Water-soluble rosin polyamide resins
This application is a continuation-in-part of application Ser. No 07/454,416, filed Dec. 21, 1989, which issued on Nov. 19, 1991, as U.S. Pat. No. 5,066,331. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     This invention relates to a novel water-soluble resin. In particular, this invention relates to a water-soluble resin for packaging ink, derived from the reaction product of a modified rosin and a bis (secondary amine) such as piperazine. 
     (2) Description of Prior Art 
     Resin used as a vehicle for water based packaging ink must exhibit properties such as solubility in water, wet adhesion to polypropylene film, hydrolytic stability, high melting point, and good pigment wetting. 
     Alcohol soluble polyamide resins have been used extensively in inks for packaging and are commercially available. These polyamides are made from dimerized fatty acids and various polyamines such as ethylene diamine or hexamethylene diamine. 
     The use of such polyamide resins in ink compositions is described in Floyd, D. E., Polyamide Resins, Reinhold Publishing Co., New York, 1958 and in the Encyclopedia of Polymer Science and Technology, Interscience Publishers, John Wiley Sons, Volume 10, New York, 1969. A typical commercial product is GAX-340 manufactured by Henkel. 
     For water based ink, a water soluble resin such as acrylic resin or a conventional soluble maleic resin may be used. Acrylic resins have good film properties, but lack adhesion to polyolefin films. 
     Conventional soluble maleic resins, which contain half-esters, are subject to a certain degree of hydrolytic instability under alkaline conditions. They also lack film toughness. 
     Water-based ink compositions are disclosed in U.S. Pat. No. 4,963,188 to be prepared by free radical polymerization of rosin and maleic anhydride. Modification of the polymer with an alcohol or an amine prior to utilization in preparing the ink composition is disclosed. 
     Recently, water soluble resins having qualities of adhesion and wettability for use in packaging ink compositions were developed as the reaction products of rosin modified by Diels-Alder reaction with an α, β unsaturated acid and a compound containing two secondary amine groups, including commercially available piperazine and N,N&#39;-dimethylethylene diamine. These resins are described in parent application Ser. No. 454,416, now patent number 5,066,331. 
     These resins were developed primarily for use in water/isopropanol-based inks for printing on film, where they perform quite satisfactorily. When using these resins in all-water systems (i.e., no alcohol), it was found that the resin solutions had relatively limited shelf stability. In many cases the solutions gel upon standing for two or three days. 
     It is therefore an object of this invention to provide improved water soluble resins having qualities of adhesion, wettability and improved stability for us in packaging ink compositions. 
     SUMMARY OF THE INVENTION 
     The above object is met by a novel resin derived from the reaction products of modified rosin and a compound containing two secondary amine groups, and further modifying said reaction products with a polyol, such as diethylene glycol. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Rosin is mainly a mixture of C 20 , fused-ring, monocarboxylic acids, typified by levopimaric and abietic acids, both of which are susceptible to numerous chemical transformations. The rosins to which this invention relates include gum rosin, wood rosin, and tall oil rosin. 
     It is generally known in the art that α, β-unsaturated acids and their anhydrides, such as maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, and fumaric acid may be reacted with abietic type rosin acids to yield C 24  or C 25  polycyclic tricarboxylic acids and anhydrides. Examples include the reaction product of levopimaric acid reacted with fumaric acid, i.e., fumaropimaric acid (I) and the product of levopimaric acid reacted with maleic anhydride, i.e., maleopimaric acid anhydride (II), as described in Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Edition, Vol. 20, Wiley-Inter-Science Publications, John Wiley &amp; Sons, New York, 1978: ##STR1## 
     The water soluble resin of the present invention is produced by reacting such a maleated or fumarated rosin acid with a compound containing two secondary amine groups, followed by reaction with a polyol. 
     Generally, the polyamine may be any polyamine of the general form: ##STR2## where R 1  =alkylene and R 2  and R 3  are alkyl or where R 1  =alkylene, R 2  +R 3  =alkylene and R 1 , R 2 , and R 3 , together with the two nitrogens to which they are bonded, form a nitrogen-containing heterocyclic ring system. Preferably, the compound containing two secondary amine groups may be a linear polyamine, such as N,N&#39;-dimethylethylene diamine, or a cyclical polyamine, such as piperazine. 
     The nitrogens of the compound containing 2 secondary amine groups react with the secondary carboxyls of the maleated or fumarated resin to form a linear oligomer with tertiary amide groups: ##STR3## where n= a positive integer and preferably n=2 or 3. 
     Use of secondary amines, rather than primary amines which would react with modified rosin in a similar way, is an essential aspect of this invention because of the lower viscosity thereby obtained. A primary amine reacted with a modified rosin forms either an imide, which has greater molecular rigidity, or a secondary amide, which is subject to interchain hydrogen bonding. 
     The reaction should be carried out at a relatively low temperature (below about 235° C., preferably about 200° C.) so that reaction of the secondary carboxyls of the rosins is favored over the tertiary ones and to avoid chain branching. Since rosin typically cannot be fully maleated or fumarated, resin made by the above process will contain a certain amount of unreacted rosin, which acts as a plasticizer and reduces the softening point of the resin. The softening point can be increased either by using a rosin that has a relatively higher content of abietic-type rosin acids, such as gum rosin, and, thus, can be maleated or fumarated to a greater extent, or by using maleated or fumarated rosin that has been vacuum stripped to remove part of the unreacted rosin. 
     A higher softening point may also be obtained by replacing part of the maleated or fumarated rosin with a dicarboxylic acid such as adipic or isophthalic acid. The dicarboxylic acid may be any dicarboxylic acid of the general form: 
     
         HOOC--R.sub.4 --COOH, 
    
     where R 4  =C 6  --C 12  alkylene, cycloalkylene or phenylene. 
     A wide range of polyols may be employed in the subsequent modification of the aminated modified rosin to provide the desired viscosity water soluble resin which possesses improved stability. All polyols tested have been shown to be effective. The polyols applicable to this invention include those with from 2 to 8 hydroxyl groups and exhibiting a molecular weight of from 62 to 600. Preferred polyols include diethylene glycol, triethylene glycol, tetraethylene glycol, glycerol, dipropylene glycol, 1,4-butanediol, pentaerythritol, sorbitol, and poly(ethylene glycol). 
     The resins of this invention may be used to prepare conventional water varnishes (based on the invention resin, water, NH 4  OH, and a defoamer), pigment (based on the invention water varnish with a pigment) bases, and water-based inks (based on the invention pigment base, a wax, and an acrylic polymer). 
    
    
     The following examples serve to illustrate the water-soluble modified resins of the present invention: 
     EXAMPLE 1 
     To a 2000 milliliter flask equipped with a mechanical stirrer and nitrogen sparge were charged 1000 grams tall oil rosin, 2.6 grams tributyl phosphite, and one drop Dow-Corning antifoam A. The charge was heated to 170° C., and 186 grams fumaric acid was added. The charge was further heated to 200° C. and held at that temperature for one hour. Then 103 grams piperazine was added, and the charge was further heated to 235° C., where it was held until the acid number was 170. Next, the batch was cooled to 205° C., and 35 grams diethylene glycol was added. Heating was continued at 205° C. until the acid number was 154. The product was a clear resin with a ring-and-ball softening point of 137° C. Solutions of this resin at 25% solids in aqueous ammonia at pH 9 to 10 were stable, remained clear, and showed no precipitation for a period of nine weeks. By contrast, a similar resin without the diethylene glycol modification gelled in aqueous ammoniacal solution in two days. 
     EXAMPLE 2 
     A series of resins were prepared using the procedure of Example 1 but replacing the diethylene glycol with equimolar amounts of other polyols. These resins are listed in Table I. All of the polyol-modified resins made had solution stabilities of greater than 30 days, except those made with pentaerythritol or sorbitol. Even these latter resins had stabilities of over three weeks, which might be acceptable in some applications. Of particular interest, due to its high softening point, is the resin containing glycerol. A higher softening point usually correlates with faster drying speed, which is highly desirable in an ink resin. On the other hand, the resins modified with PEG 400 or PPG 425 had very low softening points, which allow ink formulations with greater film flexibility. 
     
                       TABLE I                                                     
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POLYOL-MODIFIED PIPERAZINE RESINS                                         
Resin            Acid   S.p.                                              
No.   Polyol     No.    (°C.)                                      
                               Visc..sup.(a)                              
                                     Stability.sup.(b)                    
______________________________________                                    
6412-30                                                                   
      none       187    138    --     &lt;1                                  
6412-82                                                                   
      DEG        154    137    G     &gt;30                                  
6488-17                                                                   
      TEG        155    137    O-P   &gt;30                                  
6496-6                                                                    
      Gly        152    148    W+    &gt;30                                  
6496-10                                                                   
      DPG        152    142    Y-    &gt;30                                  
6496-13                                                                   
      1,4-BD     162    145    U-V   &gt;30                                  
6496-20                                                                   
      PEG200     159    132    I     &gt;30                                  
6496-28                                                                   
      PEG400     147    117    R+.sup.(c)                                 
                                     &gt;30                                  
6496-29                                                                   
      PPG425     146    120    S-    &gt;30                                  
6496-50                                                                   
      PE         165    146    U-V    29                                  
6496-53                                                                   
      Sb         150    146    S+.sup.(c)                                 
                                      27                                  
6496-55                                                                   
      TetEG      165    136    J     &gt;30                                  
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 .sup.(a) GardnerHolt viscosity of a 25% solids solution in aqueous ammoni
 at a pH of 9.6 ± 0.1.                                                 
 .sup.(b) Days standing at room temperature without gelling of a 25% solid
 solution in aqueous ammonia at a pH of 9.6 ± 0.1.                     
 .sup.(c) Solution is slightly hazy.                                      
 Key: 1,4BD = 1,4butanediol; DEG = diethylene glycol; DPG = dipropylene   
 glycol; PE = pentaerythritol; PEG200 = poly(ethylene glycol), 200 ave.   
 molecular weight; PEG400 = poly(ethylene glycol), 400 ave. molecular     
 weight; PPG425 = poly(propylene glycol), 425 ave. molecular weight; TEG =
 triethylene glycol; TetEG = tetraethylene glycol; Sb = sorbitol.         
 
    
     EXAMPLE 3 
     Table II shows the change in pH and viscosity of 25% aqueous ammonia solutions of the polyol-modified resins over 30 days. As can be seen, all of the solutions are quite stable with respect to viscosity. There is no obvious explanation for the small upward drift in pH for most of the solutions, but this behavior is not uncommon for aqueous solutions of maleic resins. 
     
                       TABLE II                                                    
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PROPERTIES OF AGED                                                        
PIPERAZINE RESIN SOLUTIONS                                                
Resin           Viscosity      pH                                         
No.    Polyol   Initial   30 Days                                         
                                 Initial                                  
                                        30 Days                           
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6488-17                                                                   
       TEG      O-P       N-O    9.56   9.83                              
6496-6 Gly      W+        W-     9.52   9.81                              
6496-10                                                                   
       DPG      Y-        Y+     9.58   9.88                              
6496-13                                                                   
       1,4-BD   U-V       U-V    9.56   9.82                              
6496-20                                                                   
       PEG200   I         I-J    9.58   9.60                              
6496-28                                                                   
       PEG400   R+        S-T    9.56   9.87                              
6496-29                                                                   
       PPG425   S-        S-T    9.60   9.75                              
6496-55                                                                   
       TetEG    J         J-K    9.66   9.65                              
______________________________________                                    
 Key: See Table I.                                                        
 
    
     It appears from the above data that a family of aqueous solution-stable ink vehicle resins with a range of softening points can be produced. 
     While the invention has been described and illustrated herein by references to various specific materials, procedures and examples, it is understood that the invention is not restricted to the particular materials, combinations of materials, and procedures selected for that purpose. Numerous variations of such details can be employed, as will be appreciated by those skilled in the art.