Understanding the science behind a windshield break and crack; how a windshield is made and the resins created to fix windshields are important for anyone in the windshield repair industry to know.

This deep understanding of windshield repair chemistry will help you buy better resin and relay to your customer that you are the expert they should trust to repair their safety device. See Lab Test Results and Scores on 12 Windshield Repair Resins here.

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An  adhesive is a substance that bonds surfaces together. Resin in polymer chemistry is a liquid substance that is convertible into polymers. A polymer is a large molecule and/or many monomers.

A monomer is a small molecule that is able to bond into long chains to identical or different molecules to form a polymer. Resins are a mixtures of monomers and polymers that can be organic or synthetic compounds. The linking up of monomers is called polymerization.

Here is a polymer: 

Understanding Adhesive Resin Science

There are two basic types of adhesive bonds- mechanical and chemical.

A  chemical bond is where the adhesive (resin) has an inter-molecular interaction with the substrate (glass).

A  mechanical bond is where the adhesive bond is by force and/or by overfilling the space with adhesive and then curing or interlocking mechanically to the surface(s) all without a molecular interaction.

Interaction- the atoms of the resin interacting with the atoms of the glass which creates a chemical bond.

Adhesion - the resins adhesion or bond to the glass. Adhesive strength is the strength of the resin's bond to the glass which can be measured by a lab test. Adhesive failure is when the resin separates from the glass.

Cohesion - the resin's bond to itself. Cohesive strength is needed when there is a gap, such as with an edge crack repair. When there is a gap a higher viscosity-thicker resin will provide more cohesive strength then a low viscosity-thinner resin. Cohesive failure is when the resin pulls apart or splits apart in the middle with resin remaining on the glass.

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

Shrinkage is created by the UV acrylic free radical tight knit double-bonding and UV curing is exothermic, meaning it releases heat. When molecules or anything double bonds it shrinks the space it is taking up. Shrinkage creates residual stress within the structure (cured resin). Low viscosity resins shrinks more than high viscosity because of the mixture having more monomer than polymer (oligomer). Oligomer raises the viscosity along with the resins strength, and durability especially when there is a gap such as with an edge crack.

Wetting is when the liquid adhesive is able to maintain contact with the substrate by molecular interaction; meaning the molecules of the resin can link to the molecules of the glass. It occurs because of inter-molecular forces between the resin and the glass surface.

Wicking is the ability of a liquid (resin) to flow into the microscopic crevices and craters on the surface of the glass without the assistance of an outside force such as gravity. Wicking is very important for good adhesion. With windshield chip repair wicking is assisted by both the vacuum and pressure cycle(s) of a windshield repair injector.

UV Curing Windshield Repair Resins Basic Ingredients:

(a) Photoinitiator triggers the curing process when it is exposed to light energy of the appropriate wavelength.

(b) Monomers are components in the formulation that is near water thin and primarily impacts the degree of adhesion to the substrate (glass).

(c) Oligomers are higher i viscosity (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.

(e) Coupling Agents are a compound which provides a chemical bond between two dissimilar materials, usually an inorganic and an organic. A silane coupling agent acts as a sort of intermediary which bonds organic materials to inorganic materials. It is this characteristic that makes silane coupling agents useful for improving the mechanical strength of composite materials, for improving adhesion, and for resin modification and surface modification.