Printer's Resource FAQ

What is moiré?

Moiré, as it relates to screen-printing, is a tertiary pattern formed from overlapping two continuous patterns. Common continuous patterns that screen printers deal with are from the following:

  • Mesh pattern
  • Film halftone pattern
  • Substrate surface pattern
Some basic causes for moiré with screen-printing may result from the following:
  • Overlapping of two halftone films at an incompatible angle.
  • Improperly angling the film dots to the mesh.
The patterns involved can be adjusted to minimize the moiré effect. They may be adjusted in the following manner:
  • Changing the angles of one of the patterns
  • Changing the frequency of one of the patterns
Here is an example of how adjusting the angle of one of the patterns may assist with minimizing moiré. Let us say that you have one continuous pattern in one film (See Diagram 1 – 0° Dots). If another similar continuous pattern is overlapped on this dot pattern at 3 degrees, moiré may result. (See Diagram 2 and Diagram 3). If we were to overlap these two continuous patterns at a compatible angle, moiré may be eliminated. In Diagram 4 we have used a 0° and 30° dot angle.

Diagram 1 - Film halftone at 0°:

Diagram 2 - Film halftone at 3°:

Diagram 3 - 0° and 3° Dots Overlapped:

Diagram 4 - 0° and 30° Dots Overlapped:

In the example above, a compatible angle for the two overlapped patterns is 30 degrees apart. It is possible to produce a set of four-color process films at compatible angles to each other. Most screen printers also have difficulties when the film is placed on the mesh. It is necessary is to conduct testing to determine what angles work best for each screen printer’s system. Different film angles may be necessary when any of the following is changed:
  • Mesh Count
  • Thread diameter
  • Mesh Manufacturer
  • Halftone line count
  • Substrate