Patent Publication Number: US-4929664-A

Title: Crosslinkable silicone polymers with talc reinforcing agents having improved non-sag and modulus properties

Description:
FIELD OF THE INVENTION 
     The present invention relates to talc reinforcing agents for use in crosslinkable silicone sealant systems. The reinforcing agents result in improved non-sag characteristics while eliminating the need to use fumed silica in the system. The reinforcing agents further improve the modulus of the system. 
     BACKGROUND ART 
     Heretofore it has been known to use calcium carbonate as a bulkifying agent or filler in one and two-part silicone sealant systems. It is necessary in this case to add fumed silica to the system in order to achieve satisfactory sag characteristics of the system. However, the fumed silica may react with the silicone polymer, and further, may contribute significantly to the cost of the final product. In the present invention, talc is used as a replacement for calcium carbonate and fumed silica. The talc reinforcing agent achieves the desired non-sag characteristic and further results in improvement in the modulus of the sealant system. 
     SUMMARY OF THE INVENTION 
     It is therefore an aspect of the present invention to provide a reinforcing agent which eliminates the need for fumed silica and which gives the desired non-sag characteristic to the silicone sealant. The reinforcing agent of the present invention results in a sag measurement as measured by the Boeing Jig test of 0.08 inches, or more preferably 0.02 inches. It is a further advantage of the reinforcing agents of the present invention to increase the modulus of the silicone system. The reinforcing agents result in improvements of 25 and preferably 50 percent of the stress at 50 percent strain. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to a reinforcing agent for producing a one-part or a two-part silicone sealant system. The reinforcing agent is a platy talc which achieves a sag of 0.08, and preferably 0.02 inches as measured by the Boeing Jig Test (full). The reinforcing agents further result in an improvement in the stress at 50 percent strain of 25 percent, and preferably 50 percent. The reinforcing agent is added in an amount of 50 to 150, and preferably 75 to 125 parts by weight per 100 parts polymer. The need for fumed silica is eliminated by the use of the reinforcing agent in accordance with the invention. 
     The reinforcing agents of the present invention can be used with a one-part or a two-part silicone system. The one-component silicone system consists of a silicone polymer of the general formula ##STR1## where the polymer is hydroxy terminated and R 1  and R 2 , independently, are aliphatic or aromatic, and preferably alkyl C 1  to C 6 , or aryl or alkyl aryl C 6  to C 12 , and more preferably alkyl C 1  or C 2 , or aryl or alkyl aryl C 6  to C 8 . The integer n is a value such that the viscosity of the polymer should be from about 5,000 to about 500,000;  and more preferably from about 18,000 to about 350,000 centistokes. 
     A crosslinking agent is used and is preferably a neutral crosslinking agent as is known in the art. Such crosslinking agents include oximes and alcohols, with oximes being preferred. The oximes have the general formula ##STR2## wherein R 1  is aliphatic, aryl, or alkylaryl having from 1 to 12 carbon atoms; and preferably alkyl having from 1 to 6, or aryl or alkylaryl having from 6 to 12 carbon atoms; and most preferably vinyl or vinyl containing alkyl having from 1 to 6 carbon atoms; and R 2  and R 3  are the same or different, and are alkyl having from 1 to 6 carbon atoms, with alkyl having 1 to 2 carbon atoms preferred. The crosslinking agent is preferably methyltris (methylethylketoximino)silane. The crosslinking agent is used in an amount from 5 to 25, and preferably 15 to 20 parts by weight per 100 parts polymer. 
     A non-reactive silicone fluid is added of the formula: ##STR3## wherein R 1  and R 2  are defined as above, and R 6  is trialkyl substituted silyl, where each alkyl is individually alkyl C 1  to C 6 , trimethylsilyl is preferred. The integer n is a value such that the viscosity of the fluid is from 50 to 20,000 centistokes, and preferably 100 to 2,000 centistokes. The fluid is added in an amount of 10 to 100; and preferably 20 to 80 parts by weight per 100 parts polymer. 
     An adhesion promoter is added. Such promoters are known in the art and include silanes, titanates, alumina zirconate, aminofunctional siloxane, and the like, and preferably aminofunctional siloxane. The promoter is added in an amount of 0.1 to 5, and preferably 0.5 to 4 parts by weight per 100 parts polymer. 
     A catalyst is added. Such catalysts are known in the art and include dialkyltin dicarboxylates, stannous octoate, titanates, amines, and the like. Preferred catalysts include dialkyltin dicarboxylates. The catalyst is used in an amount of from about 0.01 to 3 and preferably from about 0.02 to 1 part by weight per 100 parts polymer. 
     A two-component sealant system includes a polymer-based system and a curative system. The base comprises a silicone polymer of the same formula given before and having a viscosity of from about 500 to about 500,000 centistokes, and more preferably from about 500 to about 350,000 centistokes. In general, the polymer used in a two-component system preferably has a viscosity of about 20,000 centistokes. It is further possible to use a lower viscosity polymer, including one having a viscosity below 500 centistokes and omitting the non-reactive fluid. This would of course depend on the application of a sealant system. 
     A non-reactive fluid is used as defined above and may be from about 0 to about 40, and preferably 0 to 20 parts by weight per 100 parts polymer. 
     The base could optionally include antisettling agents, and coloring agents as are known in the art. The talc reinforcing agent could be added to the base, the curative, or both. 
     The two-component system further includes a curative system having a curative such as ethylorthosilicate, ethylpolysilicate, acetoxysilicate, aminosiloxane, or oximinosilanes, in an amount sufficient to react with the polymer in the system. An adhesion promoter is added to the curative system and may include those adhesion promoters noted earlier, and preferably is aminofunctional silane. An adhesion promoter is used in an amount of from about 0.1 to about 5, and more preferably 0.5 to about 4 parts by weight per 100 parts polymer. Carbon black paste can be added to the curative so that the base and the cure will have different colors in order that thorough mixing is facilitated. The carbon black is in an amount from 0 to about 10 parts, and preferably from about 3 to about 8 parts by weight per 100 parts polymer. Optionally the curative may include non-reacting fluids, catalysts, talc (or filler). The reinforcing agents of the present invention may be added to the curative system or the base, or both, in a two-component system. It is customary to add filler to the curative to bulk out the curative to bring the volume to the appropriate proportion. The curative is generally added in a ratio of from 8 to 14 parts of base per one part curative. It is critical to add a sufficient amount of curative to get a quick snap time for the two-component system. 
     The reinforcing agent of the present invention may be added to the one-component or the two-component system. The reinforcing agent is a talc, notably a platy talc. The platy talc of the present invention achieves a sag of 0.08 or less, and preferably 0.02 inches or less, as measured by the Boeing Jig Test (full). The talc further achieves improvements in stress at 50 percent strain of at least 25, and preferably at least 50 percent as measured by ASTM D-412, die C. The talc used as the reinforcing agent has a mean particle size of less than 3 μm, and preferably from about 0.5 to about 3 μm, and most preferably from about 1 to about 2 μm. The talc should have a surface area of from about 10 to about 30 meter square per gram, and preferably from about 15 to about 17 meter square per gram as measured by BET, N 2 . The reinforcing agent is added in an amount from about 50 to about 150; and preferably from about 75 to about 125 parts by weight per 100 parts polymer. A preferred platy talc is Mistron Monomix sold by Cyprus Industrial Minerals Company. 
    
    
     EXAMPLE 1 
     The following recipes were mixed together by hand in a pint can: 
     
         ______________________________________                                    
A            B        C        D      E                                   
______________________________________                                    
Silicone                                                                  
        102      102      102    102    102                               
Polymer                                                                   
BLR-3   40 + 40                                                           
Dolocron 32-15   40 + 40                                                  
Mistron                   40 + 40                                         
Mist                                                                      
Ecca-Tex                         40 + 40                                  
10R (kaolin                                                               
china clay)                                                               
Mistron                                 40 + 40                           
Monomix                                                                   
______________________________________                                    
 
    
     The silicone polymer was a hydroxy terminated polydimethyl siloxane polymer of about 80,000 centistoke viscosity. 
     About 40 grams of the filler reinforcing agent was added to the polymer with the ingredients mixed by hand, and the viscosity was checked by appearance of the mixture. A further 40 grams of filler was added, and appearance was checked again. 
     
                       TABLE I                                                     
______________________________________                                    
APPEARANCE                                                                
SAMPLES                                                                   
FILLER A       B       C       D       E                                  
______________________________________                                    
40 Grams                                                                  
       Fluid   Fluid   Fluid   Poor    Viscous                            
       Shiny   Shiny   Shiny   Disperson                                  
                                       Some                               
                               Stiff   non-sag                            
80 Grams                                                                  
       Fluid   Fluid   Fair-Good                                          
                               Still poor                                 
                                       Very                               
       Shiny   Shiny   Non-Sag dispersion                                 
                                       Viscous                            
                       Matte   (pearls Excellent                          
                       Finish  don&#39;t break                                
                                       Non-Sag                            
                               up)                                        
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     The fillers are generally described as follows: BLR-3 is a trademark for surface treated calcium carbonate sold by Pleuss-Stauffer, Inc; Dolocron 32-15 is a trademark for magnesium calcium carbonate dolomite, sold by Pfizer, Inc.; Mistron Mist is a trademark for a platy talc having a surface area of 16±1 m 2/  g (N 2  Bet) sold by Cyprus Industrial Minerals Company; Ecca Tex 1OR is a trademark for a kaolin china clay bead sold by ECC America, Inc.; and Mistron Monomix is a trademark for a platy talc having a surface area of 16±1 m 2  g, (N 2  Bet), also sold by Cyprus Industrial Minerals Company. 
     This test shows that the platy talc, Mistron Mist, and Mistron Monomix result in an improved non-sag property as compared to the sample including calcium carbonate without fumed silica. 
     EXAMPLE 2 
     A compound was made using the same silicone polymer as used in Example I and using comparable ratios of filler. The polymer was compounded using an oxime crosslinker, an adhesion promoter, and a tin catalyst. Samples A and B, the two carbonate samples, were compounded using fumed silica while samples C and D did not have the silica. Sample A, the control, contained calcium carbonate and fumed silica. 
     Sample B was made replacing calcium carbonate with magnesium calcium carbonate dolomite, (Dolocron 32-15). Sample C was made replacing calcium carbonate and fumed silica with platy talc particles having an average particle size of 3.4 micrometers, Mistron Mist. Sample D was made replacing calcium carbonate and fumed silica with platy talc particles having an average particle size of 1.5 micrometers. 
     The flow characteristics as measured by the flow meter, ASTM No. D2452 with air pressure of 60 psig; values given are number of seconds to extrude 20 grams, and full Boeing Jig Test ASTM No. D2202, with the spacer removed so that the sealant plug is pushed completely out of the cavity, are set forth in the table below for each of the samples. 
     Strain, stress at 50 percent strain, stress at 100 percent strain, tensile strength, and elongation were determined by ASTM Test Method D-412, using die C. Tear Strength was determined according to ASTM D-624, die C. Sealant hardness was determined by ASTM C-661 (Shore A). Similar aging tests were performed with aging for four weeks at 120° F., 6 months at room temperature, and six months at 120° F. The results of these tests are set forth in Tables II and III. 
     
                       TABLE II                                                    
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DATA:                                                                     
                    Flow-                                                 
                    meter    Boeing                                       
         Aging,     60 psi,  Jig,  Skin Tack                              
         Time       104&#34;     Full  Over Free                              
Material @ Temp     Sec/20 g Inches                                       
                                   Time Time                              
______________________________________                                    
Filler   Initial    14.0     .06   23   75                                
Control  4 wks 120°  F.                                            
                    13.7     .05   22   76                                
With Silica                                                               
         6 mo. RT   12.8     .05   14   33                                
         6 mo. 120° F.                                             
                    11.4     .05   21   74                                
Dolocron Initial    14.4     .05   21   65                                
32-15    4 wks 120° F.                                             
                    14.3     .05   25   60                                
         6 mos. RT  13.7     .05   14   29                                
         6 mo. 120° F.                                             
                    13.0     .04   16   32                                
Mistron Mist                                                              
         Initial    24.5     .19   70   Over 120                          
         4 wks 120° F.                                             
                    23.9     .30   70   215                               
         6 mo. RT   24.8     .39   43   102                               
         6 mo. 120° F.                                             
                    261.2    .39   17   102                               
Mistron  Initial    30.8     .04   25   85                                
Monomix  4 wks 120° F.                                             
                    35.6     .07   32   90                                
         6 mo. RT   30.1     .09   16   34                                
         6 mo. 120° F.                                             
                    64.4     .06   28   83                                
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                                           TABLE III                               
__________________________________________________________________________
CURE STABILITY OF                                                         
FILLER MODIFICATIONS                                                      
            Stress                                                        
                Stress                                                    
                     Stress                                               
            @ 50%                                                         
                @ 100%                                                    
                     @ 150%                                               
                          Max.                                            
                              Elonga-                                     
                                   Tear                                   
                                      Shore                               
Sealant                                                                   
     Aging  Strain                                                        
                Strain                                                    
                     Strain                                               
                          Stress                                          
                              tion in pli                                 
                                      A                                   
__________________________________________________________________________
Filler                                                                    
     Initial                                                              
Control                                                                   
     Mean:  25.08                                                         
                40.94                                                     
                     51.32                                                
                          149.27                                          
                              745.0                                       
                                   29.35                                  
                                      23                                  
     Std Dev:                                                             
            .51 1.40 1.02 3.28                                            
                              12.25                                       
                                   .57                                    
     120° F. 4 wk                                                  
     Mean:  23.70                                                         
                37.99                                                     
                     48.05                                                
                          128.24                                          
                              705.0                                       
                                   26.46                                  
                                      24                                  
     Std Dev:                                                             
            2.56                                                          
                .98  .85  4.37                                            
                              10.0 .69                                    
     RT 6 mo.                                                             
     Mean:  30.07                                                         
                42.69                                                     
                     50.36                                                
                          127.06                                          
                              674.0                                       
                                   26.84                                  
                                      20                                  
     Std Dev:                                                             
            1.11                                                          
                .65  .78  4.77                                            
                              29.66                                       
                                   .67                                    
     120 ° F. 6 mo.                                                
     Mean:  25.54                                                         
                39.45                                                     
                     49.55                                                
                          123.89                                          
                              694.0                                       
                                   27.19                                  
                                      19                                  
     Std Dev:                                                             
            .54 .70  .42  3.85                                            
                              16.36                                       
                                   .41                                    
Dolocron                                                                  
     Initial                                                              
32-15                                                                     
     Mean:  26.95                                                         
                53.10                                                     
                     75.85                                                
                          159.18                                          
                              508.0                                       
                                   31.19                                  
                                      28                                  
     Std Dev:                                                             
            1.99                                                          
                1.78 1.97 3.25                                            
                              38.34                                       
                                   .65                                    
     120° F. 4 wk                                                  
     Mean:  26.60                                                         
                50.11                                                     
                     72.03                                                
                          146.91                                          
                              387.5                                       
                                   27.51                                  
                                      29                                  
     Std Dev:                                                             
            .77 1.10 2.55 2.10                                            
                              9.57 .65                                    
     RT 65 mo.                                                            
     Mean:  34.91                                                         
                57.32                                                     
                     80.02                                                
                          143.14                                          
                              410.0                                       
                                   29.97                                  
                                      24                                  
     Std Dev:                                                             
            .70 1.63 2.11 5.13                                            
                              42.13                                       
                                   .75                                    
     120° F. 6 mo.                                                 
     Mean:  30.96                                                         
                52.46                                                     
                     74.31                                                
                          142.68                                          
                              403.0                                       
                                   28.45                                  
                                      23                                  
     Std Dev:                                                             
            1.86                                                          
                1.74 2.45 1.13                                            
                              12.04                                       
                                   .54                                    
Mistron                                                                   
     Initial                                                              
Mist Mean:  32.39                                                         
                64.04                                                     
                     96.13                                                
                          184.53                                          
                              382.0                                       
                                   26.80                                  
                                      28                                  
     Std Dev:                                                             
            1.53                                                          
                2.48 3.03 .87 23.08                                       
                                   .78                                    
     120° F. 4 wk                                                  
     Mean:  29.45                                                         
                58.45                                                     
                     89.08                                                
                          157.28                                          
                              275.0                                       
                                   24.94                                  
                                      27                                  
     Std Dev:                                                             
            1.02                                                          
                .53  2.30 2.71                                            
                              5.77 .43                                    
     RT 6 mo.                                                             
     Mean:  32.21                                                         
                62.75                                                     
                     92.95                                                
                          159.44                                          
                              268.3                                       
                                   26.86                                  
                                      25                                  
     Std Dev:                                                             
            1.10                                                          
                1.77 4.49 6.49                                            
                              19.41                                       
                                   .43                                    
     120° F. 6 mo.                                                 
     Mean:  16.27                                                         
                32.83                                                     
                     51.41                                                
                          113.57                                          
                              326.7                                       
                                   19.09                                  
                                      16                                  
     Std Dev:                                                             
            .89 .96  1.44 3.82                                            
                              18.89                                       
                                   .45                                    
Mistron                                                                   
     Initial                                                              
Monomix                                                                   
     Mean:  40.86                                                         
                82.10                                                     
                     116.84                                               
                          216.71                                          
                              344.0                                       
                                   32.66                                  
                                      29                                  
     Std Dev:                                                             
            2.24                                                          
                1.79 3.00 5.20                                            
                              14.75                                       
                                   .69                                    
     120° F. 4 wk                                                  
     Mean:  37.95                                                         
                73.78                                                     
                     108.03                                               
                          168.32                                          
                              230.0                                       
                                   28.89                                  
                                      31                                  
     Std Dev:                                                             
            2.35                                                          
                2.40 2.20 7.63                                            
                              8.16 .94                                    
     RT 6 mo.                                                             
     Mean:  42.35                                                         
                78.25                                                     
                     112.94                                               
                          179.80                                          
                              263.3                                       
                                   31.81                                  
                                      29                                  
     Std Dev:                                                             
            2.35                                                          
                3.05 3.87 3.02                                            
                              12.11                                       
                                   .70                                    
     120° F. 6 mo.                                                 
     Mean:  39.60                                                         
                73.04                                                     
                     106.49                                               
                          167.93                                          
                              256.7                                       
                                   27.52                                  
                                      26                                  
     Std Dev:                                                             
            2.22                                                          
                3.39 3.84 4.66                                            
                              5.16 1.21                                   
__________________________________________________________________________
 
    
     The tests above show that the platy talc in accordance with the invention results in improvements in the modulus and in the sag characteristics and eliminates the need for fumed silica. 
     While in accordance with the Patent Statutes, the best mode and preferred embodiment has been set forth, the scope of the invention is not limited thereto, but rather by the scope of the attached claims.