Abstract:
A highly reactive urethane foam for RIM to produce thin-sectioned automobile trim components having good high temperature sag performance is a quasi prepolymer system in which the polyol side is based on a relatively high molecular weight polyol combined with a known highly reactive unhindered aromatic polyamine chain extender/cross linker and with conventional short chain diols/triol extenders/cross linkers and catalysts.

Description:
INTRODUCTION 
     This invention pertains to the manufacture of thin-sectioned automobile trim components, such as bumper fascia, by injection molding of a urethane foam composition. It is more particularly concerned with an improved urethane foam composition of the prepolymer type that is especially suitable for reaction injection molding and produces a product that has surprisingly good high and low temperature properties and an excellent relatively nonporous skin. 
     A recent advance in the field of urethane technology has been the development of reaction injection molding, or RIM, systems such as ones using high pressure, multi-stream, high velocity impingement to effect essentially instantaneous mixing. As used herein, RIM means a system wherein the time from initial mixing of the urethane foam ingredients to injection in the mold cavity is less than 0.01 seconds. 
     In order to secure a good performance at high temperature without distortion, the polyol side of the urethane foam prepolymer system of this invention uses as a polymer backbone a polyol that is relatively long chain; that is, it has a molecular weight in the range of preferably 3000-6000, functionality of 2-3, and an equivalent weight of 1500-3000. These polyols have a high primary hydroxyl content. In the range of 50 to 90 percent of the hydroxyl groups are primary groups. The reaction rates of such polyols are not too fast, but in the present composition an exceptionally fast, highly reactive, unhindered aromatic polyamine chain extender/cross linker having one amino group per aromatic nucleus is used to overcome this problem in addition to which, as the amine is aromatic, it contributes to the foam&#39;s high temperature stability and resistance to sag. The bisurea linkage from the primary amine is known to have high temperature stability. 
     These aromatic amines are known and have the formula: ##STR1## Wherein n has a value in the range of 0.1 to 0.7. The use and advantage of such amines in foam systems are discussed in U.S. Pat. Nos. 3,575,896 and 3,681,291. 
     The RIM foam system of this invention, in order to tailor in specific properties, uses other recognized ingredients in the polyol blend such as alkylene diol and triol cross linker/extenders, organometal catalysts, alkylene amine catalysts, carbon black, blowing agents, and the like. The use of conventional cross linker/extenders such as butane diol, ethylene glycol, pentanediol, etc., without the aromatic polyamine does not significantly change the high temperature performance of the product. 
     The prepolymer side is quite important in the development of the foam properties. It is a quasi prepolymer of a polyoxyalkylene diol and an MDI, i.e., methylene bis (4-phenyl isocyanate), type of diisocyanate. It is known that where only one isocyanate is present per aromatic nucleus the urethane is more stable as compared to a TDI (tolulenediisocyanate) having two groups per nucleus. In addition, if a TDI is used, the elongation of the product can drop as much as 50 percent. One of the advantages of this invention is that a crude MDI can be used, thus permitting quite significant savings. The prepolymer used is characterized in part by its quite high free isocyanate content, or FNCO, of preferably 20 to 27 weight percent. 
     One skilled in the art will recognize the foam formulations of this invention as being so extremely reactive as not to be processable in conventional processing equipment. Commercially available equipment that can be used to process these compositions include: Krauss-Maffei MK-164 PU40/PU80, Cannon H100-2, and Henneke HK-1000 and KK-500 metering machines. 
     Being so highly reactive, the foam systems of this invention dramatically reduce mold-occupancy times. For a similar system without the aromatic polyamine, in-mold cure times may be in the order of 2-3 minutes whereas with this invention times of 45 to 60 seconds are easily attainable. The cure times secured with the formulations of this invention are not possible in complex moldings using standard urethane catalysts such as tert-amines and organometallics. 
     DESCRIPTION 
     The following table presents an example of the formulation of this invention and gives the ranges of the proportions of ingredients that can be used in the practice of this invention. 
     
                                           Table 1__________________________________________________________________________(parts by weight)Polyol Blend    Broad Range                  Preferred Range                                 Example A__________________________________________________________________________Long chain polyol (1)           50 to 100                  70 to 90       84.92 (1a)Short chain alkane diol/           0 to 25 (2)                  10 to 20       16.13 (1,4 butane diol)triol #1 (2)Short chain alkane diol/           0 to 25 (2)                  0.10 to 20     0.92 (ethylene glycol)triol #2 (2)Aromatic polyamine (3)           1 to 6 3 to 4         3.52 (3)Catalyst #(4)   0.1 to 3.0                  0.8 to 1.6 (alkylene amine)                                 1.20 (DABCO)Catalyst #(5)   0.01 to 0.05                  0.015 to 0.030 (organometallic)                                 0.025 (dibutyl tin dilaurate)Carbon black    0 to 40                  0.01 to 1.0    0.020Gaseous blowing agent (6)           0 to 10                  3 to 8         7.0 (trichlorofluoromethane)Water (7)       0 to 0.15                  0 to 0.08      0.04Equivalent weight            --     --            232 ± 5PrepolymerIndex*          98 to 106                  100 to 104     100FMCO % (8)      20 to 27                  22 to 24       23__________________________________________________________________________Foam Properties:Free Rise Density, pcf          11 ± 2Molded Density 55 pcf, minTensile, psi   2000 minElongation, %  250 minTear, Die &#34;C&#34;, pli          400 minHardness (Shore A)          90 minFlexural Modulus, at RT, psi          19,000 minSag, inches at 250° F          0.75 max__________________________________________________________________________ *Index is the ratio of prepolymer-NCO groups used to polyol blend reactiv hydrogen groups or equivalent (usually -OH) × 100 pcf = pounds per cubic foot pli = pounds per linear inch psi = pounds per square inch (1) A polyol having a molecular weight in the range of 3000-6000, a functionality of 2-3, and an equivalent weight of 1500-3000 such as high molecular weight polyether diols, triols, and blends. Mobay&#39;s E-9207 was used in the example. Examples of other commercially available materials are: Jefferson 6500, Union Carbide NIAX 3128, Wyandotte P-38Q, Olin Poly GX 442 and Dow 4701. (2) The alkane diols and triols can have molecular weights of 62 to 250. Examples of such cross linkers/extenders are diethylene glycol, pentane diol, trimethyol propane, and 1, 2, 6 hexane triol. (3) The aromatic amine has the formula previously given. In the example, has a value of 0.3. It was Curithane 103, sold by Upjohn Co., Polymer Chemicals Division. (4) Examples of suitable known amine catalysts are: DABCO (triethylene diamine), N-ethylmorpholine, and TMBDA (tetramethyl-butane diamine). (5) Examples of suitable known organometallic catalysts are: dibutyltin dilaurate and diacetate, stannous octoate and tin mercaptides. (6) Blowing agents that can be used are: methylenechloride, nitrogen, and DuPOnt&#39;s Freon 11 and Freon 12. (7) Water may be used but may give rise to post blowing and paintability problems. (8) The prepolymer used in the example was 91.3 parts by weight of Mobay&#39; Mondur PF. Upjohn&#39;s PAPI 901-Polymeric can also be used. The prepolymer i made from a diol as in (2) above and an aromatic diisocyanate.   Notes: 
    
     (1) A polyol having a molecular weight in the range of 3000- 6000, a functionality of 2- 3, and an equivalent weight of 1500- 3000 such as high molecular weight polyether diols, triols, and blends. Mobay&#39;s E-9207 was used in the example. Examples of other commercially available materials are: Jefferson 6500, Union Carbide NIAX 3128, Wyandotte P-380, Olin Poly GX 442 and Dow 4701. 
     (2) The alkane diols and triols can have molecular weights of 62 to 250. Examples of such cross linkers/extenders are diethylene glycol, pentane diol, trimethyol propane, and 1, 2, 6 hexane triol. 
     (3) The aromatic amine has the formula previously given. In the example, n has a value of 0.3. It was Curithane 103, sold by Upjohn Co., Polymer Chemicals Division. 
     (4) Examples of suitable known amine catalysts are: DABCO (triethylene diamine), N-ethylmorpholine, and TMBDA (tetramethylbutane diamine). 
     (5) Examples of suitable known organometallic catalysts are: dibutyltin dilaurate and diacetate, stannous octoate and tin mercaptides. 
     (6) Blowing agents that can be used are: methylenechloride, nitrogen, and DuPont&#39;s Freon 11 and Freon 12. 
     (7) Water may be used but may give rise to post blowing and paintability problems. 
     (8) The prepolymer used in the example was 91.3 parts by weight of Mobay&#39;s Mondur PF. Upjohn&#39;s PAPI 901-Polymeric can also be used. The prepolymer is made from a diol as in (2) above and an aromatic diisocyanate. 
     Examples of commercially available aromatic diisocyanates are: Upjohn&#39;s Isonate 125M (pure MDI) and Isonate 143L (&#34;liquid&#34; MDI). 
     The example of the table is used to manufacture 1975 Vega 2 + 2 uppers and lowers using a Krauss-Maffei MK-164K mixhead. The impingement pressure was 2100 ± 50 psi; the throughput was 150 ± 2 pounds per minute and the shot time was 1.8 seconds minimum - 4.0 seconds maximum. The theoretical time for any one increment of foam from mixng to injection in the mold cavity was less than 0.01 seconds. The foam ingredients were maintained at about 90° F, the mold temperature was about 130° F, and the time to the mold surfaces as required. The demolded part was given a post cure at ambient temperature for 15 minutes. Thereafter, the part was primed, baked 15 minutes at 250° F, and painted. 
     Other automobile exterior trim parts that have been made with this formulation are: 1976 Chevrolet Monza front upper fascia, Corvette fascia, and 1976 Ford Mark V sight shield. 
     As a comparison, some Vega bumper fascia were manufactured commercially from a foam composition that was substantially identical to the one in the example except that the Curithane 103 was not used with the amount of isocyanate being less so that the Index was the same. This comparative foam has the same free rise density, molded density, tensile and tear, but its elongation was 300 percent, its flexural modulus was only 12,500 psi, and its sag was 1.4 max. 
     The example of the table was repeated with some variations in the proportions of the ingredients, as follows (parts by weight): 
     
         ______________________________________         B     C      D       E    F______________________________________Long chain polyol              84.9Short chain alkane diol #1     16.13Short chain alkane diol #2     0.93DABCO                          0.4Dibutyl tin dilaurate          0.025Carbon black                   0.02Blowing agent                  7.0Aromatic polyamine           3.525   4.0    4.5   5.0  5.5Prepolymer amount*           86      87     88    88.9 89.8______________________________________ *weight amount for a theoretical Index of 100; prepolymer FNCO was 23 percent. 
    
     All of these compositions were satisfactory for the purposes of this invention.