DE3610488A1 - Process and device for producing blown films - Google Patents

Abstract

A process and a device for producing blown films have a die (2) for the extrusion of a thermoplastic molten plastic material through an annular slit (3) and for the formation of a cylindrical bubble (V), an annular air duct (8) for cooling this bubble (V), guide plates arranged opposite said die (2) and serving to lay the bubble flat and pinch rollers (15) for grasping the bubble and transforming it into a folded film. Between the die (2) and the pinch rollers (15), there is arranged a bubble twisting device (22) which encircles the bubble and exerts a torque thereon about a vertical axis. <IMAGE>

Description

Method and device for the production of

Blown film.

BACKGROUND OF THE INVENTION Technical Field of the Invention The invention relates to a method and apparatus for smoothing irregularities in the thickness of cylindrical blown films.

Background of the Invention In the blow molding of a film of thermoplastic material such as polyethylene or polypropylene, it is common practice to extrude a plastic material previously melted in an extruder through an annular slot die while introducing compressed air around the extruded material To draw out material into a cylindrical sheet called a "bubble".

The outer surface of this bubble is cooled by coolant while the bladder is guided along a predetermined distance by a conveyor device will; then it is pressed by nip rollers and folded flat and finally wound on a take-up drum.

As a result of problems related to the manufacturing process it is difficult to achieve a uniform thickness of the film caused by the above Blowing process described is produced.

For example, as shown in an exaggerated manner in Fig. 17, the cross-section of a bladder (a) usually thick-walled areas (b), thin-walled Areas (c) or bumps (d) that can be traced back to various causes, such as e.g. dimensioning errors of the ring slot width of the nozzle, irregularities in the viscosity of the molten plastic material, etc.

When the bladder (a) is folded flat according to (e) onto a winding drum (f) is wound up as shown in FIGS. 18 and 19, the bumps (d) in the respective film layers one above the other, so that the thickness (g) of the overlapping bumps will be larger compared to other areas the rolled up film, this non-uniformity in thickness corresponding to the The number of rolled up film layers increases and permanent deformations occur individual areas of the film as well as wrinkled or indented ones that remain in the end result Areas effected.

Therefore, if the film (d) is unwound around bags or the like.

To produce containers, it does not lie flat because of its surface Has ripples or irregularities that lead to difficulties when the surface is to be printed or the bags are used as packaging containers should be.

In particular, this results from the uneven film thickness Difficulty in increasing the speed of production.

Furthermore, it is difficult in an aluminum vapor deposition process that Coating foil evenly, which usually gives an inferior quality appearance is achieved, which has a detrimental effect on the value of the end product.

To address the various problems or difficulties outlined above To prevent irregularities, the general trend is to use one method to scatter in the film thickness.

In this context, a method has become known in which the nozzle rotates to reflect the position of the film relative to the take-up drum. to change the winding process. In particular, according to FIG. 20, a nozzle (q) mounted on a rotatable head (s) of an extruder (w) and is in sliding contact rotated with a sealing part (r) by a rotating drive device (p).

Furthermore, a method is known in which a stationary nozzle and nip rollers rotating about the axis of a bubble are used. One on Apparatus based on this method is described, for example, in Jp-OS 48-3534.

Both of the methods described above rely on variance the irregularities of the film thickness by shifting the film position relative to the take-up surface of a take-up drum.

As particularly shown in Fig. 21, the bumps (h) are on different locations of a film (j) axially with respect to the rotation of the winding drum offset to the variations in the radial thickness of the film layers on the take-up drum to reduce and thereby eliminate the disadvantages described above.

However, the method of rotating the nozzle includes the following Problems.

First of all, there is inevitably a sliding structure between the nozzle the rotating and the stationary parts required, causing difficulties with helps prevent plastic from leaking through the sliding parts.

Since a suitable sealing material is not available, as general approach the distance between the sliding parts as small as possible designed to increase their dimensional accuracy. When bearing for the sliding parts are used, their service life will be due to the heat of the nozzle, the high temperatures can achieve shortened.

The rotating nozzle method requires a simultaneous one Rotation of an air ring and a blower cooling the bladder, which are attached to the nozzle are attached. To avoid the rotation of these additional components is it is necessary to change the structure of the nozzle itself.

In any case, there arises the problem that the machine as a whole gets more complicated and bigger.

If still low density polyethylene (LDPE) or polyethylene high density (HDPE) is used, the machine must clean the passages for the resin will be decomposed. In the case of a complicated machine - as above described - this is very difficult.

In addition, the twisting force exerted on the bladder only plants itself limited in the section in which the blown film is formed, so that the effect a distribution of the irregularities in the film thickness is only slight.

The other method with rotating nip rollers leads to axial ones Displacements of the film wound on the take-up drum, as shown in FIG aforementioned patent application is described, whereby an edge positioning device becomes necessary, which complicates the winding mechanism.

Summary of the Invention It is an object of the invention to provide a method and an apparatus for the production of blown films by which overcomes the difficulties or disadvantages described above can, in-which a device with a relatively simple structure for twisting a Bubble is inserted through which this bubble is between the nozzle and nip rollers can be rotated.

According to one aspect of the present invention, a method for the production of blown films consists in that a) a thermoplastic material is extruded through an annular slot nozzle, b) the extruded material is cooled to form a cylindrical bubble, c) this bubble is twisted by sliding contact with a bubble holder rotating around this bubble; and d) the bubble is rolled flat by guide plates and nip rollers.

According to another aspect of the invention is an apparatus for Manufacture of blown film provided, with one for extruding a thermoplastic melted plastic mass through an annular slot and to form a cylindrical Bladder serving nozzle, with an annular air supply to cool the bladder, with guide plates arranged opposite this nozzle and used to shape the bladder flat and with nip rollers for gripping and transferring the film, #ie characterized is that between the nozzle and the squeegee rollers a surrounding the bubble and arranged thereon a twisting device which exerts a torque in the circumferential direction is.

The foregoing and other objects, features, and advantages of the invention are read in conjunction with the following description and the accompanying drawings Claims in connection with the accompanying drawings clarified, which i e For example 1, some preferred embodiments of the invention are shown.

BRIEF DESCRIPTION OF THE DRAWINGS The attached drawings show: 4 shows a schematic top view of the bubble holder according to FIG. 3, FIG. 5 shows a schematic top view of the bubble holder according to FIG. 2, FIG. 6 shows a view of the rotating bubble holder according to FIG. 5, but with a reduced circular radius of the guide surface, 7 is a schematic view to explain the twisting of the bladder, FIG. 8 is a schematic front view of a bladder twisting device with a modified structure, 9 shows a schematic vertical section of an annular bladder holder, FIG. 10 shows a schematic, perspective view of a bladder holder with a modified structure, FIG. 11 shows a schematic top view of an iris ring, FIG. 12 shows a schematic illustration of an iris ring made of wire, FIG. 13 shows a schematic view A top view of a further modified bladder holder, FIG. 14 a schematic vertical section of a rotating device deviating from the illustration according to FIG. 3, FIG. 15 a front view of a perforated tube member as a partial view which can be used instead of the cylindrical tube according to FIG. 14, FIG Fig. 16 is a front view of a slotted hose member that can be used in place of the hose member shown in Fig. 15, Figs. 17 shows a cross section of a bubble produced by the conventional blowing method, FIG. 18 shows a perspective view of a film wound on a winding drum, FIG. 19 shows a longitudinal section of a film roll formed by the conventional winding method, FIG. 20 shows a front view of the conventional nozzle lathe and FIG. 21 is a longitudinal section of a roll of film which is wound so that irregularities in the film thickness are distributed.

Description of Preferred Embodiments Before the method for the production of a blown film is explained, the corresponding device are described by means of the exemplary embodiments illustrated in FIGS. 1 to 6.

In these figures there is an extruder f and a nozzle or blow head 2 shown, which is referred to below as nozzle 2 and with an annular Slot '3 is provided on its top.

A discharge pipe 4 is provided centrally and vertically through the nozzle 2 open upper end and an air supply pipe 5 guided coaxially in the exhaust pipe 4 is included.

The lower end of the air supply pipe 5 is connected to an air compressor connected, while the lower end of the exhaust pipe 4 to the atmosphere an adjusting valve 7 is open.

An air ring duct 8 has an annular air outlet opening on its inside 8a on. The underside of the air ring channel 8 is attached to a mounting ring 9, which: is attached to the outer edge of the top of the nozzle 2. An annular one Chamber 8b of the air ring channel is connected to an air cooling device 11 via a pipe 10 connected.

At a point opposite the nozzle 2 is a frame 14 held on one side at the upper end of a rod 13, which extends from a base plate 12 extends from upward. A pair of horizontally arranged shafts 15a are as Trunnions attached to this frame 14 to secure the a couple of nip rollers 15 received / driven by a drive device 16. On the other On the side of the rod 13, a guide roller 17 is mounted at its upper end and In addition, a film winding device 20 is provided, which consists of a drive device 18 and a winding drum driven by this.

Guide plates 21 consist of two frame parts 21a that oppose each other are pivotably mounted on the frame 14, and a plurality of guide rollers 21b, which are rotatable on horizontal shafts along the frame parts 21a in suitable Are stored at intervals.

A bubble twisting or twisting device 22 is between the nozzle 2 and the nip rollers 15 and constructed as follows: The underside an annular base plate 23 with a circular opening 23a is supported by a horizontal Frame 25 over a rotation about a vertical axis permitting spherical roller bearing 24 worn.

The second and third, each provided with a circular opening 27a Base plates 27 are parallel to and in each case across the first base plate 23 fixed at certain intervals by means of a number of rods 26 extending from the base plate 23, where they are arranged at regular intervals along the outside are, extend upwards.

On each of these base plates 27 there is a rotatable bladder holder 28 attached concentrically, as will be described in more detail later.

Furthermore, one engages integrally with the outside of the base plate 23 connected ring gear 29 into a gear 30, that by one Motor 31 is driven with a reduction.

The rotatable bladder holders 28 have on the respective base plates the same construction, so that the middle of the three bladder holders in the following is described in more detail in order to avoid unnecessary repetition.

A rotatable frame with the shape of a cage open at the top and at the bottom 32 consists of an upper ring 33, a lower ring 34 with an annular Groove 34a on the inner surface and six connecting rods 35, which the upper and connect the lower ring with each other at equal intervals along their outer sides.

Six short axes 36a extend equidistantly from the top the base plate 27 from upwards, being slightly closer to the edge of the circular Opening 27a are arranged and have at their upper ends six rotatable and vertical arranged rollers 36. These rollers 36 engage in the annular Nur 34a on rotatable frame 32 with a rolling motion and store this rotatably around a vertical axis.

One on the circumferential side of the lower ring 34 is integral in its lower region The molded ring gear 37 is connected to a drive device on the base plate 27 coupled and engages in particular in a gear 39 that the output shaft of a motor 38 is attached. Accordingly, the rotatable Rotate frame 32 forwards and backwards with the corresponding direction of rotation of the motor 38.

There are 24 protruding pins 40 on the top of the upper ring 33 attached along the circular opening 33a and near the edge thereof. Outer Ends of horizontal arms 41 are pivotably mounted on pins 40 and protrude with their inner ends into the circular opening 33a (see FIG. 5).

In Figs. 3 and 4 only one of the arms 41 is shown to be in a simplified way of showing the arm construction and the type of assembly, which is described in more detail below.

A fastening member 42 with a downwardly open receiving hole 42a is rotatably mounted on the inner end of the arm 41 about a vertical axis. on the other side is a fastening member 43 with an upwardly open receiving hole 43a at the edge of the circular opening 27a of the base plate 27 by a vertical Axis rotatably mounted, in particular at a point-symmetrical position relative to the pin 40 with respect to the center point of the circular opening 34a.

A support member 44 made of flexible plastic material has the shape of a round hose and extends in an arc shape (seen from the top view) between the top ring 33 and the base plate 27, the top and bottom ends respectively are inserted in the receiving holes 42a and 43a.

24 round tubes 44 are in this way between the top ring 33 and the base plate 27 attached circularly at equal intervals so that the inner periphery of the round tubes 44 approximately an enveloping circle S according to FIG Fig. 5, although it is actually an affine circle.

As will be described later, the holding members 44 are in sliding Contact with the outer surface u (represented by an imaginary line) of a bubble offset, which is passed through the bladder holder 28, which the bladder and exerts a rotational force on it that moves the bladder about a vertical axis tried to turn.

In order to change the radius of the enveloping circle S, the motor 38 according to FIG Fig. 4 switched on to rotate the gear 39 counterclockwise. Included the rotatable frame 32 is rotated clockwise through a required angle, as shown by an arrow t. This creates the round hoses 44 offset to the imaginary (dash-dotted lines, whereby the enveloping circle under reduction changed its curve radius.

The radius of the envelope circle is correspondingly reduced according to FIG. 6 'which is formed by the 24 round tubes 44, compared to the sleeve circle according to FIG. 5.

The following description relates to the operation of the device for the production of a blown film according to the construction described above and the method of distributing the irregularities in the thickness of the blown film.

The thermoplastic plastic material heated and melted in the extruder 1 is extruded through the slot 3 of the sleeve 2 to form a bubble V. above the air supply pipe 5 flows compressed air into the bladder 3, while the outer surfaces the bladder is acted upon by cooled air from the air outlet opening 8a of the air ring channel 8 the bubble is pulled upwards by means of the squeegee roller 15. the Outer surface of the stretched upwards to a predetermined radius Bladder V becomes in sliding contact with a large number of the circular tubes 44 placed in series connection of the three bladder holders of the bladder twisting device, which is rotated by the motor 31, so that the bubble V as a whole by the forces is twisted, which attack in the circumferential direction of the bladder as it moves upward.

As shown in more detail in FIG. 7, the bubble V becomes simultaneous a force y acting in the pulling direction and one acting in the circumferential direction Subject to force 1. Accordingly, a bulge (protuberance) X, which was originally was at a position X1, helically by the twisting motion of the bladder rotates and after a certain time it reaches a position X2.

This cylindrical bubble V is guided by the guide plates 21, folded into a thin layer by means of the squeegee rollers 15 and finally opened the take-up drum 19 is wound up. Accordingly, the one on the outer surface The bulge X occurring in the bubble is even distributed in the axial direction before the nip rollers 15 can be achieved, resulting in a flat winding of the film on the winding drum 19 allowed.

Although the three rotatable bladder holders of the bladder twister 22 in the embodiment described above by a single drive device can be acted upon with a 3800 turn, it is also possible to turn 180 ° alternatively in opposite directions of rotation.

Furthermore, drive devices 45 can be rotatable separately for each Bladder holders 28 may be provided as shown by imaginary lines in FIG. 7 is., In this case, it is possible to improve the twisting effect by different Torques are exerted by the respective bladder holder.

In Fig. 8, a further embodiment is shown in which the upper Part of the air ring channel 46 above the nozzle 2 consists of a rotatable about a vertical axis Ring 46a consists.

The bladder twisting device 22 is fixed on the rotatable ring 46a mounted, which is coupled to a drive device 47. This arrangement has the advantage that the bladder twisting device 22 and the air ring channel 46 simultaneously can be driven by the drive device.

Figures 9 to 13 show further constructions of the bladder holding members 44 of the rotating bladder holders 28 of the first embodiment.

In Fig. 9, the holder 48 consists of an annular body 48a and a hollow ring body 48b, which is rotatably mounted on the body 48a and through a drive device or

a motor 49 is driven. The hollow ring body 48b is with a annular having an annular slot 28d around the inner periphery Chamber 48c provided and stands with a vertically arranged recess 48e in the Body 48a in connection. The vertical recess 48e is at a not shown Vacuum pump attached to the peripheral surface of bladder V against slot 48d suck in. Instead of the bladder holder 48, a more fixed Ring can be used.

In the embodiment shown in Fig. 10, there is a bladder holder 51 from six horizontally arranged rods 50a, which are hexagonally arranged in a Käftig 50b for making sliding contact with the peripheral surface of a bladder are arranged.

Fig. 11 shows a modification using a known iris ring 53, which within an annular frame 52 an enveloping circle by a large Forms number of spirally arranged thin plates 53a.

Fig. 12 shows a bladder holder using a known one Wire iris ring 54 made up of a large number of wires 54a instead of the above described thin plates 53a is to form an enveloping circle for the production of a to form sliding contact with the outer surface of a bladder.

In Fig. 13, a bladder holder is shown, which consists of a number of arms 58, which on the upper end face of a cylindrical body 55 at equidistant arranged pins 56 are rotatably mounted, as well as rod members 57, the from the inner free ends of the arms 58 parallel to each other in the direction of Drooping motion of the bladder.

FIG. 14 shows an embodiment of the exemplary embodiment according to FIG. 3, instead of the round hoses 44 now flexible round hoses 59 for Supply of a coolant such as cooled air can be used. In this ending Trap are the opposite # n / of the round hoses 59 each with channels 62 and 63 connected, which are fixedly attached to upper and lower rings 60, 61 and as Air supply and air discharge channels are used.

Because the round tube 59 is cooled accordingly, the bladder be adequately cooled if they are through the round tubing for the purpose of twisting is encompassed. This can improve productivity.

Instead of using the round hoses 59 according to FIG.

14, perforated guide members 64 with perforations according to FIG FIG. 15 or slotted guide members with a slot 64b according to FIG. 16 are used to improve the cooling effect.

From the above description it can be seen that according to the invention Process the irregularities in the thickness of the blown film by twisting a Bubble can be distributed between the nozzle and the squeegee rollers, reducing the Bubble safely wound onto the take-up drum with improved productivity can be.

The torque exerted on the bladder has the added effect a shift in molecular structures, increasing the tear strength and toughness the foil is increased, and at the same time the foil is still before the solidification stretched to flatten the thicker areas of the film.

The method according to the invention thereby combines the advantages of known nozzle turning process with the advantages of the squeeze roller turning process.

The method according to the invention can thereby be applied in a simple manner that the bladder twisting device is added to a known device, without this entailing large expenses for the retrofitting.

The device for the production of blown films has a relative simple structure and can thereby be manufactured at low cost.

Since there is still no additional step compared to known methods is required can increase the quality of the product while increasing the Productivity can be improved.

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Claims (17)

Method and device for the production of blown films Patent claims 1. A method for the production of blown films, characterized in that a thermoplastic, melted plastic mass through an annular slot (3) of a nozzle (2) extruded and the extruded mass is cooled to form a bubble (V), that this bubble (V) is brought into sliding contact with a rotating bubble holder and is thereby twisted and that this bubble (V) into a flat, thin path is folded by means of guide plates (21) and nip rollers (15). 2. Device for the production of blown films with one for extrusion a thermoplastic, molten plastic mass through an annular slot (3) and for forming a cylindrical bubble (V) serving nozzle (2), with an annular one Air supply (8) for cooling this bubble (V), with opposite this nozzle (2) arranged, for shaping the bladder (V) flat and with nip rollers (15) to grasp and transfer the Bubble (V) in a folded foil, characterized in that between the nozzle (2) and the nip rollers a die Bladder (V) encompassing and then exerting a torque about a vertical axis Twisting device (22) is arranged. 3. Apparatus according to claim 2, characterized in that the twisting device for the bladder a rotating, in sliding contact with the peripheral surface of the Bladder stepping bladder holder (28) and a drive device for rotating this Has bladder holder (28) around the central axis of the bladder. 4. Apparatus according to claim 2 or 3, characterized in that the twisting device (22) for the bladder rotatably over an air ring channel the nozzle (2) is mounted, wherein the twisting device (22) by a drive device of the air ring channel is driven. 5. Apparatus according to claim 2 or 3, characterized in that the twisting device (22) comprises a plurality of rotating bladder holders (28) which can be brought into sliding contact with the peripheral surface of the bladder and are independent of one another can be driven by separate drive devices. 6. Device according to one of claims 2 to 5, characterized in that that the bladder holder (28) has an iris ring, which is made of a large number of thinner Plates (53a), which are arranged in a spiral to form an enveloping circle are. 7. Device according to one of claims 2 to 5, characterized in that that the bladder holder has a plurality of elastic members forming an enveloping circle consists. 8. Apparatus according to claim 7, characterized in that the bladder holder (28) has hollow, tubular members (59; 64; 65) which allow the passage of a coolant. 9. Apparatus according to claim 8, characterized in that the bladder holder has perforated guide members (64) with perforations (64a) on the peripheral surface, from which coolant leaks. 10. Apparatus according to claim 8 or 9, characterized in that the bladder holder (28) has at least one hollow ring. 11. Device according to one of claims 8 to 10, characterized in that that the bladder holder (28) has a plurality of flexible tubes, the one Enveloping circle for make sliding contact with the bladder. 12. Device according to one of claims 7 to 11, characterized in that that the bladder holder (28; 51) has a plurality of tubes or rods (50a), those in a polygonal arrangement in a perpendicular and to movement direction The plane located near the bladder is attached and an inscribed circle to the sliding contact form with the bladder. 13. Device according to one of claims 7 to 11, characterized in that that the bladder holder (28) has a plurality of tubes or rod members (57), which are arranged parallel to the direction of movement of the bladder and around the circumferential surface the bladder extend. 14. The device according to claim 3, characterized in that the bladder holder (28) has a polygonal shape forming an inscribed circle for sliding contact forms with the bladder. 15. Device according to one of claims 3 to 5, characterized in that that the bladder holder (28i 48) has an annular body (48b). 16. The device according to claim 15, characterized in that this annular body in the region of its inner periphery has a slot (48d) and with one Vacuum pump for sucking in the peripheral surface of the bladder is connected by means of the slot (48d). 17. Apparatus according to claim 15 or 16, characterized in that that the annular body (48b) is rotatable by means of a drive device (49) is.