Patent Publication Number: US-2009236025-A1

Title: Apparatus and methods for producing foamed materials

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/038,873, filed Mar. 24, 2008, the disclosure of which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     The present invention is generally related to apparatus and methods for producing foamed materials. 
     Single component fluid materials, such as polymeric materials like thermoplastic hot melt adhesives and polymeric coatings, may be foamed before being dispensed. To that end, conventional dispensing systems may inject a gas, such as nitrogen, into solution with a single component polymeric material to transform the polymeric material into a foamed version of the material. Compressed volumes of the compressible gas are entrained in the incompressible polymeric material. When the polymeric material is dispensed and the constraint on expansion is removed, the entrained volumes of gas rapidly expand and are trapped within the polymeric material to generate a foamed fluid material. These trapped cells comprise small bubbles of gas distributed throughout the polymeric material. The resulting foamed polymeric material may then be dispensed onto a target application area. 
     A benefit of foaming polymeric materials is the reduced weight at equal volume with the same thickness. This benefit is advantageous in several applications, such as the manufacture of motor vehicles like automobiles and the manufacture of aircraft. 
     Other types of foamed materials may be formed from two or more components that may, for example, chemically react when combined. Materials of this type may, for example, include two-component and three-component adhesives. Foamed multi-component materials may be produced by conventional techniques that rely on a chemical reaction to produce entrained volumes of gas. 
     Apparatus and methods capable of foaming multi-component materials without the need for a chemical reaction would be desirable. 
     SUMMARY 
     In one embodiment, a method is provided for producing a foamed material from a catalyst-containing component, a crosslinker-containing component, and a gas. The method includes mixing the catalyst-containing component and the crosslinker-containing component to form a mixture, mechanically mixing the gas with the mixture, and dispensing the mixture as the foamed material. The gas is entrained in the mixture and, when dispensed, expands to form the foamed material. The purely mechanical approach for foaming the catalyst-containing component and the crosslinker-containing component by introducing a gas overcomes various disadvantages of conventional approaches that rely on a chemical reaction to form the entrained gas. Generally, foamed multi-component materials may, for example, be desirable in aircraft manufacturing as their use as a replacement for identical non-foamed materials reduces the weight of material used for bonding aircraft components. 
     In another embodiment, an apparatus is provided for producing a foamed material from first and second fluid components and a gas. The apparatus includes a mixing device having a mixing chamber, a first inlet communicating with the mixing chamber, a second inlet communicating with the mixing chamber, a gas port communicating with the mixing chamber, and a mixing element inside the mixing chamber. The first and second inlets are configured for respectively admitting the first and second fluid components into the mixing chamber. The apparatus further includes a gas flow control valve coupled to the gas port and configured for introducing the gas through the gas port into the mixing chamber. The mixing element is configured to mix the first and second fluid components with the gas inside the mixing chamber to form a mixture that, when dispensed, produces the foamed material. The mixing device mechanically mixes the gas with the first and second fluid components, which eliminates the need to rely on a chemical reaction to provide the entrained gas. 
     In yet another embodiment, an apparatus is provided for producing a foamed material from first and second fluid components and a gas. The apparatus includes a first mixing device having a first mixing chamber and a first mixing element inside the first mixing chamber. The first mixing element is configured to mix the first and second fluid components. The apparatus further includes second mixing device having a second mixing chamber coupled in fluid communication with the first mixing device for receiving the first and second fluid components from the first mixing device, a second mixing element inside the second mixing chamber, and a port configured to provide access into the mixing chamber. A gas flow control valve is coupled with the port and is configured for introducing the gas into the first and second fluid components in the second mixing chamber. The second mixing element is configured to mix the first and second fluid components with the gas inside the second mixing chamber to form a mixture that, when dispensed, produces the foamed material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a dispensing system in accordance with an embodiment of the invention; 
         FIG. 2  is a schematic view of a dispensing system in accordance with another embodiment of the invention; 
         FIG. 3  is a perspective view of an exemplary mixing device that may be used in the dispensing system of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view taken generally along line  4 - 4  of  FIG. 3 ; 
         FIG. 5  is a broken away, cross-sectional view of another exemplary mixing apparatus that may be used in the system of  FIG. 2 ; 
         FIG. 6  is a perspective view of a gas infeed device of the mixing apparatus of  FIG. 5 ; 
         FIG. 6A  is a cross-sectional view taken generally along line  6 A- 6 A of  FIG. 6 ; 
         FIG. 7  is a broken away, enlarged cross-sectional view of a portion of the gas infeed device of  FIGS. 6 and 6A ; 
         FIG. 8  is a broken away, enlarged cross-sectional view of a mid-portion of the gas infeed device of  FIGS. 6 ,  6 A, and  7 , showing a needle tip thereof in a first position relative to a sealing seat; 
         FIG. 9  is a view similar to  FIG. 8  showing the needle tip in a second position different from that shown in  FIG. 8 ; 
         FIG. 10  is a broken away, enlarged cross-sectional view of an end portion of the gas injection module of  FIGS. 6-9 ; and 
         FIG. 10A  is an enlarged view of encircled area  10 A of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 1  and in accordance with an embodiment of the invention, a dispensing system  10  is used to produce a foamed material  11  incorporating a gas and a multiple-component material. A first fluid component of the multiple-component material is in the form of at least one base resin which may incorporate a catalyst, an accelerator, an initiator, or another reactive species. The base resin may be a homopolymer, a copolymer, or a polymer blend. Representative base resins may include, but are not limited to, silicones, acrylics, epoxies, polysulfides, and urethanes. The number of components may include, but are not limited to, two-component materials, three-component materials, or other multi-component blends and the reaction mechanism(s) may include, but are not limited to, addition curing, radical curing and other curing chemistries. A second fluid component of the multiple-component material, which is separate and distinct from the first component, contains a base resin and a multifunctional reactive species that can serve as a crosslinker. Generally, the crosslinker is a compound (polymer or single molecule species) that has multiple functionality as reactive groups. The multiple functionality, once reacted with the base resin, results in a three-dimensional network, thereby forming a final product. The crosslinker may be an organic substance or an inorganic substance contingent upon the specific polymer system. As an example, a suitable crosslinker for an epoxy base resin is typically organic while a suitable crosslinker for a silicone base resin is typically inorganic. 
     As used herein, the first fluid component is referred to as a catalyst-containing component and the second fluid component is referred to as the crosslinker-containing component. With regard to the catalyst-containing component, it is understood that the component may contain an accelerator, an initiator, or another reactive species instead or, or in addition to, a catalyst. The isolation of the catalyst in the catalyst-containing component from the crosslinker in the crosslinker-containing component prevents curing. 
     The first and second fluid components are stored in isolation from each other to preclude chemical reaction leading to crosslinking and are only combined shortly before the time of use. When combined together, a chemical reaction initiates and curing occurs to form a cured product. Specifically, the crosslinker in the crosslinker-containing component reacts with the catalyst in the catalyst-containing component to form a polymer network via one or more of numerous reactions depending on the specific catalyst and reactant structure. However, the combination of the catalyst-containing component with the crosslinker-containing component either does not result in a chemical reaction that produces gas or chemically reacts to produce only a negligible amount of gas that is insufficient in and of itself to result in a measurable change in the dispensed weight. 
     The dispensing system  10  of the representative embodiment includes a first mixing device in the form of a static mixer  24  that is operatively coupled to first and second feeding devices  30 ,  32 . For example, the feeding devices  30 ,  32  may include respective conduits or lines  30   a ,  32   a  and respective pumps  30   b ,  32   b  that withdraw amounts of the first and second fluid components from respective supplies  13 ,  15  and direct the withdrawn the respective first and second fluid components through the lines  30   a ,  32   a , through the static mixer  24 . The pressurization supplied by the pumps  30   b ,  32   b  forces the mixture of the first and second fluid components from the static mixer  24  toward a second mixing device in the form of a dynamic mixer  40 . Specifically, the feeding devices  30 ,  32  respectively feed the first and second fluid components from the respective supplies  13 ,  15  into a mixing chamber  37  of the static mixer  24  through respective ports  13   a ,  15   a  of the static mixer  24 . 
     In the representative embodiment, a control system  42  regulates the rate and/or amounts of the first and second fluid components that are fed through feeding devices  30 ,  32  and may include, without limitation, master and slave components  42   a ,  42   b  that cooperate in this regard to maintain an appropriate mixture. Check valves  43   a ,  43   b  are respectively disposed in lines  30   a ,  32   a  to selectively permit or restrict flow of the first and second fluid components into the static mixer  24 . 
     The static mixer  24  includes a mixing element  35 , which is located inside the mixing chamber  37 , that is operative to mix the first and second fluid components with one another to form a mixture. Conventional static mixers, which have no moving parts, are devices having a series of internal baffles or elements, such as a series of alternating right- and left-hand helical elements oriented at right angles to one another. Representative static mixers are disclosed in commonly-assigned U.S. Pat. No. 5,480,589, the disclosure of which is incorporated by reference herein in its entirety. For example, and without limitation, the dynamic mixer  40  may be of a type commercially known under the name Ultra FoamMix and available from Nordson Corporation of Westlake, Ohio. The mixing chamber  37  of the static mixer  24  is connected through a line  46  with an inlet  35   a  of a mixing chamber  40   a  of the dynamic mixer  40 . The mixture is routed from the mixing chamber  37  of the static mixer  24  to the mixing chamber  40   a  of the dynamic mixer  40 . 
     A pressurized gas, such as nitrogen, dry air, or an inert gas, is fed from a supply  48  into the mixing chamber  40   a  through a gas infeed device  50 . The gas from the supply  48  is supplied into the mixing chamber  40   a  of the dynamic mixer  40  through a port  40   b , which provides fluid access into the mixing chamber  40   a . The flow of the gas through port  40   b  into the mixing chamber  40   a  of the dynamic mixer  40  may be regulated by a gas flow control valve  49  of the gas infeed device  50 . Typically, the pressure of the gas being introduced into the mixing chamber  40   a  is maintained higher than the fluid pressure of the mixture inside the mixing chamber  40   a  so that the gas flows into the mixing chamber  40   a . Generally, the specific gas pressure will depend on the viscosity and flow rate of the mixture. As used herein, the process of mechanically injecting the gas into the mixture refers to the use of a mechanism to inject the gas into the mixture, in contrast to a chemical process that generates the gas from a chemical reaction. 
     The dynamic mixer  40  includes a mixing element  51  inside the mixing chamber  40   a  that combines the gas with the first and second fluid components of the multiple-component material. Representative dynamic mixers are disclosed in commonly-assigned U.S. Pat. No. 4,778,631, the disclosure of which is incorporated by reference herein in its entirety. As used herein, the process of mechanically mixing the gas with the mixture refers to the use of a either a static or moving mixing element to accomplish the requisite mixing to form a mixture that can be ultimately dispensed as a foamed material. 
     The material mixture containing the entrained gas exits an outlet of the dynamic mixer  40  through an outlet line  54  and is directed to a dispensing device  60 . The dispensing device  60  dispenses the foamed material  11  directly onto an application target, such as a substrate or another structural component (not shown). For example, the foamed material  11  may be applied to a first structural component of an aircraft and used to bond the first component with a second structural component of the aircraft. As specific examples, the foamed material  11  may be used as a fuel tank sealant, a windshield sealant, a firewall sealant, an electric potting compound, a conductive sealant, or as an aerodynamic and corrosion inhibitive sealant. 
     Dispensing device  60  is configured in a manner understood by a person having ordinary skill in the art to dispense the foamed material in discrete volumes, such as beads or dots, to provide an interrupted, non-continuous pattern on a moving substrate, or to dispense the foamed material as continuous beads or stripes. The dispensing device  60  may comprise a gun, a module, a hand gun, etc. For example, and without limitation, dispensing device  60  may take the form of a dispensing gun known under model AG900, which is available from the Nordson Corporation of Westlake, Ohio. In one specific embodiment, the dispensing device  60  may be any conventional hot melt dispenser, including but not limited to needle valve-type dispensers, capable of selectively actuating a needle tip relative to a sealing seat for intermittently discharging amounts of the mixture the multi-component material and entrained gas from a discharge orifice and providing a positive flow cutoff. The dispensing device  60  may be pneumatically actuated by the operation of a solenoid valve that supplies air pressure to an air cylinder for moving the valve stem away from the sealing seat, thereby allowing the mixture the multi-component material and entrained gas to flow to the discharge orifice. Alternatively, the dispensing device  60  may be electrically operated and include a coil that generates an electromagnetic field for moving an armature relative to a stationary pole, in which the stem is physically coupled with the armature for moving the valve stem relative to the sealing seat. The discharge orifice of the dispensing device  60  may be defined in a nozzle that may be readily removed and exchanged with other similar nozzles for varying the configuration of discharge orifice to dispense amounts, streams, dots or beads of the multi-component material and entrained gas characterized by a different size and/or a different shape for the foamed material  11  on the substrate. The dispensing device  60  may also include a trigger that is manually actuated to initiate dispensing. 
     A foam control system  58  controls the operation of the dynamic mixer  40  and may control, for example and without limitation, the flow of gas from supply  48  into the dynamic mixer  40  via the gas flow control valve  49  and/or the flow of the material out of the dynamic mixer  40 . The foam control system  58  is electrically coupled with the gas flow control valve  49  for this purpose. 
     When the mixture of multi-component material and entrained gas is dispensed from the dispensing device  60 , the discrete volumes of gas rapidly expand and are trapped, following expansion, within the volume of the multi-component material to generate the foamed material  11 . The trapped closed cells comprise small bubbles of gas distributed throughout the bulk of the foamed material  11  and provide a structure of closed cells in the cured material. The bubble distribution may be homogeneous or inhomogeneous depending upon, among other variables, the type of base resin, the desired density reduction, the residence time in the mixing chamber  40   a  of dynamic mixer  40 , and the flow rate of the mixture of the first and second fluid components. The gas bubbles displace a percentage of the multi-component material to define cells and yield a weight reduction of the cured product, as well as to alter/improve the mechanical properties of the cured product. 
     In an alternative embodiment, the dispensing device  60  may dispense the foamed material  11  into a temporary holding container, such as a cartridge  62 , for storage and subsequent dispensing. The foamed material  11  dispensed into the cartridge  62  may be frozen (as schematically illustrated by box  64 ) to permit storage in the cartridge  62  and subsequently heated to thaw the frozen foamed material to a dispensable condition and permit dispensing of the foamed material  11  from the cartridge  62 . The curing of the material is suspended at the temperatures characteristic of the frozen condition. While frozen, the gas may be retained within the mixture of the first and second fluid components such that the foamed condition is maintained during storage and survives until the material is unfrozen and dispensed. 
     After or during use, it may be necessary to clean one or more of the components of system  10 . System  10  may be cleaned using a schematically illustrated flushing system  70 , which may be coupled to one or more of the components of system  10 . In particular, flushing system  70  may dispense a cleaning agent such as a solvent  72  having a suitably chosen density to facilitate purging of residual portions of the first and second fluid components through and out of system  10 . While the exemplary embodiment of  FIG. 1  is shown having a single flushing system  70  coupled only to the static mixer  24 , it is contemplated that other embodiments may include any number of flushing systems that may be connected to static mixer  24  and/or to any other components of a foamed producing system. Flushing may be desirable when changing the type of multi-component material being dispensed. 
     The mix control system  42  and the foam control system  58  may each have a processor (not shown), which may be any suitable conventional microprocessor, microcontroller or digital signal processor, configured to execute software that implements control algorithms to permit the operation. The control systems  42 ,  58  may also have a memory (not shown) used to store programmed instructions for the processor, as well as user input/output devices. The control systems  42 ,  58  may be integrated into a single control system. 
     With reference to  FIG. 2  in which like reference numerals refer to like features in  FIG. 1  and in accordance with an alternative embodiment, a system  100  otherwise similar to system  10  ( FIG. 1 ) includes conduits or lines  30   c ,  32   c  that respectively feed the first and second fluid components directly into the interior of the dynamic mixer  40  through respective inlets  13   b ,  15   b , without first mixing in a static mixer or another like device. In this regard, lines  30   c ,  32   c  are fluidly coupled with dynamic mixer  40  to feed polymeric components directly into the mixing chamber  40   a  of the dynamic mixer  40 . The mixing element  51  of the dynamic mixer  40 , in turn, mixes the gas and the first and second fluid components with one another to form a mixture. Foam control system  58  may control the flow of gas from supply  48  and/or fluid components from supplies  13 ,  15  into the mixing chamber  40   a  of dynamic mixer  40  prior to, during, and/or subsequent to mixing of the first and second fluid components with one another in the dynamic mixer  40 . 
     With continued reference to  FIG. 2  and further referring to  FIGS. 3-4 , details are shown of an exemplary dynamic mixer in the form of a mixing device or apparatus  120 . Mixing apparatus  120  mixes the first and second fluid components from the supplies  13 ,  15  and the gas from the supply  48  to thereby produce the foamed material  11  ( FIG. 2 ). The apparatus  120  includes first and second modules  122 ,  124  respectively controlling supplies of the first and second fluid components into a mixing module  126 . A gas infeed device or gas flow control valve in the form of a gas injection module  132  controls supply of the pressurized gas, such as nitrogen, dry air, or an inert gas, into the interior of the mixing module  126 . The mixing apparatus  120  is fluidly coupled to and feeds material containing the entrained gas to a dispenser  135 , which in turn applies the foamed material  11  onto a desired target. 
     The first module  122  is fluidly coupled to the supply  13  of the first component through an elbow fitting  141 . Elbow fitting  141  may be of a quick-release type to facilitate coupling with the supply  13  of the first fluid component or it may alternatively be of any other type such as one including a threaded coupling. Air fittings  142   a ,  142   b  fluidly couple the first module  122  with a source of process air to pressurize the interior of the first module  122  and thereby facilitate supplying the first component to the mixing module  126 . The second module  124  similarly includes an elbow fitting  143  and air fittings  144   a ,  144   b  respectively similar in structure and/or function to the elbow fitting  141  and air fittings  142   a ,  142   b  associated with the first module  122 . Second module  124  is fluidly coupled to the supply  15  of the second fluid component. 
     With specific reference to  FIG. 4 , first and second internal conduits  152 ,  154  respectively fluidly couple the first and second modules  122 ,  124  with the mixing module  126 . More particularly, the first and second conduits  152 ,  154  extend from the respective interiors of the modules  122 ,  124  to a mixing chamber  160  of the mixing module  126 . The conduits  152 ,  154  access the mixing chamber  160  through respective inlet ports  152   a ,  154   a.    
     A mixing element  166  extends within the mixing chamber  160  and rotates to mix the first and second fluid components and the pressurized gas with one another to thereby form the gas-entrained multiple-component material. To this end, the mixing element  166  includes a central shaft  168  coupled for rotation to a motor (not shown) and a generally cylindrical body  170  attached to the shaft  168 . The cylindrical body  170  includes fins  174  that are helically arranged such that, during continuous rotation of the mixing element  166 , the fins  174  tend to force the components  13 ,  15  toward the inlet ports  152   a ,  154   a , thereby retarding the flow of the gas-entrained material toward an outlet port (not shown) coupled to the dispenser  135 . The fluid components flowing through the mixing chamber  160  and the incoming pressurized gas are therefore repeatedly divided by the fins  174  into minor streams and then recombined, thus creating a substantially homogeneous blend or mixture in the mixing chamber  160 . 
     The inlet ports  152   a ,  154   a  intersect the mixing chamber  160  near the upstream end of the mixing element  166 . In one embodiment, the inlet port  152   a  is used to introduce the first fluid component and is located upstream of the inlet port  154   a  used to introduce the second fluid component. This provides a purging or flushing action of the second fluid component through the mixing chamber  160 . 
     As discussed above, the gas injection module  132  injects the pressurized gas through a gas port  175  into the mixing chamber  160 . The gas is mixed or blended with the first and second fluid components in the mixing chamber  160 . In this regard, and with reference to  FIGS. 5-10A , an alternative gas injection module  132   a  is similar in most respects to gas injection module  132  ( FIGS. 3 ,  4 ) and forms part of a mixing apparatus  120   a  that is also similar in most respects to mixing apparatus  120  ( FIGS. 3 ,  4 ). For ease of explanation, like reference numerals in  FIGS. 5-10A  refer to like features of the preceding figures. In this embodiment, the gas injection module  132   a  has a main body  163  having an inlet  188  configured to receive the pressurized gas from the supply  48 , an outlet  190  coupled with the mixing module  126 , and a gas passage  192  between the inlet  188  and outlet  190 . The gas injection module  132   a  is configured to communicate the pressurized gas from the inlet  188  through the gas passage  192  to the outlet  190  and from the outlet  190  into the mixing chamber  160 . A control orifice  194  in the gas passage  192  is configured to meter a flow rate of the pressurized gas to the outlet  190 . To this end, the control orifice  194  may, for example, have an effective diameter of about 0.001 inches to about 0.002 inches. 
     With continued reference to  FIGS. 5-10A , the gas injection module  132   a  of this embodiment also includes a flow control element  200  in the gas passage  192 . The flow control element  200  has a first condition in which the pressurized gas can flow in the gas passage  192  from the inlet  188  through the control orifice  194  to the outlet  190 , and a second condition in which the pressurized gas is blocked from flowing to the outlet  190 . The flow control element  200  may be located in the gas passage  192  between the control orifice  194  and the outlet  190 . In this representative embodiment, the flow control element  200  includes a plunger  202 , a seat  204  between the outlet  190  and the control orifice  194 , and a biasing element such as a spring  206  that applies a biasing force that urges the plunger  202  into contact with the seat  204 . The plunger  202  is thus movable relative to the seat  204  to provide the first and second conditions above described. 
     The plunger  202  is movable relative to the seat  204  to provide the first condition when a fluid pressure between the plunger  202  and the inlet  188  exceeds a sum of the biasing force provided by the spring  206  and a fluid pressure between the plunger  202  and the outlet  190 . The plunger  202  is further movable to provide the second condition described above when the fluid pressure between the plunger  202  and the outlet  190  exceeds the sum of the biasing force provided by the spring  206  and the fluid pressure between the plunger  202  and the inlet  188 . 
     With continued reference to  FIGS. 5-10A , the plunger  202  has a non-contacting relationship with the seat  204  in the first condition of the flow control element  200 , while the plunger  202  has a contacting relationship with the seat  204  in the second condition ( FIG. 10 ). The main body  163  of the gas injection module  132   a  has a sealing seat  210  ( FIGS. 8-9 ) in the gas passage  192  between the inlet  188  and outlet  190  and a gas chamber  211  between the seat  204  and the control orifice  194  having a volume, in this embodiment, of about one cubic centimeter or less. A needle tip  220  ( FIGS. 8-9 ) is movable relative to the sealing seat  210  between an open position ( FIG. 8 ) in which the needle tip  220  is separated from the sealing seat  210  to permit the pressurized gas to flow past the sealing seat  210  and a closed position ( FIG. 9 ) in which the needle tip  220  contacts the sealing seat  210  to block a flow of the pressurized gas. An actuator is mechanically coupled with the needle tip  220  and is adapted to move the needle tip  220  relative to the sealing seat  210  between the open and closed positions. The actuator in this specific embodiment takes the form of a pair of pistons  222 ,  223  ( FIG. 6A ) coupled to a needle  225  that is in turn coupled to the needle tip  220  and an air pressure supply  300  that supplies air pressure under the control of controller  302  to cause movement of the pistons  222 ,  223  so as to provide the open and closed positions. The controller  302  may be subsumed within the foam control system  58 . 
     Other structural and functional details of the exemplary gas injection module  132   a  and mixing module  126  are disclosed in commonly-assigned U.S. patent application Ser. No. 11/939,150, filed Sep. 17, 2008, and the disclosure of which is hereby incorporated by reference herein in its entirety. The systems and methods of the various embodiments may use the foamed material, for example foamed polysulfide, to produce sheets, blocks and molded parts, which may be of particular benefit in aircraft manufacturing. 
     While the invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Thus, the invention in its broader aspects is therefore not limited to the specific details, and representative apparatus and method shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants&#39; general inventive concept.