Block Rubber (TSR) in India - Indian Standard Natural Rubber (ISNR)
Indian Standard Natural Rubber (ISNR), which is the technical name for Block Rubber made in India, is natural rubber processed as per the technical specifications notified by the International Standards Organization (ISO). In India, block rubber is marketed with ISI specification, IS 4588 and therefore termed as 'Indian Standard Natural Rubber' (ISNR). This marketable form of natural rubber, is produced from Latex, Cup Lumps or Field Coagulum. The bales are marketed in bales wrapped in compact polyethylene (LDPE) , the contamination of rubber on storage, holding and transportation are fully eliminated.
ISNR is marketed in 6 well defined ISI marked grades with uniformity and consistency in quality, to meet the requirements of the global consuming industry. The standard size of the bales and its compact packaging enables mechanized handling and containerization, thereby making the transportation economical and trouble free.
Processing of natural rubber into blocks similar to synthetic rubbers adopting cost effective and modern processing methods is a notable improvement in the presentation of dry natural rubber from India. This is in line with the consumer preference in the world rubber market for Technically Specified Rubber (TSR), which has the following advantages:
a) Technically certified with supporting lab tests, rather than visually graded as in the case of RSS and Crepe grades of natural rubber.
b) Consistency in quality.
c) Compact Packaging.
d) Negligible chance of contamination during handling and transportation.
Bureau of Indian Standards (BIS) formulated specifications for ISNR in 1969 (IS 4588). IS 4588 prescribes 6 grades viz., ISNR 3 CV, ISNR 3 L, ISNR 5, ISNR 10, ISNR 20 and ISNR 50.
BUREAU OF INDIAN STANDARD SPECIFICATION OF ISNR GRADES
| Characteristic | ISNR 3CV | ISNR 3L | ISNR 5 | ISNR 10L | ISNR 20 | ISNR 50 |
|---|---|---|---|---|---|---|
| Dirt percent by mass (Max) | 0.03 | 0.03 | 0.05 | 0.10 | 0.20 | 0.50 |
| Ash, percent by mass (Max) | 0.80 | 0.80 | 0.80 | 0.80 | 0.80 | 0.80 |
| Nitrogen, percent by mass, (Max) | 0.50 | 0.50 | 0.60 | 0.75 | 1.00 | 1.50 |
| Nitrogen content,%wt. Max | 0.60 | 0.60 | 0.60 | 0.60 | 0.60 | 0.60 |
| Initial plasticity Po (Min) | As agreed to between the purchaser and the supplier | 30.00 (Min) |
30.00 (Min) |
30.00 (Min) |
30.00 (Min) |
30.00 (Min) |
| Plasticity retention index, PRI (Min) | 60.00 | 60.00 | 60.00 | 50.00 | 40.00 | 30.00 |
| Colour (Lovibond scale) | - | 6.0 | - | - | - | - |
| Mooney viscosity (1+4) at 100 C | 60+(-)5 | - | - | - | - | - |
| Accelerated storage hardening Po (max) | 8.00 | - | - | - | - | - |
| Colour code | Black | Black | Green | Brown | Red | Yellow |