Patent Document

FIELD OF THE INVENTION 
     The present invention relates to mixing of multi-component coatings, and more particularly relates to an apparatus for dynamically mixing coating components before they are applied to a surface with a spray gun. 
     BACKGROUND INFORMATION 
     Two-component coating application systems are known in which each of the components are fed through a spray gun in the desired ratio for application to a substrate. Prior to feeding the components to the spray gun, they may pass through proportioning valves which control the mix ratio of the components. A static mixer in the form of a SEMCO type spiral mixer which allows paint to flow over elements prior to application/dispensing may then be conventionally used to mix the components before they are introduced into the spray gun. However, it would be desirable to provide a multi-component spray coating system in which the components are more completely mixed prior to spray application. 
     SUMMARY OF THE INVENTION 
     In certain respects, the present invention is directed to providing a multi-component coating spray application system comprising: a source of a first coating component; a source of a second coating component; a dynamic mixer in fluid flow communication with the sources of the first and second coating components, wherein the dynamic mixer comprises a mixing chamber and a movable stirring member in the mixing chamber; and a spray gun in fluid flow communication with an outlet port of the dynamic mixer. 
     In other respects, the present invention is directed to providing a dynamic mixer for multi-component coatings comprising: a mixing chamber; a movable stirring chamber in the mixing chamber; a first inlet port connectable to a source of a first coating component; a second inlet port connectable to a source of a second coating component; and an outlet port connectable to a spray gun. 
     In further respects, the present invention is directed to providing a method of mixing multiple coating components prior to spray application. The method comprises: providing first and second coating components to a mixing chamber; mixing the first and second coating components in the mixing chamber with a movable stirring element to form a coating mixture; and feeding the coating mixture from the mixing chamber to a coating spray gun. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates a multi-component spray coating system including a dynamic mixing apparatus in accordance with an embodiment of the present invention. 
         FIG. 2  is a partially schematic side sectional view of a dynamic mixing apparatus in accordance with an embodiment of the present invention. 
         FIG. 3  is a cross-sectional view taken through section  3 - 3  of  FIG. 2 . 
         FIG. 4  is a cross-sectional view taken through section  4 - 4  of  FIG. 2 . 
         FIG. 5  is a cross-sectional view taken through section  5 - 5  of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     For purposes of the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. 
     Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard variation found in their respective testing measurements. 
     Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10. 
     In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. In addition, in this application, the use of “or” means “and/or” unless specifically stated otherwise, even though “and/or” may be explicitly used in certain instances. 
       FIG. 1  schematically illustrates a multi-component spray coating system in accordance with an embodiment of the present invention. The system includes a dynamic mixing apparatus  10  in which at least two coating components are mixed and fed to a coating spray gun  11 . As shown in  FIG. 2 , the dynamic mixer  10  includes a mixing chamber  12  having a cylindrical sidewall  13 , a base  14  and a top  15 . In the embodiment shown in  FIG. 2 , the mixing chamber  12  can be opened by means of a threaded coupling, or any other suitable connection, between the cylindrical sidewall  13  and the base  14 . As shown most clearly in  FIGS. 2 and 3 , the mixing chamber  12  has a cylindrical baffle  16  which serves to divert the incoming flow of coating components for improved mixing, as more fully described below. As shown in  FIGS. 2 and 4 , a stirring element  18  in the form of an elongated permanent magnet loosely rests on the base  14  of the mixing chamber  12 . 
     As shown in  FIGS. 1-3 , a source of a first coating component  20  flows via line  21  through a first coating component inlet port  22  into the chamber  12 . A source of a second coating component  24  is fed via inlet line  25  through a second coating component inlet port  26  into the mixing chamber  12 . As shown by arrows in  FIG. 2 , the flow paths of the first and second coating components  21  and  25  are diverted in the mixing chamber  12  by the cylindrical baffle  16 . After the first and second coating components have been mixed in the mixing chamber  12 , the resultant mixture is fed via line  27  from an outlet port  28  of the mixing chamber to the spray gun  11 . The spray gun  11  may be any suitable type of spray gun known to those skilled in the art such as those commercially available from manufacturers such as Devilbiss, Graco, Kremlin, Binks and Wagner. While a two-component coating system is shown in the figures, it is to be understood that any other multi-component coating composition may be mixed and delivered to a spray gun in accordance with the present invention. For example, a three-component coating may be dynamically mixed, in which case a third inlet port (not shown) may be added to the mixing chamber  12 . 
     As shown in  FIGS. 1 ,  2  and  5 , the dynamic mixer  10  also includes a drive chamber  32  that is used to rotate the magnetic stirring element  18  contained in the mixing chamber  12 . The drive chamber  32  has a cylindrical sidewall  33 , a base  34  and a removable top  35 . The top  35  may be engaged with the cylindrical sidewall  33  by any suitable means, such as a threaded connection, snap fit or the like. A support pin  36  extends upward from the base  34  in the axial center of the drive chamber  32 . A rotatable impeller  40  having multiple radially extending paddles  42  at its outer periphery is rotatably mounted in the drive chamber  32  by means of a central hub  43  having a cylindrical hole or recess  44  which receives the support pin  36 . The drive chamber  32  includes an inlet port  46  through which a pressurized fluid may flow  47 . In one embodiment, the pressurized fluid is provided in the form of pressurized air from any suitable type of compressed air source. An exhaust port  48  allows the air to escape from the drive chamber  32 . An elongated permanent magnet  50  is fixedly mounted on the central hub  43  of the impeller  40 . 
     As shown most clearly in  FIG. 5 , when pressurized air  47  flows through the inlet port  46 , it contacts the paddles  42  and causes the impeller  40  to rotate around its central axis. Rotation of the impeller  40  causes rotation of the permanent magnet  50  which, in turn, causes rotation of the magnetic stirring element  18  inside the mixing chamber  12 . In this manner, the first and second components of the coating are dynamically mixed in the mixing chamber  12  by rotation of the magnetic stirring element  18 . The rotational velocity or rate of the magnetic stirring element  18  may be selected as desired, for example, up to 800 rpm. For example, a rotational rate of from 120 to 240 rpm may be suitable for many coating applications. 
     The dimensions of the mixing chamber  12 , magnetic stirring element  18 , drive chamber  32  and impeller  40  may be selected by those skilled in the art without undue experimentation. For example, the mixing chamber  12  may have an inner diameter of from 2.5 to 7.5 cm, and a height of from 2.5 to 10 cm. The magnetic stirring element  18  may have a length of from 2.5 to 4.5 dependent on the size of the chamber. In one embodiment, the magnetic stirring element  18  is generally cylindrical with rounded or convex ends. A typical diameter of a cylindrical magnetic stirring element is from 2.5 to 4.5 cm. 
     The drive chamber  32  may have an inner diameter of from 6 to 12 cm, and a height of from 5 to 12 cm. The impeller  40  is sized to fit within the drive chamber  32  and may have an outer diameter of 2.5 to 5 cm. The size and number of paddles  42  of the impeller  40  may be selected by those skilled in the art based upon the desired rotation rate and size of the impeller  40 , as well as the pressure and/or flow rate of the pressurized fluid  47  through the air inlet port  46 . A typical pressure for the pressurized air flow  47  is from 6 to 8 psi. 
     The various components of the dynamic mixer  10  may be made of any suitable materials. For example, the mixing chamber  12 , drive chamber  32  and impeller  40  may be made of polymers such as PTFE, PVDF and the like. 
     The flow rates and mix proportions of the first and second coating components  21  and  25  flowing into the dynamic mixing chamber  12  may be routinely selected by those skilled in the art. For example, typical flow rates for the first and second coating components may be from 25 ml to 500 ml. Typical mix ratios of the first to second coating components may be from 1:100 to 100:1, typically from 3:1 to 2:1. 
     In order to provide more complete mixing of the first and second coating components in the mixing chamber  12 , the components are diverted by the cylindrical baffle  16  as they enter the chamber  12 . As shown in  FIG. 2 , the inlet flows of the first and second coating components are diverted from substantially horizontal radial inward flows from opposite sides of the mixing chamber  12  to a downward flow toward the magnetic stirring element  18 . As the components are mixed by the magnetic stirring element  18 , the mixture is forced upward through the outlet port  28  of the mixing chamber  12  to the spray gun  11 . Mixing times within the chamber  12  are controlled by the size of the chamber and the flow rates of the incoming first and second components  21  and  25 . Typically, mixing times of from 2 to 10 seconds are suitable for many coating compositions and applications. 
     The first and second coating components may comprise any suitable compositions. For example, the coating compositions may include a film-forming resin or base. As used herein, “film-forming” refers to resins that can form a self-supporting continuous film on at least a horizontal surface of a substrate upon removal of any solvents or carriers present in the composition or upon curing at ambient or elevated temperature. 
     Conventional film-forming resins that may be used in one or more of the components of the coating compositions include those typically used in automotive OEM coating compositions, automotive refinish coating compositions, industrial coating compositions, architectural coating compositions, powder coating compositions, coil coating compositions, and aerospace coating compositions, among others. 
     Suitable resins include, for example, those formed from the reaction of a polymer having at least one type of reactive functional group and a curing agent having functional groups reactive with the functional group(s) of the polymer. As used herein, the term “polymer” is meant to encompass oligomers, and includes without limitation both homopolymers and copolymers. The polymers can be, for example, acrylic, polyester, polyurethane or polyether, polyvinyl, cellulosic, acrylate, silicon-based polymers, co-polymers thereof, and mixtures thereof, and can contain functional groups such as epoxy, carboxylic acid, hydroxyl, isocyanate, amide, carbamate and carboxylate groups. 
     The acrylic polymers, if used, are typically copolymers of acrylic acid or methacrylic acid or hydroxyalkyl esters of acrylic or methacrylic acid such as hydroxyethyl methacrylate or hydroxypropyl acrylate with one or more other polymerizable ethylenically unsaturated monomers such as alkyl esters of acrylic acid including methyl methacrylate and 2-ethyl hexyl acrylate, and vinyl aromatic compounds such as styrene, alpha-methyl styrene and vinyl toluene. The ratio of reactants and reaction conditions are selected to result in an acrylic polymer with pendant hydroxyl or carboxylic acid functionality. 
     Besides acrylic polymers, the coating compositions can contain a polyester polymer or oligomer, including those containing free terminal hydroxyl and/or carboxyl groups. Such polymers may be prepared in a known manner by condensation of polyhydric alcohols and polycarboxylic acids. Suitable polyhydric alcohols include ethylene glycol, neopentyl glycol, trimethylol propane and pentaerythritol. 
     Suitable polycarboxylic acids include adipic acid, 1,4-cyclohexyl dicarboxylic acid and hexahydrophthalic acid. Besides the polycarboxylic acids mentioned above, functional equivalents of the acids such as anhydrides where they exist or lower alkyl esters of the acids such as the methyl esters may be used. Also, small amounts of monocarboxylic acids such as stearic acid may be used. 
     Hydroxyl-containing polyester oligomers can be prepared by reacting an anhydride of a dicarboxylic acid such as hexahydrophthalic anhydride with a diol such as neopentyl glycol in a 1:2 molar ratio. 
     Where it is desired to enhance air-drying, suitable drying oil fatty acids may be used and include those derived from linseed oil, soya bean oil, tall oil, dehydrated castor oil or tung oil. 
     Polyurethane polymers containing terminal isocyanate or hydroxyl groups may also be used. The polyurethane polyols or NCO-terminated polyurethanes which can be used include those prepared by reacting polyols including polymeric polyols with polyisocyanates. The polyurea-containing terminal isocyanate or primary or secondary amine groups which can be used include those prepared by reacting polyamines including polymeric polyamines with polyisocyanates. The hydroxyl/isocyanate or amine/isocyanate equivalent ratio is adjusted and reaction conditions selected to obtain the desired terminal group. Examples of suitable polyisocyanates include those described in U.S. Pat. No. 4,046,729 at column 5, line 26 to column 6, line 28, hereby incorporated by reference. Examples of suitable polyols include those described in U.S. Pat. No. 4,046,729 at column 7, line 52 to column 10, line 35, hereby incorporated by reference. Examples of suitable polyamines include those described in U.S. Pat. No. 4,046,729 at column 6, line 61 to column 7, line 32 and in U.S. Pat. No. 3,799,854 at column 3, lines 13 to 50, both hereby incorporated by reference. 
     A silicon-based polymer can also be used in one or more of the coating components. As used herein, by “silicon-based polymers” is meant a polymer comprising one or more —SiO— units in the backbone. Such silicon-based polymers can include hybrid polymers, such as those comprising organic polymeric blocks with one or more —SiO— units in the backbone. 
     Certain coating compositions can include a film-forming resin that is formed from the use of a curing agent. For example, the first coating component may comprise a base or film-forming resin as described above, while the second coating component may comprise a curing agent. Curing agents suitable for use in the coating compositions can include aminoplast resins and phenoplast resins and mixtures thereof, as curing agents for OH, COOH, amide, and carbamate functional group containing materials. Examples of aminoplast and phenoplast resins suitable as curing agents in curable compositions include those described in U.S. Pat. No. 3,919,351 at column 5, line 22 to column 6, line 25, hereby incorporated by reference. 
     Also suitable are polyisocyanates and blocked polyisocyanates as curing agents for OH and primary and/or secondary amino group-containing materials. Examples of polyisocyanates and blocked isocyanates suitable for use as curing agents in curable compositions that may be used include those described in U.S. Pat. No. 4,546,045 at column 5, lines 16 to 38; and in U.S. Pat. No. 5,468,802 at column 3, lines 48 to 60, both hereby incorporated by reference. 
     Anhydrides as curing agents for OH and primary and/or secondary amino group containing materials are well known in the art. Examples of anhydrides suitable for use as curing agents in the coating compositions include those described in U.S. Pat. No. 4,798,746 at column 10, lines 16 to 50; and in U.S. Pat. No. 4,732,790 at column 3, lines 41 to 57, both hereby incorporated by reference. 
     Polyepoxides as curing agents for COOH functional group containing materials are well known in the art. Examples of polyepoxides suitable for use as curing agents in the coating compositions include those described in U.S. Pat. No. 4,681,811 at column 5, lines 33 to 58, hereby incorporated by reference. 
     Polyacids as curing agents for epoxy functional group containing materials are well known in the art. Examples of polyacids suitable for use as curing agents in the coating compositions include those described in U.S. Pat. No. 4,681,811 at column 6, line 45 to column 9, line 54, hereby incorporated by reference. 
     Polyols, that is, material having an average of two or more hydroxyl groups per molecule, can be used as curing agents for NCO functional group containing materials and anhydrides and esters and are well known in the art. Examples of said polyols include those described in U.S. Pat. No. 4,046,729 at column 7, line 52 to column 8, line 9; column 8, line 29 to column 9, line 66; and in U.S. Pat. No. 3,919,351 at column 2, line 64 to column 3, line 33, both hereby incorporated by reference. 
     Polyamines can also be used as curing agents for NCO functional group containing materials and for carbonates and unhindered esters and are well known in the art. Examples of polyamines suitable for use as in the coating compositions include those described in U.S. Pat. No. 4,046,729 at column 6, line 61 to column 7, line 26, and in U.S. Pat. No. 3,799,854 at column 3, lines 13 to 50, hereby incorporated by reference. 
     It will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed in the foregoing description. Such modifications are to be considered as included within the following claims unless the claims, by their language, expressly state otherwise. Accordingly, the particular embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.

Technology Category: b