Printing technology: analysis of bronzing process of self-adhesive anti-counterfeiting labels

Self-adhesive label materials are called self-adhesive label materials in the industry. It is a composite material with paper, film or special material as the fabric, adhesive on the back, and silicon-coated protective paper as the backing paper. Today, the demand for self-adhesive labels in my country is growing rapidly at a rate of more than 20% per year. The market size of self-adhesive labels is about 450 million to 500 million square meters per year. Therefore, the application of self-adhesive is more and more extensive, and it is widely used in commercial label printing and screen printing. Among them, bronzing technology is the most important process of self-adhesive printing.

Generally speaking, self-adhesive includes a variety of bronzing processes: cold bronzing, circular bronzing, flat bronzing and other processes. According to the processing method of self-adhesive labels, its bronzing methods are divided into single bronzing and roll paper bronzing. Sheet-fed foil stamping is the same as the traditional foil stamping process, which is processed on a special foil stamping machine. Roll paper bronzing is carried out on the label linkage machine, which is the most widely used processing method. At present, bronze coils are available in the following ways:

1. Cold foil stamping on a rotating machine

This is a new hot stamping process. Instead of using a heated metal plate, the foil is transferred by means of a printing adhesive for hot stamping. The process flow is: first print UV pressure-sensitive adhesive at the position where the printed matter needs to be hot stamped, then use a UV drying device to dry the glue, then use a special metal foil to compound the pressure-sensitive adhesive, and then peel off the metal foil to make the part of the metal foil that needs to be transferred. Transfer to the surface of the print for cold foil stamping. The cold bronzing process has low cost, energy saving and high production efficiency, and can utilize existing equipment components without adding additional equipment. This is a promising new process.

2. Round press hot stamping on the round press

The hot stamping plate used for circular pressing and circular hot stamping is a cylinder, which is in contact with the impression cylinder during hot stamping to realize hot stamping. The round pressing and round bronzing is suitable for the continuous feeding rotary labeling machine, but it has certain requirements on the feeding speed, that is, it has an impact on the printing speed. But compared with flat stamping, the efficiency is greatly improved. Circular embossing rollers are expensive to manufacture and are only suitable for long-run live printing.

3. Flat hot stamping on the labeling machine

Whether the letterpress label printing machine is a flat flattening or a circular flattening device, due to the intermittent feeding of the roll paper, the bronzing method is flattened. Under normal circumstances, the bronzing table is an independent unit, and some models share a unit for bronzing and die-cutting and are used separately.

4. Multi-station flat pressing and hot stamping

Some models have a two-station hot stamping unit, such as the SMHC-45-MWL labeling machine from Shiki in Japan. One unit is close to the printing plate for horizontal hot stamping, and the other unit is a separate unit for vertical hot stamping. This model can perform two-color bronzing at the same time.

5. Flatten bronzing on a processing machine

The processor is specially designed for processing printed roll labels and labels that do not require printing. 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 that of the above-mentioned labeling machine.

According to the order of self-adhesive bronzing, it can also be divided into first bronzing process and post bronzing process. First bronzing refers to bronzing on the labeling machine first, and then printing; then bronzing refers to printing first, then bronzing. The key to bronzing first and then bronzing is the drying of the ink. Using different inks, label printing adopts two different processes: initial bronzing and post bronzing:

1. The first bronzing process

When the label machine with the intermittent feeding hot stamping part installed in the front uses normal ink to print labels, the first hot stamping process is used. Since the ink used is of oxidative polymerization drying type, it takes a certain time for the printed ink layer to dry completely, so bronzing is required. Patterns must avoid ink. The best way to avoid ink is to pre-stamp the web material before printing.

Using the first bronzing process requires the printed pattern and the bronzing pattern to be separated (juxtaposed) because the surface of the anodized aluminum is smooth, not inked, and cannot be printed. One bronzing can prevent ink from smearing and ensure the quality of label printing.

2. Post-stamping process

The labeling machine adopts the post-gilding process, the back door is installed with hot-stamping parts, and it is printed with UV ink. The roll material is printed first, and the ink is instantly dried by a UV drying device, and then stamping is performed on the surface of the material or the surface of the ink after the ink is dried. Since the ink has dried, the hot stamping pattern and the printed pattern can be side-by-side or superimposed without ink smearing.

Among the two bronzing methods, post bronzing is the ideal method, which also brings convenience to label pattern design and expands the application range of bronzing patterns. However, due to the limitation of equipment functions, the cost of label printing is relatively high. The first bronzing process is suitable for the processing of small labels with simple patterns, with low cost and a wide range of applications. It is a commonly used method in small and medium-sized printing houses.

Summary: Doing good self-adhesive bronzing is an important factor to seize the label printing market. Therefore, it is necessary to master the self-adhesive bronzing process.