Abstract:
Room-temperature-curable silicon-terminated organic sealant compositions having improved cure speeds, and metal and glass primer compositions for use therewith. These sealant compositions comprise a blend of a small amount of N-beta-aminoethyl, gamma - aminopropyl trimethoxy silane with an organosilicon-capped, isocyanate-terminated polyurethane polymer. The composition preferably further comprises a moisture-curing catalyst such as dibutyl tin diacetate.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to room-temperature-curable silicon terminated organic sealant compositions having improved cure speeds, and to metal and glass primer compositions for use therewith. This invention also relates to the use of such compositions as fast-curing sealants for vehicles and other uses. These sealants are especially useful for sealing glass to metal, such as to secure the windshield to an automobile body. 
     2. Description of the Prior Art 
     The relevent prior art is believed to be fully described in U.S. Pat. No. 3,632,557, the text of which is incorporated herein by reference. 
     That patent describes vulcanizable silicon-terminated organic polymers whose formula and preparation can be graphically described as follows: ##STR1## wherein R is a lower alkyl radical of from 1 to 6 carbon atoms; wherein R&#39; is a divalent bridging radical selected from the groups consisting of a divalent hydrocarbon radical, a divalent hydrocarbon ether radical and a divalent hydrocarbon amino radical; and wherein Z is a member selected from the group consisting of -S and -NR&#34;, where R&#34; is H or a lower alkyl radical of from 1 to 6 carbon atoms. 
     Applicants have found that these polymers have the disadvantage that they lack the curing speed required in automotive windshield sealant applications. 
     SUMMARY OF THE INVENTION 
     Applicants have found that, by blending a small amount of N-beta aminoethyl, gamma aminopropyl trimethoxy silane with the above-described prior art vulcanizable polymers, they obtain a sealant composition having outstanding cure speed. Amounts from about 0.5 to about 2.0%, based on the weight of the polymer, have been found to be particularly effective. 
     As an example of the cure rate required for automotive windshield sealants, one of the large auto companies requires a cleavage strength of at least 56 pounds/in 2  within 6 hours after the sealant is put in place. Use of the compositions disclosed in the above-mentioned U.S. patent have resulted in cure rates of 14 - 30 pounds within 6 hours, typically about 25 pounds. By contrast the sealants of the present invention have demonstrated 56 lbs/in 2  cleavage at 31/2 hours curing time. The cleavage test used is described in the Appendix. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Applicants have found that particularly good results are obtained when the organosilicon compound used in the formula on page 2 to cap the polymer is gamma aminopropyl trimethoxy silane and also when the amount of silanol curing catalyst used in the sealant composition does not exceed 0.1% based on the polymer weight. The preferred silanol condensation curing catalyst is dibutyltin diacetate. Amounts of N-beta aminoethyl gamma aminopropyl trimethoxy silane from about 0.5 to about 2.0%, based on the weight of the polymer, have been found to be required to meet the particularly demanding specifications of automotive windshield sealants, which are as follows: 
     
         ______________________________________Curing Speed    at least 56 lbs/in.sup.2 cleavage           at 6 hours after applicationAdhesion        excellent adhesion retention           after prolonged weatheringOdor            no objectionable odorViscosity (before andafter six months aging)           K value in the range of           450-850Slump           freedom from slumpHardness        Shore &#34;A&#34; Durometer reading           of less than 65______________________________________ 
    
     Description of the various tests for these specifications are set forth in the Appendix. 
     The manner of preparing a typical sealant composition of this invention is set forth in the following examples. 
     EXAMPLE 1 
     A polymer of the type described in U.S. Pat. No. 3,632,557 was prepared as follows: 
     
         ______________________________________A.   Niax PPG2025 ONE         2001.00 g(2000 Molecular Weight PolyetherDiol from Union Carbide Corporation)Hylene TM                204.00(80:20 Grade Toluene Diisocyanatefrom DuPont)Glacial Acetic Acid      0.55Dibutyltin Diacetate     0.45B.   Anhydrous Toluene        110.00C.   Anhydrous Toluene        81.00Silane A1110(gamma aminopropyl trimethoxysilane from Union Carbide Corp)                         68.30D.   Anhydrous Methanol       273.00                         2738.30 g______________________________________ 
    
     A was heated to 155°F under anhydrous conditions and maintained at that temperature for 55 minutes, at the end of which time B was added. Over the next 45 minutes the temperature was gradually reduced to 105°F. Heating was continued at about 105°F for the next 2.25 hours, at the end of which time C was added. Over the next 2.25 hours, the temperature was maintained in the range of 150°-165°F, checking for NCO until none was found. The resultant material was refluxed with D for a short time and then allowed to foam to achieve deaeration, and finally cooled. 
     EXAMPLE 2 
     A sealant was prepared as follows: 
     
         __________________________________________________________________________              Parts by                    Percent Based              Weight                    on Polymer Weight__________________________________________________________________________Polymer of Example 1              106.00                    --Carbon black (anhydrous)              40.00 37.74%Thixseal A         1.55  1.46Dibutyltin diacetate (DBTDA)              0.10  0.09N-beta aminoethyl, gamma amino- propyl tirmethoxy silane (A1120)              1.00  0.94              148.65__________________________________________________________________________ 
    
     The polymer of Example 1 and the Thixseal A (a rheology modifier from the Baker Castor Oil Co. comprising a mixture of about 58% castor wax and 42% asbestos) were added to a double planetary mixer and mixed for 3 - 4 minutes. The DBTDA was then added and mixed for 3 - 5 minutes. Then the trimethoxysilane compound was added and mixed for about 5 minutes. Finally the carbon black was added and the resultant mixture was mixed for 3/4 - 1 hour at a reduced pressure of 15 inches of mercury. All additions were carried out under anhydrous conditions. The resultant sealant was allowed to cool for 10-15 minutes, still under reduced pressure. The pressure seal was then broken and the sealant was packaged under anhydrous conditions. 
     The following properties were obtained by testing representative examples of sealants made according to Example 2. 
     
         ______________________________________Curing Speed   56 lbs/in.sup.2 at 31/2 hoursAdhesion       excellent adhesion after 1500 hrs.          Weatherometer at 190 degrees F.Odor           No objectionable odorViscosity (K value)          fresh 624  aged 30 days 660(aging at 95 degrees F)          aged 6 mos.                     718Slump          No slumpHardness       63______________________________________ 
    
     Although the sealant of this invention exhibits sealant and adhesive properties under normal conditions, in order to achieve the outstanding properties set forth above for automotive windshield use it is necessary to employ the glass and metal primers described below. 
     
         ______________________________________Glass Primer        Percent by Weight______________________________________Chlorinated Rubber    5 - 35%Carbon Black (furnace type)                 2 - 20Silane A1120 (See Ex. 2)                 0.1 - 2.0Tinuvin 327           0.1 - 2.0(2-(3&#39;,5&#39;-ditert-butyl-2&#39;-hydroxyphenyl)-5 chlorobenzotriazolefrom Ciba-Geigy)Conventional anhydrous solvent forchlorinated rubber   20 - 80Conventional plasticizer forchlorinated rubber   25 - 200% of amount                          of chlor-                          inated                          rubber used______________________________________ 
    
     The chlorinated rubber used in the glass primer should be a 5,000 - 20,000 molecular weight rubber having a 64-65% chlorine content. The chemistry and molecular structure of such rubbers is described in Treatise In Coatings, Vol. 1, Part 1 by Myers and Long (Dekker, 1967). Such rubbers can be obtained from ICI, for example Alloprene X-20, and Hercules (Parlon). Viscosity grades such as 5, 10, 20 or 125 can be used but grade 20 is preferred. 
     Conventional anhydrous aromatic hydrocarbon solvents for chlorinated rubber can be employed as solvent in the glass primer. The solvent employed must be anhydrous or the silane will be hydrolyzed and ruined. 
     The plasticizer employed in the glass primer should be selected from the group of polymeric polyester plasticizers which are compatible with chlorinated rubber. That group will be familiar to those skilled in the art. Paraplex G-56, a polymeric polyester plasticizer from Rohm &amp; Haas, is preferred. 
     The preferred glass primer composition is: 
     
         ______________________________________              Weight Percent Range______________________________________Alloprene X-20 chlorinated rubber                 15 - 20%Paraplex G-56 plasticizer                15 - 20Sterling R carbon black                 4 - 10Silane A-1120        0.5 - 1.0Tinuvin 327 U.V. screening agent                1 - 2Anhydrous toluene    50 - 60                100%______________________________________ 
    
     Metal Primer - for Acrylic Lacquered Steel 
     The metal primer is broadly the same as the broad glass primer composition, but with the following exceptions: 
     1. omit the U. V. screening agent, 
     2. as plasticizer, a conventional monomeric plasticizer for chlorinated rubber, such as diisodecyl phthalate, is preferred. However, the class of polymeric plasticizers described for the glass primer may also be used. 
     The preferred metal primer composition is: 
     
         ______________________________________              Weight Percent Range______________________________________Alloprene X-20 chlorinated rubber                 16 - 23%Diisodecyl phthalate plasticizer                 5 - 15Sterling R carbon black                2 - 5Silane A-1120        0.5 - 1.0Anhydrous toluene    60 - 70                100%______________________________________ 
    
     The normal manner of use of the primers and sealant is to brush the glass primer on the perimeter of the windshield, air dry it for a few minutes and then deposit a bead of the sealant on the primed area. The acrylic lacquered body steel is also primed by brushing on the metal primer and allowing it to air dry for a few minutes. The sealant bead on the windshield is then firmly pressed against the body steel. 
     The adhesive properties of the sealant of this invention applied as described have proved to contribute substantially to the strength (resistance to crushing) of the roof of the automobiles on which they are used. 
     The effect of various amounts of N-beta aminoethyl, gamma aminopropyl trimethoxy silane (A-1120) on the cure speed and strength of the sealant of Example 2 is shown in the table below. 
     
         ______________________________________Weight Percent A-1120            Elapsed Time(based on polymer weight)            3.5 hours    48 hours______________________________________0                 5 psi cleavage                         200 psi0.5              58           2911.0              60           3261.7              62           3932.0              60           390______________________________________ 
    
     The sealant of this invention may also contain conventional sealant additives such as fillers, reinforcers, rheology modifiers and ultraviolet light screening compounds. The carbon black of the examples of this application, although not necessary to the broad concept of this invention, is necessary to achieve the particular viscosity, slump and hardness properties required for the automotive windshield uses mentioned herein. Similarly, the Thixseal A rheology modifier, although not necessary to the broad invention, is necessary to provide the particularly demanding slump and viscosity properties of windshield sealants. Determination of effective amounts of these materials to achieve the desired properties will be within the skill of those skilled in the art. 
     It has been found that when the silanol condensation catalyst, such as dibutyl tin diacetate is employed in amounts greater than 0.1%, based on the polymer weight, the adhesive properties of the sealant suffer degradation upon aging. 
     Use of the closely related material gamma aminopropyl trimethoxy silane (A-1110) in place of A-1120 has resulted in very significantly longer cure times. For example, the time required to reach 56 lbs/in 2  was 8 hours using A-1110 versus 31/4 hours with A-1120. 
     When the preferred polymer capping organosilicon (gamma aminopropyl trimethoxy silane) is used in the reaction on page 2, 
     R is CH 3   
     R&#39; is C 3  H 6  and 
     Z is NH. 
     Although this specification has largely concerned itself with achieving the demanding properties required for automotive windshield sealants, those skilled in the art will appreciate that sealants for less demanding applications can be made outside the ranges specified herein. 
     APPENDIX 
     Test Methods 
     Cure Rate (Cleavage) 
     a 4 × 1/4 inch bead is extruded on one primed, acrylic lacquered plate. Then another plate is placed on top. The plates are pulled in a plane perpendicular to the plane of the bead. 
     Viscosity 
     Viscosity is determined by timing the flow of 20 gms. of sealant through a 0.104 inch orifice at 60 psi pressure, and again at 30 psi pressure, and inserting the two values thus obtained into the equation for K value: 
     K = P × t n  where ##EQU1## 
     Slump or Sag Characteristics 
     A 1/4 × 1/4 inch cross section sealant bead is applied to a glass plate and allowed to cure in the vertical plane. The sealant should not move downward or &#34;slump&#34; or &#34;sag&#34; but rather should remain in the original position. 
     Hardness 
     Hardness of the cured sealant is measured by a Shore &#34;A&#34;-2 Durometer.