WO2003016029A2

WO2003016029A2 - Elastomeric products

Info

Publication number: WO2003016029A2
Application number: PCT/GB2002/003736
Authority: WO
Inventors: Peter Warren
Original assignee: James Walker & Company Limited
Priority date: 2001-08-14
Filing date: 2002-08-14
Publication date: 2003-02-27
Also published as: WO2003016029A3; GB0119835D0

Abstract

A method of manufacturing an elastomeric garment comprises providing at least two layers of material, at least one of these layers comprising thermoset material, silica particles and at least 25% by volume of particulate tungsten material having a radiation absorbing capacity equivalent to that of at least 0.13 millimetres thickness of lead, and cutting the garnment to shape whilst subjecting the garnment to temperature and/or pressure to bond the at least two layers together, wherein the BET surface area of the silica particles is sufficiently large so as to enable them to promote the formation of cross-linkages between the at least two layers.

Description

ELASTOMERIC PRODUCTS

The present invention relates to the manufacture of elastomeric products.

The present invention finds particular application in the manufacture of garments made from two or more layers of thermoset material which are bonded together (at least in some areas), such as in the manufacture of gloves for, for example, surgical use. It is known to "weld" together two layers of thermoplastic material by subjecting two layers of thermoplastic material to heat and/or pressure. However, in attempts of welding vulcanised elastomers without an interfacial layer of adhesive or unvulcanised layer or thermoplastic elements contained within their structure problems are encountered in that the bond between the layers is not satisfactory. Hence, at least in some aspects, the present invention addresses these problems in relation to thermoset material.

Accordingly, in one aspect the present invention provides a method of manufacturing an elastomeric garment comprising providing at least two layers of material, at least one of these layers comprising thermoset material, silica particles and at least 25% by volume of particulate tungsten material having a radiation absorbing capacity equivalent to that of at least 0.13 millimetres thickness of lead; and cutting the garment to shape whilst subjecting the garment to temperature and/or pressure to bond the at least two layers together, wherein the BET surface area of the silica particles is sufficiently large so as to enable them to promote the formation of cross-linkages between the at least two layers.

Pursuant to the present invention it has been found that bonding strength is increased with an increase of the BET (after Brunauer, Emmett and Teller) surface area of the silica particles. Examples of suitable BET surface areas are larger than 100, 120, 140, 150, 155, 160, 165 and preferably 170 square metres per gram. It will be understood that these BET surface areas are nominal values. The amount of silica may affect the resilience of the elastomer and/or other physical properties. A preferred amount of silica is from 20 to 50pphr (parts per hundred of rubber), more preferably from 20 to 40pphr. Satisfactory results have also been obtained using 10 or 15 pphr by weight.

The degree of interfacial cross-linking may also be influenced by temperature and/or pressure to which the material is subjected and/or other additives contained in the rubber formulation.

Thus in a method of the invention the thermoset material may be heated to a temperature of from 120 to 200°C, preferably from 150 to 180°C. The thermoset material may be subjected to a pressure which would generally produce from 20 to 40% compression in thickness.

The time of treatment under temperature and/or pressure may vary but may preferably be from 2 to 20 minutes, more preferably from 3 to 5 minutes, dependent upon temperature.

The thermoset material may comprise any conventional materials known per se. Such materials include, in particular, natural rubber and synthetic thermoset rubbers. Synthetic rubbers include, inter alia, polychloroprenes, ethylene propylenes, nitriles and other known synthetic rubbers.

A particularly preferred silica component is Ultrasil (trademark) and especially Ultrasil VN3, available in the UK from Degussa.

Thus an especially preferred composite thermoset material comprises a mixture of EPDM (ethylene propylene diene monomer-derived ) rubber and silica, eg. Ultrasil VN3.

The cutting and welding may be carried out using conventional methods known per se. However, in a preferred embodiment the cutting and welding may be carried out using a profiled cutting blade. A preferred profiled cutting blade comprises a blade constructed of conventionally known material and has a proximal end and a distal cutting end. The distal cutting end is provided with a shoulder region adjacent the cutting end and which can act as a compression member during cutting.

The dimensions of the shoulder region may vary depending upon the thermoset material used in the garment and the thickness and/or width of the seam desired. The shoulder region generally comprises a substantially flat surface, substantially perpendicular to the direction of cutting. Alternatively, the shoulder region may be angled to the perpendicular, e.g. up to about 15 degrees either side of the perpendicular.

The distances of the shoulder region surface from the cutting end will vary, depending on the desired compression. Good results have been obtained with 20 to 40% compression.

If, for example, the garment comprises two 0.5mm thick sheets and a compression of 30% is desired then the shoulder could be a distance of 0.7mm from the cutting end.

It is preferred that, when being cut, the garment is placed on a suitable support such as a nylon sheet. The cutting end of the tool can then cut into the support on which the garment is placed. Using the example in the previous paragraph, the distance of the shoulder region surface from the cutting end would suitably be 1.0mm, whereby the cutting tool is controlled so that it cuts 0.3mm into the nylon sheet, leaving a distance of 0.7mm between the nylon sheet and the shoulder.

The invention also provides the use of a profiled cutting member as hereinbefore described in the manufacture of a thermoset elastomeric garment. Whilst the method of the invention may be suitable for the manufacture of any conventionally known thermoset elastomeric articles, including, for example, inflatable craft, bellows, gloves, etc., the method of the invention is especially useful in the manufacture of gloves.

The inclusion of particulate tungsten material provides a convenient x-ray attenuating or absorbing material in the elastomeric material. As this may decrease the strength of the elastomeric material, it may be desirable to provide a flexible reinforcement layer, such as a cotton layer or a layer containing a cross-linkage promoter, so as to increase the strength of the elastomeric layer. Problems may arise because the bond between the elastomeric layer and the reinforcement layer may be unsatisfactory. The present invention also addresses this problem.

The present invention also provides a method of manufacturing an elastomeric article comprising providing at least one layer of thermoset material; providing a reinforcement layer for bonding to the at least one layer of thermoset material, wherein the reinforcement layer includes a cross-linkage promoter, and bonding the reinforcement layer to the at least one layer of thermoset material, wherein cross-linkages between the at least one layer of thermoset material and the reinforcement layer are formed, aided by the presence of the cross- linkage promoter.

Preferably, the bonding is controlled to leave sufficient residual cure sites for sequent cutting and/or welding operations.

At least one layer of thermoset material preferably also includes a cross- linkage promoter, preferably the same as the reinforcement layer. Preferably, the cross-linkage promoter comprises silica. The reinforcement layer may comprise fibrous material or fabric material. The at least one layer of thermoset material may include tungsten. In another aspect the present invention provides a method of manufacturing an elastomeric article comprising providing at least two layers of material, at least one of these layers comprising thermoset material; a first step of vulcanising the thermoset material; a second step of joining the at least two layers; a third step of further vulcanising the thermoset material so as to form cross- linkages between the at least two layers, wherein the third step is carried out after the second and the second after the first step, and wherein the level of vulcanisation in the first step is controlled such that the thermoset material can be further vulcanised during the third step so as to form the cross-linkages between the at least two layers.

Controlling the level of vulcanisation may comprise controlling the duration of the first step and/or temperature, type of curative and/or amount of curative used in the first step. Preferably, a said layer is a reinforcement layer.

The present invention also extends to the use of silica as a promoter for interfacial cross-linkages between two layers of thermoset material in a method of manufacturing an elastomeric article which comprises bonding together the layers.

Preferably, priorto bonding the thermoset materials are cured, the level of the curing being controlled so as to control the cross-linkages between the at least two layers.

Preferred features to the extent not foreshadowed here are set out in the dependent claims.

The present invention also extends to starting products used in the method aspects of the present invention, such as thermoset material in sheet form containing appropriate grades of silica etc.

In any of the above aspects the thermoset material may be replaced by thermoplastic material. The present invention also provides a method comprising forming an article, preferably an elastomeric garment, comprising elastomeric material and metal particles located in cavities within the elastomeric material; and detaching the metal particles from the elastomeric matrix so as to decrease the modulus of the elastomeric material.

The present invention further provides a method of processing an elastomeric article, preferably an elastomeric garment, comprising metal particles located in cavities within the elastomeric material, the method comprising detaching the metal particles from the elastomeric matrix so as to decrease the modulus of the elastomeric material.

Preferably, detaching the metal particles comprises stretching the article, preferably so that it yields.

Detaching the metal particles may comprise at least one of stretching the article by at least 80%, heating the article, detaching the metal particles comprises exposing the article to steam, and chemically detaching the metal particles. The metal particles preferably comprise tungsten, and preferably have a diameter of between 1 and 100 micrometres, preferably 5 micrometres.

The method may comprise covering the article at least partly and preferably fully with a skin layer not comprising metal particles. The article may be covered with said skin layer either before or after the detaching step.

Preferred features of the present invention will now be described, by way of example only, with reference to the accompanying drawing, which shows a shouldered cutting tool used in the present invention, and by means of the following embodiments.

Embodiment 1 Two sheets of thermoset material were prepared and bonded together as described hereafter. The thermoset material had the following formulations:

Example 1

Example 2

Pairs of sheets of 0.5mm thickness were prepared from each of these formulations and part-cured in a curing press to an extent which would allow further curing later on, and so as to reach a handlable state. In this embodiment the top platen of the press gave a temperature of between 150 and 180°C on that side of the sheet. State-of-cure (as determined using a Monsanto ODR) was allowed to become between 10% and 30% (10% referring to 10% cross-links, 30% to 30% cross-links). The normal state-of-cure for moulded garment is about 90%. The sheets were formed with an embossed finish.

After this incomplete curing process the sheets were aligned on top of each other and cut to shape, using the cutting tool illustrated in figure 1 , with simultaneous welding near the cut. Aided by the embossed finish, the sheets did not stick together in areas other than those where they were welded together by the cutting tool. A further post-welding cure may be conducted in, for example, an oven, in order to optimise the mechanical properties of the final product.

The cutting tool 1 comprises a proximal end 2 and a distal cutting end 3. The cutting end 3 is provided with a shoulder region 4 which enables abutment against a seam of two sheets 5, 6 of thermoset material so as to compress these. Heat was applied via cutting tool 1 to the seam for 2 minutes (a preferred range being 3 to 5 minutes). The material was heated at the seam to 120°C to 200°C (a preferred range being 150°C to 180°C). Pressure was applied by means of the shoulder region 4 so as to achieve a compression of from 20% to 40%. Due to the presence of silica, and in particular the selected grade of silica, cross-linkages between the two sheets 5 and 6 were formed, which resulted in a satisfactory seam.

Embodiment 2

The technique of Embodiment 1 was used. However, tungsten powder of a nominal particle size of 5 micron was added to the formulations of thermoset material so as to provide the elastomeric material with X-ray shielding properties.

Different tungsten loadings at 30, 35, 40, 45 and 50% by volume were used. The sheets were then prepared and bonded together with simultaneous cutting to shape as described in Embodiment 1.

Embodiment 3

This is a modification of Embodiments 1 and 2, in that a reinforcement layer was bonded to a sheet of thermoset material used in Embodiments 1 and 2.

Reinforcement layers were prepared using the following formulation:

Example 3

After mixing on a laboratory mill, the compounds for the reinforcement were dissolved in toluene and coated onto a layer of 350 micrometres "Melinex" polyester film. This was dried and inverted onto a sheet of thermoset material of Embodiment 1 (without tungsten) or of Embodiment 2 (with tungsten) that had been cured for 1.6 minutes at 180°C. This gave it a state-of-cure of approximately 20%. The sheet of thermoset material and the reinforcement layer were then placed in a vulcanising press under moderate pressure for three minutes at 180°C so as to bond the two layers together. Various values of pressure, duration and temperature can be chosen for this curing step. The relevant criteria are that a satisfactory cure state of the layers and sufficient cross-linkage between the layers should be achieved. Finally, the polyester film was peeled off the two layers.

Embodiment 4

This embodiment essentially follows the technique used in Embodiment 3, but the curing step for bonding the sheet of thermoset material and the reinforcement layer together was controlled so that curing would not be complete. A glove was then formed from this laminate consisting of the sheet of thermoset material and the reinforcement layer. To this end, two portions of this laminate were laid on top of each other, with the two reinforcement layers opposing each other, i.e. the two layers of thermoset material were on the outside. Cutting and welding was then performed as described in connection with Embodiment 1 or Embodiment 2 such that, at the seam, the two reinforcement layers would be bonded together by the formation of cross-linkages therebetween. As in Embodiment 1 , aided by the embossed finish the layers did not stick together in areas other than those where they were welded together. On completion of this welding step the final product was inverted so that the reinforcement layers would be located on the outside of the resulting glove, the two thermoset layers being located on the inside of the glove. A post-welding cure may also be conducted in order to optimise mechanical properties.

Embodiment 5

This embodiment is applicable to elastomeric garments in general, i.e. not restricted to those made from thermoset material, although it will be explained with reference to thermoset material. An elastomeric, tungsten-loaded garment in sheet form was made from the formulations described above in connection with Embodiment 1 , with tungsten- loading as per Embodiment 2. Tungsten-loaded particles having a diameter of between 1 and 100 micrometers were hence located in cavities of the elastomeric material. The garment was then stretched by about 80%, which broke the mechanical bond between the tungsten particles and the elastomeric material, i.e. the tungsten particles became detached from the elastomeric matrix, and the garment yielded. This substantially decreased the modulus of the garment, and the yielded garment was useable up to an elongation of about 500%. As a result, the garment was softer, providing more touch sensitivity.

As the stretching breaks the mechanical bond between the tungsten particles and the elastomeric material there is the danger that tungsten particles located on the surface of the garment are completely separated from the garment, which may, in some cases, represent a health risk. In order to counter this the garment was covered with a skin layer such as the reinforcement layer of Embodiments 3 or 4. This skin layer can be applied before or after the "detaching".

In further experiments other particle sizes between 1 and 100 micrometers were used.

Other methods of detaching the tungsten particles from the elastomeric matrix are envisaged. These include heating the garment to about 180°C, applying steam at temperatures above those normally used for sterilisation, e.g. 160°C, detaching the particles chemically by swelling in media such as ethylene oxide, or fatiguing the material by flexing at one point.

It will be appreciated that metal particles other than tungsten particles could be used. Modifications

Although specific formulations of thermoset material have been disclosed above it will be appreciated that others will also be suitable. Likewise, any specific temperature ranges, curing times and percentages of state-of-cure have been indicated by way of example only.

Departing from the above examples, compositions with between 10 and 15 pphr of silica provided satisfactory results.

As a modification of Embodiment 3, instead of preparing a solution of the reinforcement formulation and applying this to a polyester film the reinforcement formulation can also be provided as a calendered sheet. This sheet can then be bonded to the sheet of thermoset material as described in Embodiment 3.

When welding together two sheets which are to be bonded together only in some areas, it is possible to place a separating sheet such as a sheet of fabric between the two sheets before the cutting and welding step instead of (or in addition to) forming them with an embossed finish so as to avoid the formation of cross- linkages between these two layers in certain areas.

While the present invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes may be made to the invention without departing from its scope as defined by the appended claims.

Each feature disclosed in this specification (which term includes the claims) and/or shown in the drawings may be incorporated in the invention independently of other disclosed and/or illustrated features. Several of the materials referred to in this specification are specific to certain manufacturers / suppliers. These are listed below.

Claims

1. A method of manufacturing an elastomeric garment comprising providing at least two layers of material, at least one of these layers comprising thermoset material, silica particles and at least 25% by volume of particulate tungsten material having a radiation absorbing capacity equivalent to that of at least 0.13 millimetres thickness of lead; and cutting the garment to shape whilst subjecting the garment to temperature and/or pressure to bond the at least two layers together, wherein the BET surface area of the silica particles is sufficiently large so as to enable them to promote the formation of cross-linkages between the at least two layers.

2. A method according to Claim 1 , wherein the BET surface area is between 100 and 200 square metres per gram.

3. A method according to Claim 1 , wherein the BET surface area is larger than 120, more preferably larger than 140, more preferably larger than 155, more preferably larger than 170 square metres per gram.

4. A method according to any preceding claim, wherein the BET surface area is 175 square metres per gram.

5. A method according to any preceding claim, wherein there are 20 to 50 parts of silica per 100 parts of elastomer, by weight.

6. A method according to any preceding claim, wherein during cutting the layers are subject to a temperature in the range 120° to 200°C.

7. A method according to any preceding claim, wherein during cutting the layers are subjected to pressure such as to compress them by from 20% to 40% in thickness.

8. A method according to any preceding claim, wherein the heat and/or pressure is/are applied for from 2 minutes to 20 minutes.

9. A method according to any preceding claim, wherein the cutting is effected by a shouldered cutting tool.

10. A method according to any preceding claim, wherein the thermoset material is a natural or synthetic rubber.

11. A method according to any preceding claim, wherein one of said layers comprises a reinforcement layer including a cross-linkage promoter.

12. A method according to Claim 11 , wherein the cross-linkage promoter comprises silica.

13. A method according to Claim 11 or 12, wherein the reinforcement layer comprises fibrous material or fabric material.

14. A method according to any preceding claim, wherein, prior to said bonding, said at least one layer is subject to a first vulcanisation, and subsequently, said layers are subject to a second vulcanisation so as to form cross-linkages between the layers, wherein the level of the first vulcanisation is controlled such that the thermoset material can be further vulcanised during the second vulcanisation so as to form the cross-linkages between the layers.

15. A method according to Claim 14, wherein the control of the level of the first vulcanisation comprises controlling the duration and/ortemperature, type of curative and/or amount of curative used in that vulcanisation.

16. A method comprising forming an article comprising elastomeric material and metal particles located in cavities within the elastomeric material; and detaching the metal particles from the elastomeric matrix so as to decrease the modulus of the elastomeric material.

17. A method of processing an elastomeric article comprising metal particles located in cavities within the elastomeric material, the method comprising detaching the metal particles from the elastomeric matrix so as to decrease the modulus of the elastomeric material.

18. A method according to Claim 16 or Claim 17, wherein detaching the metal particles comprises stretching the article, preferably so that it yields.

19. A method according to any one of Claims 16 to 18, wherein detaching the metal particles comprises stretching the article by at least 80%.

20. A method according to any one of Claims 16 to 19, wherein detaching the metal particles comprises heating the article.

21. A method according to any one of Claims 16 to 20, wherein detaching the metal particles comprises exposing the article to steam.

22. A method according to any one of Claims 16 to 21 , wherein detaching the metal particles comprises chemically detaching the metal particles.

23. A method according to any one of Claims 16 to 22, wherein the metal particles comprise tungsten.

24. A method according to any one of Claims 16 to 23, wherein the metal particles have a diameter of between 1 and 100 micrometres, preferably 5 micrometres.

25. A method according to any one of Claims 16 to 24, comprising covering the article at least partly and preferably fully with a skin layer not comprising metal particles.

26. A method according to Claim 25, comprising covering the article with said skin layer before the detaching step.

27. A method according to Claim 25, comprising covering the article with said skin layer after the detaching step.

28. A method substantially as herein described with reference to, or as illustrated in the accompanying drawings.