Document vV6GvxaRypYq60ovnQOdRJk28

a im nO -r Do In -e Jr.J-. th C cf . f- <f~./-- L> = /"V sn j S/v^/ t, /f <h L) V/ t/ Stsl/. /v\ & f^s-A /*$ -C- PROPOSED PUBLICATION FROM THE FABRICS & FINISHES DEPARTMENT % MODERN DEVELOPMENTS IN ORGANIC COATiNG TECHNOLOGY BY SEYMORE HOCHSERG We submit for your informofIon and comment a proposed paper on Modem Developments in Organic Coating Technology. This paper has been prepared for ora! presentation at a meeting on Frontiers of Science in Industry in Israel during the week of March 10, 1974. The paper will not be published. There is no proprietary information involved; no patent applications are contemplated on the material. We will be pleased to have any comments or suggestions that you cere to make. Unless we hear from you by March 4 we will assume you have no objections. SH/meg 2/22/7A R. W. LAURRELL R&D Manager 2/4/1 ij N42558.01 DUP030024767 MODERN DEVELOPMENTS IN ORGANIC COATING TECHNOLOGY BY SEYMORE . HO.CHBERG * CURRENT OBJECTIVES OF RESEARCH AND DEVELOPMENT: The bulk of surface coatings are used for the protection and decoration of substrates. Such specialties as fire-resistant coatings, insulation for wires, and coatings for magnet tape are somewhat smaller in volume but not insignificant. For many years the major objectives of Research and Development have been the improvement of quality, reduction in cost, new appearance effects, and enlargement of the market by extension to substrates not currently coated. While the traditional objectives are always kept in mind during continuing research and development activities, they appear now to have taken a secondary position relative to a response to certain emergencies which may turn out to be of long duration. The emergency situations are the social drives`and the consequent laws regarding toxic hazards, the problem of water and air-pollution, the recent and anticipated, shortages of fluid fuels, and the shortage of chemical products derived from petroleum. STATE CF THE ART WITH RESPECT TO: . A. QUALITY 1. Outdoor Durability - The quality of automotive finishes i is such that ten-year durability is readily achieved. The coatings can last longer than the automobiles themselves, provided one is content with a wide but limited color range. House paints properly applied over durable substrates have similar long life compared with the Substrates. Coatings for aluminum and steel strip carry long term warranties against fading and peeling, and they are expected to survive. There is little incentive for improvement of durability to exposure. Incentives for cost reduction always exist, however. * 2. High-Temperature Resistance-Coatings for wire are available in a series of classes in accordance with temperatures of use. Continuous use of over 220G with good mechanical cut-through properties can. be obtained with aromatic polyimides. At this temperature the usual metals fail by oxidation. No incentive exists for improvements above the quality of aromatic polyimides. 1 N42558.02 DUP030024768 3, Resistance to Household Deteriorating Influence-Home appliances can be coated with a variety of products which will not fail in many years of service. There is not incentive to improve colorstability, staining, resistance to grease, or resistance to soap and hot water for any of the home appliances now used. 4. Coatings for Pots and Pans-Coatings of polytetrafluoroethylene or kitchenware yield the best food release we know how to obtain. While substantial improvements can be envisaged over the polytetrafluoroethylene in scratch and stain resistance, there appears to be little hope of producing the hard, yet formable, stain-repellent material needed. 5. Maintenance Coatir.gs~Coatings for tanks, bridges, and other heavy steel construction can use some improvement. At present, the chief weakness of such finishes would appear to be related to the prepar ation of the surface for painting. Painting over rust or loose surfaces is the cause of early failure no matter what is put on top. Improvements in quality over traditional materials for these markets is apt to be small, it would be different to demonstrate and important competitively perhaps in isolated instances but not . important on a social basis. Incentives exist for reductions of cost particularly for less vigorious exposures, . B. APPEARANCE: . A wide range of colored pigments and their metallic modifica tions with aluminum pigment make possible the wide variety of automotive colors. In addition, various textures are possible through the use of large pigment particles, coarse incompatible pigment dispersions of contrasting colors and mechanical methods of introducing texture. High degrees of iridescence, as with liquid cholesteric crystals, are not ~-l yet on a practical basis, but might capture a significant market. - The iridescent, plate-like, pigment "Afflair" has some of the qualities of aluminum but it is not as bright. C. NEW SUBSTRATES: The need for painting soft substances*, in resulting in a flurry of activity. The soft substrates are plastic and rubbery materials now required in automobiles. Current materials do not perform satisfact orily over the required temperature range or are not sufficiently durable. 2 RECENT DEVELOPMENTS TO REDUCE COSTS OF MANUFACTURE AND IMPROVE QUALITY OF ORGANIC COATINGS: 1. Computers are being used to predict the course of poly merizations and .to make adjustments in processing in order to tailor-make polymers with desired properties. Not only can the molecular weight and copolymer composition be predicted, but the fine-structure of the polymer, represented by sequences in a given polymer chain, can be engineered. 2. Computers are being used to control color and to guide shading operations to yield matches of high quality with a minimum number of trial additions. Kubelka-Munk theory is used. 3. Computers are being used to provide minimum-cost solvent mixtures consistent with solvency and volatility requirements and instantly adjustable for changing market conditions. The prediction of solvency is made by using solvency parameters recently developed by Hansen and others. However, the solvency parameters have their limitations, particu larly when mixtures of polymers are involved, and particularly when the mixtures are themselves incompatible in a thermodynamic sense, but slowly separated. - 4, The high cost of white titanium dioxide pigments is resulting in research to produce small polymeric beads containing air and combinations of air with pigment. Air-droplets scatter light as a pigment does. Titanium dioxide scatters more light in an air medium than in a polymer medium. The porous polymeric beads containing titanium dioxide can conceivably save money over conventional methods of using titanium dioxide. RECENT R&D RESPONSE TO LAWS REGARDING LEAD AND MERCURY: Laws are in force to protect the consumer from the hazards of lead poisoning. Paints for sale to consumers are limited in their content of lead. Other metals are sure to be restricted, and the restrictions on lead are likely to be strengthened. Red lead, used as a standard metal--protective paint for the maintenance of ironwork, cannot be purchased in paint by the usual consumer. Other lead compounds used to prevent bleeding of colored aqueous extracts from wood can no longer be used. Substitutes for durable colored lead pigments-the chromates-are being found in expensive organic reds and yellows. 3 DUP030024770 Mercury is an effective fungicide for use in paints exposed to humid environments. It has long been used as phenyl-mercury compounds. Substitutes must be found. The search for such substitutes is time-consuming and apt to be misleading. There are at this time no foolproof materials like mercury for this purpose. * .. R&D RESPONSE TO REGULATIONS RESTRICTING . DISCHARGE OF CHROMATES AND OTHER MATERIALS FROM PLANTS: Chromates are used in pretreatments to clean aluminum and steel and provide on them an adherent layer which reduces corrosion and adheres to paint topcoats better than the metals alone. The washings are of large volume and can no longer be discharged into certain streams. The substitute treatments do not appear to provide the same degree of protection reliably. A considerable effort is expended on measurement of the wastes leaving plants in aqueous streams. RESPONSE OF R&D TO AIR-POLLUTION REGULATIONS: Air-pollution by indus'try is regulated by local and national agencies. Industrial users of paint promptly tui'ned the problem over to paint manufacturers. The regulations, of which the famous Los Angeles Rule 66 is a prime example* usuall3T differentiate between photochemically~ active and photochemically-inactive solvents. Solvents are put into classes depending on their potency - olefinic hydrocarbons are particularly bad* Limits are established on the emission of photochemically-active and inactive materials. Most individual paints had high percentages of solvent itfhieh were non-conforming to Rule 66. Exemptions from"Rule 66 Were established for aqueous finishes and others containing no more than 20% by volume of non-photochemically-active organic solvent provided thesolvent vapors do not contact flame. The response of R&D has been to concentrate on exempt type finishes i.e., less than 20% solvent (photochemically-inactive) and to convert the non-conforming current types of solvent mixtures to conforming ones by substitution of relatively innocuous for relatively obnoxious solvents. The exempt-type finishes are the so-called high-solids finishes, the aqueous finishes, and powder finishes. 4 DUP030024771 ORGANIC SOLVENT - BASED FINISHES OF HIGH SOLIDS AND THEIR APPLICATION: Enamels: Low molecular weight polymers which are crosslinked during baking are made at the lowest practical molecular weight and diluted with a minimum of solvent of conforming (Rule 66) types. Pigments are dispersed in the solutions. The quantity of solvent can be reduced and can be limited to aliphatic hydrocarbons if the polymers are stabilized against flocculation in hydrocarbon. The finishes usually comprise low molecular weight hydroxyl-terminated polyesters mixed with low molecular weight melamine-formaldehyde or capped diisocyanates or polyisocyanates,, Lacquers: Relatively high molecular weight polymers are dispersed in predominately aliphatic hydrocarbons using graft copolymers as dispersing agents. Pigments are dispersed separately. On evaporation of solvent the polymer particles coalesce. Another type of high solids finish contains high-boiling solvents which .are converted to polymeric materials after application to a substrate. Hie mechanism of conversion is usually exposure to ultra violet light or high-speed (ionizing) electrons. The organic-solvent based finishes are applied by spray, automatic or manuals can be sprayed and deposited electrostatically, and can be applied by rollers. . AQUEOUS FINISHES ; Lacquers; Ammonium salts of carboxyl-terminated polymers, usually with small amounts of auxiliary solvents, are applied by spray from relatively dilute aqueous solution. The films lose water-sensitivity on evaporation of ammonia. The polymer can be used in latex from or as micellar solutions. Enamels: Somewhat more concentrated dispersions of lower molecular weight, hydroxylated polymers are combined with melamine resins and pigment dispersions. These convert on heating to insoluble crosslinked form. Other drying mechanisms might be used. Aqueous finishes can be applied by conventional spray and dip methods. Special electrocoating methods have been developed. 5 el ec t r o c o at in g : Anodic Deposition A dilute dispersion of salts of cax^oxylated polymers is mixed with a crosslinking agent and pigments. The viscosity is barely greater than that of water. The passage of electric current through the bath of the. substrate, which is the anode, deposits a viscous mixture of vehicle ana pigment on the substrate. Coalescence of the polymer produces a film of low conductivity which limits the thickness of the deposit. The substrate is drawn from the bath with only a minor amount of entrained, uncoalesced paint. This is rinsed off. The deposit which is left on the substrate is baked to convert it to insoluble form. The electromotive force for electrodeposition is about 100-500 volts and the e.m.f. is much higher than that required for electrolytic reactions. It results in electrophoresis of the negatively charged particles toward the anode. At the anode, acids are produced through electrolysis of water, and metals are dissolved from the electrode. The acids and the metals destabilize the mixture and a viscous, slimy mass is. deposited on the anode. '..If the acidified polymer can coalesce (a Tg bath temp) it will form a coating of low conductivity and limit the thickness of the applied coating# When the deposition stops the e.m.f. across the coating will equal the applied e.m.f, and the potential gradient will be 10,000 to 100,000 volts/inch. .. The acidified deposited polymer is initially laden with water, but the flow of current causes some of the water to leave by a process of electroendosmosis, producing a denser deposit than that produced by acidification alone. .. Oxygen liberated at the anode forms bubbles in the deposit. ' The deposits are therefore initially rough. A smooth system can be obtained only if the deposited film is sufficiently fluid to smooth out by forces of surface tension. Under these conditions, edges, which are preferred positions for the initial deposit, may be left uncovered. Cathodic Deposition 1 rTM'7" ' ' m* The substrate to be coated is made the cathode. The polymer is usually in the form of polymeric amine, solubilized as a salt. 6 DUP030024773 POWDER COATINGS AND THEIR APPLICATION; Powder coatings are made of particles of 10-30 microns diameter each of which contains the pigment and the binder. The binder will usually comprise a low-molecular--weight, brittle, resin mixture which is stable enough at room temperature but which melts and reacts at oven temperatures to produce a high-molecular weight, tough polymer as required. The manufacture of powders requires the development of manufacturing techniques to yield suitable size, suitable color, and suitable flew properties and reactivity in the oven. The finished coating must also meet the service requirements. Epoxy resins and hydroxyl-containing acrylic resins or hydroxylated polyesters areused with appropriate reactive crosslinking agents. Powder coatings can be applied to a hot object by dipping it into a fluidized bed of the powder. The powder melts and sticks to the surface. The thickness depends on the local heat capacity and temperature of the object being coated. Thick coatings are readily applied by fluidized bed techniques. Thin coatings are applied by Spraying the powder, charging it electrically, and attracting it to the surface by electrostatic forces. As the powder collects, its charged particles tend to reduce the electric field, and this limits the thiekiless. The conductivity of powders determines the film thickness and must be controlled between certain limits. The application of powders for protection alone is done fairly easily, but decorative applications are difficult for a variety of reasons. Once coated and coalesced a surface can be difficult to reeoat by electrostatic deposition. ., Part of the problem with obtaining good appearances with powders is that the density of the applied powder is low, containing much air. The coalescence of the particles causes shrinkage -- not necessarily all away from the surface. Furthermore, gases are often liberated by crosslinking reactions. While smoothing by surface tension proceeds, the polymer hardens. Smoothness equivalent to that of solution applied coatings, therefore, is difficult to achieve. Powders are also available for application as dispersions in water. Such povjders can conceivably yield denser films. 7 IMPACT OF THE NEW AIR POLLUTION REGULATIONS ON FINISHES SALES: Within the last ten years the pattern of industrial finishes 'sales has changed significantly away from solvent'-thinned paints. The regulations will accelerate the change. In 1975, while solvent-thinned paints will probably still represent the majority of the Industrial paint sold, the sales of alternates will represent a substantial fraction. (See Figure 1, 2, 3, quoted from Industrial Finishing and Surface Coating, pp, 14, 15 Aug. 1973). Sales of paint to ultimate consumers will he affected less by the air-pollution regulations because the more obnoxious solvents were eliminated from these paints years ago. RESPONSE OF R&D TO POWER SHORTAGE: The shortage of power makes it necessary to reduce baking temperatures. Usually in one-package systems when reactivities are high at low baking temperatures, stability in storage is poor. The conventional air-drying oil-based systems are in reality two package systems of which one package is air. Moisture-cure, (making use of atmospheric water-vapor) of isocyanate terminated polymers, ultra-violet radiation cure, and electron-beam irradiation of vinyl monomers act like two--package systems. They are stable at room temperature, yet react rapidly under certain conditions at room temperature. Hr 8 DUP030024775  SPECIAL PROBLEMS WITH AQUEOUS FINISHES; 1. Reactivity of aluminum flake. * 2. Spraying problems with electrostatic equipment 3. Humidity control in drying. 4. Heat requirement for evaporation of water 5. Corrosion of equipment. 6. Salt-content. 7. Hydrophilic even when dry, 8. Cross-linking mechanisms need improvement. WITH ELECTROCOATING: 1. Investment in equipment, - 2. Bath composition changes - Pigment, Solvents, Binder, Sait!, Acid-base balance. 3. Control of bath composition not simple - Flushed cathodes (or anodes), reverse osmosis. , 4. Contamination with materials dragged in by the substrate. 5, Anodic electrocoating dissolves metal from the electrodes, including metal pretreatments, yielding color and poorer pretreatment surface. This is not true of cathodic deposition. 6, Gases form at the substrate, 7, Washings must be recovered (reverse osmosis). WITH POWDER COATINGS: 1. Clean-up between colors is expensive, 2. Metallic colors lack brightness, 3. Electrostatic fields do not enter cavities, 4. Recoating can be difficult. 9 DUP030024776 WITH ULTRA VIOLET CURE: 1* Line of sight cure. r'{ 2, Pigments, oxygen, exudates from substrates - interfere with polymerization. 3. Ozone, heat. WITH ELECTRON-REAM CURE; 1 Pigments, oxygen, exudates from substrates interfere, 2. Large capital investment. 3. Dangerous X-rays produced. % 10 DUP030024777 FIGURE I U. S. PAINT INDUSTRY MARKET SIZE - MILLION GALLONS * Industrial Trade Sales Total 1966 421 416 837 1968 424 419 843 1970 399 . 428 827 1971 443 431 874 1972 485 465 950 1975* 525 515 1040 1980* 630 595 1225 ^ESTIMATES C. H. Kline & Co. Marketing Guide to the Paint Industry. Industrial Finishing and Surface Coatings (Aug. 1973) pp. 14, 15 ,6 11 DUP030024778 FIGURE II U. S. PAINT INDUSTRY MARKET SIZE - MILLION GALLONS ,, ! 1 "*r'" ~ 1 1 INDUSTRIAL SALES Solvent Thinned Air Dry or Force Dry Bake Water Thinned Air Dry or Force Dry Bake 1966 1968 1970 1972 ' 1975* 131 278 128 262 123 234 103 296 98 227 3 5.5 5 ' 20 . 5 .34 8 18 73 162 Powder Epoxy Polyes ter Other 1 1 1 1.5 5.0 0.2 1.0 2.5 3 3 3.3 6.0 ^ESTIMATE C. H. Kline & Co. Marketing Guide to the Paint Industry Industrial Finishing and Surface Coating (Aug, 1973) pp. 14, 15 12 DUP030024779 Solvent Thinned Interior Exterior Water Thinned Interior Exterior Other Solvent Thinned Total FIGURE III U. S. TRADE SALES MARKET tf 1966 1968 1970 '74 92 60 75 . 58 62 1972 45 53 1975* j 9 28 136 <1 51 63 41.6 159 66 60 419 170 72 61 428 212 91 64 465 223 115 40 515 ' ' ^ESTIMATE C. H. Kline & Co. Guide to the Paint Industry Industrial Finishing and Surface Coatings (Aug. 1973) pp, ,14, 15 . ** -> 13 DUP030024780  .y^V/ijk ^v.>*iy..v,v.y\>S!y'V.-.w.v.s<:.>:t-.......^ Du J>ont de Nemours, I. , & bo. F & F Dept. UD, Division, Mar. Lab. Pro* pntes. Modern de velopments in organic coating technology, by jgeymore Hochberg. 1974 * 1 DATE ISSUED TO 1 /ft 77 /T'/Oi^vK/v 9=-^~ S7-/=i - 0/^f-/^. /np*r?if'ovt &K 735 X- /v _S>/w /n .S' * GAYLORD 40 DUP030024781 1 PATE ISSUED TO I 1 1 f DUP030024782 CURRENT OBJECTIVES OF RESEARCH AND DEVELOPMENT: The bulk of surface coatings are used for the protection and decoration of substrates. Such specialties as fire-resistant coatings, insulation for wires, and coatings for magnet tape are somewhat smaller in volume but not insignificant. For many years the major objectives of Research and Development have been the improvement of quality, reduction in cost, new appearance effects, and enlargement of the market by extension to substrates not currently coated. While the traditional objectives are always kept in mind during continuing research and development activities, they appear now to have taken a secondary position relative to a response to certain emergencies which may turn out to be of long duration. The emergency situations are the social drives and the consequent laws regarding toxic hazards, the problem of water and air-pollution, the recent and anticipated shortages of fluid fuels, and the shortage of chemical products derived from petroleum. STATE OF THE ART WITH RESPECT TO; A. QUALITY 1. Outdoor Durability - The quality of automotive finishes is such that ten-year durability is readily achieved. The coatings can last longer than the automobiles themselves, provided one is content with a wide but limited color range. House paints properly applied over durable substrates have similar long life compared with the substrates. Coatings for aluminum and steel strip carry long term warranties against fading and peeling, and they are expected to survive. There is little incentive for improvement of durability to exposure. Incentives for cost reduction always exist, however. 2. High-Temperature Resistance-Coatings for wire are available in a series of classes in accordance with temperatures of use. Continuous use of over 220C with good mechanical cut-through properties can be obtained with aromatic polyimides, At this temperature the usual metals fail by oxidation. No incentive exists for improvements above the quality of aromatic polyimides. 1 DUP030024783 3* Resistance to Household Deteriorating Influence-Home appliances can be coated with a variety of products which will not fail in many years of service. There is not incentive to improve colorstability, staining, resistance to grease, or resistance to soap and hot water for any of the home appliances now used. 4. Coatings for Pots and Pans-Coatings of polytetrafluoroethylene or kitchenware yield the best food release we know how to obtain. While substantial improvements can be envisaged over the polytetrafluoroethylene in scratch and stain resistance, there appears to be little hope of producing the hard, yet formable, stain-repellent material needed. 5. Maintenance Coatings-Coatings for tanks, bridges, and other heavy steel construction can use some improvement. At present, the chief weakness of such finishes would appear to be related to the prepar ation of the surface for painting. Painting over rust or loose surfaces is the cause of early failure no matter what is put on top. Improvements in quality over traditional materials for these markets is apt to be small, it would be different to demonstrate and important competitively perhaps in isolated instances but not important on a social basis. Incentives exist for reductions of cost particularly for less vigorious exposures. B, APPEARANCE; A wide range of colored pigments and their metallic modifica tions with aluminum pigment make possible the wide variety of automotive colors. In addition, various textures are possible through the use of large pigment particles, coarse incompatible pigment dispersions of contrasting colors and mechanical methods of Introducing texture. High degrees of iridescence, as with liquid cholesteric crystals, are not yet on a practical basis, but might capture a significant market. The iridescent, plate-like, pigment "Afflair" has some of the qualities of aluminum but it is not as bright. C. NEW SUBSTRATES; The need for painting soft substances in resulting in a flurry of activity. The soft substrates are plastic and rubbery materials now required in automobiles. Current materials do not perform satisfact orily over the required temperature range or are not sufficiently durable. 2 RECENT DEVELOPMENTS TO REDUCE COSTS OF . MANUFACTURE AND IMPROVE QUALITY OF ORGANIC COATINGS: 1. Computers are being used to predict the course of poly merizations and to make adjustments in processing in order to tailor-make polymers with desired properties. Not only can the molecular weight and copolymer composition be predicted^ but the fine-structure of the polymer, represented by sequences in a given polymer chain, can be engineered. 2. Computers are being used to control color and to guide shading operations to yield matches of high quality with a minimum number of trial additions. Kubelka-Munk theory is used. 3. Computers are being used to provide minimum-cost solvent mixtures consistent with solvency and volatility requirements and instantly adjustable for changing market conditions. The prediction of solvency is made by using solvency parameters recently developed by Hansen and others. However, the solvency parameters have their limitations, particu larly when mixtures of polymers are involved, and particularly when the mixtures are themselves incompatible in a thermodynamic sense, but slowly separated. 4, The high cost of white titanium dioxide pigments is resulting in research to produce small polymeric beads containing air and combinations of air with pigment. Air-droplets scatter light as a pigment does. Titanium dioxide scatters more light in an air medium than in a polymer medium. The porous polymeric beads containing titanium dioxide can conceivably save money over conventional methods of using titanium dioxide. RECENT R&D RESPONSE TO LAWS REGARDING LEAD AND MERCURY: Laws are in force to protect the consumer from the hazards of lead poisoning. Paints for sale to Consumers are limited in their content of lead. Other metals are sure to be restricted, and the restrictions on lead are likely to be strengthened. Red lead, used as a standard metal-protective paint for the maintenance of ironwork, cannot be purchased in paint by the usual consumer. Other lead compounds used to prevent bleeding of colored aqueous extracts from wood can no longer be used. Substitutes for durable colored lead pigments-the chromates-are being found in expensive organic reds and yellows. DUP030024785 Mercury is an effective fungicide for use in paints exposed to humid environments. It has long been used as phenyl-mercury compounds. Substitutes must be found. The search for such substitutes is time-consuming and apt to be misleading. There are at this time no foolproof materials like mercury for this purpose. R&D RESPONSE TO REGULATIONS RESTRICTING DISCHARGE OE CHROMATES AND OTHER MATERIALS PROM PLANTS: Chromates are used in pretreatments to clean aluminum and steel and provide on them an adherent layer which reduces corrosion and adheres to paint topcoats better than the metals alone. The washings are of large volume and can no longer he discharged into certain streams. The substitute treatments do not appear to provide the same degree of protection reliably. A considerable effort is expended on measurement of the wastes leaving plants in aqueous streams. RESPONSE OF R&D TO AIR-POLLUTION REGULATIONS: Air-pollution by industry is regulated by local and national agencies. Industrial;:users of&paipt promptly turned the problem over to paint manufacturers. The regulations, of which the famous Los Angeles Rule 66 is a prime example, usually differentiate between photochemicallyactive and photochemically-inactive solvents. Solvents are put into classes depending on their potency - olefinic hydrocarbons are particularly bad. Limits are established on the emission of photochemically-active and inactive materials. Most individual paints had high percentages of solvent which were non-conforming to Rule 66, Exemptions from Rule 66 were established for aqueous finishes and others containing no more than 20% by volume of non-photochemically-active organic solvent provided the solvent vapors do not contact flame. The response of R&D has been to concentrate on exempt type finishes i.e., less than 20% solvent (photochemically-inactive) and to convert the non-conforming current types of solvent mixtures to conforming ones by substitution of relatively Innocuous for relatively obnoxious solvents. The exempt-type finishes are the so-called high-solids finishes, the aqueous finishes, and powder finishes. 4 DUP030024786 ORGANIC SOLVENT - BASED FINISHES OF HIGH SOLIDS AND THEIR APPLICATION: Enamels: Low molecular weight polymers which are crosslinked during baking are made at the lowest practical molecular weight and diluted with a minimum of solvent of conforming (Rule 66) types. Pigments are dispersed in the solutions. The quantity of solvent can be reduced and can be limited to aliphatic hydrocarbons if the polymers are stabilized against flocculation in hydrocarbon. The finishes usually comprise low molecular weight hydroxyl-terminated polyesters mixed with low molecular weight melamine-formaldehyde or capped diisocyanates or polyisocyanates. Lacquers: Relatively high molecular weight polymers are dispersed in predominately aliphatic hydrocarbons using graft copolymers as dispersing agents. Pigments are dispersed separately. On evaporation of solvent the polymer particles coalesce. Another type of high solids finish contains high-boiling solvents which are converted to polymeric materials after application to a substrate. The mechanism of conversion is usually exposure to ultra violet light or high-speed (ionizing) electrons. The organic-solvent based finishes are applied by spray, automatic or manual, can be Sprayed and deposited electrostatically, and can be applied by rollers. AQUEOUS FINISHES: Lacquers: Ammonium salts of carboxyl-terminated polymers, usually with small amounts of auxiliary solvents, are applied by spray from relatively dilute aqueous solution. The films lose water-sensitivity on evaporation of ammonia. The polymer can be used in latex from or as micellar solutions. Enamels: Somewhat more concentrated dispersions of lower molecular weight, hydroxylated polymers are combined with melamine resins and pigment dispersions. These convert on heating to insoluble crosslinked form. Other drying mechanisms might be used. Aqueous finishes can be applied by conventional spray and dip methods. Special electrocoating methods have been developed. 5 DUP030024787 ELECTROCOATING: Anodic Deposition A dilute dispersion of salts of carboxylated polymers is mixed with a crosslinking agent and pigments. The viscosity is barely greater than that of water. The passage of electric current through the bath of the substrate, which is the anode, deposits a viscous mixture of vehicle and pigment on the substrate. Coalescence of the polymer produces a film of low conductivity which limits the thickness of the deposit. The substrate is drawn from the bath with only a minor amount of entrained, uncoalesced paint. This is rinsed off. The deposit which is left on the substrate is baked to convert it to insoluble form. The electromotive force for eleetrodeposition is about 100-500 volts and the e,m.f. is much higher than that required for electrolytic reactions. It results in electrophoresis of the negatively charged particles toward the anode. At the anode, acids are produced through electrolysis of water, and metals are dissolved from the electrode. The acids and the metals destabilize the mixture and a viscous, slimy mass is deposited on the anode. If the acidified polymer can coalesce (a Tg bath temp) it will form a coating of low conductivity and limit the thickness of the applied coating. When the deposition stops the e.m.f. across the coating will equal the applied e.m.f. and the potential gradient will be 10,000 to 100,000 volts/inch. The acidified deposited polymer is initially laden with water, but the flow of current causes some of the water to leave by a process of electroendosmosis, producing a denser deposit than that produced by acidification alone. Oxygen liberated at the anode forms bubbles in the deposit. The deposits are therefore initially rough. A smooth system can be obtained only if the deposited film is sufficiently fluid to smooth out by forces of surface tension. Under these conditions, edges, which are preferred positions for the initial deposit, may be left uncovered. Cathodic Deposition The substrate to be coated is made the cathode. The polymer is usually in the form of polymeric amine, solubilized as a salt. 6 DUP030024788 POWDER COATINGS AND THEIR APPLICATION: Powder coatings are made o particles of 10-30 microns diameter each of which contains the pigment and the binder. The binder will usually comprise a low-molecular-weight, brittle, resin mixture which is stable enough at room temperature but which melts and reacts at oven temperatures to produce a high-molecular weight, tough polymer as required. The manufacture of powders requires the development of manufacturing techniques to yield suitable size, suitable color, and suitable flow properties and reactivity in the oven. The finished coating must also meet the service requirements. Epoxy resins and hydroxyl-containing acrylic resins or hydroxylated polyesters are used with appropriate reactive crosslinking agents. Powder coatings can be applied to a hot object by dipping it into a fluidized bed of the powder. The powder melts and sticks to the surface. The thickness depends on the local heat capacity and temperature of the object being coated. Thick coatings are readily applied by fluidized bed techniques. Thin coatings are applied by spraying the powder, charging it electrically, and attracting it to the surface by electrostatic forces. As the powder collects, its charged particles tend to reduce the electric field, and this limits the thickness. The conductivity of powders determines the film thickness and must be controlled between certain limits. The application of powders for protection alone is done fairly easily, but decorative applications are difficult for a variety of reasons. Once coated and coalesced a surface can be difficult to recoat by electrostatic deposition. Part of the problem with obtaining good Appearances with powders is that the density of the applied powder is low, containing much air. The coalescence of the particles causes shrinkage - not necessarily all away from the surface. Furthermore, gases are often liberated by crosslinking reactions. While smoothing by surface tension proceeds, the polymer hardens. Smoothness equivalent to that of solution applied coatings, therefore, is difficult to achieve. Powders are also available for application as dispersions in water. Such powders can conceivably yield denser films. 7 DUP030024789 IMPACT OF THE NEW AIR POLLUTION REGULATIONS ON FINISHES SALES: Within the last ten years the pattern o industrial finishes sales has changed significantly away from solvent-thinned paints. The regulations will accelerate the change. In 1975, while solvent-thinned paints will probably still represent the majority of the industrial paint sold, the sales of alternates will represent a substantial fraction. (See Figure 1, 2, 3, quoted from Industrial Finishing and Surface Coating, pp. 14, 15 Aug. 1973). Sales of paint to ultimate consumers will be affected less by the air-pollution regulations because the more obnoxious solvents were eliminated from these paints years ago. RESPONSE OF R&D TO POWER SHORTAGE: The shortage of power makes it necessary to reduce baking temperatures. Usually in one-package systems when reactivities are high at low baking temperatures, stability in storage is poor. The conventional air-drying oil-based systems are in reality two package systems of which one package is air. Moisture-cure (making use of atmospheric water-vapor) of isocyanate terminated polymers, ultra-violet radiation cure, and electron-beam irradiation of vinyl monomers act like two-package systems. They are stable at room temperature, yet react rapidly under certain conditions at room temperature. 8 SPECIAL PROBLEMS WITH AQUEOUS FINISHES: 1. Reactivity of aluminum flake. 2. Spraying problems with electrostatic equipment. 3. Humidity control in drying. 4. Heat requirement for evaporation of water. 5. Corrosion of equipment. 6. Salt-content. 7. Hydrophilic even when dry. 8. Cross-linking mechanisms need improvement. WITH ELECTROCOATING: 1. Investment in equipment. 2. Bath composition changes - Pigment, Solvents, Binder, Salts, Acid-base balance. 3. Control of bath composition not simple - Flushed cathodes (or anodes), reverse osmosis. 4. Contamination with materials dragged in by the subs trate. 5. Anodic electrocoating dissolves metal from the electrodes, including metal pretreatments, yielding color and poorer pretreatment surface. This is not true of cathodic deposition, 6. Gases form at the substrate. 7. Washings must be recovered (reverse osmosis). WITH POWDER COATINGS: 1. Clean-up between colors is expensive. 2. Metallic colors lack brightness. 3. Electrostatic fields do not enter cavities. 4. Recoating can be difficult. 9 DUP030024791 WITH ULTRA VIOLET CURE 1. Line of sight cure. 2. Pigments, oxygen, exudates from substrates interfere with polymerization. 3. Ozone, heat. WITH ELECTRON-BEAM: CURE: 1. Pigments, oxygen, exudates from substrates interfere. 2. Large capital investment. 3. Dangerous X-rays produced. 10 DUP030024792 FIGURE I U, S. PAINT INDUSTRY MARKET SIZE - MILLION GALLONS Industrial Trade Sales Total 1966 421 416 837 1968 424 419 843 1970 399 428 827 1971 443 431 874 1972 485 465 950 1975* 525 515 1040 1980* 630 595 1225 ^ESTIMATES C. H, Kline & Co. Marketing Guide to the Paint Industry. Industrial Finishing and Surface Coatings (Aug. 1973) pp, 14, 15 11 DUP030024793 FIGURE II , U, S. PAINT INDUSTRY MARKET SIZE - MILLION GALLONS INDUSTRIAL SALES Solvent Thinned Air Dry or Force Dry Bake 1966 1968 1970 1972 1975* 131 278 128 262 123 234 103 296 98 227 Water Thinned Air Dry or Force Dry Bake 3 5,5 - 55 20 34 8 18 73 162 Powder Epoxy Polyester Other 1 1 1 1.5 5.0 0.2 1.0 2.5 3 3 3.3 6.0 *ESTIMATE C. H. Kline & Co. Marketing Guide to the Paint Indus try Industrial Finishing and Surface Coating (Aug. 1973) pp, 12 DUP030024794 s -c ft Solvent Thinned Interior Exterior Water Thinned Interior Exterior Other Solvent Thinned Total FIGURE III U. S. TRADE SALES MARKET 1966 1968 1970 1972 1975* 74 60 58 45 9 92 75 62 53 28 136 51 63 416 159 66 60 419 170 72 61 428 212 91 64 465 223 115 40 515 ' *e s t ima t e C. H. Kline & Co. Guide to the Paint Industry Industrial Finishing and Surface Coatings (Aug. 1973) pp. 14, 15 13 DUP030024795