Jet processing

A Gaussian distribution of particle size is the result of copolymer manufactured by suspension polymerization. A jetting process produces beads with more uniform particle size. The uniformity coefficient is a numerical method of indicating closeness of all beads to the same size. 

In the second step, a papermaking method is also used for the fine fibers, less than 0.1 tex (1 den). This process is usually followed by a high pressure water jet process instead of the third step. In the fourth step, to obtain the required properties in specific appHcations, a polyurethane is selected out of the segmented polyurethanes, which comprises a polymer diol, a diisocyanate, and a chain extender (see Urethane polymers). A DMF—water bath for coagulation is also controlled to create the adequate pore stmcture in combination with fibers. 

The ink-jet process relies on using a piezoelectric printhead that can create deformation on a closed cavity through the application of an electric field. This causes the fluid in the cavity to be ejected through the nozzle whose volume is determined by the applied voltage, nozzle diameter, and ink viscosity. The final width of the drop of the substrate is a result of the volume of fluid expelled and the thickness of the droplet on the surface. In addition, the drop placement is critical to the ultimate resolution of the display. Typical volumes expelled from a printhead are 10 to 40 pi, resulting in a subpixel width between 65 and 100 pm. Drop accuracies of +15 pm have been reported such that resolutions better than 130 ppi are achievable however, because the solvent to polymer ratio is so high, the drops must be contained during the evaporation process to obtain the desired resolution and film thickness. This containment can be a patterned photoresist layer that has been chemically modified so that the EL polymer ink does not stick to it. 

In addition to the deformation modes described above, there are some other modes of practical interest, for example, the cyclic spreading, recoiling, and oscillation mode typical of solder jetting process.[5°1 This mode leads to a final splat shape of multiple surface ripples at low substrate temperatures and hemispherical shape without surface ripples at high substrate temperatures. 

Recently methods were developed for computer-controlled ink-jet printing [16, 17], Production speed is still low (less than 20 m/min). On the product side, no problems arise with soluble dyes. However, disperse dyes and pigments must be very finely distributed to avoid blocking of the jets. Ink-jet processes are already well established in carpet printing (space dyeing). 

The jet stability and break-off behavior with respect to the fluid properties are stated in well-known theories such as Navier-Stokes equations and the Rayleigh theory. During recent years many computer simulations have aimed at predicting the jetting process in specific print heads and, more importantly, for establishing a methodology for selection of ink additives. ... 

Scale-up of an impinging jet process is simplified because the laboratory/pilot-scale feed line diameters may require only a two- or fourfold scale-up. The primary increase in scale is achieved by a longer run time. However, since the mixing device produces the same conditions of supersamration at all times during operation, the time of the run can be increased manyfold without changing the nucleation conditions. 

Gel-Cel fibers -10,20,30 - fibers obtained by Jet Process developed to improve uniformity of fibers, modify their morphology, and improve their anti-settling characteristics... 

The high-temperature demand mode ink-jet process used in printing UV-curing polymer microlenses can be used to create highly controlled spacers in flat panel displays. Figure 11-26 shows an example of printed spacer bumps that would meet the physical and thermal (in excess of 200°C) durability requirements for flat panel displays. Bumps as small as 25 pm diameter and 10 pm high can be created, and bumps this size or larger would span the requirements for most spacers in displays. 

Annular Jet Process Centrifugal suspension separation Coacervation and phase separation Cocrystallization Controlled precipitation Dispersion/suspension polymerization Dripping and jet break up Electrospraying... 

There are a number of process technologies used for annular jet processes. While there are some dominant ones, some smaller or niche processes should not be completely unmentioned. However, as the market is moving and evolving, it is not possible to give a complete overview about technologies, but the interested reader may inform himself by regularly visiting conferences and access the well-established Journals to find out about newer developments. 

At the current time, the annular jet processes most commonly used in food, pharma, cosmetic, and chemistry that produce particles of one or another kind are certainly laminar flow breakup processes. It has to be kept in mind, that the absolute majority of annular jet processes are used in other fields—as fuel engines—or to produce matrix particles, as two material nozzles used in atomization. Those, however, will not be subject to this chapter. 

For the production of core-shell encapsulated products, annular jet processes offer a large number of advantages. Already a vast amount of products is produced using these processes, ranging from chewing gums, tobacco, medical products, supplements to electronic, and chemical applications. 

Annular Jet processes are used widely in industries. A special interest and growing application are processes to produce Micrcapsules with annular gap nozzles. A selection of those processes is presented in this chapter. 

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