Flexographic printing is widely used in packaging printing fields such as label, film, paper products, electronic adhesive because of its environmental protection, adaptability to materials and high stability. In the process of high speed mass production, the quality defects such as blurred edges, overall blurring and ghosting are the most common, which will not only lead to lower product quality and scrap of mass production, but also slow down production progress and increase production cost. The fault is not caused by a single factor, but by a combination of pressure, ink, plate material, equipment parameters, and the imbalance in the coordination of the drying system. Combining with frontline production experience, this paper analyzes the core causes of fault systematically and provides standardized process control and solution.
1.Imbalance of printing pressure leads to inaccurate diffusion of pictures and texts.
Improper pressure adjustment is the main cause of text blurring. Flexographic printing adopts the principle of soft embossing and is suitable for light pressing transfer printing. If printing pressure is too high, the mesh roller and embossing roller will overexpress the flexible printing plate, leading to the spread of dot ink, resulting in the printing plate edge adhesion, dot adhesion, thick text and so on, which is also a common paste defects in the printing industry. Conversely, if the pressure is too low, the ink cannot be completely uniform transfer to the surface of the substrate, resulting in shallow text, blurred edges, local deficiencies. At the same time, the pressure imbalance between the left and right sides of the device, and the deviation of roller shaft parallelism, will result in clear text on one side and blurred images on the other, resulting in batch quality defects.
2, Ink performance is not up to standard, damage to the printing molding effect.
The viscosity, ratio, drying speed directly determines the quality of graphic and text forming. In daily production, ink dilution will lead to low viscosity, fluidity, high speed printing easy to diffuse, resulting in blurred edges and burrs; high the viscosity will cause ink too thick, ink transfer is not uniform, text depth will appear gray and fuzzy. In addition, ink mixing is not uniform, internal residual bubbles, will lead to uneven ink application in a certain area, ink drying speed and car speed do not match. If the drying speed is too fast, it is easy to cause graphics and text drying and blurring. If it dries too slowly, wet ink accumulates and adheres, causing blurring and ghosting, severely affecting the clarity of the print.
3. Defects in the process of plate and paste lead to abnormal transfer.
Flexible resin plate of the texture is relatively soft, sticker quality directly determines the accuracy of printing. When printing, if the printing plate in the process of residual bubbles, uneven paste, edges curl, uneven forces, etc., will appear local blurring, the problem of incongruence in the transfer of text and pictures. At the same time, the printing plate in long-term use, will appear wear and tear, deformation, aging, small text, small dot defects, and so on, after printing naturally become blurred. Some operators in the high-speed printing process, if the Improper selection of tape, pull the plate, will cause slight deformation of the plate, resulting in text deviation, ghosts and other continuous problems.
4, The equipment is unstable, creating motion and wobble shadows.
Under the condition of high speed printing, the stability of equipment is the foundation of precision printing. In the process of expansion and redevelopment, the excessive fluctuation of tension will cause the film and paper substrate such as tension, vibration and displacement. Every slight deviation in the imprint position can lead to ghosting and blurring of images and text. In addition, guide roll, embossing roller surface dirty, slippery, wear, deformation, and various color groups of asynchronous operation timing, will affect the stability of material feeding. The equipment is not calibrated concentricity for a long time, the transmission clearance is too big, the vibration is big when running at high speed, also is the important reason which causes the picture and text to blur.
5, dryness and environmental parameters do not match, exacerbating defects.
The drying system is the key step to ensure the shaping of graphics and text. Low drying temperature, insufficient hot air speed, air ducts blockage, etc., will lead to ink can not dry quickly, resulting in ink diffusion, graphics and text due to subsequent material stacking and friction and blurred. At the same time, workshop temperature and humidity will also affect the shape of the substrate and ink performance. If humidity is too high, the material will be stretched because of humidity, ink will slowly dry. If humidity is too low, the material will produce high static electricity, ink evaporation too fast, these will lead to poor picture and text forming quality, blurred edges.
6, Standardized Prevention and Rectification Control Plan
In view of the above reasons, the workshop needs to establish standardized machine adjustment and quality control process. In debugging, follow the principle of light pressure printing, accurately calibrate the the parallelism and printing pressure of roller shaft to prevent high pressure paste and low pressure false printing; Standardize ink blending standards, regularly test ink viscosity to ensure stable ink performance. Clean plate roller and plate before paste to ensure smooth and bubble-free surface. Regularly replace ageing and worn steel plates. Pre-production Calibrate equipment tension and correction system to remove roller surface impurities, ensure smooth feed. Finally, match the speed and drying parameters, clean the drying filter, stabilize the production environment of the workshop, eliminate the blurring of text from the source, and improve the printing yield and production stability.
