It All Starts With the Base
A glue manufacturer will make a hot melt adhesive by starting with one base material. The usual base materials are ethylene-vinyl acetates (EVA), polyolefins (PO), polyamides (PA), polyurethanes (PUR), and styrene block copolymeres. This base material will be formulated in a way that makes it have a glass transition temperature that is below the lowest service temperature but with an appropriately high melt temperature. The key to the whole thing is the high melt temperature properties, it is what makes a hot melt adhesive what it is. The next consideration is the crystallization rate. A faster rate will usually make for a higher bond strength.
Blending the Additive Ingredients
The next set of ingredients are the additives that are blended with the base material. The ones that are commonly used include tackifying resins, waxes, plasticizers, antioxidants, UV stabilizers, pigments and dyes, glitter, biocides, flame retardants, anti-static agents, and fillers to add bulk to the product with the goal of reducing costs while improving the strength of cohesion. Fillers can also have altering properties if the following are used: calcium carbonate, talc, carbon black, barium sulphate, and clays like kaolin.
Customizing the Formulations
As you can see from the list of materials above, there are more combinations and variations available than could ever be covered in any one article. The basic principles are those two categories of materials and what quantities they are combined in. What glue manufacturers will be trying to do is make a hot melt adhesive with those materials that has the appropriate open time, setting time, melt viscosity, bond formation temperature, pot life stability, and level of tack or adhesion that allows the hot melt to be used in the desired fashion. A good glue manufacturing company will have formulas prepared for every eventuality and task.
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