Cure Times of Norland Optical Adhesive


When bonding lenses with Norland Optical Adhesive the minimum full cure is estimated at 20 times the precure time using the same intensity of ultraviolet light. This is a general statement that works well in most applications.

The precure time is defined as the time it takes to initially set or gel the adhesive so that the two surfaces being bonded can no longer be moved. For example, a 15 second precure requires 5 minutes (15 sec. x 20) for minimum full cure. When different light sources are used in production for the precure and the full cure, the precure time used in this calculation must be measured using the full cure light source.

 

Factors to remember which affect the precure time are:

1. Intensity and distance of ultraviolet

    light source from surface.

2. Thickness and transmission of lens.

3. Thickness of adhesive in bondline.

4. Cure rate of adhesive.

 

Varying one or more of these can change the cure time.  Further understanding of the cure can be had from Fig.1 which illustrates the relation between the cure rate or crosslinking and the exposure time. Note that the curve is asymtotic and as the exposure time progresses the amount of crosslinking approaches 100% but theoretically never reaches it. The time chosen for minimum full cure is approximately 99.5% cross linked and for efficient production is enough for most applications exposure time.  Further exposure will bring no noticeable increase in adhesion but the additional crosslinking will lower the moisture and solvent absorption. Since the absorption of even a small amount of moisture can cause separations at the edges we recommend 4 to 8 time the minimum full cure if lenses are to be subjected to high humidity for extended periods of time.

 

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