Dispersions aminoplast

Other polycondensation reactions which lead to finely dispersed polymers in liquid polyethers are the polycondensation reactions of urea and melamine with aqueous formaldehyde [92-95]. The reaction medium is usually polyether polyols, PO homopolymers or PO-EO copolymers (random or block copolymers), with MW of 3000-5000 daltons. During the polycondensation reaction, the aminoplast polymer precipitates, being insoluble in polyether and water (water from formaldehyde solution and reaction water), is eliminated by vacuum distillation. A variant of this reaction is to develop the polycondensation in water, and water containing the aminoplast polymer (as a viscous solution) is added to a polyether polyol, under vacuum, and at high temperature (100-130 °C), water being continuously eliminated from the reaction medium. The aminoplast insoluble polymer precipitates in the form of fine particles. 

Some methylolic hydroxyl groups may react with terminal hydroxyl groups of polyether (etherification reaction). The resulting structure acts as a true NAD, having an aminoplast segment and a polyetheric segment (reaction 6.30). 

A synthetic variant is to react firstly the polyether with a small quantity of TDI. The resultant extended polyether, containing urethane groups, participates together with urea groups in polycondensation reactions with aqueous formaldehyde. Thus a true nonaqueous dispersant is formed in situ, with an aminoplast block and a polyether block, which probably assures the efficient stabilisation of the resulting aminoplast dispersion. 

Aminoplast dispersions, in spite of the accessibility and low cost of raw materials, are not produced industrially, due to the risk of toxic formaldehyde elimination, especially when the resulting aminoplast polymer polyol is used for slabstock foams and, of course, for moulded flexible foams used for seating or interior automotive parts. 

Cloetens, W.A. Lidy, B.D. Phillips and D.B. Thomas in Proceedings of the SPI/ FSK Polyurethanes World Congress, Aachen, Germany, 1987, p.480. 

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Figure 4d represents in situ encapsulation processes (17,18), an example of which is presented in more detail in Figure 6 (18). The first step is to disperse a water-immiscible Hquid or soHd core material in an aqueous phase that contains urea, melamine, water-soluble urea—formaldehyde condensate, or water-soluble urea—melamine condensate. In many cases, the aqueous phase also contains a system modifier that enhances deposition of the aminoplast capsule sheU (18). This is an anionic polymer or copolymer (Fig. 6). SheU formation occurs once formaldehyde is added and the aqueous phase acidified, eg, pH 2—4.5. The system is heated for several hours at 40—60°C.

Uses Polyol for thermoset water-reducible coatings, dispersions and emulsions crosslinked with melamines or aminoplast resins, in automotive primers, container coatings, and general industrial uses Properties Vise, liq. sol. In polar org. soivs. and water insol. in aliphatic and aromatic hydrocarbons sp.gr. 1.19 g/cc vise. 11,000 cps hyd. no. 330 flash pt. (CC) > 200 F 100% act. 

Waterborne epoxy resin (99) has been used for lamination. The epoxy copolymers PD-6049 and PD-4070 are supplied by Celanese at 69% solids in glycol ether co-solvents, which can readily be dispersed with water. When the dispersion is formulated with an aminoplast catalyst,... 

More recently, a number of interstitially crosslinked coating materials have been prepared.These are blends in which a water-soluble or water-dispersible resin, capable of crosslinking, is blended with an ordinary thermoplastic emulsion. The main resins include aminoplast, phenol-formaldehyde, polyurethane, epoxy, and drying oils. Applications include sealants, adhesives, and architectural coatings. 

Dispersant for aminoplast bead preparation Britain 755,147 1956 Monsanto... 

Anionic coatings systems for water-borne topcoats are emulsion polymers, miniemulsion polymers, polyurethane dispersions, different types of dispersions of acrylic resins in water and amino resins, water-borne polyesters, polyurethanes. Many of the polymers are hydroxyl containing and cured with various melamines and blocked isocyanates. The polymers are mainly stabilized in the water phase by neutralization of anionic groups with volatile amines (2-amino-2-methyl-l-propanol). Cross-linkers like aminoplast resins, alkoxy silanes, blocked epoxy resins, carbodi-imides can be used. 

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