Polyester coating compositions and precoated steel sheet using same
BACKGROUND OF THE INVENTION 
     This invention relates to a polyester coating composition and steel sheets precoated with the same. 
     Polyester coating compositions containing a polyester polymer and a crosslinker such as melamine resins or blocked polyisocyanates have been widely used in precoated sheet metals, automobiles and other industrial applications. For use in precoated sheet metals for indoor and outdoor uses as parts of household electrical appliances, building construction and the like in particular, the coating compositions must give a finish which is excellent not only in hardness and machinability but also in blot-proofness and luster. Heretofore, these properties have been controlled by suitably selecting the glass transition temperature (Tg), molecular weight (MW), monomer proportions, functionality and other parameters of polyester resins. However, none of prior art attempts have succeeded in providing a coating composition which satisfies with all of the above requirements, namely excellent hardness and machinability at low temperatures in particular as well as blot-proofness and luster. 
     It is, therefore, an object of the present invention to provide a polyester coating composition for use in precoated sheet metals, automobiles and other industrial applications which is excellent not only in hardness and machinability but also in blot-proofness luster and/or anti-press impression and anti-chemical properties. 
     It is another object of the present invention to provide a precoated steel sheets having a coating of the above composition. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, there is provided a polyester coating composition comprising: 
     (A) 50 to 95 parts by weight as solids of a polyester resin produced by reacting a polybasic acid component containing 0 to 85 mole % of the total acid component of an aromatic dicarboxylic acid, and a polyhydric alcohol component containing 20 to 100 mole % of the total alcohol component of a bisphenol S-alkylene oxide adduct of the formula: ##STR2##  wherein R is H or methyl, n and m are each an integer from 1 to 8, and 0 to 30 mole % of the total alcohol component of a branched chain-aliphatic glycol; and 
     (B) 50 to 5 parts by weight as solids of an aminoplast resin and/or a blocked polyisocyanate. 
     In another aspect of the present invention, there is provided a precoated steel sheet having a coating thereon formed by applying and baking the above coating composition. 
     DETAILED DISCUSSION 
     As is well-known in the art, polyester resins are a polycondensate of a polybasic acid component and polyhydric alcohol component. 
     Examples of polybasic acids includes aromatic dicarboxylic acids and anhydrides such as terephthalic acid, isophthalic acid, phthalic acid and its anhydride, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid and the like. Aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid may also be used. A small proportion of lactones such as γ-butyrolactone, and ε-caprolactone, hydroxycarboxylic acids corresponding to these lactones, aromatic hydroxycarboxylic acid such as p-hydroxybenzoic acid and p-hydroxyethoxybenzoic acid, and tri- or tetracarboxylic acids such as trimellitic acid, trimesic acid and pyromellitic acid may be incorporated to the acid component. 
     According to the present invention, the proportion of the first mentioned aromatic dicarboxylic acids in the total acid component should not be greater than 85  mole %. In other words, 15 to 100 mole % of the total acid component is occupied by other polybasic carboxylic acids. Advantageously, the acid component consists of 70 to 85 mole % of terephthalic acid and/or isophthalic acid and the balance of polybasic carboxylic acids other than aromatic dicarboxylic acids. This results in a coating film having excellent anti-press impression and anti-chemical properties. Excessive proportions of aromatic dicarboxylic acid in the total acid component will decrease the flexibity of films coated on sheet metals. 
     The alcohol component used in the synthesis of polyester resins of this invention consists of 20 to 100 moles %, preferably 40 to 90 mole % of a bisphenol S-alkylene oxide adduct as defined above. Examples of other polyhydric alcohols which may optionally be used include branched chain-aliphatic glycols such as 1,2-propanediol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,4-pentanediol, 1,4-hexanediol, 2,5-hexanediol, 3-methyl-1,5-pentanediol, 1,2-dodecanediol and 1,2-octadecanediol, and other diols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol, 1,4-cycloxanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol and bisphenol A-alkylene oxide adducts. A small proportion of tri- or tetrahydric alcohols such as trimethylolethane, trimethylolpropane, glycerine and pentaerythritol may be incorporated to the alcohol component. The proportion of branched chain-aliphatic glycols in the total alcohol component should not exceed 30 mole %. Smaller proportions of bisphenol S-alkylene oxide adducts and excessive proportions of branched chain-aliphatic glycols both adversely affect the flexibility, blot-proofness, anti-press impression and anti-chemical properties of cured films formed on precoated sheet metals. 
     Using the above-mentioned polybasic acid component and polyhydric alcohol component, a conventional polycondensation reaction may be carried out as is well-known in the art. The resulting polyester should have a molecular weight of at least 500, preferably from 2,000 to 25,000. 
     Aminoplast resins are produced, as is well-known, by reacting an amino component such as melamine, urea, acetoguanamine, benzoguanamine, stearoguanamine and spiroguanamine with an aldehyde such as formaldehyde, paraformaldehyde, acetaldehyde and glyoxal. The products may be etherified with a lower alkanol such as methanol and butanol. Melamine-formaldehyde condensates and their etherified products may preferably used in the present invention. 
     Blocked polyisocyanates are produced, as is well-known, by blocking the free isocyanate function of an organic polyisocyanate such as tolylenediisocyanate, xylylenediisocyanate, polymethylenepolyphenylene-polyisocyanate, hexamethylenediisocyanate and isophoronediisocyanate with a blocking agent. Blocked polyisocyanates of a non-yellowing polyisocyanate such as hexamethylenediisocyanate and isophrone-diisocyanate are preferably used. Commercial products are available such as Coronate 2515 from Nippon Polyurethane Co., Ltd., Takenate R-815M from Takeda Chemical Industries Ltd., Vernoc D-550 from Dainippon Ink And Chemicals, Inc., Aditol UXL-80 from Hoechst AG, and the like. 
     The coating composition of this invention comprises above-mentioned polyester resin and aminoplast and/or blocked polyisocyanate crosslinker at a weight ratio as solids of 95-50:5-50, preferably 90-60:10-40. Within this range, the resulting films may exhibit satisfactory performance. 
     The coating composition of this invention may generally used as a solution in an organic solvent which may be selected, depending upon its solubility and evaporation rate, from, for example, toluene, xylene, Solvesso 100, Solvesso 150, ethyl acetate, butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, butanol, octanol, diacetone alcohol, carbitol acetate, methoxybutyl acetate or a mixture thereof. 
     The coating composition of this invention may contain, of course, a coloring pigment such as titanium dioxide, a body pigment and other conventional additives depending upon its use or applications. For example, systems containing aminoplast crosslinkers may contain an acid catalyst such as dodecylbenzene-sulfonic acid or its amine salts, p-toluenesulfonic acid or its amine salts, or monoalkyl phosphate. Systems containing blocked polyisocyanate crosslinkers may contain a tin catalyst such as dibutyltin oxide. 
     The coating composition may be prepared using conventional dispersers or mills such as sand grinding mills, ball mills or various types of blenders. The coating composition may be applied using conventional methods such as roller coating, curtain-flow coating, airless spray coating or electrostatic coating on sheet metals such as cold rolled steel sheets, galvanized steel sheets, aluminum-zinc plated steel sheets, stainless steel sheets, tinplate steel sheets and aluminum sheets. When highter corrosion resistance is desired, a primer coating may be applied before the application of the coating composition and baked separately. The baking temperature and time may be suitably selected depending upon the size or thickness of substrate to be coated and also the curability of particular coating compositions. 
     Precoated sheet metals thus produced find a variety of uses, for example, for electrical appliances such as audio instruments, refrigerators, washers and room heaters, indoor construction materials such as partitions and curtain rails, and outdoor construction materials such as embossed sheet metals and the like. 
     The invention is further illustrated by the following examples wherein all parts and % are by weight unless otherwise indicated. 
     SYNTHESIS OF POLYESTER RESINS 
     A reactor vessel was charged with 4.0 moles of terephthalic acid, 4.0 moles of isophthalic acid, 2.0 moles of adipic acid, 5.0 moles of bisphenol S-ethylene oxide (2 moles) adduct (BSE-20, Sanyo Chemical Industries, Ltd.), 4.0 moles of 1, 6-hexanediol, 6.0 moles of ethylene glycol, and 0.05% based on the total reactants of dibutyltin oxide. The mixture was allowed to react by raising the temperature from 150° C. to 220° C. over 4 hours. Thereafter, the reaction was continued until a reduced pressure of 1 mmHg was reached over 1 hour and then at a reduced pressure of 0.3 mmHg at 260° C. for additional 3 hours to give polyester #1 shown in Table 1. 
     Analogous to the above procedure, polyesters #2 through #15 (Examples), #16 through #25 (Comparative Examples), #26 through #32 (Examples) and #33 through #38 (Comparative Examples) shown in Table 1, Table 2, Table 3 and Table 4, respectively were produced. 
     
                                           TABLE 1                                 
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         Polyester resin                                                  
Reactant, mole                                                            
         #1                                                               
           #2                                                             
             #3                                                           
               #4                                                         
                 #5                                                       
                   #6                                                     
                     #7                                                   
                       #8                                                 
                         #9                                               
                           #10                                            
                              #11                                         
                                 #12                                      
                                    #13                                   
                                       #14                                
                                          #15                             
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Terephthalic acid                                                         
         40                                                               
           40                                                             
             40                                                           
               40                                                         
                 20                                                       
                   40                                                     
                     40                                                   
                       40                                                 
                         25                                               
                           25 25 10 10 10 40                              
Isophthalic acid                                                          
         40                                                               
           40                                                             
             40                                                           
               40                                                         
                 --                                                       
                   40                                                     
                     40                                                   
                       40                                                 
                         25                                               
                           25 25 10 10 10 40                              
Phthalic acid                                                             
         --                                                               
           --                                                             
             --                                                           
               --                                                         
                 60                                                       
                   --                                                     
                     --                                                   
                       --                                                 
                         --                                               
                           -- -- -- -- -- --                              
Adipic acid                                                               
         20                                                               
           20                                                             
             --                                                           
               --                                                         
                 20                                                       
                   20                                                     
                     20                                                   
                       20                                                 
                         25                                               
                           25 25 80 80 80 20                              
1,4-Cyclohexane-                                                          
         --                                                               
           --                                                             
             20                                                           
               20                                                         
                 --                                                       
                   --                                                     
                     --                                                   
                       --                                                 
                         25                                               
                           25 25 -- -- -- --                              
dicarboxylic acid                                                         
BSE-20.sup.1)                                                             
         50                                                               
           --                                                             
             50                                                           
               50                                                         
                 50                                                       
                   30                                                     
                     80                                                   
                       50                                                 
                         80                                               
                           50 30 80 50 30 98                              
BSE-40.sup.2)                                                             
         --                                                               
           50                                                             
             --                                                           
               --                                                         
                 --                                                       
                   --                                                     
                     --                                                   
                       --                                                 
                         --                                               
                           -- -- -- -- -- --                              
Ethylene glycol                                                           
         10                                                               
           10                                                             
             10                                                           
               10                                                         
                 10                                                       
                   10                                                     
                     10                                                   
                       10                                                 
                         10                                               
                           10 10 10 10 10  2                              
1,6-Hexanediol                                                            
         40                                                               
           40                                                             
             40                                                           
               20                                                         
                 40                                                       
                   50                                                     
                     10                                                   
                       30                                                 
                         10                                               
                           20 20 10 10 10 --                              
1,4-Cyclohexane-                                                          
         --                                                               
           --                                                             
             --                                                           
               20                                                         
                 --                                                       
                   10                                                     
                     --                                                   
                       --                                                 
                         --                                               
                           20 40 -- 30 50 --                              
dimethanol                                                                
Neopentyl glycol                                                          
         --                                                               
           --                                                             
             --                                                           
               --                                                         
                 --                                                       
                   --                                                     
                     --                                                   
                       10                                                 
                         --                                               
                           -- -- -- -- -- --                              
Mn (× 10.sup.4)                                                     
         2.1                                                              
           2.0                                                            
             2.0                                                          
               2.2                                                        
                 2.1                                                      
                   2.1                                                    
                     2.3                                                  
                       1.9                                                
                         2.0                                              
                           1.9                                            
                              2.2                                         
                                 2.1                                      
                                    2.1                                   
                                       2.3                                
                                          1.8                             
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 .sup.1) Bisphenol Sethylene oxide (2 moles) adduct                       
 .sup.2) Bisphenol Sethylene oxide (4 moles) adduct                       
 
    
     
                                           TABLE 2                                 
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         Polyester resin                                                  
Reactant, mole                                                            
         #16                                                              
            #17                                                           
               #18                                                        
                  #19                                                     
                     #20                                                  
                        #21                                               
                           #22                                            
                              #23                                         
                                 #24                                      
                                    #25                                   
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Terephthalic acid                                                         
         50 50 50 50 40 25 10 40 40 25                                    
Isophthalic acid                                                          
         50 50 50 50 40 25 10 40 40 25                                    
Phthalic acid                                                             
         -- -- -- -- -- -- -- -- -- --                                    
Adipic acid                                                               
         -- -- -- -- 20 20 20 20 20 20                                    
1,4-Cyclohexane-                                                          
         -- -- -- -- -- 30 60 -- -- 30                                    
dicarboxylic acid                                                         
BSE-20   80 50 30 10 10 10 10 50 -- --                                    
BSE-40   -- -- -- -- -- -- -- -- -- --                                    
Ethylene glycol                                                           
         10 10 10 10 10 10 10 10 10 10                                    
1,6-Hexanediol                                                            
         10 40 60 50 40 40 30 -- 45 --                                    
1,4-Cyclohexane-                                                          
         -- -- -- 30 40 40 50 -- 45 90                                    
dimethanol                                                                
Neopentyl glycol                                                          
         -- -- -- -- -- -- -- 40 -- --                                    
Mn (× 10.sup.4)                                                     
         2.0                                                              
            1.9                                                           
               2.1                                                        
                  2.1                                                     
                     2.0                                                  
                        2.1                                               
                           2.1                                            
                              1.9                                         
                                 2.1                                      
                                    2.0                                   
__________________________________________________________________________
 
    
     
                       TABLE 3                                                     
______________________________________                                    
         Polyester resin                                                  
Reactant, mole                                                            
           #26     #27   #28   #29 #30   #31 #32                          
______________________________________                                    
Terephthalic acid                                                         
           42      42    42    35  35    35  35                           
Isophthalic acid                                                          
           42      42    42    35  35    35  35                           
Phthalic acid                                                             
           --      --    --    --  --    --  --                           
Adipic acid                                                               
            8       8     8    15  15    --  15                           
1,4-Cyclohexane-                                                          
            8       8     8    15  15    30  15                           
BSE-20     80      50    --    80  50    80  50                           
BSE-40     --      --    50    --  --    --  --                           
Ethylene glycol                                                           
           10      10    10    10  10    10  10                           
1,6-Hexanediol                                                            
           10      40    40    10  40    10  --                           
1,4-Cyclohexane-                                                          
           --      --    --    --  --    --  30                           
dimethanol                                                                
Mn (× 10.sup.4)                                                     
           2.1     2.0   1.9   2.2 1.8   2.0 2.2                          
______________________________________                                    
 
    
     
                       TABLE 4                                                     
______________________________________                                    
            Polyester resin                                               
Reactant, mole                                                            
              #33   #34     #35 #36   #37 #38                             
______________________________________                                    
Terephthalic acid                                                         
              50    50      20  42    25  25                              
Isophthalic acid                                                          
              50    50      --  42    25  25                              
Phthalic acid --    --      60  --    --  --                              
Adipic acid   --    --      20   8    25  25                              
1,4-Cyclohexane-                                                          
              --    --      --   8    25  25                              
dicarboxylic acid                                                         
BSE-20        80    50      50  10    80  50                              
BSE-40        --    --      --  --    --  --                              
Ethylene glycol                                                           
              10    10      10  10    10  10                              
1,6-Hexanediol                                                            
              10    40      40  40    10  20                              
1,4-Cyclohexane-                                                          
              --    --      --  40    --  20                              
dimethanol                                                                
Mn (× 10.sup.4)                                                     
              2.0   2.2     2.0 1.9   2.1 1.8                             
______________________________________                                    
 
    
    
    
     EXAMPLES 1-15 AND COMPARATIVE EXAMPLES 1-10 
     Polyester resins #1 through #25 were each dissolved in cyclohexanone to 40% concentration. 200 parts of each solution, 25 parts of Sumimal M40S (methylated melamine resin sold by Sumitomo Chemical Company, Limited, 80% nonvolatile content), 100 parts of Taipek CR-97 (titanium dioxide pigment sold by Ishihara Sango Kaisha, Ltd.), 1 part of Catalyst 6000 (dodeylbenzensulfonic acid solution sold by Mitsui Toatsu Chemicals, Inc.) and 115 parts of 1:1 mixture of cyclohexanone/Solvesso 150 were taken in a container and throughly mixed. The mixture was transferred to a paint shaker and dispersed for 1 hour. 
     Each coating composition was applied on a zinc phosphate-treated galvanized steel plate having a thickness of 0.5 mm to a dry film thickness of 16 micron using a roll coater and then baked at 250° C. for one minute. Performance of the coated steel sheet is shown in Table 5 and Table 6. 
     EXAMPLES 16-30 AND COMPARATIVE EXAMPLES 11-20 
     Polyester resins #1 through #25 were each dissolved in cyclohexanone to 40% concentration. 200 parts of each solution, 12.5 parts of Sumimal M40S, 12.5 parts of Coronate 2515 (blocked polyisocyanate sold by Nippon Polyurethane Co., Ltd., 80% nonvolatile content), 12.5 parts of Taipek CR-97, 1 part of Catalyst 6000 and 115 parts of a 1:1 mixture of cyclohexanone/Solvesso 150  were taken in a container and thoroughly mixed. The mixture was transferred to a paint shaker and dispersed for 1 hour. 
     Each coating composition was applied on a zinc phosphate-treated galvanized steel sheet having a thickness of 0.5 mm to a dry film thickness of 16 micron using a roll coater and then baked at 250° C. for one minute. Performance of the coated steel sheet is shown in Table 7 and Table 8. 
     EXAMPLES 31-45 AND COMPARATIVE EXAMPLES 21-30 
     Polyester resins #1 through #25 were each dissolved in cyclohexanone to 40% concentration. 200 parts of each solution, 25 parts of Coronate 2515, 100 parts of Taipek CR-97 and 115 parts of a 1:1 mixture of cyclohexanone/Solvesso 150 were taken in a container and thoroughly mixed. The mixture was transferred to a paint shaker and dispersed for 1 hour. 
     Each coating composition was applied on a zinc phosphate-treated galvanized steel sheet having a thickness of 0.5 mm to a dry film thickness of 16 micron using a roll coater and then baked at 250° C. for one minute. Performance of the coated steel is shown in Table 9 and Table 10. 
     EVALUATION METHODS 
     Hardness (pencil hardness) 
     Using a standard pencil according to JIS S-6006, a method according to JIS K-5400 was performed with coating films formed on the substrate sheets. 
     Flexibility 
     The coated steel sheet was bent at 5° C. in U-shape through 180° C. over a number of interposed steel sheets having a thickness of 0.5 mm which were stacked together and the occurrence of cracks in the bent area was visually observed. Flexibility is expressed in terms of the minimum number of stacked sheets at which no crack is observed. The symbol &#34;2T&#34;, for example, stands for two sheets. The smaller the number the better the product. 
     Blot-proofness 
     The coated substrate was blotted with an oily ink(red) in the area of 0.5 cm×2 cm and dried at 24° C. for 24 hours. Then the blot area was wiped with gauze impregnated with ethanol. Blot-proofness was judged in terms of the degree of remaining blot according to the following scale: 
     O:Good; Δ: Slightly bad; x: Bad 
     Gloss 
     Percent reflection at an angle of 60° C. was determined using a standard glossmeter. 
     
                                           TABLE 5                                 
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        Example                                                           
        1 2 3 4   5   6   7 8 9 10 11 12 13 14 15                         
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Polyester resin                                                           
        #1                                                                
          #2                                                              
            #3                                                            
              #4  #5  #6  #7                                              
                            #8                                            
                              #9                                          
                                #10                                       
                                   #11                                    
                                      #12                                 
                                         #13                              
                                            #14                           
                                               #15                        
Pencil hardness                                                           
        2H                                                                
          2H                                                              
            2H                                                            
              2H-3H                                                       
                  H-2H                                                    
                      H-2H                                                
                          3H                                              
                            2H                                            
                              3H                                          
                                2H 2H H  H  H  3H                         
Flexibility                                                               
        1T                                                                
          1T                                                              
            1T                                                            
              2T  2T  2T  2T                                              
                            1T                                            
                              2T                                          
                                1T 1T 1T 1T 1T 2T                         
Blot-proofness                                                            
        ◯                                                     
          ◯                                                   
            ◯                                                 
              ◯                                               
                  ◯                                           
                      ◯                                       
                          ◯                                   
                            ◯                                 
                              ◯                               
                                ◯                             
                                   ◯                          
                                      ◯                       
                                         ◯                    
                                            ◯                 
                                               ◯              
Gloss   95                                                                
          93                                                              
            96                                                            
              93  105 92  98                                              
                            94                                            
                              99                                          
                                94 90 98 93 91 103                        
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                                           TABLE 6                                 
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        Comparative Example                                               
        1  2  3   4   5   6  7  8  9  10                                  
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Polyester resin                                                           
        #16                                                               
           #17                                                            
              #18 #19 #20 #21                                             
                             #22                                          
                                #23                                       
                                   #24                                    
                                      #25                                 
Pencil hardness                                                           
        3H 2H H-2H                                                        
                  H-2H                                                    
                      H-2H                                                
                          H  H  2H H  H                                   
Flexibility                                                               
        5T 4T 4T  4T  3T  3T 3T 5T 3T 3T                                  
Blot-proofness                                                            
        ◯                                                     
           ◯                                                  
              ◯                                               
                  Δ                                                 
                      X   X  X  ◯                             
                                   X  X                                   
Gloss   94 92 89  84  83  85 81 92 82 84                                  
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                                           TABLE 7                                 
__________________________________________________________________________
        Example                                                           
        16                                                                
          17                                                              
            18                                                            
              19  20  21  22                                              
                            23                                            
                              24 25 26 27 28 29 30                        
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Polyester resin                                                           
        #1                                                                
          #2                                                              
            #3                                                            
              #4  #5  #6  #7                                              
                            #8                                            
                              #9 #10                                      
                                    #11                                   
                                       #12                                
                                          #13                             
                                             #14                          
                                                #15                       
Pencil hardness                                                           
        2H                                                                
          2H                                                              
            2H                                                            
              2H-3H                                                       
                  H-2H                                                    
                      H-2H                                                
                          3H                                              
                            2H                                            
                              3H 2H 2H H  H  H  3H                        
Flexibility                                                               
        0T                                                                
          0T                                                              
            0T                                                            
              1T  1T  1T  1T                                              
                            0T                                            
                              1T 0T 0T 0T 0T 0T 1T                        
Blot-proofness                                                            
        ◯                                                     
          ◯                                                   
            ◯                                                 
              ◯                                               
                  ◯                                           
                      ◯                                       
                          ◯                                   
                            ◯                                 
                              ◯                               
                                 ◯                            
                                    ◯                         
                                       ◯                      
                                          ◯                   
                                             ◯                
                                                ◯             
Gloss   97                                                                
          94                                                              
            94                                                            
              93  102 93  97                                              
                            94                                            
                              101                                         
                                 95 91 96 95 90 100                       
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                                           TABLE 8                                 
__________________________________________________________________________
        Comparative Example                                               
        11 12 13  14  15  16 17 18 19 20                                  
__________________________________________________________________________
Polyester resin                                                           
        #16                                                               
           #17                                                            
              #18 #19 #20 #21                                             
                             #22                                          
                                #23                                       
                                   #24                                    
                                      #25                                 
Pencil hardness                                                           
        3H 2H H-2H                                                        
                  H-2H                                                    
                      H-2H                                                
                          H  H  2H H  H                                   
Flexibility                                                               
        4T 3T 3T  3T  2T  2T 2T 4T 2T 2T                                  
Blot-proofness                                                            
        ◯                                                     
           ◯                                                  
              ◯                                               
                  Δ                                                 
                      X   X  X  ◯                             
                                   X  X                                   
Gloss   93 93 90  85  82  85 81 93 82 83                                  
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                                           TABLE 9                                 
__________________________________________________________________________
        Example                                                           
        31                                                                
          32                                                              
            33                                                            
              34  35 36 37                                                
                          38                                              
                            39                                            
                              40 41 42 43 44 45                           
__________________________________________________________________________
Polyester resin                                                           
        #1                                                                
          #2                                                              
            #3                                                            
              #4  #5 #6 #7                                                
                          #8                                              
                            #9                                            
                              #10                                         
                                 #11                                      
                                    #12                                   
                                       #13                                
                                          #14                             
                                             #15                          
Pencil hardness                                                           
        H H H H-2H                                                        
                  F-H                                                     
                     F-H                                                  
                        2H                                                
                          H 2H                                            
                              H  H  F  F  F  2H                           
Flexibility                                                               
        0T                                                                
          0T                                                              
            0T                                                            
              1T  1T 1T 1T                                                
                          0T                                              
                            1T                                            
                              0T 0T 0T 0T 0T 1T                           
Blot-proofness                                                            
        ◯                                                     
          ◯                                                   
            ◯                                                 
              ◯                                               
                  ◯                                           
                     ◯                                        
                        ◯                                     
                          ◯                                   
                            ◯                                 
                              ◯                               
                                 ◯                            
                                    ◯                         
                                       ◯                      
                                          ◯                   
                                             ◯                
Gloss   96                                                                
          93                                                              
            95                                                            
              95  102                                                     
                     94 97                                                
                          94                                              
                            97                                            
                              94 91 96 94 92 104                          
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                                           TABLE 10                                
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        Comparative Example                                               
        21 22 23 24 25 26 27 28 29 30                                     
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Polyester resin                                                           
        #16                                                               
           #17                                                            
              #18                                                         
                 #19                                                      
                    #20                                                   
                       #21                                                
                          #22                                             
                             #23                                          
                                #24                                       
                                   #25                                    
Pencil hardness                                                           
        2H H  F-H                                                         
                 F-H                                                      
                    F-H                                                   
                       F  F  H  F  F                                      
Flexibility                                                               
        4T 3T 3T 3T 2T 2T 2T 4T 2T 2T                                     
Blot-proofness                                                            
        ◯                                                     
           ◯                                                  
              ◯                                               
                 Δ                                                  
                    X  X  X  ◯                                
                                X  X                                      
Gloss   93 92 90 83 83 86 81 90 83 83                                     
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     EXAMPLES 46-52 AND COMPARATIVE EXAMPLES 31-36 
     Polyeter resins #26 through #38 were each dissolved in cyclohexanone to 40% concentration. 200 parts of each solution, 25 parts of Sumimal M40S, 100 parts of Taipek CR-97, 1 part of Catalyst 6000, and 115 parts of a 1:1 mixture of cyclohexanone/Solvesso 150 were placed in a container and thoroughly mixed. The mixture was transferred to a paint shaker and dispersed for 1 hour. 
     Each coating composition was applied on a zinc phosphate-treated galvanized steel sheet having a thickness of 0.5 mm to a dry thickness of 16 micron using a roll coater and then baked at 250° C. for one minute. Performance of the coated steel is shown in Table 11 and Table 12. 
     EXAMPLES 53-59 AND COMPARATIVE EXAMPLES 37-42 
     Polyester resins #26 through #38 were each dissolved in cyclohexanone to 40% concentration. 200 parts of each solution, 12.5 parts of Sumimal M40S, 12.5 parts of Coronate 2515, 100 parts of Taipek CR-97, 1 part of Catalyst 6000, and 115 parts of a 1:1 mixture of cyclohexanone/Solvesso 150 were taken in a container and thoroughly mixed. The mixture was transferred to a paint shaker and dispersed for 1 hour. 
     Each coating composition was applied on a zinc phosphate-treated galvanized steel sheet having a thickness of 0.5 mm to a dry film thickness of 16 micron using a roll coater and then baked at 250° C. for one minute. Performance of the coated sheet is shown in Table 13 and Table 14. 
     EXAMPLES 60-66 AND COMPARATIVE EXAMPLES 43-48 
     Polyester resins #26 through #38 were each dissolved in cyclohexanone to 40% concentration. 200 parts of each solution, 25 parts of Coronate 2515, 100 parts of Taipek CR-97, and 115 parts of a 1:1 mixture of cyclohexanone/Solvesso 150 were taken in a container and thoroughly mixed. The mixture was transferred to a paint shaker and dispersed for 1 hour. 
     Each coating composition was applied on a zinc phosphate-treated galvanized steel sheet having a thickness of 0.5 mm to a dry film thickness of 16 micron using a roll coater and then baked at 250° C. for one minute. Performance of the coated sheet is shown in Table 15 and 16. 
     EVALUATION METHODS 
     Pencil hardness and flexibity were evaluated as in preceding examples. Anti-chemical and anti-press impression properties were eveluated by the following methods. 
     Anti-chemical property 
     One drop (0.2 cc) of 0.1N sulfuric acid was placed on the coated surface and allowed to stand at 60° C. for one hour. After washing with water, the specimen was visually evaluated for the presence of a trace mark of sulfuric acid according to the following schedule: 
     O: No trace; Δ: Slight trace; x: Marked trace 
     Anti-press impression property 
     A section of refrigerator door gasket (1×2 cm) was pressed against the coated surface at a pressure of 100 g loading and maintained at 70° C. for 168 hours. The specimen was visually evaluated for the presence of an impression according to the following schedule: 
     O: No impression; Δ: Slight impression; x: Marked impression 
     
                       TABLE 11                                                    
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        Example                                                           
        46    47     48     49   50   51   52                             
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Polyester resin                                                           
          #26     #27    #28  #29  #30  #31  #32                          
Pencil hardness                                                           
          3H      2H     2H   3H   2H   3H   2H                           
Flexibility                                                               
          2T      1T     1T   2T   1T   2T   1T                           
Anti-chemical                                                             
          ◯                                                   
                  ◯                                           
                         ◯                                    
                              ◯                               
                                   ◯                          
                                        ◯                     
                                             ◯                
property                                                                  
Anti-impression                                                           
          ◯                                                   
                  ◯                                           
                         ◯                                    
                              ◯                               
                                   ◯                          
                                        ◯                     
                                             ◯                
property                                                                  
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                       TABLE 12                                                    
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        Comparative Example                                               
        31   32      33      34     35   36                               
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Polyester resin                                                           
          #33    #34     #35   #36    #37  #38                            
Pencil hardness                                                           
          3H     2H      H-2H  H-2H   3H   2H                             
Flexibility                                                               
          5T     4T      2T    3T     2T   1T                             
Anti-chemical                                                             
          ◯                                                   
                 ◯                                            
                         Δ                                          
                               X      Δ                             
                                           X                              
property                                                                  
Anti-impression                                                           
          ◯                                                   
                 ◯                                            
                         Δ                                          
                               X      Δ                             
                                           Δ                        
property                                                                  
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                       TABLE 13                                                    
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        Example                                                           
        53    54     55     56   57   58   59                             
______________________________________                                    
Polyester resin                                                           
          #26     #27    #28  #29  #30  #31  #32                          
Pencil hardness                                                           
          3H      2H     2H   3H   2H   3H   2H                           
Flexibility                                                               
          1T      0T     0T   1T   0T   1T   0T                           
Anti-chemical                                                             
          ◯                                                   
                  ◯                                           
                         ◯                                    
                              ◯                               
                                   ◯                          
                                        ◯                     
                                             ◯                
property                                                                  
Anti-impression                                                           
          ◯                                                   
                  ◯                                           
                         ◯                                    
                              ◯                               
                                   ◯                          
                                        ◯                     
                                             ◯                
property                                                                  
______________________________________                                    
 
    
     
                       TABLE 14                                                    
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        Comparative Example                                               
        37   38      39      40     41   42                               
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Polyester resin                                                           
          #33    #34     #35   #36    #37  #38                            
Pencil hardness                                                           
          3H     2H      H-2H  H-2H   3H   2H                             
Flexibility                                                               
          4T     3T      1T    2T     1T   0T                             
Anti-chemical                                                             
          ◯                                                   
                 ◯                                            
                         Δ                                          
                               X      Δ                             
                                           X                              
property                                                                  
Anti-impression                                                           
          ◯                                                   
                 ◯                                            
                         Δ                                          
                               X      Δ                             
                                           Δ                        
property                                                                  
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                       TABLE 15                                                    
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        Example                                                           
        60    61     62     63   64   65   66                             
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Polyester resin                                                           
          #26     #27    #28  #29  #30  #31  #32                          
Pencil hardness                                                           
          2H      H      H    2H   H    2H   H                            
Flexibility                                                               
          1T      0T     0T   1T   0T   1T   0T                           
Anti-chemical                                                             
          ◯                                                   
                  ◯                                           
                         ◯                                    
                              ◯                               
                                   ◯                          
                                        ◯                     
                                             ◯                
property                                                                  
Anti-impression                                                           
          ◯                                                   
                  ◯                                           
                         ◯                                    
                              ◯                               
                                   ◯                          
                                        ◯                     
                                             ◯                
property                                                                  
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                       TABLE 16                                                    
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        Comparative Example                                               
        43   44       45     46     47   48                               
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Polyester resin                                                           
          #33    #34      #35  #36    #37  #38                            
Pencil hardness                                                           
          2H     H        F-H  F-H    2H   H                              
Flexibility                                                               
          4T     3T       1T   2T     1T   0T                             
Anti-chemical                                                             
          ◯                                                   
                 ◯                                            
                          Δ                                         
                               X      Δ                             
                                           X                              
property                                                                  
Anti-impression                                                           
          ◯                                                   
                 ◯                                            
                          Δ                                         
                               X      Δ                             
                                           Δ                        
property                                                                  
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