ZINC OXIDE DISPERSION

Abstract: A zinc oxide dispersion for use in rubber compounds having at least 40, preferably 74-92 weight percent zinc oxide powder and at least five weight percent of a binder selected from the group consisting of asphalt and terpene tackifiers. The dispersion also preferably includes at least 0.5 weight percent stearifying agent such as stearic acid.

Description: ZINC OXIDE DISPERSION FIELD OF THE INVENTION This invention relates generally to zinc oxide and more particularly to a zinc oxide dispersion for use in rubber compounds . DESCRIPTION OF RELATED ART Most elastomers such as natural and synthetic rubbers require zinc oxide as a means for either activation of cure or for vulcanization. It is well known in the rubber industry that zinc oxide has a low affinity towards most elastomers and is very difficult to efficiently incorporate into a rubber matrix or compound. To overcome some of the difficulties of incorporating zinc oxide into rubber compounds, some zinc oxide dispersions have been developed to facilitate zinc oxide incorporation. However, these known zinc oxide dispersions have failings in certain regards such as cost, limited applicability, and effectiveness. There is a need for a more effective and more useful zinc oxide dispersion for use in rubber compounds. SUMMARY OF THE INVENTION A zinc oxide dispersion comprising at least 40 weight percent zinc oxide powder and at least 5 weight percent of a binder selected from the group consisting of asphalt and terpene tackifiers. A rubber compound comprising the zinc oxide dispersion and rubber selected from the group consisting of natural rubbers, synthetic rubbers, and mixtures thereof. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION Parts are parts by weight and percents are weight percents unless otherwise indicated or apparent. When a preferred range such as 5-25 is given, this means preferably at least 5 and preferably not more than 25. The invented zinc oxide dispersion has the following preferred formulation (Formulation 1) . Weight Percent Less Less Ingredient Preferred Preferred Preferred 1. Asphalt 17 11-23 5-30 2. Stearifying agent 3 1.5-6 0.5-10 3. Zinc oxide powder 80 60-90 40-96 The asphalt is preferably a blend of 55%, less preferably 45-65%, less preferably 35-75%, asphalt (preferably monor asphalt from Sun Refining) and 45%, less preferably 35-55%, less preferably 25-70%, blown asphalt. Less preferably the asphalt is 100% asphalt such as monor or 100% blown asphalt. Blown asphalt, which is asphalt, is produced by blowing air through asphalt at 400-600° F followed by cooling and is also known as oxidized asphalt. The stearifying agent is a material selected from the group consisting of fatty acids and fatty acid esters and mixtures thereof. The stearifying agent and fatty acid is preferably stearic acid, less preferably oleic, palmitic, linoleic, or linolenic acid, or a mixture thereof. The stearic acid preferably has an acid value of 193-212 and a maximum iodine value of 10. The fatty acid ester is preferably a triglyceride such as a hydrogenated triglyceride such as Neustrene 060 from Humko Chemical. The stearifying agent, which is uncrosslinked, adds lubricity to the blend as well as preferably modestly reacting with the ZnO yielding a slight degree of stearification. The zinc oxide powder is the zinc oxide powder known in the rubber compounding art. The above formulation yields a dark colored finished product that may discolor or stain white or light colored rubber compounds. Where color retention is important, an alternative formulation for the invented zinc oxide dispersion can be used, as follows (Formulation 2) . Weight Percent Less Less Ingredient Preferred Preferred Preferred 1. Terpene tackifier 16 10-22 5-30 2. Petrolatum 1 0.6-1.5 0.2-2 3. Stearifying agent 3 1.5-6 0.5-10 4. Zinc oxide powder 80 60-90 40-96 As used herein, Sta-Tac (CAS No. 26813-14-9, being 1,3-Pentadiene, polymer with 2-methy1-2-butene, molecular formula: (C 5 H 10 . C 5 H 8 ) χ ) from Arizona Chemical Co., Nevtac from Neville Chemical, and Wingtack from Goodyear are terpene tackifiers. The terpene tackifier is preferably Sta-Tac, less preferably Wingtack or Nevtac or any tackifier which is based on a terpene or polyterpene resin, or mixtures of the foregoing. The stearifying agent is as described above. Optionally, the formulations are at least 50, more preferably 60, more preferably 65, more preferably 70, 74, 75, 78, 80, 85, and 88 and not more than 90, 91, or 92, weight percent zinc oxide powder, at least 7, 8, 9, 10, 12, or 15, weight percent asphalt or terpene tackifier, and at least 1, 2, 2.5, 3 or 4, weight percent stearifying agent. In each formulation the components other than the zinc oxide form a binder or homogenizing binder or homogenizing agent or homogenizing additive or carrier or carrier system. To mix the invented dispersion, charge all the components into a heated mixer such as a Sigma Mixer at 250° F and blend together until the mixture becomes a homogeneous paste. The hot paste is then put through a forming stage such as an extruder or other apparatus to form the compound into pellets, rods or sheets. The mixing and extruding can be done on a continuous system such as a mixing extruder or other continuous system known in the art. To enhance pelletizing or other shape forming, EVA or similar thermoplastic having a melting point of about 350-400°F can be added to the mix at the rate of 3-5 parts EVA per 100 parts asphalt, or 10-15 parts EVA per 75 parts terpene tackifier. Formulation 1 (with EVA as noted) is a dark brown, hard rod, pellet, flake or sheet with a softening point of about 165-175°F and a specific gravity of about 3. Formulation 2 (with EVA as noted) is a bright white, hard pellet, flake, bead or rod with a softening point of about 130-140°F and a specific gravity of about 3. The invented zinc oxide dispersion, which is a mixture or blend or predominantly a blend, is used by adding it in the way other known zinc oxide dispersions are added to natural rubbers, synthetic rubbers, and mixtures thereof, the synthetic rubbers being preferably polychloroprene, bromobutyl, halobutyl and chlorinated polyethylene, less preferably styrene-butadiene, isobutylene-based such as butyl and isobutylene-para ethylstyrene copolymer, polybutadiene, EPDM, nitrile, acrylic, epichlorohydrin, ethylene/aerylie, EPM, isoprene-acrylonitrile, polyisoprene, polynorbornene, and styrene-isoprene. The invented zinc oxide dispersion is preferably an activator for natural and synthetic rubbers and a vulcanizer for polychloroprene and other halogenated elastomers. The rubber compounds made with the invented dispersion find particular utility for tires, tire treads, carcasses, sidewalls, coating stocks, hoses, belting, inner tubes, innerliners, general purpose rubbers, and other uses. The rubber compounds may include accelerators, retarders, other activators, other vulcanizers, antioxidants, antiozonants, protective materials, plasticizers, processing aids, stabilizers, tackifiers, extenders, fillers, reinforcing materials, blowing agents, lubricants, polymerization materials, and other rubber compounding materials known in the art. The invented zinc oxide dispersion is added to the rubber compound at a rate of 1-10, more preferably 2-6, more preferably 3-5, more preferably about 4, phr (parts per hundred parts of rubber) , by adding it right on top of the first charge of filler such as carbon black, less preferably directly with the polymer before the filler. The following Examples further illustrate various aspects of the invention. Example 1 A zinc oxide dispersion was prepared by mixing 17 parts asphalt (57% monor asphalt, 40% blown asphalt and 3% EVA) , 3 parts stearic acid and 80 parts zinc oxide powder (hereinafter the "80% ZnO dispersion"; this same dispersion was used in Examples 1-4) . This was tested against 100% ZnO powder as follows. Note that 10 parts of 100% ZnO powder has 10 parts ZnO, while 10 parts of 80% ZnO dispersion has only 8 parts ZnO. A radial auto tire sidewall composition was mixed in a laboratory Brabender at 90°C with 55 rpm rotor speed (this mixer at these settings was used in Examples 1-4) using the following sequential procedure. An exaggerated level of both zinc oxides was used in this experiment. 50 parts SIR20 natural rubber, 50 parts BR1207 synthetic rubber, and 5 parts 100% ZnO powder ("Control") or 80% ZnO dispersion ("Dispersion") were mixed for 30 seconds. 37.5 parts N330 carbon black and 4 parts Protac NPT tackifier were added and mixed for 2 minutes. 12.5 parts N330 carbon black, 8 parts Sundex 790 aromatic oil, 2 parts Sunolite 240 petroleum wax, 2 parts Flectol antioxidant, and 2 parts stearic acid were added and mixed 2 min. , discharged and cooled. 1.25 parts soluble sulfur and 1.75 parts Santocure MOR accelerator were added on a laboratory mill. The 80% ZnO dispersion incorporated into the rubber batch at a significantly faster rate compared to the 100% ZnO powder. Physical and state of cure properties were tested in accordance with ASTM methods, with the following results. Heat aged physicals are at 24 hours at 100°C. Original Cured Heat Aged Physicals Physicals Control Dispersion Control Dispersicn Shore A hardness 60 60 6 644 6644 Tensile (lb/in 2 ) 2465 2513 2 2332288 22441122 100% modulus (lb/in 2 )) 222244 234 3 32200 332277 300% modulus (lb/in 2 )) 999988 1042 1 1448888 11444455 Elongation (%) 529 538 4 41177 445500 Die-C tear (lb/in) 252 238 2 20044 223300 Trouser tear (lb/in) 82 81 9 955 9977 The mixing energy (amps at discharge) was: Control - 10.5; Dispersion - 10.25. Rheo eter data (30 min.; 160°C; 3° arc ; ODR; 100 inch-lb torque range) for max. torq. , min. torq. , TS(1), and TC(90), respectively, was: Control: 62.5, 5.3, 5.2, and 13.8, respectively; and Dispersion: 62.6, 5.6, 5.2, and 13.3, respectively. Surprisingly, the 80% ZnO dispersion was equal to or better than the control in most regards, despite having 20% less ZnO. Example 2 - Polychloroprene Compound This experiment uses a chlorinated elastomer which is very sensitive to ZnO levels. 60 parts Neoprene W, 40 parts Neoprene TM, and 4 parts Maglite D MgO were mixed 30 sec. 15 parts N990 carbon black, 2 parts Promix 130 processing aid, and 2 parts AgeRite Stalite S antioxidant were added and mixed 60 seconds. 15 parts N990 carbon black, 1 part stearic acid, 30 parts Nucap 200 hard Kaolin clay and 25 parts Sundex 790 aromatic oil were added, mixed 3 min. and discharged. Batch was cross cut 5 times on a laboratory mill, removed and cooled. The batch was returned to the Brabender and there was added and mixed for 60 seconds, 0.25 parts ETU accelerator and varying amounts of 100% ZnO powder and 80% ZnO dispersion (0, 0.33, 0.75, 1.00, 1.50, 2.00, and 3.00 phr 100% ZnO powder being Samples 0, A, B, C, D, E, and F, respectively, and 0, 0.33, 0.75, 1.00, 1.50, 2.00 and 3.00 phr 80% ZnO dispersion being Samples 0, G, H, I, J, K, and L, respectively) . The samples were then discharged, cooled and cross cut 5 times on a laboratory mill. The 80% ZnO dispersion incorporated into the rubber batch faster than the 100% ZnO powder and at the higher levels of the 80% dispersion compound nerve was reduced, resulting in improved processing properties. Test data, in accordance with ASTM methods, is as follows. Viscosity is ML(1+4)@100° C. Duro- 100% 300% 500% meter modulus modulus modulus Percent Tensileι Mooney Sample (Shore A) (psi) (psi) (psi) Elongation (psi) Viscosity 0 34 29 56 214 818 606 14.3 A 37 56 182 413 800 1070 16.9 B 39 43 177 529 770 1289 17.4 C 40 49 210 596 750 1410 16.5 D 42 63 230 664 806 1550 16.6 E 44 63 220 689 770 1500 16.8 F 45 69 228 620 781 1553 16.7 G 40 62 210 561 793 1330 16.0 H 42 63 190 536 790 1382 15.8 I 42 70 197 547 803 1417 16.2 J 44 76 220 607 806 1597 16.0 K 45 90 249 705 781 1605 16.6 L 46 84 205 661 826 1758 17.0 Rheometer data (30 min.; 350°F; 3° arc; 100 inch-lb torque range) was as follows: Max. Min. Sample Torque Torgue TS(1. TC(90. 0 8 . 61 0.64 75 27.42 A 14 . 00 0.83 42 26.75 B 17 . 08 0.83 21 26.46 C 17 . 79 0.64 08 26.71 D 22 . 28 0.83 21 25.96 E 21 . 38 0.96 38 25.83 F 21 . 32 0.77 33 25.79 O 8 . 61 0.77 75 27.46 G 16 . 18 0.83 58 26.75 H 17 . 34 0.90 75 26.96 I 19 . 78 1.03 50 26.38 J 22 . 16 1.03 13 26.17 K 22 . 16 1.35 25 26.21 L 23 . 50 1.28 88 25.63 Surprisingly, the 80% ZnO dispersion samples had overall improved cure and physical properties compared to the control samples . Example 3 To evaluate the incorporation characteristics of ZnO, both the 80% ZnO dispersion and 100% ZnO powder were added very late into the mixing cycle and only allowed to mix for a short period of time. The radial sidewall formulation of Example 1 was tested using the 80% dispersion and the 100% powder at 5 phr. The mixing procedure was as follows. The polymers were mixed for 30 seconds. 75% of the N330, the Protac NPT and the Flectol were added and mixed 2 minutes. 25% of the N330, the oil, wax, and stearic acid were added and mixed 2 min. The 100% ZnO powder ("Control") or 80% ZnO dispersion ("Dispersion") were added and mixed for 30 seconds; batch discharged and cooled. The sulfur and MOR were added on a laboratory mill, cross cut 5 times, removed and cooled. Test data, per ASTM methods, is as follows. Rheometer settings were the same as in Example 1. Control Dispersion Shore A hardness 60 60 100% modulus (lb/in 2 ) 254 219 300% modulus (lb/in 2 ) 1040 1021 Elongation (%) 560 630 Tensile (psi) 2480 2631 Mooney Viscosity 43 40 Die-C tear (lb/in) 267 276 Max. torque 62.5 62.6 Min. torque 5.3 5.6 TS(1) 5.2 5.2 TC(90) 13.8 13.3 Surprisingly, the 80% ZnO dispersion demonstrated equal or slightly better cure state and physical properties than the 100% ZnO powder, despite the fact 20% less actual ZnO powder was present. At normal rubber processing temperatures the 80% ZnO dispersion was transformed into a soft paste during mixing and incorporated into the rubber compound significantly faster than the ZnO powder. The invented dispersion improves processing properties, i.e., less nerviness and reduced viscosity of the rubber compound. Example 4 The rubber formulation of Example 3 was tested with 5 phr 100% ZnO powder ("Control") , 5 phr 80% ZnO dispersion from Example 1 ("Sample A"), 5 phr 85% ZnO dispersion (11.5 parts of the asphalt of Example 1, 3.5 parts stearic acid, and 85 parts zinc oxide powder) ("Sample B") , and 5 phr Elast-O-Zinc Curebeads from Elastochem Inc. (a commercially-available 88% ZnO powder dispersed in an organic based binder) ("Sample C") . The mixing procedure was the same as Example 3 except the ZnO was mixed for 45 seconds. Physical properties test data is as follows. Compression set was 22 hours at 158°F. Control Sample A Sample B Sample C Shore A hardness 60 60 60 60 100% modulus 254 219 220 165 300% modulus 1040 921 910 890 Elongation (%) 560 631 575 548 Tensile (psi) 2480 2632 2511 2370 Die-C tear (lb/in) 262 276 269 241 Mooney Viscosity 43 42 44 46 Rebound (%) 40.9 39 8 39. 39.0 Compression set 20.0% 20, 0% 17.0% 17.9% Surprisingly, the invented 80% and 85% dispersions demonstrated many superior physical properties over the Elast-O- Zinc commercial product. Although the preferred embodiments have been described, it is understood that various modifications and replacements of the components and methods may be resorted to without departing from the scope of the invention as disclosed and claimed herein.

Claims: WHAT IS CLAIMED IS: 1. A zinc oxide dispersion comprising at least 40 weight percent zinc oxide powder and at least 5 weight percent of a binder selected from the group consisting of asphalt and terpene tackifiers. 2. A zinc oxide dispersion according to claim 1, wherein said binder is asphalt. 3. A zinc oxide dispersion according to claim 2, said dispersion being at least 60 weight percent zinc oxide powder and at least 7 weight percent asphalt. 4. A zinc oxide dispersion according to claim 2, further comprising at least 0.5 weight percent stearifying agent. 5. A zinc oxide dispersion according to claim 4, said dispersion being at least 1.5 weight percent fatty acid. 6. A zinc oxide dispersion according to claim 3, further comprising at least 1.5 weight percent fatty acid. 7. A zinc oxide dispersion according to claim 6, said dispersion being 74-92 weight percent zinc oxide powder. 8. A zinc oxide dispersion according to claim 7, said dispersion being 78-88 weight percent zinc oxide powder, at least 10 weight percent asphalt, and at least 2 weight percent stearic acid. 9. A zinc oxide dispersion according to claim 7, said asphalt being at least 25 weight percent blown asphalt. 10. A zinc oxide dispersion according to claim 1, wherein said binder is selected from the group consisting of terpene tackifiers and mixtures thereof. 11. A zinc oxide dispersion according to claim 10, said dispersion being at least 65 weight percent zinc oxide powder and at least 7 weight percent terpene tackifier. 12. A zinc oxide dispersion according to claim 11, further comprising petrolatum and at least 0.5 weight percent stearifying agent. 13. A zinc oxide dispersion according to claim 11, further comprising at least 1.5 weight percent fatty acid, said dispersion being 74-92 weight percent zinc oxide powder. 14. A zinc oxide dispersion according to claim 12, said dispersion being 74-90 weight percent zinc oxide powder and at least 2 weight percent stearic acid. 15. A zinc oxide dispersion according to claim 14, wherein said terpene tackifier is 1, 3-Pentadiene, polymer with 2-methyl- 2-butene. 16. A rubber compound comprising a) rubber selected from the group consisting of natural rubbers, synthetic rubbers, and mixtures of any of the foregoing and b) a zinc oxide dispersion comprising at least .40 weight percent zinc oxide powder and at least 5 weight percent of a binder selected from the group consisting of asphalt and terpene tackifiers. 17. A rubber compound according to claim 16, said binder being asphalt, said dispersion being at least 60 weight percent zinc oxide powder, at least 7 weight percent asphalt, and at least 1 weight percent stearifying agent. 18. A rubber compound according to claim 17, said dispersion being 74-92 weight percent zinc oxide powder and at least 1.5 weight percent fatty acid. 19. A rubber compound according to claim 16 , wherein said binder is selected from the group consisting of terpene tackifiers and mixtures thereof, said dispersion being at least 60 weight percent zinc oxide powder, at least 7 weight percent terpene tackifier, and at least 1 weight percent stearifying agen . 20. A rubber compound according to claim 19, further comprising petrolatum, said dispersion being 74-92 weight percent zinc oxide powder and at least 1.5 weight percent fatty acid.

Inventors: HOOVER JAMES W, HOOVER, JAMES, W.
Applicants: FLOW POLYMERS INC, FLOW POLYMERS, INC.
Application year: 1999
Main classification: C08L91
IPC codes: C08K3, C08K5, C08L21