Cold Seal Adhesive Lab Report

1] Introduction:

A cold seal adhesive is a material that has good adhesion to itself at ambient temperatures, a property that is often referred to as “self-adhesion”, “auto adhesion”, or “autohesion”[1]. Cold seal adhesive comprise a special class of pressure-sensitive adhesives which possess the capability of forming a strong bond to themselves and hence also known as cohesives. Cold-seal adhesives are an established class of commercial adhesives characterized by being coated onto plastic films or other substrates to form layers that have the capability of strongly bonding to themselves when pressure is applied, but having lower adhesion to the substrates e.g. plastic films, coated papers etc. So such flexible webs bearing these cold-seal

The NR-NR interface becomes an organic part of a NR film. Diffusive bonding provides the strong interaction at the interface. Diffusion theory of polymers describes such a phenomenon with clarity. In order for diffusion bonding to take full effect, high molecular mobility at the interface, good compatibility, and sufficiently high molecular weight must be met, so that fast autohesion can occur. According to the theory of polymer interfaces, a full cohesive strength is reached when the polymer molecules at an interface diffuse a distance comparable to their radius of gyration and form large number of molecular entanglements. For high molecular weight polymers like polybutadiene and polyisoprene (NR), the interdiffusion process is completed within 3 seconds at room temperature. This implies that autohesion of NR is practically instantaneous, making it ideal for selected adhesive

Natural rubber latex (NRL) has been used in cold-seal adhesive formulations for over 100 years. The adhesives made with NRL were used in the manufacture of medical devices and food packaging products due to NRL’s excellent flexibility, high initial tack, and good tack retention properties. However, NRL has several notable disadvantages that are causing manufacturers to look at NRL-free formulations. NRL can contribute to allergic reactions due to the presence of certain natural latex proteins. Therefore, manufacturers and service providers are feeling the pressure from regulatory bodies to find alternatives. This effort is under way to protect patients, healthcare workers, food handlers and consumers from products that contain NRL. Some people know they have an allergy to NRL and take measures to prevent exposure, but others only find out after a reaction. The best approach to protect people from exposure is to avoid the use of NRL products in the first place. Another disadvantage of NRL is that it readily oxidizes and discolors at relatively low temperatures. NRL formulations require preservation against bacterial attack via the incorporation of a fungicide, and they also suffer from raw material variation. An antioxidant is a necessary ingredient, since natural rubber is prone to attack by oxygen and will deteriorate rapidly without the protection afforded