89 -10 Coatings Technology Handbook, Third Edition DK4036_book.fm Page 10 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 89.3.2.3 Polyester–Non-TGIC (β-Hydroxyalkylamide, Tetramethoxymethyl Glycoluril) As we discussed earlier, TGIC was found to have mutagenic properties. While some controversy still remains as to its hazardous nature, many coatings companies and regulatory bodies have taken a con- servative stance and limited its use. There have been regulations enacted that require warnings to be placed on labels of coatings that contain TGIC. Coatings companies have also turned to curing agents that do not have these types of hazards associated with them. The two types that are used most often are the β-hydroxyalkylamides and tetramethoxymethyl gly- coluril. The hydroxy-amides are tetrafunctional, which makes them highly reactive at curing tempera- tures. Their major drawback is that they release water from the reaction that must escape the curing film. This requires further formulation to insure defect-free films. The glycoluril is also tetrafunctional and releases a VOC, methanol, as part of the reaction process. 89.3.3 Acrylic Systems There are two primary acrylic systems: those based on hydroxy-functional acrylic resins and those using epoxy- or glycidyl-functional polymers. Carboxy-functional materials have been produced. However, they have not made much progress into the industry. 89.3.3.1 Acrylic–Isocyanate (Acrylic–Urethane) Acrylic–urethanes are formed in exactly the same way as their polyester counterparts. The acrylic resins are linear instead of aromatic. However, they use hydroxy-functionality and blocked-isocyanates to form the urethane bonds. 89.3.3.2 Acrylic–Diacid (Glycidyl–Acrylic) Epoxy- (glycidyl-) functional acrylic resins can be compared to the hybrid systems discussed earlier. They are generally reacted with dicarboxylic acids or anhydrides. The most common cross-linker is 1,12-duo- decanoic acid (1,12-dodecane dioic acid). CH 2 N CH OH R1 C CH 2 CH R1 OH O CH 2 N CH HO R1 β-Hydroxyalkylamide Crosslink Intermediate Water COOH-Polyester C CH 2 CH R1 HO O R2" O C C HO R1 " C OH O C O OH + O C C R3 " C OH O C O OH O C C R3" C OH O C O OH CH 2 N CH O R1 CH 2 CH R1 O O C C R3 " C OH O C O OH O C C R3 " C OH O C O OH CH 2 N CH O R1 C CH 2 CH R1 O O C O R2 " H O H + Thermoset Powder Coatings 89 -11 89.4 Formulation 89.4.1 Resin Systems Formulation of thermoset powder coatings is much the same as that for liquid coatings used for similar purposes. A coating may be chosen for functional or decorative purposes. All of the coating types used in powder coatings can offer decorative options. Nonetheless, it is function that dictates system choice. The resin chemistry must be chosen to suit service needs. Various pigments, fillers, and additive materials are then included to enhance decorative or functional requirements. There are two primary functions for any protective coating. They are chemical protection and exterior durability. As with many coating properties, these two tend to be in opposition. The best systems for chemical protection are usually the poorest for exterior durability. Epoxy powder coating systems deliver the best chemical and corrosion resistance. However, they have the least effective exterior durability. The double bonds in the aromatic rings are easily broken by the ultraviolet (UV) light from the sun. Glossy finishes will go flat with as little as 6 months of exposure, with film degradation following soon thereafter. Urethane systems are also very good for chemical resistance, and they have fairly good exterior durability, as well. Hybrids offer good chemical resistance, however, the polyester component makes them less effective. They are also poor in relation to exterior exposure due to the epoxy portion of the cross- link network. Acrylic and TGIC powder coatings provide the best exterior durability. Some systems can survive for up to 20 years of exposure. They offer fair to good chemical resistance. Urethane systems seem to be the best compromise between chemical and exposure properties. As mentioned, they are very good in both areas. 89.4.2 Pigments and Fillers Most pigments and fillers used in liquid coatings are suitable for use in powder coatings. 11 There are only a few special requirements for use. They must be sufficiently heat stable so they withstand the heat of extrusion and curing without degradation or color change. Normally, the heat of extrusion is 125 ° C or less for a minute or two. The heat of cure is usually 160 to 200 ° C for 10 to 20 min. Second, they must be insoluble and nonreactive in the resin system. Blooming and color shift are the most common results from pigments that are partially soluble or reactive with the binder. Some epoxy system curing agents are especially susceptible to reaction with pigments. 89.4.3 Additives 12 89.4.3.1 Flow and Leveling Flow and leveling agents are designed to minimize surface defects such as craters, pinholes, and orange peel. The mechanism of their function alters the surface tension and rheology of the coating. The likelihood of a smooth defect-free film is improved by reducing one (or both) of these properties in a coating. Most flow and leveling agents are liquids. Many are blended with inert inorganic materials to offer them in a conveniently solid form. The chemistries of these are usually polyacrylates or polysiloxanes. A few new flow agents are available, however, in solid organic form. 89.4.3.2 Debubbling (Degassing) The most common debubbling agent is benzoin (2-hydroxy-1,2-diphenyl ethanone). It is used to keep the surface of a curing film open long enough to allow for entrained air and evolved gasses to escape. Tr apped air and gas bubbles are cause for premature failure of coating films, because they make the coating brittle. The one drawback to the use of benzoin is its tendency to cause yellowing in lighter colors. A number of new advances have entered the market in an attempt to match the efficiency of benzoin without the challenge of yellowing. DK4036_book.fm Page 11 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 89 -12 Coatings Technology Handbook, Third Edition 89.4.3.3 UV Inhibitors Var ious UV light inhibitors are available to aid coating resistance to degradation by the sun’s rays. The most common are hindered amines, phosphites, sulfates, and phenolics. Most will have some positive effect on any coating’s UV resistance. However, each system will require testing to determine the best combination of inhibitors. Some systems, like epoxies and hybrids, will not develop any substantial UV resistance due to their aromatic nature. 89.4.3.4 Catalysts Catalysts or accelerators are used to reduce the reaction time or curing temperature of the resin and cross-linker. They allow for faster production time by shortening the gel or “set” time of the thermosetting coating. Energy can be conserved, because full cure may be attained at lower oven temperatures. The most common catalysts are thiazoles (used in polyesters), phosphines and ammonium halides (used in epoxies), and thiocarbamates (used in urethanes). 89.5 End Uses The following table details some of the applications currently using the chemistries discussed in this chapter. References 1. Douglas S. Richart, “Powder coatings — A review of the technology,” Am. Paint & Coat. J., April 22 (1991). 2. P. G. Clements. Patent GB 643,691; 9/27/50, Schori Metallizing Process, Ltd. 3. E. Gemmer, Patent DE 933,019; 9/15/55, Knapsack-Griesheim AG. 4. E. Gemmer, Patent U.S. 2,844.489; 7/22/58, Knapsack-Griesheim AG. 5. Patent GB 915,575. 6. E. P. Miller, “Electrostatic finishing methods,” paper presented at the Annual Meeting of the National Paint, Varnish, & Lacquer Association, Colorado Springs, CO, September 12, 1963. 7. D. A. Bates, The Science of Powder Coatings , Vol. 1. London: Scholium Intl., 1990. 8. Statistics from Powder Coatings Institute, Alexandria, VA. 9. Rohm and Haas Brochure 82F2, Primid XL-552 — A Novel Crosslinker for Powder Coatings, 1990. 10. Pulverizing Machinery (product brochure), Mikropul Corp., Summit, NJ. 11. R. Campbell and R. Kumar, “Organic pigments for powder coatings,” Am. Paint & Coat. J., April 22 (1991). 12. Josef H. Jilek, Powder Coatings (monograph). Blue Bell, PA: Federation of Societies for Coatings Te c hnology, 1991. Type Typical Applications Epoxy Shelving, transformer cases, primers, bathroom fixtures, refrigerator racks, sweepers, sewing machines, power tools, room air conditioners, office furniture, instrument cases, garden tools, kitchen furniture, fire extinguishers, toys, refrigerator liners, dryer drums, microwave ovens, mixers and blenders, fertilizers spreaders, screening, oil filters, automobile springs, hospital equipment, bus seat frames, business machines, glass bottles Hybrids Tool boxes, farm equipment, electrical control boxes, hot water heaters, hot water radiators, primer/surfacers, grain storage bins, transformer covers, 01.1 filters and air cleaners, air conditioner housings, fire extinguishers, toys, screening wire, power tools, shelving, office furniture Urethane Fluorescent light fixtures, steel and aluminum wheels, patio furniture, playground equipment, fence fittings, chrome wheels and trim, garden tractors, range side panels and broiler, ornamental iron, air conditioner cabinets, restaurant furniture supports, transformer cases TGIC Irrigation pipe and fixtures, outdoor furniture, air conditioning units, steel and aluminum, wheels, wire fencing, fence poles and fittings, farm equipment, aluminum extrusions, transformers Acrylic Range side panels, refrigerator cabinets and doors, washing machine parts, dishwasher exterior, aluminum extrusions, microwave ovens, garden tractors, automotive trim coating DK4036_book.fm Page 12 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 90 -1 90 Peelable Medical Coatings 90.1 Introduction 90- 1 90.2 Cold-Seal Coatings 90- 2 90.3 Heat-Seal Coatings 90- 2 90.1 Introduction Prepackaged sterile medical devices and supplies became necessary in the late 1960s with the growth in prepaid health insurance programs. Insurers required that health care providers itemize the cost of all the supplies used during a procedure. This led to the rapid growth in the development of disposable or single-use devices. These were packaged in paper/plastic pouches, trays, or containers and then sterilized. At the time of use, the package was torn open to expose the sterile device. When the package was torn, the device was showered with particulates and bacteria that caused a great deal of concern. At that time, the medical device industry was not regulated by the U.S. Food and Drug Administration (FDA). In 1968, the E. I. DuPont Company introduced a polyethylene, paperlike material (Tyvek ® ) that had most of the properties needed for packaging medical devices. Tyvek is a unique material that meets almost all of the critical requirements for medical packaging. It is a good bacterial filter — very porous, water- resistant, and puncture- and tear-resistant. Being made from polyethylene, it is stable during both ethylene oxide gas and radiation sterilization. It does not stand up well during steam sterilization, so only a few adhesives have been developed for this purpose. With an acceptable packaging material available, peelable coatings were developed to seal Tyvek to plastic films or thermoformed trays to form pouches and trays that could be peeled open at the point of use without compromising the sterility of the device. There are five basic types of adhesives used to seal Tyvek to plastic surfaces to form sterile packages. These are cold seal, lacquer-based heat seal, water-based heat seal, hot-melt-based heat seal and low- density polyethylene. All of these adhesives are very difficult to formulate and apply so that they meet all of the requirements of the medical device manufacturers. Some of the requirements these adhesives must meet are as follows: •Must peel cleanly without generating particles •Have a peel strength over 1 lb per inch of width and less than 3 lb per inch of width regardless of the peel angle •Be very stable both before and after sterilization (shelf life requirements can be as long as 10 years) •Meet the U.S. Pharmacopoeia requirements for medical device plastics Donald A. Reinke Oliver Products Company (Retired) DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Peelable Medical Coatings 90 -3 integrity has been maintained. A clear track through the seal area will cause the package to be rejected, because there is a path for bacteria to enter the package. Formulating a coating that is nontoxic and strong, with good hot tack and good adhesion to a variety of plastic surfaces, and that is able to peel with a controlled peel strength, is a difficult task. Several methods have been used to achieve peelability. The use of primer coats between the adhesive and the substrate is the one most often chosen; this creates a parting layer between the adhesive and the substrate. Release coating on the substrate surfaces are also used when paper is used instead of Tyvek. Most people in the industry feel that the best method is to have an adhesive with a controlled cohesive strength. When the package is peeled open, the adhesive will split with a controlled force that is below the delamination strength of the substrate. By using this method, the surface fibers of the substrate are not raised or broken. Cohesive failure of the adhesive can be achieved by formulating an adhesive that has two phases: one a strong adhesive to hold the package together and the other a weak friable material that breaks up the structure of the first phase. By varying the percentage of the two phases, the cohesive strength of the coating can be controlled within narrow limits. The nature of peelable medical packaging materials is currently undergoing a change. There is a drive to reduce the cost of medical devices, causing a shift to paper and away from Tyvek. Also, environmental concerns are pressuring medical device companies to use some method other than ethylene oxide gas sterilization. The requirement for a peelable package, however, remains strong. The medical device industry is now under the control of the FDA, which requires complete validation of processes and materials. Formulating and validating a new adhesive will generally take from 1 to 3 years. For this reason, packagers of medical devices are very reluctant to change suppliers. They do not have the engineering staff they had in the earlier years when the industry first started. To change an adhesive and develop the documentation required by the FDA is very expensive. Most companies have alternate suppliers they can use if they have problems. Further information on medical device packaging can be found in the proceedings of the Technical Association of the Pulp and Paper Industry’s Coatings and Laminations conferences during the years from 1980 through 1987. DK4036_book.fm Page 3 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 91 -1 91 Conductive Coatings 91.1 Introduction 91- 1 91.2 91.3 Commercially Available Conductive Coatings 91- 5 91.4 Applications 91- 6 91.5 New Developments 91- 7 References 91- 8 91.1 Introduction In 1986, sales in the coatings industry exceeded $10 billion, and production approached a billion gallons. 1 The breakdown of sales was $4.1 billion for architectural coatings, $3.5 billion for industrial coatings, and $2.4 billion for specialty coatings. Conductive coatings — a minuscule part of these trade sales — have been used both as industrial coatings and as specialty coatings. Regulations of the Federal Com- munications Commission (FCC), in Docket No. 20780, which regulates electromagnetic emissions from computing devices, have provided a strong impetus for the commercial development of conductive polymeric materials (including coatings and paints). Since October 1, 1983, it has been necessary for any computing device that generated signals or pulses in excess of 10 kHz to comply with the emission standards set forth in the docket. Although conductive polymeric coatings have made inroads in areas where metallic coatings previously were used, progress has been slow. A product related to conductive coatings is metallized plastic. The most important commercial pro- cesses for metallizing plastics are electroless plating, metal spraying, sputtering, and vacuum metallizing. The first commercial plating of plastics was recorded in 1905. 2 Metallizing of plastics occurred during World War II, and large-scale production started in the early 1960s. All these processes are now multi- million-dollar industries. Large quantities of plastics are metallized each year, with automotive items making up more than 60% of the market on a plated area basis. 3 There are various reasons for metallizing plastics. In the automotive industry, metallized plastic combines the consumer appeal of metal with light weight. Electroless copper metallization is an indis- pensable part of the modern electronics industry. Printed circuit boards use electroless copper to coat nonconductive plastic surfaces to define the circuit patterns. Zinc arc and flame-spray techniques provide electromagnetic interference shielding on many plastics. The plastics that account for most of the sub- strates metallized are acrylonitrile-butadiene-styrene (ABS), polypropylene, polyphenylene oxide, epoxies, phenolics, polyimides, and polyesters. The commercial process for metallization of plastics merits separate discussion and is not further considered in this chapter. Polymers (coatings) with conductivities greater than 1( Ω cm) –1 are defined as conductive polymers (also metallically conducting plastics, synmetals). 4 Unfortunately, the literature is not clear-cut, and often, materials that are semiconductors with conductivities less than 1( Ω cm) –1 are also called “conducting.” Raimond Liepins Los Alamos National Laboratory DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Metallic • Filled Polymeric • Polymeric • Organometallic Shielding from Electromagnetic Interference • The Stealth • Types of Conductive Coatings 91-2 Miscellaneous 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. [...]... Group, LLC DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM 96 Solgel Coatings 96.1 Introduction 96-1 96.2 The Solgel Process .96-1 96.3 Thin Film Applications 96-2 Lisa C Klein Rutgers–The State University of New Jersey Optical Coatings • Electronic Coatings • Abrasion Coatings • Protective Coatings • Porous Coatings • Composites 96.4 Advantages 96-3 Bibliography ... 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. .. 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. .. of release for the UV epoxy silicone coatings have remained elusive Another problem associated with these cationic cure silicone materials is substratedependent performance Excellent cure, anchorage, and release are obtained when corona-treated films © 2006 by Taylor & Francis Group, LLC DK4036_C092.fm Page 10 Thursday, May 12, 2005 9:55 AM 92-10 Coatings Technology Handbook, Third Edition 20 F S McIntyre... such as microwave, infrared, and gamma rays can be used to cure coatings However, this chapter is only concerned with electron beam and ultraviolet light radiation, which are the most important commercial processes 97-1 © 2006 by Taylor & Francis Group, LLC DK4036_book.fm Page 4 Monday, April 25, 2005 12:18 PM 97-4 Coatings Technology Handbook, Third Edition H H hν C—C C• O C• + O OR Benzoin Alkyl... 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... 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,... fluids Because these resins are normally friable solids when isolated, their blends with vinyl © 2006 by Taylor & Francis Group, LLC DK4036_C092.fm Page 8 Thursday, May 12, 2005 9:55 AM 92-8 Coatings Technology Handbook, Third Edition radiation cure of silicones requires silicone polymers incorporating radiation-sensitive organofunctional groups, as illustrated below: CH3 CH3 SiO CH3 SiO n X m X = mercaptan,... 96.1 Introduction Solgel processing is now well accepted as a technology for thin films and coatings Indeed, the solgel process is an alternative to chemical vapor deposition, sputtering, and plasma spray Not only have solgel thin films proved to be technically sound alternatives, they have been shown to be commercially viable, as well The technology of solgel thin films has been around for over 30 years... equipment is inexpensive, especially in comparison to any deposition techniques that involve vacuum Coatings can be applied to metals, plastics, and ceramics Typically, the coatings are applied at room temperature, though most need to be calcined and densified with heating Both amorphous and crystalline coatings can be obtained 96.2 The Solgel Process The solgel process is the name given to any one of . Francis Group, LLC Optical Coatings • Electronic Coatings • Abrasion Coatings • Protective Coatings • Porous Coatings • Composites 97 -1 97 Radiation-Cured Coatings 97.1 Introduction. coatings, and $2.4 billion for specialty coatings. Conductive coatings — a minuscule part of these trade sales — have been used both as industrial coatings and as specialty coatings. Regulations of the Federal. 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