Nozzle box and a stretching system with an associated nozzle box

Description

[0001] The invention relates to a nozzle box according to the preamble of claim 1, as well as a stretching system with an associated nozzle box.

[0002] Such nozzle boxes are used, for example, for heating or cooling web-like materials, particularly in the form of plastic films during plastic film production. Such a nozzle box serving as a ventilation nozzle is usually arranged transversely, i.e., generally perpendicular to the pull-off direction of the material web and thus transverse to the web travel direction, above and / or below the material web.

[0003] For example, two or more such nozzle boxes can be combined above and below a material web to form a ventilation field, namely, a so-called ventilation module. These ventilation modules, including the associated nozzle boxes, can then have a length extending transversely across the material web of up to 1.5 m, 3 m, 5 m, 7.5 m, or even up to 10 m or more.

[0004] Depending on the application, these ventilation modules can be used, for example in a preheating zone of a stretching line, to heat the air and thus the plastic film. For this purpose, the air is usually warmed and heated using a heater / heating register. If the ventilation module is used in a cooling zone, the film can also be cooled using cooled air. In this case, the ambient air is usually drawn in and blown onto the film. It is also possible for the air to be cooled beforehand, or for a mixture of ambient air and warm air to be used. In recirculation mode, cooler air (compared to the temperature of the film) is often blown onto the film.

[0005] The ventilation modules can be closed (recirculation systems) or open (ambient air is used). When heating material webs or, in particular, plastic films, a closed ventilation system is often used, which blows air into the interior of the nozzle boxes via laterally arranged fans. The air is then blown out via outlet openings or nozzle openings in the nozzle boxes towards the material web / plastic film. The blown-in air can flow back between these boxes above or below the nozzle boxes. For this purpose, so-called recirculation boxes can be provided above or below the nozzle boxes, or simply an open space can be provided to suck back the blown-out air, reheat it in the closed system, and then feed it back to the nozzle boxes via the fans. Heat exchangers, for example, can be used for heating.In this recirculation mode, the air can be circulated several times.

[0006] In a preferred variant of the invention, the aeration modules with the nozzle boxes mentioned are used in wide stretching machines or wide stretching ovens, in particular for sequential film stretching systems or also in simultaneous film stretching systems.

[0007] A nozzle box suitable for the purposes described is known, for example, from EP 0 907 476 B1. The nozzle box known from this comprises a plurality of interconnected air supply chambers running in the longitudinal direction of the nozzle box. The nozzle box itself has a ventilation or nozzle wall or side, in which a plurality of ventilation openings, i.e. outlet or discharge openings for blowing out the air, are generally formed. For this purpose, a plurality of hole-shaped ventilation openings are frequently formed in several parallel, adjacent rows. The nozzle boxes are typically mounted above and below the material web in a stretching system such that the ventilation or nozzle wall is oriented towards the material web.The design of the outlet or discharge openings themselves can be different, so that both hole-shaped and, for example, nozzle boxes with slot-shaped outlet openings can be considered.

[0008] USRE23384E, KR20110102194A and CN103206845A are other documents that disclose nozzle boxes.

[0009] An air nozzle device is also known from CN 106003679 B. A plurality of outlet openings are formed on the nozzle outlet side of a nozzle wall, which can also be arranged in specific patterns. To achieve specific effects, cylindrical elevations are provided on the inside of the nozzles (i.e., on the inside opposite the outlet side of the nozzles), thereby increasing the nozzle length.

[0010] For the sake of completeness, it should also be mentioned that, especially in the case of long nozzle boxes, these consist or can consist of at least two or more parts for production reasons, which are assembled in the longitudinal direction when used in a stretching system.

[0011] Particularly during the production and stretching of plastic films intended for use as battery separator films (i.e., particularly in a so-called wet-to-wet process), a number of additives, particularly oil, are added to the material of the plastic film to be stretched. This oil, in turn, escapes from the material of the moving material web and is separated when the film passes through an oven during the stretching process. This leads to the separated oil being deposited in the area of ​​the nozzle box's ventilation wall, especially in the nozzle boxes positioned below the advancing plastic film. From there, the separated oil can then even enter the interior of the nozzle channel via the outlet openings.

[0012] However, oil penetration is not limited to the outlet openings. Oil can enter the interior of the nozzle box through any conceivable opening, recess, or slot, including flanges, sheet metal joints, etc.

[0013] This then leads to the oil that ultimately enters the interior of the nozzle box being partially reabsorbed by the circulating air during operation and blown out. As a result, this oil reaches the surface of the plastic film being stretched, resulting in an undesirable impairment of the quality of the plastic film being produced, i.e., the film being stretched. Therefore, the object of the present invention is to create an improved nozzle box, particularly for a ventilation module, and for a stretching system with such nozzle boxes.

[0014] The problem is solved with respect to the aeration module by a nozzle box having the features of claim 1 and with respect to a stretching system by the features of claim 12. Advantageous embodiments of the invention are specified in the subclaims.

[0015] The solution according to the invention is characterized primarily by the fact that simple measures can be used to prevent oil from entering the area of ​​the nozzle openings and, through them, into the interior of the nozzle box. As a result, the gaseous treatment medium (usually in the form of air) escaping through the nozzle openings also prevents the oil deposited inside the nozzle box or oil droplets located there from swirling up and carrying them toward the film, thus preventing unwanted deposition of this oil contamination on the plastic film. When "film" is mentioned here or later, this refers to any possible material web, regardless of whether it is referred to as a plastic film or simply as film or foil, etc.

[0016] According to the invention, this is ensured by a preferably specifically designed raised section that is provided or formed around the ventilation openings. Alternatively, or preferably additionally, the ventilation wall has a specific design with opposite side flanges in the transverse direction of the nozzle box, which overlap the side walls of the nozzle box outside the interior of the nozzle box.

[0017] This raised section is introduced into the nozzle box's ventilation wall, which consists of a sheet metal wall, through a simple stamping process and is thus formed as an indentation in this sheet metal wall. In other words, the corresponding ventilation openings with the aforementioned raised sections can be created in the nozzle boxes in a single, simultaneous punching and / or stamping process.

[0018] The shape of the raised sections can be designed in different ways, with an outer boundary of the ventilation raised section that tapers at least slightly conically from the plane or the outer side of the ventilation wall in the direction of the raised section being preferred. The raised section is preferably designed in a truncated cone shape, particularly in the case of circular ventilation openings, i.e., with a flattened end face for the raised sections. This end face section surrounding the ventilation openings has a width that can preferably vary between 0.5 mm and 5 mm, for example in the case of circular or oval ventilation openings.

[0019] The opening angle of the cone or tapered section, i.e., the angle of the raised sections relative to the more or less steeply inclined outer boundary surrounding the ventilation openings, must deviate only by a very small angle from a straight line passing vertically through the ventilation wall, so that a cylinder is no longer formed. Angles of less than or equal to 89.75° are already favorable and offer advantages for a stamping process. However, the angle itself can also reach and assume smaller values, for example, 45° and less. Any values ​​between these angles are also suitable.

[0020] Furthermore, a preferred embodiment provides that the nozzle box ventilation wall provided with the ventilation openings is continuous in the transverse direction of the nozzle box, i.e., it is not composed of multiple ventilation wall sections running parallel to one another in the longitudinal direction of the nozzle box and laterally connected to one another. This prevents oil from penetrating the interior of the nozzle box through slot-like gaps formed at the lateral flanges of such a multi-part ventilation wall and from there being transported further out through the ventilation openings toward the plastic film by the supplied air.

[0021] For this purpose, the ventilation wall, which is continuous in the transverse direction of the nozzle box, is preferably provided on the outside with an angular flange which protrudes from the ventilation wall and which overlaps the adjacent side wall of the nozzle box on the outside, so that here too no oil can get into the interior of the nozzle box.

[0022] If the nozzle box, due to its great length, consists of at least two or more parts which are assembled in the longitudinal direction, specific raised ventilation wall edge sections are additionally provided on the ventilation wall (in addition to preferably overlapping wall sections), so that here too no slots are formed running from the top or outside into the interior of the nozzle box which end at the level of the top or surface of the ventilation openings, through which oil could penetrate into the interior of the nozzle box.

[0023] The above-mentioned elevation sections and especially their height can be dimensioned very small within the scope of the invention.

[0024] Finally, the aforementioned raised portion can also be designed such that not just one ventilation opening, but for example two ventilation openings (or even more) are formed in the raised plateau. In other words, a separate, independent elevation does not have to be formed for each ventilation opening. Further advantages, details, and features of the invention will become apparent from the exemplary embodiments illustrated below with reference to the drawings.

[0025] In detail: Figure 1: a schematic spatial representation of a nozzle box according to the invention; Figure 2: a schematic cross-sectional representation in the transverse direction and perpendicular to the longitudinal direction of the nozzle box according to the invention. Figure 1shown nozzle box; Figure 3: an enlarged detailed view of a ventilation opening in the region of a protrusion in cross section, which is formed on a ventilation wall of the nozzle box shown in Figures 1 and 2; Figure 4: a partial spatial view of two adjacent protrusions with ventilation openings formed therein; Figure 5: a Figures 3 and 4Slightly modified embodiment; Figures 6a to 6c: three partial vertical cross-sectional views in the longitudinal direction of two nozzle channel sections which can be assembled together at the front in these areas, namely once before assembly, during the frontal pushing together and after the completed frontal assembly of two nozzle boxes; Figures 7a to 7c: three different examples in plan view to explain how ventilation openings can be designed or arranged differently.can be aligned; Figure 8: a schematic view of a ventilation module with four nozzle boxes according to the invention, which are arranged in parallel alignment and with a lateral offset in the pull-off direction of a material web; and Figure 9: a schematic end view of several nozzle boxes arranged above and below a plastic film web in the pull-off direction of this material web, wherein drainage and / or collecting containers for collecting the oil are arranged between the nozzle boxes arranged below the material web.

[0026] Reference is made below to a first embodiment of a nozzle box according to the invention.

[0027] This nozzle box 1 has a longitudinal direction L, a transverse direction Q and a height H. It has a rectangular cross-section, although this cross-sectional shape is not mandatory.

[0028] The nozzle box 1 shown in the exemplary embodiment thus has a base 3a and two opposing side walls 3b, which, in the exemplary embodiment shown, run parallel to each other with a lateral offset and are aligned perpendicular to the base 3a. A so-called ventilation or nozzle wall 5 is provided above the base 3a at a distance H from the base 3a.

[0029] The aforementioned side walls 3b and the base 3a, as well as the ventilation or nozzle wall 5, thus surround an interior space 2, which is also referred to as a supply chamber 4 for supplying air, which can then exit through the ventilation openings discussed below. In the illustrated embodiment, the nozzle box 1 thus has, as mentioned, a rectangular cross-sectional shape, although other cross-sectional shapes are also possible. For example, the side walls can also be curved and merge continuously into a base that, for example, also has a curved cross-section, without the side walls being separated from the base by clear edges. The specific shape of the cross-section of the nozzle box is therefore not important within the scope of the invention.

[0030] A plurality of ventilation openings 7 are formed in the ventilation or nozzle wall 5 running in the longitudinal direction L, which openings are sometimes also referred to below as nozzle openings or ventilation openings or generally as openings 7, regardless of their specific opening shape (i.e., for example, as a round, slit-shaped, square opening, etc.). In the exemplary embodiment shown, these ventilation openings 7 are not only offset from one another in the longitudinal direction L in the ventilation or nozzle wall 5, but also in several rows R offset from one another in the transverse direction Q. It should be noted at this point that the shape of these ventilation openings, as well as the arrangement in the longitudinal direction L and in the transverse direction Q, can deviate as desired from the exemplary embodiment shown, i.e., these ventilation openings 7 do not necessarily have to be arranged in fixed, predetermined rows R.

[0031] From the example shown according to Figure 1 It can already be seen that the nozzle box 1 consists or can consist of two nozzle box sections 1a and 1b divided in the longitudinal direction L, which are at least indirectly fastened to one another and / or joined together at their mutually facing end faces at an interface 9 thus formed in order to increase the overall length, and in particular can be assembled on site at this interface 9.

[0032] Based on Figure 2 is a schematic cross-section in the transverse direction Q and perpendicular to the longitudinal direction L through the nozzle box 1.

[0033] It can be seen that the ventilation openings 7 are provided or formed in the ventilation or nozzle wall 5 in the form of elevations 13 or in the region of such elevations 13. Since the ventilation wall 5 consists of a metal sheet and the nozzle box 1 preferably consists of a sheet metal, in particular a metal sheet, the ventilation openings / nozzle openings 7 thus formed and the associated elevations 13 can preferably be produced in a common, simultaneous embossing and punching process.

[0034] In the illustrated embodiment according to Figure 2 and the enlarged sectional view through the elevation 13 of the ventilation opening 7 according to Figure 3 and the partial spatial representation of two elevations 13 according to Figure 4 , the circumferential outer boundary wall 15 is conical or at least slightly conical.

[0035] This outer boundary wall 15 thus rises from the ventilation wall 5 or the upper side or surface 5a of the ventilation wall 5 formed thereby in a conical, converging manner, i.e., in the illustrated embodiment, a truncated cone. The actual ventilation opening 7 is delimited by a circumferential opening edge 17, which thus forms a blunt and thus crater-free end surface for the ventilation openings 7. A so-called "crater-free" end surface is important when a foil or film is considered as the material web. This is because even if the film comes into contact with the circumferential opening edge 17 in the area of ​​the ventilation openings 7, it must be ensured that the film is not injured or damaged by crater-shaped fraying of the metal, or even tears. In the illustrated embodiment, this opening edge 17 is designed or aligned at least approximately parallel to the upper side or surface 5a of the nozzle wall 5.However, this opening edge 17 does not necessarily have to be aligned parallel to the top side or surface 5a of the nozzle wall 5. This opening edge 17 can also be curved in a perpendicular section to the top side 5a, for example, convex with an angular deviation from the top side or surface 5a that preferably becomes increasingly smaller in the direction of the ventilation openings 7.

[0036] Likewise, the opening edge 17 could preferably be aligned at at least a slight angle relative to the top side or surface 5a of the nozzle wall 5. Thus, this opening edge 17 can rise at a slight angle relative to the plane of the surface 5a from its outer edge toward the actual ventilation opening 7, for example at an angle of less than 45°, less than 30°, 25°, 20°, 15°, 10°, or less than 5°.

[0037] The height H of the elevation 13 can be very small, for example, between 0.5 mm and 10 mm. The width of the peripheral opening edge 17 can also be of the same order of magnitude.

[0038] The slightly conically diverging design of the elevations 13 is preferred because these elevations 13 are created by means of a stamping process. However, the elevations 13 are preferably produced together with the ventilation openings 7 in one processing step, for example, by a stamping and punching process.

[0039] Based on Figure 5 is different from Figure 3shown that the circumferential outer boundary wall 15 could in principle also be cylindrical, whereby in this embodiment, at least a slightly conical design is preferred, which in particular runs slightly conically diverging from the upper side 5a of the nozzle wall 5. The angle of inclination α (between the conically inclined boundary wall 15 and the plane of the associated ventilation wall 5 - Figure 3 ) can therefore be less than 90° to avoid a cylindrical configuration, for example 89.75° or less, in particular less than 89.5°, 89.25°, 89°, 88°, 87°, 86°, 85°, 84°, 83°, 82°, 81°, or 80° are advantageous. In other words, this angle can preferably also be less than 60°, 50°, 45°, or 40°, although the conical shape then becomes increasingly larger towards the surface of the ventilation wall 5.

[0040] Based on Figures 6a to 6cIn a partial longitudinal section, two adjacent ventilation walls 5 of, for example, two nozzle box sections 1a and 1b to be assembled on site are shown before their assembly, during assembly and after assembly.

[0041] It can be seen from this that the ventilation wall 5 has a ventilation wall edge section 5b projecting at least towards the end face 22, which is flanged with a next nozzle box opposite to the installation direction, i.e. preferably folded over by 180°, for example, and thus rests on the upper side 5a of the ventilation wall 5 in the form of a more or less narrow edge strip. This folded edge strip thus forms a further elevation or a further elevation section 113, wherein this elevation 113 or this elevation section 113 forms a raised section running from the left to the right side edge 20 of the nozzle box, so that no oil can penetrate into the interior of the nozzle box via a slot or mounting slot existing between two nozzle boxes assembled together at the end.This protective measure is further enhanced by the fact that one of two ventilation walls 5 to be assembled together at the end is provided in its front-side assembly area inside the nozzle box 1 with at least one material tongue 19a or a flange 19a extending over part of the longitudinal extent of the nozzle box 1, 1b. This material tongue 19a or this flange 19a projects towards the adjacent next nozzle box 1a and engages in the adjacent end face 22 of the next nozzle box 1 in a recess 19c formed there. This makes it possible to assemble two successive nozzle box sections 1a and 1b with overlapping wall sections 5 in the longitudinal direction. In this case, in . Figure 6a The two front sides of the nozzle boxes are shown in detail before their assembly, in Figure 6b during axial merging, and in Figure 6cafter the final joining, when the material tongue projecting beyond the end face 22 of one nozzle box 1b or the projecting flange 19a engages and dips into the end face 22 of the adjacent next nozzle box 1b and thereby forms the parting line 23 ( Figure 6c ) between the respective folded ventilation wall edge sections 5b above this material tongue 19a. This covers and seals the slot 23 still present at this point leading to the interior of the nozzle box.

[0042] This prevents the formation of even the smallest slits in the assembly area, through which oil initially separating on the upper side 5a of the nozzle wall 5 could penetrate into the interior 2, i.e., into the feed chamber 4. This also ensures that no oil droplets can be entrained by the air supplied to the front of the nozzle box 1 from the interior 2 and then conveyed further through the ventilation openings 7 toward the plastic film.

[0043] The overlapping arrangement of the ventilation or nozzle walls 5 in their frontal mounting area ensures that oil precipitating on the upper side 5a of the nozzle wall 5 only runs outwards - i.e. towards the opposite long sides of the nozzle box 1 - and cannot penetrate into these nozzle boxes.

[0044] In critical cases, an additional sealant could also be used, which is introduced during assembly. This sealant would then be provided in the area between the upper side of the material tongue 19a and the underside of the wall section 5e located above it. The aforementioned wall section 5c would therefore be the area that lies exactly above the corresponding section of the material tongue 19a in the finally assembled state, in other words, that wall section 5 that lies below the preferably flanged edge section 5b facing the interior 2 of the nozzle box 1. During disassembly, this seal would then have to be removed (e.g., scraped away), and a new sealant would have to be inserted during reassembly. The sealant could, for example, be a high-temperature silicone or a similar or comparable material that maintains its tightness even at high temperatures >150°C.

[0045] As a rule, however, such sealing material is not necessary at all.

[0046] Additionally, it should be noted that, for example, a reinforcement and / or stiffening 28 may, but need not, be provided on the inner side 2 of the nozzle box 1 below the ventilation or nozzle wall 5, as shown, for example, in Figures 6a to 6c. This reinforcement and / or stiffening 28 may, for example, be wall-shaped or rib-shaped or web-shaped, whereby all possible configurations are also possible here.

[0047] This goal is also served by the Figure 2edge webs 21 shown in cross-section and formed on the lateral edge regions 20 of the nozzle wall 5, which are each developed opposite the ventilation / nozzle wall 5 in such a way that they overlap the side walls 3a on the outside, i.e. do not lie in the interior 2 of the nozzle box. Above all, this ventilation / nozzle wall 5 with the ventilation openings / nozzle openings 7 is continuous in the transverse direction Q, i.e., for example, not split in two, so that here too, no slots or gaps can arise between the thus formed, separate assembly parts through which, for example, the aforementioned oil escaping from the plastic film during the stretching process can reach the interior of the nozzle box 1.

[0048] Based on Figure 7aIt is shown schematically in plan view that the ventilation openings 7 can also have completely different designs or shapes, for example they can be designed in the shape of an elongated hole, wherein these ventilation openings 7 can also be provided in several rows R next to one another.

[0049] Based on Figure 7b a similar design is shown with ventilation openings 7 in the form of elongated holes, which, however, can be provided in an inclined position, i.e. at an acute angle to the longitudinal direction L of a nozzle box 1, for example with 45° ± less than 10° or less than 25°.

[0050] Based on the representation according to Figure 7c It is shown by way of example that such elongated holes can also be formed in the transverse direction Q, i.e. perpendicular to the longitudinal direction L in the ventilation wall of a nozzle box.

[0051] What all embodiments have in common is that the elevations 13 (with at least one or more ventilation openings 7 formed thereon) are provided on the upper side 5a of the nozzle wall 5 with the formation of distances from one another, such that oil precipitating adjacent to the elevations 13 on the upper side or surface 5a of the ventilation or nozzle wall 5 can flow to the left or right edge of the nozzle box (i.e. in the transverse direction Q of the nozzle box) and from there downwards - at least with regard to the nozzle boxes arranged below the plastic film, in which the nozzle opening is aligned upwards towards the underside of the plastic film.In other words, there are many material bridges 35 that extend on the top side 5a from the left to the right side edge of the nozzle walls 5, so that oil precipitating on the top side or surface 5a of the ventilation or nozzle wall 5 can always run off past the elevations 13 to the side edge of the nozzle box.

[0052] Finally, reference is made to the representation according to Figure 8 in which nozzle boxes arranged transversely to the withdrawal direction 25 of a plastic film F can be seen, ie their frontal view, which are arranged spaced apart from one another in the withdrawal direction 25 below the plastic film F. Usually, corresponding nozzle boxes are also arranged at the same distance in the withdrawal direction and at the same vertical distance above the control film / material strip, with their ventilation openings aligned to the top of the plastic film, as shown in Figure 9 is shown.

[0053] Based on Figure 9 It is now indicated that the nozzle boxes 1 can have drainage devices 29 on the sides, usually in the form of oil troughs. These are preferably arranged at a specific angle so that the oil can drain off optimally. Thus, the oil could be collected in these troughs and drained into the collecting tank 31 via drains. Furthermore, intermediate plates could be installed between the nozzle boxes, designed like roofs, which also drain the oil into troughs. This would have the advantage of allowing the oil to be collected and, at the same time, preventing the furnace floor from becoming contaminated with oil.

[0054] This would be particularly conceivable or even necessary for a simultaneous stretching process (LISIM), because in this process both the width and the length stretching take place in the furnace. In a sequential stretching process, the length stretching takes place in a machine upstream of the furnace (MDO). A large portion of the oil is already squeezed out in the MDO and does not reach the furnace. Therefore, it is to be expected that in a simultaneous stretching process or in a transverse stretching stage following a longitudinal process, the problem of oil contamination in the furnace is even greater, and a significant advantage can be achieved through the invention.

Claims

1. Nozzle box having the following features: - side walls (3b) spaced apart from each other, a base (3a) and a ventilation wall (5) spaced apart from it, thereby forming an interior space (2), - a plurality of ventilation openings (7) arranged offset to each other is provided in the ventilation wall (5), - the nozzle box (1) is provided on its ventilation wall (5) with a plurality of protrusions (13) that are raised by at least a height (H) in relation to the sections of ventilation wall (5) or the top side or surface (5a) of the ventilation wall (5), said sections being situated adjacent to the protrusions (13), wherein the protrusions (13) are formed by embossing into the ventilation wall (5) made of a metal sheet, - the ventilation openings (7) are arranged and configured in the region of the protrusions (13) in relation to the top side or surface (5a) of the ventilation wall (5) positioned offset to each other in such a way that they are further away in relation to the interior space (2) than the top side or surface (5a) of the ventilation openings (5) adjacent to the protrusions (13), and / or the ventilation wall (5) comprises in the transverse direction (Q) of the nozzle box (1) opposing side flanges (21) that overlap the side walls (3b) of the nozzle box (1) outside the interior space (2) of the nozzle box (1).

2. Nozzle box according to claim 1, characterized in that the protrusions (13) comprise a boundary wall 15 extending around each one or around at least two or more ventilation openings (7), said boundary wall (15) extending at an acute angle of inclination α in the cross-sectional view at least in part and / or aligned at least in part perpendicular to the ventilation wall (5) away from the interior space (2).

3. Nozzle box according to claim 2, characterized in that the angle of inclination α is less than 90°, in particular less than 89.75° or less than 89.5°, 89.25°, 89°, 88°, 87°, 86°, 85°, 84°, 83°, 82°, 81°, 80°, 70°, 60°, 50°, 45° or 40°, and primarily is greater than 50°, in particular greater than 60°, 70°, 80°, 81°, 82°, 83°, 84°, 85°, 86°, 87°, 88°, 89°, 89.25° or is greater than 89.5°.

4. Nozzle box according to claim 1, 2, or 3, characterized in that the protrusions (13) are configured converging conically at least in a partial height in a direction extending away from the interior space (2).

5. Nozzle box according to claim 1, 2, 3 or 4, characterized in that the end section of the protrusion (13) situated away from the top side or surface (5a) of the ventilation wall (5) is configured to be crater-free and / or blunt, primarily in the form of an opening edge (17) surrounding the corresponding ventilation opening (7), said opening edge (17) being aligned in particular parallel to the top side or surface (5a) of the ventilation wall (5) or deviates from it less than 45°, in particular less than 30°, 20° or less than 10° or 5°.

6. Nozzle box according to any one of the claims 1 to 5, characterized in that the protrusion (13) comprises a height in relation to the top side or surface (5a) of the ventilation wall (5) that is greater than 0.5 mm or is greater than 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.0 mm or 4.5 mm, and / or the protrusion (13) comprises a height in relation to the top side or surface (5a) of the ventilation wall (5) that is less than 5.0 mm or less than 4.5 mm, 4.0 mm, 3.5 mm, 3.0 mm, 3.5 mm, 2.0 mm, 1.5 mm or 1 mm.

7. Nozzle box according to any one of the claims 1 to 6, characterized in that the ventilation openings (7) or at least a part of the ventilation openings (7) in top view are configured circular or oblong or n-polygonal in shape and that the protrusions (13) comprising ventilation openings (7) positioned preferably centrally therein comprise a shape in top view that corresponds to the shape of the ventilation openings (7) or is similar to this.

8. Nozzle box according to any one of the claims 1 to 7, characterized in that the ventilation openings are arranged or configured spaced apart in the longitudinal direction L of the nozzle box in one or in several rows provided in the transverse direction (Q) of the nozzle box (1) in such a way that the two lateral edges (20) of the ventilation wall (5) are connected to each other via bridges of material (35).

9. Nozzle box according to any one of the claims 1 to 8, characterized in that at least two ventilation openings (7) are arranged in a shared protrusion (13) that are surrounded by a shared encircling boundary wall (15).

10. Nozzle box according to any one of the claims 1 to 9, characterized in that the ventilation wall (5) comprises an ventilation wall edge section (5b) protruding on the end face in the region of at least one of its end faces (22), said ventilation wall edge section (5b) protruding on the end face being bent from the plane of the ventilation wall (5) opposite the interior space (2) and preferably resting bent over or flanged on the top side (5a) of the ventilation wall (5), thereby forming a mainly strip-shaped protrusion (113) protruding in relation to the top side or surface (5a) of the ventilation wall (5) and / or situated higher.

11. Nozzle box according to any one of the claims 1 to 10, characterized in that the nozzle box (1) in its longitudinal direction (L) comprises at least two nozzle box sections (1; 1a, 1b), wherein at least one nozzle box section (1a or 1b) is provided on the inner side the ventilation wall (5) with a material tongue extending in the assembly direction or a flange (24) that protrudes on its end face from the corresponding end face (22) of the nozzle box section (1a or 1b) and is received into a corresponding recess (19c) in the adjoining next nozzle box (1; 1b or 1a) and in doing so covers a gap (23) existing optionally between the two flanged ventilation wall edge sections (5b) adjoining each other in the interior (2) of the nozzle box (1) and seals said gap (23) in relation to the interior space (2) of the nozzle box (5).

12. Stretching unit comprising a nozzle box according to at least one of the claims 1 to 11.

13. Stretching unit according to claim 12, characterized in that the several nozzle boxes (1) arranged offset to each other in the drawing direction (A) of a plastics film (F) underneath the plastics film (F), and that a drainage device (29) and / or a receiving device (29), in particular in the form a collection container, for the oil flowing away from the top side or surface 5a of the ventilation wall (5), is provided between at least two nozzle boxes located offset to each other in the drawing direction (A).