Method for preparing modified polypropylene film

Abstract

A method for preparing a modified polypropylene film, the modified polypropylene film comprising a polypropylene film; and, an oxide layer and/or nitride layer, each of which has a thickness of 20-500 nm, on a surface of the polypropylene film; the method comprising: depositing the oxide layer or nitride layer on a surface of the polypropylene film by an Atomic Layer Deposition (ALD) process to obtain the modified polypropylene film; wherein the step of depositing the oxide layer or nitride layer comprises: placing the polypropylene film in an ALD reaction chamber; vacuumizing; heating up; introducing a carrier gas; and, passing at least two precursors into the reaction chamber alternately for reaction, resulting in the modified polypropylene film; wherein the precursors comprise a precursor for providing a metal element or Si, and a precursor for providing an oxygen or nitrogen element.

Claims

1. A method for preparing a modified polypropylene film, the modified polypropylene film comprising a polypropylene film; and, a nitride layer that has a thickness of 20-500 nm, on a surface of the polypropylene film; the method comprising: depositing the nitride layer on a surface of the polypropylene film by an Atomic Layer Deposition (ALD) process to obtain the modified polypropylene film; wherein the step of depositing the nitride layer on a surface of the polypropylene film, comprises: placing the polypropylene film in an ALD reaction chamber; vacuumizing; heating up; introducing a carrier gas; and, passing at least two precursors into the reaction chamber alternately for reaction, resulting in the modified polypropylene film; wherein the precursors comprise a precursor for providing a metal element or Si or B, and a precursor for providing a nitrogen element; wherein the modified polypropylene film has a withstanding voltage of 580 kV/mm at 140° C.

2. The method according to claim 1, wherein the metal element is at least one selected from Al, Ti, Zn, Zr, Ta, Nb, Mg, Fe, Sr and Ba; wherein, the vacuumizing achieves a vacuum degree of 250 mTorr or less; wherein, the precursors performs the reaction at a temperature no more than 100° C.

3. The method according to claim 1, wherein the nitride layer is composed of at least one selected from an aluminum nitride, a titanium nitride, a boron nitride, a silicon nitride and a tantalum nitride.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graph showing the dimensional changes of the modified polypropylene film prepared in Example 1 as a function of temperature.

(2) FIG. 2 is a graph showing the changes of storage modulus of the modified polypropylene film prepared in Example 1 as a function of temperature.

(3) FIG. 3 is a graph showing the changes of X-ray diffraction (XRD) spectrum of the modified polypropylene film prepared in Example 1 as a function of temperature.

(4) FIG. 4 is a graph showing the changes of direct voltage (DC) voltage breakdown strength of the modified polypropylene film prepared in Example 1 as a function of temperature.

(5) FIG. 5 is a graph showing the changes of the shrinkage rates of the modified polypropylene film prepared in Example 2 as a function of temperature.

(6) FIG. 6 is a graph showing the dimensional changes of the modified polypropylene film prepared in Example 3 as a function of temperature.

(7) FIG. 7 is a graph showing the shrinkage rates of the modified polypropylene films prepared by 800 ALD cycles in Examples 1, 3, 4 and 5 after being kept at 150° C. for half an hour.

DETAILED DESCRIPTION

(8) The following examples are provided only for illustration purpose in order to enable those skilled in the art to understand the technical solution of the present disclosure more clearly. It should be noted that the following examples are not intended to limit the claimed scope of the present disclosure.

(9) Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained through conventional commercial approaches or by existing known methods.

(10) Hereafter, the modified polypropylene films were prepared by using a thermal ALD device GEMSTAR TX. In the following examples, the used domestic-made polypropylene CPP films are polypropylene films purchased in China, and the imported polypropylene HCPP films are polypropylene films with high crystallinity purchased from other countries.

Example 1: Preparation of High-Temperature Resistant Modified Polypropylene Films

(11) The high-temperature resistant modified polypropylene film included a domestic-made polypropylene CPP film and an Al.sub.2O.sub.3 layer on the surface of the domestic-made polypropylene CPP film, where the Al.sub.2O.sub.3 layer had a thickness of 20-200 nm.

(12) The method for preparing the aforementioned high-temperature resistant modified polypropylene film included the following steps:

(13) Place a polypropylene film in an ALD reaction chamber; vacuumize to 250 mTorr; heat until reaching a temperature of 90° C.; introduce argon at a flow rate of 10 sccm; introduce trimethyl aluminum (TMA) and water (H.sub.2O) precursors alternately into the reaction chamber for reaction, and perform ALD cycles in which each ALD cycle consisted of TMA pulsing for 21 msec, argon sweeping for 6 sec, H.sub.2O pulsing for 21 msec and argon sweeping for 6 sec, then resulting in the modified polypropylene films.

(14) By the preparation method of this example, the modified polypropylene films were prepared through 200 (i.e., performing 200 ALD cycles), 400 (i.e., performing 400 ALD cycles) and 2000 (i.e., performing 2000 ALD cycles) ALD cycles, respectively. The Al.sub.2O.sub.3 layer became thicker as the number of deposition cycles increased.

Example 2: Preparation of High-Temperature Resistant Modified Polypropylene Films

(15) The difference between Example 2 and Example 1 only lied in that the domestic-made polypropylene CPP film was replaced by the imported polypropylene HCPP film. The rest of the preparation method was the same as that of Example 1.

(16) By the preparation method of this example, the modified polypropylene films were prepared through 400, 800 and 2000 ALD cycles, respectively. The resulted Al.sub.2O.sub.3 layer became thicker as the number of deposition cycles increased.

Example 3: Preparation of High-Temperature Resistant Modified Polypropylene Films

(17) The high-temperature resistant modified polypropylene film included a domestic-made polypropylene CPP film and a TiO.sub.2 layer on the surface of the domestic-made polypropylene CPP film, wherein the TiO.sub.2 layer had a thickness of 20-200 nm.

(18) The method for preparing the aforementioned high-temperature resistant modified polypropylene film included the following steps:

(19) Place the polypropylene film in an ALD reaction chamber; vacuumize to 250 mTorr; heat until reaching a temperature of 100° C.; introduce argon at a flow rate of 10 sccm; introduce titanium isopropylate (TIP) and water (H.sub.2O) precursors alternately into the reaction chamber for reaction; perform 800 ALD cycles in which each ALD cycle consisted of TIP pulsing for 200 msec, argon sweeping for 6 sec, H.sub.2O pulsing for 200 msec and argon sweeping for 6 sec, then resulting in the modified polypropylene films.

Example 4: Preparation of High-Temperature Resistant Modified Polypropylene Films

(20) The high-temperature resistant modified polypropylene film included a domestic-made polypropylene CPP film and a ZnO layer on the surface of the domestic-made polypropylene CPP film, wherein the ZnO layer had a thickness of 20-200 nm.

(21) The method for preparing the aforementioned high-temperature resistant modified polypropylene film included the following steps:

(22) Place the polypropylene film in an ALD reaction chamber; vacuumize to 250 mTorr; heat until reaching a temperature of 90° C.; introduce argon at a flow rate of 10 sccm and introduce diethyl zinc (DEZ) and water (H.sub.2O) precursors alternately into the reaction chamber; perform 800 ALD cycles in which each ALD cycle consisted of DEZ pulsing for 200 msec, argon sweeping for 6 sec, H.sub.2O pulsing for 200 msec and argon sweeping for 6 sec, then resulting in the modified polypropylene film.

Example 5: Preparation of High-Temperature Resistant Modified Polypropylene Films

(23) The high-temperature resistant modified polypropylene film included a domestic-made polypropylene CPP film and an AlN layer on the surface of the domestic-made polypropylene CPP film, wherein the AlN layer had a thickness of 20-200 nm.

(24) The method for preparing the aforementioned high-temperature resistant modified polypropylene film included the following steps:

(25) Place the polypropylene film in an ALD reaction chamber; vacuumize to 250 mTorr; heat until reaching a temperature of 100° C.; introduce argon at a flow rate of 10 sccm; introduce trimethyl aluminum (TMA), triethylamine and water (H.sub.2O) precursors alternately into the reaction chamber for reaction; perform 800 ALD cycles in which each ALD cycle consisted of TMA pulsing for 200 msec, argon sweeping for 6 sec, H.sub.2O pulsing for 200 msec and argon sweeping for 6 sec, then resulting in the modified polypropylene film.

(26) Tests for the Performance of the Products

(27) 1. Performance Test of Modified Polypropylene Film Prepared in Example 1

(28) 1.1. Test for Dimensional Changes as a Function of Temperature

(29) The modified polypropylene films (with an initial length of 16 mm) prepared by the method, in which 200, 400 and 2000 ALD cycles were performed respectively, of Example 1, and an unmodified CPP film (with an initial length of 16 mm) were taken and tested for the dimensional changes thereof along a stretching direction as the temperature changed. The results were shown in FIG. 1.

(30) FIG. 1 is a graph showing the dimensional changes of the modified polypropylene films prepared in Example 1 as a function of temperature. In FIG. 1, a) indicates that, during the testing process, the samples to be tested were kept at 125° C. for half an hour; and b) indicates that, during the testing process, the samples to be tested were kept at 150° C. for half an hour. As shown in FIG. 1, the CPP curve shows the relationship between the dimensional changes of the unmodified polypropylene film and the temperature, and the CPP+200 ALD cycles, CPP+400 ALD cycles and CPP+2000 ALD cycles curves show the relationship between the dimensional changes of the modified polypropylene films prepared in Example 1 and the temperature. It can be seen from the CPP curve that the unmodified CPP film has shrunk at 100° C., and has a shrinkage rate up to 3% at 150° C. In contrast, the shrinkage rates of the modified polypropylene film are far below 3% at 150° C.

(31) 1.2. Test for the Storage Modulus Changes as a Function of Temperature

(32) The modified polypropylene film prepared by the method, in which 2000 ALD cycles were performed, of Example 1 and the unmodified CPP were taken and tested for the changes of storage modulus and loss modulus as the temperature changed. The results are shown in FIG. 2. FIG. 2 is a graph showing the changes of storage modulus of the modified polypropylene film prepared in Example 1 as a function of temperature. In FIG. 2, a) shows the relationship between the changes of storage modulus and loss modulus of the unmodified CPP film and the temperature; and b) shows the relationship between the changes of storage modulus and loss modulus of the modified polypropylene film prepared by the method with 2000 ALD cycles of Example 1. It can be seen from FIG. 2 that the storage modulus of the unmodified CPP decreases rapidly with the increase of the temperature. In contrast, the storage modulus of the modified polypropylene film prepared by the method with 2000 ALD cycles of Example 1 is still 200 MPa at high temperature such as 150° C.

(33) 1.3. Test for Changes of XRD Spectrum (X-Ray Diffraction Spectrum) as a Function of Temperature

(34) The modified polypropylene film prepared by the method with 2000 ALD cycles of Example 1 and the unmodified CPP were taken and tested for the changes of XRD spectrum (X-ray diffraction spectrum) as a function of temperature. The results are shown in FIG. 3. FIG. 3 is a graph showing the changes of XRD spectrum of the modified polypropylene film prepared in Example 1 as a function of temperature. In FIG. 3, a) shows the changes of XRD spectrum of the unmodified CPP as a function of temperature, and b) shows the changes of XRD spectrum of the modified polypropylene film prepared by the method with 2000 ALD cycles of Example 1 as a function of temperature. It can be seen from FIG. 3 that the unmodified CPP film loses its crystal orientation at high temperature, while the modified polypropylene film prepared by the method with 2000 ALD cycles of Example 1 substantially does not lose its crystal orientation at high temperature.

(35) 1.4. Test for Changes of DC Voltage Breakdown Strength as Function of Temperature

(36) The modified polypropylene film prepared by the method with 2000 ALD cycles of Example 1 and the unmodified CPP were taken and tested for the changes of DC voltage breakdown strength as a function of temperature. The results are shown in FIG. 4. In FIG. 4, the CPP shows the changes of DC voltage breakdown strength of the unmodified CPP as a function of temperature, and the CPP+2000 ALD cycles shows the changes of DC voltage breakdown strength of the modified polypropylene film prepared by the method with 2000 ALD cycles of Example 1 as a function of temperature. It can be seen from FIG. 4 that the DC voltage breakdown strength of the unmodified CPP is obviously reduced at high temperature, while the DC voltage breakdown strength of the modified polypropylene film prepared by the method with 2000 ALD cycles of Example 1 has no obvious reduction at high temperature (140° C.).

(37) 2. Performance Test of Modified Polypropylene Film Prepared in Example 2

(38) The modified polypropylene films prepared by the method, in which 400, 800 and 2000 ALD cycles were performed, of Example 2 and the unmodified HCPP film (i.e., 0 cycle of ALD deposition) were taken and tested for the shrinkage rates along the stretching direction as a function of temperature. The results are shown in FIG. 5. FIG. 5 is a graph showing the changes of the shrinkage rates of the modified polypropylene films prepared in Example 2 as a function of temperature (the phrase “125° C. for half an hour” means that the sample to be tested was kept at 125° C. for half an hour, and the phrase “150° C. for half an hour” means that the sample to be tested was kept at 150° C. for half an hour). It can be seen from FIG. 5 that the shrinkage rates of the unmodified HCPP have reached above 3% at 125° C., while the shrinkage of each of the modified polypropylene films prepared in Example 2 is less than 3% after being kept at 125° C. for half an hour.

(39) 3. Performance Test of Modified Polypropylene Film Prepared in Example 3

(40) The modified polypropylene film prepared by the method, in which 800 ALD cycles were performed, of Example 3 and the unmodified CPP were taken and tested for the dimensional changes along the stretching direction as a function of temperature. The results are shown in FIG. 6. FIG. 6 is a graph showing the dimensional changes of the modified polypropylene film prepared in Example 3 as a function of temperature. In FIG. 6, the “CPP 125° C.” curve indicates the dimensional changes of the unmodified CPP along the stretching direction as a function of temperature after being kept at 125° C. for half an hour; and the “CPP 150° C.” curve indicates the dimensional changes of the unmodified CPP along the stretching direction as a function of temperature after being kept at 150° C. for half an hour; the “CPP 125° C.+800 ALD cycles” curve indicates the dimensional changes of the modified polypropylene film prepared by the method with 800 ALD cycles of Example 3 along the stretching direction as a function of temperature after being kept at 125° C. for half an hour; and the “CPP 150° C.+800 ALD cycles” curve indicates the dimensional changes of the modified polypropylene film prepared by the method with 800 ALD cycles of Example 3 along the stretching direction as a function of temperature after being kept at 150° C. for half an hour.

(41) It can be seen from FIG. 6 that the dimensional changes of the modified polypropylene film prepared by the method with 800 ALD cycles of Example 3 are significantly less than those of the unmodified CPP. The shrinkage rates of the modified polypropylene films prepared by the method with 800 ALD cycles of Example 3 are less than 2%.

(42) 4. Performance Test of Modified Polypropylene Films Prepared by the Methods with 800 ALD Cycles of Examples 1, 3, 4 and 5

(43) The modified polypropylene films prepared by the methods, in which 800 ALD cycles were performed, of Examples 1, 3, 4 and 5 respectively, and the unmodified CPP film were taken and kept at 150° C. for half an hour. Then, these films were tested for the shrinkage rates thereof along the stretching direction. The results are shown in FIG. 7.

(44) FIG. 7 is a graph showing the shrinkage rates of the modified polypropylene films prepared by the methods with 800 ALD cycles of Examples 1, 3, 4 and 5 after being kept at 150° C. for half an hour. In FIG. 7, CPP represents the unmodified CPP; CPP+TiO.sub.2 represents the modified polypropylene film prepared in Example 3; CPP+Al.sub.2O.sub.3 represents the modified polypropylene film prepared in Example 1; CPP+ZnO represents the modified polypropylene film prepared in Example 4; and CPP+AlN represents the modified polypropylene film prepared in Example 5.

(45) It can be seen from FIG. 7 that the shrinkage rate of each of the modified polypropylene films prepared by the method with 800 ALD cycles of Examples 1, 3, 4 and 5 is significantly less than that of the unmodified CPP.