Floor lacquers Quick-drying nitrocellulose-type floor finishes with good mar, scuff, and abrasion resistance can be formulated using conventional resins and plasticizers. A 26 wt. % lacquer might consist of RS nitrocellulose, l/a-second (dry), 10 parts by wt.; alkyd resin (45y0 castor oil), 5 parts bywt.; castor oil (AA) 2 parts by wt.; and dioctyl phthalate, 2 parts by wt. A good solvent system providing
good brushability and even flow out is methyl isobutyl ketone, 25 VOl. %; EAK, 15 VOl. %; ethyl alcohol, including that introduced with nitrocellulose, 20 v01. %; methyl isobutyl carbinol, 5 vol. %; toluene, 20 vol. %; and xylene, 15 vol. 70.
R. F. BULLER
Shell Chemical Corp., Union, N. J.
eckanism for ControlledTemperature Application of Lacquers
A
STUDY and evaluation of heating methods dictated four objectives for the development of a n improved paint heating system. First, find a method of heating organic finishes that will provide accurate temperature control over all ranges of operation. Secondly, develop a basic design that provides greatly reduced equipment maintenance costs. Thirdly, incorporate versatility into the design so that the equipment is equally practical for the finisher spraying one color a t one spray station or multiple colors a t many stations. Fourthly, reduce equipment costs sufficiently that increased acceptance of the hot-spray process by the finishing industry results. T h e DeVilbiss heating system consists of three basic components :
1. A heat generator which may be located outside the spraying area 2. A heat exchanger, one or more of which are located a t each spraying station 3. A heated fluid hose to carry paint from each heat exchanger to a spray gun T h e heat generator, containing a water heater and circulating pump, electrically heats water to a predetermined temperature and continually circulates the heated water throughout a closed system to one or more exchangers located in the spray booth and back to the generator. By having the thermostat react to both the heating element temperature and the return water temperature-Le., introducing thermal feedback-it has been possible to design a heating system with the double advantage of low thermal inertia and recovery from load changes without temperature drift. There is no corrosion, rusting, or evaporation of water from this system, hermetically sealed from the atmosphere, and if through accident water is lost from the system, it is replaced by means of a n automatic water-filling system. T h e DeVilbiss exchanger consists of four tubes, one within the other, that form three concentric annular spaces. Hot water a t a constant preset tempera-
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ture flows a t a fixed rate through the inner and outer annuli. Material to be heated flows (in the opposite direction to the water flow) through the center annuli. Thus, a very thin layer of lacquer is heated from both sides by a constant temperature heating medium. T o further improve the temperature control, both the lacquer and water are made to follow a spiral path through the tubes rather than being allowed to flow in a straight path. I t might be thought that this relatively small material passageway would be conducive to a clogging action. Such is not the cases for two reasons: First, when spraying takes place, the finish travels a t a relatively high velocity through the spiral passageway and actually has a scrubbing action on the walls of the tubes. Secondly, since overheating of the tube walls in the exchanger does not occur a t any time, the possibility of a baking action taking place is greatly reduced. T h e development of a heat-jacketed fluid hose was the result of a desire to eliminate pump maintenance. Thus this hose serves a dual purpose-it provides both a material handlingsystem for which maintenance requirements are negligible and affords accurate temperature control throughout the heating system. Power requirements for hot spray systems can be estimated by combining the data on the number of heat exchangers, the maximum spray rates (flow per gun in fluid ounces per minute), ambient temperature conditions, and the engineering layout of the piping system. The uses of heat as a medium to aid the spray operator to apply fuller and more uniform coats or finishes is quite generally accepted today. However, it must be appreciated that the use of heated materials is only one of three factors that must be constantly controlled. T h e second is the correct spray gun with the proper air cap and nozzle combination. The third is use of the lowest air and fluid pressure capable of doing the
INDUSTRIAL AND ENGINEERING CHEMISTRY
job required. The low pressure method for the application of heated lacquertype spray finishes has yielded proved results whenever employed. In order to employ the controlled low pressure method of application, it is necessary to ensure that the viscosity of the material being sprayed is uniform. This can only be ensured through the use of a materia1 heater. T h e lack of proper viscosity control is the oftenoverlooked answer to a high percentage of possible reasons given for orange peel, overspray, runs, blues, and low film build. I t is one of the most elusive troublemakers in the average finishing system. ASa consequence of uniform viscosities maintained in the range 140' to 150" F., regular lacquer finishes designed for cold spray applications have shown remarkably improved characteristics. In a number of cases, this has eliminated the necessity of formulating special finishes to be used in connection with a heating device. I t is not intended to imply that the equipment described here is limited to use in the 140' to 150' F. range mentioned. The point is that the present lacquer formulation being used for cold spray can be applied a t elevated temperatures, thereby resulting in savings in both material and labor. Of course, there may be situations that demand improved durability, better gloss, higher solids, or some other factor which is specially desired. Therefore, these qualities can be obtained more effectively through the use of basic formula changes. The most common error observed to date has been the effort to employ the hot spray process with high viscosity materials and reduced fluid and air pressures all a t one time. This invariably results in operator confusion. The high quality finishes being applied today no longer permit the blundering hit-or-miss methods that painters have been prone to follow since time immemorial. Therefore, it is implicit that the spray operator have proper training in the use of his gun. Consequently, it is submitted that if familiar with the customers' operating conditions, it may now be possible to help them obtain improved finishes a t a minimum reduction in material costs of from 16 to 20% plus, and in addition, enjoy the economies which have been outlined. From the foregoing it can be observed that the industry is now provided with a positive means of controlled low pressure application for the materials employed in lacquer finishing and that this has resulted, and will continue to result in improved finishes a t lower costs.
HAROLD C. FORNWALL The DeVilbiss Toledo, Ohio
Co.,
