Solvent Based Adhesive- Rubber Dissolution in Toluene
The logic behind solvent-based adhesives is that containing an adhesive inside a more malleable or spreadable substance will make it easier to apply. This allows users to be more thorough when applying the adhesive to ensure effective performance.
Solvent-based adhesives are produced when an adhesive material is blended with a suitable solvent to create an adhesive polymer solution. Rubber solutions are used in a wide range of applications, including adhesives, sealants, paints, carpet backing compounds, tire compounds, etc.
The manufacturing process, product viscosity and ingredients used vary according to the end use of the rubber solution; however, a typical batch would traditionally be prepared as follows:
- A polymer (synthetic or natural) is dissolved in a solvent, usually either liquid or low-boiling gasoline product, to produce a polymer solution. The process vessel is charged with the solvent. Many types of solvent are used, including acetone, toluene, MEK, hexane, etc.
- Rubber can be supplied in powder, crumb or block form. Blocks and large crumbs normally require chopping or granulating before they can be added to the solvent.
- The mixer is then started. Mixing continues for several hours until the rubber is fully solubilized. The polymer can take a great deal of time to dissolve, depending on the stability of the polymer and the corrosive qualities/temperature of the solvent solution.
- Finally, other ingredients such as pigments, fillers, stabilizers and lubricants are added and dispersed into the mix.
Great care is taken not to accelerate the process, as this can destabilize the chemicals leading to an ineffective bonding process as well as potentially dangerous by-products.
- Long mixing times.
- Higher operating costs and process time.
- Solvent loss.
- Synthetic rubbers such as Neoprene are extremely tough and require a certain degree of shear to disintegrate and solubilize them.
- The solids tend to form a large agglomerated mass.
Wahal Engineer’s manufactured High Shear mixer is the one step solution to the aforesaid challenges. The operation is as follows:
Step 1: The powerful suction is being created by the In-Line mixer drawing the rubber and solvent from the vessel into the rotor/stator work head.
Step 2: The materials are being forced to the periphery of the work head as a result of the Centrifugal force. Here the rubber is being subjected to a milling action in the gap between the rotor and stator.
Step 3: The product is forced out through the stator as fresh materials are drawn into the work head. In a short mixing cycle the entire contents of the vessel passes through the work head and solubilization is rapidly completed.
Advantages of the Process
- Bypassing is impossible once product is in the circulating line.
- A more energy efficient process.
- High rotor tip speed reduces process time.
- No additional pumping is required to circulate the product back into the tank.
- Shredding or granulating of rubber to a fine particle size is not required. Coarsely chopped material can be added to the vessel and finely disintegrated and solubilized the mixer. This greatly reduces overall processing time.
- Vigorous in-tank agitation ensures particles do not re-agglomerate.