Abstract:
Epoxy resins are cured with salicyloyl hydrocarbyl amines such as N,N&#39;-disalicyloyl-1,2-propylenediamine. The cured resins have an improvement in one or more properties such as color, tensile strength and flexural strength or improved pot life when compared to amine curing agents such as methylene dianiline.

Description:
BACKGROUND OF THE INVENTION 
     The present invention concerns suitable compositions containing epoxy resins and salicyloyl hydrocarbylamines and cured compositions thereof. 
     Epoxy resins have typically been cured with amines such as methylene dianiline to produce cured products with excellent properties. 
     The present invention concerns salicyloyl hydrocarbyamines as new curing agents for epoxy resins which provide cured products having excellent properties and, in some instances, have an improvement in one or more properties such as tensile strength, impact strength, color and the like. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a curable composition comprising (A) an epoxy resin having an average of more than one 1,2-epoxy group per molecule and (B) a curing quantity of at least one curing agent represented by the formulas ##STR1## wherein R is a divalent hydrocarbyl group having from 1 to about 10, preferably from about 2 to about 6, carbon atoms; R&#39; is a divalent hydrocarbyl group having from 1 to about 6 carbon atoms; R&#34; is hydrogen or a hydrocarbyl group having from 1 to about 10 carbon atoms; n has a value of zero or 1 and n&#39; has an average value of from about 1.01 to about 5, preferably from about 1.1 to about 2.5. 
     The present invention also pertains to the product resulting from the aforesaid curable compositions. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Suitable epoxy resins which can be employed herein include the glycidyl ethers of aromatic or aliphatic compounds having an average of more than one hydroxyl group per molecule. Also suitable are the epoxy resins resulting from epoxidizing compounds having an average of more than one ethylenically unsaturated group per molecule by means of a peroxygenated acid such as peracetic acid. These and other suitable epoxy resins which can be employed herein are disclosed in EPOXY RESIN HANDBOOK, by Lee and Neville, McGraw-Hill, 1967, which is incorporated herein by reference. 
     Suitable salicyloyl hydrocarbylamines which can be employed herein include salicylamide and the product resulting from reacting a hydrocarbyl salicylate with a compound having an average of more than one -NH 2  group per molecule and removing therefrom the resultant byproduct which is the hydroxyl derivative of the hydrocarbyl constituent of the hydrocarbylsalicylate. Particularly suitable hydrocarbyl salicylates from which the curing agents employed in the present invention can be prepared include methylsalicylate and phenylsalicylate wherein the byproduct would be methanol and phenol respectively. 
     Suitable amines which can be employed to prepare the curing agents employed in the present invention include, for example, ethylenediamine, propylenediamine, hexamethylenediamine, methylene-dianiline, 2,4-toluenediamine, 2,6-tolenediamine, polymethylene polyphenylamine, 1,2-phenylenediamine, 1,3-phenylenediamine, 1,4-phenylenediamine, mixtures thereof and the like. 
     The quantity of the salicyloyl hydrocarbylamine curing agents employed in the present invention varies with the particular utility, degree of cure, the particular curing agent itself, but they are usually employed in an amount which provides from about 0.1  mole to about 1 mole, preferably from about 0.15 mole to about 0.5 mole, of curing agent per epoxy equivalent contained in the epoxy resin. 
     The curable compositions of the present invention may also contain, if desired, pigments, dyes, fillers, diluents, flow control agents, fire retardant agents, accelerators, other curing agents and the like. 
     The following examples are illustrative of the invention, but are not to be construed as to limiting the scope thereof in any manner. 
     The salicyloyl hydrocarbylamine curing agents are prepared by the following general procedure. 
     A mixture of two moles of phenyl salicylate and one mole of the appropriate amine is heated at 150°-160° C. with stirring under nitrogen for 4-12 hours. The phenol liberated is removed either via washing with toluene or vacuum distillation. The residue is purified by recrystallization. Aliphatic amines generally require 4-5 hours of heating while the sterically hindered 2,6-diaminotoluene requires 12 hours. The overall yields are 75-90% after purification. Aliphatic amines can be used as received but aromatic amines should be purified by vacuum distillation from zinc dust. 
    
    
     EXAMPLE 1 
     Use of N,N&#39;-disalicyloyl-1,2-propylenediamine 
     Into separate beakers was weighed 64.9 g (0.21 mole) N,N&#39;-disalicyloyl-1,2-propylenediamine and 155.1 g (0.83 equiv.) of a diglycidyl ether of bisphenol A (DGEBA) having an average epoxide equivalent weight (EEW) of about 188. These were placed in an oven at 110°-120° C. and heated until the former was melted. The contents of the two beakers were combined, mixed and poured into cavity molds heated to 100° C. The system was cured by holding the molds at 100° C. for 1 hour (3600 s), then raising the temperature to 150° C. for an additional 2 hours (7200 s). The molds were then cooled, the specimens removed and evaluated by various tests, the results being given in Table I. 
     EXAMPLE 2 
     Use of N,N&#39;-disalicyloyl-1,2-ethylenediamine 
     64.8 g (0.22 mole) of N,N&#39;-disalicyloyl-1,2-ethylenediamine were added to 200 g (1.06 equiv.) of DGEBA having an average EEW of about 188 epoxy resin in a beaker on a hot plate at ambient temperature. The mixture was heated to 150° C. with stirring. The amide dissolved at about 125° C. The homogeneous solution was poured into a heated cavity at 150° C. and cured 2 hours (7200 s) at 150° C. followed by 2 hours (7200 s) at 175° C. The molds were cooled and the specimens evaluated. The results are given in Table I. 
     EXAMPLE 3 
     Use of N,N&#39;-disalicyloyl-1,6-hexamethylenediamine 
     58 g (0.16 mole) of N,N&#39;-disalicyloyl-1,6-hexamethylenediamine were added to beakers containing 200 g (1.06 equiv.) of DGEBA having an average EEW of about 188 epoxy resin. The mixture was heated to 150° C. while stirring. The amide dissolved in the epoxy resin at about 125° C. When the solution was thoroughly mixed and free of bubbles, it was poured into cavity molds heated to 150° C. The system was cured for 2 hours (7200 s) at 150° C. and 2 hours (7200 s) at 175° C. The molds were cooled, the specimens removed and evaluated. The results are given in Table I. 
     EXAMPLE 4 
     Use of N,N&#39;-disalicyloyl-2,4-toluenediamine 
     51.3 g (0.14 mole) of N,N&#39;-disalicyloyl-2,4-toluenediamine and 88.4 g (0.47 equiv.) of DGEBA having an average EEW of about 188 were weighed into separate beakers and placed on a hot plate and heated until the amide melted (ca 160° C.). The contents of the two beakers were then combined, rapidly mixed, and poured into cavity molds heated to 150° C. The system was cured for 1 hour (3600 s) at 150° C. and 2.7 hours (9720 s) at 170°-180° C. The molds were cooled, the specimens removed and evaluated. The results are given in Table I. 
     EXAMPLE 5 
     Use of Salicylamide 
     1.62 g (0.012 mole) of salicylamide and 6.38 g (0.034 equiv.) of DGEBA having an average EEW of about 188 were placed in a weighing pan and heated on a hot plate with stirring until the salicylamide had dissolved. When the homogeneous mixture was free of air bubbles, it was cured in an oven at 150° C. for 2 hours (7200 s) followed by 4 hours (14400 s) at 175° C. The sample was removed from the oven, cooled, and evaluated. The results are given in Table I. 
     EXAMPLE 6 
     Use of salicylamide plus benzyltrimethyl ammonium hydroxide as catalyst 
     To 15.6 g. (0.11 mole) of salicylamide in a beaker was added 3.3 g of a 35% solution of benzyltrimethyl ammonium hydroxide in methanol. To another beaker was added 64.6 g (0.34 equiv.) of DGEBA having an average EEW of about 188. Both beakers were placed on a hot plate and heated until the salicylamide was melted (ca 150° C.). The contents of the two beakers were combined, rapidly mixed, and poured in a cavity mold heated to 90° C. The system was cured for 1 hour (3600 s) at 95° C., 1 hour (3600 s) at 110° C., and 2 hours (7200 s) at 150° C. The mold was cooled and the specimens removed and evaluated. The results are given in Table I. 
     
                       TABLE I______________________________________                    HEATEXAMPLE  NOTCHED IMPACT  DISTORTION   TgNUMBER   pli.sup.1 /kgplm.sup.2                    °C.   °C.______________________________________1         0.86/15.36     123          1412        0.42/7.5        103          1203        0.08/1.43        81          1034        0.26/4.64       119          1335        N.D..sup.3      N.D..sup.3    576        N.D..sup.3      104          112______________________________________ .sup.1 pli = pounds per linear inch .sup.2 kgplm = kilograms per linear meter .sup.3 N.D. = not determined 
    
     EXAMPLE 7 
     Separate samples of amide and epoxy were weighed into aluminum dishes. Total weight of the amide and epoxy was 8-10 g. Samples with ratios of 0.15-0.5 mole amide/equiv DGEBA having an average EEW of about 188 were prepared for all the salicylamides. However, in the case of N,N&#39;-disalicyloyl-1,2-propylenediamine this range was extended to include 1 mole amine/1.0 equiv. of DGEBA. 
     In most cases, each pair of amide and epoxy components were heated to the melting point of the amide, then combined and mixed. Some amides with higher melting points were heated with the epoxy in order to solubilize the amide at a lower temperature. In each case, a homogeneous, non-gelled sample was obtained prior to being placed in the curing oven. The Tg (glass transition temperature) for these are shown in Table II. 
     
                                           TABLE II__________________________________________________________________________Tg&#39;s FOR N,N&#39;--DISALICYLOYL ALKYLENEDIAMINES ANDSALICYLAMIDE CURED DGEBA COMPOSITIONSDiamine  MOLES AMIDE/EQ. DGEBA EPOXY RESINS                                  CURING SCHEDULEDerivative  0.15     0.20        0.25           0.30              0.35                 0.40                    0.45                       0.50                          0.675                             0.75                                1.0                                  Hrs.                                     °C.                                        Hrs.                                           °C.__________________________________________________________________________1,2-propylene  115     120        138           142              118                 117                    104                        80                          76 69 66                                  1  100                                        2  1501,2-ethylene  82 110        118           120              116                 114                    111                       113                          -- -- --                                  2  150                                        2  1751,6-hexylene  57  78         83            92               91                 103                    101                        85                          -- -- --                                  2  150                                        2  1752,4-toluene  91 104        118           133              135                 138                    137                       135                          -- -- --                                  2  150                                        2  175Other:Salcylamide  liq.     gel         45            43               57                  54                     56                        77                          -- -- --                                  2  150                                        2  175__________________________________________________________________________ 
    
     EXAMPLE 8 
     Various epoxy resins were cured with N,N&#39;-disalicyloyl-1,2-propylenediamine. The results are given in Table III. 
     
                                           TABLE III__________________________________________________________________________    A.sup.1         B.sup.2              C.sup.3                   D.sup.4                        E.sup.5                             F.sup.6__________________________________________________________________________C-3, phr 49.1 68.8 53.8 23.9 17.9 61.6grams ofCuring Agent    13.2 16.3 14.0 12.7 6.1  15.2grams ofEpoxy Resins    26.8 23.7 26.0 37.3 33.9 24.8Mixingtemperature, °C.    100  100  100  100  125  100Initial GelHrs./Seconds    3/10800         2.5/9000              3/10800                   2.5/9000                        2/7200                             1.5/5400Temp °C.    100  100  100  100  100  100Post Cure #1Hrs./Seconds    2/7200         1/3600              2/7200                   1/3600                        1/3600                             2/7200Temp °C.    150  150  150  150  150  150Post Cure #2Hrs./Seconds    --   2/7200              --   2/7200                        2/7200                             --Temp °C.    --   175  --   175  175  --Tg, °C.    98   144  142  157  69   181H.D., °C.    55   104  120  143  99   178__________________________________________________________________________ Footnotes to Table III .sup.1 Epoxy Resin A was a mixture of 70% by weight of the DGEBA having a average EEW of about 188 and 30% by weight of the diglycidyl ether of a polyoxypropylene glycol having an average molecular weight of about 250, the epoxy resin having an average EEW of about 201. The average EEW of th mixture was about 190. .sup.2 Epoxy resin B was a cycloaliphatic epoxy resin having an average EEW of about 137 commercially available from Union Carbide Corporation as ERL 4221. .sup.3 Epoxy Resin C was a polyglycidyl ether of a phenolformaldehye novolac resin having an average epoxide functionality of about 2.2 and an average EEW of about 175. .sup.4 Epoxy Resin D was a diglycidyl ether of tetrabromobisphenol A having an average EEW of about 172. .sup.5 Epoxy Resin E was a solid diglycidyl ether of bisphenol A having a average EEW of about 525. .sup.6 Epoxy Resin F was a triglydicyl ether of tris(hydroxyphenyl)methan having an average EEW of about 153. 
    
     EXAMPLE 9 
     DGEBA having an average EEW of about 188 was cured with 0.25 mole of N,N&#39;-disalicyloyl-1,2-propylenediamine per epoxy equivalent employing various curing schedules. The results are given in the following Table IV. The results were compared to the epoxy resin cured with 0.50 mole of methylenedianiline (MDA) per epoxy equivalent at the 150° C. post cure. 
     
                                           TABLE IV__________________________________________________________________________EFFECT OF CURING SCHEDULE ON THE PHYSICAL PROPERTIESOF A 0.25 MOL. N,N&#39;--DISALICYLOYL-1,2-PROPYLENEDIAMNE/EQ. OF EPOXY                             Typical     All samples initially cured 1 hr at 100° C.                             Values,     followed by 2 hrs at indicated temperature                             MDA Cure,     100° C.           125° C.                 150° C.                       175° C.                             150° C.__________________________________________________________________________Barcol Hardness     14.0  13.4  15.5  13.6  N.D..sup.3Heat Distortion, °C.     102.5 123.9 121.7 122.5 160Tg (via Tma).sup.1, °C.      99.5 138.0 143   134   153Tg (via DSC).sup.2, °C.      99   130.5 139.5 122   N.D.Tensile Strength,psi/MPa   N.D.  12,762/88                 12,406/85                       N.D.  10,200/70Flexural Strength,psi/MPa   16,914           19,508/134                 20,453/141                       20,854/144                             13,500/93Flexural Modulus     5.05 × 10.sup.5           4.94 × 10.sup.5                 4.83 × 10.sup.5                       4.95 × 10.sup.5                             3.9 × 10.sup.5__________________________________________________________________________ .sup.1 TMA = thermogravimetric analysis .sup.2 DSC = differential scanning calorimeter .sup.3 N.D. = not determined