PROCESS TO PREPARE BIAXIALLY ORIENTED FILM

Abstract

The invention relates to a process for preparing a biaxially oriented film, comprising the following steps: a) Melting a composition comprising at least 50 wt % with respect to the total amount of the composition of a copolyamide comprising: i. At least 75 wt % monomeric units derived from caprolactam, and further monomeric units derived from diamines X and/or diacids Y and/or aminoacids Z in a summed amount of between 0.2 to 25 wt %; or ii. At least 75 wt % monomeric units derived from hexamethylene diamine and adipic acid, and further monomeric units derived from diamines X and/or diacids Y and/or aminoacids Z in a summed amount of between 0.2 to 25 wt %; into a polymer melt; b) Casting the polymer melt through a planar die to form a film of at least one layer and subsequently quenching the film to a temperature of below Tg of the copolyamide; c) Stretching the film obtained after quenching in a direction parallel to the machine (MD-stretching) with a factor of at least 2 at a temperature of at least Tg of the copolyamide; d) Stretching the film obtained after MD stretching in a direction transversal to the machine (TD-stretching) with a factor of at least 2 at a temperature of at least Tg+10° C. of the copolyamide; e) Cooling the obtained film after TD-stretching; f) Heat setting the film obtained after cooling, at a temperature of between Tm−70° C. and Tm of the copolyamide; in which Tg and Tm of the copolyamide are determined as described by ASTM D3418-03. The invention also relates to a biaxially oriented film and food packaging obtainable by this process.

Claims

1. Process for preparing a biaxially oriented film, comprising the following steps: a) Melting a composition comprising at least 50 wt % with respect to the total amount of the composition of a copolyamide comprising: i. At least 75 wt % monomeric units derived from caprolactam, and further monomeric units derived from diamines X and/or diacids Y and/or aminoacids Z in a summed amount of between 0.2 to 25 wt %; or ii. At least 75 wt % monomeric units derived from hexamethylene diamine and adipic acid, and further monomeric units derived from diamines X and/or diacids Y and/or aminoacids Z in a summed amount of between 0.2 to 25 wt %; into a polymer melt; b) Casting the polymer melt through a planar die to form a film of at least one layer and subsequently quenching the film to a temperature of below Tg of the copolyamide; c) Stretching the film obtained after quenching in a direction parallel to the machine (MD-stretching) with a factor of at least 2 at a temperature of at least Tg of the copolyamide; d) Stretching the film obtained after MD stretching in a direction transversal to the machine (TD-stretching) with a factor of at least 2 at a temperature of at least Tg+10° C. of the copolyamide; e) Cooling the obtained film after TD-stretching; f) Heat setting the film obtained after cooling, at a temperature of between Tm−70° C. and Tm of the copolyamide; in which Tg and Tm of the copolyamide are determined as described by ASTM D3418-03.

2. Process according to claim 1, wherein step e) is cooling the obtained film after TD-stretching to a temperature of at most Tg+10° C., and maintaining this temperature on a length of the film of at least 1× width of the film.

3. Process according to claim 1, wherein the composition comprises at least 90 wt % with respect to the total amount of the composition of the copolyamide.

4. Process according to claim 1, wherein at least one of the further monomeric units derived from diamines X, diacids Y, aminoacids Z is cyclic.

5. Process according to claim 1, wherein the further monomeric units derived from diamines X and diacids Y are cyclic.

6. Process according to claim 1, wherein the further monomeric unit derived from diamines X is chosen from the group of isophoronediamine (IPD), bis-(p-aminocyclohexane)methane (PACM), 2,2-Di-(4-aminocyclohexyl)-propane, 3,3′-dimethyl-4-4′-diaminodicyclohexylmethane, p-xylylenediamine, m-xylylenediamine, and 3,6-bis(aminomethyl)norbornane.

7. Process according to claim 1, wherein the further monomeric unit derived from diacids Y is chosen from the group of isophthalic acid (I), terephthalic acid (T), 4-methylisophthalic acid, 4-tert-butylisophthalic acid, 1,4-naphthalenedicarboxylic acid and 2,6-naphthalenedicarboxylic acid.

8. Process according to claim 1, wherein the further monomeric units derived from diamines X and/or diacids Y and/or aminoacids Z in i) or ii) in a summed amount of between 0.5 to 10 wt %, preferably between 0.8 to 5 wt %.

9. Process according to claim 1, wherein the further monomeric units derived from diamines X and diacids Y in i) or ii) are chosen from a combination of isophoronediamine (IPD), bis-(p-aminocyclohexane)methane (PACM), 2,2-Di-(4-aminocyclohexyl)-propane, 3,3′-dimethyl-4-4′-diaminodicyclohexylmethane, p-xylylenediamine, m-xylylenediamine, and 3,6-bis(aminomethyl)norbornane; and isophthalic acid (I), terephthalic acid (T), 4-methylisophthalic acid, 4-tert-butylisophthalic acid, 1,4-naphthalenedicarboxylic acid and 2,6-naphthalenedicarboxylic acid; in a summed amount of between 0.8 to 5 wt %.

10. Process according to claim 2, wherein in step e) the temperature of at most Tg+10° C. is maintained on a length of film of at least 2× width of the film.

11. Process according to claim 1, wherein the temperature in step d) is higher than the temperature in step c).

12. Biaxially oriented film, obtainable by the process according to claim 1.

13. Biaxially oriented film according to claim 12, wherein the biaxially oriented film is a multilayer film.

14. Biaxially oriented film according to claim 12, wherein the width of the film is at least 4 meter.

15. Biaxially oriented film, according to claim 12, wherein the film is at least partially printed.

16. Flexible packaging, comprising a biaxially oriented film, according to claim 12.

Description

EXAMPLES

[0065] 3-layered films were prepared. The inner layer was composed of homopolyamide PA6 or copolyamide 6/IPDT with 1 wt % comonomers. The outer layers composition contained the same (co)polyamide as the inner layer plus 1 wt % antiblock masterbatch in which the weight percentage is with respect to the total weight of composition. Antiblock masterbatch is a conventional masterbatch containing 20 wt % silica with respect to the total weight of antiblock masterbatch, for the purpose of improving the slip and antiblock characteristics of the resulting film.

[0066] The properties of the (co)polyamides used are given in Table 1. Polyamide-6/IPDT is a copolyamide in which 1.0 wt % monomeric units are derived from isophorone diamine X and terephthalic acid Y, besides 99 wt % monomeric units derived from caprolactam. Polyamide-6 is a homopolyamide consisting of monomeric units derived from caprolactam

TABLE-US-00001 TABLE 1 Properties of (co)polyamides Relative viscosity in 90 wt % formic acid Tg Tm PA6 homopolymer 2.7 53° C. 220° C. PA6/IPDT copolymer 2.8 54° C. 219° C.

[0067] The cooling temperature during step e) is shown in table 2. The difference in temperature between end of step d) and lowest temperature in step e) is shown. Results are also shown in table 2.

TABLE-US-00002 TABLE 2 Compositions and results Ex 1 Ex 2 according according Ex 3 to to according to Comparative Comparative Comparative invention invention invention example A Example B Example C Outer PA-6/IPDT + PA-6/IPDT + PA-6/IPDT + PA-6/IPDT + PA-6 + antiblock PA-6 + layers antiblock antiblock antiblock antiblock antiblock Middle PA-6/IPDT PA-6/IPDT PA-6/IPDT PA-6/IPDT PA-6 PA-6 layer Cooling in 10° C. 20° C. 30° C. 0° C.; no 10° C. 0° C.; no step e) cooling cooling Bowing 226 mm 231 mm 226 mm 246 mm 257 mm 255 mm amplitude

[0068] All films exhibited a hot air shrinkage of less than 2.7% in transversal direction, as measured at 160° C. for 5 minutes according to ASTM D 1204-02.

[0069] The process according to the invention results in a film with a low bowing amplitude. Examples 1, 2 and 3 clearly show that with a copolyamide and cooling in step e) a film is obtained with a bowing amplitude significantly lower than compared to a process in which no cooling was performed (Comparative A, or comparative C in which no cooling and a homopolyamide was used). The bowing amplitude was also significantly lower compared to the use of a homopolyamide in combination with cooling (Comparative B).