In the previous article, we learned about the first four points to improve the bonding strength of

hot melt adhesives. Today Qingdao Sainuo will continue to show you the last four points.

5. Pressure

When bonding, apply pressure to the bonding surface to make it easier for the adhesive to fill the pits on the

surface of the adherend, and even flow into the deep holes and capillaries to reduce bonding defects. For

adhesives with lower viscosity, excessive pressure will occur The ground flows, causing lack of glue. Therefore,

pressure should be applied when the viscosity is high, which will also promote the escape of gas on the surface of

the adherend and reduce the pores in the bonding area.

6. Adhesive layer thickness

Thicker adhesive layer is easy to produce bubbles, defects and early fracture. Therefore, the adhesive layer should

be made as thin as possible to obtain higher bonding strength. In addition, the thermal expansion of the thick

adhesive layer after heating causes heat in the interface area. The stress is also greater, which is more likely to

cause joint damage.

7. Load stress

The stress acting on the actual joint is complex, including shear stress, peeling stress and alternating stress.

(1) Shear stress: due to eccentric tension, stress concentration occurs at the bonding end. In addition to the shear

force, there is also a tensile force consistent with the interface direction and a tearing force perpendicular to the

interface direction. At this time, under the action of shear stress, the greater the thickness of the adherend, the

greater the strength of the joint.

(2) Try to avoid the use of joint methods that will produce peeling stress during design.

(3) Alternating stress: The adhesive on the joint is gradually fatigued due to the alternating stress, and it breaks

under conditions much lower than the static stress value. Tough and elastic adhesives (such as certain rubbery

adhesives) have good fatigue resistance.

8. Internal stress

(1) Shrinkage stress: When the adhesive is cured, the volume shrinks due to volatilization, cooling and chemical

reactions, causing shrinkage stress. When the shrinkage force exceeds the adhesion force, the apparent bond

strength will decrease significantly.

(2) Thermal stress: At high temperatures, when the molten resin cools and solidifies, volume shrinkage will occur,

and internal stress will be generated at the interface due to bonding constraints. When there is a possibility of

slippage between molecular chains, the internal stress generated disappears. The main factors affecting thermal

stress are the coefficient of thermal expansion, the temperature difference between room temperature and Tg, and

the difference in elasticity.

Qingdao Sainuo Chemical Co.,Ltd. We are manufacturer for PE wax, PP wax, OPE wax, EVA wax, PEMA, EBS,

Zinc/ Calcium Stearate…. Our products have passed the REACH, ROHS, PAHS, FDA testing.

Sainuo rest assured wax, welcome your inquiry!

Website：https://www.sanowax.com

E-mail：sales@qdsainuo.com

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Adress：Room 2702,Block B, Suning Building, Jingkou Road, Licang District, Qingdao,China