Polyimide-based adhesives have been commonly used for many applications. They are generally available in liquid forms. These are very expensive as well as difficult to handle. They can retain the bonding strength for a long time at high temperatures. These are generally applied mechanically or by dispensing with a syringe or dipping.
The most common problems when applying these adhesives are their storage, handling and short shelf life, reaction to the skin and harm caused by inhaling their vapors. The other problems include their need for high processing temperatures and pressures. Besides, high melt viscosity, poor adhesion, pinholes, bubbles and similar defects are additional problems. In a few applications, low peel resistance and lower resistance to abrasion are observed at high temperatures. Many adhesives are difficult to apply to sharp edges and odd shapes.
Pressure and Temperature
The problem of high pressure and temperature can be partially or completely lessened by use of combinations of polyisoimides. During thermal processing, these polyisoimides get isomerized to their polyimide modifications.
Polyimide systems produce polyimide coatings and these adhesives are suitable for a few applications, but the other problems limit the use of such polyimides. These problems have further been overcome by making different compositions for the coatings and adhesives by different manufacturers.
Some earlier compositions did not adhere well with both metallic as well as non-metallic surfaces particularly with fillers. The adhesives often had low peel strength, particularly at higher temperatures. This required very high temperatures and long periods, which are very costly and time consuming. Manufacturers have come with more suitable substitution.
Many manufacturers have come out with specific solutions for different applications. They recommend their different products with advanced compositions that take care of specific needs.
As many adhesives have harmful fumes, it is better to have sufficient ventilation when using them. Avoid your skin to come in contact with adhesive. Wash hands using soap and water. Keep the container air tight. Always use the manufacturer’s instructions for use.