Aqueous polymer dispersions

Abstract

A process for producing an aqueous dispersion of at least two preformed polymers each at least partially modified by grafted addition polymers produced in a solution of the polymers, comprising the steps of i) providing a solution in organic carrier liquid of a first preformed polymer, consisting of diepoxy resin, and at least one other preformed polymer excluding polyesters ii) mixing the solution containing the polymers with ethylenically unsaturated monomers, said monomers comprising an effective amount of copolymerizable dispersing moiety iii) providing an effective amount of a grafting polymerization initiator iv) allowing or causing the monomers to polymerize and graft to at least some of the preformed polymers to form a solution of modified polymers v) optionally adding crosslinking agent to solution iv) vi) dispersing the solution of modified polymers, and optionally crosslinking agent, in aqueous medium to form a stable dispersion of particles.

Claims

1. A process for producing an aqueous dispersion comprising polymer particles, said polymer particles comprising a preformed diepoxy resin and at least one other preformed polymer excluding polyester, wherein both the preformed diepoxy resin and the at least one other preformed polymer excluding polyester are at least partially modified with a grafted addition polymer comprising a copolymerisable dispersing moiety, wherein the process comprises i) providing a solution of the preformed diepoxy resin and the at least one other preformed polymer excluding polyesters in an organic carrier liquid, wherein the at least one other preformed polymer excluding polyester is selected from polyvinyl acetals; polyvinyl chloride; ethylene and its copolymers; cellulose and its copolymers; butadiene-acrylonitrile; butadiene-styrene; polyisobutylene, styrene-isobutylene; siloxanes; polyamides; polyurethanes; and polyols; ii) combining the solution of i) with ethylenically unsaturated monomers, said monomers comprising an effective amount of a copolymerisable dispersing moiety; iii) providing an effective amount of a grafting polymerisation initiator; iv) allowing or causing the monomers to polymerise and graft to at least some of both the preformed polymers to form a solution of modified polymers; v) optionally adding a crosslinking agent to the solution of iv); and vi) dispersing the solution of modified polymers with or without the optional crosslinking agent in an aqueous medium to form a stable dispersion of particles, wherein the polymer particles do not contain any phosphate diepoxy resin.

2. A process according to claim 1 wherein the particles comprise a mixture of modified polymers and optionally crosslinking agent.

3. A process according to claim 2 wherein the crosslinking agent is added to solution iv) at a chosen temperature such that the crosslinking capability is substantially preserved.

4. A process according to claim 1, wherein the at least one other preformed polymer is a polyvinyl acetal.

5. A process according to claim 4 wherein the polyvinyl acetal is a polyvinyl butyral (PVB).

6. A process according to claim 5 wherein the weight average molecular weight of the poly vinyl butyral is greater than 35000 Daltons.

7. A process according to claim 5 wherein the PVB:diepoxy ratio by weight is from 6:94 to 30:70.

8. A process according to claim 1, wherein the dispersing moiety is ionic.

9. A process according to claim 8 wherein the dispersing moiety is anionic.

10. A process according to claim 9 wherein the anionic dispersing moiety is acrylic acid, methacrylic acid, or a combination thereof.

11. A process according to claim 8 wherein at least some of the dispersing moieties are neutralised with a neutralising agent.

12. A process according to claim 11 wherein the neutralising agent comprises dimethyl ethanolamine.

13. A process according to claim 1, wherein the grafting polymerisation initiator is a peroxide.

14. A process according to claim 13 wherein the grafting polymerisation initiator is benzoyl peroxide.

15. A process according to claim 13 wherein the initiator is used in an amount of from 1 to 10% based on the weight of monomers.

16. An aqueous dispersion comprising polymer particles, said polymer particles comprising a preformed diepoxy resin and at least one other preformed polymer excluding polyester, wherein both the preformed diepoxy resin and the at least one other preformed polymer excluding polyester are at least partially modified with grafted addition polymer comprising a copolymerisable dispersing moiety, wherein the at least one other preformed polymer excluding polyester is selected from polyvinyl acetals; polyvinyl chloride; ethylene and its copolymers; cellulose and its copolymers; butadiene-acrylonitrile; butadiene-styrene; polyisobutylene, styrene-isobutylene; siloxanes; polyamides; polyurethanes; and polyols, and wherein the polymer particles do not contain any phosphated diepoxy resin.

17. The aqueous dispersion according to claim 16 further comprising a crosslinking agent.

18. The aqueous dispersion according to claim 16 wherein the preformed diepoxy resin is derived from a bisphenol A diglycidyl ether.

19. The aqueous dispersion according to claim 16 wherein the at least one other preformed polymer excluding polyester is a polyacetal.

20. The aqueous dispersion according to claim 19 wherein the polyacetal is polyvinyl butyral (PVB).

21. The aqueous dispersion according to claim 20 wherein the weight average molecular weight of the polyvinyl butyral is greater than 35000 Daltons.

22. The aqueous dispersion according to claim 20 wherein the PVB:preformed diepoxy resin ratio by weight is from 6:94 to 30:70.

23. The aqueous dispersion according to claim 16 wherein the copolymerisable dispersing moiety is ionic.

24. The aqueous dispersion according to claim 23 wherein the copolymerisable dispersing moiety is anionic.

25. The aqueous dispersion according to claim 24 wherein the anionic copolymerisable dispersing moiety is acrylic acid and/or methacrylic acid.

26. The aqueous dispersion according to claim 24 wherein at least some of the copolymerisable dispersing moiety is neutralised with a neutralising agent.

27. The aqueous dispersion according to claim 26 wherein the neutralising agent comprises dimethyl ethanolamine.

28. An aqueous dispersion obtained by the process defined in claim 1.

29. A coating composition comprising the aqueous dispersion of claim 16.

30. The coating composition according to claim 29 wherein the composition contains a crosslinking agent.

31. The coating composition according to claim 30 wherein the crosslinking agent is selected from the group consisting of phenol-formaldehyde resins, melamine-formaldehyde resins and urea-formaldehyde resins.

32. A metal substrate coated with the coating composition according to claim 29.

33. A metal substrate coated with the coating composition according to claim 30, wherein the coating is crosslinked.

34. The coated metal substrate according to claim 32 wherein the metal substrate forms a container.

35. The process according to claim 1 wherein the crosslinking agent is added to solution iv) at a chosen temperature such that the crosslinking capability is substantially preserved and at least one other preformed polymer is a polyvinyl acetal; the polyvinyl acetal is a polyvinyl butyral, and the weight average molecular weight of the poly vinyl butyral is greater than 35000 Daltons; the crosslinking agent is added to solution iv) at a chosen temperature such that the crosslinking capability is substantially preserved and at least one other preformed polymer is a polyvinyl acetal, and the dispersing moiety is ionic; the polyvinyl acetal is a polyvinyl butyral, and the weight average molecule weight of the poly vinyl butyral is greater than 35000 Daltons, and wherein the dispensing moiety is ionic; the ionic dispersing moiety is acrylic acid, methacrylic acid, or a combination thereof and at least some of the dispersing moieties are neutralised with a neutralising agent; or the grafting polymerisation initiator is a is benzoyl peroxide used in an amount of from 1 to 10% based on the weight of monomers.

36. The aqueous dispersion according to claim 16, including at least one of: a) wherein the preformed diepoxy resin is derived from a bisphenol A diglycidyl ether, and the at least one other preformed polymer excluding polyester is polyacetal; b) wherein the preformed diepoxy resin is derived from a bisphenol A diglycidyl ether, and the at least one other preformed polymer excluding polyester is polyvinyl butyral, and with a weight average molecular weight of greater than 35000 Daltons; c) wherein the preformed diepoxy resin is derived from a bisphenol A diglycidyl ether, and the at least one other preformed polymer excluding polyester is polyvinyl butyral, said polyvinyl butyral having a weight average molecular weight of greater than 35000 Daltons; d) wherein the preformed diepoxy resin is derived from a bisphenol A diglycidyl ether, and the at least one other preformed polymer excluding polyester is polyvinyl butyral (PVB), said polyvinyl butyral having a weight average molecular weight of greater than 35000 Daltons, and the PVB:preformed diepoxy resin ratio by weight is from 6:94 to 30:70; e) any one of (a) through (d) and wherein the copolymerisable dispersing moiety is ionic; and f) wherein the coplymerisable dispersing moiety is ionic or anionic, or is acrylic acid and/or methacrylic acid and is neutralised with a neutralising agent.

37. An aqueous dispersion obtained by the process defined in claim 35.

38. A coating composition comprising the aqueous dispersion of claim 36.

39. The coating composition according to claim 38 wherein the composition contains a crosslinking agent.

40. A metal substrate coated with the coating composition according to claim 39.

41. The aqueous dispersion according to claim 16, comprising the preformed diepoxy resin and the preformed polymer excluding polyester is polyvinyl acetal polymer, where the diepoxy resin and the polyvinyl acetal polymer are at least partially modified with grafted addition polymer comprising from 5 to 75% by weight of copolymerisable dispersing moiety calculated on the weight of the grafted addition polymer.

Description

EXAMPLE 1

(1) Polyvinyl butyral preformed polymer was added prior to polymerisation. The final aqueous dispersion is thought to comprise a polymer composition of diepoxy-acrylic addition polymer graft, PVB-acrylic addition polymer graft, diepoxy resin, PVB and acrylic addition polymer.

(2) The ratio of PVB:diepoxy:acrylic:X-linker is 6.0:70.4:19.1:4.5

(3) TABLE-US-00001 Ingredients pbw  1. DER 331 143.90  2. Diphenol Propane 79.41  3. Butyl Oxitol 50.45  4. Phosphonium Acetate 0.17  5. Distillate −7.14  6. Deionised Water 0.81  7. Butyl Oxitol 23.90  8. Butanol 100.65  9. Pioloform BM18 19.03 10. Methacrylic Acid 24.67 11. Styrene 31.81 12. Ethyl Acrylate 0.57 13. Benzoyl Peroxide (75%) 4.76 14. Butyl Oxitol 12.51 15. Butanol 5.65 16. Santolink EB 560 17.52 17. Dimethyl Ethanolamine 14.07 18. Deionised Water 522.25 Total 1044.99
Procedure:
1) In-Situ Preparation of Chain Extended Diepoxy Resin.

(4) A round bottom flask was fitted with a stirrer, addition ports and arranged with vacuum distillation facility.

(5) Charge ingredients 1, 2 and 3 and heat to 50° C. Add ingredient 4 and apply a vacuum (better than 75 mb). Heat to distillation and remove the stated quantity of distillate (5). Break vacuum with nitrogen.

(6) Set for direct reflux and heat to 140° C. Allow to exotherm and hold at 175-180° C. Sample for a reduced viscosity of 25-32.5 poise as measured at 25° C. and 40% nv in butyl oxitol. When at viscosity add deionised water (6) and hold at reflux for 30 minutes. Cool and thin with Butyl oxitol (7) and then butanol (8). This is the preformed diepoxy resin.

(7) 2) Add Ingredient 9 and Maintain Temperature Until Dissolved.

(8) 3) Polymerisation

(9) Heat to 115-118° C. and add a premix of ingredients 10-14 over 2.25 hours. Rinse in with butanol (15) and hold for a further 30 minutes after which polymerization is complete.

(10) 4) Crosslinking Agent Addition

(11) Cool to 100° C. and add the phenol-formaldehyde crosslinking resin (16) and hold at 90-100° C. for 15 minutes.

(12) 5) Dispersion

(13) Add dimethylethanolamine (17) and hold at 90-100° C. for 30 minutes. Heat off; add water (18) over 1 hour whilst stirring to form the dispersion. Non-volatile content by weight should be 29-31% (measured at 200° C./10 minutes)

(14) Material can be adjusted to desired application solids/viscosity by further additions of deionised water and dimethyl ethanolamine as required.

COMPARATIVE EXAMPLE A

(15) The following ingredients were used to make an aqueous dispersion of a diepoxide resin modified by grafted addition polymer (hereafter referred to as epoxide-addition polymer graft). It is thought that the polymer composition of the dispersion is a mixture of epoxide-addition polymer, epoxide resin and addition polymer result.

(16) TABLE-US-00002 Ingredients pbw 1. DER 331 143.90 2. Diphenol Propane 79.41 3. Butyl Oxitol 50.45 4. Phosphonium Acetate 0.17 5. Distillate −7.14 6. Deionised Water 0.81 7. Butyl Oxitol 18.61 8. Butanol 93.75 9. Methacrylic Acid 24.67 10. Styrene 31.81 11. Ethyl Acrylate 0.57 12. Benzoyl Peroxide 4.76 (75 wt% in carrier liquid) 13. Butyl Oxitol 12.51 14. Butanol 5.65 15. Santolink EB 560 17.52 16. Dimethyl Ethanolamine 14.07 17. Deionised Water 490.48 Total 982.00

(17) The procedure used was as follows:

(18) The apparatus was set up as for Example 1.

(19) 1) In-Situ Preparation of Chain Extended Diepoxy Resin.

(20) Charge ingredients 1, 2 and 3 and heat to 50° C. Add ingredient 4 and apply a vacuum of greater than 75 millibar (mb). Heat to distillation and remove the stated quantity of distillate (5). Break vacuum with nitrogen.

(21) Set for direct reflux and heat to 140° C. Allow to exotherm and hold at 175-180° C. Sample for a reduced viscosity of 25-32.5 poise as measured at 25° C. and 40% nv in butyl oxitol. When at viscosity add deionised water (6) and hold at reflux for 30 minutes. Cool and thin with Butyl oxitol (7) and then butanol (8).

(22) 2) Polymerisation

(23) Cool to 115-118° C. and add a premix of items 9-13 over 2.25 hours. Rinse in with butanol (14) and hold for a further 30 minutes.

(24) 3) Crosslinking Agent Addition

(25) Cool to 100° C. and add the phenol-formaldehyde resin (15) and hold at 90-100° C. for 15 minutes.

(26) 4) Dispersion

(27) Add dimethylethanolamine (16) and hold at 90-100° C. for 30 minutes.

(28) Remove heat, add water (17) over 1 hour.

(29) nv content by weight should be 29-31%.

(30) The aqueous dispersion may be adjusted to desired application solids/viscosity by further additions of deionised water and dimethyl ethanolamine.

(31) This produces an aqueous dispersion comprising a mixture of polymeric species thought to be epoxide-addition polymer graft, epoxide resin and addition polymer.

COMPARATIVE EXAMPLE B

(32) In a variation of the above, polyvinyl butyral was added after the polymerisation step and prior to the emulsification. This resulted in an aqueous dispersion where the polymer composition is thought to comprise epoxide-addition polymer graft, addition polymer, epoxy resin and polyvinyl butyral.

(33) Procedure:

(34) TABLE-US-00003 Ingredients pbw  1. DER 331 143.90  2. Diphenol Propane 79.41  3. Butyl Oxitol 50.45  4. Phosphonium Acetate 0.17  5. Distillate −7.14  6. Deionised Water 0.81  7. Butyl Oxitol 18.61  8. Butanol 93.75  9. Methacrylic Acid 24.67 10. Styrene 31.81 11. Ethyl Acrylate 0.57 12. Benzoyl Peroxide (75%) 4.76 13. Butyl Oxitol 12.51 14. Butanol 5.65 15 Butyl oxitol 5.29 16. Butanol 6.90 17. Pioloform BM18 19.03 18. Santolink EB 560 17.52 19. Dimethyl Ethanolamine 14.07 20. Deionised Water 522.25 Total 1044.99
Procedure:

(35) The apparatus was set up as for Example 1.

(36) 1) In-Situ Preparation of Chain Extended Diepoxy Resin.

(37) Charge ingredients 1, 2 and 3 and heat to 50° C. Add ingredient 4 and apply a vacuum (better than 75 mb). Heat to distillation and remove the stated quantity of distillate (5). Break vacuum with nitrogen.

(38) Set for direct reflux and heat to 140° C. Allow to exotherm and hold at 175-180° C. Sample for a reduced viscosity of 25-32.5 poise as measured at 25° C. and 40% nv in butyl oxitol. When at viscosity add deionised water (6) and hold at reflux for 30 minutes. Cool and thin with Butyl oxitol (7) and then butanol (8).

(39) 2) Polymerisation

(40) Cool to 115-118° C. and add a premix of items 9-13 over 2.25 hours.

(41) Rinse in with butanol (14) and hold for a further 30 minutes.

(42) 3) Add Ingredients 15 and 16 Followed by Item 17. Hold for Solution.

(43) 4) Crosslinking Agent Addition

(44) Cool to 100° C. and add the phenol-formaldehyde resin (18) and hold at 90-100° C. for 15 minutes.

(45) 5) Dispersion

(46) Add dimethylethanolamine (19) and hold at 90-100° C. for 30 minutes.

(47) Remove heat, add water (20) over 1 hour.

(48) nv should be 29-31%

(49) The dispersion may be adjusted to desired application solids/viscosity by further additions of deionised water and dimethyl ethanolamine.

(50) Intermediate C1

(51) Preparation of an Aqueous Dispersion of PVB-Addition Polymer Graft

(52) Preparation of PVB Acrylate Dispersion

(53) TABLE-US-00004 pbw  1. Butyl Oxitol 48.0  2. Butanol 84.8  3. Pioloform BM18 168.0  4. Methacrylic Acid 23.9  5. Styrene 44.0  6. Ethyl Acrylate 0.6  7. Benzoyl Peroxide (75%) 4.6  8. Butyl Oxitol 17.6  9. Butanol 9.0 10. Dimethyl Ethanolamine 24.7 11. Deionised Water 574.8 Total 1000.0
Procedure;

(54) To 3 L flask (fitted with a nitrogen inlet, mechanical stirrer, thermometer probe, and reflux condenser) items 1-3 are charged. The mixture is heated to 110-115° C. and held at this temperature range until all of the item 3 has dissolved. Thereafter items 4-7 are charged slowly over a two hour period and after this addition the reactor is further held for 1.5 hours at 110-115° C. The reactor content is cooled to 90-95° C. and items 8-10 are charged.

(55) Item 11 is charged under high shear over 1 hour period.

(56) The resulting product is cooled to room temperature to yield a stable aqueous dispersion with solids contents between 22-24% (measured at 200° C./10 mins)

(57) It is thought that this results in a dispersion where the polymer components are PVB-addition polymer graft, PVB and addition polymer.

COMPARATIVE EXAMPLE C

(58) Preparation of a blend of an aqueous dispersion containing PVB-addition polymer graft and epoxide-addition polymer graft.

(59) TABLE-US-00005 Ingredients 1. Aqueous dispersion of 741.6    Comparative Example A 2. Deionised water 169.1 3. Aqueous Dispersion of PVB-addition 88.5    polymer graft from Intermediate C1 4. Dimethyl Ethanolamine 0.8 1000.0
Procedure:

(60) Charge ingredient 1 and stir.

(61) Add ingredient 2 followed by 3.

(62) Adjust to viscosity with ingredient 4

(63) nv=23-24%

COMPARATIVE EXAMPLE D

(64) Intermediate D1

(65) Preparation of an Unsaturated Polyester for Use as Preformed Polymer.

(66) Set round bottomed flask for fractional distillation and pass nitrogen through flask. Charge 1101.8 g of butyl ethyl propane diol, 446.7 g of isophthalic acid, 304.2 g of 1.4 cyclohexane dicarboxylic and 1.65 g of butyl stannoic acid and raise temperature until distillation begins. Remove distillate and heat to 220° C., maintaining that temperature until the distillate is clear and the acid value of the resin is less than 10 mg KOH/g. Cool to 180° C. and add 164.5 g of maleic anhydride. Reheat to distillation temperature and maintain this temperature for 1 hour, removing any distillate produced. Change to Dean and Stark reflux and add 16.4 g of xylol to maintain a good reflux. Sample for acid value and when contents reach 5-10 mg KOH/g, then cool. Add 352.7 g of butyl oxitol and 352.7 of butanol.

(67) The polyester has an acid value of 5 to 10 mg KOH/g, solids content of 70-71% by weight and a bubble tube viscosity of 20-25 poise measured at 25° C.

COMPARATIVE EXAMPLE D

(68) The procedure according to example 1 was followed except that the PVB was replaced by the polyester, D1 and the ratio of polyester:diepoxy:acrylic:X-linker was 9.1:68.1:18.5:4.3

(69) The final aqueous dispersion is thought to comprise a polymer composition of diepoxy-acrylic addition polymer graft, polyester-acrylic addition polymer graft, diepoxy resin, polyester and acrylic addition polymer.

(70) The crosslinkable coatings of Example 1 and Comparative Examples A, B, C and D were applied to sheet metal (tin plate) by flood spinner in two coats and stoved at 188° C. for 190 seconds (to give a peak metal temperature of 188° C. for 60 seconds). Total dry film weight was approximately 8-10 microns.

(71) They were then tested according to the following tests:

(72) Joy Test

(73) A coated, stoved panel was immersed in a 1% aqueous solution of washing up liquid at 85° C. for 30 minutes. After cross-hatching, the adhesion of the stoved film to the panel was assessed by tape removal according to ISO 2409.

(74) Film Appearance

(75) A coated, stoved panel was immersed in a solution of washing-up liquid and the appearance assessed.

(76) Water Boil

(77) A coated, stoved panel was immersed for 30 minutes in boiling water. After cross-hatching, the adhesion of the stoved film to the panel was assessed by tape removal according to ISO 2409.

(78) Iron Content

(79) Coated, stoved can bodies were filled with an aqueous solution comprising 1 part citric acid and 0.6 parts citrate buffer to 100 parts of de-ionised water. After closing and pressurisation to 30-35 psi, the cans were pasteurised for 30 minutes at 85° C. After cooling to 20-22° C., a controlled semi-spherical indentation was introduced into the can side wall by means of a pendulum. Cans were then stored at 50° C. for 14 days. Assessment was made of the degree of corrosion across the can body surface by utilising the grading described in ASTM D610; the iron content of the solution was estimated by atomic absorption spectroscopy and the area of corrosion on the reverse impact site and the damage to the coating in the neck region assessed by visual inspection.

(80) Flexibility

(81) A 10×4 cm tin plate panel was coated with the test coating and stoved according to the procedure described above. The panel was bent lengthways, with the coating facing outward around a cylindrical mandrel of 5 mm diameter forming a U shape. This was retained on a base plate, one end of which was higher than the other and a weight of 2.4 kg dropped on it from a height of 65 cm. This produced a panel with a varying radius of curvature along its length. The panel was then immersed in acidified copper sulphate solution for three minutes, after which time it was removed and rinsed with water. Copper is deposited where the coating has failed to the metal. The performance of the coating was estimated by measuring the length of unaffected coating, expressed as a percentage of the total length.

(82) Table 1 is a summary of the test results

(83) Comparative Examples B and C both produce hazy and rough coatings, indicating that the polymers in these dispersions are not compatible. This produces crosslinked (or stoved) coatings that are unusable. Comparative Example D, using polyester instead of PVB, shows unacceptably poor water resistance in the water boil test and is also assessed as poor in a taste test.

(84) Surprisingly, Example 1 produces a clear and smooth coating having excellent water resistance, as demonstrated by the water boil and Joy test. The corrosion performance is also excellent as demonstrated by the very low level of iron detected in the electrolyte solution and the small area of corrosion.

(85) Surprisingly we have demonstrated that by adding a preformed polymer, such as PVB, to the ingredients before polymerisation of the ethylenically unsaturated monomers (so that the addition polymer is formed in the presence of the preformed polymer) significantly improved properties result.

(86) TABLE-US-00006 TABLE 1 Film Joy test Water boil Iron content Area of corrosion Neck damage Example Description appearance (rating) (rating) ppm square mm square mm 1 PVB added to Clear, smooth 0 1 1 0 0 diepoxy and and glossy both acrylated in situ Comparative A Diepoxide- Clear 1 1 9 50 90 addition polymer graft Comparative B PVB added to Hazy and rough N/T N/T 12 50 95 Comparative A Comparative C PVB-addition Hazy and rough 1 2 N/T N/T N/T polymer graft added to Comparative A Comparative D Polyester added Clear 0 3 N/T N/T N/T to diepoxy and Blush both acrylated in situ N/T means not tested as the stoved coating was hazy and rough and thus unusable for carbonated beverages Ratings 0 to 5 = best to worst

FURTHER EXAMPLES

(87) Examples 2 to 6 were made following the same procedure and ingredients as used in Example 1 other than the ratio of PVB:Epoxy was varied as indicated in Table 2.

(88) The coatings of Examples 2 to 7 were applied to sheet metal (tin plate) by flood spinner in two coats and stoved at 188° C. for 190 seconds. Their flexibility and water boil rating was evaluated.

(89) The compositions and performance is summarised in Table 2

(90) TABLE-US-00007 TABLE 2 Molecular Composition weight of PVB:Epoxy:Acrylic:X- Water boil Flexibility Film PVB linker rating (% pass) appearance 2 70,000-90,000 10:65:20:5 0 90 Clear, smooth and glossy 3 70,000-90,000 20:55:20:5 1 92 Slightly hazy 4 70,000-90,000 50:25:20:5 4 94 Hazy 5 70,000-90,000 75:0:20:5 5 N/T Did not form a film 6 30,000-35,000 10:65:20:5 5 89 Clear, smooth and glossy 7 250,000-350,000 10:65:20:5 3 95 Clear, smooth and glossy

(91) The data shows that the presence of the PVB polymer increases the flexibility of the coating. As the proportion of the PVB increases, the clarity of the film begins to deteriorate. Where clarity is important the PVB:Epoxy resin ratio should be less than approximately 2:1.

(92) The effect of varying the average molecular weight of the PVB from 30,000-35,000 to 250,000-350000 Daltons was evaluated in examples 2, 6 and 7. The water boil rating of example 6 was poor demonstrating that the molecular weight of the PVB used should be greater than about 35,000 Daltons.