Preparation of polyimide film by the hottest tape

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Study on the preparation of polyimide film by tape casting

polyimide is a kind of high-performance polymer material with the structural characteristics of imide ring. Its mechanical properties, electrical properties and radiation resistance are excellent, which is particularly obvious in the process of heating up [1]. Its various products such as films, adhesives, coatings, laminates and plastics have been widely used in aerospace, automotive, precision instruments and many other fields [2]. Polyimide film is the organic film with the best heat resistance at present, and its long-term use temperature is as high as 300 ℃; Because of its excellent comprehensive performance, it has many applications in aerospace industry, electrical and electronic industry, information industry and other fields [3]. The forming methods of polyimide film mainly include casting method, dipping method, extrusion stretching method and swelling stretching method. The industrial production method of benzene type polyimide film is casting stretching process [4]

in order to better guide the production, the pilot study of polyimide film prepared by convective casting method is very important. Therefore, based on pmda/ODA system, this paper has carried out a series of studies from the synthesis of polyamide acid, drying and desolvation to the characterization of mechanical properties of samples after film forming, and made a certain selection of stretching process

1 experimental part

1.1 experimental raw material

pyromellitic dianhydride (PMDA): film grade, Jiangsu Liyang Longsha Chemical Co., Ltd; 4, 4 ′ 2 diaminodiphenyl ether (ODA): industrial grade, Jiangsu Changshu Huishun Chemical Co., Ltd; N. N ′ 2 dimethylacetamide (DMAC): industrial grade, South Korea SamSung fine chemical company

1.2 test method

molar mass and its distribution: Agilent 1100 series gel permeation chromatography (GPC) instrument, column temperature 40 ℃, flow rate 1 ml/min. The mass fraction of solvent (DMAC) in polyamide acid gel film: the constant temperature oven built by the laboratory is used, and the self-made program is used to accurately determine the real-time data collected by the computer

mechanical properties: according to gb/t 1040-1992, the stress at the right angle point rises enough to produce the initial tear. Cmt24204 microcomputer controlled electronic universal testing machine produced by Shenzhen new Sansi Measurement Technology Co., Ltd. is used, and the tensile speed is 2 mm/min

x-ray diffraction analysis: adopt D8 advanced X-ray diffractometer of Bruker company in Germany, Cu target, K α X-ray, scanning angle 3 ° ~ 50 °, X-ray incident direction is perpendicular to the tensile direction of the sample

1.3 experimental process

pmda and ODA undergo ring opening polycondensation in aprotic polar solvent DMAC to produce high molar mass polyamide acid (PAA); In the polymerization process, the molar mass and distribution were measured in real time by GPC

place the polyamide acid solution on a dry, smooth and clean glass plate (12 cm × 12 cm), and then dry it in a self built constant temperature oven to prepare a polyamide acid gel film with a certain solvent content

under certain conditions, the mechanical properties of polyamide acid gel film were tested by electronic universal testing machine, and appropriate samples were selected for different proportions of tension

the stretched polyamide film is imidized at high temperature to obtain the polyimide film, and its mechanical properties at room temperature are measured by universal testing machine again

the orientation of imidized polyimide films before and after stretching was characterized by XRD

2 results and discussion

2.1 effect of reaction time on the molar mass of polyamide acid

polyamide acid is synthesized by positive feeding method, that is, PMDA is added to the DMAC polar solution of ODA in several times. With the extension of polymerization time, the weight average molar mass of polyamide acid first decreased, then increased and stabilized, then decreased, and finally basically did not change. In the initial stage of the reaction, the polycondensation products are mostly low molecular polymers, so the weight average molar mass decreases; With the progress of the reaction, the macromolecular products increase, so the weight average molar mass increases, and because the reaction is relatively stable, the amount of its molar mass used in automotive interior trim dashboard, electric tools, sports appliances, lawn mower, snow blower and other industrial parts remains basically unchanged. However, due to the exothermic reaction of the ring opening polymerization system of dianhydride and diamine, the temperature of the reaction system can gradually increase with the progress of the reaction, so that part of the polyamide acid is converted into polyimide and water is released; The generated water also causes the hydrolysis of polyimide [5], resulting in the increase of small molecules and the decrease of weight average molar mass. However, the temperature raised by the exothermic polycondensation reaction is limited after all, so the generated water is limited, making the hydrolysis reaction impossible to proceed indefinitely. Therefore, with the extension of time, the molar mass tends to a stable value, which is also the best time for the reaction

2.2 effect of drying time on the mass fraction of solvent in polyamide acid gel film

cast the polyamide acid solution evenly on a smooth and clean glass plate, and use the microcomputer controlled drying measuring device shown in Figure 2 to investigate the effect of drying time on the mass fraction of solvent in polyamide acid gel film at different temperatures (100 ℃, 110 ℃, 130 ℃, 150 ℃ and 170 ℃). The results are shown in Figure 3. Ensure the cleanness in the oil circuit

Figure 2 microcomputer controlled drying measuring device

Figure 3 Effect of drying time on solvent mass fraction

it can be seen from Figure 3 that at the same time, the higher the temperature, the lower the solvent content; At the same temperature, with the extension of time, the solvent content is lower. Therefore, increasing the temperature and prolonging the time are conducive to the removal of polyamic acid solvent, and the effect is the same; Polyamide acid gel films with different solvent contents can be prepared by controlling different drying time or temperature

2.3 selection of polyimide film stretching process

2.3.1 selection of stretching conditions

studies have shown that the performance of Kapton film produced by DuPont is much higher than that of domestic film because of the obvious orientation of Kapton film, that is, the film has been stretched. It can be seen that stretching plays a great role in improving the properties of polyimide films [6]. In the process of stretching, it is particularly important to choose the appropriate stretching conditions. Therefore, the electronic universal testing machine is used to measure the tensile strength and elongation at break of gel films with different solvent mass fractions. The results are shown in Figure 4

Fig. 4 solvent SEBS has the same elasticity, recoverability, strength, toughness and weather resistance as traditional rubber. The influence of content on the tensile properties of polyamide acid gel film

it can be seen from Fig. 4 that the higher the drying temperature is, the greater the tensile strength of polyamide acid film is, which is not conducive to stretching. At 110 ℃ and 130 ℃, the tensile strength of polyamide decreases gradually with the increase of solvent mass fraction, while the elongation at break first increases and then decreases. When the solvent mass fraction is about 30%, the elongation at break reaches the maximum, and the value at 130 ℃ is greater. Considering comprehensively, the gel film with drying temperature of 130 ℃ and solvent mass fraction of about 30% was selected

2.3.2 effect of stretching ratio on the tensile properties of polyimide film

the gel film with drying temperature of 130 ℃ and solvent mass fraction of 30% was stretched by electronic universal testing machine at room temperature for 15%, 20% and 30% respectively, and then the polyimide film was prepared by high temperature thermal imidization

Fig. 5 Relationship between mechanical properties of film and tensile ratio

see Fig. 5 for mechanical properties of polyimide film under different tensile ratios. It can be seen from Figure 5 that the tensile strength and modulus of polyimide film increase with the increase of tensile ratio. When the film is not stretched (tensile ratio is 1), the tensile strength and modulus of the film are 91.09 MPa and 1794.6 MPa respectively; When the tensile ratio reaches 1.3 times, the tensile strength reaches 154.5 MPa, which is about 1.7 times that of non tensile, while the modulus reaches 2472.4 MPa, which is 1.4 times that of non tensile. It can be seen that the mechanical properties of polyimide films have been significantly improved by stretching

2.4 orientation of stretched polyimide film

it can be seen from Figure 6 that the shape of its diffraction spectrum is basically similar. This is because the tensile strength of the film is relatively small, and its orientation is not obvious; Therefore, its peak value basically does not change [7, 8]

Fig. 6 X-ray diffraction pattern of polyimide film under different draw ratios

3 conclusion

1) polyamic acid solution is prepared by positive feeding method, and the appropriate polycondensation reaction time is 6 h. at this time, the weight average molar mass of the solution tends to be stable

2) in the drying process of constant temperature oven, the solvent content of polyamide acid gel film gradually decreases with the increase of temperature and time

3) after comparing the stretching of the gel films dried under different conditions, the analysis shows that the better stretching condition is that the temperature is 130 ℃, and the solvent mass fraction is about 30%

4) the mechanical properties of polyamic acid films stretched at room temperature with different proportions were measured after thermal amination. It was found that the tensile strength and modulus increased with the increase of tensile ratio

5) due to the small tensile ratio of the film, the spectrogram is basically similar when using wide-angle X-ray diffraction to characterize its orientation. (end)

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