Tinplate Offset Printing Technology

The printing process using a hard material such as a metal plate or a metal foil as a substrate is called metal printing. As the former metal printing substrates are mainly tinplate, it is also called tinplate printing. Although there are many types of substrates used today, such as tinplate (tinned steel sheet), chrome plated steel sheet, galvanized steel sheet, aluminum plate, aluminum foil, etc. Aluminum stamping containers, but still use tinplate printing. The printed metal plates and metal foils can be made into containers of different specifications, such as barrels and cans, and are widely used in industries such as food, beverages, chemicals, pharmaceuticals, building materials, and home appliances. Most of the tinplate printing is mainly offset printing. The so-called offset printing refers to the printing on the printing plate first printed on the intermediate carrier (blanket roller), and then indirectly printed on the substrate. Currently in the tinplate offset printing, In addition to the use of gravure offset printing for building materials and decorative panels, the others mainly use lithographic offset printing and letterpress offset printing (also known as dry offset printing).

First, the characteristics of tinplate offset printing

Tinplate printing belongs to offset printing, but it has its own characteristics compared with ordinary offset printing:

â—† The substrates printed by tinplate are all kinds of thin metal plates. At present, the substrate used for tinplate printing is commonly used tin plated steel (also known as tinplate), chrome plated steel plate, ordinary thin steel plate, and aluminum alloy plate. These metal sheets can be classified into hard sheet metal, neutral sheet metal, and soft sheet metal according to their hardness. The aluminum alloy sheet is soft, the ordinary steel sheet is neutral, and the chrome-plated steel sheet is rigid. In the printing process, depending on the softness and hardness of the substrate, roller pressure adjustments and selection of suitable liner materials are required.

â—† Coatings play a decisive role in the quality of tin printing. The coating can increase the adhesion of the metal skin and the ink layer and protect the ink film layer.

â—† Use special printing ink. Since tinplate printed substrates have a smooth surface and do not have absorption capacity, tinplate printing inks rely on oxidized conjunctiva and volatile drying. At the same time, tinplate prints are generally used for canning after printing, and the iron ink is required to be resistant to high temperature and cooking and non-toxic and harmless.

â—† Printing operation is different from ordinary offset printing. When the printing press is manufactured, the blowing force of the blowing nozzle and the suction force of the suction nozzle must be taken into consideration. At the same time, a horseshoe magnet is added at the feeding point to overcome the adsorption force between the iron sheets. During operation, adjust the volume of the mouthpiece and mouthpiece according to the weight of the substrate. Roller pressure adjustment is the key to operation. In addition to the adjustment of the thickness of the substrate, the transfer conditions of the dots must also be considered.

Second, tinplate offset printing process

The process of tinplate offset printing is: plate making - pre-press coating - printing - polishing.

1, plate making process
The photographic plate of Yintie is basically the same as the photographic plate in general printing. There are also special requirements for the characteristics of tinplate offset printing:

â—† Use an ideal screen to ensure a good reproduction of the tone. Due to the characteristics of dot duplication, in the tin printing, the dark tone and the midtone zone have two very obvious gradations. The intermediate tone level of the printed material is deepened, and the dark tone changes dramatically. This is especially true when using square dot screens. Obviously, with diamond or circular dot screens, the abrupt change in the middle tone is alleviated compared with the square dot, and the dot enlargement value is also small, which is advantageous for the reproduction of the printed iron tone. The number of screen lines also affects the reproduction of the tone. Generally, the finer the network cable is, the larger the dot enlargement value is, and the more difficult it is to copy, while the coarse screen line dot enlargement is smaller, and the dots of the non-absorbing metal sheet are enlarged excessively. Defects have also been made up.

â—† Reduce the number of colors, use standard three primary colors process to print. Multi-color printing increases the number of overprints and is prone to overprinting, frictional damage, etc., as well as man-hours and raw materials, increasing costs, prolonging the production cycle, and increasing the number of defective products. The use of the standard three-primary process to replace the multi-colored special color and auxiliary color is an ideal reproduction process.

â—† The white version is indispensable for printing iron. The tin was first printed in white before it could be printed with a fine pattern. The general printing iron is a full version of printing white, but when the non-ferrous printing, it should pay attention to the following gold can not pad white, otherwise it can not achieve the golden eye-catching effect. When making a white version, it is necessary to consider the combination of the white version and the gold version and press each other. Prevent iron edges from appearing during printing.

â—† Because the iron is processed after molding, it is necessary to leave a bite or weld at the time of plate making. When considering the bite or weld, the pattern should be centered. Otherwise, the pattern may be decentered. Especially for a square bucket, one side will deviate one side and the other side will deviate further.

2, before the printing process
Clean the dirt on the front and back surfaces of the iron sheet before painting. The coating treatment is divided into inner coating and outer coating. The inner coating refers to the inner side of the iron sheet, ie, the inner side of the sheet metal forming product, that is, the side directly contacting the contents, and is coated with a layer of protective bright oil to protect the iron sheet from being eroded by the loaded items while protecting the contents. If a food can is made, the inner coating is in direct contact with the food, and it is required to be non-toxic and odorless, and it cannot react chemically with the contained goods. After the inner coating, it is dried in a desiccator.

The outer coating (bottoming) refers to coating or printing a layer of white ink on the outer surface (ie, the printing surface) of the iron sheet, covering the area where no metallic luster is required, so that the color printed on the white is more vivid. In addition, polar groups of the white ink can also be utilized to increase the adsorption capacity on the surface thereof. Priming available roller coating and printing methods. Roller coating can be used to coat white ink thicker than printing. The white ink film layer is better in terms of softness and attachment fastness, suitable for post-processing stamping process, excellent gloss, high-temperature baking can not be discolored (yellow), and then printed after the bottom is dry.

(to be continued)