Water based systems advantages and disadvantages

Historically, wood preservatives have been thought of in terms of their solubility in either water or oil-type solvents (Ibach, 1999). Thus we have so called oil-bome and water-borne preservative systems. More recently that classification has become less relevant, because, with advances in formulation chemistry active ingredients can be formulated with either type of solvent, while others may be emulsions or suspensions. Water-based preservatives often include some type of co-solvent such as an amine or ammonia to keep one or more of the active ingredients in solution. Each solvent has advantages and disadvantages depending on the application. 

Water-based systems have good aging characteristics, resisting the effects of heat, ultraviolet (UV) light, and oxidation. Thus use of antioxidants is not normally necessary. Table 2 lists the major advantages and disadvantages of the various types of pressure-sensitive adhesives. 

The main application technique in the decorative area is still by hand (brush). Hence, future trends continue to reflect attention on worker exposure and environmental issues. This is already seen in the move to low aromatic content white spirits and isoparaffin solvents in conventional systems. High solids and waterborne technologies are being developed and both possess certain advantages and disadvantages, mainly relating to appearance and ease of use. Water-based systems bring, in principle, increased potential for water pollution, as consumers continue to rinse their brushes and paint rollers under the tap and transfer the water-soluble components such as amines and biocides to the aqueous environment. The consequence of diffuse water emissions of this type is still under debate. 

Solvent recovery and recycle has limitations in that it still depends on solvents and requires expensive equipment. If complex mixtures of solvents are used, they must be separated and cleaned up before reuse. Workers may still be exposed to hazards, and insurance rates where solvents are involved are increasing. One-hundred percent solids systems may be the wave of the future, however, at this time the technology is limited. Current hot melt systems have thermal stability problems which inhibit their use in various applications. And though problems and disadvantages remain to be solved with water-based systems, the current technology is practical and presents advantages the other alternatives cannot achieve at this time. 

Hot-melt systems are usually flexible and tough. They are used extensively for sealing applications involving paper, plastic films, and metal foil. Table 7.29 offers a general comparison of hot-melt adhesives. Hot melts can be supplied as (1) tapes or ribbons, (2) films, (3) granules, (4) pellets, (5) blocks, or (6) cards, which are melted and pressed between the substrate. The rate at which the adhesive cools and sets is dependent on the type of substrate and whether it is preheated. Table 7.30 lists the advantages and disadvantages associated with the use of water-based, solvent-based, and hot-melt thermoplastic adhesives. 

Water-based flexo inks can be formulated with either a soluble toner or with the Day-Glo EPX Series which is a tme pigment and can be formulated like a conventional pigment dispersion. The Radiant Aquabest or the Day-Glo WST can be formulated in an alkaline water-soluble system to yield strong inks. They have limited shelf life and inferior fade, but do not necessarily requite additional binder. Day-Glo EPX must be formulated with a binder such as a hard resin or can be used with one of the soluble toners such as WST. The EPX Series has several advantages over soluble toners such as much superior fade, exceUent ink stabiHty, and some hiding power over kraft-type papers. A disadvantage of the EPX is its lower tinctorial strength than other fluorescent toners. 

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