Fabric printing technology and process
Basic concepts of printing
1. Printing: The process of printing floral patterns with certain dye fastness on textiles using dyes or pigments.
2. Classification of printed matter
The objects of printing are mainly fabrics and yarns. The former attaches the pattern directly to the fabric, so the pattern is clearer. The latter is to print patterns on a collection of parallel-arranged yarns, and after weaving, the fabric will produce a hazy pattern effect.
3. The difference between printing and dyeing
1. Dyeing is to dye the dye evenly on the textile to obtain a single color. Printing is a pattern of one or more colors printed on the same textile, which is actually partial dyeing.
2. Dyeing is to prepare dye into a dye solution and dye it on the fabric through water as a medium. Printing uses slurry as the dyeing medium. The dye or pigment is mixed into the printing paste and printed on the fabric. After drying, steaming, color development and other subsequent treatments are carried out according to the properties of the dye or color to dye or fix it. On the fiber, it is finally soaped and washed to remove floating colors and paints, chemicals, etc. in the color paste.
4. Pre-printing treatment
Similar to the dyeing process, the fabric must be pre-treated 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.
5. Printing method
According to the printing process, there are direct printing, resist 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 spray printing. The first two applications are more common.
Printing methods and characteristics
According to the printing equipment, fabric printing can be mainly divided into: screen printing, roller printing, heat transfer printing, wood template printing, hollow pattern printing, tie dyeing, batik, splash printing, hand-painted printing, etc. There are two printing methods of considerable 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 include traditional wood template printing, wax valerian (i.e. wax resist) printing, yarn tie-dye printing and resist dyeing printing. Many textile printing factories mostly use screen printing and roller printing to print fabrics. Most thermal transfer printing performed by printing factories is also printed using this method.
traditional printing techniques
1. Wood template printing: A method of printing on fabric using relief wood.
2. Hollow-type printing: mainly divided into three categories: hollow-type white paste anti-dye indigo printing, hollow-type white paste anti-dye paste printing and hollow type color paste direct printing.
3. Tie-dye printing: Use cords to bundle the gray fabric, sew it into a certain fold, then bundle it firmly, and obtain the pattern after dyeing.
4. Batik printing: smear on cotton, silk and other fabrics where patterns need to appear, and then dip-dye or brush-dye to dye the wax-free parts of the fabric with color, and then remove the wax stains in boiling water or a specific solvent to make the fabric now Out of pattern.
5. Splash printing: Use acid dyes to splash or brush colors on the silk fabric at will, and then sprinkle salt on the painting while it is still wet. With the help of the neutralization effect of salt and acid dyes, a naturally flowing abstraction is formed on the silk. Pattern. Often used on silk.
6. Hand-painted printing: A printing method that uses a pen to directly dip the dye solution into the fabric to draw patterns on the fabric.
screen printing
Screen printing involves the preparation of printing screens. Screen printing screens (screens used in the printing process were once made of fine silk) are called screen printing. 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 area where the pattern will be printed. Most commercial mesh fabrics are first coated with a photosensitive film, and then the film in the pattern area is removed by photosensitivity to reveal the pattern. A screen is placed on the fabric to be printed for printing . Pour the printing paste into the printing frame, and use a scraper (a tool similar to a wiper on a car windshield) to force it through the mesh of the screen. Each color in the printing pattern needs its own A screen is used to print different colors respectively.
Hand screen printing
Hand screen printing is commercially produced on long plates (plates 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 screen frames by hand continuously along the entire platen, printing one screen frame at a time, until all the fabrics are 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.
Customer-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, novel printed aprons, curtains and shower curtains can also be printed using this printing method. 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.
Automatic screen printing Automatic screen printing (or flat screen printing) is the same as manual screen except that the process is automated, so it is faster. The printed fabric is conveyed to the screen via a wide rubber belt, rather than being placed on a long table (as in manual 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 (automatic scraping). After scraping, 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.
Rotary Screen Printing Rotary screen printing differs from other screen printing methods in several important ways. Rotary screen printing, like the roller printing to be described in the next section, is a continuous process in which the printed fabric is transported under a constantly moving rotary screen tube 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 or plastic mesh. The largest rotary screen circumference is greater than 40 inches, so the largest flower return size is also greater than 40 inches. Rotary screen printing machines with more than 20 colors have also been produced. This printing method is slowly replacing roller printing.
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 carved with very fine fine lines that are closely arranged, so it can print very detailed and soft patterns. For example, the fine and dense Perisli scroll printing 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 the special printing processing of the textile industry, five-roller printing, six-roller printing, etc. are often used to represent five sets of colors or six sets of colors). Roller printing. Roller printing is the least-used mass printing production method, and output continues to decrease every year. This method is not economical if the batch size of each pattern is not very large.
Thermal transfer printing The principle of thermal transfer printing is somewhat similar to the transfer printing method. 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. 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 required in roller printing or rotary screen printing production. Disperse dyes are the only dyes that can be sublimated and, in a sense, the only dyes that can be thermally transferred. Therefore, this process can only Used on fabrics composed of fibers that have an affinity for such dyes, including acetate fiber, acrylic fiber, polyamide fiber (nylon) and polyester fiber.
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 cycles can be obtained. Jet printing eliminates the delays and costs of engraving drums and making screens, a competitive advantage in the fast-changing textile market.
The jet printing system is flexible and fast, and can quickly switch from one pattern to another. The printed fabric is not under tension (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 fuzzing or linting. However, this process cannot print fine patterns, and the outline of the pattern is blurred. Nowadays, jet printing is almost always used for carpet printing and is not an important process for clothing textile printing. However, with research and development in mechanical and electronic control technology, this situation may change.
Basic methods of printing
Printing can be divided into direct printing, discharge printing and resist printing according to printing equipment.
1. Direct printing Direct printing is a kind of printing directly on white fabric or on pre-dyed fabric. The latter is called overprinting. Of course, the color of the printed pattern is much darker than the dyed base color. A large number of common printing methods are direct printing. If the background color of the fabric is white or mostly white, and the printed pattern looks lighter from the back than the front, then we can determine that it is a directly printed fabric (note: due to the strong penetration of printing color paste, it is suitable for light and thin products. Fabrics cannot be judged by this method). If the background color of the fabric is the same on the front and back (because it is piece dyed), and the printed pattern is much darker than the background color, then this is an overprinted fabric.
2. Discharge printing Discharge printing is carried out in two steps. The first step is to dye the fabric piece into a solid color. The second step is to print the pattern on the fabric. The printing paste in the second step contains strong bleaching agents that can destroy the background dye, so this method can produce floral cloth with a blue background and white dot pattern. This process is called whitening.
Discharge printing can be done when bleach is mixed with dyes that do not react with it in the same color paste (vat dyes are of this type). Therefore, when a suitable yellow dye (such as a vat dye) is mixed with a colored bleach, a yellow dot pattern can be printed on a blue background fabric.
Because the background color of discharge printing is first dyed using piece dyeing method, if compared with all-over printing where the background color is printed, the color of the background color is much richer and deeper. This is the main purpose of using discharge printing. Discharge printed fabrics can be printed by roller printing and screen printing, but cannot be printed by heat transfer printing. Because the production costs of discharge-printed fabrics are high compared to direct printing, the use of the required reducing agents must also be very carefully and accurately controlled. Fabrics printed in this way have better sales and higher price levels. Sometimes, the reducing agent used in this process can cause damage or damage to the fabric in the printed pattern. If the background color on both sides of the fabric is the same (because it is piece dyeing), and the pattern is white or a different color from the background color, it can be confirmed that it is a discharge-dyed printed fabric.
3. Resistant dyeing printing Resistant dyeing printing includes two stages of process:
(1) Print chemicals or waxy resin on white fabric that can prevent or prevent dye from penetrating into the fabric;
(2) Piece dyed fabrics. The purpose is to dye the base color to bring out the white pattern. Note that the results are the same as for discharge-printed fabrics, however the method of achieving this result is the opposite of discharge printing. The resist printing method is not commonly used and is generally used when the background color cannot be discharged. Compared with large-scale production basis, most resist printing is achieved through methods such as handicraft or manual printing (such as wax resist printing). Because discharge printing and resist printing produce the same printing effect, they often cannot be distinguished through naked eye observation.
4. Pigment printing The use of paint instead of dyes to produce printed fabrics has become so widespread that it has begun to be regarded as an independent printing method. Pigment printing is direct printing with paint. This process is usually called dry printing to distinguish it from wet printing (or dye printing). By comparing the hardness difference between the printed and unprinted parts of the same piece of fabric, pigment printing and dye printing can be distinguished. The paint-printed area will feel slightly harder and perhaps thicker than the unprinted area. If the fabric is printed with dye, there will be no obvious difference in hardness between the printed and unprinted parts.
Dark pigment printing is likely to feel harder and less flexible than light or pale colors. When inspecting a piece of fabric for a paint print, be sure to check all colors, as both dye and paint may be present on the same piece of fabric. White paint is also used for printing, this factor should not be ignored. Pigment printing is the cheapest printing method in printing production, because the printing of paint is relatively simple, requires the least process, and usually does not require steaming and washing.
The coatings are available in bright, rich colors and can be used on all textile fibers. Their light fastness and dry cleaning fastness are good or even excellent, so they are widely used in decorative fabrics, curtain fabrics and clothing fabrics that require dry cleaning. In addition, the paint will hardly produce large color differences on different batches of fabrics, and the coverage of the base color during overprinting is also very good.
Special printing
The basic method of printing (as mentioned above) is the printing and dyeing method used for each color in the pattern when printing a pattern on the fabric. Special printing belongs to the second category. It is classified in this way because this method can To obtain special printing effects, or because the process cost is high and it is not widely used.
1. All-over printing The background color of all-over printing is obtained by printing instead of piece dyeing. Usually in the printing process, the background color and pattern color are printed on white cloth. Sometimes allover prints are designed to mimic the effects of discharge or resist prints, which are more expensive to produce, but the different printing methods are easily identifiable from the reverse side of the fabric. The background color of all-over printing is lighter on the reverse side; because the fabric is piece-dyed first, the front and back sides of discharge dyeing or resist dyeing printing are the same color.
A common problem with all-over printing is that sometimes a large area of background cannot be covered by dark colors. When this problem occurs, if you carefully inspect the pattern on the ground, you will find some dark spots. This phenomenon is basically caused by water washing, not due to the amount of dye coverage.
High-quality all-over printed fabrics produced under strict process conditions will not have these phenomena. This phenomenon is not possible when screen printing is used for floor printing, because the color paste is applied by scraping instead of being rolled in like roller printing. Paint all over printed fabrics often have a stiff feel.