A fast drying one component bonding agent for cast PU elastomers and TPUs Cilbond 48

Transcription

1 A fast drying one component bonding agent f cast PU elastomers and TPUs Cilbond 48 Auths: Aissa Benarous, Technical Sales Direct Representing: Chemical Innovations Limited, Preston PR5 8AQ, England Due to increased demands from the polyurethane market wldwide with regard to the need f a versatile bonding agent, Chemical Innovations Ltd.,UK has developed Cilbond 48. Cilbond 48 is a one- component bonding system that can be used f the bonding of hot and cold cure PU elastomers as well as TPU s to a complete range of metals used f bonded components. The product will also bond cast elastomer PU and TPU s to epoxies, fibreglass reinfced plastics, polyamides and engineering thermoplastics such as PBT, PET, PPS, PPO, PEEK and PES. This new bonding agent does not require mixing with a curative and is suitable f use in a wide range of applications and offers excellent resistance to challenging environmental conditions and casting process parameters. In terms of environmental resistance, Cilbond 48 exhibits excellent heat resistance, salt spray resistance, boiling water resistance and resistance to oils, fuels and brake fluids. Series of tests have demonstrated the resistance of this new PU bonding agent to heat, boiling water and salt spray. The following paper presents these results and provides useful comparative data f processs of PU cast elastomers. Introduction Typical properties of this new bonding agent are provided below in Table 1. Fmulated using a fast drying solvent system, Cilbond 48 exhibits excellent application properties during the coating of many metal and plastic substrates. Me imptantly, f those metal plastic surfaces which have not gone through a methodic and though preparation and cleaning process, Cilbond 48 still exhibits strong substrate adhesion. In particular, this bonding agent is especially suitable f use where heat resistance and/ hydrolytic stability is imptant; exhibiting no failure in the cement to metal bond. End applications f this product include rollers f the paper and textile industry, solid tyres, carriage wheels, automotive bushes and suspension mounts,dunnage and any application where an engineering bond between a polyurethane elastomer and a metal plastic substrate is required. This bonding agent should also be considered f bonding PU s to a range of RFL (rescinol fmaldehyde latex) treated and untreated fabrics and cds including polyamide, Aramid, polyester and carbon fibre as used in hose and belt construction. In terms of polyurethane cast elastomers, Cilbond 48 adheres to a wide range of polyurethane systems, be it one, two three component systems. It bonds RTV (room temperature vulcanised ) polyurethanes at low temperatures of around 20 C as well as other cast polyurethanes with vulcanisation temperatures ranging between 20 C C. It also bonds various TPUs with casting temperatures of up to 230 C. Furtherme, it successfully bonds Vulkollan/NDI systems.

2 Although this bonding agent has excellent pre- bake resistance, f example 16 hours at 130 C, in many applications it can perfm without the need of a pre- bake, leading to much quicker production times. Property Table 1 Typical Physical Properties of Cilbond 48 Perfmance Appearance Viscosity no 3 Zahn 26 C Viscosity Din 26 C Non volatile solids Specific gravity@ 26C Flash Point ( Abel Pensky) Moulding Temperature Range Optimium Dry Coating Thickness Typical coverage at 25 micron dry coating thickness Shelf life Colourless liquid seconds 25 seconds 21.5% by weight C C ( cast elastomers) C (TPUs) 25micron f max adhesion & crosion resistance 15 sq m/l 12 months from date of manufacture Metal Surface Preparation To be most effective, Cilbond 48 must be applied to carefully prepared surfaces, which have been grit blasted with clean, filtered ( micron) sharp alumina sharp chilled iron grit and degreased with a solvent. Good metal preparation is vital if the environment is to be continually wet, such as f sub- sea applications. Most engineering plastics can be grit blasted, but it may be necessary to used finer grit and a lower air presure to prevent plastic flow and fibrilation. Experimental preparation Mild steel ASTM D429 test pieces were prepared accding to CIL test method 32a by MEK(methyl ethyl ketone) degreasing, micron sharp chilled iron grit blasting and then MEK degreasing. To compare the perfmance of Cilbond 48 with existing bonding agents that are specifically fmulated f use with either hot cold cure elastomers, the following bonding agent systems were spatula/knife coated onto the steel test pieces to give a recommended dried thickness of ca. 25 microns. Each coat was left to dry f at least 90 minutes. Cilbond 49SF is a bonding agent fmulated f use with hot cast elastomers and f the toughest of applications requires mixing with a curative such as Cilcure B either at 5-10%. Cilbond 41 is a bonding agent fmulated f use with cold cure elastomers and also requires the use of an added curative such as Cilcure B at 5% f the toughest applications. Cilbond 48 is a one component system that does not require a curing agent f virtually all applications. The results f these systems are presented f salt spray resistance, boiling water and dry heat resistance of the bonds. In those extremely rare conditions when it is required to achieve even higher resistance to aggressive environmental conditions such as salt

3 spray and boiling water, Cilbond 48 can be used with a curative, such as Cilcure B at 100:5 mix ratio. Bonding systems tested: Cilbond 41 Cilbond 41+Cilcure B at 100:5 mix ratio Cilbond 45SF Cilbond 48 Cilbond 49SF Cilbond 49SF + Cilcure B at 100:10 mix ratio When casting with hot cure TDI prepolymer /Ethacure 300 systems with hot cure quasi MDI systems, all coated bars were dried and then pre- baked f 105 C except CB49SF + Cilcure B which was given C. All PU s were cast using standard mix ratio and conditions, and left f 24 hours at room temperature. F Cilbond 41+B and some of the Cilbond 48 specimens, the PU cast elastomer used was a cold cure system Cilcast100 + Cilcure B. These were given no pre- bake. Half of the test pieces were stressed by directly exposing the bond line to the environmental conditions. This was achieved by tying the tail of the PU back over on itself and making it secure with a plastic tie- wrap. Salt spray testing consisted of placing both unstressed and stressed pieces into the salt spray cabinet. Each bar was checked every 24 hours f signs of failure. The test conditions were set to meet those of DIN EN ISO 9227:2006/10, 35 C with 5% salt solution. The test was run f 700 hours. Boiling water testing was conducted by placing both unstressed and stressed pieces into a hot water bath set at 99 C. Each piece was fully submerged at all times and checked every 24 hours f signs of failure. The test was run f 500 hours. Heat resistance tests were conducted by checking at which temperature, moulded peel test specimens showed signs of bond failure, either CM (cement to metal) RC (rubber (PU) to cement) fail. Results The following table presents the test results f the various combinations of materials and the time taken to reach bond failure. Hours to failure represents the time at which the test pieces were deemed to be no longer bonded to an acceptable level.

4 Table 2. Properties of the CIL PU bonding systems. Recommended System Bonding Temperature Range Salt- Spray Cilbond C 400 hours Cilbond 41 + Cilcure B (mixed at 100:5) C (plus limited use up to 180 C) Cilbond 45SF C 400 hours Pre- bake 2 95ºC 700 hours 1 105ºC ºC Boiling Water Creep Impact Bond Heat 300 hours Good Good 120ºC >>400 hours (#) Excellent Fair 140ºC ºC Cilbond C 700 hours 400 hours Excellent Very Good 150ºC ºC Cilbond 49SF C 500 hours 350 hours Very Good Excellent 130 C Cilbond 49SF + Cilcure B (mixed at 100:10) C 700 hours ºC Main Application Areas Cold cast PU, quasi prepolymers, sprayable systems, foams generally. Cold cast PU, quasi prepolymers, sprayable systems, foams generally. Improved adhesion to FBE, etc. Excellent f rotational casting of large rollers, where there is no heat input. 300 hours Good Excellent 130ºC High temperature bonding of all hot cast PU types and TPU. 500 hours Excellent Very Good 180 C Cold cast, all quasi prepolymers, Vulkollan, all hot- cure prepolymer types. High temperature bonding to hot cast PU types such as Adiprene, Vibrathane and Vulkollan and TPU where hydrolysis resistance is required. High temperature resistance and good solvent resistance. Best system f rotational casting of small to medium sized rollers. Comments Very fast amine PU cures may be difficult to bond. Limited open time. Bonds fast- cure amines. Bonds PVC, CR, CSM & some NBR compounds. F best perfmance Cilbond 45SF must be pre- baked The most versatile one- component system. Fast- drying and wks with without pre- bakes. F best perfmance Cilbond 49SF must be pre- baked. F better pre- bake resistance and longer stage of coated metals, use a cover- coat of Cilbond 49SF. Note: Very little difference was observed between stressed and unstressed parts using the above procedures, so the results apply to both. (#) The cold cast PU s fail befe the Cilbond 41+Cilcure B. Adiprene and Vibrathane are registered trademark of Chemtura Cp. Vulkollan is a registered trademark of Bayer AG.

5 Conclusions. 1. Cilbond 48 proved to be the most versatile one- component bonding system, bonding all types of PU s, from cold cure to hot cast prepolymers and TPU s. 2. Cilbond 49SF + Cilcure B gave the best salt spray and boiling water resistance on high perfmance polyether prepolymers cured with likes of Ethacure Both Cilbond 41 + Cilcure B and Cilbond 48 gave excellent salt spray and boiling water resistance with Cilcast Cilcure B, though Cilbond 48 showed slightly less cement- metal failure after the salt spray test. Recommendations Based on a whole range of tests, including the test results presented above, CIL recommends the following bonding agents to achieve the best perfmance f range of requirements. Bonding System CB48 CB49SF CB45SF CB49SF + B (100:10) Table 3. Summary of PU bonding recommendations. Salt PU types bonded Boiling Spray Water ( Hours ) ( Hours) All PU system types and processes, except on- site cold cast PU s at <<20º C Hot prepolymer systems Hot quasi systems Vulkollan TPU All systems used with 49SF plus warm rotational cast systems heat resistance of bonds ºC 130 ºC 130 ºC ºC CB41 All cold cast systems 300 (RTV PU) 400 (RTV PU) 120ºC CB41 + B (100:5) All cold cast systems and especially large rotational cast rollers and pipes, etc >400 (RTV PU) (RTV PU) 140 ºC CIL recommends that this infmation is used as a guide only and each customer application should be validated. Aissa Benarous Technical Sales Direct Chemical Innovations Ltd