A CPP membrane post-treatment method, high-strength CPP membrane

Abstract

This invention relates to the field of polypropylene membrane technology, specifically to a CPP membrane post-treatment method and a high-strength CPP membrane. The CPP membrane post-treatment method includes: placing the CPP membrane in a supercritical fluid and immersing it at a preset pressure, preset temperature, and preset time; wherein the preset pressure is 8-30 MPa, the preset temperature is 40-90°C, and the preset time is 0.5-10 h. The CPP membrane post-treatment method provided by this invention uses supercritical fluid to immerse the CPP membrane. During this process, the penetration of the supercritical fluid can change the aggregated structure of the CPP membrane, but it does not change the crystallinity of the polypropylene material. Therefore, using this method to post-treat the CPP membrane can effectively improve the tensile strength of the CPP membrane without reducing its toughness and transparency, which is of great significance for expanding the application fields of CPP membranes.

Description

Technical Field

[0001] This invention relates to the field of polypropylene film technology, and more specifically, to a CPP film post-processing method and a high-strength CPP film. Background Technology

[0002] Based on different processing methods, polypropylene films are divided into two main categories: cast polypropylene film (CPP film) and biaxially oriented polypropylene film (BOPP film). CPP film is formed by melting polypropylene (PP) granules at high temperature, extruding the molten material into a flat film shape using an extruder, and then winding and cooling it. Because it uses a unidirectional stretching process, the stretching direction of the film is the same as the extrusion direction. BOPP film, on the other hand, involves melting polypropylene (PP) granules at high temperature, extruding the molten material into a flat film shape using an extruder, and employing stretching technology in different directions to stretch the film surface in both the vertical and horizontal directions, resulting in higher tensile strength in both directions. Compared to BOPP film, CPP film has lower tensile strength, but it has the advantages of higher toughness and lower cost. To expand the application areas of CPP film, further post-processing is needed to improve its tensile strength. However, existing CPP film post-processing methods, while improving tensile strength, tend to reduce the toughness and transparency of the CPP film. Summary of the Invention

[0003] The technical problem solved by this invention is that existing CPP film post-processing methods, while improving the tensile strength of CPP films, easily lead to a decrease in the toughness and transparency of CPP films.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] A CPP membrane post-treatment method includes: placing the CPP membrane in a supercritical fluid and immersing it at a preset pressure and a preset temperature for a preset time; wherein the preset pressure is 8-30 MPa, the preset temperature is 40-90℃, and the preset time is 0.5-10 h.

[0006] Preferably, the supercritical fluid is a supercritical carbon dioxide fluid.

[0007] Preferably, the preset pressure is 12-20 MPa.

[0008] Preferably, the preset temperature is 60-80℃.

[0009] Preferably, the preset time is 1-3 hours.

[0010] Preferably, the thickness of the CPP film is 5-120 μm.

[0011] Preferably, the thickness of the CPP film is 20-50 μm.

[0012] Preferably, the CPP membrane is made of homopolymer polypropylene.

[0013] Preferably, the CPP membrane is made of copolymer polypropylene material.

[0014] The present invention also provides a high-strength CPP membrane, which is obtained by the CPP membrane post-processing method described above.

[0015] Compared with the prior art, the CPP membrane post-treatment method provided by the present invention uses supercritical fluid to impregnate the CPP membrane. During this process, the penetration of supercritical fluid can change the aggregated structure of the CPP membrane, but does not change the crystallinity of the polypropylene material. Therefore, the CPP membrane post-treatment method can effectively improve the tensile strength of the CPP membrane without reducing its toughness and transparency, which is of great significance for expanding the application fields of CPP membrane. Attached Figure Description

[0016] Figure 1 This is a graph showing the original test data of the tensile properties of the CPP film before treatment in Example 1;

[0017] Figure 2 This is a graph showing the original test data of the tensile properties of the supercritical CPP membrane in Example 1;

[0018] Figure 3 This is a graph showing the original test data of the tensile properties of the CPP film before treatment in Example 2;

[0019] Figure 4 This is a graph showing the original test data of the tensile properties of the supercritical CPP membrane in Example 2. Detailed Implementation

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0021] It should be noted that, unless otherwise specified, the features in the embodiments of this invention can be combined with each other. The terms "comprising," "including," "containing," and "having" are non-limiting, meaning that other steps and other components that do not affect the results can be added. The above terms cover the terms "composed of" and "substantially composed of." Unless otherwise specified, the materials, equipment, and reagents are commercially available.

[0022] This invention provides a CPP membrane post-treatment method, comprising: placing the CPP membrane in a supercritical fluid and immersing it at a preset pressure and temperature for a preset time; wherein the preset pressure is 8-30 MPa, the preset temperature is 40-90°C, and the preset time is 0.5-10 h. When the preset pressure is higher than 30 MPa and the preset temperature is higher than 90°C, the surface of the CPP membrane is prone to deformation.

[0023] Compared with the prior art, the CPP membrane post-treatment method provided in this embodiment of the invention uses supercritical fluid to impregnate the CPP membrane. During this process, the penetration of supercritical fluid can change the aggregated structure of the CPP membrane, but does not change the crystallinity of the polypropylene material. Therefore, by using this method to post-treat the CPP membrane, the tensile strength of the CPP membrane can be effectively improved without reducing the toughness and transparency of the CPP membrane, which is of great significance for expanding the application fields of CPP membrane.

[0024] For example, in some embodiments of the present invention, the supercritical fluid is a supercritical carbon dioxide fluid.

[0025] In some embodiments of the present invention, preferably, the preset pressure is 12-20 MPa.

[0026] In some embodiments of the present invention, preferably, the preset temperature is 60-80°C.

[0027] In some embodiments of the present invention, preferably, the preset time is 1-3 hours.

[0028] In some embodiments of the present invention, the thickness of the CPP membrane is 5-120 μm. When the thickness of the CPP membrane is less than 5 μm, the CPP membrane is prone to deformation during post-processing; when the thickness of the CPP membrane is greater than 120 μm, the preset time is too long. Preferably, the thickness of the CPP membrane is 20-50 μm.

[0029] In some embodiments of the present invention, the CPP membrane is made of homopolymer polypropylene or copolymer polypropylene.

[0030] The present invention also provides a high-strength CPP membrane, which is obtained by the CPP membrane post-processing method described above.

[0031] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0032] Example 1

[0033] A CPP membrane is placed in a supercritical carbon dioxide fluid and immersed for a preset time at a preset pressure and temperature to obtain a supercritical CPP membrane; wherein the preset pressure is 12 MPa, the preset temperature is 60 °C, the preset time is 3 h, and the CPP membrane thickness is 20 μm.

[0034] The CPP membranes before and after supercritical fluid treatment in Example 1 were tested for tensile strength, elongation at break, light transmittance, and haze. The results are shown in Table 1. Table 1 shows that compared to the CPP membrane before treatment in Example 1, the elongation at break, light transmittance, and haze of the supercritically treated CPP membrane in Example 1 did not change significantly, but the longitudinal tensile strength increased by more than 10%, and the transverse tensile strength also increased slightly. This indicates that the tensile strength of the CPP membrane in Example 1 increased after supercritical fluid treatment without reducing its toughness or transparency. It should be noted that a higher elongation at break indicates poorer toughness.

[0035] It should be noted that the original test data for the tensile properties of the CPP film before treatment in Example 1 can be found in [link to example]. Figure 1 The raw test data for the tensile properties of the supercritical CPP membrane in Example 1 can be found in [link to example]. Figure 2 . Figure 1 Curves 1-3 correspond to the longitudinal tensile strain curves of the three CPP film samples before treatment, respectively, while curves 4-6 correspond to the transverse tensile strain curves of the three CPP film samples before treatment, respectively. Analysis Figure 1 The average value of the sample results was taken to obtain the data of transverse tensile strength, longitudinal tensile strength, transverse elongation at break and longitudinal elongation at break of the CPP film before treatment, as shown in Table 1. Figure 2 Curves 1-3 correspond to the longitudinal tensile strain curves of the three supercritical CPP membranes, respectively, while curves 4-6 correspond to the transverse tensile strain curves of the three supercritical CPP membrane samples, respectively. Analysis Figure 2 The average value of the sample results was taken to obtain the data of transverse tensile strength, longitudinal tensile strength, transverse elongation at break and longitudinal elongation at break of the supercritical CPP membrane in Table 1.

[0036] Table 1

[0037]

[0038] Example 2

[0039] A CPP membrane is placed in a supercritical carbon dioxide fluid and immersed for a preset time at a preset pressure and temperature to obtain a supercritical CPP membrane; wherein the preset pressure is 15 MPa, the preset temperature is 60 °C, the preset time is 6 h, and the CPP membrane thickness is 30 μm.

[0040] The CPP membranes before and after supercritical fluid treatment in Example 2 were tested for tensile strength, elongation at break, light transmittance, and haze. The results are shown in Table 2. Table 2 shows that compared to the CPP membrane before treatment in Example 2, the elongation at break, light transmittance, and haze of the supercritically treated CPP membrane in Example 2 did not change significantly. However, the transverse tensile strength increased by approximately 6%, and the longitudinal tensile strength also increased slightly. This indicates that the tensile strength of the CPP membrane in Example 2 increased after supercritical fluid treatment without causing a decrease in the membrane's toughness or transparency.

[0041] It should be noted that the original test data for the tensile properties of the CPP film before treatment in Example 2 can be found in [link to example]. Figure 3 The raw test data for the tensile properties of the supercritical CPP membrane in Example 2 can be found in [link to example]. Figure 4 . Figure 3 Curves 1-3 correspond to the longitudinal tensile strain curves of the three CPP film samples before treatment, respectively, while curves 4-6 correspond to the transverse tensile strain curves of the three CPP film samples before treatment, respectively. Analysis Figure 3 The average value of the sample results was taken to obtain the data of transverse tensile strength, longitudinal tensile strength, transverse elongation at break and longitudinal elongation at break of the CPP film before treatment, as shown in Table 2. Figure 4 Curves 1-3 correspond to the longitudinal tensile strain curves of the three supercritical CPP membranes, respectively, while curves 4-6 correspond to the transverse tensile strain curves of the three supercritical CPP membrane samples, respectively. Analysis Figure 4 The average value of the sample results was taken to obtain the data of transverse tensile strength, longitudinal tensile strength, transverse elongation at break and longitudinal elongation at break of the supercritical CPP membrane in Table 2.

[0042] Table 2

[0043]

[0044] Example 3

[0045] A CPP membrane is placed in a supercritical carbon dioxide fluid and immersed for a preset time at a preset pressure and temperature to obtain a supercritical CPP membrane; wherein the preset pressure is 8 MPa, the preset temperature is 90 °C, the preset time is 6 h, and the CPP membrane thickness is 20 μm.

[0046] Example 4

[0047] A CPP membrane is placed in a supercritical carbon dioxide fluid and immersed for a preset time at a preset pressure and temperature to obtain a supercritical CPP membrane; wherein the preset pressure is 30 MPa, the preset temperature is 90 °C, the preset time is 0.5 h, and the CPP membrane thickness is 20 μm.

[0048] Example 5

[0049] A CPP membrane is placed in a supercritical carbon dioxide fluid and immersed for a preset time at a preset pressure and temperature to obtain a supercritical CPP membrane; wherein the preset pressure is 8 MPa, the preset temperature is 40 °C, the preset time is 10 h, and the CPP membrane thickness is 20 μm.

[0050] Example 6

[0051] A CPP membrane is placed in a supercritical carbon dioxide fluid and immersed for a preset time at a preset pressure and temperature to obtain a supercritical CPP membrane; wherein the preset pressure is 12 MPa, the preset temperature is 60 °C, the preset time is 0.5 h, and the CPP membrane thickness is 5 μm.

[0052] Furthermore, it should be noted that although the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A CPP film post-treatment method characterized by, The CPP film is placed in a supercritical fluid, and soaked at a preset pressure, a preset temperature for a preset time; wherein the preset pressure is 8-30 MPa, the preset temperature is 40-90 ℃, and the preset time is 0.5-10 h; the supercritical fluid is a carbon dioxide supercritical fluid. The preset pressure is 12-20 MPa.

2. The CPP film post-treatment method of claim 1, wherein, The preset temperature is 60-80 ℃.

3. The CPP film post-treatment method of claim 1, wherein, The preset time is 1-3 h.

4. The CPP film post-treatment method of claim 1, wherein, The thickness of the CPP film is 5-120 μm.

5. The CPP film post-treatment method of claim 1, wherein, The thickness of the CPP film is 20-50 μm.

6. The CPP film post-treatment method according to claim 5, wherein, The CPP film is made of a homopolypropylene material.

7. The CPP film post-treatment method of claim 1, wherein, The CPP film is made of a copolypropylene material.

8. The CPP film post-treatment method of claim 1, wherein, The CPP film is obtained by using the CPP film post-processing method according to any one of claims 1-8.

9. A high strength CPP film characterized by, ​

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