Filter well and method for its manufacture

DETAILED DESCRIPTION According to the present invention it has been found that a more efficient filter support surface with regard to residual liquid can be obtained if the flow channel pattern is designed more densely and with finer and more shallow channels and ridges, or ribs, in between than for the known support surface constructions.
More precisely these support ridges shall, according to the invention, have a sufficiently small width for those parts which are in contact with the filter to make essentially the whole upper surface of the filter effective, i.
e.
filtration will be carried out over the whole filter surface.
This can be achieved also for thin filters if the ridges have a width of not more than about 0.
2 mm, preferably not more than about 0.
1 mm.
"Width" hereby means the cross extension of the ridges at their broadest section.
According to a preferred embodiment the upper parts of the ridges are rounded and/or have a coarse surface, i.
e.
they are rough, in order to reduce the area of contact with the filters.
With a filter support surface of this kind a very efficient utilization of the filter can be obtained even for thin filters and at the same time a very small retained liquid volume (dead volume) after the filtration, but still with an acceptable volume flow through the filter.
A suitable distance between the support ridges is from about 0.
4 mm to about 0.
1 mm.
Such short distances prevent the filter from sinking into the channels and the channels can thus be made very shallow.
Preferably the flow channels have a depth of not more than about 0.
1 mm, especially to about 0.
05 mm or still less.
The ratio between the channel surface and the ridge surface can vary within wide limits but is preferably from about 4:1 to about 1:4, particularly from about 4:1 to 1:1.
The bottom of the flow channels should be smooth to give a small flow resistance.
The bottom portions preferably have a surface fineness (or profile depth) of less than about 0.
4 .
mu.
m, especially to about 0.
1