Flat Screen Printing with Advantages and Disadvantages

Last Updated on 03/01/2025

What is Flat Screen Printing?
Screen printing is the most widely utilized technology in the textile printing industry. Based on the type of screen used, screen printing is classified into two types: flat screen printing and rotary screen printing. In flat screen printing, flat screen is used which are made of silk threads, nylon, polyester or metal.

Flat-screen and rotary screen printing are both characterized by the fact that the printing paste is transferred to the fabric through openings in specially designed screens. The openings on each screen correspond to a pattern and when the printing paste is forced through by means of a squeegee, the desired pattern is reproduced on the fabric. A separate screen is made for each color in the pattern. Globally, approximately 61% of printed textile fabrics are produced by using the rotary screen printing method, while 23% are made using flat screen printing.

Flat Screen Printing
Fig: Flat screen printing

A variety of different machines can be used for printing fabrics. The most commonly used are described below.

Flat-bed Screen Printing Machine:
Flat-bed screen printing machine can be manual, semi-automatic or completely automatic. One type of machine, which is still commonly found in printing houses, can be described as follows. The fabric is first glued to a moving endless belt. A stationary screen at the front of the machine, is lowered onto the area that has to be printed and the printing paste is wiped with a squeegee. Afterwards the belt, with the fabric glued on it, is advanced to the pattern-repeat point and the screen is lowered again. The printed fabric moves forward step by step and passes through a dryer. The machine prints only one color at a time. When the first color is printed on the whole length of the fabric, the dried fabric is ready for the second cycle and so on until the pattern is completed.

Instead of printing one screen at a time, all the flat screens used in the design print simultaneously, on a section of fabric that has just been printed with the previous screen. The average production speed for this technology is faster than any table printing technology, usually printing cloth at 10–15 yards per minute (9–13 m/min).

In automatic flat-bed screen printing, the fabric is fixed to the moving rubber blanket of the conveyor belt and moves intermittently by a repeat length of the design. When the conveyor belt stops, all the screens lined up along the table print their impressions at the same time, thus the fabric furthest along the conveyor belt has had the most screens printed on it. At the end of the moving table, the complete design will have been printed, and the printed fabrics are automatically detached from the table for drying. The empty conveyor belt travels under the table and through washing and drying units, which clean its surface ready for the next batch of fabric. The print quality is slightly inferior to table printing due to it being wet-on-wet, but it is used for a wide range of printing applications, including fashion, interior, and bedding.

Flat Screen Preparation:
Flat screen preparation for printing involves several key steps and decisions, including:

  1. Choosing the type of fabric and the design to be printed.
  2. Choosing the size and arrangement of the repeating pattern.
  3. Breaking down the design into separate layers for each color.

These above steps are common to all printing methods. In colour separation, each colour is transferred onto a separate transparent film (diapositive), often using computer technology. The designer must ensure printing of colors with a slight overlap to avoid white gaps between them. In some cases, printing of one color on top of another produces a particular color effect. This is known as a fall-on.

The same method is used for preparing both flat and rotary screens. The flat screen is mounted on a frame and coated with a photo-sensitive polymer, such as polyvinyl alcohol, which hardens when exposed to ultraviolet (UV) light. The screen is dried and then exposed under a diapositive in a darkroom. Areas of the polymer that are blocked by the pattern remain soluble and can be washed away, leaving open spaces for the print paste to pass through. The hardened areas block the paste.

Afterward, any pinholes in the hardened areas are covered, and the screen is reinforced with a cellulose or polyurethane coating. In some cases, thermal or radiative curing of the polymer makes it harder and more resistant.

A flat screen may be produced in a single coating and exposure operation. Alternatively, in the step-and-repeat process, one repeat design is produced per exposure, the remainder of the screen being protected by dark paper. The pattern or the screen is then moved by one repeat distance and the process repeated.

The screen mesh varies from about 60 up to 150 holes per linear inch depending upon the type of pattern and the fabric. There is always a tendency for the edges of printed areas to have a serrated appearance. This comes from the arrangement of the spaces between the threads along the edge of an open area of the screen. The spreading of the paste below the screen threads reduces this, aided by using fine screens and lower viscosity pastes.

Flat screens are usually coated by means of hollow or trough shaped doctor blade, or with an angular doctor made from wood, metal or plastic. The screens are kept in an upright but slightly inclined position for coating. The filled doctor is the drawn upwards, exercising a certain amount of pressure, the speed of movement being selected as required and the doctor is slightly tilted during this operation. At the end of the movement the blade is restored from the tilted position to its original position so that the excess solution is again taken up. To make the coating thinner the doctor blade is pressed against the screen and quicker the movement of the doctor. Screens are also coated by mechanical means using special units meant for this.

Advantages of Flat Screen Printing:
In other fully mechanized machines all the colors are printed at the same time. A number of stationary screens (from 8 to 12, but some machines are equipped with up to 24 different screens) are placed along the printing machine. The screens are simultaneously lifted, while the textile, which is glued to a moving endless rubber belt, is advanced to the pattern-repeat point. Then the screens are lowered again and the paste is squeezed through the screens onto the fabric. The printed material moves forward one frame at each application and as it leaves the last frame it is finally dried and it is ready for fixation

In both machines the continuous rubber belt, after pulling away the fabric, is moved downward in continuous mode over a guide roller and washed with water and rotating brushes to remove the printing paste residues and the glue, if necessary. After this, the belt is sent back to the gluing device. In some cases the glue is applied in liquid form by a squeegee, while in other machines the belts are pre-coated with thermoplastic glues. In this case the textile is heated and then it is squeezed by a roller or simply pressed against the rubber-coated belt, causing the glue to soften and instantly adhere.

After printing, the screens and the application system are washed out. It is common practice to squeeze the color from the screens back into the printing paste mixing containers before washing them.

Disadvantages of Flat Screen Printing:

  1. The process is slower compared to rotary screen printing.
  2. The size of the design is restricted by the screen size.
  3. Requires more manual handling and monitoring, increasing labor costs.
  4. Less efficient for large-scale production compared to automated methods like rotary screen printing.
  5. Printed edges can appear jagged due to the screen’s mesh structure, especially with coarse screens.

Conclusion:
Flat screen printing is a versatile and widely used printing method in the textile industry, known for its ability to produce detailed and vibrant designs. While it offers advantages such as adaptability to various fabrics and cost-effectiveness for smaller production runs, it has limitations in speed, scalability, and design size compared to rotary screen printing. Despite these limitations, flat screen printing remains a valuable option for intricate patterns and custom designs, making it an essential technique in niche and specialized printing applications.

References:

[1] Choudhury, A. K. R. (2022). Principles of Textile Printing. CRC Press.

[2] Sinclair, R. (2015). Textiles and fashion : materials, design and technology. In Woodhead Publishing eBooks. http://ci.nii.ac.jp/ncid/BB18427651

[3] Broadbent, A. D. (2001). Basic Principles of Textile Coloration. http://182.160.97.198:8080/xmlui/handle/123456789/1125

[4] Miles, L. W. C. (2003). Textile Printing. Amer Assn of Textile.

[5] Kolanjikombil, M. (2024). Printing of Textile Substrates: Machineries and Methods. CRC Press.

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