Method for forming coating material formulations substantially comprised of a saturated resin rich phase

A method and apparatus for forming and dispensing a coating material formulation containing a liquid coating composition and a supercritical fluid as a diluent comprises a closed vessel having a hollow interior; a system for supplying fluid diluent into the vessel interior and for transforming the fluid diluent into supercritical fluid within the vessel; and, a system for introducing liquid coating composition into the vessel interior in such a way that it is sufficiently exposed to the supercritical fluid to form a fluid diluent rich phase and a liquid coating composition or resin rich phase which is saturated with supercritical fluid up to or near its saturation point for the temperature and pressure conditions within the vessel. The resin rich phase has a higher density than the fluid diluent rich phase and therefore collects on the bottom of the vessel from where it is withdrawn and supplied to coating dispensers for deposition on a substrate. The coating material formulation which is not discharged from the dispensers is preferably recirculated back into the closed vessel in such a way that it is permitted to absorb sufficient supercritical fluid to return to the saturation point.

RELATED APPLICATIONS 
This application is related to U.S. patent application Ser. No. 07/662,401, 
filed Feb. 27, 1991 and entitled "Method and Apparatus For Forming And 
Dispensing Single and Multiple Phase Coating Material Containing Fluid 
Diluent", now abandoned, and U.S. patent application Ser. No. 07/728,051, 
filed Jul. 15, 1991, entitled "Method and Apparatus for Forming and 
Dispensing Single and Multiple Phase Coating Material Containing Fluid 
Diluent," both of which are owned by the assignee of this invention and 
which are expressly incorporated herein by reference. 
FIELD OF THE INVENTION 
This invention relates to coating systems, and, more particularly, to a 
method and apparatus for combining a liquid coating composition with a 
supercritical fluid as a diluent, within a closed vessel, to produce a 
coating material solution or formulation consisting essentially entirely 
of a substantially saturated liquid coating composition or resin rich 
phase, having a predetermined proportion of liquid coating composition to 
supercritical fluid for given temperature and pressure conditions, which 
is transmitted to one or more coating dispensers for deposition on a 
substrate. 
BACKGROUND OF THE INVENTION 
A major problem of the coating and finishing industry, both in terms of raw 
material usage and in environmental effects, concerns the solvent 
components of paint. In a spray coating application of a resinous 
material, the resinous material is typically dissolved in an organic 
solvent provided with a viscosity suitable for spraying. This is required 
because it has been found that at each stage of the process for atomizing 
and conveying a resinous material in liquid form to a substrate, the 
liquid resists high speed deformation. Organic solvents are added to the 
resinous liquid because they have the effect of separating the molecules 
of resinous material and facilitating their relative movement making the 
solution more deformable at high speeds and therefore more susceptible to 
atomization. Substantial effort has been expended to reduce the volume of 
liquid solvent components in preparing high solids coating compositions 
containing about 50 percent by volume of polymeric and pigmentary solids. 
Nevertheless, most high solids coating compositions still contain from 15 
to 40 percent by volume of liquid solvent components. 
The problem with such a high volume content of liquid solvents in coating 
compositions is that during handling, atomization or deposition of the 
coating compositions, the solvents escape and can become air contaminants 
if not properly trapped. Once the coating composition is applied to a 
substrate, its solvents escape from the film by evaporation and such 
evaporated solvents can also contaminate the surrounding atmosphere. 
Additionally, since most solvents react with oxidants, pollution problems 
of toxicity, odor and smog may be created. Attempts at overcoming such 
environmental problems have proven to be costly and relatively 
inefficient. 
It has previously been proposed in Cobbs U.S. Pat. No. 4,247,581 to reduce 
solvent content in paint by mixing a liquid or gas blowing agent into the 
paint to produce an easily atomized foam solution just upstream from the 
discharge outlet of a dispensing device. Rehman et al U.S. Pat. No. 
4,630,774 disclosed an improvement of this concept wherein a foaming 
chamber and turbulence inducing device was incorporated into the coating 
dispenser to better control the formation of the foam prior to discharge 
from the outlet of the dispenser. U.S. Pat. Nos. 4,505,406; 4,505,957; 
and, 4,527,712 also disclose methods and/or apparatus for mixing liquid or 
gas blowing agents into paint formulations to reduce solvent content. Each 
of these patents are owned by the assignee of this invention. 
More recently, U.S. Pat. No. 4,923,720 to Lee et al disclosed a method and 
apparatus for the continuous production of a coating material formulation 
in which a substantial amount of the liquid solvent component is removed 
and replaced with a supercritical fluid such as supercritical carbon 
dioxide which functions as a diluent to enhance the application 
characteristics of the coating material formulation. The supercritical 
carbon dioxide and some liquid solvent material, e.g., about two thirds 
less than is required in other coating compositions, are intermixed with 
polymeric and pigmentary solids to form a coating material solution or 
formulation having a viscosity which facilitates atomization through an 
airless coating dispenser. As the coating material formulation is 
discharged from the dispensing device(s) toward a substrate, the 
supercritical carbon dioxide "flashes off" or vaporizes to assist in 
atomization of the high solids coating composition and to reduce drying 
time of the composition on a substrate. This type of coating material 
formulation, and those types of foamable formulations described above, 
have the advantage of substantially reducing the adverse environmental 
affects caused by high solvent content. 
It has been observed that in order to produce a coating material solution 
or formulation with the desired application characteristics, the relative 
proportion of the liquid coating composition and supercritical fluid 
should be maintained at a predetermined ratio or within a predetermined 
range. This produces a formulation which is either "single phase" or 
"multiple phase". A formulation is considered in single phase when the 
supercritical fluid is dissolved or dispersed within the liquid coating 
composition forming a single continuous phase of material having a given 
composition and density. A formulation is considered to be multiple phase 
when two or more phases of material are present, each having a different 
composition and density. A single phase formulation can be converted to a 
two phase formulation by adding more supercritical fluid, or by reducing 
system pressure, so that the first phase is generally continuous and the 
second phase is typically a "dispersed" phase or one having bubbles 
dispersed in the first phase. 
One problem with systems of the type disclosed in the Lee et al U.S. Pat. 
No. 4,923,720, which are designed for the continuous production of a 
coating material formulation, is an inability in some instances to control 
and/or maintain the relative proportion of liquid coating composition and 
supercritical fluid so that either a single phase or a multiple phase 
formulation is formed for transmission to coating dispensers. The 
ineffectiveness of the Lee et al system in this respect can be attributed 
to the pumping system it employs for supplying the liquid coating 
composition and/or supercritical fluid to the coating dispensers, and to 
the loss of supercritical fluid within the system caused by leakage, 
uneven mixing and the like. No provision is made in the Lee et al system 
for monitoring the liquid coating composition and/or supercritical fluid 
content within the system, nor are there any means for selectively 
altering the volume of either of these components in the course of the 
system operation. 
Many of these problems are also present in an alternative, batch-type 
system disclosed in U.S. Pat. No. 5,009,367 to Nielsen, which is owned by 
the same assignee as the Lee et al Pat. No. 4,923,720. As shown in FIG. 6 
of the Nielsen patent, the liquid coating composition and supercritical 
fluid are each weighed prior to introduction to the system, in 
predetermined proportions, and then introduced into a loop where they are 
intermixed within a static mixer in preparation for transmission to 
coating dispensers. This weighing procedure is cumbersome, and, like the 
Lee et al system, no provision is made in the Nielsen apparatus for 
adjusting the relative proportion of liquid coating composition and 
supercritical fluid once the system begins to operate. 
U.S. patent application Ser. No. 07/662,401, filed Feb. 27, 1991, and U.S. 
patent application Ser. No. 07/728,051, both entitled "Method and 
Apparatus For Forming And Dispensing Single and Multiple Phase Coating 
Material Containing Fluid Diluent", which are owned by the assignee of 
this invention, has addressed problems presented with systems of the type 
disclosed in the Lee et al U.S. Pat. No. 4,923,720 and Nielsen U.S. Pat. 
No. 5,009,367. The method and apparatus disclosed in application Ser. Nos. 
07/662,401 and 07/728,051 includes a control system which is effective to 
adjust the supply of supercritical fluid and/or liquid coating composition 
in accordance with variations in a sensed parameter, such as capacitance 
of the coating material formulation, in order to (1) maintain the coating 
material formulation in substantially single phase or in substantially 
multiple phase, as desired, in the course of an operating run; and, (2) to 
ensure that the desired ratio of liquid coating composition to 
supercritical fluid is obtained before the formulation is supplied to 
coating dispensers for deposition onto a substrate. The control system 
disclosed in application Ser. Nos. 07/662,401 and 07/728,051 is highly 
effective in forming and maintaining a coating material formulation having 
the desired supercritical fluid and liquid coating composition content, 
and provides substantial flexibility in accommodating different types of 
liquid coating compositions and different application characteristics on a 
given substrate. 
One potential limitation of the of system of Ser. Nos. 07/662,401, and 
07/728,051 however, are that they provide more control capability than may 
be required for certain applications. There has therefore been a need for 
a simpler, less expensive system of forming coating material formulations 
of the type described above for certain applications. A second limitation 
of this system is that it is relatively time consuming to clean in the 
event a change of color of the formulation is desired, and thus may not be 
readily adaptable or practically usable for multiple color applications. 
SUMMARY OF THE INVENTION 
It is therefore among the objectives of this invention to provide a method 
and apparatus for forming a coating material solution or formulation 
containing a liquid coating composition and supercritical fluid as a 
diluent, which reasonably accurately maintains the relative proportion of 
liquid coating composition and supercritical fluid during an operating 
run, which is relatively simple to operate, which is relatively 
inexpensive, and which permits the use of different color coating material 
formulations in multicolor applications. 
These objectives are accomplished in a method and apparatus for forming and 
dispensing a liquid coating formulation comprised of a liquid coating 
composition and a supercritical fluid wherein the liquid coating 
composition is sufficiently exposed to supercritical fluid within the 
interior of a closed vessel to permit the liquid coating composition to 
absorb the supercritical fluid up to its saturation point, at 
predetermined temperature and pressure conditions within the vessel, to 
produce a liquid coating composition rich phase which approaches or is at 
the equilibrium condition for the vessel conditions. This liquid coating 
composition rich phase, also known as the "resin rich phase", falls under 
the influence of gravity to the bottom of the vessel where it collects, 
and the remainder of the vessel, after the initial introduction of liquid 
coating composition, contains a fluid diluent rich phase. A coating 
material formulation, consisting substantially entirely of the resin rich 
phase, is then delivered to a coating dispenser for deposition onto a 
substrate, or, alternatively, is recirculated back into the closed vessel 
for reuse. As will later be explained in more detail, it has been observed 
that coating material formulations comprised substantially entirely of a 
saturated resin rich phase often have good application characteristics 
when dispensed. Thus, easily and reliably producing such a formulation is 
desirable. 
One aspect of this invention is predicated upon the concept of obtaining 
reliable control of the relative proportion of liquid coating composition 
and supercritical fluid forming the coating material formulation with a 
comparatively simple control system. In the presently preferred 
embodiment, means are provided for supplying liquid fluid diluent to the 
closed vessel, which is heated, including a supply tank containing the 
fluid diluent, a pump and a fluid pressure regulator interposed between 
the pump and the closed vessel. The fluid pressure regulator is set at a 
predetermined optimal pressure setting, determined experimentally during 
one system calibration procedure described below where the vessel pressure 
is varied while vessel temperature remains fixed, and this preferred 
pressure setting controls the pressure within the vessel. In an 
alternative system calibration procedure, the vessel temperature is 
varied, with the pressure being held constant, to arrive at a 
predetermined optimal temperature setting. 
The fluid pressure regulator controls the flow of fluid diluent from the 
supply tank and pump into the pressure vessel by permitting the passage of 
fluid diluent therethrough only in the event the pressure within the 
closed vessel falls below the predetermined level. The pressure regulator 
stalls the pump, and thus prevents the passage of fluid diluent 
therethrough, when the pressure within the closed vessel is at or above 
the predetermined level. As a result, fluid diluent is admitted into the 
closed vessel only as necessary to maintain the desired pressure therein. 
The fluid diluent is supplied to the vessel at a pressure above its 
critical pressure. Once in the vessel, the fluid diluent is heated above 
its critical temperature to become a supercritical fluid. The 
supercritical fluid within the vessel is dissolved within a particular 
liquid coating composition introduced into the vessel up to its saturation 
point to obtain a coating material formulation at the bottom of the vessel 
which is comprised substantially entirely of a saturated resin rich phase. 
The flow of liquid coating composition into the closed vessel is controlled 
with another relatively simple, yet reliable, control mechanism. In the 
presently preferred embodiment, means are provided for supplying liquid 
coating composition to the closed vessel including a container of liquid 
coating composition, a piston pump and a pair of flow switches each 
connected to a three-way valve. The three-way valves, in turn, are 
connected by supply lines to the closed vessel and by a control line to a 
level detector mounted to the closed vessel. This level detector is 
effective to sense the level of coating material formulation within the 
closed vessel in the course of a production run. The level detector sends 
a signal to the three-way valves to either open or close the flow of 
liquid coating composition to the closed vessel depending upon a 
predetermined, desired level of coating material formulation therein. The 
supply of liquid coating composition to the closed vessel is therefore 
dependent on the fluid level within the pressure vessel, whereas the 
supply of fluid diluent is dependent upon the pressure within the vessel. 
Since pressure and level control techniques are well developed and 
relatively inexpensive, the supercritical fluid saturated, resin rich 
phase can be reliably produced for delivery to one or more dispensing 
devices in a relatively simple and inexpensive way as compared to the 
other techniques. 
A key aspect of this invention is the provision of structure for adequately 
exposing the liquid coating composition to supercritical fluid within the 
interior of the closed vessel to produce a liquid coating composition rich 
or resin rich phase wherein supercritical fluid is dissolved within the 
liquid coating composition up to its saturation point for the temperature 
and pressure conditions within the vessel. In one presently preferred 
embodiment, adequate exposure of the liquid coating composition to the 
supercritical fluid is achieved using one or more atomizing spray nozzles, 
preferably located at the top of the vessel interior, which receive liquid 
coating composition from the three-way valves described above. The liquid 
coating composition is discharged in atomized droplets from the nozzles 
through a head or space of the fluid diluent rich phase, or supercritical 
carbon dioxide rich phase, located between the nozzles and the surface of 
the resin rich phase which is present at the bottom of the vessel. In the 
course of passage from the spray nozzles through the fluid diluent rich 
phase, the atomized droplets of liquid coating composition become 
substantially saturated with supercritical fluid thus forming more resin 
rich phase which is added to the body of resin rich phase present at the 
bottom of the vessel. Preferably, the resin rich phase which is withdrawn 
from the closed vessel but not discharged through the coating dispensers 
associated with the system is recirculated into the closed vessel at a 
location within the head or space of fluid diluent rich phase. Such 
recirculated formulation is thus re-exposed to additional supercritical 
fluid which may be dissolved therein as needed. 
In an alternative embodiment particularly adapted for high viscosity liquid 
coating compositions, sufficient exposure of the liquid coating 
composition to the supercritical fluid is achieved by a series of baffle 
plates which are provided within a baffle tube. The baffle tube is 
connected between the supply means for the liquid coating composition and 
the lower portion of the vessel. Virgin liquid coating composition is 
introduced at the top of the baffle tube which is filled with fluid 
diluent rich phase from the vessel interior. The virgin liquid coating 
composition is exposed to supercritical fluid by the baffle plates within 
the baffle tube to achieve saturation of the liquid coating composition up 
to its saturation or equilibrium point for the temperature and pressure 
conditions within the vessel. The saturated, resin rich phase thereby 
produced is collected on the bottom of the vessel for transmission to the 
coating dispensers as the coating material formulation. In the event 
coating material formulation is recirculated from the dispensers back to 
the closed vessel, a static mixer is preferably provided upstream from the 
baffle tube wherein the recirculated formulation and virgin liquid coating 
composition are initially combined and mixed prior to introduction into 
the baffle tube and vessel. The static mixer combines virgin liquid 
coating composition and the recirculated coating material formulation to 
at least partially reduce the viscosity of the virgin liquid coating 
composition in preparation for exposure to supercritical fluid within the 
baffle tube. 
One surprising finding of the applicants has been that adequate exposure of 
the liquid coating compositions, which have so far been tested, to 
supercritical fluid has been achieved using the atomization nozzle 
embodiment, and there has not yet been a need to employ the baffle tube 
embodiment. It is believed that even the higher viscosity coating material 
compositions are more easily atomized in the supercritical carbon dioxide 
environment inside the vessel than they would be in air, for example. 
Thus, it may be possible to use the spray nozzle embodiment to achieve 
adequate atomization and therefore adequate surface contact between the 
liquid coating composition particles and the supercritical fluid even with 
the higher viscosity liquid coating compositions. 
In addition to the relatively reliable and inexpensive material supply 
controls described above, another important advantage of this invention 
involves its versatility in accommodating liquid coating compositions of 
different color. The apparatus herein is essentially modular in 
construction in that a number of individual vessels can be provided, each 
connected to a separate source of liquid coating composition having a 
different color. In this embodiment, the output line from each, individual 
vessel is connected to a color change manifold of the type disclosed, for 
example, in U.S. Pat. Nos. 4,627,465 and 4,657,047 owned by the assignee 
of this invention. The color change manifold supplies the coating material 
formulation of a given color from one of the vessels to the coating 
dispensers for application on a substrate. To change colors, the color 
changer and liquid coating composition line to the dispenser are flushed 
and cleaned so that another color of coating material formulation can be 
supplied to the same dispensers with minimal downtime. This is 
advantageous in applications wherein a number of different colors must be 
utilized with the same spraying system.

DETAILED DESCRIPTION OF THE INVENTION 
The method and apparatus of this invention, and the various embodiments 
disclosed herein, are specifically intended to form a coating material 
solution or formulation in which a liquid coating composition and a 
supercritical fluid are combined within a closed vessel to form a liquid 
coating material solution or formulation for transmission to one or more 
dispensers for deposition onto a substrate (not shown). A number of terms 
are used in the following discussion to explain the method or process of 
this invention, and these terms are defined as follows. 
A "liquid coating composition" refers to materials such as paints, waxed 
base materials such as mold release agents, adhesives and other materials 
which include a solvent component and one or more components to be 
sprayed, applied or dispersed wherein a portion of the solvent component 
is replaced with a fluid diluent such as supercritical fluid in order to 
reduce solvent emissions. "Liquid coating compositions", as that term is 
applied to paints herein, is meant to refer to a mixture of solvent and 
"resin", e.g., pigments and other solids which are commonly found in 
commercially available paints. 
The term "supercritical fluid" as used herein is intended to refer to a gas 
in a supercritical state above its critical pressure and critical 
temperature. The term "liquified gas" refers to a gas in liquid state, 
which, when exposed to appropriate temperature and pressure, is capable of 
forming a supercritical fluid. The term "fluid diluent" as used herein 
refers to both supercritical fluids and liquified gases. The terms 
"coating material solution" and/or "coating material formulation" are used 
synonymously to refer to the combination of the fluid diluent or 
supercritical fluid and the liquid coating composition wherein the fluid 
diluent or supercritical fluid is substantially dissolved in the liquid 
coating composition to form a solution or at least an emulsion or 
dispersion. 
As described below in connection with an explanation of the process of this 
invention, the coating material formulation is produced by combining a 
liquid coating composition with a supercritical fluid or fluid diluent 
within a closed vessel. In the course of combining these materials, two 
distinct "phases" are produced at different locations within the vessel. 
One "phase" which is formed will be referred to herein as the "resin rich 
phase" or "liquid coating composition rich phase", and a second phase will 
be called the "fluid diluent rich phase" or "supercritical carbon dioxide 
rich phase". The terms "resin rich phase" and "liquid coating composition 
rich phase" are used synonymously to refer to a combination of 
supercritical fluid and liquid coating composition, i.e., resin and 
solvent, in which there is a relatively large percentage or proportion of 
resin and solvent compared to supercritical fluid. In this resin rich 
phase, the supercritical fluid is substantially dissolved or dispersed 
within the liquid coating composition. The terms "fluid diluent rich 
phase" and "supercritical carbon dioxide rich phase" are used synonymously 
to refer to a combination of supercritical fluid and liquid coating 
composition (resin and solvent) in which there is a relatively large 
percentage of supercritical fluid and a comparatively small amount of 
resin and solvent. Because both the resin rich phase and fluid diluent 
rich phase contain a combination of supercritical fluid, resin and 
solvent, in equilibrium with one another, each of such "phases" is 
technically considered a "coating material formulation" as that term is 
used herein. As discussed in detail below, a coating material formulation 
is removed from the vessel and supplied to one or more coating dispensers 
which consists substantially entirely of the resin rich phase because it 
is the resin rich phase, with its comparatively high proportion of resin, 
which is useful in forming an acceptable coating upon a substrate. 
The term "phase" is also used in another sense in the following description 
to explain the process of this invention. As described in detail below, 
exposure of the liquid coating composition to supercritical fluid within 
the closed vessel at predetermined pressure and temperature conditions 
results in the formation of a "saturated" resin rich phase. A saturated, 
resin rich phase refers to a condition wherein the liquid coating 
composition has absorbed all of the supercritical fluid it can, at given 
temperature and pressure conditions, while remaining in a "continuous or 
single phase" having a given composition and density. The term "single 
phase" in this context is meant to refer to a saturated state of the resin 
rich phase wherein the supercritical fluid, and liquid coating composition 
(i.e., resin and solvent), are in equilibrium with one another and are 
essentially continuous with no other material present. Depending upon 
pressure and temperature conditions within the vessel, a "two phase" 
condition can exist wherein at least some fluid diluent rich phase (i.e., 
a combination, in equilibrium, of primarily supercritical fluid with some 
resin and solvent) is dispensed within the resin rich phase (i.e., a 
combination, in equilibrium, of primarily resin and solvent with some 
supercritical fluid). Reference to "single phase" and "two phase" in this 
context is therefore concerned with the state of the resin rich phase 
which is drawn from the bottom of the vessel for delivery to the 
dispenser. As discussed below, the resin rich phase is denser than the 
fluid diluent rich phase because of the higher proportion of resin and 
solvent therein, and thus the resin rich phase naturally falls under the 
influence of gravity to the bottom of the vessel whereas the fluid diluent 
rich phase occupies the volume of the vessel above the level of the resin 
rich phase. 
A "coating dispenser" as used herein, at least in painting applications, 
refers to an airless-type spray gun capable of handling the fluid 
pressures employed in the method and apparatus of this invention. 
Preferably, the dispensers are airless spray guns of the type disclosed in 
co-pending U.S. Pat. No. 5,088,443, entitled "Method and Apparatus for 
Spraying a Liquid Coating Containing Supercritical Fluid or Liquified 
Gas," issued on Feb. 8, 1992, the disclosure of which is incorporated by 
reference in its entirety herein. Alternatively, air assisted airless-type 
spray guns can be used with the apparatus 10 of this invention such as are 
shown in U.S. Pat. No. 3,843,052 to Cowan. 
The purpose of the supercritical fluid is to act as a diluent for the 
coating composition so that the proportion or percentage of organic solids 
in the liquid coating composition can be reduced, e.g., by about 
two-thirds, compared, for example, to most commercially available high 
solids liquid coating compositions such as paint. A number of compounds in 
a supercritical state can be intermixed with a liquid coating composition, 
such as paint, to produce the coating material solution or formulation 
obtained by the means of the method and apparatus of this invention. These 
compounds include carbon dioxide, ammonia, water, nitrogen oxide (N.sub.2 
O), methane, ethane, ethylene, propane, pentane, methanol, ethanol, 
isopropanol, isobutanol, chlorotrifluoromethane, monofluoromethane, and 
others. For purposes of the present discussion, supercritical carbon 
dioxide is employed because of its non-toxic nature and because its 
critical temperature and critical pressure of 85.degree. F. and 1070 psi, 
respectively, are well within the operating ranges of standard airless 
spraying systems which could be used with the method and apparatus of this 
invention. 
The method of the present invention is first discussed followed by a 
description of an apparatus in its various embodiments, which can be used 
to practice the method of the invention. 
METHOD OF OPERATION 
The method of this invention is predicated upon the observation that 
coating material formulations consisting essentially entirely of the resin 
rich phase (i.e., primarily resin and solvent with some supercritical 
fluid) can often be sprayed onto a substrate with acceptable application 
characteristics when the resin rich phase is at or near the "two phase" or 
saturation point. As defined above, the resin rich phase becomes saturated 
at given pressure and temperature conditions when it cannot absorb any 
more fluid diluent, and wherein further attempts to dissolve additional 
fluid diluent or supercritical fluid into the resin rich phase produces a 
"two phase" mixture of resin rich phase and fluid diluent rich phase. The 
saturation point for a given resin rich phase can be "moved" or varied by 
changing pressure within the closed vessel at constant temperature, or 
conversely, by changing the temperature within the vessel at constant 
pressure. At different saturation points, the resin rich phase contains 
different proportions of resin, solvent and supercritical fluid. It has 
been observed that, in cases where the dispenser is a paint spray gun, 
saturated, resin rich phases with different proportions of resin, solvent 
and supercritical fluid produce different spray patterns of coating on a 
substrate, some of which are better than others. The method of this 
invention is therefore predicated upon the concept of producing a 
saturated, resin rich phase by combining a liquid coating composition 
(resin and solvent) with a supercritical fluid, in a simple, reliable and 
inexpensive manner, and then controlling the pressure and temperature 
within the vessel so that the resin rich phase reaches a saturation point 
where the particular proportions of resin, solvent and supercritical fluid 
forming the resin rich phase exhibit optimum application characteristics 
when sprayed onto a substrate. 
Reference is made to FIG. 1 to explain the concept of "moving" the 
saturation point of the resin rich phase, and how a "two phase" mixture of 
resin rich phase and fluid diluent rich phase can be produced. FIG. 1 
shows a phase diagram commonly known as a triangle diagram for a 
hypothetical coating material formulation at a given temperature and at 
three different pressures, e.g., P.sub.1 =1,000 psi; P.sub.2 =1,200 psi; 
and, P.sub.3 =2,000 psi. The curved lines P.sub.1, P.sub.2 and P.sub.3 
show the two phase boundary lines of the coating material formulation. For 
example, referring to the P.sub.2 curve, the area above the curve 
represents the single phase region at the P.sub.2 pressure where only a 
single phase would exist. Below the curve for P.sub.2 the formulation 
cannot exist as a single phase and separates into two phases along a "tie 
line" identified in FIG. 1. As shown in FIG. 1, assuming a liquid coating 
composition consisting of 60% resin solids and 40% solvent, as shown at 
point A, is combined with supercritical carbon dioxide at a constant 
P.sub.2 pressure of 1,200 psi, the liquid coating composition will absorb 
the supercritical carbon dioxide up to its saturation point represented by 
the point B on curve P.sub.2. Point B represents the composition of the 
resin rich phase. The tie line, mentioned above, starts at point B and 
intersects curve P.sub.2 at a point C which represents the composition of 
the supercritical carbon dioxide or fluid diluent rich phase. The resin 
rich phase and the fluid diluent rich phase are in equilibrium with each 
other at this temperature and pressure and can thus simultaneously coexist 
as two distinct phases. 
The triangle diagram illustrated in FIG. 1 is useful to determine the 
relative proportions of resin, solvent and supercritical carbon dioxide in 
both the resin rich phase and fluid diluent rich phase. To determine the 
resin composition of the resin rich phase represented by point B, for 
example, one begins at the side opposite the resin apex and counts the 
number of 10% increment lines which are crossed in order to reach point B. 
Five lines are crossed to reach point B and therefore the resin content is 
50%. Following this same procedure, the remaining components of the 
formulation are found to be 32% solvent, and 18% supercritical carbon 
dioxide. Likewise, using the same procedure, the composition of the 
supercritical carbon dioxide or fluid diluent rich phase is determined to 
be approximately 4.5% resin, 13% solvent and 82.5% supercritical carbon 
dioxide. 
The triangle diagram of FIG. 1 also illustrates the typical effect that 
pressure has on the two phase or saturation point of the resin rich phase. 
As shown in FIG. 1, as the pressure increases from P.sub.1 to P.sub.3, the 
curve is pushed down. The composition of the resin rich phase at P.sub.1 
(1,000 psi) is represented by point D, and point E represents the resin 
rich phase composition at P.sub.3 (2,000 psi). Reading the diagram, 
approximately a 12.5% supercritical carbon dioxide content is present in 
the resin rich phase at the 1,000 psi pressure. As noted above, the 
supercritical carbon dioxide present in the resin rich phase at the 1,200 
psi pressure is about 18%. Reading the diagram, it is determined that 
approximately 40% supercritical carbon dioxide is present in the resin 
rich phase at 2,000 psi. Thus, the higher the pressure at which the liquid 
coating composition and supercritical carbon dioxide are combined, the 
greater the proportion of supercritical carbon dioxide which is forced 
into or absorbed by the resin rich phase in order to reach the saturation 
point. 
While it is not shown in FIG. 1, variation in temperature within the vessel 
normally has a reverse effect on the supercritical carbon dioxide content 
of the resin rich phase, compared to pressure variation. Whereas 
increasing pressure forces more supercritical carbon dioxide into the 
resin rich phase, increasing temperature forces more supercritical carbon 
dioxide out of the resin rich phase and into the fluid diluent rich phase. 
Likewise, whereas reducing pressure results in the loss of supercritical 
carbon dioxide from the resin rich phase, reducing temperature drives 
carbon dioxide into the resin rich phase. Thus, whereas increasing 
pressure at constant vessel temperature pushes the curve down in FIG. 1, 
increasing temperature at constant vessel pressures would push the curve 
up and vice versa. 
In the presently preferred embodiment of this invention, the 
above-described method of this invention is advantageously performed 
within a closed, pressurized vessel wherein the liquid coating composition 
and fluid diluent or supercritical carbon dioxide can be introduced in a 
controlled manner and within which the pressure and temperature can be 
accurately controlled. According to the method of the present invention, 
the closed vessel is first supplied with a liquified gas through a 
pressure regulator. When using liquified carbon dioxide, for example, the 
vessel is maintained at a pressure and temperature above the critical 
pressure (1,070 psi) and critical temperature (85.degree. F.) for carbon 
dioxide to produce supercritical carbon dioxide which fills the vessel 
interior. The coating material composition is then introduced into the 
vessel in such a way that contact with, or exposure to, the supercritical 
carbon dioxide is maximized to enable the liquid coating composition to 
absorb the supercritical carbon dioxide up to its saturation point for the 
temperature and pressure conditions within the vessel. In one embodiment, 
the liquid coating composition is sprayed in atomized droplets from the 
top of the vessel which is preferably a vertically oriented, 
cylinder-shaped tank. In another embodiment, the coating material passes 
through a baffle tube containing supercritical carbon dioxide which is 
installed in the top portion of the vessel. In both embodiments, the 
liquid coating composition is allowed to become saturated with 
supercritical carbon dioxide as it passes down through the vessel so that 
a resin rich phase, saturated with supercritical carbon dioxide, collects 
on the bottom of the vessel. 
In the course of introducing virgin liquid coating composition into the 
vessel, the supercritical carbon dioxide which initially occupied the 
entire volume of the vessel absorbs solvent and resin from the liquid 
coating composition to form a fluid diluent rich phase, as defined above. 
This fluid diluent rich phase is less dense than the resin rich phase, 
because it contains a higher proportion of supercritical carbon dioxide, 
and therefore the fluid diluent rich phase remains in the upper portion of 
the vertical vessel above the level of the denser, resin rich phase which 
collects under the influence of gravity on the bottom of the vessel. The 
resin rich phase is substantially continuous with possibly small bubbles 
or microbubbles of the supercritical carbon dioxide or fluid diluent rich 
phase entrained therein. This resin rich phase, with perhaps some 
entrained fluid diluent rich phase bubbles, is then drawn off the bottom 
of the vessel and supplied to one or more dispensers such as spray guns as 
a coating material formulation for deposition on a substrate. 
The temperature can be maintained in the vessel by conventional heaters and 
temperature control means. The pressure is maintained by the pressure 
regulator which supplies the liquid carbon dioxide into the vessel. The 
amount of coating material formulation desired in the vessel can be 
maintained by simple level controls connected to the lines which supply 
virgin liquid coating composition to the vessel. It can therefore be 
appreciated that the method of this invention is useful to reliably 
produce a controlled quantity of a coating material formulation consisting 
substantially entirely of the saturated, resin rich phase, at or very 
close to its two phase point, for ready delivery to one or more coating 
dispensers such as spray guns. 
As described above, the higher density of the resin rich phase can be 
expected to separate within the vessel from the lower density fluid 
diluent rich phase by operation of gravity. But it is conceivable that for 
some coating material formulations, the difference in density between the 
two phases would not be adequate to achieve sufficient separation of the 
phases due to the chemical tendencies of some formulation compositions to 
form an emulsion. For these types of two phase compositions, other 
mechanisms known to those skilled in the art, such as a centrifuge, can be 
used to break or separate the emulsion into two substantially distinct 
phases. 
In addition, while in the above process it is generally the case and is 
preferred that only two phases be produced, e.g., a liquid coating 
composition rich phase and a fluid diluent rich phase, it is also possible 
that a "solvent rich phase" could be produced. The term "solvent rich 
phase" refers to a combination of solvent, resin and supercritical fluid 
which is predominantly comprised of solvent, and which has an intermediate 
density between the other two phases. Due to the intermediate density of 
the solvent rich phase, it would be located in the vessel above the liquid 
coating composition rich phase and below the fluid diluent rich phase. 
Because the higher density liquid coating composition rich phase resides 
at the bottom of the vessel, with or without the addition of a solvent 
rich phase, this liquid coating composition rich phase is always available 
to be drawn off the bottom of the vessel in the normal manner. It may be 
necessary, however, to adjust the level sensor if the normal level sensor 
reading is affected by the presence of the solvent rich phase. Otherwise, 
however, in all cases to date where the solvent rich phase has been 
observed, there has been an adequate head space provided for the fluid 
diluent rich phase to saturate the atomized droplets of liquid coating 
composition with supercritical fluid so the operation of the vessel 
according to the process of this invention has not been affected. 
Having described this inventive method, apparatus for practicing the 
invention are described below which illustrate that not only is the method 
herein reliable and far less complicated than other systems, but relies on 
relatively inexpensive and easy-to-use hardware. 
EMBODIMENT OF FIGS. 2 AND 3 
Referring now to FIGS. 2 and 3, one presently preferred embodiment of an 
apparatus 10 for practicing the method of this invention generally 
comprises a closed vessel 12, a fluid diluent or liquid carbon dioxide 
supply 14, a liquid coating composition or resin supply 16, and a supply 
and recirculation loop 18 for transmitting the coating material 
formulation to one or more coating dispensers 19. The liquid carbon 
dioxide supply 14 comprises a tank 20 containing liquid carbon dioxide. 
The tank 20 is connected by a line 22 to a piston pump 24, preferably of 
the type sold by the Haskell Company of Burbank, Calif. under Haskell Pump 
Model No. DSF-35. The liquid carbon dioxide is discharged from the output 
side of the piston pump 24 above the critical pressure through line 26 to 
a fluid pressure regulator 28, preferably of the type sold by Nordson 
Corporation of Westlake, Ohio under Nordson Part No. 248,830. The liquid 
carbon dioxide is discharged from the pressure regulator 28 through line 
30 to the top of closed vessel 12 as illustrated in FIG. 1. As discussed 
below in connection with the operation of apparatus 10, the liquid carbon 
dioxide is introduced into the closed vessel 12 first, at a pressure of 
about 1200 psi, which is above the critical pressure of supercritical 
carbon dioxide. The liquid carbon dioxide is heated inside the vessel to a 
temperature above the critical temperature to produce supercritical carbon 
dioxide, and thereafter liquid coating composition or resin from the resin 
supply 16 is introduced into the closed vessel 12 for combination with the 
supercritical carbon dioxide. 
In the presently preferred embodiment, the column or closed vessel 12 is a 
vertically oriented, generally cylindrical-shaped tank which is 
approximately 3 feet in height and 4 inches in diameter. A blanket heater 
32 is mounted in intimate contact with the exterior surface of the vessel 
12, and preferably is of the type sold by Watlow Cleveland Company of 
Chardon, Ohio under the Part No. 190200A. This heater 32 delivers 1500 
watts when energized with 240 volts and is effective to maintain the 
temperature of the material within vessel 12 at the desired temperature by 
means of a temperature controller 33. Temperature controller 33 is a Cal 
Series 9000 microprocessor based temperature controller Model No. 911.11F 
supplied by Cal Control Incorporated of Libertyville, Ill. The vessel 12 
also carries a level detector 34 of the type sold by the Endress & Hauser, 
Inc. of Greenwood, Ind. under the Part No. LSC1120. As described in more 
detail below, the level detector 34 is effective to sense the level of the 
saturated resin rich phase of the coating material formulation within the 
interior 13 of vessel 12 during the course of operation of apparatus 10. 
Referring to the top portion of FIG. 2, the liquid coating composition or 
resin supply system 16 comprises a resin supply container 36 connected by 
a line 38 to a piston pump 40 of the type sold by Nordson Corporation of 
Westlake, Ohio under Nordson Model No. 25B. The discharge side of piston 
pump 40 is connected through a suitable T connection (not shown) to branch 
lines 42 which are in turn connected to a pair of flow switches 44 and 46 
preferably of the type sold by or similar to Whitman Controls of Bristol, 
Conn., under Model No. P865-2. The flow switch 44 is connected by a line 
48 to a three-way, air operated valve 50, and the flow switch 46 is 
connected by a line 48 to an identical three-way valve 54. Each of the 
three-way valves 50 and 54 are preferably of the type manufactured by the 
Whitey Company of Highland Heights, Ohio under the Model No. SS-83XKF4-KL. 
As described in more detail below, each three-way valve 50 and 54 has an 
air operator or actuator 56a, 56b, respectively, preferably of the type 
manufactured by the Whitey Company under Model No. MS-153-SR. The 
three-way valve 50 is connected by a line 58 to a spray nozzle 60 mounted 
at the top of vessel 12, and three-way valve 54 is connected by a line 62 
to a spray nozzle 64 mounted at the top of vessel 12 beside the spray 
nozzle 60. A line 65 interconnects the level detector 34 with actuator 56a 
through line 66a, actuator 56b through line 66b, flow switch 44 through 
line 66c, and flow switch 46 through line 66d. As described in more detail 
below, the level detector 34 sends a signal through line 65 and then 
through lines 66a, b to the actuators 56a, 56b, respectively, which open 
or close the three-way valves 50, 54 depending upon the level of the resin 
rich phase of the coating material formulation present within the closed 
vessel 12. 
The liquid coating composition or resin supplied from the resin supply 16 
can contain impurities which could clog one or both of the spray nozzles 
60, 64. The resin supply 16 is therefore provided with an unclog 
capability depicted in FIGS. 2 and 3 to clear the nozzles 60, 64 of such 
impurities. 
FIG. 3 shows the unclogging mechanism for nozzle 60 only, but the mechanism 
for nozzle 64 is identical and directly parallels the mechanism shown in 
FIG. 3. As illustrated in FIG. 2, whenever level control 34 detects a 
resin rich phase level which is too low, it sends a "resin needed" signal 
via line 65 to the lines 66a, 66b connected to the actuators 56a, 56b for 
valves 50, 54 so that the valves 50, 54 can be rotated by actuators 56a, 
56b to the position shown in FIG. 3 to supply resin to the nozzles 60, 64. 
This same "resin needed" signal is sent via line 65 to the lines 66c, 66d 
connected to the flow switches 44, 46, respectively. As shown in FIG. 3, 
line 66c is connected to one side of a reed switch 73 which is 
spring-biased to the open condition. One magnetized contact 73a of reed 
switch 73 is supported on the outside of flow switch 44 and is connected 
by a line 78 to a timer 80. A stepped, central flow passage is formed in 
flow switch 44 which slidably receives a floating slug 74 carrying a 
magnet 75. As viewed in FIG. 3, both the floating slug 74 and magnet 75 
are formed with throughbores to permit the passage of liquid coating 
composition therethrough. A spring 76 urges the slug 74 and magnet 75 
upstream, or to the left as viewed in FIG. 3, into contact with the 
shoulder 77 formed in the wall of flow switch 44 by the stepped bore. In 
the normal operation of flow switch 44, liquid coating composition flows 
through flow switch 44, and through the bores in magnet 75 and slug 74, 
which unseats the magnet 75 from contact with shoulder 77 and pushes the 
magnet 75 and slug 74 downstream or to the right as viewed in FIG. 3 
against the force of spring 76. In the event of a clog of nozzle 60, resin 
builds up in the lines 48, 58 between the nozzle 60 and flow switch 44, 
thus reducing or stopping the flow through flow switch 44 and causing the 
magnet 75 to seat against shoulder 77 under the force of spring 76. This, 
in turn, places magnet 75 directly under the contacts 73a, 73b of reed 
switch 73. Because contact 73a of reed switch 73 is magnetized, it is 
attracted towards magnet 75 and makes contact with contact 73b to close 
the switch 73 between line 66c and line 78. 
Therefore, if resin is called for by the level detector 34, i.e., if a 
resin needed signal is sent through line 66c to flow switch 44, and the 
magnet 75 fails to unseat, the electrical circuit described above is 
completed through flow switch 44, and an unclogging procedure is initiated 
as follows. Timer 80 energizes the actuator 56 through line 82 to rotate 
the three-way valve 50 such that an internal passage 84 therein is shifted 
out of contact with an inlet port 85 formed in the three-way valve 50 
which is connected to line 48 from the flow switch 44. The internal 
passage 84 is moved by actuator 56 into contact with a vent port 86 formed 
in three-way valve 50 which opens to atmosphere. Such movement of internal 
passage 84 blocks the flow of resin from the flow switch 44 into the valve 
50, and forms a flow path from the nozzle 60 in an upstream direction 
through line 58, into the outlet 87 of internal passage 84 and then 
through the vent port 86 to atmosphere. With the three-way valve 50 in 
this position, the pressurized fluid diluent rich phase within the vessel 
interior 13 flows upstream in the reverse direction through the nozzle 60, 
line 58, internal passage 84 and out the vent port 86 in three-way valve 
50 carrying with it impurities which have clogged nozzle 60. 
In the presently preferred embodiment, the timer 80 causes the three-way 
valve 50 to rotate into this unclogging position for a fixed period of 
time, after which the valve 50 is returned to its original position to 
permit the passage of resin therethrough. In the event the unclogging 
operation is unsuccessful, slug 74 remains in contact with shoulder 77, 
and timer 80 automatically repeats the unclogging cycle. A counter 81 
counts each time the actuator 66a is energized by timer 80 within a given 
period of time, and if the clog still remains after five cycles within a 
predetermined time period an alarm 89 is sounded. If less than five cycles 
occur within such predetermined time period, the counter 81 resets itself. 
It should be understood that the identical structure described above is 
employed to clear nozzle 64 associated with three-way valve 54. 
Returning to FIG. 2 and referring to the righthand portion thereof, a 
supply and recirculation loop 18 is provided which includes a line 88, 
connected to the bottom of vessel 12, which draws a coating material 
formulation consisting substantially entirely of the resin rich phase from 
the bottom of vessel 12. Line 88 is connected to a heater 90 preferably of 
the type sold by Nordson Corporation of Westlake, Ohio under Model No. 
NH4. The coating material formulation is transmitted from the heater 90 
through line 92 to one or more coating dispensers 19. Heater 90 maintains 
the coating material at an appropriate temperature above the critical 
temperature for supercritical carbon dioxide while the coating material is 
in loop 18. The coating dispensers 19 are operative to discharge coating 
material formulation onto a substrate as required. 
When the coating dispensers 19 are not operated, or are operated 
intermittently, the coating material formulation is recirculated through a 
return line 96 and then through a restrictor 98 of the type sold by Whitey 
Valve Company of Highland Heights, Ohio under the Part No. SS-IRS6. The 
coating material then passes through a piston pump 102 of the type sold by 
Nordson Corporation of Westlake, Ohio under Nordson Model CP which pumps 
the material back into vessel 12. An accumulator 100 of the type sold by 
Parker Hannifin Corporation of Hillsborough, N.C. under the Part No. 
A2A0029A1A1E, is installed in the circulation line between restrictor 98 
and pump 102 to maintain a relatively constant input pressure at the inlet 
of pump 102. 
In an alternative embodiment, return line 96, restrictor 98 and accumulator 
100 could be removed if it is desired to "dead end" the flow of coating 
material formulation at the coating dispensers 19 and not recirculate it 
back to the vessel 12. In such embodiment, the pressure inside the vessel 
12 forces the coating material formulation through line 88, heater 90, and 
line 92 to the dispensers 19. 
OPERATION OF FIGS. 2 AND 3 EMBODIMENT 
With reference again to FIGS. 2 and 3, the operation of apparatus 10 is 
described as follows. First, the vessel heater 32 is set at an appropriate 
temperature above the critical temperature for carbon dioxide. Then, a 
fluid diluent such as liquid carbon dioxide is pumped into the vessel 
interior 13 by the liquid carbon dioxide supply 14 at a pressure above the 
critical pressure. The liquid carbon dioxide quickly achieves the critical 
temperature within the heated vessel 12 and is thereby transformed to 
supercritical carbon dioxide. Liquid carbon dioxide is continually 
supplied to the vessel 12 until the entire interior 13 of vessel 12 is 
filled with supercritical carbon dioxide to a preselected pressure of 1200 
psi, for example. 
Level detector 34 is then turned on with the result that three-way valves 
50, 54 are opened to permit the flow of "resin", i.e., liquid coating 
composition, from the resin supply 16 to the spray nozzles 60, 64. The 
spray nozzles 60, 64 atomize the liquid coating composition into 
relatively small droplets which are sufficiently exposed to the 
supercritical carbon dioxide while falling through vessel 10 that they 
become saturated with supercritical carbon dioxide and form a resin rich 
phase having a particular proportionate content of resin, solvent and 
supercritical carbon dioxide for the temperature and pressure conditions 
within the vessel 12. These saturated, resin rich phase droplets fall 
under the influence of gravity toward the bottom of vessel 12 where they 
collect and form a body of coating material formulation 104. 
In the presently preferred embodiment, the quantity of resin rich phase 
forming the coating material formulation 104 within the vessel interior 13 
is preferably maintained at a height of about 7 inches compared to the 
total height of 3 feet of the vessel 12. That portion or space 105 of the 
vessel interior 13 between the top surface 106 of the formulation 104 and 
the top of vessel 12 is filled predominantly with supercritical carbon 
dioxide rich phase, i.e., fluid diluent rich phase. After the initial 
introduction of virgin liquid coating composition into the vessel 12, the 
supercritical carbon dioxide within the vessel 12 is substantially 
converted to the fluid diluent rich phase which occupies space 105. It is 
contemplated that a small amount of fluid diluent rich phase may be 
intermixed with the resin rich phase or formulation 104 at the bottom of 
vessel 12 in the form of bubbles or microbubbles, but generally the top 
portion or space 105 of vessel 12 contains fluid diluent rich phase above 
the level of predominantly resin rich phase at the bottom of vessel 12. 
It has been observed that with some liquid coating compositions, when the 
composition is initially introduced into the vessel filled with 
essentially pure supercritical carbon dioxide, the solvent is sometimes 
immediately "stripped" from the liquid coating composition to form the 
supercritical carbon dioxide rich phase. As a result, insufficient solvent 
remains to properly form the resin rich phase so that a resin rich phase 
is initially formed which is "solvent poor" and does not produce a 
satisfactory coating on a substrate. Consequently, with these types of 
liquid coating compositions, the first "charge" of liquid coating 
composition may be dispensed from the dispensers into a waste container. 
Alternatively, prior to introducing the liquid coating composition into 
the vessel 12, a small charge of solvent can be introduced into the vessel 
from a solvent supply and pump through a suitable valve (not shown) to 
begin formation of the supercritical carbon dioxide rich phase by 
initially saturating, or partially saturating, the supercritical carbon 
dioxide with solvent prior to the introduction of the liquid coating 
composition. 
The discharge line 88 from vessel 12 is connected to the bottom of vessel 
12 in position to remove the coating material formulation 104, comprised 
substantially entirely of the resin rich phase, from the vessel 12 for 
transmission to the coating dispensers 19. It is contemplated that at 
least some pressure drop will occur in the course of transmitting the 
formulation from the vessel 12 to the coating dispensers 19. This pressure 
drop can cause the growth or formation of fluid diluent rich phase bubbles 
within the coating material formulation since lowering pressure releases 
some of the supercritical carbon dioxide from the resin rich phase into 
the fluid diluent rich phase as was explained above with reference to FIG. 
1. The presence of at least some fluid diluent rich phase bubbles can, 
however, assist in the atomization of the coating material formulation 
upon discharge from the coating dispensers 19 where dispensers 19 are 
spray guns. That is, the fluid diluent rich phase bubbles, as well as the 
dissolved supercritical carbon dioxide in the resin rich phase, rapidly 
expand upon discharge from the coating dispensers 19 to atmosphere which 
enhances the atomization of the formulation prior to deposition on a 
substrate. Moreover, the preformation of bubbles in the coating material 
formulation prior to the spray orifice can make the coating material 
easier to atomize as is taught in the prior art U.S. Pat. Nos. 4,247,581 
and 4,630,774 discussed above. 
One important aspect of this invention is the provision of means to 
relatively accurately control the proportion of liquid coating composition 
or resin, to supercritical carbon dioxide, in the coating material 
formulation to be dispensed. The desired proportion of these materials can 
vary substantially from one type of liquid coating composition to another, 
and the apparatus 10 must be capable of accommodating liquid coating 
compositions of different types and of maintaining the appropriate 
relative proportion of liquid coating composition to supercritical carbon 
dioxide during the course of an operating run. 
The preferred proportion of liquid coating composition to supercritical 
carbon dioxide is determined by alternative calibration procedures 
performed by the operator of apparatus 10. In one calibration procedure, 
vessel temperature is fixed while pressure is varied, and in the other 
calibration procedure the vessel pressure is fixed while temperature is 
varied. 
Referring to the former procedure, initially liquid carbon dioxide is 
introduced into the vessel interior 13 where it is converted to the 
supercritical state, and then liquid coating composition is added as 
described above. With vessel temperature held constant, several test 
sprays, or dispensing samples, are made of the resulting coating material 
formulation using different pressure settings of the pressure regulator 
28. 
For a given type of liquid coating composition, as discussed above, 
variation of the pressure setting of pressure regulator 28 changes the 
saturation point of the resin rich phase (i.e., the two phase point), 
resulting in variations of the relative proportion of supercritical carbon 
dioxide to liquid coating composition in the resin rich phase of the 
coating material formulation formed at the bottom of vessel 12. In the 
case where dispenser 19 is a spray gun, by changing the settings of 
pressure regulator 28, the operator can make a number of test sprays from 
coating dispensers 19 and determine which pressure setting forms a coating 
material formulation having the desired spray pattern for a given 
substrate. While the resin rich phases produced at different pressures are 
at or near their respective saturation points, some formulations produce 
superior spray patterns due to the changing supercritical carbon dioxide 
content. A pressure can therefore be selected which produces an optimal 
spray pattern, and this preferred pressure setting is then used during a 
production run for a particular liquid coating composition, with the 
temperature of vessel 12 held at the temperature setting used during the 
calibration mode. 
According to the alternative calibration procedure, the liquid carbon 
dioxide is again introduced into the vessel interior where it is converted 
to the supercritical state within vessel interior 13, and liquid coating 
composition is added as described above. With vessel pressure held 
constant, several test sprays, or dispensing samples, are made using 
different temperature settings by means of temperature controller 33. As 
discussed above, for a given type of coating material composition, 
variation of the temperature setting of temperature controller 33 changes 
the saturation point of the resin rich phase, resulting in variations of 
the relative proportion of supercritical carbon dioxide to liquid coating 
composition in the resin rich phase of the coating material formulation 
Where dispenser 19 is a paint spray gun, by changing the setting of 
temperature controller 33 the operator can make a number of test sprays 
from coating dispensers 19 and determine which temperature setting forms a 
coating material formulation having the desired spray pattern for a given 
substrate. While the resin rich phases produced at the different 
temperatures are all at or near their respective saturation points, some 
produce superior spray patterns due to their composition. A temperature 
can therefore be selected which produces the optimal spray pattern, and 
this temperature setting can be used during production runs, with the 
pressure of vessel 12 held at the pressure setting used during the 
calibration mode. 
As mentioned above, the level detector 34 functions to sense the level or 
height of the resin rich phase of coating material formulation 104 within 
the vessel interior 13 and sends a corresponding signal to the actuators 
56a, 56b associated with three-way valves 50 and 54. In the event the 
level of the resin rich phase 104 within the vessel interior 13 falls 
below the preferred level of about 7 inches, the level detector 34 signals 
the actuators 56a, 56b to open three-way valves 50, 54 to provide 
additional virgin liquid coating composition or resin into the vessel 12. 
In the embodiment of FIGS. 2 and 3, the supply of material into the vessel 
12 is supplemented by recirculation of unused coating material formulation 
through return line 96 in the event such material is not dispensed from 
the coating dispensers 19. As seen in FIG. 2, this recirculated coating 
material formulation is introduced by return line 96 into the space 105 
above the surface 106 of the coating material formulation 104 within 
vessel 12 for combination with the fluid diluent rich phase in such space 
105 so that additional supercritical carbon dioxide can be dissolved into 
the recirculated formulation, if necessary, to bring it back up to the 
saturation point. 
ALTERNATIVE EMBODIMENT OF FIG. 2A 
FIG. 2A shows various modifications of the basic system shown in FIG. 2. 
For the purposes of this discussion, the structure of FIG. 2A which is 
common to that of FIG. 2 is given the same reference numbers. 
A heater 200 is shown in the line 30 between pressure regulator 28 and 
vessel 12. In the FIG. 2 embodiment, as described above, liquid carbon 
dioxide below the critical temperature is introduced into vessel 12 and is 
transformed into supercritical carbon dioxide within the vessel 12 because 
the heater 32 maintains the vessel interior 13 at a temperature in excess 
of the critical temperature for carbon dioxide. But introducing liquid 
carbon dioxide below the critical temperature into vessel 12 may be 
undesirable in some situations, such as at high flow rates where the 
liquid carbon dioxide may have too much of a cooling effect on contents of 
vessel 12. This can cause coagulation of the liquid coating composition 
within vessel 12, because liquid carbon dioxide is not as good a solvent 
as supercritical carbon dioxide. To avoid this condition, in the 
embodiment of FIG. 2A the liquid carbon dioxide is heated above the 
critical temperature in heater 200 and thereby transformed into 
supercritical carbon dioxide before being introduced into vessel 12. 
Pressure regulator 28 maintains the liquified carbon dioxide above its 
critical pressure as in the embodiment of FIG. 2. 
Another variation shown in FIG. 2A is the placement of a temperature 
control device 202 and pressure control device 204 in the line 88 between 
the vessel 12 and the dispensers 19. Temperature control device 202 could 
be a heater such as the heater 90 shown in FIG. 2, or it could be a 
chiller. The function of the temperature control device 202 in FIG. 2A is 
to vary the temperature of the coating material formulation drawn from the 
bottom of vessel 12 to either suppress or encourage the formation of fluid 
diluent rich phase bubbles in the resin rich phase. If device 202 
increases the temperature of the formulation, then the formation and 
expansion of fluid diluent rich phase bubbles will increase since the 
increasing temperature will drive supercritical carbon dioxide out of the 
resin rich phase and into the supercritical carbon dioxide rich phase. 
Conversely, if the temperature of the formulation is reduced by device 
202, the formation of fluid diluent rich phase bubbles will be suppressed 
as the supercritical carbon dioxide in any fluid diluent rich phase 
bubbles which are present will be driven into the resin rich phase. Thus, 
device 202 can be used to control the size and number of fluid diluent 
rich phase bubbles in the formulation in line 88, which, in turn, affects 
the spray pattern from dispensers 19. 
Similarly, pressure control device 204 can be used for the same purpose. 
Pressure control device 204 can be a pump, such as a pump 102 in the 
circulation loop 18 which operates to increase the pressure in the 
formulation in line 88, or a pressure regulator to reduce the pressure of 
the formulation in line 88. By increasing the pressure, the device 204 
will drive the supercritical carbon dioxide from any fluid diluent rich 
phase bubbles into the resin rich phase suppressing bubble formation. 
Conversely, reducing the pressure will encourage bubble formation. Thus, 
like temperature control device 202, device 204 can be used to control the 
size and number of fluid diluent rich phase bubbles in the formulation 
delivered to dispensers 19 which will affect the spray pattern, or other 
dispensing pattern, produced. 
In yet another embodiment (not shown), if pressure control device 204 is a 
pump, then pump 102 and accumulator 100 could be eliminated from the loop 
18 in that they would not be necessary to circulate the coating material 
formulation around loop 18, and then return the formulation to vessel 12 
if not dispensed. 
ALTERNATIVE EMBODIMENTS OF FIGS. 4 AND 5 
With reference to FIGS. 4 and 5, alternative embodiments of this invention 
are illustrated which employ much of the same structure described above in 
connection with FIGS. 2 and 3. For purposes of this discussion, the 
structure of FIGS. 4 and 5 which is common to that of FIGS. 2 and 3 is 
given the same reference numbers. 
Referring to FIG. 4, an apparatus 108 is illustrated which is particularly 
adapted for liquid coating compositions or resins having a relatively high 
viscosity. High viscosity coating compositions may be more difficult to 
atomize with the spray nozzles 60, 64 of FIG. 2, which could reduce the 
exposure of the liquid coating composition to supercritical fluid to such 
an extent that saturation of the liquid coating composition to the two 
phase point would not occur. For such types of relatively high viscosity 
coating materials, apparatus 108 may better achieve the desired saturated 
condition. Apparatus 108 is identical to apparatus 10, except for a 
modification of the resin supply, the provision of a modified vessel 110 
and the addition of a static mixer 112 of the type preferably sold by TAH 
Industries of Inlaystown, N.J. under the Model No. TAH Series 100. 
In this embodiment, virgin liquid coating composition or resin is directed 
from a resin supply container 36 and pump 40 into a valve 113 which is 
connected by a line 115 to the static mixer 112. The flow switches 44, 46, 
three-way valves 50, 54 and actuators 56a, 56b of FIGS. 2 and 3 are 
eliminated. 
Static mixer 112 is connected by a line 118 to modified vessel 110. 
Modified vessel 110 includes a baffle tube 114 containing a number of 
angled baffle plates 116 illustrated schematically in FIG. 4. Baffle tube 
114 is mounted over an inlet 120 to the main body portion of vessel 110. 
Liquid carbon dioxide is supplied by the carbon dioxide supply 14 to the 
vessel 110 through a pressure regulator 28 and transformed within vessel 
110 into supercritical carbon dioxide in the identical manner described 
above in connection with FIGS. 2 and 3. After the initial formation of a 
resin rich phase within vessel 110, a head or space 122 of fluid diluent 
rich phase is formed within the vessel interior 111 above a coating 
material formulation 124 which collects at the bottom of vessel 110. The 
fluid diluent rich phase also enters and fills the baffle tube 114 through 
inlet 120. As the virgin liquid coating composition flows down through the 
baffle tube 114, it is continually exposed to the fluid diluent rich phase 
and absorbs supercritical carbon dioxide up to the saturation point before 
being discharged from the baffle tube 114 into the interior 111 of vessel 
110 to form the body of coating material formulation 124 at the bottom of 
vessel 110. As described above in connection with FIGS. 2 and 3, the body 
124 of coating material formulation which collects at the vessel bottom 
consists substantially entirely of a resin rich phase with some entrained 
fluid diluent rich phase bubbles. 
The coating material formulation is withdrawn from vessel 110 and enters 
loop 18 for transmission to dispensers 19, as described above. Coating 
material formulation not sprayed or dispensed from dispensers 19 enters 
return line 96 and flows through restrictor 98, past accumulator 100, and 
through pump 102 in the same manner as was described with reference to 
FIG. 2. In this embodiment, however, the outlet of pump 102 is delivered 
through line 96 into the line 115 between control valve 113 and static 
mixer 112. The recirculated coating formulation is thus merged with virgin 
coating material composition from supply 36 in line 115, and mixed 
together in static mixer 112, before being delivered into the top of 
baffle tube 114. By mixing the recirculated coating material formulation 
with the virgin liquid coating composition, the viscosity of the virgin 
liquid coating composition is at least partially reduced so that it is 
more easily saturated in baffle tube 114 with supercritical carbon dioxide 
up to the saturation point before being discharged from baffle tube 114 
into vessel 110 as the coating material formulation. 
Level detector 34 controls the level of the resin rich phase in vessel 110 
in the same manner as described with reference to FIG. 2 except that when 
the level in vessel 110 is too low, the resin needed signal is sent along 
a line 120 to valve 113 which is a simple on/off valve. This on/off valve 
113 supplies liquid coating composition through line 115 until it is shut 
off by another signal from level detector 34 via line 120. 
With references to FIG. 5, a further alternative embodiment of an apparatus 
126 of this invention is illustrated which is particularly adapted for 
applications wherein frequent color changes of the resin are required. In 
this apparatus 126, a first vessel 12a and a second vessel 12b are 
provided to receive liquid coating compositions, such as paint, of 
different color. The vessel 12a is connected to a resin supply 16a which 
provides a resin or liquid coating composition having a first color, and 
the vessel 12b is connected to a resin supply 16b which provides a resin 
having a second color. Both of the vessels 12a and 12b are supplied with 
liquid carbon dioxide from a single liquid carbon dioxide supply 14. The 
vessels 12a, 12b, the resin supplies 16a, 16b and the carbon dioxide 
supply 14 are identical in structure and function to those described above 
in connection with FIGS. 2 and 3. 
In the presently preferred embodiment, a discharge line 88a from vessel 12a 
is connected to a color change manifold 128 of the type disclosed in FIGS. 
1 and 3 of U.S. Pat. No. 4,657,047, or in U.S. Pat. No. 4,627,465, for 
example, owned by the assignee of this invention, the disclosures of which 
are incorporated by reference in their entireties herein. The color change 
manifold 128 has an inlet 151 for color A connected to line 88a from 
vessel 12a, as well as an outlet 152 from color changer 128 back into 
vessel 12a for returned or recirculated coating material formulation of 
color A. Likewise, color changer 128 has an inlet 153 for color B 
connected to line 88b from vessel 12b, as well as an outlet 154 from color 
changer 128 back into vessel 12b for recirculated coating material 
formulation of color B. If color A is selected at color changer 128, for 
example, valving in color changer 128 routes color A from inlet 151 to 
color changer outlet 155 which is connected to line 92 of loop 18. Color A 
coating material formulation is thereby delivered to spray guns 19 for 
spraying, and any unused color A formulation is returned from pump 102 and 
through return line 96 to color changer inlet 156. The color A formulation 
is then routed through valving in color changer 128 to outlet 152 so that 
it can be returned to vessel 12a. 
To change to color B, the valving for color A inlet 151 and color A outlet 
152 is first closed. Solvent 138 is then directed through solvent inlet 
157 into the color changer 128, and through outlet 155 into loop 18 so 
that all elements of the loop 18, including guns 19, are flushed of color 
A. The flushed color A and solvent are returned to color changer 128 
through inlet 156 and routed by valving in color changer 128 through dump 
outlet 158 into a dump tank 160. Pressurized air from a source 140 can 
then be admitted into the color changer manifold 128 through an inlet 159 
so that it can push any remaining solvent through outlet 155 and 
circulation loop 18, and then back into inlet 156 and through the dump 
outlet 158. The pressurized air also dries the paint flow passages of 
color changer 128 and circulation loop 18 so that color changer 128 and 
loop 18 are clean, dry and ready for color B. The structure and function 
of the apparatus 126 of FIG. 5 is otherwise identical to that described in 
connection with FIGS. 1 and 2. 
A variation of the embodiment shown in FIG. 5 is shown in FIG. 5A. Whereas 
air and solvent were used to flush paint from the color changer 128 and 
loop 18 in FIG. 5, the FIG. 5A embodiment uses supercritical fluid diluent 
as the flushing solvent. Assuming carbon dioxide is used as the fluid 
diluent, liquid carbon dioxide discharged from the outlet of pressure 
regulator 28 above the critical pressure would be heated in a heater 300 
above the critical temperature to transform the liquid carbon dioxide into 
supercritical carbon dioxide. The supercritical carbon dioxide is 
introduced into an inlet 302 to color changer 128 in place of the solvent 
supplied from supply 138 in the embodiment of FIG. 5. The supercritical 
carbon dioxide pushes the paint from the color changer 128, through loop 
18 and then back through color changer 128 into the dump tank 160. Once 
the waste material had been dumped through outlet 158 into tank 160, the 
inlet 302 is closed by valving in color changer 128, and the paint flow 
passages in color changer 128 and loop 18 are depressurized through dump 
outlet 158. Depressurization of the supercritical carbon dioxide in the 
paint flow passages dries the paint flow passages in preparation for the 
next color of coating material formulation to be sprayed. In this 
embodiment, therefore, pressurized air would not be needed to purge or dry 
the system between color changes. 
While the invention has been described with reference to a preferred 
embodiment, it will be understood by those skilled in the art that various 
changes may be made and equivalents may be substituted for elements 
thereof without departing from the scope of the invention. In addition, 
many modifications may be made to adapt a particular situation or material 
to the teachings of the invention without departing from the central scope 
thereof. 
For example, a total of two vessels 12a and 12b been illustrated in the 
apparatus 126 of FIG. 5, but it should be understood that essentially any 
number of vessels 12 could be employed, as desired. Additionally, while 
the color changer embodiment of FIG. 5 is illustrated with vessels 12a and 
12b of the type shown in FIG. 1 having spray nozzles 60, 64, it should be 
understood that two or more modified vessels 110 including baffle tube 114 
as shown in FIG. 4 could be employed in the embodiment of FIG. 5. FIG. 5 
is provided to illustrate the ease with which this invention can be 
adapted for use in applications requiring a number of different colored 
resins. 
In addition, it is noted that the liquid carbon dioxide is introduced at 
the top of the vessels 12 in the various embodiments illustrated herein, 
but it should be understood that the liquid carbon dioxide could also be 
introduced at the bottom of the vessel 12 and flow upwardly for 
combination with the liquid coating composition. 
Therefore, it is intended that the invention not be limited to the 
particular embodiment disclosed as the best mode contemplated for carrying 
out this invention, but that the invention will include all embodiments 
falling within the scope of the appended claims.