Binder solvent-based system

All of these UV-curable systems have very different chemistries than those used in solvent-based systems. Most contain a dispersant, a plasticizer (not necessary in all cases), a photopolymerizable binder, and an initiator to activate the UV curing. A typical binder/initiator system found in the literature is a polyester acrylate binder and an initiator such as 2-hydroxy-2methyl-l-phenyl-propan-l-one. The binder is a liquid low-viscosity monomer diluted into hydroxy-ethyl methacrylate. Most of the UV-curable systems contain an acrylate monomer of some sort, since they have relatively low viscosities (100 mPa s or cP) and excellent reactivity with the UV radiation. The low viscosity allows the preparation of ceramic slurries with a relatively high solids loading, and the resulting high-density green sheets have excellent mechanical properties. 

A paint grade of cerium sulfide has also been developed. The pigment has been evaluated in several coatings formulations such as automotive refinish (acrylic-isocyanate binders), general industrial solvent-based systems (polyester-melamine bin-... 

Critical to formulating a successful metallic basecoat is the selection of aluminium paste. In general the larger the particle size of the flake, the better the lustre. A polyethylene wax dispersion is also incorporated into the formulation to aid metal control and lustre. The binder in solvent based systems is a durable saturated polyester cured with a melamine formaldehyde resin and modified with CAB, to assist in film setting and hardness. 

Whilst there are some thermoset acrylic emulsions cormnerdally available, the bulk of the thermoset resins, used as the main binder system, are produced in solution. Some may then be made waterborne by neutralisation and inversion (dispersion) into a water phase. Lower molecular weights favour this qrproach. The rate of conversion from solvent based to waterborne industrial thermoset coating systems has been, and is, much slower than the conversion from architectural alkyd paints to emulsion altonatives. There are two principle reasons for this. Firstly there are problems of application and substrate wetting of many waterborne systems. Secondly, the modifications frequently required to induce water dispersibility reduce one or more of the essential performance properties required from the cured film, compared to a solvent based system. Water resistance, with many films having an increased tendency for blushing is one example. However, for some applications, such as electrodeposition, only waterborne systems will work. 

As the cylinder rotates in the press, the lower part of the cylinder is flooded with ink having a viscosity in the low centipoise range. The press ready ink may contain 7% pigment, 18% binder, such as modified rosins, nitrocellulose or a synthetic resin and 75% solvent. The solvents are usually blends of such materials as aliphatic hydrocarbons in the heptane range, toluene, acetates and alcohol. Water based systems are used in a number of applications. 

Since the 1970s a trend to use water-based coating systems and glues instead of solvent-based products has been apparent. Most water-based paints and lacquers use polyurethane or acrylate as binders. For technical reasons the systems still contain organic cosolvents as well as pigments, biocides and surfactants (Hansen et al., 1987). 

The so-called solvent-based binder systems contain polymers which solvate or swell in a solvent (e.g. water, alcohol). Typical polymers used in extrusion are PEG, PVA, agar agar and cellulose. Thermoplastic materials are polymers which when heated, soften, melt or become more pliable, and harden during cooling in a reversible physical process. Materials in this class which are used quite often for ceramic processing are PE, PP, EVA, POM and PMMA. Thermosetting materials are polymers which can be melted only once and which, after melting, harden as more heat is added. Thermoset plastics which are used in the ceramic industry are phenolic resins and different silicon resins like polysiloxane. 

One of the main advantages of thermoplastic systems for ceramic extrusion is the lower abrasivity of the feedstock material relative to other binder systems. The lower abrasivity of a extrusion feedstock prepared with a thermoplastic hinder system compared to one with a solvent-based binder for a given ceramic powder, in this case AI2O3, is shown Fig. 1. In this study a feedstock with 58 vol.-% coarse AI2O3 powder was extruded through a steel die. Looking at the surfaces of the tubes, discoloration of the material stemming from abrasion of the die can he clearly... 

Another advantage of thermoplastic binder systems over solvent-based ones is the contour accuracy of the extruded material which permits easy fabrication of fine structures (e.g. thin-walled tubes, micro-tools). For such fine structures with very small cross-sectional areas, extrusion pressures can be as high as 700 or 800 bar, and at such high pressures phase separation in feedstocks with solvent-based binder systems can occur. Even for higher pressures such phase separation effects are generally not observed when using thermoplastic binder systems. 

Co-extrusion processing using thermoplastic binder systems for ceramic bodies has been described by Van Hoy [Hoy 98]. The major binder component used in this study was ethylene vinyl acetate, and methoxypoly-ethylene glycol was used as a plasticizer. Feedstocks of alumina, a piezoelectric ceramic powder and carbon black were repeatedly co-extruded to form an array of fine M -shaped structures. With this method the size of the alumina M shapes could be reduced by a factor of 915. In this example the use of solvent-based binders would have been problematical because of drying of the feedstocks and extrudates during the co-extrusion process and during handling. 

Conductive organic coatings consist of a conductive carbon pigment in an organic binder. The most widely used systems have been solvent based. There are also water-based systems which have been developed more recently. One proprietary system uses a nickel coated carbon fibre rather than flaked graphite. 

Letterpress and flexographic systems can be used with either solvent based or aqueous based ink systems. In either case, current practice consists of mixing a solvent or water in the presence of a binder resin such as, for example, nitrocellulose, maleic anhydride, an acrylic copolymer, or various starch derivatives. The pigment is applied over the paper by the printing roller and the binder serves to hold the pigment particles in place. 

The preparation of the slurry is a critical step in the tape casting process. The factors that govern the selection of solvent, dispersant, binder, plasticizer, and other additives were described earlier in this chapter. Most tape casting operations currently use organic solvents, but the trend is towards aqueous-based systems. Other considerations in the selection of a solvent are the thickness of the tape to be cast and the surface on which the cast is to be made. Thin tapes are cast from highly volatile solvent systems (e.g., acetone or methyl ethyl ketone), whereas... 

---