GB2292152A

GB2292152A - Improvements relating to resin curing systems

Info

Publication number: GB2292152A
Application number: GB9513974A
Authority: GB
Inventors: Darren Bates
Original assignee: Sound Pipe Ltd
Current assignee: Sound Pipe Ltd
Priority date: 1994-07-13
Filing date: 1995-07-08
Publication date: 1996-02-14
Also published as: GB9414180D0; GB9513974D0

Abstract

To control when a phenolic resin system will cure, the acid catalyst is chemically blocked so that at ambient conditions, although the catalyst is mixed in the resin matrix, it will not cure. Cure can be initiated by the application of heat which "unblocks" the catalyst to enable it to commence the cure. The invention has particular application to the placement of tubular liners impregnated with the resin in pipes or passageways where the liner is inflated into the pipe or passageway before curing of the resin and then curing can be effected at the installers convenience, which is of considerable advantage.

Description

Improvements Relating to Resin Curing Systems This invention relates to resin curing systems, and in particular concerns a resin formulation designed so that the resin can be cured i.e. changed from a fluent mass to a rigid mass at the selection of the user.

There are many applications where a fluent or at least pliable resin mass is required to be cured to a solid mass to produce for example a shaped article. Some synthetic resins which are referred to as thermoplastic in nature will soften when heated and can be shaped or moulded when soft, and then cooled to form a rigid article. Other forms of synthetic resin referred to as thermosetting resins initially are fluent in nature, and remains so until mixed with a curing agent or catalyst when they change structure and become rigid. This is a one time process hence the expression thermosetting insofar as after the material has rigidified, it cannot be reconstituted into the fluent form.The present invention is concerned with thermosetting resins comprising the combination of a basic resin matrix, and a curing agent, which may be and usually is a catalyst, but the mix may also include what is referred to as an accelerator or promoter which enhances the curing reaction. Some thermosetting resins are what is referred to as ambient cure resins which means that when the curing agent and resin matrix are mixed, it is only a matter of time before the resin cures without the application of any external influence such as heat, although the presence of heat always accelerates the cure.

Other resins need the application of heat before curing will take place within a reasonable time, although even these resins will eventually cure after mixing of the resin matrix and catalyst, and without the application of external influence, but the curing time is much greater. An example of an ambient cure resin is an epoxy resin, whilst polyester resin represents a material which normally requires the application of heat to achieve cure within a reasonable time.

Epoxy resin and polyester resin mixes are used extensively in the application in which we are particularly interested, namely the formation of lining pipes formed on passageways and pipelines, in particular underground sewers or the rehabilitation of same. These processes, which are explained for example in US Patents Nos 4009163 and 4064211 involve the use of a flexible lining tube which is impregnated with the resin mix. The lining tube is then inserted into the sewer for which it is tailored, and then is inflated onto the sewer surface and held inflated whilst curing takes place. In the case of a lining tube impregnated with epoxy resin, it is simply a matter of keeping the tube in inflated condition, but if a polyester resin is used, it is usual to supply hot water to the inside of the inflated tube in order to initiate and effect the cure.In each case, when curing has been completed, the inflating pressure can be removed leaving a rigid lining pipe on the sewer surface. This process has been extremely successful throughout the world, and has been practised for many years. The main resin which is used in this process is polyester resin requiring the use of heat for the cure of same.

The process of sewer lining as indicated above can be enhanced if the resin used can be quiescent or latent in nature which means that the resin is of a type which will remain in the fluent state for a long time after mixing so that the lining tubes can be pre-impregnated with or formed by the resin mixture long before they are to be used. Indeed if this can be achieved, then lining tubes can be prepared in advance and can be stored in stock ready for subsequent orders. Additionally, the tubes can be transported all over the world upon request. Obviously, it is undesirable to provide a stock of such tubes if the resin will in the course of time cure, but if a quiescent or latent resin system can be developed, then considerable advantages can be achieved.

Another requirement is that when the lining tube is eventually placed in position of the sewer, it is desirable that curing should be effected in the shortest time possible so that the contractor can spend the minimum of time on site and therefore can complete the contract at the minimum cost to the customer. The requirement is therefore for a resin system which has a long shelf life, and a fast cure time after the cure is initiated.

Many attempts have been made to achieve this arrangement, and one particular method has been to provide a resin system which is curable by ultraviolet or other high intensity light. This system has not found commercial favour however, because of the problems concerned with taking high intensity lights into underground passageways such as sewers in which there may exist a wet and hostile environment.

The present invention is concerned with providing a latent or quiescent resin system which, after mixture of the resin ingredients, the resin will remain in the uncured state until the application of heat, and the present invention has particular application in connection with the utilisation of high reactivity ambient cure resin systems, such as those based upon the phenolic resins of which the curing agents are acids, and in accordance with the present invention, the resin system comprises a resin matrix of which the curing agent is an acid which is chemically blocked; preferably the chemical blocking is achieved in that mixed with the resin is either (i) a neutral substance which can be caused to become acidic, or (ii) an acid and an inhibiting substance of which the inhibiting effect of the inhibiting substance can be released to allow the acid to cure the resin matrix; upon the application of heat.

It can be seen therefore that an extremely simple system can result insofar as in the one case a substance such as a salt for example ammonium chloride can be mixed with a phenolic resin matrix. The mixture of these two ingredients does not cause the curing of the phenolic resin matrix, because no free curing agent acid is present, but when heat is applied, the ammonium chloride changes to ammonia and hydrochloric acid, and the hydrochloric acid then commences curing of the phenolic resin. In an alternative case, an acid and a volatile inhibiting substance for example methylamine, dimethylamine or isopropylamine is used in conjunction with the acid to inhibit the acidic effect, but the inhibiting substance is volatilized under the application of heat, leaving the acid to commence cure of the phenolic resin.

In the case of the utilisation of a compound such as a salt, that salt may have a relatively neutral pH value in the order of 6 or 7, but when the salt is heated and for example in the case of ammonium chloride, the ammonia is driven off leaving hydrochloric acid which has a pH in the order of 1, and the phenolic resin would normally commence cure when mixed with an acid of pH of 3 or less. It can be considered therefore that the salt in the change from the salt formulation to a gas and acid, moves to an activated pH level which causes curing of the phenolic resin.

Similarly, in the case of a mixture of curing acid and neutralising compound, that mixture may have a pH in the order of 13 or 14 and be relatively neutral, but when the neutralising substance which can be considered as a buffer is driven off, the pH value falls into the acidic range which results in curing of the phenolic resin.

These resin mixtures can of course be used in connection with the lining of underground sewers as described above, and the lining tubes can be pre-impregnated or resin mixtures and will remain in the resin uncured state for a long time enabling the tubes to be stored and used at will, providing the advantages described.

The lining tubes disclosed in the aforementioned US patents involve the use of fibrous felt which acts as a carrier for the resinous material. Instead of the lining tube being constructed in this way, it could be in the form of a prepreg material which comprises basically a resin matrix with fibrous reinforcement. The fibrous reinforcement can be loose fibres or a fibrous mat, as opposed to a dense felt.

Indeed, the lining tube may be constructed from a flat sheet comprising the resinous mass either impregnating material such as felt, or being in the form of a pre mixed mass, and to use the flat sheet, it is wrapped in tubular form before being placed in the pipeline or passageway. Some means may be necessary to join the overlap edges to produce a tubular form, but in other cases the edges may simply be overlapped, and will remain so as the tubular form is applied to the pipeline or passageway surface. The application of the invention to the lining of pipelines and passageways is important, but the structure of the lining as long as it embodies the resinous mass which is latent in nature by virtue of the invention, can vary within wide constructions.

When the lining tube is inserted, it may be inflated using water heated to the appropriate temperature, which typically will be in the order of 800C, which gives rise to the increase in acidity as referred to above.

In a typical mixture using a neutral salt, a 100 g of the resin may be mixed with a 10 g of the salt, and when such a mixture is subjected to heat of a temperature over 500C and preferably in the order of 800C, curing is effected in a period in the order of ten minutes, which is extremely effective. In the case of the utilisation of the phenolic resin and acid and neutraliser, 100 g of phenolic resin typically may be mixed with 10 g of the curing acid, and 5 g of the volatile neutralising substance (which may have a boiling point of the order of 35/50 C). The curing temperature again is typically in the order of 800C.

Some more specific examples are given below.

(1) A first example involves using any of the amine(s) indicated below of high pH (e.g. pH 14) to neutralise the acid catalyst "phencat 10" as sold by BP which is a toluene sulphonic/phosphoric acid which has pH 1 to pH 7, generating a stable resin system at ambient temperature with good shelflife properties. Upon heating the resin system, the low boiling point amine(s) will volatilise off quickly, leaving the active acid catalyst in the resin. Since the amine has been removed, the pH of the acid catalyst has returned to its original value of 1 and has regained its active curing properties. Examples of amines used in this chemical neutralisation technique are as follows; isopropylamine, methylamine, dimethylamine.

Properties of the Amine(s) pH Boiling point Isopropylamine 14 SOoC (40% aqueous) Methylamine 14 450C (40% aqueous) Dimethylamine 14 sooC (40% aqueous) Experiment It has been found that when 2gms (by wt) methyl amine solution is mixed with 10gms "phencat 10" acid catalyst, this generates a chemically stable (or neutral) catalyst in 100gms of phenolic resin at ambient temperature. When the phenolic system is heated in an oven at 800C, the amine volatilises off and a full cure is obtained within 15 minutes. At higher temperatures, the cure process is much quicker. See Table 2.

Amine % concentration Oven Temperature Cure Time (solution) (Oc) (mins) Methylamine 2 approx 800C 15 mins (40% aqueous) " " 500C 20 mins H n 1000C 7 mins 1100C 4 mins The respective reactions are as follow CH3NH2 + Acid

[CH3NH3 Acid ] stable (pH-14) (pH-l) amino acid complex 250C Methylamine Toluene Sulphonic pH 6-7 /phosphoric acid (Phencat 10) An initial mixing and ambient temperature the stable amino acid complex of pH 6-7 is formed. When heat at over 500C is applied the reaction reverces and the complex breaks down to methylamine and the original acid enabling cure of the resin to take place.

(2) In a second example a catalytic powder is mixed with the resin at ambient temperature but shows no reactivity and does not initiate curing of the resin. Examples of such catalytic powders are as follows; Ammonium Chloride, Ammonium Sulphate, Ammonium Nitrate. These powders or crystalline salts as they are more commonly referred to, are slightly acidic (e.g. pH 5-6) but very stable in phenolic resins. However, when a phenolic resin/ammonium chloride mixture is placed in an oven at 800C, the ammonium chloride undergoes chemical change, giving hydrogen chloride and ammonia. The hydrogen chloride is a strong acid catalyst (pH 1) and curing agent, hence a phenolic cure is obtained quickly.

Chemical Dissociation of Crystalline Salt NH + Cl NH3 + HC1 Ammonium chloride Ammonia Hydrogen chloride (NH4+)2SO42- 2NH3 + H2SO4 Ammonium Sulphate Ammonia Sulphuric Acid NH + NO3 NH3 + HNO3 Ammonium Nitrate Ammonia Nitric Acid Experimental 10g of Ammonium Chloride is mixed with 100g of Phenolic resin. This at ambient temperature is a stable resin/catalyst system with good shelf-life. Upon heating the mixture at 800C for 10 minutes, a cure is obtained.

Higher temperatures will generate a cure more quickly since the formation of Hydrogen chloride will take place more quickly.

There is prior art in the field of the use of phenolic resins as binders for example for felt manufacture, phenolic resins with acid catalysts and extending liquids, and resins for producing baking enamels, as well as prior art in the field of applying tubular linings to passageways but none of the prior patent specifications, discussed below, discloses the present invention.

Japanese Patent Application No 87-318677 This discloses a phenolic resin used as a binder for felt manufacture. The resin includes an amonium salt the purpose of which is to lower the heat treatment temperature. The advantage is reduced energy cost and improved productivity.

Japanese Patent Application No 900320047 A phenolic resin is used as a binder for fibre, wood meal, ceramic, casting sand etc which can be cured at a low temperature by using a catalyst which is a salt of an acid with a notrogen containing base. This appears similar to Japanese Patent Application 87-318677 discussed above.

Japanese Patent Application No 92-190059 This specification relates to a pre-preg of which the resin includes expandable particles. The resin is a phenol or melamine resin and the catalyst may be salt or a particular acid of amonium. The resin is for impregnating chopped strand, mat or non-woven fabrics etc. The material is used for a laminate for automobiles. There is no discussion of any chemical blocking.

European Patent Application No 0390535 This specification discloses that a rigid structure may be made by bringing together lengths of tubing or sections of tubing and impregnating same with a composition which comprises a thermosetting resin, an extending liquid for the thermosetting resin and a catalyst. The resin in one example is described as a phenolic resin and the extending liquid suitably a C1-C4 alcohol. The acid is described as suitable acidic catalyst. It is specified that the composition may include other components such as an inhibitor.

More detail is given as to the reasons for using this composition. For example at page 5 line 29 it is specified that it is desirable that the pre-catalysed thermosetting composition has an extended pot life, for example in the order of 14-25 days. The specification specifically talks about the use of resins from BP such as Cellobond J2027L and others, which may be catalysed with a catalyst such as Phencat 10.

When describing that the resin may be epoxy resin, it is specified that suitably epoxy resins include epoxy resins with blocked amine functions.

The resin systems are referred to as latent catalyst systems which in some cases can trigger polymerisation at a temperature of around 800C or upwards.

Specifically at pages 7 and 8, lines 54 to 59 page 7 and 1 to 5 page 8, an actual example of the preferred liquid composition is given.

US Patent 3474054 This patent concerns the chemistry of coating compositions which are referred to as "baking enamels". The known baking enamels have to be cured to a hard finish at a high temperature in the order of 4000F. This patent is concerned with making a composition which can be cured at a much lower temperature e.g. 1000F, but the composition will be storage stable i.e. it will have a reasonable pot life. This is done by adding an acid catalyst of a specific type to a specific resin composition. The resin composition is either an amino resin or an unmodified alkyd resin and the catalyst is an amine salt of an aromatic sulphonic acid.

French Patent Specification 2584018 This appears to relate to the provision of a tubular structure which initially is flexible, but is impregnated with a polymerisable material, and a number of examples are given, one of which is phenolic resin. The invention is concerned with the method of making the tube, and not the specific chemical composition of the resin.

European Patent Application 0620104A2 This specification discloses a pipe lining operation. The specification also discloses what is claimed to be a novel form of tube. The tube is made up by everting one impregnated tube into another. The outer impregnated tube is impregnated with a resin of a first and low viscosity with small diameter particle filler, whilst the inner tube is impregnated with a resin of high viscosity and large diameter particle filler. When the composite tube is eventually turned inside out to line the pipe, the layer with the high viscosity large diameter filler lies to the outside, and this is alleged to form a much better water barrier for the lining tube.

US Patent 4366012 This relates to vacuum impregnation of lining tubes. The patent also shows that the tube is everted into and along the passageway to line same.

Claims

1. A resin system comprising a resin matrix including an acid curing agent which is chemically blocked so that the system remains latent at ambient conditions and the curing agent can be released by the application of heat.

2. A resin system according to Claim 1, wherein the resin matrix is a high reactivity ambient cure resin matrix.

3. A resin system according to Claim 2, wherein the resin matrix is a phenolic resin matrix.

4. A resin system according to Claim 3, wherein the chemical blocking is achieved by a neutral substance which can be caused to become acidic by the application of heat.

5. A resin system according to Claim 4, wherein the neutral substance is a salt.

6. A resin system according to Claim 5, wherein the salt is ammonium chloride, ammonium sulphate or ammonium nitrate.

7. A resin system according to Claim 5 or 6, wherein the resin matrix and salt are contained in the system in the proportions by weight of 10:1.

8. A resin system according to Claim 3, wherein the chemical blocking is achieved by an acid catalyst and inhibiting substance of which the inhibiting effect is removed by the application of heat.

9. A resin system according to Claim 8, wherein said acid catalyst is the substance "Phencat 10" (sold by B.P.Plc).

10. A resin system according to Claim 9, wherein the inhibiting substance is an amine which can be driven off by heat.

11. A resin system according to Claim 10, wherein the amine is methylamine, dimethylamine or isopropylamine.

12. A resin system according to Claim 10 or 11, wherein the acid catalyst is mixed with the amine by combining 2 parts by wt of a 40% aqueous of the amine with 10 parts by wt of the acid catalyst to produce the blocked catalyst arrangement, which is mixed with 100 parts by wt of the resin matrix.

13. A flexible hardenable sheet member comprising within its wall thickness a resin system according to any preceding claim.

14. A member according to Claim 13, wherein said resin system includes fibrous reinforcing material.

15. A member according to Claim 14, wherein said fibrous reinforcing material comprises one or more layers of a fibrous fabric.

16. A member according to Claim 15, wherein said layer or each of said layers is of fibrous felt.

17. A member according to Claim 15, wherein said member is flat.

18. A member according to any of Claims 13 to 16, wherein said member is tubular.

19. A member according to Claim 18 wherein said member is inflatable by eversion and has on its outer surface a film or skin providing the means whereby the member can be inflated by eversion.

20. A member according to Claim 18 or 19, wherein the said member has an inner skin or film by which it can be inflated.

21. A method of providing a pipe comprising inflating a member according to any of claims 18 to 20 accompanied by the application of heat to unblock the curing agent to cause the resin in the member to cure causing the member to form a rigid pipe.

22. The method of claim 21 wherein the member is inflated against the inner surface of a host pipe or passageway so as to form a rigid pipe within a pipe.

23. The method of claim 22 wherein the host pipe or passageway is located underground.