Abstract:
This invention pertains to inkjet printing on fabric and to a pretreatment solution for the fabric that allows high quality printing thereon.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority under 35 U.S.C. §119 from U.S. Provisional Application Ser. No. 60/551,275 (filed Mar. 8, 2004), the disclosure of which is incorporated by reference herein for all purposes as if fully set forth. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention pertains to inkjet printing on fabric and to a pretreatment solution for the fabric that allows high quality printing thereon.  
         [0003]     Digital printing methods such as inkjet printing are becoming increasingly important for the printing of textiles and offer a number of potential benefits over conventional printing methods such as screen printing. Digital printing eliminates the set up expense associated with screen preparation and can potentially enable cost-effective short run production. Inkjet printing furthermore allows visual effects such as tonal gradients and infinite pattern repeat sizes that cannot be practically achieved with a screen-printing process.  
         [0004]     One area of textile printing ideally suited to digital printing is the flag and banner market where short runs are common. However, printing of flags and banners presents unique challenges. For example, ink is printed on one side, but must penetrate the fabric so that the image is equally visible on the back (unprinted) side as the front (printed/face) side. In addition, while the ink must travel through the fabric, it must not travel laterally causing blurring and bleeding. This seemingly contradictory set of conditions is not easily achieved.  
         [0005]     U.S. Pat. No. 5,847,740 discloses an inkjet printing process on nylon cloth.  
         [0006]     U.S. Pat. No. 6,656,228 discloses a textile pretreatment solution comprising a cationic substance, an acid generator, and an alkyl or hydroxyalkyl substituted starch. Also disclosed is a polyamide textile pretreated with the composition and inkjet printing on the pretreated textile.  
         [0007]     US2002/0081421 discloses an aqueous coating formulation for enhancing the image of acid dye based inks on fabrics. The coating formulation includes a cationic polymer or copolymer, a fabric softener, urea, and ammonium salts of multifunctional weak acids.  
         [0008]     The above-mentioned publications are incorporated by reference herein for all purposes as if fully set forth.  
         [0009]     It is an object of this invention to enable high quality inkjet printing of flags and banners  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention pertains in one aspect to a pretreatment solution for fabric. The inventive pretreatment solution is an aqueous solution comprising a polycationic compound, a viscosity builder and an acid donor.  
         [0011]     The present invention pertains, in another aspect, to a fabric that has been treated with the inventive pretreatment solution. The wet pick-up of pretreatment solution, although not specifically limited, is advantageously in the range of about 20 to about 100 grams of solution, per 100 grams of fabric. In one embodiment, the wet pick-up of pretreatment solution is in the range of about 25 to about 75 grams of solution, per 100 grams of fabric. The fabric is preferably a woven fabric comprising a synthetic polyamide fiber such as nylon 6 and nylon 6,6 fiber.  
         [0012]     In yet another aspect, the present invention pertains to an inkjet printing method wherein the pretreated fabric is imaged with an inkjet printer. The printer can be, for example, the DuPont™ Artistri™ 2020 or 3210 printer, and associated inks. Especially preferred are acid dye inks.  
         [0013]     These and other features and advantages of the present invention will be more readily understood by those of ordinary skill in the art from a reading of the following detailed description. It is to be appreciated that certain features of the invention which are, for clarity, described above and below in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination. In addition, references to in the singular may also include the plural (for example, “a” and “an” may refer to one, or one or more) unless the context specifically states otherwise.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0000]     Pretreatment Solution  
         [0014]     The inventive pretreatment solution comprises a polycationic compound, a viscosity builder, an acid donor and water. Optionally, other ingredients can be added. Ingredient percentages mentioned herein after are weight percent based on the total weight of the final solution, unless otherwise indicated.  
         [0015]     The polycationic compound is an organic compound with a plurality of cationic (protonated or quarternized) amine groups. Suitable polycationic compounds preferably comprise on average at least five cationic amine groups per molecule, and more preferably on average 10 or more cationic amine groups per molecule, and includes, for example, cationic amine polymers. The cationic polymers can be low molecular weight, for example about 500 to about 1000 (Mn), or can be higher molecular weight, for example greater than about 10000 (Mn), or even greater than about 100000 (Mn). This will depend on a number of factors such as desired cationic content, solution viscosity and other desired properties recognizable by those of ordinary skill in the art.  
         [0016]     The polycationic compound is generally present in an amount of at least about 0.2 wt % up to about 10 wt %, and more typically in the range of about 0.3 wt % to about 4 wt %, based on the total weight of pretreatment solution.  
         [0017]     Examples of suitable cationic polymers include polyethyleneimines, polyallylamines and polyvinylpyridines. Cationic polymers are available commercially, for example, under the tradenames Polycup®, Perform™ and AquaCat™ from Hercules Incorporated (Wilmington, Del., USA); “Dye Techs” from American Textile, LLC (Duluth, Ga., USA); and, “Discofix” from Apollo Chemical Corporation (Burlington, N.C., USA).  
         [0018]     The viscosity builder increases the viscosity of the medium in which it is dissolved or dispersed, and is typically a high molecular weigh natural or synthetic polymer that swells in water. Examples include starch and its derivatives; cellulose and modified cellulose; guar gum; locust bean gum; and bio-synthetic gums like xanthan, gum arabic, gum tragacanth, polyvinylpyrrolidone and polyvinylalcohol. Preferred viscosity builders are cellulose derivatives.  
         [0019]     Preferably, the viscosity builder is not anionically charged at neutral pH. Viscosity builders comprised of a substantial number of carboxylic acid groups will be anionically charged at neutral pH and are preferably avoided. The viscosity builder is generally present in the range of about 0.5 wt % to about 10 wt %, and more typically in the range of about 1 wt % to about 4 wt % weight percent, based on the total weight of pretreatment solution.  
         [0020]     An acid donor is a compound that lowers the pH of the environment upon activation by heat. Such species are typically salts of organic or inorganic acids, preferably an ammonium, alkyl ammonium or quarternary ammonium salt. Most preferably the acid donor is ammonium salt such as ammonium sulfate. Other examples include ammonium citrate, ammonium acetate and the like. The acid doner is generally present in solution at about 0.5 wt % to about 20 wt %, and more typically about 1 wt % to about 10 wt %, based on the total weight of pretreatment solution.  
         [0021]     Other optional ingredients may include, but are not limited to, humectants and biocides. A humectant is an ingredient that can retain water and includes liquids such as (poly)glycols and (ethoxylated)glycerol, and solids such as urea. Biocides prevent microbial degradation—their selection and use is generally well known in the art. In a preferred embodiment, the pretreatment solution comprises urea, preferably in an amount ranging from about 0.5 wt % to about 5 wt % based on the total weight of the pretreatment solution.  
         [0022]     The balance of the pretreatment solution is water.  
         [0023]     The ingredient levels must be sufficient to provide adequate coating weight after drying, but not so high that the solution becomes too viscous and fails to coat and penetrate the fabric evenly. The viscosity at 25° C. is preferably greater than about 100 cP and less than about 2000 cP, more preferably between about 200 and about 1000 cP, and especially between about 250 and about 500 Cp. The pH of the pretreatment solution is preferably between about 6 and about 8, and preferably about neutral.  
         [0000]     Fabric Pretreatment  
         [0024]     The fabric to be pretreated is preferably a woven fabric comprising synthetic polyamide fibers. Most commonly, the synthetic polyamide fibers are nylon-6 and/or nylon-6,6 fibers. For flag and banner stock, the fabric is generally about 70 to about 200 deniers. A commercial example of such stock Solarmax® from Glen Raven Mills.  
         [0025]     Application of the pretreatment to the fabric can be any convenient method and such methods are generally well-known in the art. One example is an application method referred to as padding. In padding, a fabric is dipped in the pretreatment solution, then the saturated fabric is passed through nip rollers that squeeze out the excess solution. The amount of solution retained in the fabric can be regulated by the nip pressure applied by the rollers. Other pretreatment techniques include spray application wherein the solution is applied by spraying on the face or face and back of the fabric. The wet pick-up of pretreatment solution is preferably between about 20 and about 100 grams of solution, and more preferably between about 25 to about 75 grams of solution, per 100 grams of fabric.  
         [0026]     After application of pretreatment the fabric is dried in any convenient manner. The final percent moisture is (approximately) equal to the equilibrium moisture of the pretreated fabric at ambient temperature, and can vary somewhat depending on the relative humidity of the surrounding air.  
         [0027]     The resins remaining in the fabric after drying provide the absorbent layer for the inkjet inks during printing. It will be appreciated that sufficient resin must be present to absorb the ink load applied. On the other hand, the presence of too much resin may prevent proper penetration. Routine optimization will reveal appropriate coating levels for a given printer and ink set.  
         [0000]     Printing Method  
         [0028]     Printing can be accomplished by any inkjet printer equipped for handling and printing fabric. Commercial printers include, for example, the Dupont™ Artistri™ 3210 and 2020 printers, and the Mimaki TX series of printers.  
         [0029]     A variety of commercial ink sets are available for use with these printers. Especially useful for printing on nylon are acid dye inks.  
         [0030]     The amount of ink laid down on the fabric can vary by printer model, by print mode (resolution) within a given printer and by the percent coverage need to achieve a given color. The combined effect of all these considerations is grams of ink per unit area of fabric for each color. In one embodiment, ink coverage is adpreferably between about 5 to about 17 grams of ink per square meter of fabric. Again, there is a balance between the ink density needed to achieve a desired color and the absorption capacity of the coating resins in the pretreatment.  
         [0000]     Post Treatment of Fabric  
         [0031]     Printed fabric will typically be post-treated according to procedures well-known in the textile art.  
       EXAMPLES  
       [0000]     Pretreatment Solutions  
         [0032]     Pretreatment solutions were prepared according to the recipes in the following table. The identity of commercial components is as follows: 
        Natrosol®=Hydroxy ethyl cellulose (Hercules Corporation)     Polucup® 172 =Cationic polymer (Hercules Corporation)     Perform® 1279 =Cationic polymer (Hercules Corporation)        
 
         [0036]     Proxel GXL=Biocide (Avecia)  
                                                 Pretreatment Solution composition, as % weight                Ingredient   Control   Inventive Solution                       Polycationic Compound   0   As indicated           Natrosol ®   2   2           Ammonium sulfate   5   5           Urea   2   2           Proxel GXL     0.2     0.2           Water (balance to 100%)   Bal   Bal                      
 
         [0037]     In the above formulation, inventive solutions contained polycationic compound as follows: 
        Solution 1a=1% Perform® 1279     Solution 1b=2% Perform® 1279     Solution 1c=3% Perform® 1279     Solution 1d=5% Perform® 1279     Solution 2a=1% Polycup® 172     Solution 2b=2% Polycup® 172     Solution 2c=3% Polycup® 172     Solution 2d=5% Polycup® 172. 
 
 Fabric Pretreatment 
       
 
         [0046]     Fabric (Solarmax®), 200 denier nylon, was treated with each solution by standard padding procedures. The wet pick-up was 40 grams per 100 g of fabric. The treated fabric was dried by allowing it to stand for at least 8 hours at ambient room temperature (about 25° C.) at which point it had reached equilibrium moisture.  
         [0000]     Printing Conditions  
         [0047]     Dried, pretreated fabric was printed with a DuPont™ Artistri™ 2020 printer at 360×600 dpi with DuPont™ Artistri™ A774, A746, A795, A768, R715, R735, A743 and A776 inks.  
         [0048]     Various flags and banners were printed to give 50%-200% ink coverage. At the 360×600 dpi setting, 50% coverage was about 5.8 grams of ink per square meter of fabric, and 200% coverage was about 23.4 grams of ink per square meter of fabric.  
         [0000]     Post Treatment  
         [0049]     Printed samples were post-treated in saturated steam at 102° C. for 30 minutes then washed twice, first in cold water for 5 minutes, then in warm water (60° C.) for 10 minutes.  
         [0000]     Evaluation  
         [0050]     Color penetration to the back side of the fabric was evaluated according to the following formula:  
         Degree   ⁢           ⁢   of   ⁢           ⁢   penetration     =           K     S   face       -     K     S   back           K     S   face         ×   100   ⁢           ⁢   %         
 
 K/S is a Kubelka-Munk function that gives a measure of reflectance of an opaque layer at a given wavelength. Measurements were made with an X-rite spectrophotometer, model SP64. K/S is calculated from the reflectance as follows, K/S=(1−R) 2 /2R where R is the minimum reflectance in fraction. 
 
         [0051]     The absolute value of degree of penetration (difference in depth of color between face and back of fabric as calculated by the equation above) should be no more than 20%, and preferably as close to zero as possible. In other words, the printed fabric should have about the same color density on both sides of the fabric.  
         [0052]     Bleed is the lateral migration of ink away from the intended location on the fabric. It is evident as “blurred” or “feathered” lines or edges rather than sharp, straight edges and also as the unintended running together of adjacent colors. The evaluation of bleed, both color-to-color (for two adjacent colors) and color-to-white, was made visually according to the following scale: 
        Very Good=little or no bleed evident (commercially acceptable)     Good=slight amount of blurring, feathering or running of colors (marginally acceptable commercially)     Poor=severe blurring, feathering or running of colors (unacceptable)        
 
         [0056]     Results  
                                                                                 Degree of Penetration (%) - Pretreatment Solutions 1a-1d                1a   1b   1c   1d                    Color            American Flag Blue   −9.08   −7.32   −9.32   0.81       American Flag Red   −5.13   8.73   1.09   9.22       Union Jack Blue   −3.28   −4.16   0   17.7       Canadian Flag Red   0.54   10.6   3.94   13.2       Italian Flag Green   −1.08   3.53   6.64   6.0       Blue   −1.79   16.6   13.6   16.2       Black   50.5   65.7   58.2   65.7       Evaluation       Color/Color Bleed   Very good   Very good   Very good   Very good       Color/White Bleed   Very good   Very good   Very good   Very good                  
 
         [0057]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
               
               
                   
               
               
                 Degree of Penetration (%) - 
               
               
                 Pretreatment Solutions 2a-2d, and Control 
               
             
          
           
               
                 Color 
                 2a 
                 2b 
                 2c 
                 2d 
                 Control 
               
               
                   
               
             
          
           
               
                 American Flag Blue 
                 −20.7 
                 15.6 
                 15.4 
                 11.4 
                 1.02 
               
               
                 American Flag Red 
                 −4.1 
                 7.6 
                 2.65 
                 10.9 
                 7.42 
               
               
                 Union Jack Blue 
                 −7.92 
                 3.24 
                 3.67 
                 10.8 
                 4.25 
               
               
                 Canadian Flag Red 
                 0.86 
                 14.9 
                 10.1 
                 10.7 
                 2.94 
               
               
                 Italian Flag Green 
                 1.83 
                 1.7 
                 −1.1 
                 −0.96 
                 0 
               
               
                 Blue 
                 1.93 
                 20.4 
                 29.2 
                 13.7 
                 16.2 
               
               
                 Black 
                 48.7 
                 47.7 
                 46.1 
                 47.7 
                 37.5 
               
               
                 Evaluation 
               
               
                 Color/Color Bleed 
                 Good 
                 Good 
                 Good 
                 Good 
                 Poor 
               
               
                 Color/White Bleed 
                 Very good 
                 Very good 
                 Very 
                 Very 
                 Poor 
               
               
                   
                   
                   
                 good 
                 good 
               
               
                   
               
             
          
         
       
     
         [0058]     As can be seen from the results, use of polycationic compounds reduced color/color and color/white bleed significantly compared to the control without cationic polymer, yet generally allowed good penetration for even color on both sides of the fabric. Although both the cationic agents were effective, the Perform® 1279 was somewhat better overall than the lower molecular weight Polycup® 172 because of the superior color/color bleed results.  
         [0059]     The poor degree of penetration results particular to the black color (&gt; than 20%) indicate the printer settings or ink formulation for that color needs to be adjusted.