Fabrication curing process

Another modification of this process was reported in 1988 (84). In this process, a precondensate of THPC and urea, plus excess urea, are neutralized to a pH of about 5.7, and the buffer salt is added. The fabric is then given a standard pad-dry-cure process followed by oxidation and laundering. The principal advantage of this modification is a reduction in both formaldehyde vapors and phosphine-like odors released during processing (84). 

THPC—Amide—PoIy(vinyI bromide) Finish. A flame retardant based on THPC—amide plus poly(vinyl bromide) [25951-54-6] (143) has been reported suitable for use on 35/65, and perhaps on 50/50, polyester—cotton blends. It is appUed by the pad-dry-cure process, with curing at 150°C for about 3 min. A typical formulation contains 20% THPC, 3% disodium hydrogen phosphate, 6% urea, 3% trimethylolglycouril [496-46-8] and 12% poly(vinyl bromide) soUds. Approximately 20% add-on is required to impart flame retardancy to a 168 g/m 35/65 polyester—cotton fabric. Treated fabrics passed the FF 3-71 test. However, as far as can be determined, poly(vinyl bromide) is no longer commercially available. 

Eabric can be cross-linked either in the dry or the wet state. If fabric is cross-linked in the dry state, smoothness returns on tumble drying. By contrast, if fabric is cross-linked in the wet state, smoothness is achieved byline-drying the fabric. This concept has been demonstrated using formaldehyde in pad—dry—cure or wet cure processes (eq. 2) (29). 

Weakening of a fabric from any cause, but particularly the weakening of a proofed fabric by the acid resulting from insufficient sweetening, after vulcanisation by the cold cure process. Tensile Strength... 

In situ frequency dependent electromagnetic-impedence measurements provide a sensitive, convenient, automated technique to monitor the changes in macroscopic cure processing properties and the advancement of the reaction in situ in the fabrication tool. This chapter discusses the instrumentation, theory, and several applications of the techniques, including isothermal cure, complex time—temperature cure, resin film infusion, thick laminates, and smart, automated control of the cure process. 

Second, by actually monitoring the state of the material, it is possible to control the fabrication process by data rather than a procedure, such as a set time temperature sequence. This means one can have a self-correcting, automated, intelligent cure process that can adapt to variations in material age, fabric permeability, tool heat transfer characteristics, and the like. 

Figure 4.21 shows the sensor output for the smart automated sensor expert system-controlled run. The resin reached the center sensor at 37 min. The viscosity is maintained at a low value by permitting slow increases in the temperature. At 60 min, fabric impregnation was complete. The resin was advanced during a 121 °C hold to a predetermined value of degree of cure of 0.35, based on the Loos model s predictions of the extent of the exothermic effect. This value of a is clearly dependent on panel thickness. Then at 130 min, the ramp to 177°C was begun. Achievement of an acceptable complete degree of cure was determined by the sensor at 190 min. Then the cure process was shut down. 

After application of the chemical finish, the fabric must be dried and if necessary, the finish must be fixed to the fibre surface, usually by additional heating in a curing step. A schematic diagram of a pad-dry-cure process is... 

Several variations on the conventional pre-cure process have been explored, including short one-step flash-dry-curing (shock condensation) of cellulosic fabrics with the risk of crosslinker migration during the quick drying. The... 

Specifically for the passivation of temperature sensitive bubble memory devices,these ultrapure materials proved to be of great value. A cure process was optimized to obtain a reliable low temperature cure without affecting the magnetic coercivities of the bubble memory devices. A positive resist process, using a simple development step to pattern via holes in devices has been optimized and successfully used to fabricate devices. The devices fabricated using the the polyimide process have been compared with conventional SiC offers reliable passivations with thinner stress free films for passivations. The fabrications involve simple inexpensive process steps and are compatible with conventional resist processes. The reliability of the imide passivated devices can be considerably enhanced by the use of ultrapure starting materials to preclude harmful ionic mobilities through passivated layers. 

In the area of liquid state rheology there is also considerable research in progress on the development of mathematical models that predict material behavior during composite fabrication cure processes. For example, the viscosity of a thermosetting matrix can be predicted for any cure cycle by using a mathematical model developed from kinetic and rheological data (26). 

Polycondensations can be carried out in an aqueous or a solvent medium, or they can be performed while the reactions are in a liquid or in a molten state. In industry, reactions of polyfunctional monomers leading ultimately to the tridimenaonal-network molecules of thermosetting resins are usually interrupted at a stage where the polymers still are soluble and fusible. They then are shipped to the fabricators, who convert them by heat curing processes into the final thermosetting product. 

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