NON-BLACK SYNTHETIC RUBBER FORMULATIONS

Abstract: The invention disclosed relates to an injection mouldable non-black bromobutyl rubber formulation which provides twenty-four hour protection from penetration by H-agent and as such is particularly suitable for use in gas masks. The novel rubber formulation comprises bromobutyl rubber and appropriate additives to improve physical properties of the resulting material. Significantly, an alcohol phosphate is included as part of the accelerator in an amount of 0.5 to 2.1 pph of bromobutyl rubber.

Description: NON-BLACK SYNTHETIC RUBBER FORMULATIONS This invention relates to rubber compositions, and in particular to synthetic rubber compositions for use in gas masks and other items requiring CW agent penetration resistance. Natural rubber has been the choice of rubber chemists for gas mask facepieces since the introduction of respiratory protecting gas masks towards the end of World War I. It has many advantages over synthetic elastomers for facepiece use including comfort, high resiliency, high strength, easy processing and moulding, non-dermatitic properties and good low temperature flexibility. However as protective equipment develops and improves, the materials they are made from require an ever increasing performance. With the advent of new mask designs some of the properties of the material require improvement. For example, it is highly desirable to maximize the Modulus 500% to the range of 900-1600 psi, while keeping the Permanent Set at 500% below about 12%. With this in mind, applicant has concentrated on providing an improved rubber composition for facepiece use that would exhibit such improved properties. Various synthetic rubber formulations were evaluated. The material studies were based upon the knowledge that when the final material was chosen it would be susceptible to the present commercial injection moulding operation now used in industry. The basic property which influences the material selection is its impermeability to chemical warfare (CW) agents, specifically H and GB agents. The standard selected for comparison was twenty-four (24) hour protection against H-agent (dichlorodiethyl sulfide) . This standard is accepted by many countries. According to the invention, applicant has now developed a novel non-black injection mouldable synthetic rubber composition, which provides twenty-four hour protection from penetration by H-agent, comprising: SUBSTITUTE SHEET bromobutyl rubber 100.0 silica 28.0 - 31.5 fatty acid cure promoter 0.5 - 1.0 silane coupling agent (S-containing) 1.9 - 2.0 reinforcing filler 5.0 - 7.5 icrocrystalline wax 0.5 - 1.0 low-temperature plasticizer 0 - 8.0 rubber accelerator 2.5 - 3.0 process aid 0 - 2.2 alcohol phosphate 0.5 - 2.1 metal oxide curing agent 5.0 - 5.5 pigment 4 - 5 2-mercaptobenzothiazyl disulfide 0 - 1.0 sulfur 0. 0.25 diethylene glycol 0 - 3 wherein all proportions are expresse in parts by weight per one hundred parts of bromobutyl rubber (pph) . The silica employed is a nόn-dusting precipitated hydrated silica - 97.2% Si0 2 - particle size 100-300 microns, sold under the trade mark Zeosil 175. A similar material sold under the trade mark Zeosil 125 may also be employed. The purpose of this component is to maximize Modulus 500% and Tensile strength. The fatty acid cure promoter employed is preferably stearic acid, although other fatty acid cure promoters ® could also be employed, such as Octoate Z, a trademark for a mixed fatty acid cure promoter. The silane coupling agent is one which contains sulfur, such as vinyl mercaptosilane which is bifunctional polysulphide organosilane, sold under the trade mark SI-69. This component aids the silica to SUBSTITUTE SHEET achieve the required 500% Modulus, i.e. 900-1600 psi, while keeping the Permanent Set at 500% below about 12%. The reinforcing filler is a treated calcined clay- anhydrous aluminum silicate treated with a silane coupling agent. This component contributes to the optimisation of 500% Lodulus and Permanent Set at 500%. Such materials include those sold under the trade marks Burgess KE and Nucap 100. Various ester plasticizers have been employed in some formulations to provide good low temperature flexibility and improve resilience; including ® dibutylsebacate (DBS) Kodaflex . TX-IB, dicapryl phthalate, dioctyl phthalate (DOP) and dioctylazelate (DOA) . The first three have been found to be equally applicable. The microcrystalline wax employed is preferably ® ® Sunproof Canadian, although Sunproof Improved has also been employed. The metal oxide curing agent employed is zinc oxide. Other curing agents such as lead oxide (Pb3©4) could also be employed. Perhaps the most significant improvement in properties is achieved by the accelerator system employed. The most difficult problem to overcome was having raised the Modulus 500% to levels in the range of 900-1600 psi, it was found that the Permanent Set was too high. This problem was overcome by including an alcohol phosphate, which was found to lower Permanent Set at 500% to below the useful maximum of about 12%, while maintaining Modulus 500% in the range of 900-1600 psi. A suitable alcohol phosphate is sold under the trade mark Zelec NE which is a neutralized alcohol phosphate. The rubber accelerator per se is selected from Methazate, a trade mark for zinc dimethyldithiocarbamate; Tetrone A, a trade mark for dipentamethylene-thiuram SUBSTITUTE SHEET tetrasulfide; and Robac P25, also a trade mark for dipentamethylene-thiura tetrasulfide. ® A process aid (peptizing agent) such as Strucktol (an acidic fatty acid) may be used with the accelerator in amounts up to about 2.2 pph to lubricate the polymer chain and reduce power requirements of the internal mixer. Low-temperature T2 stiffening may be improved by the inclusion of a suitable plasticizer, e.g. TP-90-B, a trade mark for di(butoxy-ethoxy-ethyl) formal; and diethylene glycol. Improved adhesion to metal, e.g. aluminum inserts in gas masks may be achieved by including in the formulations MBTS (2-mercaptobenzothiazyl disulfide) and sulfur. An appropriate adhesive is employed to bind the rubber material to a surface. Chemlok 205-220 (See page 193 of Chemical Dictionary) has been found acceptable for bonding to metal surfaces. The pigments are selected to give an olive-drab colouration to the resulting material. Accordingly, the pigment composition typically comprises finely divided, BIK N-231 (Black) (0.17 pph); Yellow 2087 or 2089 (1.83 - 2.28 pph); and Green 4099 (1.65 - 2.61 pph). The results shown in the specific examples which follow illustrate the improved properties of the preferred formulations according to the invention. SUBSTITUTE SHEET EXAMPLE 1 (Lot 008 ) Bromobutyl X2 100.00 ■ 5 Stearic Acid 1.04 Zeosil 175 31.30 SI-69 1.96 10 Burgess KE 5.22 Sunproof CDN 1.04 Diethylene Glycol 2.61 TP-90-B 7.83 Black N-231 0.17 15 Green 4099 1.83 Yellow 2087 2.35 Added on Mill: 20 Zinc Oxide 5.48 Methazate 2.87 Alcohol Phosphate 0.47 164.17 25 Bromobutyl X2 is a trade name for a bromobutyl rubber material available from Polysar of Sarnia, Canada. The various properties of this material cured for about 12 minutes at about 160o C, in the form of slabs and 30 buttons, are provided in table 1 which follows. SUBSTITUTE SHEET Tftgre i SPEC. RHEOMETER (viscosity) APP. T90 4.6 DENSITY 1.14 HARDNESS O REX SHORE 46 45 ± 5 42 MIN. 1500 2173 MIN. 500% 725 900-1600 1200 11.5-18.5 13.8 TEAR STRENGTH Die "C" MIN 150 187 PERMANENT SET 500% 10/10 12% MAX 9.6 AGEING 96H/80 °C OK T.S. Δ % -15+20 -7.9 EL. Δ % ± 20 -17.2 TEAR STRENGTH Δ % - 20 MAX +11.2 HARNDESS O AΔ % 0 OZONE ASTM D518-B PASS PPHM/400°/4H 100% STIFFNESS T2 MAX. -25 PASS BAYSORE RESILIENCE 10 SUBSTITUTE Srtct ' f Physical test results on the compression moulded tensile sheets and on the facepieces, show that all the physical properties required are within the specification (SPEC) as recited in Table 1. The action of the alcohol phosphate has held the Permanent Set % below 12. This was also enhanced by the treated silicate reinforcing filler. Initially, applicant started by replacing the carbon black in the black rubber formulations as described in our co-pending Canadian application Serial No. 485,232 filed 26 June, 1985, with silica and a silane coupling agent in order to raise the modulus and tensile values. However, this deteriorates the Permanent Set to levels of 20 - 30%, as well as giving low Rheometer Modulus and extremely long raise before a rheometer plateau is reached. Having established that silane is needed to raise the Modulus to the specification levels indicated in Table 1, and that higher Modulus values create higher Permanent Set, it was necessary to determine how to lower Permanent Set without affecting Modulus. This led to the investigation of alcohol phosphate and treated silicate. We were also able to bring cure injection times down to 180 sees from a previous high of 600 sees. Physicals on the facepieces are within specification as of 240 sees. SUBSTITUTE SHEE ' EXAMPLE 2 Verifying the ef ect of the alcohol phosphate on the Permanent Set, and also comparing various precipitated silicas and treated silicates. TABLE 2 (A) (B) (C) Zinc Oxide 5.48 5.48 5.48 Accelerator additions: Al) Methazate 3.00 A2) Methazate Alcohol Phosphate A3) Methazate Alcohol Phosphate Neutralized Bl) Methazate Alcohol Phosphate B2) Methazate Alcohol Phosphate Strucktol A-60 Cl) Methazate Alcohol Phosphate SUBSTITUTE SHEET These trials indicate that once again the Modulus 500% values are just within or on the lower limit of the specification. It is also apparent that the alcohol phosphate is responsible for lowering the Permanent Set to values within lspecification, i.e. below about 12%, while maintaining the Modulus 500% in specification, i.e. 900 - 1600 psi. EXAMPLE 3 a) Continuing investigation of the effect of Alcohol Phosphate on Permanent Set, i.e. with and without. b) Investigating the effect of % volatiles on the physicals. c) Comparing Bromobutyl versus Chlorobutyl. d) Mill mixed in Lab at 70°C. e) Methazate versus Robac P 25. SUBSTITUTE SHEET (A2) Same formulation as (Al) except that Bromobutyl X2 and Zeosil 175 was heated at 100°C for 24 hours, to drive off volatiles, and mixed immediately upon removal from oven. A31 & A41 - Methazate 3.00 A32 & A42 - Robac P 25 3.00 Confirmation that there is improvement in Permanent Set of 10% points when using the alcohol phosphate neutralized. Robac P 25 shows an improvement Tensile, Modulus, lower Viscosity, higher Tear - but at a loss of 3 - 4% points in Permanent Set. The most interesting of all, were the results of the Chlorobutyl - higher modulus and especially a gain in resilience. However, one major disadvantage is the extremely slow cure rate. Accordingly, bromobutyl is preferred. SUBSTITUTE SHEET EXAMPLE 4 A study was undertaken to evaluate the adhesion problem encountered with the metal (anodized aluminum) insert in the XC4 Mask. Adhesion in the range of 40-50 lb/min. is required. Four formulations were evaluated, together with different acceleration systems. Two types of adhesives were used: a) Chemlok #205 primer followed by Chemlok #234 B b) Chemlok ® #250 Trials were made by compression moulding onto aluminum strips, which were only cold solvent degreased. The same procedure that was used on the inserts. SUBSTITUTE SHEET Bromobutyl X2 Zeosil 175 SI-69 Burgess KE Sunproof CDN Stearic Acid Diethylene Glycol TP-90-B DBS Yellow 2087 N-231 Black Yellow 2089 Green 4099 Alcohol Phosphate Acidic Zinc Oxide MBTS Sulphur Acceleration systems: Al, Bl, Cl - Methazate 3.13 A2, B2, C2 - Methazate 3.13 Tire sulphur 0.16 C3 - Methazate ' 3.13 Alkyl Phosphate Acidic 2.35 - Tetrone A 2.50 Formulations A to C exhibit a lack of adhesion to an anodized aluminum surface using one coat of Chemlok #250. A second coat improved adhesion marginally, but still remained unsatisfactory. Formulation D which contains MBTS and. sulphur was found to adhere better to aluminum surfaces. SUBSTITUTE SHEET

Claims: THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS: 1. A non-black injection mouldable synthetic rubber composition, which provides twenty-four hour protection from penetration by H-agent, comprising: bromobutyl rubber 100.0 silica 28.0 - 31.5 fatty acid cure promoter 0.5 - 1.0 silane coupling agent (S-containing) 1.9 - 2.0 reinforcing filler 5.0 - 7.5 microcrystalline wax 0.5. - 1.0 low-temperature plasticizer 0 - 2.5 rubber accelerator 2.5 - 3.0 process aid 0 - 2.2 alcohol phosphate 0.5 - 2.1 metal oxide curing agent 5.0 - 5.5 pigment 4 - 5 2-mercaptobenzothiazyl disulfide 0 - 1.0 sulfur 0 - 0.25 diethyleneglycol 0 - 3 wherein all proportions are expressed in parts by weight per one hundred parts of bromobutyl rubber (pph) . SUBSTITUT TE" °H? J ' _- 2. A rubber composition according to Claim 1, wherein the rubber accelerator is selected from the group consisting of zinc dimethyldithiocarbamate and dipentamethylene-thiuram tetrasulfide. 3. A rubber composition according to Claim 2, wherein the low temperature plasticizer is selected from the group consisting of dibutylsebacate, dicapryl phthalate, dioctyl phthalate and dioctylazelate. 4. A rubber composition according to Claim 3, wherein the alcohol phosphate is a neutralized alcohol phosphate. 5. A rubber composition according to Claim 4, wherein the fatty acid cure promoter is stearic acid. 6. A rubber composition according to Claim 5, wherein the metal oxide curing agent is zinc oxide. 7. A rubber composition according to Claim 1, 4 or 6, including as adhesion to metal promoter about 1.0 pph of MBTS and about 0.25 pph of sulfur. 8. A rubber composition according to Claim 6, wherein the pigment consists of a mixture of finely divided pigments to provide an olive-drab colouration to the resulting material. SUBSTITUTE SHEE t 9. A rubber composition according to Claim 1, consisting essentially of: Bromobuty1 rubber 100.00 Stearic Acid 1.04 Silica 31.30 Bifunctional polysulfide organo silane 1.96 Anhydrous aluminum silicate treated with a silane coupling agent 5.22 Microcrystalline wax 1.04 Diethylene Glycol 2.61 Di-butoxy-ethoxy-ethyl adipate 7.83 Black N-231 0.17 Green 4099 1.83 Yellow 2087 2.35 Zinc Oxide 5.48 Zinc dimethyldithiocarbamate. 2.87 Alcohol Phosphate 0.47 wherein all proportions are expressed in parts by weight per one hundred parts of bromobutyl rubber (pph) . SUBSTiTU i _ SHEET 10. A rubber composition according to Claim 1, consisting essentially of: Bromobutyl rubber 100.00 Stearic Acid 1.04 Silica 31.30 Bifunctional polysulfide organo silane 1.96 Anhydrous aluminum silicate treated with a silane coupling agent 5.22 Microcrystalline wax 1.04 Diethylene Glycol 2.61 Di-butoxy-ethoxy-ethyl adipate 7.83 Black N-231 0.17 Green 4099 1.83 Yellow 2087 2.35 Zinc Oxide 5.48 Zinc dimethyldithiocarbamate 3.00 Alcohol Phosphate 2.00 wherein all proportions are expressed in parts by weight per one hundred parts of bromobutyl rubber (pph) . 11. A rubber composition according to claim 10, " additionally consisting essentially of in association with the zinc dimethyl- dithiocarbamate, a fatty acid peptizing agent in an amount of 2.00, wherein all proportions are expressed in parts by weight per one hundred parts of bromobutyl rubber (pph) . SUBSTITUTE SHEET 12. A rubber composition according to Claim 1, consisting essentially of: Bromobutyl rubber 100.00 Stearic Acid 0.52 Silica 31.30 Bifunctional polysulfide organo silane 1.96 Anhydrous aluminum silicate treated with a silane coupling agent 5.22 Microcrystalline wax 1.04 Diethylene Glycol 2.61 Di-butoxy-ethoxy-ethyl adipate 7.83 Black N-231 0.17 Green 4099 1.83 Yellow 2083 2.61 Zinc Oxide 5.48 Zinc dimethyldithiocarbamate 3.00 Alcohol Phosphate 2.00 wherein all proportions are expressed in parts by weight per one hundred parts of bromobutyl rubber (pph) . SUBSTITUTE SHEET 13. A rubber composition according to Claim 1, consisting essentially of: Bromobutyl rubber 100.00 Stearic Acid 0.52 Silica 31.30 Bifunctional polysulfide organo silane 1.96 Anhydrous aluminum silicate treated with a silane coupling agent Microcrystalline wax Diethylene Glycol Di-butoxy-ethoxy-ethyl adipate Black N-231 Green 4099 Yellow 2083 Zinc Oxide Dipentamethylene-thiuram tetrasulfide Alcohol Phosphate • wherein all proportions are expressed in parts by weight per one hundred parts of bromobutyl rubber (pph) . SUBSTITUTE SHEET 14. A rubber composition according to Claim 1, consisting essentially of: Bromobutyl rubber 100.00 Stearic Acid 0.52 Silica 33.94 Bifunctional polysulfide organo silane 2.09 Anhydrous aluminum silicate treated with a silane coupling agent 3.92 Microcrystalline wax 0.78 Diethylene Glycol 2.61 Di-butoxy-ethoxy-ethyl adipate 7.83 Black N-231 0.16 Yellow 2089 2.35 Green 4099 1.65 Alcohol Phosphate 2.09 Zinc Oxide 5.48 Zinc dimethyldithiocarbamate 3.13 . wherein all proportions are expressed in parts by weight per one hundred parts of bromobutyl rubber (pph) . 15. A rubber composition according to Claim 14, additionally consisting essentially of : Sulfur 0.16 wherein all proportions are expressed in parts by weight per one hundred parts of bromobutyl rubber (pph) . SUBSTITUTE SHEET 16. A rubber composition according to Claim l, consisting essentially of: Bromobutyl rubber 100.00 Stearic Acid 1.00 Silica 28.00 Bifunctional polysulfide organo silane 2.00 Anhydrous aluminum silicate treated with a silane coupling agent 7.50 Microcrystalline wax 0.50 Diethylene Glycol 2.00 Di-butoxy-ethoxy-ethyl adipate 5.00 Dibutyl sebacate 2.50 Yellow 2087 2.28 Black N-231 0.17 Green 4099 1.65 Alcohol Phosphate 1.50 Zinc Oxide 5.00 2-mercaptobenzothiazyl disulfide 1.00 sulfur 0.25 Dipentamethylene-thiuram tetrasulfide 2.50 wherein all proportions are expressed in parts by weight per one hundred parts of bromobutyl rubber (pph) . SUBSTITUTE SHEET

Inventors: CLARK JOHN R, COLLYER JOHN C, CLARK, JOHN, R., COLLYER, JOHN, C.
Applicants: HER MAJESTY THE QUEEN AS REPRE, HER MAJESTY THE QUEEN AS REPRESENTED BY THE MINIST
Application year: 1992
Main classification: A62D5
IPC codes: A62D5, C08L23