There are several reasons why PTFE is difficult to adhere: First, the surface energy is low, and the critical surface tension is generally only 31 to 34 dyne/cm. Due to the low surface energy and large contact angle, the adhesive cannot fully wet PTFE, which can not adhere well to PTFE; Second, the crystallinity is large, the chemical stability is good, and the swelling and dissolution of PTFE are both To be more difficult than non-crystalline polymers, when the adhesive is coated on the surface of PTFE, it is difficult for the polymer chains to spread and entangle with each other in the chain domain, and no strong adhesion force can be formed. Third, the PTFE structure Highly symmetrical, it is also a nonpolar polymer. The adhesion of the adhesive to the PTFE surface is caused by the van der Waals force (intermolecular force). Van der Waals force includes orientation force, inducing force, and dispersive force. The surface of the non-polar high-molecular material does not have the conditions for forming the orientation force and the inducing force, but can only form a weaker dispersion force, and thus the adhesion performance is poor.
Based on the above understanding, in general, in order to solve the problem of difficult adhesion of PTFE, people mainly proceed from the surface modification and the synthesis of new adhesives.
▲ Surface treatment method
◆ Sodium-naphthalene complex chemical treatment
◆ High temperature melting method
◆ Radiation grafting
◆ Low temperature plasma technology
◆ Laser processing method (additive manufacturing method, material modification, micro laser laser activation, electroless copper plating)