Self-adhesive labels are printed on a composite material, such as paper, film, or other specialty materials, with an adhesive coating on the back and a silicone-coated protective paper as the backing. These products are typically single-sheet composite printed products with an adhesive coating on the back, allowing them to be adhered to the desired location. Self-adhesive printing involves the process of transferring ink and other substances through a printing plate under pressure to a pre-coated adhesive layer on the back of the printing material.
01 Letterpress Self-adhesive labels are printed using letterpress printing, using a photosensitive resin plate. The printed labels have the advantage of rich ink color. However, the quality of letterpress printing equipment varies greatly. Some still use rotary presses, some use standardrotary presses, while others have adopted specialized slant-back, satellite, or unit-type self-adhesive label presses, so it’s difficult to generalize when transitioning to self-adhesive label printing.
02 Offset Printing
Offset printing is the primary method used by label printing plants in my country to print paper self-adhesive labels. Offset printing is characterized by detailed graphics and rich gradations, making it suitable for high-volume printing. Furthermore, single-machine printing equipment can be used for multiple purposes, making it well-suited to the specific characteristics of the Chinese label market. However, sheet-fed offset printing is not suitable for printing on non-absorbent films, as film labels are typically printed roll-to-roll and require volatile drying inks.
03 Flexographic Printing Currently, the quality of flexographic printing is comparable to that of offset printing, and even offers unique advantages. This printing process offers advantages such as simple machine construction, low cost, and print quality comparable to offset and gravure printing. Furthermore, it boasts a thicker ink layer than offset printing. Flexographic printing utilizes water-based and UV-curable inks, which are environmentally friendly. However, due to the greater elasticity of flexographic printing, tonal reproduction differs from that of gravure and conventional letterpress printing. The dot gain from highlights to midtones in flexographic printing is larger, resulting in lower print contrast and a tendency for highlight gradations to appear discontinuous. When printing labels with fine graphics, frequency-modulated screens can be used in highlights to compensate for gradation defects, while amplitude-modulated screening can be used in shadows or midtones to improve quality. Label printing shops without flexographic presses can consider installing a stacked narrow-web flexographic press specifically designed for self-adhesive label printing. This press is suitable for printing film labels. Since flexographic presses typically use rotary die-cutting, the high cost of die-cutting rollers and long production cycles make them suitable only for long-run jobs and unsuitable for the high demand for short-run self-adhesive label production in China. However, this type of label printing equipment is easily adaptable and can be integrated with the film slitting, seaming, and sealing processes.
04 Gravure Printing
Gravure printing utilizes a short-path inking system for ink supply, web-based printing, and a high degree of automation. It uses solvent-based inks, resulting in a fast drying process, making it a popular choice for film printing. Generally, gravure presses operate at high speeds, and many also feature a drum die-cutting unit at the back end for die-cutting and creasing, making it suitable for printing a variety of labels. However, due to the long production cycle and high costs associated with gravure platemaking, it is only suitable for large-scale label production.
05 Gluing Self-adhesive labels are made of either water-based or hot-melt adhesives. Hot-melt adhesives are increasingly used in the labeling industry due to their advantages, such as small size and low price. Hot-melt adhesive equipment is also environmentally friendly, efficient, reusable, and easy to use. The hot-melt adhesive process consists of unwinding, coating, cooling, laminating, and winding.
06 Hot Stamping
Hot stamping, as an important metallic surface finishing method, is an effective way to enhance the visual appeal of products such as labels, cartons, and labels, and is widely used. Hot stamping and cold stamping, the two main methods, each have their advantages and disadvantages. In practical applications, the appropriate method should be selected based on the specific situation, primarily considering cost and quality. Hot stamping technology involves transferring hot stamping foil to the substrate using a dedicated metal stamping plate through heat and pressure. The advantages of hot stamping technology include high quality, high precision, and clear, sharp edges. The printed image also has a high gloss and a bright, smooth surface. Hot stamping foils offer a wide range of options, including foils in various colors, glossy finishes, and suitable for various substrates. 3D hot stamping, using a 3D hot stamping plate, imparts distinct three-dimensional depth to printed images and text, creating a relief effect and strong visual impact. 3D hot stamping can also impart a unique tactile quality to packaging. Hot stamping, due to its numerous advantages, has gained widespread popularity among users and consumers. However, hot stamping requires specialized equipment, a heating device, and the production of hot stamping plates. Therefore, achieving high-quality hot stamping results also comes at a higher cost.
07 Post-Processing Edit To protect the printed image and enhance the quality of self-adhesive labels, many labels undergo post-printing finishing treatments such as lamination, varnishing, and hot stamping. Hot stamping methods can be categorized as sheet-fed or web-fed, depending on the processing method used. Sheet-fed hot stamping is similar to traditional hot stamping and is performed on a dedicated hot stamping machine. Web-fed hot stamping is performed on a labeling machine and is the most widely used process.
There are several methods for hot stamping web materials:
① Flatbed hot stamping on a labeling machine
② Multi-station flatbed hot stamping
③ Flatbed hot stamping on a processing machine
④ Round hot stamping on a rotary press
⑤ Cold hot stamping on a rotary press
This is a new hot stamping process that eliminates the use of heated metal plates. Instead, it uses a printed adhesive to transfer metal foil to achieve hot stamping. The process involves first printing a UV pressure-sensitive adhesive on the desired area of the printed product. The adhesive is dried in a UV drying unit, and then a special metal foil is laminated with the pressure-sensitive adhesive. The foil is then peeled off, and the desired area of the foil is transferred to the printed product, achieving cold hot stamping. Cold foil stamping offers low costs, energy savings, and high production efficiency. It utilizes existing equipment and components, eliminating the need for additional equipment, making it a promising new process.
Glazing is primarily used for surface coating of mirror-finish coated paper and coated paper labels to enhance surface gloss, provide stain and moisture resistance, and protect the image. Depending on the processing method, glazing of self-adhesive label materials can be categorized as sheet-fed glazing or web-fed glazing. Web-fed glazing is the most commonly used method in self-adhesive label printing. Web-fed self-adhesive labels are glazed on rotary labeling machines, typically using UV varnishing, which involves applying a uniform layer of UV varnish to the printed image. For flexo labels printed with water-based inks, glazing is an essential step. Lamination: Laminating with a liner is performed on the labeling machine using a specialized laminating film with a liner, which is then laminated using a laminating device. This traditional lamination method has been replaced by linerless laminating processes. Linerless film lamination is performed on a labeling machine. The lamination principle is similar to that of liner-based film lamination. Linerless film relies on its surface smoothness (surface tension) to replace the backing paper after rewinding. Once the adhesive adheres to the surface, it can be peeled off without leaving any adhesive residue. Linerless film is made of low-surface-tension BOPP film. Linerless film offers low cost and is currently the most widely used laminating material.
