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Dry natural rubber graded or the bases of technical parameters are called Technically Specified Rubbers. The International standards Organization (ISO) first came out with the draft Technical Specifications for Natural Rubber during 1964. Based on these specifications, Malaysia introduced their Standard Malaysian Rubber (SMR) scheme in 1965 and since then all the Natural Rubber producing countries started producing and marketing NR as Technically Specified Rubbers. The TSR's are mostly the block types made adopting new methods of processing. The blocks are generally 33 1/3kg bales in the International market and 25kg in India. All the block rubbers are also guaranteed to conform to certain technical specifications as laid out by the national schemes or by the ISO_2000 standard.
   
   
  Among these forms types, the first three are in the dry form and almost of the total NR produced in the world is at present marketed in these 3 forms.  
 
   
Sheet Rubber   Crepe Rubber   T.S.R
         
       
Preserved Latex        
 
     
 
The nomenclature of Technically Specified Rubbers consists of a 3 or 4 letter country scheme code, which is followed by a numeral which indicates the maximum permissible dirt content in that grade expressed as a hundredth of a percent. All major NR producing countries including India have their national schemes.

The share of TSR in the export market of NR accounts a little over 60%. Also in the international market, TSR's are the major volume grades of dry rubber in production and exports in the major NR exporting countries of the world. In Malaysia, the TSR is designated as Standard Malaysian Rubber (SMR). In Indonesia, the designation given is Standard Indonesian Rubber (SIR). In Thailand the TSR's are called Standard Thai Rubber (STR). In India, the TSR's are designated as Indian Standard Natural Rubber (ISNR).

The advantages claimed for the Technically Specified Rubbers over the conventional sheet and crepe grades of rubbers are the following:
  • Being available in a limited number of well defined grades, correct choice of grades according to requirements by the consumers, is rather easy.

  • Being possible to assess the actual content of foreign and volatile matter, mistakes can be avoided in deciding the actual worth of the material.

  • Being marketed as compact, polythene wrapped bales, degradation of the rubber on storage, handling and transportation can be prevented

  • Being in standard size and compact, considerable savings can be made in transport through mechanized handling and containerization
From a consideration of all the above, it can be noted that Technically Specified Natural Rubbers are well known as the modern form of Natural Rubber, designed mainly.
  • To meet the requirements of the rubber consumers better,

  • To ensure value for the money of paid by the consumers and

  • To ensure, better uniformity and consistency in the quality of NR.
This would mean that marketing NR as Technically specified Rubber is a notable technical improvement when compared to marketing NR as visually graded and packed sheets or crepes.

The different grade of TSR’s Specified by ISO

The international standards Organization (ISO) have specified 6 different grades of Technically Specified Rubber. The specifications in force at present are given in the following tables:

TSR's Specified by ISO under ISO-2000

Parameters Grades
TSR - CV TSR - L TSR - S TSR -10 TSR - 20 TSR - 50
Dirt content, %wt, Max 0.05 0.05 0.05 0.10 0.20 0.50
Ash content, %wt, Max 0.60 0.60 0.50 0.75 1.00 1.50
Nitrogen content,% wt, Max 0.60 0.60 0.50 0.60 0.60 0.60
Volatile matter % wt, Max 0.80 0.80 0.80 0.80 0.80 0.80
Initial Wallace plasticity Po, Min - 30 30 30 30 30
Plasticity Retention Index (PRI Min 60 60 60 50 40 30
Colour, Max (Lovibond units) - 6 - - - -
Money viscosity 60±5 - - - - -

It is understood that these specifications are now under revision, and the revised specifications may be finalized soon. In the revised specifications, it is likely that more grades may be introduced. The detailed characteristics of the different grades of TSR's are as follows:

   
 

TSR-CV

TSR-CV is produced from high quality field latex. Rubber is viscosity stabilized at narrow money viscosity range. The accelerated storage hardening of this grade of rubber will be within 8 units.
 
Packing;
  It is presented in a modern 1.2 metric tonne pallet which facilitates handling, transportation and store space utilizations. Each pallet consists of 36 bales of 331/3 kg net. Each bale is wrapped in high quality polythene bag which is dispersible and compatible with rubber at 110°C.
 
General Characteristics;
  TSR-CV Rubbers are generally softer than conventional grades. Coupled with its constant viscosity feature, it provides a unique cost advantage in eliminating the pre mastication process and high reject rates, when used in open mill the rubber forms coherent band almost instantaneously thus increasing the milling through put. The non scorch characteristics of the rubber will permit higher curing temperature to be adopted without risk of rejects.
 
Additional benefits of TSR-CV
 
  • Reduction on mixing period giving higher throughput.
  • Reduction of scraps and rejects.
  • Better resistance to chipping and chunking of, off the road tyres
  • Better green strength
  Uses
  Can be used for high quality products such as mechanical mountings for engine and machinery, railway buffers, bridge bearings, vehicle suspension systems and general automotive components large truck tyre tread, conveyor belt covers, cushion gum for rethreading, wind-shield wiper blades, masking tapes, brake assembly units, injection molded products including rubber/metal bonded components, low density sponge, tee gum cushion compounds, springs, industrial rolls, inner tubes and cement.
   

 

TSR-L

It is a light colour rubber produced from high quality latex, having low ash and dirt content.
 
Packing
  Packed and presented in the same way as TSR-CV
 
General characteristics
  The attractive features of TSR - L is the light colour property together with its cleanliness and excellent heat ageing resistance. Technologically TSR - L exhibits excellent vulcanization properties having high tensile strength, modulus and elongation at break for both black and non black mix. Higher hardness product can also be obtained with suitable compounding.
 
Uses
  Can be used for light colored and transparent products such as surgical/pressure sensitive tapes, spread textiles, rubber bands, hot water bottles, surgical/pressure sensitive tapes, spread textiles, rubber bands, hot water bottles, surgical and pharmaceutical products, large industrial rollers for paper printing industry, gas masks, swim fins and caps, sport foot wear, rubberized curtaining , bicycle tubes, chewing gum, tennis balls, cable sheaths, washing machine gaskets and adhesive solutions and tapes.
   

 

TSR-5

It is produced from fresh coagulam and or from unsmoked sheets, Ribbed smoked sheets and Air dried sheets.
 
Packing
  It is packed and presented in the same way us that of TSR-CV and TSR-L.
 
General Characteristics
  TSR-5 has superior strength property together with low mill shrinkage and good tack. It processes better especially in extrusion, calendaring, and joining of cycle inner tubes.
 
Uses
  Can be used with benefit for general purpose friction and extruded products, small components in passenger vehicles, resilient bush/mountings, sealing rings, cushion gum, brake seals, bridge bearing, ebonite battery plate, separators, adhesives, plant linings etc.

 

TSR-10

TSR - 10 is produced from clean and fresh field coagulam or from unsmoked sheets.
 
Packing
  It is packed and presented in the same way as that of TSR-CV, TSR-L and TSR-5.
 
General characteristics
  TSR - 10 has good technological properties similar to those of RSS-2 and RSS-3, but has the advantage over RSS from (1) lower viscosity and (2) easier mixing characteristic (slightly more rapid breakdown) as well as being technically specified and packed in modern packing.
 
Uses
  Can be used for tyres, inner tubes, cushion gum stocks, joint rings by injection molding, raincoat proofing, microcellular sheets, for upholstery and packing, conveyor belts and foot wears.

 

TSR-20

It is a large volume grade of technically specified natural rubber. It is produced mostly from field coagulam, with lower grades of RSS and or unsmoked sheets.
 
Packing
  It is packed and presented in the same way as that of TSR-CV, TSR-L, TSR-5 and 10.
 
General Characteristics
  TSR-20 has excellent processing characteristics and good physical properties. Its low viscosity and easier mixing characteristic (compared with the RSS grades) will reduce the mastication and mixing period considerably.
 
Uses
  Used mostly for tyres, cushion gum stock, bicycle tyres, raincoat proofing, micro-cellular sheet for upholstery and packing, conveyor belts, foot wear and other general products.

 

TSR-50

It is the lowest grade of TSR and is produced from old dry field coagulam or partly degraded rubber.
 
Packing
  IIt is packed and presented in the same way as that of other grades of TSR.
 
General Characteristics
  The rubber usually will be having low viscosity and easier mixing characteristics compared with lower grades of RSS, ESC and remilled crepes.
 
Uses
  Can be used for producing camel back, low quality foot wears and black molded articles etc.