GB2053927A - Improvements in the manufacture of rubber products - Google Patents

Abstract

White factice for incorporation into rubber compositions for the manufacture of very thin rubber products in such as bathing caps and hospital sheeting, is first mixed with a sufficient quantity of a powder to provide a powder coating on each and all of the ultimate particles, this mixing being achieved e.g. by means of rotatable paddle blades within a mixing container. The factice/powder mix is then transferred to a processing container in which the factice particles are subjected to the impacting action of e.g. an edged blade revolving at a high speed in excess of 1,000 r.p.m. The edge of the blade cuts through the particles in an atmosphere loaded with the powder which coats the freshly exposed surfaces and prevents them adhering together again. The factice is produced by sulphurisation of vegetable oils in known manner.

Description

SPECIFICATION Improvements in the manufacture of rubber products This invention is concerned with improvements in, or relating to the manufacture of sulphurised vegetable oils.

It is well known that many vegetable oils such as rape oil, palm oil, cotton seed oil, etc. may be reacted with sulphur chloride to produce a material known commercially as white factice.

This material is used chiefly in the rubber trade where it may be used as a filler or extender, when it is sometimes referred to as white rubber substitute. The white factice is also incorporated into rubber because of certain characteristics it imparts during the processing of the rubber or to the finished rubber article. For example, it exerts a softening action on the rubber compound which enables the rubber compound to be calendered or moulded more easily and it imparts a "handle" or texture to the finished rubber article which improves its suitability for some purposes.In the manufacture of such sulphurised oils, after the reaction of the vegetable oil and sulphur chloride, the resulting mass is cooled and then ground down by any of the known techniques such as by passing the product through a two roll mill in which the rolls are preferably travelling at different surface speeds and exerting a shearing action. The product is then a soft spongy mass of granules which are slightly self tacky so that under slight pressure they compact into a light, porous spongy mass which requires significant effort to disintegrate it into its original granules or ultimate particles. Such a force is provided by the rubber mixing machinery in commercial use and no difficulty is experienced in breaking down the factice agglomerates and incorporating the factice into a rubber compound in this way.A facticeloaded rubber compound prepared in this way is suitable for many applications such as the manufacture of erasers or sheeting calendered on to a fabric base. However, factice prepared in this way usually contains a proportion of its weight in the form of firm resilient granules of non-standard composition varying in size from 0.1 mm to 0.5 mm in their greatest dimension. The presence of these non-standard bodies prevents the use of the factice in very thin rubber products such as bathing caps and hospital sheeting which may have a thickness of no more than 0.2 mm. As a result, alternative materials of possibly a more expensive and less satisfactory character may have to be used.

The object of the present invention is to provide a means of removing these resilient granules from the factice and thereby rendering it suitable for use in rubber articles of thickness down to 0.2 mm or even less. It is impracticable to attempt to screen them out as the factice immediately clogs the screen. They cannot be ground down to a finer size because being resilient, they merely become deformed on passing through the nip or gap of the grinding plant and recover on emerging. For the same reason, once the factice has been incorporated into the rubber and evenly dispersed, these granules are unaffected by the rolls of the mixing mill and retain their original form.

In the present invention the first stage is to mix into the factice a proportion of a suitable powder.

Such a powder may be one which is incorporated into rubber as an inert filler as, for example, china clay or whiting. Other suitable powders are mineral colours such as yellow ochre, red iron oxide or green chromium oxide, or opaque bases like zinc oxide, titanium dioxide and magnesium carbonate. It is clearly an advantage if the powder used is one which in any case would be used in the rubber mixture, when the only processing alteration is an adjustment of the formula to accommodate the additional powder being added with the factice.

The proportion of powder to factice can be anything above a specific minimum providing it does not exceed the total proportion required by the mix formula. The minimum proportion is that necessary to provide a coating on each and all of the ultimate factice particles and depends on the particle size of the powder and the size of the factice particles. With powders of exceptionally small particle size such as titanium dioxide it may be found that 5% on the wieght of the factice is sufficient whilst with coarse powders such as ground limestone it may be necessary to use 20%.

The powder and factice are intimately mixed by any of the conventional methods used for mixing materials of this nature. A widely used mixer has a vertical shaft carrying rotatable paddle blades within a suitable container. The action of such a mixer is to reduce the lumps of factice to granules of roughly 1.0 mm to 4.0 or 5.0 mm. Such granules remain in discreet form and do not agglomerate together under the pressure of the paddle blades because of the coating of powder.

Prolonged stirring does not significantly reduce the size of the granules. This is because the granules, which comprise agglomerates of factice particles held together by their self tacky surfaces, have the resilient characteristics of rubber.

We have found that to reduce the granules to their ultimate particles it is necessary to exert an impacting action on each granule or suh-granule and at the same time coat the freshly exposed surfaces with powder to prevent them adhering together again. We have found that this can be done by using an edged blade revolving at very high speed in an enclosed container, the speed of the revolving blade preferably exceeding 1,000 r.p.m. The edge cuts through the granules because of its high velocity, reducing them to their ultimate factice particles in an atmosphere loaded with powder. The final product is a free flowing powder which can be readily screened.

Although the factice powder can be screened at any time after its preparation, we have found it advantageous to incorporate a screen of the desired mesh size in the outlet from the processing container. By this means any unbroken granules are retained in the processing area until they have been broken down and the firmer nonstandard material is removed from the factice powder unless it is of insignificant dimensions and passes through the mesh of the screen. A convenient size of screen is 60 mesh although for very refined work 100 mesh may be used and the product passing it is then suitable for thin rubber products.

Claims (20)

1. A process for the treatment of white factice produced by sulphurisation of a vegetable oil to disperse resilient granules therein, comprising the steps of mixing with the factice a quantity of powder which is at least sufficient to provide a powder coating on each and all of the ultimate factice particles, and exerting an impacting action on the granules to reduce them to their ultimate particles whiie at the same time coating the freshly exposed surfaces with powder to prevent them adhering together again.

2. A process according to claim 1, wherein the powder is mixed with the factice by means of a rotatable paddle blade or blades within a mixing container in which the mixing action reduces initial lumps of factice to granules of roughly 1.00 mm to 4.0 or 5.0 mm in size.

3. A process according to either one of the preceding claims, wherein said impacting action to reduce the granules is done by means of an edged blade revolving at high speed in an enclosed processing container, with the edge of the blade cutting through the granules and reducing them to their ultimate factice particles in an atmosphere loaded with powder, whereby the final product is a free-flowing powder.

4. A process according to claim 3, wherein said blade is revolved at a speed in excess of 1,000 r.p.m.

5. A process according to claim 3 or 4, wherein the free-flowing powder product is screened at the outlet from the processing container.

6. A process according to claim 5, wherein the screening employs a screen of 60 mesh at said container outlet.

7. A process according to claim 5, wherein the screening employs a screen of 100 mesh at said container outlet.

8. A process according to any one of the preceding claims, wherein the powder mixed with the factice is of small particle size aliowing a minimum quantity of about 5% of the weight of the factice to be used.

9. A process according to any one of claims 1 to 7, wherein the powder mixed with the factice is of a fairly coarse nature and a minimum quantity of about 20% of the weight of the factice is required.

10. A process according to claim 9, wherein said powder is ground limestone.

11. A process according to any one of claims 1 to 9, wherein the powder mixed with the factice is one which is commonly incorporated into rubber compounds as an inert filler.

12. A process according to claim 11, wherein said inert filler powder is china clay or whiting.

13. A process according to any one of claims 1 to 9, wherein the powder mixed with the factice is a mineral colour such as yellow ochre, red iron oxide or green chromium oxide.

14. A process according to any one of claims 1 to 9, wherein the powder mixed with the factice is an opaque base like zinc oxide, titanium dioxide and magnesium carbonate.

1 5. White factice in the form of a free-flowing powder produced by a process in accordance with any one of the preceding claims.

16. A rubber compound containing white factice according to claim 1 5.

1 7. A rubber compound according to claim 16, wherein the powder mixed with the factice during the production thereof is one used in the rubber compound mix, the formula of the latter being adjusted to accommodate the additional powder added with the factice.

1 8. A thin rubber product containing white factice according to claim 1 5.

1 9. Apparatus for carrying out a process according to claims 2 and 3, comprising said mixing container with rotatable paddle blades mounted on a vertical shaft, and said processing container with enclosed rotatable edged blade.

20. A process for dispersing lumps and granules in white factice to produce a free-flowing powder product, substantially as described.