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Natural Rubber (NR) is processed into blocks adopting new processing techniques. It is a notable improvement in the presentation of dry Natural Rubber. In India, block rubbers are to be marketed with ISI (Indian Standards Institution) specifications and therefore, this rubber is termed as Indian Standard Natural Rubber (ISNR).
Process Flow
Production of ISNR
Production of ISNR involves a series of unit operations such as pre-cleaning, blending, final size reduction, drying and packing. The raw rubber in the form of latex and/ or Field Coagulam (FC) is converted in to Blocks after pre-cleaning operations to remove foreign matter, washed, dried at a temperature not exceeding 110C, compressed into blocks of standard size and shape and wrapped in low density polythene film. Grading is done by taking samples from bales representing each lot and testing for dirt, ash, volatile matter, nitrogen content, initial plasticity and plasticity retention index. Block rubber is then packed in dispersible polythene, palletized if required and marketed. The weight of each bale is 25 Kg.

Indian Standard Natural Rubber can be produced both from field latex, sheet rubber and from Field Coagulam (FC) like cup lumps, tree lace etc. The various grades of ISNR that we produce in our factories are ISNR 3L, 5, 10, 20 and 50. The following table indicates detailed specification for each grade.
Sl No. Characteristics ISNR3L ISNR5 ISNR10 ISNR20 ISNR50
1 Dirt Content (Percent by mass, Max.) 0.03 0.05 0.10 0.20 0.05
2 Volatile Matter (Percent by mass, Max.) 0.80 0.80 0.80 0.80 0.80
3 Ash (Percent by mass, Max.) 0.50. 0.50 0.75 1.00 1.50
4 Nitrogen (Percent by mass, Max.) 0.60 0.60 0.60 0.60 0.60
5 Initial Plasticity (Min) 30 30 30 30 30
6 Plasticity Retention Index (PRI)(Min) 60 60 50 40 30
7 Colour (Lovibond scale) (Max) 6.0 - - - -
Quality Control
The grading of Block Rubber is based on the technical specifications published by the Bureau of Indian standards in IS : 4588 - 1986. Specification for Raw Natural Rubber (Fourth Revision). This Indian standard prescribes three different grades of Field Coagulam (FC) based Block rubber namely ISNR - 10, ISNR - 20 and ISNR - 50. INDIAR is processing ISNR-20 Grade which is in demand in Tyre and Non-Tyre industries. The factory has a fully equipped lab, complete with two Wallace Plastimeters for testing and grading the products.
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INDIAR - Quality Control Lab 1 INDIAR - Quality Control Lab 2
Block Rubber Exports
The ISNR - 20 Grade Block Rubber which is produced in the INDIAR received a great response from the world market. Three containers exported to Singapore on an experimental basis created very good response. The society now receives a lot of export orders but as the production is not sufficient to meet the needs of our local customers, we will think about exporting only after the completion of factory expansion project.
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