EP0345666A2 - Spray head for liquids - Google Patents

Abstract

In a spray head for spraying liquids, in particular adhesives, such as melting adhesives or lacquers, having at least one feed channel for the liquid, having at least one feed channel for a gas stream, and having an outlet orifice for the liquid/gas mixture, the feed channel or every heat channel respectively for the liquid ends in a first, longitudinally extended intermediate chamber; the feed channel or every feed channel respectively for the gas stream ends in a second, longitudinally extended intermediate chamber; the two longitudinally extended intermediate chambers are connected via retention chambers which taper in the direction of transport, in which chambers the gas and the liquid are strongly accelerated, to a common slot-shaped nozzle gap. <IMAGE>

Description

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

The term "liquid media" is intended to cover all sprayable media, but in particular adhesives and lacquers which have to be sprayed on as a gas / medium mixture in many applications, for example for painting surfaces, but also for coating webs, such as, for example Textiles. In particular, the spraying of thermoplastic, high-polymer materials that are used as hot melt adhesives is intended.

Spray heads of the type specified are known, for example, from DE-PS 35 43 469, DE-PS 29 24 174 and US Pat. No. 4,669,661. At least one feed channel for the liquid medium, at least one feed channel for a gas stream and a common outlet opening for the mixture of liquid medium / gas are provided. The outlet openings are each designed as round nozzles, the so-called "spray cone" and to create a circular application pattern. If larger areas have to be sprayed, several such spray heads or a single spray head with several round nozzles are arranged in a row on a line or else staggered or stepped above the surface to be sprayed, so that the individual spray cones of the various round nozzles touch or overlap and so that in principle it is possible to work across the board.

With such spray cones, however, the volume flows in the center of the cone are usually different than in the edge area; in addition, the individual spray cones generally have different volume flows; Therefore, a uniform, area-wide application, such as is required, for example, for coating substrates with adhesives, in particular hot melt adhesives, is not possible using this spray principle.

For spraying hot melt adhesives in particular, no spray head has been known to date which can produce a line or strip-shaped application pattern using a single nozzle.

The invention is therefore based on the object of creating a spray head for spraying liquid media, in particular adhesives, such as hot melt adhesives, or lacquers of the type specified, in which the disadvantages mentioned above do not occur. In particular, a spray head is to be proposed which delivers a completely uniform spray pattern over the entire width of the surface to be coated, as cannot be achieved with the spray heads customary hitherto.

This is achieved according to the invention by the features specified in the characterizing part of claim 1. Appropriate embodiments are defined by the features of the subclaims.

The advantages achieved by the invention are based on the design of a spray head with a surface nozzle, which delivers a line or strip-shaped application with a very homogeneous spray density over the entire surface, so that completely uniform spray patterns can also be achieved.

For this purpose, the two materials, i.e. the liquid medium and the gas, are each fed from their supply lines to an elongated intermediate chamber and thus expanded to the desired application width. From these intermediate chambers, the still separated materials reach the common, slit-shaped nozzle gap via stowage chambers; the first contact between the two materials takes place at the end of the two stowage chambers at the entry surface of the nozzle gap, whereby according to a preferred embodiment the two streams meet at a relatively large angle and thereby mix intimately with one another. Particularly good results are obtained with an angle of incidence of approximately 90 °.

The gas stream, which strikes the stream from the liquid medium almost perpendicularly and leaves its storage chamber at high speed, conveys the liquid medium pneumatically and thereby mixes intimately with it, so that a very homogeneous mixture of liquid medium / gas leaves the slit-shaped nozzle gap and acts as a line. or strip-shaped application pattern is sprayed onto the web to be coated.

According to a preferred embodiment, the device is designed in a modular construction and consists of two separate, interconnectable main components, namely the gas supply part and the supply part for the liquid medium provided with the usual valve.

The respective elongated intermediate chamber is formed in plate-shaped mouthpieces, the edges and surfaces of which form the storage spaces or the slot-shaped nozzle gap with one another or with the opposite surfaces of the main parts.

According to a preferred embodiment, the two plate-shaped mouthpieces are displaceably mounted, so that the shape and size of the storage spaces and the slot-shaped nozzle gap can be varied and adapted with different requirements and properties of the materials to be processed.

The two main parts are heated and together by one heat Surround me insulation to ensure a uniform temperature, which is particularly important for the processing of hot melt adhesives.

By exchanging the two plate-shaped mouthpieces, for example, spreading chambers of different lengths and thus corresponding line or strip-shaped application patterns can be realized.

In principle, it is possible to design the outer surfaces of the two mouthpieces in such a way that a flat surface results in the area of the outlet of the slot-shaped nozzle gap. According to a preferred embodiment, however, the outlet of the slot-shaped nozzle gap is provided with a tear-off edge, so that in this area the corresponding outer surfaces of the two mouthpieces should meet at an angle which is less than 90 ° and, according to a preferred embodiment, between 30 and 60 °, in particular between 40 and 50 °.

Since the sprayed mixture perfectly detaches from the slot-shaped nozzle gap through this tear-off edge, material webs passed by can also be coated uniformly at a relatively short distance. This can rule out that external influences, in particular the room temperature and any air movements, have an effect on the application pattern, as is the case when spraying from relatively great heights, as was previously required to achieve large application areas when using round nozzles was.

It has proven to be expedient if a surface of the storage space for the liquid medium, according to a preferred embodiment the bottom surface facing the leaked mixture, is provided with a groove-like pattern at least shortly before the liquid medium strikes the gas stream and is marked as " Quasi slot "is formed. This results in a uniform distribution of the liquid medium over the entire width of the storage space, the liquid medium leaving the storage space in the form of individual “flow threads” and thereby being able to mix very well and homogeneously with the gas stream.

These grooves produced by milling according to a preferred embodiment should have a depth of 0.1 to 1.0 mm, in a preferred embodiment of 0.2 to 0.6 mm, in order to ensure the perfect passage of the liquid medium in connection with its even distribution to ensure over the entire length of the storage space and thus the slot-shaped nozzle gap. No firm specifications can be made for the width of the grooves or millings and in particular for the width of the blocking area between two adjacent grooves, since these parameters also depend on the type of application pattern to be achieved. By designing this area appropriately, a kind of "mask effect" can be achieved, so that unusual spray patterns can also be realized, for example spray patterns in which coated areas alternate with uncoated areas over the entire length of the slot-shaped nozzle gap.

By adjusting the mouthpiece with the elongated intermediate chamber for the gas flow, this can be regulated and thus adapted to different requirements and / or properties of the materials to be processed.

The slit-shaped nozzle gap has the same thickness over its entire length, so that the gas flow and the liquid medium entrained by it mix thoroughly in the slit-shaped nozzle gap, atomized at the tear-off edge of the nozzle gap, where there is only little adhesion, and sprayed onto the one to be coated Material web to be sprayed on.

• Fig. 1 einen vertikalen Schnitt durch einen Sprühkopf für das Ver­sprühen von Schmelzklebstoffen,
• Fig. 2 im vergrößerten Maßstab eine Figur 1 entsprechende Dar­stellung des eigentlichen Auslaßbereiches dieses Sprüh­kopfes,
• Fig. 3 eine Draufsicht auf das den Stauraum für das flüssige Me­dium bildende Mundstück,
• Fig. 4 einen Schnitt längs der Linie A-B von Figur 3,
• Fig. 5 im vergrößerten Maßstab eine Ansicht des Details X von Figur 3,
• Fig. 6 eine Draufsicht auf das den Stauraum für den Gasstrom bil­dende Mundstück,
• Fig. 7 einen Schnitt längs der Linie A-B von Figur 6, und
• Fig. 8 eine Ansicht von oben auf dieses Mundstück.

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

• 1 is a vertical section through a spray head for spraying hot melt adhesives,
• 2 on an enlarged scale a representation corresponding to FIG. 1 of the actual outlet area of this spray head,
• 3 is a plan view of the mouthpiece forming the storage space for the liquid medium,
• 4 shows a section along the line AB of FIG. 3,
• 5 is an enlarged view of the detail X of Figure 3,
• 6 is a plan view of the mouthpiece forming the storage space for the gas flow,
• Fig. 7 is a section along the line AB of Figure 6, and
• Fig. 8 is a top view of this mouthpiece.

The spray head shown in the figures, generally indicated by the reference numeral 10, is designed in a modular construction and has two main parts which are firmly connected to one another, in particular screwed together, namely a first part 12 for the supply of a hot melt adhesive and a second part 14 for the supply of the gas , especially air. The top and the side surfaces of these two main parts 12, 14 are surrounded by a schematically indicated thermal insulation 16.

The part 12 for the supply of the hot-melt adhesive is provided with the usual bores 18 for heating elements, in particular resistance heating elements (not shown) and has a bore 20 which runs in the vertical direction from top to bottom and which at its lower end is in a region 21 merges with a reduced diameter, so that a shoulder-shaped shoulder is formed.

In this bore 21, a valve needle 22 can be pushed back and forth, which is provided with a piston 24 at its upper end. This piston 24 is either acted upon alternately on both sides with compressed air or only acted upon on one side with compressed air and adjusted in the other direction by a spring, so that the piston 24 and thus the valve needle 22 are moved back and forth accordingly.

At the upper end of part 12 there is a schematically indicated adjusting mechanism 28, which is provided with manually adjustable actuating members 26 and with which the stroke of the valve needle 22 can be adjusted.

The valve needle 22 runs at its lower end into a tip 22a, the side surface of which comes into contact with the shoulder of the channel 20 and thereby closes the lower end 21 of the channel 20, so that no more hot melt adhesive can escape.

The liquefied and thus flowable hot melt adhesive is supplied to the channel 20 under pressure in the usual way, so that the hot melt adhesive can emerge down the channel 20 through the gap between the lower tip 22a and the shoulder when the valve needle 22 is raised, while lower position of the valve needle 22, the tip 22a rests on the shoulder and thus blocks the channel 20, so that the flow of the hot melt adhesive is not possible.

The part 14 for the supply of air is also heated and has a plurality of bores 30 which are connected to an air source (not shown) and open into a common outlet channel 32.

A plate-shaped element 34, hereinafter referred to as "mouthpiece", is screwed onto the underside of part 12 and has the shape shown in FIGS. 1 and 2, namely on its surface facing the underside of part 12 with a groove 36 which is rectangular in cross section is provided, which extends almost over the entire length of the first mouthpiece 34, as can be seen from Figure 3. This groove 36 is somewhat wider than the lower, narrow end of the channel 20 in the part 12. As a result, the tip 22a of the valve needle 20 penetrating the groove 36 cannot hinder an adjustment of the first mouthpiece 34 in the direction of the double arrow 38 shown in FIG .

In order to make this adjustment possible, there are 34 in the first mouthpiece the elongated holes 40 shown in Figure 3 are formed, passed through the screws (not shown) and screwed into the underside of part 12.

By loosening the screws, the first mouthpiece 34 can be moved in the direction of the double arrow 38.

The groove 36, which is aligned with the lower, narrow end of the bore 20, is adjoined by a beveled edge 42 which finally ends at the left, upper edge of the plate-shaped first mouthpiece 34 again at the level of the flat top of the first mouthpiece 34.

The gap thus formed, which tapers to the left as shown in FIG. 2, between the oblique edge 42 and the underside of the part 12 serves as storage space 43 for the hot melt adhesive supplied via the narrow bore 20 and the groove 36.

As can be seen from FIGS. 3 and 5, the beveled surface 42 adjoining the groove 36 is provided with grooves 44, which extend from the groove 36 into the region of the edge 48 and the hot melt adhesive on its way from the groove Divide 36 to edge 48 into a large number of individual "threads".

These grooves 44 can, for example, have the shape shown in FIG. 5, namely triangular in cross section; the triangular grooves 44 are separated from one another by trapezoidal webs 46, the intermediate webs 46 and thus the blocking regions being somewhat wider than the grooves 44 in the embodiment shown, so that the ratio of blocking area / flow area is greater than 50%.

By adapting the shape and / or the size of the webs 46 or the grooves 44 accordingly, the respectively desired conditions can be set and certain application patterns, in particular with coating-free strips, can also be achieved.

In principle, it is also possible to apply this groove structure to the surface to provide the underside of part 12; according to a preferred embodiment, however, the first mouthpiece 34 is formed with the grooves 44 in the manner described.

Adjoining the edge 48 of the first mouthpiece 34 is a downwardly sloping, bevelled surface 50 which forms one side of the slot-shaped nozzle gap 51 and which slopes obliquely outwards at an angle of somewhat more than 90 ° to the underside of the part 12 and thus to the top of the first mouthpiece 34.

At the lower end of the surface 50 there is a short surface 52 which runs parallel to the top of the mouthpiece 34 and merges into the underside of the first mouthpiece 34 via a beveled intermediate piece 54.

The right-hand side of the part 14 for the air supply as shown in FIGS. 1 and 2 is provided with an elongated recess 56 which is rectangular in cross section and in which there is also a plate-shaped second mouthpiece 58. This second mouthpiece 58 is thus clamped in the recess 56 between the two opposite surfaces of the parts 14 and 12 by tightening the fastening screws for the two parts 12, 14.

The second mouthpiece 58 can be moved in the direction of the double arrow 60 along the side wall of the part 12 upwards or downwards. For this purpose, an adjusting screw 62 is screwed into the underside of part 14, which is provided with a disk-shaped or tab-shaped projection 64. The outwardly projecting edge of this projection 64 engages in a groove 66 in the outside of the second mouthpiece 58. By turning the adjusting screw 58, the projection 64 is displaced in the direction of the double arrow 60, so that the second mouthpiece 48 is taken along.

At the upper edge of Figure 2, a gap 68 between the two adjacent surfaces of the parts 12, 14 is indicated. This gap 68 only arises after loosening the fastening screws between the two Parts 12, 14. Now, by turning the adjusting screw 62, the second mouthpiece 58 can, as explained, be displaced in the direction of the double arrow 60. If the fastening screws are now tightened again, the gap 68 closes and the second mouthpiece 58 is clamped in the recess 56 between the two parts 12, 14 and thereby fixed.

A corresponding adjustment mechanism can be provided for the adjustment of the first mouthpiece 34.

The second mouthpiece 58 has a passage 70 which adjoins the channel 32 and which, viewed perpendicular to the plane of the drawing according to FIGS. 1 and 2, extends over the entire depth of the part 14. As can be seen from FIGS. 1 and 2, the passage 70 extends downward at an angle of approximately 30 ° to the channel 32, so that the air flow supplied is deflected accordingly.

The deflected air flow passes from the passage 70 into a storage space 72 which is formed between the opposite side wall of the first part 12 and a bevelled edge of the second mouthpiece 58. As can be seen, this storage space 72 tapers towards the edge 48 in a manner similar to the storage space 42 for the hot melt adhesive.

At the end of the bevelled surface of the second mouthpiece 58 forming the storage space 72, there is another, bevelled surface 74, which lies opposite the surface 50 of the first mouthpiece 34 and together with this forms the slit-shaped nozzle gap 51 which, depending on the Properties of the hot melt adhesive, in particular its flow properties, and the application requirements have a thickness of 0.1 to 1.0 mm, in particular 0.2 to 0.6 mm.

At the lower end of the surface 74 there is an upwardly sloping surface 76 which finally merges into the left-hand side wall of the second mouthpiece 58. In a side view, the second mouthpiece 58 has the wedge shape shown in FIG. 2, at least in its lower part.

Due to the described design of the outlet area of the slot Shaped nozzle gap between the two surfaces 50, 74 thus creates a tear-off edge, as is necessary for the correct application of the sprayed hot melt adhesive in the direction of the arrow according to FIG. 1 onto the web of material transported in the direction of the arrow, for example a textile web 78.

When this spray head is in operation, the liquefied and thus flowable hotmelt adhesive is supplied under pressure via the bore 20 of the groove 36 in the first mouthpiece 34 and the air with overpressure via the bores 30, the channel 32 and the passage 70 in the second mouthpiece 58.

From these intermediate chambers 36, 70, which serve as spreading chambers and which extend approximately over the entire length of the slot-shaped nozzle gap 51, the hot-melt adhesive and the air each pass separately into the associated storage spaces 43, 72, the cross-sections of which taper in the direction of transport, so that results in a relevant speed increase of hot melt adhesive and air.

The two strongly accelerated media meet at the edge 48 at approximately a right angle and from there reach the slot-shaped nozzle gap 51 between the two surfaces 50, 74. As can be seen in particular from FIG. 2, the strongly accelerated air flow experiences only a relatively small amount Deflection, since its storage space 72 extends approximately in the direction of the slot-shaped nozzle gap 51; however, the accelerated hot melt adhesive is deflected by an angle of almost 90 ° and thereby intimately mixed with the air stream which takes the hot melt adhesive with it and subsequently serves as a "driving means" for the hot melt adhesive.

This mixing between air and hot melt adhesive is supported by the grooves 44, since the hot melt adhesive emerges in many individual threads at the edge 48 and is immediately entrained in the slot-shaped nozzle gap 51 by the air flow.

By the described adjustment of the two mouthpieces 34, 58 in In the direction of the double arrows 38, 60, the storage spaces 48, 72 and the slit-shaped nozzle gap 51 can be adjusted and certain operating conditions can be adapted.

Since the mouthpieces 34, 58 are only screwed on, there is a modular structure, so that they can be exchanged without problems and thus adapted to other requirements.

In a corresponding manner, the two parts 12, 14 can also be replaced individually and replaced by other parts.

Claims (15)

1. spray head for spraying liquid media, in particular adhesives such as hot melt adhesives or paints,
a) with at least one feed channel for the liquid medium,
b) with at least one feed channel for a gas stream, and
c) with an outlet opening for the mixture of liquid medium / gas,
characterized by the following features: d) the or each feed channel (21) for the liquid medium ends in a first, elongated intermediate chamber (36); e) the or each feed channel (32) for the gas flow ends in a second, elongated intermediate chamber (70); f) the two elongated intermediate chambers (36; 32, 70) are connected to a common slit-shaped nozzle gap (51) via stowage chambers (43, 72) tapering in the transport direction, in which the gas and the liquid medium are strongly accelerated. 2. Spray head according to claim 1, characterized in that the gas flow and the flow of the liquid medium after leaving their storage spaces (43, 72) meet at an angle of more than 45 °. 3. Spray head according to claim 2, characterized in that the two streams meet at an angle of approximately 90 °. 4. Spray head according to one of claims 1 to 3, characterized in that the gas flow in the transition from its storage space (72) in the slot-shaped nozzle gap (51) undergoes only a relatively small deflection, while the flow of the liquid medium in the transition from its storage space (43) to the slot-shaped nozzle gap (51) is strongly deflected, in particular at an angle of at least 60 °. 5. Spray head according to one of claims 1 to 4, characterized by a first part (12) for the supply of the liquid medium and by a second part (14) for the supply of the gas, the two parts (12, 14) attached to each other are. 6. Spray head according to one of claims 1 to 5, characterized in that the two parts (12, 14) are heated. 7. Spray head according to one of claims 1 to 6, characterized by two separate mouthpieces (34, 58) which together form the slot-shaped nozzle gap (51) and with the opposite surfaces of the parts (12, 14) the storage spaces (43, 72) . 8. Spray head according to claim 7, characterized in that the mouthpieces (34, 58) elongate, the intermediate chambers forming recesses or passages (36, 70) and beveled, the storage spaces (43, 72) have surfaces. 9. Spray head according to one of claims 7 or 8, characterized in that the two mouthpieces (34, 58) are adjustable. 10. Spray head according to one of claims 7 to 9, characterized in that the adjoining and the slot-shaped nozzle gap (51) forming surfaces of the two mouthpieces (34, 58) are designed so that there is a tear-off edge. 11. Spray head according to one of claims 1 to 10, characterized in that a surface of the storage space (43) for the liquid medium is provided with such a structure that on the trailing edge (48) on which the liquid medium on the gas stream hits, forms a multitude of individual threads. 12. Spray head according to claim 11, characterized in that the structure is formed by grooves in the corresponding surface (42) of the first mouthpiece (34) and / or the opposite surface of the first part (12). 13. Spray head according to one of claims 11 or 12, characterized in that the structure is formed by milling (44). 14. Spray head according to one of claims 11 to 13, characterized in that the structure (44, 46) at least partially blocks the passage of the liquid medium, so that coating-free zones are formed. 15. Spray head according to one of claims 1 to 14, characterized in that the slot-shaped nozzle gap (51) has a thickness of 0.1 to 1.0 mm, in particular 0.2 to 0.6 mm.

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