Abstract:
A dyeing system composition for use in printing articles formed from cellulose prior to dyeing. The dyeing system composition includes the use of both a dye blocking print paste and a dye enhancing print paste to selectively decrease or increase the shade of dyed portions of a cellulose article such as a woven cotton fabric.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates generally to printing cellulosic articles and, more particularly, to a new and improved method of screen printing fabrics, in which the fabric article is first selectively printed with a chemical system including a dye blocking print paste and a dye enhancing print paste and subsequently dyed to bring out the print. 
     (2) Description of the Prior Art 
     Traditional screen printing of garments is done by printing ink, binder, thickener and softener combinations on dyed or white prepared for print (PFP) garments. A detailed description of the screen printing process is published in the Encyclopedia of Textiles, Second Edition, 1972 Prentice-Hall, Inc., Englewood Cliffs N.J., the disclosure of which is hereby incorporated by reference in its entirety. The following discussion is taken from the above-referenced Encyclopedia of Textiles. 
     The screen printing method in textiles is basically a stencil process. A wooden or metal frame is covered with a bolting cloth, which may be made of silk, fine metal thread, or nylon. The fabric is covered with a film and the design areas are cut out of the film just as in stencil making. The frame is then laid on the fabric and color is brushed or squeezed through the open areas of the film by the use of a big rubber knife or squeegee. 
     Originally, the design was cut out of film and then adhered to the screen. Today the cutting is done mechanically by a photo-chemical process which reproduces the design exactly as it was painted in the art which is being reproduced. 
     In printing, one screen is used for each color and these are accurately registered one on the other by the use of fixed stops attached to an iron rail running the length of the table. The length of the table determines the number of yards which can be printed at one laying; this varies depending on the available space, though 30 yards is considered the smallest space which is practical for economic production. 
     While screen printing, either by hand or machine, is a slower and more expensive process than roller printing, it has several virtues. From the point of view of design, pattern repeats can be much larger than in roller printing. Also, since the process is slower, pigment colors can be laid on in heavy layers to produce a handicraft effect. From an economic point of view, it does not require as large an investment as roller printing because the runs can be shorter, especially in the hand operation. This has encouraged smaller converters to adopt the screen method and to experiment more with design than they would be able to do in the roller method, where they would be required to contract for a minimum of about 8000 yards per pattern. 
     One of the most important physical parameters for good screen printing is that the print paste is thick enough to stand in a gel state until it is dried and cured. This assures clean crisp definition of the print. 
     However, the print paste still must flow readily and evenly. These two properties are defined as the rheology of the print paste and the most desirable property is called pseudo-plastic or the ability of the paste to become less viscous when moved by pump or mechanical device and to thicken or become more viscous when it stills. 
     Because of the nature of the print paste, screen prints are generally opaque and rubbery to the touch. In addition, these prints are not very durable especially when washed. There has been much work done in developing softer prints that do not crack and peel after washing and these softened prints are called &#34;plastisols,&#34; but they are still based on pigments, binder, thickener and are still a surface coating which can be &#34;felt&#34;. 
     Thus, there remains a need for a new and improved method of screen printing in which the garment or fabric may be printed using traditional screen printing techniques while, at the same time, provides printed areas which can not be rubbed off or felt to the touch. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a dyeing system composition for use in printing articles or fabrics formed from cellulose prior to dyeing. In the preferred embodiment, the dyeing system composition includes the selective use of both a dye blocking print paste and a dye enhancing print paste to selectively decrease or increase the shade of the dyed portions of a cellulose article, such as a woven or knitted cotton or cotton/polyester article or fabric. 
     In the preferred embodiment, the dye blocking print paste includes a thickener and a dye blocking agent. The dye blocking agent includes a pre-catalyzed cross-linking glyoxal resin and a dye resist. Also, in the preferred embodiment, the dye enhancing print paste includes a thickener and an epoxy functional quaternary ammonium enhancing agent. The thickener for both print pastes, preferably, is an acid/alkali stable hydroxypropyl guar derivative, polyscaharride, dispersed in an invert emulsion. 
     Accordingly, one aspect of the present invention is to provide a dye blocking print paste for use in printing articles formed from cellulose prior to dyeing. The composition includes: (a) a thickener; and (b) a dye blocking agent, the dye blocking agent including a cross-linking resin and a dye resist. 
     Another aspect of the present invention is to provide a dye blocking print paste for use in printing articles formed from cellulose prior to dyeing. The composition includes: (a) a thickener; and (b) a dye blocking agent, the dye blocking agent including a pre-catalyzed cross-linking resin and a dye resist. 
     Still another aspect of the present invention is to provide a dyeing system composition for use in printing articles formed from cellulose prior to dyeing. The composition includes: (a) a dye blocking print paste, the dye blocking print paste including: (i) a thickener and (ii) a dye blocking agent, the dye blocking agent including a pre-catalyzed cross-linking resin and a dye resist; and (b) a dye enhancing print paste, the dye enhancing print paste including: (i) a thickener and (ii) an enhancing agent. 
     These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment when considered with the examples. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is performed in the reverse order of traditional garment or fabric screen printing. According to the present invention, the garment or fabric is print prepared (e.g. scoured and bleached white) or griege (unprepared) with a chemical system including a dye blocking print paste and a dye enhancing print paste. 
     The dye blocking print paste includes a wetting agent, a thickener paste; and a dye blocking agent, the dye blocking agent including a cross-linking resin and a dye resist to selectively decrease the shade of the dye. In the preferred embodiment, the dye enhancing print paste includes a wetting agent, thickener and a dye enhancing agent which is used to selectively increase the shade of the dye. 
     In the preferred embodiment, the thickener paste for both the dye blocking and the dye enhancing print paste is an acid/alkali stable hydroxypropyl guar derivative, polyscaharride, dispersed in an invert emulsion. Specifically, the polysaccharide concentrate includes about 35 weight percent water, 10 weight percent emulsifier, 10 weight percent polysaccharide and 45 weight of a petrol solvent. 
     Also, the cross-linking resin used in the dye blocking agent is preferably a pre-catalyzed glyoxal resin although it is believed that a self-catalyzed glyoxal resin might also work. In the preferred embodiment, the dye resist used in the dye blocking agent is a low molecular weight polyacrylic acid having a molecular weight of about 2000. One suitable dye resist is sold under the tradename BURCO® Dye Resist 118 by Burlington Chemical Company, Inc. of Burlington, N.C., the assignee of the present invention. 
     Finally, the enhancing agent used in the dye enhancing print paste is preferably an epoxy functional quaternary ammonium compound. One suitable dye resist is sold under the tradename BURCO® DCE by Burlington Chemical Company, Inc. of Burlington, N.C., the assignee of the present invention. 
     The cellulosic article, garment or fabric is then dyed to the desired shade with the blocking and enhancing print pastes selectively either reducing the amount of dye on the fabric or enhancing the dye on the fabric. If we measure the background and set it arbitrarily as 100%, the enhanced regions are 250% deeper in color and the blocked regions are 90% lighter than the background. 
     Further examples of the present invention can be seen in a camo print on 100% cotton knit fabric where various concentrations of the enhancer chemical are printed on and then dyed. 
    
    
     The present invention can be best understood by a review of the following examples: 
     EXAMPLES 1-2 
     A dye blocking print paste was prepared using both pre-catalyzed glyoxal resin and a conventional glyoxal resin according to the amounts in weight percent shown in Table 1. Cotton fabric was printed with the dye blocking print paste, the print paste was allowed to dry and cure and conventional reactive and direct dyeing were made. The results are shown in Table 1, below: 
     
                       TABLE 1______________________________________        Pre-        Catalyzed       Poly-        Glyoxal  Glyoxal                        acrylic                              Wetting                                     ShadeEx. Paste    Resin    Resin  Acid  Agent  Difference______________________________________1   15 wt. % 15 wt. % --     5 wt. %                              0.1 wt. %                                     -90%2   15 wt. % --       15 wt. %                        5 wt. %                              0.1 wt. %                                     No                                     Effect!______________________________________ 
    
     As can be seen, only the dye blocking print paste including a pre-catalyzed glyoxal resin was effective in blocking the dye. 
     EXAMPLES 3-6 
     A dye blocking print paste was prepared using pre-catalyzed glyoxal resin according to the amounts in weight percent shown in Table 2. Cotton fabric was printed with the dye blocking print paste, the print paste was allowed to dry and cure and conventional reactive and direct dyeing were made. The results are shown in Table 2, below: 
     
                       TABLE 2______________________________________        Pre-        catalyzed       Poly-        Glyoxal  Glyoxal                        acrylic                              Wetting                                     ShadeEx. Paste    Resin    Resin  Acid  Agent  Difference______________________________________3   15 wt. % 15 wt. % --     5 wt. %                              0.1 wt. %                                     -90%4   15 wt. % 10 wt. % --     5 wt. %                              0.1 wt. %                                     -60%5   15 wt. %  5 wt. % --     5 wt. %                              0.1 wt. %                                     -30%6   15 wt. % 2.5 wt. %                 --     5 wt. %                              0.1 wt. %                                     -10%______________________________________ 
    
     As can be seen, the dye blocking print paste having between about 5 to 15 wt. % pre-catalyzed glyoxal resin produced a linear relationship between the weight percent of resin and the shade difference in blocking the dye. 
     EXAMPLES 7-10 
     A dye blocking print paste was prepared using pre-catalyzed glyoxal resin according to the amounts in weight percent shown in Table 3 and both with and without polyacrylic acid. Cotton fabric was printed with the dye blocking print paste, the print paste was allowed to dry and cure and conventional reactive and direct dyeing were made. The results are shown in Table 3, below: 
     
                       TABLE 3______________________________________        Pre-        catalyzed      Poly-        Glyoxal  Glyoxal                       acrylic                              Wetting                                     ShadeEx. Paste    Resin    Resin Acid   Agent  Difference______________________________________7   15 wt. % 15 wt. % --     5 wt. %                              0.1 wt. %                                     -90%8   15 wt. % 15 wt. % --    --     0.1 wt. %                                     -60%9   15 wt. % 2.5 wt. %                 --    --     0.1 wt. %                                     No                                     Effect!10  15 wt. % --       --    15 wt. %                              0.1 wt. %                                     No                                     Effect!______________________________________ 
    
     As can be seen, the addition of polyacrylic acid improved the effectiveness of the dye blocking print paste 50% when comparing Example 7 to Example 8. In addition, only the dye blocking print paste including a pre-catalyzed glyoxal resin was effective in blocking the dye even when the amount of polyacrylic acid was increase to 15 wt. %. 
     Dyeings were than made using the thickener of the present invention along with a conventional epoxy functional quaternary ammonium compound to form a dye enhancing print paste. This compound has been used in the past to react with cellulose to yield a permanent cationic site on the cellulose to improve dye yield. If we measure the background and set it arbitrarily as 100%, the enhanced regions were 250% deeper in color than the background when dyed with fiber reactive and direct dyes. 
     Finally, fabric was screen printed using a combination of the blocking print paste and enhancing print paste according to the present invention. Dyeing to the desired shade with the blocking and enhancing print pastes selectively either reduced the amount of dye on the fabric or enhanced the dye on the fabric. If we measure the background and set it arbitrarily as 100%, the enhanced regions were 250% deeper in color and the blocked regions were 90% lighter than the background! 
     Certain modifications and improvements will occur to those skilled in the art upon a reading of the foregoing description. By way of example, while the preferred embodiment of this invention is directed to printing cotton and cotton/polyester fabrics, it could be easily adapted to printing other cellulosic articles. Also, non-polymer organic acids, such as citric acid, maleic acid and BTCA, other cationics and other thickeners may work. It should be understood that all such modifications and improvements have been deleted herein for the sake of conciseness and readability but are properly within the scope of the following claims.