CN112574445A - Preparation method of self-reinforced polyimide film - Google Patents

Abstract

The invention belongs to the technical field of preparation of polyimide films, and provides a preparation method of a self-reinforced polyimide film. Because the polyimide solid powder has a crystalline structure, the polyimide solid powder is added into polyimide precursor polyamide acid (PAA), and in the film-making process, the mechanical property of the product can be improved and the water absorption and the thermal expansion coefficient can be reduced by means of the self-higher molecular weight through inducing the crystallization of the polymer.

Description

Preparation method of self-reinforced polyimide film

Technical Field

The invention belongs to the technical field of polyimide film preparation, and particularly relates to a preparation method of a self-reinforced polyimide film.

Background

Polyimide (PI) contains imide rings on a main chain, is a polymer with a highly regular chemical structure, has excellent chemical stability, wear resistance, flame retardance, high temperature resistance, low temperature resistance, corrosion resistance, radiation resistance, outstanding mechanical property and dielectric property, and is widely applied to the fields of aviation, aerospace, microelectronics, nano-scale liquid crystal, separation membranes, laser and the like. In recent years, the research, development and utilization of polyimide are one of the most promising engineering plastics in 21 st century in various countries. Polyimide, because of its outstanding characteristics in performance and synthesis, has been fully recognized as a structural material or a functional material with great application prospects.

The research shows that the polyimide film with a crystalline structure has better mechanical property, heat resistance and solvent resistance compared with the film with an amorphous structure.

Disclosure of Invention

The invention provides a preparation method of a self-reinforced polyimide film.

The invention is realized by the following technical scheme: a preparation method of a self-reinforced polyimide film comprises the steps of adding polyimide solid powder into polyamide acid PAA solution, controlling the heating rate to be 5 ℃/min, heating to 300 ℃ to react for 30min, inducing polymer crystallization, and naturally cooling to prepare the self-reinforced polyimide film.

The method comprises the following specific steps:

(1) mixing 4, 4' -diaminodiphenyl ether ODA and N-methylpyrrolidone NMP, stirring to dissolve ODA in NMP, adding pyromellitic dianhydride PMDA in three batches, and stirring for 12 hours in ice bath to obtain a PAA solution with 10wt% of solid content; the intrinsic viscosity numbers are respectively 0.86dl/g, 1.49dl/g and 2.11 dl/g; corresponding molecular weight 3.29X 10⁴，6.43×10⁴，9.83×10⁴；

(2) Diluting the three PAA solutions with different intrinsic viscosities to 5wt% by using NMP; in N₂Stirring at 180 deg.C for 3 hr under reflux condensation, vacuum filtering the precipitated solid to remove NMP, cleaning with anhydrous ethanol, vacuum filtering, oven drying at 180 deg.C for 3 hr, and grinding to obtain the final productThree different molecular weight PI powders; the theoretical molecular weights of the three PI powders are 3.06X 10⁴，5.98×10⁴，9.14×10⁴(ii) a The PAA solution with larger intrinsic viscosity can not obtain PI powder by the method;

(3) adding PI powder with three molecular weights into a polyamic acid solution with an intrinsic viscosity of 2.11dl/g according to the weight percentages of 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt% and 0.5wt%, respectively, stirring for 3h to prepare a composite solution, and uniformly coating the composite solution on a glass plate by using a scraper with the thickness of 150 mu m;

(4) and (3) putting the glass plate coated with the solution into an oven, raising the temperature to 300 ℃ at the rate of 5 ℃/min, standing for 30min, naturally cooling, and taking out the film.

In the invention, because the polyimide solid powder has a crystal structure, the polyimide solid powder is added into polyimide precursor polyamide acid (PAA), and the heat resistance, rigidity and dimensional stability of a product can be improved, the mechanical property is improved, and the water absorption and thermal expansion coefficient are reduced by inducing polymer crystallization in the film preparation process.

Drawings

FIG. 1 is SEM pictures of PI powders with different molecular weights; in the figure: a is L-PI powder; b is M-PI powder; c is H-PI powder;

FIG. 2 is an XRD pattern of three PI powders;

FIG. 3 is an XRD pattern of a PI/PI powder composite film;

FIG. 4 is an XRD pattern of PI composite films with different amounts of PI powder added in Experimental example 2;

FIG. 5 is a polarized light microscope photograph of PI composite films with different amounts of PI powder added; the left side of the figure is magnified by 400 times, and the right side of the figure is an enlarged view of the figure in a black frame in the left side; wherein: a is a polarization microscope photo of the PI composite film with 0.1wt% of H-PI powder addition; b is a polarization microscope photo of the PI composite film with the addition amount of the H-PI powder being 0.2 wt%; c is a polarized light microscope photo of the PI composite film with the addition amount of the H-PI powder being 0.4 wt%; d is a polarization microscope photo of the PI composite film with the addition amount of the H-PI powder being 0.5 wt%.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments; all other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1: a preparation method of a self-reinforced polyimide film comprises the steps of adding polyimide solid powder into polyamide acid PAA solution, controlling the heating rate to be 5 ℃/min, heating to 300 ℃ to react for 30min, inducing polymer crystallization, and naturally cooling to prepare the self-reinforced polyimide film.

The method comprises the following specific steps:

1. adding ODA and NMP into a three-neck flask, stirring to dissolve ODA in a solvent, then adding PMDA in three batches, and stirring for 12 hours in ice bath to obtain a PAA solution with 10wt% of solid content. The intrinsic viscosity numbers are respectively 0.86dl/g, 1.49dl/g and 2.11 dl/g; corresponding molecular weight 3.29X 10⁴，6.43×10⁴，9.83×10⁴；

2. The three PAA solutions with different intrinsic viscosities are diluted with NMP in N₂Stirring for 3h at 180 ℃ under the reflux condensation condition in the atmosphere, removing NMP from the precipitated solid through vacuum filtration, washing with absolute ethyl alcohol, continuing vacuum filtration, placing in a drying oven for drying for 3h at 180 ℃, and grinding to obtain three kinds of PI powder with different molecular weights. SEM photographs of the three PI powders are shown in fig. 1; the XRD patterns of the three PI powders are shown in fig. 2.

From FIG. 1, it can be seen that: a is L-PI powder with theoretical molecular weight of 3.06 × 10⁴(ii) a B is M-PI powder with theoretical molecular weight of 5.98 × 10⁴(ii) a C is H-PI powder with theoretical molecular weight of 9.14 × 10⁴. As can be seen from the figure, the higher the molecular weight of the PI powder, the longer the molecular chain, the weaker the ability to rearrange regularly, and the less perfect the crystallization. The molecular weight of A is lowest, the molecular chain is easy to move, the crystallization is complete, regular spherical crystals are formed, and the size of the crystals is about 5 mu m; b, the molecular weight is intermediate, the molecular chain moves for the second time, a beam-shaped crystal is formed, and the longitudinal dimension is about 4 mu m; c has the highest molecular weight and the molecular chain movesThe capability is weak, the crystallization is imperfect, but beam-shaped crystals are formed, the regularity is low, and the longitudinal dimension of the crystals is about 1.3-2.6 mu m.

As can be seen from fig. 2: the PI powder with three molecular weights has obvious diffraction peaks at 2 theta =11.72 degrees, 13.8 degrees, 14.76 degrees, 23 degrees and 27 degrees, and the lower the PI molecular weight (L-PI), the higher the diffraction peak intensity and the sharper the peak shape, which indicates that the crystallization is more perfect. The higher the PI molecular weight (H-PI), the lower the diffraction peak intensity, indicating a lower degree of perfection of the crystal.

3. Three kinds of PI powders with different molecular weights were added to a polyamic acid solution with an intrinsic viscosity of 2.11dl/g in an amount of 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, respectively, and stirred for 3 hours to prepare a composite solution, which was uniformly coated on a glass plate using a doctor blade having a thickness of 150 μm.

4. Placing in an oven, heating to 300 deg.C at a rate of 5 deg.C/min, standing for 30min, naturally cooling, and taking out the film.

Experimental example 1: testing and characterizing the prepared self-reinforced polyimide film

1. Observing the aggregation structure of the composite film by a polarizing microscope: the prepared composite film is placed under a polarizing microscope to observe the aggregation structure of the composite film, the magnification of an eyepiece and an objective lens is 10 multiplied by 10, and the magnification of a camera is 4 times respectively when photographing.

2. Testing the aggregation state structure of the composite film by using a wide-angle X-ray diffractometer: the composite film aggregate structure was examined using a wide angle X-ray diffractometer (WAXD) with an X-ray source CuKa (λ =0.15418), Ni filtering, room temperature test conditions, 30kV × 20mA operating conditions, 1 ° divergence slit, 1 ° scattering slit, 0.04mm receiving slit, test angle range of 5 ° <2 θ <35 °, scanning at 0.08 °/sec.

3. Observing the appearance of the PI powder by using a scanning electron microscope: the powder was subjected to a gold-spraying treatment, and the morphology thereof was observed with a Scanning Electron Microscope (SEM) and the acceleration voltage was measured at 20 kV.

4. And (3) testing mechanical properties: the composite film was cut into 10mm wide strips, and the thickness of the film was measured with a digital coating thickness gauge, generally taking the value at the minimum thickness, and then stretched with an electronic universal tester, wherein the stretching rate was 5mm/min.

5. Coefficient of Thermal Expansion (CTE) test: the CTE is tested by a dynamic mechanical thermal analyzer in an air atmosphere with a pre-stress of 0.5N, the testing temperature range is 50-400 ℃, the temperature rise rate is 10 ℃/min, and the specification of a film sample is 3.5 multiplied by 0.3cm²。

6. Water absorption test: cutting the polyimide film into 2X 2cm according to GB/T1034-1998²The square of (2) was kept in an oven at 23 ℃ for 24 hours, then placed in water, and the surface of the film was kept at a constant temperature of 23 ℃ for 24 hours without any contact with anything. The sample was removed from the water, wiped dry immediately and the weight of the sample was measured within 1 min.

Experimental example 2: performance comparison of PI composite films prepared from PI powders with different molecular weights

ODA and NMP were added to a three-necked flask, and stirred to dissolve ODA in the solvent, then PMDA was added in portions, and stirred for 12 hours in ice bath to obtain a PAA solution with 10wt% solid content. The intrinsic viscosity numbers are respectively 0.86dl/g, 1.49dl/g and 2.11dl/g, and then PI powders with three different molecular weights are prepared, and the theoretical molecular weights of the three PI powders are respectively 3.06 multiplied by 10⁴，5.98×10⁴，9.14×10⁴. Adding 0.3wt% of PI powder with different molecular weights into the polyamic acid solution with the intrinsic viscosity of 2.11dl/g, and stirring for 3 hours to prepare a composite solution. Here, the experimental formulation of the data in Table 1 is described in detail, and then the experimental results are analyzed in detail.

TABLE 1 comparison of PI composite film properties prepared from PI powders of different molecular weights

Because the L-PI powder has strong crystal-inducing and crystal-conducting capacity, the PI/L-PI composite film prepared from the low-molecular-weight PI powder has obvious crystallization phenomenon (see figure 3), the PI powder with three molecular weights is filled into the PI, and the prepared PI/PI powder composite film is 2 theta =6^o，9^o,11⁰，21⁰Obvious diffraction appears on the left and rightAnd the diffraction peak of the PI/M-PI composite film is sharper and the composite film prepared by the L-PI is sharper compared with the PI/H-PI powder composite film, which shows that the L-PI powder has the strongest induced crystallization capability, and the M-PI powder is inferior and the H-PI powder is weaker.

Crystallization causes the polyimide molecular chains to be arranged closely, the free volume is reduced, and the water absorption is lower; meanwhile, the thermal expansion of the amorphous region is inhibited by the tightly-packed chain molecules in the crystal region, so that the thermal expansion coefficient is lower. However, the crystal size of the L-PI powder is 5 μm (see figure 1), and the L-PI powder has a larger size, so that the L-PI powder does not play a good role in promoting the mechanical property. For H-PI powder, crystallization is incomplete, the longitudinal dimension of the formed beam-shaped crystal is about 1.3-2.6 mu m (see figure 1), the beam-shaped crystal plays a role of heterogeneous nucleation when being compounded with a PI precursor, and PI crystallization is induced, but the prepared PI/H-PI composite film has a weaker crystallization degree than the PI/L-PI composite film (see figure 3), so the water absorption rate and the thermal expansion coefficient are higher, but are slightly lower than those of a pure PI film by 34% and 67%; because the crystal size is small, the good reinforcing effect is achieved, in addition, the improvement of the mechanical property is also promoted due to the high molecular weight of the H-PI powder, and the tensile strength and the elastic modulus are respectively improved by 27 percent and 20 percent. The crystallization ability of the PI/M-PI composite film is between the two, the crystal size and the molecular weight of the M-PI powder are between the two, and therefore various properties listed in the table 1 are between the two.

The theoretical molecular weight of the PI powder is higher, and the prepared composite film has good comprehensive effect. Mainly due to the advantages of induced crystallization and high molecular weight.

Experimental example 2: comparison of the addition amount of PI powder: the H-PI powder was added to the polyamic acid solution at 0wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5 wt%. The results obtained are shown in Table 2. The result showed that the effect was best when the amount of PI powder added was 0.5 wt%.

TABLE 2 Properties of polyimide composite films

The addition amount in Table 2 was 0, and the case in Table 1 was not added, as compared with a pure polyimide film, i.e., a conventional film. The mechanical property of the prepared PI/H-PI composite film is improved by adding the H-PI powder, and the water absorption and the thermal expansion coefficient are reduced. This is because: on one hand, the added polyimide powder and the base material polyimide have good cohesiveness, the interface strength of the polyimide powder and the base material polyimide is improved, and the mechanical property of the composite film is improved. On the other hand, the H-PI powder induces PI crystallization, and the PI crystallization gradually presents a more regular and well-like reticular texture (see figure 5) with the increase of the addition amount of the H-PI powder, and the crystallization is more obvious (see figure 4).

As shown in FIG. 4, the PI/H-PI composite films prepared by different addition amounts of H-PI powder are all 2 theta =6^o,12^o,22^oThe diffraction peak appears, and the diffraction peak becomes sharper with the increase of the addition amount, which shows that the crystallization inducing capability of the H-PI powder is further increased.

As shown in fig. 5, when the addition amount of the H-PI powder is gradually increased from 0.1wt% to 0.5wt%, the crystallization becomes more and more obvious, and when the addition amount is gradually increased, the bright points become more and more, the color becomes darker, a more regular reticular texture similar to a "well shape" appears, the reticular structure has a distinct bright and dark crystal band, and this phenomenon indicates that the orientation of two crystal bands at the bright and dark intervals is different, the bright band is due to the regular arrangement of spherulites, the orientation is performed along one direction, so that the rigidity of the segment is increased, the dark band is caused by the randomly arranged segment, and the bright and dark bands in the graph are regularly distributed.

In summary, when the amount of H-PI powder added is 0.5wt%, the overall performance of the composite film is best.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (2)

1. A preparation method of a self-reinforced polyimide film is characterized by comprising the following steps: adding polyimide solid powder into polyamide acid PAA solution, controlling the heating rate to be 5 ℃/min, heating to 300 ℃, reacting for 30min, inducing the polymer to crystallize, and naturally cooling to prepare the self-reinforced polyimide film.

2. The method for preparing a self-reinforced polyimide film according to claim 1, wherein: the method comprises the following specific steps:

(1) mixing 4, 4' -diaminodiphenyl ether ODA and N-methylpyrrolidone NMP, stirring to dissolve ODA in NMP, adding pyromellitic dianhydride PMDA in three batches, and stirring for 12 hours in ice bath to obtain a PAA solution with 10wt% of solid content; the intrinsic viscosity numbers are respectively 0.86dl/g, 1.49dl/g and 2.11 dl/g; corresponding molecular weight 3.29X 10⁴，6.43×10⁴，9.83×10⁴；

(2) Diluting the three PAA solutions with different intrinsic viscosities to 5wt% by using NMP; in N₂Stirring for 3h at 180 ℃ under reflux condensation conditions in the atmosphere, carrying out vacuum filtration on precipitated solids to remove NMP, washing with absolute ethyl alcohol, continuing vacuum filtration, placing in a drying oven for drying for 3h at 180 ℃, and grinding to obtain three PI powders with different molecular weights; the theoretical molecular weights of the three PI powders are 3.06X 10⁴，5.98×10⁴，9.14×10⁴；

(3) Adding PI powder with three molecular weights into a polyamic acid solution with an intrinsic viscosity of 2.11dl/g according to the weight percentages of 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt% and 0.5wt%, respectively, stirring for 3h to prepare a composite solution, and uniformly coating the composite solution on a glass plate by using a scraper with the thickness of 150 mu m;

(4) and (3) putting the glass plate coated with the solution into an oven, raising the temperature to 300 ℃ at the rate of 5 ℃/min, standing for 30min, naturally cooling, and taking out the film.

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