Printing technology: analysis of stamping process of self-adhesive labels

The self-adhesive label material in the industry is called a self-adhesive label material, which is a composite material with paper, film or special material as the fabric, the back side coated with adhesive, and the silicon coated protective paper as the bottom paper. The demand for self-adhesive labels in China is growing rapidly at a rate exceeding 20% ​​every year. The size of the sticker market is about 450 to 500 million square meters per year. Therefore, the current application of stickers is more and more extensive, widely used in commercial label printing and screen printing. Among them, bronzing technology is the most important process for sticker printing.

In general, the stickers include a variety of bronzing processes: cold bronzing, round bronzing, flat bronzing and other processes. According to the processing method of self-adhesive labels, its bronzing methods are divided into sheet bronzing and roll bronzing. The single-sheet bronzing process is the same as the traditional bronzing process and is processed on a dedicated bronzing machine. Roll paper bronzing is done on the label linkage, which is the most widely used processing method. At present, there are several ways to stamp the reel material:

1. Cold bronzing on the rotary machine

This is a new hot stamping process. Instead of using heated metal printing plates, the method of printing adhesives is used to transfer the metal foil to achieve hot stamping. The process flow is: first print the UV pressure-sensitive adhesive at the position where the stamping needs to be gilded, dry the adhesive through the UV drying device, and then use special metal foil to combine with the pressure-sensitive adhesive, and then peel off the metal foil, so the metal The part of the foil that needs to be transferred is transferred to the surface of the printed product to achieve cold bronzing. The cold bronzing process has low cost, saves energy, and has high production efficiency. It can use existing equipment parts without adding additional devices. It is a promising new process.

2. Round stamping on the rotary machine

The bronzing plate used for the round pressing and round bronzing is in the form of a roller. During the bronzing, it is in contact with the imprinting roller to realize the bronzing. Round pressing round hot stamping is suitable for use in continuous paper-conveying rotary labeling machines, but it has certain requirements on the paper feeding speed, that is, it has an effect on the printing speed. However, compared with flat stamping, it greatly improves efficiency. The round pressing round hot stamping roller has high manufacturing cost, so it is only suitable for long version live hot stamping.

3. Flat stamping on the labeling machine

Regardless of the flattening or round flattening equipment of the letterpress label printing machine, due to the intermittent feeding of the roll paper, all the bronzing adopts the flattening method. In general, the bronzing station is an independent unit, and some models share a single unit for bronzing to die cutting, which is used separately.

4. Multi-station flat pressing and bronzing

Some models have a two-station bronzing unit, such as the Japanese Shiki's SMHC-45-MWL labeling machine. One unit is close to the printing plate to complete horizontal bronzing, and the other unit is a separate unit to complete longitudinal bronzing. This model can perform two-color bronzing at the same time.

5. Flat pressing on the processing machine

The processing machine is specially designed for processing printed roll labels and labels that do not need to be printed. Hot stamping is a function of the processing machine. The hot stamping device on the processing machine generally adopts the flat pressing method, and its working principle is the same as the above labeling machine.

According to the order of self-adhesive hot stamping, it can also be divided into first hot stamping process and second hot stamping process, where first hot stamping refers to first hot stamping on the label machine, and then printing; and then hot stamping refers to printing first, and then hot stamping. The key to bronzing first and bronzing is the drying of ink. Different inks are used, and label printing requires two different processes of first and second stamping:

1. First bronzing process

When the label machine installed with intermittent paper-feeding bronzing parts is printed with ordinary ink, the first bronzing process is used. Since the ink used is an oxidative polymerization drying type, the ink layer after printing needs a certain time to dry completely, so bronzing Patterns must avoid ink. The best way to avoid ink is to pre-gilding the roll material before printing.

The use of the first bronzing process requires that the printed pattern and the bronzing pattern are separated (parallel) because the surface of the anodized aluminum is smooth, no ink, and cannot be printed. Bronzing first prevents ink smearing and guarantees label printing quality.

2. Post bronzing process

The post bronzing process is applied to the label machine where the bronzing parts are installed on the back door, and UV ink is used for printing. The reel material is printed first, and the ink is dried instantaneously through the UV drying device, and then the surface of the material after the ink is dried or the surface of the ink is gilded. Since the ink has dried, the bronzing pattern and the printed pattern can be juxtaposed or overprinted, and ink smearing will not occur.

Among the two methods of hot stamping, post bronzing is an ideal method, which also brings convenience to the design of label patterns and expands the application range of bronzing patterns. However, due to the limitations of device functions, the cost of label printing is relatively high. The first hot stamping process is suitable for the processing of small labels with simple patterns, low cost, and a wide range of applications. It is a common method for small and medium-sized printing plants.

Summary: Doing a good job in self-adhesive bronzing is an important factor in seizing the label printing market, so mastering the self-adhesive bronzing process is necessary.