Self-adhesive material and its effect on label printing

With a number of adhesive manufacturers have launched into production. The requirements for self-adhesive materials and related printing processes also have their own characteristics. This article proposes a brief introduction to the constituents of adhesive materials and their effects on the printing process. Discuss with everyone.

Simply put, ordinary adhesive materials are mainly composed of three parts: surface materials, glue, and bottom paper. Surface material is divided into paper surface material and film surface material. The classification of glue is more complex. It is divided into permanent glue, semi-permanent glue and removable glue for use. The commonly used classification is glassine paper (translucent, suitable for photoelectric control and automatic labeling), film Bottom paper (mostly PET film, high transparency, high tensile strength, suitable for high-speed labeling systems and highly transparent labels) Cowhide backing paper (used for labeling at home, mostly for manual labeling. It is also commonly used for offset printing and self-adhesive materials. The end of paper).

The above is a brief description of the composition of common self-adhesive materials. In addition, there are some special adhesive materials, and their composition forms are not the same, such as in mould label, special hot melt adhesive on the back of the face material, and non-backed paper, and RFID labels (the back of the face material is accompanied by Sensing coils, mostly used for logistics labels), multi-layer adhesives (with multi-layer backing paper and multi-layer glue, for logistics labels, and applications on blood bags).

The printing of sticker materials is not different from the principle of ordinary printing, but the structure of self-adhesive materials is different from ordinary printing paper. So its printing process still has its own characteristics.

The first is the printing method. At present, in the United States, self-adhesive printing is mainly based on flexographic printing. In Europe, there are flexographic and rotogravure editions. In China, flexo printing and offset printing are supplemented by flexo printing. In the past two years, flexo has developed rapidly in China. As for printing inks of adhesive materials, the domestic market generally uses U V relief inks and high-viscosity solvent oils to print clear, beautiful, full-color, flawless labels. Especially color label printing. Should avoid the production of white spots, ghosting (silk bars), inaccurate colors, poor ink adhesion, insufficient color, and missing prints. To do this, in addition to the need to ensure good quality control of the label, the key is to control the relevant links during the printing process, so as to fundamentally eliminate the occurrence of bad prints.

Self-adhesive material is the carrier of label printing. The ingredients of the adhesive material, such as the surface material, directly determine the quality of the label printing. The properties of glue, coating quality, backing paper properties and quality all affect the printing quality of labels. The qualified self-adhesive material should be clean and tidy surface material and the non-silicone surface of the backing paper is free of dirt, paper powder, glue coating is even and smooth, the backing paper is flat and has certain tensile strength and toughness. This is very important for label printing.

Adhesive paper can be roughly divided into paper and film. Different materials have different requirements for the printing process. Paper surface materials can be divided into model paper (double adhesive tape), coated paper, mirror ink viscosity should not be too low (ink should not be transferred too much viscosity reducing agent). The ink absorbency of coated paper is one of the most suitable paper types for printing. (For individual coated paper imported from Europe, the phenomenon of hair growth occurs when the coated paper is printed with a flat press-engraved relief pattern due to its different density and surface coating properties. At this time, you can try to reduce the press pressure, increase the viscosity of the ink, and if it still cannot be improved, you can only change the paper type). Mirror coated paper is relatively poor ink absorption. Therefore, some viscosity-reducing agents may be added in the ink, and the printing pressure may be appropriately increased (not necessarily, depending on the actual situation). Some European imports of mirror coated paper surface coating too dense. The surface is too closed. Therefore, ink absorption is poor, when the offset press is printed. It's easy to be scratched, sometimes with your fingers to wipe off the ink. This kind of mirror coated paper can only be used for letterpress or flexo printing. Mirror coated paper also has a feature. That is, flakes can occur, especially when printing with flexo. The improvement method is to properly increase the UV lamp power or drying intensity. Flake off and the quality of the mirror coating can be gently tearing along the direction perpendicular to the direction of the paper according to the degree of crispness of the paper and the status of the coating on the surface of the fracture surface can roughly determine the degree of powder off. Mirror coated paper itself has a high gloss. Therefore, the label printed with mirror coated paper has enough luster as no special requirements. The label surface does not need to be coated or coated. However, if the printing speed is too fast (over 50 m/min. Relief), the viscosity of the ink is so high that the ink will not cure until it is completely level. At this time, the surface gloss of the label will be greatly reduced to achieve the desired effect, especially for solid color printing. This should be noted more. The thermal transfer printing paper has a slightly better ink absorption than the coated paper thermal paper and is better than the thermal transfer printing paper printing these two types of materials. The viscosity of the ink should not be too low. When using UV ink to print thermal paper, the UV lamp power should be moderately high and the paper surface will be heated yellow. If it is too low, the ink will not dry completely.

Membrane adhesive surface materials can be divided into PE (polyethylene), PP (polypropylene), PET (polyester tandoori), PVC (polyvinyl chloride), synthetic paper and special materials.

The vast majority of film surface materials are non-absorbent face materials (except for individual synthetic papers). The ink absorption is poor. In order to improve the ink absorption and ink adhesion. Need to do surface coating or corona treatment. Surface coating is a layer of special chemical substance commonly known as bridging agent on the surface of the material. Can significantly improve the material surface properties. Corona treatment is based on high-frequency high-voltage electric breakdown through the surface of the membrane material. The dense tiny pinholes are formed while the oxygen near the surface of the material under high voltage generates strong oxidizing ozone molecules. Adsorption of ink on the surface of the material tends to penetrate these tiny pinholes and is pulled by ozone molecules. So corona also improves the material's ink absorption and surface tension. After surface coating or corona treatment, the surface tension of the material can reach 38 dyne/cm. There is no problem with printing ink. Usually adhesive material suppliers will do surface coating or corona treatment when producing materials. However, the effect of corona treatment gradually decreases over time. Therefore, it is recommended that the printing machine should be equipped with a corona device. Online corona treatment before printing.

The corona effect can only last about 4 months. In areas where relative humidity exceeds 60%. This cycle is shorter.

Most film materials have no special requirements for ink. But except PVC material. Due to PVC material special. It is recommended to use special inks for PVC materials. The reason is that PVC material contains some plasticizers. Plasticizers are chemically unstable. Over time, it will gradually seep to the surface of the material. This will significantly reduce the ink adhesion. Within a few weeks after printing, there was a large area drop of the ink layer.

For the printing of film adhesive materials. Static electricity has always been a thorny issue. Membrane materials generate static electricity in the process of unwinding, printing, die cutting, and winding and slitting. Static electricity will absorb the dust in the air. As a result, white spots are printed. Many machine suppliers have considered electrostatic problems. In addition to the static bar installed on the machine. But the effect is not good. It is recommended that copper wire brushes be added after the material is unrolled, before the printing group and before the die-cutting station. Copper brush distance material 3 ~ 5cm. The copper wire brush of the whole printing press needs to be connected with copper wire. Then access the underground 1.5 meters. It is not good to only access the machine without accessing the underground. Because quite a lot of printing plants use terrazzo or concrete floors. The conductive effect is not enough. It was also suggested to keep the printing shop constant at 25°C. Relatively moderate not less than 70%. It also reduces the generation of static electricity.

One common cause of white spots is paper dust and airborne dust that is adsorbed on the surface of the material. Self-adhesive material suppliers in the cutting of self-adhesive materials. The tool, knife holder and cleaning roller should be cleaned in time. Also keep the cutting environment tidy. Try to avoid paper powder and air dust. For printing plants. More attention should be paid to the cleanliness of the environment. When printing, a soft cotton cloth can be used to wrap the square wooden stick. Then press on the unwinding splicing platform. Can improve the white spots caused by paper powder. Note that the cotton cloth stained with paper powder should also be removed when changing paper rolls.

The adhesive layer of the adhesive material also affects the printing effect. The common problem is uneven and spilled glue. Uneven coating is mainly dotted plastic or linear glue-free. This will affect the letterpress printing. White dots or blank lines appear at poor glue application. If it is flexo printing. It is usually not affected. Because the flexographic printing pressure is much lower than the letterpress. Overfill refers to glue overflow from both ends of the roll. Spilled glue stuck to the printing press. When serious, you cannot open the book. There are many reasons for overflowing. The common reason is that the paper roll tension is too high. Coated weight is too high. The humidity is too high and the glue is too fluid. 2. Slightly talc or gently spray some silicone oil spray on both ends of the film. Can prevent the overflow of glue. If you find glue overflow. Should try to reduce the material tension. Turn down the uv light power. Slow down the printing speed.

The backing paper of self-adhesive material mainly influences the die cutting of the label. At the same time, the flatness and tensile strength of the bottom paper will also affect the printing quality. The requirements for the bottom paper of the film material are higher than those of the paper material. The poor tensile strength of the bottom paper will result in overprinting. Even broken paper for PE materials. The tensile properties of the backing paper are particularly important. PE material tensile strength is much lower than PP, PET and so on. So when printing materials. Machine tension should not be too high. Otherwise it will cause significant deformation of the material. Lead to overprinting. Not allowed to die cut.

The above has made some brief introductions to the influence of various constituent elements of the adhesive material on the printing quality. It should be noted that there are many factors that affect sticker printing. Such as material properties and quality, ink, machinery and equipment, drying process, printing process, technical level of employees and the environment temperature and humidity. Will have an impact on the quality of the print. Therefore, when the quality of printed parts is abnormal. Should be comprehensive analysis. Exclude one by one. Take appropriate measures. Remove interference problems.

The printing quality of domestic stickers has been not inferior to those of Europe and the United States. Some well-known companies in the Shanghai-Ninghang District and the Pearl River Delta region that have developed self-adhesive printing products have also successfully entered the international market. But so far. Not much. It has been reported that Americans do not use an annual amount of 15 square meters. European per capita use of adhesive about 10 square meters. The per capita annual amount in China is less than 1 square meter, which can be seen. The development prospect of China's adhesives is huge. At the same time, market competition is becoming more and more intense. All of these have constantly put forward higher requirements for the variety, quality, and quality of adhesive materials.

Reprinted from: Printed Today