Rubber Grades

Natural Rubber (NR) is produced from the crop harvested from rubber plantations both in the latex form as well as in the field coagulam form. Latex is a milky white dispersion of rubber in water and field coagulam is the auto coagulated latex on the tapping panel (tree lace) and the collection cups (shell scrap and cuplumps). Both the latex and field coagulam harvested from rubber plantations being highly susceptable to degradation by contamination on keeping, have to be processed into marketable forms that will allow safe storage and marketing.

The most important forms in which NR is processed and marketed are the following:

Among these 4 forms/types, the first three are in the dry form and almost 90% of the total NR produced in the world are at present marketed in these 3 forms. In the international market, these 3 broad types of dry NR, are available as over 40 grades consisting of ribbed smoked sheets and air dried sheets, crepes, which includes latex based and field coagulam derived estate brown crepes, remilled crepes etc. and Technically Specified Rubber in block form. In addition, there are a small number of speciality natural rubbers including chemically modified products and blends/composites. Among the 3 types, crepes are now of minor significance in the world market, probably less than 75,000 tonnes per year since field coagulam grade block rubbers have virtually replaced brown crepes excepting in India and only SriLanka and India continues to produce latex crepes. This would mean that sheet rubber and block rubber are the dominant types of dry NR available in the world market and this dominance reduced the number of grades used in any volume to the 10-15 within these types. However, an attempt is made to give the details of each type of NR with the grade descriptor both for the benefit of producers, marketers and consumers of NR in India as well as in the world

Creps

Grades available in the international markets and grade descriptions

Crepe is a crinkly lace rubber, obtained when coagulated latex or any form of field coagulam(tree lace, shell scrap, and earth scrap etc.) is passed several times through heavy rolls called crepers and the resultant material air dried at ambient temperature. There are different types of crepe rubber depending upon the type of starting materials from which they are produced. The different types of crepe rubbers, for which grade descriptions are given in the Green Book are the following:

Pale Latex Crepes

There are 8 grades under this category. All these grades must be produced from the fresh coagula of natural liquid latex under conditions where all processes are carefully and uniformly controlled. The rubber is milled to produce thin and thick crepes. The grade descriptions for the various grades are as given below
• No : IX Thick pale crepe
• No : IX Thin pale crepe

The difference between the grades is only in thickness. Deliveries of the grades must consist of dry, firm rubber of very light uniform colour. Discolouration, regardless of cause, dust, specks, sand or other foreign matter, oil or their stains, or any evidence of oxidation or heat, not permissible
• No.1 Thick pale crepe
• No.1 Thin pale crepe

Deliveries must consist of dry, firm rubber of light colour with very slight variation in shade permissible. Discolouration, regardless of cause, dust, specks sand or other foreign matter, oil or other stains or any evidence of oxidation or heat not permissible
• No.2 Thin pale crepe
• No.2 Thick pale crepe

Deliveries must consist of dry, firm rubber, slightly darker than No.1 Thick or Thin pale crepe with slight variation in shade permissible. Slightly mottled rubber will not be objected to provided this condition does not exist in more than 10% of the number of bales included in the delivery, lot or tender as determined by the number of bales inspected. Discolouration, regardless of cause, dust, specks, sand or other foreign matter, oil or other stains or any evidence of oxidation or heat, not permissible, other than those specified above as permissible.
• No. 3 Thick pale crepe
• No. 3 Thin pale crepe

Deliveries must consist of dry, firm rubber of yellowish colour with variation in shade permissible. Mottled and streaked rubber are permissible provided this condition does not exist in more than 20% of the number of bales included in the delivery, lot or tender as determined by the number of bales inspected. Discolouration, regardless of cause, dust, specks, sand or other foreign matter, oil or other stains or any evidenc of oxidation or heat, not permissible other than specified above as permissible.

Estae Brown Crepes

There are six grades under this category. All these grades are made from lump and other high grade rubber scrap(field coagulam) generated on rubber estates. Tree bark scrap, if used must be pre-cleaned to separate the rubber from the bark. Power wash mills are to be used in milling these grades into a form of thick and thin brown crepes. The grade descriptions for the different grades of Estate Brown Crepes are as follows
• No: IX Thin Brown Crepe
• No: IX Thick Brown Crepe

The difference between the grades is only in the thickness. For these two grades, deliveries must consist of dry, cean rubber light brown in colour. Discolouration, regardless of cause, specks, sand or other foreign matter, oil or other stains or any evidence of oxidation or heat not permissible.
• No: 2x Thin Brown Crepe
• No: 2x Thick Brown Crepe

For both these grades deliveries must consist of dry, clean rubber brown light in colour. Discolouration, regardless of cause, specks, sand or other foreign matter, oil or other stains or any evidence of oxidation or heat, not permissible
• No: 3x Thin Brown Crepe
• No: 3x Thick Brown Crepe

For both these grades, deliveries must consist of dry rubber brown to dark brown in colour. Discolouration, regardless of cause, specks, sand or other foreign matter, oil or other stains or any evidence of oxidation or heat, not permissible, except little specks of bark which will not be objected to.

Thin Brown Crepes(Remills)

There are 4 different grades coming under this category. These grades are manufactured on power wash mills from wet slab, unsmoked on estates or small holdings. Tree bark scrap, if used must be pre-cleaned to separate the rubber from the bark. Earth scrap and smoked scrap are not permissible in these grades. The grade descriptions for the different grades coming under this category are as follows:
• No: 1 Thin Brown Crepe

Deliveries must consist of dry, clean rubber, light brown in colour. Mottled rubber permitted to some extent. Discolouration, regardless of cause, sludge, specks of bark, sand, dirty packing, or all other foreign matter, oil or other stains or any evidence of oxidation or heat not permissible.
• No: 2 Thin Brown Crepe

Deliveries must consist of dry, clean rubber, light to medium brown in colour. Mottled rubber permitted, to a little more in extent. Discolouration, regardless of cause, sludge, specks of bark, snad, dirty packing, or all other foreign matter, oil or other stains or any evidence of oxiation or heat not permissible.
• No: 3 Thin Brown Crepe

Deliveries must consist of dry, clean rubber medium brown to medium dark brown in colour. Mottled rubber permitted. Discolouartion, regardless of cause, sludge, specks of bark,sand , dirty packing, or all other foreign matter, oil or other stains or any evidence of oxidation or heat not permissible
• No: 4 Thin Brown Crepe

Deliveries must consist of dry rubber, medium dark brown to dark brown in colour. Mottled rubber and small minute specks of barks willnot be objected to. Discolouration, regardless of cause, sludge, sand, dirty packing, or all other foreifn matter, oil or other stains or any evidence of oxidation or heat not permissible

Thick Blanket Crepes(Ambers)

There are 3 grades under this category. These grades are manufactured on power wash mills from wet slab, unsmoked sheets, lump and other high grade scrap generated on estates or small holdings. Tree bark scrap, if used must be pre-cleaned to separate the rubber from the bark. Earth scrap is not permissible in these grades. The grade descriptions of the 3 different grades coming under this category are as follows:
• No: 2 Thick Blanket crepe(Amber

Deliveries must consist of dry, clean rubber, light brown in colour. Mottled rubber permitted to some extent. Discolouration, regardless of cause, sludge, specks of bark, sand, dirty packing or all other foreign matter, oil or other stains or any evidence of oxidation or heat not permissible.
• No. 3 Thick Blanket crepe(Amber)

Deliveries must consist of dry, clean rubber, medium brown to brown in colour. Mottled rubber permitted. Dis-colouration, regardless of cause, sludge, specks of barks, sand, dirty packing, or all other foreign matter, oil or other stains or any evidence of oxidation or heat not permissible.
• No: 4 Thick Blanket crepe(Amber)

Deliveries must consist of dry rubber, brown to dark brown in colour. Mottled rubber permitted. Discolouration, regardless of cause, sludge, specks of bark, sand, dirty packing or all other foreign matter, oil or other stains or any evidence of oxidation or heat not permissible

Flat Bark Crepes

There are two grades of rubber under this category. These grades are produced on power wash mills out of all types of scrap natural rubber in uncompounded form including earth scrap. The descriptions of these two grades are as follows

Standard Flat Bark crepe

The rubber must be dry, very dark brown to black in colour is medium hard to soft in texture. Sludge,cotton, sand, dirty packing, and other foreign matter, except fine bark particles not permissible. Heated and discoloured rubber not permissible.
• Hard Flat Bark crepe

The rubber must be dry, very dark brown to black in colour and is produced in the form of thick, firm, comparatively tough crepe. Sludge, cotton, sand, dirty packing and other foreign matter, except fine bark particles, are not permissible. Heated and discoloured rubber not permissible

Pure Smoked Blanket crepe

This grade is made by milling on power wash mills smoked rubber derived exclusively from Ribbed smoked sheet(including block sheets),or Ribbed smoked sheet cuttings. No other type of rubber shall be used and no non-rubber material shall be added. Rubber of this type must be dry, clean, firm, tough and retains an easily detectable smoked sheet odour. Sludge,oil spots, heat spots, sand, dirty packing and foreign matter not permissible. Colour variation from brown to very dark brown permissible.

The different grades of TSR's Specified by ISO

The international standards Organisation(ISO) have specified 6 different grades of Techitcally Specified Rubber. The specifications inforce at present are given in the following tables

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
Nitrogencontent,%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 specificatios may be finalised 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

Description
TSR-CV is produced from high quality field latex. Rubber is viscosity stabilized at narrow money viscosity range. The acclerated 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 nett. 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 premastication 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 buf fers, bridge bearings, vehicle suspension systems and general automotive components large truck tyre tread, conveyor belt covers, cushion gum for retreading, wind-shield wiper blades, masking tapes, brake assembly units, injection moulded products including rubber/metal bonded components, low density sponge, tee gum cushion compounds, springs, industrial rolls, inner tubes and cement.

TSR-L

Description
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 vulcanisate 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 coloured 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, swin fins and caps, sport foot wear, rubberised curtaining , bicycle tubes, chewing gum, tennis balls, cable sheaths, washing machine gaskets and adhesive solutions and tapes.

TSR-5

Description
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, calendering, 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, seperators, adhesives, plant linings etc.

TSR - 10

Description
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 moulding, raincoat proofings, microcellulor sheets, for upholstery and packing, conveyor belts and foot wears.

TSR-20

Description
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 proofings, micro-cellular sheet for upholstery and packing, conveyor belts, foot wear and other general products.

TSR-50

Description
It is the lowest grade of TSR and is produced from old dry field coagulam or partly degraded rubber.

Packing
It 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 moulded articles etc.

Sheet Rubber

Grades available in the international markets and in India, the grade descriptions and packing specifications

NR in sheet forms are the oldest and the most popular type. Being the simplest and easiest to produce on a small sacle, small holder’s rubber in most of the countries are processed and marketed as sheet rubber. Two types of sheet Rubbers are produced and marketed in the international market, namely the Ribbed smoked sheets(RSS) and the Air Dried Sheets(ADS). Among these two types, Ribbed smoked sheet is the most popular and is available for volume consumption.

Ribbed Smoked Sheets (RSS)

Ribbed smoked sheets are marketed based on visual assessment of quality. To establish acceptable grades for commercial purposes, the international Rubber Quality and Packing conference, have stipulated the grade description and the details are given in the Green Book.

The International Grade Descriptions for Rss

Only deliberately coagulated rubber latex processed into rubber sheets, properly dried and smoked can be used in making RSS. The following prohibitions are also applicable to the RSS grade

• Wet, bleached, undercured and virgin rubber and rubber that is not completely visually dry at the time of buyer’s inspection is not acceptable(except slightly undercured rubber as specified for RSS-No: 5)
• Skim rubber made of skim latex shall not be used in whole or in part in the patches as required under packing specifications. Prior to grading RSS, the sheets are separated, inspected and any blemishes are removed by cutting with a pair of scissors.

Grade Descriptions

No: IX RSS

The grade must be produced under conditions where all processes are carefully and uniformally controlled. Each bale must be packed free of mould but very slight traces of dry mould on wrappers or bale surfaces adjacent to wrapper found at time of delivery will not be objected to provided there is no penetration of mould inside the bale. Oxidised spots or streaks, weak, heated, undercured, oversmoked, opaque and burnt sheets are not permissible.

The rubber must be dry, clean, strong, sound and evenly smoked and free from blemishes, specks, rust, blisters, send, dirty packing and any other foreign matter. Small pinhead bubbles if scatteres, will not be objected to.

No: RSS

Each bale must be packed free of mould but very slight traces of dry mould on wrappers or bale surfaces adjacent to wrapper found at the time of delivery will not be objected to provided there is no penetration of mould inside the bale. Oxidised spots or streaks, weak, heated, undercured, oversmoked, opaque and burnt sheets are not permissible.

The rubber must be dry, clean, strong sound and from blemishes, rust, blisters, sand, dirty packing and any other foreign matter, except slight specks. Small pinhead bubbles, if scattered, will not be objected to.

No:2 RSS

Slight rust, and slight amount of dry mould on wrappers, bale surfaces and interior sheets, found at time of delivery will not be objected to, provided these conditions either singly or in combination, do not exist to an objectionable extent on and in more than 5% of the number of bales included in the delivery, lot or tender as determined by the number of bales inspected.

Small bubbles and slight specks of barks, if catteres, will not be objected to.

Oxidised spots or streaks, weak, heated, undercured, oversmoked, opaque and burnt are not permissible. The rubber must be dry, clean, strong, sound and free from blemishes, blisters, sand, dirty packing and all other foreign matter other than specified above as permissible.

No: 3 RSS

Rust and dry mould on wrappers, bale surfaces and interior sheets, found at time of delivery will not be objected to, provided these conditions, either singly or in combination, do not exist to an objectionable extent on and in more than 10% of the number of bales included in the delivery, lot or tender as determined by the number of bales inspected. Slight blemishes in clour, small bubbles ans small specks of bark permissible. Oxidised spots or streaks, weak, heated, undercured, oversmoked, opaque and burnt sheets are not permissible. The rubber must be dry, strong and free of blemishes, blisters, sand dirty packing and all other foreign matter other than specified above as permissible.

No: 4 RSS

Rust, dry mould on wrappers, bale surfaces and interior sheets, found at time delivery will not be objected to provided these conditions, either singly or in combination, do not exist to an objectionable extent on or in more than 20% of the number of bales included in the delivry, lot or tender as deteremined by the number of bales inspected.

Medium size bark particles, bubbles, translucent stains, slightly sticky and slightly over smoked rubber as permissible but should not be evident to a marked degree. Oxidised spots, or streaks, weak, heated, undercured opaque and burnt sheets are not permissible. The rubber must be dry, firm and free of blemishes, blisters, sand, dirty packing and all other foreign matter other than specified above as permissible.

No: 5 RSS

Rust, dry mould on wrappers, bale surfaces and interior sheets, found at time of delivery will not be objected to provided these conditions, either singly or in combination, do not exist to an objectionable extent on or in more than 30% of the number of bales included in the delivery, lot or tender as determined by the number of bales inspected.

Types of Creps Produced and Marketed in India

The types and grades of crepe rubbers produced and marketed in India are the following

Pre-Coagulated crepe

This is the most pure form of Natural Rubber and is prepared from field latex under controlled conditions, which includes removal of the undesired colouring matter present in latex through the process of fractional coagulation. The pre-coagulated crepe rubber must have paper white colour and generally conforms to the specifications for thin PLC-IX given in the Green Book

Pale Latex crepes

There are 4 grades coming under this category. The grades are PLC_IX, PLC_1, PLC_2 and PLC_3 fair average quality(FAQ). No special grade descriptions are available for these grades and hence the grade descriptions given in the Green Book for thin PLC_IX, 1, 2 and 3 are usually adopted for fixing the grade of pale latex crepes in India

Estate Brown crepes

There are 4 different grades coming under this category. They are EBC-super IX, EBC-IX, 2x and 3x. Among these, EBC-super IX, grade is the light coloured Estate Brown crepe, produced mostly from fresh cup-lumps generated on estates. No special grade descriptions are issued for this grade. Hence light coloured Estate Brown crepes meeting the specifications of thin EBC-IX given in the Green Book, are graded and marketed as EBC-super IX. For EBC-2x and EBC-3x, the grade descriptions given in the Green Book are adopted in India also

Remilled crepes

They are 3 different grades coming under this category. They are Remilled crepe 2,3 and 4. These grades are made from waste slab coagulam, unsmoked sheets and field coagulam. The grade descriptions given for Thin Brown crepes(Remills) in the Green Book are adopted for fixing the grade of the rubber coming under this category.

Smoked Blanket crepe

This grade if rubber is derived exclusively from Ribbed smoked sheet or sheet cuttings. The specification given for pure smoked Blanket crepe in the Green Book is being adopted for grading this type of crepe.

Flat Bark crepe

This grade of.rubber is made from all types of low grade scrap including earth scrap. The grade description given for standard flat Bark crepe in the Green Book is being adopted in grading this type of crepe rubber

Packing Specifications for crepe Rubbers in India

For packing pre-coagulated crepe and pale latex crepes, the maximum weight of the rubber in each bale should be 50 kg nett. In respect of packing materials and procedures for packing, the specifications stipulated in the Green Book are generally adopted. However, these grades are commonly packed as 50 kg bales, wrapped in polythene and Jute hessian.

Packing Specifications for Estate Brown crepes and Remilled crepes

Among the Estate Brown crepes, ESC-SIX, is packed as 50Kg. bales, wrapped in polythene and jute hessian as in the case of pale latex crepes. The lower grade of Estate Brown crepes and Remilled crepes are packed as 50Kg. bare backed bales doped on all sides with a bale coating solution.

Packing of Flat Bark crepe

Flat Bark crepes are also packed as 50kg.bare backed bales doped on all sides with the recommended bale coating solution.

Sole Crepes made in India

Sole crepes in 4 different thickness are made by a few estates in India. The standard thicknesses are 1/20″, 3/16″,1/3″ and 1/4′. These grades of rubber are made from fresh latex coagulam and must have white colour, completely free of extraneous matter and dirt and conforming strictly to specifications of length, breadth, thickness and weight.

Packing of sole crepes

Sole crepes are laminated with tissue wrapped with polythene and jute hessian and the bale sizes, varying from 55 to 71 kg.

Technically Specified Natural Rubber

Dry natural rubber graded or the basis of technical parameters are called Technically Specified Rubbers. The International standards Oraanisationil(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.

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 mechanised handling and containerisation

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.

Have Any Questions?

Visit Us Daily