WO2004020111A1

WO2004020111A1 - Liquid spray method

Info

Publication number: WO2004020111A1
Application number: PCT/JP2003/010784
Authority: WO
Inventors: Masafumi Matsunaga; Takayuki Aoyagi; Kouki Terao
Original assignee: Nordson Corporation
Priority date: 2002-08-30
Filing date: 2003-08-26
Publication date: 2004-03-11
Also published as: JP2004089976A; TW200404607A; TWI294310B; JP4437272B2; AU2003256086A1

Abstract

A liquid spray method includes: dispensing liquid (LQ) from a liquid dispensing opening (7b); expelling a first compressed gas (FG) from a first compressed gas outlet (17b) around the liquid dispensing opening (7b) to atomize the liquid (LQ) to form a particle expelling flow; and expelling a second compressed gas (SG) from a plurality of second compressed gas outlets (10b) toward the particle expelling flow to impinge a part of the second compressed gas onto the particle expelling flow to swirl the particle expelling flow while finely atomizing the particles.

Description

DESCRIPTIOPN

LIQUID SPRAY METHOD

Technical Field

The invention relates to a liquid or a melt spray method. Background Art

Two methods discussed below are conventionally known as methods and devices in which a swirl is imparted to a liquid or a melt by using a compressed gas while spraying the liquid or the melt.

(1) JP 5-212334 A discloses an improved swirl spray nozzle suited to the manufacture of one fine thread (filament) by attenuating a rubber hot melt adhesive, which is an example of a melt, while the rubber hot melt adhesive is being dispensed and swirled from a nozzle member. This apparatus is widely used in bonding processes in the manufacture of disposable diapers, napkins, and the like because the transfer efficiency of 100% can be accomplished by imparting a continuous swirled filament.

Further, a method is proposed in JP 9-136053 A as manufacturing a filament that does not have a swirl hook. This method is proposed for solving a hook phenomenon upon the start of filament dispensing in the above method. Directionality is imparted in a pendent direction to a hot melt adhesive upon the start of the dispensing by being sprayed pressurized air from an air hole, which is formed separately from a plurality of air nozzles used in swirling.

Meanwhile, pressurized air from the other air nozzle holes are brought into contact with the hot melt adhesive, and the hot melt adhesive is attenuated and swirled to form a filament without the hook. (2) A method of manufacturing suitable swirled fiber-shaped filaments, circle-shaped beads, dot patterns, or fine particles of a liquid or a melt is proposed in JP 4-4060 A by the applicants of the present invention. This method is capable of handling a wide range of applications, and solves all of the problems of the method discussed in the above- item (1) . With this method, a compressed gas dispensing opening used for dispensing the filaments or the fine particles is forcibly rotated, so that the liquid or the melt can be dispensed in a desired form, and therefore the form does not tend to vary due to the type or the viscosity of the liquid or the melt employed.

However, the nozzles described in JP 5-212334 A and JP 9-136053 A are designed so as to be suitable for granulation using materials that tend to form fiber-shaped filaments, such as hot melt adhesives. On the other hand, the manufacture of fine particles of melts at room temperature, such as liquid coatings, adhesives, paraffin wax, and the like has been frequently tested due to their good transfer efficiency. Spray coating of the fine particles has also been attempted.

However, the nozzles cited in the aforementioned publications are made with the goal of forming filaments and fibers, and are not designed for atomization. Therefore, the average spray particle diameter is not less than 50 μm, even for liquids having a low viscosity on the order of 50 mPa-s, and for paraffin wax having a lower viscosity on the order of 10 mPa-s, and there are cases where particles of 200μm or more are mixed. Further, the average particle diameter of solder resist, which has a viscosity of, for example, 300 mPa-s, is several hundreds of micrometers, and thus these nozzles are not suited to coating printed substrates. On the other hand, it is possible to make the average spray particle diameter equal to or less than

12μm with liquids having a viscosity of 50 mPa-s, so- called a minimum atomizing range, by employing spraying or centrifugal atomization according to the method described in JP 4-4060 A. However, such an apparatus is complex and expensive, and further, a large installation space is required. In addition, it is necessary to use an explosion proof AC servomotor or the like in a rotary apparatus used for a compressed gas nozzle for high precision applications where a flammable liquid such as an organic solvent is used, leading to further increase in cost as well as installation space. Even though the required characteristics are present, the number of applications where this method can be used is limited. The development of functional coatings and the like has been advancing recently. Demand has increased for spraying techniques that are capable of making very fine particles, finer than those made by using conventional spray nozzles, by coating a film out of contact with a substrate without damaging the substrate, or by wet-on-wet overlapping application in which a usage (transfer) efficiency on the same order as that found with contact roll coaters, screw coaters, and slotted nozzle coaters can be obtained. There is a fervent desire for devices and methods with which a high coating film performance, as well as a high usage (transfer) efficiency of the coating material, can be obtained in a process for manufacturing: a reflection preventing film having a thickness on the order of 0.1 μm, which is used in a flat panel display; or an electrode coated with an electrode ink (a dispersion made from carbon carrying platinum particles and a polymer solution for application to both sides of an electrolyte membrane) for electrodes used in the fuel cell proposed by U.S. Patent No. 5,415,888.

Disclosure of Invention

In view of the problems discussed above, an object of the present invention is to provide a liquid spray method in which: fine particles of liquid or a melt are made having a high quality level equivalent to, or surpassing, those of a liquid or a melt made by spraying or centrifugal atomization; the liquid or the melt can be applied possessing a swirl that generates a vortex action in the fine particles and possessing a high transfer efficiency to a substrate; and the fine particles are granulated (or atomized) and used as granulation material in pharmaceuticals, foods, chemicals, and the like.

In order to solve the above-mentioned problems, there is provided a liquid spray method as described below. That is, there is provided a liquid spray method, including: dispensing at least one liquid from a liquid dispensing opening; expelling a first compressed gas from a first compressed gas outlet provided around the liquid dispensing opening and granulating the liquid dispensed from the liquid dispensing opening to form a liquid particle expelling flow; and expelling a second compressed gas from a plurality of second compressed gas outlets toward the liquid particle expelling flow to impinge at least a part of the second compressed gas onto the liquid particle expelling flow to swirl and atomize the liquid particle expelling flow. Due to this arrangement, the object of the present invention is attained.

Brief Description of Drawings

Fig. 1 is an overall system diagram (partially sectional longitudinal diagram) of a liquid spray apparatus that shows an embodiment of a liquid spray apparatus used in implementing a liquid spray method according to the present invention.

Fig. 2 is a longitudinal sectional diagram taken along the lines II-II in Fig. 1, which shows an automatic dispensing valve and a nozzle assembly. Fig. 3 is a bottom view of the automatic dispensing valve and the nozzle assembly, as viewed in the direction indicated by the arrow III in Fig. 1

Fig. 4 is an enlarged view of a portion designated by the reference sign A in Fig. 1.

Fig. 5 is an enlarged view of a portion designated by the reference sign B in Fig. 3.

Fig. 6 is a diagram showing an example of a pulse (intermittent) spray cycle pattern of liquid. Fig. 7 is a diagram showing another example of a pulse (intermittent) spray cycle pattern of liquid.

Best Mode for Carrying Out the Invention The present invention is explained below based on the preferred embodiments while referring to the accompanying drawings. Note that dimensions, material properties, shapes, relative disposition, and the like of structural components described in the embodiments below do not limit the scope of this invention thereto, unless so specified in particular.

Fig. 1 to Fig. 5 are diagrams that show embodiments of a liquid spray apparatus used in implementing a liquid spray method according to the present invention. Fig. 1 is an overall system diagram of a liquid spray apparatus (partially sectional longitudinal diagram) . Fig. 2 is a longitudinal sectional diagram taken along the lines II-II in Fig. 1, which shows an automatic dispensing valve and a nozzle assembly. Fig. 3 is a bottom view showing the automatic dispensing valve and the nozzle assembly, as viewed in the direction indicated by the arrow III in Fig.l. Fig. 4 is an enlarged diagram of a portion designated by the reference sign A in Fig. 1. Fig. 5 is an enlarged diagram of a portion designated by the reference sign B in Fig. 3.

A pump 3 pumps up a liquid stored in a tank 2. A liquid supply pipe 4 for transporting the liquid pumped by the pump 3 is connected to a liquid automatic dispensing valve 1. The pipe 4 and a liquid return pipe 4b are connected to the automatic dispensing valve 1 by connectors 4a. A compressed air pipe 8 for operating a piston lc incorporated in the automatic dispensing valve 1, to thereby open and close a needle la coupled to the piston lc with respect to a valve seat lb, is connected to the automatic dispensing valve 1 through a connector 8c. An air regulator 8a and a solenoid valve 8b are disposed in the compressed air pipe 8 on the upstream side and on the downstream side, respectively. A spring (compression coil spring) Id always urges the needle to seat the needle la on a valve seat lb. A nozzle assembly 5 is attached to the automatic dispensing valve 1. As shown in Fig. 2, a first compressed gas supply pipe 13 for supplying a first compressed gas (compressed air or the like) is connected to the nozzle assembly 5 through a connector 13e. An air regulator 13a and a solenoid valve 13b are disposed in the first compressed gas pipe 13 in the order from the upstream side to the downstream side. A solvent supply pipe 13c is connected to the portion 13d of the first compressed gas pipe 13. Further, as shown in Fig. 1, a second compressed gas supply pipe 11 for supplying a second compressed gas (compressed air or the like) is connected to the nozzle assembly 5 through connectors lid. An air regulator 11a and a solenoid valve lib are disposed in the second compressed gas pipe 11 in the order from the upstream side to the downstream side .

As shown in Fig. 4 in detail, in a lower end portion of a main body 5a of the nozzle assembly 5, a liquid nozzle 7, an intermediate (solvent) disk 9, and an annular compressed gas nozzle 10 are placed in mutual pressure contact, and are securely attached to the main body 5a by screwing a fastener 5c onto the main body 5a. An upper surface of the liquid nozzle 7 is in pressure contact with a lower end surface of the main body 5a of the nozzle assembly. An elongated cylindrical protrusion is formed in a central portion of a lower surface side of the liquid nozzle 7, and projects and extends downwardly in a distal end direction, through a low height stepped disk portion. A liquid passage 7a is formed passing through the low height stepped disc portion and a longitudinal direction center portion of the cylindrical protrusion.

An outer periphery of the upper surface of the intermediate (solvent) disk 9 is in pressure contact with an outer periphery of the lower surface of the liquid nozzle 7. A circular cavity 9d is formed in the center portion of the upper surface of the intermediate (solvent) disk 9. The low height stepped disk portion of the liquid nozzle 7 is fitted in the circular cavity 9d. An inverted conical protruding portion 9f that protrudes downwardly in the distal end direction is formed in the center portion of the lower surface side of the intermediate disk 9, through the cylindrical portion 9e. An internal hole 17 is formed in a longitudinal direction center portion of the intermediate disk 9. An annular gap 17a is formed between the internal hole 17 and a cylindrical protruding portion 7d of the liquid nozzle 7. Further, an inner hole lOd is formed in the center portion of the annular compressed gas nozzle 10, and the cylindrical portion 9e of the intermediate disk 9 is fitted into the inner hole lOd. The upper surface of the compressed gas nozzle 10 is in pressure contact with the lower surface of the intermediate disk 9. Second compressed gas passages 10a are formed in the compressed gas nozzle 10. The second compressed gas passages 10a (eight holes in this embodiment) are directed in a downward oblique direction (refer to Fig. 4), and also directed to be slightly off a longitudinal center axis of the liquid passage 7a of the liquid nozzle 7 (refer to Fig. 5) , and are drilled and formed at nearly equal intervals in a circumferential direction in the compressed gas nozzle 10.

In addition, a plurality of first compressed gas passages 16 are formed at equal intervals in the liquid nozzle 7, in the circumferential direction at an outer circumference side of the liquid passage 7a. The passages 16 pass completely through the nozzle 7 in the longitudinal direction. In addition, a plurality of second compressed gas passages 7c are formed at equal intervals in the circumferential direction of the liquid nozzle 7, and pass completely through the nozzle 7. Further, an upper side annular groove 9a having a rectangular shape cross-section is formed in an upper surface of the intermediate disk 9 at a position opposing to the second compressed gas passages 7c of the liquid nozzle 7. A lower side annular groove 9c is formed in a lower surface of the intermediate disk 9 in a position that is nearly co- radial with the upper side annular groove 9a. The upper side annular groove 9a and the lower side annular groove 9c are in communication with each other through intercommunication holes 9b that are disposed and drilled at equal intervals in the circumferential direction. An annular groove 10c having a triangular cross-section is formed in the compressed gas nozzle 10. The annular groove 10c is co-radial with respect to the lower side annular groove 9c, and becomes a starting point of the second compressed gas passages 10a.

On the other hand, a first compressed gas annular groove 15a is formed in the lower end surface of the main body 5a of the nozzle assembly 5 at a radial position substantially corresponding with that of the first compressed gas passages 16 of the liquid nozzle 7. A first compressed gas supply passage 15 that extends in the longitudinal direction and is in communication with the annular groove 15a is formed in the main body 5a of the nozzle assembly 5. The first compressed gas supply passage 15 is in communication with the first compressed gas pipe 13. Further, a second compressed gas annular groove 5b is formed in the lower end surface of the main body 5a of the nozzle assembly 5 in a position on the outside of the first compressed gas annular groove 15a and in a radial position substantially corresponding with that of the second compressed gas passages 7c of the liquid nozzle 7. A second compressed gas supply passage lie that extends in the longitudinal direction and is in communication with the annular groove 5b is formed in the main body 5a of the nozzle assembly 5. The second compressed gas supply passage lie is in communication with the second compressed gas pipe 11.

A liquid supply flow passage 6 is formed in the main body 5a of the nozzle assembly 5 on a longitudinal centerline in alignment with the liquid passage 7a of the liquid nozzle 7. The liquid supply flow passage 6 is in communication with the liquid passage le in which a valve mechanism comprising the needle la and the valve seat lb of the liquid automatic dispensing valve 1 is disposed. The liquid passage le of the automatic dispensing valve 1 is in communication with the liquid supply pipe 4 through the valve mechanism.

By this means, an annular space 16a having a necessary capacity is formed between a lower surface of the low height stepped disk portion of the liquid nozzle 7 and a bottom surface of the circular cavity 9d of the upper surface center portion of the intermediate disk 9. The annular space 16a is in communication with the annular gap 17a that is formed between the outer circumferential surface of the cylindrical protruding portion 7d of the liquid nozzle 7 and an inner circumferential surface of the inner hole 17 of the intermediate disk 9. The annular gap 17a forms a first compressed air passage (flow passage), and an annular opening of the lower end of the annular gap 17a forms a first compressed gas outlet 17b. Further, the annular space 16a serves as a supply passage for the first compressed gas, as discussed above. The annular space 16a also can store a necessary amount of a solvent, which is supplied through the first compressed gas supply pipe 13 from the solvent supply pipe 13c during the spraying operation or during the cessation of the spraying operation, and causes the solvent to pass through the annular gap 17a and flow out from the compressed gas outlet 17b, either by itself or along with the compressed gas, moistening a liquid dispensing opening 7b. In this type of structure, the liquid is transported from the liquid tank 2 to the pipe 4 by the pump 3. The liquid passes through the liquid passage le in which the valve mechanism (the needle la and the valve seat lb) of the liquid automatic dispensing valve 1 is disposed. The liquid passes through the liquid supply flow passage 6 of the nozzle assembly 5 and the liquid passage 7a of the liquid nozzle 7, and is dispensed from the liquid dispensing opening 7b of the liquid nozzle 7. When the liquid is not dispensed, that is when the valve mechanism is closed, the liquid passes through the liquid return pipe 4b and returns to the tank 2. Further, the first compressed gas is transported to the pipe 13 through the regulator 13a and the solenoid valve 13b by a first compressor (not shown) , which is a compressed gas source. In addition, the first compressed gas passes through the compressed gas supply passage 15 of the nozzle assembly 5, the annular groove 15a, the passage 16 of the liquid nozzle 7, the annular space 16a, and the annular gap 17a, and is sprayed out from the compressed gas outlet 17b, which is an annular opening at the distal end.

As is clear from the above discussion, the annular first compressed gas outlet 17b is formed around the liquid dispensing opening 7b. Further, as shown in the enlarged diagram of Fig. 4, the liquid dispensing opening 7b of the liquid nozzle 7 is formed in an inner portion of the internal hole 17, that is at a position further inside than the lower end opening of the internal hole 17, in this embodiment. In other words, the liquid dispensing opening 7b is actually further inside than the outlet through which the first compressed gas expands and is released into the atmosphere. The first compressed gas is expelled from the compressed gas outlet 17b, which is the annular opening for the first compressed gas. A structure in which the first compressed gas outlet 17b and the liquid dispensing opening 7b are combined thus forms a so-called internal mixing two- fluid spraying means . Fine granulation or atomization of the liquid is therefore extremely good, Further, the second compressed gas is transported to the pipe 11 through the regulator 11a and the solenoid valve lib by a second compressor (not shown) that is a compressed gas source. In addition, the second compressed gas is made to flow through the second compressed gas supply passage lie of the nozzle assembly 5, the annular groove 5b, the second compressed gas passage 7c of the liquid nozzle 7, the upper side annular groove 9a of the intermediate disk 9, the intercommunication holes 9b, the lower side annular groove 9c, the annular groove 10c of the compressed gas nozzle 10, and a plurality of the second compressed gas passages 10a disposed in a circumferential direction. Then the second compressed gas is expelled from second compressed gas outlets 10b of the distal end openings. The following may be finely granulated or atomized and applied as the liquid used for spraying in the present invention, for example: liquid coatings having a viscosity from 30 to 70 mPa-s such as acrylic epoxy waterborne coatings that are used as inside surface coatings of beverage cans; dispersions that contain carbon particles with a particle diameter of 0.1 to 80 μm that are dispersed in a liquid having a viscosity from 20 to 80 mPa-s and are used as inside surface coatings of alkaline dry cells; solder resist having a viscosity of 50 to 300 mPa-s and used in coating printed substrates; dispersions (electrode inks) made from carbon carrying platinum particles and a polymer liquid in order to be applied to both sides of electrolyte membranes, which are used as fuel cell electrodes; and the like. Further, melts of paraffin waxes, microcrystalline waxes, polyethylene waxes, otsu-type blown asphalt, and the like having a viscosity of 5 to 800 mPa-s may be finely granulated or atomized and applied as the melt in the present invention.

A liquid spray method by using the liquid spray apparatus thus structured is explained next.

The liquid that is stored in the tank 2 is pumped up and pressurized by the pump 3, and is transported via the pipe 4 into the automatic dispensing valve 1. The solenoid valve 8b is then excited, compressed air is transported to the compressed air pipe 8 from the compressed air source, and the compressed air is transported to the lower surface of the piston lc of the automatic dispensing valve 1 via the air regulator 8a. The piston lc moves upward against an urging force of the spring Id due to the air pressure of the compressed air. The needle la moves away from the valve seat lb, and the automatic dispensing valve 1 opens (refer to Fig. 1 and Fig. 2) . The liquid thus passes through the liquid passage le of the automatic dispensing valve 1 and the liquid supply flow passage 6 in almost the center of the nozzle assembly 5. In addition, the liquid passes through the liquid passage 7a of the liquid nozzle 7, and is dispensed from the liquid dispensing opening 7b as a dispensed liquid flow LQ. When the solenoid valve 13b of the first compressed gas pipe 13 is excited, the first compressed gas is transported from the first compressor (not shown) , which is a compressed gas source, via the regulator 13a (refer to Fig. 2) . The first compressed gas passes through the compressed gas supply passage 15 of the nozzle assembly 5, the annular groove 15a, the passages 16 of the liquid nozzle 7, the annular space 16a, and the annular gap 17a. The first compressed gas is expelled from the compressed gas outlet 17b, which is the annular opening at the distal end, in a direction indicated by a dotted line arrow (FG) in Fig. 4. The dispensed flow LQ of the liquid that is dispensed from the liquid dispensing opening 7b of the liquid nozzle 7 as discussed above is granulated or atomized, and a particle expelling flow is formed. The combination of the first compressed gas outlet 17b and the liquid dispensing opening 7b is an internal mixing two-fluid spraying structure as discussed above. Therefore the dispensed liquid flow LQ contacts the high-pressure compressed gas from the perimeter in the inner portion of the inner hole 17 to cause the intermixing of both of the liquid and the compressed gas before the compressed gas exits the lower end opening of the inner hole 17 to be released to the atmosphere and expanded. The liquid is thus finely granulated or atomized in a favorable manner. Note that the present invention is not limited to only application of the internal mixing two-fluid spraying structure as the method of making the liquid particulate spray flow using the first compressed gas. It is also possible to apply an external mixing ,two-fluid spraying structure.

In the nozzle assembly 5, the solenoid valve lib of the second compressed gas pipe 11 is excited, and the second compressed gas is transported from the second compressor (not shown) , which is a compressed gas source, via the regulator 11a (refer to Fig. 1) . The second compressed gas flows through the gas passage lie of the nozzle assembly 5, the annular groove 5b, the passage 7c of the liquid nozzle 7, the upper side annular groove 9a of the intermediate disk 9, the intercommunication holes 9b, and the lower side annular groove 9c. In addition, the second compressed gas flows to the annular groove 10c of the compressed gas nozzle 10, and to the plural second compressed gas passages 10a that are disposed at nearly equal intervals in the circumferential direction. The second compressed gas is expelled from each of the second compressed gas outlets 10b of the distal end opening in a direction indicated by dotted line arrows (SG) in Fig. 4 and Fig. 5.

The second compressed gasses SG that are each expelled from the plurality of the second compressed gas outlets 10b are expelled in directions that are slightly off (offset from) a longitudinal centerline of the liquid passage 7a and the liquid dispensing opening 7b of the liquid nozzle 7, and expand. Therefore at least a portion of each of the second compressed gasses SG collides with and contacts the liquid particle expelling flow, which has been granulated or atomized by the first compressed gas as discussed above, thus forming a liquid fine particle swirl FW (refer to Fig. 2) . The liquid that has not yet been granulated or atomized is finely granulated or atomized by the collisions and the contact with the second compressed gasses SG. This promotes fine granulation or atomization of the liquid particle expelling flow. As shown in Fig. 2, the liquid fine particle swirl FW then reaches the substrates SB, which are sent sequentially by conveying means such as a conveyor, at a position directly below the nozzle assembly 5, for example. Fine particles FP that form the swirl FW are applied to a surface of the substrate SB, thus forming a thin coating film CF. A liquid fine particle group forms the swirl FW during application of the fine particles FP to the substrate SB, and therefore each of the fine particles FP contacts the substrate SB in a state where it is caught in the inside of the swirl FW. The amount of the fine particles FP that rebound due to collisions with the substrate SB and are carried away is thus extremely small, and the development of turbulence due to collisions of the gas that forms the swirl FW with the substrate SB is also suppressed as much as possible. The transfer efficiency for the fine particles is thus increased greatly.

With the liquid spray apparatus of this embodiment, the solvent supply pipe 13c is connected to the first compressed gas supply pipe 13 through a solvent supplying port 13d as shown in Fig. 2. A solvent is supplied to the solvent supply pipe 13c, and the solvent mixes with the first compressed gas. The solvent can thus be sent with the first compressed gas along the first compressed gas supply passage, that is, along the compressed gas supply passage 15 of the nozzle assembly 5, the annular groove 15a, the passage 16 of the liquid nozzle 7, the annular space 16a, the annular gap 17a, and the compressed gas outlet 17b, which is the annular opening at the distal end. The solvent can thus always moisten the liquid dispensing opening 7b of the liquid nozzle 7 during spraying operations. Even if a liquid that contains volatile components is sprayed, a skinning phenomenon caused by buildup of liquids such as coatings in the vicinity of the liquid dispensing opening 7b can be prevented, and narrowing and clogging of the flow passage can be prevented. The amount of the liquid dispensed can thus be stabilized, and a constant coating film thickness and a constant coating film weight can be maintained. Further, the solvent passes alone through the solvent supply pipe 13c when spraying of the first compressed gas is stopped, for example, when spraying operation is stopped, and is transported within the system. A fixed amount of the solvent accumulates in the annular space 16a, passes through the annular gap 17a and the compressed gas outlet 17b, and flows out. The solvent can thus moisten the liquid dispensing opening 7b of the liquid nozzle 7. In addition, the present invention can also be structured by incorporating the solvent supply pipe 13c within the first compressed gas supply passage (denoted by reference numerals 13, 15, 15a, 16, 16a, and 17a) , and disposing the dispensing opening thereof in the vicinity of the liquid dispensing opening 7b of the liquid nozzle 7. The liquid dispensing opening 7b can be moistened instantaneously when spraying operations stop if the solvent supply pipe is thus structured. The skinning phenomenon in the vicinity of the liquid dispensing opening 7b due to the volatilization of volatile components in the liquid, and due to drying of the liquid itself, during stoppage for a predetermined period of time can thus be prevented.

The internal mixing two-fluid spraying structure is employed in this embodiment, and granulation or atomization is performed satisfactorily. On the other hand, volatile components contained in coatings or adhesives, for example, evaporate instantaneously so that the skinning in the vicinity of the first compressed gas outlet 17b and the liquid dispensing opening 7b easily occurs, and continuous operation becomes impossible in many cases. However, the solvent moistens the vicinity of the first compressed gas outlet 17b and the liquid dispensing opening 7b in this embodiment. The spray caused by finely granulating or atomizing the liquid can therefore be performed very smoothly and continuously without the occurrence of skinning.

In addition, in particular, an amount of a liquid containing solid particles such as carbon particles, which is a so-called dispersion type or powder slurry liquid, can be dispensed stably and continuously while effectively preventing clogging of a narrow gap between the needle la and the seat lb of the liquid automatic dispensing valve 1 due to the solid particles agglutinating in the narrow gap. This can be achieved by performing the liquid spraying operation described above by continuously performing the supply and the expelling of the first and the second compressed gases, and dispensing the liquid by high-speed intermittent operations. That is, for example, the period of time that the needle la is open, and the period of time that the needle la is closed, may each be set to extremely short given periods of time. The period of time that the needle la is open (liquid dispensing time) may be set to 15 ms (milliseconds), and the period of time that the needle la is closed (liquid supply stopping time) may be set to 30 ms . Opening and closing operations of the needle la may then be repeatedly performed cyclically, the opening degree of the needle la and the seat lb may be set to be larger by a predetermined amount, and the dispensing amount may be set to be larger by a predetermined amount than the flow rate during continuous dispensing. A so- called pulse (intermittent) spraying operation is thus performed. It is thought that clogging can be effectively prevented due to an action whereby, even if agglutinated solid particles are starting to clog the space between the needle la and the seat lb, such foreign matters to be clogged are pushed away by impacts of the needle la with the seat lb that accompany the high speed closing operations. Note that this type of intermittent opening/closing operation of the needle la can be performed by connecting a controller with a built-in timer (not shown) to the solenoid valve 8b of the compressed air pipe 8 that controls the opening and^' closing of the needle la, and setting the timing at which the needle la is opened and closed. If dispensing by high-speed intermittent operations is performed at a frequency equal to or greater than 60 cycles/minute with the present invention, clogging due to solid particles in the liquid agglutinating in the space between the needle la and the seat lb can be effectively prevented.

In addition, at least the first compressed gas can also be synchronously supplied and expelled intermittently by intermittent liquid dispensing operations. A controller with a built-in timer (not shown) may also be connected to the solenoid valve 13b attached to the first compressed gas supply pipe 13, and the supply time and the supply stoppage time for the first compressed gas may each be set to 30 ms, for example, as shown in Fig. 7. On the other hand, the needle la may be set to open within the period of time during which the first compressed gas is supplied and expelled (30 ms) , for example, only for 20 ms, to dispense the liquid for 20 ms . In this case, after lapse of 5 ms (ti) since the start of gas supply, liquid supply is started, and liquid dispensing is stopped 5 ms (t₂) before the gas spraying is stopped. Therefore, the cycle of liquid dispensing for 20 s and no liquid dispensing for 40 ms is repeated. Further, the second compressed gas can also be intermittently supplied and expelled in a manner similar to the first compressed gas.

By thus expelling at least the first compressed gas for a predetermined short period of time that is slightly longer than the period of time the liquid is dispensed, it becomes possible to effectively eliminate the generation of large droplets upon the start of dispensing and end of dispensing. Spraying operations are possible with suitable fine granulation or atomization from the start of dispensing to the end. By thus supplying and expelling at least the first compressed gas intermittently, which effectively contributes to fine granulation or atomization, a rebound (reflections due to impinge of the compressed gas on the substrate SB) caused by continuous supply of the first compressed gas can be prevented. As a result, the amount of removed liquid particles and the amount of removed solid fine particles contained in the liquid are significantly reduced, and the transfer efficiency is effectively increased. Suitable fine granulation or atomization can be achieved from the start of spraying to the end of spraying with the present invention if at least the first compressed gas is expelled for a time longer than the liquid dispensing by 1 ms to 200 ms, regardless of whether the compressed gas is supplied and expelled continuously or intermittently.

With the liquid spray method of the present invention, in addition to the case in which the fine particles of the liquid obtained through spraying is coated on the substrate SB, it is possible to perform granulation or atomization by spraying within the air For example, by heating a substance (paraffin wax, which is a biodegradable material, for example) having a softening point (65°C, for example) that is higher than the temperature of air, which is an atmosphere within which spraying of the substance as a liquid is to be performed, to a temperature (100°C, for example) higher than its softening point and melting it to make it into a melt; heating first and second compressed gases via a hot current of air generating apparatus to a temperature (120°C, for example) higher than the softening point of the substance; and spraying the hot melt into the air from the liquid dispensing opening 7b, the melt is solidified by cooling within the air to be granulated or atomized into fine particles. Then, the particles that freely fall can be collected. Note that a biodegradable package provided with a barrier film can also be manufactured by spraying the hot melt paraffin wax directly onto a substrate, such as a pulp-mold package.

Further, with the present invention, the liquid passage 7a and the liquid dispensing opening 7b of the liquid nozzle 7 may be made into dual structures and different liquids are dispensed from an inside passage and an outside passage to be subjected to fine granulation or atomization. Accordingly, the two liquids can be combined and sprayed outside of the nozzle assembly and can be applied to a substrate, for example. A coating that is the same as if formed by mixing the two liquids in advance can thus be made . Note that although compressed air is normally used as the first and the second compressed gasses explained above, other gasses can also be used in accordance with the properties and the behavior of the liquid to be dispensed. For example, if the liquid is flammable, nitrogen gas or carbon dioxide gas can be used.

Further, the intermediate disk 9 and the compressed gas nozzle 10 are formed separately, but both may also be integrally formed as a unit. In addition, the intermediate disk 9, the compressed gas nozzle 10, and the liquid nozzle 7 may all be integrally formed as a unit. Experimental examples of coating and the like in accordance with the liquid spray method of the present invention are discussed next. (Experimental Example 1)

An acrylic epoxy waterborne coating (NV: 20%, viscosity: 20 sec/FC#4 (FORD cup #4, corresponding to approximately 40 mPa-s measured by a B-type viscometer) was used as a coating liquid, and 100 mm x 100 mm aluminum foil was used as a substrate. Experiments were performed under the following conditions:

(1) liquid pressure (dispensing pressure of the pump 3) : 0.06 MPa;

(2) first compressed gas: air from the first compressor at 0.05 MPa; (3) second compressed gas: air from the second compressor at 0.15 MPa;

(4) dispensed liquid flow rate: 10 ml/min;

(5) distance between nozzle (lower end of the opening of the inner hole 17 of the liquid nozzle 7) and the substrate: 100 mm;

(6) speed of conveyor used in conveying the substrate: 0.3 m/min; (7) diameter of the nozzle dispensing opening (liquid dispensing opening 7b) : 0.7 mm;

(8) coating pattern width: nearly circular, 25 mm; (9) traverse speed of the automatic dispensing valve 1 and the nozzle assembly 5 during coating: 24 m/min; traverse stroke: 270 mm; traverse cycle: 30 c/min; and

(10) number of samples: three (3). Spraying was performed from the liquid dispensing opening 7b of the nozzle assembly 5 while the combination of the automatic dispensing valve 1 and the nozzle assembly 5 traversed the aluminum foil used as the substrate SB, which was conveyed by conveyor, under the conditions stated above. The results of the experiment showed that the fine granulation or atomization during spraying was satisfactory, and that the leveling state of the coated surface was also satisfactory. Then, the substance was set up for three minutes at room temperature and then dried for two minutes at 200°C, and the weight thereof was measured. The weight value after subtracting the weight of the aluminum foil, which was measured in advance, was 161.3 mg. A transfer efficiency of 80.7% was thus found from the theoretical weight of 200 mg (the specific gravity of the solid content was approximately one (1), and therefore the theoretical weight equals the flow rate during the six (6) seconds in which coating was performed on the substrate, multiplied by the solid content) . Further, a mirrored surface equivalent to that of the aluminum foil surface was observed on the coated surface after drying. (Comparative Example 1)

Another experiment was performed under the same conditions as Experimental Example 1 except that a two-fluid spray gun manufactured by Nordson

Corporation (a gun provided with compressed gas expelling openings around the vicinity of a liquid dispensing opening, trade name: AD-29 gun) was used, and only the first air from the first compressor was expelled from the compressed gas expelling openings as an atomization air. The coating pattern was an elliptical pattern having a minor axis of 15 mm and a major axis of 35 mm, and the major axis was set as the direction in which the substrate SB was moved. Sampling was performed similarly. Large particles were observed visually, and bubbles were developed on the wet surface. Drying was performed under the same conditions as Experimental Example 1, and the weight of the coating film was measured to be 98.6 mg. The transfer efficiency was 49.3%. Approximately 20 micro-bubbles were observed in the coating film after drying. Further, a fluorescent lamp reflected onto the coated surface showed a jagged, saw tooth-like surface .

(Comparative Example 2)

Sampling was performed under the same conditions as those of Experimental Example 1 except for the condition in which the nozzle disclosed in JP 5-212334 A was used and only the second air from the second compressor was used. Large spray particles were visually observed on the whole, on the order of two times as large as those in Experimental Example 1 Further, particles larger than those of Comparative Example 1 were observed scattered in the sprayed liquid. The wet surface was less satisfactory than that of Comparative Example 1, and many micro-bubbles developed in the coating film after drying. Even craters that were generated due to contaminants, oil, or the like acting as seeds were seen here and there. However, the weight after drying was 163.4 mg, giving a transfer efficiency of 81.7%, nearly the same as that of Experimental Example 1. (Experimental Example 2)

An experiment was performed next using a carbon dispersion as the coating liquid. The carbon dispersion had a viscosity of 40 mPa-s, analogous to the carbon ink that is coated for use in inner surfaces of alkaline dry cells and electrodes in fuel cells. The three spray nozzles described above were used as spray nozzles. That is, the combination of the automatic dispensing valve 1 and the nozzle assembly 5 used in implementing the method of the present invention, the AD-29 two-fluid spray gun, and the nozzle disclosed in JP 5-212334 A were used.

Tests were performed using the same wet flow rate of the solvent type carbon dispersion in each of the nozzles .

The spraying pattern began to become disrupted from the second sampling in each of the cases, and the weight was reduced by half. The carbon particles agglutinated and a clogging developed in the narrow clearance between the needle and the seat by operating with the automatic dispensing valve open. It was confirmed that the flow rate was unstable, and the experiment was stopped. (Experimental Example 3)

The coating of Experimental Example 2 was used, and the pulse (intermittent) spray method disclosed in JP 61-161175 A, Spray method for two fluids", proposed by the inventors of the present invention was applied to the combination of the automatic dispensing valve 1 and the nozzle assembly 5 used in implementing the present invention. The first and the second compressed airs were supplied and expelled continuously. The period of time that the carbon dispersion was sprayed (the period of time that the needle was open) was set to 15 ms, and the amount of closed time (the period of time that the needle was closed) was set to 30 ms . In order to make the spray flow rate from the nozzle the same in both cases, the flow rate during continuous operation was increased by three times to be 30 ml/min by making the opening between the needle and the seat larger. The pulse (intermittent) spray flow rate was approximately 10 ml/min. The flow rate was measured immediately after starting the experiment, after three (3) minutes, after five (5) minutes, and after ten (10) minutes by using a graduated cylinder. The flow rate was stable

In addition, even when the flow rate during continuous dispensing was set to 10 ml/min, which is the same as that in Experimental Example 2, the pulse settings were set to those used in Experimental Example 3 to set the pulse flow rate to approximately 3.3 ml/min, the flow rate was stable. This is thought to be because, even if agglutinated carbon particles begin to clog the space between the needle and the seat, a pushing out action works due to very high speed closing operations of the needle la accompanied with impacts. Dry fine particles can be made if the per minute flow rate is reduced. By using this phenomenon, an effect can be achieved in which drying is quickened without causing the electrolytes of fuel cells to swell. This phenomenon is therefore useful. (Experimental Example 4)

The flow rate of the coating dropped by approximately half to be 6 ml/min when spraying operations performed under the conditions of

Experimental Example 1 were stopped for five (5) minutes and then restarted. This was caused as a result of a phenomenon in which built-up coating caused skinning in a tip of the coating dispensing nozzle, that is, around the liquid dispensing opening 7b, and the flow passage was narrowed. When coating spraying operations were performed by: supplying ion exchange water as a solvent to the solvent supply pipe 13c connected to the first compressed air supply pipe 13 shown in Fig. 2 at a flow rate of 1 ml/min; guiding the ion exchange water to the compressed gas outlet 17b, passing through the annular space 16a of the first compressed gas supply passage inside the nozzle assembly 5, and the compressed gas passage 17a; and atomizing the ion exchange water by using air from the first compressor, there was no adverse influence to the coated surface before and after drying, and there was no change in the weight of the coating film. Further, there was no build-up of the coating onto the nozzle tip (in the vicinity of the liquid dispensing opening 7b) . That is, skinning did not develop. Further, it was confirmed that there were no problems with normal operation, with no changes in the flow rate of the coating, after spraying operations were stopped for five (5) minutes. However, the flow rate dropped to half or less after a 45 minute break for lunch. When the ion exchange water was also made to flow when the spraying operations were interrupted, and the tip of the coating dispensing nozzle was always kept moistened, no change in the flow rate was observed even if the spraying operations were interrupted for one hour. In addition, no problems of change in flow rates due to skinning developed even for cases in which a structure was employed with an internal mixing spraying means, with which best granulation or atomization with the first air is achieved, in other words the liquid dispensing opening 7b, disposed in a dispensing opening formed in a position at which the first compressed gas actually goes out into the atmosphere. That is, even when the liquid dispensing opening 7b is disposed inside the lower end of the opening of the inner hole 17 of the intermediate disk 9, there is no problem of change in flow rate due to the skinning. In this experiment, as shown in the enlarged view of Fig. 4, the structure used was one in which the outlet of the coating dispensing nozzle (the liquid dispensing opening 7b) was placed inside the expelling opening for the first compressor air (the lower end of the opening of the inner hole 17 within the cylindrical protruding portion 7d of the tip portion of the liquid nozzle 7) by 0.5 mm. Note that a structure in which the liquid dispensing opening protrudes by an amount on the order of 0.1 mm to 0.8 mm is generally used for normal two-fluid spraying. Internal mixing two-fluid spraying is an ideal spray method with satisfactory fine granulation or atomization, but is normally not used because volatile components in coatings or adhesives instantaneously evaporate to cause skinning at the air expelling opening. This problem can be resolved in accordance with the present invention. (Experimental Example 5)

Paraffin wax, a biodegradable material, having a softening point of 65°C was heated to 100°C and melted, the opening diameter of the dispensing nozzle (the opening diameter of the liquid dispensing opening 7b) was set to 0.2 mm, and the liquid pressure was set to 0.12 MPa. A structure in which there is internal mixing with the first air at 0.1 MPa was used, and the pressure of the second air was set to 0.3 MPa. Hot current of air of 120°C was supplied from the air supply source via a hot current of air generating apparatus, and granulation or atomization was performed by spraying within the air. The spray dispensing amount was 7 g/min. Fine particles that freely fall down after being solidified in the air were measured. The fine particles were found to be spherical shape with an average particle diameter of 12 μm. Needless to say, a biodegradable package provided with a barrier film made by performing spraying directly onto a substrate, such as a pulp mold container, can also be made. (Experimental Example 6)

The liquid dispensing opening was made into a dual structure. Volumetric pumps were used in order to supply one part by weight of isocyanate, which is . a hardening agent, from an inside dispensing opening, and 10 parts by weight of polyol, which is a base material, from an external dispensing opening. Spray coating was performed on the substrate SB. The viscosity of polyol was 18 sec/FC#4. The performance of the coating film as determined by rubbing test after flushing the film with solvent and then drying was the same as that found when spraying two liquids mixed in advance. This establishes that spraying of a plurality of liquids externally mixed can also be performed by the present invention. The present invention is not limited to the embodiments discussed above. Many other embodiments can also be implemented without deviating from the characteristic features of the present invention. The embodiments discussed above therefore do not exceed simple examples in every facet, and should not be interpreted as limiting. The scope of the present invention is determined by the scope of the claims, and is not bound to the statements within this description. In addition, variations and changes to the present invention that are within a scope equivalent to that of the claims all fall within the scope of the present invention.

As is apparent from the description above, the liquid spray method according to the present invention has excellent effects such as fine particles of a liquid or a melt can be made having a high quality level equivalent to, or surpassing, those of a liquid or a melt made by spraying or centrifugal atomization; and the liquid or the melt can be applied possessing a swirl that generates a vortex action in the fine particles and possessing a high transfer efficiency to a substrate. The liquid spray method also has an excellent effect such that the fine particles are granulated or atomized and can be used as granulation material in pharmaceuticals, foods, chemicals, and the like.

Claims

1. A liquid spray method, comprising: dispensing at least one liquid from a liquid dispensing opening; expelling a first compressed gas from a first compressed gas outlet formed around the liquid dispensing opening to atomize the liquid dispensed from the liquid dispensing opening to form a particle expelling flow; and expelling second compressed gas from a plurality of second compressed gas outlets toward the particle expelling flow to impinge at least a part of each of the second compressed gas onto the particle expelling flow to swirl the particle expelling flow while finely atomizing the particle expelling flow.

2. A liquid spray method according to claim 1, wherein the liquid is a melt.

3. A liquid spray method according to claim 1 or 2, wherein said expelling the first compressed gas includes forming the particle expelling flow by using internal mixing two-fluid spraying means in which the liquid dispensing opening is disposed further inside than a position at which the first compressed gas is actually expelled into the atmosphere and expands after being expelled from the first compressed gas outlet.

4. A liquid spray method according to any one of claims 1 to 3, wherein the liquid contains volatile components, and at least the first compressed gas contains a solvent.

5. A liquid spray method according to any one of claims 1 to 4, further comprising: supplying a solvent from a solvent supplying port or a dispensing opening provided in at least a flow passage for the first compressed gas to the flow passage when the expelling of the first compressed gas is ceased, to flow the solvent as a solvent film out of the first compressed gas outlet to moisten the liquid dispensing opening with the solvent.

6. A liquid spray method according to any one of claims 1 to 5, wherein at least the liquid is dispensed by high-speed intermittent operations at a frequency equal to or greater than 60 cycles/minute.

7. A liquid spray method according to any one of claims 1 to 6, wherein at least a duration of the expelling of the first compressed gas is longer than a duration of the dispensing of the liquid by 1 to 200 milliseconds before a beginning and after an ending of the dispensing of the liquid, respectively.