Mioré between film and mesh
Avoiding moiré between film and mesh
In half-tone printing, an additional moiré effect can result from unsuitable angling between the half-tone film and the screen printing mesh. This effect is most plainly visible in monochrome prints, whereas multi-color printing tends to conceal it.
The greatest risk of interference between the film angle and the symmetrical mesh geometry occurs at 0° / 45° / 90°.
This is why the half-tone angle and the mesh threads should never run parallel to each other. In offset printing, the recommended angle for the dominant color is 45° which, when laid onto the mesh, can result in moiré.
There are two possibilities for preventing all this: angle the mesh, or angle all four colors with respect to the mesh.
(or all at 22,5 °)
On economic grounds, we recommend stretching the mesh straight but pre-angling the diapositives of all separation.
With five, six and more colors, angling should be chosen so that pale colors fall at the same angle as their deep complements, e.g. deep red with pale blue, deep blue with pale red. An additional grey should be angled so as not to coincide with other strongly grey-like colors.
The moiré can be wholly or partially eliminated in the following ways:
By the type of stencil:
The moiré effect is less apparent with an indirect stencil, since the influence of the mesh is less pronounced than in the case of direct stencils.
By the fineness of the mesh:
The finer the mesh in relation to the half-tone count, the less visible is the moiré effect.
Recommended ratio between mesh count and the fineness of the half-tone:
Mesh count/cm :
Screen pitch lpcm
SEFAR PET 150-31yellow
3.75 : 1
5.00 : 1
i.e. the mesh number is divided by the ratio.