Therban Advanced Technology

Transcription

1 ELASTOMERE UND KUNSTSTOFFE ELASTOMERS AND PLASTICS Novel HNBR Molecular weight Processability Flow behavior Injection moulding HNBR (hydrogenated nitrile butadiene rubber) is a high performance elastomer, known for its excellent heat/oil resistance and superior mechanical properties. However, it is also an elastomer with relatively high Mooney viscosity (ML 1þ4, 100 8C > 55), due to the limitation of its feedstock NBR s finishing process. This paper discusses a novel approach to improve the processibility of HNBR while equal physical properties and aging resistance are retained. The HNBR rubber compound based on this new approach can be mixed in a shorter time, (faster black incorporation time BIT), have a much improved flow which yield to faster mould filling and shorter cycle time in injection moulding process. Therban Advanced Technology Der neue niedermolelkulare HNBR neuer HNBR, Molmasse Verarbeitbarkeit Fließverhalten Spritzgießen HNBR (hydriertes Poly(butdien-coacrylnitril) ist ein Hochleistungselastomer, bekannt durch seine ausgezeichnete Hitze/Úl-beständigkeit und hochwertigen mechanischen Eigenschaften. Darüber hinaus ist es aufgrund des zu seiner Herstellung eingesetzten NBR ein Rohstoff mit einer relativ hohen Mooney-Viskosität (ML 1þ4, 100 8C > 55). Der vorliegende Beitrag stellt einen neuen Ansatz vor um die Verarbeitbarkeit des HNBR zu verbessern, wobei die physikalischen Eigenschaften und die Alterungseigenschaften unverändert bleiben. Die neue HNBR-Type kann in kürzerer Zeit gemischt werden (geringere black incorporation time ), weißt ein besseres Fleißverhalten und Werkzeugfüllung auf und ermöglicht damit kürzere Taktzeiten im Spritzgießprozess. Therban Advanced Technology The New Low Molecular Weight HNBR Hydrogenated nitrile butadiene rubber (HNBR) is known for its unique combination of excellent mechanical properties, superior oil/chemical resistance, good low temperature flexibility and stability to thermal oxidative degradation. It s main application is in the automotive and oil exploration industries, where a good balance of properties at low and high temperature and good resistance to aggressive heat/ fluid aging are required. In most of those applications, an improvement in rubber processibility is desirable. The manufacturing of HNBR involves emulsion polymerization of NBR, followed by hydrogenation of NBR in solution at high pressure and temperature. In general, the Mooney viscosity (ML 1þ4, 100 8C) of a HNBR product is nearly twice of that of its NBR feedstock due to the conversion of the C ¼ C double bonds to a single bond sequences along the polymer chains. Therefore, all commercial HNBR grades have relatively high Mooney viscosity due to the limitations of current commercial NBR finishing technology. To develop a low molecular weight HNBR grade with much improved processibility while maintain its superior mechanical strength and heat/oil resistance has been one of the many challenges for researchers working in HNBR development. It has been shown, that improved processibility can be achieved with addition of low molecular weight fatty acids Those additives can either derive from the polymerisation or are added intentionally or at a later stage in the compounding step. Nevertheless, this approach can lead to mould fouling especially in combination with high shear process steps such as injection moulding. In addition efforts have been taken in recent years to produce a low Mooney HNBR by applying high shear stress (at a shearing rate of 500-5,000 S 1 ) in the presence of an antioxidant and in the absence of an oxygen-donor. This approach can lower the Mooney viscosity by at least 15 points [1]. However, the control of the mechanical shear process and chemical environment to produce a constant Mooney polymer is rather difficult, and the resulting polymer has a wider molecular weight distribution which yields less favourable physical properties [2]. This paper discusses newly developed lower molecular weight HNBR products with narrow molecular weight distribution (HNBR-AT ¼ Advanced Technology). The lower molecular weight of this type of polymer provides significant improvement in rubber processing, while their slightly narrower molecular weight distribution allows superior mechanical performance. The low Mooney HNBR also permits formulations with fewer or no plasticizers, therefore improvement in heat aging resistance can be achieved. In addition, no mould fouling occurs when properly compounded. Raw polymer properties of therban AT The specific polymer properties of HNBR- AT (Therban AT 3404 ML1þ4/100 ¼ 39) are best demonstrated by a comparison of the properties with those of standard HNBR grades. The standard Therban grades A 3407 (ML1þ4/100 ¼ 71) and Therban A 3406 (ML1þ4/100 ¼ 56) with a higher mooney viscosity were thus chosen as references. The results of the analytical characterisation of all three polymers are summarised in Tab. 1. The amount of residual double bonds (RDB) as well as the content of bound acrylonitrile (ACN) in the polymer is comparable for the three Therban grades. This sug- R. Parg, C. Wrana, D. Achten, Leverkusen Corresponding author: R. Parg Lanxess AG LXS-TRP-MK-AD-SE Gebäude K10, Raum Leverkusen Tel.: 02 14/ Fax: 02 14/ KGK Kautschuk Gummi Kunststoffe 58. Jahrgang, Nr. 3/

2 Tab. 1. Analytical Properties of the Raw Polymers Property Therban A 3407 Therban A 3406 Therban AT 3404 RDB [%] < 1 < 1 1,2 ACN [%] T G [8C] 24,8 25,3 24,5 M N [kg/mol] M W [kg/mol] PD (M N /M W ) 2,9 2,9 2,5 gests an identical microstructure of the polymers. The glass transition temperatures (Tg) of the three polymers (measured by DSC; Perkin Elmer, heating rate 20 K/ min) are the same within the limits of experimental accuracy. This is a further indication that the microstructure of all three polymers are similar, since the glass transition is mainly influenced by the microstructure of statistical main chain segments of the polymer. A comparison of the GPC measurements, (performed with a V2000 from Waters) yields significant differences between the three samples. The highest values of the molecular weight averages M N and M W were found for Therban A 3407 and the lowest for the Therban AT The polydisperisty (PD) of the grades A 3407 and A 3406 are comparable and significantly larger than the value of the Therban AT The good empirical correlation between the molecular weight average M W and the Mooney viscosity can be qualitatively explained by the influence of the molecular weight and the molecular weight distribution on the rheological properties. A relation between the molecular weight, the molecular weight distribution (MWD) and the rheological data, which is based on molecular parameters, can be established by a characterisation of the dynamicmechanical properties in the regime of the viscous flow. From the frequency dependent dynamic-mechanical data the viscosity of each polymer was extrapolated using the Software NLREG [3]. Fig. 1 shows a comparison of the polymer viscosities at a temperature of 100 8C. The lowest viscosity was observed for the Therban AT A quantitative relation between the molecular weight, the MWD and the rheological data can be achieved by the analysis of the dynamic-mechanical properties with a generalized mixing rule in a double reptation model. A detailed description of this method can be found in [4]. Fig. 1. Viscosity at 100 8C from Dynamic-mechanical Measurements Fig. 2. Molecular Weight Distribution from Dynamical-Mechanical Data Fig. 2 shows the result of this analysis. The molecular weight distribution of the three polymers was thereby calculated solely from the viscoelastic properties. The comparison of the molecular weight distributions of the three polymers (Fig. 2) demonstrates that the lower polymer viscosity of the Therban AT 3404 (Fig. 1) can be attributed to the lower molecular weight as well as a narrower MWD. Application Due to the inherent visco-elastic properties of the rubber raw materials and the need to incorporate and disperse ingredients/fillers into the rubber phase shear intense processes such as mixing and subsequent processing/shaping steps e.g. moulding, extrusion, calandering are applied. Within those processing steps the required compound viscosity is schematically drawn in Fig. 3. Especially within the injection moulding (IM) technology, low compound viscosities are preferred as the geometry of the mould design can be very complex for e.g. technical demands of the end article. In addition not only the size of the nests but also the numbers are essential for economical reasons. For extrusion, lower viscosity compounds are not as essential as for IM, however smooth surface finish and pronounced edges of e.g. profiles require a rubber recipe optimization and/or the choice of e.g. polymeric raw materials with adapted microstructure e.g. LCB (long chain branching). Within compression moulding / building processes the need for a lower viscosity of a rubber compound might also derive from the need to penetrate rubber compounds through fiber reinforcement sublayers, e.g. within the building process of timing belts. Considering the viscosity dependence of the various processing techniques three representative applications o-ring, cable and timing belt compounds were investigated. The unaged and aged physical data for standard compounds based on Therban 3406 / 3407 and new compounds based on Therban AT were compared. O-Ring applications The three Therban grades were compounded in a peroxide cured standard black O- ring recipe. In addition, blends of Therban AT with A 3407 were also prepared (see Tab. 2 compound 1 3 and 4 6 respectively. O-Ring application: Unaged physical properties The physical data of the 3407 HNBR compound shown in Tab. 3 was set as the 100 % reference for the subsequent comparison in the spider graph shown in Fig. 4. (Compounds 1 3 from table 2 are shown). As can be seen, the use of Therban AT has a significant impact of the compound viscosity. The compound viscosity of compound 1 (80 ML) is reduced to 56 ML (compound 3). In addition, the effect of a lower molecular weight polymer is seen in a slightly reduced tensile strength and redu- 110 KGK Kautschuk Gummi Kunststoffe 58. Jahrgang, Nr. 3/2005

3 Tab. 2. O-ring Recipe o-ring recipe Therban A Therban A Therban AT Vulkanox ZMB2/C5 0,4 0,4 0,4 0,4 0,4 0,4 Rhenofit DDA-70 1,4 1,4 1,4 1,4 1,4 1,4 Corax N Zinkoxyd aktiv Maglite DE Diplast TM 8-10/ST TA/C 1,5 1,5 1,5 1,5 1,5 1,5 PERKADOX B-GR ced stresses at 50 %, 100 % and 200 % of elongation. This can be explained with the increased amount of chain ends, which yields to a less perfect network and a reduced amount of stress bearing chain segments between mechanically active cross links. This effect is also seen in the compression set data, which increases from 37 to 40 %, when vulcanisates of compound 1 and 3 are compared. O-Ring application: Aged physicals Following an ageing procedure either in hot air (Fig. 5) or in IRM 903 (Fig. 6) a slight reduction of the tensile strength (approx. by 2 MPa) and a reduced modulus (approx. by 1,5 MPa) when compound 1 is compared with compound 3. Fig. 3. Viscosity Requirements for Different Rubber Processes Tab. 3. Reference Data for A 3407 in O-ring Recipe 3407 compound ML1þ4, 100 8C 80 tensile strength MPa 26,2 elongation at break % 216 M 50 MPa 4,7 M100 MPa 11,8 M150 MPa 19,1 M200 MPa 24,7 hardness 23 8C, shore A 80 CS DIN A 37 O-Ring application: Processability and mould fouling In order to simulate the processability of the IM process rheovulcameter experiments were performed with a spiral (Fig. 7) and a ramification tool (Fig. 8). Within the less geometrically demanding spiral tool, the throughput rate of the Therban compounds could be increased by a factor of 200 % when compound 3 with 100 % Therban AT is compared to compound 1 based on A In addition, by blending e.g. 50 % of Therban AT into the standard HNBR A 3407 (compound 5) the throughput rate is nearly doubled. Within the more geometrically demanding ramification tool, a throughput increase of approx 120 % was achieved for compound 3 in comparison to compound 1. Mould fouling experiments were performed on a Klöckner DESMA D ZO IM machine. The mould vulcanisates of compound 1 3 are shown in Fig. 9 and the injection conditions are listed below: Fig. 4. Unaged Physicals in O-Ring Applications Fig. 5. Aged Physicals in O-Ring Applications KGK Kautschuk Gummi Kunststoffe 58. Jahrgang, Nr. 3/

4 find manifold applications in cables for e.g. military use. Barrel temperature: 90 8C Injection Pressure: variable Mould Temperature: 190 8C Mould pressure 50 ton Shot size: 75 g Number of cycles: 100 Neither the Therban 3407, 3406 nor the new Therban AT 3404 showed any exudation effects on the mould or on the vulcanisates after 100 cycles of the various compounds were injected. FRNC cable applications Fig. 6. IRM Aged Physicals in O-Ring Applications A special FRNC (flame-retardant-non-corrosive) cable recipe (Tab. 4) with peroxide cure was applied since Therban grades Cable application: Unaged physical properties Again for comparison purposes, compound 1 was set as the 100 % reference. The unaged physical data of compound 1 are shown in Tab. 5. Similar to the aforementioned O-ring example a significant drop in compound viscosity is observed when Therban AT, compound 3, is compared to the standard A 3407 compound. (from 86 to 59 ML, Fig. 10). A slight tendency to somewhat longer scorch times is observed, but no in depth study was undertaken to explain this effect. The reduction in tensile strength and stresses at different strains derive as previously explained from the effect of the reduced molecular weight of the Therban 3404 AT. Tab. 4. FRNC Therban Cable Recipe Cable recipe Therban A Therban A Therban AT Apyral 120 E Zinc-Borate Stabaxol P Zinkstearat EDENOL Rhenofit DDA-70 1,4 1,4 1,4 Silan Si Silquest RC-1 Silane Rhenofit TRIM/S 0,7 0,7 0,7 PERKADOX B-GR Tab. 5. Physical Properties of A 3407 in a FRNC Cable Recipe 3407 compound ML1þ4, 100 8C 86 t 10 0,6 t 90 4,9 tensile strength 12,9 elongation at break 240 M 50 3,8 M 100 7,9 M ,5 hardness 23 8C 78 Fig. 7. Spiral Tool, 50 bar, Mould Temperature 180 8C, Die Temperature C, Injection Time 100 sec, Vulcanisation Time 10 min Fig. 8. Ramification tool, 50 bar, Mould Temperature 180 8C, Die Temperature 100 8C, Injection Time 100 sec, Vulcanisation Time 10 min 112 KGK Kautschuk Gummi Kunststoffe 58. Jahrgang, Nr. 3/2005

5 Fig. 9. Mould Fouling Experiments Cable applications: Processing and finishing In order to investigate the impact of the throughput efficiency an extrusion experiment was performed (Fig. 11). The mass output of compound 3 with Therban AT is increased by 50 g/min when compared with compound 1. The torque and extrusion pressure are reduced significantly. Within an assumption of a linear function in between extrusion pressure and troughput the theoretical mass output of compound 3 at 119 bar is 393 g/min, which is 60 % higher than the mass throughput with compound 1. In addition, the finishing of the extrudate is significantly improved, as no slip-stick effects are observed at the edges of the Garvey profile (Fig. 11). Fig. 10. Unaged Physical Properties in a FRNC Cable Recipe Belt applications Identical investigations were performed with a standard peroxide cured timing belt recipe (Tab. 6). Again for comparison purposes compound 1 was set as the 100% reference. The unaged physical data of compound 1 is shown in Tab. 7. Similar to the aforementioned investigations within O-ring and cable applications a significant impact on the compound ML viscosity was observed when Therban AT was used as a 50 % polymer basis. Other physicals e.g. tensile strength and stresses at different strains are slightly reduced whilst compression set and hardness remains unchanged (Fig. 12). Following a hot air aging procedure for 7 days at 150 8C a slight reduction in tensile strength and stresses at 50 % and 100 % deformation arose when compound 3 and 1 are compared (Fig. 13). Fig. 11. Extrusion Experiment with a Garvey Profile Tab. 6. Acrylate Reinforced Timing Belt Recipe (ART ¼ 70 Weight% Therban C3446/30 Weight% Zink diacrylates) timing belt recipe Therban LA Therban A Therban AT Therban ART KA N Zinkoxid aktiv Maglite DE Vulkanox ZMB2/C5 0,4 0,4 0,4 Rhenofit DDA-70 1,4 1,4 1,4 PERKADOX B-GR Tab. 7. Unaged Physical Data of A 3407 in a Timing Belt Recipe 3407 compound ML1þ4, 100 8C 80 tensile strength 26,2 elongation at break 216 M 50 4,7 M ,8 M ,1 M ,7 hardness 23 8C 80 hardness 70 8C 77 KGK Kautschuk Gummi Kunststoffe 58. Jahrgang, Nr. 3/

6 Fig. 12. Unaged Physicals of a Timing Belt Recipe Fig. 13. Aged Physicals of a Timing Belt Recipe Fig. 14. Dynamic Stress/Strain Behaviour of Vulcanisates under Pulsed Excitation Fig. 15. Life Time Prediction of Vulcanisates Life time prediction of the vulcanisates in a timing belt Following a tear analyzer investigation of the 3 compounds no significant changes within the measuring accuracy were observed when stress/strain behaviour (Fig. 14) and the resulting life time prediction (Fig. 15) following a constant strain method were observed. Conclusion 1. A new type of Therban with low molecular weight and narrow molecular weight distribution has been developed. 2. The lower molecular weight of Therban AT leads to considerably improved processibility such as fast mould filling and fast extrusion rate and easy mix. 3. The narrower molecular weight distribution ensures that the excellent physical properties of the Therban are maintained. 4. Due to the lower molecular weight of Therban AT the desired compound viscosities can be produced with little or no addition of plasticizer; this results consequently in improved heat ageing resistance. 5. Therban AT should be particulary interesting for IM other moulding application. References [1] Fujii Yoshinori, Ikeda Atsumi, JP , [2] S. Guo, paper presented at ACS Meeting, Columbus (2004). [3] LREG, program for nomlinear regularization, Version Rheology 2.0, (2001) Material Research center Freiburg. [4] C. Wrana et. al., presented at the 6th Fall Rubber Colloquium, Hannover (2004). 114 KGK Kautschuk Gummi Kunststoffe 58. Jahrgang, Nr. 3/2005