Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D1/00—Processes for applying liquids or other fluent materials
  • B05D1/02—Processes for applying liquids or other fluent materials performed by spraying
  • B05D1/025—Processes for applying liquids or other fluent materials performed by spraying using gas close to its critical state
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F35/00—Accessories for mixers; Auxiliary operations or auxiliary devices; Parts or details of general application
  • B01F35/20—Measuring; Control or regulation
  • B01F35/21—Measuring
  • B01F35/211—Measuring of the operational parameters
  • B01F35/2111—Flow rate
  • B01F35/21112—Volumetric flow rate
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F35/00—Accessories for mixers; Auxiliary operations or auxiliary devices; Parts or details of general application
  • B01F35/80—Forming a predetermined ratio of the substances to be mixed
  • B01F35/82—Forming a predetermined ratio of the substances to be mixed by adding a material to be mixed to a mixture in response to a detected feature, e.g. density, radioactivity, consumed power or colour
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F23/00—Mixing according to the phases to be mixed, e.g. dispersing or emulsifying
  • B01F23/40—Mixing liquids with liquids; Emulsifying

Definitions

• This invention pertains to mixing and proportioning a compressible fluid and a non-compressible fluid.
• the compressible fluid is a supercritical fluid
• the non-compressible fluid is a coating composition
• the resultant mixture is applied to a substrate by spraying techniques.
• Coating compositions are complex mixtures which often include binders, pigments, surfactants, flow-control agents, and organic solvents.
• Organic solvents serve a variety of purposes related to viscosity reduction, film formation and adhesion. In spraying paints and coatings, organic solvents reduce their viscosity. This viscosity reduction is needed to enable atomization when the material is sprayed and also to facilitate droplet coalescence on the surface, thus giving a coherent, uniform film. Spray atomization requires a very low viscosity to produce the fine droplets needed for high-quality coatings.
• VOC volatile organic compounds
• U.S. Patent No. 4,923,720 discloses methods and apparatus for the production of the high solid coating formulation in which substantial amounts of the liquid solvent component have been removed and replaced with a non-toxic and environmentally compatible supercritical fluid, such as supercritical carbon dioxide. This coating composition is then sprayed onto a substrate at which time the supercritical carbon dioxide vaporizes to assist spray atomization.
• a non-toxic and environmentally compatible supercritical fluid such as supercritical carbon dioxide.
• This coating composition is then sprayed onto a substrate at which time the supercritical carbon dioxide vaporizes to assist spray atomization.
• the relative proportion of the liquid composition and supercritical carbon dioxide should be maintained at a predetermined ratio or within a predetermined range.
• one requirement of U.S. Patent No. 4,923,720 is to control the relative proportion of liquid coating composition and supercritical fluid.
• the liquid coating composition and supercritical fluid are each introduced into the system by a separate pump. However, the volume of the supercritical carbon dioxide is varied depending upon the system pressure and temperature. This can result in deviation of the
• U.S. Patent No. 5,215,257 discloses an improved method and apparatus for forming and dispensing a coating material formulation or solution containing a fluid coating composition and a fluid diluent, such as a supercritical carbon dioxide.
• the control system opens and closes the supply of supercritical carbon dioxide and/or liquid coating composition in accordance with variation of capacitance in the formulation.
• the devices requires predetermined set point values to control supercritical carbon dioxide concentration in the coating formulation.
• the correlation between the carbon dioxide concentration in the coating formulation and the values obtained by capacitance sensor can vary significantly depending upon system pressure, temperature and coating formulation.
• compositions having both liquid and gas components in a multiple phase solution it has been found that controlling carbon dioxide concentration is difficult.
• the signal from the capacitance sensing circuit produces a relatively widely fluctuating signal due to the formation of bubbles.
• Another deficiency of the apparatus is that the device requires the feed coating capacitance information of formulation before carbon dioxide addition to calculate control set point values with respect to carbon dioxide concentration.
• Aforementioned U.S. Patent No. 4,923,720 discloses an apparatus capable of pumping and proportioning a coating formulation and liquid carbon dioxide.
• volumetric proportioning of the coating formulation stream and the supercritical carbon dioxide stream is carried out by means of reciprocating pumps which displace a volume of fluid from the pump during each one of its pumping cycles.
• One reciprocating pump is used to pump the coating formulation which is slaved to another reciprocating pump which is used to pump the liquid carbon dioxide.
• the piston rods for each pump are attached to opposite ends of a shaft that pivots up and down on a center fulcrum.
• the volume ratio is varied by sliding one pump along the shaft, which changes the stroke length.
• liquid carbon dioxide is relatively compressible at ambient temperature, the temperature at which it is typically stored in a pressurized container. Such compressibility may undesirably cause fluctuations and oscillations of the amount of carbon dioxide that is present in the admixed coating formulation that is to be sprayed. This occurs due to the incompatible pumping characteristics of the relatively non-compressible coating formulation and the relatively compressible liquid carbon dioxide. With the coating formulation, pressure is immediately generated in the reciprocating pump as soon as its volume is displaced. Inasmuch as the liquid carbon dioxide is substantially compressible, a larger volume is needed to be displaced in order to generate the same pressure. Because mixing occurs when the flow of the coating formulation and of the Uquid carbon dioxide are at the same pressure, the flow rate of carbon dioxide lags behind the flow rate of the coating formulation.
• U.S. Patent No. 4,621,927 discloses a mixture control apparatus controlling a flow rate of a second fluid to be mixed with a first fluid so as to prepare a third fluid having a predetermined concentration.
• a set point variable of the flow rate of the second fluid is calculated in accordance with the flow rate of the third fluid so as to improve controllability of the apparatus.
• the invention in U.S. No. 4,621,927 cannot control the mixture of compressible fluid(s) and non-compressible fluid(s) because the thermodynamic properties of the fluids are influenced by variables such as pressure, temperature, and concentration.
• the present invention measures the volumetric flow of the non-compressible fluid stream before and after the addition of compressible fluid to determine and to control the amounts of compressible fluid.
• This invention simply and accurately proportions the fluids because it has been surprisingly discovered that the density of the non-compressible fluid and compressible fluid mixture does not vary significantly in many systems as long as the solubility limit of the compressible fluid in the non-compressible fluid mixture is not exceeded.
• compressible fluid is meant to include a material whose density is afiected by a change in pressure to an extent of at least about 5%. As used herein, all fluids are understood to be at one atmosphere pressure and 0°C unless otherwise noted.
• the present invention in its broader embodiment comprises an apparatus for continuously mixing a substantially compressible fluid and a substantially non-compressible fluid in a predetermined proportion which includes: a) means for supplying substantially compressible fluid; b) means for supplying substantially non-compressible fluid; c) means for measuring the volumetric flow rate of the substantially non-compressible fluid; d) means for generating a signal based upon the volumetric flow rate of the substantially non- compressible fluid; e) means for forming a mixture of the measured substantially non-compressible fluid and substantially compressible fluid, such that the density of the resulting mixture behaves substantially like a non-compressible fluid; f) means for measuring the volumetric flow rate of said mixture; g) means for generating a signal based upon the flow rate of the substantially compressible fluid and substantially non-compressible fluid mixture; and h) means for controlling the flow rate of the substantially compressible fluid in response to the signals generated in (d) and (g).
• coating formulation or “coating composition” are understood to mean a typical, conventional coating composition which does not have any supercritical fluid admixed therewith.
• admixed liquid mixture or “admixed coating formulation” are meant to include an admixture of a coating formulation with at least one supercritical fluid.
• the present invention also comprises a method for forming a mixture of a substantially compressible fluid and a substantially non- compressible fluid in a predetermined proportion which comprises: a) providing a non-compressible fluid; b) measuring said non-compressible fluid's volumetric flow rate; c) providing a compressible fluid; d) mixing the compressible fluid with the non-compressible fluid such that the density of the resulting mixture behaves substantially as a non-compressible fluid; e) measuring the volumetric flow rate of the mixture; and
• substantially as a non-compressible fluid is understood to include a mixture whose density is unaffected by a change in concentration of the components in the mixture of less than about 10%, preferably of less than 5% , and most preferably of less than 2%.
• the difficulties associated with handling a compressible fluid are substantially eliminated.
• the density of the resulting fluid mixture is also measured to ensure that the fluid mixture is behaving substantially as a non-compressible fluid.
• Figure 1 is a phase diagram for a supercritical carbon dioxide, polymer and solvent system.
• Figure 2 is a graph of the density versus composition of ethanol/water and isopropyl alcohol/water systems.
• Figure 3 is a graph of the density versus composition of a dimethyl sulfoxide/acetone system.
• Figure 4 is a graph of the density versus composition of an acrylic polymer/methyl aryl ketone solution.
• Figure 5 is a graph of the density versus composition of a polymeric coating composition/carbon dioxide solution.
• Figure 6 is a diagram of the apparatus suitable for proportioning and spraying a compressible fluid and non-compressible fluid.
• Figure 7 is a diagram of the apparatus used to conduct the experimental trials described herein.
• Figures 8-11 are graphical representations of flow rate versus time for the spray application of various coating mixtures.
• Figures 12 and 13 are graphs of the density versus composition for two coating compositions in carbon dioxide.
• Figures 14 and 15 are graphs of the density versus composition for two coating compositions in ethane.
• the coating compositions employed in this invention are broadly defined to include paints, lacquers, adhesives and the like. Such coating materials may also include those that are typically utiHzed in the agricultural field such as, but not limited to, fertilizers, herbicides and insecticides.
• the coating compositions employed in the present invention typically comprises a solids component containing at least one polymeric component, pigments, melting agents, cross-linking agents, ultraviolet light stabilizers.
• a solvent fraction is also employed, including active solvents, coupling solvents and water.
• Other liquid components often found in coating compositions may also be used such as curing agents, plasti ⁇ zers, surfactants and the like.
• the components of both the solvent fraction and the liquid fraction of coating compositions are well known to those with skill in the art. A more thorough discussion of the components found in coating compositions can be found in U.S. Patent No. 5,171,613.
• critical temperature is defined as the temperature above which a gas cannot be liquefied by an increase in pressure.
• critical pressure is defined as that pressure which is just sufficient to cause the appearance of two phases at the "critical temperature”.
• the compressibility of supercritical fluids is great just above the critical temperature where small changes in pressure result in large changes in the density of the supercritical fluid.
• the "liquid ⁇ like" behavior of a supercritical fluid at higher pressures results in greatly enhanced solubilizing capabilities compared to those of the "subcritical" compound, with higher diffusion coefficients and an extended useful temperature range compared to liquids.
• Compounds of high molecular weight can often be dissolved in the supercritical fluid at relatively low temperatures.
• An interesting phenomenon associated with supercritical fluids is the occurrence of a "threshold pressure" for solubility of a high molecular weight solute. As the pressure is increased, the solubility of the solute will often increase by many orders of magnitude with only a small pressure increase.
• the solvent capabilities of the supercritical fluid are not essential to the broad aspects of the present invention.
• Near- supercritical liquids also demonstrate solubility characteristics and other pertinent properties similar to those of supercritical fluids.
• the solute may be a liquid at the supercritical temperatures, even though it is a solid at lower temperatures.
• fluid "modifiers” can often alter supercritical fluid properties significantly, even in relatively low concentrations, greatly increasing solubility for some ⁇ olutes. These variations are considered to be within the concept of a supercritical fluid as used in the context of this invention. Therefore, as used herein, the phrase "supercritical fluid” denotes a compound above, at, or slightly below the critical temperature and pressure (the critical point) of that compound.
• supercritical carbon dioxide fluid is preferably used with the coating formulations.
• nitrous oxide (N2O) is a desirable supercritical fluid for admixture with the coating formulations.
• any of the supercritical fluids and the mixtures thereof are to be considered as being applicable for use with the coating formulations.
• the solvency of supercritical carbon dioxide is substantially similar to that of a lower aliphatic hydrocarbon and, as a result, one can consider supercritical carbon dioxide as a replacement for the hydrocarbon solvent of a conventional coating formulation.
• there is a safety benefit also, because carbon dioxide is non-flammable.
• Coating formulations are commonly applied to a substrate by passing the coating formulation under pressure through an orifice into air in order to form a liquid spray, which impacts the substrate and forms a liquid coating.
• orifice sprays three types are commonly used; namely, air spray, airless spray, and air- assisted airless spray.
• Air spray, airless spray, and air-assisted airless spray can also be used with the liquid coating formulation heated or with the air heated or with both heated. Heating reduces the viscosity of the liquid coating formulation and aids atomization.
• the present invention can also be applied by electrostatic applications as described in U.S. Patent No. 5,106,650.
• the constituents of that mixture usually need to be present in particular, accurately proportionated amounts in order for the mixture to be effective for its intended use.
• the underlying objective is to reduce the amount of organic solvent present in a coating formulation by the use of supercritical fluid. Understandably, with this objective in mind, it is generally desirable to utilize as much supercritical fluid as possible while still retaining the ability to effectively spray the liquid mixture of coating formulations and supercritical fluid and also obtain a desirable coating on the substrate. Accordingly, here too, it is particularly preferred that there be prescribed, proportionated amounts of supercritical fluid and of coating formulation present in the liquid coating mixture to be sprayed.
• the preferred upper limit of supercritical fluid addition is that which is capable of being miscible with the coating formulation. This practical upper limit is generally recognizable when the admixture containing coating formulation and supercritical fluid breaks down from one phase into two fluid phases.
• the vertices of the triangular diagram represent the pure components of an admixed coating formulation which for the purpose of this discussion contains no water.
• Vertex A is an organic solvent
• vertex B is carbon dioxide
• vertex C represents a polymeric material.
• the curved line BFC represents the phase boundary between one phase and two phases.
• the point D represents a possible composition of a coating formulation in which supercritical carbon dioxide has not been added.
• the point E represents a possible composition of an admixed coating formulation, after admixture with supercritical carbon dioxide.
• the amount of supercritical fluid, such as supercritical carbon dioxide, that can be mixed with a coating formulation is generally a function of the miscibility of the supercritical fluid with the coating formulation as can best be visualized by referring to Figure 1.
• the composition of the admixed liquid coating mixture approaches the two-phase bovmdary represented by line BFC. If enough supercritical carbon dioxide is added, the two-phase region is reached and the composition correspondingly breaks down into two fluid phases. Sometimes, it may be desirable to admix an amount of supercritical fluid (in this case, supercritical carbon dioxide) which is even beyond the two phase boundary. Generally, however, it is not preferable to go much beyond this two phase boundary for optimum spraying performance and/or coating formation.
• supercritical fluid in this case, supercritical carbon dioxide
• proper proportionation is also desirable to provide optimum spraying conditions, such as, formation of desired admixed viscosity, formation of desired particle size, formation of desired sprayed fan shape, and the like.
• the non-compressible fluid in the present invention is typically in the liquid state.
• the liquid state is characterized by the strong interaction of the molecules, which distinguishes liquids from gases, and the state of disorder of the molecular motion, which distinguishes liquids from solids. The behavior of liquids are generally well understood and their properties tend not to vary significantly over discrete ranges.
• Figure 2 is a plot of liquid density versus composition of water and ethanol and water and iso-propyl alcohol at atmospheric pressure at 20 °C. With the addition of ethanol or isopropyl alcohol to the mixture, the density of the mixture gradually decreases to the density of the undiluted alcohol.
• Figure 3 demonstrates a similar result with a plot of the liquid density of dimethyl sulfoxide and acetone at atmospheric temperature and pressure.
• apparatus which by taking advantage of the relative constant density, is capable of pumping, pressurizing, proportioning, heating, and mixing a coating composition with carbon dioxide to form an admixed liquid mixture through only volumetric measurements.
• the coating composition and supercritical carbon dioxide is provided at the precisely desired proportions ready for being sprayed.
• the apparatus depicted herein is able to simply and elegantly proportion the liquid mixture by making use of the constant density phenomena described herein.
• this discussion is focused on carbon dioxide it is not limited to this material and the present invention may include any compressible fluid.
• carbon dioxide is supplied as a liquid from any suitable source (9), such as a tank or cylinder.
• the liquid carbon dioxide is supplied on a continuous basis.
• the carbon dioxide is then fed to carbon dioxide feed pump (7) through an optional 0-3000 psi pressure indicator (8).
• the carbon dioxide is sent to a control valve (10) then heated to about 30-80°C in the preheater (3) and then sent to mixer (5).
• the coating is supplied by a pump (1) through an optional pressure gauge (2), through a flow meter (4) to the preheater (3).
• the coating composition is then sent to the mixing unit (5) to form the admixed liquid mixture.
• the flow rate of the coating composition and carbon dioxide are then measured by the second flow meter (11).
• An optional thermocouple (6) is preferably provided.
• An optional density meter (17) is preferably provided to monitor the density of the admixed coating formulation. In a most preferred embodiment a density meter is employed to ensure that the flow rate of carbon dioxide does not become so large as to create a significant change in the density of the admixed coating formulation.
• a sight gauge (18) is preferably employed for phase analysis.
• the admixed coating formulation mixture can then be adjusted to desired final temperature by an optional heater (not shown) and provided through a conduit (13) to the spray gun (14).
• the mixture of coating and carbon dioxide also can be recirculated through the heater (12) and recirculation pump (16) to maintain constant spray temperature if desired.
• a multi-channel flow ratio computer (15) receives the signals of the flow rates from both the flow meters and is used to output signal to control the flow rate of the carbon dioxide via control valve (10).
• volumetric flow meter used in the present invention is not critical. Any suitable volumetric flow meter such as gear meters, turbines and rotameters and the like may be used of which gears meters are preferred.
• Apparatus suitable for studying the controllability of compressible fluid, specifically carbon dioxide, was constructed and is depicted in Figure 7.
• the unit was comprised of feed pumps for coating formulation (101) and carbon dioxide (107), two flow gear meters (104) and (111), a control valve (110), heaters (103), a micro-processor based flow controller (115) and a homogeneous mixing unit for the two fluids (105).
• the coating material was fed from a container, and pressurized to 1500-2200 psig at room temperature by an air-driven liquid coating pump.
• the coating material was preheated to 30-40°C through a heater (103).
• the flow rates of coating material were measured by a precision gear meter (104).
• Liquid carbon dioxide was fed from a cylinder, and pressurized to 1500-2200 psi at room temperature by an air-driven carbon dioxide liquid pump (107). Then carbon dioxide was preheated to 30-40°C through a heater (103). These two fluids were mixed through a mixing unit (105), which was comprised of a sparger, and two KenicsTM mixers.
• the flow rates of the mixture of coating material and carbon dioxide were measured by a precision gear meter (111), and heated in heater (112) to 45-60°C before spray application.
• the mixture of coating and carbon dioxide were re-circulated through the spray gun (114) to maintain constant spray temperature.
• a multi-channel flow ratio computer received signals of the flow rates from both gear meters, displayed the totaled flow rates, and was used to manipulate the position of a carbon dioxide control valve (110) to control a required carbon dioxide concentration in the coating mixture.
• the flow rate of carbon dioxide was also monitored with a mass flow meter (109), and the data from gear meters (a) and (b) were interfaced to a computerized data acquisition system (116).
• Figure 8 is a plot of coatings flow rate versus time (120 seconds) for continuous spraying of an admixed coating formulation from a spray apparatus depicted in Figure 7.
• the coating formulation was a mixture of acrylic and melamine polymers and organic solvents.
• Point #1 in the Figure 8 is the coatings flow rate measured by a precision gear meter (104).
• Point #2 in the Figure 8 is the flow rate of the admixed coatings formulation flow rate measured by a precision gear meter (111). From the disclosure of this invention, carbon dioxide flow rate is the difference between the readings of gear meter (111) and the readings of gear meter (104).
• Figure 9 illustrates carbon dioxide flow rates from a spray unit using the coating formulation described in Table 1 in an apparatus similar to Figure 7 determined by two methods; 1) calculating the differences in flow rate between the two flow gear meters from Figure 7, and 2) actual carbon dioxide flow rates measured by the mass flow meter (109).
• the differences in the graphs is believed to be caused by response time delays and the effect of data averaging in the mass flow meter, because it requires 0.2-0.5 second time delays for the flow calculations to be conducted
• overall flows for 120 seconds were 89.0 cubic centimeters (cc) from this invention, and 89.5 grams from mass flow meter, indicating that the:
• Density of the mixture of coatings and carbon dioxide is close to 1.0 grams/cc, which is almost the same as the density of coating material alone;
• the combination of two volumetric flow meters can be used to measure and accurately control carbon dioxide concentrations.
• Figure 10 shows three plots of flow rates; Dcoating composition,; 2) mixture of coating composition and carbon dioxide; and 3)carbon dioxide for a 90 second continuous spray interval using the coating formulation in Example 1. Apparatus similar to that disclosed in Figure 7, without a recirculation loop was used.
• Line #1 in Figure 10 indicates coatings flow rates measured by a precision gear meter.
• line #2 in Figure 10 was the coatings and carbon dioxide mixture flow rates measured by a precision gear meter.
• Line #3 in Figure 10 carbon dioxide flow rates calculated from the differences between the readings of the gear meter and the readings of the flow meters.
• the totalized flow rates of coatings and mixture of coatings and carbon dioxide for 90 seconds were 219.5 cc and 310.9 cc, respectively. Therefore, carbon dioxide flows for 90 seconds were 91.4 cc from the method of the present invention, and 92.0 grams as measured by the mass flow meter, indicating that the combination of the two volumetric flow meters can be used to accurately measure and control carbon dioxide flowrates.
• Figure 11 shows two flow rates: 1) coatings; and admixed coating formulations intermittently sprayed for 800 seconds from a spray unit described in Figure 7 without a recirculation loop.
• Point #1 in the Figure 11 indicates coatings flow rates measured by a precision gear meter 104.
• Point #2 in the Figure 11 indicates the flow rate of coating and carbon dioxide flow mixture measured by a precision gear meter 111.
• the totalized flow rates of coatings and admixed coating formulation for 800 seconds were 2195 cc and 3109 cc, respectively. Therefore, carbon dioxide flows for 800 seconds were 914 cc as measured by the method of the present invention, and 920 grams from mass flow meter.
• the Example once again demonstrates that the combination of two volumetric flow gear meters can be used to measure and control carbon dioxide concentrations accurately.
• Relative error is defined as (C02 from this invention-C02 from mass meter )/C ⁇ 2 from mass meter.
• the total amount of carbon dioxide mixed with a coating formulation and sprayed from apparatus depicted in Figure 7 was measured.
• the amount of carbon dioxide used was measured using a mass flow meter and two volumetric gear meters.
• the coating formulation consisted of 69 weight percent AT-954 Acrylic, available from Rohm & Haas, and 31 weight percent MAK.
• the pressure and temperature at the coatings and carbon dioxide mixing unit were maintained at 1600 psi and 36°C, respectively.
• a clear solution appearance is indicative of a single phase solution.
• a hazy appearance indicates that the solution is in two distinct phases.
• This Example demonstrates the highly accurate proportionation of the fluids when the single phase solution is maintained. When a two phase solution is created, the density of the solution typically begins to change rapidly and the accuracy of the proportionation apparatus is diminished.
• Example 1 The apparatus of Example 1 was used to spray the formulation of Table 1 with carbon dioxide at 1500 psi and 50°C.
• densities of coating formulation and supercritical carbon dioxide were 0.9652g/cc and 0.3978 g cc, respectively.
• carbon dioxide into the formulation (a) up to 30 percent, the mixture densities decreased less than 1.2 percent.
• mixture densities decreased significantly, and the coating formulation displayed two distinct phases; a carbon dioxide rich phase and a polymer rich phase.
• Figure 13 is a graph of mixture density of the coating formulation listed below with carbon dioxide at 1500 psi and 50°C as measured by the spray unit depicted in Figure 6.
• the densities of the coating formulation and supercritical carbon dioxide were measured as 0.9700 g/cc and 0.3978 g/cc, respectively.
• the mixture density significantly decreased, and the mixture separated into distinctive two phases.
• Figure 14 is a plot of mixture density of coating formulation from Example 8 with supercritical ethane at 1500 psi and 50°C measured from a spray unit in Figure 5.
• the densities of the coating formulation and supercritical ethane were measured as 0.9652 g/cc and 0.203 g/cc, respectively.
• the mixture was a single clear phase.
• the mixture density decreased more than 19 percent.
• Figure 15 is a plot of mixture density of coating formulation from Example 7 with supercritical ethane at 1500 psi and 50°C measured from the spray unit depicted in Figure 6.
• the densities of 100 percent of coating formulation and supercritical ethane were measured as 0.9652 g/cc and 0.203 g/cc, respectively.
• the mixture showed a single clear phase.
• the mixture densities decreased more than 11.7 percent.
• Figures 12-15 clearly demonstrate that the unexpected constant density properties of the admixed coating formulations especially when using supercritical carbon dioxide as a viscosity reducing agent.
• the density of the mixture can vary significantly with increasing compressed fluid levels.
• the ethane mixtures did not exhibit a substantially constant density region when admixed, therefore the present invention would not be suitable for accurately proportionately these mixtures.

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• 1994
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