Urea-formaldehyde resins butanol-modified

Unmodified urea-formaldehyde resins are unsuitable for use in surface coatings formulations, due to their lack of solubility in common solvents and incompatibility with other resins. This limitation can be substantially overcome when the resins are modified by alcohols, such as n-butanol. Very commonly, butylated urea-formaldehyde resins are blended with alkyd resins to provide good flexibility and adhesion in coatings. Furfuryl alcohol-modified urea resins are used to bind foundry cores formed in preheated pattern boxes, due to their capability of rapid core production. 

Unmodified urea-formaldehyde resins are not suitable for use in surface coating formulations because they are insoluble in common solvents, do not interact readily with other resins and are comparatively unstable. These limitations are substantially overcome when the resins are modified by alcohols. n-Butanol is the alcohol most widely used for this purpose and a typical process might be as follows. 

Tollens described resins produced from the condensation of urea and formaldehyde in 1884, and John patented this polymer (UF) in 1918. In 1936, Henkel patented comparable resins (MF) based on melamine instead of urea. Both resins, which were referred to as amino resins, are insoluble in common solvents and used as additives for curing other coatings. For example, the addition of MF reduces the curing time of alkyd resins by 50%. Soluble amino resins, which can be used as coatings, are produced when modified by etherification with butanol. 

Formaldehyde. Pure formaldehyde, CH2O, is a colorless, pungent smelling reactive gas (see Formaldehyde). The commercial product is handled either as soHd polymer, paraformaldehyde (13), or in aqueous or alcohoHc solutions. Marketed under the trade name Formcel, solutions in methanol, / -butanol, and isobutyl alcohol, made by Hoechst-Celanese, are widely used for making alcohol-modified urea and melamine resins for surface coatings and treating textiles. 

Amino Resins. Formaldehyde-modified amino resins (i.e., melamine, benzogua-namine, and urea resins) are the most important resins for the heat curing of hydroxyfunctional polyester resins. These resins are readily available with a low molecular mass (very good polyester compatibility, but less reactive) or in precondensed form (limited compatibility, but very reactive). In order to prevent premature reaction in the wet paint, the amino resins are blocked by etherification with, for example, methanol or butanol. Sulfonic acids (e.g., p-toluenesulfonic acid, dodecyl-benzenesulfonic acid) have proved suitable for accelerating the deblocking of amino resins during heat curing. These acids must also be used in blocked form (ammonium salts, thermolabile adducts). 

To a mixture of 9 gm (0.05 mole) of benzoguanamine, 60 gm (1.0 mole) of urea, and 260 gm of 37% (3.2 moles) formaldehyde is added 10% aqueous sodium carbonate to bring the pH to 8.0. Then 370 gm (5.0 moles) of Az-butanol is added, and the solution is heated to 80°C for 40 min. Fifteen grams of concentrated hydrochloric acid is added, and the mixture is heated to 93 over 30 min with removal of water. The mixture is kept at 93 for 2 hr, evaporated to 66.5% solid, and diluted with xylene to 50% resin solids. The resin (3gm) is blended with 7.0 gm of soybean oil-modified alkyd resin, coated, and baked at 130°C for 30 min to give a heat-stable coating, resistant to bending. 

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