In order to protect the quality of self-adhesive labels and the quality of labels, many surface coatings have been selected for lamination, glossing, and bronzing.
First, sticker UV coating
The glazing process is mainly applied to the surface coating of mirror coated paper and coated paper labels. The purpose is to increase the glossiness of the surface and achieve the functions of antifouling, moisture prevention and pattern protection. According to the processing method, the coating of the self-adhesive label material is divided into light on a single sheet of paper and light on a web of paper, wherein the light on the web of paper is the most commonly used method in the label printing process.
The coating of web labels was carried out on a turn label machine. At present, the UV coating process is commonly used, that is, a layer of UV coating is evenly coated on the printed pattern surface. For water-based ink flexo labels, glazing is an indispensable process.
UV glazing process should pay attention to the following issues:
1. Verification of Varnish Quality
UV Varnish varieties are numerous, have a certain storage period, and have certain requirements for the environment, so that before the use of Sichuan should check the color of coating oil and its drying after quantitative coating, and additives matching Situation, but also pay attention to observe whether there is a reaction with the printing ink used. General requirements of the first glazing test, and then put into normal production.
2. Coating thickness
The leveling properties of UV varnish are not as good as those of solvent type varnish. If the coating amount is too large, streaks will appear on the surface after polishing, which will affect the light reflection effect. If the coating amount is too large, the glazing oil will not dry completely, and only the surface layer will be dry, resulting in adhesion after rewinder.
3. Varnish viscosity and surface tension
Varnish viscosity has an effect on its leveling properties, drying speed, and surface gloss. According to different paper, adjust the appropriate viscosity. While controlling the viscosity, it is also necessary to pay attention to the variation of the surface tension of the coating oil. The surface tension of the varnish must be less than the surface tension of the ink layer of the printed matter. In this way, the varnish can completely wet the varnish surface to avoid quality problems such as pinholes and streaks.
4. Speed, coating amount, pressure, drying temperature
The coating speed, coating amount, pressure, and drying temperature of the coating are mutually restricted, and the relationship between the coating and the absorption of the coating oil on the surface of the paper must be properly adjusted.
5. Regularly check the UV drying device
The UV lamp in the UV drying device gradually reduces the effective power with the use of time. The effective time of the UV lamp is 1000 hours. The effective power should be regularly tested during production and should be replaced when the time of use is close to 1,000 hours.
Second, sticker hot stamping
1. Hot stamping method
According to the processing method of self-adhesive labels, the bronzing method is divided into sheet-fed bronzing and web bronzing. The sheet-fed bronzing process is the same as the traditional bronzing process and is processed on a special gilding machine. Web bronzing is accomplished on the label linkage mechanism and is the most widely used processing method. At present, there are several ways to roll foil material:
1 label machine flat press flat hot stamping
No matter whether it is a flat press or a round press-type device, the letterpress label printing press adopts a flat press mode because the paper is fed intermittently. In general, the stamping station is an independent unit, and there are also some models of bronzing that share one unit for die-cutting and are used separately.
2 multi-station flat press hot stamping
Some models have a hot stamping unit with two stations, such as Shiki's SMHC-45-MWL labeler. One unit is close to the printing plate to complete horizontal bronzing, and the other is a stand-alone unit to complete vertical bronzing. The model can be double-colored at the same time.
3 flat press on the processing machine
The processing machine is designed to process printed roll labels and labels that do not need to be printed. Hot foil stamping is a function of the processing machine. The hot stamping device on the processing machine generally adopts the flat pressing method. Its working principle is the same as the above labeling machine.
4 rounds on the rotary press
The bronzing plate used for round press bronzing is in the form of a roll, and it is in contact with the embossing roll when it is bronzing to achieve bronzing. Round round hot stamping is suitable for use on continuous transfer paper label converting machines, but it has certain requirements on the paper feed speed, that is to say it has an impact on the printing speed. However, compared to the flat bronzing, the efficiency has been greatly improved. Round press hot stamping roll is expensive to manufacture, so it is only suitable for long live stamping.
5 turn cold stamping machine
This is a new technique for bronzing. Instead of using heated metal plates, it uses printing adhesives to transfer metal foils to achieve bronzing. The process flow is: First, the UV-sensitive adhesive is printed on the location where the printed product needs to be gilded, the adhesive is dried by the UV drying device, and then the special metal foil is used to compound the pressure-sensitive adhesive, and then the metal foil is peeled off. Thus, the metal The part of the foil that needs to be transferred is transferred to the surface of the print to achieve cold stamping. The cold bronzing process is low in cost, saves energy, and has high production efficiency. It can utilize existing equipment components without adding additional devices. It is a promising new process.
2. First hot stamping and hot stamping
Self-adhesive bronzing is also divided into bronzing and bronzing. First gilding refers to bronzing on the labeling machine and then printing; then bronzing refers to printing first, and then bronzing. The key to bronzing and post-bronzing is the drying of the ink. There are two situations in the relationship between bronzing patterns and printed patterns: juxtaposition and overprinting. Because of the different inks used, the labels must be printed using the first and second hot stamping processes respectively.
1 first hot stamping process
When the label machine installed with the intermittent paper-feeding stamping unit uses ordinary ink to print the label, the first stamping process is used. Since the used ink is an oxidative polymerization-drying type, the ink layer after printing needs a certain time to be completely dried, so the hot stamping is performed. Pattern must avoid ink. The best way to avoid ink is to pre-foil the roll material before printing.
The use of the first bronzing process requires that the printing pattern and the bronzing pattern be separated (side by side) because the surface of the galvanized aluminum is smooth, free from ink, and cannot be printed. The first hot stamping can prevent the ink from getting dirty and ensure the label printing quality.
After 2 hot stamping process
After the bronzing process is applied to the labeling machine where the bronzing components are mounted on the back door, the printing uses UV ink. The web material is printed first, and the ink is instantaneously dried by a UV drying device, and then gilded on the surface of the ink or the ink surface after the ink is dried. Since the ink is dry, the hot stamping pattern and the printed pattern can be either side-by-side or overprinting, and no ink pick-up will occur.
Two kinds of gilding methods are ideal methods for post-bronzing, which also brings convenience to the label pattern design and expands the application scope of hot stamp patterns. However, due to the limitation of the function of the device, the cost of label printing is relatively high. The first bronzing process is suitable for the processing of small labels with simple patterns. The low cost and wide range of applications are commonly used by small and medium sized printing plants.