Die-cutting of self-adhesive materials and its technical points (below)

Effect of Adhesive on Die-Cut

There are four types of adhesives commonly used in adhesive materials: acrylic water-based latex, rubber-based hot-melt adhesives and solvent-based rubber or acrylic adhesives, of which the most widely used are latex and hot-melt adhesives.
Due to the different raw materials and formulas of the adhesives, their physical and chemical properties are also different. The water emulsion is composed of tiny capsules, the cohesion force is relatively small, and the adhesive film is easily separated. The hot melt adhesive is composed of a rubber material with a large cohesive force, and it is difficult to separate the adhesive films. Therefore, when die-cutting, if it is a water emulsion material, the label will be exhausted even if the adhesive layer is not cut or completely cut off, because the pulling force at the time of waste can easily pull off the adhesive layer. When die-cutting hot-melt adhesive type adhesive materials, if the die cutting is not in place, the labels are not peeled off together with the waste paper edge, and the bottom paper is cut through. Because the hot melt adhesive layer can only be completely discharged when it is completely cut (or mostly cut), the uncut plastic film will be peeled off together with the label, which increases the difficulty of die cutting.

For this reason, die-cutting latex-type self-adhesive materials are relatively easy, and the hot-melt adhesive-type self-adhesive materials have higher requirements for die-cutting technology. This is also the main reason for the large consumption of processed hot melt adhesive materials and low production efficiency.

The effect of bottom paper on die-cutting

The quality of the bottom paper is the key to the quality of die-cutting. The thickness, flatness, fiber structure and strength of the bottom paper directly affect the quality of die-cutting. At present, the commonly used bottom paper is divided into two major categories, namely, opaque bottom paper and translucent bottom paper. Opaque paper-backed self-adhesive materials generally have a ration of more than 90g/m2, and have a certain degree of stiffness. They are suitable for sheet-fed printing and web-fed printing. Finished labels are mostly used for manual labeling. Transparent backing paper self-adhesive material is generally weighed 60 ~ 70g/m2, bottom paper fiber has a certain density or tightness, mainly used for web printing, not suitable for single sheet printing, finished label for automatic labeling.

Self-adhesive materials require a good flatness of the backing paper, a uniform thickness, a uniform light transmittance, and a higher density, so as to facilitate complete die-cutting of the surface material.

1. Opaque backing paper

The commonly used opaque backing paper is distinguished by color, and can be divided into two types, yellow and white. In terms of structure, it is divided into pre-coated PE coating and no-PE coating. Coating PE coating has two purposes: one is to seal the pores on the surface of the paper to make it smooth and smooth, and apply silicone oil on it to reduce the coating amount, which can reduce the cost; the other is to improve the die-cutting characteristics because PE The coating is equivalent to a layer of cushion, has a certain toughness and elasticity, can reduce the bottom paper breakage. Practice shows that the bottom paper with PE coating has far lower fracture resistance than the bottom paper material without PE coating.

Since thick-bottomed paper labels are mainly used for manual labeling, the quality of unqualified die-cutting has a certain influence on manual labeling. For example, when die-cutting is continued, hand-waste will be peeled off together with the label; if the backing paper is cut through or cut through half It is also very difficult for operators to uncover the mark.

When the opaque backing paper is die-cut on a flat die-cutting die-cutting machine, the common fault is the bottom paper breakage. Therefore, on the basis of ensuring the precision of the die cutter and the flatness of the liner, a flatness, fiber tension, and a uniform thickness should be selected as much as possible. Paper to improve die-cutting quality.

Translucent bottom paper

Translucent paper is also called thin-bottom paper. At present, the adhesive material for label printing is commonly used for glassine paper (glass bottom paper). There are two indicators of the glassine base paper will affect die-cutting quality: one is the thickness uniformity, and the second is the fiber structure. The thickness of the backing paper is most important, especially when circular die cutting, because the size of the die cutter roll is determined by the thickness of the bottom paper. If the thickness of the backing paper is not uniform, the cutting edge will cut through or cut off. Papers cause troubles in the waste disposal process.

The fiber structure of the glassine base paper mainly influences the die cutting speed for round die cutting, because the fiber strength directly affects the waste breaking speed. The faster the speed, the greater the pulling force, the easier the waste discharge. If the material itself is strong, the cutting speed can be increased. However, for slower flattened die-cuts, the fiber structure has little effect on die-cut quality. In addition, the toughness and fracture resistance of fibers have a great influence on the quality of die-cutting. The backing paper with good fiber toughness may not be problematic in die cutting with low precision, but if the backing paper is brittle and has poor toughness, Only die-cutting can be performed on equipment with high precision and good die-cutting quality. This shows that the accuracy of the equipment is also one of the factors that affect die-cutting quality.

We have encountered such cases: There are two self-adhesive materials with the same surface material and different backing papers. Processing on two labeling equipments at the same time results in die cutting on high precision equipment. The cutting quality is normal, while the die-cutting on the equipment with low precision, the poor toughness of the bottom paper fiber material often has problems and cannot be produced normally. This case shows that the quality of die-cutting is related to the self-adhesive material itself, and it is also related to the precision of the equipment.

Die cutting technology

Since the various properties of self-adhesive label materials, such as the strength of the adhesive surface material, the characteristics of the adhesive, and the strength of the bottom paper have a certain influence on the die-cut quality of the label, the adhesive material and the label processing are selected. Among them, there should be certain requirements, the use of high-quality materials or the corresponding die-cutting process to improve the quality of the label cutting. Through many years of practice, the author summarizes the problems encountered in the work and proposes several considerations for the correct choice of self-adhesive materials and effective improvement of die-cutting quality.

1) Do not die-cut film materials with die-cut sheets that have been die-cut. Because the edges are worn, it is not suitable for re-cutting the film.

2) When flat and die-cutting, try to reduce the die-cutting area, especially the full-size small label, because the layout is large and there are many rows of cutters, and the quality is difficult to guarantee.

3) When the flat plate is cut and die-cut, the pad plate should be replaced frequently, especially the long-lived ones, because the cut marks will affect the die-cut quality of the new label.

4) Always check the die-cut quality, especially for the automatic labeling. In order to avoid the emergence of large quantities of quality problems. The specific inspection method is to use a signal pen on the bottom paper to check the penetration of the cut paper.
5) Die-cutting large-area, complex-patterned labels, to professional manufacturers to make die-cuts, this can guarantee die-cutting accuracy.

6) To maintain the sharpness of the blade, create a file and record the use of each die-cut version so that the blades can be replaced in time.

7) It is necessary to die-cut thin-film adhesive materials, especially PET materials, with a special blade with a small angle and high hardness.

Source: Comin Media - "Printing Technology - Label Special Issue"