07/15/2024
Viscosity – Does it Matter?
Adhesive Chemistry- UV Acrylic adhesives are comprised of three primary components: (1) Photoinitiator, (2) Monomer, and (3) Oligomer (resin). The photoinitiator triggers the curing process when it is exposed to light energy of the appropriate wavelength. The Monomer component in the formulation is near water thin and primarily impacts the degree of adhesion to the substrate (glass). The Oligomer is thicker and provides most of the post-cure mechanical properties such as strength, hardness, elongation, elasticity, shrinkage control, cohesion, durability and bond to the PVB etc. An oligomer is a custom-made intermediate molecule that turns into a polymer, also called a giant molecule upon curing. Oligomer is much thicker than monomers and increases viscosity. The higher the viscosity the higher the oligomer content. OLIGOMER content should be your priority with chips and cracks.
FLOW - Centipoise (CPS) is the rate of flow of a liquid. The lower the CPS number, the faster the rate of flow - water for example is zero. But the lower the CPS, the lower the oligomer content, along with lower strength and its ability to withstand stress without yielding. So, what does this mean to windshield repairing- The higher the viscosity the stronger the resin. This is true of all adhesives. Krazy Glue / Super Glue for example are acrylic adhesives. They have Regular water thin glue and Extra Strength Gell- written right on the tube and package. Windshield chip resins lower than 40 cps are mostly all monomer and do not have enough oligomer to restore the windshield to 100% new laminated glass strength or meet the insurance policy requirement to the consumer of pre-loss condition in most repair systems. A repair system consists of the (1) resin, (2) tool-injector (3) tool-holding structure, (4) methods to fill, such as flexing, (5) curing method CUP or no CUP, (6) curing light intensity and (7) curing light uniformity. Each of which affects the outcome.
If you have FLOW as your priority to fill stone-breaks, then you have an outdated tool. (1) An injector with sufficient vacuum and pressure will force the wicking and deeper wetting into the glass with thicker resins-more oligomer. That happens more efficiently with an O-ring sealed piston because they have more vacuum and more pressure to inject thicker resins. (2) If you must manually flex legs with a 15cps, 18cps or 20 cps resin you are fighting your tools holding structure. If you must pull out the piston and stick a probe down onto the impact point to flex (apply compression) the break open or remove air bubbles, that is your holding structure not suppling flex/compression on the break but causing tension instead of pure compression to the break area (pulling up on the glass). This comes from your holding structure’s shape, suction cup durometer (stiffness), suction cup size and suction cup placement.
At our shop we repair chips with 50-100 cps resin all with ROLAGS or ASTM D790 tests scores of 110%, 115% and 136% new laminated glass strength. I have not had to flex a leg since I made the First Flexing Bridge ever made in 2017 - the Wonder Bar Bridge. My technician Brian does the same and reports 95% less manually flexing as does other users.
OLIGOMER should be your priority with chips and cracks, not FLOW.
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