Chemical-resistant films in high optical quality

Abstract

The present invention relates to a process for producing transparent polymeric films or plastics moldings of particularly high chemical resistance, having more particularly a very good resistance towards oil-in-water and water-in-oil emulsions, and of high optical quality.

Claims

1. A process for producing a polyamide film or a polyamide moulding, by extruding a polyamide moulding composition through an extrusion film die comprising a die body and a die lip, the process comprising: melting the polyamide moulding composition at a temperature of between 250 and 330 C. in a multi-screw extruder comprising a first extruder zone, a second extruder zone, and a transition region, where the temperature of the second extruder zone and the transition region is 10 C. higher than the first extruder zone; extruding the melted polyamide moulding composition through a die lip having a temperature of between 290 and 370 C.; removing an extruded composition having a thickness between 10 m and 10 mm with at least one roll or at least one belt; and conveying and at the same time cooling the extruded composition, wherein: the composition comprises, in polymerized form, an aromatic, aliphatic or cycloaliphatic dicarboxylic acid and a cycloaliphatic diamine, the polyamide moulding composition has a carboxyl endgroup fraction, an amino endgroup fraction, or both, of less than 35 mmol/kg, and a temperature of the die lip, which is an exit region, is higher than a temperature of the die body by 10 C. to 100 C.

2. The process according to claim 1, wherein the polyamide moulding composition comprises in polymerized form an aliphatic or cycloaliphatic dicarboxylic acid and a cycloaliphatic diamine.

3. The process according to claim 1, wherein the polyamide moulding composition comprises in polymerized form an aromatic dicarboxylic acid and a cycloaliphatic diamine.

4. The process according to claim 2, wherein: the polyamide moulding composition comprises in polymerized form an aliphatic or cycloaliphatic dicarboxylic acid and a cycloaliphatic diamine; and the polyamide moulding composition has an amino endgroup fraction of less than 35 mmol/kg.

5. The process according to claim 3, wherein: the polyamide moulding composition comprises in polymerized form an aromatic dicarboxylic acid and a cycloaliphatic diamine; and the polyamide moulding composition has an amino endgroup fraction of less than 35 mmol/kg.

6. The process according to claim 1, wherein a pressure at a die outlet is such that all volatile constituents are fully dissolved.

7. The process according to claim 1, wherein the die body has a temperature of between 250 C. and 330 C., and the die lip has a temperature of between 290 C. and 370 C.

8. The process according to claim 1, wherein the polyamide moulding composition has a maximum water content of 0.1% by weight.

9. The process according to claim 1, wherein the die lip comprises a heating system, which is inserted within the die lip.

10. The process according to claim 9, wherein the insert heating system is at least one selected from the group consisting of heating cartridges and flat radiators.

Description

(1) The drawings: The numerals in brackets in the text below relate to the drawings, FIG. 1 and FIG. 2.

(2) FIG. 1 shows a prior-art film die having a lip gap (3) and without lip heating system (4).

(3) FIG. 2 depicts a film die used in accordance with the invention, with a heating system (4) for the die lip (2). (1) is the die body.

General Working Example

(4) The water content was determined by the Karl-Fischer method.

(5) The endgroup determinations are made by titration.

(6) Production of the Polyamide Films/Mouldings

(7) The polyamide film is produced by conventional methods, such as extrusion through a slot die, for example, as in the case of flat film extrusion, blown film extrusion or solution casting.

(8) The plastics moulding may, if desired, also be realized in multi-layer configuration, by adhesive bonding, extrusion coating or laminating in downstream operating steps.

(9) The examples were produced on a commercial flat film extrusion line from Collin. In this case, the polyamide is fed preferably in pellet formalthough the form of addition has no effect on the capacity to perform the inventionto a hopper, from which it is conveyed into the extruder. The extruder is composed of a usually metallic barrel, which is heated from the outside, and an extruder screw, which rotates in the extruder about its own axis and therefore conveys the polymer from the feed section after the hopper opening through the extruder. In alternative embodiments, twin-screw or multi-screw extruders can also be used. Through the external heating and the shearing of the polymer in the extruder, the polymer melts and, after the tip of the extruder screw, enters the extrusion die in the form of a film die (or, generally, slot die). Here, the polyamide melt is converted into a flat form and emerges flatly through the nozzle gap from the film die. The film die may also be fed with melt from two or more extruders, thus producing multi-layer films. The plastics web is subsequently cooled on at least one roll and thereafter wound.

(10) The extruder used for the trials, with a closed barrel, two extruder zones heatable separately from one another, and with no devolatilization opening, has a screw diameter of 35 mm with an L/D ratio (Length of the screw/Diameter of the screw) of 25. A commercial three-zone screw is used. For the purposes of the trials, the following temperature settings were made on the extrusion line:

(11) TABLE-US-00001 Intake (zone after the hopper): 240 C. Extruder zone 1: 280 C. Extruder zone 2: 290 C. Transition region: 290 C. Film die: 290 C. Lip heating system: 350 C. (Exception: Comparative Example C4 without lip heating system: 290 C.)

(12) In the trial set-up, the films are produced in single-layer form by what is called the chill roll process, and have a thickness of 50 m. Subsequently the films are inspected for their quality. This is done by visual comparison and evaluation, the comparison being with a reference specimen of marketable grade in terms of optical quality. By optical quality here is meant parameters including streaks, surface quality, number of gel bodies, number of impurities, and number of particles of degraded material. All of the specimens considered to be marketable received an evaluation of (+). The specimens which were just no longer marketable received an evaluation of (), and the specimens which were distinctly or very distinctly unmarketable received the evaluations () and () respectively.

(13) Chill roll process: Melt web is deposited onto a chill roll, at a point at which the other side of the film is not in roll contactthat is, there is no counter-roll or polishing nip.

(14) Polyamide PA1 comprises PA PACM 12 polyamides from Evonik Degussa GmbH, based for example on the composition of TROGAMID CX7323. PA1 is a low-viscosity PA PACM 12, which according to the prior art can be used especially for injection moulding applications.

(15) Polyamide PA2 is a medium-viscosity PA PACM 12.

(16) TABLE-US-00002 Material Water Amino Carboxyl Exam- identifi- Film content endgroups endgroups Endgroup ple cation quality by KF mmol/kg mmol/kg total C1 PA1 <0.01 47 69 116 C2 PA1 0.05 61 69 130 1 PA1 + <0.01 31 67 98 C3 PA2 n.d. 55 47 102 2 PA2 + 0.014 20 68 88 3 PA1 + 0.024 20 88 108 4 PA1 + <0.02 16 75 91 5 PA1 + 0.019 10 79 89 6 PA1 + <0.02 11 73 84 7 PA1 + 0.02 21 69 90 8 PA2 + 0.009 26 64 90 C4 PA2 0.009 26 64 90

(17) The examples denoted with a C are non-inventive, comparative examples. In these polyamides, both endgroups are present each at more than 35 mmol/kg in the polyamide. The visual assessment reports that these films have bubbles and/or streaks in a relevant amount (). The best result is shown by Comparative Example C1, which had no bubbles and few streaks.

(18) From Example 3especially by comparison with Comparative Example C3it is evident that the film quality is determined not by the chain length, which can be read from the endgroup total, but rather from the proportion of the individual endgroup types.

(19) In Comparative Example C4, the same polyamide was used as in Example 7, the temperature of the die lip being set identically to the temperature of the entire film die and of the extruder. In this example, after an extrusion period of 15 minutes, distinct deposits are found on the die lip, and, accordingly, numerous streaks are found on the film.