Method for reducing block of ethylene interpolymers containing --COOH groups
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of application Ser. No. 423,981 filed Sept. 27, 1982 which is a divisional of application Ser. No. 332,435 filed Dec. 21, 1981. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention concerns the treatment of particulate interpolymers of ethylene having pendant carboxyl groups. 
     Particles of ethylene interpolymers having pendant carboxyl groups tend to stick together or cohere during storage, particularly in a warm environment. This is particularly present when the amount of monomer or monomers containing the carboxyl group is present in the polymer in amounts of 10% by weight and above. These polymers tend to bridge together in handling systems, during shipping, storage, and in fabricating equipment lines due to the tendency to stick and block, particularly when such polymers are in the form of pellets or chips. This results in an economic loss, in terms of slow downs, to physically unblock the storage bins and sometimes in shutdowns of production lines. 
     G. R. Looney et al. in U.S. Pat. No. 3,753,965 discloses a method for deblocking particles of the polymers containing ethylene and acrylic acid by treating such polymers in a solution of a base material. 
     It may be desirable to perform the treatment step simultaneously while chopping strands of the polymer into pellets or the like. 
     The present invention provides alternate treatment solutions which, in some instances, are superior to those employed by Looney. Also, the treatment solutions of the present invention do not, in most instances, significantly adversely affect the physical properties of the polymer. 
     SUMMARY OF THE INVENTION 
     The present invention pertains to a method for surface treating particles of an interpolymer of ethylene and a polymerizable ethylenically unsaturated monomer containing carboxyl groups, said interpolymer containing up to about 50, preferably from about 10 to about 40, weight percent of carboxyl group containing monomer so as to reduce the tendency of such polymer to block and stick, which process comprises contacting such particles with a member selected from the group consisting of 
     (A) a solution containing from about 0.10 to about 5, preferably from about 0.125 to about 0.75 weight percent of a tertiary organic amine represented by the formula ##STR1##  wherein R is an x valent a hydrocarbon radical having from 1 to about 24 carbon atoms which can be unsubstituted or contain one or more substituent groups selected from carboxyl, hydroxyl, amino, halo, or alkyl; each Z is independently hydrogen or a monovalent metal selected from group I of the Periodic Table and x has a value equal to the valence of R; and 
     (B) at least one material or a mixture of materials selected from 
     (1) a solution containing from about 0.1 weight percent to that which provides a saturated solution, preferably from about 0.125 to about 1.5 weight percent of a carboxylic acid having the general formula ##STR2##  wherein R is a hydrocarbon group having from 1 to about 24 carbon atoms which can be unsubstituted or contain or or more substituent groups selected from carboxyl, hydroxyl, amino, halo, or alkyl; or 
     (2) a solution containing from about 0.1 weight percent to that which provides a saturated solution, preferably from about 0.125 to about 1.5 weight percent of a carboxylic acid salt represented by the general formula ##STR3##  wherein R is a saturated or unsaturated aliphatic or aromatic organic radical having from 1 to about 24 carbon atoms which can be unsubstituted or contain one ormore substituent groups selected from carboxyl, hydoxyl, amino, halo, or alkyl; M is a y valent metal selected from Groups I-A or II-A of the Periodic Table; and wherein x=y and each have a value or from 1 to 2 inclusive; 
     and wherein said treatment is conducted in sufficient quantities at a sufficient temperature for a sufficient time so as to provide the resultant treated particles, after drying; with reduced blocking and/or sticking properties. 
     The present invention also pertains to an improvement in a process for reducing the blocking and/or self-sticking characteristics of interpolymers of etylene and one or more polymerizable ethylenically unsaturated monomers, at least one of which contains a --COOH group, by treating such polymers with a solution containing a compound of a Group I-A metal at a concentration, temperature and time sufficient to reduce such blocking and/or self-sticking characteristics; said improvement comprising employing as the Group I-A metal compound, a mixture comprising 
     (A) at least one Group I-A or I-B metal salt of ethylenedinitrilotetraacetate and 
     (B) at last one organic compound of said group I-A metal. 
     As used herein, the term Periodic Table refers to the Periodic Table of the Elements published by Sargent-Welch Scientific Company, catalog number S-18806. The term Group refers to the group designations, columns, in that Table. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Particular compounds which can be employed in the process of the present invention include, for example, solutions of mixtures of sodium benzoate and trisodium phosphate, sodium citrate and trisodium phosphate, sodium acetate and sodium carbonate, sodium benzoate and sodium carbonate, sodium citrate and sodium carbonate, sodium stearate and sodium carbonate, sodium stearate and trisodium phosphate, sodium salicylate and sodium carbonate, sodium salicylate and trisodium phosphate, sodium acetate and tetrasodium ethylenedinitrilotetraacetate and the like. 
     Also suitable for solutions of stearic acid, acetic acid, propanoic acid, butanoic acid, mixtures thereof and the like. 
     The acids and/or salts are employed as aqueous solutions or as solutions in an organic solvent such as alcohols or the like such as, for example, ethyl alcohol or isopropyl alcohol. 
     The particles, usually in the form of pellets or chips, are treated by contacting them with the treating solution at a temperature of from about 0° C. to about 85° C., preferably at about 15° C. to about 30° C., for from about one second to about two hours, preferably for from about five seconds to about 45 seconds. The total concentration of the solution is usually from about 0.01% to about 10%, preferably from about 0.25% to about 1.5% by weight of solute in the chosen solvent and at a solution pH of from about 2 to about 13.5. 
     When employing the solutions at a pH of about 10 or less, the treatment effect progresses very slowly such as to render the process economically impractical for commercial operations. However, when using solutions of carboxylic acids, adequate antiblocking is effective at lower pH values. When treating polymers containing greater than about 15 weight of a carboxylic acid containing monomer, solutions greater than about 12.5 pH are not deemed to be commercially practical over longer periods of time due to a tendency toward corrosion of the process equipment. Also, at temperatures below about 15° C. some of the treating materials are not readily soluble in the solvent. The maximum temperature employed should be below the melting point or the low end of the melting range of the polymer being treated. For most of such polymers, the upper limit on the treatment range is about 75° C. 
     Suitable interpolymers containing pendant --COOH groups which can be cmployed herein include ethylene/acrylic acid copolymers, ethylene/methacrylic acid, ethylene/acrylic acid/acrylate ester terpolymers, blends thereof and the like. 
    
    
     The following examples are illustrative of the present invention and are not to be construed as to limiting the scope thereof in any manner. 
     EXAMPLE I 
     Treatment 
     A 500 grams sample of pellets of ethylene/acrylic acid copolymer containing 20.5 weight percent acrylic acid and with a melt index of 25 was placed in a 2000 cc beaker containing 1500 cc of various previously prepared aqueous treatment solutions of a composition indicated in the following Table I. The pellets were allowed to come in contact with the treatment solution for 3 minutes at ambient temperature (23° C.±1°). The solution was drained and the treated pellets were spread onto an aluminum sheet and placed in a forced-draft oven and dried for 30 minutes at 50° C. The pellets were removed from the oven after 30 minutes and allowed to cool for 15 minues to room temperature (23° C.±1°) before being tested. 
     Blocking or Sticking Test 
     Samples treated were tested by the following procedures: 
     Melt Index 
     ASTM D1238, condition (B). 
     Rigidity 
     ASTM D747. 
     pH 
     Standard pH determination procedures were used, using a Leeds Northrup pH meter model 7411. 
     Na PICK-UP 
     The resin is partially dry ashed in a platinum crucible followed by complete ashing in a muffled furnace of 500° C. The ash is taken up in a slightly acidic solution and introduced in Spectraspan III emission spectroplotomer which utilizes DC current as the energy source. Plasma is used to excite the Na ions and emit its characteristic spectrum. 
     Drop Test 
     A test to determine the extent of pellet blocking employed a 13.2 mm inside diameter Plexiglass cylinder and a 12.7 mm outside diameter solid rod of Plexiglass, which will just fit into the cylinder. A known weight of 488 grams (to simulate the force exerted on the pellets at the bottom of a full 20 foot silo) was placed on the rod, pushing down on 3.5 grams of pellets inside the cylinder. The whole apparatus was placed in an oven at 50° C. (the estimated maximum temperature attained in silos or hopper cars). The extent of the blocking was expressed as the height in inches that the inverted cylinder had to be dropped to dislodge the pellets completely. Each copolymer sample was tested in multiplicate (6 times) and the average value was used as its blocking value. The higher the number, the worse the material blocks. 
     Results of various treating solutions are given in the following Table I. 
     
                       TABLE I                                                     
______________________________________                                    
TREATING        SAMPLE NUMBER                                             
MATERIAL        A        B       C     D                                  
______________________________________                                    
sodium, acetate. wt. %                                                    
                0        0.75    0     0.375                              
trisodium phosphate, wt. %                                                
                0        0       0.75  0.375                              
Drop Test, inches                                                         
                &gt;21      10      10.8  5                                  
cm.             &gt;53.4    25.4    27.4  12.7                               
______________________________________                                    
 
    
     EXAMPLE 2 
     In a manner similar to Example 1, various treating solutions were employed at various concentrations to treat two different polymers. The results are given in Table II. 
     EXAMPLE 3 
     In a manner similar to Example 1, various treating solutions were employed at various concentrations. The polymer treated was an ethylene acrylic acid copolymer containing 20% acrylic acid by weight . 
     The polymer employed in samples A through O had a melt index of about 13.1 before treatment whereas the polymer employed in samples P through Y had a melt index of about 25 before treatment. The results are given in Table III. 
     
                                           TABLE II                                
__________________________________________________________________________
Polymer                                                                   
       Sodium                                                             
            Sodium                                                        
                 Sodium                                                   
                      Sodium                                              
                            Sodium                                        
                                 Acetic                                   
                                     Stearic                              
and    Acetate                                                            
            Benzoate                                                      
                 Citrate                                                  
                      Salicylate                                          
                            Strearate                                     
                                 Acid                                     
                                     Acid                                 
Results                                                                   
       0.75.sup.4                                                         
            0.5.sup.4                                                     
                 0.5.sup.4                                                
                      0.5.sup.4                                           
                            0.5.sup.4                                     
                                 0.5.sup.4                                
                                     1.0.sup.4                            
__________________________________________________________________________
Polymer A.sup.1                                                           
pH     7.95 7.2  7.1  5.65  9.4   N.D.*                                   
                                     N.D.                                 
Drop Test                                                                 
inches 6.8  9.3  9.5  &gt;10   4.5  N.D.                                     
                                     5.8                                  
cm     &gt;17.3                                                              
            23.7 24.1 &gt;25.4 11.4 N.D.                                     
                                     33                                   
Melt Index                                                                
       12.9 N.D. N.D. N.D.  N.D. N.D.                                     
                                     13.0                                 
Rigidity                                                                  
psi    3970 N.D. N.D. N.D.  N.D. N.D.                                     
                                     3960                                 
kg/cm.sup.2                                                               
       279                           278                                  
Na Pick-up.sup.2                                                          
       N.D. N.D. N.D. N.D.  N.D. N.D.                                     
                                     N.D.                                 
ppm                                                                       
Polymer B.sup.3                                                           
pH     7.95 7.2  7.1  5.65  9.4  N.D.                                     
                                     N.D                                  
Drop Test                                                                 
inches &gt;10  &gt;10  &gt;10  &gt;10   &gt;10  N.D.                                     
                                     N.D.                                 
cm     &gt;25.4                                                              
            &gt;25.4                                                         
                 &gt;25.4                                                    
                      &gt;25.4 &gt;25.4                                         
                                 N.D.                                     
                                     N.D.                                 
Polymer C.sup.5                                                           
pH     N.D  N.D. N.D. N.D.  N.D.   2.8                                    
                                     5.75                                 
Drop Test                                                                 
inches N.D. N.D. N.D. N.D.  N.D.  5.4                                     
                                     5.4                                  
cm     N.D. N.D. N.D. N.D.  N.D. 13.7                                     
                                     13.7                                 
Melt Index                                                                
       N.D. N.D. N.D. N.D.  N.D. 14.9                                     
                                     19.2                                 
__________________________________________________________________________
 Footnotes to Table II                                                    
 *Not Determined                                                          
 .sup.1 Polymer A was an ethylene/acrylic acid copolymer containing about 
 20% acrylic acid by weight and having a melt index of about 13.1.        
 .sup.2 Na pickup by the polymer was obtained about 3 minutes a treatment 
 at room temperature.                                                     
 .sup.3 Polymer B was an ethylene/acrylic acid copolymer containing about 
 20% acrylic acid by weight and having a melt index of about 25.          
 .sup.4 Concentration in weight percent based on weight of additive plus  
 weight of water.                                                         
 .sup.5 Polymer C was an ethylene/acrylic acid copolymer containing about 
 20% acrylic acid by weight and having a melt index of about 15.          
 
    
     
                                           TABLE III                               
__________________________________________________________________________
Treating Material                                                         
and         SAMPLE NUMBER                                                 
Results     A    B    C    D    E    F   G    H   I   J    K              
__________________________________________________________________________
Treating Material.sup.1                                                   
Trisodium Phosphate                                                       
            0    0    0.75 0.375                                          
                                0    0   0    0   0   0    0              
Sodium Acetate                                                            
            0    0.75 0    0.375                                          
                                0    0   0    0   0   0    0              
Sodium Benzoate                                                           
            0    0    0    0    0.5  0   0.25 0   0   0    0              
Sodium Carbonate                                                          
            0    0    0    0    0    0.5 0.25 0   0   0    0              
Sodium Citrate                                                            
            0    0    0    0    0    0   0    0   0   0    0              
Sodium Salicylate                                                         
            0    0    0    0    0    0   0    0.5 0   0.25 0              
Sodium Hydroxide                                                          
            0    0    0    0    0    0   0    0   0.5 0.25 0              
Tetrasodium Ethylene                                                      
            0    0    0    0    0    0   0    0   0   0    0.75           
Dinitrilotetraacetate                                                     
pH          --   7.95 11.5 11.4 7.2  11  10.9 9.7 12.6                    
                                                      11.7 10.9           
Results                                                                   
Melt Index.sup.3                                                          
            13.1 12.9 N.D..sup.2                                          
                           12.9 N.D..sup.2                                
                                     N.D..sup.2                           
                                         12.9 N.D..sup.2                  
                                                  N.D..sup.2              
                                                      12.8 N.D..sup.2     
Rigidity                                                                  
psi         3850 N.D..sup.2                                               
                      N.D..sup.2                                          
                           4100 N.D..sup.2                                
                                     N.D..sup.2                           
                                         4000 N.D..sup.2                  
                                                  N.D..sup.2              
                                                      4070 N.D..sup.2     
kg/cm.sup.2 271            288           281          286                 
Drop Test                                                                 
inches      &gt;21  6.8  4.4  3.2  9.3  2.4 0.91 5.7 3.6 2.3  3.8            
cm          53.3 17.3 11.2 8.1  13.6 6.1 2.31 14.5                        
                                                  9.1 5.8  9.7            
__________________________________________________________________________
Treating Material                                                         
and         SAMPLE NUMBER                                                 
Results     L    M    N    O    P    Q    R    S   T   U   V              
__________________________________________________________________________
Treating Material.sup.1                                                   
Trisodium Phosphate                                                       
            0    0    0.25 0.25 0.25 0.375                                
                                          0.375                           
                                               0.375                      
                                                   0.5 0.5 0.5            
Sodium Acetate                                                            
            0.375                                                         
                 0    0.25 0    0    0.375                                
                                          0    0   0.5 0   0              
Sodium Benzoate                                                           
            0    0    0    0.25 0    0    0.375                           
                                               0   0   0.5 0              
Sodium Carbonate                                                          
            0    0    0    0    0    0    0    0   0   0   0              
Sodium Citrate                                                            
            0    0    0    0    0.25 0    0    0.375                      
                                                   0   0   0.5            
Sodium Salicylate                                                         
            0    0    0    0    0    0    0    0   0   0   0              
Sodium Hydroxide                                                          
            0    0    0    0    0    0    0    0   0   0   0              
Tetrasodium Ethylene                                                      
            0.375                                                         
                 0    0    0    0    0    0    0   0   0   0              
Dinitrilotetraacetate                                                     
pH          10.5 --   11.2 11.3 11.2 11.2 11.3 11.3                       
                                                   11.3                   
                                                       11.3               
                                                           11.3           
Results                                                                   
Melt Index.sup.3                                                          
            12.8 25.0 N.D..sup.2                                          
                           N.D..sup.2                                     
                                N.D..sup.2                                
                                     N.D..sup.2                           
                                          N.D..sup.2                      
                                               N.D..sup.2                 
                                                   N.D..sup.2             
                                                       N.D..sup.2         
                                                           N.D..sup.2     
Rigidity                                                                  
psi         4170 N.D..sup.2                                               
                      N.D..sup.2                                          
                           N.D..sup.2                                     
                                N.D..sup.2                                
                                     N.D..sup.2                           
                                          N.D..sup.2                      
                                               N.D..sup.2                 
                                                   N.D..sup.2             
                                                       N.D..sup.2         
                                                           N.D..sup.2     
kg/cm.sup.2 293                                                           
Drop Test                                                                 
inches      2.8  &gt;21  5.6  6.6  5.5  5    6    5.6 5.1 6.7 4.7            
cm          7.1  53.3 14.2 16.8 14   12.7 15.2 14.2                       
                                                   13  17  11.9           
__________________________________________________________________________
 Footnotes to Table III                                                   
 .sup.1 Values expressed for the treating material are wt. % in an aqueous
 solution.                                                                
 .sup.2 N.D. = Not determined                                             
 .sup.3 The melt index values are those measured after treatment except fo
 the control samples A and M.