Metal Printing Prepress

The general process flow of metal printing is: plate making → pre-press coating → printing → drying → coating → molding. Therefore, the prepress processing of metal printing includes platemaking and bottom handling.

First, the plate process requirements

The photographic plate of Yintie is basically the same as that of photolithography in general printing, but for the characteristics of metal printing, its platemaking process also has its special requirements.

Use an ideal screen to ensure a good reproduction of the tone. Due to the characteristics of dot duplication, the dark tone and intermediate tone region in metal printing have two very obvious gradations. The intermediate tone level of printed material is deepened, and the dark tone is dramatically graded, especially when a square dot screen is used; diamonds are more obvious; Point or round point screen, the middle tone of the mutation phenomenon than the square network points have been eased, the dot gain value is also small, the iron tone reproduction is more favorable. The number of screen lines also affects the reproduction of the tone. Generally, the finer the network cable is, the larger the dot value is, and the more difficult it is to copy. The dots of the coarse cable line are smaller, and the dots are increased in the non-absorbing iron sheet printing. Excessive defects have also been made up.

Reduce the number of colors, use standard three primary colors process to print. Multi-color printing increases the number of overprints, and the special colors and assists of overprinting plates are more ideal for the copying process.

White version of the application. The metal sheet must be printed in white before it can be printed with a fine pattern. However, there are gold to print when you pay attention to the following golden pad can not be white, otherwise it can not reach the golden eye-catching effect. When making a white version, special attention should be paid to the combination of the white and gold versions to prevent the edges from being exposed during printing.

Since the iron is processed after molding, it is necessary to leave a bite or weld at the time of plate making. Consider the case of bite, weld, the pattern should be centered, otherwise it is easy to cause the pattern off-center.

Second, the bottom coating process before printing

The coating treatment is divided into inner coating and outer coating. Inner coating refers to the inner side of the sheet metal forming product, that is, the side in direct contact with the contents, and is coated with a layer of protective bright oil to protect the iron sheet from being eroded by the loaded items and at the same time protect the contents. If the food cans are made, the inner coating will be in direct contact with the food, requiring no toxicity and odorlessness, and no chemical reaction with the food.

After the inner coating, it is dried in a desiccator.

The outer coating (bottoming) is a place where no metallic luster is required on the printing surface, and a layer of white ink is applied or printed to make other colors more vivid against white; the use of polar groups of white ink can also increase the surface Adsorption capacity. Priming available roller coating and printing methods. Roller coating can be used to coat white ink thicker than printing. The white ink film layer has good softness and fastness of adhesion, suitable for stamping processing in the subsequent process, good gloss, and no discoloration (yellowing) after baking at high temperature.

The basic requirements for primer coating are: good affinity for white paint or ink, good adhesion to substrates, good leveling, suitable heat-curing properties and good flexibility; light color , Dry yellowing after film formation; Good water resistance.

There are generally two types of primers: one is a primer coated with a rubber roller, which is a 350 amino acid alkyd paint; the other is an on-machine-printed primer, which is generally 6012 insulating varnish. .

Source: Qilu Graphic Arts