Abstract
When metals and NBR vulcanizates are put into contact an adhesive force is generated between them. The phenomenon is called fixing, and the adhesive force generated is defined as the fixing strength. The fixing strength is divided into an initial fixing at 30 min after loading and an after-fixing which thereafter occurs successively. The former fixing strength is exhibited by the physical adsorption forces of the NBR segments to the metal surfaces. The latter are based on the formation of first-order bonds which are brought about by the chemical reactions between the metals and NBR vulcanizates. These fixing strengths were influenced by the environmental factors such as testing time, temperature, and humidity; by the surface factors such as the surface roughness of the metals and NBR vulcanizates, the hardness of the NBR vulcanizates, and the surface conditions; and by material factors such as the kinds of metals and rubbers, the fillers, and other ingredients in vulcanizates. From the above results, the fixing phenomenon is explained as follows. At first, the segment molecules of the NBR vulcanizates diffuse to the metal surfaces and then the nitrile groups in the NBR vulcanizates are adsorbed on the surfaces of the metals. At this time, secondary-order bond forces are generated between the two materials. Succeedingly, the chemical reactions occur at the contact parts between the two materials and then are combined by first-order bonds. As a result, a high fixing strength, as cohesive failure, is generated. The fixing mechanism leads to the four indicators of fixing prevention: (1) the control of the contact areas, (2) the suppression of molecular motion of the NBR segments, (3) the inhibition of interfacial reactions, and (4) the introduction of inactive crosslinks and side chains. In this paper, the surface curing of the NBR vulcanizates, which leads to the suppression of molecular motion of NBR segments, and the blooming method which leads to the inhibition of interfacial reactions, were investigated. The former method is not always effective for preventing the fixing because it is difficult to produce the NBR vulcanizates with less fixing properties under ordinary industrial conditions. However, stearamide and methylene bis-erucamide are very effective blooming agents to prevent fixing, because they provide barrier films onto the surfaces of NBR vulcanizates.