UV RESISTANT SURFACING MATERIALS FOR COMPOSITE PARTS

Abstract

A surfacing material that can provide improved UV resistance while providing good surface properties. The surfacing material includes a resin layer formed from a curable resin composition containing: (A) one or more cycloaliphatic epoxy resin(s), each having two or more epoxy groups per molecule; (B) an epoxy-amine adduct having two or more epoxy groups per molecule and obtained by a reaction of (i) an epoxy compound having two or more alicyclic epoxy groups per molecule with (ii) an amine compound having two or more amino groups per molecule; (C) a curing agent and/or a catalyst; (D) ceramic microspheres; and (E) a flow control agent in the form of inorganic particles, which are not ceramic microspheres.

Claims

1. A surfacing material comprising at least one resin layer formed from a curable resin composition comprising: (A) one or more cycloaliphatic epoxy resin(s), each having two or more epoxy groups per molecule; (B) an epoxy-amine adduct having two or more epoxy groups per molecule and obtained by a reaction of (i) an epoxy compound having two or more alicyclic epoxy groups per molecule with (ii) an amine compound having two or more amino groups per molecule; (C) a curing agent and/or a catalyst; (D) ceramic microspheres; and (E) a flow control agent in the form of inorganic particles, which are not ceramic microspheres.

2. The surfacing material of claim 1, wherein the curable resin composition further comprises: (F) an inorganic pigment selected from metal oxides and carbon black.

3. The surfacing material of claim 1, wherein the curable resin composition further comprises: (G) a toughening agent that is not an epoxy-amine adduct and is selected from: thermoplastic polymers, elastic polymers, and core-shell rubber (CSR) particles.

4. The surfacing material according to claim 1, wherein the one or more cycloaliphatic epoxy resin(s) is/are represented by the following general Formula I: ##STR00012## where X represents a single bond or a linkage group; the linkage group is selected from: divalent hydrocarbon groups, carbonyl group (—CO—), ether bond (—O—), ester bond (—COO—), amide bond (—CONH—), carbonate bond (—OCOO—), and groups containing two or more of said groups linked to each other.

5. The surfacing material according to claim 4, wherein the divalent hydrocarbon groups are selected from: straight or branched chain alkylene groups having 1 to 18 carbon atoms, including methylene, methylmethylene, dimethylmethylene, ethylene, propylene, and trimethylene groups; and divalent alicyclic hydrocarbon groups, including 1,2-cyclopentylene, 1,3-cyclopentylene, cyclopentylidene, 1,2-cyclohexylene, 1,3-cyclohexylene, 1,4-cyclo-hexylene, and cyclohexylidene groups.

6. The surfacing material according to claim 1, wherein the one or more cycloaliphatic epoxy resin(s) is/are selected from polyepoxides having he following chemical structures: ##STR00013## where n is an integer from 1 to 30; ##STR00014## where a, b, c, d, e, f independently denote an integer of 0 to 30.

7. The surfacing material according to claim 1, wherein the one or more cycloaliphatic epoxy resin(s) is/are selected from polyepoxides having he following chemical structure: ##STR00015## where R represents a group corresponding to a q-valent (q-hydric) alcohol R—(OH)q, except for removing —OH(s) in a number of q there from; p is an integer from 1 to 50; and q is an integer from 1 to 10.

8. The surfacing material according to claim 1, wherein the one or more cycloaliphatic epoxy resin(s) has/have a viscosity of 2500 mPa.s or less at 25° C., as determined by Brookfield Viscometer.

9. The surfacing material according to claim 1, wherein the one or more cycloaliphatic epoxy resin(s) is/are selected from: cyclohexanedimethanol diglycidyl ether; cyclohexanediol diglycidyl ether; poly[(2-oxiranyl)-1,2-cyclohexanediol] 2-ethyl-2 (hydroxymethyl)-1,3-propanediol ether; 3′,4′-epoxycyclohexane)methyl 3,4-epoxy-cyclohexylcarboxylate; 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate; 3′,4′-epoxycyclohexyl)-3,4-epoxycyclohexane; and hexahydrophthalic acid diglycidylester.

10. The surfacing material according to claim 1, wherein the epoxy-amine adduct has from 2 to 10 epoxy groups per molecule, and the epoxy groups are positioned at the molecular chain ends of the epoxy-amine adduct.

11. The surfacing material according to claim 1, wherein the epoxy-amine adduct is represented by Formula II: ##STR00016## where X is, in each occurrence, independently selected from a single bond and a divalent group having at least one atom; R.sup.2 is a divalent organic group having a carbon atom at each bonding site; and n is an integer of 1 or higher.

12. The surfacing material according to claim 1, wherein the epoxy-amine adduct is a reaction product of a cycloaliphatic epoxy compound and an amine selected from: polypropylene glycol 130 bis(2-aminopropyl ether; triethyleneglycol diamine; trimethylolpropane polyoxypropylene triamine, and poly(oxy-1,4-butanediyl), alpha-(4-amino-butyl)-omega-(4-aminobutoxy).

13. The surfacing material according to claim 1, wherein the curing agent and/or catalyst (C) is/are selected from: (i) amine-containing compound; (ii) Lewis acid-amine complex; (iii) acid anhydride; and (iv) cationic catalyst.

14. (canceled)

15. The surfacing material according to claim 1, wherein the curable resin composition further comprises a curing accelerator selected from: imidazole, dihydrazide, aliphatic polyamine, alkyl and aryl substituted ureas and bisureas.

16. The surfacing material according to claim 13, wherein the Lewis acid-amine complex is selected from: BF.sub.3.n-hexylamine, BF.sub.3.monoethylamine, BF.sub.3.benzylamine, BF.sub.3.diethylamine, BF.sub.3.piperidine, BF.sub.3.triethylamine, BF.sub.3.aniline, BF.sub.4.n-hexylamine, BF.sub.4.monoethylamine, BF.sub.4.benzylamine, BF.sub.4.diethylamine, BF.sub.4. piperidine, BF.sub.4.triethylamine, BF.sub.4.aniline, PF.sub.5.ethylamine, PF.sub.5.isopropylamine, PF.sub.5.butylamine, PF.sub.5.laurylamine, PF.sub.5.benzylamine, and AsPF.sub.5laurylamine.

17. The surfacing material according to claim 13, wherein the acid anhydride is selected from: methyltetra-hydrophthalic anhydride, methylhexahydrophthalic anhydride, dodecenylsuccinic anhydride, methyl-endomethylene-tetrahydrophthalic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyl nadic anhydride, carbic anhydride, methylcyclohexenedicarboxylic anhydride, and mixtures thereof.

18. The surfacing material according to claim 17, wherein the acid anhydride is used in combination with a curing accelerator selected from diazabicycloun-decene, phosphorous compounds, tertiary and quaternary amines.

19. The surfacing material according to claim 13, wherein the cationic catalyst is selected from: aryldiazonium salts, aryliodonium salts, arylsulfonium salts, and blocked acids.

20. (canceled)

21. The surfacing material according to claim 1, wherein the curable resin composition does not contain any aromatic epoxy resins.

22-24. (canceled)

25. The surfacing material according to claim 1, wherein the flow control agent (E) is selected from: talc, mica, calcium carbonate, alumina, and silica.

26. (canceled)

27. (canceled)

28. The surfacing material according to claim 3, wherein the toughening agent (G) is selected from: (i) polyvinyl acetal resins (PVB); (ii) polyvinyl formal resins; (iii) a thermoplastic copolymer of polyethersulfone (PES) and polyetherethersulfone (PEES); and (iv) core-shell rubber (CSR) particles.

29-46. (canceled)

Description

EXAMPLES

[0119] The following examples serve to give specific embodiments of the surfacing films formed according to the present disclosure but are not meant in any way to limit the scope of the present disclosure.

[0120] Eight surfacing films were prepared based on the formulations shown in Table 2-9. For comparison, a comparative surfacing film was prepared according to the formulation shown in Table 11.

Example 1

[0121] A curable resin composition for forming a surfacing film was prepared according to Table 2. The epoxy-amine adduct (B) was prepared by reacting 8.8 g (grams) of 3′,4′-Epoxycyclohexane) methyl 3,4-epoxycyclohexylcarboxylate with 20.6 g of poly[(2-oxiranyl)-1,2-cyclohexanediol] 2-ethyl-2 (hydroxymethyl)-1,3-propanediol ether and 8.8 g of polytetrahydrofuranamine (elastomer) at 150° C. for 1 hour.

[0122] Each epoxy-amine adduct was prepared by adding the components into a mixing vessel and mixing the components using a high-speed shear lab mixer. The epoxy resins and the amine compound were added to the mixing vessel, and the mixture was heated up gradually under shear mixing (1000-3000 rpm) to the designated adduct reaction temperature and held at the reaction temperature for specified time period. After the hold time, the reaction product was cooled down to ˜30° C.-40° C., and then the epoxy-amine adduct was discharge for further use in preparing the curable composition of Table 2.

TABLE-US-00003 TABLE 2 Components wt % Cycloaliphatic Epoxy (A) (3′,4′-Epoxycyclohexane)methyl 3,4- 4.4 epoxycyclohexylcarboxylate Poly[(2-oxiranyl)-1,2-cyclohexanediol] 2-ethyl-2 4.4 (hydroxymethyl)-1,3-propanediol ether Epoxy-amine adduct (B) 38.2 Curing agent/Catalysts (C) Boron trifluoride ethylamine complex 4.4 Ceramic microspheres (D) 16.1 Flow control agent (E) Fumed silica 5.9 Pigments TiO.sub.2 22 UV stabilizers/additives Phenolic antioxidant: 1.1 Pentaerythritol Tetrakis(3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate Triazine UV absorber: 1.2 2-[4-[(2-Hydroxy-3-dodecyloxypropyl)oxy]-2-hydroxyphenyl]- 4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine Liquid hindered amine (HAL): 1.2 Decanedioic acid, bis(2,2,6,6-tetramethyl-1-(octyloxy)- 4-piperidinyl ester Conductive Additives Carbon black particles 0.5 TOTAL (wt %) 100

[0123] A surfacing film was prepared by adding the components disclosed in Table 2 into a mixing vessel and mixing the components using a high-speed shear lab mixer. The epoxy resins (A) and epoxy-amine adduct (B) were added first. Methyl ethyl ketone (MEK) solvent was added, as necessary, to control the viscosity of above mix to about 80 wt % solids. The temperature of the composition was kept below about 70° C. during mixing.

[0124] To form a surfacing film, the prepared composition was strained, de-aired, and deposited as a resin film. Straining was performed through a filtration media (nylon mesh screen). De-airing was performed such that the solid content of the composition was about 80 wt %. The strained and de-aired composition was then coated as a film having a film weight of about 50-200 gsm by a film coater, and then dried so as to achieve less than 2% by weight volatiles. A carrier (glass or polyester type carrier with areal weight of 10-20 gsm) was pressed into the resin film under light pressure to embed the carrier to the film.

Example 2

[0125] A curable resin composition for forming a surfacing layer was prepared according to Table 3. The epoxy-amine adduct (B) was prepared by reacting 9.6 g of epoxidized Hydrogenated Bisphenol A with 22.5 g of poly[(2-oxiranyl)-1,2-cyclohexanediol] 2-ethyl-2 (hydroxymethyl)-1,3-propanediol ether and 9.6 g of polytetrahydrofuranamine (elastomer) at 135° C. for 1.5 hour. The epoxy-amine adduct was prepared with the same procedure as described for the epoxy-amine adduct in Example 1.

TABLE-US-00004 TABLE 3 Components wt % Cycloaliphatic Epoxy (A) Epoxidized Hydrogenated Bisphenol A 4.8 Poly[(2-oxiranyl)-1,2-cyclohexanediol] 2-ethyl-2 4.8 (hydroxymethyl)-1,3-propanediol ether Epoxy-amine adduct (B) 41.7 Curing agent/Catalysts (C) Dicyandiamide (DICY) 2.6 Aliphatic Bisureas (for DICY) 2.2 Aliphatic polyamines (Ancamine 2014FG) 3.9 Ceramic microspheres (D) 14.4 Flow control agent (E) Fumed silica 6.4 Pigments TiO.sub.2 19.2 TOTAL (wt %) 100

[0126] A curable surfacing film having a carrier embedded therein and areal weight of about 150 gsm was formed from the resin composition of Table 3 as described in Example 1. The carrier used was a 10 gsm glass scrim.

Example 3

[0127] A curable resin composition for forming a surfacing layer was prepared according to Table 4. The epoxy-amine adduct (B) was prepared by reacting 8.6 g of epoxidized hydrogenated Bisphenol A with 19.9 g of poly[(2-oxiranyl)-1,2-cyclohexanediol] 2-ethyl-2 (hydroxymethyl)-1,3-propanediol ether and 8.6 g of polytetrahydrofuranamine (elastomer) at 135° C. for 1.5 hour. The epoxy-amine adduct was prepared with the same procedure as described in Example 1.

TABLE-US-00005 TABLE 4 Components wt % Cycloaliphatic Epoxy (A) Epoxidized Hydrogenated Bisphenol A 5.7 Poly[(2-oxiranyl)-1,2-cyclohexanediol] 2-ethyl-2 2.9 (hydroxymethyl)-1,3-propanediol ether Epoxy-amine adduct (B) 37.1 Curing agent/Catalysts (C) Dicyandiamide (DICY) 2.3 Accelerators Aliphatic Bisurea (for DICY) 2 Isophthalic dihydrazide (IDH)) 5.7 Ceramic microspheres (D) 12.9 Flow control agent (E) Fumed silica 5.7 Additional Toughening Agent Polyvinyl acetal polymers 4.3 Pigments TiO.sub.2 17.1 UV stabilizers/additives Pentaerythritol Tetrakis(3-(3,5-di-tert-butyl-4- 1.4 hydroxyphenyl)propionate 2-[4-[(2-Hydroxy-3-dodecyloxypropyl)oxy]-2- 1.4 hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine Decanedioic acid, bis(2,2,6,6-tetramethyl-1-(octyloxy)- 1.4 4-piperidinyl ester Conductive Additives Carbon black particles 0.6 TOTAL (wt %) 100

[0128] A curable surfacing film having a carrier embedded therein and areal weight of about 150 gsm was formed from the resin composition of Table 4 as described in Example 1. The carrier used was a 10 gsm glass scrim.

Example 4

[0129] A curable resin composition for forming a surfacing layer was prepared according to Table 5. The epoxy-amine adduct (B) was prepared by reacting 8.8 g epoxidized hydrogenated Bisphenol A with 20.5 g of poly[(2-oxiranyl)-1,2-cyclohexanediol] 2-ethyl-2 (hydroxymethyl)-1,3-propanediol ether and 8.8 g of polytetrahydrofuranamine (elastomer) at 135° C. for 1.5 hour. The procedure for forming the epoxy-amine adduct was the same as described in Example 1.

TABLE-US-00006 TABLE 5 Components wt % Cycloaliphatic Epoxy (A) Epoxidized Hydrogenated Bisphenol A 4.4 Poly[(2-oxiranyl)-1,2-cyclohexanediol] 2-ethyl-2 4.4 (hydroxymethyl)-1,3-propanediol ether Epoxy-amine adduct (B) 38.1 Curing agent/Catalysts (C) Dicyandiamide (DICY) 1.5 Accelerators Aliphatic polyamines (Ancamine 2014FG) 4.4 2-Methylimidazoleazine 1.8 Ceramic microspheres (D) 13.2 Flow control agent (E) Fumed silica 5.9 Additional Toughening Agent Polyvinyl formal resin 5.9 Pigments TiO.sub.2 17.6 UV stabilizers/additives Light stabilizer: 1.46 (3,5-di-tert-butyl-4-hydroxybenzoic acid, n-hexadecyl ester Triazine UV absorber: 1.46 2,4-bis(2,4-dimethylphenyl)-6-(2-hydroxy-4- octyloxyphenyl)-1,3,5-triazine TOTAL (wt %) 100

[0130] A curable surfacing film having a carrier embedded therein and an areal weight of about 150 gsm was formed from the resin composition of Table 5 using the method as described in Example 1. The carrier used was a 10 gsm glass scrim.

Example 5

[0131] A curable resin composition for forming a surfacing layer was prepared according to Table 6. The epoxy-amine adduct (B) was prepared by reacting 8.8 g of 3′,4′-Epoxycyclohexyl)-3,4-epoxycyclohexane) with 20.6 g of Poly[(2-oxiranyl)-1,2-cyclohexanediol] 2-ethyl-2 (hydroxymethyl)-1,3-propanediol ether and 8.8 g of polytetrahydrofuranamine (amine-terminated Elastomer) at 150° C. for 1 hour.

TABLE-US-00007 TABLE 6 Components wt % Cycloaliphatic Epoxy (A) (3′,4′-Epoxycyclohexyl)-3,4-epoxycyclohexane 4.4 Poly[(2-oxiranyl)-1,2-cyclohexanediol] 2-ethyl-2 2.2 (hydroxymethyl)-1,3-propanediol ether Epoxy-amine adduct (B) 28.5 Curing agent/Catalyst (C) Methyl nadic anhydride mixture with carbic anhydride 29.6 Accelerators Accelerator for acid anhydride 0.5 1,8-diazabicyclo[5.4.0] undecene-7 (DBU) Ceramic microspheres (D) 12.1 Flow control agent (E) Fumed silica 4.4 Pigments TiO.sub.2 16.4 UV stabilizers/additives (3,5-di-tert-butyl-4-hydroxybenzoic acid, n-hexadecyl ester 1 2,4-bis(2,4-dimethylphenyl)-6-(2-hydroxy-4-octyloxyphenyl)- 1 1,3,5-triazine TOTAL (wt %) 100

[0132] A curable surfacing film having a carrier embedded therein and areal weight of about 150 gsm was formed from the resin composition of Table 6 using the method as described in Example 1. The carrier used was a 10 gsm glass scrim.

Example 6

[0133] A curable resin composition for forming a surfacing layer was prepared according to Table 7. The epoxy-amine adduct (B) was prepared by reacting 5.0 g of (3′,4′-epoxycyclohexane)methyl 3,4-epoxycyclohexylcarboxylate with 4.9 g of (3′,4′-epoxycyclohexyl)-3,4-epoxycyclohexane 23.2 g of Poly[(2-oxiranyl)-1,2-cyclohexanediol] 2-ethyl-2 (hydroxymethyl)-1,3-propanediol ether and 9.9 g of polytetrahydrofuranamine (elastomer) at 150° C. for 1 hour.

TABLE-US-00008 TABLE 7 Components wt % Cycloaliphatic Epoxy (A) (3′,4′-Epoxycyclohexyl)-3,4-epoxy cyclohexane 4.9 Poly[(2-oxiranyl)-1,2-cyclohexanediol] 2-ethyl-2 5.0 (hydroxymethyl)-1,3-propanediol ether Epoxy-amine adduct (B) 43 Curing agent/Catalyst (C) Cationic catalyst 1 Benzyl(4-hydroxyphenyl)methylsulfonium, hexafluoroantimonate (4-Hydroxyphenyl)methyl(1-naphthylmethyl)sulfonium, 1 hexafluoroantimonate Ceramic microspheres (D) 18.2 Flow control agent (E) Fumed silica 6.6 Pigments TiO.sub.2 24.8 UV stabilizers/additives (3,5-di-tert-butyl-4-hydroxybenzoic acid, n-hexadecyl ester 1.7 2,4-bis(2,4-dimethylphenyl)-6-(2-hydroxy-4-octyloxyphenyl)- 1.7 1,3,5-triazine TOTAL (wt %) 100

[0134] A curable surfacing film having a carrier embedded therein and areal weight of about 150 gsm was formed from the resin composition of Table 7 using the method as described in Example 1. The carrier used was a 10 gsm glass scrim.

Example 7

[0135] A curable resin composition for forming a surfacing layer was prepared according to Table 8. The epoxy-amine adduct (B) was prepared by reacting 8.8 g (3′,4′-Epoxycyclohexane)methyl 3,4-epoxycyclohexylcarboxylate) with 20.6 g of poly[(2-oxiranyl)-1,2-cyclohexanediol] 2-ethyl-2 (hydroxymethyl)-1,3-propanediol ether and 8.8 g of polytetrahydrofuranamine (amine-terminated elastomer) at 150° C. for 1 hour.

TABLE-US-00009 TABLE 8 Components wt % Cycloaliphatic Epoxy (A) (3′,4′-Epoxycyclohexyl)-3,4-epoxycyclohexane 4.4 Poly[(2-oxiranyl)-1,2-cyclohexanediol] 2-ethyl-2 4.4 (hydroxymethyl)-1,3-propanediol ether Epoxy-amine adduct (B) 38.2 Curing agent/Catalyst (C) Boron (2-propanamine) trifluoro-, adduct with butyl 4.4 glycidyl ether Ceramic microspheres (D) 13.2 Flow control agent (E) Fumed silica 5.8 Additional Toughening Agent Polyvinyl acetal polymers 7.3 Pigments TiO.sub.2 17.6 UV stabilizers/additives Pentaerythritol Tetrakis(3-(3,5-di-tert-butyl-4- 1.4 hydroxyphenyl)propionate 2-[4-[(2-Hydroxy-3-dodecyloxypropyl)oxy]-2-hydroxyphenyl]- 1.4 4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine Decanedioic acid, bis(2,2,6,6-tetramethyl-1-(octyloxy)- 1.4 4-piperidinyl ester Conductive Additives Carbon black particles 0.5 TOTAL (Wt, %) 100

[0136] A curable surfacing film having a carrier embedded therein and areal weight of about 150 gsm was formed from the resin composition of Table 8 using the method as described in Example 1. The carrier used was a 10 gsm glass scrim.

Example 8

[0137] A curable resin composition for forming a surfacing layer was prepared according to Table 9. The epoxy-amine adduct (B) was prepared by reacting 9.7 g of Epoxidized Hydrogenated Bisphenol A with 22.6 g of poly[(2-oxiranyl)-1,2-cyclohexanediol] 2-ethyl-2 (hydroxymethyl)-1,3-propanediol ether and 9.7 g of polytetrahydrofuranamine (elastomer) at 135° C. for 1.5 hour.

TABLE-US-00010 TABLE 9 Components wt % Cycloaliphatic Epoxy (A) Epoxidized Hydrogenated Bisphenol A 4.85 Poly[(2-oxiranyl)-1,2-cyclohexanediol] 2-ethyl-2 4.85 (hydroxymethyl)-1,3-propanediol ether Epoxy-amine adduct (B) 42 Curing agent/Catalyst (C) Dicyandiamide (DICY) 2.6 Accelerator Aliphatic Bisurea (for DICY) 4.8 Ceramic microspheres (D) 14.5 Flow control agent (E) Fumed silica 6.5 Additional Toughening Agent PES-PEES co-polymer 1 CSR particles 6.4 Alicyclic epoxy with 25-30 wt % CSR particles (MX 553) Pigments TiO.sub.2 12.5 TOTAL (wt %) 100

[0138] A curable surfacing film having a carrier embedded therein and areal weight of about 150 gsm was formed from the resin composition of Table 9 using the method as described in Example 1. The carrier used was a 10 gsm glass scrim.

Surfacing Film Evaluation

[0139] Test panels were prepared using the surfacing materials produced according to Examples 1-8. Each test panel is a composite panel fabricated by placing a surfacing material on a tool, followed by laying up of prepreg plies (CYCOM 5276-1 from Cytec Industries Inc., carbon fibers/epoxy based prepregs) to form a prepreg layup. The prepreg layup was then cured at a temperature about 177° C. for 2 hours under 80 psi in an autoclave.

[0140] After curing, the composite panels surfaced with the surfacing films were inspected for surface appearance defects (pits, pin holes). Then the composite panels were evaluated for its Tg, UV stability (color shift under UV exposure), paint stripper resistance, dry and wet paint adhesion with or without UV exposure.

[0141] Table 10 shows the surface properties and test results for the test panels. The test panel number corresponds to the Example number.

TABLE-US-00011 TABLE 10 Test Panels 1 2 3 4 5 6 7 8 T.sub.g (° C.) 242 217 233 181 246 263 238 231 UV Stability (Color Change ΔE* after UV irradiation) Day 0 0 0 0 0 0 0 0 0 Day 1 0.8 1.9 1.7 2.1 1.3 1.5 1.5 1.9 Day 4 1.64 2.4 2.3 2.7 2 2.4 2.1 2.2 Day 7 2.1 2.7 2.5 3.4 2.4 2.9 2.3 2.5 Paint stripper resistance Day 0 0 0 0 0 0 0 0 0 Day 1 0.61 0.68 0.75 0.88 0.78 0.85 0.64 1.25 Day 2 0.95 1.03 1.08 1.15 0.95 1.10 0.90 1.45 Day 4 1.33 1.38 1.50 1.55 1.30 1.45 1.38 1.60 Day 7 1.49 1.70 1.75 1.88 1.78 1.88 1.78 1.78 Surface pencil hardness Day 0 9 H 9 H 9 H 9 H 9 H 9 H 9 H 9 H Day 1 9 H 9 H 9 H 9 H 9 H 9 H 9 H 9 H Day 2 9 H 9 H 9 H 9 H 9 H 9 H 9 H 9 H Day 4 9 H 9 H 9 H 8 H 9 H 8 H 9 H 9 H Day 7 9 H 8 H 8 H 7 H 7 H 7 H 9 H 8 H Paint adhesion Dry scribe w/UV 7 days 10 10 10 10 10 10 10 10 Dry scribe w/o UV 10 10 10 10 10 10 10 10

[0142] All the surfacing film examples, when tested alone, have shown excellent UV stability with minimal noticeable color change (ΔE*<1) after UV irradiation for extended time period (>7+ days). Most of the test panels surfaced with the curable UV stable surfacing films also showed good paint stripper resistance with T.sub.g greater than 200° C.

[0143] The glass transition temperature (Tg) of the cured surfacing films was determined by using either a modulated DSC (TA 2910) or a thermal mechanical analyzer (TMA 2940, TA Instruments) under nitrogen at ramp of 10° C/min within 30° C.-300° C. temperature range.

UV Stability Testing

[0144] The UV resistance or UV stability of composite panels (in the form of 3″×6″ specimen size, with 0.15 mm thickness) surfaced with the surfacing film, was measured according to ASTM G154. ASTM G154 refers to a Standard Test Method for accelerated weather testing of UV stability of coating films by exposing the surface under fluorescent UV light sources. The cured test panels were irradiated by UVA lamp (340 nm wavelength) at 1.55 W/m2 for various time periods. Instrument used for UV testing is a QUV accelerated weathering tester

[0145] Each test panel surfaces with curable composition film was prepared and exposed to QUV test conditions specified. The test panels were taken out periodically to test its color change. The color change (CIELAB ΔE*) of the test panels was measure by X-Rite SP 62 Spectrophotometer. The Color difference (ΔE*) before and after UV exposure was measured and reported. The smaller of color difference, the more UV stable of the test panel. The Color difference (ΔE*) less than 2.5 is considered barely noticeable color change with good UV stability.

Paint Stripper Resistance Testing

[0146] Paint stripper resistance of unpainted, surfaced composite panels (2″×2″ specimen size, with 0.15 mm thickness) were measured by measuring the paint stripper fluid uptake and surface pencil hardness change over the immersion period (up to 168 hours at ambient room temperature) of benzyl alcohol—based paint stripper solution (Cee Bee 2012A available from McGean or Turco 1270-6 available from Henkel) used for aerospace composite structure paint-stripping process. The weight of each test panel was measured before and after paint stripper soak at interval of 24 hours, 48 hours and up to 168 hours (7 days). The paint stripper fluid uptake (weight change over immersion time, expressed in wt.%) of the tested panel was measured at same test intervals up to 168 hours (7 days) immersion.

[0147] The surface of each unpainted test panel was immersed the benzyl alcohol—based paint stripper solution for up to 168 hours at ambient room temperature, and then tested for pencil hardness change during the immersion period according to ASTM D3363. ASTM D3363 refers to a Standard Test Method for determining the surface hardness of clear and pigmented organic coating film on a substrate. The pencil hardness scale is as follows: 6B (softest), 5B, 4B, 3B, 2B, B, HB, F, H, 2H, 3H, 4H, 5H, 6H, 7H, 8H, 9H (hardest). The pencil hardness of the test panel was measured before and after soaking in the paint stripper at interval of 24 hours, 48 hours and up to 168 hours (7 days). Pencil hardness that changes more than 2H level upon 24 hour immersion is not considered as having good paint stripper resistance.

Dry and Wet Paint Adhesion With or Without UV Exposure

[0148] Dry and wet scribe paint adhesion of painted composite panels (in the form of 3″×6″ specimen size, with 0.15 mm thickness) surfaced with the surfacing film, with or without UV exposure prior to painting, were measured according to ASTM D3359. ASTM D3359 refers to a Standard Test Method for assessing the surface adhesion of coating films to substrates by applying and removing pressure-sensitive tape over cuts made in the film (cross-hatch scribe tape test). The cured test panels were exposed to zero (without UV), 200 kJ/m.sup.2 or 1000 kJ/m.sup.2 ultraviolet (UV-A) radiation in accordance with AATCC Test Method 16, Option 3. Instrument used for UV testing is a Xeno Weather-o-meter, such as Atlas CI3000 FadeoMeter. Each test panel surface was prepared (cleaned, with and without sanding) and applied with an exterior decorative paint coating used in aerospace painting (epoxy paint primer followed by a polyurethane based top-coat). Subsequently, dry paint adhesion test was conducted in accordance with ASTM D3359. For conducting wet paint adhesion, the UV exposed test panels were painted and then immersed in de—ionized water at 75° F. for 7 days. Wet paint adhesion test was then conducted in accordance with ASTM D3359.

Example 9

Comparison

[0149] For comparison, a surfacing film was prepared based on the formulation shown in Table 11. Amounts are in weight percentage (wt %).

TABLE-US-00012 TABLE 11 Components wt % Tetraglycidyl 4,4′-diaminodiphenylmethane 10 Triglycidyl ether of aminophenol 12 Pre-react adduct of Bisphenol A, Bis-A epoxy, 30 and Hycar elastomer Bisphenol A diglycidyl ether with CSR particles 12 (25 wt %) Dicyandiamide 2.3 4,4′-Methylene bis(phenyldimethylurea) 2.3 Ceramic microspheres 23 Fumed silica 2.5 TiO.sub.2 pigment 5.9 Total 100

[0150] The surfacing film based on the Table 11 composition was prepared in a similar procedure as described in Example 1. A composite test panel was prepared using the comparative surfacing film of Table 11. The cured test panel was tested to determine its Tg, UV stability, paint stripper resistance, and paint adhesion, using the test procedures described previously. The comparative test results are shown in Table 12.

TABLE-US-00013 TABLE 12 Comparative Example T.sub.g (° C.) 175 UV Stability (Color Change ΔE* after UV irradiation) Day 0 0 Day 1 13 Day 4 17 Day 7 19.5 Paint stripper resistance Day 0 0 Day 1 0.48 Day 2 0.95 Day 4 1.41 Day 7 1.70 Surface pencil hardness Day 0 9H Day 1 9H Day 2 8H Day 4 7H Day 7 6H Paint adhesion Dry scribe w/UV 7 days 10 Dry scribe w/o UV 10

[0151] As can be seen from Table 12, the aromatic epoxy based surfacing film showed significant color change under UV exposure, indicating its high UV sensitivity and is not UV resistant.