CN112574445B

CN112574445B - Preparation method of self-reinforced polyimide film

Info

Publication number: CN112574445B
Application number: CN202011430734.5A
Authority: CN
Inventors: 翟燕; 谢建新; 李欣健; 梁红玉; 贺秀丽
Original assignee: Taiyuan Institute of Technology
Current assignee: Taiyuan Institute of Technology
Priority date: 2020-12-09
Filing date: 2020-12-09
Publication date: 2023-05-02
Anticipated expiration: 2040-12-09
Also published as: CN112574445A

Abstract

The invention belongs to the technical field of preparation of polyimide films, and provides a preparation method of a self-reinforced polyimide film, wherein polyimide solid powder is added into polyamide acid PAA solution, then the temperature rising rate is controlled to be 5 ℃/min to 300 ℃ for reaction for 30min, polymer crystallization is induced, and then the self-reinforced polyimide film is prepared by natural cooling. Since the polyimide solid powder has a crystal structure, and is added into polyimide precursor polyamide acid (PAA), the mechanical property of the product can be improved and the water absorption and thermal expansion coefficient can be reduced by inducing the crystallization of the polymer and the higher molecular weight of the product in the film preparation process.

Description

Preparation method of self-reinforced polyimide film

Technical Field

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

Background

Polyimide (PI) contains imide ring on its main chain, is a polymer with highly regular chemical structure, and has excellent chemical stability, wear resistance, fire resistance, high temperature resistance, low temperature resistance, corrosion resistance, radiation resistance, outstanding mechanical properties and dielectric properties, so that it is widely used in the fields of aviation, aerospace, microelectronics, nanometer, liquid crystal, separation membrane, laser, etc. In recent years, research, development and utilization of polyimide have been carried out in one of the most promising engineering plastics in the 21 st century. Polyimide has been widely recognized in its great application prospect, because of its outstanding characteristics in terms of performance and synthesis, whether as a structural material or as a functional material.

It has been found that polyimide films having a crystalline structure are superior in mechanical properties, heat resistance, and solvent resistance to films having 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 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 ℃ for reaction 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 the ODA in the NMP, adding pyromellitic dianhydride PMDA in three batches, and stirring for 12 hours under ice bath to obtain PAA solution with 10 weight percent of solid content; intrinsic viscosity is 0.86dl/g, 1.49dl/g, 2.11dl/g, respectively; corresponding to a molecular weight of 3.29X 10 ⁴ ，6.43×10 ⁴ ，9.83×10 ⁴ ；

(2) The three PAA solutions with different intrinsic viscosity are diluted to 5wt% by NMP; at N ₂ Stirring for 3h at 180 ℃ under the condition of reflux condensation in atmosphere, vacuum filtering the precipitated solid to remove NMP, washing with absolute ethyl alcohol, vacuum filtering, drying for 3h at 180 ℃ in an oven, and grinding to obtain three PI powders with different molecular weights; the theoretical molecular weight of the three PI powders is 3.06X10 respectively ⁴ ，5.98×10 ⁴ ，9.14×10 ⁴ The method comprises the steps of carrying out a first treatment on the surface of the PAA solutions with higher intrinsic viscosity cannot obtain PI powder by this method;

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

(4) And (3) placing the glass plate coated with the solution in an oven, heating to 300 ℃ at a heating rate of 5 ℃/min, staying for 30min, naturally cooling, and taking out the film.

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

Drawings

FIG. 1 is a SEM photograph of PI powders of 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 for 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 PI powder addition amounts in Experimental example 2;

FIG. 5 is a polarized light micrograph of PI composite film with different PI powder loadings; the left magnification of the drawing is 400 times, and the right drawing is an enlarged drawing of the drawing in the black frame in the left drawing; wherein: a is a polarized light microscopic photograph of the PI composite film with the addition amount of H-PI powder of 0.1 wt%; b is a polarized light microscopic photograph of the PI composite film with the addition amount of H-PI powder of 0.2 wt%; c is a polarized light microscopic photograph of the PI composite film with the addition amount of the H-PI powder of 0.4 and wt percent; d is a polarization microscope photograph of the PI composite film with the addition amount of the H-PI powder being 0.5 and wt percent.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments; all other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

Example 1: a preparation method of 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 ℃ for reaction 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 solvent, and separating into three partsPMDA was added in batch and stirred under ice bath for 12h to give a PAA solution of 10wt% solids. Intrinsic viscosity is 0.86dl/g, 1.49dl/g, 2.11dl/g, respectively; corresponding to a molecular weight of 3.29X 10 ⁴ ，6.43×10 ⁴ ，9.83×10 ⁴ ；

2. The three PAA solutions with different intrinsic viscosity are diluted by NMP and are in N ₂ Stirring for 3h at 180 ℃ under the condition of reflux condensation in the atmosphere, filtering out NMP from the precipitated solid by vacuum suction, washing with absolute ethyl alcohol, continuing vacuum suction filtration, drying for 3h at 180 ℃ in an oven, and grinding to obtain three PI powders 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 obtained that: a is L-PI powder, and the theoretical molecular weight is 3.06X10 ⁴ The method comprises the steps of carrying out a first treatment on the surface of the B is M-PI powder with theoretical molecular weight of 5.98X10 ⁴ The method comprises the steps of carrying out a first treatment on the surface of the C is H-PI powder, and has a theoretical molecular weight of 9.14X10 ⁴ . 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 the lowest, the molecular chain is easy to move, the crystallization is perfect, regular spherical crystals are formed, and the crystal size is about 5 mu m; the molecular weight of B is centered, the molecular chain moves for a second time to form a beam-shaped crystal, and the longitudinal dimension is about 4 mu m; the molecular weight of C is highest, the molecular chain movement capability is weaker, the crystallization is imperfect, but the bunchy crystals are also formed, the degree of regularity is lower, and the longitudinal dimension of the crystals is about 1.3-2.6 mu m.

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

3. Three kinds of PI powders having different molecular weights were added to a polyamic acid solution having 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 with a doctor blade having a thickness of 150. Mu.m.

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

Experimental example 1: the prepared self-reinforced polyimide film is subjected to test characterization

1. Observing the aggregation state structure of the composite film by a polarized light microscope: and (3) placing the prepared composite film under a polarizing microscope to observe the aggregation state structure, wherein the magnification of an eyepiece and an objective lens is 10 multiplied by 10, and the magnification of a camera during photographing is 4 times respectively.

2. Testing the aggregation state structure of the composite film by using a wide-angle X-ray diffractometer: the composite film aggregation structure was examined using a wide angle X-ray diffractometer (WAXD), the X-ray source was CuKa (λ=0.15418), ni filtered, the test conditions were room temperature, operating conditions 30kV X20 mA, the divergent slit was 1 °, the receiving slit was 0.04mm, the angular range of the test was 5 ° <2θ <35 °, and the scan was performed at a speed of 0.08 °/sec.

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

4. Mechanical property test: cutting the composite film into strips of 10mm width, measuring the thickness of the film by a digital coating thickness gauge, generally taking the value of the minimum thickness, and then stretching by an electronic universal tester, wherein the stretching rate is 5mm/min, and recording the tensile strength, elongation at break and elastic modulus.

5. Coefficient of Thermal Expansion (CTE) test: CTE is tested by a dynamic mechanical thermal analyzer, air atmosphere, prestress of 0.5N, test temperature range of 50-400 ℃, heating rate of 10 ℃/min and film sample specification of 3.5 multiplied by 0.3cm ² 。

6. Water absorption test: the polyimide film was cut into 2X 2cm pieces according to GB/T1034-1998 ² Is kept at the constant temperature of 23 ℃ for 24 hours, then is placed in water, the surface of the film is not contacted with anything, and is kept at the constant temperature of 23 ℃ for 24 hours. The sample was removed from the water, immediately wiped dry, and the weight of the sample was measured within 1 min.

Experimental example 2: performance comparison of PI composite film prepared from PI powder with different molecular weights

ODA and NMP were added to a three-necked flask, stirred to dissolve the ODA in the solvent, then PMDA was added in portions and stirred under an ice bath for 12 hours to give a PAA solution of 10% by weight solids. Intrinsic viscosity of 0.86dl/g, 1.49dl/g, and 2.11dl/g, respectively, and preparing three PI powders with different molecular weights, wherein theoretical molecular weights of the three PI powders are 3.06X10 respectively ⁴ ，5.98×10 ⁴ ，9.14×10 ⁴ . 0.3wt% of PI powder with different molecular weights is added into polyamide acid solution with intrinsic viscosity of 2.11dl/g, and the mixture is stirred for 3 hours to prepare composite solution. Here, the experimental proportioning relationship of the data in Table 1 is described in detail, and then the experimental results are analyzed in detail.

TABLE 1 comparison of the Performance of PI composite films prepared from PI powders of different molecular weights

Because of the strong crystal-inducing capability of L-PI powder, the PI/L-PI composite film prepared by low molecular weight PI powder has obvious crystallization phenomenon (see figure 3), three molecular weight PI powders are filled into PI, and the prepared PI/PI powder composite film is in 2θ=6 ^o ，9 ^o ,11 ⁰ ，21 ⁰ The diffraction peak appears obviously on the left and right sides, and compared with the PI/H-PI powder composite film, the PI/M-PI composite film has a sharp diffraction peak, the composite film prepared by L-PI is more sharp, which indicates that the L-PI powder has the strongest crystallization induction capability, the M-PI powder is inferior, and the H-PI powder is weaker.

Crystallization makes polyimide molecular chains closely arranged, and free volume is reduced, resulting in lower water absorption; and simultaneously, the linking molecules tightened between the crystal regions inhibit the thermal expansion of the amorphous regions, so that the thermal expansion coefficient is lower. However, the L-PI powder has a crystal size of 5 μm (see FIG. 1), and the L-PI powder has a larger size and does not have a good promotion effect on the improvement of mechanical properties. For H-PI powder, the longitudinal dimension of the formed beam-shaped crystals is about 1.3-2.6 mu m (see figure 1), and the beam-shaped crystals play a role in heterogeneous nucleation when being compounded with a PI precursor to induce PI crystallization, but the prepared PI/H-PI composite film has weaker crystallization degree than that of a PI/L-PI composite film (see figure 3), so that the water absorption rate and the thermal expansion coefficient are slightly higher, but are 34 percent and 67 percent lower than those of a pure PI film; the crystal size is small, so that a good reinforcing effect is achieved, in addition, the high molecular weight of the H-PI powder also plays a role in promoting the improvement of mechanical properties, and the tensile strength and the elastic modulus are respectively improved by 27% and 20%. The PI/M-PI composite film has crystallization capability between the two, crystal size and M-PI powder molecular weight between the two, so that the various properties listed in the table 1 are between the two.

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

Experimental example 2: PI powder addition amount comparison: 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 results showed that the PI powder addition of 0.5wt% worked best.

TABLE 2 Properties of polyimide composite film

The case of the addition amount of 0 in table 2 is compared with the case of the pure polyimide film, i.e., the conventional film, and the case of no addition in table 1. The mechanical properties of the prepared PI/H-PI composite film are improved by adding the H-PI powder, and the water absorption rate and the thermal expansion coefficient are reduced. This is because: on one hand, the polyimide powder added has good cohesiveness with the polyimide as a base material, and the interface strength of the polyimide powder and the polyimide is improved, so that the mechanical property of the composite film is improved. On the other hand, H-PI powder induces PI crystallization, and as the addition amount of H-PI powder increases, a more regular network structure similar to a 'well shape' is gradually displayed (see figure 5), and the crystallization is more obvious (see figure 4).

As shown in fig. 4, PI/H-PI composite films prepared with different amounts of H-PI powder added were all at 2θ=6 ^o ,12 ^o ,22 ^o Diffraction peaks appear when the addition amount is increased, and the diffraction peaks are more sharp, which shows that the H-PI powder induces crystallization energyThe force is further increased.

As shown in FIG. 5, when the addition amount of H-PI powder was gradually increased from 0.1wt% to 0.5wt%, crystallization became more and more evident, and when the addition amount was gradually increased, bright spots became more and more intense, and a more regular "well-like" network structure was developed, which had distinct bands of alternate bright and dark bands, indicating that the orientations of the two bands of alternate bright and dark bands were different, the bright bands were oriented in one direction due to the regular arrangement of spherulites, the rigidity of the segments was increased, and the dark bands were caused by the randomly arranged segments, and the bright and dark bands in the figure were regularly distributed.

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

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims

1. A preparation method of a self-reinforced polyimide film is characterized in that: adding polyimide solid powder into polyamide acid PAA solution, controlling the heating rate to be 5 ℃/min, heating to 300 ℃ for reaction for 30min, inducing polymer crystallization, and naturally cooling to prepare the self-reinforced polyimide film;

the method comprises the following specific steps:

(2) The three PAA solutions with different intrinsic viscosity are diluted to 5wt% by NMP; at N ₂ Stirring for 3h at 180 ℃ under the condition of reflux condensation in atmosphere, vacuum filtering the precipitated solid to remove NMP, washing with absolute ethyl alcohol, vacuum filtering, drying for 3h at 180 ℃ in an oven, and grinding to obtain three PI powders with different molecular weights; the theoretical molecular weight of the three PI powders is 3.06X10 respectively ⁴ ，5.98×10 ⁴ ，9.14×10 ⁴ ；

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