There are 12 common defects that occurred in flexographic printing.
- Dot Gain
- Gear Marks
- Halo
- Feathering
- Doughnuts
- Skip out
- Misregistration
- Mottled image
- Filling in
- Bridging
- Pinholing
- Dirty Print
Dot Gain
The dot gain occurs in almost every print. It causes problems when it is too much.
What are the causes?
This is because of too much pressure between the printing sleeve or cylinder or plate and substrate. Another reason is thick or swollen sleeves or plates from aggressive inks, solvents or cleaning agents. The swelling is avoidable by in-the-round elastomer sleeves. It is very durable and resistant to swelling.
These are the common causes:
- Incorrect ink viscosity
- Too much anilox cell volume
- Dots dipping into the anilox
- Press damage or wear
- Dirty image carrier
- Placing the tape at a wrong thickness
Gear Marks
This is also known as chatter or banding. To avoid this avoid, regular monitoring and maintenance.
How does it look like?
There are alternating lines of light and dark which typically run perpendicular to web direction on press.
What are the causes?
It is because of press mechanics and higher pressure. Also, the host may be responsible for bad printing quality. These gear marks are sometimes clearly heard from the press.
With time, the gears are worn and the teeth are eroded away or even break out. The uneven size of gears causes imbalance and bouncing.
Some other causes:
Poor drive gear lubrication, the pressure tolerance between elastomer and photopolymer sleeves, inadequate cleaning
HALO
As we know the flexographic printing is a pressure-sensitive process. This is the most common cause that occurred due to pressure changes in flexo printing.
How does it look like?
The ink is extended beyond the edges of the selected printing area on the substrate
What are the Causes?
The most common is too much pressure which pushes ink out as there is no place to go. If the pressure is variable the halo is different on locations on a substrate. It can solve by adjusting pressure from print cylinder to substrate
It is because of too much ink transfer, mismatch speed of cylinder-to-web speed
Feathering
The changes in pressure cause the defect but there are also some possible errors that make printing improper
How does it look like?
The ink is extended beyond the selected printing area which creates uneven edges and it looks like a bird’s feather
What are the Causes?
As the ink builds up around the dots it increases the printing surface area. There is high pressure between the print cylinder and substrate or between the print cylinder and anilox in the process.
Other causes
There is dried ink on the image carrier. There is also debris on the substrate. The ink drying is very quick and ink surface tension is high
Doughnuts
This is not the food item but the expensive cause to solve in Flexographic Printing
How does it look like?
There are screen dots that appear slurred and blank or semi-blank space in the middle. It looks like doughnuts.
What are the Causes?
Pressure is one of the main causes of doughnuts and cylinder or plate swelling. The inks and solvents damage the products and cause the swell and distort and make images blurry. The solution is more solvent resistant, direct-laser engrave elastomer sleeves.
There are also some other causes like pressure, print-to-web speed, ink transfer, etc.
Skip Out
The ink must be wet out completely on substrate and Press mechanics is very important. If there is wobbling, the printing parts make contact with the substrate. Also, you may face issues like ink composition in maintenance and cleaning.
How does it look like?
The printing area is too light or miss.
What are the Causes?
Even the small vibration and other micro errors in press mechanics can impact contacts between print cylinder and substrate.
There are also some other causes like high or low areas on the image carriers, bent shafts. Pressure, ink viscosity, and pH, maintenance, and cleaning
Misregistration
For excellent flexographic printing quality, the precise alignment of ink combinations on the substrate. If there is a small fraction of an inch, the design and color are faulty.
How does it look like?
The colors or design is not aligned and causes color shifting. There are cracks between colors or blurred at some places.
What are the causes?
It is because the improper plate position or orientation. For perfect print, every plate must be aligned
There are also some other causes like cylinder concentricity, Cylinder or plate or sleeve condition, gear condition. If the rollers dragged or rotate unevenly. Not proper working of web guide, substrate tension, or tolerance is incorrect.
Mottled Image
This is a common defect for package printing as it requires solid color. The ink is not wet enough on a substrate.
How does it look like?
There is unevenness in print density and shade variations as the printed area required solid color. It has looked like an orange peel and bumpy.
What are the causes?
It may be because of the poor ink transfer between anilox, image carrier, and substrate. Make sure that all print transferring parts are clean. It is because of surface tension, ink viscosity, pressure.
Bridging or Filling In
As these errors are different technically and for flexo printing it is the same. There are various reasons which allow more ink on the image carrier.
How does it look like?
In the areas of the letters the graphic is low quality and has low resolution and connected with each other. Also, the excess ink fills in where it supposes to print.
What are the causes?
The pressure and press mechanics together push the ink where it doesn’t need to be. Ink viscosity, Anilox cell volume or cell count, or engraving angle are the possible causes.
Pinholing
Some of the substrate areas are not fully printed and look like incomplete printing.
How does it look like?
There are small unprinted spots of a size of a pinhole
What are the Causes?
The most probable reason is dirty anilox which interrupts the ink transfer. Also, the ink dries quickly. Other causes are high ink viscosity, lost cell volume of Anilox, some irregular or damage substrate surface. Also, the incorrect surface tension chain between image carrier and substrate.
Dirty Print
This defect directly affects the image quality.
How does it look like?
There are speckles in the ink which look contaminated or it is proof of extra dot.
What are the Causes?
As the name suggests there are contaminants in the flexographic printing room. The machinery generates static electricity and it attracts ducts and other small particles to ink anilox, image carrier, or substrate.
We provide a full Flexographic Printing Defects Troubleshooting Kit for identifying and fix the defect
This guide has about every defect, causes of defects, and information about how to fix it.
