Analysis Of Current Mainstream Printing Technology

1、 Screen printing

Screen printing includes the preparation of printing screens. Printing screens (screens used for printing were once made of fine silk, which is called screen printing. Although silk screens are no longer used, screen printing is still often used in the printing process.) Made of polyester fiber or metal wire fabric. The screen fabric shall be coated with an opaque non porous film. Where there are patterns, the opaque film should be removed and the screen with fine mesh should be left. This area is where the pattern will be printed. Most commercial screen fabrics are first coated with a layer of photosensitive film, and then the pattern is displayed by removing the film at the pattern part through photosensitive method. 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 the scraper (a tool similar to the windshield wiper). Each color in the printed pattern needs a separate screen to print different colors. Example 3 Three screen frames are needed for color printing, and three colors are printed on the fabric respectively. In addition, the pattern of each color in the pattern must be accurately positioned on the screen so that the pattern position is accurate after printing, avoiding the phenomenon that the green stem of a rose is printed in the middle of the red petals. Printing to pattern refers to the industrial term that all patterns and colors are accurately printed on the fabric. There are three methods to realize screen printing, and the application principle of each method is basically the same. The first is manual screen printing, which was very popular in the 1920s and is still widely used today. Until the mid-1950s, when modern technology gave this process automation, manual screen printing was the only screen printing method. The second method is called automatic screen printing (also called flat screen printing and automatic flat screen printing). In the mid-1960s, there was further development. The screen shape changed from manual and automatic flat screen to round screen. The third method is called circular screen printing.

2、 Manual screen printing

Manual screen printing is commercially produced on long platens (platens up to 60 yards). The printed cloth roll is smoothly laid on the platen, and the surface of the platen is pre coated with a small amount of viscous substances. Then the printer moves the screen frame continuously by hand along the whole platen, printing one screen frame at a time until the fabric is completely printed. Each screen frame corresponds to a printed pattern. The production speed of this method is 50-90 yards per hour. Commercial manual screen printing is also widely used to print cut pieces. In the garment piece printing process, the garment making process and the printing process are arranged together. Before the pieces are sewn together, the customized or unique patterns are printed on the pieces. Because manual screen printing can produce large screen frames for large flower patterns, fabrics such as beach towel, novel printed apron, curtain and shower curtain can also be printed by this printing method. Hand screen printing is also used to print limited, highly fashionable women clothing And printing small quantities of products for market exploration.

3、 Automatic screen printing

Automatic screen printing (or flat screen printing) is the same as manual screen printing except that the process is automatic, so it is faster. The printed fabric is conveyed to the screen by wide rubber belt instead of being placed on the bench (like manual screen printing). Like manual screen printing, automatic screen printing is also an intermittent rather than a continuous process. In this process, the fabric is moved under the screen, and then stopped. The scraper on the screen scratches (automatic nail 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 can only be used for the whole roll of fabric, and the cut pieces are generally not printed in this way. As a commercial production process, the output of automatic screen printing (i.e. flat screen printing) is declining due to the preference for rotary screen printing with higher production efficiency.

4、 Rotary screen printing

Rotary screen printing is different from other screen printing methods in several important aspects. Like the drum printing described in the next section, the rotary screen printing is a continuous process. The printed fabric is conveyed to the bottom of the moving rotary screen vase through wide rubber belts. Among screen printing, the production speed of rotary screen printing is the fastest, more than 3500 yards per hour. Use seamless perforated metal mesh or Plastic Web. The circumference of the largest round mesh is greater than 40 inches, so the maximum return size is also greater than 40 inches. Rotary screen printing machines with more than 20 colors have also been produced, and this printing method is slowly replacing drum printing.

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5、 Drum printing

Drum printing, like newspaper printing, 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 drum printing, the pattern is printed on the fabric through carved copper rollers (or rollers). The copper cylinder can be carved with closely arranged fine lines, so it can print very fine and soft patterns. For example, the fine and dense Pelizley vortex tweed printing is a kind of pattern printed by roller printing. The flower tube carving shall be completely consistent with the design drawings of the pattern designer, and each kind of design and color requires a carving roller. (on spin In specific printing processing, five roll printing, six roll printing, etc. are often used to indicate five or six color roller printing. Drum printing is a mass printing production method with the least use, and the output continues to decline every year. If the production volume of each pattern is not very large, this method will not be economical. In most cases, the cost of drum preparation and equipment adjustment is high and consumption is long, which makes this method of printing less economical. However, drum printing is often used for printing with extremely thin line patterns, such as the Pedsley vortex tweed printing and the main printing patterns printed in large quantities in many seasons. The size of the carved flower tube depends on the printing machine and the printing pattern. Most printing machines can be equipped with a flower tube with a maximum circumference of 16 inches, which means that the size of the printing pattern cycle cannot exceed 16 inches. The width of the flowerpot should be slightly larger than the width of the printed fabric so that the fabric, including the selvage, can be printed with patterns inside. Once ready, the printing cylinder can be used almost limitlessly, and there is no problem in printing millions of yards of fabric.

6、 Color fixation after screen printing and drum printing

Once the fabric passes through the screen or drum printing, the color is positioned on the cloth, and further processing is required to fix the color. Dyes used as printing colorants must be able to combine with fibers. The printed fabric can be fixed in the steam whose temperature is close to or sometimes exceeds the boiling point of water (high-pressure steam); This step is called steaming. After steaming, the fabric should go through a soap bath to remove other substances used in the printing paste and color paste formula. Finally, the fabric goes through several washing and drying processes. A large amount of water and heat energy are consumed in the printing process. If pigments rather than dyes are used in printing, the fabric needs to undergo dry heat treatment up to 210 ℃ to solidify the resin of the fixing paint. This process is called baking, and no further treatment is required. Printing with pigments instead of dyes can save a lot of water and energy. The textile industry usually refers to the fabrics printed with dyes as wet printed fabrics, and the fabrics printed with pigments as dry printed fabrics. This is because the wet printed cloth needs steam steaming and subsequent water washing as part of the whole process. On the other hand, the printed fabric only needs to be simply dry and hot baked as part of the dyeing process, without water washing.

7、 Heat transfer printing

The principle of heat transfer printing is somewhat similar to that of transfer printing. In thermal transfer printing, patterns are first printed on paper with disperse dyes and printing inks, and then printing paper (also called transfer paper) is stored for use by textile printing plants. When printing the fabric, the transfer paper and the unprinted face to face are stuck together through the heat transfer printing machine (as shown in Figure 9-10). The dye on the transfer paper sublimates and transfers to the fabric at such a high temperature under the condition of about 210 ℃ (400T). The printing process is completed without further treatment. The process is relatively simple and does not require the necessary expertise in drum printing or rotary screen printing. Disperse dyes are the only dyes that can be sublimated and, in a sense, the only dyes that can be used for thermal transfer printing. Therefore, this process can only be used on fabrics composed of fibers that have affinity for such dyes, including acetate fibers, acrylonitrile fibers, polyamide fibers (nylon) and polyester fibers. For thermal transfer printing, textile printing plants should purchase such printing paper from highly specialized printing paper manufacturers. Transfer paper can be printed according to the requirements of pattern designers and customers (ready-made patterns can also be used for transfer paper printing). Heat transfer printing can be used to print garment pieces (such as edge printing, chest pocket embroidery, etc.), in which case a specially designed pattern should be used. As a complete textile printing method, heat transfer printing stands out from the printing process, thus eliminating the use of huge and expensive dryers, steaming machines, washing machines and stenters. As the printing paper can be inspected before printing, the inaccurate printing and other defects can be eliminated. Therefore, the heat transfer printing fabric rarely appears defective. The production rate of continuous heat transfer printing is about 250 yards per hour.

8、 Jet printing and its development prospect

Jet printing is to spray small dye droplets and stay in Textile The nozzle and pattern forming used to spray dye solution can be controlled by computer at the precise position of, and complex patterns and precise pattern circulation can be obtained. Jet printing eliminates the delay and cost increase caused by engraving rollers and screen making, which is a competitive advantage in the fast changing textile market. The jet printing system is flexible and fast, and can quickly transfer from one pattern to another. The printed fabric is not subject to tension (that is, the pattern will not be distorted due to stretching), and the fabric surface will not be rolled, thus eliminating potential problems such as fabric fuzzing or fuzzing. However, this process cannot print fine patterns, and the pattern outline is vague. Now jet printing is almost used for carpet printing, not an important process of clothing textile printing. However, with the research and development of mechanical and electronic control technology, this situation may change.