Patent Publication Number: US-4256158-A

Title: Pneumatic tire with puncture-sealing lining comprising a vulcanizable layer and a dispersed vulcanization component

Description:
The present invention relates to improvements in pneumatic tires containing means intended to assure the sealing of puncture holes. 
     The applicants&#39; studies and research have led to the development of complex linings forming at least a part of the covering of the cavity of the tire, in which complex linings there are superimposed sequentially a layer of a vulcanizable sealing mixture, a vulcanized elastomeric partition and a layer of a vulcanizing mixture capable of vulcanizing the vulcanizable sealing mixture, that is to say of cross-linking the quantity of vulcanizable sealing mixture which, under the influence of the escaping air, has penetrated into a puncture hole, in this way effecting a permanent repair of the puncture hole. 
     This automatic repair complex lining may have, separately or simultaneously, a number of drawbacks. It may, for example, operate only imperfectly when the tire is not at its operating temperature, namely upon the starting of the vehicle or after only a very brief run or in very cold weather. Furthermore, a drop in effectiveness of the complex lining with time can be noted. This drop is due to the migration of the cross-linking agents through the vulcanized elastomeric partition interposed between the vulcanizable sealing mixture and the vulcanizing mixture, but it may also be due to an increase in the viscosity of the products which slows down the flow of the products in the puncture hole and therefore slows down the cross-linking reaction. 
     The object of the present invention is to overcome these drawbacks by use of a simple lining. For this purpose, the pneumatic tire of the present invention has, between two vulcanized elastomeric partitions, a layer of a vulcanizable sealing mixture which extends at least in part over the inner wall of the tire. The tire is characterized by the fact that the layer of vulcanizable sealing mixture has a base of at least one vulcanizable elastomer of low molecular weight, preferably less than 30,000, contains at least one component of a vulcanization system for the vulcanizable elastomer and has an apparent viscosity of between 10 3  and 10 7  N/s/m 2  and preferably between 6×10 4  and 10 6  N/s/m 2  at 60° Celsius measured with a Weissenberg rheogoniometer at a shear velocity gradient of 10 -2  to 10°s -1  ; at least one other component which forms the vulcanization system with the component contained in the vulcanizable sealing mixture being contained in a dispersion within the cavity of the tire. 
     The vulcanization system is formed, as known per se, of at least one vulcanization and at least one vulcanization accelerator. Thus, one of said components of the vulcanization system is contained either in the vulcanizable sealing mixture or in the dispersion within the cavity of the tire, in accordance with the principle of the invention. 
     The vulcanizable sealing mixture preferably contains up to 75% by weight of a pulverulent or granular filler having a particle size less than 250 microns and/or of a fibrous filler formed of fibers having a length at least equal to 0.5 mm and a diameter between 0.005 and 0.040 mm. This filler increases the sealing power of the vulcanizable sealing mixture and makes it possible to regulate the viscosity thereof. 
     Either the vulcanization accelerator(s) or the vulcanization agent(s) can be placed in fluid dispersion, for example by spraying, within the cavity of the tire, after having been previously placed in suspension or in solution in a liquid. 
     However, there may also be used either granular particles of an ultra-light cellular material, such as those used as support lining of a safety tire in accordance with U.S. Pat. No. 4,003,419, or ultra-light very smooth gasfilled microspheres, such as those used as support lining of a safety tire in accordance with U.S. Pat. No. 4,037,636, the disclosures of which patents are incorporated by reference herein. At least some of the granular particles or spheres are at least partially coated with either the vulcanization agent or with the vulcanization accelerator in powdered state or contained in a suspension or solution, for example, in the lubricant, the carriers of which are the granular particles in accordance with U.S. Pat. No. 4,003,419. 
     In a third embodiment, there is used a liquid or gel in which the other component of the vulcanization system is placed in solution or suspension. This liquid or gel may be a lubricant present in sufficient amount within the cavity of the tire (in the absence of a support lining) to avoid damage to the tire when it travels with an inflation pressure which is less than normal pressure. 
     Variant embodiments of the invention are illustrated by the following examples: 
     EXAMPLE I: VULCANIZATION ACCELERATOR IN THE CAVITY OF THE TIRE 
     
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                         Parts                                            
                         by Weight                                        
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Vulcanizable Sealing Mixture:                                             
depolymerized natural rubber                                              
                           80                                             
polyisobutylene (average molecular                                        
                           20                                             
weight 15,000)                                                            
carbon black               125                                            
zinc oxide                 10                                             
Lubricant Containing the Vulcanization Accelerator:                       
silicone emulsion          65                                             
ethanol                    30                                             
synthetic oil having a base of ether                                      
                           5                                              
of polyglycols                                                            
quaternary ammonium (alkyldimethyl-                                       
                           300    ppm                                     
benzylammonium chloride)                                                  
sodium isopropylxanthate   5                                              
sulfur                     5                                              
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     EXAMPLE II: ONE OF THE COMPONENTS OF THE VULCANIZATION SYSTEM IN THE VULCANIZABLE SEALING MIXTURE 
     
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                    Parts                                                 
                    by Weight                                             
______________________________________                                    
Vulcanizable Sealing Mixture:                                             
polyisobutylene-isoprene copolymer                                        
                      100                                                 
 (average molecular weight 30,000)                                        
vulcanized rubber powder (particle size:                                  
                      180                                                 
 90% of particles of a diameter less than                                 
 160 microns)                                                             
manganese dioxide     10                                                  
cobalt naphthenate    1                                                   
Vulcanization Agent Contained in the                                      
Cavity of the Tire:                                                       
parabenzoquinone dioxime.                                                 
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     This vulcanization agent can be dispersed: 
     either on the surface of granular particles or spheres, at least partially coating them, 
     or in a lubricant used alone or in combination with granular particles or spheres. 
     Lubricant: 
     
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       water           50 cc                                              
       ethanol         30 cc                                              
       polyglycols     20 cc                                              
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     EXAMPLE III: GELATED LUBRICANT 
     
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                       Parts                                              
                       by Weight                                          
______________________________________                                    
Vulcanizable Sealing Mixture:                                             
1,2-polybutadiene (80%) of low molecular                                  
                         50                                               
weight (average molecular weight 30,000)                                  
polyisobutylene (average molecular weight                                 
                         50                                               
about 12,000)                                                             
carbon black             115                                              
zinc oxide               4                                                
phenol resin             10                                               
antioxidant              2                                                
Gelated Lubricant:                                                        
silicone emulsion        65                                               
ethanol                  30                                               
synthetic oil having a base of                                            
                         5                                                
ethers of polyglycols                                                     
quaternary ammonium(alkyldimethyl-                                        
                         300     ppm                                      
benzylammonium chloride)                                                  
sulfur                   6                                                
zinc isopropylxanthate   1                                                
diethylammonium diethyl dithiocarbamate                                   
                         3                                                
silica                   5                                                
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     The drawing shows diagrammatically, in meridian or transverse section in 
     FIG. 1, a tire 1 whose inner wall 2 is provided with a layer 3 of vulcanizable sealing mixture. 
     FIG. 2, the detail view, shown on a larger scale than in FIG. 1, is a portion of the tire included within the circle A. The layer 3 is covered with a vulcanized elastomeric partition 4 on the side of the cavity 5 of the tire 1. The layer 3 is compartmentalized by circumferential vulcanized elastomeric partitions 6 in order to prevent the vulcanizable sealing mixture from accumulating below the meridian zone of the crown under the effect of centrifugal force. The different forms of the dispersion of the vulcanization agent or vulcanization accelerator present in the cavity 5 of the tire 1 are indicated symbolically by the dots 7. This cavity 5 is closed by the rim 8 on which the tire 1 is mounted. 
     It is obvious that the layer 3 may extend either under the entire inner wall 2 or only over one or more portions thereof.