Common problems and solutions of offset printing
Date: Sep 27 2024 From: Star Color
Offset printing is a widely used flatbed printing technology, mainly known for its printing effect and economy, and occupies an important position in the printing industry. In practical operation, offset printing often encounters various problems that affect the quality and production efficiency of printed materials. As practitioners in the printing industry for over 10 years, let's explore some common problems and solutions in offset printing.
Ink transfer issue
1. Ink cannot be transferred from the ink fountain to the ink roller
Phenomenon: Poor ink fluidity, short ink quality, resulting in reduced or interrupted ink supply, and lighter color of printed products.
Reason: Ink has poor fluidity, low viscosity, and high thixotropy.
resolvent:
Regularly stir the ink in the ink fountain to maintain its fluidity.
Add ink with high viscosity and good fluidity, or high viscosity resin oil to improve the fluidity of the ink.
2. Ink accumulates on the rubber blanket and cannot be transferred to the paper
Phenomenon: Ink accumulates on the rubber blanket and cannot be smoothly transferred to the paper.
Reason: Ink viscosity is low, water resistance is poor, there are too many pigments and fillers in the ink, the fineness is not enough, and paper powder is mixed into the ink.
resolvent:
Reduce the content of dampening solution.
Add ink with high viscosity and good water resistance.
Reduce the amount of anti sticking and anti stripping agents used.
Replace the paper and choose a paper with higher surface strength.
3. Ink cannot be transferred from the ink roller
Phenomenon: Poor ink transfer between ink rollers.
Reason: Ink has poor water resistance, excessive use of printing solution leads to ink emulsification, low viscosity, and poor fluidity.
resolvent:
Reduce the water supply or add isopropanol to the solution to improve wetting and increase volatility.
Add ink with high viscosity and good fluidity.
Quality issues with printed materials
1. Uneven ink color and unclear patterns in printed materials
Phenomenon: The color of the printed product is uneven, and the edges of the pattern are blurred.
Reason: The ink is too thick and sticky, causing it to dry on the printing plate and ink roller. The printing plate cylinder liner and rubber cylinder liner are not suitable.
resolvent:
Reduce the viscosity of ink with ink adjusting oil.
If drying is too fast, add anti caking agents appropriately.
Adjust the printing plate and rubber blanket pad again.
2. Paper surface fuzz
Phenomenon: The surface of the paper becomes fuzzy during printing, which affects the printing quality.
Reason: Ink viscosity is high, paper surface strength is low, printing speed is too fast, and pressure is too high.
resolvent:
Reduce printing speed.
Add a release agent to the ink to reduce its viscosity.
Replace paper with high surface strength.
3. Circular white spots
Phenomenon: Circular white spots appear in the graphic and textual parts of the printed product.
Reason: Ink skin mixed in, paper scraps, dust and other foreign objects mixed in the ink.
resolvent:
When taking ink, avoid bringing ink skin into the ink.
Do a good job in environmental cleaning and regularly clean the paper scraps on the paper feeding and receiving devices.
Overprint issue
1. Inaccurate overprinting
Phenomenon: When printing in multiple colors, the overprinting between each color is inaccurate.
reason:
Low typesetting accuracy, improper coordination of graphic or rule line positions.
Frequent exposure to the printing plate results in poor overprinting.
resolvent:
Improve the accuracy of typesetting and use a high-power magnifying glass for inspection.
Reduce the number of plate exposures. If multiple plate exposures are necessary, use plate paper for zone exposure.
2. Poor wet to wet overprinting
Phenomenon: The ink used for post printing cannot adhere smoothly to the ink used for pre printing.
reason:
The viscosity of the post printing ink is too high, and the first printing ink is slow to fix and has a large ink supply.
Printing ink dries too quickly, the interval between front and back printing is too long, and the first color powder is sprayed too much.
resolvent:
Reasonably grasp the interval time of overprinting.
Reduce the amount of powder sprayed on the first color.
If crystallization has occurred, it can be remedied by printing a layer of glossy oil.
Other issues during the printing process
1. Dirty version
Phenomenon: Ink stains appear on non graphic parts of the printed product.
reason:
The preparation of the printing plate is poor, and the non graphic and textual parts have not reduced their ability to sense grease.
The water roller is dirty or stained with ink.
Ink has poor water resistance, and excessive water supply can cause ink emulsification.
resolvent:
Prepare the printing plate to reduce the grease sensitivity of non graphic parts.
Keep the water roller clean and avoid getting ink on it.
Adjust the ink balance and reduce the water supply.
2. Rubbing dirt
Phenomenon: When printing materials are stacked, the ink on the front side sticks to the printing materials on the back side.
reason:
Ink has poor dryness and slow curing.
Excessive ink usage leads to poor adhesion on the surface of the paper.
resolvent:
Improve the drying speed of ink and add desiccants.
Reduce ink usage and choose paper with strong absorbency.
Printing machine and blanket maintenance
1. Plastic deformation of rubber blanket
Phenomenon: The uneven thickness of the rubber blanket after long-term use affects the printing quality.
reason:
The tightness of the rubber blanket is not appropriate.
Uneven printing pressure.
resolvent:
The tightness of the rubber blanket should be moderate to avoid being too tight or too loose.
Regularly clean the rubber blanket to remove impurities such as paper wool and paper powder.
2. Printing pressure adjustment
Phenomenon: Inappropriate printing pressure leads to a decrease in printing quality.
resolvent:
Adjust the appropriate printing pressure based on the characteristics of paper and ink.
Ensure that the axis of the drum is parallel and operate in a standardized manner when installing the rubber blanket.
The above are the common problems and solutions encountered in the offset printing process, hoping to be helpful to everyone.
There are various problems encountered during the offset printing process, and most of them can be effectively solved through analysis and reasonable adjustments. In practical operation, operators should be familiar with the operating process of printing machines, the setting of printing process parameters, and the characteristics of printing materials, in order to ensure the quality and production efficiency of printed materials. At the same time, regular maintenance and upkeep of printing machines and their accessories are also important steps in ensuring printing quality.
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