METHOD OF FORMING A GASKET

Abstract: A method of forming a gasket in situ which comprises injecting into a gasket space a curable composition comprising one or more polymeric or polymerisable materials and an appropriate cure system, the curable composition having a viscosity at 25 DEG C in the range of from 2,000-500,000 mPas and comprising an entrained gas in an amount sufficient to increase the unit volume of the composition by at least 0.1 %, and curing the curable composition.

Description: METHOD OF FORMING A GASKET This invention relates to a method of forming gaskets, more particularly a method of forming a gasket by injection of a curable composition into a gasket space, and to a mechanical assembly comprising a gasket between two components of said assembly. It has been proposed to provide a gasket composition which can be injected between two components, for example in an engine or other machine, and which will then polymerise in situ. For example, the two components can be assembled face-to-face, and a polymerisable gasket composition injected under pressure into a gap or groove in one of the faces, so that the composition flows along the gap or groove until it is distributed throughout the gap or groove, and forms a sealing path around the area of the mating surfaces. The composition is then cured in situ to form the gasket. An example of such a prior art method is described in US-A-5116558 which discloses a method of forming a gasket in situ between two components which includes injecting into a groove in at least one of the said components a curable composition including one or more free-radical polymerisable vinyl esters, and ingredients of a rapid free-radical cure system therefor, the cure system being inactivated prior to injection of the 5 composition, and the composition having a viscosity at 25°C m the range from 200 to 500,000 Pas, and permitting the composition to cure. Preferred compositions have a Brookfield viscosity at the time of the injection from about 2,000 to about 15,000 mPas at 10 25°C and gel to a non-flowable state within five minutes of the initiation of cure and had the consistency of a flexible solid upon full cure. US-A-5116558 provides full details of usable 15 polymerisable vinyl esters and free radical cure systems for use m the method to which the reader is referred for further information. Preferred compositions m accordance with US-A- 20 5116558 also incorporate ingredients for expanding the volume of the composition m situ at room temperature, preferably two reactive ingredients which react at room temperature to produce a gas m situ m the composition, the two reactive ingredients being isolated from each 25 other prior to injection of the composition. The object of the incorporation of ingredients for expanding the volume of the composition is stated to be to compensate for shrinkage which might occur upon polymerisation. The entire disclosure of US-A-5116558 is incorporated herein by reference for all purposes. Certain problems have been found to arise with the use of the method of US-A-5116558 : 1. Compositions within the preferred range of 2,000 to 15,000 mPas tend to leak from the gasket space when injected under medium pressure. A possible solution to this problem would be to use compositions of higher viscosity. However higher viscosities lead to difficulties in uniformly distributing and reacting the ingredients for expanding the volume of the composition and thus this is not a viable choice in the prior art method . 2. The preferred method of expanding the volume of the composition involves the reaction of an acid and a bicarbonate m aqueous solution The presence of water in the composition is, however, deleterious in that it tends to reduce the adhesion of the gasket to the components. 3. Whilst certain other methods of overcoming volume reduction upon polymerisation, involving the incorporation of low boiling solvents or the chemical decomposition of blowing agents are disclosed, these are stated to have various disadvantages and are not recommended. According to the present invention, the aforementioned problems are obviated by using a curable composition of a viscosity sufficient to avoid substantial leakage from the gasket space under the conditions of injection, and to obtain the necessary volume expansion by entraining a gas m the mjectable composition. EP-A-0604926 discloses a method for fabricating a gasket m situ between two components which includes extruding onto a seal region of a substrate a curable composition including foamable organosiloxane base and a curing agent portion where, upon combining said base and said curing agent, foam is formed and a curing occurs by hydrosilation reaction, and where, prior to extrusion from the mixing chamber, the composition or components of the composition are injected with an amount of inert gas. This gas acts to stabilise the cell structure formed by the foaming reaction. In a first aspect, therefore, the invention provides a method of forming a gasket m situ which comprises injecting into a gasket space a curable composition comprising one or more polymeric or polymerisable materials and an appropriate cure system, the curable composition having a viscosity at 25°C in the range of from 2000 to 500,000 mPas and comprising an entrained gas m an amount sufficient to increase the unit volume of the composition by at least 0.1%, and curing the curable composition, the curing reaction taking place substantially without the production of further gaseous components. According to the present invention, the necessary volume expansion is obtained solely by entraining a gas in the mjectable composition, and the curing reaction takes place substantially without the production of further gaseous components. Thus the entrained gas acts to obtain a foamed structure m the present invention as opposed to acting as a nucleation site for subsequent reaction-induced foam cells in EP-A-0604926. Thus the gasket formulation can be selected entirely for its other characteristics and is not dependent on a foaming reaction. Moreover, the bubble size is more precisely controllable so that large bubbles can be avoided which may reduce adhesion and which may form uncontrollably when chemically formed. Moreover, water can be avoided which is necessarily present either as a precursor in siloxane curing systems or as a by-product in acrylic systems. Water may likewise adversely affect adhesion. Finally, by injecting the composition with entrained gas under pressure, the gas bubbles are compressed so that their subsequent expansion can accommodate both leaking gasket composition prior to complete curing thereof, as well as inevitable contraction of the composition during said curing, and still preferably leaving residual gas pressure greater than atmospheric after curing so that expansion and contraction of the bubbles can accommodate relative movement of the components being sealed together by the gasket . The gasket can be of any suitable shape depending upon the size and configuration of the gasket space. Normally the gasket space comprises a groove m one of two components joined together to form a mechanical assembly. For example, each component may be provided with flat faces, such as are provided on mating flanges. Thus, m another aspect, the present invention provides a mechanical assembly comprising two components joined together and having mating surfaces defining between them a gasket space for sealing said components with respect to one another, a passage through one component from the gasket space to an outside surface of the assembly, said space being filled with a gasket comprising a cured composition of one or more polymeric or materials injected into said space along said passage prior to curing thereof and comprising at least 0.1% by volume of an entrained gas under greater than atmospheric pressure, the curing reaction having taken place substantially without the production of gaseous components. In a preferred method according to the invention the curable composition comprises one or more free- radical polymerisable vinyl esters and a free-radical cure system therefore which will preferably cause the composition to gel to a non-flowable state in, for example, less than five minutes, more preferably less than three minutes, from the commencement of curing. The cure system usually comprises a free-radical polymerisation initiator and, if required for activation of the initiator, a polymerisation activator. An example of a suitable cure system is a redox cure system. In a preferred embodiment of a method of the invention, the curable composition is a multi-part composition wherein one part comprises an initiator and another part comprises the activator, and the method includes mixing the parts at the time of injection to form a fluid having the appropriate viscosity. Preferably the parts before mixing are of substantially equal viscosity, and are mixed m substantially equal proportions . In a particularly preferred embodiment, the free- radical polymerisable vinyl esters comprise: a) a moderate-to-long chain di- or poly- functional prepolymer (A) having vinyl reactive ends ; and b) a monomer (B) which is: (l) reactive with said moderate-to-long chain prepolymer; and (n) soluble or miscible with the moderate-to-long chain prepolymer. Suitable moderate-to-long chain prepolymers (A) and monomers (B) are described m US-A-5116558 and also in US-A-4439600, the entire contents of which are incorporated herein by reference for all purposes. The moderate-to-long chain di- or poly- functional prepolymers (A) having vinyl reactive ends preferably comprise polyether-urethane and/or polyester-urethane derivatives which may be synthesised by reacting a polyester diol or a polyether diol with a diisocyanate and reacting the resulting product with a polymerisable acrylic or methacrylic acid ester, or vinyl reactive alcohol such allyl alcohol, to produce end-capping. The monomer (B) preferably comprises a mono- functional short chain monomer which is copolyτnerisable with the end caps of the moderate-to-long chain prepolymer (A) and miscible with or soluble m the prepolymer (A) . Preferably the monomer is of low volatility, enhances the flow characteristics of the prepolymer, has a good high temperature performance, high cross-linking ability and reacts efficiently with the prepolymer. The monomer (B) can, for example, comprise a monomethacrylate or monoacrylate ester of an aryl, alkyl or arylalkyl alcohol, or their arylammo, alkylamino and arylalkylamino methacrylate or acrylate esters . Alternatively, polymerisable vinyl ester monomers may be used such as, for example, as described in US-A- 4451615 and US-A-4180640, the entire disclosures of which are incorporated herein by reference for all purposes. Variations in softness and hardness of the gasket may be achieved by varying the levels and type of monomer used, as discussed in US-A-4439600 , the entire disclosure of which is also incorporated herein by reference for all purposes. The free-radical polymerisable initiator preferably comprises an organic peroxide, hydroperoxide, perester or peracid, as described, for example, m US-A- 4439600 and US-A-4451615. If desired, the curable composition can also comprises an accelerator of free-radical polymerisation such as, for example, those described in US-A-3491076 , US-A-4287330, and US-A-4180640 , the entire disclosures of which are included herein by reference for all purposes . 10 In order to achieve the required viscosity for the mjectable composition, it may be necessary, and is indeed often preferable, to incorporate a viscosity control agent. Normally such agents will be used to increase the viscosity of the composition. Suitable viscosity control agents include, for example, finely divided particulate materials such as, for example, fumed silica. In a preferred method according to the invention, the components of the composition are made up at a lower viscosity, and a sufficient quantity of the viscosity control agent added to bring the composition up to the desired viscosity. Preferably the quantity of viscosity control agent added is from about 1 to about 10 parts by weight, based on the weight of the composition. The curable composition can, if desired, also comprise a wide variety of plasticisers , adhesion promoters, dyes and similar materials, which may be used m appropriate amounts as desired. In a preferred embodiment of the invention, the composition is provided in two parts. Part I preferably comprises a pre-polymer (A) , a short chain monomer (B) 11 and an initiator (C) , together with a metal chelatmg agent inhibitor and a free radical inhibitor (antioxidant) . Part II preferably comprises a prepolymer (A) , a short chain monomer (B) , and a transition metal activator together with a viscosity control agent and an inhibitor. Part II does not contain a source of free radicals. Activation of the initiator (C) does not occur until the two parts I and II are mixed. The two parts I and II are preferably formulated so that they can be mixed m easily controlled proportions, preferably equal proportions. Preferably the two parts I and II are mixed m a chamber at or slightly upstream from the injection nozzle. The metal chelatmg agent is preferably present part I in a small amount which is not sufficient to interfere with the activating action of the metallic salt activator when the two parts are mixed. The mixed composition preferably begins to gel after two to three minutes at ambient temperature . The Brookfield viscosity of the composition at the time of injection is preferably in excess of 20,000 mPas, more preferably from 30,000 to 50,000 mPas or 12 higher. With certain compositions it is found that viscosities lower than 20,000 mPas can tend to cause leakage from the gasket space under the injection pressure, and also can lead to coalescence of the entrained gas bubbles . The entrained gas is preferably one that does not react with the components of the composition, and preferably has an oxygen content sufficiently low to prevent oxygen inhibition of the cure reaction. Suitable gases include, for example, nitrogen, carbon dioxide and inert gases such as helium. The amount of the entrained gas is preferably sufficient to increase the unit volume of the curable composition by at least 1.0%, preferably at least 5%, more preferably from 5-20%. Preferably the curable composition comprising the entrained gas is injected into the gasket space under pressure through a one-way valve, so that the gas has residual positive (that is to say greater than atmospheric) pressure after curing. 13 In a preferred method according to the invention, there are provided two or more reservoirs of uncured polymeric or polymerisable component materials which are capable of reacting when mixed to form a cured polymeric material with the desired properties. The uncured component materials are pumped into a mixer, which may be a static mixer, but is preferably dynamic, that is to say driven by a motor. The gas may be entrained in the curable composition by any suitable method. For example, the gas may be entrained in one or more of the uncured component material reservoirs and/or injected into one or more of the feeds into the mixer and/or injected into the mixer itself. Where a motorised mixer is used, this can also serve to break down the gas particles to a suitable size. Preferably the entrained gas particles have a diameter of less than 1mm, more preferably less than 0.1mm, on injection into the gasket space. After mixing and introducing the entrained gas the curable composition is injected into the gasket space. In a preferred method according to the invention, the 14 curable composition is injected through a one-way valve, such as, for example, a rubber duck bill valve, which is connected to the gasket space at least until the resin has cured, and may be left permanently m position. The use of a duck bill valve is preferred over other types of one-way valve m that it can have a lower back pressure, is usually cheaper, and does not usually require a threaded seat . The injection step may be continued until a preset "back pressure" or "no flow condition" is obtained, which has been pre-determmed to correspond to a desired degree of filling of the groove (normally 100%) . Usually it will not be necessary to make specific provision for venting of the air originally present m the gasket space, since it has been found m practice that venting of this air can be effected through small gaps which remain between the mating surfaces of the components between which the gasket is situated. The use of a one-way valve is particularly desirable in order to avoid de-pressuπsation by gas expansion before the curable composition cures However the use of a one-way valve is not absolutely essential and the curable composition could be injected, for 15 example, through a syringe. Before injecting the curable gasket composition, it is advisable to remove any contamination from the surfaces of the components by oil or grease, since this may compromise adhesion. As previously stated, the use of the entrained gas significantly helps to negate the effects of contraction of the composition on curing. However, a further substantial advantage of the method of the invention is that it permits the production of a semi-foamed gasket the volume of which can increase slightly as the mating surfaces of the components move apart, and contract as they come closer together. This cyclic process is continuous on any vibrating equipment, such as an automobile engine, and but for the permitted volume expansion and contraction, would cause the gasket material either to lose adhesion or to tear within itself, depending upon whether the cohesive strength or adhesive strength of the curable composition is greater. The method of the present invention also enables higher viscosity injectable curable gasket compositions to be used, thus reducing seepage of material from the 16 gasket space through any remaining air gaps . Higher viscosity compositions also have a lower mobility of gas bubbles, reducing the possibility of coalescence prior to curing . Finally, it has been found possible with preferred compositions according to the invention for injection to be carried out at relative low pressures, for example, up to about 10 Bar. The invention is illustrated by the following Example and with reference to the accompanying drawing which is a schematic representation of the mixing and injecting process of the present invention, as well as a mechanical assembly incorporating the present invention. EXAMPLE A two part composition is made up as follows: Part 1 Parts by Weight Diacrylate terminated Polyurethane resin 64 Methacrylic Acid 6 17 Phenolic Antioxidant 0.3 Ethylene Diamine Tetra Acetic Acid 0.1 Organic hydroperoxide 1 Curing accelerator 0.4 Fumed silica * 5.7 Part 2 Diacrylate terminated Polyurethane Resin 75 C 13 Methacrylate 21 Phenolic Antioxidant 0.3 Copper Napthenate (8% Cu) 0.3 Saccharin 0.8 Fumed Silica * 3.4 * Viscosity Control Agent - Actual quantity adjusted to give 35,000 mPas at 25°C. The diacrylate terminated aliphatic polyurethane resin used in this Example has an approximate average molecular weight of 20,000 . The organic hydroperoxide of Part 1 initiates the free radical polymerisation process when activated. However, the organic hydroperoxide requires the presence of a suitable metal ion for activation. Activation of the hydroperoxide is prevented in Part 1, prior to mixing with Part 2, by means of the EDTA stabiliser whereby any trace amounts of metals which may be present in Part 1 are complexed by the stabiliser and prevented from activating initiation of the polymerisation. Part 2 contains the initiation activator copper napthenate. Part 2 does not contain a source of free radicals . With reference to the drawings Parts 1 and 2 are in respective containers 10,12 and pumped by respective pumps P1,P2, in a ratio of 1:1, into a dynamic mixer 14. The mixer comprises stators 15 and rotors 17, the rotors being driven by motor 16. A suitable mixer is made and sold by Bartec. Nitrogen gas is injected into the mixture by another pump P3 in proportion to the pumping of Parts 1 or 2. The mixed composition had a viscosity of 35,000 mPas at 25°C measured on a Brookfield RVT viscometer with spindle 4 at 20 rpm. The mixture, after passing through the mixer 14, exits through line 18 to an injector 20 mated with a port 22 of a mechanical assembly 30. 19 Assembly 30 comprises two components 34,36 mated together and joined by means not shown. A gasket space 32 is defined between mating surfaces of the two components, and comprises a groove formed one, or perhaps both, of the components 34,36. A passage 38 connects the gasket space 32 with the port 22. A duckbill valve 40 is disposed in the port 22. The mixture is injected between the two flanges at a pressure of approximately 5 Bar through the one-way valve 40.. The groove 32 is, in the present Example, 3mm wide, 1.5mm deep by 45cm long, and it was filled in approximately 15 seconds. Air in the groove is vented through the gaps which exist between mated surfaces, although a special port for this purpose could be provided. The composition gelled in situ to a non-flowable state in 2-3 minutes after mixing, although the injector 20 was disconnected from the port 22 after completion of the injection. The valve 40 prevents escape of the mixture after such disconnection. The flexible gasket formed was tested to resist 1 bar (at 25°C) oil pressure five minutes after injection. A pressure regulator 42 cuts off supply to the injector 20 when it is to be disconnected from the port 20 22 on detection, by a sharp increase in injection backpressure, of the gasket space 32 being filled. Cut-off is effected by disabling pumps PI, P2 and P3. The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or seeps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) , may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar 21 features . The invention is not restricted to the details of the foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. 22

Claims: CLAIMS 1. A method of forming a gasket m situ which comprises injecting into a gasket space a curable composition comprising one or more polymeric or polymerisable materials and an appropriate cure system, the curable composition having a viscosity at 25°C in the range of from 2,000-500,000 mPas and comprising an entrained gas an amount sufficient to increase the unit volume of the composition by at least 0.1%, and curing the curable composition, the curing reaction taking place substantially without the production of further gaseous components. 2. A method according to claim 1, wherein the gasket space comprises a groove m one of two mating components . 3. A method according to claim 1 or 2 , in which the curable composition comprises one or more free-radical polymerisable vinyl esters and a free-radical cure system therefore. 4. A method according to claim 3 , m which the cure system comprises a free-radical polymerisation initiator and, if required for activation of the 23 initiator, a polymerisation activator. 5. A method according to any of the preceding claims, in which the curable composition is a multi-part composition wherein one part comprises an initiator and another part comprises an activator, and the method includes mixing the parts at the time of injection to form a fluid having the appropriate viscosity. 6. A method according to claim 5 , in which the parts before mixing are of substantially equal viscosity, and are mixed in substantially equal proportions . 7. A method according to claim 3 , in which the free-radical polymerisable vinyl esters comprise: a) a moderate-to-long chain di- or poly- functional prepolymer (A) having vinyl reactive ends; and b) a monomer (B) which is: (i) reactive with said moderate-to-long chain prepolymer; and (ii) soluble or miscible with the moderate-to-long chain prepolymer. 8. A method according to claim 4 , in which the free-radical polymerisable initiator comprises an 24 organic peroxide, hydroperoxide, perester or peracid. 9. A method according to any of the preceding claims, in which the curable composition also comprises a free-radical polymerisation accelerator. 10. A method according to any of the preceding claims, in which the curable composition comprises a viscosity control agent. 11. A method according to claim 10, in which the viscosity control agent comprises a finely divided particulate material. 12. A method according to claim 11, in which the finely divided particulate material is fumed silica. 13. A method according to claim 7, in which the curable composition is provided in two parts, the first part comprising said pre-polymer (A) , said monomer (B) and an initiator (C) , together with a metal chelating agent inhibitor and a reducing agent, and the second part comprising said pre-polymer (A) , said monomer (B) , and a metallic salt activator together with a filler and an inhibitor. 14. A method according to any of the preceding claims, in which the curable composition has a viscosity 25 of at least 20,000 mPas . 15. A method according to any of the preceding claims, in which the curable composition has a viscosity of from 30,000-50,000 mPas . 16. A method according to any of the preceding claims, in which the entrained gas is one that does not react with the components of the composition, and has an oxygen content sufficiently low to prevent oxygen inhibition of the cure reaction. 17. A method according to claim 16, in which the gas comprises nitrogen, carbon dioxide or an inert gas such as helium. 18. A method according to any of the preceding claims, in which the amount of the entrained gas is sufficient to increase the unit volume of the curable composition by at least 1.0%. 19. A method according to any of the preceding claims, in which the amount of entrained gas is sufficient to increase the unit volume of the curable composition by from 5-20%. 20. A method according to any of the preceding claims, wherein the curable composition comprising the 26 entrained gas is injected into the gasket space through a one-way valve. 21. A method according to claim 20, in which the one-way valve is a duck bill valve. 22. A method according to any of the preceding claims, in which there are provided two or more reservoirs of uncured polymeric or polymerisable component materials which are capable of reacting when mixed to form a cured polymeric material with the desired properties and the uncured component materials are pumped into a mixer prior to injection. 23. A method according to claim 22, in which the gas is entrained in one or more of the uncured component material reservoirs and/or is injected into one or more of the feeds into the mixer and/or is injected into the mixer itself. 24. A method according to any of the preceding claims, in which the curable composition s injected into the gasket space at a pressure of up to 10 bar. 25. A mechanical assembly comprising two components joined together and having mating surfaces defining between them a gasket space for sealing said components with respect to one another, a passage 27 through one component from the gasket space to an outside surface of the assembly, said space being filled with a gasket comprising a cured composition of one or more polymeric or materials injected into said space along said passage prior to curing thereof and comprising at least 0.1% by volume of an entrained gas under greater than atmospheric pressure, the curing reaction having taken place substantially without the production of gaseous components. 26. An assembly as claimed in claim 25, further comprising a port in said passage controlled by a one way valve adapted to maintain the pressure of said entrained gas above atmospheric during curing of said composition. 27. An assembly as claimed in claim 26, in which said valve is a duck-bill valve. 28. An assembly as claimed in any of claims 25 to 27, wherein said gasket is formed by a method as claimed in any of claims 1 to 24. 29. A method of forming a gasket from a curable composition comprising an entrained gas substantially as hereinbefore described with reference to the Example and/or accompanying drawing. 28 30. A mechanical assembly including a gasket substantially as hereinbefore described with reference to the Example and/or accompanying drawing. 29

Inventors: AL-OMRAN AWNI, JONES ROBERT, WAKE SIMON JOHN, AL-OMRAN, AWNI, JONES, ROBERT, WAKE, SIMON, JOHN
Applicants: AL OMRAN AWNI, CANNING PLC W, JONES ROBERT, WAKE SIMON JOHN, AL-OMRAN, AWNI, JONES, ROBERT, W. CANNING PLC, WAKE, SIMON, JOHN
Application year: 1999
Main classification: C08J9
IPC codes: B29C45, C08F290, C08L75, F16J15