CA1125712A - Method and apparatus for dispensing heat sensitive liquid polymeric compositions - Google Patents

Abstract

METHOD AND APPARATUS FOR DISPENSING HEAT
SENSITIVE LIQUID POLYMERIC COMPOSITIONS

Abstract of the Disclosure A method and apparatus for dispensing heat sensitive liquid polymeric compositions. The apparatus includes a reservoir containing the liquid, a gear pump receiving the liquid from the reservoir and pressurizing the liquid as it passes therethrough, and cooling means associated with the gear pump for cooling the pump to prevent thermal degradation, e.g., fusion of the liquid in the pump. The invention is particularly useful for dispensing liquid adhesive compositions, including cold glues, plastisols, and other dispersed liquid systems. A gas may be introduced into the liquid in a two stage gear pump to produce a gas/liquid mixture wherein the gas subsequently expands to form a foam.

Description

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Backgroulld of the Invention This invention is directed to the dispensing of heat sensitive liquids for application onto substrates. ~ore parti-cularly, this invention is directed to the dispensing under pressure of heat sensitive liquid adhesive compositions, including cold glues and plastisols. Among other applications, the inven-tion is particularly useful for producing foams of liquid adhe-sives, including plastisols.
Apparatus for dispensing liquid adhesive compositions are known to -the art. For example, the Scholl et al patents, U.S. Pat. Nos. 4,059,466 and 4,059,714, both issued on Nove~ber 22, 1977, and assigned to the assiqnee of this invention, disclose apparatus for producing and dispensing thermoplastic or so-called "hot melt" liquid adhesive foams. Such foamed adhesives PreSent se~eral advantages over non-foamed adhesives. For exa~ple, after deposition, a foamed liquid adhesive displays a longer "open" time period during which it remains sufficiently fluid to be re oeptive 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 Scholl et al patents cited above disclose the use of motor d~iven gear pumps for mixing and dispensing the liquid adhesive with a foaming agent and for supplying the mixtNre under pressure, as, for example, 300 pounds per square inch, to a conventional adhesive dispensing gun. Canadian Application Ser. No.
321 555 filed February 15, 1979, assigned to the assignee of this in-vention, discloses a particularly preferred ~orm of pump. In such pumps, the liquid flow is "segmented," as discrete v~lumes, in the inter-tooth spa oes of the gears. The action of the meshing gear teeth on-mab/

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~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 melt thermoplastic !
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. That is, in a gear pump, for example, 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 pump parts retain a significant amount of this frictional heat. They are thus rapidly heated as such com-positions pass through the pump. However, such compositions are heat sensitive and tend to fuse and thicken when heated above about 120-200~ 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 unpre-dictably 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 addi-tion, 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 of the liquid adhesive composition in the pump makes it difficult to maintain an effective and smoothly running liquid adhesive dispensing system.

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This problem is so severe that the art teaches not to use rotary pumps in systems involving heat sensitive materials, such as liquid plastisols. For example, U.S.
Patent No. 2,763,475 to Dennis teaches at column 3, lines 51-57 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.
Summary of the Invention It has been among the principal objects of this invention to provide an improved system for dispensing heat sensitive liquid polymeric compositions, such as cold glues and plastisols, which employs a rotary type pump but which prevents thermal degradation such as fusion of the liquid passing through the pump. It has therefore been an objective of this invention to provide a method and apparatus for dispensing of heat sensitive liquid polymeric compositions in apparatus including a rotary pump, e.g., a gear type pump, while preventing thermal degradation of the liquid passing through the apparatus to achieve effective and sus-tained smooth operation of the dispensing system.
To accomplish this objective, the invention of this application incorporates a novel pump and dispensing system for 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 improved apparatus of the present invention comprises a ro-tary pump for receiving liquid polymer from a source of liquid polymer, agitating the liquid polymer in the ws/ j ~resellce of a gas -to distribu-te the gas throughout the liquid polymer and pressllrizing the liquid and gas dispersion so as to force the gas into solution with the liquid polymer. Means for cooling the rotary pump is provided to prevent thermal reaction of the liquid polymer due to the heat generated in the pump and means is provided for dispensing the liquid polymer and gas solution at a pressure below the solution maintenance pressure of the gas and liquid polymer solution whereby the gas is released from solution to form a polymer foam.
Thus, the method of the present invention is generally comprised of the steps of mechanically agitating the liquid polymer in the presence of a gas so as to obtain a mixture of the gas in the liquid polymer, pressurizing the mixture of liquid and gas in a rotary pump so as to force the gas into solutlon with the li~uid polymer, cooling the rotary pump so as to prevent thermal reaction of the liquid polymer due to the heat generated in the pump and dispensing the liquid and gas solution at atmospheric pressure whereby the gas is released from solution and forms a polymer foam.
In one present embodiment of the 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 block further includes a cooling water f 10W
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 -3a-S /
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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 utilizing 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 less than about 80F, 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 shutdown, it may be quickly and smoothly restarted. This invention thus permits conventional hot melt dispensing apparatus Y~S/

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I i 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 o~ 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 are characterized 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 butyral, cellulous acetate-butyrate, polyvinylidene flouride, 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 pro-duce a stable foam on discharge which can then be fused or cured by the application of heat or by other means.
~hese and other objects and advantages of this inven-tion will be more readily apparent from the following detailed description of the invention taken with the accompanying drawings.

5'l 12 Brief Descr~ption of the Dra~7in~s Fig. 1 is a pers~ective view with parts br~ken away of one embodlment of a dispensing apparatus inoorporating the in-vention of this application.
Fig. 2 is a perspective view of the gear pump and mani-fold block of the dispensing apparatus shcwn in Fig. 1.
Fig. 3 is a perspective view with parts broken away showing another embodiment of the in~7ention of this application.
Referring first to Figs. 1 and 2, the dispensing ap-paratus of this invention co~prises a housing 10 in which there is located a material reservoir 12, a gear pump 14, and a mani-fold block 16. The reserv~ir 12 includes side walls 17 and down-wardly sloping bottom walls 18 and 19 which direct the material in the reservoir 12 toward an inlet 20 of the pump 14. m e pump then mo~es t~e material into the manifold block 16 frcm which it is directed to one or more oonventional applicators or dis~ensers via hoses or oonduits 21.
The gear pump 14 is a two stage gear pump having inter-meshing geared teeth (not shown) which operate as multiple small pistQns to pull inccming liquid into the pump, pressuri æ it, and dispense it fr~m the pump outlet. Such pumps generally create a suction on the inlet opening 2n so as to draw the liquid into the pu~p. In the illustrated entodiment, gas as for example, air, nitro~en or carbon ~ioxide is also supplied to the pump 14 through pump inlet 22 via the inlet tube 24, the outlet of which ter-munates at the entran oe port 22 of the pump. Such a gas in-jection system is completely disd osed in U.S. Pat. No. 4,059,714 for "Hot ~elt Thermoplastic Adhesive Foam System," which app-lication is assigned to the assionee of this invention.

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The two p~airs of inten~esllincJ c~ars 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 as, for example, a pneuma-tie motor 32, while the other 30 is an idler shaft. A more ccmplete description of a presently preferred gear pump 14 utili æd in the practioe of this invention may be found in the aforementioned Canadian application Ser. No. 321 555 for "Gear Pump with ~eans for Dispersing Cas Into Liquid," whieh ap lieation is assigned to the assignee of this applieation.
The pump 14 is mounted on the manifold block 16 which may be formed of a suitable heat eondueting material sueh as aluminu~. The ~nifold block 16 is ported such that the liquid material flcwing fmm the outlet port (not shcwn) of the pump 14 flows into a vertieal inlet port of the manifold. m is inlet port communicates with a longitudinal passa~e 34, a transverse passage 36, and a longitudinal passage 38 on the front side of the bloek lèading to the conduits 21. Conventlonal liquid dis-pensers, as, for exa~ple, conventional hot melt applieator guns or dispensers of the type shcwn in U.S. Reissue Pat. Nb. 27,865 or U.S. Pat. No. 3,690,518 may be attached to the manifold bloek either direetly or by hoses 21. The numker of outlet conduits and eonnected dispensers will vary depenc~ng on the particular applieation to which the system is applied.
Intersecting the longitudinal passage 34 and extending coaxially with it is a fil~er mounting bore which accommDdates a conventional filter 40, one end of which co~prises a plug 42 threaded into a threaded end seetion of the bore. A co~plete description of the filter assembly may be found in U.S. Pat. No.

3,224,590 which issued December 21, 1965. Liquid material flcw-ins into the manifold block 16 flows through the passaqe 34 and then through the filter 40 to the transverse passage 36 of - ~b/

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t~le n~nif`old blc~k and the lnterconnected longitudinal passases 38. A preferred form of manifold block is completely described in the aforen,entioned U.S. Pat. No. 3,964,645.
A pair of transverse fluid flow passages 44 and 46 lie on a horizontal plane above the material fl~ passages 34, 36 and 38 and generally in the area directly kelow where the pump 14 is mounted on the manifold block~ me transverse passaaes 44 and 46 are joined at their interior ends by a longitudinal passageway 48 entering the side of the block. m is longitudinal passa~eway 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 pre-ferred 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 cc~municate through hoses 52 via 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. Ihe cooling liquid thus enters the manifold block 16, passes throu~h one of the transverse passages 44, flows through the longitudinal passageway 48a, and exits -through the other transve se passage 46. The ~low of cooling water into and out of the manifold blo~k is thus in a continuous loop, the direction of which is shcwn by the arrows in lines 53.
The pnDximate location of the cooling passaaeway 44, 46, 48a in associati~ with the location of the pump 14 cools the manifold block whîch in tu m cools the pump 14. This cooling action ~b/

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¦extracts the substantial frictional heat generated by the pump thus preventing the heating of the liquid material in the pump.
Referring to Fig. 3, there is illustrated another em- j bodiment of the cooling apparatus for the liquid material passing through ,he 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 circum-¦
ference 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 of the invention thus produces more direct application of cooling water to the pump than in the pre-vious embodiment. In either case, however, ~he throughput of cooling liquid in association with the pump prevents heating of the liquid material passing through the pump to provide smooth, sustained operation of the apparatus without heating of the material being dispensed.
Example I
A dispersion of Dow Saran 506 (a product of Dow Chemical¦
Company~ was prepared using Santicizer 148 (a product of the,Mon- !
santo Company) as the primary plasticizer. Saran 506 is a poly-vinylidene 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 stabilizer, sold under the trademark Advastab TM 181 by Cincinnati Milacron, Inc. ~he composition was as follows:
Dow Saran 506 50.0 parts Santicizer 52.5 parts Epoxidized soybean oil 5.0 parts I llZS71Z

Citriflex A-4 5.0 parts Advastab TM 181 2.0 parts This material was placed in a Nordson Corporation Model XI ~ot Melt Dispenser with a two stage pump, water cooled mani-fold and a Nordson H-20 gun. The Model XI dispenser corresponds to the apparatus shown in U. S. Pat. No. 4,059,714 and the H-20 gun corresponds to the apparatus shown in U. S. Reissue Pat. No.
27,865. Water at a temperature of about 55 F was continuously circulated through the manifold at a rate of about 10-15 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 dispersion was noted.
With water continuously circulating through the mani-fold in accordance with the apparatus described above, the tem-perature of the pump was consistently held below 105-110 F. With no pump cooling, pump temperatures reached 150-200~ F 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 II
Using the apparatus described in Example I, a polyvinyl !
acetate white glue formulation (sold under the trademark Swift 46297) was foamed for 50 minutes using CO2. Pump temperatures recorded at the top of the pump never exceeded 69 F, and the urp turned freely.

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E~ample 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 efficacy of the invention. A vinyl chloride plastisol sold under the trademark "Geon 128" by the B. F.
Goodrich Company was used. The conditions were as follows:
flow rate of manifold cooling water 11~5 milliliters/sec., tem-perature of cooling water 54 F, air pressure on pump 50 pounds, discharge pressure at gun 700-750 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 83 F and steady. Conditions ¦
were changed 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 shutdown 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 shutdown overnight to see if the pump would still turn freely the next day without cleaning out of the pump. When the pump was shut-down, it took only five to ten minutes to come to room tempera-ture. The next morning the pump was started and turned rela-tively freely with little or no slowdown.
Although this invention has been described in terms of certain preferred embodiments, it will be recognized that other forms may be adopted by those skilled in the art within 57 ~Z
,, 1, the scope of the invention. For example, although this invention has been described with particular application to a two-stage gear pump, it will be recognized that 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 adhe-sives such as cold glues and plastisols which exhibit heat sen-sitivity in the form of fusing or coalescence of the resin par-ticles, it will be recognized that this invention is applicable to the dispensing of any material which exhibits effects of heat sensitivity including, for example, change of color, charring, molecular breakdown, premature setting-up, and the like. The invention is thus applicable to the aforementioned cold glues and plastisols, thermoplastic resins, such as degradable poly-vinyl chloride, thermosetting resins, such as epoxys, polyesters, polyamides, and the like.
e claim:

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
(1) An improved apparatus for dispensing a heat sensitive liquid polymer foam comprising:
a source of said liquid polymer, a rotary pump for receiving said liquid polymer from said source, agitating said liquid polymer in the presence of a gas to distribute said gas through-out said liquid polymer, and pressurizing said liquid and gas dispersion so as to force said gas into solu-tion with the liquid polymer, means associated with said rotary pump for cooling said rotary pump to prevent thermal reaction of said liquid polymer due to the heat generated in said pump, and means for dispensing the liquid polymer and gas solution at a pressure below the solution mainten-ance pressure of said gas and liquid polymer solution whereby said gas is released from solution to form a polymer foam.

(2) The apparatus of claim 1 wherein said rotary pump means is a gear pump.

(3) The apparatus of claim 2 wherein said gear pump is a two stage pump comprising two pair of serially arranged intermeshing gears.

(4) The apparatus of claim 1 further comprising a heat conductive manifold upon which said rotary pump means is mounted and wherein said means for cooling said rotary pump means comprises means for circulating a cooling fluid through said manifold.

(5) The apparatus of claim 1 wherein said means for cooling said rotary pump means comprises a jacket surrounding said rotary pump means through which a cooling fluid may flow.

(6) The apparatus of claim 4 or 5 wherein said cooling fluid is water.

(7) The apparatus of claim 1 further comprising means for heating said source of said liquid polymer.

(8) An apparatus for dispensing a heat sensitive liquid polymer foam comprising:
a reservoir adapted to receive and contain said liquid polymer, a rotary pump at least partially mounted in said reservoir for agitating said liquid polymer in the presence of a gas to distribute said gas throughout said liquid polymer and pressurizing said liquid and gas dispersion so as to force said gas into solution with the liquid polymer, means for cooling said rotary pump to prevent thermal reaction of said liquid polymer due to the heat generated in said pump, and a dispenser selectively operable to dispense said liquid and gas solution at a pressure below the solution maintenance pressure of said gas and polymer solution whereby said gas is released from solution to form a polymer foam.

(9) The apparatus of claim 8 wherein said rotary pump is a gear pump.

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(10) The apparatus of 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 said cooling means comprises means for continuously circulating cooling fluid through said manifold.

(11) The method of dispensing a heat sensitive liquid polymer foam which comprises the steps of:
mechanically agitating the liquid polymer in the presence of a gas so as to obtain a mixture of said gas in the liquid polymer, pressurizing the mixture of liquid and gas in a rotary pump so as to force the gas into solution with the liquid polymer, cooling said rotary pump so as to prevent thermal reaction of said liquid polymer due to the heat generated in said pump, and dispensing the liquid and gas solution at atmospheric pressure whereby said gas is released from solution and forms a polymer foam.

(12) The method of claim 11 wherein said liquid is a thermally fusible cold glue or plastisol.

(13) The method of claim 11 wherein said liquid is maintained by the cooling step at a temperature below about 110° F.

(14) The method of claim 11 wherein the cooling step is continuous.