Compositions: coating or plastic – Coating or plastic compositions – Marking
FIELD OF THE INVENTION
The invention relates to the use of tartaric acid diesters to reduce the surface tension in water-based systems.
BACKGROUND OF THE INVENTION
The ability to reduce the surface tension of water is of great importance in waterborne coatings, inks, adhesives, fountain solutions and agricultural formulations because decreased surface tension translates to enhanced substrate wetting in actual formulations. Surface tension reduction in water-based systems is generally achieved through the addition of surfactants. Performance attributes resulting from the addition of surfactants include enhanced surface coverage, fewer defects, and more uniform distribution. Equilibrium surface tension performance is important when the system is at rest. However, the ability to reduce surface tension under dynamic conditions is of great importance in applications where high surface creation rates are utilized. Such applications include spraying, rolling and brushing of coatings or spraying of agricultural formulations, or high speed gravure or ink-jet printing. Dynamic surface tension is a fundamental quantity which provides a measure of the ability of a surfactant to reduce surface tension and provide wetting under such high speed application conditions.
Traditional nonionic surfactants such as alkylphenol or alcohol ethoxylates, and ethylene oxide (EO)/propylene oxide (PO) copolymers have excellent equilibrium surface tension performance but are generally characterized as having poor dynamic surface tension reduction. In contrast, certain anionic surfactants such as sodium dialkyl sulfosuccinates can provide good dynamic results, but these are very foamy and impart water sensitivity to the finished coating.
In addition to the development of high-performance surfactants, there is considerable interest in the industry in surfactants with improved environmental characteristics. Environmental concerns have led to an increased use of environmentally compatible surfactants as alternatives have become available. In addition, the use of less favorable products, such as alkylphenol ethoxylate (APE) surfactants, has declined. This is, in part, due to the poor environmental characteristics of APE surfactants, such as incomplete biodegradation and a suspicion that they may function as endocrine mimics. The demand for high-performance, eco-friendly surfactants has stimulated efforts in new surfactant development. From this work a new family of surfactants, referred to as alkyl polyglycoside (APG) surfactants, has emerged as a readily biodegradable, environmentally-friendly alternative to conventional surfactants. These materials, however, can be foamy and thus, are not suitable for a variety of coating, ink, adhesive and agricultural applications where the generation of foam is undesirable. Moreover, many APG surfactants possess poor color characteristics and are solids or pastes. This latter property complicates handling and necessitates the formation of blends which contain significantly less than 100% active ingredient. Thus, not only is it desirable to obtain surfactants which exhibit excellent surface tension reducing capabilities and low foam under dynamic application conditions, but it is also highly desirable that such new surfactants are environmentally-friendly, are liquids and possess little or no color.
There is a need for surfactants which exhibit good equilibrium and dynamic surface tension properties, are low-foaming, are low viscosity liquids to facilitate handling, have low color and low odor characteristics and would be widely accepted in the waterborne coating, ink, adhesive, fountain solution and agricultural formulation industries. Moreover, since there is substantial interest in the development of environmentally-friendly surfactants, an essential attribute would be that these surfactants not only possess the aforementioned desired performance attributes but also are derived from naturally occurring compounds or their synthetic equivalents or possess favorable biodegradation and toxicity properties.
The importance of reducing equilibrium and dynamic surface tension in applications such as coatings, inks, adhesives, fountain solutions and agricultural formulations is well-appreciated in the art.
Low dynamic surface tension is of great importance in the application of waterborne coatings. In an article, Schwartz, J. “
The Importance of Low Dynamic Surface Tension in Waterborne Coatings
”, Journal of Coatings Technology, September 1992, there is a discussion of surface tension properties in waterborne coatings and a discussion of dynamic surface tension in such coatings. Equilibrium and dynamic surface tension were evaluated for several surface active agents. It is pointed out that low dynamic surface tension is an important factor in achieving superior film formation in waterborne coatings. Dynamic coating application methods require surfactants with low dynamic surface tensions in order to prevent defects such as retraction, craters, and foam.
Efficient application of agricultural products is also highly dependent on the dynamic surface tension properties of the formulation. In an article, Wirth, W.; Storp, S.; Jacobsen, W.
“Mechanisms Controlling Leaf Retention of Agricultural Spray Solutions
”; Pestic. Sci. 1991, 33, 411-420, the relationship between the dynamic surface tension of agricultural formulations and the ability of these formulations to be retained on a leaf was studied. These workers observed a good correlation between retention values and dynamic surface tension, with more effective retention of formulations exhibiting low dynamic surface tension.
Low dynamic surface tension is also important in high-speed printing as discussed in the article “
Using Surfactants to Formulate VOC Compliant Waterbased Inks
”, Medina, S. W.; Sutovich, M. N.
Am. Ink Maker
1994, 72 (2), 32-38. In this article, it is stated that equilibrium surface tensions (ESTs) are pertinent only to ink systems at rest. EST values, however, are not good indicators of performance in the dynamic, high speed printing environment under which the ink is used. Dynamic surface tension is a more appropriate property. This dynamic measurement is an indicator of the ability of the surfactant to migrate to a newly created ink/substrate interface to provide wetting during high speed printing.
U.S. Pat. No. 5,098,478 discloses water-based ink compositions comprising water, a pigment, a nonionic surfactant and a solubilizing agent for the nonionic surfactant. Dynamic surface tension in ink compositions for publication gravure printing must be reduced to a level of about 25 to 40 dynes/cm to assure that printability problems will not be encountered.
U.S. Pat. No. 5,562,762 discloses an aqueous jet ink of water, dissolved dyes and a tertiary amine having two polyethoxylate substituents and that low dynamic surface tension is important in ink jet printing.
Esters of tartaric acid (2,3-dihydroxy-butanedioic acid), also called tartrates, are known. Tartaric acid has been utilized to produce surfactants.
EP 0 258 814 B1 discloses mono-, di- or tri-esters of carboxylic hydroxyacids of the structure:
as surface active agents, where X=CH
COOR″ or H; Y=OH or H; R, R′ and R″=H. alkaline earth or alkali metal, ammonium group or a radical from etherified C
alkyl polysaccharides or hydroxy C
Aratani et al., “
Preparation and Properties of Gemini Surfactants From Tartric Acid”, Commun. Jorn. Com. Esp. Deterg.,
1998, 28, 48 prepared anionic surfactants from tartaric acid by alkylation of the hydroxy groups and conversion of the carboxyl groups of the resulting tartaric acid ether to hydrophilic moieties. The surfactants studied were of the following structure, where R=alkyl group, A=CO
and X=Cl, Br, I.
Ono, D., et al., “
Preparation and Properties of Bis
Lassila Kevin Rodney
Slone Caroline Sassano
Air Products and Chemicals Inc.
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