Improving the adhesion between vulcanized rubber and metal is a separate science, and it is sometimes difficult to achieve good adhesion. Even if the initial bonding performance is sometimes good, the bonding, corrosion resistance and resistance to moisture aging may be poor after aging. The initial bonding performance is not an accurate predictor of the bonding performance after aging. In addition, standard bonding tests in the laboratory do not fully reflect the actual rubber-to-metal bonding of rubber products in production.
The most common rubber-to-metal bond is the rubber-to-wire bond, which in this case is actually copper-plated wire, and some other rubber-to-metal bonds are described below. The following experimental schemes or ideas may improve the bonding between rubber and metal.
1. NR
Usually natural rubber bonds better to copper-plated steel wire.
2. Cobalt salts
Cobalt salts can usually be added to rubber formulations to improve the adhesion of rubber to brass-plated steel wire. Cobalt salts affect the production of copper sulfide on the wire surface, which helps to "anchor" the rubber to the wire, and they improve the initial and aging adhesion of the rubber to the brass-plated wire. Increasing the amount of cobalt salts reduces moisture aging properties and accelerates sulfur vulcanization. In fact, increasing the amount of cobalt salts improves the initial bonding but reduces the bonding after moisture aging. Therefore, in order to balance the various properties, it is necessary to choose the appropriate amount of cobalt salt, sulfur and accelerator.
3. Resorcinol formaldehyde resin and hexamethoxy melamine
Usually resorcinol formaldehyde resin and hexamethoxy melamine are used with cobalt salt to improve the initial bonding and aging bonding, because HMMM and RF will crosslink in situ during the vulcanization process to protect the system from moisture erosion.
4. High sulfur and low promotion
For good adhesion of rubber to copper-plated steel wire, the insoluble sulfur content of the vulcanization system should be high while the accelerator content should be relatively low, as this ensures a high level of CuxS formation on the wire surface.
5. DCBS
In the bonding system rubber, DCBS is a commonly used accelerator, it can reduce the vulcanization speed better than other sub-sulfur amide accelerators, and thus help to improve the bonding performance. Increase the ratio of sulfur / DCBS dosage, can improve both the initial bonding performance and moisture aging bonding performance.
6. Silica
In the wire bonding compound, white carbon black is often used to replace part of the carbon black, because white carbon black can promote the generation of ZnO at the interface, thereby improving the initial bonding properties and the bonding properties after aging.
7. Carbon black N326
In the steel wire bonding adhesive, N326 is often chosen a carbon black, because this carbon black can give the adhesive very good Green strength, even at low dosage can still have good reinforcement, and easy to penetrate into the wire to promote the bonding effect.
8. stearic acid and zinc oxide effect
In the bonding adhesive material, too much stearic acid will reduce the adhesive material after moisture aging bonding, especially in the case of high amounts of naphthenic cobalt. Too much stearic acid can be corrosive to brass and therefore have a negative effect on wire bonding. Usually the zinc oxide film formed on the brass surface is melted off by the stearic acid. To avoid this, the stearic acid should be consumed quickly in the vulcanization and the zinc oxide chosen should be highly reactive so that it can react quickly with the stearic acid. In addition, the zinc oxide/stearic acid ratio should be high.
9. Effect of vulcanization conditions
After increasing the vulcanization temperature from 130°C to 190°C, the extraction force of rubber/wire decreases linearly.
10. Peroxide vulcanization and cross-linking aid
The use of co-crosslinkers will improve the bonding properties of peroxide vulcanized rubbers. In some cases, increasing the amount of zinc methacrylate (Saret 633), a crosslinking aid, improves the bonding properties of steel wires with aluminum, zinc or brass plating on the surface to the rubber.
11. In the neoprene and brass-plated steel wire bonding adhesive, to minimize the amount of sulfur, generally 0.5 parts (mass), the amount of sulfur in the natural adhesive material is generally at least 3 parts (mass).
12. Metal surface treatment
In order to get a better rubber and metal bonding properties, the metal surface should be kept clean and properly treated before use.
