Abstract:
Disclosed is a synergistic catalytic combination of 1,2-dimethylimidazole with tris(3-dimethylaminopropyl)amine and a salt of 1,8-diazabicyclo(5,4,0)undecene-7. The combination catalyst is useful in polyurethane systems such as elastomers, microcellular, rigid, semirigid, and flexible foams, such as integral skin semiflexible foams used in the manufacture of steering wheels.

Description:
BACKGROUND OF THE INVENTION 
     In preparing polyurethane foams advantages have been achieved by the use of the combination of a triethylenediamine-type of amine catalyst and an organic tin salt. With the multiplicity of raw materials used, namely, polyols, isocyanates, blowing agents, surfactants and additives, catalysis of polyurethane reactions has required continual modification mostly because of economic and ecological factors. Shortened demolding times for example, in rigid, flexible and microcellular molding operations are desirable to effect savings in labor and fixed costs. Moreover, the versatility of urethane has lead to the development of numerous production techniques; freerise molding, injection, casting, spray and others. Each require a specific reactivity profile, attainable in most cases only through catalysis. These developments and requirements have created a need for improved catalysts. Moreover, a commonly used catalyst for making urethane foams is triethylenediamine such as DABCO available from Air Products Co., which is a solid material. While effective as a catalyst for this purpose, solid catalysts are somewhat difficult to work with and liquid or semi-liquid catalytic materials would be desirable. 
     SUMMARY OF THE INVENTION 
     The improved catalyst of the present invention comprises a blend of 1,2-dimethylimidazole and tris(3-dimethylaminopropyl)amine together with 1,8-diazabicyclo-5,4,0-undecene 7 (DBU) blocked with 2-ethylhexanoic acid. The latter materials are available from Abbott Laboratories as POLYCAT 9 and POLYCAT SA-102, respectively. Other salts of DBU can be used such as for example those formed with phenol, formic acid, acetic acid, oleic acid or paratoluene sulfonic acid. A mixture of from about 20-80% 1,2-dimethylimidazole; 8-60% tris(3-dimethylaminopropyl)amine (PC-9); and 2-50% 1,8-diazabicyclo-5,4,0-undecene 7 blocked with 2-ethylhexanoic acid (SA-102) will provide a satisfactory combination. A preferred mixture is from 25-50% 1,2-dimethylimidazole; 40-60% PC-9; and 2-30% DBU salt. If desired, the 1,2-dimethylimidazole and PC-9 can be combined in a blend to be subsequently mixed with the SA-102. A blend of 40% 1,2-dimethylimidazole and 60% PC-9 for example, can be used satisfactorily. The combination catalyst can be used in polyurethane systems such as elastomers, microcellular, rigid semirigid and flexible foams. Specific examples such as shoe soles and integral skin semiflexible foams such as are used in the manufacture of automotive steering wheels. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In order to illustrate the manner in which catalytic combinations of the present invention can be prepared and used, reference is made to the following examples, which, however, are not meant to limit or restrict the scope of the invention in any respect. 
    
    
     EXAMPLE 1 
     Polyester Base Microcellular Foam (Shoe-Soles) 
     The following cup pours were made: 
     Polyester polyol with 3% trichlorotrifluoromethane (polyol blend): 100 grams 
     Polyisocyanate: Mondur E501 90 grams 
     Component temperature=40° C. 
     Room temperature=71°-73° F. 
     Relative humidity=42-46% 
     Cup size=pint 
     Mixing speed=3000 RPM 
     
         ______________________________________    Catalyst    Triethylene-              PC9 = 0.42 PC9 = 0.42    diamine, 0.65%              SA102 = 0.18                         SA102 = 0.28______________________________________Mix Time, Sec.      6            6         6Cream Time, Sec.      8-9         15         14-16Tack Free, Sec.      30-35       50         35-37Pull, Sec. 65-85       80-90      50-52Remarks    Slow hard cure                  Very Soft  Very soft______________________________________ 
    
     EXAMPLE 2 
     Microcellular Polyester Base Resins 
     Based on the cup pour results of Example 1, a ratio of 2/1: PC9/SA102 was utilized to determine molding characteristics of the two component blend of Example 1. 
     
         ______________________________________Formula______________________________________Polycat 9:  100 parts                =     0.50 PHR                             (parts per hun-Polycat SA102:        50 parts                =     0.25 phR                             dred of resin       150 parts             polyol blend)______________________________________ 
    
     Reactivity 
     Mix time=6 seconds 
     Cream time=13 seconds 
     Tack free=39-40 seconds 
     Pull=50-51 seconds. 
     Molding characteristics 
     
         ______________________________________Mix time = 6 secondsAmount of   Polyol Blend                   =       237   gramsfoam mixed  Polyisocyanate                   =       213   grams       Catalyst    =       1.78  grams -    451.78 grams______________________________________ 
    
     Mold Dimension: 5×10×1 inch 
     Mold temperature=140° F. 
     Mold release=chem trend P5 Cl 
     Demold time=3 minutes 
     Results--Bottom of part green, cheesey, very soft, upper part satisfactory. 
     EXAMPLE 3 
     Evaluation of Methylimidazoles as a Co-catalyst for Improving Demold Characteristics of Polyester Base Resins Systems 
     
         ______________________________________Foam RatioPolyol Blend: 100 parts (237 grams)Polyisocyanate: 90 parts (213 grams)      Catalyst      PC9 = 0.50   PC9 = 0.50      SA102 = 0.20 SA102 = 0.22      1,Methyl-    1,Methyl-      Imidazole = 0.20                   Imidazole = 0.22______________________________________Room temperature        70             70°F.Component tempera-        40 C.          40 C.ture °C.Relative humidity        60%            60%Foam ratio:  100/90         100/90Polyester/ISOMix time, Sec.         8Cream time, Sec.        14String time, Sec.        30Rise time, Sec.        50Tack free, Sec.        40Density, LBS/FT.sup.3Pull, Sec.   52Molded Part, Mixed        450 grams      450 gramsMold temperature        128° F. 135° F.Results      NG, cheesy,    Slight improve-        soft           ment; still cheesy______________________________________ 
    
     Same conditions as Example 2 plus 0.2 or 0.22 1-methyl-imidazole. No improvement noted. 
     EXAMPLE 4 
     Evaluation of 1,2-Dimethylimidazole as a Co-catalyst to Improve Demold Time of Polyester Based Microcellular Foam Formulations 
     
         ______________________________________Formulation______________________________________Polyol Blend:        100      partsPolycat 9:           0.50     partsPolycat SA102:       0.20     partsPolyisocyanate:      90.0     parts1,2-Dimethyl-imidazole:                0.2 to 0.4                         parts______________________________________Molded 10&#34; × 5&#34; × 1&#34; partsAluminum mold       PC9 = 0.50     PC9 = 0.50       SA102 = 0.20   SA102 = 0.20       1,2 Dimethyl-  1,2 Dimethyl-       Imidazole = 0.20                      Imidazole = 0.40       per 100 parts Resin                      per 100 parts Resin______________________________________Resin       237 grams      237 gramsE501        213 grams      213 gramsMix time    10             103000 RPMMold release agent       P5 Cl          P5 ClMold temperature       130°-135° F.                      130°-135° F.Demold after       Fair-Slight    Fair3 minutes   Loss of skin   Slight loss of skin______________________________________ 
    
     EXAMPLE 5 
     
         ______________________________________               Blend A   Blend BFormulation         % Weight  % Weight______________________________________1,2 Dimethyl Imidazole               40.00     33.00Tris (3-Demethylaminopropyl)               60.00     67.00amine (Polycat 9)   100.00    100.00______________________________________    Triethyl- Blend A = Blend B =                                Belnd A =    enediamine              0.90      0.80    0.80    0.65      SA102 =   SA102 = SA102 =    Control   0.20      0.20    0.20______________________________________Cream time,    9         10        12      11sec.Top of Cup,    25        24        27      26sec.String time,    28        27        30      28sec.Tack free,    32        31        36      34sec.Pull time,    45        47        59      55sec.Density  14.5      15.0      14.9    15.3LBS/FT.sup.3______________________________________ 
    
     EXAMPLE 6 
     Polyester Base Microcellular Shoe-Soles 
     Comparison between Blend A, Blend B (see example 5) and triethylenediamine. 
     
         ______________________________________Formulation Control   1        2      3______________________________________Triethylenediamine       0.65      --       --Blend A     --        0.90     --     0.80Blend B     --        --       0.80   --SA102       --        0.20     0.20   0.20Polyisocyanate       90.0      90.0     90.0   90.0Polyol Blend       --        100.0    100.0  100.0Component   40° C.                 40° C.                          40° C.                                 40° C.temperatureMold temperature       125°-                 125°-                          125°-                                 125°-       130° F.                 130° F.                          130° F.                                 130° F.Mold release agent       DPM286    DPM286   DPM286 DPM286Mix time, sec.       6         6        6      6       80/72     80/72    80/72  80/72Demold time 3 min.    31/2 min.                          41/2 min.                                 4 min.Shore A Hardness       60        62       60     63Weight of Part       105       108      109    106Mold Dimension: 5 × 10 × 0.25 inchTotal Weight of Components: 152 grams______________________________________ 
    
     EXAMPLE 7 
     The formulation used in the preparation of the microcellular shoe sole system is shown below: 
     
         ______________________________________Polyester resin Witco F108                 83.01,4 Butane Diol       17.0Water                 0.2Trichloromonofluoromethane                 4.0Polyisocyanate Mondur E-501 100 Index______________________________________ 
    
     The results are summarized in the following table. 
     
         ______________________________________MICROCELLULAR SHOE SOLEPOURS BASED ON POLYESTER RESIN      Control             1A       2A       3A______________________________________1/3 Triethylenediamine        0.60              0      02/3 DipropyleneglycolPolycat 77 (N,N,N&#39;,        0.40              0      0N&#34;,N&#34;--Pentamethyl-dipropylenetriamine)2:1 Blend, Polycat 9:1,        0        0.80     0.80   0.802-DimethylimidazoleSA102        0        0.05     0.10   0Components temper-        40       40       40     40ature °C.Foam ratio: polyol        105/108  105/108  105/108                                 108/108blend isocyanateMix time, sec.        8        8        8      8Cream time, sec.        10       11       10     11String time, sec.        28       33       28     36Rise time, sec.        40       42       38     48Pull time, sec.        61       72       49     81Density, LBS/FT.sup.3        14.40    16.14    15.14  16.45Remarks      No ShrinkageMolded pad density,        31.0     32.3     32.6   30.8LBS/FT.sup.3Mold temperature, °F.        128°                 130°                          130°                                 128°Mold release agent        M 286    M 286    M 286  M 286Demold time minutes        3        31/2     21/2   5______________________________________ 
    
     The following table records the results of a reactivity study as between various imidazole compounds. As is apparent, 1,2-dimethylimidazole produced improved results with respect to a faster initiation time, rise time, foaming time, a faster rate of rise, time to maximum rate of rise, gel time and time to peak pressure. The formulation used comprised 100 parts polyol, 1.5 parts silicone surfactant, 36.5 parts trichlorofluoromethane, 122.8 parts methylene diisocyanate and 1.6 parts of the imidazole catalyst. 
     
                       TABLE 1______________________________________Rigid          1,Methyl-                   2,Methyl- 1,2-Dimethyl-   PC 8   imidazole                   imidazole imidazole______________________________________Foam      15.51    12.94    15.69   15.01Height, inchesInitiation     66       64       81      44Time, secondsRise time,     108      93       142     69SecondsFoaming time,     42       29       61      25SecondsRate of Rise,     29.04    34.49    17.47   49Inches/minutesTime to dx/dt,     69       67       86      47SecondsPressure, 3.06     3.88     2.41    3.83PSIGGel time, 94       66       97      51SecondsTime to Peak     207      144      231     123Pressure,Seconds______________________________________ 
    
     Referring to the examples, it can be seen in Example 1 that the two component system approaches but does not produce the reactivity of the commonly utilized solid catalyst, triethylenediamine. In this example, the noted catalyst or combination catalyst was added to the polyol blend and polyisocyanate. In Example 3, no improvement was noted in comparison to the results obtained in Example 2 when 1-methyl imidazole was added to the two component systems. In Example 4, improved results are apparent with the addition of 1,2-dimethylimidazole in comparison to the addition of the 1-methylimidazole added in Example 3 or the two component systems of Example 2. 
     In Example 5 it can be seen that the combination catalyst of the invention produces results comparable to the commonly used catalyst triethylenediamine with increased amounts of 1,2-dimethylimidazole producing generally more advantageous results. Examples 6 and 7 illustrate the comparable or improved demold time resulting from the use of the combination catalyst of the present invention. Being semiliquid in form, the combination catalyst provides the further advantage of ease of handling as well as faster processing time.