Piperazine and alkanolamine accelerator for epoxy curing
United States Patent Waddill PIPERAZINE AND ALKANOLAMINE ACCELERATOR FOR EPOXY CURING Harold George Waddill, Austin, Tex.  
 Assignee: Jefferson Chemical Company, Inc.,  
 Houston, Tex.  
 Filed: Mar. 9, 1973 Appl. No.: 339,608  
 inventor:  
 References Cited UNITED STATES PATENTS 7/l969 Endors et al. 260/47 EN 2/l972 Bentley et al. 260/47 EN 2/1974 Godfrey et al. 260/47 EN [451 Apr. 1, 1975 Primary Examiner-Benjamin R. Padgett Assistant Examinerlrwin Gluck Attorney, Agent, or Firm-James L. Bailey; John R. Kirk, Jr.; Terrence D. Dreyer [57] ABSTRACT Epoxy resins, of the polyglycidyl ether of a polyhydric phenol type, are cured by incorporating therein a polyoxyalkylenepolyamine and an accelerator combination of piperazine and an alkanolamine, the combination having a combined weight ratio of between about 1:8 to 1:1. The accelerator combination is synergistic for accelerating the curing of a polyglycidyl ether of a polyhydric phenol cured with a polyoxyalkylenepolyamine at ambient or elevated temperatures. The epoxy resin products are useful in protective coatings, adhesives, seamless and terrazzo flooring, castings, laminates, and in grouting, potting, encapsulating, caulking and sealing compositions.  
 4 Claims, N0 Drawings PIPERAZINE AND ALKANOLAMINE ACCELERATOR FOR EPOXY CURING BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an improved process for curing epoxy resins and the resin product thus produced.  
 2. Description of Prior Art US. Pat. No. 3,467,393 to Legler I969) teaches the use of a polyoxyalkylenepolyamine for curing a polyglycidyl ether of a polyhydric phenol. Homans US. Pat. No. 2,783,214 (1957) discloses the curing of an epichlorohydrin-bisphenol resin-forming material at ambient temperature with a specific mixture of amines, i.e., a major amount of triethylene tetramine and a minor amount of triethanolamine, in the presence of a highly reactive substance which will polymerize spontaneously in the presence of the stated amines.  
  In several applications, accelerated curing of epoxy resins at ambient temperatures is essential. A typical situation is the use of an epoxy resin as an adhesive in a flammable environment. Many known prior art processes for preparing low temperature cured epoxy resins are disadvantageous inasmuch as the resultant epoxy resins have inferior physical properties, e.g., brittleness, loss in resistance to water absorption, strength, and the impairment of electrical properties. On the other hand. epoxy resins of the polyglycidyl ether of a polyhydric phenol type cured with a polyoxyalkylenepolyamine exhibit superior physical properties. However, curing with polyoxyalkylenepolyamines at ambient temperatures is too slow for use in many applications.  
  There are a few prior art processes known for accelerating the cure of epoxy resins cured with a polyoxyalkylenepolyamine. For example, Lee, Henry and Neville, Kris, Handbook of Epoxy Resins, McGraw-Hill Book Co., N.Y., 1967, p. 7-14, describes the use of N-(Z-aminoethyl)piperazine as an epoxy curing agent accelerator. US. Pat. No. 3,639,928 to Bentley et al. discloses a process for accelerating the curing of epoxy resins cured with a polyoxyalkylenepolyamine by incorporating therein an accelerator mixture of N-(3-aminopropyl)piperazine and salicylic acid. However, known prior art processes and accelerators still appear to be too slow for many applications of epoxy resins requiring cures at ambient temperatures. On the other hand, it has been found that epoxy resins can be cured at ambient temperature with a polyoxyalkylenepolyamine in very short periods of time by using an accelerator combination of the instant invention with the polyoxyalkylenepolyamine.  
 SUMMARY OF THE INVENTION The invention is an improved process for curing epoxy resins of the polyglycidyl ether of a polyhydric phenol type which are cured with a polyoxyalkylenepolyamine and the accelerator combination therefor. The rate of cure of the epoxy resins with the polyoxyalkylenepolyamine is rapidly accelerated by the use of an accelerator combination of piperazine and an alkanolamine, wherein the accelerator combination has a weight ratio of about 1:8 to 1:1 piperazine to alkanolamine. The cured epoxy resin products are useful in protective coatings, adhesives, seamless and terrazzo flooring, and as castings, potting, encapsulating, grouting, caulking and sealing compositions and like applications wherein accelerated curing is convenient or essential.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS More particularly, the instant invention is an improved process for accelerating the curing of a polyglycidyl ether of a polyhydric phenol cured with a polyoxyalkylenepolyamine which comprises the steps of combining with a polyglycidyl ether of a polyhydric phenol, a polyoxyalkylenepolyamine and an accelerator combination of piperazine and an alkanolamine,  
 said combination having a weight ratio of about 1:8 to  
  1:1 piperazine to alkanolamine, and allowing the mixture to cure and the resins obtained therefrom. Examples of the types of polyglycidyl ethers of polyhydric phenols to which the invention is applicable include the diglycidyl ether of isopropylidenediphenol and its congeners.  
 Polyoxyalkylenepolyamines of the formula;  
  R .r 2] y where R is a hydrocarbon radical, A is an alkylene radical having from two to four carbon atoms, x has an average value from 1 to 10, and y is an integer from 2 to 4 representing the valence of R, are useful in the practice of the instant invention. Preferred examples of the polyoxyalkylenepolyamines include polyoxypropylene diamines of the formula;  
 (I) ri niacn (0on mr H3 CH3 where x 2 to 40, polyoxypropylene triamines of the formula;  
 where R is a lower alkyl and x y z 3 to 40, and polyoxypropylene diamines of the formula;  
 (III) R CH3 where.r+z=2to l0 andy= l to 50.  
  Examples of preferred alkanolamines useful in the invention include mono-, diand triethanolamine, hydroxy ethoxyethylamine, N-aminoethylethanolamine, N, N bis (hydroxypropyl), N-hydroxyethylamine, and the like.  
  The particular order of mixing of the above described components is not critical in the practice of the instant invention. For example, the polyoxyalkylenepolyamine, piperazine and alkanolamine components may be blended in any desired order or manner to provide a homogenous mixture of accelerated curing agents. The mixture may then be incorporated into or mixed with the above described resin component at time of use to give an accelerated self-curing resin at ambient temperature.  
  In a preferred method of practicing the invention, the piperazine and alkanolamine components are first blended. The blend is then added to the polyoxyalkylenepolyamine component and this overall mixture is Should fire retardance be required for the epoxy resins cured by the process and composition of the present invention, it will be understood that various fire retardants for epoxy resins in compositions known in the art finally admixed with the above-described resin compo- 5 can be utilized without departing from the intended nent at time of use. The blend of piperazine and alkascope of the invention. Experiments have shown that nolamine component is capable of being stored for long well known epoxy resin fire retardants, for example, periods of time, if desired. various halogenated compounds, phosphate com- It is essential in the practice of the instant invention pounds, even including piperazine phosphate, and the that the accelerator combination of piperazine and allike, can be utilized in effective amounts in the abovekanolamine components be utilized in a weight ratio of described inventive process without affecting the synbetween about 1:8 to about 1:1 piperazine to alkanolaergistic effect of the accelerator combination of piperamine. I have found that the utilization of these compozine and alkanolamine components upon the accelernents within the described combined weight ratio is ated curing rate. Preferably, where fire retardance is highly synergistic for accelerating the self-curing of the desirable, an effective amount of piperazine phosphate above-described epoxy resin types cured with said pois incorporated into the above-described mixture of lyoxyalkylenepolyamines at ambient temperature. Acepoxy resin, polyoxyalkyleneamine, and accelerator cordingly, experiments have shown that where piperacombination. Accordingly, the piperazine phosphate zine or an alkanolamine is utilized alone, or where the may be added at any time during the mixing of the comweight ratio of the components is without the preponents without affecting the described synergistic efscribed range, the rate of curing at ambient temperafect. ture is drastically reduced. The above-described mixture of epoxy resin, polyox- The combined weight of piperazine and alkanolayalkylenepolyamine, and accelerator combination of mine components present when mixed with the polyoxpiperazine and alkanolamine is also preferably allowed yalkylenepolyamine may range from about 1 to 100 to self-cure at ambient room temperatures of between parts by weight per 100 parts by weight of the polyoxabout 0 to about 45 C. However, the mixture can be yalkylenepolyamine. The optimum amount may vary cured or post-cured at elevated temperatures up to somewhat for a given application depending upon the about 175 C., if desirable and convenient. particular epoxy resin, polyoxyalkylenepolyamine and The following Examples and Tables illustrate the lk l i b i ili d d i b t d t mined practice of the invention in more detail but are not to empirically for the most effective amount. be construed as limitative- In the curing of epoxy resins, the curing-hardening agent is usually added in an amount that will provide EXAMPLES one reactive NH in the combined harde e -Curing The epoxy resin formulations set forth in the followcomponents for each epoxy group in the epoxy resin ing Table l were prepared in separate containers at component. These are known in the art as stoichiometroom t pe at re (abo t 25 C Eq al amounts of ric quantities. Usually the stoichiometric quantities can epoxy resin for each example were mixed with stoichiobe calculated from a knowledge of the chemical struC- metric amounts of the curing agent consisting of a poture and analytical data the Particular components lyoxyalkylenediamine either with or without an addibeing utilized. However, many times the stoichiometric 4O ti l accelerator eomponent Th l i or i quantity is found empirically. A particular example of quired for a solid t b gi f r ing was noted in ea h such a method is measuring the maximum exotherm case. A portion of each formulation was coated on a temperature during the curing of the epoxy resin at difsteel t st panel by means of a 6-mil applicator blade, ferent hardening-curing agent concentrations. A graph and allowed to cure at room temperature. The times of the exotherm temperature vs. the concentration of required t reach the set-to-touch (STT) and throughhardening-curing agent will exhibit a maximum at or dry (TD) stages of cure, as determined by a Gardner near the stoichiometric quantity. circular drying time recorder, were also noted. As illus- For the purposes of the instant invention, the stoichitrated by the gel time and drying time of Example 4 the metric amount of the hardening-curing agent is CalCuaccelerator combination of piperazine and alkanolalated by adding together the number of equivalents on mine is strongly synergistic for accelerating the rate of the basis of weight per replaceable NH group in the cure of the epoxy resin cured with polyoxyalkpolyoxyalkylenepolyamine, piperazine and alkanolaylenepolyamine. Accordingly, the accelerator combimine components utilized. Preferably, these componation of triethanolamine and piperazine was over nents are utilized in amounts that will provide up to 10 twice as effective as either agent alone in producing the percent excess of the stoichiometric amount. gel time.  
 TABLE 1 Grams Gel Time STT TD Ex. No. ER D-2302 TEA P Min. Hrs. Hrs.  
 I too 30 295 9.0 12.5 2 I00 30 6.3 41.5 5.6 8.1 3 [00 27.4 2.3 82.5 19.0 23.0 4 27.4 5.4 2.3 17.0 4.0 6.2  
 &#39;Diglycidyl other of isopropylidenetliphenol having an equivalent weight per epoxide of 191. &#34;Jeffummc&#34; product manufacture by Jefferson Chemical Company, Inc., a polyoxypropylenediamine of structure I hanng an average molecular weight of about 230 and an equivalent weight per active hydrogen of about 58.  
 Triethannlaminc iperazine EXAMPLES 5-8 Epoxy resin formulations in Table 2 were prepared in accordance with the procedure set forth in Examples l4. The gel times were noted in each case. The strongly synergistic effect of the accelerator combination of piperazine and triethanolamine is again illustrated by Example 8.  
 TABLE 2 Grams Gel Time Ex. No. ER D-400 TEA P Min.  
 Same as in Table l leffamlne product. a polyoxypropylenediamine of structure 1 having an average molecular eight of about 400 and an equivalent weight per active hydrogen of about 105 Trlethanolamme &#39;Piperazlne EXAMPLES 9-12 TABLE 3 Grams Gel Time Ex. No. ER D-230 DEA P Min.  
 Same as Table l &#34;Samcs as Table l &#39;Dmthanolaminc Pipcranne EXAMPLES 13-16 TABLE 4 Grams Gel Time Ex. No. ER T-403 TEA P PP Min.  
  6 TABLE 4-Continued Grams Gel Time Ex. No. ER T-403 TEA P PP Min.  
 Same as in Table l -.leffamine product. a polyoxypropylenediamine of structure 1 having an average molecular weight of about 400 and an equivalent weight per active hydrogen of about 80.  
 &#34;Triethanolamine Piperazine Piperazine phosphate monohydrate. a flame retardant.  
 EXAMPLES 17-20 The epoxy resin formulations in the following Table 5 were prepared in accordance with the process of Examples l4, the gel times being noted. Example 20 shows the synergistic accelerated curing rate produced by the combination of piperazine and the 2 mol propylene oxide adduct of monoethanolamine.  
 TABLE 5 Grams Gel Time Ex. No. ER D-230 A P Min Same as Table 1 Same as Table 1 Reaction product of monoethanolamine (1 mol) and propylene oxide (2 mols); N-N-histZ-hydroxypropyll N-hydroxyethyl) amine.  
 Same as in Table l Comparable results to those illustrated in the Tables and Examples set forth hereinabove are obtained by using accelerator combinations within the invention disclosed but not specifically illustrated. Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and, therefore, only such limitations should be imposed as indicated in the appended claims.  
 What is claimed is:  
  1. As a composition of matter, an accelerator combination that is synergistic for accelerating the curing of a polyglycidyl ether of a polyhydric phenol cured with a polyoxyalkylenepolyamine, said accelerator combination comprising piperazine and an alkanolamine in a combined weight ratio of about 1:8 to about 1:1 piperazine to said alkanolamine.  
  2. An accelerator combination of claim 1 wherein said alkanolamine is selected from the group consisting of mono-, di-, or triethanolamine, hydroxy ethoxyethylamine, N-aminoethylethanolamine, N,N-bis(hydroxypropyl), N-hydroxyethylamine, and mixtures thereof.  
  3. An accelerator combination of claim 1 wherein the alkanolamine is triethanolamine.  
  4. An accelerator combination of claim 1 wherein the weight ratio of piperazine to triethanolamine is about 1:4 to 1:2.