What are hot melt adhesives used in?

- Dec 16, 2019-

EVA hot melt adhesive bonding is widely applicable, such as PA (polypropylene), PA (polyethylene) and other non-polar materials, can also achieve a better bonding effect.

The rubber layer has good resistance to low temperature, water and moisture.

Due to the poor rigidity of EVA, compared with polyester and polyamide hot melt adhesive, the softening point is relatively low, and its global softening point is around 100*C, so its use scope is limited.

The basic components of EVA hot melt adhesive are EVA resin, adhesive resin, wax and stabilizer.

EVA resin is a short branched chain composed of polar acetic acid gene introduced into the ethylene branched chain, disrupting the original crystallization state, leading to EVA tending to "plasticizing effect", reducing the crystallinity of ethylene on the branched chain, increasing the distance between polymer chains, making EVA resin more flexible and elastic.

VA content in EVA resin can range from low to high percentage.

Therefore, the percentage of VA and MI (melting index, reflecting molecular weight) in the resin are the most important factors that directly determine and influence the properties of EVA.

Generally, the content of VA is high, the adhesive force rises, the wettability of the adhesive material is good, the curing time is slow, the heat resistance decreases.

High melt index, indicating low molecular weight, colloidal viscosity, wettability, good heat resistance, viscosity is unchanged.

Compared with EEA (ethylene-ethyl acrylate), EAA (ethylene-propylene ester) and EMA (methyl propylene ester ethyl ester), EVA has a higher tensile breaking strength in ethylene-matrix copolymer, which varies with the content of VA.

If the MI of EVA is different, the rupture tensile strength changes more.

The tensile strength at the yield point of EVA decreases with the increase of VA content. If the VA content is above 25%, it becomes very small.

The bending rigidity of EVA is equal to that of soft PVC, which decreases with the increase of VA, while the bending rigidity decreases with the increase of MI.

EVA resin has a good coordination, it can be mixed with other kinds of resin, in order to improve physical properties.

Such as EVA resin mixed with nitric acid fiber, so that the nitric acid fiber has excellent flexural resistance, friction resistance and thermal bonding.

Adding 5%~10% EVA to rigid PVC improves fluidity and impact resistance.

EVA was mixed with polyamide resin to develop good bending resistance and pigmentation at low temperature.

The viscous resin includes rosin, rosin ester, polyterpene resin, low molecular weight polystyrene and C5, C9 olefine resin.

The thermal stability of viscosifying resin should be paid attention to. Generally, olefin resin is better than rosin derivative.

But rosin derivatives can provide good adhesive strength.

Common waxes are paraffin wax, microcrystalline wax, synthetic wax, low molecular weight polyethylene, etc.

In EVA hot melt adhesive, the role of wax is to reduce viscosity, improve wettability, reduce curing time, and reduce cost.

But it causes brittleness and reduces adhesion.

The dosage in the formula should be careful, the effect of microcrystalline wax on the adhesive force is minimal compared with other waxes.

Synthetic wax is better than microcrystalline wax and paraffin wax in improving the heat resistance and reducing the cost of glue.