Sixth, screen printing and drum printing fixed color
Once the fabric is screened or roller-printed, the color is positioned on the cloth and further processing is required for fixing.
Dyes used as print colorants must be able to bind fibers. The printing fabric can be fixed in a vapor whose temperature is close to or sometimes exceeds the boiling point of water (high-pressure steaming); this step is called steaming. After steaming, the fabric is passed through a soap bath to remove print paste and other materials used in the color paste formulation. Finally, the fabric goes through several washing and drying steps. In the printing process, a large amount of water and heat are consumed.
If a pigment, not a dye, is used in the print, the fabric needs to be subjected to a dry heat treatment up to about 210° C. to cure the fixed coating resin. This step is called baking and no longer requires further processing. Printing with pigments instead of dyes can save a lot of water and energy.
The textile industry generally refers to dye-printed fabrics as wet printed fabrics, while pigment-printed fabrics refer to dry printed fabrics. This is because wet printed fabrics require steam steaming and subsequent water washing as part of the overall process. On the other hand, calico fabric simply requires dry heat curing as part of the coloring process and does not require water washing.
Seven, thermal transfer printing
The principle of thermal transfer printing is somewhat similar to the transfer printing process. In thermal transfer printing, patterns are first printed on paper with disperse dyes and printing inks, and then printed paper (also known as transfer paper) is stored for use in textile printing plants.
During fabric printing, the heat transfer printing machine (shown in Figure 9-10) is used to attach the transfer paper and the unprinted face to face and pass the machine under conditions of approximately 210°C (400T) at such high temperatures. The dye on the transfer paper sublimates and is transferred to the fabric to complete the printing process without further processing. The process is relatively simple and does not require the specialized knowledge necessary for the production of cylinder printing or rotary screen printing (see Figure 9-11).
Disperse dyes are the only dyes that can be sublimed. In a sense, they are the only dyes that can be used for thermal transfer printing. Therefore, this process can only be used on fabrics that have affinity for such dyes, including acetate fibers and acrylics. Nitrile fiber, polyamide fiber (nylon) and polyester fiber. In thermal transfer printing, fabric printing plants purchase this type of printing paper from highly specialized printing paper manufacturers. The transfer paper can be printed according to the requirements of the designer and customer (ready-to-use designs can also be used for transfer printing).
Thermal transfer printing can be used to print clothing (such as border printing, chest pocket embroidery, etc.), in which case special designs are used. Thermal transfer printing stands out from the printing process as a complete fabric printing method, thus eliminating the need to use large and expensive dryers, steamers, washing machines, and tenters.
Since the printed paper can be inspected before printing, this eliminates inaccuracies and other illnesses. Therefore, thermal transfer printing fabrics rarely appear defective.
The speed of production of continuous thermal transfer printing is about 250 yards per hour.
Eight, jet printing and its development prospects
Jet printing is to spray small droplets of dye and stay in the precise position of the fabric. The nozzle and pattern used to jet the dye liquid can be controlled by computer, and complicated patterns and precise pattern cycles can be obtained.
Jet printing eliminates the delays and cost increases caused by engraving cylinders and screens. This is a competitive advantage in the rapidly changing textile market. The jet printing system is flexible and fast, and can quickly transfer from one pattern to another. The printed fabric is free from tension (that is, it will not be twisted due to stretching) and the fabric surface will not be pressed, thus eliminating potential problems such as fuzzing or napping of the fabric. However, this process cannot print fine patterns and the outline of the pattern is blurred.
Jet printing is almost always used for carpet printing, and it is not an important process for textile printing. However, with the research and development of mechanical and electronic control technologies, this situation may change. At present, several jet printers have been put into textile printing production, including Millitron liquid jet printers developed by Millilin and his company.