Ghosting in Flexo Printing: Causes & Solutions Guide

Giới thiệu

Ghosting in flexographic printing, a problem that causes much annoyance to press operators and print buyers, is the faint appearance of a previously printed image or pattern in another area of the substrate. This can greatly affect the appearance and quality of the printed material, which may cause customer complaints and loss of material. The first step in addressing and eradicating ghosting is to understand the root causes of this problem so as to achieve a high quality flexographic output. Just as a laser printer user may refer to the terms of use to solve a problem, this guide is similar in that it provides flexo professionals with information on how to deal with a ghosting issue.

The Causes of Ghosting in Flexo Printing

Several factors within the flexographic printing process can contribute to the appearance of ghosting. These often relate to inconsistencies in ink transfer, drying, or the physical condition of the printing components. Let’s examine some of the most common culprits.

Insufficient Ink Transfer Due to Low Anilox Volume

The anilox roller is the most important component of the flexographic inking system as it is responsible for metering and transferring the right amount of ink to the printing plate. Applying an anilox with the wrong volume is somewhat like putting the wrong paper type into the paper tray of a printer. It has a surface area of thousands of small cells, the volume of which defines the amount of ink that is transferred to the plate. When an anilox roller with a low cell volume is used for a specific job, it is impossible to store and deposit the required amount of ink to create the necessary ink film thickness on the substrate. This can result in a faint or ghost printing, especially in areas of solid color or where high ink density is needed. The first impression might get the required number of impressions in a single rotation while the subsequent impressions in the same rotation may be weak and hence the ghost image.

Rapid Ink Drying on the Anilox Roller Surface

Another cause of ghosting is when the ink dries up very fast on the surface of the anilox roller. This premature drying can be caused by high temperature in the pressroom, the drying profile of the ink or even excessive air flow over the roller. As the ink starts to dry on the anilox surface, it may partially or fully close the tiny cells on the surface of the roller, thus preventing it from picking up and depositing a uniform layer of fresh ink. This blockage causes an uneven deposit of ink on the printing plate, which produces a faint image in the next revolution. This can sometimes be even worse when using thick paper since it absorbs more ink and dries very fast. The freshly applied ink might initially give a good coverage on the printed area but as the partially dried ink on the anilox does not allow fresh ink to be supplied to the surface uniformly, the ghost image appears.

Ink Viscosity Too High or Too Low for Proper Flow

Ink viscosity, which is the measure of the ability of the ink to resist flow, is one of the most important factors that affect the efficiency of the ink transfer in flexographic printing. If the ink viscosity is high, the ink will not easily transfer from the ink pan to the anilox roller and from the anilox to the printing plate. This restricted flow can lead to a weak or ghosted print due to an insufficient and uneven ink film on the plate. On the other hand, if the ink viscosity is low with high humidity, the ink may flow too easily, which can cause problems such as flooding, dot gain, and may also be a cause of ghosting since the ink does not form a continuous film. The ideal ink viscosity is the one that will flow smoothly through the inking system and provide a uniform layer of ink on the printing plate and substrate without giving a starved appearance of the ghosting effect. Getting the right ink viscosity is as important as getting the right individual toner formulations for a laser printer to produce the right color.

Worn or Improperly Mounted Printing Plates

Proper mounting and using quality plates is as crucial as using genuine brother drum units in a laser printer. The printing plates themselves are directly involved in the process of transferring the ink from the anilox roller to the substrate. Printing plates may deteriorate, get damaged or may not have the right surface texture as it was when it was new. This wear can be expressed in the form of a decrease in the height of the image areas or in the destruction of the plate surface, which affects the uniformity of ink deposition and transfer. Likewise, if the printing plates are not properly fixed on the plate cylinder, they may not come in contact with the anilox roller or the substrate in a uniform manner. This can lead to an uneven pressure and poor ink transfer across the printed image and may lead to ghosting. Less contact may result in less ink being deposited on the paper and this may create an impression that is faint and may be referred to as a ghost.

Step-by-Step Troubleshooting Guide for Flexo Ghosting

Identifying the Root Cause

The first step in addressing the issue of ghosting is to carefully analyze each part and environment of the flexographic printing process. First, one should observe the printed substrate to determine the nature of the ghost image. Is it a faint repetition of a specific element, or a general lack of density in certain areas? Next, it is necessary to pay attention to the anilox roller, which is a key component of the printing unit. Look for any signs of ink deposits on the cells, any signs of wear and tear on the roller surface or any irregularities in the roller. Evaluate the ink itself. Is the viscosity within the recommended range for the job? Is the ink fresh and has it been stored in the right manner to ensure that it has not expired? Finally, inspect the printing plates. Check for any signs of wear and tear, damage or improper installation of the part. The process of ruling out possible causes of ghosting through observation and inspection is important in identifying the cause of the problem.

Immediate Actions and Adjustments

Once you have a better understanding of the potential causes, there are several immediate actions and adjustments you can make in an attempt to reduce the ghosting. It is always advisable to make some changes and then make a test print to see the outcome. If you think that there is poor ink transfer, try to increase the press speed for a short time or adjust the impression to have a better contact between the anilox, the plate and the substrate. If the problem is suspected to be due to rapid ink drying, then it is advisable to lower the temperature in the pressroom or add a retarder to the ink (depending on the manufacturer’s guidelines). If the problem is ink viscosity, then it should be brought to the right range by using the right thinners or thickeners. If there is dried ink on the anilox, clean it using the right cleaning solutions and methods as described above. For plates, make sure that the plates are well fixed and properly installed and check for worn out or damaged plates. These immediate changes can sometimes help to alleviate the problem of ghosting, especially if the cause is not complex. Similar problems in other printing technologies can be solved by cleaning the drum unit or removing any lint from the system.

When to Consider Equipment Upgrades

Although most cases of ghosting can be fixed and managed, there are cases where the root of the problem may be attributed to the limitations or wear and tear of the printing equipment. If you are still experiencing ghosting even after following all the troubleshooting and maintenance procedures, then it is high time to upgrade your equipment. For instance, if your anilox rollers are worn out or damaged in a way that compromises their ink metering capacity, you can replace them with new rollers with the right cell volumes and counts to enhance the ink transfer and reduce ghosting. Sometimes, the problem may lie in the basic structure or state of the printing press, for example, a worn out drum unit mechanism may be causing uneven pressure or vibrations that result in ghosting. Likewise, the ink pumps or viscosity control systems may have become obsolete and may not be able to deliver the right ink properties for the best print quality, which is why an upgrade is beneficial.

Preventive Strategies: Best Practices to Minimize Ghosting

Regular Maintenance and Cleaning

It is therefore important to set a strict regimen for the maintenance and cleaning of the flexographic printing equipment to avoid ghosting. This involves thorough washing of the anilox rollers to ensure that they are free from ink deposits, dust, lint or any other material that may hinder the flow of ink through the cells. It is recommended that cleaning be done according to the manufacturer’s instructions and using the right cleaning agents. Likewise, the printing plates should be checked for wear and tear, damage, and adhesion to the plate cylinder. Establish a mechanism for replacing worn plates as soon as possible. Other press parts that need to be maintained include the doctor blades and impression rollers, which also play a role in enhancing the quality of the prints and avoiding problems like ghosting. In addition to these general cleaning and maintenance schedules, it is also advisable to occasionally verify the warranty status of your machine, and by referring to a machine warranty calculator if any, to understand the terms and conditions of the warranty to guide your maintenance so as not to go against the warranty period for some parts.

Proper Ink Management

Ink management is an important factor that should be observed to ensure that the ink used is of good quality and does not cause ghosting. This involves ensuring that inks are stored in a cool dry place, away from direct sunlight as this affects the viscosity and the rate at which they dry. It is also important to make sure that the inks are well stirred before use to avoid having a blotchy appearance. Ink viscosity should be checked and controlled on a regular basis during the print run by using viscosity control systems or by other means. Do not mix inks and ensure that the inks are stored according to their shelf life.

Optimizing Press Settings

This is due to the fact that the settings of the flexographic press must be adjusted considering the type of work as well the material intended for printing to prevent ghosting. This involves the selection of the impression cells, the level of pressure that is exerted between the anilox roller, the printing plate, and the substrate. Too much pressure causes deformation of the plate and excessive ink expulsion while too little pressure leads to inadequate ink transfer resulting in ghosting. Changes to thicker paper may require change to the pressure settings. Like with the press speed, it is equally important to balance the press speed with the ink’s drying characteristics and the nature of the substrate. This may not provide adequate duration for the ink to dry or transfer to the paper which can result in ghosting. In this case, the press settings need to be altered in relation to the print job specifications, the type of ink used, the substrate, and the print’s defining features.

Press Setting	Impact on Ghosting	Optimization Strategy
Impression Settings	Insufficient pressure: poor transfer	Adjust for optimal contact, avoid excessive squeeze
Tốc độ báo chí	Too fast: hinders transfer/drying	Match speed to ink/substrate drying needs
Anilox Roller Pressure	Incorrect pressure: affects metering	Follow manufacturer’s recommendations
Drying System	Insufficient/excessive drying	Optimize temperature/airflow for proper drying
Web Tension	Inconsistent: exacerbates ghosting	Maintain consistent tension

Partner with KETE for High-Quality, Ghost-Free Flexo Printing Machine

It’s worth mentioning that KETE has been selling over 2000 machines per year for more than 15 years and currently operates in more than 80 countries. Our policy ‘Quality First, Customer Foremost’ has enabled us to design ghosting-free flexo printing machines. With KETE, you can also enjoy our high-speed presses of up to 250m/min as well as our environmentally friendly, food-grade water-based inks. Our flexo printing machines are robust and adaptable, able to handle both thick paper stock as well as plain paper, showcasing unrivaled flexibility in printing. In addition, we offer ISO 9001, CE, Rohs certifications, and pre-shipment testing to guarantee you our high-performance, accurate ghost-free print machines, backed by our 2-year warranty with no repair fees and expert technical support.

Phần kết luận

Like most issues in engineering, ghosting in flexo printing can be managed and mitigated by recognizing the root causes, creating a method for solving it, and applying consistent preventive measures. By monitoring flexographic printing ghosting issues, considering the transfer of ink, drying attributes, the operational state of your printer, and following recommended practices for maintenance and upkeep of the entire system, maintenance of the fuser, and ensuring the correct drum unit works with the printer, are critical for other printers, and so it is correct with regard to your flexo press. It is possible to achieve reduced flexo printing ghosting occurrences, greater image clarity, and sharpness of details which in turn increases the standing of the business as a leading provider.