WHAT ARE THE PHYSICAL FACTORS THAT AFFECT THE PHYSICAL STRENGTH OF THE BOND?

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Double Sided PVC Foam Tape

1. When the adhesive is well infiltrating the surface of the adhered material (contact angle θ <90 °), the roughness of the surface is conducive to improving the degree of wetting of the adhesive liquid on the surface, increasing the density of the contact point between the adhesive and the adhered material, which is beneficial Improve bonding strength. Conversely, when the adhesive is impregnating the adhered material poorly (θ> 90 °), the roughness of the surface is not conducive to the improvement of the bonding strength.

2. Surface treatment:

The surface treatment before bonding is the key to successful bonding, and its purpose is to obtain a strong and durable joint. Due to the existence of a "weak boundary layer" formed by an oxide layer (such as rust), a chrome layer, a phosphating layer release agent, etc., the surface treatment of the adherend will affect the bonding strength. For example, the surface of polyethylene can be oxidized with hot chromic acid to improve the bonding strength. When heated to 70-80oC for 1-5 minutes, a good bondable surface will be obtained.This method is suitable for polyethylene plate thick-walled tubes Wait. When the polyethylene film is treated with chromic acid, it can only be carried out at room temperature. If it is carried out at the above temperature, the surface treatment of the film is treated by plasma or micro flame.

When the surface of natural rubber, styrene-butadiene rubber, nitrile rubber and neoprene rubber is treated with concentrated sulfuric acid, the rubber surface is expected to be slightly oxidized, so the sulfuric acid should be thoroughly washed off in a short time after the acid is applied. Excessive oxidation leaves more fragile structures on the rubber surface, which is not conducive to bonding.

When partially bonding the surface of the vulcanized rubber, the surface treatment removes the release agent, and it is not appropriate to use a large amount of solvent to wash, so as not to diffuse the release agent to the treatment surface and hinder the adhesion.

For the surface treatment of aluminum and aluminum alloys, it is hoped that aluminum crystals are generated on the aluminum surface, while the naturally oxidized aluminum surface is a very irregular and quite loose aluminum oxide layer, which is not conducive to bonding. Therefore, the natural alumina layer needs to be removed. However, excessive oxidation will leave a weak layer in the bonded joint.

3. Penetration:

The bonded joints are often infiltrated into some other low molecular weights due to the ambient atmosphere. For example, when the joint is in a humid environment or underwater, water molecules penetrate into the adhesive layer; the polymer adhesive layer is in an organic solvent, and solvent molecules penetrate into the polymer. The penetration of low molecules first deforms the adhesive layer and then enters the interface between the adhesive layer and the adherend. The strength of the adhesive layer is reduced, resulting in the destruction of the bond.

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