There are several methods of textile printing, two of which are of commercial importance: screen printing and rotary screen printing. The third method is thermal transfer printing, which is of r...
There are several methods of textile printing, two of which are of commercial importance: screen printing and rotary screen printing. The third method is thermal transfer printing, which is of relatively low importance. In recent years, digital printing has developed strongly, and the color and printing clarity have become higher and higher. It has developed from the original proofing to a mass production line. Other printing methods rarely used in textile production are: wood template printing, wax valerian (i.e. wax resist) printing, yarn tie-dye printing and resist dyeing printing.
1. Screen printing
Screen printing involves the preparation of a printing screen. The screen used in the printing process was once made of fine silk. The process is called screen printing. Today, silk screens are no longer used, but the name screen printing is still often used in the printing process. Made of nylon, polyester or wire fabric with a fine mesh stretched tightly over a wooden or metal frame. The screen fabric should be coated with an opaque, non-porous film. Where there are patterns, the opaque film should be removed, leaving a screen with fine mesh. This area is where the pattern will be printed. Most commercial mesh fabrics are first coated with a photosensitive film, and then the film in the patterned area is removed by photosensitivity to reveal the pattern. Print by placing a screen over the fabric to be printed. Pour the printing paste into the printing frame and use a scraper to force it through the mesh of the screen.
Each color in the printing pattern requires a separate screen in order to print different colors separately. For example, 3-color printing requires 3 screen frames to print 3 colors on the fabric respectively. In addition, each color pattern in the pattern must be accurately positioned on the screen so that the pattern position is accurate after printing, to avoid a phenomenon such as the green stem of a rose being printed in the middle of the red petals. Printing is an industrial term that refers to the accurate printing of all pattern colors on fabrics.
There are three methods to achieve screen printing, and the application principles of each method are basically the same. The first is hand screen printing, which was very common in the 1920s and is still widely used today. Until the mid-1950s, when modern technology enabled this process to be automated, manual screen printing was the only screen printing method. The second method is called automatic screen printing (also known as flat screen printing and automatic flat screen printing). In the mid-1960s, there was further development, and the shape of the screen changed from manual and automatic flat screens to round screen shapes. The third method is called circular screen printing or rotary screen printing, which is currently the most widely used screen printing method.
2. Hand-made screen printing
Hand screen printing is commercially produced on long pallets (up to 60 yards long). The printed cloth roll is spread smoothly on the table, and the surface of the table is pre-coated with a small amount of sticky substance. The printer then moves the frames by hand continuously along the entire platen, printing one frame at a time, until all the fabric is printed. Each screen frame corresponds to a printing color. The production speed of this method is 50-90 yards per hour. Commercial hand screen printing is also used extensively to print cut garments. In the garment printing process, the garment making process and the printing process are arranged together. Customized or unique patterns are printed on the pieces before they are sewn together. Because hand screen printing can produce large frames for large flower patterns, fabrics such as beach towels, innovative printed aprons, curtains and shower curtains can also be printed with this printing method.
Hand-screen printing
Hand screen printing is also used to print limited edition, highly fashionable women’s clothing and to print small batches of products intended for market launch.
3. Automatic screen printing
Automatic screen printing (or flat screen printing) is the same as manual screen printing except that the process is automated, so it is faster. The printed fabric is transported to the screen via a conveyor belt, rather than being placed on a long table (as in manual screen printing).
Screen printing
Like manual screen printing, automatic screen printing is an intermittent rather than a continuous process. In this process, the fabric moves under the screen and then stops. The scraper on the screen performs scraping and printing. After scraping and printing, the fabric continues to move under the next screen frame. The production speed is about 500 yards per hour. Automatic screen printing can only be used for the entire roll of fabric, and cut pieces of clothing are generally not printed using this method. 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.
4. Rotary screen printing
Rotary screen printing differs from other screen printing methods in several important ways. Rotary screen printing, like the drum printing to be described in the next section, is a continuous process. The printed fabric is transported under the continuously moving rotary screen tube through a conveyor belt. Among screen printing, rotary screen printing has the fastest production speed, greater than 3,500 yards per hour. Use seamless perforated metal or plastic mesh. The circumference of a large rotary screen is greater than 40 inches, so the size of a large flower return is also greater than 40 inches. Rotary screen printing machines with more than 20 colors have also been produced. This printing method has gradually replaced roller printing.
Rotary screen printing
5. Roller printing
Roller printing is like newspaper printing. It is a high-speed process that can produce more than 6,000 yards of printed fabric per hour. This method is also called mechanical printing. In roller printing, the pattern is printed on the fabric through an engraved copper roller (or roller). The copper roller can be engraved with very fine fine lines that are closely arranged, so it can print very detailed and soft patterns. For example, the fine, dense Perisli scroll tweed print is a type of pattern printed by roller printing. The flower tube engraving should be completely consistent with the design drawings of the pattern designer. Each color requires an engraving roller. In specific printing processing in the textile industry, five-roller printing, six-roller printing, etc. are often used to represent five-color or six-color roller printing.
Roller printing is a low-use mass printing production method. In recent years, the output has continued to decline every year because this method is not economical if the batch size of each pattern is not produced in very large quantities. In most cases, the high cost and time consuming nature of drum preparation and equipment adjustments make printing using this method less economical. However, roller printing is often used for prints with very fine line patterns such as paisley tweed prints and staple prints that are printed in large quantities for many seasons.
The size of the engraving tube depends on the printing machine and printing pattern. Most printing machines can be configured with a floral tube with a maximum circumference of 16 inches, which means that the size of the printing pattern loop cannot exceed 16 inches. The width of the floral tube should be slightly larger than the width of the printed fabric so that the fabric, including the edges, can be completely printed with the pattern. Once prepared, the printing cylinder can be used almost unlimitedly, typically printing millions of yards of fabric without issue.
6. Color fixation after screen printing and roller printing
Once the fabric has been screen or roller printed, the color is positioned on the cloth and requires further processing to fix the color.
Dyes used as printing colorants must be able to bind to fibers. The printed fabric can be solidified by placing it in steam with a temperature close to or sometimes exceeding 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 the printing paste and other substances used in the color paste formulation. 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 be subjected to dry heat treatment of up to about 210°C to solidify the resin that holds the coating. This step is called baking and no further treatment is required. Printing with pigments instead of dyes saves a lot of water and energy.
In the textile industry, fabrics printed with dyes are usually called wet printed fabrics, while fabrics printed with pigments are called dry printed fabrics. This is because wet calico requires steaming, and subsequent washing. The latter simply requires dry heat baking as part of the coloring process and does not require water washing.
7. Thermal transfer printing
The principle of thermal transfer printing is somewhat similar to transfer printing. During thermal transfer printing, patterns are first printed on paper with disperse dyes and printing inks, and then the printing paper (also called transfer paper) is stored for use in textile printing factories.
Thermal transfer printing
When the fabric is printed, it passes through a thermal transfer printing machine, so that the transfer paper and the unprinted paper are pasted face to face, and pass through the machine at about 210°C (400T). At such a high temperature, the dye on the transfer paper sublimates and transfers. onto the fabric, completing the printing process and requiring no further processing. The process is relatively simple and does not require the expertise necessary in roller printing or rotary screen printing production.
Disperse dyes are the only dyes that can sublime, and 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 composed of fibers that have an affinity for such dyes, including acetate fibers and acrylic fibers. Nitrile, polyamide (nylon) and polyester. When doing thermal transfer printing, fabric printing factories purchase this 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).
Thermal transfer printing can be used to print garment parts (such as edge printing, breast pocket embroidery, etc.), in which case specially designed patterns should be used. Thermal transfer printing stands out from the printing process as a complete fabric printing method, thus eliminating the need for large and expensive dryers, steamers, washers and tenters.
Since the printing paper can be inspected before printing, inaccurate registration and other defects are eliminated. Therefore, defects in thermal transfer printed fabrics are rare.
The production speed of continuous thermal transfer printing is approximately 250 yards per hour.
8. Digital printing and its development prospects
Digital 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 cycles can be obtained.
Digital printing eliminates the delays and added costs of engraving drums and making screens, a competitive advantage in the fast-changing textile market. The digital printing system is flexible and fast, and can quickly switch from one pattern to another; the printed fabric is not tension-free (that is, the pattern will not be distorted due to stretching), and the surface of the fabric will not be rolled. , thus eliminating potential problems such as fabric fluffing or fluffing, and is especially suitable for printing small batches and multiple varieties of printing patterns. With the development of technology, there are more and more choices of printing colors and the clarity is getting higher and higher. The Italian MS digital printing machine JP5 evo can have 4-8 printing heads, a width of 180 cm, and a printing accuracy of 600*600dpi. Italy’s Reggiani can already produce 8-16 printing heads, with a printing speed of 400 square meters per hour and a printing accuracy of 2400dpi × 2400dpi.
Italian MS digital printing machine
Italian Reggiani digital printing machine
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