Offset printing belongs to flat printing, which is the most common printing technology in packaging printing. It has outstanding advantages in high quality and efficiency in the field of large-scale printing, and the printing materials are also very extensive. Flat printing is an indirect printing process that involves restoring images and text to the surface of the printing material through the action of a printing plate and an eraser drum.
Due to the good elasticity of the rubber drum, the wear of the printing plate is correspondingly reduced, which is very helpful for improving printing accuracy and production efficiency. For example, it is now easy for a single sheet offset press to achieve a printing speed of 15000 or even 18000 sheets per hour. After adopting CTP (Computer Direct Plate Making Technology), the printing accuracy reaches 300-400 lines, and it also has good adaptability to substrates with different surface structures, such as various special papers and art papers.
Offset printing can be divided into water (wetting solution) offset printing and anhydrous offset printing. Water offset printing is known in the industry as it utilizes the principle that oil (offset ink) and water (wetting solution) are immiscible. The blank part of the printing plate is hydrophilic and hydrophobic, while the image and text part of the printing plate is hydrophobic and hydrophobic. By using the principle of mutual exclusion between oil and water, the printing plate is first coated with water to form a hydrophilic and ink repellent water film on the blank part; Then, the printing plate is inked to allow the text and images to adhere to the ink. Under the pressure of printing, the text and images on the printing plate are transferred to the surface of the substrate through a rubber drum. Water offset printing technology is more commonly used.
Flat printing can be divided into: flat printing and drum printing (also known as drum printing).
Flat sheet printing: Flat sheet printing machines can only feed single sheets of paper, and images and texts are also printed on single sheets of paper or materials. The quality of flat printing is slightly better than that of rotary printing, but the printing speed is slightly slower than that of rotary printing. Flat printing machines are divided into three types: large, medium, and small.
Miniature printer: The maximum printing size is 14 inches * 17 inches (about 35cm * 43cm), and there are monochrome machines, two color machines, or business card printing machines. It is usually used for printing a small number of short editions, such as commercial forms, notes, official document formats, and business cards.
Medium size machine: The maximum printing size is 49 inches * 74 inches (approximately 64cm * 96cm). This type of machine is the most commonly used and has the widest market application range, such as the common split, four open, six open, or eight open machines. The printing quantity is usually around 3000 sheets, suitable for commercial printing such as four color printed brochures.
Large scale printer: The maximum printing size is 49 inches * 74 inches (approximately 125cm * 188cm), which is not commonly seen in the market. It is usually a fully powered or ultra wide width printing machine, with a large printing quantity and can achieve five to eight color printing.
Drum printing: The feeding system of the drum printing machine is a roll, and the printing material width has different specifications. After the machine completes printing, it usually automatically cuts into the required flat sheet size according to the design requirements. The drum printing speed is fast, suitable for large-scale production. Like flat sheet printing, drum printing is classified into different types based on the acceptable width of the printing material. Generally, narrow format drum printing can only print single or dual colors, while wide format drum printing can complete multi color printing at once or print on both sides simultaneously.
Roll sheet paper can also be cut into flat sheets using a flat sheet printing machine cutting equipment, and then printed on the flat sheet printing machine.
Offset printing technology has a high popularity rate, complete equipment types, complete supporting facilities, and a solid market foundation, making it the most widely used printing technology in the world, especially in the field of paper printing. There are mainly books, brochures, promotional materials, single pages, packaging materials, letterhead seals, label cards, exquisite calendars, etc. Although gravure and flexographic printing manufacturers have also been involved due to their unique advantages, offset printing has always held the largest market share and will continue to maintain this pattern in the foreseeable future.
Waterless offset printing has the advantages of easy operation, good image restoration, high product quality, and is beneficial for environmental protection. Silicone rubber printing plates, specialized inks, and temperature control are known as the three major elements that make up anhydrous offset printing. Waterless offset printing is not widely used in the market mainly because this printing technology still has certain drawbacks. This is mainly manifested as high printing plate costs. Waterless offset printing uses a special type of silicone rubber coated printing plate and specialized ink for printing. The printing plate is a flat concave structure, and due to material reasons, the printing plate is prone to wear and tear. The printing plate material is special and domestically produced is rare, so the price will be higher. There are also many special requirements for specialized inks. Therefore, the overall cost is relatively high. In addition, waterless offset printing requires strict temperature control, and different colored inks have different color restoration under different temperature conditions, requiring careful technical control of the process flow. So, waterless offset printing is only suitable for low-speed small format printing, and its printing resistance is low.
