“I see that Dymax has just introduced a new line of equipment that cures at 405 nm. Are there any benefits to curing in the visible light range?”
Earlier this year Dymax released two new curing systems, the BlueWave® LED DX-1000 VisiCure™ Spot/Flood Lamp and the BlueWave® LED VisiCure™ Spot Lamp, along with a line of LED needle bonders that cure in the visible light range. These new VisiCure™ light-curing systems use LEDs that produce visible light energy in a relatively narrow wavelength band, as contrasted to a typical broad band, high-pressure UV bulb. These systems offer all the traditional benefits of LED-curing such as cooler curing temperatures, longer bulb life, and less energy consumption with the added benefit of curing in the visible portion of the spectrum. The main benefit of curing with visible light is that it can cure adhesives through UV-blocking substrates and select translucent colored materials. Increased safety is another important benefit of visible light-curing systems. With visible light output, UV-related shielding and protective equipment can be minimized. As with any process, testing must be done to ensure acceptable results. For further information, please contact Dymax Application Engineering.
"In my application I have a process where I apply UV adhesive between two pieces of plastic and I am seeing a short contraction period followed by a longer expansion period. Is it possible for UV adhesive to behave this way? How much does UV adhesive shrink during cure? Could this cause a pulling force between two plastic materials? If under an opposite force could the UV adhesive relax and expand somewhat?"
When light-curable adhesives cure, whether curing with UV light or visible light, crosslinks are forming between polymer chains. This pulls the chemical chains closer to each other very rapidly. We typically see a 1-2% linear shrinkage, which could translate into a 2-5% volumetric shrinkage. This may stress some plastics or optical components. There is a relaxation effect, usually over the next few hours or overnight, where the chains relax slightly as they rotate into an optimum alignment. In the spirit of valentine’s day – polymer chains like to spoon together and snuggle. If they are at odd angles to each other, they are still touching, but want to find that alignment where they are in the same direction and bending the same way. Chemical bonds can stretch and spin around their axes and allow for this relaxation. Also good to note, a product with a low modulus will stretch easier under stress, and a product with a very high modulus will not stretch much at all. A silicone (on one extreme) can have a modulus as low as 300 psi, whereas an epoxy can have a modulus as high as 2,000,000 psi. Many UV-curable adhesives are urethane acrylates and can vary in their modulus’ over a very wide range. The product data sheet should list this value.
Adhesives, Medical, Structural