Basic concept of printing
1. Printing
The process of printing floral patterns with a certain color fastness on textiles with dyes or pigments.
2. Classification of printed objects
The main objects of printing are fabrics and yarns. The former attaches the pattern directly to the fabric, so the pattern is clearer. The latter is to print the pattern on the assembly of yarns arranged in parallel, and after weaving, the fabric produces a pattern effect with a hazy style.
Third, the difference between printing and dyeing
1. Dyeing is to dye the dye evenly on the textile to obtain a single color. Printing is to print patterns of one or more colors on the same textile, which is actually partial dyeing.
2. Dyeing is to mix the dye into a dye solution and dye it on the fabric through water as a medium. In printing, the dye or pigment is used as the dyeing medium, and the dye or pigment is mixed into a printing paste for printing on the fabric. After drying, the subsequent treatments such as steaming and color development are carried out according to the nature of the dye or color to make it dye or fix On the fiber, it is finally soaped and washed with water to remove the floating color and the paint and chemicals in the color paste.
Four, pre-processing for printing
Similar to the dyeing process, the fabric must be pretreated before printing to obtain good wettability so that the color paste can evenly enter the fiber. Plastic fabrics such as polyester sometimes need to be heat-set to reduce shrinkage and deformation during the printing process.
Five, the method of printing
According to the printing process, there are direct printing, anti-dye printing and discharge printing; according to the printing equipment, there are mainly roller printing, screen printing and transfer printing. From the printing method, there are manual printing and mechanical printing. Mechanical printing mainly includes screen printing, roller printing, transfer printing and liquid jet printing. The first two applications are more common.
Printing method and its characteristics
According to the printing equipment, fabric printing can be divided into: screen printing, roller printing, heat transfer printing, wood template printing, hollow pattern printing, tie dyeing, batik, splash printing, hand-painted printing, etc. Among them, there are two printing methods of commercial importance: screen printing and roller printing. The third method is thermal transfer printing, which is of relatively low importance. Other printing methods that are rarely used in textile production are traditional wood template printing, wax printing (that is, wax proof) printing, yarn tie-dye printing and anti-dye printing. Many textile printing factories mostly use screen printing and roller printing to print fabrics. Most thermal transfer printing performed by printing factories are also printed in this way.
Traditional printing technology
1. Wood template printing: the method of printing on the fabric on the embossed wood.
2. Hollow type printing: mainly divided into three categories: hollow type white paste anti-dyeing indigo printing, hollow type white paste anti-dyeing paste printing and hollow type color paste direct printing.
3. Tie-dye printing: bind the fabric with a string, sew it into a certain fold, and then bind it firmly to obtain a pattern after dyeing.
4. Batik printing: smear the areas that need to show patterns on cotton, silk and other fabrics, then dip or brush dye to make the non-wax parts of the fabric dyed into color, and then remove the wax stains in boiling water or a specific solvent to make the fabric appear Out the pattern.
5. Splash printing: use acid dyes to splash or brush colors on the silk fabric, and then sprinkle salt on the screen while it is still wet, and use the neutralization effect of salt and acid dyes to form a natural flowing abstraction on the silk Pattern. Often used in silk.
6. Hand-painted printing: A printing method in which a pen is directly dipped in the dye solution to draw patterns on the fabric.
Screen printing
Screen printing includes the preparation of a printing screen. The printing screen (the screen used in the printing process was once made of fine silk. This process is called screen printing. It is made of fine mesh nylon, polyester fiber or metal wire fabric. The screen fabric should be coated with an opaque non-porous film. Where there are patterns, the opaque film should be removed, leaving a fine mesh screen. This The area is the part where the pattern will be printed. Most commercial screen fabrics are first coated with a layer of photosensitive film, and then the film on the pattern part is removed by the photosensitive method to show the pattern. Place a screen on the fabric to be printed for printing Pour the printing paste into the printing frame, and force it through the mesh of the screen through a scraper (a tool similar to a windshield wiper on a car). Each color in the printing pattern needs its own needs A screen, the purpose is to print different colors.
Manual screen printing
Manual screen printing is commercialized on the long platen (platen length is 60 yards). The printed cloth rolls are spread smoothly on the platen, and the surface of the platen is pre-coated with a small amount of viscous material. Then the printing worker moves the screen frame by hand continuously along the entire platen, printing one screen frame at a time, until the fabric is completely printed. Each screen frame corresponds to a printing color. The production speed of this method is 50-90 yards per hour. Commercial manual screen printing is also widely used to print tailored garment pieces. In the garment printing process, the garment making process and the printing process are arranged together. Before the garment pieces are sewn together, the customized or unique patterns are printed on the garment pieces. Because manual screen printing can produce large screen frames for large floral patterns, fabrics such as beach towels, novel printed aprons, curtains and shower curtains can also be printed by this printing method. Hand screen printing is also used to print limited, highly fashionable women’s clothing and to print small batches of products for market exploration.
Automatic screen printing
Automatic screen printing (or flat screen printing) is the same as manual screen printing except that the process is automated, so the speed is faster. The printed fabric is transported to the screen through a wide rubber belt, instead of being placed on a long table (like manual screen printing). Like manual screen printing, automatic screen printing is also an intermittent rather than continuous process. In this process, the fabric is moved under the screen and then stopped. The scraper on the screen performs scraping (automatic scraping). After scraping, the fabric continues to move under the next screen frame. The production speed is about 500 yards per hour. . The automatic screen printing roller can only be used for the whole roll of fabric, and the cut piece is generally not printed in this way. As a commercial production process, the output of automatic screen printing (referring to flat screen printing) is declining due to the preference for rotary screen printing with higher production efficiency.
Rotary screen printing
Rotary screen printing differs from other screen printing methods in several important ways. Rotary screen printing is the same as the cylinder printing described in the next section. It is a continuous process. The printed fabric is transported to the bottom of the continuously moving cylinder through a wide rubber belt. Among screen printing, rotary screen printing has the fastest production speed, which is greater than 3,500 yards per hour. Use seamless perforated metal mesh or plastic mesh. The circumference of the largest cylinder is greater than 40 inches, so the largest flower back size is also greater than 40 inches. Rotary screen printing machines with more than 20 sets of colors have also been produced, and this printing method is slowly replacing drum printing.
Roller printing
Cylinder printing is like newspaper printing. It is a high-speed process that can produce more than 6000 yards of printed fabric per hour. This method is also called mechanical printing. In cylinder printing, the pattern is printed on the fabric through an engraved copper cylinder (or roller). The copper cylinder can be engraved with very delicate fine lines that are closely arranged, so that very delicate and soft patterns can be printed. For example, the fine and dense Paleysley swirl pattern printing is a type of pattern printed by roller printing. The engraving of the flower tube should be exactly the same as the design draft of the pattern designer. Each design needs an engraving roller. Roller printing. Roller printing is the least used mass printing production method, and the output continues to decrease every year. If the batch for producing each pattern is not very large, this method is not economical.
Heat transfer printing
The principle of thermal transfer printing is somewhat similar to the transfer printing method. In thermal transfer printing, first use disperse dyes and printing inks to print patterns on paper, and then store the printing paper (also called transfer paper) for use in textile printing plants. When fabric printing, through a thermal transfer printing machine, the transfer paper and the unprinted surface are stuck together, and the machine passes through the machine at about 210°C (400T). Under such high temperature, the dye on the transfer paper sublimates and transfers. On the fabric, the printing process is completed without further processing. The process is relatively simple and does not require professional knowledge required in the production of roller printing or rotary screen printing. Disperse dyes are the only dyes that can be sublimated. In a sense, they are the only dyes that can transfer flowers. Therefore, this process can only It is used on fabrics composed of fibers that have affinity for such dyes, including acetate fibers, acrylonitrile fibers, polyamide fibers (nylon) and polyester fibers.
Jet printing
Jet printing is to spray small droplets of dye and stay on the precise position of the fabric. The nozzle and pattern formation used to spray the dye solution can be controlled by a computer, and complex patterns and precise pattern circulation can be obtained. Jet printing eliminates the delay and cost increase caused by engraving rollers and making screens. This is a competitive advantage in the fast-changing textile market. The jet printing system is flexible and fast, and can quickly change from one pattern to another. The printed fabric is not under tension (that is, the pattern will not be twisted due to stretching), and the surface of the fabric will not be rolled , Thus eliminating potential problems such as fabric fuzzing or raising. However, this process cannot print fine patterns, and the outlines of the patterns are blurred. Now jet printing is almost used for carpet printing, not an important process for garment textile printing. However, with the research and development of mechanical and electronic control technology, this situation may change.