A method for preparing a flexible conductive PVC-based composite film

Abstract

The present invention discloses a method for preparing a flexible conductive PVC-based composite film, comprising the steps of preparing a mixed diluent, preparing a casting solution, preparing a coagulation bath, coating the casting solution with a doctor blade, forming the film by phase conversion, extracting the diluent, and performing a heat treatment. The method comprises the following steps: using a ternary mixed diluent comprising a water-soluble diluent having a strong interaction with PVC and two water-insoluble diluents having a weak interaction with PVC, uniformly dispersing an unmodified carbon nanomaterial in a PVC solution, adopting a TIPS and NIPS composite method to prepare a flexible conductive PVC-based composite film, then adopting an in-situ template method to distribute the carbon nanomaterial dispersed in the water-insoluble diluent phase having a weak interaction with PVC to the upper surface and the surface of the three-dimensional network pore wall of the PVC-based composite film through a diluent extraction process, and finally heat-treating the composite film to obtain a flexible conductive PVC-based composite film. The present invention has a simple preparation process, can meet the needs of industrial large-scale production, and has broad application prospects in the field of flexible conductive materials.

Description

Technical Field

[0001] The present invention relates to the technical field of composite film preparation, and in particular to a method for preparing a flexible conductive PVC-based composite film. Background Art

[0002] With the growing demand for wearable devices, the research and development of wearable flexible devices has attracted widespread attention. Flexible conductive materials, like blood vessels and nerves in living organisms, are an essential component of flexible devices. Electrode materials in traditional devices are primarily metals, but due to their inflexibility, they are prone to fracture and failure during stretching, making them unable to meet the development needs of flexible devices. Therefore, the research on flexible conductive materials is of great significance.

[0003] Currently, there are three main types of flexible conductive materials. The first is metal-based flexible conductive materials, which design traditional metal materials into stretchable structures. For example, metal electrodes such as gold and platinum are designed into frustum structures for use in flexible sensor devices. These structures have excellent conductivity, but the processing process usually requires micromachining methods such as photolithography, electron beam deposition, and reactive ion etching. The operation is complex and costly, making them unsuitable for large-scale applications. The second is carbon-based flexible conductive materials, which process carbon nanomaterials such as carbon nanotubes, graphene, and biomass-derived carbon fibers into flexible conductive materials. However, their high price limits their application. The third is polymer-based flexible conductive materials. Commonly used polymers can be divided into intrinsically conductive polymers and composite conductive polymers. Intrinsically conductive polymers include poly (3-hexylthiophene), polyaniline, polypyrrole, etc., which have conjugated structures containing unsaturated bonds and are easily oxidized, resulting in poor conductivity in practical applications and limiting their application. The matrix of the composite conductive polymer is a polymer material that is not conductive itself. Conductive polymer materials are typically formed by uniformly dispersing conductive fillers (such as carbon nanotubes) within a single or multi-phase polymer matrix through various processing methods (melting, solution, or other molding techniques). Composite conductive polymer flexible conductive materials have become a key research and development area in the field of flexible conductive materials in recent years due to their advantages such as light weight, good processability, and adjustable conductivity. These materials allow for a wide range of conductive fillers and polymers to be selected based on the specific application scenarios.

[0004] Polyvinyl chloride (PVC) has the characteristics of a general-purpose resin. It is a high-strength, corrosion-resistant, oxidation-resistant, and high-temperature resistant material. It is often used in cables, films, pipes, and other fields. It has good stability, chemical resistance, corrosion resistance, good film-forming properties, and high mechanical properties. In addition, the PVC structural unit contains a strong polar group, the chlorine group, which has good compatibility with carbon nanotubes, making it a good flexible matrix material.

[0005] Due to the strong interaction between carbon nanotubes, agglomeration is very likely to occur when blended with polymers, and carbon nanotubes are randomly dispersed in the polymer matrix. Therefore, it is usually necessary to add more carbon nanotubes to improve the conductive properties of the polymer. However, adding a high content of carbon nanotubes will cause a series of new problems, such as processing difficulties and poor mechanical properties, which hinders its development and application.

[0006] It can be seen that in order to give PVC good conductivity without destroying the surface properties and conductive properties of nanocarbon materials, it is urgent to develop a reasonable preparation process to solve the above problems. Summary of the Invention

[0007] The object of the present invention is to provide a method for preparing a flexible conductive PVC-based composite film, which can solve the technical problems involved in the background technology.

[0008] The technical solution of the present invention is:

[0009] A method for preparing a flexible conductive PVC-based composite film comprises the following steps:

[0010] (1) Solvent preparation: a water-soluble diluent having a strong interaction with PVC and two water-insoluble diluents having a weak interaction with PVC are mixed, and the mixture is mechanically stirred to form a ternary mixed diluent; wherein the mass fraction of the diluent having a strong interaction with PVC is 50-74%, and the mass fraction of the two water-insoluble diluents having a weak interaction with PVC is 4-20% in total;

[0011] (2) Preparation of casting solution: PVC and unmodified nano-carbon material are placed in the ternary mixed diluent prepared in step (1), and after mechanical stirring at a certain temperature, vacuum degassing is performed to prepare a PVC casting solution;

[0012] (3) Preparation of coagulation bath: The coagulation bath is deionized water;

[0013] (4) Scraping the casting liquid: Scrape the PVC casting liquid onto the nonwoven fabric using a scraper;

[0014] (5) Phase inversion molding: The nonwoven fabric containing the PVC casting solution is immediately immersed in a coagulation bath, taken out and dried at room temperature to obtain a dried film;

[0015] (6) Diluent extraction and heat treatment: The obtained controlled dry film is placed in a weak non-solvent to extract the diluent to obtain an extracted film, and then the extracted film is placed in an oven for heat treatment to obtain a flexible conductive PVC-based composite film.

[0016] As a preferred improvement of the present invention, in step (2), the solid content of the PVC casting solution is 15-25%.

[0017] As a preferred improvement of the present invention, in step (2), the ratio of the PVC to the unmodified nano-carbon material is 3-48:1.

[0018] As a preferred improvement of the present invention, in step (2), the temperature of the casting solution is 25-80° C., and the stirring time of the casting solution is 6-24 h.

[0019] As a preferred improvement of the present invention, in step (2), the nano-carbon material is carbon nanotubes, and the content thereof is 0.5%-5%.

[0020] As a preferred improvement of the present invention, in step (1), the diluent having a strong interaction with PVC and being soluble in water is one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, triethyl phosphate, trimethyl phosphate, and dimethyl sulfoxide; the diluent having a weak interaction with PVC and being insoluble in water is any two of benzophenone, methyl isobutyl ketone, diisobutyl ketone, dimethyl phthalate, dibutyl phthalate, dioctyl phthalate, dimethyl isophthalate, methyl salicylate, triacetin, diphenyl carbonate, cyclohexanone, and butyl acetate.

[0021] As a preferred improvement of the present invention, in step (3), the conductivity of the deionized water is ≤16 MΩ·cm; and the coagulation bath temperature is 25-45°C.

[0022] As a preferred improvement of the present invention, in step (4), the casting liquid is scraped onto the surface of the non-woven fabric to form a flat film, specifically, the casting liquid is coated on the non-woven fabric with a thickness of 50-150 μm at a speed of 1.0-5.0 m / s, and after air cooling for 1-30 seconds, it is solidified in a coagulation bath; the thickness of the flat film is 100-400 μm; the non-woven fabric is one of polyethylene terephthalate non-woven fabric and polyamide non-woven fabric.

[0023] As a preferred improvement of the present invention, in step (5), the immersion time in the coagulation bath is 1-2 hours.

[0024] As a preferred improvement of the present invention, in step (6), the weak non-solvent is one of methanol, ethanol, and propanol; the temperature in the drying oven is 40-60° C.; and the heat treatment time is 1-60 min.

[0025] The beneficial effects of the present invention are as follows:

[0026] 1. Combining the NIPS method with the TIPS method, by adjusting the relationship between heat transfer and mass transfer during the film formation process, allows both thermally induced phase separation and solvent-induced phase separation to exist in the system. This makes it easier to obtain or control the formation of a honeycomb pore structure, avoids the accumulation of carbon nanomaterials, and improves their dispersion in the polymer matrix and the mechanical properties of PVC-based conductive materials.

[0027] 2. By using a weak non-solvent to extract a diluent that has a weak interaction with PVC and is insoluble in water, the carbon nanomaterial dispersed in the diluent phase that has a weak interaction with PVC and is insoluble in water migrates. During the diluent extraction process, the carbon nanotubes are distributed to the upper surface of the PVC-based composite film and the surface of the three-dimensional network pore walls, thereby improving the connectivity of the conductive network and the conductive properties of the PVC-based composite film. This allows the flexible conductive PVC-based composite film prepared by the present invention to be used in the field of flexible conductive applications.

[0028] 3. The preparation process of the present invention is simple, can meet the needs of industrial large-scale production, and has broad application prospects in the field of flexible conductive materials. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in this field can implement it. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0031] Example 1

[0032] Example 1 provides a method for preparing a flexible conductive PVC-based composite film, comprising the following steps:

[0033] (1) Solvent preparation: N,N-dimethylformamide, diphenyl carbonate, and triacetin are mixed in a ratio of 12:1:1, and mechanically stirred to prepare a ternary mixed diluent; wherein the mass fraction of the diluent having a strong interaction with PVC is 71%, and the mass fraction of the two diluents having a weak interaction with PVC and being insoluble in water is 12% in total;

[0034] (2) Preparation of casting solution: 16% by mass of PVC and 1% of unmodified nano-carbon material were placed in the ternary mixed diluent prepared in step (1), and the mixture was mechanically stirred for 10 h at 70° C. and then vacuum degassed to prepare a PVC casting solution;

[0035] (3) Preparation of coagulation bath: The coagulation bath is deionized water and the coagulation bath temperature is 25°C;

[0036] (4) Casting liquid blade coating: The PVC casting liquid is applied to the nonwoven fabric using a blade coating machine. Specifically, the casting liquid is applied to the surface of a polyethylene terephthalate nonwoven fabric with a thickness of 100 μm at a speed of 3.0 m / s. The thickness of the flat film is 150 μm.

[0037] (5) Phase inversion molding: The nonwoven fabric containing the PVC casting solution was immediately immersed in a coagulation bath for 1 h, taken out and dried at room temperature to obtain a dried film;

[0038] (6) Diluent extraction and heat treatment: The obtained controlled-dry film is placed in ethanol for diluent extraction to obtain an extracted film, and then the extracted film is placed in an oven at a temperature of 40°C for heat treatment for 5 minutes to obtain a flexible conductive PVC-based composite film.

[0039] Example 2

[0040] Example 2 provides a method for preparing a flexible conductive PVC-based composite film, comprising the following steps:

[0041] (1) Solvent preparation: N,N-dimethylformamide, benzophenone, and dioctyl phthalate are mixed in a ratio of 10:1:1, and mechanically stirred to prepare a ternary mixed diluent; wherein the mass fraction of the diluent having a strong interaction with PVC is 70%, and the mass fraction of any two diluents having a weak interaction with PVC and being insoluble in water is 14% in total;

[0042] (2) Preparation of casting solution: 15% by mass of PVC and 1% of unmodified nano-carbon material were placed in the ternary mixed diluent prepared in step (1), and the mixture was mechanically stirred for 12 h at 60° C. and then vacuum degassed to prepare a PVC casting solution;

[0043] (3) Preparation of coagulation bath: The coagulation bath is deionized water and the coagulation bath temperature is 35°C;

[0044] (4) Casting liquid blade coating: The PVC casting liquid is applied to the nonwoven fabric using a blade coating machine. Specifically, the casting liquid is applied to the surface of a polyethylene terephthalate nonwoven fabric with a thickness of 80 μm at a speed of 3.0 m / s. The thickness of the flat film is 150 μm.

[0045] (5) Phase inversion molding: The nonwoven fabric containing the PVC casting solution was immediately immersed in a coagulation bath for 1.5 h, taken out and dried at room temperature to obtain a dried film;

[0046] (6) Diluent extraction and heat treatment: The obtained controlled-dry film is placed in ethanol for diluent extraction to obtain an extracted film, and then the extracted film is placed in an oven at a temperature of 50°C for heat treatment for 5 minutes to obtain a flexible conductive PVC-based composite film.

[0047] Example 3

[0048] Example 3 provides a method for preparing a flexible conductive PVC-based composite film, comprising the following steps:

[0049] (1) Solvent preparation: N,N-dimethylformamide, dimethyl phthalate, and dibutyl phthalate are mixed in a ratio of 10:1:1, and mechanically stirred to prepare a ternary mixed diluent; wherein the mass fraction of the diluent having a strong interaction with PVC is 70%, and the mass fraction of any two diluents having a weak interaction with PVC and being insoluble in water is 14% in total;

[0050] (2) Preparation of casting solution: 15% by mass of PVC and 3% of unmodified nano-carbon material were placed in the ternary mixed diluent prepared in step (1), and the mixture was mechanically stirred for 12 h at 60° C. and then vacuum degassed to prepare a PVC casting solution;

[0051] (3) Preparation of coagulation bath: The coagulation bath is deionized water and the coagulation bath temperature is 35°C;

[0052] (4) Casting liquid blade coating: The PVC casting liquid is applied to the nonwoven fabric using a blade coating machine. Specifically, the casting liquid is applied to the surface of the polyethylene terephthalate nonwoven fabric with a thickness of 80 μm at a speed of 3.0 m / s. The thickness of the flat film is 220 μm.

[0053] (5) Phase inversion molding: The nonwoven fabric containing the PVC casting solution was immediately immersed in a coagulation bath for 1.5 h, taken out and dried at room temperature to obtain a dried film;

[0054] (6) Diluent extraction and heat treatment: The obtained controlled-dry film is placed in ethanol for diluent extraction to obtain an extracted film, and then the extracted film is placed in an oven at a temperature of 50°C for heat treatment for 15 minutes to obtain a flexible conductive PVC-based composite film.

[0055] Example 4

[0056] Example 4 provides a method for preparing a flexible conductive PVC-based composite film, comprising the following steps:

[0057] (1) Solvent preparation: N,N-dimethylformamide, methyl salicylate, and methyl isobutyl ketone are mixed in a ratio of 8:1:3, and mechanically stirred to prepare a ternary mixed diluent; wherein the mass fraction of the diluent having a strong interaction with PVC is 50%, and the mass fraction of any two diluents having a weak interaction with PVC and being insoluble in water is 26% in total;

[0058] (2) Preparation of casting solution: PVC with a mass fraction of 23% and unmodified nano-carbon material with a content of 1% are placed in the ternary mixed diluent prepared in step (1), and the mixture is mechanically stirred at a temperature of 80° C. for 24 hours and then vacuum degassed to prepare a PVC conductive film casting solution;

[0059] (3) Coagulation bath preparation: The coagulation bath is deionized water and the coagulation bath temperature is 45°C;

[0060] (4) Casting liquid blade coating: The PVC casting liquid is applied to the nonwoven fabric using a blade coating machine. Specifically, the casting liquid is applied to the surface of a polyethylene terephthalate nonwoven fabric with a thickness of 150 μm at a speed of 3.0 m / s. The thickness of the flat film is 150 μm.

[0061] (5) Phase inversion molding: The nonwoven fabric containing the PVC casting solution is immediately immersed in a coagulation bath for 2 h, taken out and dried at room temperature to obtain a dried film;

[0062] (6) Diluent extraction and heat treatment: The obtained controlled-dry film is placed in acetone for diluent extraction to obtain an extracted film, and then the extracted film is placed in an oven at a temperature of 50°C for heat treatment for 60 minutes to obtain a flexible conductive PVC-based composite film.

[0063] Example 5

[0064] Example 5 provides a method for preparing a flexible conductive PVC-based composite film, comprising the following steps:

[0065] (1) Solvent preparation: N,N-dimethylformamide, dimethyl isophthalate, and methyl salicylate are mixed in a ratio of 34:2:3, and mechanically stirred to prepare a ternary mixed diluent; wherein the mass fraction of the diluent having a strong interaction with PVC is 68%, and the mass fraction of any two diluents having a weak interaction with PVC and being insoluble in water is 10% in total;

[0066] (2) Preparation of casting solution: 17% by mass of PVC and 5% by mass of unmodified nano-carbon material were placed in the ternary mixed diluent prepared in step (1), and the mixture was mechanically stirred for 18 hours at 75°C and then vacuum degassed to prepare a PVC conductive film casting solution;

[0067] (3) Preparation of coagulation bath: The coagulation bath is deionized water and the coagulation bath temperature is 40°C;

[0068] (4) Casting liquid blade coating: The PVC casting liquid is applied to the nonwoven fabric using a blade coating machine. Specifically, the casting liquid is applied to the surface of a polyethylene terephthalate nonwoven fabric with a thickness of 100 μm at a speed of 3.0 m / s. The thickness of the flat film is 120 μm.

[0069] (5) Phase inversion molding: The nonwoven fabric containing the PVC casting solution was immediately immersed in a coagulation bath for 1 h, taken out and dried at room temperature to obtain a dried film;

[0070] (6) Diluent extraction and heat treatment: The obtained controlled-dry film is placed in acetone for diluent extraction to obtain an extracted film, and then the extracted film is placed in an oven at a temperature of 50°C for heat treatment for 15 minutes to obtain a flexible conductive PVC-based composite film.

[0071] The conductive properties of the composite films provided in Examples 1-5 are shown in Table 1.

[0072] Table 1 Conductive properties of composite films in implementation cases

[0073] Example Film thickness / μm Square resistance / Ω Conductivity / (S / cm) Example 1 150 14900 0.0051 Example 2 150 13780 0.0061 Example 3 220 1290 0.049 Example 4 150 6110 0.011 Example 5 120 87 1.5

[0074] As can be seen from Table 1, when the carbon content and the extractant are the same, the higher the content of the water-insoluble diluent with low interaction with PVC, the higher the conductivity of the composite membrane; when the carbon content is the same and the ratio of the water-soluble diluent with high interaction with PVC to the water-insoluble diluent with low interaction with PVC is equivalent, the conductivity obtained varies greatly with different extractants; when the extractant is the same and the ratio of the water-soluble diluent with high interaction with PVC to the water-insoluble diluent with low interaction with PVC is equivalent, the higher the carbon content, the higher the conductivity of the composite membrane; in addition, when the extractant is the same, a composite membrane with a high content of the water-insoluble diluent with low interaction with PVC and a low carbon content has a higher conductivity than a composite membrane with a low content of the water-insoluble diluent with low interaction with PVC and a high carbon content.

[0075] The beneficial effects of the present invention are as follows:

[0076] 1. Combining the NIPS method with the TIPS method, by adjusting the relationship between heat transfer and mass transfer during the film formation process, allows both thermally induced phase separation and solvent-induced phase separation to exist in the system. This makes it easier to obtain or control the formation of a honeycomb pore structure, avoids the accumulation of carbon nanomaterials, and improves their dispersion in the polymer matrix and the mechanical properties of PVC-based conductive materials.

[0077] 2. By using a weak non-solvent to extract a diluent that has a weak interaction with PVC and is insoluble in water, the carbon nanomaterial dispersed in the diluent phase that has a weak interaction with PVC and is insoluble in water migrates. During the diluent extraction process, the carbon nanotubes are distributed to the upper surface of the PVC-based composite film and the surface of the three-dimensional network pore walls, thereby improving the connectivity of the conductive network and the conductive properties of the PVC-based composite film. This allows the flexible conductive PVC-based composite film prepared by the present invention to be used in the field of flexible conductive applications.

[0078] 3. The preparation process of the present invention is simple, can meet the needs of industrial large-scale production, and has broad application prospects in the field of flexible conductive materials.

[0079] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and the embodiments. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A method for preparing a flexible conductive PVC-based composite film, characterized in that: The steps include: (1) Solvent preparation: a water-soluble diluent having a strong interaction with PVC and two water-insoluble diluents having a weak interaction with PVC are mixed, and the mixture is mechanically stirred to form a ternary mixed diluent; wherein the mass fraction of the diluent having a strong interaction with PVC is 50-74%, and the mass fraction of the two water-insoluble diluents having a weak interaction with PVC is 4-20% in total; (2) Preparation of casting solution: PVC and unmodified nano-carbon material are placed in the ternary mixed diluent prepared in step (1), and after mechanical stirring at a certain temperature, vacuum degassing is performed to prepare a PVC casting solution; (3) Preparation of coagulation bath: The coagulation bath is deionized water; (4) Scraping the casting liquid: Scrape the PVC casting liquid onto the nonwoven fabric using a scraper; (5) Phase inversion molding: The nonwoven fabric containing the PVC casting solution is immediately immersed in a coagulation bath, taken out and dried at room temperature to obtain a dried film; (6) Diluent extraction and heat treatment: The obtained controlled dry film is placed in a weak non-solvent for diluent extraction to obtain an extracted film, and then the extracted film is placed in an oven for heat treatment to obtain a flexible conductive PVC-based composite film; the weak non-solvent is one of methanol, ethanol, and propanol.

2. The method for preparing a flexible conductive PVC-based composite film according to claim 1, wherein: In step (2), the solid content of the PVC casting solution is 15-25%.

3. The method for preparing a flexible conductive PVC-based composite film according to claim 1, wherein: In step (2), the ratio of the PVC to the unmodified nano-carbon material is 3-48:

1.

4. The method for preparing a flexible conductive PVC-based composite film according to claim 1, wherein: In step (2), the temperature of the casting solution is 25-80° C., and the stirring time of the casting solution is 6-24 hours.

5. The method for preparing a flexible conductive PVC-based composite film according to claim 1, wherein: In step (2), the nano-carbon material is carbon nanotubes, and the content is 0.5-5%.

6. The method for preparing a flexible conductive PVC-based composite film according to claim 1, wherein: In step (1), the diluent having a strong action on PVC and being soluble in water is one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, triethyl phosphate, trimethyl phosphate, and dimethyl sulfoxide; the diluent having a weak action on PVC and being insoluble in water is any two of benzophenone, methyl isobutyl ketone, diisobutyl ketone, dimethyl phthalate, dibutyl phthalate, dioctyl phthalate, dimethyl isophthalate, methyl salicylate, triacetin, diphenyl carbonate, cyclohexanone, and butyl acetate.

7. The method for preparing a flexible conductive PVC-based composite film according to claim 1, wherein: In step (3), the conductivity of the deionized water is ≤16 MΩ·cm; and the coagulation bath temperature is 25-45°C.

8. The method for preparing a flexible conductive PVC-based composite film according to claim 1, wherein: In step (4), the casting liquid is scraped onto the surface of the nonwoven fabric to form a flat film, specifically, the casting liquid is coated on the nonwoven fabric with a thickness of 50-150 μm at a speed of 1.0-5.0 m / s, and after air cooling for 1-30 seconds, the flat film is solidified in a coagulation bath; the thickness of the flat film is 100-400 μm; the nonwoven fabric is one of polyethylene terephthalate nonwoven fabric and polyamide nonwoven fabric.

9. The method for preparing a flexible conductive PVC-based composite film according to claim 1, wherein: In step (5), the immersion time in the coagulation bath is 1-2 hours.

10. The method for preparing a flexible conductive PVC-based composite film according to claim 1, wherein: In step (6), the temperature in the oven is 40-60° C.; and the heat treatment time is 1-60 min.