Coatings Technology Handbook Episode 3 Part 3 pptx

Conductive Coatings 91 -5 A new class of low-dimensional materials — for example, polymeric metallophthalo-cyanines with such metals as aluminum, chromium, tin, and gallium at the center of the ring — has been synthesized and made conducting [~1 ( Ω⋅ cm) –1 ] by halogen doping (partial oxidation). 34,35 Var ious transition metal ions have been coordinated with conjugated ligands to synthesize polymers with metal ions within the main chain. 36 Ligands such as tetrathiosquarate, tetrathionaphthalene, tetrathi- afulvalene, and tetrathiooxalate have been used. The tetrathiooxalate complexed with nickel ions gave linear polynickel tetrathiooxalate oligomers with conductivities as high as 20 ( Ω⋅ cm) –1 . A completely different approach to depositing conducting organometallic coatings involves the use of a low-pressure plasma (LPP) environment. The LPP environment may be used to deposit a polymeric organometallic coating (or powder) from organometallic monomers, 37–42 or it may be used to convert a deposited organometallic coating into a metallic one. 20,43,44 The metals introduced in the organometallic coatings by LPP/organometallic monomers were iron, tin, mercury, tantalum, lead bismuth, and metal coatings by the LPP posttreatment were gold, platinum, palladium, silver, and lead. The generation of metal surface coatings from certain organometallic coatings can be also achieved by thermal means (controlled pyrolysis). 20 The advantage of the LPP process is that it permits a metallic coating to be formed on a heat-sensitive substrate without the use of elevated temperatures. The process also permits formation of adhering gold and platinum coatings otherwise difficult to deposit on plastic substrates. None of the conducting organometallic coatings or their deposition processes have gone beyond the research stage. However, the conducting organometallic coatings effort is very new compared with the other types mentioned before. 91.3 Commercially Available Conductive Coatings Whereas the metallized plastics effort is a multimillion-dollar industry, the commercial application of conductive polymer coatings as a paint, lacquer, ink, adhesive, or a solution of some kind forms a very small industry indeed. Below are summarized several typical products available commercially. A proprietary aluminum containing paint, AG 9680, manufactured by A.I. Technology, Inc., Princeton, New Jersey, is claimed to approach the shielding effectiveness of 70 to 75 dB, an effectiveness similar to that of pure silver. A silver-filled silica matrix elastomer, Aremco-Shield 615, has been developed by Aremco Products, Inc., Ossining, New York. This material has been formulated into a conductive paint that can be applied by either brush or spray; it cures at room temperature and bonds to metals, glass, and plastics. N N N N N N N N N N N N N N N N M X X N N N N M X N N N N M DK4036_book.fm Page 5 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 91 -6 Coatings Technology Handbook, Third Edition A silver lacquer (Eccocoat CC-2) and an elastomeric, silver-filled, conductive coating (Eccocoat CC- 40) have been developed by Emerson and Cuming, Canton, Massachusetts. The lacquers and the elas- tomer coatings may be applied by dipping, spraying, silk screening, roll coating, or brushing. In most cases, a simple spray coat is adequate to produce a highly conductive surface [up to 20 ( Ω⋅ cm) –1 ] using the air-dry method. Oven curing will give improved conductivity. A rather extensive series of conductive coatings under the trade name Evershield has been developed by the E/M Corp. of West Lafayette, Indiana. The series of products consists of a graphite-filled acrylic resin system, EC-G-102, intended mainly for applications for electrostatic charge dissipation; a high performance nonoxidizing copper-filled acrylic resin system, EC-C-301, is suitable for spray gun appli- cation. The coating has an attenuation performance of 50 to 70 dB at 10 to 1000 MHz. A popular nickel- filled acrylic resin system, EC-N-501, easily paintable and with superior adhesion characteristics for a wide variety of plastic substrates, is also available. It has an attenuation performance of 50 to 60 dB at 30 to 1000 MHz. 91.4 Applications 91.4.1 Shielding from Electromagnetic Interference The advent of the FCC Docket 20780, which regulates electromagnetic emissions from computing and communication devices used in industrial and residential locations, has really provided a stimulus for the industry to come up with cost-effective methods for limiting the level of electromagnetic interference (EMI). To meet the set standards, the manufacturers have adopted a variety of methods for controlling EMI. These methods have ranged from redesigned basic circuitry to incorporation of conductive shielding materials in the devices. The incorporation of conductive shielding may take different routes: 45 •Use of metal enclosures •Metallic foil tapes •Metal coatings on plastic enclosures •Conductive paints on plastic enclosures •Conductive plastic enclosures • Flexible laminates with metal foil The shielding effectiveness of a homogeneous medium, such as a conductive coating, is related to the propagation of the electromagnetic field through the coating. The shielding effectiveness is directly related to the electronic and magnetic properties of the coating; therefore, for best shielding effectiveness, materials with both high relative magnetic permeability and high electrical conductivity are necessary. Thus, it has been found that the various metals and alloys form the following “series” in decreasing order of effectiveness: Ag > Cu > Au > Al > Zn > brass > Ni > Sn > steel > stainless steel Currently, the most cost-effective and the most problem-free materials for shielding are claimed to be nickel-filled acrylic or polyurethane conductive paints. 46 91.4.2 The Stealth One of the more glamorous applications of conducting coatings has been in the “stealth” technology. be said about its materials technology. The so-called stealth materials can provide a minimal radar profile for military aircraft and naval vessels. This profile is achieved primarily by a combination of geometric design and materials properties. The active components consist of several classes of materials: carbon fiber composites, radar-absorbing coating, ferrite layers, and interference layers in the form of certain pigment-filled polymer coatings. 21 From other EMI work, it had been known for years that incorporating DK4036_book.fm Page 6 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Until the Pentagon revealed the top-secret Stealth (Figure 91.1) fighter on November 10, 1988, little could 91-8 Coatings Technology Handbook, Third Edition References 1. T. J. Miranda, in Applications of Polymers. R. B. Seymour and H. F. Mark, Eds. New York: Plenum Press, 1988. 2. H. Narcus, Trans. Eelctrochem. Soc., 88, 371 (1945). 3. J. I. Kroschwitz, Ed in-Chief, Encyclopedia of Polymer Science and Engineering, Vol. 9. New York: Wiley, 1985. 4. C. C. Ku and R. Liepins, Electrical Properties of Polymers, Chemical Principles. New York: Hanser, 1987. 5. G. J. Shawham and B. R. Chuba, in “Materials — Pathway to the future,” SAMPE, 33, 1617 (1988). 6. Y. Ikenaga, T. Kanoe, T. Okada, and Y. Suzuki, Ausz. Eur. Patentanmeld. I, 3(12), 485 (1987). 7. P. S. C. Ho, P. O. Hahn, H. Lefakis, and G. W. Rubloff, Ausz. Eur. Patentanmeld. I, 2(29), 1367 (1986). 8. S. John and N. V. Shanmugam, Met. Finish., 84(3), 51 (1986). 9. R. Liepins, Camille Dreyfus Laboratory Annual Report, Research Triangle Institute, Research Tr iangle Park, NC, December 31, 1970, and unpublished results after 1970. 10. J. Fredrich, I. Loeschcke, and J. Gahde, Acta Polym., 37(11–12), 687 (1986). 11. L. J. Krause, “Electroless metal plating of plastics,” U.S. Patent 4,600,656 (July 15, 1986). 12. R. Cassat, “Metallizing electrically insulating plastic articles,” U.S. Patent 4,590,115 (May 20, 1986). 13. R. Cassat and M. Alliot-Lugaz, “Metallization of electrically insulating flexible polymeric films,” U.S. Patent 4,564,424 (January 14, 1986). 14. D. E. Davenport, in Conductive Polymers. R. B. Seymour, Ed. New York: Plenum Press, 1984, p. 39. 15. J. E. McCaskie, in Modern Plastics Encyclopedia 1985–1986, 62, No. 10A. J. Aranoff, Ed. New York: McGraw-Hill, 1985, p. 381. 16. V. Krause, Kunsts. Plast. (Munich), 78(6), 17 (1988). 17. R. A. Baldwin, A. J. Gould, B. J. Green, and S. J. Wake, British Patent 2,169,925A (July 23, 1986). 18. A. Yanagisawa, H. Koyama, K. Suzuki, and T. Nakagawa, Proceedings of the 31 st International SAMPE Symposium, April 7–10, 1986, p. 1583. 19. J. C. Cooper, Ru. Panayappan, and R. C. Steele, in Proceedings of the 1984 IEEE National Symposium on Electromagnetic Compatibility, April 24–26, 1984, San Antonio, TX, p. 233. 20. R. Liepins, B. Jorgensen, A. Nyitray, S. F. Wentworth, D. M. Sutherlin, S. E. Tunney, and J. K. Stille, Synth. Met., 15, 249 (1986). 21. A. Wirsen, “Electroactive polymer materials.” National Technical Information Service Publication PB86-185444, January 1986. 22. W. Werner, M. Monkenbusch, and G. Wegner, Makromol. Chem., Rapid Commun., 5, 157 (1984). 23. H. Naarmann and N. Theophilous, Synth. Met., 22, 1 (1987). 24. T. Yamamoto, K. Sanechika, and A. Yamamoto, J. Polym. Sci., Polym. Lett. Ed., 18, 9 (1980). 25. S. Hotta, T. Hosaka, and W. Shimotsuma, Synth. Met., 6, 317 (1983). 26. S. T. Wellinghoff, Z. Deng, J. Reed, and J. Racchini, Polym. Prepr., 25(2), 238 (1984). 27. A. G. MacDiarmid, J. C. Chiang, M. Halpern, W. S. Huang, S. L. Mu, N. L. D. Somasiri, W. Wu, and S. I. Yaniger, Mol. Cryst. Liquid Cryst., 121, 173 (1985). 28. J. C. Chiang and A. G. MacDiarmid, Synth. Met., 13, 183 (1986). 29. W. S. Huang, A. G. MacDiarmid, and A. P. Epstein, J. Chem. Soc. Chem. Commun., 1784 (1987). 30. R. B. Bjorklund and B. Liedberg, J. Chem. Soc. Chem. Commun., 1293 (1986). 31. S. P. Armes and B. Vincent, J. Chem. Soc. Chem. Commun., 289 (1987). 32. S. P. Armes, J. F. Miller, and B. Vincent, J. Colloid Interface Sci., 118(2), 410 (1987). 33. S. P. Armes, M. Aldissi, and R. D. Taylor, “Non aqueous polypyrrole colloids,” LA-UR-88-3855, submitted to J. Chem. Soc. Chem. Commun. 34. P. M. Kuznesof, R. S. Nohr, K. J. Wynne, and M. E. Kenney, J. Macromol. Sci. Chem., A16(1), 299 (1981). 35. T. J. Marks, Science, 227, 881 (1985). 36. J. R. Reynolds, J. C. W. Chien, F. E. Karasz, and C. P. Lillya, Polym. Prepr., 25(2), 242 (1984). DK4036_book.fm Page 8 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Conductive Coatings 91-9 37. R. Liepins and K. Sakaoku, J. Appl. Polym. Sci., 16, 2633 (1972). 38. E. Kny, L. L. Levenson, W. J. James, and R. A. Auerbach, J. Phys. Chem., 84, 1635 (1980). 39. G. Smolinsky and J. H. Heiss, Org. Coat. Plast. Chem., 28, 537 (1968). 40. R. K. Sadhir and W. J. James, in Polymers in Electronics. T. Davidson, Ed. ACS Symposium Series No. 242 Washington, DC: American Chemical Society, 1984. 41. R. Liepins, M. Campbell, J. S. Clements, J. Hammond, and R. J. Fries, J. Vac. Sci. Technol., 18(3), 1218 (1981). 42. E. Kny, L. L. Levenson, W. J. James, and R. A. Auerbach, Thin Solid Films, 85, 23 (1981). 43. R. Liepins, “Method of forming graded polymeric coatings on films,” U.S. Patent 4,390,567 (June 28, 1983). 44. R. Liepins, “Method of forming metallic coatings on polymer substrates,” U.S. Patent 4,464,416 (August 7, 1984). 45. R. W. Simpson, Jr., in Proceedings of the 1984 IEEE National Symposium on Electromagnetic Com- patibility, April 24−26, 1984, San Antonio, TX, 1984, p. 267. 46. D. Staggs, in Proceedings of the 1984 IEEE National Symposium on Electromagnetic Compatibility, April 24–26, 1984, San Antonio, TX, 1984, p. 43. 47. B. Bridge, M. J. Folkes, and H. Jahankhani, in Inst. Phys. Conf. Ser. No. 89, Session 8, p. 307, 1987. 48. T. A. Hoppenheimer, High Technology, December, 58 (1986). 49. R. H. Baughman, R. L. Elsenbaumer, Z. Igbal, G. G. Miller, and H. Eckhardt, in Electronic Properties of Conjugated Polymers. H. Kuzmany, M. Mehring, and S. Roth, Eds. New York: Springer-Verlag, 1987, p. 432. 50. K. J. DeGraffenreid, in Proceedings of the 1985 IEEE International Symposium on Electromagnetic Compatibility, April 24–26, 1984, San Antonio, TX, 1985, p. 273. 51. Emerson and Cuming, Technical Bulletin 4-2-14, Canton, MA. 52. M. Gazard, J. C. Dubois, M. Champagne, F. Garnier, and G. Tourillon, J. Phys. Paris Colloq., C3, 537 (1983). 53. F. Garnier, G. Tourillon, M. Gazard, and J. C. Dubois, J. Electroanal. Chem., 148, 299 (1983). 54. W. J. Miller, in Modern Plastics Encyclopedia 1985−1986, 62, No. 10A. J. Aranoff, Ed. New York: McGraw-Hill, 1985, p. 380. 55. H. E. Coonce and G. E. Macro, in Proceedings of the 1985 IEEE International Symposium on Electromagnetic Compatibility, April 24–26, 1984, San Antonio, TX, 1985, p. 257. 56. H. Munstedt, in Electronic Properties of Polymers and Related Compounds. H. Kuzmany, M. Mehring, and S. Roth, Eds. New York: Springer-Verlag, 1985, p. 8. 57. M. E. Gross, A. Appelbaum, and P. K. Gallagher, J. Appl. Phys., 61(4), 1628, (1987). 58. R. Liepins, B. S. Jorgensen, and L. Z. Liepins, “Process for introducing electrical conductivity into high-temperature polymeric materials” (submitted for patent). 59. T. Hioki, S. Noda, M. Kakeno, A. Itoh, K. Yamada, and J. Kawamoto, in Proceedings of the Inter- national Ion Engineering Congress, September 12–16, 1983. Kyoto, Japan, 1984, p. 1779. 60. A. Auerbach, Appl. Phys. Lett., 47(7), 669 (1985). 61. A. Auerbach, J. Electrochem. Soc., 132(6), 1437 (1985). 62. J. Y. Lee, H. Tanaka, H. Takezoe, A. Fukuda, and E. Kuze, J. Appl. Polym. Sci., 29, 795 (1984). 63. T. Cacouris, G. Scelsi, R. Scarmozzino, R. M. Osgood, Jr., and R. R. Krchnavek, Meter. Res. Soc. Proc., 101, 43 (1988). 64. J. E. Bouree and J. E. Flicstein, Mater. Res. Soc. Proc., 101, 55 (1988). 65. A. Gupta and R. Jagannathan, Mater. Res. Soc. Proc., 101, 95 (1988). 66. L. Baufay and M. E. Gross, Mater. Res. Soc. Proc., 101, 89 (1988). 67. A. M. Lyons, C. W. Wilkins, Jr., and F. T. Mendenhall, Mater. Res. Soc. Proc., 101, 67 (1988). DK4036_book.fm Page 9 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 92 -1 92 Silicone Release Coatings 92.1 Introduction 92- 1 92.2 Thermal-Cured Silicone Release Agents 92- 2 92.3 Radiation-Curable Silicone Release Agents 92- 7 92.4 The Future 92- 9 References 92- 9 92.1 Introduction Silicone release coatings are vitally important to the tag and label industry, which could not exist in its present form without reliable release agents. Silicones possess unique physical and chemical properties that make this class of substances ideal for the purpose of releasing pressure-sensitive adhesives. Silicone release agents worth $130 to $150 million were sold worldwide in 1988, contributing to products with a total value that exceeds $3 billion. The term “silicones” as commonly used refers to linear (two-dimensional) polydimethylsiloxanes, which may be structurally depicted as follows: where x is an integer greater than 1. Silicon is tetrafunctional, so an infinite number of silicone polymers may be devised with different organic groups replacing methyl, or with three-dimensional resin structures wherein silicon atoms are incorporated in the polymer structure via three or four —Si–O— linkages. Since, however, the low surface tension, nonpolarity, chemical inertness, and low surface energy respon- sible for the outstanding release characteristics of silicone coatings all derive from the linear dimethyl- silicone structure, this discussion focuses on linear polymers. Silicone coatings that release pressure-sensitive adhesives have been in use for some 35 years. The chemistry and applications of silicone release coatings have undergone remarkable change during this time, with the pace of development accelerating in recent years. In the face of increasingly sophisticated and demanding requirements, silicones remain the only proven means of providing pressure-sensitive adhesive release for the tag and label industry. The liner most often used is paper, usually a machine-calendered (i.e., supercalendered kraft), clay- coated, or glassine paper designed to minimize penetration during coating and curing of silicone. Good CH 3 CH 3 SiO x Richard P. Eckberg General Electric Company DK4036_C092.fm Page 1 Thursday, May 12, 2005 9:55 AM © 2006 by Taylor & Francis Group, LLC The laminate structure normally used by the label industry is illustrated in Figure 92.1. Silicone Release Coatings 92 -3 where n can vary from about 50 to more than 4000, while m is much less than n ; m normally is 10 to 50. SiH is a very reactive chemical species that readily condenses with silanol (SiOH) groups, forming extremely stable siloxane bonds and liberating hydrogen in the process: ≡ SiOH + ≡ SiH → ≡ SiOSi ≡ + H 2 Many different catalysts accelerate or initiate this condensation reaction; metal soaps and driers such as dibutyltin acetate are the most efficient and economical, and are therefore in general use. Condensation cure systems are applied as solutions in organic solvents (toluene or heptane, or mixtures thereof), or as oil-in-water emulsions, because in the absence of a dispersing medium, a catalyzed mixture of a silanol-stopped silicone plus polymethyl-hydrogen-siloxane cross-linker sets up to an insoluble cross-linked gel in a few minutes at room temperature. There is no known means of retarding the condensation reaction sufficiently at room temperature to permit solvent-free coating without rendering the composition uncurable at oven temperatures. Solvent (or water in the case of emulsions) therefore acts as a bath life extender through the dilution effect, while also permitting easy, convenient coating of the silicone material. Although use of solvents or water mandates high oven temperature and solvent recovery, and entails fire or explosion risk, such materials are readily coated via simple techniques such as direct gravure, reverse roll, metering rod, and doctor blade. Coating out of a solvent vehicle also gives the silicone supplier wide latitude in silanol molecular weight; such dispersion products as General Electric SS-4191 consist of approximately 30 wt% solutions of high molecular weight silanol gums (MW in aromatic solvents). Even at 70% solvent, these products as furnished have viscosities exceeding 10,000 cps, requiring further dilution to about 5 wt% silicone solids with more solvent to render them coatable. The cross-linker is normally packaged in the silanol solution; catalyst is added to the fully diluted bath at time of use. Controlling silanol molecular weight is a proven means of controlling the release characteristics of the cured condensation-cross-linked coating. Long chains of polydimethyl-siloxane between cross-linking sites provide a rubbery, elastomeric coating; shorted intercross-link intervals lead to higher cross-link density and a harder, more resin-like coating. The rubbery coatings provide tight (high) release, which displays a marked dependence on delamination speed in comparison to the low (easy) release independent of stripping speed obtained from highly cross-linked silicone films. Accordingly, silicone suppliers offer several different molecular weight silanol-based dispersion products, permitting the end user to obtain a desired range of release. The relationship between silanol chain length and nominal release level is Addition cure silicones resemble condensation cure silicones in some respects: both types of system rely on thermally accelerated cross-linking reactions between polymethyl-hydrogen siloxane cross-linker molecules and a separate reactive dimethylsiloxane polymer. Addition cure processes utilize catalyzed reaction of unsaturated organic groups attached to otherwise unreactive dimethylsilicones with SiH groups present on the cross-linker. Polymers in use are vinyl-functional silicones, the general structure of which may be represented as follows: The curing reaction is an addition to the SiH group across the olefin double bond, also known as a hydrosilation process: CH 3 CH 3 CH 3 CH 3 SiO CH 3 CH 3 Si—CH X CH CH 3 SiO Y CH—SiO H 2 C CH 2 CH 2 X + Y = 50 to >4000; Y ≥ 0 DK4036_C092.fm Page 3 Thursday, May 12, 2005 9:55 AM © 2006 by Taylor & Francis Group, LLC graphically shown in Figure 92.2. Silicone Release Coatings 92 -5 Addition cure silicone release agents are available as solvent-free, low viscosity vinyl silicone fluids, as solvent-dispersed vinyl silicone gums (analogous to most silanol-based condensation cure products), and as emulsions. In each case, sufficient vinyl functionality is built into the linear silicone molecules to promote formation of highly cross-linked resinous cured coatings. These products therefore provide uniformly low (premium) release from most pressure-sensitive adhesives. Controlled release is not obtained by varying molecular weight of these vinyl silicone polymers (unlike the silanol case), and thus a different approach has been taken by silicone suppliers to combine the advantages of addition cure chemistry (particularly solventless packages) with a controllable range of release. Studies of cured dimethylsilicone release coatings by electron spectroscopy for chemical analysis have confirmed that the surface is much more organic than would be predicted from the stoichiometry of the (CH 3 ) 2 SiO polymer unit. 16 An adhesive in a laminate construction is therefore largely in contact with unreactive, bulky, freely rotating methyl groups; more polar —Si—O—Si— polymer backbones concen- Since the surface orientation of Si—CH 3 groups governs the release characteristics of highly cross- linked nonelastomeric silicone coatings, it follows that breaking up this nonpolar, featureless “methyl landscape” by inclusion of materials that alter the polarity of the silicone should alter the release of the coating. This is, in fact, accomplished by adding vinyl-functional silicone resins to the basic linear vinyl silicone polymers. 17 “Resin” is here defined as nonlinear silicone structures bearing high concentrations of functionally. Solventless high release additives are therefore mixtures of vinyl silicone resins with vinyl silicone fluids. Because these resins are normally friable solids when isolated, their blends with vinyl FIGURE 92.3 Cure time as a function of temperature. TIME TO CURE INCREASING TEMPERATURE IDEAL CURE UNCURED REGION CURED REGION OBSERVED CURE O OO O Si DK4036_C092.fm Page 5 Thursday, May 12, 2005 9:55 AM © 2006 by Taylor & Francis Group, LLC trate beneath the coating surface. A depiction of this postulated structure is offered in Figure 92.4. 92 -8 Coatings Technology Handbook, Third Edition radiation cure of silicones requires silicone polymers incorporating radiation-sensitive organofunctional groups, as illustrated below: In addition, UV cure normally requires high concentrations of photosensitizers or photoinitiators, such as benzophenone, benzoin ethers, and cationic-type “onium” salts. The presence of polar organo- functional moieties plus photocatalysts in radiation-cured release agents causes significant performance differences between radiation-cured and conventional thermally cured silicones. Nonetheless, industry demands for low (or “zero”) temperature processing of silicone coatings to permit use of thermally sensitive films and to prevent demoisturization of papers have prompted considerable efforts by major silicone suppliers to develop, then improve, radiation-curable products. Radiation-curable silicones are now available from several sources. Acrylated and methacrylated silicones were the focus of the earliest patented work in this area. 21 Acrylated silicones specifically developed for release applications were introduced by Goldschmidt 22 and are in commercial use at a small number of coating facilities equipped to perform EB cure. These materials have an important performance drawback inherent in free radical acrylate cross-linking chemistry: because cure is subject to severe inhibition by atmospheric oxygen, efficient inerting (<500 ppm O 2 ) of EB or UV cure chambers with nitrogen is essential for fast, complete cure to occur. While nitrogen blanketing is not impossible, inerting adds complexity and cost to the coating operation. Cure chemistry pioneered by W. R. Grace & Company overcomes oxygen inhibition problems that interfere with radiation cure of acrylates. Mercapto-olefin addition is initiated by UV light in the presence of suitable photosensitizers, or by EB radiation. The reaction is analogous to hydrosilation: —RSH + CH 2 = CHR ′ ® —RSCH 2 CH 2 R ′ The chemistry has been extended to release coatings by development of mercaptoalkyl-functional silicone polymers. 23–26 While mercaptovinyl silicone systems can be UV cured in ambient atmosphere, market acceptance of products based on this technology has been slowed by their objectional odor (skunk fragrance is derived from mercaptans) and by the tendency of unreacted mercaptan residues in the cured coatings to chemically react and bond (via addition) to free acrylate usually present in cross-linkable acrylic pressure-sensitive adhesives. The same issues affect hybrid acrylic silicone-mercaptosilicone sys- tems developed to take advantage of the oxygen insensitivity of mercapto-olefin addition. 27 Certain “onium” (sulfonium and iodonium) salts are known to be capable of initiating photopoly- merization of epoxides 28 and vinyl ethers. 29 Epoxy-functional silicones are readily prepared, 30 so appli- cation of cationic UV cure to silicones was an obvious extension of the technology. 31–33 A major performance advantage inherent in epoxy silicone-iodonium salt photocurable systems results from the non-free-radical nature of this cross-linking. This particular cure mechanism is not subject to oxygen inhibition, making UV-curable epoxy silicone based release agents particularly well suited to wide web converting operations, as nitrogen blanketing is not needed. The epoxy silicone UV cure system has been shown to combine exceptionally fast UV cure response with premium, stable release versus cross-linkable acrylic, styrene-butadiene rubber, and hot-melt adhe- sives. 16 As with other radiation-curable silicone release systems, 34 however, controlled release additives capable of providing a broad, predictable range of release for the UV epoxy silicone coatings have remained elusive. Another problem associated with these cationic cure silicone materials is substrate- dependent performance. Excellent cure, anchorage, and release are obtained when corona-treated films CH 3 CH 3 SiO m CH 3 n X SiO X = mercaptan, methacrylate, acrylate, epoxy, vinyl ether DK4036_C092.fm Page 8 Thursday, May 12, 2005 9:55 AM © 2006 by Taylor & Francis Group, LLC 92 -10 Coatings Technology Handbook, Third Edition 20. F. S. McIntyre et al., in Proceedings of the 1987 TAPPI Polymers, Laminations, and Coatings Con- ference, San Francisco, 1988. 21. J. D. Nordstrom et al., U.S. Patents 3,577,256; 3,650,813. 22. G. Koerner et al., U.S. Patent 4,306,050. 23. R. Viventi, U.S. Patent 3,8166,282. 24. J. Bokerman et al., U.S. Patent 4,052,059. 25. J. A. Colquhoun, U.S. Patent 4,070,525. 26. R. P. Eckberg et al., U.S. Patent 4,558,147. 27. F. Hockemeyer et al., U.S. Patent 4,571,349. 28. J. V. Crivello et al., J. Polym. Sci., 17 , 977, 1047 (1979). 29. J. V. Crivello et al., in Radcure IV Proceedings , Chicago, 1982. 30. F. D. Mendecine, U.S. Patent 4,046,930. 31. R. P. Eckberg et al., U.S. Patent 4,279,717. 32. R. P. Eckberg et al., U.S. Patent 4,421,904. 33. R. P. Eckberg et al., U.S. Patent 4,547,431. 34. R. H. Bickford, in Radtech ’88 Conference Proceedings , New Orleans, 1988. 35. G. R. Homan et al., U.S. Patent 4,525,566. 36. T. J. Drahnak, U.S. Patent 4,510,094. 37. R. P. Eckberg, U.S. Patent 4,670,531. 38. J. V. Crivello et al., U.S. Patent 4,617,238. 39. S. C. Lapin, in Radcure ’88 Conference Proceedings , Baltimore, 1988. DK4036_C092.fm Page 10 Thursday, May 12, 2005 9:55 AM © 2006 by Taylor & Francis Group, LLC [...]...DK4 036 _book.fm Page 1 Monday, April 25, 2005 12:18 PM 93 Silicone Hard Coatings Edward A Bernheim Exxene Corporation 93. 1 93. 2 93. 3 93. 4 93. 5 Introduction 93- 1 Substrates 93- 2 Uses 93- 2 Application of the Coating . 93- 2 Conclusions . 93- 3 93. 1 Introduction Silicone (polysiloxane) hard coatings are finishes of superior abrasion... Silicone coatings are solvent-borne coatings Some of the possible solvents are alcohols and glycol ethers This includes such alcohols as isopropanol, propanol, ethanol, n-butanol, isobutanol, and methanol Polysiloxane coatings are applicable to many substrates, but the majority of applications are on nonmetallic surfaces, especially plastics Silicone coatings can be dyed or pigmented, but for the most part. .. in the late 1 930 s The technology of PSAs and adhesive products is covered extensively in the Handbook. 3 94.2 Adhesives The basis of a PSA is an elastomer made tacky by addition of tackifying resins Natural rubber was the first material used and still is among the most important elastomers for compounding of PSAs The general composition of such compounded adhesives is as follows Elastomer, 30 to 60% Tackifier,... resistance, 5-min curing, and tinted coatings Many of these properties can be combined in one coating The coatings are used in such diverse areas as the automotive, electronic, computer hardware, architectural and architectural glazing, recreation, sporting goods, protective eyewear, safety, and optical industries 93- 1 © 2006 by Taylor & Francis Group, LLC DK4 036 _book.fm Page 1 Monday, April 25, 2005... Silicone coatings are used on cast sheet stock, extruded sheet stock, molded parts, lenses, windows, films, etc The application methods are also quite varied Some of the methods are spraying, flow coating, spin coating, dip coating with various withdrawal speeds and, with some formula modifications, pad coating and roller coating The coatings are not suitable for screen or gravure application Hard silicone coatings. .. Plasticizer, 0 to 30 % *Deceased 94-1 © 2006 by Taylor & Francis Group, LLC DK4 036 _book.fm Page 1 Monday, April 25, 2005 12:18 PM 95 Self-Seal Adhesives 95.1 Introduction 95-1 Adhesion and Cohesion • Seal Performance Larry S Timm 95.2 Application Techniques 95 -3 Findley Adhesives, Inc Handling • Procedures 95.1 Introduction Cohesives, often referred to as “self-seal adhesives,” are coatings which... surfaces, especially plastics Silicone coatings can be dyed or pigmented, but for the most part these coatings are used as clear top coatings They have excellent light transmission and actually improve the optical properties of the material that is coated Some of the plastics that are used with polysiloxane coatings are polycarbonate, acrylic, polyarylate, polysulfone, vinyls, nylons, polyester, cellulose... chains and joining at the now-available bonding sites produces a molecular inseparable condition referred to as a cohesive seal (Figure 95.1, Figure 95.2, and Figure 95 .3) In application, the greater the number of bonding sites utilized to impart adhesion, the smaller the number remaining to facilitate subsequent adhesion Laboratory evaluation on the functionality of self-seal formulations confirms the significance... by Taylor & Francis Group, LLC DK4 036 _book.fm Page 1 Monday, April 25, 2005 12:18 PM 94 Pressure-Sensitive Adhesives and Adhesive Products 94.1 Introduction 94-1 94.2 Adhesives 94-1 94 .3 Adhesive Properties 94-2 Tack • Peel Adhesion • Shear Resistance • Other Tests • Dynamic Mechanical Analysis 94.4 Products .94-5 Tapes • Labels • Other Products 94.5 Processing ... polyester, cellulose acetate, cellulose acetate-butyrate, and polyolefins, just to name a few Despite this plethora of materials, acrylics and polycarbonates are generally the plastics of choice Silicone hard coatings do not have automatic adhesion to all plastic surfaces Materials such as polycarbonate and acrylics will, in many cases, have tape adhesion without need of surface treatment, etch, or primer coat . 1 93. 2 Substrates 93- 2 93. 3 Uses 93- 2 93. 4 Application of the Coating 93- 2 93. 5 Conclusions 93- 3 93. 1 Introduction Silicone (polysiloxane) hard coatings are finishes of superior. as a hydrosilation process: CH 3 CH 3 CH 3 CH 3 SiO CH 3 CH 3 Si—CH X CH CH 3 SiO Y CH—SiO H 2 C CH 2 CH 2 X + Y = 50 to >4000; Y ≥ 0 DK4 036 _C092.fm Page 3 Thursday, May 12, 2005 9:55 AM ©. DK4 036 _C092.fm Page 10 Thursday, May 12, 2005 9:55 AM © 2006 by Taylor & Francis Group, LLC 93 -1 93 Silicone Hard Coatings 93. 1 Introduction 93- 1 93. 2 Substrates 93-