The tape manufacturers around the world use various types of pressure sensitive adhesives or PSAs as it is commonly known. The PSAs are silicone, solvent, hotmelt, rubber or water based and more often than other, the adhesive base used mainly depends on the application of the tape being manufactured.
In this blog, we will be looking at natural rubber adhesive, especially PLC rubber grade. The tape manufacturers prefer using natural rubber (NR) or synthetic rubber (SR) adhesive as it is cost effective. The synthetic rubber is also often referred to as SBS, SIS, Hotmelt etc. The market offers various grades of natural rubber – from premium to low grades, but is broadly divided into the following grades:
- RSS (Ribbed Smoked Sheet) Rubber / Sheet Rubber
- ISNR (Indian Standard Natural Rubber) / Block Rubber
- Crepe Rubber
RSS: Ribbed Smoked Sheet Rubber are coagulated rubber sheets processed from fresh field latex sourced from well managed rubber plantations adopting modern processing methods.
ISNR: The natural rubber is processed into blocks adopting cost effective and modern processing methods.
Crepe Rubber: Crepe rubber is processed from fresh latex coagulum, fresh field coagulum or from cutting of RSS. When any of these materials, after necessary preliminary treatment, is passed through crepe making machines, a crinkly and lace like rubber is obtained. This rubber when dried is known as crepe rubber.
The most effective natural rubber used in PSAs is PLC (Pale Latex Crepe) rubber, which is nothing but a transparent crepe rubber that is processed from fresh field latex. The crepe rubber undergoes process of fractional coagulation or bleaching to remove yellow colouring pigment and give it a translucent/transparent appearance. Sometimes, a combination of both the methods are used to remove the enzymatic discolouration or colouring matter.
The covalent or molecular weight of the translucent rubber is systematically broken down by passing it through calendaring/roller machines which helps in reducing the molecular weight of the rubber. The reduction in molecular weight helps to reduce the shear force (energy and time) required during the mastication* process. The crepe rubber is passed through above processes several times and the end product derived is translucent PLC rubber with low molecular weight.
Due to the transformation, the translucent PLC rubber with lower mastication and reduced molecular weight is most suitable for manufacturing colourless adhesive in time saving manner and at the same time it also has better dissolvability in toluene when compared to other forms of rubber.
