What factors affect the viscosity of pur hot melt adhesive?

2021/08/06

    The principle of cooling and solidification of pur hot melt adhesive is that the heated pur hot melt adhesive will have an irreversible chemical reaction with moisture in the air, and the pur hot melt adhesive after solidification will not be affected by high temperature, low temperature, and other environments. Pur hot melt adhesive In fact, it penetrates into the object to be bonded and combines with its molecular structure to destroy the surface layer of the object, thereby firmly bonding the two objects. So what can we use to change the stickiness of pur hot melt adhesive?

 

1. Surface treatment

The surface of many objects is often covered by a layer of oxide, phosphating layer or mold release agent, etc. to form a "weak boundary layer", which will directly affect the bonding strength, so it is best to put the surface of these objects before bonding. The oxide layer, etc. is treated first to improve the bonding strength.

 

2. Improve surface roughness

The surface of the adherend is too smooth, and the pur hot melt adhesive can penetrate less molecules, thereby reducing the bonding strength. The roughening process of the surface of the object can also affect the adhesion. Therefore, we can also increase the bonding strength of the hot melt adhesive by increasing the roughness of the surface of the bonded object.

 

3. Adhesive layer thickness

Pur hot-melt adhesive bonding does not mean that the more glue you use, the stronger the adhesion. The thicker the glue layer is easy to produce bubbles, which will cause defects or early fractures, so we try our best to glue The thickness is thinner, so that a higher bonding strength can be obtained. In addition, the thermal expansion of the thick adhesive layer after heating makes the thermal stress caused by the bonding surface relatively large, and it is difficult to achieve the molecular damage on the surface of the bonding site, and the bonding will not be firm.

 4. pressure

Glue on the surface of the bonded object, and apply pressure to the two bonded objects in time, so that the pur hot melt adhesive fills the holes on the surface of the bonded body, and even flows into the deep holes and capillaries to reduce bonding defects. Therefore, properly apply pressure during bonding. It can also promote the escape of gas on the surface of the bonded object, reduce the bonding area of the hole, and increase the bonding firmness.