Since the inception of the "Modern Ceramics Era," usually defined as during or slightly after World War II, there have been several advances in ceramic processing technology. One of the newest and most prolific of these advances has been the development and implementation of tape casting as a manufacturing process for the production of thin sheets of ceramic materials. Glenn Howatt is universally regarded as the "father" of tape casting since he had the first publications and patent describing this process.
Tape casting is also known as doctor blading and knife coating, and under these names the process is well known in many industries including paper, plastic, and paint manufacturing. The "doctor" is a scraping blade for the removal of excess substance from a moving surface being coated. The technique has long been utilized in the paint industry to test the covering power of paint formulations. Films of paint a few mils (<50 microns) thick are uniformly coated on a standard black and white background and the degree to which the background is hidden is measured optically. Howatt’s patent was the first documented use of this technique to form ceramics. His patent teaches "forming ceramic materials into flat plates, especially useful in the electric and radio fields." This is still the principle application today, although the use extends far beyond the field envisioned in 1952.
The chief advantage of the tape casting process is that it is the best method for forming large area, thin, flat ceramic or metallic parts. These are virtually impossible to press and most difficult if not impossible to extrude. The difficulties are compounded in dry pressing when the plate is to be pierced with numerous holes because of the increased problem of uniform die fill. Punching via holes and slots of various sizes and shapes into unfired tape is relatively easy and essential to the multilayered ceramic packages being designed and manufactured today. The thin ceramic sheets are essentially two dimensional structures since they are large in the X and Y directions and very thin in the Z dimension. In today’s technology very thin is defined in microns, with tapes as thin as 1 micron being reported by equipment manufacturers. Tape Casting Warehouse, Inc. personnel have cast tapes on a standard tape casting machine which range from 12 microns on the thin side to over 3 mm on the thick side. The prime dried thickness range for tape casting is generally accepted as being from 0.025 mm to 1.27 mm..
In the ceramics industry, tape casting is a process which is most analogous to traditional slip casting. The similarity occurs since it is a fabrication technique which utilizes a fluid suspension of ceramic or metallic particles as the starting point for processing. However, there are subtle differences. Tape casting is usually based upon a non-aqueous solvent as the liquid system. In recent years there has been increased emphasis with excellent success on the utilization of aqueous based tape casting systems. In most tape casting processes, however, the use of non-aqueous solvents is required since the drying process is evaporative from the surface rather than absorptive into a plaster of Paris mold. It is interesting to note that Howatt taught the use of porous plaster batts as the tape casting surface and that water was one of the liquid mediums he utilized. The use of a porous casting surface has been replaced in modern tape technology by the use of a non-absorptive carrier. In the 1950s the American Lava Corporation developed and received a patent which describes this advance in the technology. John L. Park, Jr. described the use of a moving polymer carrier as a casting surface in this seminal patent. This was the turning point in tape casting processing technology since it was the first time that the process was demonstrated to be continuous and dried unfired tapes could be rolled-up on the polymer carrier for use in downstream processing. It also opened up the possibility of roll-to-roll or continuous in-line processing. Since the Park patent issued there have been many refinements with respect to slurry formulation and equipment design, however the basic process has remained very close to that original conceptual design.