What is a mix ratio?
The mix ratio of 2 part epoxy adhesive is used to determine the amount of resin and catalyst needed to achieve the listed properties of the epoxy.
2 part epoxy adhesives are often supplied in a dual cartridge with the appropriate mix nozzle to ensure the correct mix ratio and that sufficient mixing occurs simply by dispensing through the nozzle. For many, this method of dispensing is ideal as it eliminates concerns related to the correct ratio and to adequate mixing.
In some situations very small amounts of epoxy are required and the nozzles are not cost effective. In these cases you may prefer measuring and mixing by hand.
Mixing 2 part epoxy by hand?
Choosing Meter Mix Dispense Equipment
In other applications the dual cartridges are impractical due to large quantities used. Dispensing equipment can be used to assure the correct mix ratio, then the adhesive is dispensed through a static mix tip.
NOTE: There are many different varieties of static mix nozzles. It is important to use the one specified by the manufacturer to ensure proper mixing occurs. The number of elements in the nozzle dictate the number of stirs the adhesive gets while passing. Nozzles can range from say 24 to 56 elements so the nozzle with 24 elements only stirs the adhesive 24 times – the one with 56 has more than double the amount of stirs.
How exact does this ratio need to be?
Regardless of how you get there, weighing or measuring, aim for as close to 100% accuracy as possible. To achieve the results stated on the data sheet, you want the mix ratio to be spot on and ensure complete mixing. Although formulations and sensitivities to specific epoxy features may vary, it’s best to control the mix ratio within no more than +/- 5%. If you don’t maintain an accurate mix ratio and thorough mixing; bond strength, chemical resistance, and Tg can decrease whilst outgassing will increase due to un-reacted epoxy ingredients.
1:1 mix ratio 2 part epoxy adhesives are less sensitive to exact ratio than 10:1 mix ratio epoxies.
When is it Ok to disregard the mix ratio?
Unless your mother insists or you are under advice of the epoxy manufacturer, stick to the stated ratio on the technical data sheet. (If your mother insists, I’d still ask a chemist at the manufacturer.) Altering mix ratio will affect curing: you may have a soft cure or no cure or slower cure or a very fast cure that could create heat (exotherm) and it will affect the final properties.
The epoxy manufacturer may suggest altering the stated mix ratio for your application to achieve different results. Your results won’t match those listed on the technical datasheet but they may be better for your application. Manufacturers know how to dial in these ratios to affect pot life, cure speed, hardness, and adhesion.
For more tips on implementing a 2 part epoxy epoxy process, contact Permabond.