44 -1 44 HVLP: The Science of High-Volume, Low-Pressure Finishing 44.1 The Principles behind HVLP 44- 1 44.2 The Benefits of HVLP 44- 1 44.3 HVLP versus Conventional Air Spray 44- 3 44.4 HVLP versus Airless and Air-Assist/Airless 44- 3 44.5 HVLP versus LVLP 44- 4 44.6 Compliant Technologies: HVLP and Electrostatic 44- 4 44.7 Components of an HVLP System 44- 4 44.8 Differences between HVLP Systems 44- 5 44.9 Operating an HVLP System 44- 7 44.10 The Use of Air Cap Test Kits 44- 7 44.1 The Principles behind HVLP High-volume, low-pressure (HVLP) atomization utilizes a high volume of air delivered at 10 psi or less to atomize fluid material into a soft, low-velocity pattern. This reduction in the velocity of the airstream over the 40 to 70 psi typically delivered by conventional spray methods results in a more controlled spray pattern, less bounceback, and enhanced transfer efficiency. Transfer efficiency can be defined as the amount of paint sprayed that goes onto the part as compared to the amount lost due to overspray and bounceback. In general, HVLP can be used with most low-to-medium solids materials including two-component paints, urethanes, acrylics, epoxies, enamels, lacquers, stains, and primers. Some HVLP application 44.2 The Benefits of HVLP High transfer efficiency enhances both productivity and finish quality. Less overspray improves visibility, which limits operator error. It also reduces deposits on adjacent surfaces, which typically results in a dry, sandy finish. Reducing overspray will reduce spray booth maintenance, filter replacement, waste disposal, Depending on the application, two-thirds or more of every gallon of material sprayed by conventional methods can be lost to overspray. But with HVLP, typically one-third or less is lost to overspray. Pro- ductivity does not suffer either because more paint is applied per pass, and fewer passes are required. But while finish quality and materials savings are important benefits, perhaps the most compelling reason to consider HVLP is the current trend toward legislated transfer efficiency requirements. The Steve Stalker ITW Industrial Finishing DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC and materials costs (Figure 44.1 and Figure 44.2). equipment can atomize higher viscosity materials and/or higher fluid flow rates. 44 -6 Coatings Technology Handbook, Third Edition the air from a turbine is not always controllable; pressure is not always sufficient to provide effective atomization with higher viscosity materials; and turbines generally require a higher level of maintenance. The second design (Figure 44.8) diverts shop air through an air conversion unit, which reduces atomization air pressure to 10 psi or less before the air reaches the spray gun. When fitted with air heaters, the heat can be adjusted or eliminated. They can also be regulated to deliver consistent pressure. Plus, they are more reliable than turbine generators. However, larger internal diameter (ID) air hose and a separate air conversion are required. The final design also utilizes shop air (Figure 44.9). However, it reduces the air pressure to the required 10 psi or less within the gun. This design eliminates the need for a separate air conversion unit while delivering the same degree of control over air pressure. In addition, it offers added convenience because it can be connected with a standard air line (1/4 ″ fitting and 3/8 ″ or 5/16 ″ air hose). FIGURE 44.7 Turbine generator air supply configuration. FIGURE 44.8 Shop air supply with air conversion unit configuration. FIGURE 44.9 Shop air supply with gun air conversion configuration. Turbine Unit Material Supply 50–100 PSI Air Supply Optional Heater Material Supply Air Conversion Unit 50–100 PSI Air Supply Material Supply DK4036_book.fm Page 6 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 45 -1 45 A Practical Guide to High-Speed Dispersion 45.1 What Is a Disperser? 45- 1 45.2 How Does It Work? 45- 1 45.3 What Is the Difference between a Disperser and an Agitator? 45- 2 45.4 When Do I Need to Use a Disperser rather than an Agitator? 45- 3 45.5 What Are the Limitations of a Disperser? 45- 3 45.6 What Different Types of Dispersers Are Available, and What Type Is Best for Me? 45- 4 45.7 How Do I Select the Proper Size Disperser? 45- 5 45.8 How Do I Select the Proper Size Tank for My Disperser? 45- 5 45.9 How Do I Select the Proper Size Blade for My Disperser? 45- 5 45.10 What Other Factors Affect the Performance of My Disperser? 45- 6 45.11 How Do I Operate My Disperser for Optimum Performance? 45- 7 45.12 What Safety Measures Must I Follow and Why? 45- 7 Every year, new people join the various businesses that use mixing machines in their laboratories and manufacturing facilities. What seems obvious to many experienced personnel can be complicated and frustrating to these newcomers. The purpose of this chapter is to present a fundamental explanation of the “what, how, when, and why” about high-speed dispersers. This chapter is dedicated to those new- comers who will become the experts of the future. 45.1 What Is a Disperser? A disperser is a type of mixer used to rapidly break apart lumps of powdery material, uniformly distrib- uting and wetting them in a liquid. It is also used to dissolve soluble solids in a liquid. 45.2 How Does It Work? A disperser works on the principle of energy transfer. A disc-type blade is mounted at the bottom end Herman Hockmeyer Hockmeyer Equipment Corporation DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC How Do I Know When It Is Time to Replace My Blade? • What Type of Blade Works Best on My Disperser? of the mixing shaft and rotated at relatively high tip speed (Figure 45.1). (Tip speed is the speed at the III -1 III Materials DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 46 -1 46 Acrylic Polymers 46.1 Introduction 46- 1 46.2 Chemistry and Manufacture 46- 1 46.3 Versatility of Acrylics 46- 2 46.4 46.5 Coating Techniques 46- 8 46.1 Introduction Since their introduction decades ago, acrylic polymers have gained a strong foothold in the coatings and allied industries as a result of their improved flexibility and adhesion compared to polyvinyl acetate emulsions, phenolics, and styrene-butadiene latex combined with their moderate cost. In addition, their significantly improved outdoor durability, including resistance to ultraviolet degradation, has mandated their use in several applications. In many respects, the name “acrylic” has become synonymous with a high performance level in a polymer system. Presently, acrylics are available in three physical forms: solid beads, solution polymers, and emulsions. The emulsion form is by far the dominant form in use today. This is due generally to the ease of tailoring properties, and the lower hazards and manufacturing costs compared to the solid and solution polymers. 46.2 Chemistry and Manufacture 46.2.1 Monomers Acrylic monomers are esters of acrylic and methacrylic acid. Some common esters are methyl, ethyl, isobutyl, n -butyl, 2-ethylhexyl, octyl, lauryl, and stearyl. The esters can contain functional groups such as hydroxyl groups (e.g., hydroxyethyl methacrylate), amino groups (e.g., dimethylaminoethyl methacry- late), amide groups (acrylamide), and so on, in addition to the carboxylic acid functionality of the unesterified monomer. Acrylic monomers can be multifunctional (e.g., trimethylolpropane triacrylate, or butylenes glycol diacrylate, to mention two). The polymer chemist has a wide range of monomers to select from when designing a specialty polymer system. Typically, mixtures of comonomers are chosen for the properties they impart to the polymer. Adhesive strength, for example, is increased by using monomers with low glass transition temperatures such as butyl acrylate or 2-ethyl hexylacrylate. Members of the carboxylic acid group of acrylic and methacrylic acids also tend to increase the adhesive properties of polymers. Cohesive strength is usually imparted by the harder acrylic monomers such as methyl methacrylate and methyl acrylate. Molecular weight is also a significant contributing factor, and these two parameters must be carefully balanced by the polymer chemist. Ronald A. Lombardi ICI Resins US James D. Gasper ICI Resins US DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Monomers • Polymerization Methods Coatings • Adhesives • Inks Glass Transition Temperature • Emulsion Acrylics Gravure Coaters • Flexographic Coaters • Wire-Wound Rod Application Areas 46-4 Coaters • Knife over Roll Coaters • Reverse Roll Coaters 46 -6 Coatings Technology Handbook, Third Edition 46.4.2.1 Heat-Sealable Adhesives Heat sealing is used for bonding two substrates where one or both are impervious to water. Typically, the more heat- and solvent-resistant substrate is coated first, and the solvent or water is driven off in an oven. At this point, the web can be wound up on itself (if the dried adhesive is tack free or nonblocking) and heat sealed to the secondary substrate at a later date. Alternatively, the adhesive-coated substrate can be laminated simultaneously to the second substrate to form the finished product. The latter case is the laminating adhesive technique, discussed later. When heat is applied to activate or soften the adhesive, two conditions must be met for adequate bonding: 1. The adhesive must have sufficient flow at the activation temperature to properly wet out the secondary substrate. 2. The adhesive must have a chemical affinity or specific adhesion to the particular substrate. This comprises the secondary chemical bonding forces, which give rise to what we call adhesive bonding. Many applications involving food packaging fall into this category. Examples include lidding-type adhesives for coffee creamers and jams and the blister packaging of pharmaceuticals. 46.4.2.2 Laminating Adhesives Laminating adhesives function much the same as heat-seal adhesives except that the temperature neces- sary to activate the adhesive is much lower. Where heat-seal adhesives may require an activation tem- perature of 120 ° C (250 ° F), laminating adhesives can be designed to function anywhere between room temperature and 90 ° C (200 ° F). Recently, new low temperature curing types of adhesive have, to some degree, replaced two-component solvent-polyurethane adhesives in the flexible packaging area. 13 Design- ing a room temperature curing mechanism into an acrylate system further enhances opportunities to replace solvent systems. 14 Considerable progress has also been made using low temperature curing acrylics in the industrial area. 15 Typical applications include vinyl-to-wood laminating and bonding vinyl to ABS for automotive interiors. 46.4.2.3 Pressure-Sensitive Adhesives The pressure-sensitive method of bonding is often called the “one-way” bonding method. The adhesive is coated onto the substrate either directly or by transfer coating. The adhesive is protected by a release liner until it is ready to be used. When application is desired, the liner is removed and the adhesive- coated substrate is bonded to the other substrate using pressure alone. Pressure actually activates the adhesive, hence the name of this method. Upon firm pressure, the tacky adhesive mass actually flows and bonds itself both mechanically and chemically to the other surface. However, to be functional, a pressure-sensitive adhesive must be more than just very tacky. Flypaper has a very high degree of tack but lacks internal strength or cohesiveness. A functional pressure-sensitive material will have high tack or adhesive strength combined with high cohesive strength, the basis require- ment for any adhesive. Pressure-sensitive adhesives are used in many tape areas such as packaging, masking, electrical mend- ing, medical, and mounting. The graphic arts area includes vinyl decals and special decorative films such as clear and metallized polyester films. These areas generally require an outstanding balance of properties that must be retained under severe outdoor exposure and temperature extremes. Such properties as outstanding resistance to ultraviolet light degradation and plasticizer migration are required. Adhesives for this area must produce clear and colorless films, dictating the use of acrylics exclusively. 16 Solvent-based polystyrene acrylics (PSAs) have been traditionally used in these areas. More recently, they have been replaced in varying degrees with their emulsion counterparts. 17 However, there still exist technical areas in which the solvent systems prevail. 18 These include applications requiring high levels of heat, water, and solvent resistance. DK4036_book.fm Page 6 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 46 -10 Coatings Technology Handbook, Third Edition increases coating weight, whereas slowing the applicator roll decreases coating weight. The primary reason for using a reverse roll coater is that a precise, uniform coating weight across the web can be attained. Dried film tolerances of ~0.0001 in. are possible. The other desirable feature is that coating weight thickness is independent of the backing weight variation. This is exactly opposite to the relationship on a knife over roll coater. Coating thickness in a reverse roll coater is generally a function of the following: • Gap between applicator and metering roll •Applicator roll speed •Adhesive solids, viscosity, and rheology Two primary coating supply systems are used when applying adhesives or coatings by reverse roll. For higher viscosities (10,000 to 20,000 cp), a nip-fed arrangement is utilized. For lower viscosities (3000 to 10,000 cp), a pan-fed system is preferred. The principal drawback to the reverse roll coater is the expense, as high precision rolls and bearings are required. However, the initial investment is usually outweighed by the improvement in quality of the finished product. References 1. J. A. Brand and L. W. Morgan, U.S. Patent 4,546,160; S. C. Johnson & Son, Inc. 2. K. W. Free, U.S. Patent 3,821,330; E. I. Dupont de Nemours and Co. 3. K. Shimada et al., U.S. Patent 3,968,059; Mitsubishi Raon Co. Ltd. 4. H. F. Mark, Encyclopedia of Polymer Science and Technology, Vol. 5. New York: Wiley, 2003, pp. 801–859. 5. B.F. Goodrich Chemical Company, Latex Product Date, Bulletin L–12, p. 14. 6. Rohm and Haas Company, Bulletin SP197, Special Products Department. 7. B.F. Goodrich Chemical Company, Latex Bulletin L–10, p. 4. 8. B.F. Goodrich Chemical Company, Latex Bulletin L–19, p. 12. 9. R. A. Heckman, J. Prot. Coat. Linings, 3 . 10 (1986). 10. J. E. Fitzwater, Jr., J. Water-Borne Coat., 8 , 3 (1985). 11. J. E. Fitzwater, Jr., J. Water-Borne Coat., 7 , 3 (1984). 12. G. Pollano and A. Lurier, J. Water-Borne Coat., 9 , 1 (1986). 13. P. Foreman, Paper Film and Foil Converter, November 1982. 14. R. A. Lombardi, Adhes. Age, February 1987. 15. A. H. Bealieu and F. P. Hoenisch, J. Water-Borne Coat., 10 , 1 (1987). 16. D. Satas, Handbook of Pressure Sensitive Adhesive Technology, 2nd ed. New York: Van Nostrand Reinhold, 1989. 17. R. A. Lombardi, Higher Performance Water-Borne Pressure Sensitive Adhesives. Pressure Sensitive Ta pe Council Seminar, Itasca, IL, 1987. 18. F. T. Koehler and J. A. Fries, Acrylic Emulsion PSAs: Performance vs. Acrylic Solutions. Spring Seminar, Adhesive and Sealant Council, Atlanta, 1985. 19. G. Sen, Am. Ink Maker, 65, 12 (1987). 20. M. T. Nowak, Am. Ink Maker, 62, 10 (1984). DK4036_book.fm Page 10 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC 47 -1 47 Vinyl Ether Polymers 47.1 General 47- 1 47.2 Monomers 47- 1 47.3 Production of Polymers 47- 1 47.4 Products on the Market 47- 2 47.5 Properties 47- 2 47.6 Applications 47- 3 Bibliography 47- 3 47.1 General The general formula for vinyl ether polymers used in the production of adhesives and coatings is as follows. The consistency of these polymers depends on their molar mass and ranges from viscous oils to rubbery solids. Vinyl ether was first converted into a resinous polymer more than a century ago. Between 1920 and 1930, it became readily accessible by the techniques of Reppe chemistry and thus attracted industrial interest. Means were then investigated for polymerizing it. In 1938 the large-scale production of vinyl ether polymers commenced in the Ludwigshafen works of the former IG-Farbenproduktion (now the Carbide Corporation, which relinquished the field in 1976. 47.2 Monomers The Reppe reaction between acetylene and an alcohol gives rise to vinyl ether: HC ≡ CH + H–OR → CH 2 = CH–OR It is still the only method of producing vinyl ethers that has acquired industrial significance. The 47.3 Production of Polymers Vinyl ethers can be easily polymerized in bulk or in solution, by batch or continuous techniques. Owing to the considerable heat of reaction, careful control and elaborate equipment are essential. The monomers and the initiator are metered continuously into the reactor, and the polymerization reaction sets in within a few minutes. After the reactor has been completely charged, it is closed, and polymerization proceeds further under pressure. The boiling point of the monomer or the solvent governs the rate at which the Helmut W. J. Müller BASF AG, Ludwigshafen/Rhein DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC main production site of BASF AG). GAF Corporation started production after 1940, followed by Union properties of the constituent monomers are listed in Table 47.1. 48 -1 48 Poly(Styrene-Butadiene) 48.1 Introduction 48- 1 48.2 Emulsion Polymerization 48- 1 48.3 Characteristics of Styrene-Butadiene Latex 48- 3 48.4 Uses 48- 3 Bibliography 48- 4 48.1 Introduction Styrene-butadiene (SB) polymers are used in coatings formulations primarily to improve coating strength, printability, gloss, pigment and fiber binding, and substrate bond strength. The styrene-butadiene poly- mers are produced primarily by emulsion polymerization to form a latex. A latex is a dispersion of finely divided spherical particles of polymer in water. The monomer ratios of styrene and butadiene can be adjusted to give the desired amount of flexibility or stiffness. Polystyrene latex contains hard polymer particles that will not form a continuous film upon drying at room temperature. Polybutadiene latex contains very soft, gummy polymer particles that will produce a weak, sticky film when dried. By copolymerization of styrene and butadiene monomers and adjustment of the monomer ratios, it is possible to obtain a copolymer with a wide range of intermediate properties. Thus, a copolymer latex with a high styrene content will produce a very tough, durable film but will not have the flexibility and adhesive performance of a latex with a high butadiene content. The temperature at which the copolymer changes from a brittle to a rubbery state is known as the g the T g of SB copolymers. As the concentration of styrene in the copolymer increases, the T g also increases. This property is important in coatings for determining durability of the dried film and optimizing curing conditions. A typical latex will contain 45 to 55% polymer, with the balance being water. cross-linking, and molecular weight can all be controlled, and this is accomplished through free radical emulsion polymerization. 48.2 Emulsion Polymerization Emulsion polymerizations require an emulsifier or surfactant composed of a hydrophobic and a hydro- philic portion to give the latex colloidal stability. As low levels of surfactant are added into the aqueous solution in a reactor vessel, the surfactant will saturate the water phase, and as the concentration is critical micelle concentration. As the styrene and butadiene monomers are added, they will diffuse through the water phase and into the micelles until an equilibrium is obtained. The majority of poly- Randall W. Zempel Dow Chemical Company DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM © 2006 by Taylor & Francis Group, LLC Ta ble 48.1 illustrates the typical properties of a styrene-butadiene latex. The particle size, composition, glass transition temperature (T ). Figure 48.1 illustrates the effect of the concentration of styrene on increased, the surfactant molecules will aggregate to form micelles. This concentration is known as the merization occurs within these monomer-swollen micelles. Figure 48.2 is a representation of the process. [...]... April 25, 2005 12: 18 PM 49-6 Coatings Technology Handbook, Third Edition 27 28 29 30 31 32 33 34 35 36 37 38 39 Thiokol Chemical Corp., British Patent 2,325,561 C H Sheppard and R J Jones, U.S Patent 3,931,354 R A Gray, J Coat Technol., 57(7 28) , 83 (September 1 985 ) K Hamann et al., U.S Patent 3,770, 688 W L Vaughn, U.S Patent 3 ,80 3, 087 Union Chemique Belgique, British Patent 1,441 ,81 4 Ford Motor Co.,... Patent 1,441 ,81 4 Ford Motor Co., British Patent 1,424,9 68 W J Morris, J Coat Technol., 56(715), 49 (August 1 984 ) B K Christmas, Mod Paint Coat., 152 (October 1 984 ) A R Siebert et al ACS Org Coat Plast Chem Div Prepr 34(91), 759 (1974) F B Jones et al., U.S Patent 3 ,80 3, 089 C A McPherson and J K Gillham, ACS Org Coat Plast Chem Div Prepr., 38( 1), 229 (19 78) R S Drake et al., Epoxy Resin Chemistry II ACS Symposium... Tunkel et al., Kauchuk Rezina, (3), 8 (1974) H Okamoto et al., Nippon Gomu Kyokaishi, 49(6), 520 (1976) B N Pronin et al., Vysokomol Soed A, 19(3)5, 455 (1977) M Roux-Michollet et al., ACS Polym Div Prepr., 19(2), 369 (19 78) A H Frazer and E J Goldberg, U.S Patent 2 ,88 8,440 Phillips Petroleum Co., U.S Patent 3 ,86 0,566 Product Research Chemical Corp., Belgian Patent 82 1,959 K Marabushi, U.S Patent 4,205,150... Skillicom, U.S Patent 3,607 ,84 5 P A E Guinet and R P Puthet, U.S Patent 3,409,573 E J Goethals, Ed., Telechelic Polymers: Synthesis and Applications Boca Raton, FL: CRC Press, 1 988 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 © 2006 by Taylor & Francis Group, LLC DK4036_book.fm Page 1 Monday, April 25, 2005 12: 18 PM 50 Polyesters 50.1 Introduction... Preparation of Polyester Coatings 50-7 Solvent-Borne Polyester Coating • High Solids Paints • Waterborne Paints • Solvent-Free Coatings H F Huber Hüls Troisdorf AG D Stoye Hüls Troisdorf AG 50.7 Properties and Applications of Polyester Coatings .50-9 Sheet and Coil Coatings • Can Coating • Automotive Paints • Industrial Paints • Two-Component Paints • Powder Coating • Radiation-Curable Coatings • Adhesives... polybutadienes to toughen epoxy coatings Jones and coworkers37 devised on epoxy coating cured by a mercaptan-terminated polymer McPherson and Gillham 38 characterized epoxy resin coatings cured by carboxylated telechelic polybutadiene by torsional pendulum analysis, noting effects of molecular weight and compatibility of the components Drake et al.39 reviewed elastomer-modifier, epoxy-based coatings A steel coating... shown are some oligomers for incorporation into ultraviolet or electron beam (EB) coating systems 49-1 © 2006 by Taylor & Francis Group, LLC DK4036_book.fm Page 4 Monday, April 25, 2005 12: 18 PM 49-4 Coatings Technology Handbook, Third Edition TABLE 49.2 Telechelic Polymer Cure Systems Curative Telechelic Species Polymerizable oligomer Polyisocyanates Tetramethyldiamine Diisocyanates Hexachloro p–xylylene... Mercaptan-terminated butadiene copolymer Hydroxy-terminated polysiloxane Peroxide Ref 55 56 57 58 59, 60 61 62 63 22 64 65 66 67 68 69 70 71 72 73 74 75 Not all the liquid polymer coatings are based on telechelic functionality Gray29 described a randomly functional hydroxyacrylic oligomer synthesis for use in melamine resin cured coatings Hamann and coworkers30 devised a coating composed from a phenolic adduct to... April 25, 2005 12: 18 PM 49 Liquid Polymers for Coatings 49.1 Introduction 49-1 49.2 Fluid Properties 49-1 49.3 Commercial Liquid Polymers 49-1 Polymers with Random Functionality • Telechelic Polymers • Curing Robert D Athey, Jr Athey Technologies 49.4 Applications .49-3 49.5 Conclusions .49-5 References .49-5 49.1 Introduction High solids coatings are an... Washington, DC: American Chemical Society, 1 983 DeSoto Inc., U.S Patent 3,933,760 Mitsubishi Gas Chem Ind., German Patent 2,533 ,84 6 J E French, ACS Org Coat Plast Chem Div Prepr., 35(2), 72(1975) W H McDonald, U.S Patent 4,091,050 Pechiney St Gobain German Patent 2,052,961 A Vranken and P Dufour, German Patent 2,450,621 K Ko et al., German Patent 2,533 ,84 6 J M Moisson-Frankhauser et al., British Patent . 47.1. 48 -1 48 Poly(Styrene-Butadiene) 48. 1 Introduction 48- 1 48. 2 Emulsion Polymerization 48- 1 48. 3 Characteristics of Styrene-Butadiene Latex 48- 3 48. 4 Uses 48- 3 Bibliography. 2,325,561. 28. C. H. Sheppard and R. J. Jones, U.S. Patent 3,931,354. 29. R. A. Gray, J. Coat. Technol., 57 (7 28) , 83 (September 1 985 ). 30. K. Hamann et al., U.S. Patent 3,770, 688 . 31 19(2), 369 (19 78) . 70. A. H. Frazer and E. J. Goldberg, U.S. Patent 2 ,88 8,440. 71. Phillips Petroleum Co., U.S. Patent 3 ,86 0,566. 72. Product Research Chemical Corp., Belgian Patent 82 1,959. 73.