BIAXIALLY ORIENTED FILM HAVING A PARTICLE-CONTAINING POROUS LAYER

Abstract

The invention relates to a biaxially oriented single-layer or multilayer porous film which comprises at least one porous layer and said layer comprises at least one propylene polymer, at least one -nucleating agent and particles, said particles having a melting point of over 200 C. and at most an agglomerate or at most a particle having a particle size of >1 m being detectable on a REM recording of a film sample of 10mm2.

Claims

1.-26. (canceled)

27. A biaxially oriented, single- or multi-layered porous film which comprises at least one porous layer and this layer contains at least one propylene polymer, at least one -nucleation agent and particles, wherein the particles have a melting point of more than 200 C. and at most one agglomerate or at most one particle with a particle size of >1 m is detectable on a SEM image of a 10 mm.sup.2 film sample of the biaxially oriented, single- or multi-layered porous film.

28. The film as claimed in claim 27, wherein the porosity is produced by transformation of -crystalline polypropylene upon stretching the film, wherein at least one -nucleation agent is present in the film.

29. The film as claimed in claim 27, wherein the film contains 2% to 60% by weight of particles with respect to the weight of the porous layer.

30. The film as claimed in claim 27, wherein the -nucleation agent is a calcium salt of pimelic acid and/or of suberic acid and/or an iron oxide and/or nickel pimelate.

31. The film as claimed in claim 27, wherein no agglomerates and no particles with a particle size of >1 m can be detected on a SEM image of a 10 mm.sup.2 film sample.

32. The film as claimed in claim 27, wherein the particles have a mean particle size of <1 m.

33. The film as claimed in claim 27, wherein the particles are not vacuole-initiating particles.

34. The film as claimed in claim 27, wherein the porous layer of the film contains at least 65% by weight of propylene polymers.

35. The film as claimed in claim 27, wherein the porous layer of the film contains 50% to 85% by weight of propylene polymer, 15% to 50% by weight of propylene block copolymer and 50 to 10000 ppm of -nucleation agent.

36. The film as claimed in claim 27, wherein the density of the film is in the range 0.1 to 0.5 g/cm.sup.3 and it has a Gurley value of less than 150 s.

37. The film as claimed in claim 27, wherein the particles are inorganic spherical particles.

38. The film as claimed in claim 27, wherein the particles are not vacuole-initiating particles, wherein vacuole-initiating particles are particles which, upon biaxial stretching of a polypropylene film without -nucleation agents, reduce the density of the polypropylene film to <0.85 g/cm.sup.3.

39. The film as claimed in claim 27, wherein the particles are inorganic particles.

40. The film as claimed in claim 27, wherein the particles are TiO.sub.2.

41. The film as claimed in claim 27, wherein the particles are organic particles.

42. A process for the production of a porous film by process A or process B wherein process A comprises the following steps: (i) extruding an at least single-layered polypropylene film, in which propylene polymer and -nucleation agent and particles with a melting point of more than 200 C. are melted in an extruder and extruded through a flat nozzle onto a take-off roller, (ii) next, the extruded molten film is cooled and solidified, with the formation of -crystallites, (iii) next, the film from step (ii) is stretched in the longitudinal direction and thereafter in the transverse direction, and (iv) the process speed is 5 to 200 m/min or process B which comprises the following steps: (i) extruding an at least single-layered polypropylene film, in which propylene polymer and no -nucleation agent and particles with a melting point of more than 200 C. are melted in an extruder and extruded through a flat nozzle onto a take-off roller, (ii) next, the extruded molten film is cooled and solidified, with the formation of -crystallites, (iii) next, this film is stretched in the longitudinal direction and thereafter in the transverse direction, wherein the film is produced at a process speed of 5 m/min to 200 m/min and in that at most one agglomerate or at most one particle with a particle size of >1 m is detectable on a SEM image of a 10 mm2 film sample of the biaxially oriented, single- or multi-layered porous film.

43. The process as claimed in claim 42, wherein the particles are mixed with at least one polypropylene to form a batch and the particle-containing batch is mixed with polypropylene and melted in the extruder.

44. The process as claimed in claim 42, wherein a dispersing agent is added during the manufacture of the particle-containing batch.

45. A high energy or high performance systems containing the film as claimed in claim 27.

46. A biaxially oriented, single- or multi-layered film A or B which comprises A. at least one porous layer and this layer contains at least one propylene polymer, a -nucleation agent and particles, wherein the particles have a melting point of more than 200 C. and a mean particle size of <1 m or B. at least one porous layer and this layer contains at least one propylene polymer and particles, wherein the particles have a melting point of more than 200 C. and a particle size of <1 m, wherein the porous layer contains no -nucleation agents.

47. The film as claimed in claim 46, wherein the film is film B and further contains no block copolymers and the porous layer has a Gurley value of less than 500 s.

48. The biaxially oriented, single- or multi-layered film as claimed in claim 46, wherein at most one agglomerate or at most one particle with a particle size of >1 m is detectable on a SEM image of a 10 mm.sup.2 film sample of the biaxially oriented, single- or multi-layered porous film.

Description

EXAMPLES

Example A

Batch Production

[0111] In a first step, a batch formed from polymer and particles was produced which was then used in the subsequent experiment. This batch was produced as follows:

[0112] 60% by weight of a TiO.sub.2 pigment (Huntsmann TR28) together with 0.04% by weight of calcium pimelate as the nucleation agent (calcium pimelate) were mixed, melted and granulated in a twin-screwed extruder at a temperature of 230 C. and with a screw rotation speed of 270 rpm with 39.96% by weight of granulated isotactic polypropylene homopolymer (melting point 162 C., MFI 3 g/10 min). The SEM images of the batch exhibited finely divided TiO.sub.2 particles with a particle size of 20 to 500 nm with no agglomerates over 1 m. The activity of the batch was at a value of 91% for the second heating.

Example B

Film Production

Film Example: 1

[0113] After the extrusion process, a double-layered pre-film was extruded from a wide slit nozzle at an extrusion temperature of 240 C. to 250 C. The throughputs of the extruder were selected here such that the ratio of the thicknesses of the layers A:B was 1:2. The multi-layered pre-film was initially drawn off onto a cooling roller and cooled. Next, the pre-film was oriented in the longitudinal and transverse directions and finally fixed. The layers of film had the following composition:

Composition of Layer A:

[0114] 40% by weight TiO.sub.2 batch in accordance with Example A formed from:

TABLE-US-00001 60% by weight TiO.sub.2 Approx. 39.96% by weight propylene homopolymer 0.04% by weight nucleation agent
respectively with respect to the batch 60% by weight of polypropylene mixture, formed from:

[0115] Approx. 60% by weight propylene homopolymer (PP) with an n-heptane soluble fraction of 4.5% by weight (with respect to 100% PP) and a melting point of 165 C.; and a melt flow index of 3.2 g/10 min at 230 C. and 2.16 kg load (DIN 53 735), and

[0116] Approx. 39.96% by weight of propylene-ethylene block copolymer with an ethylene fraction of approx. 5% by weight with respect to the block copolymer and a melt flow index (230 C. and 2.16 kg) of 6 g/10 min

[0117] 0.04% by weight of nano Ca pimelate as the -nucleation agent

[0118] respectively with respect to the mixture.

Composition of Layer B:

[0119] Approx. 80% by weight of propylene homopolymer (PP) with an n-heptane soluble fraction of 4.5% by weight (with respect to 100% PP) and a melting point of 165 C.; and a melt flow index of 3.2 g/10 min at 230 C. and 2.16 kg load (DIN 53 735), and

[0120] Approx. 19.96% by weight of propylene-ethylene block copolymer with an ethylene fraction of approx. 5% by weight with respect to the block copolymer and a melt flow index (230 C. and 2.16 kg) of 6 g/10 min

[0121] 0.04% by weight of nano Ca pimelate as the -nucleation agent.

[0122] The layers of film additionally contained stabilizers and neutralization agents in the usual quantities. The nano Ca-pimelate was produced as described in Examples 1a or 1b of WO2011047797.

[0123] After extrusion, the polymer mixture was drawn over a first take-off roller and a further roller trio, cooled and solidified, then longitudinally stretched, transversely stretched and fixed; in detail, the following conditions were selected: [0124] Extrusion: extrusion temperature 245 C. [0125] Cooling roller: temperature 125 C. [0126] Take-off speed: 1.5 m/min (dwell time on the take-off roller: 55 sec) [0127] Longitudinal stretching: preheat rollers: 92 [0128] stretching roller T=90 C. [0129] Longitudinal stretching by factor of 3.6 [0130] Transverse stretching: heating zone T=145 C. [0131] Stretching zone T=145 C. [0132] Transverse stretching by factor of 4.8 [0133] Convergence: 13%

[0134] A roll of 1500 m run length was run with no tearing. The porous film produced in this manner was about 30 m thick and had a density of 0.33 g/cm.sup.3 and had a uniform, white-opaque appearance. The porosity was 66% and the Gurley value was 160 s. SEM images of the surface of side A exhibited no TiO.sub.2 agglomerates and no particles with a particle size of >1 m on an examined surface area of 10 mm.sup.2.

Film Example 2

[0135] A double-layered film was produced as described in Film Example 1, with the difference that the take-off speed was increased to 2.5 m/min. The composition of the layers as well as the other process conditions were unchanged. Despite the increased take-off speed, 800 m run lengths were prepared without tearing. The thickness was reduced to 20 m in this case. Despite the shorter dwell time on the take-off roller, the Gurley value was surprisingly reduced to approx. 140 seconds. In this film too, no TiO.sub.2 agglomerates and no particles with a particle size of >1 m on a surface area of 10 mm.sup.2 were identified on side A using SEM.

Film Example 3

[0136] A double-layered film was produced as described in Film Example 1, with the difference that the layer B now had the same composition as layer A. The composition of layer A as well as the process conditions were unchanged. Thus, in fact, a single-layered film was produced. The thickness of the film was 31 m and the Gurley value was surprisingly reduced to less than 100 seconds. This composition also exhibited very good run stability, and thus a roll with a 2000 m run length was produced. Both sides of the film exhibited no TiO.sub.2 agglomerates and no particles with a particle size of >1 m on a surface area of 10 mm.sup.2 in SEM.

Film Example 4

[0137] An actual single-layered film with 24% by weight of TiO.sub.2 was produced as described in Film Example 3. The take-off speed (as in Film Example 2) was increased to 2.5 m/min. the (same) composition of the layers A and B as well as the remaining process conditions were unchanged. With the increased take-off speed of 2.5 m/min, a roll of 1000 m run length was produced without tearing. The thickness here was reduced to 20 m and the Gurley value surprisingly remained below 100 seconds, as was the case for Ex 3. In this film, on both sides, no agglomerates and no particles with a particle size of >1 m on a surface area of 10 mm.sup.2 were identified using SEM.

Film Example 5

[0138] A single-layered film with 24% by weight of TiO.sub.2 was produced as described in Film Example 3, with the difference that the polypropylene mixture now did not contain any nucleation agents and thus had the following composition: approx. 60% by weight of propylene homopolymer (PP) with a n-heptane soluble proportion of 4.5% by weight (with respect to 100% PP) and a melting point of 165 C.; and a melt flow index of 3.2 g/10 min at 230 C. and under 2.16 kg load (DIN 53 735), and approx. 40% by weight of propylene-ethylene block copolymer with an ethylene fraction of approx. 5% by weight with respect to the block copolymer and a melt flow index (230 C. and 2.16 kg) of 6 g/10 min.

[0139] Otherwise, the composition of the layer and the composition of the TiO.sub.2 batch as well as the process conditions were unchanged compared with Example 3.

[0140] Here again, a roll of 1000 m run length could be prepared without tearing. The thickness of the film was 28 m. Surprisingly, the Gurley value, as was the case with Film Example 3, remained below 100 seconds. In this film too, in both layers no agglomerates and no particles with a particle size of >1 m over a surface area of 10 mm.sup.2 were identified using SEM.

Film Example 6

[0141] A double-layered film was produced as described in Film Example 1, with the difference that in layer A, the concentration of TiO.sub.2 batch was increased to 60% and the fraction of polypropylene mixture was reduced to 40% so that 36% by weight of TiO.sub.2 was present in layer A. The composition of layer B as well as the process conditions were unchanged. Here again, this composition exhibited very good run stability and a roll with a 1000 m run length was produced. The thickness of the film was 27 m and the Gurley value was surprisingly reduced to less than 100 seconds. Side A of the film exhibited no agglomerates of >1 m over a surface area of 10 mm.sup.2 using SEM. However, one particle with a particle size of approx. 1.2 m was identified.

Film Example 7

[0142] A double-layered film was prepared under the same conditions and using the same formulation as in Film Example 2. However, the take-off speed was increased to 5 m/min, and thus the final film speed was increased to 19 m/min. In order to produce a film with the same thickness under these conditions, the extrusion throughput was also doubled. This composition also exhibited a very good run stability at the higher process speed and a roll with a 1000 m run length was produced. The thickness of the film was 27 m and the Gurley value compared with Example 2 was raised to 170 seconds, wherein the -content measured for the pre-film was reduced slightly to 57%. Side A of the film exhibited no agglomerates and no particles with a particle size of >1 m over a surface area of 10 mm.sup.2 using SEM.

Film Example 8

[0143] A double-layered film was prepared under the same conditions and using the same formulation as in Film Example 2. However, the take-off speed was increased to 7.5 m/min, and thus the final film speed was increased to 28 m/min. In order to produce a film with the same thickness under these conditions, the extrusion throughput was also doubled. This composition also exhibited a very good run stability at the higher process speed and a roll with a 1000 m run length was produced. The thickness of the film was 24 m and the Gurley value compared with Example 7 was raised to 198 seconds, wherein the -content measured for the pre-film was reduced slightly to 54%. Side A of the film exhibited no agglomerates and no particles with a particle size of >1 m over a surface area of 10 mm.sup.2 using SEM.

Film Example 9

[0144] A double-layered film was prepared under the same conditions and using the same formulation as in Film Example 2. However, the take-off speed was increased to 10 m/min, and thus the final film speed was increased to 37 m/min. In order to produce a film with the same thickness under these conditions, the extrusion throughput was also doubled. This composition also exhibited a very good run stability at the higher process speed, and a roll with a 1000 m run length was produced. The thickness of the film was 24 m and the Gurley value compared with Example 8 was raised to 222 seconds, wherein the -content measured for the pre-film was reduced slightly to 51%. Side A of the film exhibited no agglomerates and no particles with a particle size of >1 m over a surface area of 10 mm.sup.2 using SEM.

Film Example 10

[0145] A double-layered film was prepared under the same conditions and using the same formulation as in Film Example 2. However, in layer A and layer B, the propylene-ethylene block copolymer was changed by increasing the proportion of propylene homopolymer (PP). This composition again exhibited a very good run stability, despite missing the block copolymer, and a roll with a 1000 m run length was produced. The thickness of the film was 27 m and the Gurley value was 170 seconds. This composition also exhibited a very good run stability, and so a roll with 1000 m run length was produced. Side A of the film exhibited no agglomerates and no particles with a particle size of >1 m over a surface area of 10 mm.sup.2 in SEM.

Comparative Example 1

[0146] A film was produced under the same conditions as in Film Example 1, with the difference that for layer A the same mixture as for layer B was used, and thus the TiO.sub.2 addition was dispensed with. The composition of layer B as well as the process conditions were unchanged. In actual fact, a single-layered film was produced. The thickness of the film was 29 m and the Gurley value was 200 seconds.

Comparative Example 2

[0147] A film was produced under the same conditions as in Film Example 1, with the difference that the take-off speed here was increased to 2.5 m/min. With the higher take-off speed, 500 m run length were prepared without tearing. The thickness was reduced to 20 m and the Gurley value increased to 280 seconds.

Comparative Example 3

[0148] A double-layered film was produced under the same conditions as in Film Example 1, with the difference that the composition of the batch for layer A was changed. The TiO.sub.2 was replaced by an Al.sub.2O.sub.3 with a mean particle diameter of 3 m. The composition of the polypropylene mixture for layer A, the composition of layer B as well as the process conditions were unchanged. However, in fact a film could not be produced because of the large amount of tearing.

Comparative Example 4

[0149] A double-layered film was produced under the same conditions as in Film Example 1. However, the TiO.sub.2 was introduced by direct addition to the extruder instead of using a batch. Frequent tearing occurred during production. The few films which were produced in principle had the same properties as the film of Example 1. Side A of the film displayed several agglomerates with a size of 1 to 3 m over a surface area of 10 mm.sup.2 using SEM.

TABLE-US-00002 Comp Ex 1 Comp Ex 2 Ex 1 Ex 2 Ex 3 Ex 4 Ex 5 Ex 6 Particle / / TiO.sub.2 TiO.sub.2 TiO.sub.2 TiO.sub.2 TiO.sub.2 TiO.sub.2 material Mean particle nm 200 200 200 200 200 200 size Particle shape spherical spherical spherical spherical spherical spherical Conc of % 0.04 0.04 0.04 0.04 0.04 0.04 0 0.04 nucleation agent Film structure single- single- double double single- single- single- double layer layer layer- layer- layer layer layer layer- A/B A/B A/B Conc. of TiO.sub.2 % by 0 0 24 24 24 24 24 36 in layer A wt Ratio A/B 1:2 1:2 1:2 Run length m 500 500 1600 800 2000 1000 1000 800 without tearing Take-off speed m/min 1.5 2.5 1.5 2.5 1.5 2.5 1.5 1.5 Agglomerates 0 0 0 0 0 1 with a size >1 m over 10 mm.sup.2 Process speed m/min 5.92 9.25 5.92 9.25 5.92 9.25 5.92 5.92 Thickness m 29 20 30 20 31 20 28 27 Density kg/m.sup.3 0.32 0.33 0.34 0.35 0.35 0.37 0.37 0.33 Porosity % 60.5 59.5 58.5 57.5 57.5 55.5 55.5 59.5 Maximum pore nm 65 63 79 76 146 152 146 84 size Mean pore size nm 57 54 58 57 119 109 112 67 Gurley value s/100 cm.sup.3 199 280 160 138 91 98.9 99.9 144 -content, pre- % 66 64 63 64 66 62 61 66 film Ex 7 Ex 8 Ex 9 Ex 10 Particle material TiO.sub.2 TiO.sub.2 TiO.sub.2 TiO.sub.2 Mean particle size nm 200 200 200 200 Particle shape spherical spherical spherical spherical Conc of nucleation % 0.04 0.04 0.04 0.04 agent Film structure double layer- double layer- double layer- double layer- A/B A/B A/B A/B Conc of TiO.sub.2 in % by 24 24 24 24 layer A wt Ratio A/B 1:2 1:2 1:2 1:2 Run length without m 1000 1000 1000 1000 tearing Take-off speed m/min 5 7.5 10 2.5 Agglomerates with a 0 0 0 0 size >1 m over 10 mm.sup.2 Process speed m/min 18.50 27.75 37.00 9.25 Thickness m 27 24 21 30 Density kg/m.sup.3 0.37 0.39 0.41 0.34 Porosity % 55.5 53.5 51.5 58.5 Maximum pore size nm 64 66 69 76 Mean pore size nm 56 57 57 57 -content, pre-film % 55 53 50 72 Gurley value s/100 cm.sup.3 170 196 222 170