|Title of Invention||
"A DISPERSION COMPOSITION FOR PRODUCING RUBBER"
|Abstract||A process for the production of rubber from latex comprises adding acid to the latex at the point of its collection from a rubber (Hevea) tree so as to cause coagulation of the latex. The acid is typically formic acid and is preferably added to the latex as part of a dispersion which also comprises tetrabis (2-ethylhexyl) thiuriam disulphide and/or tetramethylthiuriam disulphide together with ZnO and KC1. The product thus obtained can be processed like conventionally produced rubbers and compares favourably in terms of its properties. It can be stored for several weeks before being processed and does not produce an offensive odour during either such storage or further processing.|
|Full Text||This invention relates to an improved process for the production of rubber from latex and, more particularly, to such a process which involves performing the coagulation of the latex at the point of its collection from a rubber (Hevea) tree.
Latex is traditionally extracted from rubber trees by a method known as "tapping". This can be achieved either by a bark excision technique, in which a strip of bark is cut out of the tree trunk so as to initiate latex flow (subsequent tappings being carried out by excising a thin layer of bark from the same cut), or by a bark incision technique, according to which one or more punctures are made into the bark to initiate the latex flow. The latex flowing out of the tree is usually collected in a cup or polybag which is attached to the tree trunk. Tapping may be conducted repeatedly and at regular intervals, typically every alternate day, from the same rubber tree.
Latex forms rubber by coagulation. According to the conventional procedure, latex that has been collected from rubber trees is removed and subjected to a subsequent acid coagulation step in a factory. Latex which is left untreated, whether it remains in the collecting cup or polybag on the tree or if it is removed and stored, will after a few days undergo auto-coagulation to form "cuplump" and which has the appearance of lumps that are blackish irf colour. Cuplump produces a very strong and unpleasant odour after only a few days and which is due to bacterial action causing protein breakdown. In contrast, acid coagulated latex has the appearance of lumps that are white in colour and does not emit any detectable odour.
Both acid coagulated latex and cuplump are then usually treated by the Hevea Crumb process which was developed in the 1960s and has been widely employed ever since (British Patent No. 1075234).
The Hevea Crumb process involves crepeing the acid coagulated latex or the cuplump so as to cause the lumps to crumble. The material is then dried and the resulting "biscuits" are baled and graded according to colour and dirt content. Rubber produced in Malaysia is classified according to the various grades of Standard Malaysian Rubber (SMR). SMR L (latex grade) is produced from acid coagulated latex and is the highest quality. SMR 10 and SMR 20 are produced from cuplump and the numerals refer to the dirt content. The SMR 10 and SMR 20 grades of rubber are used to make products such as tyres for automobiles.
The SMR 10 and SMR 20 grades of rubber have both found good markets, particularly in Europe and the USA. As noted above, the auto-coagulated cuplump from which these grades of rubber are produced develops a highly unpleasant smell within a few days. Furthermore, these grades of rubber also produce an offensive odour during their subsequent processing and this causes objections to their use in some countries. In particular, the drying of cuplump material produces foul smells, which are environmentally unacceptable, and scrubbers need to be installed in the production line to absorb 90% of the odour. Additionally, countries such as Japan prefer the RSS (Ribbed Smoke Sheet) grade of rubber since this is latex base material. For RSS production, the field latex is collected and subsequently coagulated at a factory in a container using formic acid. The coagulum is then creped into rubber sheets and the sheets are dried in a smoke house.
There is therefore a need for an improved process for the production of rubber from latex and, in particular, a process which avoids the production of a rubber product that has an offensive odour in the raw state and/or during its subsequent processing. The present invention seeks to provide such a process.
According to the present invention there is provided a process for the production of rubber from latex which comprises adding
acid to the latex at the point of its collection from a rubber tree so as to cause coagulation of the latex. The invention also provides coagulated latex which results from such a process and, furthermore, rubber in finished form that has been produced through the use of such a process.
It is the addition of the acid which causes the latex to coagulate. Preferably, formic acid is employed. The acid needs to be added in an amount of at least 0.6% by weight on the weight of wet field latex and, more preferably, at a level of about 4%. The quantity of acid added to the latex has an effect on the rate at which it coagulates and, in general, the presence of larger amounts will serve to accelerate coagulation.
Preferably, the acid is added to the latex as part of a
dispersion which also comprises one or more of the following components:-
• Tetrabis (2-ethylhexyl) thiuriam disulphide and which has the
This compound is readily available and is, for example, sold under the brand name TOT-N by Ouchi Shinko Chemical Industrial Co Ltd of Tokyo, Japan. It is known as a new accelerator for use both in dry rubber and latex compound to overcome the problem of volatile nitrosamines.
• Zinc oxide (ZnO).
• Potassium chloride (KCI).
Tetramethylthiuriam disulphide (TMTD), which is known for use in the preservation of latex concentrate and is also a fast cure accelerator commonly employed as a secondary accelerator in rubber compounding operations, may be present in addition to, or in place of, the
tetrabis (2-ethylhexyl) thiuriam disulphide. TMTD is readily available and is, for example, sold by Bayer of Germany and ICI of the United Kingdom. It is to be understood that the ZnO and KCI components may also be supplemented or replaced by similar materials which have the same effect. For example, NaCI could be used instead of, or as well as, KCI.
A typical dispersion suitable for use in the process of this invention would comprise at least 0.6% formic acid, at least 0.0125% tetrabis (2-ethylhexyl) thiuriam disulphide and/or at least 0.0125% tetramethylthiuriam disulphide, together with at least 0.0125% ZnO and at least 0.01% KCI; all of these percentages being by weight on the weight of the wet field latex being treated.
While the acid causes coagulation of the latex, it is believed that the other components of the dispersion as set out above serve to prevent or delay the breakdown of protein which would otherwise occur through bacterial action and which is accompanied by the aforementioned unpleasant odour.
The process of this invention is characterised by the fact that the coagulation of the latex is performed at the point of its collection from a rubber tree. The latex is conventionally collected in either a cup or polybag attached to the tree and, most conveniently, the coagulation step of this invention is performed by simply dripping the acid into such a container. It is to be understood, however, that the latex could be removed from the cup or polybag before the acid coagulation step is actually performed. The essential feature is that the coagulation is caused to occur at the time that the latex is collected from the rubber tree or within a very short period of time thereafter.
Preferably, the acid is added to the latex as part of a dispersion of the type described above. Most conveniently, the dispersion is dripped into the latex as a pre-formed mixture. It is to be understood, however, that the acid and one or more of the other components of the
dispersion could be dripped into the latex separately and either simultaneously or in rapid succession.
When the acid coagulated lumps are removed, the remaining serum may be poured onto the ground to act as a fertiliser. The coagulum which is obtained using the process of this invention is white in colour and can be stored for periods of at least three weeks, either at the point of its collection on a rubber tree or after its removal to a storage site, without developing an offensive odour or showing other signs of degradation. It can be processed like conventionally produced rubbers and compares favourably in terms of its properties. Furthermore, it has been found that the rubber produced according to the process of this invention does not give off offensive odours during its subsequent processing.
In a conventional SMR factory two separate production lines are required, namely one for the processing of SMR L rubber (i.e. latex grade rubber obtained from latex that has been subjected to an acid coagulation treatment in a factory) and another for the handling of SMR 10 and SMR 20 (i.e. lower grade rubbers that have been produced from auto-coagulated cuplump). However, with the acid coagulated latex which results from the process of the present invention only a single standard production line is required and which employs the following steps:-
(Steps Removed)The requirement for only a single standard (uniprocess) production line in a factory is obviously desirable in terms of overall efficiency and cost savings and has led to the Applicants naming the product Standard Uniprocess Malaysian Rubber (or SUMAR). The advantages of the process of this invention include the following:-
• It is capable of producing rubber that is of latex grade
(i.e. having a dirt content of below 0.02%).
• It produces rubber that exhibits good physical properties and
which can be further processed in a conventional manner.
• The rubber product does not produce or develop an offensive
odour, even if stored for several weeks before being further
processed, and also does not produce an offensive odour
during its subsequent processing. Furthermore, the process
does not produce any pollution. It can therefore be regarded
as environmentally friendly.
• The process is efficient and can produce a saving of labour
costs both in the rubber tree plantations and in the rubber
processing factories. It is thus highly cost competitive.
• The process can be employed regardless of whether the
eventual rubber product is required to be a general purpose
rubber or a more specialised type of rubber. The appropriate
chemical is simply included in the dispersion which is dripped
into the latex at the point of its collection from a rubber tree.
For example, rubber of a light colour is obtained by adding
sodium bisulphide; viscosity stabilised rubber can be
produced by adding hydroxy neutral sulphate (HNS); and
deproteinised natural rubber is prepared by adding a suitable
The present invention will now be further illustrated by reference to the following Examples.
There now follows a technical evaluation of the rubber which is formed by the acid coagulation of latex using the process of this invention.
Properties of Raw Rubber
Table 1 sets out the characteristics and properties currently specified by Malaysia as being required of the various grades of Standard Malaysian Rubber (SMR).
Table 2 shows the results that were achieved when a sample of rubber produced according to the method of the present invention (designated "New Rubber") was evaluated against the specification requirements set out in Table 1. Samples of SMR L, SMR 10, SMR 20 and RSS 3 obtained from commercial sources were also tested under the same conditions for comparative purposes. It will be seen that the New Rubber has a very low dirt content level, better even than that of SMR L, and a high Po value. However, the PRI value is lower than that of SMR L, but better than that of RSS 3 and comparable to those of SMR 10 and SMR 20.
Properties of Gum Vulcanisates
Samples of SMR L, SMR 20, RSS 3 and a product obtained using the process of this invention (designated "New Material") were evaluated and the results obtained are shown in Table 3. It is well known that acid coagulated rubber produced by conventional processes (for example, SMR L) has a slower cure time than rubber obtained from latex that was not acid coagulated (for example, SMR 10 and SMR 20). It is also known that if rubber is washed properly the cure time can be improved, as illustrated by the cure time obtained for the sample of RSS 3 in Table 3. Surprisingly and advantageously, however, the New Material is seen to have a faster cure time even though its manufacture involved acid
coagulation. While most of the other physical properties set out in Table 3 remain similar to those exhibited by the previously known rubbers, it will be seen that the New Material exhibits better tear, tensile and compression set characteristics.
Mixing Studies of Black Mix in Brabender
The mixing behaviour of samples of three rubbers, namely the New Rubber obtained using the process of this invention, SMR 20 and RSS 3, were evaluated in a Brabender mixer using a black compound (i.e. natural rubber with carbon black as filler). The following results were obtained:-
Total mixing energy
New Rubber (166) > RSS 3 (163) > SMR 20 (159) Nm - min
New Rubber (126°C) > RSS 3 (121°C) > SMR 20 (121°C)
New Rubber (23.7 Nm) > RSS 3 (23.4 Nm) > SMR 20
While there is an indication in these results that the New Rubber has higher total mixing energy, higher final temperature and higher final torque, it should be noted that the differences are only marginal. Properties of Black Vulcanisates (50 pphr HAF) Samples of a rubber obtained using the process of this invention (designated New Rubber) and the rubbers SMR 20 and RSS 3 were evaluated and the results obtained are set out in Table 4 and Table 5. The results indicate that the New Rubber can be processed in the same way as conventional rubber materials and has a number of advantageous characteristics.
Table 1 (Table 1 Removed)
10 Where Po is Initial Plasticity
PRI is Plasticity Retention Index Mv is Mooney viscosity
Table 2 (Table Removed)
Table 3 (Table Removed)
Where TS is Tensile Strength
EB is Elongation at Break
IRHD is International Rubber Hardness Durometer
Table 4 (Table 4 Removed)
Table 5 (Table 5 Removed)
1. A dispersion composition for use in a process for producing rubber from latex, said composition is capable of being added to the latex at the point of its collection from a rubber tree to obtain a coagulated latex, said composition comprising at least 0.6% formic acid, at least 0.0125% terabis (2-ethylhexyl) thiuriam disulphide and/or at least 0.0125% teramethylthiuriam disulphide, at least 0.0125% zinc oxide, and at least 0.01% potassium chloride, all percentages being by weight on the weight of wet field latex.
2. The dispersion composition as claimed in claim 1, wherein the amount of formic acid is about 4% by weight on the weight of wet field latex.
3. A coagulated latex obtained by the use of the dispersion composition as claimed in claim 1.
4. A rubber obtained from the coagulated latex as claimed in claim 3.
5. The dispersion composition for use in a process for producing rubber from
latex, a coagulated latex and a rubber substantially as herein described.
|Indian Patent Application Number||2619/DEL/2005|
|PG Journal Number||52/2010|
|Date of Filing||30-Sep-2005|
|Name of Patentee||THE BOARD OF THE RUBBER RESEARCH INSTITUTE OF MALAYSIA|
|Applicant Address||260 JALAN AMPANG, 50450 KUALA LUMPUR, MALAYSIA.|
|PCT International Classification Number||C08C 1/15|
|PCT International Application Number||N/A|
|PCT International Filing date|