METHOD OF BONDING WITH WATER-BASED ADHESIVES

Abstract: A method of bonding in which water-based adhesives, i.e., aqueous polymeric dispersions or emulsions, are extruded from the discharge outlet (26) of a dispensing device (10) as a bead (12) which is impinged by air jets (14) directed at an angle and tangent to the periphery of the bead. The viscosity of the water-based adhesive, hydraulic pressure at which the adhesive is extruded from the dispensing device, diameter of the discharge outlet and pressure of the air jets are controlled such that the extruded bead is attenuated by the air jets to form an elongated, thin adhesive strand or fiber (16) which is deposited in a spiral pattern (31) on a first substrate (32) for subsequent bonding to a second substrate.

Description: Method of Bonding With Water-Based Adhesives Field of the Invention This invention relates to adhesive bonding, and, more particularly, to a method of depositing an attenuable, aqueous polymeric dispersion or emulsion in a spiral spray pattern of elongated adhesive strands or fibers onto a first substrate for subse¬ quent bonding to a second substrate. Background There are a number of industrial applica- tions for adhering different types of products. In applications wherein quick setting time is desirable, hot melt thermoplastic adhesives have been widely used. The strength of the bond obtained with hot melt thermoplastic adhesives is determined, at least in part, by the area of interface or surface contact between the adhesive and substrate, i.e., the greater the area of contact, the stronger the bond. In most cases, hot melt adhesives have been dispensed in a thick, extruded bead, which, because of the relatively high viscosity and high surface tension of such adhesives, is difficult to spread over as large a surface area as desired.. Additionally, hot melt adhesive cools quite quickly when it is applied to a substrate which further adds to the difficulty of spreading a bead over a larger area. Another problem with hot melt adhesives is that some substrates to be bonded are heat sensitive and can be damaged or destroyed by contact with hot melt adhesives which can have an application tempera¬ ture of 300°F or higher. This is of particular concern in applications such as the bonding of the polyethylene backing sheet to the non-woven pad of hygienic articles wherein the backing sheet is heat sensitive and can be damaged, or its appearance adversely affected, by relatively thick, high tempera¬ ture beads of hot melt adhesive. In order to reduce these problems with hot melt adhesives, methods and apparatus have been developed to form hot melt thermoplastic adhesives in an elongated, thin bead or fiber which is deposited atop the substrate. Elongated beads or fibers of adhesive have been produced in prior art spray devices which include a nozzle formed with an adhesive dis- charge opening and one or more air jet orifices through which a jet of air is ejected. A bead of adhesive is extruded from the adhesive discharge opening in the nozzle which is then impinged by the air jets to attenuate or stretch the adhesive bead forming an elongated, thin fiber for deposition onto the substrate. This elongated, thin strand or fiber of adhesive has a reduced application temperature compared to that of a relatively thick, extruded bead. Examples of spray devices capable of forming adhesive fibers are disclosed in U.S. Patent Nos. 2,626,424 to Hawthorne, Jr.; 3,152,923 to Marshall et al; 4,185,981 to Ohsato et al; and, Patent Nos. 3,911,173; 4,031,854; and, 4,098,632 all to Sprague, Jr. The formation of elongated fibers or strands has also permitted hot melt adhesives to be spread or deposited over a larger area than thick, extruded beads. A substantially spiral-shaped spray pattern of adhesive fibers has been obtained in the prior art by impacting the adhesive bead discharged from the nozzle with air jets directed substantially tangent to the periphery of the extruded adhesive bead. These tangentially applied air jets cause the elongated adhesive fiber to move in a twisting, spiral path toward a substrate, thus forming a spray pattern which is relatively wide compared to the width of an extruded bead. Spiral spray patterns of adhe'sive fibers are formed in the methods and apparatus taught in the '424 Hawthorne, Jr. patent, '981 Ohsato et al patent, and the Sprague, Jr. patents mentioned above. Sumnary of the Invention Water-based adhesives or so-called "cold adhesives" have been proposed as alternatives to hot melt thermoplastic adhesives in some applications, but were never considered as candidates for the formation of elongated, thin adhesive strands or fibers. This is due, in part, to the fact that water-based adhe¬ sives do not have the inherent disadvantages of hot melt adhesives which were the motivating factors in forming hot melt adhesives in elongated strands or fibers. Water-based adhesives are dispensed at ambient temperatures and therefore the problem of thermal damage to a substrate is eliminated. More¬ over, water-based adhesives do not cool when applied to a substrate, unlike hot melt adhesives which quickly cool and thereafter become more difficult to spread. Additionally, the method of applying hot melt adhesives in the form of elongated, thin fibers described above had not been seriously considered as being feasible for use with water-based adhesives. Because water-based adhesives comprise a dispersion or emulsion of polymeric particles in an aqueous carrier, it was expected that any attempt to form elongated adhesive fibers from water-based adhesives, in the same manner as hot melt adhesives, would either produce adhesive droplets or break up the emulsion. In fact, this expectation was borne out in early attempts to form water*-based adhesives in elongated strands or fibers wherein adhesive droplets were formed when an extruded bead of such adhesives was impacted by air jets, instead of attenuated or elon¬ gated adhesive strands or fibers as obtained with hot melt adhesives. As a result, water-based adhesives, i.e., aqueous polymeric dispersions or emulsions, had not been employed in the same applications where hot melt thermoplastic adhesives are currently dispensed in elongated, fiber-like strands onto a substrate. It was therefore among the objectives of this invention to provide a method of bonding in which aqueous polymeric dispersions or emulsions can be employed to form an attenuated, elongated adhesive strand or fiber for bonding two substrates to one another. This objective is accomplished in a method of bonding wherein an aqueous polymeric dispersion or emulsion, i.e., a water-based adhesive, is extruded in a bead from the discharge outlet of a dispensing device. This extruded bead of water-based adhesive is then attenuated by one or more jets of air ejected from air jet bores in the dispensing device to form an elongated adhesive strand or fiber having a small diameter compared ' to that of the extruded bead. In a preferred embodiment, these air jets contact the extr ded bead along its periphery to impart a swirling or twisting motion to the attenuated, elongated adhesive strand or fiber thereby forming a spiral spray pattern on a first substrate for subsequent bonding to a second substrate. In one aspect of this invention, it has been found that several operating conditions of the dis¬ pensing device must be controlled to obtain relatively- thin, elongated adhesive fibers in an acceptable pattern from certain types of water-based adhesives. These parameters include the diameter of the adhesive discharge outlet of the dispensing device from which the adhesive bead is extruded, the hydraulic pressure required to extrude an adhesive bead from the dis- charge outlet at a given weight per unit of time, e.g., grams per second, and the pressure of the air delivered to the air jet bores of the dispensing device for discharge of the air jets which impact the adhesive bead. It has been observed that for certain types of water-based adhesives, e.g., ethylene vinyl acetate emulsions having a viscosity of between about 800-1,200 centipoise (cps) , the operating parameters of the dispensing device mentioned above can be adjusted within ranges to produce a controlled spiral pattern of elongated adhesive fibers on a substrate. Experiments have been conducted on this type of adhesive using a dispenser having a discharge outlet about 0.125 inches long, which varied from about 0.012 to 0.020 inch in diameter, wherein the hydraulic pressure at which the adhesive was delivered to such discharge outlet was varied from about 50 to 500 psi and wherein the pressure of the air delivered to six 0.050 inch long, 0.018 inch diameter air jet bores of the dispenser was varied from about 2 to 30 psi. Greater hydraulic pressures, i.e., near the 500 psi level, are required with smaller diameter discharge outlets and lesser hydraulic pressures near the 50 psi level are used with larger diameter discharge outlets. Under these operating conditions of the dispensing device for such ethylene vinyl acetate polymers, acceptable elongated strands or fibers in the desired spiral pattern have been obtained. In another aspect of this invention, it has been found that other types of water-based adhesives are unacceptable for use in forming elongated adhesive fibers or strands without modification. One group of water-based adhesive, e.g., ethylene vinyl acetate emulsions those having a viscosity of more than about 10,000 cps, tend to break up into non-uniform blobs and broken strings when ejected from the discharge outlet of the spray device. This problem has been solved by diluting the dispersion or emulsion, e.g., by adding additional water, until the viscosity decreases to a level in the range of about 200 to 10,000 cps, and preferably in the range of about 800 to 4,000 cps. At this viscos¬ ity, such ethylene vinyl acetate dispersions or emulsions have been both extruded in a bead and formed into an elongated fiber or strand. The operating conditions of the dispenser which have been employed to obtain acceptable adhesive fibers using these types of adhesives include a discharge outlet diameter in the range of about 0.016 to 0.030 inches, a hydraulic pressure of the adhesive delivered to the discharge outlet in the range of about 100 to 200 psi and a pressure of the air delivered to the air jet bores in the dispenser in the range of about 2 to 6 psi. In another aspect of this invention, other aqueous polymeric emulsions or dispersions, e.g., styrene butadiene, do not form uniform elongated adhesive fibers at the desired viscosity level. It is believed that the reason for such failure is that shear forces and elongational stresses are imposed on the extruded bead of such material by the air jets which cannot be supported by the emulsion, and which cause the emulsion to break up into droplets or blobs. In order to successfully form elongated adhesive strands or fibers from this group of aqueous polymeric dispersions or emulsions, a water-soluble polymer such as hydroxypropyl methyl cellulose has been added. The water-soluble polymer creates a continuous polymer phase between the particles of styrene butadiene which is capable of supporting the elongational stress applied to the extruded bead by the air jets to form an attenuated adhesive fiber instead of breaking up into droplets. Beginning with a styrene butadiene emulsion and then adding an effective, amount of 1% hydroxypropyl methyl cellulose to obtain an emulsion with a viscosity of about 3,000 cps, the operating conditions of the dispenser employed to obtain an acceptable adhesive strand or fiber include a dis¬ charge outlet diameter of the dispenser in the range of about 0.016 to 0.030 inches, a hydraulic pressure of the adhesive delivered to the discharge outlet of about 40 psi and a pressure of the air delivered to the air jet bores in the dispenser of about 3 psi. Description of the Drawings • The structure, operation and advantages of a presently preferred embodiment of this invention will become further apparent upon consideration of the following description taken in conjunction with accompanying drawings, wherein: Fig. 1 is a schematic, elevational view of a dispensing device for attenuating water-based adhe- sives; Fig. 2 is an enlarged cross sectional view of that portion of the dispenser through which the water-based adhesive is extruded and impacted with air jets; and Fig. 3 is a view of the pattern of elongated adhesive strands or fibers on a first substrate in preparation for bonding to a second substrate. Detailed Description of the Invention Referring to Figs. 1 and 2, a dispensing device or dispenser 10 is schematically illustrated which is capable of extruding an adhesive bead 12 and impacting the adhesive bead 12 with air jets 14 to form an attenuated or elongated adhesive strand or fiber 16. The details of the operation of dispenser 10 form no part of this invention per se and thus are described briefly herein. A complete discussion of the operation of dispenser 10 is given in U.S. Patent No. 4,785,996 to Ziecker et al, assigned to the same assignee as this invention, the disclosure of which is incorporated by reference in its entirety herein. For purposes of the present discussion, the dispenser 10 has a dispenser body 18 which is con¬ nected by a line 20 to a source of water-based adhe¬ sive (not shown) , and by a line 22 to a source of pressurized air (not shown) . The base of the dispen¬ ser body 18 mounts a nozzle 23 which supports a nozzle plate 24 having a throughbore 26 which communicates with an adhesive passageway within the dispenser 10. The throughbore 26 terminates in a discharge outlet 28 through which the adhesive bead 12 is extruded, and has a length of about 0.125 inch. The nozzle plate 24 is also formed with six air jet bores 30, two of which are shown in Fig. 2, each having a length of about 0.050 inch and a diame¬ ter of about 0.018 inch. These air jet bores 30 communicate with an air delivery passageway formed in the dispenser body 18 and discharge individual jets 14 of pressurized air at an angle with respect to the longitudinal axis of the throughbore 26, and substan¬ tially tangent to the periphery of the adhesive bead 12 extruded from the throughbore 26. These air jets 14 are effective to both attenuate or stretch the adhesive bead 12 to form the thin, elongated adhesive fiber 16, and to impart a twisting or swirling motion to the adhesive fiber 16 so that the adhesive fiber 16 is laid down in a spiral pattern 31 upon a first substrate 32. See Fig. 3. The first substrate 32 can then be brought into contact with a second substrate 34 to form a bond therebetween, as illustrated sche¬ matically in Fig. 3. The term "water-based adhesive" as used herein is meant to refer to an aqueous polymeric dispersion or emulsion consisting of a polymeric material and water carrier, usually with a surfactant or other additives as is well understood in the art. The polymeric material or base can consist of any of the following: polyvinyl acetate, ethylene vinyl acetate, -ethylene and acrylic polymers, polyvinyl chloride, butadiene acrylonitrile, butadiene styrene, butyl, ethylene propylene polymers, fluoro polymers, natural rubber, polybutadiene, polychloroprene, polyisobutylene, polyisoprene, polysulfide, poly- urethane, silicone, and miscellaneous polymers. Generally, these aqueous polymeric emulsions have a solids content in the range of about 30% to 75%, and more preferably in the range of about 50% to 66%, by weight. In an alternative embodiment, the term "water-based adhesive" is also meant to refer to an aqueous polymeric emulsion or dispersion of the type described above with the addition of a water-soluble polymer such as hydroxypropyl methyl cellulose. As discussed below, this type of "water-based adhesive" employs the water-soluble polymer as an extender to create a continuous polymer phase with the polymer particles in the water carrier and thereby prevent the emulsion or dispersion from breaking up under the influence of elongational forces applied by the air jets 14 to the extruded bead 12 so as to permit the formation of an elongated adhesive fiber 16. Experiments have been conducted in which an acceptable adhesive pattern 31 of elongated adhesive fibers 16 has been obtained. In Examples 1-5 given below, a copolymer ethylene vinyl acetate emulsion was used having a viscosity in the range of about 800 to 1,200 centipoise (cps) and a solids content of about 66%, which is commercially available from Air Products and Chemicals, Inc. under the designation 465 DEV. The viscosity was measured using a Brookfield visco- eter. Model LVF (No. 3 spindle, 60 rpm, at 77°F). Example 1 polymer base: ethylene vinyl acetate viscosity: 800 - 1,200 cps hydraulic pressure: 500 psi air jet pressure: 2 psi increased to 30 psi nozzle diameter: 0.012 In this example, the air jet pressure was increased from about 2 psi to about 30 psi, holding all the other parameters constant, which produced acceptable elongated adhesive fibers 16 at pattern widths on the substrate ranging from about 0.125 inch at 2 psi to about 0.825 inch at 30 psi. Example 2 polymer base: ethylene vinyl acetate viscosity: 800 - 1,200 cps hydraulic pressure: 235 psi air jet pressure: 2 psi increased to 30 psi nozzle diameter: 0.014 inch In this example, the air jet pressure was increased from about 2 psi to about 30 psi, holding all the other parameters constant, which produced acceptable elongated adhesive fibers 16 at pattern widths on the substrate ranging from about 0.468 inch at 2 psi to about 0.563 inch at 30 psi with a maximum pattern width of 0.938 inch at 15 psi. Example 3 polymer base: ethylene vinyl acetate viscosity: 800 - 1,200 cps hydraulic pressure: 225 psi air jet pressure: 2 psi increased to 30 psi nozzle diameter: 0.016 inch In this example, the air jet pressure was increased from about 2 psi to about 30 psi, holding all the other parameters constant, which produced acceptable elongated adhesive fibers 16 at pattern widths on the substrate ranging rom about 0.313 inch at 2 psi to about 0.750 inch at 30 psi. Example 4 polymer base: ethylene vinyl acetate viscosity: 800 - 1,200 cps hydraulic pressure: 150 psi air jet pressure: 2 psi increased to 30 psi nozzle diameter: 0.018 inch In this example, the air jet pressure was increased from about 2 psi to about 30 psi, holding all the other parameters constant, which produced acceptable elongated adhesive fibers 16 at pattern widths on the substrate ranging from about 0.563 inch at 2 psi to about 1.00 inch at 30 psi with a maximum pattern width of 1.125 inch at 15 psi. Example 5 polymer base: ethylene vinyl acetate viscosity: 800 - 1,200 cps hydraulic pressure: 50 psi air jet pressure: 4 psi nozzle diameter: 0.020 inch Under these conditions, an acceptable elongated adhesive fiber 16 was produced on a sub¬ strate. With reference to the results obtained in Examples 1-5, one further parameter was involved, i.e., in each Example the weight of adhesive dis¬ charged from the discharge outlet 28 was .01 grams per inch of the substrate 32 at a line speed of 150 feet per minute. This explains the decrease in hydraulic pressure as the diameter of the discharge outlet 28 was increased. In other words, greater hydraulic pressure is required with a smaller diameter discharge outlet 28 in order to discharge .01 grams per inch at 150 feet per minute than the hydraulic pressure required to discharge the same weight of adhesive from a larger diameter discharge outlet 28. See Examples 1 and 5. Two trends can be observed from the results of Examples 4-8. First, the width of the spiral pattern 31 tends to increase as the pressure and velocity of the air jets discharged from air jets bores 30 is increased. This is generally true regard¬ less of the diameter of the discharge outlet 28. Additionally, the width of the spray pattern 31 tends to increase as the diameter of the discharge outlet 28 increases. Pattern widths were obtained from the operating conditions of Examples 1-5 in the range of about .125 inch to 1.125 inches. In another group of experiments, a different type of ethylene vinyl acetate emulsion was employed which is commercially available from National Starch and Chemical Corporation under the designation Impervo 14-9004. This ethylene vinyl acetate-based adhesive has 60% solids and a viscosity of 35,000 cps. It was discovered that such water-based adhesive produced droplets or blobs when extruded from the discharge outlet 28 of nozzle plate 24 and not a continuous extruded bead. It was unexpectedly discovered that elon¬ gated adhesive fibers 16 could be produced from this type of ethylene vinyl acetate emulsion by diluting the emulsion with de-ionized water. Additional experiments were conducted in which de-ionized water was added to the National Starch and Chemical Corporation adhesive designated Impervo 14-9004 in an effective amount to reduce the viscosity of the emulsion from 35,000 cps to a range of about 1,000 to 10,000 cps and most preferably to a range of about 800 to 6,000 cps. Specific results of such experiments are given in Examples 6, 7 and 8 below. Example 6 polymer base: ethylene vinyl acetate viscosity: 1,000 cps hydraulic pressure: 100 psi air jet pressure: 2 psi nozzle diameter: .016 to .030 inches. Under these conditions, a stable pattern 31 of an elongated adhesive fiber 16 was obtained on a substrate located at about 1 inch from the discharge outlet 28. The width of the pattern 31 was about 0.7 inches. Example 7 polymer base: ethylene vinyl acetate viscosity: 3,200 cps hydraulic pressure: 100 - 200 psi jet pressure: 2 - 4 psi nozzle diameter: 0.016 to 0.030 inches Under these conditions, a stable pattern 31 of an elongated adhesive fiber 16 was obtained on a substrate located at about 1 inch from the discharge outlet 28. The width of the pattern 31 was about 0.9 inches. Example 8 polymer base: ethylene vinyl acetate viscosity: 6,000 cps hydraulic pressure: 200 psi air jet pressure: 6 psi nozzle diameter: 0.016 to 0.030 inch This combination oi parameters produced a very fine elongated adhesive fiber 16 having a pattern width of about 0.8 inch. As mentioned above, the term "water-based adhesive" as used herein is also meant to refer to an aqueous polymeric dispersion or emulsion of polymeric particles in a water medium with the addition of a water-soluble polymer in amounts in the range of about 0.25% to 5% by weight. It has been found that water- based adhesives with certain polymer bases are incap¬ able of sustaining the elongational forces applied by the air jets discharged from air jet bores 30 and tend to break up in coarse droplets or blobs at the desired viscosity without the addition of a continuous polymer phase with the particles of the polymer base so that the emulsion or dispersion can sustain such forces. One example of a water-based adhesive with a water-soluble polymer additive which has been success¬ fully attenuated to form acceptable elongated adhesive fibers 16 is as follows. In this example, a water- based adhesive was employed which is commercially available from National Starch and Chemical Corpora¬ tion under the designation 33-4037. This adhesive has a styrene butadiene polymer base. The virgin adhesive 33-4037 has 60% solids and a viscosity of 9,000 cps which was diluted with water and 1% hydroxypropyl methyl cellulose to a viscosity of about 3,000 cps in the Example given below. Example 9 polymer base: styrene butadiene water-soluble polymeric additive: 1% hydroxypropyl methyl cellulose viscosity: 3,000 cps hydraulic pressure: 40 psi air jet pressure: 3 psi nozzle diameter: 0.016 to .030 inches In this example, an aqueous polymeric dispersion or emulsion having styrene butadiene as the polymer base, when diluted with an effective amount of 1% hydroxypropyl methyl cellulose, was used effec¬ tively in the formation of elongated adhesive fibers 16 under the operating conditions of the dispenser 10 given above. It is believed that the 1% hydroxypropyl methyl cellulose is effective to provide a continuous polymeric phase between the particles of styrene butadiene within the water matrix so as to permit such dispersion or emulsion to sustain the elongational force imposed by the impact of the air jets 14 and thus permit the successful formation of an elongated adhesive bead 16. While 1% hydroxypropyl methyl cellulose was employed in this Example, it is contem¬ plated that this or another water-soluble polymer could be employed in a concentration in the range of about 1/4% to 5% by weight. In each of the Examples 1-9 given above, and in the accompanying discussion, an "elongated adhesive fiber 16" is formed which is identified as having a diameter comparatively smaller than that of the extruded bead 12. Although difficult to precisely measure, elongated adhesive fibers 16 have been produced from the method and under the conditions described above having a diameter in the range of about 0.008 to 0.0055 inch. Under some operating conditions of dispenser 10, particularly using smaller discharge outlets 28, e.g., 0.012 to 0.016 inch, the elongated adhesive fiber 16 tends to fuse together in the spiral pattern 31 making it difficult to accu¬ rately measure the diameter of the fiber 16. Additionally, the foregoing description and examples have discussed the air jets 14 which impinge the extruded bead 12 in terms of air pressure, e.g., 2 to 30 pounds per square inch. This discussion is made with reference to the nozzle plate 24 as disclosed in detail in U.S. Patent No. 4,785,996 to Ziecker et al, mentioned above. As set forth in that patent, the diameter of the air jet bores 30 in nozzle plate 24 are in the range of about 0.017 to 0.019 inches. The velocity of the air jets 14 discharged therefrom can therefore be calculated or measured. While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is in¬ tended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims: 1. A method of adhesive bonding, comprising: extruding a bead of an attenuable, aqueous polymeric dispersion; attenuating said bead of aqueous polymeric dispersion with a jet of air to form an elongated, adhesive strand; depositing said elongated, adhesive strand onto a first substrate for subsequent bonding to a second substrate. 2. The method of claim 1 in which said step of extruding a bead comprises extruding a bead of an attenuable, aqueous polymeric dispersion having a viscosity in the range of about 200 centipoise to about 10,000 centipoise. 3. The method of claim 1 in which said step of extruding a bead comprises extruding a bead of an attenuable, aqueous polymeric dispersion consisting essentially of a water carrier and polymeric particles dispersed or emulsified within said water carrier, said polymeric particles comprising about 30% to 75% of said attenuable, aqueous polymeric dispersion. 4. The method of claim 1 in which said step of extruding a bead comprises extruding a bead of an attenuable, aqueous polymeric dispersion consisting essentially of a water carrier and polymeric particles dispersed or emulsified within said water carrier, said polymeric particles comprising about 50% to 66% of said attenuable, aqueous polymeric dispersion. 5. The method of claim 1 in which said step of extruding a bead comprises extruding a bead of an attenuable, aqueous polymeric dispersion consisting essentially of a water carrier, polymeric particles dispersed or emulsified within said water carrier and an effective amount of a water-soluble polymer as an aid in forming said strand. 6. A method of adhesive bonding, comprising: extruding a bead of attenuable, aqueous polymeric dispersion; attenuating and rotating said bead of aqueous polymeric dispersion with a jet of air to form an elongated, adhesive strand which rotates in a spiral, twisting motion; depositing said spiraling elongated, adhe¬ sive strand onto a first substrate for subsequent bonding to a second substrate. 7. The method of claim 6 in which said step of attenuating and rotating said bead comprises impacting said bead with a jet of air directed at an angle relative to the longitudinal axis Df said bead to attenuate said bead forming an elongated adhesive strand, and at the periphery of said bead to impart a spiral motion to said elongated adhesive strand. 8. A method of adhesive bonding, comprising: ejecting a bead of an attenuable, aqueous polymeric dispersion from the discharge outlet of a spray device; impacting said bead with jets of air ori¬ ented at an angle relative to the longitudinal axis of said discharge outlet so that said bead is attenuated to form an elongated adhesive fiber; and simultaneously directing said air jets at the periphery of said bead to impart a twisting motion to said elongated adhesive fiber to form a controlled, spiral spray pattern of said elongated adhesive fiber on a first substrate for subsequent bonding to a second substrate. 9. The method of claim 8 in which said step of ejecting said bead of an attenuable, aqueous polymeric dispersion comprises delivering said attenuable, aqueous polymeric dispersion to said discharge outlet of said nozzle at a pressure in the range of about 40 pounds per square inch to about 500 pounds per square inch. 10. The method of claim 8 in which said step of directing said air jets at the periphery of said bead comprises delivering air to air jet discharge orifices in said spray device at a pressure in the range of about 2 pounds per square inch to about 30 pounds per square inch. 11. The method of claim 8 in which said step of ejecting a bead of attenuable, aqueous polymeric dispersion comprises ejecting said bead through a discharge outlet in said spray device having a diame- ter in the range of about 0.012 inches to about 0.030 inches. 12. The method of claim 8 in which said step of extruding a bead comprises a bead of an attenuable, aqueous polymeric dispersion having a viscosity in the range of about 200 centipoise to about 10,000 centi- poise. 13. A method of adhesive bonding, comprising: extruding a bead of an attenuable, aqueous polymeric dispersion consisting essentially of a water carrier and polymeric particles dispersed Dr emulsi- fied in said water carrier; attenuating and rotating said bead of aqueous polymeric dispersion to form an elongated, adhesive strand which rotates in a spiral, twisting motion; depositing said spiraling elongated, adhe¬ sive strand onto a first substrate for subsequent bonding to a second substrate. 14. The method of claim 13 in which said step of extruding a bead comprises extruding a bead of an attenuable, aqueous polymeric dispersion having a viscosity in the range of about 200 centipoise to about 10,000 centipoise. 15. A method of adhesive bonding, comprising: extruding a bead of an attenuable, aqueous polymeric dispersion consisting essentially of a water carrier, polymeric particles dispersed or emulsified in said water carrier and an effective amount of a water-soluble polymer in said water carrier as an aid in forming an elongated strand of adhesive; attenuating and rotating said bead of aqueous polymeric dispersion to form said elongated adhesive strand which rotates in a spiral, twisting motion; depositing said spiraling elongated adhesive strand onto a first substrate for subsequent bonding to a second substrate. 16. The method of claim 15 in which said step of extruding a bead comprises extruding a bead of an attenuable, aqueous polymeric dispersion consisting essentially of a water carrier, polymeric particles dispersed or emulsified in said water carrier and about 0.25% to 5% water-soluble polymer in said water carrier.

Inventors: LADER HARRY J, REHMAN WILLIAM R, RICHARDS STEPHEN, SAIDMAN LAURENCE B, LADER, HARRY, J., REHMAN, WILLIAM, R., RICHARDS, STEPHEN, SAIDMAN, LAURENCE. B.
Applicants: NORDSON CORP, NORDSON CORPORATION
Application year: 1990
Main classification: B32B7
IPC codes: B05B7, B05C5, B05D1, B05D5, C09J5