Softening Point vs. Adhesion

Solvents in the adhesive evaporating.

You are not giving enough information; i.e., application, type of UV adhesive nor type of polymer substrate.

It appears that you may be doing a destructive test to determine the separation of the two components. If this is not the case then you are using the wrong base polymer if what you are doing is an environmental test. The base polymer must be able to withstand the heat by itself but you are stating that it doesn't, therefore, you may not have the correct polymer. If this is not the case then why must it pass "a heat test that is at the softening point of the polymer."

Environmental tests are developed to accelerate aging in real life situations but can not exceed recommended use temperatures of the product.

Now, I just thought of something else. Presuming that adhesion is taking place in all areas of the laminate except the edge, like you said, then I would presume that something happened to that edge that is affecting its molecular weight. If this is the case then the edge has lost some of its properties which could affect the necessary cohesive forces to have a successful bond. Many factors could cause this, excessive heat prior to bonding; i.e., cutting edge of laminate with a saw and then using a flame to clean rough edge, etc. (not enough information given). Try cutting a section of the laminate yourself, clean edge with a blade and then use your UV bonding and heat test. What happens? Is the heat applied at 90 degress to the laminate or at an angle that would hit the edge too?

There are a lot of unknowns to successfully troubleshoot this problem without guessing.

Polarizer window, urethane UV adhesive, waterjet cutting of finished laminate to size. Because of optical properties I can't change the polymer that is causing the trouble: cellulose diacetate retarder. Customer states that laminate must tolerate 4 hrs in 70C oven without delaminating. Yes, I know that cell. diacetate can absorb ~5% water with prolonged exposure. Could the uv cured adhesive also absorb water during waterjet cutting (short exposure time) and with heat, release it as water vapor causing the edge de-lamination?

The best thing for you to do is to contact the material supplier for the laminate and the supplier for the UV adhesive. Have them help you resolve the issues.

This is one supplier that you can contact to discuss your application and testing methods.

http://www.dymax.com/products/plastic/plastic_substrate_selector.php

It seems very odd that a test for a product would be developed at a level that starts to exceed the intended use properties of the materials used. As a supplier you can't afford to make rejects and may also have an obligation to educate the customer. Do your homework and ask the experts, as noted above. Let me know what you find out.