PROCESS FOR PREPARING A BIAXIALLY ORIENTED MULTILAYERED FILM

Abstract

The invention relates to a process for preparing a biaxially oriented multilayered film, the film comprising at least one layer comprising a polyolefin composition and at least one layer comprising a polyamide composition, the process comprising the steps of: a) Melting a polyamide composition comprising: i. a semi-crystalline polyamide Y comprising: monomeric units derived from caprolactam in an amount of at least 75 wt %; monomeric units derived from an aliphatic diamine in an amount of between 2.5 and 12.5 wt %; monomeric units derived from an aromatic diacid in an amount of between 2.5 and 12.5 wt %; wherein the weight percentage is given with respect to the total weight of the polyamide Y; ii. an amorphous polyamide in an amount of between 2.5 and 50 wt % with respect to the total weight of the polyamide composition; wherein the amorphous polyamide comprises: monomeric units derived from an aliphatic diamine X in an amount of between 30 and 70 wt %; monomeric units derived from an aromatic diacid in an amount of between 30 and 70 wt %; wherein the weight percentage is given with respect to the total weight of the amorphous polyamide; b) Melting a composition comprising a polyolefin; c) Co-extruding at least the melts obtained from a) and b) to form a film of at least two layers; d) Cooling the film to a temperature of at most 50 C., while the film is transported in a direction, referred to as machine direction; e) Stretching the film obtained in step d) with a stretch ratio of at least 13, at a temperature between the Tg of polyamide Y and Tm of the polyolefin, wherein the stretch ratio is defined as being the product of the stretch ratio parallel to the machine direction and the stretch ratio perpendicular to the machine direction. The invention also relates to a biaxially oriented multilayered film obtainable by the process.

Claims

1. Process for preparing a biaxially oriented multilayered film, the film comprising at least one layer comprising a polyolefin composition and at least one layer comprising a polyamide composition, the process comprising the steps of: a) Melting a polyamide composition comprising: b) Melting a composition comprising a polyolefin; c) Co-extruding at least the melts obtained from a) and b) to form a film of at least two layers; d) Cooling the film to a temperature of at most 50 C., while the film is transported in a direction, referred to as machine direction; e) Stretching the film obtained in step d) at a temperature between the Tg of polyamide Y and Tm of the polyolefin; wherein the polyamide composition comprises: i. a semi-crystalline polyamide Y comprising: monomeric units derived from caprolactam in an amount of at least 75 wt %; monomeric units derived from an aliphatic diamine in an amount of between 2.5 and 12.5 wt %; monomeric units derived from an aromatic diacid in an amount of between 2.5 and 12.5 wt %; wherein the weight percentage is given with respect to the total weight of the polyamide Y; ii. an amorphous polyamide in an amount of between 2.5 and 50 wt % with respect to the total weight of the polyamide composition; wherein the amorphous polyamide comprises: monomeric units derived from an aliphatic diamine X in an amount of between 30 and 70 wt %; monomeric units derived from an aromatic diacid in an amount of between 30 and 70 wt %; wherein the weight percentage is given with respect to the total weight of the amorphous polyamide; and wherein in step e) the film is stretched with a stretch ratio of at least 13, the stretch ratio being defined as the product of the stretch ratio parallel to the machine direction and the stretch ratio perpendicular to the machine direction.

2. Process according to claim 1, wherein the amorphous polyamide comprises monomeric units derived from an aromatic diacid selected from terephthalic acid (T), isophthalic acid (I), and naphthalic acid.

3. Process according to claim 1, wherein the amorphous polyamide is PA-XI/XT, wherein X denotes the monomeric units derived from an aliphatic diamine X and I and T denote monomeric units derived from an aromatic diacid isophthalic acid (I) and terephthalic acid (T) respectively.

4. Process according to claim 3, wherein the molar ratio isophthalic acid over terephthalic acid is at least 1.5.

5. Process according to claim 1, wherein the amorphous polyamide comprises monomeric units derived from an aliphatic diamine X selected from 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane and 1,7-diaminoheptane.

6. Process according to claim 1, wherein the amorphous polyamide is PA-6I/6T.

7. Process according to claim 1, wherein the polyamide Y is PA-6/6T, wherein the amount of 6T is between 5 and 25 wt % with respect to the total weight of polyamide Y.

8. Process according to claim 1, wherein the polyamide composition employed at step a) substantially consists of PA-6/6T and PA-6I/6T.

9. Process according to claim 1, wherein the composition of step b) comprises a polyolefin selected from polyethylene, polypropylene, polybutylene, polyoctene, polymethylpentene and copolymers thereof.

10. Process according to claim 1, wherein the process further comprises a step of providing an adhesive layer between the layers originating from a) and b), by co-extruding in step c) a functionalized polyolefin.

11. Process according to claim 10, wherein the functionalized polyolefin is selected from maleic-anhydride functionalized polyethylene, epoxy functionalized polyethylene, maleic-anhydride functionalized polypropylene and epoxy functionalized polypropylene.

12. Process according to claim 1, wherein the stretching ratio is at least 15.

13. Process according to claim 1, wherein stretching in step e) is first performed in a direction parallel to the machine direction and subsequently in a direction perpendicular to the machine direction.

14. Process according to claim 1, wherein stretching in step e) is performed simultaneously in a direction parallel to the machine direction and in a direction perpendicular to the machine direction.

15. Biaxially oriented multilayered film obtainable by the process according to claim 1, comprising at least one layer comprising a polyolefin composition and at least one layer comprising a polyamide composition, and having a stretch ratio of at least 13, wherein the stretch ratio is defined as being the product of the stretch ratio parallel to the machine direction and the stretch ratio perpendicular to the machine direction, wherein the polyamide composition comprises: i. a semi-crystalline polyamide Y comprising: monomeric units derived from caprolactam in an amount of at least 75 wt %; monomeric units derived from an aliphatic diamine in an amount of between 2.5 and 12.5 wt %; monomeric units derived from an aromatic diacid in an amount of between 2.5 and 12.5 wt %; wherein the weight percentage is given with respect to the total weight of the polyamide Y; ii. an amorphous polyamide in an amount of between 2.5 and 50 wt % with respect to the total weight of the polyamide composition; wherein the amorphous polyamide comprises: monomeric units derived from an aliphatic diamine X in an amount of between 30 and 70 wt %; monomeric units derived from an aromatic diacid in an amount of between 30 and 70 wt %; wherein the weight percentage is given with respect to the total weight of the amorphous polyamide.

Description

[0063] The invention will now be elucidated by the following examples.

Multilayer Film Production

Comparative Experiment 1

[0064] 5-layer films were prepared by a co-extrusion cast process. Three single screw extruders were applied: single screw extruder 1: screw diameter 30 mm, L/D=30; single screw extruder 2: screw diameter 25 mm, L/D=25; single screw extruder 3: screw diameter 30 mm, L/D=25. PA-6 Tg=52.3 C. (commercial DSM PA-6 film grade F132C1) was fed to extruder 1 with barrel setting temperatures of barrel 1/2/3/4/5 240/270/265/260/267 C. respectively; screw rotation speed was 30 rpm. As adhesive layer a functionalized polyolefin being a functionalized PP material (commercial grade Yparex OH213) was fed to extruder 2 with barrel setting temperatures of barrel 1/2/3/4 170/220/230/240 C respectively; screw rotation speed was 28 rpm. Polypropylene copolymer (PP) (commercial grade Borealis RD204CF) with a Tm of 151.3 C. was fed to extruder 3 with barrel setting temperatures of barrel 1/2/3/4 170/210/220/230 C respectively; screw rotation speed was 142 rpm. The three extruders were connected to a feed block where the flow pattern of the three different types of polymers resulted in a 5-layer system: a PA-6 mid-layer, two PP layers at the outside and two PP-tie layers in between; PP/PP-tie/PA/PP-tie/PP. This feed block is connected to a film die with a slot die with adjustable die-width. Temperature setting of feed block and film die was 250 C. The length of the slot die was 300 mm and the die-width was 1 mm. The film was taken up and cooled on a chill role with a chill role temperature of 20 C. By adjusting the winding speed of the chill role to 5.1 m/min, the thickness of the 5-layer cast film was fixed at 250 m and resulted in individual layer thicknesses of PP/PP-tie/PA/PP-tie/PP: 95/5/50/5/95 m. The film was collected at a role and directly after production the film was packed in an alumina bag to prevent contact with moisture as much as possible.

Comparative Experiment 2

[0065] For this comparative experiment, PA-6 material from comparative experiment 1 was replaced by a granular mixture of 80 wt % PA-6 (commercial DSM PA-6 film grade F132C1) and 20 wt % of Novamid X21; PA-6I/6T; an amorphous polymer based on hexamethylene diamine, terephthalic acid (T) and isophthalic acid (I) with molar ratio I/T=2. Except for this polyamide material replacement, the procedure to obtain the 5-layer film was identical to the procedure as described in comparative experiment 1. The melt of the 5-layer film material at die-exit was optical transparent indicating that the mixing efficiency of the single layer extruder was sufficient to obtain proper mixing of PA-6 and PA-6I/6T at a scale smaller than the wavelength of light.

Example 1

[0066] For this example, PA-6 material from comparative experiment 1 was replaced by a granular mixture of 90 wt % DSM product Novamid 2620; PA-6/6T with a Tg of 57.5 C. (a copolymer based on 90 wt % caprolactam and 10 wt % 6T (6: hexamethylene diamine; T: terephthalic acid) and 10 wt % of Novamid X21; PA-6I/6T (I/T molar ratio=2). Except for this polyamide material replacement, the procedure to obtain the 5-layer film was identical to the procedure as described in comparative experiment 1. The melt of the 5-layer film material at die-exit was optical transparent indicating that the mixing efficiency of the single layer extruder was sufficient to obtain proper mixing of Novamid 2620 and Novamid X21 at a scale smaller than the wavelength of light.

Example 2

[0067] For this example, PA-6 from comparative experiment 1 was replaced by a granular mixture of 80 wt % DSM product Novamid 2620; PA-6/6T with a Tg of 57.5 C. (a copolymer based on 90 wt % caprolactam and 10 wt % 6T (6: hexamethylene diamine; T: terephthalic acid) and 20 wt % of Novamid X21; PA-6I/6T. Except for this polyamide material replacement, the procedure to obtain the 5-layer film was identical to the procedure as described in comparative experiment 1. The melt of the 5-layer film material at die-exit was optical transparent indicating that the mixing efficiency of the single layer extruder was sufficient to obtain proper mixing of Novamid 2620 and Novamid X21 at a scale smaller than the wavelength of light.

Stretching Experiments

[0068] Comparative experiment 1

[0069] Planar sequential stretching experiments on the 5-layer films were performed on a batchwise Karo-IV laboratory stretching device as commercialized by Brueckner Machinenbau GmbH.

[0070] After opening the alumina bag containing the film role of the above described film as produced in comparative experiment 1, sheets with lateral dimensions 90*90 mm.sup.2 were cut from the film and stored under dry conditions. A sheet was positioned in the clamping device of the Karo stretcher. In the first oven where the MD (machine direction) stretching step occurs, temperature setting=70 C.; in the second oven where the TD (transverse direction) stretching step occurs, temperature setting=120 C. The film is transported in the first oven and kept in this oven for 16 s. The film is stretched at a speed of 200%/s. Subsequently, the film is transported to the second oven, kept for 15 s and stretched at a stretching speed of 100%/s. The maximum stretching ratio obtained without rupture setting in is .sub.MD*.sub.TD=3.1*3.1=9.6. For higher stretching levels rupture of the film sets in.

Comparative Experiment 2

[0071] Comparative experiment 1 was repeated with only one change: instead of film from comparative experiment 1 film from comparative experiment 2 was used. The maximum stretching ratio obtained without rupture setting in was .sub.MD*.sub.TD=2.8*4.0=11.2.

Example 1

[0072] Comparative experiment 1 was repeated with only one change: instead of film from comparative experiment 1 film from example 1 was used. The maximum stretching ratio obtained without rupture setting in for this film was surprisingly high: .sub.MD*.sub.TD=3.7*4.2=15.5.

Example 2

[0073] Comparative experiment 1 was repeated with only one change: instead of film from comparative experiment 1 film from example 1 was used. The maximum stretching ratio obtained without rupture setting was even higher compared to example 1: .sub.MD*.sub.TD=3.8*4.6=17.5.

[0074] These examples clearly show that the maximum level of planar stretching of these 5-layer films was governed by the layer comprising polyamide and that changes in the type of polyamides applied in the polyamide layer strongly affect the maximum level of stretching. A composition comprising PA-6/6T and PA-6I/6T clearly showed significant higher maximum stretching levels compared to the comparative experiments.

[0075] In view of the similarity of the stretching processes and conditions, it is in the line of expectation that the observed improvement in stretchability for sequential planar stretching processes also holds for simultaneous planar stretching processes and for so-called double-bubble and triple-bubble tubular stretching processes.