Abstract:
Cure of an epoxy resin by an aliphatic amine is accelerated by a calcium sulfonate or calcium hydrocarbyl sulfate salt. The calcium salt is preferably a salt of a detergent-range sulfonic acid or hydrocarbyl sulfuric acid which is soluble in either the amine or the epoxy resin.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to the cure of epoxy resins. In one aspect, the invention relates to acceleration of aliphatic amine cure of epoxy resins. 
     Certain common accelerators for aliphatic amine cure of epoxy resins, such as alcohols, phenols and carboxylic acids, tend to give a relatively low degree of acceleration. Others, such as calcium nitrate tetrahydrate, overcome this problem but must be added as third components, whether or not dissolved in a solvent. Calcium nitrate, when dissolved in an epoxy resin, tends to cause advancement of the resin and to lose activity on storage. If dissolved in the amine curing agent, it tends to give a copious precipitate in the presence of traces of water (from atmospheric moisture or the water of hydration of calcium nitrate tetrahydrate). 
     It is therefore an object of the invention to provide an epoxy resin/amine system which exhibits accelerated cure. It is a further object of the invention to provide an aliphatic amine-cured epoxy resin system having an amine-soluble accelerator component. 
     SUMMARY OF THE INVENTION 
     According to the invention, cure of an epoxy resin by an aliphatic amine is accelerated by a calcium sulfonate or calcium hydrocarbyl sulfate salt. The calcium salt is preferably a salt of a detergent-range sulfonic acid, or a detergent-range hydrocarbyl sulfuric acid, which is soluble in either the amine or the epoxy resin. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The epoxy resin component of the invention composition can be any epoxy-functional compound having an average of more than one vicinal epoxide group per molecule. Preferred epoxy resins are diglycidyl ethers of a bisphenol prepared by the reaction of epichlorohydrin with a compound containing two hydroxyl groups, such as bisphenol-A or bisphenol-F, carded out under alkaline reaction conditions. Such an epoxy resin can be represented by the structural formula ##STR1## which n is a number within the range of 0 to about 2 and R is a direct bond or a divalent hydrocarbyl group. Suitable epoxy resins have molecular weights within the range of 300 to 3000, preferably about 300 to about 1000. The commercially available EPON® Resin 828, a reaction product of epichlorohydrin and bisphenol-A having an epoxide equivalent weight (ASTM D-1652) of about 182 and an n value in the formula above of about 0.2, is the preferred epoxy resin for use in the invention compositions. 
     The aliphatic amine curing agent component of the invention compositions can be any compound having two or more active amine groups. Preferred amines include C 5-15  aliphatic and cycloaliphatic diamines and polyamines such as 2-methyl-1,5-pentanediamine, 1,2-diaminocyclohexane, triethylenetetramine, diethylenetriamine, 1,4- or 1,3-diaminocyclohexane, isophoronediamine, 1,3-bis(aminomethyl)benzene, 1,3-bis(aminomethyl)cyclohexane, isomeric mixtures of bis(4-aminocyclohexyl)methane, oligo(propylene oxide)diamine and adducts of the above amines with epoxy resins, epichlorohydrin, acrylonitrile, ethylene oxide, and the like. 
     The amine will be present in the composition in an amount effective to cure the epoxy resin, generally an amount within the range of about 0.6 to about 2 equivalents, based on the epoxy resin. 
     The calcium sulfonate or calcium hydrocarbyl sulfate accelerator component of the invention composition can be described by the chemical formulae 
     
         Ca(OSO.sub.2 R).sub.2 or Ca(OSO.sub.2 OR).sub.2 
    
     in which R is a C 6-25  hydrocarbon or hydrocarbon-containing group. R can be, for example, C 6-20  aliphatic, C 12-25  alkaryl, or, CH 3  (OCH 2  CH 2 ) n  O-- where n is greater than about 2. Some or all of the hydrogen atoms may alternatively be replaced by halogens. Such calcium sulfonates and calcium hydrocarbyl sulfates include, for example, calcium dodecylbenzene sulfonate, calcium dodecyl sulfate, calcium hexanesulfonate, calcium 3-oxaheptyl sulfate, calcium perfluorooctane sulfonate, calcium 2-hydroxyoctadecane sulfonate, etc. The preferred accelerators, because of their commercial availability and demonstrated effectiveness, are detergent-range (C 12-20 ) alkaryl sulfonates such as those commercially available from Stepan Company under the trade name Ninate 401. The accelerator can be conveniently added to the resin or amine component as a solution in an organic solvent. 
     The calcium sulfonate or calcium hydrocarbyl sulfate is present in the epoxy/amine formulation in an amount effective to accelerate cure of the epoxy by the amine, generally an amount within the range of about 0.1 to about 10 parts per hundred parts by weight of epoxy resin. 
     The invention compositions can be prepared by blending the epoxy, the amine and the calcium sulfonate or calcium hydrocarbyl sulfate in any order desired. The compositions can be provided as a two-container system, with the calcium sulfonate or calcium hydrocarbyl sulfate present as an additive in the epoxy resin or, preferably, in the amine. 
     Cure of the invention compositions can be effected by exposure to a temperature of 0° to 100° C. for 1 to 24 hours. Certain of the compositions are curable at room temperature over a time of about 8 to 24 hours. 
     The invention compositions are useful for coatings, adhesives, flooring, casting and composites fabrication. 
    
    
     EXAMPLE 1 
     Accelerator Activity of Calcium Sulfonate Compared with Calcium Nitrate. 
     A mixture (Accelerator A) was prepared by mixing 59 parts by weight of Ca(NO 3 ) 2 .4H 2  O with 41 parts by weight of polyethylene glycol 400 and stirring until the mixture became a homogeneous liquid. Accelerator A, Stepan Ninate 401 calcium dodecylbenzenesulfonate solution and salicylic acid (the latter predissolved in 2-methyl-1,5-pentanediamine) were then mixed with EPON® Resin 828 and 2-methyl-1,5-pentanediamine in the indicated proportions and the mixtures (mass 75-80g) were then tested for gel time (with no external heat applied) in a Shyodu gel timer with a rotating probe, and also on thin film gel plates at 90° C. and 120° C. Additional mixtures of the epoxy resin with 2-methyl-1,5-pentanediamine and the accelerators were prepared and poured into casting molds made of two 1/8 (3.18 mm) thick glass plates separated by a 1/8&#34; (3.18 mm) thick polytetrafluoroethylene spacer. The castings were allowed to cure overnight at room temperature and were then cured for 2 hours at 80° C. the following day. Physical properties of the castings were determined and are shown in Table 1. 
     
                                           TABLE 1__________________________________________________________________________                1     2     3     4     5     6     7__________________________________________________________________________Composition:Epoxy Resin, grams   128   128   128   128   128   128   128epoxy equivalents    0.681 0.681 0.681 0.681 0.681 0,691 0.6812-methyl-1,5-pentanediamine, grams                22    22    22    22    22    22    22NH equiv.            0.757 0.757 0.757 0.757 0.757 0.757 0.751Accelerator A, grams       1.28  1.92Ninate 401, grams                      1.28  2.56  3.84Salicylic acid, grams (predissolved in amine)            2.56NH/epoxy ratio, eq/eq                1.11  1.11  1.11  1.11  1.11  1.11  1.11Uncured properties:Shyodu gel time, min.                88.5  10.2  7.6   33.3  12.0  10.7  22.3Thin film gel time, sec., 90° C.                340   180   280   180   170   200120° C.       95    25    72    46    39    53Cured properties:Rheometrics tan δ peak, °C.                113   110   117   107   105   105   116R.T. dry flexural (ASTM D-790)Yield strength, MPa  102 ± 1                      104 ±  1                            106 ± 1                                  105 ± 1                                        105 ± 1                                              105 ± 1                                                    116 ± 1Tangent modulus, GPa 2.66 ± 0.02                      2.67 ± 0.03                            2.73 ± 0.03                                  2.70 ± 0.02                                        2.69 ± 0.03                                              2.67                                                    2.96 ± 0.03Break elongation, %  ≧6.5                      ≧6.5                            ≧6.5                                  ≧6.4                                        ≧6.5                                              ≧6.4                                                    ≧6.5Compact tension fracture toughness, K.sub.q,                1.94 ± 0.11                      1.94 ± 0.09                            1.76 ± 0.14                                  1.88 ± 0.15                                        1.83 ± 0.09                                              1.75                                                    1.51 ± 0.07MPa-m.sup.1/2 (ASTM E 399-83)93° C. H.sub.2 O pickup, %: 1 day                1.742 weeks              2.64Room temp. methyl ethyl ketone pickup, %:1 day                0.33  0.25  0.23  0.29  0.29  0.20  0.362 weeks              3.16  5.01  4.48  6.32  5.49  disint.                                                    6.27Room temp. CH.sub.2 Cl.sub. 2 pickup, %, 1 day                disint.                      disint.                            disint.                                  disint.                                        disint.                                              disint.                                                    disint.__________________________________________________________________________ 
    
     From Table 1 above can be seen the accelerator effect of the Ninate 401. On a weight basis, Ninate 401 is a weaker accelerator than Accelerator A but slightly stronger than salicylic acid. On the basis of calcium content, however, Ninate 401 (3.73% calcium by weight) is almost as active as the calcium nitrate-based Accelerator A (10% calcium by weight). 
     EXAMPLE 2 
     Comparison of Stability of Calcium Sulfonate Accelerator and Calcium Nitrate Accelerator as Solutions in 2-Methyl-1,5-Pentanediamine. 
     Mixtures of Ninate 401 (or Accelerator A), with 2-methyl-1,5-pentanediamine and water were prepared in small vials as shown in Table 2 below. 
     
                       TABLE 2______________________________________Mixture #    1      2      3    4    5    6    7    8______________________________________2-methyl-1,5-    5.5    5.5    5.5  5.5  5.5  5.5  5.5  5.5pentane-diamine,gramsAccelerator    0.96   0.96   0.96 0.96A, gramsNinate 401,                      0.96 0.96 0.96 0.96gramsWater, grams    0.11   0.30 1.00      0.11 0.30 1.00Precipitate    Yes    Yes    Yes  Yes  No   No   No   Noafter 1 day?Precipitate    Yes    Yes    Yes  Yes  No   No   No   Yesafter 2months?______________________________________ 
    
     From Table 2 can be seen that the mixtures containing Ninate 401 showed much greater resistance to precipitate formation, even in the presence of water. All of the mixtures containing Accelerator A showed heavy precipitate formation after 1 day, whereas all the Ninate 401 mixtures (except the one with the highest amount of added water) were free of precipitate even after 2 months. Table 3 below shows that Ninate 401/2-methyl-1,5pentanediamine mixtures showed no loss of accelerator activity after storage for six days, when the amine mixtures were mixed with EPON Resin 828 and gel tests were run as in Example 1. 
     
                       TABLE 3______________________________________Mixture #                1       2______________________________________2-methyl-1,5-pentanediamine, grams                    55      55Ninate 401, grams        3.2     9.6Amount of above amine mixture used for gel                    11.64   12.92tests, gAmount of EPON ® Resin 828 used for                    64      64gel tests, gShyodu gel time, min., initially                    33.3    10.7after 6 days             25.9    9.4Thin film gel time, sec., initially, 90° C.                    280     170120° C.           72      39Thin film gel time, sec., after 6 days, 90° C.                    290     175120° C.           70      25______________________________________ 
    
     EXAMPLE 3 
     Comparison of Calcium Naphthenate with Accelerator A and Ninate 401 as an Accelerator for Aliphatic Amine Cure of Epoxies. 
     A calcium naphthenate mixture (Nuodex) containing 10% calcium was tested as an alternative accelerator to Accelerator A and Ninate 401 for the cure of EPON Resin 828 with 2-methyl-1,5-pentanediamine, as shown in Table 4 below. One can see from the results shown below that calcium naphthenate had little or no accelerator activity, even though it was soluble in the resin/amine mixture. This suggests that calcium salts of anions with relatively high basicity and nucleophilicity, such as most carboxylate anions, may not be generally effective as accelerators. 
     
                       TABLE 4______________________________________Mixture #            1       2      3______________________________________EPON ® Resin 828, grams                64      64     642-methyl-1,5-pentanediamine, grams                11      11     11Calcium naphthenate, grams   0.64   1.28Shyodu gel time, min.                88.5    80.5   92.9______________________________________ 
    
     EXAMPLE 4 
     Acceleration of Amine Cure of Epoxy Resin using Ninate 401 anti Other Accelerators. 
     Mixtures of EPON Resin 828 with Amicure PACM (mixture of isomers of bis(4-aminocyclohexyl)methane) and accelerators were prepared and Shyodu gel time was determined as in previous examples. Table 5 shows the relative effect of these materials as accelerators. 
     
                       TABLE 5______________________________________Mixture #       1       2      3     4    5______________________________________EPON ® Resin 828, grams           58      58     58    58   58Amicure PACM, grams           17      17     17    17   17Accelerator A, grams    0.58Ninate 401, grams              0.59  1.16Salicylic acid, grams                     0.59(predissolved in amine)Shyodu gel time, min.           202     24.3   126.3 68.2 81.1______________________________________