Abstract:
A printing ink composition containing resin and glycerine, wherein the composition has less than 5 wt. % volatile organic compounds and has no hazardous air pollutants and a method of preparing such composition.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to printing ink compositions having less than 5 percent by weight (wt. %) of volatile organic compounds (VOCs) and no hazardous air pollutants. More specifically, this invention relates to the use of glycerine in printing ink formulations to dissolve the resin, thereby reducing the need for employing VOCs.  
         BACKGROUND OF THE INVENTION  
         [0002]    VOCs are photoreactive chemicals that contain elemental carbon that can lead to ozone formation. In the printing ink industry, VOCs are used to control the properties of the printing ink. Each VOC is property specific. For example, an alcohol is used to decrease the drying rate of an ink and a glycol would be used to increase the drying rate of the same ink. These chemicals may also affect the printability properties of the ink such as lay, color, shade and strength, and rub resistance to name a few and may further affect the processing and rheological (flow) properties of the printing ink as well.  
           [0003]    The benchmark for desired reaction rates of hydrocarbon-based compounds or VOCs is ethane. If a compound has a reaction rate with the hydroxyl radical and ultraviolet (“UV”) light that is faster than ethane, the compound reacts too close to the ground and consequently generates ozone and smog. Such compounds are defined as volatile organic compounds (VOCs). On the other hand, if a compound has a reaction rate that is slower than ethane, then the compound reaches higher into the atmosphere before reacting with the hydroxyl radical and UV light. In such instances, such compound does not contribute to the formation of ground based ozone and smog and therefore, is not considered a VOC.  
           [0004]    The printing ink industry has a need to reduce VOC emissions as a result of state and federal health, safety and environmental laws and regulations, which affect printers. This has caused the industry to search for alternate chemicals, which would reduce the VOC levels and yet maintain or even enhance the properties of the ink. Another concern is the presence hazardous air pollutants (HAPs) employed in printing inks which under the Federal Clean Air Act (FCAA) and Environmental Protection Agency (EPA), printers will perhaps be required to keep HAPs emission inventories.  
           [0005]    Diethylene glycol, a common ingredient in aqueous letterpress printing inks, is an example of a VOC, while ethylene glycol is considered to be a VOC and a HAP.  
           [0006]    In the United States, if a manufacturer emits air pollutants which must be controlled (such as VOCs or HAPs), the federal guidelines dictate adopting one of two courses of action to mitigate their emissions. The first is using engineering controls such as thermal or catalytic afterburners. This of course is a primary economic concern from the capital and operation perspective. The second is employing an alternate technology to reduce the amounts of VOCs and HAPs.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention provides a printing ink composition comprising a resin and glycerine having less than 5 wt. % VOC and no HAPs.  
           [0008]    The present invention also provides a printing ink composition additionally comprised of monoethanolamine, having less than 3 wt. % VOC and no HAPs.  
           [0009]    The present invention further provides a method of preparing an aqueous letterpress or flexographic printing ink compositions containing resin and using glycerine to dissolve the resin, wherein said ink composition has less than 5 wt. % VOC and no HAPS.  
           [0010]    Other objects and advantages of the present invention will become apparent from the following description and appended claims.  
         DETAILED DESCRIPTION OF THE INVENTION  
         [0011]    It has been surprisingly found that the use of glycerine as a primary solvent for a printing ink resin imparts good flow properties and sufficient press stability to the ink without compromising on print quality and allows for the production of printing inks having no HAPs and a VOC content of less than 5 wt. %.  
           [0012]    Preferably, the resin suitable for use in the present invention is maleic, acrylic or a combination thereof and the glycerine is preferably present at a concentration of about 25 to 80 wt. %, more preferably at 40 to 60 wt. %.  
           [0013]    Commercial letterpress or flexographic water-washable printing inks, such as HydroSet (available from Sun Chemical Corporation, Fort Lee, N.J.) typically consists of a conventional pigment dispersion in an aqueous acrylic resin, blended with a maleic and acrylic resins dissolved in propylene glycol (PG) and diethylene glycol (DEG). Both of these glycols are VOCs and present in the diethylene glycol is ethylene glycol, which is a HAPs.  
           [0014]    HydroSet has a history of good printing performance and customer satisfaction. Therefore, a successful low VOC, HAPs free alternate to HydroSet would be required to exhibit the printing and end-use press performance the letterpress and flexographic printing industries have come to expect from HydroSet, as well as offering the equivalent manufacturing ease in production. Acceptable press performance requires that the printing ink stay wet (or “open”) upon reaching the printing press, but dry rapidly enough on the substrate being printed so as not to smear or “track” on the substrate. The prints must also offer the color strength and gloss equivalent to the standard established by HydroSet.  
           [0015]    A number of solvent and resin combinations were evaluated as possible alternates to HydroSet. All except one, where the vehicle selected is dissolved in glycerine, failed in performance related either to its insufficient press stability or to poor print quality. Since glycerine is a no-HAPs and non-VOC material, the use of the glycerine as a vehicle as demonstrated below in the examples, provided the press stability and print quality equivalent to printing inks formulated with the “standard” HydroSet.  
           [0016]    Accordingly, under the present invention low VOC letterpress and flexographic printing inks for use in paper packaging, for example, (hereafter referred to as “Compliant Ink”) were formulated having a much lower VOC content than other commercially available letterpress and flexographic printing inks used in paper packaging. In addition, unlike many of the currently available printing inks for this particular application, the ink contained no HAPs materials. Lab evaluation of open time and press stability was made by observing the change in tack of the ink as it was run on an Inkometer; a machine with rotating rollers that simulates the action of rollers on a printing press. Ink transfer and print quality were evaluated with the use of a Vandercook proofing press.  
           [0017]    Table 1 shows the composition for a typical non-Compliant water-washable letterpress or flexographic ink (HydroSet) used for paper packaging where the VOC content is 374.5 grams/liter (29.1%). The percentages expressed below are based on the total weight of the printing ink.  
                                     TABLE 1                       INGREDIENT               DESCRIPTION   INGREDIENT (wt.)   VOC CONTENT (%)                                Maleic Resin   26.3   0       Acrylic Resin   5.3   0       Diethylene   16.2   16.2       Glycol       Ethylene   9.9   9.9       Glycol       Water   7.2   0       Monoethanolamine   1.9   1.9       No. 2 Cup   3.0   1.1       Grease       Pigment   4.2   0       Clay   25.0   0       Wax   1.0   0       TOTAL   100.0   29.1                  
 
           [0018]    Table 2 shows a composition for a Compliant Ink where the VOC content is only 24.4 grams/liter (1.9%).  
                                                 TABLE 2                                   INGREDIENT   INGREDIENT               DESCRIPTION   (wt.%)   VOC CONTENT (%)                                        Maleic Resin   10.7   0           Acrylic Resin   5.9   0           Glycerine   43.6   0           Water   7.8   0           Monoethanolamine   1.9   1.9           Pigment   4.4   0           Clay   24.7   0           Wax   1.0   0           TOTAL   100.0   1.9                      
 
           [0019]    The invention is illustrated in even more detail by the following specific examples, but those of ordinary skill in the art will understand that the inveniton is not limited to the details thereof and that changes may be made without departing from the scope of the invention. 
       
    
    
     EXAMPLE 1  
       [0020]    HydroSet 74 Red (available from Sun Chemical Corporation, Fort Lee, N.J.) was used as a standard for comparing the performance and properties of the experimental ink formulas under the present invention.  
         [0021]    Results for the Tack Stability Test for HydroSet 74 Red were:  
                                                                 ELAPSED               TIME (minutes)   TACK                                        1   11.0           2   14.0           3   17.0           4   18.5           5   21.0                      
 
         [0022]    The results indicate that tack began decreasing at 13 minutes, an indication that the ink was drying on rollers. The tack was checked on a Twing-Albert Inkometer at 800 RPM. Tack of production batches were read at 1 minute. For evaluation of reformulation variables, tack was read at 1, 2, 3, 4, and 5 minutes and then allowed to run until the ink dried, with a notation of the lapsed time until drying on the rollers occurred.  
         [0023]    After the tack was verified to be within specification, the sample was readied for printing on a Vandercook Proof Press. Using an S &amp; V Volummeter, the standard print film thickness was obtained by filling the volummeter to 13 clicks. The ink was applied to the bed of the press and rolled out to a uniform thickness with a hand brayer (i.e. plate). The ink thus transferred was transferred 6 times, each time in a different direction. GCMI Edition VIII stock was used as the substrate and strips of each were put together for a single print on three different substrates. The stock was inserted in the press grippers and the prints were made by bringing the substrate into contact with the ink. The plate should be adequately shimmed so as to insure proper print impression. The prints were then air dried for color comparison and for rub test performance. The prints were dried at 100° F. for 8 minutes.  
       EXAMPLE 2  
       [0024]    The stability of several experimental variations of HydroSet 74 Red using different solvents were evaluated. The open time test results are shown below in Table 3.  
                           TABLE 3                           Resin       Open Time       Resin Type   Solvent   Solvent   (minutes)                   Maleic/Acrylic   EG/DEG   DEG   13.0       Maleic   PG   PG    4.0       Maleic   PG   DEG    5.0       Maleic/Acrylic   PG   PG    3.5       Maleic/Acrylic   PG   DEG    3.5       Maleic/Acrylic   PG   DEG + 6% Cup   Dried Immed.               grease                          
 
         [0025]    We observed that none of the printing inks formulated with resin and propylene glycol had adequate open time. Furthermore, the addition of 6% cup grease caused the printing ink containing propylene glycol to dry immediately on the rollers, even before the ink had spread evenly across the rollers. This indicates that the cup grease contributes not only to tack and rheology of an ink, but also to its drying rate.  
       EXAMPLE 3  
       [0026]    Printing inks containing both glycerine and Polyglycol E300 (a polyethylene glycol) were formulated and selected for evaluation as representative non-VOC and non-toxic printing inks (i.e. compliant inks) under the present invention. Data were obtained (see Table 4) for a standard HydroSet 74 Red and six experimental variations.  
         [0027]    VOC data was derived by computation, with inks containing ethylene glycol, diethylene glycol, and propylene glycol considered 100% VOCs. The VOC data does not include the amines in the ink, which are estimated to be below 32 gram/liter.  
         [0028]    Method for Calculating Theoretical VOC (Grams/Liter)  
         [0029]    The following method was used for calculating theoretical VOC (gms/L). While this method is useful for experimental formulation, samples should also be subjected to the standard industry accepted Method 24 analysis for certifiable VOC determination.  
         WT/GAL INK÷WT/GAL WATER=SPECIFIC GRAVITY  (1)  
         [0030]    Thus, for a production sample of HS 74 Red (HydroSet): 10.74 lbs./gal.÷8.345 lbs./gal.=1.287 specific gravity  
         SPEC. GRAV. OF INK×1,000 GRAMS=GRAMS/LITER OF INK  (2)  
         [0031]    Water weighs 1,000 grams/liter. Multiplying the specific gravity of the ink by 1,000 grams will give the grams per liter weight of the ink. Thus: 1.287×1,000 grams=1,287 grams/liter  
         % VOCs×INK GRAMS/LITER=VOC GRAMS/LITER  (3)  
         [0032]    To determine grams of VOCs per liter, multiplying the percentage by weight of VOCs in the formula by the ink&#39;s gram weight per liter.  
         [0033]    The standard HydroSet 74 Red contains 9.9% ethylene glycol and 16.2% diethylene glycol, both of which are VOCs. In addition, the formula contains up to 2.5% MEA, another VOC. This gives a total of 28.6% VOCs by weight. Thus: 0.286×1,287 grams=368 grams/liter  
         [0034]    The solvents shown below represent the liquid portions of the resin cuts and any free liquid incorporated into the ink. This does not include the water possibly present in the maleic anhydride pigment dispersion. Solvents used were ethylene glycol (EG); glycerine; diethylene glycol (DEG); Polyglycol E300 (P300); propylene glycol (PG) and water.  
         [0035]    Tack Stability Tests were conducted using a Model B45 (manual) Thwing-Albert Inkometer at 800 RPM. Tack readings were made at 1, 2, 3, 4, and 5 minutes of elapsed time. Samples that showed good stability were run longer. Two samples demonstrated excessive tack increases and were removed from the Inkometer well before 5 minutes had elapsed. The tack increase values shown in Table 4 are the difference between the 5 minute reading and the 1 minute reading.  
                                             TABLE 4                               VOC   TACK       RESIN   % SOLVENT   (gms/L)   INCREASE                                Maleic/Acrylic (standard)    9.9 EG   336   5.4           16.2 DEG       Maleic   28.2 P300   0   0           11.0 GCN       Maleic   17.6 DEG   227   0           10.8 GCN            6.5 P300       Maleic/Acrylic   18.8 P300   0   2.7            9.2 H 2 O       Maleic/Acrylic   33.0 P300   0   3.6            8.5 H 2 O       Maleic/Acrylic   18.8 PG   242   12.3           11.0 GCN       (at 3 min.)       Maleic/Acrylic   18.8 PG   242   16.7 (at 3 min.)           11.0 P300       27.2 (at 4 min.)                  
 
         [0036]    The tack for the standard formula (i.e. HydroSet) had increased 15.2 points at 10 minutes and began decreasing at 11.5 minutes, which was an indication that the ink was drying on the print rollers. The polyglycol/glycerine solvent combination showed no tack increase at 10 minutes and had an increase of only 0.2 points after 15 minutes. The polyglycol/water solvent combination had a total tack increase of 6 points at 10 minutes.  
       EXAMPLE 4  
       [0037]    Maleic/Acrylic resin ink formulations having different solvents were evaluated for tack and print appearance and compared to the standard (HydroSet). The results are shown in Table 5.  
                   TABLE 5                       FORMULATION   TACK AND APPEARANCE                   All glycerine - no cup grease   tack-10 at 1-3 minutes       Maleic/Acrylic resin   tack-11 at 4-20 minutes           Appearance comparable to           HydroSet with slightly faster drying.       Glycerine/DEG - no cup grease   tack-11 at 1-20 minutes       Maleic/Acrylic resin   Transfer not as good as all glycerine           formulation.       Glycerine/water - no cup grease   Dried on Inkometer.       Maleic/Acrylic resin       Polyglycol E300/PG/Water/   Dried on Inkometer, but maintained       Maleic/Acrylic   some tack.                  
 
         [0038]    The observations on the drying rates for the above formulas were summed up as follows:  
                           TABLE 6                                       Drying Results (compared to           Solvent   Std.)                           Glycerine   comparable to Std.           Glycerine/Water   faster than Std.           Glycerine/PG (or)   slower than Std.           Glycerine/DEG           PG/Water   set comparable, final dry               slower than Std.                      
 
         [0039]    The results of the experimental data in Examples 1 to 4 clearly show that glycerine formulations are the best suited to give printing results that are comparable to the commercial standard (HydroSet) without exceeding the 5 wt. % VOC limit.  
         [0040]    The invention has been described in terms of preferred embodiments thereof, but is more broadly applicable as will be understood by those skilled in the art. The scope of the invention is only limited by the following claims.