COMPOSITIONS OF POLYEPOXIDE/POLYAMINE ADDUCTS AND BLOCKED ISOCYANATES

Abstract: Automotive primer surfaces require fast cure times, resistance to chipping and lower volatile solvent contents due to environmental considerations. A coating composition capable of curring within 15 minutes which is suitably chip resistant and has acceptable higher solids levels has been formulated from (A) an adduct of (1) an epoxy resin having an average epoxide equivalent weight of from 140 to 1000 and (2) a polyamine having at least two primary and/or secondary amine groups, and (B) a substantially fully blocked polyisocyanate being blocked with ketoximes, aldoximes, lactams, N-hydroxy-imides or alcohols. The composition contains from 0.9 to 20 moles of polyamine per epoxide equivalent and from 0.75:1 to 2:1 ratios of latent NCO groups in component (B) per amine group in component (A). These formulations can additionally be employed as coil coatings and exterior coatings for beverage cans.

Description: COMPOSITIONS OF POLYEPOXIDE/POLYA INE ADDUCTS AND BLOCKED ISOCYANATES The present invention concerns compositions of polyepoxide/polya ine adducts and blocked polyisocyanates. German 1,086,372 describes varnishes resistant to chemicals and solvents prepared from a polyamide (the reaction production of a dimer acid and a polyamine) and a trimethyolpropane/toluene diisocyanate prepolymer blocked with a phenol. Cure will take place at room temperature. Addition of an epoxy resin to the above blend results in improved adhesion (German 1,090,803). Flexibility of epoxy resins cured with polya ines at room temperature can be improved by conducting the cure in the presence of a TMP/TDI prepolymer capped with nonylphenol (Ger. Offen. DE 2,152,606). In U.S. 3,321,548 resinous coatings with a fairly high degree of crosslinking and rigidity are obtained by reacting a phenol-blocked isocyanate with functionality of at least three with an amine terminated epoxy resin derived from an epoxy resin and an aromatic amine. Phenol-capped isocyanates are not acceptable in the present invention because they react with the amine-capped epoxy at room temperature and, therefore, do not have sufficient stability to formulate a one- package system. U.S. 3,886,228 provides compositions from a polyamine terminated imide and an isocyanate or phenol blocked prepolymer. Again, these are room temperature curing and unacceptable as ' single-package systems. Amine terminated polyamide systems stable at room temperature are provided by blocking the isocyanate prepolymer with an alcohol. These systems are cured above 350°F (177°C) (U.S. 2,995,531). Mixtures crosslink- able at elevated temperatures are obtained from a trimethylolpropane/toluene diisocyanate prepolymer capped with ε-caprolactam and cured with 3,3'-dimethyl 4,4'diaminodicyclohexyl methane (Ger. Offen. DE 2,131,299). Chain extended, substantially linear elastomers prepared from a diamine and a ketoxime blocked diisocy¬ anate are described in Canadian 788,481. Electrodepositable compositions are described in U.S. 4,104,147 and 4,115,226. These are based on intermediate molecular weight amine terminated epoxies cured with blocked isocyanates, but these must be used in aqueous dispersions to provide suitable application viscosity. Amine terminated epoxies capped with an anhydride to give anodic electrodepositable coatings which may be cured with a blocked isocyanate are described in U.S. 4,176,221. Automotive primer-surfacers are typically • cured at 275 to 325°F (135° to 163°C). To be useful, such coatings must cure sufficiently within 15 minutes (900 s) at 275°F (135°C) to give suitable properties. Such a coating must pass a number of tests, one of the most important being a chip resistance test described in Society of Automotive Engineers (SAE) Test Method J400. A chip rating of 6 to 7 is generally acceptable by the automotive companies. Recent environmental pressures have required that newer coatings have a lower volatile content. The present invention provides coating composi¬ tions with higher solids, i.e. non-volatiles content, which are capable of curing within 15 minutes (900 s) at 275°F (135°C) and provide suitable chip resistance. The present invention is directed to a composi¬ tion curable at temperatures above 120°C which comprises (A) an adduct of (1) an epoxy resin having an average of more than one epoxy group per molecule and an average epoxide equivalent weight of from 140 to 1000 and (2) a polyamine compound having at least two amine groups selected from primary amine groups, secondary amine groups or mixture of such groups per molecule; and (B) a material containing an average of more than one NCO group per molecule which NCO groups have been blocked with ketoxi es, aldoximes, lactams, N-hydroxy- -imides or alcohols; -<_.- wherein components (A-l) and (A-2) are employed in quantities which provide from 0.9 to 20, preferably from 0.9 to 10, most preferably from 0.9 to 2 moles of polyamine compound per epoxide equivalent; and components (A) and (B) are employed in quantities which provide a ratio of latent NCO groups in component (B) per primary and/or secondary amine group in component (A) of from 0.75:1 to 2.0:1, preferably from 0.9:1 to 1.5:1. If desired, the excess polyamine can be removed prior to reacting the polyamine-epoxy resin adduct with the blocked isocyanate. A latent NCO group is defined as that which has been rendered inactive, but upon heating will provide a reactive NCO group. The capped isocyanates contain latent NCO groups. Compositions of the present invention may additionally contain from 10 to 60, preferably from 15 to 50, percent by weight based on the total composition of a suitable solvent. Suitable epoxy resins which can be employed herein include the glycidyl ethers of aliphatic, cyclo- aliphatic and aromatic polyhydric materials. Particularly suitable are the glycidyl ethers of polyhydric phenols, polyhydric bisphenols and polyhydric alcohols such as, for example, the glycidyl ethers of resorcinol, catechol, hydro uinone, bisphenol A, glycidyl ethers of aliphatic polyols such as 1,4-butane- diol, dipropylene glycol, tripropylene glycol, a poly¬ propylene glycol of 400 molecular weight, dibutylene glycol, tributylene glycol, an adduct of bisphenol A with four moles of ethylene or propylene oxide or glycidyl ethers of cycloaliphatic polyols such as 1, -cyclohexanedimethanol, bis(hydroxymethylcyclohexyl)- methane, hydrogenated bisphenol A or mixtures thereof. Also suitable as epoxy resins for use herein are the elastomer or rubber modified epoxy resins in which a carboxyl-containing elastomer or rubber is reacted with an epoxy resin in such proportions that the resultant product is terminated by epoxy groups. The reaction between the epoxy resin and the carboxyl- -containing rubber can be catalyzed if " desired by a suitable catalyst such as triphenyl phosphine. Suitable carboxyl-containing rubber materials include, for example, carboxyl-terminated polybutadiene-acrylonitrile polymers such as those produced by B. F. Goodrich and sold under the trademark Hycar CTBN. These and other elastomer or rubber modified epoxy resins which can be employed herein include, those disclosed in PRODUCT BROCHURE-RLP-2-"Tough Epoxy Resins with Hycar Reactive Liquid Polymers", March 1980 by B. F. Goodrich Chemical Group, by J. A. Clarke in U.S. 3,509,230 and by R. R. Shelley, Jr. and J. A. Clarke in U.S. 3,947,522. Suitable amine materials which can be employed herein to prepare the amine terminated adducts with the epoxy resins include, for example, aliphatic amines, cyclic aliphatic amines and heterocyclic saturated amines. Particularly suitable amine materials include, for example, aminoethyl piperazine, ethylenediamine, diet ylenetriamine, trimethylenediamine, tetramethylene- diamine, penta ethylenediamine, hexamethylenediamine, trimethyl hexamethylenediamine, l,4-bis(aminomethyl)- cyclohexane, l,4-bis(aminocyclohexyl)methane, isophorone diamine, or mixtures thereof. Also suitable as the amine component herein are the polyamides which are the reaction products of dimer and trimer fatty acids with an aliphatic diamine or triamine such as, for example, ethylenediamine or diethylenetriamine. The ratio of the amine component to the epoxy may vary over a wide range. The moles of amine to equivalents of epoxy can vary from 0.9 to 20 moles of amine to equivalents of epoxy. At the lower ratio of amine to epoxy some molecular weight build-up will occur. At the higher ratio of amine to epoxy molecular weight build-up will be minimized, however, large quantities of unreacted amine will be present. Although the excess amine may be removed, for example by distilla¬ tion, it is preferable to use a lower ratio of amine to epoxy. A ratio of about 2 moles of polyamine per equivalent of epoxy will provide . minimum molecular weight build-up while minimizing the amount of unreacted amine. Suitable polyisocyanates which can be employed herein include aliphatic, cycloaliphatic or aromatic polyisocyanates which have an average of more than one -NCO group per molecule. Particularly suitable polyisocyanates include, for example, toluene diisocyanate, methylenediphenyl ' diisocyanate, isophorone diisocyanate, methylene bis- (cyclohexylmethylisocyanate), hexa ethylene diisocyanate, trimethyl hexamethylene diisocyanate, and mixtures thereof. Also suitable as polyisocyanates are the isocyanate prepolymers prepared from the aforementioned polyisocyanates and a polyhydric material such as, for example, aliphatic diols, polyoxyalkylene diols, aliphatic triols and polyoxyalkylene triols. Particularly suitable polyhydric materials which can be employed to prepare the prepolymers include, for example, polyalkylene diols such as polypropylene or polybutylene glycols having a molecular weight from 200 to 2000, polyesters such as, for example, poly(propylene glycol) adipate, polycaprolactonediols or triols, and mixtures thereof. Suitable ketoximes which can be employed herein as the capping or blocking agent for the polyisocyanate include, for example, acetone ketoxime, methyl ethyl ketoxime, cyclohexanoneoxime, and mixtures thereof. Suitable aldoximes which can be employed herein to prepare the capped or blocked polyisocyanate include, for example, acetaldoxime, propionaldoxime, and mixtures thereof. Suitable N-hydroxyimides include, for example, N-hydroxysuccinimide, N-hydroxymaleimide, N-hydroxy- phthalimide, and mixtures thereof. Suitable alcohols which can be employed as the capping or blocking agent for the polyisocyanates include, for example, sec-butanol, 2-ethyl hexanol, t-butanol, and mixtures thereof. Suitable lactams which can be employed as the capping or blocking agent for the polyisocyanates include, for example, ε-caprolactam, 2-pyrrolidine, and mixtures thereof. When it is desired for the capped or blocked polyisocyanate to be deblocked at temperatures of from 250° to 325°F (120° to 163°C), it is preferred to employ an aldoxime, ketoxime or lactam as the capping or blocking agent. When it is desired for the blocked polyisocyanates to become deblocked at higher temper- atures, it is preferred to employ an alcohol as the blocking or capping agent. Suitable solvents which can be employed herein include, for example, glycol ethers, ketones, esters, aromatic hydrocarbons, and mixtures thereof. The curable compositions of the present invention can be employed as automotive primer surfacers, coil coatings, and exterior coatings for beverage cans. If desired, one or more additives such as, for example, fillers, pigments, dyes, or flow control agents can be added to the curable and/or coating compositions of the present invention. The following examples are illustrative of the present invention but are not to be construed as to limiting the scope thereof in any manner. EXAMPLES 1 THROUGH 13 Preparation of Polyepoxide/Polyamine Adducts For Adduct A, a 500 ml flask was charged with 31.76 g (0.25 mole) of 2-aminoethylpiperazine (AEP -molecular weight 129) and 25 g of 2-methoxypropanol. A solution of 100 g (0.22 eq. ) of a diglycidyl ether of bisphenol A having an average epoxide equivalent weight (EEW) of 450 in 100 g of 2-methoxypropanol was added during 90 minutes (5400 s) while maintaining the temperature at 30°C. The solution was stirred an additional 4.5 hours (16200 s) at room temperature. The product was a pale yellow liquid having a Gardner viscosity of Y-, approximately 1600 cps (1.6Pa-s), at 51 percent solids at room temperature. For Adducts B through G, the method for preparing Adduct A was followed using epoxy resins which were diglycidyl ethers of bisphenol A having EEWs of 450, 238 and 186, and using as amines 2-aminoethylpiperazine and diethylenetriamine (DETA, molecular weight 103). For Adducts E, F and G, a 250 ml flask was employed instead of a 500 ml flask. A summary of the adducts is given.in Table I. TABLE I Moles Amine Amine Solution Equiv. Solvent, Epoxy Resin Epoxy Final Viscosity Adduct Amine g mole cf EEW g equiv. Resins Solids % Gardener cps (Pa- s) A AEP 31.76 0.25 25 450 100 0.22 1.1:1 51 Y 1600 (1. .6) B DETA 50.4 0.49 33.6 450 200 0.44 1.1:1 60 N.D. C AEP 119.2 0.92 79.0 238 200 0.84 1.1:1 60 Z-Z-l 2500 (2 .5) D DETA 95.2 0.92 63.5 238 200 0.84 1.1:1 60 Z-2 3600 (3. ■ 6) E DETA 80.1 0.77 36.0 186 128. ,9 0.70 1.1:1 70 N.D. F DETA 154.2 1.49 36.0 186 55. ,9 0.30 5.0:1 70 N.D. G DETA 177.9 1.72 36.0 186 31. .95 . 0.17 10.1:1 70 N.D. N . D . - Not determined . Example 1 was prepared by mixing 11.3 g (0.02 equiv.) with 5.3 g (0.02 equiv.) of Blocked Isocyanate H, an aliphatic/aromatic, ketoxime blocked polyisocyanate commercially available from Mobay Chemical Co. as Mondur HCB. Example 2 was prepared by mixing a like amount of Adduct A with 3.1 g (0.02 equiv.) of Blocked Isocyanate I. Blocked Isocyanate I was prepared by reacting 0.2 equiv. of a polyoxypropylene glycol having an average molecular weight of 400 and 0.8 equiv. of 2-ethylhexanol with 1.0 equiv. of 80/20 2,4-/2,6-toluene diisocyanate mixture. Films of the two examples were drawn down on Bonderite 40 treated steel panes using a No. 22 wire wound rod and cured at 350°F (177°C) for 15 minutes (900 s) . Blocked Isocyanate J was prepared as follows: A 500 ml flask was charged with 336 g (1.0 equiv.) of an adduct of trimethylolpropane (TMP) and an 80/20 mixture of 2,4-/2,6-toluene diisocyanate (TDI) commercially available from Spencer-Kellog as P49-75S (75% solids in ethyl acetate). Methyl ethyl ketoxime (87.1 g, 1.0 mole, 1.0 equiv.) was added dropwise during 40 minutes (2400 s) while applying cooling as required to keep the temperature below 60°C. Forty g of methyl ethyl ketone were added, and stirring was continued an additional 90 minutes (5400 s). An addi¬ tional 80 g of methyl ethyl ketone and 20 g of 2-methoxy¬ propanol were added, giving a final product at 60.2 percent solids and containing 14.9 percent ethyl acetate, 21.3 percent methyl ethyl ketone and 3.6 percent 2-methoxypropanol. This product had a latent NCO equivalent weight of 563 and a Garnder viscosity of X. Latent NCO equivalent weight means the weight which would provide one NCO equivalent upon removal of the blocking agent. Blocked Isocyanate K was prepared as follows: A one-liter flask was charged with 174 g (2.0 equiv.) of TDI. The contents were heated to 50°C and 205 g (1.0 equiv.) of a polypropylene glycol of about 425 molecular weight commercially available ' from The Dow Chemical Company as P425 containing 0.87 g of dibutyltin dilaurate (20 percent solids in methyl ether ketone) was added during 30 minutes (1800 s) while maintaining the temperature below 70°C with occasional cooling. Fifty ml of methyl ethyl ketone were added, stirring continued for an additional 40 minutes (2400 s) at 55°C. Heating was discontinued and 87.1 g of methyl ethyl ketoxime (1.0 mole, 1.0 equiv.) were added while applying cooling to keep the temperature below 55°C. An additional' 25 ml of methyl ethyl ketone and 25 g of 2-methoxypropanol were added to give a total of 100 g of solvent added or 82.3 percent solids. The product had a latent NCO equivalent weight of 565 and a Gardner viscosity of Z. The product gradually crystallized on prolonged standing but could be liquified by heating to between 40 and 60°C. Examples 3 through 6 were prepared using Adducts A, B, C and D and Blocked Isocyante J. Examples 7 through 13 were prepared using Adducts A through G and Blocked Isocyanate K. The compositions of Examples 1 through 13 were employed to prepare cured films. The films were drawn down on Bonderite 40 treated steel panels using a No. 22 wire wound rod. Films from Examples 1 and 2 were cured at 350°F (177°C) for 15 minutes (900 s). Fil s from Examples 3 through 10 were cured at 275°F (135°C) or 325°F (163°C) for 30 minutes (1800 s). Films from Examples 11 through 13 were cured at 300°F (149°C) for 15 minutes (900 s). Summaries of the compositions and the methyl ethyl ketone (MEK) rubs and reverse impact are presented in Table II. TABLE II Example Example Example Ex 1 2 3 Blocked Isocyanate g, equiv. NCO H/5.3/0.02 1/3.1/0.02 J/17.0/0.03 J/1 Polyepoxide/Polyamine Adduct A/11.3/0.02 A/11.3/0.02 A/34.7/0.036 B/2 Latent NCO/ Pri . Amine Group 1:1 1:1 0.8:1 Cure at 350°F (177°C) N.D. MEK Double Rubs >100 >100 Reverse Impact, 50 >160 in-lb (J) (5.7) >(18.1) • Cure at 325°F (163°C) N.D. N.D. MEK Double Rubs >100 > Reverse Impact, F40 in-lb (J) (F4.5) (F Cure at 300°F (149°C) N.D. N.D. N.D. MEK Double Rubs Reverse Impact, , in-lb (J) Cure at 275°F (135°C) N.D. N.D. MEK Double Rubs >100 > Reverse Impact, F40 in-lb (J) ((FF44..55)) ((FF TABLE II (con . ) Example Example Example Example Example 6 7 8 9 10 Blocked Isocyanate g, equiv. NCO J/17.0/0.03 K/17.0/0.03 K/17.0/0.03 K/17.0/0.03 K/17.0/0.03 Polyepoxide/Polyamine ., Adduct D/17.0/0.035 A/34.7/0.036 B/27.7/0.035 C/18.3/0.03 D/17.0/0.035 Latent NCO/ Pri. Amine Group 0.9:1 0.08:1 0.9:1 1:1 0.9:1 Cure at 350°F (177°C) N.D. N.D. N.D. N.D. N.D. MEK Double Rubs Reverse Impact, 1 in-lb (J) Cure at 325°F (163°C) MEK Double Rubs >100 >100 >100 >100 >100 Reverse Impact, F40 F40 P140 F12Θ F60 in-lb (J) (F4.5) (F4.5) (P15.8) (F13.6) (F6.8) Cure at 300°F (149°C) N.D. N.D, N.D. N.D. N.D. MEK Double Rubs Reverse Impact, in-lb (J) Cure at 275°F (135°C) MEK Double Rubs >100 >100 >100 >100 >100 Reverse Impact, F40 F40 P140 F120 P140 in-lb (J) (F4.5) (F4.5) (P15.8) (F13.6) (P15.8) TABLE II (con . ) Example Example Example 11 12 13 Blocked Isocyanate g, equiv. NCO K/55.8/0.1 K/55.8/0.1 K/55.8/0.1 Polyepoxide/Polyamine Adduct E/23.8/0.07 F/6.7/0.06 G/5.8/0.063 Latent NCO/ Pri. Amine Group 1.4:1 1.7:1 1.6:1 Cure at 350°F (177°C) N.D. N.D. N.D. MEK Double Rubs Reverse Impact, in-lb (J) Cure at 325°F (163°C) N.D. N.D. N.D. MEK Double Rubs Reverse Impact, in-lb (J) Cure at 300°F (149°C) >200 47 69 MEK Double Rubs P160 P160 P160 Reverse Impact, (P18.1 ) (P18.1) (P18.1) in-lb (J) Cure at 275°F (135°C) N.D. N.D. N.D. MEK Double Rubs Reverse Impact, in-lb (J)

Claims: 1. A composition which is curable at temper¬ atures above 120°C which comprises (A) an adduct of (1) an epoxy resin having an average of more than one epoxy group per molecule and an average epoxide equivalent weight of from 140 to 1000 and (2) a polyamine compound having at least two amine groups selected from primary amine groups, secondary amine groups or mixture of such groups per molecule; (B) a material containing an average of more than one NCO group per molecule, which NCO groups have been substantially fully blocked with ketoximes, aldoximes, lactams, N-hydroxy-imides or alcohols; wherein components (A-l) and (A-2) are employed in quantities which provide from 0.9 to 20 moles of polyamine compound per epoxide equivalent; and components (A) and (B) are employed in quantities which provide a ratio of latent NCO groups in component (B) per primary and/or secondary amine group in component (A) of from 0.75:1 to 2:1. 2. A composition of Claim 1 wherein components (A-1) and (A-2) are employed in quantities which provide from 0.9 to 10 moles of polyamine compound per epoxide equivalent; and components (A) and (B) are employed in quantities which provide a ratio of latent NCO groups in component (B) per primary and/or secondary amine group in component (A) of from 0.9:1 to 1.5:1. 3. The composition of Claim 1 additionally containing from 10 to 60 percent by weight based on the total composition of a suitable solvent. 4. The composition of Claim 3 wherein the solvent is present in quantities of from 15 to 50 percent by weight.

Inventors: CAVITT MICHAEL B, HICKNER RICHARD A, CAVITT, MICHAEL, B., HICKNER, RICHARD, A.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1985
Main classification: C08L63
IPC codes: C08G18