WO2007091061A1

WO2007091061A1 - Reducing mitrosamine formation in rubber products

Info

Publication number: WO2007091061A1
Application number: PCT/GB2007/000424
Authority: WO
Inventors: James Richard Allan Pollock
Original assignee: Broadlab Limited
Priority date: 2006-02-08
Filing date: 2007-02-08
Publication date: 2007-08-16
Also published as: GB2435042A; GB0602431D0; GB0702532D0

Abstract

This invention relates generally to rubber products. In particular, but not necessarily restricted thereto, the present invention relates to rubber products which are handled or worn by human beings; more particularly, the present invention relates to a reduction of the effects of nitrosatable substances associated such rubber products. One skilled in the art will appreciate that the polymer contained in natural rubber latex and certain other rubber lattices can be cross-linked without prior coagulation as the product is, in effect, a latex of vulcanized rubber. In manufacturing industries, natural rubber latex is usually pre-vulcanized by heating with dispersions of sulphur and an accelerator, such as zinc diethyldithiocarbamate, to 50-80 °C. The reaction proceeds much more rapidly than the vulcanization of dry rubber at the same temperature with the same vulcanizing ingredients. However, certain ingredients used in manufacture of rubber products such as dithiocarbamate accelerators (vulcanization agents) and substances formed therefrom during vulcanisation are believed to react with nitrites present in human and animal body fluids to produce unacceptable levels of potentially carcinogenic nitrosamines. Furthermore, new constraints of a toxicological nature have appeared in recent years based on various national and regional regulations. The present invention seeks to provide an improved rubber composition. In particular, it seeks to provide a method of producing rubber products, especially those which come into contact with human and/ or animal body fluids which have a reduced tendency to produce nitrosamines during such contact.

Description

REDUCING MITROSAMINE FORMATION IN RUBBER PRODUCTS

FIELD OF THE INVENTION

This invention relates generally to rubber products. In particular, but not necessarily restricted thereto, the present invention relates to rubber products which are handled or worn by human beings; more particularly, the present invention relates to a reduction of the effects of nitrosatable substances associated therewith.

BACKGROUND TO THE INVENTION

It is known that polymers contained in natural rubber latex and certain other rubber lattices can be cross-linked without prior coagulation as the product is, in effect, a latex of vulcanized rubber. In manufacturing industries, natural rubber latex is usually pre- vulcanized by heating with dispersions of sulphur and an accelerator, such as zinc dialkyldithiocarbamates and metal alkylxanthates, may also be required. The reaction proceeds much mote rapidly than the vulcanization of dry rubber at the same temperature with the same vulcanizing ingredients. Some non-rubber constituents of ammonia-preserved natural rubber latex also act as accelerators. Natural rubber latex can also be pre-vulcanized by heating with peroxides and by irradiation. Thiazoles are sometimes used as secondary accelerators. Accelerators are widely available in the form of their zinc salts and therefore frequently used in such form.

However, certain ingredients used in the manufacture of rubber products such as dithiocarbamate accelerators (vulcanization agents) and substances formed therefrom are believed to react with nitrites present in human and animal body fluids to produce unacceptable levels of potentially harmful nitrosamine compounds. Thus, it is believed, that concentrations of nitrosatable secondary amines or their derivatives in rubber latex products need to be kept to a minimum. The main sources of secondary amines and their derivatives, and hence of nitrosamines, in rubber latex products are thiurams and dithiocarbamates such as zinc dialkyldithiocarbamates or zinc dibenzyldithiocarbamate accelerators. The dialkyldithiocarbamates and zinc dibenzyldithiocarbamate accelerators produce dialkylamines and dibenzylamines and derivatives thereof which are readily nitrosated, yielding objectionable levels of nitrosamines. Furthermore, new constraints of a toxicological nature have appeared in recent years based on the strict European regulations which limit the amount of nitrosamines and nitrosatable substances that can migrate into solution and be present in fluids. European standard, EN12868, exists to maintain levels in certain products to tolerable levels, in view of the carcinogenic effect of nitrosamines.

In the case of toy balloons, since saliva in the mouth and acids in the stomach will react with nitrosatable compounds being vulcanisation by-products of the rubber balloon products, it is now stated on the packaging of such toy balloons that the balloon must be inflated with an inflator. These nitrosatable products will be present on surfaces of the balloon and will leach from any parts of the balloon having a substantial thickness; Not only will there be issues of safety regarding the inflation of balloons by mouth, care should be taken with babies who may wish to play with the balloon (when inflated or deflated) and perhaps chew the same.

Latex balloons were first manufactured in 1847, in the United Kingdom. The product, the market and the technology have naturally made giant strides since then. In recent years a number of European governments and environmental bodies have been investigating the levels of nitrosamines and nitrosatable compounds in foods and everyday consumer products. Nitrosamines form a group of substances that have been found by researchers to be potential carcinogens. .

Within the EU, legislation only exists for infant's teats and soothers. In Germany, approximately 10 years ago, and in The Netherlands, approximately one year ago, guidelines were given for the levels of nitrosamines / nitrosatable substances in toy balloons. These guidelines were based largely on the legislation for teats and soothers and the limits set for toy balloons reflect migration per unit area rather than per unit weight, as for teats and soothers. Teats and soothers, like balloons are dipped latex products. Whilst, teats and soothers have prolonged oral contact with infants and balloons are typically inflated only once, it is upon first use that maximum leaching of any nitrosamines / nitrosatable substances will occur. New balloons are frequently inflated orally, several at a time; the nitrosamines and other release agents are responsible for the sour taste that is left in one's mouth. It is also the case that when a balloon, that has been inflated orally, is burst in the vicinity of children and adults then those children and adults will be sprayed with a carcinogen-rich saturated vapour. Ideally balloon pumps are employed, but this is not widespread. Thus, the issues that arise through an infant's use of teats or soothers equally apply to oral balloon inflation and there are in place strict controls on the levels of nitrosamines / nitrosatable substances. Similar nitrosatable activity will occur in the use of rubber gloves, footwear, and condoms.

In order to prevent or at least reduce the formation of nitrosamines during the vulcanization of rubber, two methods have been variously adopted, namely to avoid secondary amines, or to avoid / eliminate nittosating agents.

In the vulcanization of rubber, nitrosamines are primarily formed by the nitrosation of secondary amines, as discussed above. These secondary amines are, in turn, cleavage products of the accelerator required for vulcanization. Oxides of nitrogen (NOx) are present in the air and also in components of the rubber mix. Recommendations for minimizing carcinogenic nitrosamines include the use of high-ammonia natural rubber latex concentrate or low-ammonia concentrates free of secondary preservatives which give rise to secondary amines and the use of dithiocarbamate accelerators of low water solubility such as zinc dibenzyldithiocarbamate, which liberate amines of high molecular weight and low solubility in water.

In a report entitled "Nitrosamine Solutions", by Robinson Brothers Limited, ref 03/2003, the use of inhibitors is discussed and dismissed; chemicals such as ascorbic acid, α-tocopherol, calcium oxide and formaldehyde resins were employed. It was suggested that nitrosamine inhibitors should be used as a last resort and in combination with accelerators.

EP-A- 0 476 334 teaches of the use of alkaline earth oxides and hydroxides to reduce nitrosamine content in rubber compounds.

JP58002337 advises that to prevent the formation of nitrosamine caused by the nitrogen- containing vulcanization accelerator and vulcanization assistant in the vulcanization reaction, by adding vitamin E or caffeic acid or ferulic acid to a natural rubber or synthetic rubber composition.

US2004106743 teaches of a composition which is without precursor of at least one carcinogenic nitrosamine and which comprises a selected rubber capable of vulcanization at a temperature of between 95 - 140° C and that the vulcanization system employs sulphur, at least one accelerator compound selected from the group consisting of benzothiazyl disulfide and mercaptobenzothiazole and at least one ultra-accelerator compound selected from the group consisting of tetrabenzylthiuram disulfide and zinc dibenzyldithiocarbamate.

OBJECT OF THE INVENTION

The present invention seeks to provide an improved rubber composition. In particular, it seeks to provide a method of producing rubber products, especially those which come into contact with human and/or animal body fluids. The present invention also seeks to provide rubber products such as gloves, toy balloons, condoms and teats that are safe to use.

STATEMENT OF THE INVENTION

In accordance with a first aspect of the invention there is provided a method of producing a rubber product wherein a compound of the sulphamyl group is provided whereby the formation of nitrosamines from nitrosatable substances from product is significantly reduced.

The method can comprise the step of adding a compound of the sulphamyl group to a rubber product, wherein the sulphamyl compound is applied to a surface of a rubber product as a powder, an aerosol, an aqueous solution — by spraying or rinsing - which solution is subsequently dried. The sulphamyl solution conveniently comprises an aqueous solution of ammonium sulphamate having a concentration in the range of 0.1 — 1.0 mg/1, preferably in the range 0.25 — 0.5mg/l, the method including the step of drying at an elevated temperature until dry.

The method can comprise the step of adding the sulphamyl compound to a pre- vulcanisation rubber composition, whereby the sulphamyl compound is distributed within a completed product. Conveniently, the sulphamyl compound is mixed as an aqueous solution with a pre-vulcanisation product whereby the sulphamyl compound is distributed within a completed product, in a range of 0.001 — 0.1 percent composition. Preferably, the sulphamyl compound comprises a 0.03 — 0.01 percentage composition within a completed product.

A sulphamyl compound conveniently comprises a compound of the formula RSO₂NH₂, where R is NH₄O, NH₂, OH or metal-ion-O.

In accordance with a second aspect of the invention, there is provided a rubber product in which any nitrosatable substances are substantially prevented from forming nitrosamines upon contact with body fluid, for example gloves, footwear, toy balloons, condoms and teats. The use of a compound of the sulphamyl group will have been applied to the product in either a pre-vulcanisation stage or in a post-vulcanisation stage. The compound may have been added to a pre-vulcanisation rubber compound as a powder. The compound may have been applied to a surface of a post-vulcanisation rubber product as an aerosol, powder, spray or solution to a surface of the rubber product.

The present invention also resides in a rubber product being one of a glove, footwear, toy balloon, condom and teat, wherein the surface of the rubber has traces of a compound of the sulphamyl group thereon.

The present invention also resides in a rubber product being one of a glove, footwear, toy balloon, condom and teat, wherein the body of the rubber has traces of a compound of the sulphamyl group therein, having been added to the product in a pre-vulcanisation stage.

Upon contact with a rubber product, which has free nitrosatable substances associated therewith, either as a surface product or as a leachable substance, the sulphamyl group will limit the conversion of the nitrosatable substances when in contact with body fluids and thereby to substantially prevent the formation of nitrosamines from nitrosatable substances.

BRIEF DESCRIPTION OF THE TABLES

For a better understanding of the present invention, reference will now be made, by way of example only, to the Tables as shown in the accompanying drawing sheet, wherein: -

Table 1 is a comparison of a reduction in nitrosamines from nitrosatable substances;

Table 2 shows a comparison between a concentration of ammonium sulphamate in the treated latex and an amount of nitrosatable substances in rubber product; and,

Table 3 shows a single result for when a concentration of a sulphamate is present in the treated latex and an amount of nitrosatable substances in rubber product.

DETAILED DESCRIPTION QF THE INVENTION

There will now be described, by way of example only, the best mode contemplated by the inventor for carrying out the present invention. In the following description, numerous specific details are set out in order to provide a complete understanding to the present invention. It will be apparent to those skilled in the art, that the present invention may be put into practice with variations of the specific.

As is well known, rubber is farmed in countries such as Malaysia, from rubber trees, where latex is obtained after cutting through the bark of a rubber tree, where the latex flows as a liquid therefrom. Latex collected in the field is subsequently concentrated (generally by centrifugiog, to ϊemoγe part of the unwanted serum) to a dry rubber content of about 60%. It is then preserved with ammonia to stabilise it and to combat against bacterial growth. This stabilised latex becomes the starting material for all natural latex products, whether produced by dipping (gloves, balloons, condoms, catheters, baby soothers and dental dams) or foaming (latex foam or sponge) or extrusion (latex thread, more commonly known as 'elastic').

To make latex gloves, liquid latex concentrate is first mixed with various compounding chemicals which are essential to produce a strong and stable film after which hand- shaped formers are dipped into the latex mix to acquire a thin layer of the material. Dipping can be done either in the presence or absence of a destabilising chemical (coagulant dip or straight dip respectively). The product is then cured at about 100°- 120°C to turn the liquid latex into a film.

Inventor has found that the incorporation of substances containing the sulphamyl group RSO₂NH₂, where R is NH₄O, NH₂, OH or metal-ion-O in rubber product, can reduce the subsequent formation of nitrosamines upon contact with fluids similar in composition to that of body fluids following exposure to rubber products having nitrosatable substances associated therewith.

In accordance with a first aspect of the invention, a vulcanised rubber product is vulcanised and formed into a desired shape. The product is then sprayed with a 0.35mg/ml aqueous solution of ammonium sulphamate, which is sprayed onto an inside surface thereof by means of a spray nozzle arrangement. This method of application is particularly suitable for rubber gloves, toy balloons and condoms and similar products. Conveniently, this is performed during manufacturing, wherein the product is arranged upon a former on which it is made. The spray is then dried at 60⁰C for a period of twenty minutes in an atmosphere of 10% humidity. The interior surface of products such as toy balloons are conveniently treated by an elongate probe with a nozzle at a distal end thereof, whereby to be readily inserted into such a product. The spraying of exterior surfaces is also recommended. Similar methods can be practiced for gloves and condoms alike, where a thickness of typically 0.2 - 0.5 mm enables the products to be sufficiently well treated whereby the formation of nitrosamines from nitrosatable substances is very much reduced.

Table 1

Referring to Table 1, toy balloons, each of dry weight of about 2g, were treated by the application of an aqueous solution of ammonium sulphamate (0.35 mg/litre) to the inside surface of each balloon, which was subsequently dried at 60⁰C for a period of twenty minutes. The balloons were subjected to the test for the measurement of nitrosatable substances which are stated in European standard EN 12868.

A rubber latex composition of a type which would be useful in making toy balloons, condoms and babies bottles teats and soothers was mixed with ammonium sulphamate solution in water so that the concentration of ammonium sulphamate in the solid rubber obtainable from that latex would be 0.03%, and a thin rubber sheet was cast from this latex so obtained. This rubber sheet (A) and one prepared from the same latex but without the addition of the ammonium sulphamate were examined for nitrosatable substances by the method as prescribed in European standard EN 12868 "Nitrosamines and nitrosatable substances in babies bottles and soothers". It was found that the amount of nitrosatable substances was ten times greater in the untreated product. Specifically, the amount of nitrosatable substances per kilogramme of rubber for treated rubber sheet was 5.2 micrograms; whilst in the untreated rubber the amount was 51.6 micrograms.

In accordance with a second aspect of the invention, for any such products, the original latex may have such sulphamyl substances incorporated into a pre-vulcanisation rubber mixture. This is a preferred method of treatment for the manufacture of products such as footwear (for example plimsolls and trainers) and teats, for feeding bottles of babies, dummies (also known as soothers). Products such as teats have significantly thicker walls of product (for example, between 1 - 5mm), which may mean that a solution applied only on one or both surfaces may not be sufficient, especially considering that teats and the like are subject to sterilisation procedures, typically involving boiling water, which will result in the loss of any non-bound surface compounds, quite readily. Accordingly such techniques are not appropriate to eliminate significant quantities of nitrosatable product. Accordingly, by having sulphamyl products contained within the formed rubber product, nitrosatable products upon coming into contact with body fluids will combine /react with the sulphamyl compounds either within the rubber product or upon being leached from the rubber product, whereby the chances of formation of nitrosamines is substantially reduced. As will be appreciated, lower concentrations of active substance in the original treated latex will provide lower degrees of protection from the formation of nitrosamines from nitrosatable substances. When the concentration of ammonium sulphate in the treated latex was between 0.005% and 0.02%, the results were as follows:-

Table 2

The use of a sulphamide in place of the ammonium sulphamate has also shown to be effective in reducing the conversion of nitrosatable substances into nitrosatnines:- Table 3

Thus it is readily shown that the effect of the use of a sulphamyl group can provide a significant reduction in the amount of nitrosatable substances in rubber product.

Claims

CLAIMS:

1. A method of producing a rubber product wherein a compound of the sulphamyl group is provided whereby the formation of nitrosamines from nitrosatable substances in said product is significantly reduced.

2. A method according to claim 1, wherein the sulphamyl compound is applied to a surface of a rubber product as a powder.

3. A method according to Claim 1, wherein the sulphamyl compound is applied to a surface of a rubber product as an aqueous solution, which solution is subsequently dried.

4. A method according to Claim 3, wherein the sulphamyl solution comprised an aqueous solution of ammonium sulphamate of a concentration in the range of 0.1 - 1.0 mg/1, preferably in the range 0.25 — 0.5mg/l, the method including the step of drying at an elevated temperature until dry.

5. A method according to Claim 1, wherein the sulphamyl compound is applied to a surface of a rubber product as an aerosol.

6. A method according to Claim 1, wherein the sulphamyl compound is applied to a rubber product by means of rinsing in solution, which product is subsequently dried.

7. A method according to Claim 1, wherein the sulphamyl compound comprises part of a pre-vulcanisation rubber composition, the sulphamyl compound being mixed as an aqueous solution with a pre-vulcanisation product whereby the sulphamyl compound is distributed within a completed product, in a range of 0.001 - 0.1 percent composition.

8. A method according to claim 7, wherein the sulphamyl compound comprises a 0.03 — 0.01 percentage composition within a completed product.

9. A method according to any one of Claims 1 - 8, wherein the sulphamyl compound comprises a compound of the formula RSO₂NH₂, where R is NH₄O, NH₂, OH or metal-ion-O.

10. A rubber product being one of a glove, footwear, toy balloon, condom and teat, wherein the surface of the rubber product has traces of a compound of the sulphamyl group thereon.

11. A rubber product according to Claim 10, wherein the sulphamyl compound comprises a compound of the formula RSO₂NH₂, where R is NH₄O, NH₂, OH or metal- ion-O.

12. A rubber product being one of a glove, toy balloon, condom and teat, wherein the body of the rubber has traces of a compound of the sulphamyl group therein, having been added to the product in a pre-vulcanisation stage.

13. A rubber product according to Claim 12, wherein the sulphamyl compound comprises a compound of the formula RSO₂NH₂, where R is NH₄O, NH₂, OH or metal- ion-O.