Screen Printing
Screen printing refers to the use of a mesh screen as a printing plate, which is made into a screen printing plate with images through photosensitive plate making methods. Screen printing consists of five main elements: the screen printing plate, squeegee, ink, printing table, and substrate. The basic principle of screen printing is that ink can pass through the mesh holes of the image part of the screen printing plate, while the non-image part cannot. During printing, ink is poured onto one end of the screen printing plate, and a squeegee is used to apply pressure to the inked areas of the screen printing plate while moving evenly towards the other end of the screen printing plate. The ink is squeezed from the mesh holes of the image part onto the substrate as the squeegee moves.
Stencil printing is the simplest form of perforated plate printing and originated in the late 19th century. This type of printing is done on special wax paper, which is then typed or written on with an iron pen to create a wax paper stencil. Ink is then rolled onto the wax paper stencil, resulting in the desired printing effect on the substrate. Among perforated plate printing methods, screen printing is the most widely used.
Screen printing involves stretching fabric, synthetic fiber fabric, or metal mesh on a frame and making a screen printing plate using hand-cut lacquer film or photosensitive plate making methods. Modern screen printing technology utilizes photosensitive materials to create screen printing plates through photolithography methods, where the mesh holes in the image part of the screen printing plate are open, while the mesh holes in the non-image part are blocked. Screen printing is used for various applications such as painting, printmaking, posters, business cards, book covers, product packaging, labels, textile printing, glass, metal, and other flat substrates.
Direct plate making method: The direct plate making method involves first placing a photosensitive film with the photosensitive side facing up on a workbench, placing a stretched mesh frame on the film, pouring photosensitive emulsion into the mesh frame, and using a soft squeegee to evenly coat the mesh frame with pressure. After thorough drying, the plastic film base is removed, leaving the photosensitive film-coated screen ready for exposure. After exposure and development, a screen printing plate is created.
Process flow: Screen stretching - degreasing - drying - peeling off the film base - exposure - development - drying - plate repairing - mesh sealing
Indirect plate making method: In the indirect plate making method, the indirect film is first exposed, hardened with 1.2% H2O2, and then developed with warm water. After drying, a peelable graphic film is made, which is then placed on the stretched screen mesh, squeezed tightly to the wet screen mesh, and the film base is removed. After drying with air, a screen printing plate is produced.
Screen printing originated in China more than two thousand years ago. Even in ancient times, methods such as paste-resistant printing appeared during the Qin and Han dynasties. By the Eastern Han Dynasty, paste-resistant wax dyeing methods were widespread, and the quality of printed products improved. By the Sui Dynasty, people began using frames with stretched silk nets for printing, evolving from paste-resistant printing to screen printing. According to historical records, exquisite clothing worn in the Tang Dynasty's palace was printed using this method. By the Song Dynasty, screen printing continued to develop, and improvements were made to the originally used oil-based paints by adding starch-based gums to dyes, enabling screen printing to produce more vibrant colors.
Screen printing consists of five main elements: screen printing plate, squeegee, ink, printing table, and substrate. The basic principle of screen printing is that ink can pass through the mesh holes of the image part of the screen printing plate, while the non-image part cannot. During printing, ink is poured onto one end of the screen printing plate, pressure is applied to the inked areas of the screen printing plate with a squeegee, and the ink is squeezed from the mesh holes of the image part onto the substrate as the squeegee moves towards the other end of the screen printing plate. Due to the viscosity of the ink, the print adheres within a certain range. Throughout the printing process, the squeegee maintains continuous line contact with the screen printing plate and the substrate, with the contact line moving with the squeegee. The tension of the screen printing plate itself generates a reactive force against the squeegee, called rebound force. As a result of the rebound force, the screen printing plate and the substrate only have linear contact during printing, while other parts of the screen printing plate are separated from the substrate. This allows the ink to break away from the screen printing plate during printing, ensuring printing dimensional accuracy and avoiding smudging on the substrate. After the squeegee passes over the entire surface, it is lifted, and the screen printing plate is lifted, lightly scraping the ink back to its initial position. This completes one printing cycle.
Screen printing has strong adaptability: Offset, relief, and intaglio printing methods can generally only be used on flat substrates. However, screen printing can be used not only on flat surfaces but also on curved, spherical, and irregular surfaces. Furthermore, screen printing can be applied to both hard and soft substrates, without being limited by the texture of the substrate. In addition to direct printing, screen printing can also be used for indirect printing as needed, by first screen printing onto gelatin or silicone plates, and then transferring it to the substrate. Therefore, screen printing has strong adaptability and a wide range of applications.
Strong three-dimensional effect: The ink layer thickness of conventional offset and relief printing is generally around 5 microns, while intaglio printing is around 12 microns, and flexographic printing (aniline) is 10 microns. However, the ink layer thickness of screen printing far exceeds the thickness of these ink layers, generally reaching around 30 microns. Thick screen printing ink layers result in rich texture and a strong three-dimensional effect, which other printing methods cannot compare with. Screen printing can not only print in single color but also perform color overlay and halftone color printing.
Strong light resistance: Due to its porous nature, screen printing can use various inks and coatings. It can not only use paste, adhesives, and various pigments but also use coarser pigments. In addition, screen printing ink mixing is simple. For example, light-resistant pigments can be directly added to ink, which is another major feature of screen printing. Screen-printed products have the great advantage of strong light resistance. Practical tests have shown that, compared with the maximum density value range measured after one impression using black ink on copperplate paper, offset printing is 1.4, relief printing is 1.6, intaglio printing is 1.8, while the maximum density value range of screen printing can reach 2.0. Therefore, screen-printed products have stronger light resistance than other types of printed products and are more suitable for outdoor advertising and signage.
Large printing area: The maximum area size printed by conventional offset and relief printing methods is generally the full sheet size. Beyond the full sheet size, mechanical equipment limitations apply. However, screen printing can be used for large-area printing. Today, screen printing products can have a maximum size of up to 3 meters by 4 meters, or even larger.
The above four points are the differences between screen printing and other printing methods, as well as the characteristics and advantages of screen printing. Understanding the characteristics of screen printing allows for leveraging its strengths when choosing a printing method, achieving ideal printing results.
Screen printing usually comes in two forms: manual printing and mechanical printing.
Manual printing refers to the entire process from continuous paper to receiving paper, including moving the printing plate up and down, as well as squeegee printing, which are all manual operations.
Mechanical printing refers to the printing process being completed by mechanical actions. It can be further divided into semi-automatic and fully automatic printing, where semi-automatic means that substrate insertion and removal are manually operated, while printing is mechanically completed, and fully automatic means that the entire printing process is mechanically completed.
There is also a rapid and simple curved surface screen printing method called "direct surface screen printing," where the screen printing plate is removed and directly pressed against the substrate for printing. This method can be used to print a large number of processed products, such as latex plastic barrels, pure water buckets, basins, thermos bottles, cups, bowls, plates, and other products. This method can also be used to print signage on cars or print on irregular surfaces.
Preparation of direct surface screen: First, dry and repair the photosensitive text and graphics film, then remove it, and cut it to size. Use wooden or aluminum strips as frames to firmly attach them to the ends of the screen with adhesive tape or directly with adhesive. This creates the required direct surface screen. Operating method for direct surface screens: Depending on the substrate, different inks are prepared: firstly, using flat plates and dishes, prepare the ink, then one person holds the direct screen with both hands and presses it firmly against the substrate, while another person evenly coats the ink on the screen using the squeegee on the ink plate. After that, the squeegee is evenly placed on the plate to carry out uniform printing.
If the area to be printed is too large, ink can be poured onto the plate as needed, but care should be taken not to let the ink flow out of the substrate. Pay attention to the ink mixture not being too thin or too dry, and maintain moderate humidity. For small-area printing of text or graphics, one person can operate by tightly attaching one end of the direct screen to the substrate as needed, and then using the other hand to pull the screen tightly against the substrate for printing. When starting printing, always start lightly from the end where the tape is attached. If two people are operating, the same principle applies. This printing method is convenient to operate, flexible in substrate requirements, suitable for large and small quantities, and has the advantages of low cost and energy savings.
Screen printing is not only suitable for general paper printing but also has a very wide range of applications. For example, ceramics, glass, printed circuit boards, etc. Depending on the substrate, the printing process may vary. Although there are inseparable connections between different series, each has its own special characteristics due to the different chemical and physical properties of the substrates. Therefore, they are usually divided into several major categories based on the different substrates: paper printing, plastic printing, ceramic printing, glass printing, circuit board printing, metal printing, textile printing, etc. This forms their relatively independent printing systems.
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