Abstract:
The invention is water-based printing inks and coatings formulated with stable low viscosity grind bases made from modified rosin grinding resins. These grinding resins are produced via the fusion esterification of fortified rosin with hydroxyacrylic resins and various polyols. Suitable hydroxyacrylic resins are prepared by copolymerizing an hydroxyalkylacrylate or methacrylate with alkyl acrylates, cycloalkyl acrylates, methacrylates, or styrene. These hydroxyacrylic resins can be made to contain a wide range of molecular weights and hydroxyl contents, thereby permitting formulation of a wide variety of soluble grinding resins and printing inks.

Description:
This application is a continuation-in-part of our commonly assigned, co-pending U.S. patent application Ser. No. 7/967,052 filed Oct. 28, 1992 now U.S. Pat. No. 5,216,071; which is a continuation-in-part of our commonly assigned, co-pending U.S. patent application Ser. No. 07/923,543 filed Aug. 3, 1992 now U.S. Pat. No. 5,189,090, entitled &#34;Hydroxyacrylic Modified Rosin Resins For Water-Based Coatings&#34;; which, in turn, was a continuation-in-part of U.S. patent application Ser. No. 07/796,651 filed Nov. 22, 1991, and expressly abandoned on Aug. 14, 1992. 
    
    
     FIELD OF INVENTION 
     This invention relates to novel water-based inks and coatings formulated utilizing grind bases produced from hydroxyacrylic modified rosin based ink pigment grinding resins. 
     BACKGROUND OF THE INVENTION 
     Impelled by environmental concerns and increasing governmental regulations on the volatile organic content of coatings, the applications of water-based flexographic and rotogravure inks are increasing in the ink industry. A typical water-based ink system is formulated by the addition of a binder resin (usually acrylic polymer latices) to a grind base. Grind bases are prepared by using grinding resins to disperse pigments. Pigments are crystalline solids composed of agglomerates, aggregates, and primary particles which vary in size from 0.02 to 0.50 microns. During the grinding process, agglomerates and aggregates are broken down into primary particles which possess strong tendencies to reassociate in an ink. The finer the particle size of the pigment, the greater the color strength, but the more difficult the pigment becomes to disperse. Grinding resins help prevent the particles from reassociating by increasing both the electrostatic and steric repulsion between pigment particles. 
     An ink formulator must consider the compatibility of the various ink components when selecting the grind resins to be used. Grind bases (i.e., pigment dispersions) are let down with a variety of alkali-soluble resins or alkali-insoluble resin emulsions to achieve the properties desired for the end use of the ink. If the grind resins and the let-down resins are not compatible, the result may be pigment flocculation, viscosity increase, loss of color strength, and other problems. 
     Soluble maleic resins have been used for several years in water-based inks and coatings. Typically these resins are partial esters of maleated or fumarated rosin with various polyols having acid numbers greater than 140. However, when used in aqueous pigment grinding media, these traditional maleic resins exhibit a major shortcoming--the viscosities of the resultant pigment dispersions tend to be unstable over time. 
     It is known to correct this problem by modifying maleic resins with styrene-allyl alcohol (SAA) copolymer, thereby producing pigment grinds with stable viscosities. SAA is a hard (softening point of 95°-110° C.) thermoplastic, low molecular weight polymer manufactured by the Monsanto Corporation. However, SAA copolymers have two significant disadvantages: 1) they are relatively expensive, and 2) they are currently commercially available in only two grades--RJ-100 (which has a molecular weight of 2340) and RJ-101 (which has a molecular weight of 1700). Thus, the range of maleic resins which may be formulated utilizing SAA is severely limited. 
     Therefore, it is the object of this invention to formulate water-based inks and coatings containing stable viscosity pigment grinds produced from soluble maleic grinding resins which are not SAA modified. 
     SUMMARY OF THE INVENTION 
     The object of this invention is met by replacing traditional SAA resins with hydroxyacrylic resins in an esterification reaction with fumarated or maleated rosin and a polyol. The hydroxyacrylic resins are produced by copolymerizing an hydroxyalkylacrylate or methacrylate with alkyl acrylates, cycloalkyl acrylates, methacrylates, or styrene. In addition to being relatively inexpensive to make, such hydroxyacrylic resins can be prepared to contain a wide range of molecular weights and hydroxyl contents. This versatility allows formulation of a wide variety of soluble maleic resins capable of being used as grind resins or let down resins for water-based ink vehicles and inks. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The process for producing the desired maleic resin comprises reacting in a fusion esterification reaction: 70-96% by weight of fumarated rosin, maleated rosin, or combinations thereof; 2-18% by weight of a polyol or combination of polyols; and 2-40% by weight of a hydroxyacrylic resin or combination of hydroxyacrylic resins. The resulting maleic resin may be utilized as a grind resin or as a let down resin, depending upon the requirements of the coating formulator. 
     Rosins which are suitable for use in the reaction include, but are not limited to, the following: 
     wood rosin, 
     tall oil rosin, and 
     gum rosin. 
     Tall oil rosin is preferred, more preferably fortified tall oil rosin made by reacting the rosins with varying amounts of fumaric acid, maleic anhydride, or maleic acid. Fortification of rosin is well known in the art, as evidenced by U.S. Pat. No. 2,994,635, which is hereby incorporated by reference. 
     Polyols which are suitable for use in the reaction include, but are not limited to, the following: 
     glycerol, 
     sorbitol, 
     pentaerythritol, 
     neopentyl glycol, 
     ethylene glycol, 
     diethylene glycol, 
     dipropylene glycol, 
     polyethylene glycol, and 
     combinations thereof. 
     Suitable polyethylene glycols and polyethylene glycol mixtures have a molecular weight in the range of 100-5,000. 
     Hydroxyacrylic resins suitable for use in formulating these maleic grinding resins are produced by reacting in a free radical addition polymerization reaction: 
     (a) 50.0-89.5 parts by weight of a member selected from the group consisting of styrene, alkyl acrylates, cycloalkyl acrylates, methacrylates, and combinations thereof where the alkyl or cycloalkyl group contains 1-18 carbon atoms, 
     (b) 10.0-50.0 parts by weight of a hydroxy-containing monomer, or combination of monomers, having the chemical structure: ##STR1## where R 1  is a hydrogen or methyl group and R 2  is a C 2  -C 4  alkylene, 
     (c) 0.5-12.0 parts by weight of a peroxide or azo catalytic initiator, and 
     (d) up to 10.0 parts by weight of a mercaptan-containing chain transfer agent. 
     Suitable hydroxyacrylic polymer resins have a molecular weight in the range of 1,000-9,000. Depending on the type of solvent employed in the polymerization reaction, it may be necessary to add a chain transfer agent to achieve the desired molecular weight. (For example, chain transfer agents may not be necessary when diethylene glycol, dipropylene glycol, and similar solvents are utilized.) Chain transfer agents which are suitable for use in the above reaction must contain a single mercaptan group and include, but are not limited to, the following: 
     dodecyl mercaptan, 
     mercaptoacetic acid, 
     mercaptopropionic acid, 
     octyl mercaptan, 
     2-mercaptoethanol, and 
     combinations thereof. 
     Catalytic peroxide or azo initiators suitable for use in the above reaction include, but are not limited to, the following: 
     azo-bis-isobutyonitrile, 
     benzoyl peroxide, 
     di-tert-butyl peroxide, 
     t-butyl peroctoate, 
     t-butyl peroxybenzoate, and 
     combinations thereof. 
     Solvents which are suitable for use in the polymerization reaction include, but are not limited to, the following: 
     methyl isobutyl ketone, 
     toluene, 
     ethanol, 
     isopropanol, 
     t-butanol, 
     diethylene glycol, 
     dipropylene glycol, and 
     combinations thereof. 
     In view of the teachings contained herein, it is well within the ability of a skilled artisan to utilize these solvents to produce hydroxyacrylic resins and maleic resins having different viscosities and solids levels. For ease of manipulation, it is preferable to produce hydroxyacrylic resins having a 50-80% solids level. 
     However, it is further preferred to utilize solid acrylate resins (preferably which have been ground or flaked) as produced via a continuously stirred-tank reactor method (see Example 5) in the practice of this invention for the following reasons. The above referenced solvents used in the polymerization reaction are water-miscible. When one produces the rosin grinding resin from the hydroxyacrylic resin using the standard non-solid acrylate resin procedure those solvents are distilled off. However, water from the esterification reaction also distills off to mix with the solvents. As it is uneconomical to separate this mixture into its solvent and water components, the usual practice is to incinerate the mixture. 
     In contrast, the solvent used in the procedure to produce flaked acrylate resin is stripped off during processing; thereby preventing the solvent from combining with water during the esterification step. This lowers both the cost and environmental impact of the procedure by allowing the solvents to be recycled. 
     In order to use solid acrylate resin it is necessary to utilize 10-32% by weight of a hydroxyacrylic resin during the fusion esterification reaction. 
     As appreciated in the art, the exact components and properties of components desired for any given ink application can vary, and, therefore, routine experimentation may be required to determine the optional components and proportions of components for a given application and desired properties. 
     The following examples are provided to further illustrate the present invention and are not to be construed as limiting the invention in any manner. 
    
    
     EXAMPLE 1 
     A hydroxyacrylic resin was produced via the following procedure. To a 500-ml flask fitted with a mechanical stirrer, reflux condenser, and two addition funnels was charged 60 g of methyl isobutyl ketone (MIBK). To the first addition funnel was charged 56.5 g of styrene, 43.5 g of 2-hydroxyethyl methacrylate, and 4.0 g of 2-mercaptoethanol. To the second addition funnel was added 20.0 g of MIBK and 2.0 g of t-butyl peroxybenzoate. The flask was heated to reflux (110° C.), and the contents of the two addition funnels were added concurrently over one hour. Refluxing was continued for three hours, after which a solution of 20.0 g of MIBK and 2.0 g of t-butyl peroxybenzoate was added over ten minutes. Refluxing was continued for three more hours. The resultant hydroxyacrylic resin solution had a solids content of 54% and a Gardner-Holt viscosity of J. 
     EXAMPLE 2 
     A hydroxyacrylic resin was produced via the following procedure. To a 500-ml flask fitted with a mechanical stirrer, reflux condenser, and two addition funnels was charged 60 g of toluene. To the first addition funnel was charged 45.5 g of styrene, 21.5 g of 2-ethylhexyl acrylate, 33.0 g of 2-hydroxyethyl methacrylate, and 6.0 g of 2-mercaptoethanol. To the second addition funnel was added 20.0 g of toluene and 2.0 g of t-butyl peroxybenzoate. The flask was heated to reflux (110° C.), and the contents of the two addition funnels were added concurrently over one hour. Refluxing was continued for three hours, after which a solution of 20.0 g of toluene and 2.0 g of t-butyl peroxybenzoate was added over ten minutes. Refluxing was continued for three more hours. The resultant acrylic resin solution (hereafter referred to as hydroxyacrylic resin no. 1) had a solids content of 53% and a Gardner-Holt viscosity of K. 
     A series of hydroxyacrylic resins were prepared using the above procedure wherein the composition of the resins and the solvents utilized were varied. The results are listed in Table I below. 
     
                       TABLE I______________________________________Hydroxyacrylic Resins                                 Gardner-                                 HoltResin No.   Composition*               Solvent    % Solids                                 Viscosity______________________________________1       45.5   Styrene  Toluene  51.3   E   21.5   2-EHA   33.0   HEMA   6.0    2-ME2       45.5   Styrene  Ethanol  50.2   A   21.5   2-EHA   33.0   HEMA   6.0    2-ME3       45.5   Styrene  Isopropanol                            49.9   E   21.5   2-EHA   33.0   HEMA   6.0    2-ME4       45.5   Styrene  t-Butanol                            50.9   T+   21.5   2-EHA   33.0   HEMA   6.0    2-ME5       51.0   Styrene  Isopropanol                            50.1   B-C   27.0   2-EHA   22.0   HEA   6.0    2-ME______________________________________ *2-EHA =  2ethylhexyl acrylate HEA = hydroxyethyl acrylate HEMA = hydroxyethyl methacrylate 2ME = 2mercaptoethanol 
    
     A polymer-modified maleic rosin resin was produced via the following procedure. ROSIN SS (250.0 g) was melted in a 1000-ml three-necked, round-bottomed flask. (ROSIN SS is a tall oil based rosin manufactured by Westvaco.) The flask was equipped with a Dean-Stark trap, condenser, nitrogen inlet, thermocouple, heating mantle, and heating tape. Fumaric acid (62.0 g) was added to the molten rosin at 150° C., and this mixture was heated to 200° C. and stirred for three hours. Next, a blend of triethylene glycol (17.5 g) and glycerol (10 g) was slowly added. The reaction mixture was stirred for one hour, and then hydroxyacrylic resin no. 1 (84.9 g at 53% solids in toluene) was added. The reaction was then held at 210° C. for three hours to produce a polymer-modified rosin resin (hereafter referred to as maleic resin no. 1). 
     A series of polymer-modified maleic rosin resins were prepared by following the above procedure and substituting the respective hydroxyacrylic resins listed in Table I. FILTREZ 5014® (a widely used SAA-containing rosin resin manufactured by the Filtered Rosin Products Corporation) was employed as a control against which the maleic resins were evaluated (via making different pH-level varnishes from the resins). The varnishes were made by mixing each respective maleic resin (35 parts), water (51.8 parts), isopropanol (7 parts), concentrated ammonium hydroxide (6 parts), and FOAMBLAST 1005 (0.2 parts) in a Waring Blender. (FOAMBLAST 1005 is a defoaming agent manufactured by the Ross Chemical Company.) The varnishes were allowed to stand overnight to let the air and foam dissipate. The results are given in Table II below. 
     
                       TABLE II______________________________________Maleic Resins          Varnish                                     Gardner-   Acid   Softening                  HoltResin No.   No.    Point, °C.                    No.  pH  % Solids                                     Viscosity______________________________________(Control)   171    143       A    8.2 35.4    Z5Filtrez                  B    8.9 34.8    R-50141       181    128       A    8.1 34.8    X-Y                    B    8.8 35.9    S+2       150    138       A    8.2 35.0    Z                    B    8.8 34.0    M-N3       169    131       A    8.2 35.1    X-Y                    B    8.7 34.5    N4       178    139       A    8.1 34.0    Z2+                    B    8.8 35.4    N5       181    132       A    8.3 34.7    F-G                    B    8.8 34.0    E______________________________________ 
    
     Half of the varnishes listed in Table II above (i.e., the B varnishes) were utilized to produce a series of grind bases via the procedure of combining 49.5 g of varnish, 50.0 g of phthalocyanine blue G.S. high-solids presscake (manufactured by Sun Chemical Company), and 0.5 g of FOAMBLAST 1005 in a Waring Blender. After five minutes of predispersion, the batch was poured in a &#34;quicky mill&#34; with 100.0 g of shot and placed on a Red Devil paint shaker for one hour. The grind bases were evaluated for viscosity, and the results are shown in Table III below. 
     
                                           TABLE III__________________________________________________________________________Phthalo Blue Grind BasesVarnish Grind     ShellFrom  Base     Cup        Grind Base Viscosity (sec)Resin No. pH  No.        1 Day            8 Days                15 Days                     22 Days                          29 Days__________________________________________________________________________Control 8.8 3  19  22  30   27   24     4  15  17  15   18   161B    8.6 3  64  77  77   74   92     4  37  43  46   61   762B    8.7 3  47  81  69   120  85     4  36  48  47   60   783B    8.5 3  68  72  86   92   &gt;120     4  48  52  56   56   624B    8.7 3  42  59  72   71   72     4  34  37  40   42   395B    8.3 3  23  30  41   42   44     4  16  21  25   28   26__________________________________________________________________________ 
    
     Water-based inks for printing on paper were produced from the grind bases described in Table III using the following formulation: 
     
         ______________________________________Grind base         60 parts by weightJONREZ E-2003      40 parts by weight.______________________________________ 
    
     (JONREZ E-2003 is an acrylic emulsion manufactured by Westvaco, Inc.) The hydroxyacrylic resin-based inks exhibited superior characteristics when compared to the SAA-containing control ink. 
     Water-based inks for printing on plastic film (such as polyethylene or polyester) were also produced from the grind bases described in Table III using the following formulation: 
     
         ______________________________________Grind base         55 parts by weightJONREZ E-2050      48 parts by weightJONREZ W-2320       5 parts by weightIsopropyl alcohol   2 parts by weight.______________________________________ 
    
     (JONREZ E-2050 is an acrylic emulsion manufactured by Westvaco, Inc. JONREZ W-2320 is a wax emulsion manufactured by Westvaco, Inc.) These hydroxyacrylic resin-based inks exhibited superior characteristics when compared to the SAA-containing control ink. 
     Thus, as indicated in Table I a variety of hydroxyacrylic resins can be produced in a number of solvents by following the above procedures. These hydroxyacrylic resins can be utilized to produce maleic resins (Table II), grind bases (Table III), and printing inks which compare favorably with their SAA-based counterparts. 
     EXAMPLE 3 
     A hydroxyacrylic resin was produced without employing a chain transfer agent via the following procedure. To a 500-ml flask fitted with a mechanical stirrer, reflux condenser, and an addition funnel was charged 70.80 g of dipropylene glycol To the addition funnel was charged 92.85 g of styrene, 31.40 g of hydroxyethyl acrylate, 19.45 2-ethylhexyl acrylate, and 11.50 g of t-butyl peroxybenzoate. The flask was heated to 150° C., and the contents of the addition funnel was added over a period of one hour. Heating was continued for at a temperature of 150° C. for four hours, after which the resultant hydroxyacrylic resin solution was allowed to cool. 
     A polymer-modified maleic rosin resin was produced using this hydroxyacrylic resin solution via the following procedure. To a 1000-ml three-necked, round-bottomed flask equipped with a Dean-Stark trap, condenser, nitrogen inlet, thermocouple, heating mantle, and heating tape was charged 400.0 g of ROSIN SS. The rosin was heated to 200° C., at which time 102.0 g of fumaric acid and one drop of ANTIFOAM A was added to the rosin. (ANTIFOAM A is a defoaming agent manufactured by Dow Corning, Inc.) This mixture was held at 200° C. and stirred for three hours, after which 16.0 g of glycerine was added. The reaction mixture was stirred at 200° C. for one hour, at which time 84.0 g of the hydroxyacrylic resin solution was added. This reaction mixture was held at 200° C. for four hours before cooling, thereby producing a polymer-modified rosin resin having an acid number of 188 and a softening point of 132° C. 
     EXAMPLE 4 
     A hydroxyacrylic resin was produced without employing a chain transfer agent via the following procedure. To a 500-ml flask fitted with a mechanical stirrer, reflux condenser, and an addition funnel was charged 56.00 g of diethylene glycol. To the addition funnel was charged 92.85 g of styrene, 31.70 g of hydroxyethyl acrylate, 19.45 2-ethylhexyl acrylate, and 11.50 g of t-butyl peroxybenzoate. The flask was heated to 150° C., and the contents of the addition funnel was added over a period of one hour. Heating was continued for at a temperature of 150° C. for four hours, after which the resultant hydroxyacrylic resin solution was allowed to cool. 
     A polymer-modified maleic rosin resin was produced using this hydroxyacrylic resin solution via the following procedure. To a 1000-ml three-necked, round-bottomed flask equipped with a Dean-Stark trap, condenser, nitrogen inlet, thermocouple, heating mantle, and heating tape was charged 400.0 g of ROSIN SS. The rosin was heated to 200° C., at which time 102.0 g of fumaric acid and one drop of ANTIFOAM A was added to the rosin. This mixture was held at 200° C. and stirred for three hours, after which 16.0 g of glycerine was added. The reaction mixture was stirred at 200° C. for one hour, at which time 84.0 g of the hydroxyacrylic resin solution was added. This reaction mixture was held at 200° C. for four hours before cooling, thereby producing a polymer-modified rosin resin having an acid number of 187 and a softening point of 133° C. 
     EXAMPLE 5 
     A solid flaked copolymer was made using a continuously-stirred tank reactor via the following procedure. A feed mixture of 78.0 parts of styrene, 32.4 parts of dipropylene glycol, 22.0 parts of hydroxyethyl methacrylate, 12.0 parts of di-tert-butyl peroxide and 3.0 parts of 2-mercaptoethanol was fed into the reactor at a rate of 7.3 g/minute. The temperature of the reactor was 160° C. and its pressure was held at 80 psig. The residence time of the mixture in the reactor was about 135 minutes. 
     The stream leaving the reactor discharged continuously into a heated flash vessel, which operated at about 10 mm Hg, absolute pressure. Average temperature of the resin in the flash vessel was 175° C. The stripped resin leaving the flash vessel had less than 0.03 wt. % styrene and less than 0.03 wt. % 2-hydroxyethyl methacrylate. Residual dipropylene glycol was about 3 wt. %. The resin yield was about 0.74 grams of resin per gram of feed mixture. 
     The cooled resin (which was subsequently flaked) was clear, glassy, and shatterable. Hydroxyl value was about 150 (mg KOH/g) and acid value was about 4.5 (mg KOH/g). The resin had a weight average molecular weight of 2550. 
     A polymer-modified maleic rosin resin was produced using this hydroxyacrylic copolymer via the following procedure. To a 1000-ml three-necked, round-bottomed flask equipped with a Dean-Stark trap, condenser, nitrogen inlet, thermocouple, heating mantle, and heating tape was charged 200.0 grams of ROSIN SS. The rosin was heated to 200° C., at which time 51.0 grams of fumaric acid and one drop of ANTIFOAM A was added. The mixture was held at 200° C. and stirred for three hours, after which 8.0 grams of glycerin and 6.0 grams of dipropylene glycol were added. The reaction mixture was stirred at 200° C. for one hour, at which time 72 grams of the flaked acrylic resin was added. This reaction mixture was held at 200° C. before cooling, thereby producing a polymer-modified rosin resin having an acid number of 160 and a softening point of 132° C. 
     Pigment grinds were made with this resin as described in Example 2. A pigment grind at pH 8.3 had an initial #3 Shell cup viscosity of 18 seconds and a viscosity after four weeks of 22 seconds. A pigment grind made at pH 8.9 had an initial viscosity of 25 seconds and a viscosity after four weeks of 28 seconds. 
     Many modifications and variations of the present invention will be apparent to one of ordinary skill in the art in light of the above teachings. It is therefore understood that the scope of the invention is not to be limited by the foregoing description, but rather is to be defined by the claims appended hereto.