The development of offset printing plates can be traced back to the late 19th and early 20th centuries, and its technology has undergone many improvements and innovations, gradually becoming one of the most commonly used printing methods in the modern printing industry.

1. Early stage (19th century to early 20th century)

Offset printing originated from lithographic printing technology, the core principle of which is based on the repulsion of oil and water. The earliest lithographic presses used stone plates (lithography), which utilized limestone surface treatment to form hydrophilic and lipophilic areas. Subsequently, metal plates (e.g. zinc, aluminum) gradually replaced lithographic plates, improving durability and printing efficiency.

2. Protein Plate and Flat Gravure Plate (mid-20th century)

- Protein Plate: Plates are made on metal plates by coating them with a protein-sensitive liquid, and UV exposure is used to form the image. However, it was gradually eliminated due to low print resistance and complicated plate making.

- Flat Gravure Plate: A slightly concave graphic area is corroded on the surface of the metal plate to enhance the ink adhesion ability, and the print resistance is better than that of the protein plate, but the process cost is higher.

3. Popularization of PS plate (Presensitized plate) (late 20th century)

PS plate (Presensitized Plate) became the mainstream, its substrate is aluminum plate, the surface coated with photosensitive resin layer. Through exposure and development to form a lipophilic graphic area, with convenient plate making, high print resistance (up to hundreds of thousands of prints), is still the most widely used offset printing plate.

4. Digital Innovation of CTP Plate (Computer to Plate Making) (21st Century)

With the development of digital technology, CTP (Computer-to-Plate) technology to replace the traditional film plate-making process, directly to the digital file output to the printing plate, higher precision, efficiency, and support for high-resolution graphics, becoming the mainstream choice for modern offset printing.

Current common types of offset printing plates are:

1. PS plate (pre-coated photopolymerized plate)

- Structure: Aluminum substrate + burrified layer (to enhance adhesion) + photopolymeric resin layer.

- Features: standardized plate making process, low cost, strong printing resistance (100,000-500,000 prints), suitable for high-volume printing, such as books and magazines, packaging and so on.

2. CTP Plate (Digital Direct Platemaking)

- Classification: Including thermal plates (imaging by laser heating) and photopolymerized plates (UV exposure).

- Advantages: eliminates film link, reduces errors, supports fine dots (e.g., more than 200 lines/inch), suitable for high-precision color printing, such as picture books and high-grade packaging.

3. Multi-layer metal plate

- Structure: Composite of copper, chrome and other metal layers, utilizing the hydrophilic/oleophilic properties of different metals.

- Characteristics: extremely high print resistance (millions of prints), but high cost of plate making, mostly used for long version printing (such as banknotes, stamps).

4. Paper-based plate

- Usage: paper as the substrate, coated photopolymerization layer, low cost, but low print resistance (thousands of prints), suitable for small offset presses or short-run printing (e.g., bills, labels).

Offset printing plate from the early lithographic plate, protein plate development to today's PS plate, CTP plate, reflecting the plate making technology from manual to digital leap. The current mainstream types are centered on PS and CTP plates, balancing efficiency and quality; multilayer metal and paper-based plates play a role in specific areas. The future trend may further develop towards environmentally friendly materials (e.g. chemical-free plates) and intelligent plate making.