APPARATUS AND METHOD FOR COATING PARTICULATE MATERIAL WITH BINDER RESIN PRIOR TO FORMING PARTICLE BOARD

Abstract: An apparatus is disclosed for the continuous dispensing and blending of a fluid material with a particulate material in predetermined quantities. A master control is provided for synchronizing the startup and interruption of the systems for furnishing the particulate material and the fluid material and for operation of the blending apparatus, thereby facilitating the continuous operation thereof. The system is particularly adapted for use in the coating of wood furnish with binder adhesive prior to the pressing and heating of the wood furnish to form particle boards and the like.

Description: The present invention relates to an apparatus and a method for continuously coating particulate material with a fluid material, of the type stated in the first part of claims 1 and 9. An apparatus and a method of the same kind are known from DE-A-2 138 082. Particle boards, and other composites derived by binding together particulate material using an adhesive binder, are prepared by coating the particulate material with the adhesive binder and forming the coated particles into a mat which is then subjected to the action of heat and pressure in order to prepare the final composite. In commercial production processes the coating of the particles, the formation of the mat, and the pressing operation are carried out in a substantially continuous manner (cf. for example, US-A-3 796 529 and US-A-4 320 715). Illustratively, the particulate material and the binder are brought together and blended using various types of mechanical blender and then passed to a storage bin or the like. From the latter the coated particles are dispensed on to a moving belt to form a mat which is subsequently conducted on the moving belt through a zone in which the mat is subjected to heat and pressure to form the particle board. The adhesive used to prepare particle boards has hitherto commonly been a phenol--formaldehyde resin, but, more recently, polyisocyanates, particularly polymethylene polyphenyl polyisocyanates, have been used as the adhesive binder. Various methods of mechanically blending the particulate material and the binder have been described and employed in the art. Since the cost of the binder is a significant proportion of the total cost of the raw materials in production of the particle boards, it is desirable that the mixing of the binder and the particulate material be carried out as efficiently as possible without any significant loss of binder in the process. Centrifugal blenders have been employed in which the binder is dispensed through rotating radial dispensing arms in a housing through which the particulate material is being fed. Document US-A-4,320,715 discusses this type of centrifugal blender and notes certain drawbacks. The patent describes a different form of blending in which the particles are caused to fall downwardly on the periphery of a blender vessel with a spray of fluid coating material being directed outwardly against the falling furnish by use of a series of rotating inverted conical atomizer disks. The above types of systems appear to be reasonably satisfactory when phenol-formal-dehyde is employed as the binder resin. However, in the case of the polyisocyanate binders, the quantity of binder being applied to the particulate material is significantly less and cannot be easily dispensed in a uniform manner using the above types of operation. Further, in a particular method of employing polyisocyanates as the binder resin, the polyisocyanate is emulsified in water and the emulsion is applied to the particulate material. Such emulsions of polyisocyanate have only a limited stability and, if prepared and stored prior to a production run, can be rendered useless or unsatisfactory if any breakdown of the production line occurs involving long delays which extend beyond the useful life of the emulsion. When using polyisocyanates as the binder in coating particulate material, particularly for particle boards, it is highly desirable that the coating operation can be interrupted at any given moment in order to accommodate shutdowns of the production line in which the coated particles are being converted to finished boards. The previous types of blender used with phenol-formaldehyde resin binders are not readily adapted to such interruption in operation. Further, it is desirable, when using the polyisocyanate in the form of an aqueous emulsion, to provide systems which do not require production and storage of the emulsion in a preliminary step, but which permit the emulsion to be formed in situ at the time of dispensing and blending with the particulate material. Further, the above mentioned DE-A-2 138 082 discloses an apparatus and method for coating wood chips with what is generically described as a glue. This apparatus uses two mixers the first being a "leveling mixer" with a complicated baffle system comprising elements which are required to fluidize the wood chips before they ever enter the second gluing mixer. In addition, there must be a critical speed difference between the rotation of an actual mixing element in the first leveling mixer (15 rpm) as opposed to a mixing element in the second mixer (1000 rpm). Because of the high rotational speed of the second mixer, the chips are flung to the outside and form a ring of material. This ring or tube of particulate material has been flung there on the inside edge of the housing by the very high rotational speed of the mixing element of the second mixer. The particulate matter enters the second mixer through an opening and the glue is sprayed through nozzles, provided in the wall of the second mixer. Accordingly, the particles and glue enter at separate openings in this second mixer. Furthermore, the glue is mixed in a tubular configuration of particles. Finally, prior art document US-A-3 796 412 ciscloses an apparatus for controlling the moisture content of granular material in which a main control valve is controlled by a control circuit having electrical measurement means for the measurement of the power input or the driving torque of drive means for a mixing drum, the feed of water to the mixing drum being controlled as a function of the power input or driving torque. It is an object of the present invention to provide an apparatus and a method which meet the above mentioned requirements and facilitate operations which utilize polyisocyanate as the binder either in neat form or in the form of an aqueous emulsion. To solve this object the present invention provides an apparatus and a method as stated in claims 1 and 9, respectively. The apparatus also comprises means for feeding two or more components, required for preparation of a fluid coating material, in predetermined proportions to a mixing head from which the resulting fluid coating material is dispensed to the inlet port of the blender and mixed with the particulate material. This invention will be more fully understood from the following description of preferred embodiments in conjunction with the drawings, in which: FIGURE 1 shows, partly in schematic form and partly in cross-section, an embodiment of an apparatus in accordance with the invention. FIGURE 2 shows a cross-sectional view of a modification of the fluid material dispensing orifice shown in FIGURE 1. FIGURE 3 shows a cross-sectional view of a further modification of the fluid material dispensing orifice shown in FIGURE 1. FIGURE 4 shows, in schematic form, an alternative embodiment of the fluid material dispensing system shown in FIGURE 1. FIGURE 5 shows a cross-sectional view taken along the line 5-5 in FIGURE 4. In the particular embodiment shown schematically in FIGURE 1, a blender 2 is shown with a substantially cylindrical housing 4 provided with an inlet port 6 and an exit port 8. An agitator 10 is disposed within said housing 4 and is provided with a series of paddle members 14 disposed along the axis 12 thereof and mounted by means of bearings 16 and 16a for rotation about its axis. Said agitator is rotated by means of variable speed motor 18. The actual shape and pitch of the plurality of paddle members 14 can be varied in accordance with the relative positions of said paddle members along the axis 12 of the agitator. The paddle members 14 which are adjacent to the inlet port 6 are preferably so shaped and pitched as to facilitate the propulsion of material being fed through the inlet port towards the exit port of the blender 2. Those paddle members 14 which are closest to the exit port 8 of the blender are so shaped and pitched that they tend to retard the progress of particulate material through the blender providing some holdup and increasing the efficiency with which the particular material can be blended with the fluid coating material. The blender 2 is provided optionally with baffle members [not shown in FIGURE 1] which project inwardly from the interior of the housing 4 into one or more of the spaces between the adjacent paddle members 14. Particulate material, illustratively wood furnish, is charged to the inlet port 6 of the blender 2 by feeding from a storage container 20, which can take any appropriate form, to a continuously travelling belt 22 which transports said particulate material and deposits same [at the end 24 of said belt] on to a chute 26 inclined to the horizontal and having its lower end 28 disposed above the inlet port 6. The continuous belt 22 is controlled by drive means 30 which can be an electrically actuated drive mechanism or any other suitable such mechanism. Fluid coating material is introduced through inlet port 6 via orifice 32 to which said fluid material is fed from storage tank 34 by means of constant delivery pump 36 through appropriate conduits 38. In an optional embodiment the orifice 32 is provided with a spray jet of appropriate design to dispense said fluid material in any desired spray pattern. Fluid pressure regulator 40 serves to maintain the pressure and rate of flow of the fluid material at any desired level. Shutoff valve 42 controls the flow of fluid material to the orifice 32. The shutoff valve 42, the agitator motor 18 and the drive means 30 for the continuous belt feed for the particulate material are all operatively connected for simultaneous actuation or deactuation to master control means 45. Thus, the startup of flow of the fluid material and of the particulate material to the blender, as well as operation of the agitator in the blender, can be accomplished simultaneously by operation of master control means 45. Similarly, the three different operations can be terminated simultaneously by operation of master control means 45. The respective rates of flow of the particulate material and the fluid coating material can be adjusted and maintained in any particular desired relationship by suitable adjustment of the rate of feed of the particulate material and by rate of flow of the fluid coating material. The control of the former rate can be accomplished by adjusting the rate of operation of the continuous belt 22. The rate of dispensing of the fluid coating material from orifice 32 can be controlled by adjustment of the pressure maintained by the pressure regulator 40. The blend of particulate material and coating material exiting from the blender 2 via exit port 8 is removed by a continuous conveyor belt 44 to a storage container [not shown] from which the coated material can be supplied on demand to the continuous forming operation to produce particle board. In operation of the apparatus shown in FIGURE 1 the particulate material and the fluid coating material each enter the blender 2 in predetermined ratio of proportions and are therein mixed and conveyed by means of the agitator 12 with paddles 14. It is found that the arrangement shown in FIGURE 1 produces uniform distribution of the fluid material in the particulate material and gives rise to an homogeneous blended material which emerges from the exit port 8 of the blender 4. The operation can be interrupted at any time by operation of the master control means 45. The latter can take any appropriate form. Illustratively, it can provide an electrical impulse which closes or opens appropriate switches on electrically controlled drive mechanisms 18 and 30 and, at the same time, operates a solenoid or like device which controls the opening or closing of the shutoff valve 42. The apparatus therefore provides a very convenient mode of controlling the blending operation both as to the maintenance of appropriate ratios of the particulate material and fluid coating material and also enables the total operation to be interrupted at any given time by operation of one master control. The rate of dispensing of the fluid coating material from orifice 32 to the inlet port 6 of blender 4 can be controlled accurately by utilizing the embodiment shown in partial cross-section in FIGURE 2. In this modification a nipple member 46 provided with a single annular passage 48 is interposed between the shutoff valve 42 and the orifice 32. The nipple member 46 serves a dual purpose. Firstly, it acts as a metering device for the fluid coating material being dispensed through conduit 38. The amount of material which passes through the annular passage 48 at any given pressure can be readily determined and a calibration curve derived thereby showing rate of passage of fluid v. pressure. Using the calibration curve so derived, it is possible to adjust rates of flow of fluid material at any time by appropriate adjustment, using pressure regulator 40, of the pressure of fluid material in the conduit 38 preceding the metering device. The nipple member 46 can be retained in the conduit 38 in any suitable manner. In the particular embodiment shown in FIGURE 2 the nipple is inserted in the end of main conduit 38 and held in place therein by brazing, soldering or any other suitable means. A second conduit 38a is attached to the end of the main conduit 38 by appropriate means, e.g. by appropriate threads formed on the overlapping portions of the inner surface of the conduit 38a and the outer surface of conduit 38. The second function which nipple 46 serves is to give rise to a stream of atomized liquid which exits from the orifice 32 in a substantially linear path. This is in contrast to the uncontrolled spray pattern which occurs in the absence of the nipple member in the conduit or the spray pattern which is formed when the orifice 32 is provided with a standard spray nozzle as discussed above. The calibration of the metering device formed by the use of the nipple 46 as shown in FIGURE 2 can be achieved by collecting the appropriate amount of material over a given time which leaves the orifice 32 at a given pressure. However, in order to check the calibration while in actual operation, a 3-way valve 50 is interposed in conduit 38a between the nipple 46 and the orifice 32 and thereby provides a means of sampling the stream of fluid passing through the nipple member 46 through a side arm 52 into a suitable receptacle. This particular arrangement is illustrated in FIGURE 3 where the various other numerals identifying elements have the same meaning as in FIGURES 1 and 2. In a further modification of the apparatus according to the invention the fluid coating material can be prepared in situ by admixing streams of two or more separate components, such as, for example, water and an emulsifiable isocyanate, followed by dispensing of the so produced fluid coating material directly into the blender 2. An embodiment of this modification of the dispensing means for the fluid coating material is illustrated schematically in FIGURE 4. Two separate streams of components for production of the fluid coating composition are each fed separately from appropriate storage tanks 54 and 56 via pumps 58 and 60, respectively, pressure regulators 62 and 64, respectively, and stop valves 66 and 68, respectively, to a mixing head 70. In the latter the two components undergo impingement mixing under pressure and the resulting mixture is dispensed through orifice 32′ into the inlet port 6 of the blender 4 as shown in FIGURE 1. The two stop valves 66 and 68 are operatively connected to each other and to the master control device 45 so that these valves can be actuated or deactuated synchronously with the drive means 30 of the particulate material conveyor and the drive means 18 of the blender agitator shown in FIGURE 1. FIGURE 5 shows a cross-sectional view taken through the line 5-5 in FIGURE 4 and illustrates the manner in which the two components of the fluid coating material are brought together in the mixing chamber of the mixing head 70. As shown in FIGURE 5 the two individual components enter the mixing chamber via the conduits 38 leading into the passageways 72 and 74, respectively, and thence through orifices 76 and 78 into the mixing chamber 80. As will be seen from FIGURE 5 the orifices 76 and 78 are disposed at an angle to the longitudinal axis of the passageways 72 and 74, respectively, thereby directing fluid passing therethrough in a peripheral trajectory into mixing chamber 80 as illustrated by the arrows. These streams of fluid so entering the mixing chamber 80 impinge on each other under pressure and are mixed by the turbulence so created before being dispensed through the nozzle 32′. If desired, the conduits 38 and 38′ leading into the mixing head 70 shown in FIGURE 4 can be provided with nipple members as shown in FIGURE 2. Calibration devices as shown in FIGURE 3 can also be introduced in the conduits 38 and 38′ between the stop valves 66 and 68 and the mixing head. The proportions in which the two components are being dispensed into the mixing head 70 can be readily adjusted through a wide range by appropriate adjustment of the relative rates of flow of the two components. In a particular embodiment one component is formed by water and the second component is a polyisocyanate admixed with appropriate emulsifying agent or agents so that the two components when brought together in the mixing head 70 form an isocyanate emulsion. Where such a combination is used and the components are to be fed in a fixed ratio to the mixing head, it is appropriate to employ as the pumps two piston type pumps in which the lengths of the pistons in the two pumps are different and correspond to the difference in rate of supply of the two components to the mixing head. The two pumps can then be driven from a common source and geared together so that the two components are delivered to the mixing head in any constant preselected ratio. While the process and apparatus of the invention has been described above in relation to several specific embodiments, it will be appreciated that other modifications can be made that are not essential to the novel combination defined in the appended claims and that such modifications and equivalents are also, therefore, intended to be comprehended by said claims.

Claims: Apparatus for continuously coating particulate material with a fluid material which comprises: blender means (2) comprising a substantially cylindrical housing (4) having an inlet port (6) and an exit port (8); agitator means (10) mounted within said housing (4) and adapted to provide mixing and uniform distribution of said fluid material and said particulate material and their propulsion through said blender means (2); means (20, 22, 26) for feeding particulate material at a predetermined rate to the inlet port (6) of said blender means (2); means (32, 34, 36, 38, 40) for feeding fluid coating material at a predetermined rate to said blender means (2) through a fluid dispensing orifice (32); means (44) for transporting coated particulate material from said exit port (8) of said blender means (2) to storage means; and master control means (45) for synchronously actuating and deactuating each of said particulate material feeding means (20, 22, 26) and said fluid coating material feeding means (32, 34, 36, 38, 40); characterized in that said fluid coating material feeding means (32, 34, 36, 38, 40) feeds the fluid material to said inlet port (6) of said blender means (2) and comprises a nipple member (46) having a single annular passage (48), said nipple member (46) acting as a metering device for the fluid coating material and serving to give rise to a stream of atomized liquid which exits from said orifice (32), in a substantially linear path, and said master control means (45) also synchronously actuates and deactuates said agitator means (10). Apparatus according to Claim 1 wherein said fluid coating material feeding means (32, 34, 36, 38, 40) comprises: reservoir means (34) for storing said fluid coating material; pump means (36) for delivering said fluid coating material under pressure from said reservoir means (34) via conduit means (38) to said orifice (32) disposed in said inlet port (6) of said blender means (2); and valve means (42) interposed between said pump means (36) and said orifice (32) said valve means (42) being operatively connected to said master control means (45) for actuating or deactuating thereof synchronously with said agitator means (10) and said particulate materials feeding means (20, 22, 26). Apparatus according to Claim 2 wherein said fluid coating material feeding means also comprises pressure regulating means (40) interposed between said pump means (36) and said valve means (42). Apparatus according to Claim 2 wherein said nipple member (46) is interposed between said valve means (42) and said fluid dispensing orifice (32). Apparatus according to Claim 1 wherein said fluid coating material feeding means comprises means (70) for admixing at least two fluids in predetermined proportions. Apparatus according to Claim 5 wherein said fluid coating material feeding means comprises: a plurality of reservoir means (54, 56) for storing individual components required to produce a fluid coating material; pump means (58, 60) for delivering each of said individual components under pressure from said reservoirs (54, 56) via conduit means (38, 38′) to a mixing chamber (70); a dispensing orifice (32′) for delivering said admixed components to the inlet port (6) of said blender means (2); valve means (66, 68) controlling the supply of each component to the mixing chamber (70), each of said valve means being operatively connected to said master control means (45) for actuation or deactuation thereof synchronously with each other and with said agitator means (10) and said means (20, 22, 26) for feeding particulate material. Apparatus according to Claim 6 wherein said fluid coating material feeding means also includes means (62, 64) for metering said individual components in predetermined proportions to said mixing chamber (70). Apparatus according to Claim 6 wherein said mixing chamber (70) is circular in cross-section and the inlet ports (72, 74) thereto are disposed in the periphery of said mixing chamber (70) and aligned to deliver said individual components to said mixing chamber (70) in peripheral trajectories which intersect. A method for continuously coating particulate material with fluid material which comprises the steps of continuously feeding particulate material and fluid material separately in predetermined proportions to a blending zone; continuously blending said particulate material and fluid material in said blending zone with uniform distribution of said materials therein; continuously conveying the blended materials to a storage zone, and providing master control means for simultaneously discontinuing said feeding of said particulate material and said fluid material; characterized in that said particulate material and said fluid material are fed to the blending zone through a common inlet port wherein said fluid material is fed to said blending zone through a nipple member (46) having a single annular passage (48) acting as a metering device for the fluid material and serving to give rise to a stream of atomized liquid which exists from an orifice (32) in a substantially linear path, and said master control means simultaneously also discontinue said blending of said materials.

Inventors: MCCLELLAN, THOMAS ROY, MURRAY, PAT LOGAN
Applicants: THE DOW CHEMICAL COMPANY
Application year: 1984
Main classification: B27N1
IPC codes: B01F15, B01F7, B27N1, B05C3