Organosilicon coating, polytetrafluoroethylene composite film and preparation method and application thereof

Abstract

The invention belongs to the technical field of membrane materials, and particularly relates to an organic silicon coating, a polytetrafluoroethylene composite membrane as well as a preparation method and application thereof. The organic silicon coating disclosed by the invention is prepared from the following components in parts by weight: 5 to 20 parts of hexamethylcyclotrisiloxane, 5 to 15 parts of octamethylcyclotetrasiloxane, 0.5 to 5 parts of anchoring agent, 0.5 to 5 parts of platinum catalyst, 0.1 to 0.5 part of reaction inhibitor and 100 to 500 parts of methylbenzene. The organic silicon coating is used, a compact hole sealing coating is formed on the modified surface of the surface modified polytetrafluoroethylene film, original micropores of the polytetrafluoroethylene film can be isolated, the sealing performance is good, and the problem that the barrier property of the polytetrafluoroethylene film is poor is solved. Meanwhile, both the organic silicon coating and the polytetrafluoroethylene have very high temperature resistance, and can stay in an autoclave at 280 DEG C for 3 hours without the occurrence of curling, melting, cracking and other abnormalities. And the composite film has good high temperature resistance and good barrier property, and meets the molding requirements of a thermosetting prepreg system.

Description

Technical Field

[0001] The invention belongs to the technical field of membrane materials, and specifically relates to an organic silicon coating, a polytetrafluoroethylene composite membrane, and a preparation method and application thereof. Background Art

[0002] The traditional autoclave molding process uses nylon and polyethylene composite film or pure nylon as vacuum bag film, which can play a role in barrier and pressure retention, but is limited by the melting point of the material. The use temperature of polyethylene cannot exceed 120°C, and the use temperature of nylon cannot exceed 250°C. With the rapid development of BMI resin prepreg and thermosetting prepreg, the curing process temperature needs to reach 250°C to 300°C. Ordinary nylon and polyethylene composite film or pure nylon vacuum bag film can no longer meet the requirements of this process.

[0003] Film materials that can withstand 250℃ to 300℃ are generally polytetrafluoroethylene or polyimide (PI). PI film can withstand 400℃, but the material cost is expensive, and PI film is relatively hard. It is generally only suitable for molds with small fluctuations and poor conformability. At the same time, due to the "break" effect of PI, once there is a hole, there is a risk that the entire film may break. Therefore, polytetrafluoroethylene film with better flexibility becomes the first choice, but the current polytetrafluoroethylene film has poor sealing and barrier properties, and cannot meet the use requirements of high-temperature vacuum bag film. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide an organosilicon coating, a polytetrafluoroethylene composite film, and a preparation method and application thereof. The organosilicon coating of the present invention is used to prepare a sealing coating on the modified surface of the surface-modified polytetrafluoroethylene film, and the formed polytetrafluoroethylene composite film has good sealing performance and excellent barrier properties, meeting the use requirements of high-temperature vacuum bag films.

[0005] The invention provides an organic silicon coating, comprising the following components in parts by weight: 5 to 20 parts of hexamethylcyclotrisiloxane, 5 to 15 parts of octamethylcyclotetrasiloxane, 0.5 to 5 parts of an anchoring agent, 0.5 to 5 parts of a platinum catalyst, 0.1 to 0.5 parts of a reaction inhibitor and 100 to 500 parts of toluene.

[0006] Preferably, the anchoring agent includes 3-glycidyloxypropyltriethoxysilane, and the reaction inhibitor includes 2-methyl-3-butyn-2-ol.

[0007] The present invention also provides a polytetrafluoroethylene composite membrane, comprising a surface-modified polytetrafluoroethylene membrane and a sealing coating covering the modified surface of the surface-modified polytetrafluoroethylene membrane, wherein the sealing coating is made of the organic silicon coating described in the above technical solution.

[0008] Preferably, the surface-modified polytetrafluoroethylene membrane comprises a sodium-modified polytetrafluoroethylene membrane or a plasma-modified polytetrafluoroethylene membrane.

[0009] Preferably, the sodium modified polytetrafluoroethylene membrane is obtained by soaking the polytetrafluoroethylene membrane in a sodium naphthalene solution; the sodium naphthalene solution comprises the following components in parts by weight: 5 to 10 parts of naphthalene, 1 to 3 parts of sodium and 80 to 100 parts of tetrahydrofuran.

[0010] Preferably, the plasma-modified polytetrafluoroethylene membrane is obtained by plasma treatment of a polytetrafluoroethylene membrane, and the conditions of the plasma treatment include: a pressure of 0.15*133.3 Pa, a radio frequency of 45 to 55 W, argon and oxygen gases, an argon flow rate of 5 to 7 L / min, and an oxygen flow rate of 3 to 5 L / min; and a plasma treatment time of 30 to 90 seconds.

[0011] Preferably, the sealing coating has a gram weight of 1 to 10 g / m 2 .

[0012] The present invention also provides a method for preparing the polytetrafluoroethylene composite film described in the above technical solution, comprising the following steps:

[0013] The polytetrafluoroethylene membrane is subjected to surface modification treatment to obtain a surface modified polytetrafluoroethylene membrane;

[0014] The modified surface of the surface-modified polytetrafluoroethylene membrane is coated with the organic silicon coating to obtain a polytetrafluoroethylene composite membrane.

[0015] Preferably, after coating, the process further comprises: drying and heat curing; the drying temperature is 50-70° C. and the time is 1-3 minutes; the heat curing temperature is 120-150° C. and the time is 30-60 seconds.

[0016] The present invention also provides the use of the polytetrafluoroethylene composite film described in the above technical solution or the polytetrafluoroethylene composite film obtained by the above preparation method as a vacuum bag film.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention provides an organosilicon coating, comprising the following components in parts by weight: 5 to 20 parts of hexamethylcyclotrisiloxane, 5 to 15 parts of octamethylcyclotetrasiloxane, 0.5 to 5 parts of an anchoring agent, 0.5 to 5 parts of a platinum catalyst, 0.1 to 0.5 parts of a reaction inhibitor, and 100 to 500 parts of toluene. The organosilicon coating of the present invention is used to prepare a sealing coating on the modified surface of a surface-modified polytetrafluoroethylene film, and the formed polytetrafluoroethylene composite film has good sealing performance and excellent barrier properties, and meets the use requirements of high-temperature vacuum bag films.

[0019] The present invention also provides a polytetrafluoroethylene composite film, which includes a surface-modified polytetrafluoroethylene film and a sealing coating. The surface modification can reduce the surface energy of the polytetrafluoroethylene film, so that it can be composited with the sealing coating; the organic silicon coating forms a dense sealing coating on the surface of the surface-modified polytetrafluoroethylene film, which can isolate the original micropores of the polytetrafluoroethylene film, has good sealing performance, and solves the problem of poor barrier properties of the polytetrafluoroethylene film. At the same time, the organic silicon coating and polytetrafluoroethylene have high temperature resistance and can stay in a 280°C autoclave for 3 hours without abnormal phenomena such as curling, melting, and rupture, meeting the use requirements of high-temperature vacuum bag films. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 This is a thermal gravimetric curve of the plasma-treated film of Example 2;

[0022] Figure 2 This is a thermogravimetric curve of the composite film of Example 3;

[0023] Figure 3 is a photoelectron spectroscopy (XPS) graph of the original film used in the examples;

[0024] Figure 4 This is the photoelectron spectroscopy (XPS) diagram of the sodium-treated film of Example 1;

[0025] Figure 5 This is a photoelectron spectroscopy (XPS) diagram of the plasma-treated film of Example 2;

[0026] Figure 6 This is the photoelectron spectroscopy (XPS) diagram of the composite film of Example 3;

[0027] Figure 7 This is a photoelectron spectroscopy (XPS) diagram of the composite film surface after alcohol friction treatment in Example 3;

[0028] Figure 8 This is a photoelectron spectroscopy (XPS) diagram of the composite film of Example 8;

[0029] Fig. 9 These are photos of the composite film autoclave of Example 5 before and after use, where the left photo is a photo taken at room temperature, and the right photo is a photo taken after high-temperature use at 280°C. DETAILED DESCRIPTION

[0030] The invention provides an organic silicon coating, comprising the following components in parts by weight: 5 to 20 parts of hexamethylcyclotrisiloxane, 5 to 15 parts of octamethylcyclotetrasiloxane, 0.5 to 5 parts of an anchoring agent, 0.5 to 5 parts of a platinum catalyst, 0.1 to 0.5 parts of a reaction inhibitor and 100 to 500 parts of toluene.

[0031] In the present invention, the weight portion of the hexamethylcyclotrisiloxane (D3) is preferably 10 to 15 parts, and the hexamethylcyclotrisiloxane is the main ingredient of the sealing liquid.

[0032] Based on 1 part by weight of hexamethylcyclotrisiloxane, the weight of the octamethylcyclotetrasiloxane (D4) is preferably 10 to 15 parts, and the octamethylcyclotetrasiloxane is the main ingredient of the sealing liquid.

[0033] Based on 1 part by weight of hexamethylcyclotrisiloxane, the weight of the anchoring agent is preferably 0.5 to 1 part; the anchoring agent preferably includes 3-glycidyloxypropyltriethoxysilane, and the anchoring agent is a silane coupling agent, which can improve the adhesion of the coating.

[0034] Based on 1 part by weight of hexamethylcyclotrisiloxane, the weight of the platinum catalyst is preferably 0.5 to 1 part. The platinum catalyst can catalyze the curing process.

[0035] Based on 1 part by weight of hexamethylcyclotrisiloxane, the weight of the reaction inhibitor is preferably 0.1 to 0.2 parts. The inhibitor preferably includes 2-methyl-3-butyn-2-ol, which can slow down the reaction speed of the curing process and prevent explosion.

[0036] Based on 1 part by weight of hexamethylcyclotrisiloxane, the weight of toluene is preferably 100 to 300 parts, specifically 100 parts, 300 parts or 500 parts.

[0037] In the present invention, the organosilicon coating more preferably comprises the following components in parts by weight: 10 to 15 parts of hexamethylcyclotrisiloxane, 10 to 15 parts of octamethylcyclotetrasiloxane, 0.5 parts of anchoring agent, 0.5 to 5 parts of platinum catalyst, 0.1 parts of reaction inhibitor and 100 to 500 parts of toluene.

[0038] The present invention also provides a polytetrafluoroethylene composite membrane, comprising a surface-modified polytetrafluoroethylene membrane and a sealing coating covering the modified surface of the surface-modified polytetrafluoroethylene membrane, wherein the sealing coating is made of the organic silicon coating described in the above technical solution.

[0039] In the present invention, the surface modified polytetrafluoroethylene membrane preferably includes sodium modified polytetrafluoroethylene membrane or plasma modified polytetrafluoroethylene membrane. The surface modified polytetrafluoroethylene membrane used in the present invention is convenient for subsequent compounding with the sealing coating.

[0040] In the present invention, the sodium modified polytetrafluoroethylene membrane is preferably obtained by soaking the polytetrafluoroethylene membrane in a sodium naphthalene solution; the sodium naphthalene solution preferably includes the following components in parts by weight: 5 to 10 parts of naphthalene, 1 to 3 parts of sodium and 80 to 100 parts of tetrahydrofuran, specifically 10 parts of naphthalene, 3 parts of sodium and 87 parts of tetrahydrofuran; the soaking time is preferably 3 to 7 minutes, specifically 5 minutes, and the surface of the polytetrafluoroethylene membrane is corroded during the soaking process, which is convenient for compounding with the coating material. After the soaking, it is preferably further washed and dried, and the washing preferably includes washing with tetrahydrofuran and washing with water in sequence to wash away the sodium naphthalene solution and tetrahydrofuran; the present invention has no special requirements for the drying conditions.

[0041] In the present invention, the plasma modified polytetrafluoroethylene film is preferably obtained by plasma treatment of polytetrafluoroethylene film, and the conditions of the plasma treatment include: the pressure is preferably 0.15*133.3Pa, the radio frequency is preferably 45-55W, specifically 50W, the gas is argon and oxygen, the argon flow rate is preferably 5-7L / min, specifically 6L / min, and the oxygen flow rate is preferably 3-5L / min, specifically 4L / min; the plasma treatment time is preferably 30-90 seconds, specifically 60 seconds. During the plasma treatment, the surface roughness of the polytetrafluoroethylene film increases (dyne value greater than 40), and the oxygen atoms in the gas are transferred to the film surface to form active groups, which are convenient for compounding with the coating material.

[0042] In the present invention, the surface energy of the surface-modified polytetrafluoroethylene membrane is lower than that of the unmodified polytetrafluoroethylene membrane, and the reduction of the surface energy is conducive to compounding with the coating.

[0043] In the present invention, the thickness of the polytetrafluoroethylene film in the surface modified polytetrafluoroethylene film is preferably 30 to 150 microns, specifically 30 microns, 50 microns, 75 microns, 100 microns, 125 microns or 150 microns, the room temperature tensile strength is preferably ≥30 MPa, and the elongation at break is preferably ≥300%. The present invention has no special requirements on the source of the polytetrafluoroethylene film, and it can be a commercially available product.

[0044] In the present invention, the sealing coating is a silicone coating, and the weight of the sealing coating is preferably 1 to 10 g / m 2 , specifically 1g / m 2 , 1.6g / m 2 , 2.3g / m 2 3.8g / m2 , 3.9g / m 2 or 4.1 g / m 2 .

[0045] The present invention also provides a method for preparing the polytetrafluoroethylene composite film described in the above technical solution, comprising the following steps:

[0046] The polytetrafluoroethylene membrane is subjected to surface modification treatment to obtain a surface modified polytetrafluoroethylene membrane;

[0047] The modified surface of the surface-modified polytetrafluoroethylene membrane is coated with the organic silicon coating to obtain a polytetrafluoroethylene composite membrane.

[0048] In the present invention, unless otherwise specified, the materials and equipment used are commercially available products in the art.

[0049] In the present invention, the coating method preferably includes rolling, scraping or spraying.

[0050] In the present invention, the coating is preferably performed on one side of the surface of the surface-modified polytetrafluoroethylene membrane, and the other side is not coated.

[0051] In the present invention, after the coating, it is preferred that the coating further includes: drying and heat curing; the drying temperature is preferably 50-70°C, specifically 60°C, and the time is preferably 1-3 minutes, specifically 2 minutes; the heat curing temperature is preferably 120-150°C, and the time is preferably 30-60 seconds.

[0052] The present invention also provides the use of the polytetrafluoroethylene composite film described in the above technical solution or the polytetrafluoroethylene composite film obtained by the above preparation method as a vacuum bag film.

[0053] The present invention solves the problem that the surface of polytetrafluoroethylene is non-polar and has poor affinity with other materials by modifying the surface of polytetrafluoroethylene; and solves the problem that a large number of micropores of about 200 nm exist on the surface of polytetrafluoroethylene and the gas barrier effect is poor by preparing an organic silicon sealing coating on the modified surface. The present invention provides a vacuum bag film with excellent heat resistance, good barrier performance and good coating adhesion.

[0054] In order to further illustrate the present invention, the organosilicon coating, polytetrafluoroethylene composite film and preparation method and application thereof provided by the present invention are described in detail below in conjunction with the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0055] In the embodiment of the present invention, the anchoring agent used is 3-glycidyloxypropyltriethoxysilane, and the inhibitor is 2-methyl-3-butyn-2-ol.

[0056] Example 1

[0057] A naphthalene sodium solution is prepared according to the following weight parts: 10 parts of naphthalene, 3 parts of sodium and 87 parts of tetrahydrofuran; a polytetrafluoroethylene film with a thickness of 50 microns is then immersed in the prepared naphthalene sodium solution for 5 minutes; the surface of the polytetrafluoroethylene film after immersion is cleaned with tetrahydrofuran and water in turn; and the polytetrafluoroethylene film with sodium on the surface is obtained after drying.

[0058] Example 2

[0059] A 50-micron-thick polytetrafluoroethylene film was placed in a reaction chamber with a pressure of 0.15*133.3Pa, a radio frequency of 50W, argon and oxygen gases, gas flow rates of 6L / min and 4L / min respectively, and a treatment time of 60 seconds to obtain a plasma-treated polytetrafluoroethylene film.

[0060] Example 3

[0061] The sodium-treated polytetrafluoroethylene film obtained in Example 1 was used as a substrate, and a sealing coating was applied on its surface by knife coating, followed by drying and curing at a drying temperature of 60° C. for 1 minute, and a curing temperature of 120° C. for 1 minute.

[0062] The formula of the sealing coating, in parts by weight, includes: 15 parts of hexamethylcyclotrisiloxane (D3), 10 parts of octamethylcyclotetrasiloxane (D4), 0.5 parts of anchoring agent, 0.5 parts of platinum catalyst, 0.1 parts of inhibitor, and 100 parts of toluene.

[0063] Example 4

[0064] The sodium-treated polytetrafluoroethylene film prepared in Example 1 was used as a substrate, and the sealing coating was coated on its surface by knife coating, followed by drying and curing at 60° C. for 1 minute, and at 150° C. for 30 seconds.

[0065] The formula of the sealing coating, in parts by weight, includes: 10 parts of hexamethylcyclotrisiloxane (D3), 15 parts of octamethylcyclotetrasiloxane (D4), 0.5 parts of anchoring agent, 0.5 parts of platinum catalyst, 0.1 parts of inhibitor, and 100 parts of toluene.

[0066] Example 5

[0067] The plasma-treated polytetrafluoroethylene film obtained in Example 2 was used as a substrate, and a sealing coating was applied on its surface by knife coating, followed by drying and curing at a drying temperature of 60° C. for 1 minute, and a curing temperature of 120° C. for 1 minute.

[0068] The formula of the sealing coating, in parts by weight, includes: 15 parts of hexamethylcyclotrisiloxane (D3), 10 parts of octamethylcyclotetrasiloxane (D4), 0.5 parts of anchoring agent, 0.5 parts of platinum catalyst, 0.1 parts of inhibitor, and 100 parts of toluene.

[0069] Example 6

[0070] The plasma-treated polytetrafluoroethylene film obtained in Example 2 was used as a substrate, and a sealing coating was applied on its surface by knife coating, followed by drying and curing at a drying temperature of 60° C. for 1 minute, and a curing temperature of 150° C. for 30 seconds.

[0071] The formula of the sealing coating, in parts by weight, includes: 10 parts of hexamethylcyclotrisiloxane (D3), 15 parts of octamethylcyclotetrasiloxane (D4), 0.5 parts of anchoring agent, 0.5 parts of platinum catalyst, 0.1 parts of inhibitor, and 100 parts of toluene.

[0072] Example 7

[0073] The sodium-treated polytetrafluoroethylene film prepared in Example 1 was used as a substrate, and the sealing coating was coated on its surface by knife coating, and then dried and cured at a drying temperature of 60° C. for 2 minutes and a curing temperature of 120° C. for 1 minute.

[0074] The formula of the sealing coating, in parts by weight, includes: 15 parts of hexamethylcyclotrisiloxane (D3), 10 parts of octamethylcyclotetrasiloxane (D4), 0.5 parts of anchoring agent, 0.5 parts of platinum catalyst, 0.1 parts of inhibitor, and 300 parts of toluene.

[0075] Example 8

[0076] The plasma-treated polytetrafluoroethylene film obtained in Example 2 was used as a substrate, and a sealing coating was applied on its surface by knife coating, followed by drying and curing at a drying temperature of 60° C. for 3 minutes, and a curing temperature of 120° C. for 1 minute.

[0077] The formula of the sealing coating, in parts by weight, includes: 15 parts of hexamethylcyclotrisiloxane (D3), 10 parts of octamethylcyclotetrasiloxane (D4), 0.5 parts of anchoring agent, 0.5 parts of platinum catalyst, 0.1 parts of inhibitor, and 500 parts of toluene.

[0078] The original film (untreated) used in the example and the polytetrafluoroethylene composite film prepared in the example were tested for surface dyne value, and the results are shown in Table 1, wherein the conditions of the alcohol friction treatment include: the alcohol is medical alcohol with a volume concentration of 75%, the friction frequency is 30 times / minute, and the friction time is 15 minutes.

[0079] Table 1 Changes in surface dyne value before and after coating

[0080]

[0081] It can be seen from the data in Table 1 that the surface dyne values ​​of the original film and the coating surface are both less than 21, indicating that the release property of the composite film is still very good; after being rubbed with alcohol, the dyne value of the coating surface is still low, indicating the stability of the coating adhesion.

[0082] Table 2 Tensile strength and elongation at break of films of Examples 1 to 8

[0083]

[0084] It can be seen from the data in Table 2 that after different treatments and coatings, the changes in the mechanical properties (tensile strength and elongation at break) of the film meet the needs of vacuum bagging films and can be used in industrial production.

[0085] Table 3 Gas permeability of original film, Example 5 and Example 7 composite film (GB / T 1038-2000)

[0086]

[0087] It can be seen from the data in Table 3 that the gas permeability is reduced by coating, and the barrier performance required by the vacuum bag film is achieved. The gram weight of the coating of the composite film of Example 5 is greater than that of Example 7, and the gas barrier performance of the composite film of Example 5 is more excellent.

[0088] Figure 1 This is the thermal gravimetric curve of the plasma-treated film in Example 2. Figure 2 The thermal gravimetric curve of the composite film of Example 3 is shown in FIG. The red line in the figure is the thermal gravimetric curve, and the blue line is the curve after the thermal gravimetric derivative is obtained. Figure 1 and Figure 2 It can be seen that the decomposition temperature of the film of Example 2 is 560°C, and the decomposition temperature of the composite film of Example 3 is 582.98°C, which has excellent heat resistance and can meet the use requirement of 280°C.

[0089] Figure 3 to Figure 8 They are the photoelectron spectroscopy (XPS) graphs of the original film, Example 1, Example 2, Example 3, the composite film after the surface of Example 3 was rubbed with alcohol, and the composite film of Example 8. Figure 3 It can be seen that the original film contains a large amount of fluorine, but after the sealing coating is improved, the film is Figure 6 ) as an example, only silicon can be detected on its surface, indicating that the coating has effectively covered the surface. After the surface was rubbed with alcohol and tested again, the element content remained basically unchanged, indicating that the coating has good adhesion and will not fall off.

[0090] Fig. 9 The photos of Example 5 composite film autoclave before and after use, the left photo is at room temperature, and the right photo is after high temperature use at 280°C (3 hours). At room temperature, the film is tightly bonded to the sealing strip, and has good airtightness. After high temperature use, the film still maintains its own color, and no abnormalities such as brittle cracking and melting occur, showing excellent temperature resistance.

[0091] Although the above-mentioned embodiments have made a detailed description of the present invention, they are only some embodiments of the present invention, rather than all embodiments. People can also obtain other embodiments based on the embodiments of the present invention without creative work, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. An organosilicon coating, characterized in that: The invention comprises the following components in parts by weight: 5 to 20 parts of hexamethylcyclotrisiloxane, 5 to 15 parts of octamethylcyclotetrasiloxane, 0.5 to 5 parts of anchoring agent, 0.5 to 5 parts of platinum catalyst, 0.1 to 0.5 parts of reaction inhibitor and 100 to 500 parts of toluene.

2. The organosilicon coating according to claim 1, characterized in that: The anchoring agent includes 3-glycidyloxypropyltriethoxysilane, and the reaction inhibitor includes 2-methyl-3-butyn-2-ol.

3. A polytetrafluoroethylene composite membrane, characterized in that: The invention comprises a surface-modified polytetrafluoroethylene film and a sealing coating layer covering the modified surface of the surface-modified polytetrafluoroethylene film, wherein the sealing coating layer is made of the organic silicon coating according to claim 1 or 2.

4. The polytetrafluoroethylene composite membrane according to claim 3, characterized in that: The surface modified polytetrafluoroethylene membrane includes a sodium modified polytetrafluoroethylene membrane or a plasma modified polytetrafluoroethylene membrane.

5. The polytetrafluoroethylene composite membrane according to claim 4, characterized in that: The sodium modified polytetrafluoroethylene membrane is obtained by soaking the polytetrafluoroethylene membrane in a sodium naphthalene solution; the sodium naphthalene solution comprises the following components in parts by weight: 5 to 10 parts of naphthalene, 1 to 3 parts of sodium and 80 to 100 parts of tetrahydrofuran.

6. The polytetrafluoroethylene composite membrane according to claim 4, characterized in that: The plasma-modified polytetrafluoroethylene membrane is obtained by subjecting the polytetrafluoroethylene membrane to plasma treatment. The conditions of the plasma treatment include: a pressure of 0.15*133.3 Pa, a radio frequency of 45 to 55 W, argon and oxygen gases, an argon flow rate of 5 to 7 L / min, and an oxygen flow rate of 3 to 5 L / min; and a plasma treatment time of 30 to 90 seconds.

7. The polytetrafluoroethylene composite membrane according to claim 3, characterized in that: The sealing coating has a gram weight of 1 to 10 g / m 2 .

8. The method for preparing a polytetrafluoroethylene composite membrane according to any one of claims 3 to 7, characterized in that: The following steps are involved: The polytetrafluoroethylene membrane is subjected to surface modification treatment to obtain a surface modified polytetrafluoroethylene membrane; The modified surface of the surface-modified polytetrafluoroethylene membrane is coated with the organic silicon coating to obtain a polytetrafluoroethylene composite membrane.

9. The preparation method according to claim 8, characterized in that: The coating process further includes: drying and heat curing; the drying temperature is 50-70° C. and the time is 1-3 minutes; the heat curing temperature is 120-150° C. and the time is 30-60 seconds.

10. Use of the polytetrafluoroethylene composite film according to any one of claims 3 to 7 or the polytetrafluoroethylene composite film obtained by the preparation method according to any one of claims 8 to 9 as a vacuum bag film.

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