In 1995 I evaluated several UV adhesives for bonding to soda-lime float 'window' glass, and environmental resistance. This report summarizes my testing results with 'Norland Optical Adhesive 61' manufactured by Norland Products, Inc., 2540 Route 130, Suite 100, P.O. Box 637, Cranbury NJ 08512; (609) 395-1966, FAX (609) 395-9006. Contact Norland directly for current pricing and availability information.
Norland describes '61' as a proprietary mercapto-ester that's tough (slightly flexible), providing excellent adhesion to glass and metal, and fair adhesion to plastic. Clear; refractive index = 1.56; >90% transmission from 0.4 to 2.5 microns. Preferred adhesive for precision optical bonding. Low shrinkage and resiliancy of adhesive minimizes strain. Used for optics exposed to temperature extremes (can withstand -150 to +125o C). Shelf life is 4 months (store at 5-22o C). Environmental resistance was empirically estimated by accelerated age-testing. This consisted of several samples, each exposed to various conditions for various times of up to one week: 100o C dry, 90o C water, 20o C water pH=6 (tap water), 20o C water pH=11 (NaOH), 20o C water pH=3 (HCl). Weight loss/gain for all samples was nil. 'Clouding' of all samples was nil. The 20o C water pH=6 (tap water) samples were tossed into the strainer bowl of my shop sink and after two years they showed no sign of clouding although they did eventually begin to turn a slight straw color. Strain seen as birefringence in a polariscope was 'satisfactory'.'61' is supplied in a nice syringe with a very satisfactory reusable cap. It's 'water thin' when first applied, but a short (5 sec) uv exposure (pre-cure) with a battery operated UV-lamp results in a slight thickening which allows minor adjustments to be made. Final UV cure (like setting in the sun for an hour, or 10 min. with a 'germicidal' UV Hg lamp followed by 'ageing' (which occurs over about 1 week, but can be greatly accelerated with heat: overnight at 50o C works well) yields the final bond. Two issues of concern were oxygen inhibition and bubble formation during polymerization. These are both a problem with many UV adhesives, but not with '61'. Oxygen inhibition yields an 'uncurable' sticky surface when unpolymerized adhesive is exposed to air. Bubble formation is typically due to contraction during polymerization and solvent trapping. '61' is a single-component, 100% solids, solvent-free material and cures bubble-free. Outgassing in vacuum was not measured.
Excess adhesive may be cleaned-up with acetone or alcohol after the pre-cure. Fully cured parts can be separated by soaking in acetone for up to several days. This can be done relatively safely in a coffee can with a sheet of glass for a lid.
Last edited 02-18-03