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.
Third, the adhesive material of the film
1. Adhesive label coating method
Stickers are usually coated with transparent BOPP film on paper-based adhesive materials, which can achieve the purpose of protecting pattern, waterproof, anti-corrosion, and increasing the three-dimensional sense of the label. Other types of films, such as PET, PVC can also be used as composite films, but the application is not universal. Due to the high cost, the paper web reel film has gradually been replaced by a UV coating process.
Self-adhesive labels are divided into sheet-fed and web-covered films according to the printing and processing methods of raw materials. A sheet of paper is laminated on a laminator. Reel material is compounded on a label machine's compound station or on a dedicated laminator.
1 sheet-covered film
According to the function of the film coating equipment and the characteristics of the composite film, the sheet-fed self-adhesive labels have two kinds of film coating methods:
The coating compound - complete on the laminator. The compounding process is as follows: firstly, the adhesive is coated on the surface of a roll of BOPP film, and the solvent in the adhesive is volatilized through a drying device; then, the sheet of paper is combined with the film of the roll in the compound station and is heated; The roller squeezes the two together to complete the lamination process.
Pre-coating film composite - The surface of the composite film is pre-coated with an adhesive. There are two types of films: hot melt adhesive and pressure sensitive adhesive. The laminating machine is provided with a heated impression cylinder. When the film is covered with the film, the pre-coating film is in contact with a single sheet of paper. Under the action of the hot-pressing cylinder, the adhesive is melted, so that the film is integrated with the paper bonding. If you use a pressure-sensitive composite membrane, you can turn off the heating power and rely on pressure to compound.
2 roll cover
According to the different equipment, web cover can be divided into:
Bottom paper composite film composite - on the label machine, using a special composite film with a bottom paper, under the role of composite devices covered film. This is a traditional film coating method. In recent years, it has been replaced by a process using a non-backed paper composite film.
Non-backed paper compound film composite - on the labeling machine, the principle of film coating is basically the same as the composite technology with bottomed paper composite film. The bottomless paper film is replaced by the surface smoothness (surface tension) of its own material instead of the bottom paper. After the adhesive is adhered to the surface thereof, it can be peeled off without residual glue traces. The material used for the bottomless paper film is a low surface tension BOPP film. The bottomless film coating has a low cost and is currently the most widely used coating material.
Dry coating - on laminators or gravure presses, mainly used for film coating. Reel material dry film is suitable for high-volume label products, with good coating quality and low cost. After the roll label is coated with a film, the secondary processing such as die cutting, waste discharge and the like is generally performed on the processing machine, such as some battery labels and alcohol labels.
UV coating process - the latest foreign technology, mainly used in the unit type rotary labeler with UV drying device. The principle of the process is that the surface of the coating material is first printed with an UV adhesive by an ordinary printing unit, and the adhesive is cured by a UV drying device to become a pressure-sensitive adhesive. Then the ordinary BOPP film (general compound surface has been corona treatment) is compounded with the roll material at the coating station to complete the coating process. The UV coating film has a low cost and a small change in the tension of the composite film. It does not require a special film and is suitable for high-speed production. UV coating is a promising process and is currently applied in developed countries in Europe and America.
2. Technical requirements for the lamination process
There are many factors involved in the lamination process. It is necessary to understand the influence of various process parameters on the quality of the lamination, and correctly handle the relationship between them to achieve the best results. The technical parameters and precautions involved in the lamination process can be found in the attached table.
Technical parameters and precautions involved in the lamination process
Technical parameters precautions
The drying temperature is controlled between 50-70°C, which can fully volatilize the solvent without overheating the film.
The temperature of the compound temperature impression cylinder is controlled at 70-90°C, which not only dissolves the adhesive, but also does not overheat the film.
Composite pressure ensures that the axial pressure of the impression cylinder is consistent and the pressure should be kept within 150-250kg/cm2
Adhesive coating should be thin, controlled at 3-8g/cm2, thickness 5-8μm, to avoid overcoating
The machine speed sheet should be controlled at 35-45 sheets/minute, the web should be at 3-10 meters/minute, and also related to other parameters
The tension of the film is adjusted to the minimum level so as to achieve the correct coating and compounding. To avoid excessive tension
Roller precision The impression cylinder requires a smooth, clean surface with no scratches or dents. To ensure that the environmental factors such as ellipticity and concentricity are kept clean, an air purification device is required. Control workshop temperature and humidity, prevent paper or film deformation
The thickness of the ink should be deep and shallow, so as to prevent the surface tension from declining due to the excessive thickness of the ink layer.
Ink drying ink should be thoroughly dried to avoid blistering
The ink additive controls the amount of the desiccant to prevent crystallization of the ink layer. Crystallized ink surface will appear film is not strong. (Wen / Fu Qiang)