Preparation method for reducing crust of polyimide foam material
By prefilling small molecule solvents in a closed mold and rapidly heating imidation, the problem of crusting of polyimide foam materials during foaming is solved, the uniformity and production efficiency of the material are improved, and the cost.
Patent Information
- Application Number
- CN202411564213.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-05
- Publication Date
- 2025-01-03
AI Technical Summary
Polyimide foam materials are prone to crust during foaming, resulting in uneven material structure, large waste and low production efficiency. The existing methods reduce the temperature gradient to reduce crust but will prolong the foaming time and affect the foam structure.
The sealed mold is prefilled with small molecule solvents such as water vapor or tetrahydrofuran, and the foamable precursor is prepared by reaction between dianhydride and diamine, and the imidation is rapidly heated and imidized in the mold to reduce the viscosity of the precursor skin, improve fluidity, and reduce Crouching phenomenon.
It effectively reduces the crusting phenomenon of polyimide foam material, improves the uniformity and production efficiency of foam material, and reduces production costs.
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Abstract
Description
Technical Field
[0001] The invention belongs to the field of polymer foaming materials, and in particular relates to a preparation method for reducing skinning of polyimide foam materials. Background Art
[0002] Polyimide is an aromatic heterocyclic polymer compound containing an imide ring in the molecular chain. It is a polymer material with the highest temperature resistance, the best mechanical properties, dielectric properties, and corrosion resistance. It is also an indispensable material in aerospace, electronics, and national defense. It has important value in technology and business and is the "gold" of special plastics. Polyimide foam materials not only maintain the excellent heat resistance and flame retardancy of its resin, but also have outstanding wave transmission properties, light weight, good flexibility and resilience, and are easy to use. Therefore, they are extremely important in military equipment. They are also ideal foam materials for aircraft and other aircraft, and are used in the thermal insulation of space shuttle bulkheads, ship cabins, vehicles and other fields.
[0003] Since polyimide foam contains a large number of aromatic hybrid structures in the molecular chain, the material is difficult to melt or dissolve. Extrusion, reaction injection foaming and other methods with high technical maturity are not suitable for the continuous production of polyimide foam. Due to factors such as cost, quality, cost-effectiveness, large-scale production, and technical routes, there are not many products that can truly achieve the industrialization of polyimide foam. Especially in the foaming stage, heat is transferred from the outside to the inside, and the small polyamide acid molecules on the outside of the raw material are first polymerized at high temperature, resulting in increased viscosity and reduced fluidity, which is easy to produce crusting; as the internal temperature of the raw material gradually increases and foaming occurs, the volume of the raw material will expand rapidly, and the crust on the outside of the raw material will crack severely due to poor fluidity, and the cracks will even affect the structure of the main foam material. The density and pore structure of the crust are significantly different from those of the main foam material, which affects industrial production and product quality control; and the crust must be removed before use, causing great waste. The traditional method to reduce crusting is to reduce the heating rate and temperature gradient so that the inside and outside of the raw material reach the foaming temperature almost at the same time. However, this will inevitably prolong the foaming time, reduce production efficiency, and affect the foam structure. Therefore, a new and easy-to-use method is urgently needed to minimize the skinning generated during the production of polyimide foam. Summary of the invention
[0004] The purpose of the present invention is to provide a method for preparing a polyimide foam material with reduced skinning, thereby solving the problem of severe skinning or even cracking in the existing foaming method, further shortening the foaming time and improving the production efficiency.
[0005] To achieve the above-mentioned purpose, the present invention provides the following technical scheme: The present invention discloses a preparation method for reducing skinning of polyimide foam material, comprising using dianhydride and diamine to prepare a polyamic acid foamable precursor; using a closed mold for foaming molding, wherein the mold can be pre-filled with a certain pressure of water vapor, low molecular alcohol, tetrahydrofuran and other gases; rapidly heating for foaming and imidization to obtain a polyimide foam material with little skinning.
[0006] The present invention provides a method for preparing a polyimide foam material to reduce skinning, which specifically comprises the following steps: (1) preparing a foamable precursor by reacting dianhydride and diamine in a solvent, mixing with a catalyst and a surfactant, and drying; (2) Using a foamable precursor, adding a small molecule solvent in a closed mold for heating and foaming to prepare a foam prepolymer; (3) Opening the mold, imidizing the foam prepolymer at high temperature to prepare polyimide foam.
[0007] The foamable precursor is prepared by reacting dianhydride and diamine in a solvent, and is mixed with a catalyst and a surfactant and dried.
[0008] Preferably, the dianhydride includes one or more of pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, diphenyl ether tetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, bisphenol A type diphenyl ether dianhydride, triphenyl diether tetracarboxylic dianhydride, cyclobutane tetracarboxylic dianhydride, ethylenediamine-N, N'-disuccinic anhydride, and cyclopentanetetracarboxylic dianhydride.
[0009] Preferably, the diamine includes one or more of p-phenylenediamine, m-phenylenediamine, benzyl diamine, diamino diphenyl ether, ethylenediamine, propylenediamine, butylenediamine, pentanediamine, hexamethylenediamine, and methylpentanediamine.
[0010] Preferably, the solvent includes one or more of water, methanol, ethanol, propanol, butanol, ethylene glycol, acetone, tetrahydrofuran, and ethyl acetate.
[0011] Preferably, the catalyst includes one or more of imidazole, sulfuric acid, phosphoric acid and hydrochloric acid.
[0012] Preferably, the surfactant includes one or more of silicone oil, cottonseed oil, castor oil, coconut oil, palm wax, beeswax, spermaceti, isooctyl alcohol, isopentanol, diisobutyl carbinol, glycerol monostearate, tributyl phosphate.
[0013] The drying method includes one or more of natural volatilization, heating drying, vacuum drying, and rotary evaporation.
[0014] The heating foaming method includes one or more of gas heating, resistance wire heating, and infrared heating.
[0015] The closed mold can be made of materials with good heat transfer performance such as graphite and stainless steel, and can withstand a pressure of 0.1~1.0MPa.
[0016] The small molecule solvent includes one or more of water, methanol, ethanol, propanol, butanol, tetrahydrofuran, and ethyl acetate.
[0017] Compared with the prior art, the present invention has the following beneficial effects: The preparation method for reducing the skinning of polyimide foam material of the present invention reduces the viscosity of the skin of the precursor during foaming and improves the fluidity of the skin of the precursor by pre-filling a certain volume of small molecule solvent in a closed mold, thereby reducing the skinning of the polyimide foam material and improving the uniformity of the foam material, thereby improving the yield rate of the foam material production. At the same time, since the viscosity of the skin layer is reduced during foaming, it can be quickly heated for foaming and imidization, thereby improving the production efficiency and effectively reducing the production cost. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 It is the cross-sectional structure of the foam material prepared after adding water in a closed mold.
[0019] Figure 2 It is the cross-sectional structure of the foam material prepared by adding ethanol in a closed mold.
[0020] Figure 3 It is the cross-sectional structure of the foam material prepared by adding water and tetrahydrofuran in a closed mold.
[0021] Figure 4 It is the cross-sectional structure of the foam material prepared by adding tetrahydrofuran in a closed mold.
[0022] Figure 5 It is the surface structure of foam materials produced in an open mold. DETAILED DESCRIPTION
[0023] The present invention is further described below in conjunction with specific examples. The following examples are provided for a better understanding of the present invention, are not limited to the best mode of implementation, and do not limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts falls within the protection scope of the present invention.
[0024] In the embodiments, if specific experimental steps or conditions are indicated, the conventional experimental steps or conditions described in the literature in the field can be used. If the manufacturer of the reagents or instruments is not indicated, they can be obtained from commercial conventional reagents.
[0025] Example 1: A) Add 322g of dried benzophenone tetracarboxylic dianhydride to a mixed solvent containing 450g of tetrahydrofuran and 100g of methanol, and add 2g of imidazole and 0.5g of silicone oil, stir, heat to 60°C and reflux for 2h, cool to room temperature and then add 200g of diaminodiphenyl ether, heat to 60°C again, stir for 1h to obtain a foaming precursor solution; the foaming precursor solution is rotary evaporated at room temperature for 3 hours to obtain a foaming precursor. B) Take 2g of the foaming precursor and place it in a mold, add 0.1g of water, cover it with a lid, seal it, quickly heat it to 160°C, and keep it warm for 2h to obtain a foam prepolymer. C) Open the mold lid, heat the foam prepolymer to 250°C and keep it warm for 2h, cool it, demould it, and obtain a polyimide foam material.
[0026] The polyimide foam material prepared in Example 1 was cut open to obtain a cross-sectional structure as shown in FIG. Figure 1 As shown. Figure 1 It can be seen that the foam material is uniform as a whole, has no cracks in the skin, and has a thickness of less than 2 mm, indicating that the skinning phenomenon has been effectively suppressed.
[0027] Example 2: A) 156g of dried benzophenone tetracarboxylic dianhydride and 98g of cyclobutane tetracarboxylic dianhydride were added to a mixed solvent containing 300g of tetrahydrofuran and 100g of acetone, and 5ml of 10% sulfuric acid and 1g of diisobutyl carbinol were added, stirred, heated to 60°C and refluxed for 2h, cooled to room temperature, and then 54g of p-phenylenediamine and 58g of hexamethylenediamine were added, and the temperature was raised to 60°C again. After stirring for 1h, a foaming precursor solution was obtained; the foaming precursor solution was freeze-dried for 16h to obtain a foaming precursor powder. B) 2g of the foaming precursor powder was placed in a mold, 0.2g of ethanol was added, the lid was covered, the temperature was quickly raised to 160°C, and the temperature was kept for 2h to obtain a foam prepolymer. C) The mold lid was opened, the foam prepolymer was heated to 250°C and kept warm for 2h, cooled, demolded, and a polyimide foam material was obtained.
[0028] The polyimide foam material prepared in Example 2 was cut open to obtain a cross-sectional structure as shown in FIG. Figure 2 As shown. Figure 2 It can be seen that the foam material is uniform as a whole, has no crack peaks in the skin layer, and has a thickness of less than 0.1 mm, indicating that the skinning phenomenon has been effectively suppressed.
[0029] Example 3: A) 156g of dried benzophenone tetracarboxylic dianhydride and 148g of biphenyl tetracarboxylic dianhydride were added to a mixed solvent containing 300g of tetrahydrofuran and 100g of ethylene glycol, and 10ml of 10% hydrochloric acid and 1g of tributyl phosphate were added, stirred, heated to 60°C and refluxed for 2h, cooled to room temperature and then 60g of ethylenediamine was added, heated to 60°C again, stirred for 1h, and a foaming precursor solution was obtained; the foaming precursor solution was vacuum dried at 30°C for 30min to obtain a foaming precursor. B) 2.5g of the foaming precursor was placed in a mold, 0.5g of water and 0.3g of tetrahydrofuran were added, the lid was covered, sealed, and the temperature was quickly raised to 160°C and kept warm for 2h to obtain a foam prepolymer. C) The mold cover is opened, the foam prepolymer is heated to 250°C and kept warm for 2 hours, cooled, and demolded to obtain a polyimide foam material.
[0030] The polyimide foam material prepared in Example 3 was cut open to obtain a cross-sectional structure as shown in FIG. Figure 1 As shown. Figure 3 It can be seen that the foam material is uniform as a whole, has no crack peaks in the skin layer, and has a thickness of less than 0.1 mm, indicating that the skinning phenomenon has been effectively suppressed.
[0031] Example 4: A) Add 240g of dried cyclopentanetetracarboxylic dianhydride to a mixed solvent containing 400g of tetrahydrofuran and 100g of methanol, and add 2g of imidazole and 0.5g of silicone oil, stir, heat to 60°C and reflux for 2h, cool to room temperature, add 108g of p-phenylenediamine, heat to 60°C again, stir for 1h, and obtain a foaming precursor solution; heat the foaming precursor solution at 60°C and dry for 8 hours to obtain a foaming precursor. B) Take 1g of the foaming precursor and place it in a mold, add 0.2g of tetrahydrofuran, cover it with a lid, seal it, quickly heat it to 160°C, and keep it warm for 2h to obtain a foam prepolymer. C) Open the mold lid, heat the foam prepolymer to 250°C and keep it warm for 2h, cool it, demould it, and obtain a polyimide foam material.
[0032] The polyimide foam material prepared in Example 4 was cut open to obtain a cross-sectional structure as shown in FIG. Figure 4 As shown. Figure 4 It can be seen that the foam material skin has no crack peaks and the thickness is less than 0.2 mm, indicating that the skinning phenomenon has been effectively suppressed.
[0033] Comparative Example 1: A) Add 322g of dried benzophenone tetracarboxylic dianhydride to a mixed solvent containing 450g of tetrahydrofuran and 100g of methanol, and add 2g of imidazole and 0.5g of silicone oil, stir, heat to 60°C and reflux for 2h, cool to room temperature and then add 200g of diaminodiphenyl ether, heat to 60°C again, stir for 1h to obtain a foaming precursor solution; rotary evaporate the foaming precursor solution at room temperature for 3 hours to obtain a foaming precursor. B) Take 2g of the foaming precursor and place it in an open mold, directly and quickly heat it to 160°C, and keep it warm for 2h to obtain a foam prepolymer. C) Heat the foam prepolymer to 250°C and keep it warm for 2h, cool it, demould it, and obtain a polyimide foam material.
[0034] The polyimide foam material prepared in Comparative Example 1 was photographed to obtain a surface structure such as Figure 5 As shown. Figure 5 It can be seen that the cortex of the foam material is cracked, and the crack peaks are large and deep, indicating that the crusting phenomenon is very obvious.
Claims
1. A method for preparing a polyimide foam material to reduce skinning, characterized in that: include: A) preparing a foamable precursor by reacting dianhydride and diamine in a solvent, mixing with a catalyst and a surfactant, and drying; B) using a foamable precursor, adding a small molecule solvent in a closed mold for heating and foaming to prepare a foam prepolymer; C) Opening the mold, imidizing the foam prepolymer at high temperature to prepare polyimide foam.
2. The preparation method according to claim 1, characterized in that: The dianhydride in the foamable precursor includes one or more of pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, diphenyl ether tetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, bisphenol A type diphenyl ether dianhydride, triphenyl diether tetracarboxylic dianhydride, cyclobutane tetracarboxylic dianhydride, ethylenediamine-N, N'-disuccinic anhydride, and cyclopentanetetracarboxylic dianhydride.
3. The preparation method according to claim 1, characterized in that: The diamine in the foamable precursor includes one or more of p-phenylenediamine, m-phenylenediamine, benzyl diamine, diamino diphenyl ether, ethylenediamine, propylenediamine, butylenediamine, pentanediamine, hexamethylenediamine, and methylpentanediamine.
4. The preparation method according to claim 1, characterized in that: The solvent in the foamable precursor includes one or more of water, methanol, ethanol, propanol, butanol, ethylene glycol, acetone, tetrahydrofuran, and ethyl acetate.
5. The preparation method according to claim 1, characterized in that: The catalyst in the foamable precursor includes one or more of imidazole, sulfuric acid, phosphoric acid and hydrochloric acid.
6. The preparation method according to claim 1, characterized in that: The surfactant in the foamable precursor includes one or more of silicone oil, cottonseed oil, castor oil, coconut oil, palm wax, beeswax, spermaceti, diethylhexanol, isooctyl alcohol, isopentanol, diisobutyl carbinol, glycerol monostearate, and tributyl phosphate.
7. The preparation method according to claim 1, characterized in that: The drying of the foamable precursor includes one or more of natural volatilization, heating drying, vacuum drying, and reduced pressure distillation.
8. The preparation method according to claim 1, characterized in that: The closed mold can be made of materials with good heat transfer performance such as graphite and stainless steel. The mold can withstand a pressure of 0.1-1.0 MPa.
9. The preparation method according to claim 1, characterized in that: The heating and foaming method includes one or more of gas heating, resistance wire heating and infrared heating.
10. The preparation method according to claim 1, characterized in that: The small molecule solvent includes one or more of water, methanol, ethanol, propanol, butanol, tetrahydrofuran, and ethyl acetate.