GB2222217A - Method of joining pipes and epoxy adhesive therefor - Google Patents

Abstract

A method of joining pipes comprising overlapping the circumference of a pipe end (21) with a larger diameter cylindrical fitting (22) to make a close radial fit, applying adhesive (A) having a viscosity in the range from 0.5 to 200 centipoises to the edge of the overlap, allowing the adhesive to be drawn between the pipe and fitting, and thereafter curing the adhesive. A particularly suitable adhesive for use in the method comprises a heat curable adhesive composition comprising an epoxy resin, a curing agent, a reactive diluent and a wetting agent, the said composition having a viscosity in the range from 0.5 to 200 centipoises. <IMAGE>

Description

METHOD OF JOINING PIPES AND ADHESIVE THEREFOR The invention relates to a method of joining pipes, particularly copper pipes, and to an adhesive composition for use in the method, and to a container for storing and dispensing adhesive for use in the present invention.

Normal domestic and industrial copper piping has traditionally been soldered together using end-feed capillary fittings. A pipe end is inserted within a cylindrical fitting of larger diameter to make a close radial fit and then molten solder is applied around the circumference of the join of the fitting and pipe end. As there is a close radial fit capillary action arising from surface tension helps to draw the solder between the fitting and the pipe. When the solder sets a firm bond is formed between the two parts.

Normally when joining two pipes together one pipe end will be inserted into either end of a short cylindrical fitting. However, occasionally, one pipe end is inserted within another pipe end of slightly larger diameter thereby avoiding the need for a separate cylindrical fitting.

This method of joining copper pipes has the disadvantage that a lot of heat must be provided to melt the solder and normally a blow lamp or similar would be employed. In the case of domestic plumbing maintenance where perhaps only one joint needs to be repaired it is burdensome for the householder to have to obtain a blow lamp.

Another method of joining such pipes, or pipes and fittings, together which has been employed is to use an epoxy adhesive. The adhesive is smeared around the pipe end of smaller diameter, the pipes are then pushed together and overlapped and heat is applied to the outside to cure the epoxy. Such a process is messy and non-water tight bonds are often formed due to patchy application of the adhesive. It has not been possible to apply such epoxy adhesives in a manner similar to that in which solder is applied because epoxy resinous compounds have a comparatively high viscosity of several hundred thousand, for example about 400,000 centipoises. Molten solder, on the other hand, has a viscosity of between about 1.0 and 2.0 centipoises.

It has now surprisingly been found that pipe, particularly copper pipe, can be successfully joined together to form a strong and uniform bond by employing adhesive.

In accordance with the present invention there is provided a method of joining pipes comprising overlapping the circumference of a pipe end with a larger diameter cylindrical fitting to make a close radial fit, applying adhesive having a viscosity in the range from 0.5 to 200 centipoises to the edge of the overlap, allowing the adhesive to be drawn between the pipe and fitting, and thereafter curing the adhesive. The action of surface tension draws the adhesive between the pipe and fitting.

In order to ensure adequate bonding the close radial fit (by radial fit is meant the distance between the outer surface of the inner pipe and the inner surface of the cylindrical fitting) should preferably be less than 0.18 millimeter, preferably greater than 0.02 millimeter.

While the adhesive employed in the method of the present invention is conveniently an epoxy adhesive, any other curable adhesive having a viscosity in the desired range may be employed, provided that after curing that adhesive forms a strong bond which is resistant to water as this is obviously essential for plumbing joints. For example, epoxy, novolak or resorcinol resins may be employed. Conveniently, a heat curable adhesive will be used but, adhesives which are curable by radiation, for example UV-radiation or X rays may be used if convenient sources of such radiation are available. Depending on the nature of such radiation it may cure the adhesive by any of three ways. First, it may penetrate the outer pipe to reach the adhesive and initiate a polymerisation reaction.Secondly, if it cannot penetrate the outer pipe it may initiate a polymerisation reaction in part of the adhesive which is exposed and cause polymerisation of the bulk of the adhesive through chain reactions. Thirdly, it may cause the pipe to heat up and lead to heat curing.

If the adhesive is heat curable it will preferably be one which cures at a comparatively low temperature to avoid the need for severe heat application. Suitably the adhesive will be one which will cure at 1500C or below and preferably in the range of 50-1000C. The heat necessary to raise a copper pipe to such a temperature can be applied by using a hot air gun and thus pipes may be joined using such adhesive by supplying heat from a suitable domestic source such as a hair dryer, paint stripper, or electric fan heater.

The pipes joined in accordance with the present invention may be joined by the use of an end-feed capillary fitting or by inserting one pipe end within another pipe end of slightly larger diameter. The invention is particularly useful for joining pipes which comprise copper or a copper alloy.

The adhesive employed in the method of the present invention preferably has a viscosity of only up to 100 centipoise, more preferably only up to 50 centipoise. This enables the adhesive to flow well enough to be drawn between the pipe and fitting by surface tension. The viscosity values given herein for the adhesive of the present invention are those at 250C.

Some epoxy adhesives which have a viscosity falling within the desired range are already known.

For example, GB 1544278 discloses a pumpable epoxy resin composition which comprises an epoxy resin, a curing agent therefor and a liquid diluent, while GB 1554429 discloses a method of making flexible sheet material which involves the use of an epoxide-solvent mixture. However, the diluents employed to provide these epoxy adhesives with their low viscosities are solvents such as toluene and methyl ethyl ketone.

While such epoxies can be employed in the method of the present invention they have disadvantages arising from the fact that they are heat-curable and solvent is driven off during the heating. Thus, if such epoxies are used in the method of the present invention the heating must be carried out very slowly to ensure that all the solvent is driven off before the curing commences otherwise bubbles of solvent vapour may be trapped and lead to a weaker, less watertight joint. A further problem is that it may be difficult for the solvent vapour to escape from the enclosed region of a joint because of surface tension.

Encyclopaedia of Polymer Science and Technology, Interscience, volume 6 1967 p 240 discloses epoxy adhesives containing reactive diluents and having viscosities in the range 200 to 1500 centipoise. Such epoxies do not have low enough viscosities to produce good joints according to the present invention and also do not wet the surfaces to be joined adequately.

An adhesive which can be used in the method of the invention and which reduces or obviates the problems associated with these known adhesives is thus desirable.

Thus, the present invention also provides a heat curable adhesive composition comprising an epoxy resin, a curing agent, a reactive diluent and a wetting agent, said composition having a viscosity in the range from 0.5 to 200 centipoise.

By employing a reactive diluent to reduce viscosity the problems associated with release of solvent vapour are avoided. By "a reactive diluent" is meant a diluent which has a lower viscosity than the epoxy resin and thus reduces the viscosity of the adhesive composition but which can react with the curing agent. Preferred reactive diluents contain epoxy groups. A wetting agent is included in the composition to faciliate flow of the adhesive over the surface of the joint to be soldered and wetting of that surface.

Preferably the composition will have a viscosity of only up to 100 centipoise, more preferably only up to 50 centipoise.

The reactive diluent is preferably present in an amount of only up to 25 weight percent of the composition.

Examples of reactive diluents that may be used include both monofunctional and multi functional compounds.

Examples of reactive diluents containing one reactive epoxy group include butyl glycidyl ether, alkyl glycidyl ethers where the alkyl group contains between 8 and 14 carbon atoms, 2 ethyl hexyl glycidyl ether, phenyl glycidyl ether, cresol glycidyl ether, and para tertiary butyl phenyl glycidyl ether.

Examples of reactive diluents containing more than one reactive epoxy group include poly glycidyl ether of an aliphatic polyol, triglycidyl ether trimethylol propane, cyclo aliphatic diglycidyl ether, neopentyl glyol diglycidyl ether, butane diol 1,4-diglycidyl ether, and 1,6-hexanediol diglycidyl ether.

A wetting agent is added to the composition of the present invention to improve the bonding of the adhesive to the surface to which it is applied. Where the surface is a copper pipe suitable wetting agents include silanes, zirconates and titanates. Examples of such wetting agents include gamma-glycidyloxypropyltrimethoxysilane, gamma-aminopropyltriethoxysilane, beta-(3,4 epoxycyclohexyl) ethyltrimethoxysilane, isopropyl triisostearoyl titanate, isopropyl (trimethyl amino ethylamino) titanate, isopropyl tri(dioctyl phosphato) titanate, and isopropoxy zirconium tristearate.

Examples of epoxy resins that may be used in the composition of the present invention include glycidyl ether epoxy resins, for example the glycidyl ether of the following compounds: bisphenol A, bisphenol F, hydrogenated bisphenol A,tetrabromobisphenol A, phenol novolaks, brominated phenol novolaks, cresol novolaks, and hydantoin. Triglycidyl epoxy resins such as triglycidyl isocyanurates and triglycidyl-paraaminophenol derived resins may be used, as may tetraglycidyl epoxy resins such as tetraglycidyl methylene dianiliine ether resins.

Curing agents for use with the epoxy resins may be selected from the conventional known hardeners.

Preferably liquid curing agents will be employed.

Examples of these include polyamines such as, ethylene diamine, diethylene triamine, triethylenetetraminine, diethylene aminopropylene, and menthane diamine; piprazines such as, N amino ethyl piprazine; modified polyamines such as, olefin oxide polyamine adducts; polyamines such as, alkyl alkenyl imidazolines; acid anhydrides such as, dodecenyl succinic, and methyl nadic.

The epoxy resin of the present invention may be supplied as a one-pack epoxy resin in which all the ingredients are mixed and stored together before use or as a two-pack adhesive in which the curing agent is stored separately from the epoxy resin until the ingredients are mixed together just before use. A two-pack adhesive is preferred because it can be stored for longer periods at higher temperatures.

Also, there are very few curing agents suitable for one pack adhesives which are in liquid form. It is preferred not to use solid curing agents as these will not flow as well.

Thus the present invention further provides a kit comprising the components for producing an adhesive composition as defined above, in which the curing agent is stored separately from the epoxy resin.

In a preferred embodiment the kit consists of a container for the components of the adhesive composition in which the curing agent is stored separately from the epoxy resin comprising a flexible housing the interior of which is divided into at least two compartments, one containing curing agent and the other containing epoxy resin, said at least two compartments being separated by a friable membrane which is arranged so that it can be broken by deformation of the housing to enable mixing of the curing agent and epoxy resins.

Thus, the curing agent is stored in one compartment on one side of the membrane while the epoxy resin is stored in the compartment on the other side. After the membrane has been broken by deformation of the housing the two components can easily be mixed by shaking the container because the viscosity of the ingredients is comparatively low. In accordance with the invention the viscosity of the adhesive when mixed is in the range of from 0.5 to 200 centipoises.

Preferably the housing will be provided with a dispensing nozzle. The nozzle will have a dispensing oriface which is closed to the outside atmosphere during storage but will be easily opened when needed to allow adhesive to be dispensed from the container.

For example, the nozzle may have a permanent dispensing oriface covered with a cap which can be removed when required or the oriface may be provided with a seal which can be punctured when required.

The method of joining pipes, adhesive, and kit of the present invention will now be described by way of example with reference to the accompanying drawings and the following examples.

In the accompanying drawings Figure 1 is a sectional view through a horizontal pipe joint formed according to the method of the present invention Figure 2 shows a vertical pipe joint formed according to the method of the present invention.

Figure 3 is a cross-sectional view lengthwise through a container according to one embodiment of a kit for producing an adhesive composition according to the invention, and Figure 4 is a cross-sectional view lengthwise through a container according to another embodiment of a kit for producing an adhesive composition according to the invention.

Example A two-pack epoxy adhesive with a low viscosity was formulated. Use of a low viscosity aids the "wetting" of the fittings and also allows capillary action to draw the adhesive into the joint in the manner which occurs with presently used solders.

The formulation employed was made by mixing the following components A and B together in the ratio 102:30 A:B.

Part A Shell epoxy resin Epikote 828 80 parts by weight Butane diol 1,4 diglycidyl ether 20 parts by weight Union Carbide Silane A187 2 parts by weight 102 Part B Trimethylhexamethylenediamine 30 Epikote 828 is a trade name of the Shell Chemical Company and used to describe a liquid glycidyl ether of Bisphenol A. Silane A187 is a trade name of the Union Carbide Company and used to describe gamma-glycidoxypropyltrimethoxysilane.

The formulation was used to make joints between copper pipe ends and capillary fittings.

The procedure used to make the joints will now be described with reference to Figures 1 and 2 of the accompanying drawings: Referring to the drawing, Figure 1 shows two copper pipe fragments 21 inserted within a copper end feed capillary fitting 22 of slightly larger diameter than the pipe fragments.

Before assembly the outer ends 24 of the pipe fragments and the inner ends 26 of the capillary fitting are cleaned with wire wool. The joints are then assembled. The circumference of each end 24 is overlapped by the larger diameter cylindrical fitting to make a close radial fit. In the case of nominal 15 mm copper pipe the fit is about 0.0635 millimeters.

The epoxy adhesive having the formulation described above was then applied by a pipette to the edge of the overlap in a line round the circumference of each pipe end 24 as indicated by A in the sectional view of Figure 1. The joint was then cured in an oven at 1000C.

Figure 2 illustrates a similar pipe joint which is mounted vertically and similar pieces are indicated with the same reference numerials as for Figure 1. However, in this case the pipe was maintained in a vertical orientation both during and after application of the adhesive and during curing in the oven. It will be seen from the results shown in Table 1 below that the method of the present invention is equally effective in bonding vertical pipes and in bonding horizontal pipes despite the effect of gravity.

Several joints formed in this way were tested for leakage by passing water from a hot water tap through them. None of the samples leaked.

The joints were also tested for tensile strength using an Instron Tensometer Model 6025. The results of the tensile strength tests are given below in Table 1.

Table 1 Tensile Results (peak) Cured horizontally Cured vertically /kiloNewtons /kiloNewtons 7.15 6.66 6.22 6.95 7.12 7.00 6.71 7.25 These results can be compared with the results obtained for testing copper pipe on its own and pre-soldered Yorkshire fittings and hand soldered capillary fittings for which the results are shown in Table 2 below.

Table 2 Tensile Results (peak) Copper Pipe Yorkshire Pre- Hand Soldered 15 mm Diameter Soldered Fitting Capillary Fitting /kiloNewtons /kiloNewtons /kiloNewtons 8.28 7.42 8.29* 8.26 7.34 8.25* 7.39* 8.15 8.11 For the samples marked with an asterisk the copper pipe itself failed before the joint.

Joints were also formed using adhesives having the compositions described in Table 3 below. Strong leak-proof bonds were obtained in each case.

The viscosity values quoted for the adhesives were measured using the German "DIN 125" standard at 250C. The shear rates used were in the range 129.8 min~l to 780 min1.

Table 3 Diglycidyl ether of bisphenol A - 75 75 50 75 Diglycidyl ether of bisphenol F - - - 25 Cycloaliphatic diepoxide 100 - - - Phenyl glycidyl ether - 25 25 25 Gamma glycidyl oxypropyl trimethoxysilane 2.0 2.0 2.0 2.0 2.0 Trimethylhexamethylene diamine 30.0 30.0 - 30.0 30.0 2 methyl pentamethylene diamine - - 30 - Viscosity (centipoises) 81 105 49 93 49 Figures 3 and 4 illustrate two examples of a container for use in the present invention.

Referring to Figure 3 the container comprises a generally cylindrical housing 1 of flexible plastics material sealed across one end 6 and, at the other end provided with a nozzle 3 which is closed by a cap 4.

The housing 1 contains a friable membrane 2 of thin glass which forms a closed cigar shaped compartment which contains curing agent 5. The compartment formed between the membrane 2 and the housing 1 contains epoxy resin 7.

When it is desired to use the container the housing is bent in the middle so that it folds back onto itself thereby causing the membrane 2 to break and release the curing agent 5 so that it can mix with the epoxy resin 6. Mixing can be improved by shaking the container vigorously. The cap 4 may then be removed and the housing squeezed so as to expel adhesive from the nozzle.

Referring to Figure 4 a container again comprises a generally cylindrical housing 1 sealed at one end 6 and provided with a nozzle 3 at the other end.

However, in this case a friable membrane 12 is positioned in the plane of the cross-section of the housing so as to divide the housing into two compartments 13 and 14. One compartment 13 contains epoxy resin while the other compartment 14 contains curing agent. In this embodiment the nozzle is sealed by a sealing member 15 of thin metal.

When it is desired to use the adhesive the housing 1 is squeezed so as to fracture the membrane 12 and permit mixing of the epoxy resin with the curing agent. The tube may be shaken to effect the mixing. The sealing member 15 at the end of the nozzle 3 can then be punctured by a sharp instrument to permit flow of the adhesive from the container.

Claims (22)

CLAIM8

1. A method of joining pipes comprising overlapping the circumference of a pipe end with a larger diameter cylindrical fitting to make a close radial fit, applying adhesive having a viscosity in the range from 0.5 to 200 centipoises to the edge of the overlap, allowing the adhesive to be drawn between the pipe and fitting, and thereafter curing the adhesive.

2. A method as claimed in claim 1 in which the radial fit is in the range of 0.02 mm to 0.18 mm.

3. A method as claimed claim 1 or claim 2 in which the adhesive is cured by heating.

4. A method as claimed in any one of claims 1 to 3 in which the cylindrical fitting is an end feed capillary fitting.

5. A method as claimed in any one of claims 1 to 3 in which the cylindrical fitting is a pipe end.

6. A method as claimed in any one of claims 1 to 5 in which the pipe end and the cylindrical fitting are of copper or a copper alloy.

7. A method as claimed in any one of claims 1 to 6 in which the adhesive has a viscosity of up to 100 centipoises.

8. A method as claimed in any one of claims 1 to 6 in which the adhesive has a viscosity of up to 50 centipoises.

9. A method as claimed in any one of claims 1 to 8 in which the adhesive is as defined in any one of claims 11 to 15 below.

10. A method of joining pipes as claimed in claim 1 substantially as described herein with particular reference to the Example.

11. A heat curable adhesive composition comprising an epoxy resin, a curing agent, a reactive diluent and a wetting agent, the said composition having a viscosity in the range from 0.5 to 200 centipoises.

12. An adhesive composition as claimed in claim 11 which has a viscosity of up to 100 centipoises.

13. An adhesive composition as claimed in claim 11 which has a viscosity of up to 50 centipoises.

14. An adhesive composition as claimed in any one of claims 11 to 13 which cures at l500C or below and preferably in the range of 50-1000C.

15. An adhesive composition as claimed in any one of claims 11 to 14 in which the epoxy resin is selected from glycidyl ether epoxy resins, triglycidyl ether epoxy resins, triglycidyl epoxy resins, triglycidyl-para-aminophenol derived resins and tetraglycidyl epoxy resins.

16. An adhesive composition as claimed in any one of claims 11 to 15 in which the curing agent is selected from polyamines, piprazines, modified polyamines, imidazolines and acid anhydrides.

17. A adhesive composition as claimed in any one of claims 11 to 16 in which the reactive diluent is selected from butyl glycidyl ether, alkyl glycidyl ethers where the alkyl group contains between 8 and 14 carbon atoms, 2-ethyl hexyl glycidyl ether, phenyl glycidyl ether, cresol glycidyl ether, tertiary butyl phenyl glycidyl ether, poly glycidyl ether of an aliphatic polyol, triglycidyl ether trimethylol propane, cycloaliphatic diglycidyl ether, neopentyl glyol diglycidyl ether, butane diol 1,4-diglycidyl ether, and 1,6-hexanediol diglycidyl ether.

18. An adhesive composition as claimed in any one of claims 11 to 17 in which the wetting agent is selected from silanes, zirconates and titanates.

19. A heat curable adhesive composition as substantially as illustrated by any of the formulations contained in the Example.

20. A kit comprising the components for producing an adhesive composition as defined in any one of claims 11 to 19 in which the curing agent is stored separately from the epoxy resin.

21. A kit as claimed in claim 16 which consists of a container for the components of the adhesive composition in which the curing agent is stored separately from the epoxy resin comprising a flexible housing the interior of which is divided into at least two compartments, one containing curing agent and the other containing epoxy resin, said at least two compartments being separated by a friable membrane which is arranged so that it can be broken by deformation of the housing to enable mixing of the curing agent and epoxy resin.

22. A kit as claimed in claim 21 the container of which is provided with a dispensing nozzle.