DE102010042882A1 - Film-forming die for forming single layer or multilayer film, has recesses that are formed in initial partial region of melt channel and tapered towards end of melt channel - Google Patents

Abstract

The die has a melt portion that is formed between the boundary walls (5,6) and provided with a melt line which is opened. A melt channel is formed in the melt portion and comprised with partial regions (11-14) in the boundary walls. The recesses (3,7) are formed in the initial partial regions of the melt channel and tapered towards the end of melt channel.

Description

The invention relates to a film blowing head for producing a film tube of single-layer or multilayer film. Such film blowing heads are known.

As a rule, they have in common that they are supplied with melt from one or more extruders. This melt often passes through a pre-distributor from which melt is distributed to a larger number of melt lines. During their further course through the die, the melt lines open into melt gaps, which can be converted into a film or a film layer by their flat surface expression of the circular-cylindrical melt strand in its cross-section, which emerges from the melt lines. If a single-layer film is produced, a single such gap is needed. In the production of a film with a number n of layers usually n such column are needed.

After the melt line has flowed into the melt gap, the melt lines pass into melt channels formed by depressions in one or both boundary walls of the melt gap. The melt channels run along the boundary walls of the melt gap to distribute melt in the melt gap. As they pass through the melt gap, the melt channels taper more and more until finally they completely merge into the melt gap.

The pamphlets EP 1055504 B1 . DE20307412 U1 such as US 5716650 B show, inter alia, the aforementioned facts. In a comparison of the basic structure of the blowing heads shown in the three publications, however, there are fundamental differences:
The US 5716650 B shows a film blowing head, which consists essentially of a stack of round plates having a round recess in their center (round perforated discs). The outer diameter and the diameter of the round recess are the same for the round plates of a blow head. The stack of round plates is - provided in the region of the round recess - with an inner mandrel and has a total circular cylindrical shape. The melt is supplied to the multilayer blower head shown with initially externally extending melt lines in the radial direction from the outside. The individual plates define the individual melt gaps, each forming a film layer. The melt lines direct the melt to the gaps. After reaching the column, the gaps change to melt channels, which spiral in the film gap in the direction of the center of the circular cylinder. As a rule, the melt lines are formed only by a groove in one of the two plates delimiting the respective gap. The US 5716650 B however, shows a film blowing head in which the channels are formed by grooves in both plates delimiting the respective gap.

On their way toward the center of the blow head, the spiraling grooves (their depth in the split walls decreases) until the grooves finish completely. At the places where the grooves end, the melt has gone completely into the gap. On its remaining way through the gap, the melt is further fixed to its "new" areal shape. Eventually, the gaps forming the film sheets terminate in the multilayer gap that exists between the inner mandrel and the plates. Due to the confluence of the different film layers, a melt stream is formed which already contains the layers of the later multi-layer film. The extrusion of this melt stream takes place through an annular gap, which is typical for film blowing heads. Film blowing heads of the type described above, which are formed from a stack of plates, are often referred to in the English language "stack die".

The EP 1055504 B1 shows such a stack, which, however, has some structural differences to the stack US 5716650 B having.

In the multi-layer gap open individual gaps, which are introduced in the radial direction of the blowing head from the inside and from the outside to the multi-layer gap. Individual discs have conical shapes. Often, the use of a melt pre-distributor, the melt distributed inside a closed component on several lines, in connection with such a film blowing head is recommended.

An alternative design of a Folienblaskopfes is in the DE 203 07 412 U1 shown. In the case of these blowing heads, the melt gaps that form the individual layers are already circular-cylindrical about the main axis of symmetry of the likewise circular-cylindrical blow head.

Along this melt gaps extending melt channels in the manner of helices, which also in the direction of the junction of the melt channel in a common melt channel at the top axial Taper the end of the blow head by the decrease in their depth in the boundary walls of the melt channels until they pass completely into the melt channel. It should be noted that also the DE 203 07 412 U1 in contrast to many other prior art documents shows melt channels formed by recesses in both boundary walls of the melt channels.

Apparently, both by the DE 203 07 412 U1 as well as through the US 5716650 B avoiding the formation of streaks or specks in the film. However, the measures proposed in these two documents are not able to completely eliminate the formation of streaks and specks, so that the need of the art persists for a remedy to these two problems.

The object of the present invention is therefore to propose a film blowing head, can be produced with the film with fewer specks and stripes.

Generally, the present invention is directed to a blow head according to the US 5716650 B and solves this problem by the inclusion of the features of the characterizing part of claim 1.

Surprisingly, it has been found that the formation of specks and the like subsides when the melt channel is only formed by recesses in one of the two boundary walls of the melt channel in a region of the at least one melt channel. This circumstance may be related to the fact that the entire melt strand is pressed onto one side of the melt gap by the measure mentioned and thus better durchgewalkt. This measure achieves an even better effect if the melt strand at the beginning of the melt channel remains in a shape of round or oval cross-section. In this case, if the round or oval cross-section is symmetrical with respect to the melt gap, it can distribute itself uniformly in the region of the two boundary walls at the beginning. It can also be seen from these statements that it is advantageous if the melt channel is formed in its initial region by recesses in its two boundary walls.

When the depth of the recesses forming the melt channel increases in at least one of the two boundary walls in at least a portion of the melt channel in the transport direction of the melt, the through-flowing of the melt in the channel is promoted. This effect also occurs when the depth in both walls increases. By this measure, however, the volume of the melt channel increases relatively strong, so that a backflow of melt from the channel must be obtained in the gap. Therefore, the latter measure (increase in depth in both walls in the direction of transport of the melt) should only be used moderately.

Often, areas will be used in which at a height of the melt channel, the depth of the recesses in a boundary wall decreases and increases in the other. Astonishingly, when the depth at a height of the melt channel varies in both walls by the same amount but with different signs, results are worse than in melt channels where the amounts are different.

It seems obvious that the course of the depth of the channel in the two boundary walls is a periodic function, with a phase shift of 90 ° in the case of angle functions ensuring that one boundary wall has a maximum depth at one boundary wall and the other at the other boundary wall Boundary wall a minimum depth is recorded. The course of the two functions (the "melt channel height") will also decay in the course of the channel. It has proven to be advantageous to deviate from this generally advantageous rule in at least one region of the at least one channel and to subject the course of the channel depth in the two boundary walls to two different functions.

For this measure, especially the middle areas of a melt channel are recommended. For the purposes of this document, the course of a melt channel can be divided into four areas. A start area, a first and a second middle area and an end area.

Further embodiments of the invention will become apparent from the description and the claims.

The individual figures show:

1 A schematic Funktionsssizizze a Folienblaskopfes 1

2 An enlarged section 1

3 A development of a melt distributor

4 A section AB through a first melt channel

5 A section AB through a second melt channel

6 A section AB through a third melt channel

7 A section AB through a fourth melt channel

8th A section AB through a fifth melt channel

9 A development of a melt distributor

10 A first recess in a boundary wall

11 A second recess in a boundary wall

12 A third recess in a boundary wall

1 shows an example of a Einschichtblaskopfes 1 that just has a melt gap 4 has, which has a circular cylindrical shape. The likewise circular cylindrical blow head 1 and the melt gap 4 are arranged symmetrically in this case to the main axis of symmetry of the blow head. The melt gap of such a blow head 1 gets from an inner spine 5 and a housing 6 limited. In order to achieve a greater abstraction on other blast head types such as Stack Blowheads, however, should at this point of inner 5 and outer boundary wall 6 to be spoken. Stack The blow heads would be in this context of upper and lower boundary walls the speech.

2 shows again a more detailed view of a melt channel, the here - as often shown in the prior art - only through a recess 3 or groove in the inner boundary wall 5 is realized.

3 shows a development of the peripheral surface of the mandrel 5 and thus the melt distributor of the blow head 1 , Of particular interest is the location of the cutting line AB and the recess to be recognized as a groove 3 ,

4 now illustrates how the groove / recess 3 of the blowhead 1 in the section AB runs. The depth T1 of the melt channel 3 coming from the inner boundary line 8th of the melt gap 4 is measured off, steadily decreases until the channel has finally passed into the gap.

5 shows a section AB through another melt channel 10 that of both recesses 3 in the inner boundary wall 5 as well as recesses 7 in the outer boundary wall 6 is formed. In the drawing it can be seen that the depths T1 and T2 are in the direction of the height of the melt channel 10 "Similar" decrease. As a function of the height h of the melt channel 10 take the two depths T1 and T2 with the same sign and equal amounts. With the height h of the melt channel 10 is a running variable that represents the length of the melt channel along the direction of the melt channel. So it is unequal, for example, to the cylindrical coordinates z, since the melt channel 10 does not run exclusively in the axial direction.

In the example shown, the diameter D of the channel thus decreases uniformly and steadily as a function of the height h.

In 6 an embodiment of a melt channel is presented, which illustrates several aspects of the invention:
In the starting area 11 of the melt channel 10 There are recesses in both boundary walls 5 and 6 , However, the course of the depths T1 and T2 in the boundary walls is very different. He obeys another function and the course is not out of phase. In the first middle area 12 this is exactly the case:
The depth T1 has at the height h of the melt channel 10 a maximum at which the depth T2 has a minimum. In general, T1 and T2 are in the first middle range 12 in that their slopes T1 'and T2' are of the same magnitude and sign. Such a course as a function of the height h of the melt channel 10 For example, if you set T1 and T2 as a function of phase-shifted trigonometric functions. So the depths of the recesses could be set as follows: T1 (h) = Acos (h) e ^{(-1 / 5h)} T2 (h) = Acos (h + Π / 2) ^{(-1 / 5h)} with A = constant

As a result, very rounded courses of the depths of the recesses result 3 and 7 , which are between relative minima and maxima 16 and 17 vary. The melt line in question tapers as a function of the height h. The phase shift by + Π / 2 causes, as mentioned, that their slopes T1 'and T2' of the same magnitude and different signs. Such a course of the depth is as mentioned, in particular in at least one central region 12 and 13 of the melt channel 10 advantageous.

For the purposes of this application, it can be said that the two functions shown above have "the same course" but are - as mentioned - out of phase.

It is particularly surprising that a deliberate deviation from the above established rule in at least one region of the melt channel brings benefits.

In the end of the in 6 shown melt channel 10 are only recesses in the inner boundary wall 6 to see.

In the end area 14 the course of the function T1 (h) is thus subject to a clearly different course than the course of the function T2 (h), which continues periodically.

A similar, slightly rounded area can be achieved by the following functions: T1 (h) = 0 T2 (h) = Acos (h + Π / 2) e ^{(-1 / 5h)}

In the middle areas 12 and 13 would T1 (h) = k with k = constant and k> 0 more advantageous.

The person skilled in the art will recognize in the course of the depth T1 (h) and T2 (h) of the recesses 3 and 7 in the 6 and 7 several relative extrema in which the first derivative of depth T1 (h) and T2 (h) after running variable h is zero. These relative extrema include the relative maxima 16 and 17 in 6 , It has been found that it is advantageous to provide less than four relative extremes per boundary wall.

Also, two or three Extrama have their advantages in certain applications.

7 shows an embodiment of the course of a melt channel 10 that the in 6 Melting channel very similar. at 7 is the course of the midline 21 of the melt channel 10 and the midline 18 of the melt gap 4 to be observed.

The center line 18 gives in at 7 selected perspective, the center of the extension of the melt gap in the r-direction again.

The center line 21 gives in at 7 selected perspective, the middle of the extension of the melt channel 10 in the r direction again. At Stack The blow heads, which exist on flat perforated discs, one would at this point, the extension of melt channels and gaps in the axial direction z of the blow head based.

In the end area 14 of in 7 imaged melt channel 10 there is no crossing of the two center lines 18 and 21 , For stack The blow heads, which consist of flat perforated disks, would be based on the extension in the axial direction of the blower head at this point.

8th shows an embodiment of a melt channel, the only in the initial area 11 through recesses 3 . 7 in both boundary walls 5 . 6 is formed.

9 shows once again a settlement of the peripheral surface of an inner mandrel 5 , at the same time the inner boundary wall of a melt gap 4 represents. However, in 9 in contrast to 3 only four recesses 3a to d in the boundary wall 5 presented in order to better understand details.

The melt, not shown, penetrates from the melt lines 22 in the area of the melt channels 10 , among other things, from the aforementioned recesses 3a to be formed. The melt is then initially largely through the melt channels 10 in the direction of the variable h - ie in the direction of the axes of the melt channels 10 - directed. However, a certain amount of melt constantly flows into the melt gap 4 , Here, the melt under considerable pressure changes its direction of movement and strives largely in the axial direction z of the film blowing head 1 to the extrusion gap. This circumstance is indicated by the arrows 23 symbolizes.

In 9 are the areas 11 to 14 on the first of the circumferential in the circumferential direction φ 3a based. In the starting area 11 the recess 3a in the circumferential direction φ until the beginning of the next recess 3b is enough, is the recess 3a in the axial direction z, the first recess. It is therefore easy to see that the recess 3a in this area is not melt, which would have come from another recess, is overflowed. The starting area 11 can therefore be called zeroth overflow area in this context.

In the first middle area 12 becomes the recess 3a already overflowed by melt coming out of the recess 3b originates and has penetrated from this into the melt gap. The first middle area 12 can therefore also be called the first overflow area.

Accordingly, the second middle region 13 second overflow area and the end area 14 third overflow area can be called. The in this publication for the beginning area 11 , the first middle area 12 , the second middle area 13 and the end area 14 proposed measures are particularly advantageous when they relate to the said different overflow areas. As a rule, the recesses of such blow heads will have an even greater number of different overflow areas. Accordingly, one can go to the length of areas 11 to 14 For the purposes of this document say that they are approximately between a quarter and a tenth of the length of the respective melt channel.

In the context of 9 As already stated elsewhere, it is particularly advantageous if at least one melt channel in its initial region of recesses 3 . 7 in its two boundary walls 5 . 6 is formed. As also mentioned, additional benefits are added if at least one of the in direction h of the channel 10 following areas through recesses 3 . 7 is formed in only one wall. Most advantageous this appears in the end 14 (last overflow area).

If the recesses 3 . 7 in the first zero overflow area 11 together the melt channel 10 then it will bring additional benefits if the recess that ends first does not end directly after passing through the zeroth overflow region, but only after that. It is advantageous if the recess 7 in the outer boundary wall first ends.

An exception to this rule form the outermost column of a blowhead with circular cylindrical melt gaps and the top column of a stack The blowhead: Here should the recesses 7 in the outermost boundary wall 6 or the upper boundary wall run longer than the recesses 3 in the other wall 5 ,

What the path length of the shorter recesses after the end of the first overflow area 11 As far as concerns are concerned, it has been found to be quite in the range of the length of an area 11 . 12 . 13 . 14 can lie. This additional length of the respective shorter recess 3 . 7 over the first overflow area 11 In addition, it can be more advantageous at 10 to 30% but at 15 to 25% of the total length of the respective melt channel 10 lie.

The following 10 to 12 deal with the design of the recesses 3 . 7 in the two different boundary walls 5 . 6 are introduced and together a melt channel 10 form. For illustrative purposes, the width of the recesses in the three figures has been exaggerated relative to the length (extending in the "h" direction).

In 10 is the recess 3 shown. She has a border 27 which lies on both sides of the recess. recesses 3 . 7 The type shown in the figures are usually with milling tools in the boundary walls 5 . 6 introduced the melt gaps. In the 10 The recess shown tapers continuously from its beginning to its end. From what is stated in the present document, it can be seen that, apart from certain periodic and aperiodic fluctuations, tapering of the recesses is desirable because the melt is successively removed from the melt channel 10 to the melt gap 4 to be delivered. The recess 3 is easily as a milling groove, in which the milling tool is moved in the milling process in the direction of extension of the groove and thereby continuously from the respective boundary wall 5 is pulled out, produced.

In 11 is a recess 7 in a boundary wall 6 shown. The recess 7 is shorter than the recess in this embodiment 3 in 10 (the reference numerals 3 and 7 such as 5 and 6 could be for the purpose of 10 to 12 also be reversed). The reason for the shortening is a significant increase in the speed with which the recess 7 rejuvenates after the line 29 that the areas 11 and 12 separates, "happened" in "h-direction".

The recess 7 out 11 can therefore be prepared by the milling tool initially the same as the beginning of the recess 7 produces, as in the recess 3 out 10 has happened. After passing the line 29 becomes the milling tool 29 but faster from the boundary wall 6 pulled out as at the recess 3 in 10 ,

If the two recesses 3 out 10 and 7 out 11 together form a boundary channel, and the axes of symmetry 24 and 25 the two recesses aligned with each other, would the respective boundary channel 10 in his starting area 11 formed by two symmetrical recesses. In the first middle area 12 who is following the line 29 follows, and in which the recess 7 more tapered than the recess 3 (for the purpose of this publication "Rejuvenation area"), the two recesses would 3 and 7 continue to lie one above the other. However, both edges would 28 the recess 7 (in "r-direction") over the recess 3 lie. It has been found that such an arrangement brings problems and that it is advantageous if at least one of the two boundary walls 28 the recess 7 not in r-direction over the recess 3 lies. This is possible, for example, if the in 12 illustrated recess 7 together with the recess 3 out 10 forms a melt channel. If these two recesses arranged to each other, that their symmetry lines 24 and 25 In the r-direction aligned with each other, then lie the two right outer boundary lines 27 and 28 one above the other. Only the circumferential φ left boundary line 28 lies after the line 29 to its 28 end - ie in the rejuvenation area - above the recess 3 , Such a kind of arrangement of the recesses 3 . 7 in which at least two of the edges 27 and 28 lie on each other (here in the beginning area 11 ) and in the region in which a recess tapers more strongly (tapering region) are superimposed, has proved in tests to be advantageous.

At the recess 7 out 12 come two symmetry lines 25 and 26 that enclose the angle α. The symmetry lines 24 . 25 and 26 Also indicate the way that the main axis of symmetry of the milling tool in the manufacture of the recesses 3 and 7 sweeps.

In the 1 to 12 were details of Folienblasköpfen 1 with circular cylindrical melt gaps 4 explained. In this type of blowing head, the application of the present invention has particular advantages. However, the equipment of stack-the blow heads with the features shown is advantageous. Many of the statements made above are directly transferable to stack die heads. Often it is only necessary to swap in the figures, the z and the r coordinates, to the statements of the film blowing heads 1 with circular cylindrical melt gaps 4 on the stack to transfer the blow heads. LIST OF REFERENCE NUMBERS 1 2 3 Recess / groove in the inner boundary wall 4 melt gap 5 Inner mandrel, inner boundary wall of the melt gap 6 Housing, outer boundary wall of the melt gap 7 Recess / groove in the outer boundary wall 8th Inner boundary line of the melt gap 9 Outer boundary line of the melt gap 10 melt channel 11 initial region 12 First middle range 13 Second middle range 14 end 15 16 Relative maximum T1 17 Relative maximum T2 18 Centerline of the melt gap 4 19 Arrows (flow direction of the melt) 20 Magnifying glass (detail of figure 2) 21 Centerline of the melt channel 10 22 melt line 23 Arrow melt transport 24 Symmetry axis of the recess 3 25 Symmetry axis of the recess 7 26 Symmetry axis of the recess 7 after change of direction 27 Edge of the recess 3 28 Edge of the recess 7 29 Line between areas 11 and 12 z Axial cylindrical coordinates r Radial cylindrical coordinates φ Cylindrical coordinates in the circumferential direction H Running variable (coordinate) in the spatial direction along the course of the melt channel / "height" T1 Depth of the recess in the inner wall in the direction of the radial cylindrical coordinates of the boundary line 8th the melt gap measured T2 Depth of the recess in the outer wall in the direction of the radial cylindrical coordinates of the boundary line 9 the melt gap measured α Angle between the symmetry lines 25 and 26 3a First recess / groove in the inner boundary wall 3b Second recess / groove in the inner boundary wall 3c Third recess / groove in the inner boundary wall 3d Fourth recess / groove in the inner boundary wall

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1055504 B1 [0004, 0006]
• DE 20307412 U1 [0004, 0008, 0009, 0010]
• US 5716650 B [0004, 0004, 0004, 0006, 0010, 0012]

Claims (11)

Foil blowing head ( 1 ) for producing a film tube made of single-layer or multilayer film, 1 ) at least one melt gap ( 4 ) to form a film layer which ( 4 ) between two boundary walls ( 5 . 6 ), wherein at least one melt line ( 22 ) in the melt gap ( 4 ), which - within the melt gap ( 4 ) in a first melt channel ( 4 ), at least in a sub-area ( 11 . 12 . 13 . 14 ) of the course of the at least one first melt channel ( 10 ) of recesses ( 3 . 7 ) in the two boundary walls ( 5 . 6 ) of the melt gap ( 4 ) is formed - and the melt in the melt gap ( 4 ) while he ( 10 ) in its course in the transport direction of the melt (h) tapers and finally in its ( 10 ) End area ( 14 ) all the way into the melt gap ( 4 ), characterized in that the at least one first melt channel ( 10 ) in one of its subareas ( 11 . 12 . 13 . 14 ) only of recesses ( 3 . 7 ) in one of its two boundary walls ( 5 . 6 ) is formed. Foil blowing head ( 1 ) according to claim 1, characterized in that the at least one first melt channel ( 10 ) in its end region ( 14 ) only of recesses ( 3 . 7 ) in one of its two boundary walls ( 5 . 6 ) is formed. Foil blowing head ( 1 ) according to one of the preceding claims, characterized in that the depth (T1, T2) of the recesses ( 3 . 7 ) in at least one of the two boundary walls ( 5 . 6 ) in at least one subarea ( 11 . 12 . 13 . 14 ) of the at least one first melt channel ( 10 ) in the transport direction of the melt this melt channel ( 10 ) increases. Foil blowing head ( 1 ) according to one of the preceding claims, characterized in that the amount of change in the depth (T1, T2) of the recesses ( 3 . 7 ) in the two boundary walls ( 5 . 6 ) at a height (h) of the at least one first melt channel ( 10 ) in at least one subarea ( 11 . 12 . 13 . 14 ) of the melt channel ( 10 ), which is preferably not the end region ( 14 ) is, in the transport direction of the melt (h) in the melt channel ( 10 ) is different. Foil blowing head ( 1 ) according to the preceding claim, characterized in that the change in the depth (T1, T2) of the recesses ( 3 . 7 ) in one of the two boundary walls ( 5 . 6 ) in at least one section ( 11 . 12 . 13 . 14 ) of the at least one first melt channel ( 10 ), preferably not the end portion ( 14 ) is, in the transport direction (h) of the melt in the melt channel ( 10 ) is subject to a different function than changing the depth (T1, T2) of the recesses ( 3 . 7 ) in the other of the two boundary walls ( 5 . 6 ). Foil blowing head ( 1 ) according to one of the preceding claims, characterized in that the depth (T1, T2) of the recesses ( 3 . 7 ) in at least one of the two boundary walls ( 5 . 6 ) less than four relative extremes ( 16 . 17 ) having. Foil blowing head ( 1 ) according to one of the preceding claims, characterized in that - the center line ( 21 ) of the at least one first melt channel ( 10 ), which is the center of the extent of the at least one melt channel in the direction of its extension transversely to the transport direction ( 23 ) of the melt in the at least one melt gap ( 4 ) and transversely to the transport direction of the melt in the at least one melt channel ( 10 ), - in at least one subarea ( 11 . 12 . 13 . 14 ) of the course of the melt channel between a maximum ( 16 . 17 ) the depth (T1, T2) of the recesses in a first boundary wall ( 5 . 6 ) and between a maximum ( 16 . 17 ) the depth of the recesses in the remaining second boundary wall ( 5 . 6 ) the center line ( 18 ) of the at least one melt gap ( 4 ), - Which ( 18 ) the middle of the extension of the melt gap ( 4 ) in the direction of its extension transversely to the transport direction (h) of the melt in the at least one melt channel ( 10 ) and transversely to the transport direction ( 23 ) of the melt in the melt gap ( 4 ) indicates, - does not cross. Foil blowing head ( 1 ) according to one of the preceding claims, characterized in that The at least one first melt channel ( 10 ) a zeroth overflow area ( 11 ), which is not overflowed by melt and an overflow area ( 12 . 13 . 14 ), which is overflowed by the melt of at least one second melt gap, has, and wherein the at least one first melt channel ( 10 ) in the entire zeroth overflow area ( 11 ) of recesses ( 3 . 7 ) in both boundary walls ( 5 . 6 ) of the melt gap ( 4 ) is formed. Foil blowing head ( 1 ) according to the preceding claim, characterized in that the at least one first melt channel ( 10 ) also in the starting area ( 12 ) of the overflow area, which directly adjoins the zeroth overflow area ( 11 ), of recesses ( 3 . 7 ) in both boundary walls ( 5 . 6 ) of the melt gap ( 4 ) is formed. Foil blowing head ( 1 ) according to the preceding claim, characterized in that the at least one first melt channel ( 10 ) also in the starting area ( 12 ) of the overflow area ( 12 . 13 . 14 ), of the ( 12 ) directly to the zeroth overflow area ( 11 ), of recesses ( 3 . 7 ) in both boundary walls ( 5 . 6 ) of the melt gap ( 4 ), and that this initial region ( 12 ) has a length which is at 10 to 30%, but preferably at 15 to 25% of the total length of the at least one first melt channel ( 10 ) lies. Foil blowing head ( 1 ) according to one of the preceding claims, characterized in that - the at least one first melt channel ( 10 ) at least in one of its subareas ( 11 . 12 . 13 . 14 ) of recesses ( 3 . 7 ) in both boundary walls ( 5 . 6 ) of the melt gap ( 4 ), that this subarea ( 11 . 12 . 13 . 14 ) then into a subarea ( 11 . 12 . 13 . 14 ), in which one of the two recesses ( 3 . 7 ) are more rejuvenated than the other ( 3 . 7 ) - and that in this rejuvenation area a boundary wall ( 26 . 27 ) of a recess ( 3 . 7 ) and a boundary wall ( 26 . 27 ) of the other recess ( 3 . 7 ) are aligned with each other.

Images