Fabric Dyeing and Finishing


Dyeing is the whole process that dyes are combined with fabric fibers by chemical or physical chemical means to make the fabric have a certain color.

(1) Classification by equipment

Printing by equipment classification mainly has the following four aspects:

①  flat screen printing circular screen printing roller printing transfer printing

1, flat screen printing

Flat screen printing has three kinds of manual table plate and semi-automatic plate, automatic plate. In the flat screen printing method, the screen is the main printing tool. There is empty mesh where there is a pattern, and the mesh is coated where there is no pattern. During printing, the color paste is scraped through the mesh and transferred to the fabric. Flat screen printing is characterized by less restrictions on unit pattern size and color number, convenient plate making, large length of flower cycle (cycle), bright color pattern, printing fabric withstand small tension, therefore, especially suitable for easy deformation of knitted fabrics, silk, wool fabrics and chemical fiber fabrics printing. But its production efficiency is relatively low, suitable for small batch, multi – variety production.

(2) semi-automatic lithographic screen printing

Semi-automatic screen printing machine printing, is manual put cloth, automatic control of the mechanism to move the screen frame and scraper. Most pulping equipment is automatic pulping, but there are also manual pulping. The printing table plate is a hot table plate, because of the use of semi-automatic machinery, two ends of the printing table plate need to be equipped with automatic printing steering device. If no steering table, reverse method can also be used to solve the problem.

The screen frame of semi-automatic screen printing machine is generally made of aluminum alloy material. Screen frame after taut mesh and plate called color frame or flower frame. The color frame is mounted on an automatic printing device, which controls its movement, lifting and scraping of the scraper. The scraper is a scraping tool for screen printing. It’s made of synthetic rubber. The selection of scraper should be based on the fabric thickness, printing process, color printing properties to be selected.

Semi-automatic screen printing machine can print wide fabric, but it is easy to produce edge bubble defects, which can be solved by proper adjustment of scraper pressure.

(3) Automatic lithographic screen printing

During running, put cloth, lifting and scraping are automatically completed by machinery.

Lithographic screen printing with two types: frame moving type and cloth moving type.

Frame moving screen printing : the fabric to be printed is glued to a hot (or cold) platform at a temperature of about 45. In turn, the color paste on the screen that is taut on the frame and made of patterns is printed on the fabric with a rubber scraper, and then a set of colors is printed on the fabric into a complete pattern, one by one.

Moving screen printing system is printed on automatic screen printing machine. This machine does not heat the table, its length is short, the table is covered with a seamless ring rubber guide belt, to be printed fabric flat paste in the guide belt, and with the guide belt travel a flower back distance, then stop, screen frame lifting frame is automatically down to the screen close to or close to the fabric, scraper according to the electromagnetic control of the number of reciprocating scraping OARS; After the color paste is printed on the fabric, the screen frame is lifted up, and the guide belt is moved forward according to the specified distance, so that the printing step is automatically completed one board after another. After printing, the fabric is dried in the drying equipment. Cloth moving screen printing according to the scraping mode has two kinds of meridional scraping and weft scraping; According to the different type of scraper, there are two kinds of rubber scraper and electromagnetic metal rod.

2. Rotary screen printing

Rotary screen printing machine is produced based on the flat screen printing machine, the flat screen is changed into a cylindrical nickel screen, the mesh is hexagonal, the squeezer is made of chromium, molybdenum, vanadium, steel alloy.

During printing, the circular net rotates in a fixed position on the fabric, and the fabric moves forward with the guide tape running in the cycle. Printing color paste by the circular mesh inside the squeegee and through the mesh printed on the fabric, circular mesh printing is automatic pulp. After the full set of color printing, enter the drying equipment. Rotary screen printing machine is usually composed of four parts: cloth feeding device, printing machine head, drying device and cloth dropping device.

At present, the rotary screen printing machine usually has eight colors, twelve colors, sixteen colors, twenty-four colors and other rotary screen printing machines. the width mainly has 640mm and 904mm (circular mesh circumference) and so on. Most of them are 640mm rotary screen printing machines. Rotary screen printing machine has a lot advantages: simple operation, low labor intensity, high yield, suitable for all kinds of fabric printing, at the same time, it is suitable for a variety of small batch fabric printing.

The feeding device of rotary screen printing machine has two kinds: cloth cart and cloth roll. When the cloth is rolled, the swinging cloth roller can be pressed on the cloth roll, and the cloth can be input into the printing device by rotation of the cloth roller. The printing is completed when the fabric is moved forward by rubber tracks that run in cycles. The track is first coated with a thin layer of thermoplastic resin on the surface of the rubber roller, which can flat paste the fabric. An infrared radiant heater is installed next to the roller to heat the resin on the track. Thermoplastic resin coating can process 20 ~ 1 million meters of fabric. If found viscosity is not good, can be recoated.

Printing device Circular screen printing device includes circular screen, scraper, pulp feeding device, etc.

Circular screen is the printing machine’s pattern. Made of nickel metal, also known as nickel mesh, hexagonal mesh. The two ends of the circular net are fixed with a dull head to prevent the deformation of the circular net during printing, which affects the accuracy of the flower and can withstand the pressure of the printing ink and the scraper. In order to improve the elasticity of the circular net and reduce the pressure, the circular net should be deviated from the center line of the support roll, which is generally deviated from about 16mm. Each screen stand has a reading device that shows the upward pressure of the scraper on each side.

Scraper The scraper of rotary screen printing machine is installed on the scraper rack on the center line of the rotary screen. The scraper holder is equipped with both the scraper and the slurry feeding pipe. The scraper is made of chromium, molybdenum, vanadium and steel alloy. It has the characteristics of small friction coefficient and arbitrary adjustment of Angle. When printing, the blade of the scraper and the inner circle of the net are tangent. The scraper mainly exerts pressure on the color paste, and scraping is auxiliary compound action. Rotary screen printing machine scraper pressure and position can be adjusted to adapt to a variety of patterns and a variety of thick and thin color printing fabric.

Printing device rotary screen printing machine is automatic pulp. Each round net is equipped with a slurry feeding system. Supply of color paste, the machine will be on the plastic tube set on the metal feed pipe, and the other end of the machine tube into the color paste bucket, pump input circular mesh, automatic control of the height of the color paste by the electrode.

Rotary screen printing machine adopts loose hot air drying. After printing, it is separated from the rubber crawler, and then imported into the drying part. The cloth is loosely placed on the polyester net and dried by hot air. The cloth is pulled into the car by the electric pulling shaft.

Rotary screen printing machine has the advantages of low labor intensity, high production efficiency and strong adaptability to fabric. Suitable for chemical fiber fabric, knitted fabric, light fabric printing. The effect of lively pattern and bright color can be obtained, and color defects can be avoided. However, due to the limitations of the circular network structure, the effect of fine lines is not very ideal.

3. Roller printing (copper roller printing)

In roller printing, the pattern is printed on the fabric by an engraved copper roller (or roller). Copper rollers can be carved with very fine lines in close rows, so that they can print very detailed, soft patterns. The engraving should be exactly the same as the design drawing of the pattern designer. Each color needs its own engraving roller. Roller printing is the least used mass printing production method, the output continues to decline every year. This method would not be economical if the quantities of each pattern were not very large. In most cases, the high cost of drum preparation and equipment adjustment makes printing using this method less economical. Roller printing is often used for prints with very fine line patterns. Most printing machines can be configured with a flower tube with a maximum circumference of 16 inches, which means that the size of the pattern cycle cannot exceed 16 inches. The width of the flower tube should be slightly larger than the width of the printed fabric so that the fabric, including the edge, can be fully printed with the pattern. Once ready, the rollers can be used almost unlimited, generally printing millions of yards of fabric without problem.

The roller printing machine is composed of cloth feeding device, printing machine head, drying machine, cloth discharging device, transmission equipment and other main parts. As shown in Figure 2-12. The cylinder printed by the roller is a hollow cylinder made of red copper, containing more than 97.5% copper and 2%~2.5% zinc. According to the pattern carved on the copper roller, it is divided into two types of embossed and concave printing machines. Embossed roller printing machine is mainly used for woolen stripe printing, concave roller printing machine is used for cotton, T/C and chemical fiber fabric printing; According to the arrangement form of the flower tube, it can be divided into three types: radial, vertical and oblique; It can be divided into single-side roller printing machine and double-side roller printing machine according to whether the fabric is printed on one side or two sides. According to the number of printing sets can be divided into four color, six color, eight color and ten color roller printing machine. During printing, the color paste in the pulp tray is transferred to the cylinder by the pulp roller, and the color paste on the surface of the cylinder is scraped by the pulp scraper. The color paste stored in the concave grain of the cylinder is squeezed by the cylinder and the pressure roller, and the color paste is transferred to the fabric to complete the printing process. One flower tube prints a set of colors. If several flowers are printed together at the same time, several sets of colors can be printed, and they fit together in a certain position to form a pattern on the fabric. The coordination of each flower is regulated by the floral device.

As patterns are often multi-colored, the matching between colors should be carried out as original, so each flower cylinder on the printing machine has an adjustment device for the level of the flower cylinder, a matching device for the radial and axial direction of the flower cylinder, and a pressure adjustment device between the flower cylinder and the pressure roller. Adjusting these devices of each flower cylinder, as well as adjusting the pressure of the flower cylinder and the tension of the rubber interlining cloth, cotton interlining cloth and the fabric to be printed, can complete the pattern matching of the colorful flower cylinder and print the required printing pattern.

Post time: Mar-27-2023

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