Dispersion Resin

Dispersion Resins. Polytetrafluoroethylene dispersions in aqueous medium contain 30—60 wt % polymer particles and some surfactant. The type of surfactant and the particle characteristics depend on the appHcation. These dispersions are appHed to various substrates by spraying, flow coating, dipping, coagulating, or electro depositing. 

Urea.—Forma.IdehydeResins. Cellular urea—formaldehyde resins can be prepared in the following manner an aqueous solution containing surfactant and catalyst is made into a low density, fine-celled foam by dispersing air into it mechanically. A second aqueous solution consisting of partially cured urea—formaldehyde resin is then mixed into the foam by mechanical agitation. The catalyst in the initial foam causes the dispersed resin to cure in the cellular state. The resultant hardened foam is dried at elevated temperatures. Densities as low as 8 kg/m can be obtained by this method (117). 

There are two principal PVC resins for producing vinyl foams suspension resin and dispersion resin. The suspension resin is prepared by suspension polymerization with a relatively large particle size in the 30—250 p.m range and the dispersion resin is prepared by emulsion polymerization with a fine particle size in the 0.2—2 p.m range (245). The latter is used in the manufacture of vinyl plastisols which can be fused without the appHcation of pressure. In addition, plastisol blending resins, which are fine particle size suspension resins, can be used as a partial replacement for the dispersion resin in a plastisol system to reduce the resin costs. 

Vinyl organosol coatings, which incorporate a high molecular weight thermoplastic PVC organosol dispersion resin, are extremely flexible. Soluble thermosetting resins, including epoxy, phenoHc, and polyesters, are added to enhance the film s product resistance and adhesion. 

Water-dispersible resins contain carboxyhc groups which are neutralized using base or amine compounds. This solubilizes the resin in solution and also promotes pigment wetting. Film formation occurs by the evaporation of volatiles foUowed by cross-linking through ambient cure oxidative reactions or elevated temperature reactions. Solvents, most commonly glycol ethers, are used to promote film formation and improve film quahty. 

L. Eoff, J. Chatterji, A. Badalamenti, and D. McMechan. Water-dispersible resin system for wellbore stabilization. In Proceedings Volume. SPE Oilfield Chem Int Symp (Houston, TX, 2/13-2/16), 2001. 

Because of the low level of emulsifiers and protective colloids, the suspension polymer types are most suitable for electrical applications and end uses requiring clarity, This form is also employed in the bulk of extrusion and molding applications. Cost is lower than for emulsion and solution forms. The emulsion or dispersion resins are employed mainly for organosol and plastisol applications where fast fusion with plasticizer at elevated temperature will occur as a result of the fine particle size of the resin. 

Fig. 14 (a) Shadowed sample of dispersed resin G. The insets are dark-field images. Low-intensity bright-field diffraction contrast images of (b) TE-30 (bottom) and (c) TE-3698 (top), and TE-3170 (bottom). The upper part of b (d) has Pt/C-shadowed TE-30 particles the insets in c are enlargements of some of the particles. All scale bars in a given figure part represent the same scale unless otherwise identified. 

Overall rheology is determined by the selection of the dispersion resin but the viscosity of a paste is influenced by many factors—the types and amounts of the constituents in the formulation, the methods of mixing, and the temperature. Further brief comments on the effects of constituents would include ... 

During sulfite pulping the fatty acid esters are saponified to an extent determined by the conditions. Some of the resin components can also become sulfonated, resulting in increased hydrophilicity and better solubility. However, the partial removal of resin that always occurs during sulfite cooking and subsequent mechanical treatment is mainly associated with the formation of finely dispersed resin particles in stable emulsions. The dissolved lignosulfonic acids act as detergents with respect to the lipophilic resin components. 

Use Lubricants in greases, oil dispersions, resin-bonded films, dry powders, etc., especially at ex-... 

Pliovic [Goodyear], TM for homopolymers, vinyl dispersion resin, plastisol, and organosol compounds. 

An area of interest at that time was the incorporation of colloidal silica into emulsion systems. Typical emulsions included floor waxes or rubber latices. Conventional wax compositions ordinarily included certain extenders or modifiers in the wax dispersions. These may comprise wax-soluble or water-dispersible resins (natural or synthetic). These formulations can produce coatings with a pleasing appearance however, many lack slip resistance. The incorporation of colloidal silica into the formulation produces coatings that prevent slipping. 

In 1960, the American Society for Testing and Materials (ASTM) completed work on tests and standardizations and issued D1755, "Specification for Poly(Vinyl Chloride) Resins. In this specification, type GP refers to general purpose resins, and type D refers to dispersion resins (which will be discussed later). A similar specification for copolymer resins has been issued as ASTM D2427-78. 

Dispersion Resins. These materials used in plastisols or organosols have a very fine particle size, in the range of 0.1 to 2 Um and are made by emulsion polymerization followed by spray drying. 

ASTM D1755-81 gives the classification for these resins. The following characteristics of dispersion resins are of significance ... 

In addition to general purpose and dispersion resins, mention... 

The weighed average residual concentration of VCM in PVC resin after stripping may not exceed 2000 ppm for dispersion resins and 400 ppm for all other resins including latex resins, averaged separately for each type. 

Liquid State. The liquid state in most thermoplastics is produced by heating until molten in vinyls it is generally obtained by dispersing resin particles in plasticizer to produce a plastisol and in rubber it is obtained by use of latex. In thermosetting plastics, the monomers are reacted only up to low molecular weight reactive prepolymers, which are still liquid or at least readily fusible at low temperature. 

The voltage requirement is largely dictated by the nature of the dispersed resin in the bath. Installations are usually operated at between 200 and 400 V, although some are reportedly operated as low as 50 V and others as high as 1000 V. 

Figure 2 shows typical steps in the manufacture of an emulsion resin. Basically, the vinyl chloride monomer is added to a pressure vessel (reactor) where in contact with the emulsifier and the initiator the polymerization is carried out under conditions of controlled pressure and temperature. Since it is uneconomical to carry out the reaction to 100% conversion, unreacted monomer is removed in a stripping vessel. If the polymer is to be applied via the latex (water-based coating) technique, the manufacturing process can now be considered complete. If a dispersion resin is to be produced, then latex from the blend tank is transferred to a spray dryer where water is removed. These very small polymer particles... 

The average particle size varies from approximately 2 to 8 ym in diameter with extremes falling below 0.6 and above 20 um. Note that average opening of a 325-mesh screen is 43 ym. This means that all the dispersion resin particles would show up as 100% through the 325 mesh in a conventional screen analysis. 

In 19A7 the first true dispersion resins were introduced in the United States. These emulsion-type polymers could be prepared with 100% solids with relatively simple "stir-in" techniques. Paste-type dispersions are noted to have been developed somewhat earlier and independently in Europe. 

Because water is the fluid component, very low viscosities at relatively high solids (50%) are attainable. Latexes are usually cheaper than solution vinyls but similar in cost to dispersion resins. As with organosols and solution vinyls, coating thickness is limited due to the evaporation of the fluid component. Note that more heat is usually required to remove water than organic solvents, and corrosion of equipment must be considered. 

The primary reason for utilizing a dispersion resin system is to obtain the benefit of fluid properties. With viscosity characteristics in mind, we must consider this qualification for the plasticizers used in plastlsols. 

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