Described below is a process for producing a microsieve.
Microsieves are nowadays increasingly being used for demanding separation tasks, for example in medical technology or biotechnology. For instance, the enrichment or extraction of particular cells from human blood can be effected by filtration of the blood through a microsieve (microfiltration). Microsieves, in contrast to the known micro filters made from sponge-like polymeric or ceramic membranes, have a defined pore geometry and are therefore much more efficient and have better classification.
For optimization of a filtration method, a freely selectable pore geometry and pore density and distribution of the microsieve are desirable. In contrast to sponge-like filter membranes, the particles retained barely penetrate into the surface, if at all, in the case of microsieves. Thus, they are firstly more easily identifiable microscopically and secondly can be detached more easily from the filter if required by further analysis methods.
One type of known microsieves is that of the track-etched membranes. In the case of these, a polymer film is bombarded with heavy ions and the trace left behind in the film by the heavy ions is subsequently broadened by an etching operation to give a pore. As a result of the production process therefor, these membranes have a spatially irregular pore distribution. According to the pore size, the maximum number of pores per unit area is limited to a considerable degree. For example, it is only possible with track-etched membranes in the case of a pore diameter of 8 micrometers to achieve a pore fraction of the total area of the membrane of 5% at most. Moreover, a multitude of pores pass through the base material of the membrane not at right angles but obliquely. Furthermore, double pores occur, which give rise to a common pore having a diameter greater than the nominal diameter.
WO 2011/139445 A1 discloses a method for producing microsieves, in which a photostructurable dry resist film, for example epoxy resin film, is structured by a photolithographic operation to give a microsieve. This is followed by detachment for dissolution of the microsieve from the carrier used in the production, for example by etching. A disadvantage of the known method is that it imposes lower limits on the thickness of the microsieve, since it is very difficult to process epoxide films thinner than about 10 μm.
The problem addressed is that of specifying an improved process for producing a microsieve, with which the disadvantage mentioned at the outset is avoided. More particularly, the production of microsieves thinner than 10 μm is to be enabled.