, in particular after ageing in steam/salt water/humidity. This leads to the conclusion that should be incorporated at temperatures of more than 10 C. The reason for this phenomenon becomes evident from an examination of the TGA scan for (Figure 1). It is important to mention that between 40 and 70 C, loses its water of crystallisation and become active. The dehydrated remains stable between 7- C and only starts to decompose at temperatures above C. It should be stressed that this solely involves the TGA scan for, in rubber, on the other hand, decomposition sets in at temperatures much higher than C. It is to be expected that during this decomposition, participates in the crosslinking reaction and will finally be used up. If the temperature is only 130 C, the reaction will probably be incomplete and the will not react and probably remain in the system in its dehydrated form. This unreacted has a tendency to absorb water of crystallisation from the atmosphere, as shown in Figure. This moisture absorption tends to have a negative impact on the adhesion properties, in particular where ageing in humidity or steam is concerned. It is therefore advisable to ensure that all the participates in the desired reaction during the vulcanisation. 3. Impact of zinc plays a decisive role in the activation of. Several mixing sequences were employed to demonstrate this phenomenon (mixing sequences 1, and 3, see Section. Experimental part ). The sequence of the addition of zinc was varied. The formulations are given in s, 3 and 4. The adhesion values are listed in 6. It is evident that when zinc is added in the non-productive phase in which the output temperature is between 10 and 1 C, the presence of significantly improves the adhesion properties after ageing. This is in conformity with the explanations given in section 3. The picture changes greatly when the zinc is added during the productive phase of the mixing process (mixing sequence, see Section Experimental part ). Although T/4 International Polymer Science and Technology, Vol. 30, No. 3, 003

5 Figure 1 TGA scan of Figure TGA scan of a sample ( ) the output temperature was kept at 10-1 C, the presence of had negative consequences for the adhesion values, as shown in 6. This leads to the conclusion that zinc is necessary for the activation of the reaction of. In order to identify the minimum quantity of zinc required for this activation, mixing sequence 3 was used in which phr of zinc was added in the nonproductive phase and the remaining 6 phr in the productive phase. The corresponding adhesion values are given in 6. It is interesting that phr of zinc are sufficient to activate the reaction of and hence facilitate the maintenance of adhesion after ageing. The complete impacts of the differences in the mixing sequences are more clearly evident in diagrams, as shown in Figure 3 (A), (B) and (C). 3.3 Influence of inorganic sodium salts on the adhesion properties During the reaction of, it is possible that of sodium salts, such as sodium thiosulfate, sodium sulfate etc. may form. These concomitant materials could have deleterious impact on important properties. It was on this basis that the impact of the addition of sodium thiosulfate and sodium sulfate on adhesion were investigated. The corresponding formulations are shown in 4. The vulcanisation characteristics are shown in 7. It is established that both and sodium thiosulfate increase the mixtures scorching tendency although sodium sulfate has a negligible impact only. The adhesion values are shown in 8. Once again, the impact is clear: maintains adhesion on International Polymer Science and Technology, Vol. 30, No. 3, 003 T/

6 Figure 3 Mixing sequence 1 (a), (b) and 3 (c) 7. Vulcanisation characteristics of the mixtures at 10 C Properties Degree of crosslinking, N m Scorch time ts, min ptimum vulcanisation time t, mi O n T/6 International Polymer Science and Technology, Vol. 30, No. 3, 003

7 8. Adhesion values (vulcanisation: 10 / t C ) Properties, mixtures Non-aged, N () A ged in hot air, 3 d/10 C () A ged in steam, d/11 C (60) Aged in salt (solution), 14 d/rt (40) A ged in humidity, 9 % RH, d/80 C (40) Values in brackets indicate the degree of cover exposure to different ageing conditions. The incorporation of sodium sulfate or sodium thiosulfate has no negative impact on adhesion to steel cord (compare the values for mixture 09 with those for mixtures 11 and 1). REFERENCES W.J. van Ooji, Rubber Chem. Technol., (1979) 60. S. Buchan, Rubber to Metal Bonding Crosby Lackwood and Sons, London, W.E. Weening, Kautschuk Gummi Kunststoffe, 31 (1978) 7 4. G.R. Hamed and T. Donatelli, Rubber Chem. Technol., 6 (1983) 0. R.N. Datta and F.A.A. Ingham, Kautschuk Gummi Kunststoffe, (1999) 3 6. A.G. Buswell, D.C. Eaten and C.R. Tidswell, Rubber World, 1973 () (197) 3 7. W.J. van Ooji, Rubber Chem. Technol., 7 (1984) L.R. Baker, Technol. 1 (1981) W.J. Ooji, W.E. Weening and P.F. Murray, Rubber Chem. Technol., 4 (1981) 7 1 A. Orband, G. Anthoine and H. Roebuck, Kautschuk Gummi Kunststoffe, 39 (1986) 37 1 G. Anthoine and D.G. Lloyd, Ind. Gomma 74 (198) 9, 3, 36 D.G. Lloyd, Gummi Fasern Kunststoffe, 41 (1988) 84, 86, 88, O. Uchino, T. Imori and M. Yoshida, JP , K.-D. Albrecht, Rubber Chem. Technol., 46 (1973) 981 R.F. Seibert, Rubber Division, ACS, Orlando, Florida, Oct -9, 1993, paper No. (No date given) International Polymer Science and Technology, Vol. 30, No. 3, 003 T/7

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