EP0225624A2 - Spray head for spraying a thermoplastic material, particularly a fusible glue - Google Patents

Abstract

1. A spray head for spraying a thermoplastic hot-melt adhesive a) having at least one feed channel (14) for the heated hot-melt adhesive, b) having an outlet at the lower end of the feed channel (14), c) having a tapered feed channel (52) for a stream of gas, d) having a mixing chamber (54) into which both the feed channel (14) for the heated hot-melt adhesive and the gas feed channel (52) open, and e) having a nozzle opening (58, 80) connected to the mixing chamber (54) for the atomized hot-melt adhesive, characterised by the following features : f) outlets (86, 88, 90, 92) for gas jets directed onto the emerging, atomized hot-melt adhesive are arranged distributed symmetrically round the nozzle opening (58, 80) ; g) seen in plan view on the nozzle openings (58, 80), the gas jets extend from the outlet (86, 88, 90, 92) parallel to one another in pairs and past the nozzle opening (58, 80) ; and h) the streams of gas for the mixing chamber (54) on the one hand and the outlets (86, 88, 90, 92) on the other hand are adjustable independently of one another (60, 64).

Description

The invention relates to a spray head for spraying a flowable thermoplastic of the type specified in the preamble of claim 1.

DE-OS 2 836 545 or DE-OS 3 416 105 discloses devices for spraying application compositions, in particular hot-melt adhesives, but also plastics, in which the flowable application composition is supplied from one source to a spray head, which is supplied via a second Line receives a gas. The spray head simultaneously releases the heated, flowable application composition and the gas, generally air, so that the emerging application composition is atomized by the pressurized gas and applied to the substrate to be coated in the form of a spray curtain or mist.

DE-PS 2 924 174 discloses a spray head for spraying a flowable hot-melt adhesive in which the heated adhesive emerges from a central feed channel. The gas outlet openings are directed against the axis of the outlet opening of the adhesive feed channel and form a gap opening which is directly concentrically surrounding the outlet opening for the adhesive, the jet direction of which forms an acute angle with the axis of the outlet opening. A disadvantage of this configuration is the unfavorable mixing of heated adhesive and the gas, generally compressed air, so that optimal spray patterns cannot be achieved. In particular, once a spray pattern has been specified, it can no longer be varied.

A similar spray head emerges from DE-PS 2 405 450, the gas outlet device having an annular, conical channel which surrounds the outlet opening for the heated adhesive and to which the thread to be extruded from the outlet opening for the adhesive is inclined. Since the inlet openings for the annular, conical gas channel are arranged offset on one another on opposite sides of the outlet opening for the adhesive, there is a swirling of the gas in the feed channel, i.e. the exiting gas flow gives the adhesive thread leaving the outlet opening a rotational movement component. In this way, uniform dimensions of the adhesive layer can be achieved in a simple manner, these dimensions being able to be varied as required, namely by appropriately adapting the speed of the emerging gas stream.

However, this known spray head still does not work optimally, since the mixing of heated adhesive and compressed gas leaves something to be desired. In addition, the shape of the emerging, atomized adhesive threads can no longer be influenced.

The invention is therefore based on the object of providing a spray head for spraying a flowable thermoplastic material of the type specified, in which the disadvantages mentioned above no longer occur.

In particular, a spray head is to be proposed which ensures good mixing of plastic and compressed gas, generally compressed air.

This is achieved according to the invention by the features specified in the characterizing part of claim 1.

Expedient embodiments are defined by the features of the subclaims.

The advantages achieved by the invention are based in particular on the fact that in the mixing chamber which is provided in the outlet area of the spray head, the heated plastic on the one hand and the compressed gas on the other hand are optimally mixed thoroughly, i.e. a finely atomized plastic curtain from the narrow opening or narrow openings of this mixing chamber can emerge; In this way, the plastic can be applied to the surface to be coated as a thin, finely divided film. The impact area for the plastic can easily be changed by changing the nozzle shape, the flow angle of the plastic, the distance between the spray head and the surface to be coated, the speed of the air and plastic flow and finally by appropriate design of the inlet openings for the plastic or the compressed air into the mixing chamber and the outlet opening (s) of the mixing chamber can be varied.

It is essential that the plastic is not in the form of a con continuous thread, but as an even, thin film on the surface to be coated and there shows an optimal adhesion.

It has proven to be advantageous if the gas is brought into the mixing chamber through a flow channel which is provided with flow guide elements, so that there is an optimal swirling of the plastic with the compressed gas in the mixing chamber.

The outlet opening of the mixing chamber can be designed as a thin outlet slot with a width of about 0.3 mm or as a circular outlet opening with a corresponding diameter. Finally, it is also possible to provide a plurality of outlet openings with a circular diameter, for example arranged on a straight line.

In order to also be able to influence the atomized plastic emerging from the outlet opening of the mixing chamber, according to a preferred embodiment, additional gas outlet openings are provided on the outside of the spray head, which are offset from one another and each direct a gas flow onto the atomized plastic. This allows the atomized plastic to be given a specific shape and directional component.

These additional gas outlet openings are either located on two oppositely arranged knobs with offset gas outlet openings or in an outer, bead-shaped ring on the outside of the spray head with corresponding gas outlet openings.

According to a preferred embodiment, the gas flows that are fed to the mixing chamber, on the one hand, and the gas flows on the outside of the nozzle, on the other hand, are independent of one another set to predetermined flow values, that is to say pressure and / or volume, so that the corresponding parameters can be regulated independently of one another.

• Fig. 1 eine schematische Darstellung einer Vorrichtung zum Versprühen eines fließfähigen thermoplastischen Kunst­stoffes mittels eines stationären Sprühkopfes,
• Fig. 2 einen vertikalen Schnitt durch den unteren Teil des Sprühkopfes mit der Düse,
• Fig. 2a im vergrößerten Maßstab einen vertikalen Schnitt durch das untere Ende des Sprühkopfes,
• Fig. 3 eine Ansicht von unten auf die Düse,
• Fig. 4 einen vertikalen Schnitt durch eine weitere Aus­führungsform des unteren Teil des Sprühkopfes,
• Fig. 5 eine Ansicht von unten auf diesen Sprühkopf,
• Fig. 6 einen vertikalen Schnitt durch eine dritte Aus­führungsform des unteren Teils eines Sprühkopfes,
• Fig. 7 eine Ansicht von unten auf die Düse dieses Sprüh­kopfes
• Fig. 8 eine schematische Ansicht eines Schmelzklebstoff-Musters, wie es sich bei mehreren, nebeneinander angeordneten Aus­führungsformen nach Fig. 6, 7 ergibt, und
• Fig. 9 eine schematische Ansicht eines Schmelzklebstoffmusters, wie es sich bei mehreren, in einer Reihe angeordneten Sprühköpfen nach den Figuren 6 und 7 ergibt, wenn die Achse der Gasaustrittsöffnungen schräg in Bezug auf die Richtung der Relativbewegung zwischen dem zu beschichten­den Substrat und den Sprühköpfen angeordnet ist.

The invention is explained in more detail below using exemplary embodiments with reference to the accompanying schematic drawings. Show it

• 1 is a schematic representation of a device for spraying a flowable thermoplastic by means of a stationary spray head,
• 2 shows a vertical section through the lower part of the spray head with the nozzle,
• 2a on an enlarged scale a vertical section through the lower end of the spray head,
• 3 is a bottom view of the nozzle,
• 4 shows a vertical section through a further embodiment of the lower part of the spray head,
• 5 is a bottom view of this spray head,
• 6 shows a vertical section through a third embodiment of the lower part of a spray head,
• Fig. 7 is a bottom view of the nozzle of this spray head
• Fig. 8 is a schematic view of a hot melt adhesive pattern, as it results in several, side by side embodiments of Fig. 6, 7, and
• Fig. 9 is a schematic view of a hot melt adhesive pattern, as is the case with several spray heads arranged in a row according to Figs. 6 and 7, when the axis of the gas outlet openings is arranged obliquely with respect to the direction of the relative movement between the substrate to be coated and the spray heads is.

FIG. 1 shows a device, generally indicated by reference number 10, for spraying thermoplastic materials, in particular hot melt adhesives, with a liquefaction device 12, which may have the structure known from DE-OS 2 836 545, for example. The liquefaction device 12 has on its top a filler cap 14 for the plastic to be refilled.

Further details will be described below with reference to "hot melt" or "hot melt adhesive".

The device 10 also contains a hot melt hose 16, which is shown larger in the left part of FIG. 1 than in the right part. This hot melt hose 16 opens into a spray head 18, on the underside of which a nozzle 19 is provided for spraying the hot glue onto a material web 20 which is moved in the direction of the arrow and is to be coated with the hot glue; the sprayed hot glue emerging is indicated in FIG. 1 with dashed lines.

The hot melt hose 16 has a connection piece 22 at its inlet end and a connection piece 24 at its outlet end, which are attached to the liquefaction device 12 or the spray head 18 by corresponding counterparts.

At the inlet end of the hot melt hose 16, three lines are led through the outer wall thereof, namely a compressed air inlet hose 28, which opens into a shut-off element designed as a solenoid valve 30, which is acted upon by the compressed air flowing in the direction of the arrow, and two connected to the liquefaction device 12 via plugs Lines, namely a supply line 32 connected to a hot strip in the interior of the hot melt hose 16 and a control line 34.

At the outlet end, an outlet hose 36 for warm air penetrates the outer wall of the hot melt hose 16 and opens into the lower part side of the spray head 18.

The hot melt hose 16 has, for example, the construction as is known from DE-OS 3 416 105, i.e. the air line is integrated in the hot melt hose 16, so that the compressed air supplied and the heated hot melt in the hot melt hose. are kept at the specified temperature.

As an alternative to this, hot melt hose 16 and compressed air line can also be designed separately.

In the outlet hose 36 there is an adjustable throttle 39 for setting the amount of compressed air supplied to the spray head 18.

Viewed in the flow direction of the compressed air, the compressed air line branches in front of the solenoid valve 30, that is to say a line leads to the solenoid valve 30, while a bypass 38 bypassing the solenoid valve 30 is connected to the compressed air hose 28 at a point which is downstream of the solenoid valve 30 when viewed in the flow direction is.

Through this bypass 38, a small amount of compressed air flows in comparison with the amount of operating air, not only during a spraying process but also during the breaks in operation.

The spray device 10 shown in FIG. 1 has the following mode of operation: in the liquefaction device 12, the hot glue filled through the cover 14 is heated and thereby liquefied; since the shut-off device for the supply of the liquefied hot glue is still closed (this shut-off device is generally located in the liquefaction device 12 and is not shown in FIG. 1), no hot glue can escape at the spray head 18.

However, a relatively small amount of compressed air flows continuously through the bypass 38, which is negligible in comparison with the amount of compressed air required during operation; this amount of compressed air Flows through the hot melt hose 16, the part 36 with the throttle 39 and constantly emerges from the nozzle 19 of the spray head 18.

At the beginning of a spraying process, a corresponding switching signal is given, whereby the valve 30 in the compressed air line 28 and the shut-off element of the liquefaction device 12 are opened at the same time. The heated and thereby liquefied hot glue is introduced into the hot glue hose 16 by a high-pressure displacement pump (not shown) in the liquefaction device 12 via the connection 22. At the same time, the solenoid valve 30 is opened so that the total amount of compressed air available flows through the hot glue hose 16 and the air hose 36 into the spray head 18 via the solenoid valve 30 and the air hose 28.

At its outlet end, the hot melt leaves the hot melt hose 16 via the nozzle 24 at approximately the same temperature that it has when it enters the hot melt hose 16; the compressed air also leaves the hot melt hose 16 via the gas line part 36 at approximately the same temperature as the hot melt.

The compressed air heated in this way is introduced into the spray head 18 into the hot glue stream in such a way that it is atomized, the temperature-controlled air stream having such a temperature that on the one hand it does not lead to premature solidification of the hot glue applied, but on the other hand it does not lead to overheating of the hot glue and therefore to impair its properties when leaving the spray head 18.

Since a relatively small amount of air constantly flows from the bypass 38 through the hot melt hose 16 to the spray head 18, the opening can NEN of the solenoid valve 30 and the shut-off for the hot melt take place simultaneously.

Fig. 2 shows a vertical section through the lower part of the spray head 18 with the screwed, approximately cup-shaped nozzle 19. You can see the connection 24 for the supply of the heated plastic, which then through a central supply channel 40 in a support 42 for the nozzle 19 flows down. This nozzle carrier 42 is approximately cylindrical in shape and receives in its central feed channel 40 for the heated hot glue a mandrel 44 with a tip which extends to the lower end of the feed channel 40 and thus of the nozzle carrier 42. At this lower end, the central feed channel 40 for the heated hot glue also tapers.

In Figure 2, an opening 43 is also indicated, which is connected to the line 36 for the compressed air. A flow channel 46 runs downward from this opening 43 in the nozzle carrier 42 and opens into an annular channel 48 which is formed between a stepped area 50 with a reduced diameter of the nozzle carrier 42 on the inside and the inside wall of the nozzle 19 on the outside. From this ring channel 48, the compressed air flows through an inward and downward channel 52 into a mixing chamber 54, which is delimited at the lower end by the inner wall of the nozzle 19 on the one hand and the lower, conical end of the nozzle carrier 42 on the other and in turn tapers downwards (see also Fig. 2a).

The flow channel 52 is provided with flow guide elements 52a (see FIG. 2a), namely in the embodiment shown with grooves or ribs in the outer wall of the lower, conical, stepped region 50 of the nozzle carrier 52, as a result of which the Can influence the angle at which the compressed air in the mixing chamber meets the hot glue emerging from the opening. As an alternative to the illustrated embodiment, knurling can also be provided, for example, not only on the area 50 of the nozzle carrier, but also on the inner surface of the nozzle 19, in order to make the compressed air flow entering the mixing chamber laminar or turbulent as required.

The compressed air is thus fed to the mixing chamber 54 in such a way that the mixing chamber 54 optimally mixes the heated hot glue from the central channel 40 and the swirling compressed air.

At its lower end, the nozzle 19 has a cylindrical projection 56 in plan view (see FIG. 3) with a central, slot-shaped outlet opening 58 for the mixing chamber 54, from which the atomized hot glue emerges downwards. This outlet opening has a width of approximately 0.3 mm.

As an alternative to the embodiment according to FIGS. 2 and 3, the outlet opening can also be formed by a single central bore with a circular cross section in the projection 56 or else by a plurality of bores with a circular cross section arranged next to one another on a straight line. Such holes should have a diameter of about 0.3 mm.

The compressed air on the one hand and the heated hot glue on the other hand are thoroughly mixed in the mixing chamber 54 so that the atomized hot glue leaves the outlet opening 58 as a "hot glue curtain" and can be applied to the substrate 20 as a uniform, thin layer.

FIGS. 4 and 5 show an embodiment in which a control valve 60 for the compressed air is provided at the opening 43, so that the quantity and / or pressure of the compressed air supplied to the nozzle 19 can be adjusted.

The compressed air then passes from the opening 43 in a manner similar to the embodiment according to FIGS. 2 and 3 to a mixing chamber in which the heated hot glue is atomized.

The nozzle holder 42 contains a second compressed air connection 62 with a second control valve 64. This connection 62 is connected via a flow channel 66 in the nozzle holder 42 to a flow channel 68 in the nozzle 19. A half-ring line (not shown) in the transition area between nozzle carrier 42 and nozzle 19 connects the two channels 66, 68 to a further flow channel 70 on the opposite side of the nozzle 19, ie, the two flow channels 68, 70 in the nozzle 19 symmetrically Arranged in the middle of the nozzle 19.

The two flow channels 68, 70 in the nozzle 19 end in hemispherical knobs 72, 74 which are located on the lower outside of the nozzle 19 and are provided with outlet openings 76, 78. In the vertical section according to FIG. 4, it can be seen that these outlet openings 76, 78 are directed obliquely downward onto the atomized hot glue which leaves the nozzle 19 via the outlet opening.

From the top view of the nozzle 19 according to FIG. 5, it can be seen that the two knobs 72, 74 and the outlet opening 80 of the nozzle 19 lie on a straight line. However, the outlet openings 76, 78 of the knobs 72, 74 are arranged parallel to one another in such a way that the exiting air jets flow past the outlet opening 80 (see FIG. 5), ie the "hot melt curtain" emerging from the outlet opening 80 is drawn from both sides acted upon by the air jets from the knobs 72, 74 and thereby receives a certain shape.

The shape of this hot glue curtain can be influenced by appropriate spatial configuration of the knobs 72, 74 and thus the air jets generated by them.

FIGS. 6 and 7 show an embodiment which differs from the embodiment according to FIGS. 4 and 5 in that a circumferential bead ring 82 is provided on the lower outside of the nozzle 19 and is connected to the two flow channels 68, 70. The bead ring 82 contains a circumferential ring channel 84 which is provided with outlet openings on the inside of the ring bead 82.

In the embodiment according to FIGS. 6 and 7, a total of four outlet openings 86, 88, 90 and 92 are used, which are arranged symmetrically to the outlet opening 80 of the nozzle 19, that is to say in each case at angular intervals of 90 °.

These outlet openings 86, 88, 90, 92 direct fine air jets onto the hot glue curtain emerging from the outlet opening 80, as a result of which a specific spray pattern can be achieved. By changing the positions of the outlet openings accordingly, this spray pattern can be varied as required.

The outer air jets can also be used in one embodiment of a spray head without a mixing chamber 54 in the nozzle 19, that is to say when the heated hot glue has been atomized in the usual way by the compressed air.

Good results are achieved if the thermoplastics and in particular hot melt adhesives have a viscosity in the range between 0 and 1,000,000 and in particular between 0 and 750,000 cp.

The compressed air or, more generally, the atomizing gas should be heated, with temperatures in the range between 50 ° C. and 200 ° C. having proven suitable.

FIG. 8 shows a spray pattern as can be achieved with several spray heads according to the embodiments according to FIGS. 4 and 5. The axes that connect the outlet openings 76, 78 of the nozzle heads 18 run perpendicular to the direction of the relative movement between the substrate 20 and the spray heads, which results in patterns 100 that run at right angles to this direction. The direction is indicated in Fig. 8 by the arrow.

This alignment particularly advantageously utilizes the maximum width of the individual oval patterns 100.

Another, particularly useful spray pattern is shown in Figure 9; the axes connecting the openings 76, 78 are inclined with respect to the direction of the relative movement between the substrate 20 and the spray head 18, as can be seen from FIG. 9. The optimal angle can be set as required.

The spray pattern in this embodiment is denser than in the spray pattern according to FIG. 8 if all other influencing parameters are kept the same. In some cases, the overlap between the individual spray patterns 100 can be reduced.

Claims (15)

1. spray head for spraying a thermoplastic, in particular a hot melt adhesive, a) with at least one feed channel for the heated plastic, b) with an outlet opening at the lower end of the feed channel, c) with a conical feed channel for a gas stream, and d) with an outlet opening for the gas channel, which directs a gas flow onto the emerging plastic,
characterized by the following features: e) both the feed channel (40) for the heated plastic and the gas channel (52) open into a mixing chamber (54) from which the atomized plastic emerges via a narrow opening (58). 2. Spray head according to claim 1, characterized in that a flow channel (52) for the gas to the mixing chamber (54) extends from an annular channel (48). 3. Spray head according to one of claims 1 or 2, characterized in that a cup-shaped nozzle (19) is screwed onto a cylindrical nozzle carrier (42), and that the flow channels (48, 52) for the gas between the nozzle carrier (42) and the inner surface the nozzle (19) are formed. 4. Spray head according to one of claims 2 or 3, characterized in that the flow channel (52) for the gas between the annular channel (48) and the mixing chamber (54) with flow guide elements, in particular ribs and / or grooves, is provided. 5. Spray head according to one of claims 1 to 4, characterized in that the outlet opening (58, 86, 88, 90, 92) of the spray head (19) has a width of about 0.3 mm. 6. Spray head according to one of claims 1 to 5, characterized in that the outlet opening (58) is designed as a narrow gap. 7. Spray head according to one of claims 1 to 5, characterized in that the outlet opening is formed by at least one circular bore. 8. Spray head according to one of claims 1 to 7, characterized in that the mixing chamber (54) has a cylindrical shape. 9. Spray head according to one of claims 1 to 8, characterized in that the cylindrical mixing chamber (54) has a diameter of about 1.5 mm. 10. Spray head, in particular according to one of claims 1 to 9, characterized in that further gas outlet openings (76, 78; 86, 88, 90, 92) are provided on its underside, which direct gas jets onto the emerging, atomized plastic. 11. Spray head according to claim 10, characterized in that two opposite, hemispherical knobs (72, 74) with gas outlet openings (76, 78) are provided. 12. Spray head according to claim 11, characterized in that the gas jets from the two outlet openings (76, 78) run parallel to one another past the outlet opening (80). 13. Spray head according to claim 10, characterized in that a bead ring is provided with outlet openings. 14. Spray head according to claim 13, characterized in that the outlet openings (86, 88, 90, 92) of the bead ring (82) are arranged symmetrically. 15. Spray head according to one of claims 10 to 14, characterized in that the gas flows for the mixing chamber (54) on the one hand and the knobs (72, 74) or the annular bead (82) on the other hand are independently adjustable.

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