Norland Blocking Adhesive NBA 108

Introduction

NBA 108 is a single component, UV curing adhesive used for temporary bonding of lenses to metal polishing mounts or where bonded components need to be easily separated in the future. The adhesive cures in minutes at room temperature by exposure to longwave UV light and eliminates the heat induced strain typical of the old fashioned hot pitch blocking methods. 

NBA 108 is specifically formulated to provide low shrinkage and low strain to further minimize any potential strain on the lens during the blocking process. This blocking adhesive is formulated to be used with polishing processes that use large amounts of liquid or use heavy grinding.  Debonding is accomplished by soaking parts in acetone. The adhesive cures only by exposure to UV light in the range of 350 to 380 nanometers. The adhesive needs to be exposed to 6 joules/cm squared of UV energy to be fully cured.

Recommended light sources include mercury lamps, sun lamps, fluorescent black lights and xenon lamps. Norland Products sells a variety of light sources optimized for curing our adhesive. Cure times are typically in the 1 to 5 minute range depending on intensity of UV light and distance away from surface. Lenses typically separate after soaking in acetone for 10 to 60 minutes.

Debonding time is a function of surface area. Plano surfaces will require more time than surfaces with only slight edge contact, therefore annular ring designs of the mounting block are most efficient. Relief grooves or slots in the metal block may also be used for promoting the deblocking process by allowing the solution to come in contact with more of the adhesive. Lenses may also be debonded

by heating between 80 and 100° C. After separation, the components and tools are cleaned in the detergent/water solution. Shelf life of the liquid is at least 6 months at room temperature if stored in the original container away from UV light. Prolonged skin contact should be avoided and affected areas should be washed with soap and water. Avoid prolonged vapor inhalation and use in a well ventilated area.

Typical Properties of NBA 108 

Solids :                     100%

Viscosity at 25° C:     550cps

Refractive Index
of Cured Polymer:     1.51

Elongation at Failure 18%  

Modulus (psi)            710               

Tensile Strength (psi) 101               

Hardness - Shore D:    25