CA1259735A

CA1259735A - Adhesive system for production of spiral wound membrane elements for use in organic fluid mixture separations

Info

Publication number: CA1259735A
Application number: CA000454141A
Authority: CA
Inventors: William M. King; William W. Wight
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1983-05-13
Filing date: 1984-05-11
Publication date: 1989-09-19
Also published as: DE3473470D1; US4464494A; EP0127364A1; JPS59215375A; JPH0370755B2; EP0127364B1

Abstract

ABSTRACT OF THE DISCLOSURE

In fabricating a reverse osmosis spiral wound apparatus for the separation of organic fluid mixtures, especially for the separation of dewaxing solvents containing ketone from dewaxed oil by per-meation through a permeable membrane such as pretreated regenerated cellulose or asymmetric polyimide a special epoxy adhesive formulation is used to form the membrane element edge seals which serve to define separate permeate zones and feed stream zones. This special adhesive formulation is characterized by having a relatively long pot life, (i.e. will not set too quickly) permitting it to be easily handled during application to the membrane edges in the course of element fabrication, as well as being flexible (trimable) and of proper viscosity.

Description

g~25~

1 In fabricating a reverse osmosis spiral

2 wound apparatus for the separation of organic fluid

3 mixtures, especially for the separation of dewaxing

4 solvents containing ketone from dewaxed oil by per-meation through a permeable membrane a special epoxy 6 adhesive formulation is used to form the membrane 7 element edge seals which serve to define separate 8 permeate zones and feed stream zones. This special 9 adhesive formulation is characterized as having a relatively long pot life, (e.g. pot life of about 30 11 minutes or longer meaning the formulation will not set 12 too quickly) permitting it to be easily handled during 13 application to the membrane edges in the course of 14 element fabrication, as well as being flexible, trimable and of proper viscosity to permit winding of 16 multi-leaf elements. The adhesive also thoroughly wets 17 the membrane and the permeate spacer when the membrane 18 edge seals are formed thus insuring the absence of edge 19 seal leaks. This adhesive is resistant to solvents such as water, methanol, methyl ethyl ketone, methyl 21 isobutyl ketone, toluene, ethers, benzene, hexane, 22 dioxane, DMF, per halogenated hydrocarbon (e.g.
23 generally of the Freon*type) but is not resistant to 24 materials such as acetic acid, NMP or incompletely halogenated hydrocarbons such as methylene chloride or 26 chloroform.

27 The special adhesive which meets these 28 criterion comprises a ketone resistant epoxy formu-29 lation which is (1) a reaction product of bisphenol-A
and epichlorohydrin, (2) a thickening agent ~such as 31 fumed silica), ~3) a polyamide or amidoamine low 32 temperature low exotherm curing agent such as one 33 identified as Versamid 140* (4) a diluent selected from 34 DMF~ methanol, isopropanol, acetone, hexane, toluene, * Trade Mark -` ~2~ 3~

1 m2,hylenechloride, methyl ethyl ketone, tetrahydro~
2 furan, dimethylsulfoxide, dimethylacetamide and 3 preferably (5) a urethane flexibilizer (such as Estane 4 5707F-l~. Use of such flexibilizer requires that the diluent solvent selected be, or at least include GMF, 6 THF or other solvent in which the polyurethane is 7 soluble. This formulation will include the above 8 components 1, 2, 3 and 4 in a ratio based on parts by 9 weight of about 100/0-15/~0-70/8-32, preferably about 100/10/60/12. The formulation comprising components 1, 11 2, 3, 4 and 5 will have the above identified materials 12 present in a ratio based on parts by weight of about 13 100/0-15/~0-70/8-32/2-8, most preferably 100/10/60/
14 12/4. The edge seal adhesive will cure in from 1-21 days at a temperature of from about 25-60C. Lower 16 temperatures require longer times but are preferred so 17 as to avoid damage to the membrane materials which can 18 result from exposure to elevated temperatures. A curing lg temperature of about 25C requiring a curing time of about 7~21 days is preferred.

21 Waxy hydrocarbon streams are solvent dewaxed 22 employing any one of a number of different processes.
23 Representative, non-limiting examples include solvent 24 dewaxing processes employing indirect heat exchange in scraped surface chillers wherein waxy oil and solvent, 26 at approximately the same temperature, are mixed in 27 such a manner so as to effect complete and thorough 28 solution of the oil in the solvent before being cooled 29 or chilled. This solution is then cooled in the scraped surface chiller at a uniform, slow rate under con-31 ditions which avoid agitation of the solution as the 32 wax precipitates out.

*Trade Mark ~2~d35 1 Another well-known method of solvent 2 dewaxing involves conventional, incremental solvent 3 addition. In this method, solvent is added to the oil 4 at several points along a chilling apparatus. The waxy oil is first mixed with solvent then chilled until some 6 wax crystallization has occurred and the mixture has 7 thickened considerably. A first increment of solvent is 8 introduced at this point in order to maintain fluidity, g cooling continues and more wax is precipitated. A
second increment of solvent is added to maintain fluid-11 ity. This process is repeated until the desired oil-wax 12 filtration temperature is reached, at which point an 13 additional amount of solvent is added in order to 14 reduce the viscosity of the mixture to that desired for the filtration step. In this method the temperature of 16 the incrementally added solvent should also be about 17 the same as that of the wax/oil/solvent mixture at the 18 point of introduction. If the solvent is introduced at 19 a lower temperature, shock chilling of the slurry usually occurs, resulting in the formation of small 21 and/or acicula shaped wax crystals with attendant poor 22 filter rate.

23 Still another well-known process is the 24 DILCHILLR process wherein a waxy oil is introduced into an elongated, staged cooling zone or tower at a 26 temperature above its cloud point and incrementally 27 introducing cold dewaxing solvent into said zone, along 28 a plurality of points or stages therein, while main-29 taining a high degree of agitation so as to effect . . . ~
3a RRegistered service mark of Exxon Research and 31 Engineering Company.

373~:i 1 substantiall~ instar. aneous mixing of the solvent and 2 wax/oil mixture as they progress through said zone and 3 resulting in the precipitation of at least a portion of 4 the wax present in the waxy oil. ~he basic concept is shown in U.S. Patent No. 3,773,650 while a modification 6 thereof which employs the aforementioned high agitation 7 chilling zone augmented by a subsequent, separate and 8 distinct scraped surface chilling zone is presented in 9 U.S. Patent 3,775,288.

11 Typical ketone containing dewaxing solvents 12 are (a) the aliphatic ketones having from 3 to 6 carbon 13 atoms and mixtures thereof, such as acetone, methyl 14 ethyl ketone (MEK) and methyl isobutyl ketone (MIBK), and (b) mixtures of the aforesaid ketones with C6-Clo 16 aromatics such as benzene, xylene and toluene. Pre-17 ferred solvents are MEK/MIBK and MEK/toluene.

18 Solvent dewaxing may be practiced on any 19 waxy hydrocarbon oil stock, preferably waxy petroleum oil stock or distillate fraction thereof, more pre-21 ferably waxy lube oil, transformer oil, white oil or 22 fuel oil stocks. Illustrative, non-limiting examples of 23 waxy stocks are (a) distillate fractions that have a 24 boiling range within the broad range of about 500F to about 1300F, with preferred stocks including the 26 lubricating oil and specialty oil fractions boiling 27 within the range of between about S00F and 1200F, (b) 28 briqht stocks and deasphalted resids having an initial 29 boiling point about 800F, and (c) broad cut feedstocks that are produced by topping or distilling the lightest 31 material off a crude oil leaving a broad cut oil, the 32 major portion of which boils above about 500F or 33 650F. Additionally, any of these feeds may be 34 hydrocracked prior to distilling, dewaxing or topping.

~5~3~3~

1 The distillate fractions may come from any source such 2 as the paraffinic crudes obtained from Aramco, Kuwait, 3 the Pan Handle, North Louisiana, etc., naphthenic 4 crudes, such as Tia Juana, Coastal crudes, etc. r as well as the relatively heavy feedstocks, such as bright 6 stocks having a boiling range of 1050~F and synthetic 7 feedstocks derived from Athabasca Tar Sands, shale, 8 etc.

9 Spiral wound elements are well known in the separations art and generally comprise a perforated 11 central tube which collects the permeate, which tube is 12 surrounded by layers of permeation membrane, and 13 alternating layers between the membrane layers of feed 14 spacers and permeate spacers with the edges of the membrane layers surrounding the permeate spacers being 16 sealed to sandwich the permeate spacer into a closed 17 envelope in fluid communication with the perforated 18 central tube leaving the perforated central tube as the 19 only permeate outlet. Spiral wound elements take many varied forms and are generally described in US Patent 21 3,417,870, USP 3,173,867, USP 3,367,594, USP 3,386,583, 22 USP 3,397,790, USP 3,813,334, USP 3,966,616, USP
23 3,668,837~ USP 3,852,198. What is common to most 24 spiral wound elements, however, is the formation of a membrane edge seal around the permeate spacer layer to 26 define a permeate zone isolated from the feed stream 27 zone.

28 Spiral wound elements for the practice of 29 the separation of dewaxing solvents containing ketone from dewaxed oil can be made from specially pretreated 31 regenerated cellulose as disclosed in EP Publication 32 No. 13834. ~urther, the spiral wound elements re~uire 33 the use of a perforated central mandrel (tube) for the 34 collection of permeate, feed spacers, permeate spacers, - 6 ~ 3~
1 (as described above) and also antitelescoping rings, 2 various seals and an outer wrapper. In fabricating the 3 spiral wound elements useful for the separation of 4 organic fluids, especially dewaxing solvent containing S ketone from dewaxed oil the central mandrel, permeate 6 spacer, feed spacer, antitelescoping rings, seals and 7 outer wrapper are all made of materials now currently 8 in use in producing spiral wound elements for aqueous 9 separations. Thus, the central mandrel for example, may be made o~ metal, Nylon 6 or other solvent resistant 11 plastic, the permeate spacer may be made of ~elamine 12 formaldehyde impregnated polyester (e.g. SIMPLEX*), the 13 feed spacer may be made of polypropylene mesh ~e.g.
14 VEXAR*),the anti-telescoping ring of Nylon 6, the seals lS of butyl rubber and the outer wrapper of epoxy rein-16 forced fiberglass (eOg. fiberglass and Ciba Geigy Epoxy 17 OS00 + 2964 hardner).

18 However, in producing a spiral wound element 19 for use in the hostile environment of organic solvents, especially dewaxing solvents containing ketone and 21 dewaxed oil, the membrane edge seal adhesive must be 22 specially formulated.

23 It has been discovered that the membrane 24 edge seal adhesive which meets the requirements of useful pot life (for manageability and ease of 26 handling) is flexible --(thereby permitting the 27 multi-leaf membrane-permeate spacer-membrane sandwich 28 to be trimmed), is resistant to organic solvent, 29 especially dewaxing solvents containing ketones and is of the proper viscosity to penetrate the permeate 31 spacer and membrane surface at the membrane edge (so as 32 to form the above described envelope) while not running 33 out of the edge or over the entire surface, comprises 34 an epoxy resin formulation which is (1) a reaction *Trade Mark ~2~3'73~

1 product of bisphenol-A and epichlorohydrin having a 2 viscosity in the range of about 7000 to 20,000 cen-3 tipoise preferably 10,000 to 16,000 centipoise with a 4 weight per epoxide (WPE) of about 175-210, preferably about 185-195, (2) a thickening agent [such as Cabosil*
6 M-5], (3) a polyamide or amidoamine low temperatures, 7 low exotherm curing agent such as a condensation 8 product of polyamine with fatty acids or dimer acids, 9 and having an amine value of between about 85-620, preferably about 370-620, more preferably about 370-400 11 or 580-620, (4) a diluent from the group of DMF, 12 methanol, isopropanol, acetone, hexane, toluene, 13 methylene chloride, methylethyl ketone, tetrahydro-14 furan, dimethylsulfoxide, dimethylacetamide, and preferably (5) a high molecular weight polyurethane 16 flexibilizer (such as Estane 5707F-l). The use of a 17 polyurethane flexibilizer requires that the diluent 18 should be, or at least should include-DMF, THF or other 19 solvent in which the urethane component is soluble in order to dissolve the polyurethane. This ~ormulation 21 will include the above components 1/2/3/4 in a ratio, 22 based on parts by weight of about 100/0-15/40-70/8-32, 23 most preferably about 100/10/60/12.

24 The formulation comprising components 25 1/2/3/4/5 will employ the components in a ratio based 26 on parts by weight about lnO/0-15/40-70/8-32/2-B, most 27 preferably about 100/10/60/12/4.

28 The use of a flexibilizer makes the multi-29 leaf element membrane edges readily trimable. Vse of the formulation without the polyurethane flexibilizer 31 will yield an adhesive which forms a strong, solvent 32 resistant edge seal but which rapidly becomes brittle 33 and hard a~ter curing making trimming difficult if not 34 impossible unless care is taken to insure that trimming *Trade Maxk ~25~317~;

1 is pe-.formed before the adhesive becomes Drittle. By 2 adding the polyurethane flexibilizer the edge seal 3 remains pliable and somewhat rubbery for a relatively 4 long time, thus facilitating ~rimming during element fabrication.

6 The use of the solvent, surprisingly, 7 permits the formation o~ an adhesive which upon curing 8 is more solvent resistant than the formulation without 9 the solvent.

~he most preferred formulation co~prises 11 Epon 828*, Cabosil M5*, a curing agent identified as 12 Versamid 140*(from Henkel), a flexibilizer identified 13 as Estane 5707F-l*~B.F. Goodrich) and DMF solvent in a 14 ratio 100/10/60/4/12. Elements made using-the adhesive have membrane edge seals which cure at about 25C over 1~ a period of about 21 days. The edge seals are flexible 17 (do not crack) can be trimmed and stand up well to use 18 conditions.

19 The various components which go to make up the adhesive formulation of the present invention are 21 available from commercial sources. Suitable reaction 22 products of bisphenol A and epichlorohydrin are 23 a~ailable, for example, from Shell Chemical Company 24 under the designation Epon 828*, Epon 830, Epon 825 and Epon 826; from Reichold Chemical Company under the 26 designation EpoTuf* 37-139, EpoTuf 37-140, EpoTuf 27 37-141; from Ciba Geigy Corporation under the desig-28 nation Araldite* 6005, 6010 and 6020; from Celanese 29 Corporation as Epi-ReZ*508, 509 and 510; and from Dow 30 Chemical Company under the designation D.E.R. 330, 331, 31 332, 317 and 337. Suitable low temperature, low 32 exotherm polyamide or amidoamine curing agents are 33 available, for example from Henkel Corp. under the *Trade Mark ~25~3~

des.gnation Versamid*L~0 (which has an amine value of 2 about 370-400), Versamid 115, Versamid 125 and versamid 3 150 or Genamid*2000 (which has an amine value of about 4 5~0-620~ and Genamid 250; from Ciba Geigy Corporation under the designation 815, 82S and 840 and from Shell 6 Chemical Company under the designation V-15, V-25 and 7 V-40. Suitable high molecular weight thermosetting 8 polyurethanes are available, for example, from s. F.
9 Goodrich under the designation Estane 5701, 5713, and 10 5707 F-l. Suitable thickening agents are available, for 11 example, from Cabot Corporation under the designation 12 CabosiI*M-5, Cabosil MS-7 and MS-5 and from Degussa 13 Corporation under the designation Aerosil* 200, 300 and 14 380. These fumed silica thickening agents can also be 15 combined with some aluminum oxide (<50%) such as that 16 available from Degussa under the designation aluminum 17 oxide-C. The thickening agent is used to improve the 18 anti-slump character of the adhesive, i.e., insure that 19 it is not too fluid so it will not run out of the edge 20 of the element or flow into the interior of the element 21 before the adhesive sets.

22 Examples I - XXIV - Solvent Resistance 23 The following Tables show the ketone resis-24 tance of coupons made by sandwiching adhesive filled 25 permeate spacers (melamine formaldehyde impregnated 26 Dacron (Simplex~ ) between two pieces of PM250 Regen-27 erated Cellulose (ENKA*; 17.5.c~, about 12,000 molecular 28 weight cut off). One layer of PM250 was removed from 29 one face of the coupon before the coupons were immersed 30 in methyl ethyl ketone at room temperature for one 31 month. Thus, the adhesive on the exposed face of the 32 coupon was directly exposed to the ketone solvent.

33 Components are reported in parts by weight.

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' Example XX~

2 Examples of adhesive systems with room 3 temperature cures that are ketone resistant yet are 4 unsuitable for use in spiral-wound elements.

Formulation l:

6 Epoxy Resin Ciba Geigy 0500*lO0

7 Cabosil M5 Thickener 10

8 Ciba Geigy Curing ~gent 2964**86

9 Estane 5707F-l 2 lO DMF 8 ll Formulation 2:

12 Epoxy Resin Epon 828 100 13 Cabosil M5 Thickener lO
14 Triethylenetetramine 5.5 15 Diethylenetriamine 5.5 16 Estane 5707F-1 2 18 * Ciba Geigy 0500 epoxy is a low viscosity, high l9 functionality (~3) amine based resin These two formulations are ketone resistant with good 21 bond strength to steel, fabrics and membranes, but the 22 adhesive systems have short (less than 20 minutes) pot 23 lives and exotherm during cure in 8-inch diameter 24 elements. The higher temperatures thus produced during cure cause these adhesives to become very hard and very 26 brittle very ~uickly, thereby making the trimming of 27 the spiral-wound membrane elements impossible.

** Trade Mark ~5~73~

F~rmula i~

2 Epoxy resin Epon 828 100 3 Cabosil 10 4 Versamid 140 50 DMF

6 This formulation without Estane 5707F-l is ketone 7 resistant, however, the resultant adhesive system after 8 cure is brittle and makes trimming the element very 9 difficult, if not impossible, because the brittle

10 adhesive tends to introduce cracks in the membrane

11 during the trimming operation.

12 However, since the adhesive cures slowly, if

13 care is taken the edges can be trimmed while the

14 adhesive is stlll pliable. Preferably, however, the

15 formulation will include a polyurethane flexibilizer to

16 facilitate such handling.

17 EXAMPLE XXVI

18 Epon 828 was combined with Epon 871 in the

19 ratio 70% Epon 828, 30% 871 and then combined with

20 Cabosil M5, Versamid 140 and DMF in a ratio based on

21 parts by weight of 100 (total of both Epons)/10/60/12.

22 The adhesive was destroyed by ketone. Epon 871 is a

23 flexible epoxy and was added to make the system

24 flexible and trimable. Epon 871 is an aliphatic epoxy.

25 Aliphatic epoxy resins do not exhibit good solvent

26 resistance properties. Use of this resin destroys the

27 ketone resistance of the adhesive.

12 59'73~

1 EXAMPLE X~VI T

2 Polyimide membranes prepared and used in 3 accordance with the procedure described and claimed in 4 United States Patent 4,532,041, "Assymetric Polyimide Reverse Osmosis Membrane, Method for Prepa-6 ration of Same and Use Thereof For Organic Liquid 7 Separation", Wan, Shuey, inventors, were fabricated 8 into a spiral-wound element measuring 8 inches x 40 9 inches (having a surface area of about 225 sq. feet) using the preferred adhesive formulation described 11 above. The element was tested for the separation of 12 different.grades of dewaxed oil feeds from MER/MIBK
13 (60/40) over a period of time. The element showed good 14 performance and was still satisfactorily operating in the test unit after about 6 months under real con-16 ditions, (operating pressure about 400 psi, temperature 17 about 45C).

- r

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A solvent resistant adhesive for use in producing membrane edge seals in the production of elements which are suitable for organic fluid separations, which adhesive comprises an epoxy resin formulation which is (1) a reaction product of bisphenol-A and epichlorohydrin, (2) a thickening agent, (3) a low temperature, low exotherm polyamide or amidoamine curing agent, and (4) a diluent wherein the components 1/2/3/4 are present in a ratio based on parts by weight of about 100/0-15/40-70/8-32.

2. The adhesive formulation of claim 1 wherein the reaction product of bisphenol and epichlorohydrin has a viscosity in the range of about 7000 to 20,000 centipoise at 25°C (ASTM D445) with a weight per epoxide (WPE) of about 175-210.

3. The adhesive formulation of claim 2 wherein the reaction product of bisphenol-A and epichlorohydrin has a viscosity in the range of about 10,000 to 16,000 centipoise at 25°C (ASTM D445) with a weight per epoxide (WPE) of about 185-195.

4. The adhesive formulation of claim 3 wherein the thickening agent is fumed sililca.

5. The adhesive formulation of claim 1, 3 or 4 wherein the polyamide or amidoamine curing agent is a condensation product of a polyamine with fatty acids or dimer acids and wherein the curing agent has an amine value of between about 85-620.

6. The adhesive formulation of claim 1, 3 or 4, wherein the polyamide or amidoamine curing agent is a condensation product of a polyamine with fatty acids or dimer acids and wherein the curing agent has an amine value of between about 370-400.

7. The adhesive formulation of claim 1, 3 or 4, wherein the polyamide or amidoamine curing agent is a condensation product of a polyamine with fatty acids or dimer acids and wherein the curing agent has an amine value of between about 580-620.

8. The adhesive formulation of claim 1, 3 or 4, wherein the polyamide or amidoamine curing agent is a condensation product of a polyamine with fatty acids or dimer acids and wherein the curing agent has an amine value of between about 370-400; and the diluent is selected from dimethylformamide, methanol, isopropanol, acetone, hexane, toluene, methylene chloride, methylethyl ketone, tetrahydrofuran, dimethylsulfoxide, and dimethylacetamide.

9. The adhesive formulation of claim 1, 3 or 4, wherein the polyamide or amidoamine curing agent is a condensation product of a polyamine with fatty acids or dimer acids and wherein the curing agent has an amine value of between about 370-400; the diluent is selected from dimethylformamide, methanol, isopropanol, acetone, hexane, toluene, methylene chloride, methylethyl ketone, tetrahydrofuran, dimethylsulfoxide, and dimethylacetamide, and the components 1/2/3/4 are present in a ratio based on parts by weight of about 100/10/60/12.

10. The adhesive formulation of claim 1, 3 or 4, wherein the polyamide or amidoamine curing agent is a condensation product of a polyamine with fatty acids or dimer acids and wherein the curing agent has an amine value of between about 370-400: and the diluent is selected from dimethylformamide, methanol, isopropanol, acetone, hexane, toluene, methylene chloride, methylethyl ketone, tetrahydrofuran, dimethylsulfoxide, and dimethylacetamide, and the components 1/2/3/4 are present in a ratio based on parts by weight of about 100/10/60/12, said formulation further comprising component (5) a high molecular weight polyurethane flexibilizer.

11. The adhesive formulation of claim 1, 3 or 4, wherein the polyamide or amidoamine curing agent is a condensation product of a polyamine with fatty acids or dimer acids and wherein the curing agent has an amine value of between about 370-400; and the diluent is selected from dimethylformamide, methanol, isopropanol, acetone, hexane, toluene, methylene chloride, methylethyl ketone, tetrahydrofuran, dimethylfulfoxide, and dimethylacetamide, said formulation further comprising component (5) a high molecular weight polyurethane flexibilizer, and said components 1/2/3/4/5 being present in a ratio based on pacts by weight of about 100/0-15/40-70/8-32/2-8.

12. A method for producing membrane edge seals by means of an adhesive in the production of elements for use in organic fluid separations wherein the adhesive comprises an epoxy resin formulation which is (1) a reaction product of bisphenol-A and epichlorohydrin, (2) a thickening agent, (3) a low temperature, low exotherm polyamide or amidoamine curing agent, and (4) a diluent wherein the components 1/2/3/4 are present in a ratio based on parts by weight of about 100/0-15/40-70/8-32.

13. The method of claim 12 wherein the membrane edge seal produced using the adhesive is in a spiral wound element.

14. The method of claim 12 wherein the reaction product is bisphenol-A and epichlorohydrin has a viscosity in the range of about 7,000 to 20,000 centipoise at 25°C (ASTM D445) with a weight per epoxide (WPE) of about 175-210.

15. The method of claim 14 wherein the reaction product of bisphenol-A and epichlorohydrin has a viscosity in the range of about 10,000 to 16,000 centipoise at 25°C (ASTM D445) with a weight per epoxide (WPE) of about 185-195.

16. The method of claim 15 wherein the thickening agent is fumed silica.

17. The method of claim 14 wherein the polyamide or amidoamine curing agent is a condensation product of a polyamine with fatty acids or dimer acids and wherein the curing agent has an amine value of between about 85-620.

18. The method of claim 17 wherein the curing agent has an amine value of between about 580-620.

19. The method of claim 17 wherein the curing agent has an amine value of between about 370-400.

20. The method of claim 19 wherein the diluent is selected from dimethylformamide, methanol, isopropanol, acetone, hexane, toluene, methylene chloride, methylethyl ketone, tetrahydrofuran, dimethylsulfoxide, dimethylacetamide.

21. The method of claim 20 wherein the components 1/2/3/4 are present in a ratio based on parts by weight of about 100/10/60/12.

22. The method of claim 21 wherein the adhesive formulation further comprises component (5) a high molecular weight polyurethane flexibilizer.

23. The method of claim 22 wherein components 1/2/3/4/5 are present in the ratio based on parts by weight of about 100/0-15/40-70/3-32/2-8.