GB2047810A - Rotary pumps - Google Patents

Abstract

An apparatus for dispensing a heat-sensitive liquid polymeric composition includes a source of the liquid e.g. a reservoir 12, a rotary pump such as a gear pump 14, receiving the liquid and pressurizing the liquid as it passes therethrough, and cooling means 44, 46, 52, 54 associated with the pump for cooling the liquid therein to prevent thermal degradation thereof. The liquid may be an adhesive composition. A gas may be introduced into the liquid in the pump to produce a gas/liquid mixture, wherein the gas subsequently expands, and the pump may have two pairs of gears operating in series relationship. The cooling means may comprise a block of aluminium 16 on which the pump is mounted and containing passages 36, 38 and 44, 46 for the outgoing liquid and for the coolant, respectively. <IMAGE>

Description

SPECIFICATION Apparatus and method for dispensing heat sensitive liquid polymeric compositions This invention relates to the dispensing of heat sensitive liquids for application to substrates. Particularly, this invention is directed to the dispensing under pressure of heat sensitive liquid adhesive compositions, including cold glues and plastisols.

Among other applications, the invention is particu larly useful for producing foams of liquid adhesives including plastisols.

Apparatus for dispensing liquid adhesive compos itions are known. For example, U.S. Patent Nos.

4,059,466 and 4,059,714 disclose apparatus for producing and dispensing thermoplastic or so-called "hot-melt" liquid adhesive foams. Such foamed adhesives present several advantages over nonfoamed adhesives. For example, after deposition, a foamed liquid adhesive displays a longer "open" time period during which it remains sufficiently fluid to be receptive for adhering a substrate to it. Further, a foamed liquid adhesive displays better adhesive strength per unit weight and thus reduces the quantity of adhesive required for a given bond.

The patents referred to earlier disclose the use of motor driven gear pumps for mixing and dispensing the liquid adhesive with a foaming agent and for supplying the mixture under pressure as, for example, 300 pounds per square inch, to a conventional adhesive dispensing gun. U.S. Patent Application No. 884,826 discloses a particularly preferred form of pump. In such pumps, the liquid flow is "segmented" as discrete volumes in the intertooth spaces of the gears. The action of the meshing gear teeth on the segmented portion of the fluids mixes and pressurizes the fluids. Gear pumps are relatively simple and efficient means for mixing and pressurizing viscous fluids, and they are widely used in liquid dispensing apparatus such as in hot meltthermoplastic adhesive dispensing systems.

Cold glues and plastisols are widely used throughout industry for adhering substrates one with another in many diverse applications. However, when such compositions are used with liquid dispensers having rotary pumps such as gear pumps, serious problems are encountered. For example, in a gear pump, the action of the intermeshing gears of the pump on the fluid generates an appreciable amount of frictional heat. Cold glues and plastisols have very poor heat transfer characteristics; and therefore the pumps parts retain a significant amount ofthis frictional heat. They are thus rapidly heated as such compositions pass through the pump. However, such compositions are heat sensitive and tend to fuse and thicken when heated above about 120 to 200"F as can occur in any pump which generates an appreciable amount of heat, such as a rotary pump.As a result, the fused thickened material clogs the pump such that the pump parts do not turn freely. This slows down the pump and unpredictably varies the pressure of the liquid generated by the pump causing non-uniform dispensing of the liquid. The material can also plug pump inlet and outlet ports and make it difficult if not impossible to restart the pump after a shutdown. In addition, in systems in which a gas is injected into the material to produce a gas/liquid foaming composition, the thickening of the viscous liquid prevents easy formation of the foam. All in all, the fusion ofthe liquid adhesive composition in the pump makes it difficult to maintain an effective and smoothly running liquid adhesive dispensing system.

This problem is so severe that it is generally recommended not to use rotary pumps in systems involving heat sensitive materials, such as liquid plastisols. For example, U.S. Patent No.2,763,475 states that a positive displacement type of pump such as a piston pump or diaphragm pump should be employed in a liquid plastisol system and that any pump which generates an appreciable amount of frictional heat, such as a gear pump or centrifugal pump should be avoided.

We have sought to provide an improved method and apparatus for dispensing heat sensitive liquid polymeric compositions such as cold glues and plas tisolswhich employs a rotary type pump but which prevents thermal degradation such as fusion of the liquid passing through the pump.

Accordingly the present invention provides an apparatus for dispensing heat sensitive liquid polymeric compositions wherein the temperature of the liquid is always maintained at a temperature well below that which would cause deleterious effects on the material. This invention is particularly applicable to the dispensing of liquid adhesives such as cold glues and plastisols.

The apparatus comprises an apparatus for dispensing a heat sensitive liquid polymeric composition comprising a source for a liquid polymeric composition, a rotary pump adapted to receive the liquid from the source and to discharge it under pressure, and means associated with the rotary pump for cool ingthe rotary pump to prevent thermal degradation ofthe liquid in the pump.

In one embodiment of the present invention, the adhesive material is contained in a reservoir. The adhesive flows from the reservoir into a two-stage gear pump where it is pressurized in the intertooth spaces of the intermeshing gears. The gear pump is mounted on a heat conductive manifold block containing material flow passages for conducting the adhesive material exiting the pump to an adhesive dispensing gun from which the adhesive is dispensed at atmospheric pressure. The manifold btock further includes a cooling water flow passage located directly below the pump. Cooling water continuously flows through this passage into and out of the manifold block to cool the block and in turn the gear pump. The flow of cooling water through the manifold block thereby cools the gear pump and prevents the material passing through the gear pump from being heated by the pump parts.

We have found that using this system liquid adhesives such as white glues and plastisols may be raised to a high pressure as, for example, 300 pounds per square inch, in the gear pump without appreciably raising the temperature of the material.

That is, material supplied to the reservoir at room temperature passes through the gear pump at a temperature of less than about 80"F which is well below the fusion temperature of the material. The apparatus runs smoothly and continuously without any clogging or slowing of the gear pump. In addition, when the apparatus is shut down, it may be quickly and smoothly restarted. This invention thus permits conventional hot melt dispensing apparatus to be employed in dispensing heat sensitive liquids such as cold glues and plastisols.

In another embodiment of the invention, the apparatus includes means for injecting an inert gas such as carbon dioxide into the liquid passing through the gear pump such that the gas is simultaneously injected and mixed into the liquid in the gear pump. When the pressurized adhesive/gas solution is subsequently dispensed from a conventional adhesive dispenser, the gas comes out of solution and becomes trapped in the adhesive to form a closed cell solid adhesive foam having the desirable adhesive characteristics described hereinabove.

The method and apparatus of this invention are useful with heat sensitive liquids generally, including but not limited to liquid adhesives. These liquids are generally "viscous" in that they have viscosities generally greater than about 1000 centipoise. Examples of some viscous liquids with which the invention is useful include cold or non-hot melt liquid starch base adhesives including the "dextrin" glues; resin glues such as polyvinyl acetate; plastisols such as polyvinyl chloride, polyvinylidene chloride, polyvinyl butytal, cellulous acetate-butyrate, polyvinylidene fluoride, polymethyl methacrylate; natural resins; hide or animal glues; and the like.

The compositions may further include additives such as plasticizers, stabilizers and pigments and may be injected with an inert gas, such as air, nitrogen and carbon dioxide, to produce a stable foam on discharge which can then be fused or cured by the application of heat or by other means.

The invention is further illustrated in the accompanying drawings, wherein: Figure lisa perspective view with parts broken away of one embodiment of a dispensing apparatus incorporating an embodiment of the present invention; Figure 2 is a perspective view of the gear pump and manifold block of the dispensing apparatus shown in Figure 1; and Figure 3 is a perspective view with parts broken away showing another embodiment of the present invention.

Referring first to Figures 1 and 2, the dispensing apparatus of this invention comprises a housing 10 in which there is located a material reservoir 12, a gear pump 14 and a manifold block 16. The reservoir 12 includes side walls 17 and downwardly sloping bottom walls 18 and 19 which direct the material in the reservoir 12 toward an inlet 20 of the pump 14.

The pump then moves the material into the manifold block 16 from which it is directed to one or more conventional applicators or dispensers via hoses or conduits 21.

The gear pump 14 is a two stage gear pump having intermeshing geared teeth (not shown) which operate as multiple small pistonsto pull incoming liquid into the pump, pressurize it and dispense it from the pump outlet. Such pumps generally create a suction on the inlet opening 20 so as to draw the liquid into the pump. In the illustrated embodiment, gas, for example air, nitrogen or carbon dioxide, is also supplied to the pump 14 through pump inlet 22 via inlet tube 24, the outlet of which terminates at the pump inlet 22. Such a gas injection system is disclosed in U.S. Patent No.4,059,714.

The two pairs of intermeshing gears of the pump 14 are mounted on a pair of parallel shafts 28 and 30.

One of these shafts 28 is driven by a motor, for example, a pneumatic motor 32 while the other 30 is an idler shaft. A more complete description of a preferred gear pump 14 used in the apparatus of the present invention is found in the aforementioned U.S. Patent Application No. 884,826.

The pump 14 is mounted on the manifold block 16 which may be formed of a suitable heat conducting material such as aluminium. The manifold block 16 is ported such that the liquid material flowing from the outlet port (not shown) of the pump 14 flows into a vertical inlet port of the manifold. This inlet port communicates with a longitudinal passage 34, a transverse passage 36, and a longitudinal passage 38 on the front side of the block leading to the conduits 21. Conventional liquid dispensers, as for example, conventional hot melt applicator guns or dispensers of the type shown in U.S. Reissue Patent No. 27,865 or U.S. Patent No. 3,690,518 may be attached to the manifold block either directly or by hoses 21. The number of outlet conduits and connected dispensers will vary depending on the particular application to which the system is applied.

Intersecting the longitudinal passage 34 and extending coaxially with it is a filter mounting bore which accommodates a conventional filter 40, one end of which comprises a plug 42 threaded into a threaded end section of the bore. A complete description of the filter assembly is found in U.S.

Patent No. 3,224,590. Liquid material flowing into the manifold block 16 flows through the passage 34 and then through the filter 40 to the transverse passage 36 of the manifold block and the interconnected longitudinal passages 38. A preferred form of manifold block is described in the aforementioned U.S. Patent No.3,964,645, A pair of transverse fluid flow passages 44 and 46 lie on a horizontal plane above the material flow passages 34, 36 and 38 and generally in the area directly below where the pump 14 is mounted on the manifold block. The transverse passages 44 and 46 are joined at their interior end by a longitudinal passageway 48 entering the side of the block. This longitudinal passageway is closed by a plug 50 inserted therein to form a closed loop defined by passages 44 and 46 and that portion 48a of passage 48 extending - therebetween. In one presently preferred form, the passages 44, 46 and 48 may be drilled in the block 16 about 1/16" to 1/8" below the top surface 49 of the block 16.

The transverse passageways 44 and 46 communicate through hoses 51 vai lines 53 with a source of cooling liquid, for example, water which passes through a cooling or refrigeration unit 54 before entering the block 16. The cooling liquid thus enters the manifold block 16, passes through one of the transverse passages 44, flows through the longitud inal passageway 48a, and exits through the other transverse passage 46. The flow of cooling water into and out ofthe manifold block is thus in a continuous loop, the direction of which is shown by the arrows in lines 53. The proximate location ofthe cooling passageway 44, 46, 48a in association with the location of the pump 14coolsthe manifold block which in turn cools the pump 14.This cooling action extracts the substantial frictional heat generated by the pump thus preventing the heating of the liquid material in the pump.

Referring to Figure 3, there is illustrated another embodiment of the cooling apparatus for the liquid material passing through the pump 14. In this embodiment, the pump 14 mounted to the top 49 of the manifold block 16 is surrounded by a jacket 56 having an internal annular groove 58 surrounding the outer circumference of the pump 14. Cooling liquid, e.g. water, from the cooling unit 54 flows into and out of the jacket 56 via the flow paths 60, 62 illustrated thus surrounding the pump 14 with coolant. This embodiment thus produces more direct application of cooling water to the pump than in the previous embodiment.In either case, however, the throughput of cooling liquid in association with the pump prevents heating ofthe liquid material passing through the pump to provided smooth, sustained operation of the apparatus without heating of the material being dispensed.

The present invention is further illustrated in the following Examples.

Example I A dispersion of Dow Saran 506 (a product of Dow Chemical Company) was prepared using Santicizer 148 (a product of the Monsanto Company) as the primary plasticizer. Saran 506 is a polyvinylidene chloride (PVDC) and polyvinylchloride copolymer at least 80% PVDC. Other materials added as stabilizers included epoxidized soybean oil, Citriflex A-4 (a product of the Pfizer Company), and an organotin stabil per sold under the trade mark Advastab TM 181 by Cincinnati Milacron, Inc. The composition was as follows: Dow Saran 506 50.0 parts Santicizer 52.5 parts Epoxidized soybean oil 5.0 parts Citriflex A-4 5.0 parts AdvastabTM 181 2.0 parts This material was placed in a Nordson Corporation Model XI Hot Melt Dispenser with a two-stage pump, water cooled manifold and a Nordson H-20 gun.The Model XI dispenser corresponds to the apparatus shown in U.S. Patent No. 4,059,714 and the H-20 gun corresponds to the apparatus shown in U.S. Reissue Patent No. 27,865. Water at a temperature of about 55"F was continuously circulated through the manifold at a rate of about 10 to 15 ml/sec. The composition was foamed using CO2 as the gaseous foaming agent. A billowing foam was produced at the nozzle.

The foam was dispensed for about one-half hour.

The pump was then turned off and allowed to sit for 10 to 15 minutes with the material in it. The pump was then restarted with no difficulty. No fusion of the disperson was noted.

With water continuously circulating through the manifold in accordance with the apparatus described above, the temperature of the pump was consistently held below 105 to 110 F. With no pump cooling, pump temperatures reached 150 to 2000F within 30 minutes of operation and plastisol solidification occurred within the pump when operation was interrupted for a brief time making it impossible to restart operation until the pump was dismounted, disassembled, and the solidified plastisol removed manually.

Example lI Using the apparatus described in Example I, a polyvinyl acetate white glue formation (sold under the trade mark Swift 46297) was foamed for 50 minutes using CO2. Pump temperatures recorded at the top of the pump never exceeded 69"F and the pump turned freely.

Example III Using the apparatus described in Example I, another white glue (Swift 42802) was foamed for more than one hour. Pump temperatures recorded at the top of the pump peaked at 70"F. The pump turned freely throughout.

Example IV Using the apparatus of Example I, long-term runs were made to demonstrate the efficacy of the apparatus of the present invention. A vinyl chloride plastisol sold underthetrade mark"Geon 128" by the B.F. Goodrich Company was used. The conditions were as follows: flow rate of manifold cooling water 11.5 Millilitres/sec., temperature of cooling water 54"F, air pressure on pump 50 pounds, discharge pressure at gun 700 to 750 psig, CO2 injection to pump 0.4 scfh. After one hour of operation, the pump temperature as recorded at the top of the pump was 830F and steady. Conditions were charged slightly to raise the air pressure on the pump to 55 pounds and the CO2 injection to 0.45 scfh, and the apparatus was run for one more hour.Pump temperature was 89"F and the pump ran smoothly. The unit was then shut down for one hour and then restarted. The pump ran smoothly and freely.

After four hours of continuous operation, the highest pump temperature recorded was 97"F. The unit was shut down overnight to see if the pump would still turn freely the next day without cleaning out ofthe pump. When the pump was shut down, it took only five to ten minutes to come to room temperature. The next morning the pump was started and turned relatively freely with little or no slowdown.

Although this invention has been described with particular application to a two-stage gear pump, the invention is applicable to a variety of rotary pumps, for example, one-stage gear pumps, screw pumps, vane pumps and the like.

Moreover, although the description of this invention has been directed particularly to the dispensing of liquid adhesives such as cold glues and plastisols which exhibit heat sensitivity in the form of fusing or coalescence of the resin particles, this invention is applicable to the dispensing of any material which exhibits effects of heat sensitivity including, for example, change of colour, charring, molecular breakdown, premature setting-up, and the like. The invention is thus applicable to the aforementioned cold glues and plastisols, thermoplastic resin, such as degradable polyvinyl chloride, thermosetting resins such as epoxys, polyesters, polyamides, and the like.

Claims (15)

1. An apparatus for dispensing a heat sensitive liquid polymeric composition comprising a source for a liquid polymeric composition, a rotary pump adapted to receive the liquid from the source and to discharge it under pressure, and means associated with the rotary pump for cooling the rotary pump to prevent thermal degradation of the liquid in the pump.

2. An apparatus as claimed in claim 1, wherein the rotary pump is a gear pump.

3. An apparatus as claimed in claim 2, wherein the gear pump is a two-stage pump comprising two pairs of serially arranged intermeshing gears.

4. An apparatus as claimed in any of claims 1 to 3, further comprising a heat conductive manifold upon which the rotary pump is mounted and wherein the means for cooling the rotary pump comprises means for circulating a cooling fluid through the manifold.

5. An apparatus as claimed in any of claims 1 to 3, wherein the means for cooling the rotary pump comprises a jacket surrounding the rotary pump through which a cooling fluid may flow.

6. An apparatus as claimed in claim 4 or 5, wherein the cooling fluid is water.

7. An apparatus as claimed in any of claims 1 to 6, comprising means for injecting a gas into the liquid in the rotary pump to produce a foamable liquid/gas solution.

8. An apparatus for dispensing a heat sensitive liquid polymeric composition comprising a reservoir adapted to receive and contain a liquid polymeric composition, a dispenser selectively operable to dispense the liquid and a rotary pump at least partially mounted in the reservoir for supplying the liquid from the reservoir to the dispenser, and means for cooling the rotary pump to prevent thermal degradation of the liquid.

9. An apparatus as claimed in claim 8, wherein the rotary pump is a gear pump.

10. An apparatus as claimed in claim 9, further comprising a manifold upon which the gear pump is mounted and through which the liquid is supplied to the dispenser and wherein the cooling means com prises means for continuously circulating cooling fluid through the manifold.

11. A method of dispensing a heat sensitive liquid polymeric composition which comprises introducing a liquid polymeric composition into a cooled rotary pump, and discharging the liquid from the rotary pump under pressure.

12. A method as claimed in claim 11, wherein the liquid is a thermally fusible cold glue or plastisol.

13. A method as claimed in claim 11 or 12, wherein the liquid is maintained at a temperature below 110"F.

14. A method as claimed in any of claims 11 to 13, wherein the cooling is continuous.

15. An apparatus for dispensing a heat sensitive liquid polymeric composition substantially as herein described and with reference to the accompanying drawing.