What is screen printing? Describe the screen printing process.

Screen printing

The term textile printing is a combination of fabric printing with 1 to 20 colors depending on the design and color. Printing is the process of painting the design was drawn by an artist and fixation to the fabric or materials with a mixture of different chemicals and dyes with the help of applying different types of machinery and technology. There are various methods for textile printing, first comes developing the design. This is why design is called the heart of printing. To create a textile printing design, each design has to be converted into a 100% vector image by using graphic software. Depending on how many colors are used in a design, all the color needs a separate file for each color, a separate rotary screen is used for developing the design. Then each separated color file has to be transferred to the separate Rotary screen. For that, various machinery and chemicals are used.

The steps of rotary screen preparation are given below

Screen rounding and degrease: The new screen is removed from the packet and the tension ring is carefully attached to both sides of the screen, which can be easily removed from the screen or reconnected. After attaching the tension ring, the screen has to be kept in the polymer machine at a temperature of 160/160 degrees for 40-60 minutes. The amount of grease applied to the screen hardens the screen due to the grease hitting and rounding the diameter of the screen perfectly. And this process is called screen rounding. After rounding the screen, the screen needs to be degreased. A degreaser is a type of soapy water that can clean the grease or oily substance on the screen. The screen is degreased with foam by mixing one part of water with four parts of degreaser and inserting the screen inside the developing stand. Alternatively, after soaking the screen in a degreaser tank for 15/20 minutes and washing it with water, it becomes a screen degreaser. After rounding the screen, the screen has to be inserted inside the lighting stand and needs checking by turning on the light. Whether the mesh hole is closed or if there is any dirt on the screen if any hole is closed or dust is on the screen, it should be cleaned with an air compressor or water gun machine. Then the screen is polymerized at the temperature of 40-120 C for 20/30 minutes or at normal humidity with water for 4/6 hours to achieve a suitable form for coating.

Screen coating

The screen is coated in light yellow lightroom. Excessive light dissipates the heat of the emulsion. To keep the temperature of the emulsion perfect, AC should be installed in the screen preparation room, if the emulsion contains any tiny sand particles or any other dirt or dust. However, during screen coating, those sand particles will form a pinhole on the screen or appear in the form of a pinhole. The screen preparation room should be reserved at all times so that the pinhole in the screen is not created by the sand particles entering the screen preparation room. The screen preparation room should be maintained at all times so that no sand particles from outside can enter the room. 

There are generally three types of chemicals used in screen coating 

a. Universal emulsion

b. Sensilax sensitizer

c. Water

A screen coating needs 200 grams of chemicals. In 100g of emulsion, 10% water, 5% sensitizer and the rest are photo emulsions. Many times the percentage of chemicals has to be changed depending on the thickness and sharpness of the design… In this case, 20% of the water has to be used and at the same time, an exposer uses his practical experience to do this. Many new chemical companies are currently marketing readmit emulsions. It is usually used to make emulsions according to design variations. For best results, mixing emulsion has to be mixed very well by stirring with a stick. Using high mesh polyester or bolting cloth, filter 2/3 times. It is more convenient to do screen coating after filtering emulsion. Because by then there is foam in the emulsion, which needs 4/5 hours to dissolve. As the screen coating with foam mixed emulsion does not penetrate the emulsion perfectly on the screen.

Screen coating is done in two ways

a. Coating machine

b. Manual process

a. Coating machine: 200 gm of the prepared emulsion is added into a clean scraper ring and coated on the clean screen with a speed of 10-12 min. then dried at 350c - 400c and 60% relative humidity in an oven with circle wind and on more than ± 20c temperature differences. Coat the binder evenly on both surfaces beating the enduring and the nicked screen with a scraper coating and removing the excessive binder. 

Advantages

a. Uniform and smooth coating

b. Variable speed for coating

c. The coating goes down over the hard beam

d. Easy to operate

b. Manual process: If there is any problem in the coating machine or there is no coating machine then the exposers do screen coating on the basis of their skill hand. Manually coating the screen does not make the emulation penetration 100% perfect on the screen, resulting in various problems, but not so much the problem with the local design. Moreover, in the case of export design, this manual system is not acceptable, as well as manually screen coating is not perfect and time is wasted. For this reason, the screen coating is no longer done manually. Exposers often solve many screen problems by reducing or increasing the viscosity of the emulsion, for example, making emulsions depending on the exposure or sharpness of the design. After coating the screen, the screen has to be kept upright for 15/20 minutes so that the emulsion applied on the screen comes down by rolling. Then the screen has to be kept in the emulsion machine at the temperature of 30/35 degrees Celsius for 20/25 minutes. This dries the emulsion applied to the screen. If there is no clematises machine, it can be dried in a light-dark room with normal fan air, in this case, it takes more time, about 2/3 hours. If the emulsion screen is not exposed within 4/5 hours, the emulsion temperature is lost. However, in a dark room with AC, the coated screen can be done for up to 18 hours.

Screen expose

After the screen coating, the screen has to be exposed. The device by which the screen is exposed is called the rotary screen exposing machine. There are also three types of exposing machines,

1. Manual exposing machine

2. Inkjet exposing machine

3. Laser exposing machine

When designers did the manual design, they used to expose it in the manual exposing machine. There were various problems with manual exposure but even after manual exposure was given, the main material for giving manual exposure is design film. With this film, part by part exposure was given and the cost would be less. With the change of technology, the CAD exposing process started instead of manual. First Inkjet then laser exposing system is started. Any critical design can be perfectly exposed in an inkjet and laser exposing machine. In this case, there are some conditions, the coated screen must be inserted inside the rubber tube of the exposing machine. Then with the help of an automatic air system, you have to tighten the screen with air and tape on both sides of the screen to prevent air from escaping.

Screen developing wash

After exposing the screen, the screen has to be developed within 10/15 minutes. If waiting for a long time, the emulsion of the screen becomes hard, so there is a problem with the screen wash. The exposing screen has to be carefully immersed in water in the developing tank. Make sure that the screen does not rub against the body of the developing tank. Because the tank is rubbed hard, the screen emulsion is likely to go up. Under the developing tank has two semicircular stands, above which, carefully soak the screen on it in water for 10/15 minutes. The screen should be removed from the developing tank and the outside and inside of the screen should be cleaned with water under high pressure through a shower. And sometimes, rub lightly with foam. In this way, the design area is opened from the screen at water pressure. Then insert the screen inside the lighting stand and check each motif of the design. If a motif is not fully open, it must be opened with the help of a water gun machine. At this time, it is very carefully noted that the extra area of the design is not open. Thus the exposing screen has to be developed by the water very carefully. After that, it is necessary to remove the water from the screen, for this removing the screen from the light stand, and keep it upright for 10/15 minutes. Then the emulsion on the screen surface should be kept inside the polymerized at the temperature of 120 degrees Celsius for 20 minutes to harden it.

End ring gluing

To remove the screen from polymerizing, end ring gluing is done. And before doing the end ring gluing should be cleaned well. After that, the end ring adhesive should be applied manually on both sides of the end ring (front side and back side) of the screen. After applying the adhesive, the adhesive should be dried for 10/15 minutes. Then with the help of the end ring gluing machine, put the end ring inside the screen and hit for 10 minutes. After hitting the end ring will be firmly attached to the screen. If the end ring does not attach perfectly, then the screen will be destroyed by opening the end ring during fabric production. For this, the end ring should be applied very carefully. After inserting the end ring, the screen has to be checked by inserting it into the check stand. If a pinhole or extra area of the design area is opened on a screen, it should be closed with a brush with a photo emulsion. In this way, the screen has required to check more times, then it will be suitable for production.