solutions t page 15 tested in the tension plane. Shear force is the force applied when substrates in a bonded joint are pulled parallel from one another along a plane. Compression is the optimal force to place on an adhesively bonded assembly. Compressive force is the force applied to an assembly when the bonded substrates are pushed together perpendicularly by an outside force. Peel and Cleavage forces are similar to each other and are the least desirable forces to apply to any bonded assembly. Peel and cleavage forces are applied to the leading edge of an assembly. These forces apply an uneven distribution of stress to the edge of the bonded materials. Once the adhesive begins to pull apart along the leading edge, the fractures being created in the adhesive begin to spread through the bond line.
Improve bonding through surface preparation Surface preparation and pretreatment methods have been accepted to allow adhesives to bond well to plastics, such as polyolefins which are commonly labeled as difficult-to-bond. There are five common types of surface preparation to improve bond capabilities: abrasion, acid etching, flame treatment, corona treatment and plasma. Abrasion is a process of mechanically roughening the surface of a material to enlarge the surface area at the bond line. A surface cleaning should be performed after the abrasion to remove any debris from the process. Acid etching is an effective method of increasing surface area in a manner similar to abrasion. Acid etching can be hazardous due to the chemicals required to perform the process, and it also can be time consuming. page 18 u
16 | plastics business • summer 2014