Rubber-laminated material for gaskets
BACKGROUND OF THE INVENTION 
     The present invention relates to a material for gaskets in which a rubber layer is laminated on a one or each of opposite surfaces of a metal plate, and the gasket produced from the material has an advantage in that it is excellent in adhesion to fluids (an antifreeze and hot water) to be used in an engine cooling system of a car so that no layer separation is cause. 
     A rubber-laminated material for gaskets is formed in such a manner that a metal substrate formed, for example, of a carbon steel plate, a stainless steel plate, an aluminum alloy plate, a plated steel plate, or the like is coated with rubber and formed into a sheet. The thus obtained material is punched into predetermined shapes so as to be used as gaskets for various equipment. 
     FIG. 1 is a section showing the conventional rubber-laminated material for gaskets. The process of producing the illustrated material for gaskets will be described in the order of steps or producing. A substrate steel plate 1 is alkali-degreased, surface-roughed with a shot blast or a Scotch brush, and then phosphate-treated, so that chemical conversion treated layers 2 are formed. Chromic acid treatment is sometimes performed as the chemical conversion treatment for an aluminum alloy plate. Thereafter, coating of a primer mainly containing phenol resin (pure phenol resin or denatured phenol resin such as cresol denatured phenol resin or cashew denatured phenol resin) is performed to thereby form primer layers 3. Then, each of the primer layers 3 is coated to a predetermined thickness with a rubber solution prepared in such a manner that a carbon reinforcing filler, a generally-used vulcanizing agent, and an additive are added to nitrile rubber and the nitrile rubber is dissolved in toluene, an ester group solvent, and a ketone group solvent, and the rubber solution is dried and vulcanized, so that a rubber layer 4 is formed. The rubber layer 4 is coated, in accordance with a use condition of a gasket, with dispersion such as graphite, molybdenum disulfide, or the like, so that a non-adhesive layer 5 is formed. (Up to here, refer to the specification of U.S. Pat. No. 2,957,784.) 
     In the foregoing conventional rubber-laminated gasket, however, there has been caused a problem in that in the case of using the gasket in an engine cooling system of a car, the primer layers 3 of phenol group resin are invaded by an antifreeze or hot water so that the rubber layers 4 are separated from the metal 1, while the oil resistance and the Freon resistance are sufficient in the case of using the gasket in a refrigerator compressor. 
     The following five points are considered to be the reasons of the layer separation. 
     (I) Since a hydroxyl group (--OH) and a methylol group (--CH 2  OH) of phenol resin which are the principal components of the primer layers 3 are hydrophilic, hot water penetrates into the primer layers 3 and the adhesion surfaces to thereby cause swelling of the phenol resin and reduction of the adhesive force of the surface, so that the separation is caused. 
     (II) Weak acid phenol resin is reaction-decomposed by an alkali rust preventive (an amine group or a phosphate) contained in an antifreeze, so that the separation is caused. 
     (III) Pores are formed in the rubber layers 4 by solvent vapor or a vulcanized gas generated when the rubber layers 4 are formed. Hot water or an antifreeze penetrates into the pores to thereby accelerate the reasons I and III. 
     (IV) Since the chemical conversion treated layers 2 are porous, water molecules are arranged or a moist metallic salt is formed on the metal surface to break the adhesion force between the metal and the primer. 
     (V) An anode-cathode reaction (an electrochemical reaction) is caused between a metal surface of a gasket end portion formed by punching and the porous, chemical conversion treated layers to thereby generate a hydrogen gas on the chemical conversion treated surface at the cathode side, so that the separation is caused. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a rubber-laminated material for gaskets in which in the case of using the gasket in an engine cooling system of a car or the like, separation of rubber layers from a metal substrate due to fluids (hot water and an antifreeze) of the cooling system is not caused and therefore no leakage of the fluids through the gasket is caused. 
     Another object of the present invention is to provide a rubber-laminated material for gaskets in which chemical conversion treated layers having high adhesion to primer layers of phenol group resin are provided. 
     The rubber-laminated material for gaskets according to the present invention has features in that a layer subjected to chromium sealing treatment with a chromic (III) acid or a chromic (VII) acid (particularly, two layers, one being a phosphate (zinc phosphate, iron phosphate) treated layer, the other being a chromium sealing treated layer) is formed on a chemical conversion treated surface of a metal plate, in that a rubber layer laminated on a one surface or each of opposite surfaces is composed of nitrile rubber (particularly, nitrile rubber containing wax having a water repellency effect), and in that a primer layer interposed between the metal plate and the rubber layer is composed of high-reactive xylene denatured phenol resin (particularly, high-reactive xylene denatured phenol resin and epoxy resin) having an oxymethylene group or an acetal group. By the foregoing features and combination thereof, the orientation of water molecules onto the metal surface is prevented, the rust preventing force is improved, the penetration of hot water and an antifreeze from the rubber layer is suppressed, the antifreeze resistance, the hot water resistance, and the like of a primer are improved, so that the foregoing problems in the prior are solved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a section showing the conventional rubber-laminated material for gaskets; and 
     FIG. 2 is a section showing the rubber-laminated material for gaskets according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The configuration, operation and effects of the present invention will be described in detail hereunder with reference to examples of the present invention. 
     EXAMPLE 1 
     FIG. 2 is a section showing the rubber-laminated material for gaskets according to the present invention. 
     The process of producing the illustrated material for gaskets will be described in the order of steps of producing. First, a steel plate cold-rolled in cut length (SPCC) 11 having a thickness of 0.25 mm is prepared. The surfaces of the steel plate are treated with an alkali group degreaser, and roughed with a Scotch bright. Next, iron phosphate treatment is performed and a chromium sealing layer 13 is further formed on each of the porous, iron phosphate treated layers 12 under the condition that a treatment temperature is 65° C., a process time is 5 seconds and an amount of chromium adhesion is 10 mg/m 2 , so that a rust prevention, chemical conversion treated coating is formed. 
     Next, 11 weight percent of high-reactive xylene denatured phenol, 2.6 weight percent of phenol novolac epoxy resin, and 6 weight percent of an primer NBR rubber compound having a composition as showing in Table 1 are dissolved into 80.4 weight percent of a mixture solvent of methyl ethyl ketone and methyl isobutyl ketone at a ratio of 9:1 to thereby prepare a primer. The opposite surfaces of the treated steel plate are coated with the primer by use of a reverse roll coater, and heated in an oven at 160°-170° C. for about 2-4 minutes, so that primer layers 14 each having a thickness of 5 μm are formed on the opposite surfaces. 
     Next, 40 weight percent of NBR rubber compound for laminate having a composition as shown in Table 1 is dissolved into 60 weight percent OF mixture solvent of toluene and propyl acetate at a ratio of 3:1 to thereby prepare rubber solution for laminate. The primer layers 14 are coated with the rubber solution by using a roll coater or a knife coater, dried at 60°-100° C. for 20 minutes so that the solvent is volatilized, and then coated with graphite dispersion. Then, the thus treated primer layers 14 are vulcanized at 180°-200° C. for 10-20 minutes, so that rubber layers 15 and non-adhesive layers 16 are formed on the opposite surfaces respectively so as to have a thickness of 50 μm on each surface. Thus, a rubber-laminated material for gaskets having the whole thickness of 0.35 mm was obtained. 
     
                       TABLE 1                                                     
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            NBR          (Unit: PHR)                                      
            rubber compound                                               
                         NBR rubber compound                              
Composition for primer   for rubber layer                                 
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nitrile rubber                                                            
            100          100                                              
hydrozincite                                                              
             3-10         5-15                                            
stearic acid                                                              
            0.3-1.0      0.5-1.0                                          
carbon      100-150      100-150                                          
coumarone-indene                                                          
            20-60        0-5                                              
resin                                                                     
aging inhibitor                                                           
             0-5         5-8                                              
plasticizer --           10-20                                            
retarder    --           1-2                                              
wax         --            5-10                                            
sulfur      0.5-4        0.5-4                                            
vulcanization                                                             
            --           2-6                                              
accelerator                                                               
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     EXAMPLES 2-6 
     Rubber-laminated materials for gaskets were obtained under the producing conditions of Table 2 in the same manner as in Example 1. 
     
                                           TABLE 2                                 
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                Embodiments                         Comparative           
Example         1     2     3     4     5     6     Example               
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kind of metal plate                                                       
                SPCC  SPCC  SUS   SUS   aluminum                          
                                              aluminum                    
                                                    SPCC                  
thickness of metal plate (mm)                                             
                 0.25  0.25  0.20  0.20  0.6   0.6   0.25                 
surface roughing method                                                   
                Scotch                                                    
                      Scotch                                              
                            Scotch                                        
                                  Scotch                                  
                                        --    --    Scotch                
                bright                                                    
                      bright                                              
                            bright                                        
                                  bright            bright                
degreasing method                                                         
                alkali                                                    
                      alkali                                              
                            alkali                                        
                                  alkali            alkali                
                degrease                                                  
                      degrease                                            
                            degrease                                      
                                  degrease          degrease              
chemical conversion                                                       
                ion   ion   --    --    chromic                           
                                              chromic                     
                                                    ion                   
treatment method                                                          
                phosphate                                                 
                      phosphate         acid  acid  phosphate treatment   
                treatment                                                 
                      treatment         treatment                         
                                              treatment                   
                                                    chromium sealing      
primer components (weight %)                                              
high-reactive xylene                                                      
                11    11    11    11    11    11    --                    
denatured phenol resin                                                    
phenol novolac epoxy resin                                                
                 2.6  --     2.6  --     2.6  --    --                    
pure phenol resin                                                         
                --    --    --    --    --    --    11                    
rubber for primer                                                         
                 6     6     6     6     6     6     6                    
(composition: see Table 1)                                                
solvent         80.4  83    80.4  83    80.4  83    83                    
rubber layer thickness (μm)                                            
                50    50    30    30    30    30    50                    
(composition: see Table 1)                                                
non-adhesive layer                                                        
                graphite                                                  
                      graphite                                            
                            graphite                                      
                                  graphite                                
                                        graphite                          
                                              graphite                    
                                                    graphite              
whole thickness (mm)                                                      
                 0.35  0.35  0.26  0.26  0.66  0.66  0.35                 
lattice pattern cutting test                                              
spiral scorling test                                                      
antifreeze resistance                                                     
                100/100                                                   
                      100/100                                             
                            100/100                                       
                                  100/100                                 
                                        100/100                           
                                              100/100                     
                                                    0/100                 
(120° C. × 168 hours)                                        
hot water resistance                                                      
                no    no    no    no    no    no    separation between    
(95° C. × 72 hours)                                          
                separation                                                
                      separation                                          
                            separation                                    
                                  separation                              
                                        separation                        
                                              separation                  
                                                    surface blister and   
                                                    primer                
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                                                    metal                 
 
    
     The operation and effects of the present invention related to the Examples 1-6 are as follows. 
     First, the operation and effects (a) through (d) are generated by using high-reactive xylene denatured phenol as the principal component of the primer. 
     (a) Since the high-reactive xylene denatured phenol has less number of hydrophilic functional groups and hydroxyl groups compared with the conventional pure phenol resin (the same applies to the denatured phenol resin such as cashew denatured phenol resin, cresol denatured phenol resin, or the like), the hot water resistance and the alkali resistance have been improved. 
     (b) The high-reactive xylene denatured phenol is weak alkali because an alkali catalyst is used as synthetic catalyst. Therefore, the durability against antifreeze property (the alkalinity) added with an alkali rust preventive has been improved. 
     (c) Since an oxymethylene group or an acetal group has been led as the molecular end and binding group in the high-reactive xylene denatured phenol, the cross-linking density has been increased in comparison with the conventional denatured phenol resin. Therefore, the hot water resistance and the alkali resistance have been improved. 
     (d) In the high-reactive xylene denatured phenol, it is preferable to remove, through refining, a cross-linking preventing component, non-reactive phenol which is a hydrophilic component, a low-melting point component and an amine compound are generated at the time of resin synthesis. As a result, the resin cross-linking density is increased to thereby prevent hot water and an antifreeze from penetrating into the resin. 
     Thus, there is one subject of the present invention in that the hot water resistance and the antifreeze resistance are improved by using special high-reactive xylene denature phenol resin as the principal component of the primer in place of the conventional phenol group resin. 
     Second, while water repellency wax has been conventionally used as an ozone deterioration inhibitor, the wax is used to fill pores generated in the rubber layers in drying and vulcanization of rubber to thereby prevent hot water and an antifreeze from penetrating into the primer layers and the adhesion surfaces to thereby improve the adhesion. As the wax, it is preferable to use wax in which isoparaffin wax is richly contained so that the mixing ratio of normal paraffin wax to isoparaffin wax is selected to be within a range of 20-40: 80-60 and in which the bloom speed into the rubber surface is low. It is suitable to select the quantity of addition to rubber to be 5 phr-10 phr. The penetration prevention effect is reduced if the quantity of addition is smaller than 5 phr, and on the contrary the adhesion in the normal state is reduced if the quantity of addition exceeds 10 phr. 
     Third, by the chromium sealing, the rust prevention effect on the porous phosphate group treated surfaces is improved, formation of moisture and a moist salt on the metal surface is prevented, and an electrochemical reaction is suppressed, so that separation between rubber and metal is prevented. 
     Fourth, since epoxy resin is neutral, the durability against an alkali antifreeze and water is excellent. The antifreeze resistance and the hot water resistance of the primer mainly containing high-reactive xylene denatured phenol have been further improved by addition of epoxy resin to the primer. 
     It is suitable to select the quantity of addition of epoxy resin to be 2.0-3.0 weight percent. The effect on the antifreeze resistance and hot water resistance is reduced if the quantity of addition is made smaller than 2.0 weight percent, and, on the contrary, the adhesion between the rubber layer and the primer layer is reduced if the quantity of addition is made larger than 3.0 weight percent. 
     There is the other subject of the present invention in that the geometric effect upon the hot water resistance and the anti-freeze resistance is generated by combining the foregoing first, second, third, and fourth operations. 
     EXAMPLES 7-9 
     To perform the phosphate treatment and the chromium sealing treatment (processing liquid temperature: 50° to 85° C., processing time: 3 to 40 seconds, and adhesion amount: 2 to 200  mg/cm 2 ) as the chemical conversion treatment as shown in Examples 7-9 of Table 3 is effective also in the case of using phenol group resin in place of high-reactive xylene denatured phenol resin as the principal component of the primer. That is, not only the orientation of moisture and mist salts on the metal surface is prevented but an electrochemical reaction is suppressed, so that separation of the primer layers due to hot water is improved. 
     
                                           TABLE 3                                 
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               Embodiments          Comparative                           
Example        7      8      9      example                               
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kind of metal plate                                                       
               SPCC   SPCC   SPCC   SPCC                                  
thickness of metal plate (mm)                                             
                0.25   0.25   0.25   0.25                                 
surface roughing method                                                   
               Scotch Scotch Scotch Scotch                                
               bright bright bright bright                                
degreasing method                                                         
               alkali alkali alkali alkali                                
               degrease                                                   
                      degrease                                            
                             degrease                                     
                                    degrease                              
chemical conversion                                                       
               ion    ion    zinc   ion                                   
treatment method                                                          
               phosphate                                                  
                      phosphate                                           
                             phosphate                                    
                                    phosphate                             
               treatment                                                  
                      treatment                                           
                             treatment                                    
                                    treatment                             
               chromic                                                    
                      chromic                                             
                             chromic                                      
               sealing                                                    
                      sealing                                             
                             sealing                                      
primer components (weight %)                                              
pure phenol resin                                                         
               11     --     --     11                                    
high-reactive xylene                                                      
               --     11     11     --                                    
denatured phenol resin                                                    
rubber for primer                                                         
                6      6      6      6                                    
(composition: see Table 1)                                                
solvent        83     83     83     83                                    
rubber layer thickness (μm)                                            
               50     50     50     50                                    
(composition: see Table 1)                                                
non-adhesive layer                                                        
               graphite                                                   
                      graphite                                            
                             graphite                                     
                                    graphite                              
whole thickness (mm)                                                      
                0.35   0.35   0.35   0.35                                 
spiral scorling test                                                      
(hot water resistance)                                                    
condition (95° C. × 168 hours)                               
               no separation                                              
                      no separation                                       
                             no separation                                
                                    separation between surface            
                                    blister and primer metal              
condition (95° C. × 500 hours)                               
               no separation                                              
                      no separation                                       
                             no separation                                
                                    separation between surface            
                                    blister and primer metal              
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