GB1565688A

GB1565688A - Process for manufacturing tubes

Info

Publication number: GB1565688A
Application number: GB49075/76A
Authority: GB
Original assignee: BOULAIN R
Current assignee: BOULAIN R
Priority date: 1975-11-28
Filing date: 1976-11-24
Publication date: 1980-04-23
Also published as: NL7613279A; JPS5284262A; DE2653211B2; IT1125230B; DE2653211C3; FR2332851A2; DE2653211A1; FR2332851B1; NL187261C

Description

(54) IMPROVEMENTS IN OR RELATING TO A PROCESS FOR MANUFACTURING TUBES (71) I, ROBERT GEORGES PIERRE BOULAIN, a French Citizen of 26, Rue de la Prairie, 28260 Anet, France, do hereby declare the invention for which I pray that a patent may be granted to me and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to a tube and to a process of fabrication of elastomer or plastics material tubes, and to an apparatus for manufacturing such tubes.

According to one aspect of this invention there is provided a tube, said tube comprising an outer tubular member formed from a gelled aqueous dispersion of a sensitized elastomer or plastics material as herein defined, said outer tubular portion having an internal coating of butyl rubber.

In this specification the term aqueous dispersion of a sensitized elastomer or plastics material is used to mean a liquid aqueous dispersion of an elastomer or plastics material, which, when heated, will gell or congeal to form a solid having elastomeric or plastic properties. An example of such a dispersion is natural latex which, on heating gells to form natural rubber.

Preferably said butyl rubber comprises poly-isobutylene and said poly-isobutylene may contain a proportion of poly-isoprene molecules.

Advantageously said poly-isobutylene is vulcanized.

A tube as described above may be intended for use as an inner tube for a bicycle, the thickness of the inner coating of butyl rubber being between 0.03 mm and 0.25 mm. Preferably the thickness of the inner coating of butyl rubber is between 0.05 mm and 0.15 mm, and preferably the thickness of the tube excluding the thickness of the inner coating of butyl rubber is between 0.15 mm and 0.60 mm.

According to a second aspect of this invention there is provided a method of manufacturing a tube according to the first aspect of the invention, said process comprising the steps of passing a sensitized aqueous dispersion of an elastomer or plastics material, as herein defined, from a supply chamber to a shaping device and extruding said dispersion to form an outer tubular element, the dispersion being heated in the shaping device to initiate gelling thereof, said method including the step of applying a continuous inner coating of butyl rubber on the inside of said outer tubular element.

Preferably said coating of butyl rubber comprises poly-isobutylene, and advantageously said poly-isobutylene contains a number of poly-isoprene molecules.

The method may comprise the further step of continuously vulcanizing the inner coating of butyl rubber simultaneously with the step of vulcanizing the gelled dispersion forming the outer tubular element.

Preferably the step of extruding the dispersion through a shaping device comprises the steps of extruding the dispersion downwardly through an orifice defined by two vertical co-axial forming tubes constituting said shaping device, causing liquid butyl rubber emulsion to flow through a channel passing through the inner of said two forming tubes and to flow over a part spherical element located within the said outer tubular element which is extruded from the lower part of said orifice, which part spherical element has an upstanding cylindrical flange on the upper surface thereof, said butyl rubber emulsion being supplied at a controlled rate so that said butyl rubber emulsion overflows from the flange to descend by gravity around said part spherical element, said extruded outer tubular element passing over the part spherical portion and entraining the said butyl rubber emulsion so that the butyl rubber emulsion forms a continuous coating of substantially uniform thickness on the interior of the said tubular element, said butyl latex emulsion gelling to constitute said butyl rubber coating.

Advantageously the method may comprise the further step of injecting air into the interior of the interiorly coated tubular element through a channel extending through said two forming tubes and terminating at the lower region of said part spherical element.

Said injected air may be hot air or warm air.

Preferably the butyl rubber emulsion to be supplied to said part spherical portion is thermally insulated from the warm or hot air being injected into the said tubular element, the butyl rubber emulsion thus being prevented from premature de-stabilization under the effect of heat.

The method may comprise the further step of supplying a cooling medium to a space defined between a supply channel for the butyl rubber emulsion and said supply channel for the warm or hot air, the cooling medium being circulated to prevent premature de-stabilization of the butyl rubber emulsion before it reaches said part spherical portion.

The method may comprise the step of supplying said dispersion of elastomer or plastics material to said shaping device at a point lower than the upper most point of the space defined between the butyl rubber supply channel and the warm or hot air supply channel in which said cooling medium is circulated.

Also the method may comprise the step of passing the dispersion forming said outer tubular element through a heating collar to complete gelling of the said outer tubular element before the inner coating of butyl rubber is applied to the tubular element.

Alternatively said inner coating of butyl rubber is provided by a spray system adapted to be provided with a reciprocal movement and adapted to spray the butyl rubber emulsion on the inside of the said tubular element before the inner surface of said tubular element comes into contact with hot air, stabilizers which prevent clogging of the spray device being added to the butyl rubber emulsion.

According to a third aspect of this invention, there is provided an apparatus for manufacturing a tube according to said one aspect, and for performing a method in accordance with said second aspect, said apparatus comprising two coaxial forming tubes defining an orifice, means for extruding a sensitized aqueous dispersion of elastomer or plastics material as herein defined through said orifice, means for heating said dispersion to initiate gelling thereof, and means for applying butyl rubber to the interior of the tubular element thus extruded.

Preferably the apparatus further comprises a central channel passing through said two coaxial forming tubes to inject air into the interiorly coated tubular element.

A supply channel for butyl rubber emulsion may be provided which extends through said two coaxial forming tubes. Said butyl rubber emulsion supply channel may be thermally insulated.

Preferably said air supply channel extends between said two forming tubes and said butyl rubber emulsion supply channel comprises one or more tubes also passing between said two forming tubes, spaced upper plug means and lower plug means being provided, each of said plug means sealing the space in the interior of the innermost of said two forming tubes, the two plug means thus defining a closed space which extends across the inner of the two forming tubes and which embraces the butyl rubber supply channel and the hot or warm air supply channel, means being provided for circulating a cooling medium within said closed space.

Advantageously the butyl rubber supply channel is located equi-spaced from the inner forming tube and the air supply channel. Said forming tubes may be substantially vertical and said warm air supply channel may terminate at its lower end in a part spherical portion having upstanding flanges on the upper surface thereof, said butyl rubber emulsion being directed onto said part spherical portion from said butyl rubber supply channel so that, in use, the butyl rubber is entrained on the interior surface of a tube extruded through said orifice. Conveniently said sensitized emulsion of elastomer or plastics material may be introduced to said orifice at a point between said two forming tubes at a point intermediate said two plugs. Preferably a heating collar is provided embracing said two forming tubes to initiate gelling of said dispersion of elastomer or plastics material.

Advantageously said heating collar is located substantially at the level of said lower plug means.

The present invention provides a tube in which a thin coating of butyl rubber is applied, preferably substantially continuously, to the inside of the tube to give the tube produced increased air impermeability.

The provision of the thin coating of butyl rubber still permits the tube to be inflated at a high pressure and the increased air impermeability enables tubes manufactured in accordance with the present invention to retain a high inflated pressure for at least 24 hours.

It has been found that preferred tubes made in accordance with the present invention combine the advantages of light weight mechanical strength of natural rubber tubes produced from aqueous dispersion, in that thev can be inflated to very high pressures without any risk of bursting, with the advan tages of very much greater air impermeability than can be obtained with tubes such as inner tubes for tyres produced by moulding or extruding poly-isobutylene in the dry state.

In the prior proposed production of tubes such as inner tubes for tyres poly-isobutylene is crushed in the presence of a number of additives of the plasticizer type, anti-oxygen agents or vulcanization agents, together with reinforcing agents and "de-stringing" agents of the carbon black and oil types. These additives appreciably reduce the air impermeability of poly-isobutyl inner tubes produced by moulding or extrusion.

A tube in accordance with the present invention differs from these prior proposed tubes in that it comprises an inner layer of butyl rubber on the interior of a tube formed from an aqueous dispersion, which may be a natural rubber tube. As has been described above in an apparatus for performing the invention a device may be provided which, by spraying or scraping, enables a continuous inner coating of the poly-isobutylene to be provided, the inner coating being thin and of substantially constant thickness.

In a preferred embodiment of the present invention the uniform thickness of the inner coating is ensured by providing a scraping device, and butyl rubber is supplied through a tube which is parallel with the two nested forming tubes through which the elastomer or plastics material tube is extruded. A central hot air injection tube is also provided to inject air into the manufactured tube to cause the natural latex to gel and to cause vulcanization of the butyl rubber. The butyl rubber is supplied through at least one tube which is nested within the two forming tubes and which is maintained parallel with the central hot air injection tube and equidistant from the forming tubes and the said central tube by means of two plugs which act as spacers.A flow of cooling water can be provided between the central hot air injection tube and the two forming tubes to prevent the passage of hot air through the central tube from causing premature de-stabilization of the said butyl rubber. Gelling of the natural latex tube is produced preferably by means of a heating collar, the top part of which is at the level of the lower plug, while the central hot air injection tube terminates at the bottom in a hollow hemisphere forming a flaring or trumpet shaped mouth for the tube, or, alternatively, a sphere through which the tube extends diametrically. The hemisphere of sphere provided at the lower end of the hot air injection tube urges the butyl rubber into contact with the natural rubber tube.

The butyl rubber emulsion leaves the or each supply tube at a controlled rate of flow and spreads, under the influence of gravity, over the top of the hemisphere or sphere.

The hemisphere or sphere may be provided with an upstanding flange of circular configuration on the upper surface thereof which defines a butyl rubber emulsion reservoir.

The butyl rubber overflowing from the reservoir in a thin uniform layer flows down the exterior of the hemisphere or sphere and then contacts the inner surface of the natural rubber tube, which is already partially gelled, to form a thin uniform layer on the inside of the natural rubber tube. As the natural rubber tube leaves the forming tubes its diameter initially decreases and then the diameter increases again so that it can pass the portion of the hemisphere or sphere having the largest dimension, thus entraining by friction a small quantity of butyl rubber emulsion present on the upper surface of the hemisphere or sphere, this butyl rubber emulsion then flowing past the hemisphere or sphere.

The natural latex is supplied to the forming tubes through a collector ring, which supplies the natural latex to the space between the concentric forming tubes through a collector ring, which supplies the natural latex to the space between the concentric forming tubes.

The butyl rubber emulsion supply is at a higher level than the forming tube and the inner forming tube continues upwardly above the collector ring to provide a support for a plug supporting the upper part of the butyl rubber supply.

It is to be understood that cold air may be injected through the central tube instead of hot air, to slow down the natural latex tube gelling process, and if cold air is to be injected in this way there is no reason to provide the flow of cooling water between the central tube and the forming tubes to prevent possible premature de-stabilization of the butyl rubber emulsion inside the supply tube or tubes, and in such a case the space between the two plugs can simply be filled with air at ambient temperature.

In order that the present invention may be more readily understood and so that further features thereof may be appreciated the invention will now be described by way of example, with reference to the accompanying drawing whose single figure schematically illustrates the different stages of a process in accordance with the invention.

In the single figure of the drawings there is illustrated a natural latex supply pipe 2a which forms a circular ring around an inner forming tube Sa, and the arrangement is such that natural latex flows to this ring, and the flows downwardly from the ring under the influence of gravity between an outer forming tube 4a and the said inner forming tube Sa. Natural latex is, of course, a dispersion of sensitized material as herein defined. The inner forming tube Sa is continued upwardly above the circular ring 18.

A hot air injection tube 15a is provided, this tube being centrally disposed. It is to be understood that this tube 1 Sa may be used to inject cold air rather than hot air. Two symmetrical butyl rubber emulsion supply tubes 19 are also provided.

A single supply tube may be found sufficient, but the required rate of flow of butyl rubber emulsion may necessitate the use of two tubes, and if two tubes are utilised it is preferred that the tubes are located with their axes in the same diametric plane.

Two flow tubes 20, 21 are provided to produce a flow of cooling air or water in a space 24 between the tubes lSa and the tube 5a. The three tubes 15a and 19, and the flow tubes 20 and 21 are held in position by means of plugs 22 and 23.

The tube lSa is shown as being provided with a hemispherical flaring lower portion 25, and hot air passing through the tube lSa leaves through this hemispherical flaring portion and is thus located on the interior of the manufactured tube. The hot air causes the natural latex tube 8b to gel, and the inner butyl rubber lining 26 to vulcanize or dry. It is to be understood that a heating collar 27 surrounding the forming tubes 4a, 5a which is connected to an electrical supply (not shown) raises the temperature of the tube 8b and initiates the gelling of this tube, whilst the tube is still between the forming tubes 4a and Sa.As the tube 8b emerges from the forming tubes the tube 8b initially shrinks and is then compelled to flare out again to be able to slide over the outer surface of the hemispherical portion 25. As the tube 8b slides over the surface a part of the butyl rubber emulsion present between the hemisphere and the tube 8b is entrained with the tube 8b and produces the inner lining 26.

By suitably adjusting the rate of flow of butyl rubber emulsion through the supply tubes 19 the annular space 28 between the hemisphere and the flange 29 is filled with butyl rubber emulsion until butyl rubber emulsion overflows at a sufficient rate to form a thin sheet which then flows downwardly over the upper surface of the hemisphere 25 to form the inner lining 26.

The thickness of the inner lining 26 is very much less than the thickness of the natural rubber tube 8b and in order to simplify the drawing the respective thicknesses are not shown to scale and consequently it is to be understood that the drawing is diagrammatic in this respect.

If the tube 15a is a glass tube the hemispherical portion 25 may be produced, for example, by blowing, but it is to be under stood that the hemispherical portion 25 may be replaced by a spherical portion through which the tube 1 spa extends diametrically, the spherical portion acting in the same way as the hemispherical portion 25 to deflect the flow of the butyl rubber emulsion. Of course, a flange similar to the flange 29 may be provided at the top of the spherical portion.

It is to be understood that various changes, improvements or additions can be made to the embodiments of the process just described without departing from the scope of the present invention as defined in the appended claims.

In the illustrated embodiment of the invention the butyl rubber emulsion supply tube is thermally insulated with respect to the hot air injection tube 15a the butyl rubber emulsion supply then passing inside this tube to lead to an emulsion spray device e.g. an annular device which sprays the emulsion onto the interior of the tube 8b. In such an embodiment, in order to obtain a perfectly continuous poly-isobutylene lining, stabilizers have to be introduced into the emulsion and the spray head has to be given a reciprocating rotary or longitudinal movement.

The thickness of the butyl rubber polyisobutylene coatings which can be obtained by utilizing processes in accordance with the invention can vary from 0.03 mm approximately to 0.25 mm maximum of final dry product. Preferably the thicknesses between 0.05 mm and 0.15 mm. The thickness of the tube excluding that of the inner coating may be between 0.15 and 0.60 mm.

The inner coating vulcanizes at the same time as the elastomer tube gels, some molecules of poly-isoprene and vulcanization agents of known types being added to the poly-isobutylene for this purpose.

Various experimental tests that have been conducted show that with a rubber inner tube of a thickness of 0.50 mm and produced by extrusion with an addition of 50% carbon black and 20% oils, and having a dry polyisobutylene film inner lining having a thickness of 0.1 mm, i.e. a thickness of one-fifth of that of the extruded rubber inner tubes, the water vapour transmission obtained per 24 hours is of the order of 0.24 g per element of an area of approximately 650 cm squared.

Corresponding tests made with prior proposed tubes, i.e. tubes without the inner polyisobutylene film exhibit a water vapour transmission per 24 hours of the order of 100 g per element of area of approximately 650 cm squared. Thus the water vapour transmission of a tube made in accordance with the invention is about 1/415 of that obtainable with a prior proposed tube.

Of course, the above ratios for the water vapour transmission closely reflect the corresponding ratios for air transmission and provide a guide to the air impermeability.

It should be noted that the use of butyl rubber rather than other substances known for their air impermeability, such as polyvinylidene chloride, for example, is due to the fact that the elasticity of butyl rubber films is slightly greater than that of natural rubber tubes, while the elasticity of polyvinylidene chloride films is considerably less, and this would give rise to cracking of the said films on high-pressure inflation of a tube formed with an inner lining of polyvinylidene chloride. The most preferred starting material is the artificial butyl latex sold by Esso under the Trade name "Latex Enjay Butyl BP 100".

One of the advantages of the above described process lies in the fact that the butyl latex is applied with an appreciable pressure against the inside of the natural latex tubes, so that the coating is mechanically bonded intimately to its support, prior to the molecular bridges which can be produced, where applicable, on vulcanization.

It should also be noted that the said natural rubber latex may be replaced, with any latex e.g. polychloroprene latex, which, on gelling, provides an elastomer having the mechanical properties required for the use in question. It is to be understood that the above described method is expecially useful in the manufac ture of inner tubes for racing bicycles, but tubes in accordance with the invention may be used for other purposed, e.g. as surgical tubes.

WHAT I CLAIM IS: 1. A tube, said tube comprising an outer tubular member formed from a gelled aqueous dispersion of a sensitized elastomer or plastics material as herein defined, said outer tubular portion having an internal coating of butyl rubber.

2. A tube according to claim 1 wherein said butyl rubber comprises polyisobutylene.

3. A tube according to claim 2 wherein said poly-isobutylene contains a proportion of poly-isoprene molecules.

4. A tube according to claim 2 or 3 wherein said poly-isobutylene is vulcanized.

5. A tube according to any one of the preceding claims for use as an inner tube for a bicycle, the thickness of the inner coating of butyl rubber being between 0.03 mm and 0.25 mm.

6. A tube according to claim 5 wherein the thickness of the inner coating of butyl rubber is between 0.05 mm and 0.15 mm.

7. A tube according to claim 4 or S wherein the thickness of the tube excluding the thickness of the inner coating of butyl rubber is between 0.15 mm and 0.60 mm.

8. A method of manufacturing a tube according to claim 1, said process comprising the steps of passing a sensitized aqueous dispersion of an elastomer or plastics material, as herein defined, from a supply chamber to a shaping device and extruding said dispersion to form an outer tubular element, the disper sion being heated in the shaping device to initiate gelling thereof, said method including the step of applying a continuous inner coating of butyl rubber on the inside of said outer tubular element.

9. A method according to claim 8 wherein said coating of butyl rubber comprises poly-isobutylene.

10. A method according to claim 9 wherein said poly-isobutylene contains a number of poly-iosprene molecules.

11. A method according to any one of claims 8 to 10 comprising the further step of continuously vulcanizing the inner coating of butyl rubber simultaneously with the step of vulcanizing the gelled dispersion forming the outer tubular element.

12. A method according to any one of claims 8 to 11 wherein the step of extruding the dispersion through a shaping device comprises the steps of extruding the dispersion downwardly through an orifice defined by two vertical co-axial forming tubes constituting said shaping device, causing liquid butyl rubber emulsion to flow through a channel passing through the inner of said two forming tubes and to flow over a part spherical element located within the said outer tubular element which is extruded from the lower part of said orifice, which part spherical element has an upstanding cylindrical flange on the upper surface thereof, said butyl rubber emulsion being supplied at a controlled rate so that said butyl rubber emulsion overflows from the flange to descend by gravity around said part spherical element, said extruded outer tubular element passing over the part spherical portion and entraining the said butyl rubber emulsion so that the butyl rubber emulsion forms a continuous coating of substantially uniform thickness on the interior of the said tubular element, said butyl latex emulsion gelling to constitute said butyl rubber coating.

13. A method according to claim 12 comprising the further step of injecting air into the interior of the interiorly coated tubular element through a channel extending through said two forming tubes and terminating at the lower region of said part spherical element.

14. A method according to claim 13 wherein said injected air is hot air or warm air.

15. A method according to claim 14 wherein the butyl rubber emulsion to be supplied to said part spherical portion is thermally insulated from the warm or hot air being injected into the said tubular element, the butyl rubber emulsion thus being prevented from premature de-stabilization under the effect of heat.

16. A method according to claim 15 comprising the further step of supplying a cooling medium to a space defined between a supply channel for the butyl rubber emulsion and said supply channel for the warm or hot

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. rubber tubes, while the elasticity of polyvinylidene chloride films is considerably less, and this would give rise to cracking of the said films on high-pressure inflation of a tube formed with an inner lining of polyvinylidene chloride. The most preferred starting material is the artificial butyl latex sold by Esso under the Trade name "Latex Enjay Butyl BP 100". One of the advantages of the above described process lies in the fact that the butyl latex is applied with an appreciable pressure against the inside of the natural latex tubes, so that the coating is mechanically bonded intimately to its support, prior to the molecular bridges which can be produced, where applicable, on vulcanization. It should also be noted that the said natural rubber latex may be replaced, with any latex e.g. polychloroprene latex, which, on gelling, provides an elastomer having the mechanical properties required for the use in question. It is to be understood that the above described method is expecially useful in the manufac ture of inner tubes for racing bicycles, but tubes in accordance with the invention may be used for other purposed, e.g. as surgical tubes. WHAT I CLAIM IS:

1. A tube, said tube comprising an outer tubular member formed from a gelled aqueous dispersion of a sensitized elastomer or plastics material as herein defined, said outer tubular portion having an internal coating of butyl rubber.

air, the cooling medium being circulated to prevent premature de-stabilization of the butyl rubber emulsion before it reaches said part spherical portion.

17. A method according to claim 16 comprising the step of supplying said dispersion of elastomer or plastics material to said shaping device at a point lower than the upper most point of the space defined between the butyl rubber supply channel and the warm or hot air supply channel in which said cooling medium is circulated.

18. A method according to any one of claims 8 to 17 comprising the step of passing the dispersion forming said outer tubular element through a heating collar to complete gelling of the said outer tubular element before the inner coating of butyl rubber is applied to the tubular element.

19. A method according to any one of claims 8 to 11 wherein the said inner coating of butyl rubber is provided by a spray system adapted to be provided with a reciprocal movement and adapted to spray the butyl rubber emulsion on the inside of the said tubular element before the inner surface of the said tubular element comes into contact with hot air stabilizers which prevent clogging of the spray device being added to the butyl rubber emulsion.

20. An apparatus for manufacturing a tube according to claim 1, and for performing the method of claim 8, said apparatus comprising two coaxial forming tubes defining an orifice, means for extruding a sensitized aqueous dispersion of elastomer or plastics material as herein defined through said orifice, means for heating said dispersion to initiate gelling thereof, and means for applying butyl rubber to the interior of the tubular element thus extruded.

21. An apparatus according to claim 20 further comprising a central channel passing through said two coaxial forming tubes to inject air into the interiorly coated tubular element.

22. An apparatus according to claim 20 or 21 wherein a supply channel for butyl rubber emulsion is provided which extends through said two coaxial forming tubes.

23. An apparatus according to claim 22 wherein said butyl rubber emulsion supply channel is thermally insulated.

24. An apparatus according to claim 23 wherein said air supply channel extends between said two forming tubes and said butyl rubber emulsion supply channel comprises one or more tubes also passing between said two forming tubes. spaced upper plug means and lower lower plug means being provided, each of said plug means sealing the space in the interior of the innermost of said two forming tubes, the two plug means thus defining a closed space which extends across the inner of the two forming tubes and which embraces the butyl rubber supply channel and the hot and warm air supply channel, means being provided for circulating a cooling medium within said closed space.

25. An apparatus according to claim 24 wherein the butyl rubber supply channel is located equi-spaced from the inner forming tube and the air supply channel.

26. An apparatus according to claim 22 or any claim dependent thereon wherein said forming tubes are substantially vertical and wherein said warm air supply channel terminates at its lower end in a part spherical portion having upstanding flanges on the upper surface thereof, said butyl rubber emulsion being directed onto said part spherical portion from said butyl rubber supply channel so that, in use, the butyl rubber is entrained on the interior surface of a tube extruded through said orifice.

27. An apparatus according to claim 24 or any claim dependant thereon wherein said sensitized emulsion of elastomer or plastics material is introduced to said orifice at a point between said two forming tubes at a point intermediate said two plugs.

28. An apparatus according to any one of claims 20 to 27 wherein a heating collar is provided embracing said two forming tubes to initiate gelling of said dispersion of elastomer or plastics material.

29. An apparatus according to claim 28 when dependant directly or indirectly on claim 24 wherein said heating collar is located substantially at the level of said lower plug means.

30. A tube substantially as herein described with reference to and as shown in the accompanying drawing.

31. A method of making a tube substantially as herein described with reference to the accompanying drawing.

32. A tube whenever made by a method according to any one of claims 8 to 19 or claim 31.

33. An apparatus for making a tube substantially as herein described with reference to and as shown in the accompanying drawing.