Polymer blend systems for water-borne paints
Introduction
One of the largest concerns for the coatings industry is to reduce volatile organic compounds (VOC). Water-borne paints are the most practical and effective solution. Emulsion paints have been used in large quantities to coat buildings for more than 50 years as they are very easy to apply and low in price. Electrodeposition coatings also have been widely used in the industrial coating field prior to the anti-pollution age because of this unique character.
However, all classes of traditional paints are currently being converted into waterborne paints, and all new water-borne paints require new aqueous resins. Development of new aqueous resins is a more sophisticated technology than that of solvent-borne resins, since there are many restrictive limitations due to the special nature of water. The resin blend technique is a simple and useful technique in coatings technology, and is very important in water-borne paints.
This article is divided into three parts. The first part presents a new blend system of a high molecular weight emulsion polymer produced by emulsion polymerization and water-soluble resins. This system is currently applied to a quick-drying paint applicable to metal surfaces. A high performance emulsion paint obtained by a blend of acrylic emulsions and urethane dispersions is also described. The second part provides the blend of water-borne alkyd and water-borne acrylic resins. The former is main binder and the latter is a pigment dispersing resin. Excellent water-borne alkyd paints, which can take the place of conventional alkyd paints, are obtained. Force-drying acrylic water-borne paints prepared by colloidal dispersion are described in the third part. In all these cases, we confirmed that crosslinking of the blended resins gives a high level of performance to the new water-borne coatings.
Other uses for resin blends, such as those for industrial baking paints and are special examples of the resin blend, such as strengthening hiding power with a microvoid emulsion [1], or a moisture permeable coating with a hydrophilic microgel [2], etc. are not discussed.
Section snippets
Water-borne resins used in the blend system
Aqueous resins are classified into four types as shown in Table 1. The water-soluble resins containing appreciable amounts of hydrophilic groups are rarely used as binder components in water-borne paint because of the poor water resistance of the paint. However, they are available as pigment dispersants, viscosity control agents and so on.
Colloidal dispersions having an appropriate amount of hydrophilic groups can be used as a main binder for baking paints, and their film properties are
Disadvantages of current high molecular weight emulsions
Conventional emulsion paints are of high molecular weight emulsions. The film formation of emulsion paints is performed by coalescence of emulsion particles. The good mechanical and chemical properties of these paint films originate from the high molecular weight resins of emulsion polymers.
Emulsion paints are generally preferred to coat alkaline surfaces, such as those of mortar and cement where alkyd paints cannot be applied because oxidative polymerization is obstructed. Emulsion paints
Problems with alkyd resin emulsion
A low molecular weight emulsion easily forms a pore-free film upon evaporation of water at room temperature, however, the crosslinking reaction is essential to obtain satisfactory properties of paints. Alkyd resins are conventionally studied as a resin curable at ambient temperature. In study of emulsions of air-drying alkyd resins 13, 14, 15, difficulty in manufacturing fine emulsions has retarded practical use. Dispersing alkyd resin in water is usually performed in the presence of
Blend system of colloidal dispersion
Air-drying short oil-length alkyd resins are usually used for force-dried industrial paints. However, when these resins are applied in aqueous form, rather longer drying time is necessary because of the retarding action of the amine neutralizer in the oxidative crosslinking. It is most desirable to use reactive microgel as a multifunctional crosslinkable agent to reinforce the film hardness [27]. An admixture of the polyfunctional acrylic emulsion can also improve the drying rate, but this
Conclusions
Blending of well designed aqueous resins and latices reinforces their advantages to each other and produces excellent water-borne paints. Blending of a minor amount of special aqueous resins can compensate for the disadvantages of the blend resins.
Crosslinking is a key factor for high performance in air-drying aqueous paint. That is to say, it is most important that all blended resins are joined by crosslinking. For this purpose, compatibility of the resins is also very significant in order to
References (27)
Prog. Org. Coat.
(1992)- et al.
Prog. Org. Coat.
(1988) Prog. Org. Coat.
(1992)- et al.
Prog. Org. Coat.
(1986) - et al.
Prog. Org. Coat.
(1986) J. Coat. Technol.
(1987)- et al.
J. Polym. Sci. Polym. Chem. Ed.
(1985) J. Oil Colour Chem. Assoc.
(1978)J. Oil Colour Chem. Assoc.
(1979)- et al.
J. Coat. Technol.
(1996)