Recyclable PET film

Abstract

The present invention relates to a multilayer, coextruded polyester film including at least one outer layer (A) and a base layer (B), in which the at least one outer layer (A) includes, to an extent of at least 60 wt %, a polyester or a copolyester formed from units derived from aliphatic dicarboxylic acids and diols, wherein the units derived from dicarboxylic acids are selected from one or more dicarboxylic acids from the group of succinic acid, adipic acid, suberic acid, azelaic acid and sebacic acid, and the units derived from diols are selected from one or more diols from the group of ethylene glycol, 1,3-propanediol, 1,4-butanediol and neopentyl glycol.

The present invention further relates to a process for producing the film according to the invention, to the use thereof and to a process for recycling the polyester film according to the invention.

Claims

1. A multilayer, coextruded polyester film comprising at least one outer layer (A) and a base layer (B), wherein the at least one outer layer (A) consists to an extent of at least 60 wt % of a polyester or a copolyester consisting of units derived from aliphatic dicarboxylic acids and diols, wherein the units derived from dicarboxylic acids are selected from one or more dicarboxylic acids from the group consisting of succinic acid, adipic acid, suberic acid, azelaic acid and sebacic acid, and the units derived from diols are selected from one or more diols from the group consisting of ethylene glycol, 1,3-propanediol, 1,4-butanediol and neopentyl glycol.

2. The polyester film according to claim 1, wherein the units derived from dicarboxylic acids consist of 70 to 100 mol % of units derived from succinic acid and 0 to 30 mol % of units derived from adipic acid, and the units derived from diols consist of 0 to 20 mol % of units derived from ethylene glycol, 0 to 20 mol % of units derived from 1,3-propanediol and 80 to 100 mol % of units derived from 1,4-butanediol, wherein the units derived from dicarboxylic acids and the units derived from diols in each case sum to 100 mol %.

3. The polyester film according to claim 1, wherein the at least one outer layer (A) is a first outer layer (A) and the polyester film additionally comprises a second outer layer (A) which has been applied to the surface of the polyester film opposite the first outer layer (A).

4. The polyester film according to claim 1, wherein the polyester film comprises an outer layer (C) which has been applied to the surface of the polyester film opposite the first outer layer (A).

5. The polyester film according to claim 1, wherein the at least one outer layer (A) has a thickness of 0.5 μm to 6 μm.

6. The polyester film according to claim 5, wherein the at least one outer layer (A) has a thickness of 1 μm to 3 μm.

7. The polyester film according to claim 1, wherein a coating has been applied to the at least one outer layer (A).

8. The polyester film according to claim 7, wherein the coating has been applied using an in-line process.

9. The polyester film according to claim 7, wherein the coating is an adhesion promoting coating or an anti-adhesion coating.

10. A process for producing a polyester film according to claim 1, wherein said process comprises initially melting the polyester/the polyester mixture of the individual layers of the film in extruders, forming the resulting melts into flat melt films in a multilayer nozzle, pressing the flat melt films through a wide-slot die and cooling and solidifying the pressed flat melt films by hauling off the pressed film onto a cooling roll and one or more haul-off or take-up rolls, biaxially stretching solidified film and subsequently heat-setting and winding up the biaxially stretched film, wherein the at least one outer layer (A) consists to an extent of at least 60 wt % of a polyester or a copolyester consisting of units derived from aliphatic dicarboxylic acids and diols, wherein the units derived from dicarboxylic acids are selected from one or more dicarboxylic acids from the group consisting of succinic acid, adipic acid, suberic acid, azelaic acid and sebacic acid, and the units derived from diols are selected from one or more diols from the group consisting of ethylene glycol, 1,3-propanediol, 1,4-butanediol and neopentyl glycol.

11. The process according to claim 10, wherein said process further comprises coating the film with a coating composition during the production process.

12. A process for recycling a polyester film comprising the steps of comminuting a multilayer polyester film according to claim 1 comprising at least one outer layer (A) and a base layer (B), contacting the comminuted polyester film with an aqueous alkali metal hydroxide-containing solution, separating the comminuted polyester film, wherein the comminuted polyester film no longer comprises an outer layer (A), drying the comminuted polyester film.

13. The process according to claim 12, wherein the aqueous alkali metal hydroxide-containing solution is an NaOH-or KOH-containing solution.

14. The process according to claim 12, wherein the aqueous alkali metal hydroxide-containing solution is a 1 to 10 wt % aqueous NaOH- or KOH-containing solution and has a temperature of 60° C. to 98° C.

15. The process according to claim 14, wherein the aqueous alkali metal hydroxide-containing solution has a temperature of 80° C. to 95° C.

16. The process according to claim 12, wherein the contacting with the aqueous alkali metal hydroxide-containing solution step is performed for a period of 5 to 30 minutes.

17. The process according to claim 12, wherein the contacting with the aqueous alkali metal hydroxide-containing solution step is performed for a period of 7 to 15 minutes.

18. A carrier film comprising polyester film according to claim 1.

19. The carrier film according to claim 18, wherein said carrier film is label film or embossing film.

20. A process for producing a polyester film, comprising employing a recycled polyester film obtained by a process according to claim 12 in polyester film production.

Description

EXAMPLES

Raw Materials Used

[0078]

TABLE-US-00001 PET 1 Polyethylene terephthalate (PET), PET 4004 (manufacturer: Invista & Fibres GmbH, Germany), PET 2 Polybutylene succinate (PBS), BIOPBS ® FZ71 (manufacturer: PTT MCC Biochem Co., Ltd). MB1 Masterbatch of 98.5 wt % of PET 4004 and 1.5 wt % of amorphous SiO2, SYLOBLOC ® 46 (manufacturer: Grace GmbH, Worms, Germany); average particle diameter d50 according to data sheet 2.9-3.5 μm. • C 1 (Silicone) An aqueous dispersion according to EP-0769540 A2 example 3 was prepared. The United States equivalent of EP-0769540 A2 is U.S. Pat. No. 5,672,428, which is hereby incorporated by reference herein in its entirety. This dispersion makes it possible to provide a polyester film with a siliconized surface. C 2 (Adhesion promoter) An aqueous dispersion according to EP-0144948 A2 example 1 was prepared. The United States equivalent to EP-0144948 is U.S. Pat. No. 4,571,363, which is hereby incorporated by reference herein in its entirety. This dispersion makes it possible to provide a polyester film with an acrylate-based adhesion promoting coating.

Production of an Uncoated Film

[0079] Specimens having a 2-layered AB construction were produced, wherein the outer layer (A) had a thickness of about 10% of the total film thickness and represents the readily soluble layer. The base layer (B) consists only of conventional 30 polyester without further additives. The raw materials were melted by extrusion and coextruded in a wide-slot die to form the so-called pre-film. The pre-film which had a total thickness of 613 μm had a specimen having dimensions of about 11×11 cm cut out of it and biaxially oriented with a stretching frame. At a stretching temperature of 95° C. the film was stretched by a factor of 3.5 in the machine direction (MD) and by a factor of 3.5 in the transverse direction (TD) and subsequently thermoset for a duration of 30 seconds at a temperature of 225 ° C. The resulting biaxially stretched polyester film had a total thickness of about 50 μm, wherein the outer layer (A) accounted for about 5 μm thereof.

TABLE-US-00002 TABLE 1 Formulations and measured values of the examples Total film Total film Thickness thickness thickness reduction before after of outer Ex- Outer Base solution solution layer A ample layer A layer B test [μm] test [μm] [μm] 1 92% 100% PET 1 49 43 6 PET 2 8% MB1 CE1 92% 100% PET 1 50.6 50.6 0 PET 1 8% MB1 CE2 40% 100% PET 1 49 49 0 PET 2 52% PET 1 8% MB1

Example 1

[0080] In addition to the readily soluble polyester (PET 2) an SiO.sub.2-containing masterbatch was additionally introduced into the outer layer (A) to afford the windability of the film. The mixture of polyester and masterbatch did not result in any discernible streaks or gels in the film and optical appearance is very good. The solubility test disclosed that the outer layer (A) had completely dissolved under the simulated washing conditions. The remaining base layer (B) remained optically untouched in the solution and was able to be separated without issue.

Comparative Example 1

[0081] A film was produced as in example 1 but using PET 1 instead of PET 2. The outer layer (A) was not able to be removed in the solubility test.

Comparative Example 2

[0082] The readily soluble polyester (PET 2) from example 1 was incorporated into the outer layer (A) in a lower concentration such that the proportion was not more than 40 wt %. This composition means that the outer layer (A) is no longer sufficiently soluble and it was no longer separable from the base layer (B) in the washing test. The outer layer (A) became whitish-matt and opaque and exhibited a tendency for sticking to itself and to the vessel wall. Removal of the thus incipiently dissolved outer layer (A) was achieved only using additional mechanical measures, for example by scraping with a wooden spatula. However, this behaviour is not tolerable for a processing of plastic wastes that is to be operated on an industrial scale.