FLUORORESIN POROUS FILM AND PREPARATION METHOD THEREOF

Abstract

The present invention relates to a fluororesin porous film in which, based on the total thickness of the fluororesin porous film composed of a single 5 m to 300 m layer, a thickness ratio of nodes distributed on any one surface shows a difference of 5% or more compared to a thickness ratio of nodes distributed on the other surface forming the remaining part, a method for preparing the same, and a vent filter including the porous film.

Claims

1. A fluororesin porous film comprising a fluororesin and nodes, the film composed of a single layer of 5 m to 300 m, wherein, based on a total thickness of the fluororesin porous film, a thickness ratio of the nodes distributed on one surface of the film has a difference of at least 5% compared to a thickness ratio of the nodes distributed on the other surface of the film.

2. The fluororesin porous film according to claim 1, wherein the difference is 5% to 40%.

3. The fluororesin porous film according to claim 1, wherein a thickness of the nodes distributed on one surface is in the range of 0.1 m to 10 m, and a thickness of the nodes distributed on the other surface is in the range of 0.105 m to 15 m.

4. The fluororesin porous film according to claim 1, wherein the film has water pressure resistance of 10 to 300 kPa under air permeability of 0.5 to 100 s/100 cc.

5. The fluororesin porous film according to claim 1, wherein the film has an average pore size of 150 nm to 900 nm and a maximum pore size of 300 nm to 2500 nm.

6. A method for preparing a fluororesin porous film comprising the steps of: preparing a preform using a fluororesin containing composition; extruding the preform stretching the extruded preform; and positioning one surface of the stretched preform in contact with a heating device equipped with a roll and then firing it the surface of the stretched preform that is in contact with the heating device at 300 to 500 C. for 1 second to 120 seconds.

7. The method for preparing a fluororesin porous film according to claim 6, wherein the heating device includes a heating roll, a nipping roll, or a roll equipped with a tension adjusting means for of applying a force in the Z-axis direction.

8. The method for preparing a fluororesin porous film according to claim 6, wherein the step of stretching the extruded preform includes: i) uniaxially stretching the extruded preform under the condition where a longitudinal or transverse stretch ratio is 2 to 50 times; or ii) uniaxially stretching the extruded preform under the condition where a longitudinal or transverse stretch ratio is 2 to 50 times, and biaxially stretching the uniaxially stretched preform at least one time under the condition where a longitudinal or transverse stretch ratio is 2 to 50 times.

9. The method for preparing a fluororesin porous film according to claim 1, wherein the fluororesin includes at least one fluorine-based compound selected from the group consisting of polytetrafluoroethylene (PTFE), a tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), a tetrafluoroethylene-hexafluoropropylene copolymer (FEP), an ethylene-tetrafluoroethylene copolymer resin (ETFE), a tetrafluoroethylene-chlorotrifluoroethylene copolymer (TFE/CTFE), and an ethylene-chlorotrifluoroethylene resin (ECTFE).

10. A vent filter comprising the fluororesin porous film of claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0060] FIG. 1 schematically shows a method of reducing porosity by firing only the surface with heat in the porous film of the present invention.

[0061] FIG. 2 is a graph showing the relationship between the water pressure resistance and the air permeability according to examples of the present invention and comparative examples.

[0062] FIG. 3 is a scanning electron microscope image showing differences in node distribution on a first surface and a second surface of the surfaces of the porous films of Comparative Example 1 and Example 1.

[0063] FIG. 4 is a scanning electron microscope image showing differences in node distribution on a first surface and a second surface of the surfaces of the porous films of Comparative Example 2 and Example 2.

[0064] FIG. 5 is a scanning electron microscope image showing differences in node distribution on a first surface and a second surface of the surfaces of the porous films of Comparative Example 3 and Example 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0065] Hereinafter, the present invention will be described in more detail by way of the following examples. However, these examples are set forth to illustrate the invention, and the scope of the invention is not limited thereto.

Example 1: Preparation of PTFE Porous Film

[0066] 100 parts by weight of polytetrafluoroethylene powder (CD145E, AGC) was mixed with 22 parts by weight of a liquid lubricant (trade name: Isopar H, Exxon Co.) to prepare a single-layer preform.

[0067] Then, the single-layer preform was extruded at a temperature of 50 C. at a rate of 50 mm/min to prepare a sheet having a thickness of about 300 The sheet thus prepared was heated at a temperature of about 200 C. to completely dry the liquid lubricant.

[0068] After the drying step, the preform was uniaxially stretched under the conditions shown in Table 1 below.

[0069] Subsequently, the stretched preform was fired at a temperature of 360 C. for 10 seconds by using a heating roll to obtain a PTFE porous film.

Example 2: Preparation of PTFE Porous Film

[0070] 100 parts by weight of polytetrafluoroethylene powder (CD145E, AGC) was mixed with 26 parts by weight of a liquid lubricant (trade name: Isopar H, Exxon Co.) to prepare a single-layer preform.

[0071] Then, the single-layer preform was extruded at a temperature of 50 C. at a rate of 50 mm/min to prepare a sheet having a thickness of about 300 The sheet thus prepared was heated at a temperature of about 200 C. to completely dry the liquid lubricant.

[0072] After the drying step, the preform was uniaxially stretched under the conditions shown in Table 1 below.

[0073] Subsequently, the stretched preform was fired at a temperature of 360 C. for 10 seconds by using a heating roll to obtain a PTFE porous film.

Example 3: Preparation of PTFE Porous Film

[0074] 100 parts by weight of polytetrafluoroethylene powder (6J, MDF) was mixed with 22 parts by weight of a liquid lubricant (trade name: Isopar H, Exxon Co.) to prepare a single-layer preform.

[0075] Then, the single-layer preform was extruded at a temperature of 50 C. at a rate of 50 mm/min to prepare a sheet having a thickness of about 300 m. The sheet thus prepared was heated at a temperature of about 200 C. to completely dry the liquid lubricant.

[0076] After the drying step, the preform was uniaxially stretched under the conditions shown in Table 1 below.

[0077] Subsequently, the stretched preform was fired at a temperature of 360 C. for 10 seconds by using a heating roll to obtain a PTFE porous film.

Comparative Example 1: Preparation of PTFE Porous Film

[0078] A PTFE porous film was obtained in the same manner as in Example 1, except that in the firing step, a hot air system was used instead of a heating roll.

Comparative Example 2: Preparation of PTFE Porous Film

[0079] A PTFE porous film was obtained in the same manner as in Example 2, except that in the firing step, a hot air system was used instead of a heating roll.

Comparative Example 3: Preparation of PTFE Porous Film

[0080] A PTFE porous film was obtained in the same manner as in Example 3, except that in the firing step, a hot air system was used instead of a heating roll.

Experimental Examples

[0081] The air permeability, the maximum pore size, the node thickness, and the water pressure resistance were measured for the examples and comparative examples according to a conventional method, and the results are shown in Table 1 and FIGS. 2 to 5.

TABLE-US-00001 TABLE 1 Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 1 Example 2 Example 3 Kind of resin CD145E CD145E 6J CD145E CD145E 6J Isopar content 22 26 22 22 26 22 (parts by weight) Stretch 200 200 300 200 200 300 temperature ( C.) Stretch ratio X2.5 X2.5 X3 X2.5 X2.5 X3 Heat setting 360 C. 360 C. 360 C. 360 C. 360 C. 360 C. method firing firing firing Hot air Hot air Hot air system by system by system by system system system heating roll heating roll heating roll Air 46 21 9 46 20 10 permeability (s/100 cc) Max. Pore size 690 998 1353 790 1178 1903 (nm) First surface 39.4% 34% 14.5% 4.5% 3% 0.5% vs. second surface node thickness difference Water 180 125 60 165 105 45 pressure resistance (kPa)

[0082] As can be seen in Table 1 and FIGS. 2 to 6 above, it can be confirmed that the PTFE porous films prepared in Examples 1 to 3 have improved water pressure resistance characteristics under the same air permeability condition as compared to Comparative Examples 1 to 3.

[0083] In particular, it can be confirmed that the present invention can effectively prevent penetration of water because the thickness of nodes on one surface shows a difference of 14.5% to 39.4% compared to the thickness on the other surface (second surface) in forming of the porous film.