The present invention relates to a screen-type printing stencil having therein holes arranged in a pattern.
Screen printing, whether of the type employing flat-bed printing stencils or of the type employing cylindrical screen printing stencils in rotary screen printing machines, requires that the boundary areas between the different printed colors be smeared as little as possible.
The object of the present invention is accordingly to provide a screen-type printing stencil having therein openings patterned to reduce smearing.
This object is achieved according to the present invention by providing that the pattern of the openings or holes is formed by repetition of a primary pattern or pattern period formed by at least three holes none of which can be brought into coincidence or superimposition by rectilinear shifting toward each other.
In this connection it is of advantage if the pattern period includes holes of at least two different geometrical shapes and/or different sizes.
A particularly advantageous embodiment of a screen-type printing stencil according to the present invention is obtained when the pattern period has at least one hole which is equilateral and at least two elongated holes or six pentagonal holes.
When at least two elongated holes are provided, it is advantageous if the equilateral hole is hexagonal and if there are present three elongated, congruent, rhomboidal holes, the longitudinal axes of which extend at an angle of 60.degree. with each other. The sides of each rhomboidal hole extend in directions parallel with respective sides of the hexagonal hole.
When six pentagonal holes are provided, it is of advantage that the equilateral hole be a regular hexagon and that the six pentagonal holes be shifted with respect to each other by 60.degree. symmetrically around the hexagonal hole. Each side of the hexagonal hole faces a parallel side of equal length of one of the pentagonal holes. The mutually facing sides of adjacent of the pentagonal holes are always parallel with each other, and the outer sides adjacent thereto are always aligned with each other and jointly form a regular hexagon.
The above features of the screen-type printing stencil of the invention avoid the occurrence of intervals, which would otherwise exert a disadvantageous effect on printing, especially the printing of fine line patterns.
Further, a particular advantage of the invention is that the screen-type printing stencils of the invention produce sharper pattern outlines, since the inner tensions of the photolacquer exert their effect in an advantageous manner, i.e. the photolacquer does not pull back in the area of holes, which would lead to irregular edges.