Abstract:
This invention relates to novel polyamines which are the reaction product of 
     A) at least one nonaromatic diamine containing from 2 to 40 carbon atoms, wherein the amine groups are primary amine groups; and 
     B) at least one epihalohydrin of the formula                            
      where R is hydrogen or methyl and X is chlorine or bromine; and the coatings resulting from the reaction between the above reaction product and nonaromatic epoxy resins.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of provisional application Serial No. 60/116,377, filed on Jan. 19, 1999. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to polyamines and to compositions produced by the reaction of the polyamines with epoxy resins. 
     BACKGROUND OF THE INVENTION 
     Certain aromatic polyamines are known for use as hardening agents for epoxy resins. However, coatings obtained from the reaction between these polyamines and epoxy resins, especially aromatic epoxy resins, often yellow with age, rendering them of limited usefulness. 
     SUMMARY OF THE INVENTION 
     Polyamines have now been discovered that can be reacted with nonaromatic epoxy resins, i.e. epoxy resins based on aliphatic or cycloaliphatic polyols to form coatings having a high resistance to yellowing with age and with exposure to ultraviolet radiation. 
     The polyamines of the invention are the reaction products of 
     A) at least one nonaromatic diamine containing from 2 to 40 carbon atoms, wherein the amine groups are primary amine groups; and 
     B) at least one epihalohydrin of the formula                           
      where R is hydrogen or methyl and X is chlorine or bromine; wherein the mole ratio of component A) to component B) is about 2:1. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term “about”. 
     The polyamines of the invention, which are the reaction products of components A) and B) given above, preferably have the formula                           
     wherein R is hydrogen or methyl, and R′ is a C 2-40  aliphatic, cycloaliphatic, aliphatic cycloaliphatic, or polyoxyalkylene group, wherein the first three of these groups can optionally contain one or more nonconjucated double bonds. However, other nonaromatic diamines can also be used in the practice of the invention. 
     Examples of the nonaromatic diamines of component A) include, but are not limited to, the following: 1,3-bis(aminomethyl)cyclohexane, ethylenediamine, diethylenetriamine, triethylenetetramine, hexamethylenediamine, 2-methyl-1,5-pentanediamine-, 1,6-hexamethylenediamine, 2-heptyl-3,4-bis(9-aminononyl)-1-pentylcyclohexane(dimeryldiamine), polyoxyalkylene diamine, e.g. polyoxypropylene diamine, isophoronediamine, norbornodiamine, 2.5(2.6)-bis(aminomethyl)bicyclo(2.2.1) heptane, 4,4′-dicyclohexylmethane diamine, 1,4-diaminocyclohexane, menthanediamine, and bis(aminomethyl)cyclohexane. 
     Preferred nonaromatic diamines include those based on (i.e. containing) straight or branched chain saturated aliphatic groups, and those based on at least one cycloaliphatic group, optionally containing one or more nonconjugated double bonds. 
     Component B) is preferably epichlorohydrin, although epibromohydrin, 2-methyl epichlorohydrin, and 2-methyl epibromohydrin can also be used as component B). 
     The reaction between about 2 moles (e.g. from 2 to 2.1 moles) of component A) and one mole of component B) can be carried out by slowly adding component B) to component A) under a nitrogen atmosphere at a temperature in the range of from 200 to 100° C., preferably from 23 ° to 60° C. with stirring. After completion of the addition, from 0.5 to 1 mole of alkali metal hydroxide, preferably sodium hydroxide (a 50% aqueous solution for example) is added slowly with stirring. After this addition the mixture is heated to a temperature in the range of 650° to 95° C. for a period of several hours. The reaction mixture is then filtered to remove insoluble salts, and the reaction product isolated from the filtrate, e.g. by the removal of volatile components therefrom using vacuum distillation. 
     The polyamine of formula I can then be reacted with a nonaromatic epoxy resin at ambient temperatures to produce the coatings of the invention. The nonaromatic epoxy resin is based on an aliphatic or cycloaliphatic polyol, e.g. the polyglycidyl ether of polyether polyol, cycloaliphatic diepoxides, diglycidyl ether of hydrogenated Bis-phenol A, and the like. 
     The polyamine of formula I can be mixed with the nonaromatic epoxy resin in various proportions to form the coatings of the invention. However, weight ratios of (0.25 to 0.60):1 (polyamine:epoxy resin) are most suitable. 
     The coatings of the invention are light-stable and are accordingly very useful for outdoor applications. The coatings resist yellowing even after long periods of time exposed to daylight, which of course contains significant quantities of ultraviolet light. 
    
    
     The invention will be exemplified but not limited by the following examples. 
     EXAMPLES 
     Example 1 
     349.30 grams (2.051 moles) of isophoronediamine were added to a reaction vessel at 24° C. under a nitrogen atmosphere. 92.50 grams (1.000 moles) of epichlorohydrin was then added slowly with stirring over a period of one hour, while controlling the exothermic reaction to a reaction temperature of 45-50° C. After the addition, the mixture was stirred at 52° C. for 30 minutes. Then 79.20 grams (0.990 moles) of 50% NaOH was added over a period of 30 minutes at a temperature of 43-46° C. The resulting mixture was heated to 70° C. and held at this temperature for one hour. The temperature was then raised to 90° C. and held at this temperature with stirring for an additional hour. The temperature was reduced to 70° C. and 2.70 grams (0.025 moles) of Na 2 CO 3  were added over 5 minutes, and the mixture stirred at 70° C. for 3 hours. 513.1 grams of crude reaction product were obtained, including a salt precipitate. 
     The reaction mixture was filtered to give 206.0 grams of filtrate and 252.0 grams of suspended solids on the filter paper. The suspended solids were added to 200 grams of water with stirring. Two layers separated. The top oily layer was separated off and added to the filtrate to give 396.60 grams of crude reaction product, which was then vacuum stripped (30 mm, 100° C.) to remove volatile components to give a residual reaction product (285.79 grams). 
     Example 2 
     315.7 grams (2.05 moles) of 2,5(2,6)-bis(aminomethyl) bicyclo(2.2.1)heptane and 79.20 grams (0.99 moles) of 50% NaOH solution were added to a reaction flask under a nitrogen atmosphere. Then 92.50 grams (1.00 mole) of epichlorohydrin were added with stirring over a period of about 1.5 hours. During this period the temperature rose from 28° to 84° C. The mixture was then held at 84-90° C. with stirring for 2 hours. The mixture was cooled to 70° and 2.70 grams (0.025 moles) of Na 2 CO 3  were added and held with stirring at 70° C. for 3 hours. Next, 225.0 grams of water were added and the resulting mixture cooled to 40° C. The mixture was vacuum stripped (15 mm at 105° C.) and filtered under nitrogen to give a clear filtrate reaction product (140.42 grams). 
     Example 3 
     293.71 grams (2.53 moles) of 2-methyl-1,5-pentanediamine and 98.41 (1.23 moles) of 50% NaOH were added to a reaction flask under a nitrogen atmosphere. Then 114.22 grams (1.23 mole) of epichlorohydrin were added with stirring over a period of 2 hours during which the temperature rose from 23° to 101° C. The mixture was stirred at 85-90° C. for 2.5 hours, and then cooled to 70° C. 3.33 grams (0.031 moles) of Na 2 CO 3  were slowly added and the resulting mixture held with stirring at 65-70° C. for 3 hours. The mixture was cooled to room temperature, filtered, and the filtrate vacuum stripped (10 mm at 95° C.). The residue was filtered in a filter press to give 235.9 grams of filtrate reaction product. 
     Example 4 
     494.1 grams (2.05 moles) of polyoxypropylenediamine and 81.2 g (1.02 moles) of 50% NaOH solution were added to a reaction flask under a nitrogen atmosphere. Then 92.5 grams (1.00 mole) of epichlorohydrin were added with stirring over a period of about 1.5 hours, during which time the temperature rose from 29° C. to 108° C. The mixture was stirred for 2 hours at 91° C., and then cooled to 70° C. 2.7 grams (0.025 moles) of Na 2 CO 3  were added and the resulting mixture held at 65-72° C. with stirring for 3 hours. The mixture was heated to 120° C. and filtered in a filter press under pressure. The distillate was vacuum stripped (20 mm at 120° C.) to give 479.0 grams of residual reaction product. 
     Example 5 
     965.5 grams (6.27 moles) of 2,5(2,6)-bis (aminomethyl) bicyclo (2.2.1) heptane and 242.8 grams (3.0 moles) of 50% NaOH solution were added to a reaction flask under a nitrogen atmosphere with stirring. Then 283.4 grams (3.06 moles) of epichlorohydrin were added with stirring over a period of about 2 hours, during which time the temperature rose from 24° C. to 91° C. The reaction mixture was maintained with stirring at 86-91° C. for 2 hours, and cooled to 70° C. Then 8.3 grams (0.078 moles) of Na 2 CO 3  were added and the resulting mixture maintained with stirring at 65-70° C. for 3 hours. The reaction mixture was next heated to 80° C. and filtered through a filter press. The filtrate was vacuum stripped (10 mm at 150° C.) and cooled to 80° C. 849.39 grams of reaction product were obtained as the residue. 
     Example 6 
     582.5 grams (4.1 moles) of 1,3-bis(aminomethyl) cyclohexanone and 159.6 grams (1.98 moles) of 50% NaOH were added to a reaction flask under a nitrogen atmosphere. Then 185.1 grams (2.0 moles) of epichlorohydrin were added with stirring over a period of about 2.5 hours, during which time the reaction temperature was allowed to rise from 24° C. to 85° C. The reaction mixture was stirred at 90-95° C. for 2 hours, cooled to 50° C., 54 grams (0.05 moles) of Na 2 CO 3  added, and stirred for an additional 3 hours at 65-70° C. The reaction mixture was cooled, filtered in a filter press and the filtrate vacuum stripped (20-30 mm at 100-102° C.). The hot residue (70° C.) was again filtered, resulting in 616.73 grams of filtrate reaction product. 
     Example 7 
     The following nonaromatic epoxy resin compositions and hardener compositions were mixed together at ambient temperatures, and the resulting mixtures (A-K) were coated on steel panels, allowed to harden, and tested as shown in Table 1 below: 
     
       
         
               
               
               
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Component 
                 A 
                 B 
                 C 
                 D 
                 E 
                 F 
                 G 
                 H 
                 I 
                 J 
                 K 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Nonaromatic epoxy resin compositions. Numbers represent weight ratios of ingredients. 
               
             
          
           
               
                 Epalloy ® 5000 1   
                 100 
                   
                 100 
                   
                 100 
                   
                 100 
                   
                 100 
                   
                   
               
               
                 Epalloy ® RK851 2   
                   
                 100 
                   
                 100 
                   
                 100 
                   
                 100 
                   
                 100 
                 80 
               
               
                 Photomer 4399 3   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 10 
               
               
                 UC ERL 4206 4   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 10 
               
             
          
           
               
                 Nonaromatic polyamine hardener compositions. Numbers represent weight ratios of ingredients. 
               
             
          
           
               
                 NBDA Epi-Adduct 5   
                 28 
                 31 
                 13.8 
                 15 
                 28 
                 31 
                 28 
                 31 
                 25 
                 25 
                 15 
               
               
                 Benzyl alcohol 
                   
                   
                   
                   
                 22 
                 9 
               
               
                 Dowanol ® PM 6   
                   
                   
                   
                   
                   
                   
                   
                   
                 28 
                 31 
               
               
                 Versamine ® EH50 7   
                   
                   
                   
                   
                   
                   
                 10 
                 10 
               
               
                 AEEA 8   
                   
                   
                 2.3 
                 5 
                   
                   
                   
                   
                   
                   
                 2.5 
               
               
                 AEP 9   
                   
                   
                 4.6 
                 5 
                   
                   
                   
                   
                   
                   
                 2.5 
               
               
                 TMD 10   
                   
                   
                 2.3 
                   
                   
                   
                   
                   
                   
                   
                 5 
               
               
                 Mix Weight Ratio: 
               
               
                 Resin 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
               
               
                 Hardener 
                 28 
                 31 
                 23 
                 25 
                 50 
                 40 
                 38 
                 41 
                 53 
                 56 
                 25 
               
               
                 Vis. of Hardener 
                 110,000 
                 110,000 
                 700 
                 750 
                 550 
                 4,100 
                 13,000 
                 15,000 
                 150 
                 170 
                 500 
               
               
                 (Cps. @ 25° C.) 
               
               
                 Set to touch time (hrs.) 
                 3.5 
                 1 
                 4 
                 1.5 
                 3 
                 1.5 
                 1.5 
                 0.75 
                 3.5 
                 1.5 
                 1 
               
               
                 Tack free time (hrs.) 
                 5.5 
                 2.25 
                 8 
                 2.5 
                 3.5 
                 2 
                 3.5 
                 2 
                 5.5 
                 2.5 
                 1.5 
               
               
                 Thru cure time (hrs.) 
                 8 
                 3 
                 12 
                 &gt;24 
                 4.5 
                 3 
                 4.5 
                 2.5 
                 6.5 
                 3.5 
                 5.0 
               
               
                 Tg (° C.) 11   
                 109 
                 118 
                   
                   
                 53 
                 101 
                 110 
                 120 
                 95 
                 110 
               
               
                 QUV Exposure 12   
               
               
                 (D65) after 7 days: 
               
               
                 DL 13  (darkening) 
                 −4.22 
                 −5.08 
                 −3.69 
                 −3.62 
                 −4.06 
                 −5.08 
                 −0.76 
                 −0.89 
                 −4.48 
                 −3.66 
                 −3.65 
               
               
                 Db 14  (yellowing) 
                 17.93 
                 21.75 
                 14.40 
                 16.78 
                 19.84 
                 20.95 
                 4.87 
                 5.97 
                 20.34 
                 22.99 
                 15.36 
               
               
                 DE 15  (overall) 
                 18.61 
                 22.07 
                 15.16 
                 16.98 
                 20.26 
                 21.67 
                 5.14 
                 6.29 
                 20.99 
                 23.41 
                 16.22 
               
               
                 Repeat QUV on force cured 
               
               
                 panels - 24 hours @  140° F. 
               
               
                 DL 
                 −3.10 
                 −4.03 
                   
                   
                   
                   
                 −0.39 
                 −1.92 
               
               
                 Db 
                 17.79 
                 23.24 
                   
                   
                   
                   
                 4.92 
                 6.67 
               
               
                 DE 
                 18.16 
                 23.70 
                   
                   
                   
                   
                 5.04 
                 7.05 
               
               
                   
               
               
                 Notes for Table 1  
               
               
                   1 Diglycidyl ether of hydrogenated Bis-phenol A  
               
               
                   2 Predominantly the diglycidyl ether of hydrogenated Bis-phenol A  
               
               
                   3 Dipentaerythritol pentaacrylate  
               
               
                   4 Vinyl cyclohexenedioxide  
               
               
                   5 The reaction product produced by the process of Example 2  
               
               
                   6 Propylene glycol monoether from Dow Chemical Co.  
               
               
                   7 Tertiary amine from Henkel Corporation  
               
               
                   8 Aminoethyl ethanolamine from Union Carbide Corp.  
               
               
                   9 Aminoethyl piperazine from Dow Chemical Co.  
               
               
                   10 Trimethyl hexamethylenediamine from Hüls Corp.  
               
               
                   11 Tg is the glass transition temperature in degrees centigrade  
               
               
                   12 QUV Exposure is the Q Panel Ultraviolet exposure carried out according to ASTM Method G53.  
               
               
                   13 DL is the difference in lightness and darkness  
               
               
                   14 Db is the difference in yellowing  
               
               
                   15 DE is the difference in the overall coloring  
               
             
          
         
       
     
     Example 8 
     The following epoxy resin compositions and hardener compositions were mixed together at ambient temperatures, and the resulting mixtures (A-J) were coated on steel panels, allowed to harden, and tested as shown in Table 2 below: 
     
       
         
               
               
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Component 
                 A 
                 B 
                 C 
                 D 
                 E 
                 F 
                 G 
                 H 
                 I 
                 J 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Epoxy resin compositions. Numbers represent weight ratios of ingredients. 
               
             
          
           
               
                 Epalloy ® 5000 
                 100 
                   
                 100 
                 100 
                   
                   
                 100 
                   
                   
                   
               
               
                 Epalloy ® RK851 
                   
                 100 
                   
                   
                 100 
               
               
                 DER 331 16   
                   
                   
                   
                   
                   
                   
                   
                 100 
                   
                 100 
               
               
                 Shell DPL 700 17   
                   
                   
                   
                   
                   
                 100 
               
               
                 Eponox ® 1510 18   
                   
                   
                   
                   
                   
                   
                   
                   
                 100 
               
             
          
           
               
                 Polyamine hardener compositions. Numbers represent weight ratios of ingredients. 
               
             
          
           
               
                 NBDA Epi-Adduct 5   
                 28 
                 31 
                 28 
                 28 
                 31 
                   
                   
                   
                   
                   
               
               
                 Versamine ® C-31 19   
                   
                   
                   
                   
                   
                   
                 39 
                   
                   
                 45 
               
               
                 Versamine ® EH-50 
                 10 
                 10 
                 10 
                 5 
                 5 
                   
                   
                   
                 10 
               
               
                 Dowanol ® PM 
                 12 
                 9 
                   
                 17 
                 14 
               
               
                 Benzyl alcohol 
                   
                   
                 12 
               
               
                 Shell DPC 750 20   
                   
                   
                   
                   
                   
                 38 
               
               
                 NBDA Epi Adduct 
                   
                   
                   
                   
                   
                   
                   
                 42 
               
               
                 in PM Solvent 21   
                   
                   
                   
                   
                   
                   
                   
                   
                 36 
               
               
                 Mix Weight Ratio: 
               
               
                 Resin 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
               
               
                 Hardener 
                 50 
                 50 
                 50 
                 50 
                 50 
                 38 
                 39 
                 42 
                 46 
                 45 
               
               
                 Viscosity 
                 570 
                 1100 
                 1525 
                 250 
                 560 
               
               
                 Gel Time 
                 57′ 
                 26′ 
                 41′ 
                 63′ 
                 32′ 
                 32′ 
                 146′ 
                 34′ 
                 67′ 
                 43′ 
               
               
                 BK Cure (hrs.) 22 : 
               
               
                 Set to touch 
                 1 
                 1 
                 2 
                 3 
                 1 
                 3 
                 8 
                 1 
                 2 
                 3 
               
               
                 Tack free 
                 3.5 
                 2 
                 3¼ 
                 4 
                 2 
                 4 
                 13 
                 2 
                 4 
                 5 
               
               
                 Thru cure 
                 8 
                 2.5 
                 4.5 
                 10 
                 2.5 
                 8 
                 22 
                 3 
                 5 
                 8 
               
               
                 Gloss Before - 
               
               
                 20° 
                 63.8 
                 84.6 
                 72.1 
                 86.0 
                 83.3 
                 90.3 
                 89.0 
                 101.7 
                 86.9 
                 100.7 
               
               
                 60° 
                 89.1 
                 94.3 
                 93.5 
                 92.8 
                 94.2 
                 95.3 
                 94.9 
                 103.1 
                 90.1 
                 103.0 
               
               
                 QUV Exposure 
               
               
                 (D65) after 1 week: 
               
               
                 DL (darkening) 
                 −2.87 
                 −2.10 
                 −3.73 
                 −1.60 
                 −2.01 
                 −2.43 
                 −2.71 
                 −5.96 
                 −3.13 
                 −5.29 
               
               
                 Db (yellowing) 
                 10.43 
                 7.28 
                 19.19 
                 5.90 
                 7.89 
                 11.70 
                 16.26 
                 25.2 
                 12.50 
                 26.77 
               
               
                 DE (overall) 
                 11.05 
                 7.95 
                 19.79 
                 6.45 
                 8.59 
                 12.08 
                 16.84 
                 23.96 
                 13.11 
                 24.36 
               
               
                 Gloss After 1 week: 
               
               
                 20° 
                 3.2 
                 37.3 
                 21.1 
                 22.7 
                 32.9 
                 89.6 
                 86.6 
                 85.0 
                 86.2 
                 85.3 
               
               
                 60° 
                 19.3 
                 78.3 
                 62.9 
                 55.1 
                 70.4 
                 70.4 
                 95.5 
                 93.8 
                 94.0 
                 94.3 
               
               
                 QUV Exposure 
               
               
                 (D65) after 2 weeks: 
               
               
                 DL (darkening) 
                 −2.58 
                 −2.46 
                 −3.71 
                 −2.38 
                 −2.78 
                 −3.31 
                 −3.64 
                 −7.36 
                 −2.73 
                 −6.39 
               
               
                 Db (yellowing) 
                 7.96 
                 8.82 
                 18.06 
                 7.20 
                 11.53 
                 14.14 
                 19.34 
                 25.24 
                 9.68 
                 26.31 
               
               
                 DE (overall) 
                 8.67 
                 9.57 
                 18.69 
                 7.95 
                 17.31 
                 14.65 
                 19.97 
                 26.29 
                 10.39 
                 27.09 
               
               
                 Gloss After 2 weeks: 
               
               
                 20° 
                 3.0 
                 30.5 
                 15.9 
                 22.8 
                 31.2 
                 78.1 
                 72.0 
                 78.8 
                 84.9 
                 74.9 
               
               
                 60° 
                 18.0 
                 75.4 
                 59.0 
                 63.4 
                 71.8 
                 92.5 
                 89.5 
                 95.8 
                 93.3 
                 90.7 
               
               
                 QUV Exposure 
               
               
                 (D65) after 3 weeks: 
               
               
                 DL (darkening) 
                 −2.39 
                 −2.92 
                 −3.79 
                 −2.74 
                 −3.48 
                 −3.93 
                 −4.24 
                 −8.06 
                 −2.46 
                 −7.13 
               
               
                 Db (yellowing) 
                 7.50 
                 11.66 
                 18.30 
                 9.19 
                 16.77 
                 16.43 
                 21.28 
                 26.74 
                 8.13 
                 27.92 
               
               
                 DE (overall) 
                 8.24 
                 12.46 
                 18.96 
                 9.98 
                 17.51 
                 17.01 
                 22.09 
                 27.93 
                 8.86 
                 28.57 
               
               
                 Gloss After 3 weeks: 
               
               
                 20° 
                 2.85 
                 36.5 
                 22.6 
                 28.7 
                 26.3 
                 81.3 
                 58.4 
                 73.3 
                 84.7 
                 69.1 
               
               
                 60° 
                 17.2 
                 78.9 
                 60.3 
                 62.9 
                 68.7 
                 93.9 
                 87.5 
                 97.4 
                 93.7 
                 89.2 
               
               
                   
               
               
                 Notes for Table 2  
               
               
                   16 Bisphenol A/epichlorohydrin epoxy resin from Dow Chemical Co.  
               
               
                   17 A blend of hydrogenated Bisphenol A/epichlorohydrin based epoxy resin with a multifunctional acrylate monomer from Shell Chemical Co.  
               
               
                   18 Hydrogenated Bisphenol A - epichlorohydrin epoxy resin from Shell Development Corp.  
               
               
                   19 A modified cycloaliphatic amine from Henkel Corporation.  
               
               
                   20 A cycloaliphatic amine from Shell Development Corp.  
               
               
                   21 The reaction product obtained from the process of Example 5 diluted in a mixture of propylene glycol monomethyl ether from Dow Chemical Co.  
               
               
                   22 BK Cure is measured by coating a 1″ × 12″ glass strip with the epoxy resin composition and immediately attaching a timer with a prong in contact with the bottom of the glass strip, wherein the timer moves up the strip at a rate of 2″ per hour. When the prong no longer scratches the coating, the length of the scratched surface is measured, which gives the time required for the coating to cure.