Polyimide laminated body as well as preparation method and application thereof

Abstract

The invention discloses a polyimide laminated body as well as a preparation method and application thereof. The structure of the polyimide laminated body comprises a substrate layer, wherein the substrate layer is a glass fiber sheet of which the surface is pretreated by an epoxy silane coupling agent; the polyimide layer is obtained by uniformly mixing raw materials including polyimide, hexamethyldisilazane, nano silicon dioxide powder and a curing agent, coating the surface of the substrate layer with the mixture, and carrying out hot pressing. The polyimide laminated body has high toughness, high temperature resistance and long-term use stability, is not easy to break and layer in long-term use, and can be used for a long time at the temperature of 270 DEG C or below.

Description

Technical Field

[0001] This invention relates to the field of high-temperature resistant materials technology. More specifically, it relates to a polyimide laminate, its preparation method, and its applications. Background Technology

[0002] The development of technologies in specialized fields such as electronics, electrical appliances, and aerospace has placed higher demands on laminated products, especially on their high-temperature resistance. Currently, the maximum operating temperature of epoxy resin laminates is only 180℃. As the temperature increases, their heat resistance and electrical insulation properties decrease significantly, making it difficult to meet current requirements for laminated products.

[0003] Polyimide contains imide rings (-CO-N-CO-) in its main chain and is a high-performance polymer material with good heat resistance, low-temperature resistance, and flame retardancy. However, although existing polyimide resin laminates have a high glass transition temperature (above 200℃), their laminated products have poor toughness and are prone to cracking and delamination after long-term use. Summary of the Invention

[0004] To address the above problems, the present invention aims to provide a polyimide laminate, its preparation method, and its applications. This polyimide laminate possesses high toughness, high temperature resistance, and long-term stability; it is not prone to breakage or delamination during prolonged use and can be used continuously at temperatures below 270°C.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a polyimide laminate, wherein the structure of the polyimide laminate comprises: A substrate layer, wherein the substrate layer is a glass fiber sheet pretreated with an epoxy silane coupling agent; and The polyimide layer located on the surface of the substrate layer is obtained by hot pressing a mixture of raw materials containing polyimide, hexamethyldisilazane, nano-silica powder and curing agent onto the surface of the substrate layer.

[0006] Furthermore, in the raw materials forming the polyimide layer, hexamethyldisilazane is used as a modifier. During the mixing process, it is modified on the surface of the nano-silica powder, which reduces the agglomeration of the nano-silica powder, improves the bonding strength between the nano-silica powder and the polyimide, improves the structural stability of the polyimide laminate, and thus improves its toughness.

[0007] Furthermore, in the raw materials, the mass ratio of polyimide, hexamethyldisilazane, nano-silica powder and curing agent is 10:0.1-1:1-2:0.1-1.

[0008] Furthermore, the raw material also includes a first solvent, preferably dimethylformamide. The amount of the first solvent added to the raw material is sufficient to dissolve all components and obtain a solution.

[0009] Furthermore, the curing agent is selected from polyisocyanate. The presence of the curing agent plays a role in cross-linking and curing, thereby improving the structural stability of the polyimide laminate.

[0010] Furthermore, the preparation of the polyimide includes the following steps: The pyromellitic dianhydride, p-phenylenediamine, and norbornene dianhydride were dissolved in anhydrous ethanol at a mass ratio of 1:1.2:0.2. The system was then heated to 80-100°C and refluxed for 1-3 hours. After cooling, the polyimide was obtained.

[0011] In the above-mentioned method for preparing polyimide, pyromellitic dianhydride and p-phenylenediamine are selected as reaction monomers. The resulting polyimide has a stable structure and good heat resistance, which is far superior to that of polyimides commonly used in this field.

[0012] In the above-mentioned method for preparing polyimide, norbornene dicarboxylic anhydride is used as a capping agent for the reaction of dianhydride and diamine to control the molecular length of the polymerization reaction. Furthermore, norbornene dicarboxylic anhydride has active alkenyl groups, which can provide reactive sites during curing, thereby further improving the structural stability and heat resistance of the polyimide laminate.

[0013] Furthermore, the thickness of the polyimide layer is 0.1-1.5 mm.

[0014] Furthermore, the thickness of the substrate layer is 0.1-1 mm.

[0015] Furthermore, the total thickness of the laminate is 0.5-2 mm.

[0016] Furthermore, the surface-pretreated glass fiber sheet is a glass fiber sheet whose surface has been treated with an epoxy silane coupling agent. Surface pretreatment of the glass fiber sheet makes it easier for the surface of the glass fiber sheet to bond with the polyimide adhesive, enhancing the toughness of the polyimide laminate and preventing problems such as breakage and delamination during long-term use.

[0017] Furthermore, the method for preparing the pretreated glass fiber sheet is as follows: dissolve the epoxy silane coupling agent in a second solvent to obtain a solution, and spray the solution onto the surface of the glass fiber sheet.

[0018] For example, the second solvent is selected from ethanol.

[0019] Furthermore, the epoxy silane coupling agent is γ-glycidoxypropyltrimethoxysilane.

[0020] Furthermore, the hot pressing temperature is 220-380℃ and the pressure is 1-20 MPa.

[0021] In a second aspect, the present invention provides a method for preparing the polyimide laminate as described in the first aspect above, the method comprising the following steps: The raw materials containing polyimide, hexamethyldisilazane, nano silica powder and curing agent are coated on the substrate layer and hot-pressed to obtain a polyimide layer laminated on the substrate layer.

[0022] Thirdly, the present invention provides the application of the polyimide laminate described in the second aspect above in the preparation of high-temperature resistant aerospace components and high-voltage motor insulation materials.

[0023] The beneficial effects of this invention are as follows: This invention addresses the problems of poor toughness and easy breakage / delamination in existing polyimide laminates. The provided polyimide laminate utilizes pyromellitic dianhydride and p-phenylenediamine as reactant monomers, and norbornene dianhydride as a capping agent to synthesize the polyimide precursor. The anhydride and amine reaction products have a high proportion of benzene ring structures, resulting in structural stability and good heat resistance. Norbornene dianhydride is used as a capping agent to regulate the reaction molecular length during polymerization and provides reactive sites during curing. Hexamethyldisilazane is used to modify the surface of nano-silica powder, making it oleophilic, reducing the agglomeration of the nano-silica powder, increasing the bonding strength between the nano-silica powder and polyimide, improving the structural stability of the polyimide laminate, and thus enhancing its toughness. γ-glycidyl etheroxypropyltrimethoxysilane is used to modify the surface of the glass fiber sheet, making it easier for the glass fiber sheet surface to bond with the polyimide adhesive, enhancing the toughness of the polyimide laminate and preventing breakage / delamination during long-term use.

[0024] The polyimide laminate provided in this invention has a flexural strength higher than 450 MPa at 20°C, a flexural strength higher than 300 MPa at 270°C, and a thermal decomposition initiation temperature higher than 550°C. The polyimide laminate products of this invention can be used for extended periods below 270°C. Detailed Implementation

[0025] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0026] Example 1 A method for preparing a polyimide laminate includes the following steps: 1) Pyromellitic dianhydride, p-phenylenediamine and norbornene dianhydride were dissolved in anhydrous ethanol at a molar ratio of 1:1.2:0.2. The system was then heated to 85°C and refluxed for 2 hours. After cooling, polyimide was obtained. 2) Add the polyimide, hexamethyldisilazane, nano silica powder, and polyisocyanate obtained in step 1) to the solvent dimethylformamide in a weight ratio of 10:0.8:1.5:0.8, stir and mix well to obtain polyimide solution. 3) Dissolve γ-glycidoxypropyltrimethoxysilane in ethanol to prepare a 3% (w / w) modified solution, and then spray the modified solution onto the surface of the glass fiber sheet to perform surface pretreatment on the glass fiber sheet. 4) Coat the polyimide solution obtained in step 2) onto the glass fiber sheet pretreated in step 3); then imidize it at a temperature of 260°C and a pressure of 10 MPa to obtain the polyimide laminate.

[0027] The polyimide laminate prepared in Example 1 has a thickness of 1.5 mm, a flexural strength of 500 MPa at 20°C, a flexural strength of 350 MPa at 270°C, and a thermal weight loss initiation temperature of 560°C.

[0028] Example 2 A method for preparing a polyimide laminate includes the following steps: 1) Pyromellitic dianhydride, p-phenylenediamine and norbornene dianhydride were dissolved in anhydrous ethanol at a molar ratio of 1:1.2:0.2. The system was then heated to 85°C and refluxed for 2 hours. After cooling, polyimide was obtained. 2) Add the polyimide, hexamethyldisilazane, nano silica powder, and polyisocyanate obtained in step 1) to the solvent dimethylformamide in a weight ratio of 10:0.8:2:1, stir and mix well to obtain polyimide solution. 3) Dissolve γ-glycidoxypropyltrimethoxysilane in ethanol to prepare a 3% (w / w) modified solution, and then spray the modified solution onto the surface of the glass fiber sheet to perform surface pretreatment on the glass fiber sheet. 4) The polyimide adhesive obtained in step 2) is coated onto the glass fiber sheet pretreated in step 3); then imidization is carried out at a temperature of 270°C and a pressure of 12 MPa to obtain the polyimide laminate.

[0029] The polyimide laminate prepared in Example 2 has a thickness of 1.5 mm, a flexural strength of 460 MPa at 20°C, a flexural strength of 310 MPa at 270°C, and a thermal weight loss initiation temperature of 560°C.

[0030] Example 3 A method for preparing a polyimide laminate includes the following steps: 1) Pyromellitic dianhydride, p-phenylenediamine and norbornene dianhydride were dissolved in anhydrous ethanol at a molar ratio of 1:1.2:0.2. The system was then heated to 85°C and refluxed for 2 hours. After cooling, polyimide was obtained. 2) Add the polyimide, hexamethyldisilazane, nano silica powder, and polyisocyanate obtained in step 1) to the solvent dimethylformamide in a weight ratio of 10:0.2:1.2:0.3, stir and mix well to obtain polyimide filament; 3) Dissolve γ-glycidoxypropyltrimethoxysilane in ethanol to prepare a 3% (w / w) modified solution, and then spray the modified solution onto the surface of the glass fiber sheet to perform surface pretreatment on the glass fiber sheet. 4) Coat the polyimide solution obtained in step 2) onto the glass fiber sheet pretreated in step 3); then imidize it at a temperature of 260°C and a pressure of 10 MPa to obtain the polyimide laminate.

[0031] The polyimide laminate prepared in Example 3 has a thickness of 1.5 mm, a flexural strength of 460 MPa at 20°C, a flexural strength of 330 MPa at 270°C, and a thermal weight loss initiation temperature of 557°C.

[0032] Example 4 A method for preparing a polyimide laminate includes the following steps: 1) Pyromellitic dianhydride, p-phenylenediamine and norbornene dianhydride were dissolved in anhydrous ethanol at a molar ratio of 1:1.2:0.2. The system was then heated to 85°C and refluxed for 2 hours. After cooling, polyimide was obtained. 2) Add the polyimide, hexamethyldisilazane, nano silica powder, and polyisocyanate obtained in step 1) to the solvent dimethylformamide in a weight ratio of 10:1:1:0.9, stir and mix well to obtain polyimide solution. 3) Dissolve γ-glycidoxypropyltrimethoxysilane in ethanol to prepare a 3% (w / w) modified solution, and then spray the modified solution onto the surface of the glass fiber sheet to perform surface pretreatment on the glass fiber sheet. 4) Coat the polyimide solution obtained in step 2) onto the glass fiber sheet pretreated in step 3); then imidize it at a temperature of 260°C and a pressure of 10 MPa to obtain the polyimide laminate.

[0033] The polyimide laminate prepared in Example 4 has a thickness of 1.5 mm, a flexural strength of 455 MPa at 20°C, a flexural strength higher than 310 MPa at 270°C, and a thermal weight loss initiation temperature of 550°C.

[0034] Comparative Example 1 When pyromellitic dianhydride was replaced with phthalic anhydride (OPDA), and the other conditions were the same as in Example 1, the results showed that the flexural strength of the obtained polyimide laminate decreased to 300 MPa at 20°C, the strength at 270°C was less than 150 MPa, and the thermal weight loss initiation temperature decreased to 450°C.

[0035] Comparative Example 2 Omit the nano silica powder, and keep the other conditions the same as in Example 1. The results show that the flexural strength of the resulting laminate decreased by 15% and the coefficient of thermal expansion (CTE) increased by 20%, demonstrating the contribution of the nanofiller to toughness and dimensional stability.

[0036] Comparative Example 3 o-phenylenediamine was used as an aromatic diamine to replace p-phenylenediamine, and the other conditions were the same as in Example 1. The thickness of the prepared polyimide laminate was 1.5 mm, and the performance test results were as follows: the flexural strength at 20°C was 320 MPa, the flexural strength at 270°C was 180 MPa, and the thermal weight loss initiation temperature was 480°C.

[0037] Compared with Example 1, p-phenylenediamine has the advantages of having a para-amino group, less steric hindrance, and a more regular molecular chain. As one of the reaction monomers, it contributes to the excellent mechanical properties and high-temperature resistance of the laminate.

[0038] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A polyimide laminate, characterized in that, The structure of the polyimide laminate includes: A substrate layer, wherein the substrate layer is a glass fiber sheet pretreated with an epoxy silane coupling agent; and The polyimide layer located on the surface of the substrate layer is obtained by hot pressing a mixture of raw materials containing polyimide, hexamethyldisilazane, nano-silica powder and curing agent onto the surface of the substrate layer.

2. The polyimide laminate according to claim 1, characterized in that, The mass ratio of polyimide, hexamethyldisilazane, nano-silica powder and curing agent in the raw materials is 10:0.1-1:1-2:0.1-1.

3. The polyimide laminate according to claim 1, characterized in that, The curing agent is selected from polyisocyanate.

4. The polyimide laminate according to claim 1, characterized in that, The preparation of the polyimide includes the following steps: The pyromellitic dianhydride, p-phenylenediamine, and norbornene dianhydride were dissolved in anhydrous ethanol at a mass ratio of 1:1.2:0.

2. The system was then heated to 80-100°C and refluxed for 1-3 hours. After cooling, the polyimide was obtained.

5. The polyimide laminate according to claim 1, characterized in that, The thickness of the polyimide layer is 0.1-1.5 mm; the thickness of the base layer is 0.1-1 mm; and the total thickness of the laminate is 0.5-2 mm.

6. The polyimide laminate according to claim 1, characterized in that, The method for preparing the pretreated glass fiber sheet is as follows: dissolve the epoxy silane coupling agent in ethanol to obtain a solution, and spray the solution onto the surface of the glass fiber sheet.

7. The polyimide laminate according to claim 1, wherein the epoxy silane coupling agent is γ-glycidoxypropyltrimethoxysilane.

8. The polyimide laminate according to claim 1, characterized in that, The hot pressing temperature is 220-380℃ and the pressure is 1-20Mpa.

9. The method for preparing the polyimide laminate according to any one of claims 1-8, characterized in that, Includes the following steps: The raw materials containing polyimide, hexamethyldisilazane, nano-silica powder and curing agent are coated onto the substrate layer and hot-pressed to obtain a polyimide layer laminated on the substrate layer.

10. The use of the polyimide laminate as described in any one of claims 1-8 in the preparation of high-temperature resistant components for aerospace or insulating materials for high-voltage motors.