In the printing process of cartons, we often encounter problems such as blurred handwriting contours, corrugated crushing, ink filling between imprinted voids, poor overprinting / overprinting quality, and how to deal with low-gram base paper and how to print large corrugated boxes The problem is also a technical problem that carton companies are very concerned about.
In view of the quality problems that often occur in the production process of carton color boxes, we share some of the experience and lessons learned by our peers as follows:
The ink on the paper is scratched or ripped
Due to the different materials, paper structure and production process of whiteboard paper, coated paper, offset paper, when the temperature is low in winter and the ink viscosity is large, the hanging surface layer or coating layer of whiteboard paper often has sticky hair or sticky ink on the printed part. The phenomenon of breakage seriously affects the appearance quality of the printed matter.
Solution
Wetting powder and alcohol can be added to the fountain solution (the proportion is from 5% to 20%) to reduce the tension on the edge of the inked area, or according to different types of ink, the corresponding ink adjustment oil, debonding agent or diluent can be used. Reduce the viscosity of the ink.
Control the printing workshop and room temperature, generally controlled at 19 ℃ ~ 28 ℃, it is best to enter the winter to properly heat the ink, which is conducive to improve the fluidity of the ink and reduce the viscosity of the ink.
Use strong whiteboard paper, and the printing pressure should not be too high.
There should not be too much liner paper under the blanket, and the pad should not be soft. After using the blanket for a period of time, it should be cleaned with a cleaning agent.
Color paper ink drying is slow
This phenomenon is easy to cause the printed matter to be sticky and bring some difficulties to the post-processing. This problem can be controlled from the following three aspects.
Switch to a base paper with slightly stronger ink absorption properties: for example, coated whiteboard paper has stronger absorption performance than bleached linerboard whiteboard paper.
Choose quick-drying ink or add the appropriate amount of drying aid according to the characteristics of the ink, and reduce the amount of ink applied to the ink area.
Properly extend the interval between post-processing or disperse the printed matter to dry.
Differences in ink shades and color appearance appear in the same batch of prints
Use the following methods to control to get better results:
The inks needed for the same batch of products are best prepared in one go. When preparing the inks, the required inks, as well as diluents, debonding agents, desiccants and other auxiliaries must be measured with a weighing instrument, otherwise the ink will be dispensed multiple times. And random ink distribution will also cause differences in hue.
The absorption performance, whiteness, and thickness of the base paper (whiteboard paper) used in the same batch of products must be consistent. The thicker base paper will cause increased printing pressure and lead to heavy ink color, and the unevenness of the white background of the paper will also cause ink shade and color Changes in appearance.
The ink and ink balance on the printing roller should be well controlled, and the empty car should be strictly controlled, because after each empty car, the ink color of the first dozen printed products is obviously darker and thicker. If the frequency of empty cars is higher, Then there are naturally many prints with different shades of ink.
For products that require multiple overprints, the previous ink should be allowed to dry before the subsequent overprint.
Wrinkles appear when printing on white paper
When printing color-printed sheets with whiteboard paper, if the moisture content of the paper is not uniform, there will be lotus leaf edges, wavy edges or excessive drying due to the environment, leading to the evaporation of water at the edge of the paper and the occurrence of tight edges. In addition, the stand-alone printing color; After printing and wetting for many times, the whiteboard paper will wrinkle during the color printing process.
To solve the wrinkling of whiteboard paper during the color printing process, we must first control the moisture content of the base paper before entering the factory. And the whiteboard paper is best placed in the offset printing workshop one to two weeks before printing on the machine, so as to keep the moisture content of the paper and the humidity of the printing workshop in balance. If the air humidity of the printing workshop is relatively dry, it is best to spray some water on the ground to adjust the air humidity to prevent the edge of the paper from evaporating and causing wrinkles caused by tight edges. The other is to replace or remove uneven base paper.
Color printing veneer appears fluted
The causes of color printing overlays are paper thickness, paper flow direction, binder solid content, sizing amount on corrugated peak, pressure after overlay, and moisture content of paperboard.
The problem of dew can be controlled by the following ways:
Appropriately increase the gram of the color printing face paper, and take advantage of the fact that the base paper absorbs water and the transverse expansion is greater than the longitudinal expansion. The longitudinal grain of the color printing face paper and the corrugation form a "+" cross-fit.
Increase the solid content of the adhesive, reduce the moisture in the adhesive, and adjust the gap between the applicator roller and the pressure roller of the laminating machine (or laminating machine) to ensure that the color printing paper and the corrugated paper are well bonded Under the circumstances, try to reduce the amount of sizing on the corrugated peak.
After laminating, drying treatment is carried out, and the moisture is controlled at 9 ± 2% to shrink the fiber of the color printing facial paper, which can also reduce the fluting.
Adhesive or corrugated collapse appears on the veneer
Overlay adhesives are currently mostly oxidized starch adhesives. If the oxidized starch adhesive is not sufficiently oxidized during the preparation process, or if the starch is oxidized too deeply, it will cause the quality of the adhesive to be unstable, resulting in opening. . In addition, if the amount of sizing is adjusted too small, gluing will also occur if there is too little sizing on the corrugated peak. If the laminating is done by hand laminating, each layer of tile paper or liner paper is not mounted flat and it will also cause glue opening.
Carry out veneer on the veneer; or mount the veneer by hand. If the amount of glue applied to the corrugated peak is too large, it is easy to cause the corrugated peak to absorb too much glue and become soft. Corrugated collapse will occur after being pressed with the tissue . In addition, excessive sizing amount not only wastes glue, but also makes it difficult to dry the products after veneering. Therefore, the amount of sizing should be strictly controlled.
Color printing products appear discolored during post-processing and loading and unloading
From the surface phenomenon, the discoloration is mainly due to the friction between the products in the post-processing, handling and loading and unloading processes. In fact, this problem is also closely related to the ink preparation method. In the production process of color printing products, we often find that the ink The viscosity is too large, causing the ink roller to emit ink unevenly and the printed matter is sticky by the ink sticky hair. In order to solve this problem, a debonding agent is often added to the ink. If a debonding agent is used uniformly for inks with different characteristics, the phenomenon of discoloration will be quite serious, because the characteristics of different types of inks are different. As an example, Type 05 and Type 01 resin inks of Shanghai Ink Factory, if improper debonding agent is used during ink adjustment, it will cause crystallization of the ink (the ink printed on the product has powdery characteristics) and cause the product to discolor. Type 05 bright quick-drying resin ink can only add 0592 type debonding agent, and the amount should be controlled within 3%, while type 01 resin ink can use 3% red dry oil and 6 # adjustment ink Adjust its viscosity, generally do not add debonding agent, otherwise it will also cause color printing products to fade.
In addition to the preparation of ink, attention should be paid to the product and product as much as possible during the post-processing and handling of the product. Discoloration caused by dry friction between the product and equipment, product and tool, because the ink is not dry In this case, the dry rub resistance is poor, even if the new RMB is rubbed with rough paper, it will also fade.
If the product is discolored, the remedy is to cover the surface of the printed product with another film or apply a layer of gloss paste to solve the problem of discoloration.
