Die head and process to manufacture multilayer tubular film

Abstract

In the case of a die head and a process to produce multilayer tubular film made from thermoplastic polymers, the advantages of radial distributors and axial distributors should be combined. This is achieved in that at least one distributor is a plate distributor and at least one distributor is an axial distributor, whereby the plate distributor is located in an annular element of the axial distributor upstream of the melt merge zone to the ring-shaped die.

Claims

1. A die head for producing a multilayer tubular film from thermoplastic polymers, the die head comprising: a mandrel surrounded by a plurality of annular elements; at least one melt feeder; a plurality of melt channels arranged concentrically around a central axis of the die head, wherein the plurality of melt channels are delimited by the mandrel and the plurality of annular elements; a ring-shaped die into which the plurality of melt channels discharge; and a plurality of distributors for distributing a melt from the at least one melt feeder to the ring-shaped die; wherein at least one of the plurality of distributors is an axial distributor and at least one of the plurality of distributors is a plate distributor, the plate distributor having a plurality of distributor plates with plate distributor melt channels located in between and arranged in an annular element of the plurality of annular elements upstream of where the melt merges into the ring-shaped die and whereby the plate distributor is delimited in a radial direction on a first side by a respective melt channel to which the plate distributor discharges and on a second opposite side by the annular element of the plurality of annular elements.

2. The die head of claim 1, wherein the plurality of distributors includes plate distributors located at different melt channels of the plurality of melt channels.

3. The die head of claim 1, wherein the plurality of distributors includes plate distributors located at a same melt channel of the plurality of melt channels and configured either on top of or opposite each other.

4. The die head of claim 1, wherein the plurality of distributors includes plate distributors and axial distributors located at a same melt channel of the plurality of melt channels.

5. The die head of claim 1, wherein the annular element of the plurality of annular elements with the plate distributor arranged in the annular element of the plurality of annular elements is designed in a modular way to comprise a base annular element, a plate distributor stack, and a mounting ring.

6. The die head of claim 1, configured such that merging of the melt from the plate distributor melt channels into the plurality of melt channels takes place at an acute angle.

7. The die head of claim 1, wherein the axial distributor or plate distributor of an outside melt channel of the plurality of melt channels is located at an inside wall of a housing.

8. The die head of claim 1, configured such that a layer thickness distribution in the multilayer tubular film produced is set as a function of pressure drops in the axial distributor and in the plate distributor.

9. The die head of claim 8, wherein the pressure drops are set across cross-sections in the axial distributor and in the plate distributor.

10. The die head of claim 9, configured such that adaptation of the cross-sections of the axial distributor and the plate distributor for thickness and type of melt takes place in at least one of a predistributor, a feed line from the predistributor to axial and radial distribution channels of the respective axial and plate distributors, a distribution geometry, and a merging of melt streams.

11. The die head of claim 1, wherein the axial distributor or the plate distributor of an inside melt channel of the plurality of melt channels is located at an outside wall of a mandrel of the die head.

12. The die head of claim 1, wherein the axial distributor comprises at least one spiral on an outside cylindrical surface or on an inside cylindrical surface of at least one annular element of the plurality of annular elements.

13. A method for production of multilayer tubular film made from thermoplastic polymers in a blown film line, the method comprising providing the die head of claim 1, forming at least one of the layers of the multilayer tubular film from one or several layers in an axial distributor of the die head of claim 1 and from one or more layers in a plate distributor of the die head of claim 1, and discharging melt from the plate distributor into the axial distributor.

14. The method of claim 13, further comprising operating the plurality of distributor plates in parallel mode.

15. The method of claim 13, further comprising operating the plurality of distributor plates in series mode.

16. The method of claim 13, further comprising operating the plurality of distributor plates in a combination of parallel and series mode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other details, features and advantages are also disclosed herein and from the following description of the associated drawings in which a preferred embodiment of is shown by way of example.

(2) The drawings show:

(3) FIG. 1: A die head according to the disclosure;

(4) FIG. 2: A die head with plate distributor in parallel operation according to the disclosure; and

(5) FIG. 3: A die head with plate distributor in series operation according to the disclosure.

DETAILED DESCRIPTION

(6) In FIG. 1, a die head in a preferred embodiment is shown in section.

(7) The die head (1) combines an axial distributor with a plate distributor. The die head (1) surrounds an inside cylindrical mandrel (2). The mandrel (2) in this example is surrounded by concentric annular elements (3, 4, 5, 6, 7), whereby the outermost annular element (7) simultaneously constitutes the housing. The mandrel (2) itself also constitutes an annular element. Between the mandrel (2) and the inside annular element (3), as well as between the individual annular elements are ring-shaped dies, the melt channels (8, 9, 10, 11, 12). The mandrel (2), the first (3) and the third annular element (5) all exhibit a spiral (13, 14, 15) on their outside cylindrical surface. The sixth annular element (7), the housing, exhibits a spiral (16) on its inside cylindrical surface. The depth of the spirals (13, 14, 15, 16) decreases towards the ring-shaped die (17). The second (4) and fourth annular element (6) have no spirals but rather smooth cylindrical surfaces. The third annular element (5) has a plate distributor (18). On its inside cylindrical surface, there is a recess to accommodate a plate distributor stack (21) and it has a mounting ring (24). The plate distributor stack (21) comprises several distributor plates (25) which constitute the plate distributor stack (21) and the melt feed units (not shown here). Plate distributor melt channels (26) are located between these. The plate distributor (18) has a melt feeder (not visible here), a spiral distributor, melt channels (26) and melt outlets (27). The distributor plates (25) are connected to each other by means of a bolted connection or another separable connection and are fixed on the mounting ring (24). The plate distributor stack (21) with mounting ring (24) is then installed in the die head (1) with the third annular element (5), the base annular element. The plate distributor stack (21) discharges its melt streams from the plate distributor melt channels (26) one by one into the melt channel (10). The melt channels (8, 9, 10, 11, 12) are united upstream of the ring-shaped die (17) to form an annular slit.

(8) The melt is transported by several melt feed units (28) into the die head (1), and is then conveyed via different predistributors (not shown here) to the start of the spirals (13, 14, 15, 16) and the plate distributor (18).

(9) The melt is distributed uniformly by the axial distributor, here an axial spiral distributor, over the circumference of the respective melt channels (8, 9, 11, 12) before being conveyed towards the ring-shaped die (17). Another melt stream is fed via a predistributor (not shown) to the plate distributor stack (21) and is distributed in the same such that it discharges as a uniform molten tube stream via the distributor outlets (27) into the melt channel (10). The plate distributor is thus located concentrically in the axial distributor. In the melt channel (10), the melt streams from the individual plate distributor melt channels (26) are united one after the other. This united melt stream is then united consecutively with the melt streams from the melt channels (8, 9, 11, 12) before being routed to the ring-shaped die (17) where the melt stream discharges as a multilayer molten tube.

(10) Because the spiral discharge of the outside layers of the molten tube, i.e. the inside and outside layer, takes place towards the centre of the molten tube, which subsequently make contact with the melt of the other layers, a multilayer film can be produced without streaks and corrugations.

(11) If die head for multilayer tubular film of over 5 thick layers is to be used, correspondingly more annular elements are located between the outside ring element and the mandrel. If a die head for multilayer tubular film of less than 5 thick layers is to be used, correspondingly less annular elements are located between the outside annular element and the mandrel.

(12) The plate distributor can also be adapted regarding the number of layers by employing more or less plates.

(13) FIG. 2 shows a die head (1) in parallel operation. In comparison with the die head in FIG. 1, this die head (1) has two plate distributors (18, 19). A plate distributor (18) is located in the annular element (4), the associated plate distributor stack (21) discharges the melt into the melt channel (9). The second plate distributor (19) is positioned in the annular element (5). The plate distributor stack (22) of the distributor (19) discharges the melt into the melt channel (10). This melt stream is then united consecutively with the melt streams from the other melt channels (8, 9, 11) before being routed to the ring-shaped die (17) in order to exit the die head (1) as a molten tube.

(14) FIG. 3 shows a die head (1) in series operation. It also has two plate distributors (18, 20). The plate distributors (18) and (20) are positioned on top of each other in the same annular element (5). Both plate distributor stacks (21) and (23) discharge their melt into the same melt channel (10). This united melt stream is then united consecutively with the melt streams from the melt channels (8, 9, 11, 12) before being routed to the ring-shaped die (17) in order to exit the die head (1) as a molten tube.

LEGEND

(15) 1 Die head

(16) 2 Mandrel

(17) 2, 3, 4, 5, 6, 7 Annular elements

(18) 8, 9, 10, 11, 12 Melt channels

(19) 13, 14, 15, 16 Spirals

(20) 17 Ring-shaped die

(21) 18, 19, 20 Plate distributors

(22) 21, 22, 23 Plate distributor stacks

(23) 24 Mounting ring

(24) 25 Distributor plates

(25) 26 Plate distributor melt channels

(26) 27 Plate distributor melt outlet

(27) 28 Melt feeder