PVC band is also a problem that often occurs in the coating production process.
Problem: PVC cracking often occurs on the four-door and two-cover thin seal strips, and there are many vertical cracks (as shown in Figure 2). There are many reasons for PVC cracking, PVC material elongation at break, PVC coating. Thickness, amount of hemmed glue and hemming bite force will all have an effect.
Reason: If the tensile strength of PVC material is not enough, it will lead to PVC cracking. Generally, the elongation at break of PVC glue is between 100% and 140%, and the PVC rubber with elongation at break <100% is easy to crack. Low PVC glue is also easy to crack.
Protection method: The amount of glue on the body flange also needs attention. The inner and outer plates of the four doors and two covers will expand due to thermal expansion and contraction when heated in the drying room. When the amount of the folded edge is insufficient, the outer plate is opened outward. Producing a large tensile force, if it exceeds the tensile limit of PVC glue, PVC glue will fold the bite force is also an important factor. The PVC glue on the upper part of the folding edge of a certain model is often cracked. The occlusal biting force is too high, the measured value is 3.1mm, and the hem biting force is required to be (2.4±0.3)mm. After the hem biting force is reduced to 2.4mm, the PVC cracking problem is solved.