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.$Page break $
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 pressure