GAS-TIGHT TRACK-ETCHED MEMBRANES FOR EMERGENCY VENTING

Abstract

The invention provides a gas-tight membrane for use as a burst membrane, especially for emergency venting in connection with batteries, e.g. for cars, e-bikes, handheld devices, electronic cigarettes, energy storing devices or heavy-duty tools. The membrane comprises a basic membrane having indentations obtained by an incomplete track-etch treatment applied to the basic membrane. Further, the invention provides a method for preparing the gas-tight membrane by an incomplete track-etch treatment applied to both sides of a basic membrane.

Claims

1. Use of a gas-tight membrane comprising a basic membrane having indentations on one or both sides of the membrane, which indentations are partially developed pores obtained by an incomplete track-etch treatment applied to the basic membrane as a burst membrane, especially for emergency venting in connection with batteries, e.g. for cars, e-bikes, handheld devices, electronic cigarettes, energy storing devices or heavy-duty tools.

2. Gas-tight membrane suitable for the use according to claim 1, comprising a basic membrane having indentations both sides of the membrane, which indentations are partially developed pores, the pores on both sides having an asymmetrical orientation against each other.

3. Gas-tight membrane according to claim 2, wherein the pores have a conical or cylindrical shape.

4. Gas-tight membrane according to claim 2, wherein the pores on different sides of the membrane have the same or different penetration depth.

5. Gas-tight membrane according to claim 2, having 1,000 to 110.sup.10 partially developed pores per cm.sup.2, preferably 110.sup.6 to 510.sup.8 partially developed pores per cm.sup.2 on one or both sides of the membrane and/or wherein the pore size is 0.1 to 20 m, preferably 1 to 10 m, as determined by electron microscopy.

6. Gas-tight membrane according to claim 2, wherein the standard deviation of the distribution of partially developed pores per square unit is up to 30%, preferably from 1% to 10% and typically between 2% to 5%.

7. Gas-tight membrane according to claim 2, wherein the standard deviation of pore size is between 3% and 10% and/or wherein the deviation of a median burst pressure is equal to or below 50%, preferably equal to or below 25% and most preferably equal to or below 20%.

8. Gas-tight membrane according to claim 2, wherein the membrane comprises partially developed pores on both sides of the membrane in a manner, which provides for different burst pressures for the different sides.

9. Gas-tight membrane according to claim 2, wherein the membrane material is selected from polyethylene terephthalate (PET), polycarbonate (PC), polyimide (PI), polyvinylidene fluoride (PVDF), polyethylene naphthalate (PEN), polyether ether ketone (PEEK), and ethylene tetrafuoroethylene (ETFE).

10. Gas-tight membrane according to claim 2, wherein the membrane thickness lies between 5 and 200 m, preferably 10 to 75 m, and/or wherein a pore-free bridge of membrane material constitutes between 10% and 50% of the thickness of the basic membrane.

11. Method for producing a gas-tight membrane according to claim 2 by an incomplete track-etch treatment applied to both sides of a basic membrane, in which the incomplete track-etch treatment comprises the steps: an irradiation treatment by heavy ions with a lower energy than needed to penetrate the whole thickness of the basic membrane, optionally a subsequent UV activation, and an etching treatment, to obtain indentations on both sides of the basic membrane, wherein the incomplete track-etch treatment is performed under conditions preventing the formation of pores that completely penetrate the thickness of the basic membrane.

12. Method according to claim 11, wherein the basic membrane comprises a polymer foil such as a PET, PC, PI, PEN, PVDF, PEEK, or ETFE foil.

13. The method according to claim 11, wherein track-etch treatment on both sides of the basic membrane is carried out under the same of different conditions, in particular using the same or different ion energy in the irradiation treatment and/or the same of different time and conditions in the etching treatment.

Description

FIGURES

[0036] FIG. 1 shows a one-sided gas-tight track-etched membrane (symbolical representation, the tracks can be conical or cylindrical);

[0037] FIG. 2 shows a two-sided gas-tight symmetrical track-etched membrane (symbolical representation, the tracks can be conical or cylindrical);

[0038] FIG. 3 shows a two-sided gas-tight asymmetrical track-etched membrane (symbolical representation, the tracks can be conical or cylindrical);

[0039] FIG. 4 shows a two-sided gas-tight asymmetrical track-etched membrane produced as double-version of FIG. 1 (symbolical representation, the tracks can be conical or cylindrical); and

[0040] FIG. 5 shows a scanning electron microscope image with a cross section of gas-tight track-etched membrane

EXAMPLE

[0041] A raw PET foil (23 m thickness, Mitsubishi Hostaphan RN MED) was irradiated with heavy ions (Kr) at the accelerator. The UV activation of latent tracks was on purpose avoided. The irradiated foil was then etched, but the etching was stopped, before the etching fronts from both sides of the membrane met each other and the pores were developed into go-through pores. The control of the etching was done with airflow measurements and water entry pressure measurements. These and other applicable measurements can be used to control the production and grade the membrane for different burst pressures, depending on the configuration of test setup. FIG. 5 shows a scanning electron microscope image with a cross section of gas-tight track-etched membrane with pore density of 110.sup.8 pores/cm.sup.2, thickness 22 m, water entrance pressure about 3 bar (indirect burst pressure measurement). The burst pressure is measured by sealing 25 mm membrane discs with O-rings and applying an increasing water under pressure until the membrane breaks and give a leakage that is detected via electrical contact above and below membrane.

LIST OF REFERENCES

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