Coatings Technology Handbook 2010 Part 11 ppsx

70 -1 70 Silane Adhesion Promoters References 70- 3 Silane adhesion promoters are organofunctional silicon compounds that promote adhesion of coatings to substrates, especially improving their resistance to debonding under humid conditions. It must be emphasized that these silanes are not related to polydimethylsiloxane fluids, which cause cratering and poor repaintability in coatings. Silane adhesion promoters may help overcome such problems of poor wetting and intercoat adhesion in coatings. Silane adhesion promoters are generally formulated into primers or added at relatively low levels to coatings, in contrast to silicone resins, which are typically used at about 30% level in silicone-alkyd or silicone-acrylic formulations. These silanes are ambifunctional compounds of the general structure (CH 3 O) 3 Si–R–X, where X is an organofunctional group chosen for compatibility with the organic coating and the alkoxysilane portion provides bonding to mineral substrates. 1 The alkoxysilane may be prehydrolyzed to silanols that are reactive with hydrate metal oxide surfaces and contribute siloxane cross-links. Methoxysilanes also react directly with metal hydroxides and then cross-link in the presence of atmospheric moisture. Silane adhesion promoters are often effective in improving the adhesion of coatings to plastic surfaces or to oily metal surfaces. As additives in paints, they may be useful in improving intercoat adhesion. A recent trend is to formulate adhesion promoters by mixing silane monomers, partially prehydrolyzing the silanes, or by mixing silanes with polymer precursors such as epoxies and melamines. Silane adhesion promoters are offered by silane manufacturers Dow Corning Corporation, Union Carbide Corporation, Petrarch Chemicals Division of Dynamit Nobel, and Peninsular Chemical Research, as well as by pro- prietary formulators such as Hughson Chemical Division of Lord Corporation. Adhesion promoters Walker 2 reviewed a study of silane primers and additives for adhesion of a two-part epoxy paint with polyamide cure, and a two-part aliphatic isocyanate adduct cured polyester paint on mild steel, aluminum, cadmium, copper, and zinc surfaces. Silanes were tested as primers (essentially monolayer coverage on aluminum, indicate that the diamine-functional silane gave uniformly improved retention of adhesion under wet conditions and gave greater recovery of adhesion when the panels were dried. Methacrylate-, epoxy-, and mercaptofunctional silanes were also useful as adhesion promoters. Results were similar on cadmium, copper, and zinc. Paints with some silane additives showed little deterioration in performance during 9 months of storage. Some general recommendations on use of silane adhesion promoters of Table 70.1 for coating on glass, 3 Edwin P. Plueddemann Dow Corning Corporation DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC supplied by Dow Corning and recommended for coatings are described in Table 70.1. metal), and as 0.1 to 0.4% additive based on total paint. Results, summarized in Table 70.2 for iron and aluminum, and steel are summarized in Table 70.3. 71 -1 71 Chromium Complexes 71.1 Introduction 71- 1 71.2 Manufacture 71- 1 71.3 Methacrylic Acid Types 71- 1 71.4 End Uses 71- 2 71.5 Application Methods 71- 3 71.6 Governmental and Other Regulations 71- 4 71.1 Introduction Chromium complexes are widely used for changing the characteristics of paper, glass, and other hydroxylic surfaces, and the surfaces of materials such as polyethylene, which can be made functional by corona discharge and similar methods. These binuclear compounds have the approximate formula shown in in effect converted to –R groups. The radical R is of two general types: long chain saturated hydrocarbon, incorporated by the use of a fatty acid, and unsaturated hydrocarbon, incorporated as methacrylic acid. The fatty acids are used to change the physical properties of the surface, whereas the function of the methacrylic acid is to change its chemical properties. The chromium in these complexes is exclusively trivalent. As is discussed below, the health hazard associated with hexavalent chromium compound is not present in these products, which have the approval of the U.S. Food and Drug Administration (FDA). 71.2 Manufacture The starting point for these materials is a solution of a basic chromium chloride, which is converted to the complex by reaction with the appropriate acid. The products are green solutions, with such depth of color that they appear black. In addition to being classed as flammable liquids, they are corrosive, since some of the chlorine (see Figure 71.1) is hydrolyzed and therefore exists in the form of HCl. In use, both hazards are removed by dilution and neutralization. 71.3 Methacrylic Acid Types The du Pont Company makes methacrylatochromium complexes under the name Volan bonding agent. Although the methacrylic acid types are used to coat substrates, the coating is always reacted further before the end use is reached. They are therefore not normally considered to be coatings per se, and are discussed only briefly. A methacrylate group can polymerize with any other molecule undergoing vinyl polymerization. If Volan-treated glass fiber, for instance, is impregnated with an unsaturated polyester, then when the latter J. Rufford Harrison E. I. du Pont de Nemours & Company DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Release • Water Resistance • Grease Resistance Figure 71.1. The chromium end of the molecule attaches itself to the substrate, whose –OH groups are 72 -1 72 Nonmetallic Fatty Chemicals as Internal Mold Release Agents in Polymers 72.1 Introduction 72- 1 72.2 Test Procedure 72- 2 72.3 Experimental 72- 2 72.4 Results 72- 3 72.5 Conclusions 72- 7 Acknowledgment 72- 7 72.1 Introduction A major problem in injection molding is removal of the part from the mold. If the part has a large surface area or a certain type of surface, it may be almost impossible to remove the piece without damage. The force of the ejector can be increased to some extent, but this increases the possibility of damage to the piece. The use of some type of mold treatment is well known in the industry. The most common treatment is spraying a silicon- or fluorocarbon-type mold release agent directly on the mold. This procedure makes it considerably easier to remove the piece from the mold, but unfortunately it causes other problems. The spray-on mold release is typically good for eight to 10 moldings and then must be resprayed. Continued respraying eventually causes a buildup on the mold, which must be removed. Both the respraying and the cleaning cause an increase in cycle time. The use of an internal mold release agent can eliminate or lessen the problems of spray-on mold release. It would not be necessary to continually spray the mold, and there would not be as much buildup on the mold when internal mold release agents are used. One theory about how mold release additives work is that the additive exudes to the surface in the time between injection and ejection and serves to lubricate the boundary area during ejection. The mold release agent may also serve to reduce electrostatic attraction during ejection in some cases. If these assumptions are true, then a number of things can affect the usefulness of an additive: solubility in the resin, rate of migration in the resin, lubricity of the additive, melting point of the additive, and ability of the additive to reduce electrostatic attraction, to name some. Since most of these interrelationships are not well known, it follows that a large part of mold release is done on a trial-and-error basis. Eventually what will and will not work can be predicted for a given resin, but these predictions are made only on the basis of how similar compounds behave. Kim S. Percell Witco Corporation Harry H. Tomlinson Witco Corporation Leonard E. Walp Witco Corporation DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Results • Polyolefins 72 -4 Coatings Technology Handbook, Third Edition 72.4.1.2 Acetal The most effective mold release agents in acetal are fatty amides in general and fatty bisamides amides in particular. Ethylene bisoleamide shows 25.1% reduction of mold release force at 5000 ppm but causes a visible darkening of the resin during processing. Ethylene bisstearamide, a saturated amide, is nearly as good, showing 23.3% reduction at a level of 5000 ppm; it does not cause any color problems. Other secondary amides, such as stearyl stearamide and stearyl erucamide, give mold release improvement nearly as good as the bisamides (see Table 72.3). Primary amides such as erucamide, oleamide, and stearamide also show good mold release enhancement in acetal. None of the nonamide materials examined has the mold release effectiveness of the amides. The best ester mold release agent is cetyl palmitate, which exhibited a 16.5% reduction in mold release force at a 5000 ppm treatment level. The optimum amount of ethylene bisstearamide is 5000 ppm. When used above that level, there is little increase in effectiveness; below that amount, the maximum effectiveness is not reached. The use of fatty amides as mold release agents has negligible effect on mechanical properties (see Table 72.4). 72.4.1.3 Polybutylene Terephthalate Fatty bisamides are the best mold release agents in polybutylene terephthalate (PBT). Both saturated and unsaturated bisamides show about 10% reduction of ejection force when used at a level of 5000 ppm. The bisoleamide, however, causes some darkening of the resin during processing (see Table 72.5). TA BLE 72.3 Effectiveness of Mold Release Agents in Acetal Release Agent Level (ppm) Reduction of Ejection Force (%) N , N ′ -Ethylene bisstearamide 7500 26.0 N , N ′ -Ethylene bisoleamide a 5000 25.1 N , N ′ -Ethylene bisstearamide 5000 23.3 Stearyl stearamide 5000 21.1 Stearamide 5000 20.4 Erucamide 5000 21.8 N , N ′ -Ethylene bisstearamide 2500 15.2 N , N ′ -Ethylene bisstearamide 1000 5.3 Fluorocarbon spray-on — 22.1 a Causes resin to darken during processing. TA BLE 72.4 Mechanical Properties of Acetal with N,N ′ - Ethylene Bisstearamide Present Property N,N ′ -Ethylene Bisstearamide (ppm) 0 2500 5000 Te nsile strength at yield, psi 9965 9883 9818 Elongation at break, % 36 39 41 Izod impact, ft-lb/in. 1.30 1.32 1.35 TA BLE 72.5 Effectiveness of Mold Release Agents in PBT Release Agent Level (ppm) Reduction of Ejection Force (%) N,N ′ -Ethylene bisoleamide 5000 9.8 N,N ′ -Ethylene bisstearamide 5000 9.4 Stearamide 5000 6.7 Erucamide 5000 6.2 N,N ′ -Ethylene bisstearamide 2500 7.7 N,N ′ -Ethylene bisstearamide 1000 2.7 Fluorocarbon spray-on — 8.8 a May cause resin to darken during processing. DK4036_book.fm Page 4 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 72 -6 Coatings Technology Handbook, Third Edition mold release agents, although not as good as erucamide (see Table 72.9). Secondary amides and bisamides are not as good mold release agents as the primary amides. In addition to primary fatty amides, ethoxylated fatty amines are useful mold release agents in HDPE. At a level of 5000 ppm, ethoxylated oleyl amine and ethoxylated tallow amine show nearly a 20% decrease in mold release force (see Table 72.9). The use level is higher than the primary amide usage level, but the ethoxylated amines are also known as antistatic agents and therefore could solve two problems with one additive. Fatty esters have also been tested for mold release, but with the exception of glyceryl monostearate, they do not have much usefulness as mold release agents. GMS, used at a level of 5000 ppm, shows a 14.8% reduction of ejection force, but this is not as good as the primary amides or the ethoxylated amines. The use of primary amides or ethoxylated amines as mold release agents in HDPE has negligible effect on mechanical properties when tested at room temperature (see Table 72.10). 72.4.2.3 Linear Low-Density Polyethylene The results of testing for mold release in linear low-density polyethylenes (LLDPEs) are quite similar to The primary amides can be used at lower concentrations, because they are more efficient in LLDPE. Erucamide shows 30.3% reduction of mold release force when used at a level of 1000 ppm, while in HDPE it must be used at a level of 5000 ppm to achieve the same effect. The ethoxylated amines are also useful mold release agents and exhibit the same increased efficiency reported for the primary amides (see Table 72.11). As in HDPE, the ethoxylated amines are also useful as antistatic agents. TA BLE 72.8 Mechanical Properties of Polypropylene with and without Glyceryl Monostearate Property Glyceryl Monostearate, 45% α -ester (ppm) 0 2500 Te nsile strength at yield, psi 4848 505 Elongation at break, % 295 60 Izod impact, ft-lb/in. 0.65 0.72 TA BLE 72.9 Effectiveness of Mold Release Agents in HDPE Release Agent Level (ppm) Reduction of Ejection Force (%) Erucamide 5000 30.8 Erucamide 2500 20.2 Stearamide 5000 26.7 Ethoxylated oleyl amine 5000 18.9 Ethxylated tallow amine 5000 19.8 Glyceryl monostearate 5000 14.8 Fluorocarbon spray-on — 20.7 TA BLE 72.10 Mechanical Properties of HDPE with Various Additives Property Level (ppm) Tensile Strength at Yield (psi) Elongation at Break (%) No additive — 3810 551 Erucamide 2500 3825 410 Erucamide 5000 3840 513 Ethoxylated oleyl amine 5000 3813 402 Ethoxylated tallow amine 5000 3877 425 DK4036_book.fm Page 6 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC those in HDPE. Erucamide is the most effective mold release agent (see Table 72.11). 73 -1 73 Organic Peroxides 73.1 Introduction 73- 1 73.2 Types and Properties 73- 1 73.3 Application in Coatings 73- 4 73.4 Safety Factors and Producers 73- 5 73.5 Future Trends 73- 5 References 73- 5 73.1 Introduction Organic peroxides are derivatives of hydrogen peroxide, HOOH, wherein one or both hydrogens are replaced by an organic group (i.e., ROOH or ROOR). 1–5 They are thermally sensitive and decompose by homolytic cleavage of the labile oxygen–oxygen bond to produce two free radicals: (73.1) The temperature activity of organic peroxides varies from below room temperature to above 100 ° C, depending on the nature of the R groups. In addition to thermal decomposition, certain organic peroxides can be decomposed by activators or promoters at temperatures well below the normal decomposition temperature. A major application of these compounds is as free radical initiators in the polymerization of vinyl and diene monomers in the plastics and coatings industries. They are also used as cross-linking and modifying agents for polyolefins, as vulcanizing agents for elastomers, and as curing agents for polyester resins. 73.2 Types and Properties Peroxide manufacturers now offer over 50 different organic peroxides in more than 100 formulations including dilutions in solvents, pastes, and filler-extended grades. In most cases, these formulations are designed for specific applications and to allow shipping and handing with a reasonable degree of safety. peroxides are commonly reported in terms of half-life ( t 1/2 ) temperature, that is, the time at which 50% of the peroxide has decomposed at a specified temperature. Table 73.1 lists the 10-hour t 1/2 temperature ranges for the major organic peroxide types. Peroxides of certain types, such as hydroperoxides and ketone peroxides, are primarily used in combination with promoters and are employed at temperatures much lower then their measured 10-hour t 1/2 temperature. ROOR RO OR ′ →⋅+⋅ ′ ∆ Peter A. Callais Pennwalt Corporation DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Peroxide Selection • Radical Types The major classes of commercial organic peroxides are shown in Table 73.1. Decomposition rates of 73 -6 Coatings Technology Handbook, Third Edition 15. t-Amyl Peroxides (product bulletin), Lucidol Division, Pennwalt Corporation, Buffalo, NY, 1985. 16. M. Takahashi, Polym. Plast. Technol. Eng., 15 , 1 (1980). 17. L. W. Hill and Z. W. Wicks, Jr., Prog. Org. Coat., 10 , 55 (1982). 18. R. H. Kuhn, N. Roman, and J. D. Whitman, Mod. Paint Coat., 71 (5), 50 (1981). 19. R. F. Storey, in Surface Coatings , A. L. Wilson, J. W. Nicholson, and H. J. Prosser, Eds. London: Elsevier Applied Science, 1987, p. 69. 20. C. J. Bouboulis, U.S. Patent 4,739,006 (1988). 21. D. Rhum and P. F. Aluotto, U.S. Patent 4,075,242 (1978). 22. Y. Eguchi and A. Yamada, U.S. Patent 4,687,882 (1987). 23. W. R. Berghoff, U.S. Patent 4,716,200 (1987). 24. R. A. Gray, J. Technol., 57 (728), 83 (1985). 25. R. Buter, J. Technol., 59 (749), 37 (1987). 26. D. Rhum and P. F. Aluotto, J. Technol., 55 (703), 75 (1983). 27. V. R. Kamath and J. D. Sargent, Jr., J. Coat. Technol., 59 (746), 51 (1987). 28. V. R. Kamath, U.S. Patent pending. 29. F. M. Merrett, Trans. Faraday Soc., 50 , 759 (1954). 30. D. H. Solomon, J. Oil Colour. Chem. Assoc., 45 , 88 (1962). 31. J. Sanchez, U.S. Patent 4,525,308 (1985). 32. A. J. D’Angelo and O. L. Mageli, U.S. Patents 4,304,882 (1981), 3,952,041 (1976), 3,991,109 (1976), 3,706,818 (1972), and 3,839,390 (1974). 33. A. J. D’Angelo, U.S. Patent 3,671,651 (1972). 34. R. A. Bafford, U.S. Patent 3,800,007 (1974). 35. R. A. Bafford, E. R. Kamens, and O. L. Mageli, U.S. Patent 3,763,112 (1973). 36. O. L. Mageli, R. E. Light, Jr., and R. B. Gallagher, U.S. Patent 3,536,676 (1970). 37. H. Ohmura and M. Nakayama, U.S. Patent 4,659,769 (1987). 38. C. S. Sheppard and R. E. MacLeay, U.S. Patents 4,042,773 (1977) and 4,045,427 (1977). 39. T. N. Myers, European Patent Appl., 223,476 (1987). 40. P. A. Callais, V. R. Kamath, and J. D. Sargent, Proc. Water-Borne Higher Solids Coatings Symp., 15 , 104 (1988). DK4036_book.fm Page 6 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 74 -1 74 Surfactants for Waterborne Coatings Applications 74.1 Introduction 74- 1 74.2 Chemistry 74- 1 74.3 Theory 74- 2 74.4 Foam Control 74- 3 74.5 Wetting 74- 4 74.6 Conclusion 74- 5 74.1 Introduction As governmental regulations become increasingly restrictive, waterborne coatings appear to be the logical choice for many paint manufacturers. However, the technological switch from solvent to waterborne systems requires an understanding of the challenges that lay ahead with respect to wetting, foam control, and coverage over difficult-to-wet substrates. This chapter will help explain the important contribution of wetting agents and defoamers to the emerging technology of waterborne coatings. Topics will include the chemistry of several surfactants along with a thorough analysis and understanding of surface tension. Surface tension reduction and mechanisms relating to foam stabilization will be reviewed. 74.2 Chemistry All surfactants fall into two classifications, nonionic and ionic. Within the ionic category, surfactants can be further subdivided into anionic, cationic, or amphoteric types. For coatings, most surfactants utilized are either nonionic or anionic. For wetting agents, the products we will compare include alkylphenol ethoxylates, sodium dioctyl sulfosuccinates, sodium laurel sulfates, block copolymers of ethylene and propylene oxides, alkyl benzene sulfonates, and, finally, a specialty class called acetylenic glycols. We start with this. Acetylenic glycols are a chemically unique group of nonionic surface active agents that have been especially designed to provide multifunctional benefits to a wide array of waterborne coating products. Two key benefits include an unusual combination of wetting and foam control properties. Characterized as an acetylenic diol, we have a 10-carbon backbone molecule with a triple bond, two adjacent hydroxyl groups, and four symmetrical methyl groups. Based on acetylene chemistry, this product is unlike any other surfactant molecule. The combination of the triple bond and the two hydroxyl groups creates a domain of high electron density, making this portion of the molecule polar and thus Samuel P. Morell S. P. Morell and Company DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 75 -1 75 Surfactants, Dispersants, and Defoamers for the Coatings, Inks, and Adhesives Industries 75.1 Introduction 75- 1 75.2 Wetting and Dispersing Process 75- 2 75.3 Silicones and Surface Flow Control Agents 75- 6 75.4 Defoaming Additives 75- 9 75.5 Conclusion 75- 12 References 75- 12 75.1 Introduction Over the history of coatings, inks, and adhesives, many evolutionary changes have occurred; not only have the ingredients used to make the formulations been changed, but also the physical characteristics of the formulations along with their application, cure, and performance parameters have changed. Of course, each trend poses challenges to both raw material suppliers and formulators alike. Because additives are used to enable and enhance system performance, the evolution of resins, pigments, solvents, and application technologies pose special challenges for additive suppliers. Resin and solvent combinations used in the good old days were typically quite low in surface tensions in comparison to modern formulations. Today’s more environmentally friendly formulations with little or no solvents, or in the case of aqueous formulations, with little or no cosolvents, require increased use of interfacially active materials in order to provide adequate substrate wetting, surface flow, and the prevention of foaming and air entrapment. John W Du BYK-Chemie USA DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC The Wetting and Dispersing Process • Waterborne Systems • Background • Chemical Structure of “Silicones” • Surface Solvent-Based Systems • Classification • Summary Phenomena and the Elimination of Defects • Summary Selection Criteria and Test Methods • Summary The Nature of Foam • Defoamers versus Air Release Agents • for Aqueous Systems • Defoamers for Solvent-Based Systems • The Mechanisms of Defoaming and Air Release • Defoamers [...]... means for particulates to associate with each other without actually coming in contact This association allows large domains of controlled flocculates to move as a single unit while maintaining the individual particle-to-particle spacing that is required for stability This type © 2006 by Taylor & Francis Group, LLC DK4036_book.fm Page 8 Monday, April 25, 2005 12:18 PM 75-8 Coatings Technology Handbook, ... Surface Coatings, 2nd ed Chichester: John Wiley, 1985, pp 622–625 13 J W Simmons, R M Thorton, and R J Wachala, “Defoamers and antifoams,” in Handbook of Coatings Additives L J Calbo, Ed New York: Marcel Dekker, 1987 14 M S Gebhard and L E Scriven, “Formulation and dissipation of air bubbles in spray-applied coatings, ” in Proceedings of the Twenty-first Waterborne, Higher Solids, and Powder Coatings. .. in Coatings Technology Handbook II, Chap 71 D Satas and A Tracton, Eds New York: Marcel Dekker, 2000, pp 595–608 © 2006 by Taylor & Francis Group, LLC DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM 76 Pigment Dispersion 76.1 Introduction 76-1 76.2 A Brief Introduction to Pigments 76-2 Pigment Definition • Pigment Particles 76.3 The Dispersion Process 76-4 Pigment Wetting • Particle... used to generate hammer-tone finish coatings © 2006 by Taylor & Francis Group, LLC DK4036_book.fm Page 13 Monday, April 25, 2005 12:18 PM Surfactants, Dispersants, and Defoamers 75-13 10 W Heilin and S Stuck, “Polysiloxane zur Erhöhung der Kratzfestigkeit von Beschictungsoberflächen,” Farbe und Lack, 101, 376 (1995) 11 L H Brown, “Silicone additives,” in Handbook of Coatings Additives L J Calbo, Ed New... dispersion process involves the breaking down and separation of the aggregated and agglomerated particles that are present in all pigments in their normal form after their manufacture Dispersion is not considered to be a process of pulverization but rather a process of particle separation, homogeneous distribution of the particles in a medium, and stabilization of the resultant system to prevent reaggregation,... collapse Consequently, particulate spacing, steric hindrance, and dispersion stabilization are lost 75.2.4.2 Controlled Flocculation Additives If the pigment affinic groups are not confined to a small region of the additive molecule but rather are distributed in a specific fashion over the entire molecule, then such an additive will be capable of simultaneously contacting two or more pigment particles in a bridge-like... condition of controlled flocculation and the normal flocculated state Without additives, the pigment particles make direct contact with one another in uncontrolled flocculation In contrast, no direct pigment-to-pigment contact occurs in controlled flocculation; additive molecules are always present between the pigment particles Ordinary flocculation without additive (resulting in direct pigment-to-pigment contact)... multiple pigment affinic groups, arranged in such a manner that all of the groups are available for adsorption onto a pigment particle’s surface Following additive adsorption, the binder-compatible molecular chains of the additive can then extend into the liquid binder Enveloping the pigment particles with additive and preventing direct pigment–pigment contact, these binder-compatible chains of the deflocculating... Surface Treatment of Pigments: Application 76 -11 Organic Pigments • Inorganic Pigments Theodore G Vernardakis BCM Inks USA, Inc 76.9 The Characterization and Assessment of Dispersion 76-17 76.10 Conclusion .76-17 References 76-18 76.1 Introduction The dispersion of pigments in fluid media is of great technological importance to the coatings manufacturers who deal with pigmented... waterborne coatings, thereby avoiding wetting problems They can often be used to replace fluoro surfactants However, fluoro surfactants, in addition to reducing surface tension (and being more expensive), also exhibit a pronounced tendency to stabilize foam It is important to note that silicone surfactants do not stabilize foam 75.3.3.6 Controlled Incompatibility The compatibility of any particular silicone . 72 -4 Coatings Technology Handbook, Third Edition 72.4.1.2 Acetal The most effective mold release agents in acetal are fatty amides in general and fatty bisamides amides in particular particle-to-particle spacing that is required for stability. This type DK4036_book.fm Page 5 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 75 -8 Coatings Technology. (1995). 11. L. H. Brown, “Silicone additives,” in Handbook of Coatings Additives . L. J. Calbo, Ed. New York: Marcel Dekker, 1987. 12. S. Paul, “Methods used to reduce foaming,” in Surface Coatings