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blog Roll paper rotogravure printing and post-processing tips

by:SWIFT     2019-09-24
Paper packaging solutions occupies a considerable proportion in the packaging solutions industry. In a sense, the products packaged with coated copperplate paper generally have relatively high grades and quality, and they require higher requirements for printing. Therefore, it is necessary to conduct detailed studies on the printing and post-processing processes of paper. At present, paper printing methods mainly include offset printing, flexo printing (including UV) and gravure printing. From the standpoint of product exquisiteness, offset printing and gravure printing are more prominent, and offset printing is more frequently used for printing flat sheets. The famous ROLAND and HEIDELBERG are The field is almost universal; in gravure printing, gravure is more widely used, CERRUTI, W &H and BOBST are leading the way. The author shared some of his experiences in copper plate paper and kraft paper gravure with the general readers in order to achieve the purpose of attracting valuable opinions. The application of gravure printing on paper is actually very extensive. However, in contrast, gravure printing is used more in the plastic printing industry, especially in the flexible packaging solutions industry. In recent years, with the rapid development of flexible packaging solutions, gravure printing is almost linked with plastic printing. In fact, gravure printing was first applied to paper. In modern paper gravure printing technology, the use of bronzing, embossing, die-cutting, and other technologies in tandem has made its performance means richer and its application range more extensive. Paper and plastic films will exhibit very different properties in the same gravure printing due to their different properties. In the early days of flexible packaging solutions, the equipment used for plastic gravure printing and paper gravure printing was completely different and incompatible. With the development of modern technology, paper and plastic dual-use gravure printing machines have been developed, which greatly reduces the investment cost of paper gravure printing equipment. The application of paper gravure printing is also more popular. In order to simultaneously take into consideration the different material printing on one device, it is necessary to distinguish from the device configuration, raw material control, and plate rollers in order to obtain exquisite prints at the same time. The main raw material of raw paper is raw wood pulp. According to the different types of pulp and whether the surface is coated with calendering, it can be divided into different types of coated paper, offset paper, moisture-proof paper, kraft paper, and medical paper. But its basis is the natural polymer of cellulose molecular structure. Unlike synthetic polymers such as plastics, cellulose is a hydrophilic polymer, while the latter is completely hydrophobic. Secondly, as far as the commonly used paper is concerned, the mechanical properties of the paper are much higher than those of plastic films, and the longitudinal elastic modulus of the tensile modulus is small. It is these two points that have caused the unique process details in the gravure printing of paper. Cellulose has a certain degree of water absorption. Therefore, for the commonly used coated paper, offset paper, and kraft paper, the moisture content is an important factor in indicating the quality of the paper. The paper will swell after absorbing water, and will shrink after losing water, which is a characteristic that plastic film does not have. The common substation gravure printing machine adopts the automatic color registration system for tracking each color of the overprinting marks, and performs vertical and horizontal overprinting by means of following colors to track the previous color or fixedly track the principle of the first color; after each color printing, it enters the high temperature airflow drying. The ink layer is dried in the drying tunnel to prevent the printed ink from being contaminated and dissolved by the latter color to cause so-called 'biting'. Such a process is suitable for a non-absorbent plastic film, and for a sheet whose external dimensions are affected by the moisture content, the negative influence thereof must be carefully considered and eliminated. The author in the actual production, often found that the former color of the overprint mark in the width direction will be less than about 0.5-0.8 mm after the color, resulting in horizontal overprint deviation of defective products. From the point of view of occurrence, the deviation of the second to third colors from the first color transverse overprint is greater, and the deviation of the second colors from the other colors is smaller. The fundamental reason for the above-mentioned unfavorable phenomena is that after the printing is finished, the paper is drying itself while it enters the drying path of the drying ink, and the water contained in the base paper is also heated and dried, and shrinkage occurs after the water is dehydrated. In the longitudinal direction, due to the presence of tension, the contraction amplitude is relatively small, while the lateral direction is relatively large. Since the size has become smaller after the latter color has been reached in the width direction, the overprint system cannot accomplish the goal of automatic correction and will continuously alarm. Related tags: Customized food packaging solutions bags, aluminum film bags manufacturers,
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