Lithographic plates refers to various printing plates used for lithography (such as offset printing). There are many types of lithographic plates, which are differentiated by different plate-making processes and materials.

The following are some of the main types of lithographic plates:

1. Photosensitive protein plate:

This plate is usually made of aluminum or zinc plate as the base, with the image part covered with a hardened protein film, and the blank part is covered with an inorganic salt layer. Although its production process is simple and low-cost, it is almost no longer used due to its low print durability (generally 5,000 to 10,000 prints).

2. Plat-concave plate:

This plate uses zinc plate as the base, and the image part is 5 to 8 μm lower than the plate surface after corrosion treatment, and is coated with an oleophilic base paint. Although it is superior to the protein plate in terms of printing capacity and printing quality, it is not common now because of the complexity of plate making.

3. Multi-layer metal plate:

This type of plate is made of two metals with different hydrophilicity and oleophilicity, such as a two-layer flat-concave plate with chrome-plated copper or a three-layer flat-concave plate with copper-plated iron and then chrome-plated or nickel-plated. However, due to problems such as poor dot reproduction and long plate making cycle, it is rarely seen now.

4. Pre-coated photosensitive plate (PS plate):

This is the most commonly used lithographic printing plate. PS plate is known for its stable printing quality and simple plate making process, and is suitable for large-scale printing. Due to its high quality, stability and efficiency, PS plate has become the standard choice for modern offset lithographic printing plates.

In summary, among all the above-mentioned lithographic plates, pre-coated photosensitive plate (PS plate) is the most commonly used one. It not only solves many problems of early plates, such as poor dot reproduction and low printing durability, but also greatly improves printing efficiency and product quality. With the development of technology, PS plate has been continuously improved and perfected, making it an indispensable part of the modern printing industry. Therefore, for most modern printing plants, PS plate is their first choice for lithographic printing.

Factors to consider when choosing lithographic Printing plates:

- Printing quality: The printing quality of different plates may vary.

- Cost: Choose the right plate according to the project budget.

- Production volume: Short-run printing and mass production may have different requirements for plate materials.

- Environmental protection: Some environmentally friendly materials may be more suitable for projects with environmental requirements.