Moulding tool for moulding a ceramic green body and use of said moulding tool

#The present invention relates to a moulding tool for moulding a ceramic green body in the production of at least one optical lens made of an opto-ceramic. The invention furthermore addresses a process for producing the lenses mentioned before. Also, the invention is directed to the use of a moulding tool for producing opto-ceramic lenses.

#Transparent ceramics suited as materials for lenses are hereinafter referred to as opto-ceramics. Such materials have very convenient properties (refractive indices, dispersions) and contribute to an improvement of optical imaging systems. In special cases new imaging concepts are only possible with such new optical material options. Especially the possibilities of more compact construction of for example digital cameras or improved of simplified colour corrections (chromatical or apochromatical) or mentioned here.

#The lenses that can be produced with the moulding tool according to the invention and by making use of the new and advantageous process claimed herein consist of opto-ceramics. Such materials are defined afterwards. The term “consist of” in the sense of this invention does not exclude the presence of remaining binders or other additives present in the final lens besides the single phase, poly crystalline material (see below). Such compounds may be present depending on what concise process was used for producing the respective lens.

#The objects, features and advantages of the invention will now be illustrated in more detail with the aid of the following description of the preferred embodiments, with reference to the accompanying figures in which:

#FIGS. 1a and 1b are diagrammatic cross-sectional views illustrating a preferred slip casting process using a mould according to the present invention;

#FIGS. 2a, 2b, 2c and 2d are diagrammatic cross-sectional views illustrating a preferred centrifugal slip casting process using a mould according to the present invention;

#Particularly preferred are the moulding tools according to the present invention for casting (slip casting, pressure slip casting, vacuum slip casting, centrifugal slip casting, gel casting) or for plastic moulding processes (extrusion) or for hot casting or die casting or pressing, for example uniaxial pressing.

#Particularly preferred is the slip casting shown in FIG. 1 or allied processes, wherein a suspension 2 is cast into the mould 1 together with a preferably nanoscale powder (see FIG. 1a). Because of the porosity of the mould, moisture is drawn from the suspension by capillary forces (pointed out with arrows 4). A sherd 5 (ceramic green body) is formed on the walls of the mould (see FIG. 1b). The cavities developing due to the shrinkage are filled by casting more fresh slip into the mould. As a version the pressure slip casting as well as vacuum pressure casting can be applied, too.

#The materials used for slip casting for the moulding tool are gypsum, resins, polymers, ceramics or zeoliths with suitable open pore structures. With respect to suspensions of nanoscale grains structures should be used that are substantially nanoscale, too. The pores must be open in any case, the pore diameters should reach from about 50 nm to about 5000 nm. The surface of the mould should be as even as possible, in order to limit eventual post-processing to a minimum (average roughness RMS smaller than about 100 nm, preferably smaller than about 50 nm, particularly preferred smaller than about 25 nm more preferred even smaller than 3 nm). Herein RMS means the so called root mean squared roughness and is calculated from the mean of the squared deviations.