Printing Methods
Lithography (Planographic Printing)
Lithography is a printing method where the image area and the non-image (blank) area of the printing plate are almost on the same plane, utilizing the principle that oil and water are immiscible.
▶ Plate Characteristics
• The image area is ink-receptive (oleophilic);
• The blank area (non-image information) is water-receptive (hydrophilic, using dampening solution);
• The image area and blank area are on the same plane.
▶ Principles of Lithography
In lithography, the image and non-image areas on the printing plate are almost on the same level. During printing, to enable the ink to distinguish between these areas, the dampening system first supplies water to the non-image areas, protecting them from being wetted by the ink. Then, the inking system supplies ink to the plate. Since the non-image areas are protected by water, the ink can only adhere to the image areas. The ink on the plate is first transferred to a rubber blanket, and then, using the pressure between the blanket cylinder and the impression cylinder, the ink on the blanket is transferred to the substrate to complete the printing process. Thus, lithography is an indirect printing method.
Gravure Printing (Intaglio)
In gravure printing, the image area is lower than the blank area. This method is commonly used for printing valuable securities such as banknotes and stamps.
▶ Plate Characteristics
• The image area is recessed (etched or engraved);
• The blank area (non-image) is raised, forming the supporting surface of the plate;
• The blank areas are on the same plane, while the image areas vary in depth to create different levels of tone (gradients).
▶ Principles of Gravure Printing
In gravure printing, the entire surface of the plate is covered with ink. Then, a special doctor blade mechanism is used to scrape away the ink from the blank areas, leaving ink only in the recessed cells of the image area. Under significant pressure, the ink is then transferred to the surface of the substrate to obtain the printed product. Gravure printing is a direct printing method. The image area is recessed, with the depth of the recesses varying according to the image's layers, while the blank areas are raised and situated on the same plane.
Relief Printing (Letterpress)
In relief printing, the image area is raised and significantly higher than the blank area. The principle is similar to a seal or stamp. Early woodblock printing, movable type printing, and later lead type printing all belong to relief printing.
▶ Plate Characteristics
• The image area is raised;
• The blank area (non-image) is recessed;
• The image areas are on the same plane, while the blank areas can be on different levels.
▶ Principles of Relief Printing
The principle of relief printing is relatively simple. The inking system first ensures the ink is evenly distributed, and then transfers it to the plate via ink rollers. Because the image area is much higher than the non-image area, the ink can only be transferred to the image areas, while the non-image areas remain ink-free. The paper-feeding mechanism delivers the paper to the printing unit. Under the joint action of the plate device and the impression device, the ink from the image area is transferred to the substrate, completing the printing of a product.
Screen Printing (Porous Printing)
In screen printing, the image area consists of holes or a mesh, and ink is transferred through these holes onto the substrate surface. Common types include stencil and silk screen printing.
▶ Plate Characteristics
• The image areas (to be printed) allow ink to leak through;
• The blank areas are blocked, preventing ink from passing through.
▶ Principles of Screen Printing
The principle of screen printing is that under the action of a squeegee, the ink in the screen frame leaks through the mesh (image area) onto the substrate. The non-image areas of the screen are blocked, so no ink passes through, thereby completing the printing process.
Product Application & Detail Examples
