Airtight track etch film for emergency venting

Abstract

The present invention provides a gas-tight film for use as a rupture film, in particular for emergency venting in connection with batteries, such as for automobiles, electric bicycles, handheld devices, electronic cigarettes, energy storage devices or heavy tools. The film comprises a base film having an indentation obtained by an incomplete track etch treatment applied to the base film. In addition, the present invention provides a method of preparing a hermetic film by applying an incomplete track etching treatment to both sides of a base film.

Description

Technical Field

[0001] The invention relates to gas-tight membranes comprising a base membrane having indentations on one or both sides, a method for producing the gas-tight membranes of the invention and their use as burst membranes in various forms of application. Background Art

[0002] The production of "classical" track-etched membranes (TEM) includes high-energy heavy ion irradiation of polymer foils, followed by activation of the latent tracks, for example by UV light, and subsequent etching. The production of a large number of commercially available TEMs currently focuses on providing through holes that penetrate the entire thickness of the membrane, and these holes have the highest possible pore size and uniformity of pore density throughout the membrane over hundreds of square meters. Exemplary methods for producing track-etched membranes are described in the following publications or in patent documents such as US 3 612 871 B2, DD-AP 235 923 and DE 195 36 033 A1.

[0003] It is well known that if some production requirements of common TEMs are not fully followed, the produced TEMs may have incompletely developed or unevenly distributed pores. Such waste byproducts of common TEM production were previously considered to be unattractive commercially and have not been optimized for commercialization. Summary of the invention

[0004] The present invention aims to provide a gas-tight track-etched membrane which can be used as a rupture membrane in many applications. Thus, in a first aspect, the present invention relates to the use of a gas-tight membrane as a rupture membrane, in particular for emergency venting associated with batteries, such as for automobiles, electric bicycles, handheld devices, electronic cigarettes, energy storage devices or heavy tools, the gas-tight membrane comprising a base membrane having indentations on one or both sides of the base membrane, the indentations being partially developed pores obtained by an incomplete track-etching process applied to the base membrane.

[0005] In a second aspect, the invention relates to a gas-tight membrane suitable for use as a rupture membrane as described above, said gas-tight membrane having indentations on both sides of the membrane which are partially developed holes, the holes on both sides having an asymmetric orientation relative to each other.

[0006] In a third aspect, the present invention relates to a method for producing the gas-tight membrane of the present invention by applying an incomplete track etching treatment to both sides of a base membrane, wherein the incomplete track etching treatment comprises the following steps: irradiation treatment with heavy ions having an energy lower than the energy required to penetrate the entire thickness of the base membrane; optionally, subsequent activation with UV or DMF; and an etching step to obtain indentations on both sides of the base membrane, wherein the incomplete track etching treatment is carried out under conditions that prevent the formation of holes that completely penetrate the membrane. DETAILED DESCRIPTION

[0007] The invention presented here describes a new type of gas-tight track-etched membrane (GT TEM) that was previously unavailable. Through certain targeted manipulations of production parameters, a series of GT TEMs can be produced that include partially developed holes that do not penetrate the entire thickness of the membrane. The manipulation of production parameters sets a certain penetration depth of the partially developed holes and, more importantly for the intended application of emergency venting, a certain thickness of the hole-free "bridge" between the two sides of the partially developed holes. The thickness of the "bridge" and the shape and density of the holes set in the membrane are related to the force required to rupture the membrane.

[0008] like Figure 1 As shown, the airtight membrane used as a rupture membrane according to the present invention can have partially developed holes on one side. Alternatively, as shown Figure 2 As shown, a membrane used as a rupture membrane may have partially developed holes on both sides of the membrane. Figure 2 A symmetrical orientation of the holes relative to each other and a symmetrical orientation of the hole depth relative to the remaining "bridge" are shown. However, further preferred embodiments of the present invention include Figure 3 The hole depths shown are asymmetrically oriented with respect to the "bridge", or as Figure 4 Asymmetric orientation of the hole depths relative to each other and optionally also relative to the "bridge" is shown. All conceivable sizes, depths and relative configurations of holes on one or both sides of the membrane are considered to be within the scope of the present invention, and the skilled person can readily make the selection of the appropriate configuration based on the intended use of the gas-tight membrane as a rupture membrane.

[0009] The pores of the gas-tight membrane used as a rupture membrane according to the invention are preferably conical or cylindrical in shape. In addition, the pores on different sides of the membrane may have the same or different penetration depths, also resulting in a symmetrical or asymmetrical configuration with respect to a "bridge" between the two sides of a partially developed pore or with respect to a "bridge" between one side of a partially developed pore and a side without pores.

[0010] The gas-tight membrane used as a rupture membrane can have the same range of pore density and pore size as is usually applied to "classical" track-etched membranes, however, the difference is that according to the present invention, the pores do not penetrate completely through the membrane, but are only present as indentations on one or both sides. In a preferred embodiment, the gas-tight membrane used as a rupture membrane shows 1,000 to 1×10 10 Partially developed pores / cm 2 , preferably the airtight film has 1×10 6 Up to 5×10 8 Such indentations or partially developed holes / cm 2 This number of partially developed pores may be present on one or both sides of the membrane, and the pore density may be the same or different for both sides of the membrane. Determination of pore density can be done on an electron microscope, using 2 x 0.5 cm 2 On a sample of 100-200 nm, 6-12 spatially distributed images with 100-400 pores per image are used. This pore density can then be correlated with continuous online current measurements during irradiation, which reflect the pore density over the entire length of the membrane.

[0011] Also considering the pore size, the gas-tight membrane used as a rupture membrane according to the present invention is very similar to the known "classical" track-etched membrane and can have the same pore size on the surface, preferably a pore size of 0.1 to 20 μm, preferably 1 to 10 μm, and again, the important difference is that for the gas-tight membrane of the present invention, the pores do not completely penetrate the membrane. For a cylindrical pore shape, the pore size is consistent from the membrane surface to the bottom of the hole, while for a conical pore shape, the pore size on the surface has a maximum diameter and gradually decreases toward the bottom of the hole. In addition, the pore size on both sides of the membrane with indentations on both sides can be the same or different.

[0012] For many applications of the membrane, it is important that the pores are particularly evenly distributed and, according to the invention, the gas-tight membrane preferably used as a rupture membrane shows a standard deviation of a distribution of partially developed pores per square unit of at most 30%, preferably 1% to 10%, most preferably between 2% and 5%, taking into account both sides of the membrane independently, as measured with online current measurement during irradiation. In the context of the present invention, a square unit refers to any suitable square size for determining the standard deviation of the pore distribution.

[0013] In a similar manner, the pore size is also preferably highly consistent and uniform over the membrane area, and in particularly preferred embodiments of the present invention, the standard deviation of the pore size varies between 3% and 10%. In particular, the uniformity and consistency of the pore distribution and pore size can be important factors for use as a rupture membrane. Considering preferred embodiments with respect to these features, the present invention allows the medium burst pressure applied to the membrane to have a deviation of 50% or less, preferably 25% or less, and most preferably 20% or less, and again, this property applies independently to each of the two sides of the membrane. The burst pressure can be measured by sealing with an O-ring The membrane is then filled with increasing amounts of water under pressure until the membrane ruptures and a leak occurs, which is detected via electrical contacts above and below the membrane.

[0014] Considering the various membrane configurations described above, it is apparent that a membrane used as a rupture membrane may contain partially developed pores on both sides of the base membrane in a manner that provides different rupture pressures for different sides. This is particularly true if the pore depths on the two sides are different, however, the pore density on the two sides and other factors that affect the rupture pressure may also vary. Using such a membrane configuration to achieve different rupture pressure sensitivities may be very advantageous depending on whether the pressure is applied from one side or the other.

[0015] Like the classical track etching membrane, the airtight membrane used as the rupture membrane according to the present invention can also be made of a membrane material selected from polyethylene terephthalate (PET), polycarbonate (PC), polyimide (PI), polyvinylidene fluoride (PVDF), polyethylene naphthalate (PEN), polyetheretherketone (PEEK), ethylene tetrafluoroethylene (ETFE) and other polymers or composite materials with similar properties. Based on the properties of PET and the fact that the material is environmentally friendly, but also based on its rupture properties, PET is the most preferred membrane material of the present invention.

[0016] The film thickness can be adjusted and selected depending on the intended use. In the context of the present invention, typical film thicknesses are between 5 and 200 μm, with preferred film thicknesses, in particular for rupture films, being 10 to 75 μm.

[0017] Likewise, the non-porous "bridge" of membrane material typically constitutes 10% to 50% of the thickness of the base membrane, depending on the desired sensitivity of the membrane, however, higher or lower values ​​may also be used depending on the intended application.

[0018] It is obvious to those skilled in the art that many of the above explanations about the preferred embodiments apply to specific situations, especially the specific use of the membrane as a rupture membrane. For specific applications as a rupture membrane, adjustments and variations of such preferred embodiments may be necessary and advantageous. Such adjustments and variations can be easily made by those skilled in the art based on his knowledge and the overall information provided herein.

[0019] Rupture membranes are often used in devices where a fault or external condition can lead to a pressure increase or other condition that can damage the device or endanger surrounding objects or articles. Rupture membranes can be used in safety engineering and applications such as pressure sensors, but can also be used in explosion pressure absorption systems, where the membrane can prevent fire and explosion.

[0020] Therefore, preferred uses of the gas-tight membrane as a rupture membrane include applications in emergency venting, in particular battery-related applications, such as for automobiles, electric bicycles, handheld devices, energy storage devices or heavy tools. In addition, other applications in which overpressure can be prevented by rupturing the corresponding material in a predetermined fashion to achieve controlled deflation are potential uses of the membrane, such as in vehicle airbags.

[0021] The membrane can be used for applications as described above with external triggers such as needles, edges or the like as well as without external triggers. In the latter case, the membrane ruptures based on its own perforation because the membrane includes millions of weak points that yield in response to the applied pressure.

[0022] According to a second aspect, the invention provides a gas-tight membrane, which is particularly suitable for the above-mentioned use as a rupture membrane. The gas-tight membrane comprises a base membrane having indentations on both sides of the base membrane, the indentations being partially developed holes, the holes on both sides having an asymmetric orientation relative to each other.

[0023] The other properties of the membrane correspond to the above description of the intended use as a rupture membrane. The gastight membrane according to the second aspect of the present invention may have a thickness of about 1,000 to 1×10 10 Pieces / cm 2 Partially developed holes, preferably 1×10 6 Up to 5×10 8 Partially developed pores / cm 2 The pore size as determined by electron microscopy may be about 0.1 to 20 μm, preferably 1 to 10 μm.

[0024] The standard deviation of the distribution of partially developed pores per square unit is preferably at most 30%, more preferably 1% to 10%, typically between 2% and 5%. The standard deviation of the pore size is preferably between 3% and 10%. The deviation of the median burst pressure is preferably equal to or lower than 50%, more preferably equal to or lower than 25%, most preferably equal to or lower than 20%.

[0025] The membrane material may be selected from polyethylene terephthalate (PET), polycarbonate (PC), polyimide (PI), polyvinylidene fluoride (PVDF), polyethylene naphthalate (PEN), polyetheretherketone (PEEK) and ethylenetetrafluoroethylene (ETFE).

[0026] The membrane thickness is preferably between 5 and 100 μm, more preferably between 10 and 75 μm.The non-porous bridges of membrane material may constitute 10% to 50% of the thickness of the base membrane.

[0027] The penetration depth of the holes on different sides of the membrane can be the same or different. The hole can have a conical or cylindrical shape, wherein the shape can be different or the same on different sides of the membrane. Other properties such as the number of holes, the density of holes, etc. can also be the same or different for both sides. For example, if the pressure when the membrane ruptures is higher on one side than on the other side, the different properties on both sides are advantageous. Therefore, according to a particularly preferred aspect of the present invention, the airtight membrane comprises partially developed holes on both sides of the membrane in the following manner, the manner being to provide different rupture pressures for different sides.

[0028] Regarding the third aspect of the invention, i.e. the method for producing the above-mentioned airtight membrane, this method includes an incomplete track etching treatment applied to both sides of the base membrane. This incomplete track etching treatment includes a step of irradiation treatment by heavy ions with an energy lower than the energy required for the heavy ions to penetrate the entire thickness of the base membrane. Optionally, subsequent UV activation can be carried out in accordance with the prior art to produce a track etched membrane. In addition, and the etching treatment step is carried out to remove the polymer material contained in the potential track formed by the heavy ion treatment and the optional subsequent UV activation to obtain indentations on both sides of the base membrane, the etching treatment step is a standard step in the production of classical membranes with fully developed pores.

[0029] The incomplete track etching process is carried out under conditions that prevent the formation of holes that completely penetrate the thickness of the base film. The energy of the heavy ions is selected to be so low that it cannot completely penetrate the polymer film material. In addition, the production process can be carried out with or without subsequent UV activation. Omitting the UV activation step is also a point to suppress the possibility of the membrane being completely penetrated by holes. In the above case, due to the low energy of the heavy ions, and optionally also due to the lack of UV activation or insufficient UV activation, complete penetration of the holes is avoided. In addition, the oxygen concentration during the UV activation treatment can be adjusted to avoid the development of completely penetrating holes.

[0030] Finally, the etching step can also be adjusted to avoid the pores from developing completely. For example, etching can be stopped before the pores have fully penetrated the thickness of the membrane, and a less aggressive etching solution can be applied.

[0031] If the energy of the heavy ions is high enough to completely penetrate the polymer material, it is possible to produce, for example, Figure 2 A hermetic membrane with partially developed pores on both sides is shown. The latent tracks are then left completely or partially undeveloped by applying too little or no UV activation and / or too little or no oxygen concentration and / or incomplete etching to both sides.

[0032] Depending on the conditions applied to each side of the membrane, a symmetrical or asymmetrical membrane can be obtained. Asymmetry can also be added by a protective layer on one side or by applying different etching conditions to both sides of the polymer foil. Likewise, etching is stopped before the pores have completely penetrated the thickness of the membrane.

[0033] Alternatively, asymmetric forms of hermetic track-etched films (e.g., Figure 4 ). Then, as described above, the tracks are left undeveloped and etching is stopped before the pores have completely penetrated the thickness of the membrane.

[0034] Based on the above examples, it will be readily understood by those skilled in the art that by adjusting the conditions for producing a classical track-etched film as described above, various different configurations and variations of the gas-tight film for use according to the invention can be obtained. As described for the gas-tight film itself, also for the production method of the invention, the features and conditions can be easily adjusted to provide the best possible gas-tight film for the intended use.

[0035] The following examples and drawings further illustrate the present invention: BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1A single-sided airtight track-etched membrane is shown (symbolically, the track can be conical or cylindrical);

[0037] Figure 2 A double-sided airtight symmetrical track-etched membrane is shown (symbolically, the track can be conical or cylindrical);

[0038] Figure 3 A double-sided airtight asymmetric track-etched membrane is shown (symbolically, the track can be conical or cylindrical);

[0039] Figure 4 Shown as Figure 1 Double-sided gas-tight asymmetric track-etched membranes produced in a dual version (symbolically, the track can be conical or cylindrical); and

[0040] Figure 5 Scanning electron microscope image showing a cross section of a hermetic track-etched membrane

[0041] Example

[0042] The original PET foil (thickness 23um, Mitsubishi HostaphanRN MED) was irradiated with heavy ions (Kr) at the accelerator. UV activation of potential tracks was intentionally 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 hole developed into a through hole. The control of the etching was completed with air flow measurement and water inlet pressure measurement. Depending on the configuration of the test device, these and other applicable measurements can be used to control the production and classification of membranes with different burst pressures. Figure 5 Scanning electron microscope image showing a cross section of a hermetic track-etched membrane with a pore density of 1×10 8 Holes / cm 2 , thickness 22um, water inlet pressure about 3 bar (indirect burst pressure measurement). The burst pressure is measured by the following, sealed with an O-ring The membrane is then filled with increasing amounts of water under pressure until the membrane ruptures and a leak occurs, which is detected via electrical contacts above and below the membrane.

[0043] References

[0044] Apel P. Yu. and Dmitriev SN (2011), Micro- and nanoporous materials produced using accelerated heavy ion beams, Adv. Nat. Sci: Nanosci. Nanotechnol. 2 (2011) 013002 http: / / iopscience.iop.org / 2043-6262 / 2 / 1 / 013002;

[0045] Apel P. (2001), Track etching technique in membrane technology, Radiation measurements 34, pp 559-566;

[0046] Fischer BE and Spohr R. (1983). Production and use of nuclear tracks: imprinting structure on solids. Rev. Mod. Phys. 55 907.

[0047] Spohr R. (1997) Ion track technology-apersisting challenge, New Astronomy Reviews 42 (1998) 189-203;

[0048] Apel P. Yu. (1995) Heavy particle tracks in polymers and polymeric track membranes, Radiation measurements 25, 1-4, pp 667-674 (1995);

[0049] Spohr R. (2001), Etch hints for polymers with high track-etch-rate, European Research Training Network EuNITT, Report M2.1;

[0050] DeSorbo W. (1979), Ultraviolet effects and aging effect on etching characteristics of fission tracks in polycarbonate film, Nucl. Tracks, Vol. 3, pp 13-32, 1979;

[0051] Spohr R. (2009), Ion Tracks for micro and nanofabrication, Uppsala PhD Thesis 700, http: / / kth.diva-portal.org / smash / get / diva2:280068 / FULLTEXT02.pdf.

Claims

1. Use of a gas-tight membrane as a rupture membrane, in particular for emergency venting associated with batteries, such as for automobiles, electric bicycles, handheld devices, electronic cigarettes, energy storage devices or heavy tools, the gas-tight membrane comprising a base membrane having indentations on one or both sides of the base membrane, the indentations being partially developed holes obtained by an incomplete track etching process applied to the base membrane.

2. An airtight membrane suitable for use according to claim 1, comprising a base membrane having indentations on both sides of the base membrane, the indentations being partially developed pores, the pores on both sides having an asymmetric orientation relative to each other. The airtight membrane according to claim 2 , wherein the pores have a conical or cylindrical shape.

4. A gas-tight membrane according to claim 2 or 3, wherein the holes on different sides of the membrane have the same or different penetration depths.

5. The airtight film according to any one of claims 2 to 4, having 1,000 to 1×10 10 Partially developed pores / cm 2 , preferably 1×10 6 Up to 5×10 8 Partially developed pores / cm 2 , and / or wherein the pore size determined by electron microscopy is from 0.1 to 20 μm, preferably from 1 to 10 μm.

6. A gastight membrane according to any one of claims 2 to 5, wherein the standard deviation of the distribution of partially developed pores per square unit is at most 30%, preferably 1% to 10%, typically between 2% and 5%.

7. A gastight membrane according to any one of claims 2 to 6, wherein the standard deviation of the pore size is between 3% and 10%, and / or wherein the deviation of the median burst pressure is equal to or lower than 50%, preferably equal to or lower than 25%, most preferably equal to or lower than 20%.

8. A gastight membrane according to any one of claims 2 to 7, wherein the membrane comprises partially developed holes on both sides of the membrane in such a way as to provide different bursting pressures for different sides.

9. The airtight membrane according to any one of claims 2 to 8, wherein the membrane material is selected from polyethylene terephthalate (PET), polycarbonate (PC), polyimide (PI), polyvinylidene fluoride (PVDF), polyethylene naphthalate (PEN), polyetheretherketone (PEEK) and ethylenetetrafluoroethylene (ETFE).

10. The gastight membrane according to any one of claims 2 to 9, wherein the membrane has a thickness between 5 μm and 200 μm, preferably 10 μm to 75 μm, and / or wherein the non-porous bridges of membrane material constitute 10% to 50% of the thickness of the base membrane.

11. A method for producing an airtight membrane according to any one of claims 2 to 10, wherein the airtight membrane is produced by applying an incomplete track etching process to both sides of a base membrane, wherein the incomplete track etching process comprises the following steps: - irradiation treatment with heavy ions having an energy lower than that required to penetrate the entire thickness of the base film, -optionally, subsequent UV activation, and - Etching treatment, To obtain indentations on both sides of the base film, The incomplete track etching process is performed under conditions that prevent the formation of pores that completely penetrate the thickness of the base film.

12. The method according to claim 11, wherein the base film comprises a polymer foil, such as PET, PC, PI, PEN, PVDF, PEEK or ETFE foil.

13. A method according to claim 11 or 12, wherein the track etching treatment on both sides of the base film is carried out under the same or different conditions, in particular using different same ion energies in the irradiation treatment and / or using different same times and conditions in the etching treatment.

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