Jan. 13, 2023
In the printing process of cartons, we often encounter problems such as fuzzy handwriting outlines, corrugated crushing, filling ink between imprinted spaces, and poor overprinting/overprinting quality. In addition, how to deal with low-weight base paper and how to print large corrugated boxes The problem is also a technical issue that carton companies are very concerned about.
Aiming at some quality problems that often occur in the production process of carton color boxes, RX packaging shares some experiences and lessons accumulated by its peers as follows:
1. The ink part of the paper is brushed or torn
Due to the different materials, paper structures and production processes of white board paper, coated paper, and offset paper, when the temperature is low in winter and the viscosity of the ink is high, the liner layer or coating layer of the white board paper often has sticky hairs or sticky ink parts. The broken phenomenon seriously affects the appearance quality of printed matter.
Wetting powder and alcohol (5% to 20%) can be added to the fountain solution to reduce the tension on the edge of the inked part, or according to different types of inks, corresponding varnishes, debonding agents or diluents can be selected to Reduce the viscosity of the ink. Control the printing workshop and room temperature. Generally, it is advisable to control it at 19°C to 28°C. It is best to heat the ink properly in winter, which will help improve the fluidity of the ink and reduce the viscosity of the ink. Choose white board paper with strong nap, and the printing pressure should not be too high. The backing paper under the blanket should not be too much, and the pad should not be soft. After the blanket has been used for a period of time, it should be cleaned with a cleaning agent.
2. Color paper ink drying speed is slow
This phenomenon is likely to cause the printed matter to be stuck and cause some difficulties in post-processing. This problem can be controlled from the following three aspects. Use base paper with slightly stronger ink absorption performance: for example, coated white board paper has stronger absorption performance than bleached liner paper white board paper in this respect. Choose quick-drying ink or add a corresponding amount of drying aid according to the characteristics of the ink, and reduce the amount of ink applied to the inked part. Appropriately extend the interval between post-processing or spread out the printed matter to dry.
3. Different shades of ink and differences in color appearance appear in the same batch of printed matter
Better results can be obtained by controlling it in the following ways:
The ink required for the same batch of products should be prepared at one time. When preparing the ink, the required ink, as well as additives such as thinner, debonding agent, and desiccant must be measured with a scale, otherwise the ink will be prepared multiple times. And random ink matching will also cause differences in hue.
The absorption performance, whiteness and thickness of the base paper (white board paper) used in the same batch of products should be consistent. The thicker base paper will increase the printing pressure and cause the ink to be thick. The different white backgrounds of the paper will also cause ink depth and color Changes in appearance.
The balance of ink and ink on the printing roller should be well controlled, and empty runs should be strictly controlled, because after each empty run, the ink color of the first dozen or so prints printed is obviously darker and thicker. If the frequency of empty runs is high, Then there are naturally many prints with different shades of ink.
For products that need to be overprinted multiple times, the previous primer should be completely dried before subsequent overprinting.
4. Wrinkles appear during printing on white board paper
When using white board paper to print color-printed sheets, if the moisture content of the paper is uneven, there will be lotus leaf edges, wavy edges, or tight edges due to excessive moisture evaporation at the edge of the paper due to excessive drying of the environment, and stand-alone overprinting; After repeated printing and wetting, the white board paper will wrinkle during the color printing process.
In order to solve the wrinkling of white board paper during the color printing process, it is first necessary to control the water content of the base paper into the factory. And before the white board paper is printed on the machine, it is best to put it in the offset printing workshop one to two weeks in advance, so that the moisture content of the paper and the humidity of the printing workshop can be kept in balance. If the air humidity in the printing workshop is relatively dry, it is best to properly spray some water on the ground to adjust the air humidity, so as to prevent the paper edge from evaporating more water and causing tight edges to cause wrinkling. The other is to replace or remove uneven base paper.
5. There is a dew on the color printing veneer
The reasons for the corrugation of the color printing veneer are the thickness of the paper, the direction of the silk flow of the paper, the solid content of the adhesive, the amount of glue on the corrugated peak, the pressure after the veneer, and the moisture content of the cardboard.
The desolation problem can be controlled by the following methods:
Appropriately increase the grammage of the color printing surface paper, and make use of the characteristic that the horizontal expansion of the base paper is greater than the vertical expansion after absorbing water, and the longitudinal silk flow of the color printing surface paper and the corrugation are cross-bonded in a "+" shape.
Increase the solid content of the adhesive, reduce the moisture in the adhesive, and adjust the gap between the sizing roller and the pressure roller of the laminating machine (or laminating machine), so as to ensure that the color printing surface paper and the corrugated paper are well bonded. In some cases, try to reduce the amount of sizing on the corrugated peak. After the veneer is dried, the water content is controlled at 9 ± 2% to shrink the fibers of the color printing surface paper, which can also reduce the flute.
6. Glue opening or corrugated collapse occurs on the veneer
Most of the veneer adhesives are now oxidized starch adhesives. If the starch oxidation of the oxidized starch adhesives is not sufficiently oxidized during the preparation process, or the starch is oxidized too deeply, the quality of the adhesives will be unstable, resulting in glue opening. . In addition, if the amount of sizing is too small, too little sizing on the corrugated peaks will cause glue opening. If the veneer is laminated by hand, each layer of tile paper or the inner paper of the surface is not mounted evenly, which will also lead to glue opening.
Carry out veneer on the veneer machine; or use hand-mounted glue to veneer, if the amount of glue applied to the corrugated peak is too large, it is easy to cause the corrugated corrugated to absorb too much glue and become soft, and the corrugated corrugated will collapse after being pressed with the facial paper . In addition, excessive glue application not only wastes glue, but also makes it difficult to dry the products after veneering. Therefore, the amount of sizing should be strictly controlled.
7. Color printing products fade during post-processing and loading and unloading
From the surface phenomenon, the color fading is mainly caused by the friction between the products in the post-processing and handling process. In fact, this problem is also closely related to the ink mixing method. In the production process of color printing products, we often find that the If the viscosity of the ink is too high, it will cause the ink roller to send out ink unevenly and the printed matter will be damaged by the sticky hair of the ink. In order to solve this problem, a debonding agent is often added to the ink. If a debonding agent is uniformly used for inks with different characteristics, the phenomenon of color fading will be quite serious, because the characteristics of different types of inks are different. Take the 05 and 01 resin inks of Shanghai Ink Factory as an example. If the detackifier is not used properly during ink adjustment, it will cause ink crystallization (the ink printed on the product will appear powdery) and cause serious color loss of the product. Type 05 bright and fast-drying resin ink can only be added with type 0592 detackifier, and the amount of addition should be controlled within 3%, while type 01 resin ink can use 3% red dry oil and 6# varnish to Adjust its viscosity. Generally, do not add a debonding agent, otherwise it will also cause the color printing product to fade.
In addition to the attention should be paid to the deployment of ink, in the process of post-processing, handling and loading and unloading of products, it is also necessary to control the color fading caused by dry friction between products and products, products and equipment, products and tools, because the ink is not completely dry. Under normal circumstances, the dry friction resistance is poor, even if the new RMB is wiped dry with rough paper, it will also fade.
If the product fades, the remedy is to cover the surface of the printed product with a layer of film or add a layer of gloss paste to solve the problem of color fading.