Contam ination insensitive UV curable adhesives RUSS CROOK'·· and DIANE GU ILFOYLE' Agerr Syst~ms. 9999 Hamilton Boult\·ard. Brtlnlgsvllle. PA 180Jf...9JS9 :Corning !rte.. SP·PR~OI. Corning. NY I
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Surface Treatment Figure 4. Effect of the use of siloxane primers on the average lap shear strength on 304 Stainless Steel adherends.
to heavily contaminated surfaces have been successful. A 161% increase in the average lap shear strength was measured by using 50% (wt/wt) siloxane resin A and a proprietary component-S used as a toughener. Figure 5 shows data that the new formulation not only enhances the average lap shear strength, but the contamination insensitivity of the adhesive joint is also preserved. Since component 8 acts as a toughening component to the siloxane based formulations, the effect of contamination level on lap shear strength is not statistically distinguishable for concentrations of the siloxane based resin A below 50 pph. However, as the concentration of resin A is increased to 75 pph (the brittle siloxane component), the average lap shear strength becomes statistically dependent on the level of silicone surface contamination. Addition of component 8 to the formulation has significantly enhanced the average lap shear strength of the contamination insensitive formulations. Highest average lap shear strength and insensitivity to surface contamination was observed when the si loxane resin was blended at 50 pph (wt/wt) with the toughening epoxy resin. The adhesive formu lation MCG-47 is superior to most UV curable (e.g. Chipshield 2400) and many two-part (e.g. Epotek 353ND) structural adhesives on clean surfaces. Both Chipshield 2400 and Epotek 353ND have been shown to be extremely sensitive to 2 silicone surface contamination allowing no more than 0.047 mg/cm before physically falling apart when removed from the bonding fixture.
