INTEGRATED PROCESS FOR PRODUCING POLYESTER TAPE

Abstract

The present invention relates to an integrated process for the production of polyester tape, comprising the steps of a) preparing feed polyester comprising a polymerisation reaction in one or more reactors in series and measuring the viscosity of the obtained feed polyester, b) feeding the feed polyester obtained from step a) and optional additives to a melt mixing device, mixing said feed polyester and said optional additives so as to form a molten polyester composition and measuring the viscosity of the obtained polyester composition, c) extruding the molten polyester composition through a film extrusion die thereby forming a molten film of said polyester composition, d) preparing a polyester tape from said molten polyester film, said preparing comprising trimming the edges of the film at a stage where said film is below its melting temperature, e) feeding at least a part of the trimmed edges obtained in step d) in-line to the melt mixing device in step b) wherein the amount of trimmed edges and optional further additives fed to the melt mixing device in step b) is controlled on the basis of the measured viscosity of the polyester composition.

Claims

1. An integrated process for the production of polyester tape, comprising the steps of a) preparing feed polyester comprising a polymerisation reaction in one or more reactors in series and measuring the viscosity of the obtained feed polyester, b) feeding the feed polyester obtained from step a) and optional additives to a melt mixing device, mixing said feed polyester and said optional additives so as to form a molten polyester composition and measuring the viscosity of the obtained polyester composition c) extruding the molten polyester composition through a film extrusion die thereby forming a molten film of said polyester composition, d) preparing a polyester tape from said molten polyester film, said preparing comprising trimming the edges of the film at a stage where said film is below its melting temperature, e) feeding at least a part of the trimmed edges obtained in step d) in-line to the melt mixing device in step b) wherein the amount of trimmed edges and optional further additives fed to the melt mixing device in step b) is controlled on the basis of the measured viscosity of the polyester composition.

2. The process of claim 1 wherein the viscosity of the polyester composition is controlled such that the viscosity varies at most 10% with respect to a target value.

3. The process of claim 1 wherein the trimmed edges are transported to the melt mixing device at least in part in an environment having a relative humidity of at most 10% when measured at 25° C. and atmospheric pressure.

4. The process of claim 1 wherein the trimmed edges are transported at least in part through protective tubes.

5. The process of claim 1 wherein the polyester is polyethylene terephthalate (PET) or polyethylene naphthalate (PEN).

6. The process of claim 1 wherein the polyester is polyethylene terephthalate and the intrinsic viscosity of the feed polyester is at least 0.5 dl/g.

7. The process of claim 1 wherein the additives in step b) comprises at least a chain extender.

8. The process of claim 7 wherein the chain extender is a linear chain extender.

9. The process of claim 1 wherein the feed polyester is prepared using a melt polymerisation process in one or more melt polymerisation reactors and wherein the polyester melt from said one or more reactors is fed directly to the melt mixing device of step b).

10. The process of claim 1 wherein the viscosity of the feed polyester and/or the polyester composition is the melt viscosity.

11. The process of claim 1 wherein the tape is a uniaxially oriented polyester tape and wherein : step c) further comprises cooling of the molten polyester film to below its melting temperature step d) further comprising slitting the polyester film into a plurality of tapes followed by drawing said plurality tapes at a draw ratio of at least 3:1 at a temperature of from 80° C. to 120° C. and heat setting said drawn tapes at a temperature of at least 150° C.

12. An apparatus for carrying out the process of claim 1 comprising: one or more reactors for the polymerisation of feed polyester, an output of said reactors being connected to an input of at least one melt mixing device, and means for measuring the viscosity of the feed polyester, at least one melt mixing device for melt mixing the feed polymer and optional additives, so as to form a polyester composition, said melt mixing device having an output connected to a film extrusion die, and means for measuring the viscosity of said polyester composition, a film extrusion die for forming a molten film of the polyester composition, a polyester tape manufacturing line in series with the film extrusion die for the manufacture of polyester tape, said polyester tape manufacturing line having edge trim means and means for feeding edge trim to an input of said melt mixing device.

13. The process of claim 2, wherein the viscosity of the polyester composition varies at most 5% with respect to the target value.

Description

[0128] FIG. 1 schematically illustrates an embodiment of the system 100 for continuous production of polyester tape according to the present invention.

[0129] In unit 101, feed polyester having a desired melt viscosity is prepared. The polymerisation is performed under control of a first melt viscosity control unit 109 which measures the melt viscosity of the feed polyester melt exiting from the unit 101. The dotted lines indicated with reference numerals 112 and 117 indicate the control loop signals, wherein signal 112 is an input for control unit 109 and signal 117 is an output signal from control unit 109. The viscosity in unit 101 may be controlled in a known manner, for example by controlling either one or more of temperature, pressure, (co)monomer ratio, catalyst concentration etc.

[0130] The feed polyester melt is fed to a melt mixing device unit 102. Optionally, a part of the feed polyester melt is fed to a unit 110 for the preparation of polyester granules or flakes.

[0131] Melt mixing device unit 102 is fed with a polymeric anti-splitting additive from an additive feed unit 107.

[0132] Unit 102 prepares a polyester melt composition suitable for film production and feeds it to a polyester film production unit 103. The polyester film production unit 103 prepares a polyester film from the polyester melt composition and feeds the polyester film to a polyester tape production unit 104. The film production unit 104 comprises a flat die for extruding the polyester film and a chill roller for receiving and chilling the polyester film.

[0133] Polyester tape production unit 104 receives the polyester film from the polyester film production unit 103 and comprises an edge trimming device which trims the polyester film edges, to ensure an even thickness throughout the width of the polyester film and further to ensure a constant width of the polyester fil. The edge trims are collected by edge trim collection unit 106.

[0134] The polyester film is slit in the tape production unit 104 into tapes by slitting knives, wherein the knives are spaced with a predetermined width. Occasionally some of the produced tapes may break after slitting. The broken tapes are collected by broken tape collection unit 105. The broken tape collection unit 105 comprises any suitable container placed near the slitting knives for picking up the broken tapes.

[0135] The collected edge trim and broken tape are collected in a feed back unit 116 where they may optionally be shredded and fed back to melt mixing device unit 102.

[0136] A second melt viscosity control unit 108 measures the melt viscosity of the polyester melt composition and controls the supply of polymeric anti-splitting additive and/or other additives like chain extenders to be fed from unit 107, and the supply from feed back unit 116 of the shredded edge trims from unit 106 and the broken tapes from unit 105. The dotted lines indicated with reference numerals 111, 113 and 114 indicate the control loop signals, wherein signal 111 is an input for control unit 108 based on measurement of the melt viscosity of the polyester composition, signals 113 and 114 are output signals from control unit 108. The viscosity in unit 102 may be controlled by varying the amount of edge trim recycle fed to melt mixing device unit 102 and/or by controlling the amount of additive, such as chain extenders, fed from unit 107. Other additives that influence the melt viscosity of the polyester composition prepared in unit 102 may be controlled also based on output signal(s) 113. For the purpose of explanation only a single control unit with single output signals is shown in FIG. 1. However a skilled person will understand that in fact units 108 and 109 may have multiple outputs based on the number of parameters to be controlled.

[0137] FIG. 2 schematically illustrates an embodiment of the unit 101 for the preparation of the feed polyester composition. Polyester preparation unit 101 has a paste mixing vessel 202, at least one esterification reactor 203, a first pre-polycondensation reactor 204, a second pre-polycondensation reactor 205, and a finisher reactor 206. Various variations to these reactors are possible. Industrial polymerization lines with a single pre-polymerisation reactor, and also polymerization lines with just one paste mixing vessel, one esterification reactor and one finisher are also known.

[0138] In the above described polyester preparation unit 101, a dialcohol-based compound and a dicarboxylic acid-based compound 201 are fed to paste mixing vessel 202. The paste is then fed into the at least one esterification reactor 203. The output of esterification reactor 203 is fed into the pre-polycondensation reactor 204. The output of the second pre-polymerisation reactor 205 is the first polyester melt composition, This first polyester melt composition is fed into and subjected to the finisher reactor 206.

[0139] The melt viscosity of the output of the finisher reactor 206, the feed polyester melt, is controlled by viscosity control unit 109 shown in FIG. 1. The melt viscosity is preferably controlled by varying the under pressure or vacuum of finisher reactor. As set out above, when the melt viscosity is higher than a target viscosity, the vacuum is reduced, i.e.

[0140] pressure increases, whereas if the melt viscosity is lower than the target viscosity, the vacuum is increased, i.e. pressure is reduced.

[0141] FIG. 3 schematically illustrates an embodiment of the melt mixing device unit 102 for preparing the polyester melt composition suitable for film production from the feed polyester. Unit 102 comprises an extruder 301, the feed back unit 116 for shredded edge trim and/or broken tape, and the feed unit 107 for one or more additives. Compounding unit 102 has an inlet 304 for the feed polyester melt composition from the polyester preparation unit 101, see FIG. 1, i.e. from the finisher reactor 206 (see FIG. 2) and an outlet 305 for feeding the third polyester melt composition to the flat die of the polyester film production unit 103.

[0142] The (polymeric) additives in feed unit 107 comprise the anti-splitting additives such as LLDPE, LDPE and the like. In a preferred embodiment feed unit 107 is also used to add chain extenders. The feed back unit 116 can have an impeller 309 to add the edge trim and broken tape shreds into the extruder 301. The extruder 301 is preferably a high shearing twin screw extruder as described above.

[0143] FIG. 4 schematically illustrates an alternative embodiment of the melt mixing device unit 102 for preparing the polyester melt composition suitable for film production from the feed polyester. Compared to FIG. 3 feed unit 107 and feed back unit 116 are combined in a single feed stream to melt mixing device 301. In addition to that a degasser 310 is added to the extruder so as to remove low molecular weight materials and residual moisture from the melt mixing device.