Microscopic degradation mechanism of polyimide film caused by surface discharge under bipolar continuous square impulse voltage

Polyimide （PI） film is an important type of insulating material used in inverter-fed motors. Partial discharge （PD） under a sequence of high-frequency square impulses is one of the key factors that lead to premature failures in insulation systems of inverter-fed motors. In order to explore the damage mechanism of PI film caused by discharge, an aging system of surface discharge under bipolar continuous square impulse voltage （BCSIV） is designed based on the ASTM 2275 01 standard and the electrical aging tests of PI film samples are performed above the partial discharge inception voltage （PDIV）. The chemical bonds of PI polymer chains are analyzed through Fourier transform infrared spectroscopy （FTIR） and the dielectric properties of unaged and aged PI samples are investigated by LCR testers HIOKI 3532-50. Finally, the micro-morphology and micro-structure changes of PI film samples are observed through scanning electron microscopy （SEM）. The results show that the physical and chemical effects of discharge cut off the chemical bonds of PI polymer chains. The fractures of ether bond （C-O-C） and imide ring （C-N-C） on the backbone of a PI polymer chain leads to the decrease of molecular weight, which results in the degradation of PI polymers and the generation of new chemical groups and materials, like carboxylic acid, ketone, aldehydes, etc. The variation of microscopic structure of PI polymers can change the orientation ability of polarizable units when the samples are under an AC electric field, which would cause the dielectric constant e to increase and dielectric loss tan ~ to decrease. The SEM images show that the degradation path of PI film is initiated from the surface and then gradually extends to the interior with continuous aging. The injection charge could result in the PI macromolecular chain degradation and increase the trap density in the PI oolvmer bulk.

Hierarchically Multifunctional Polyimide Composite Films with Strongly Enhanced Thermal Conductivity

The development of lightweight and integration for electronics requires flexible films with high thermal conductivity and electromagnetic interference(EMI) shielding to overcome heat accumulation and electromagnetic radiation pollution.Herein,the hierarchical design and assembly strategy was adopted to fabricate hierarchically multifunctional polyimide composite films,with graphene oxide/expanded graphite(GO/EG) as the top thermally conductive and EMI shielding layer,Fe_(3)O_(4)/polyimide(Fe_(3)O_(4)/PI) as the middle EMI shielding enhancement layer and electrospun PI fibers as the substrate layer for mechanical improvement.PI composite films with 61.0 wt% of GO/EG and 23.8 wt% of Fe_(3)O_(4)/PI exhibits high in-plane thermal conductivity coefficient(95.40 W(m K)^(-1)),excellent EMI shielding effectiveness(34.0 dB),good tensile strength(93.6 MPa) and fast electric-heating response(5 s).The test in the central processing unit verifies PI composite films present broad application prospects in electronics fields.

Surface investigation on Upilex-S polymide film iradiated by vacuum ultraviolet radiation

Vacuum ultraviolet radiation of Upilex-S polyimide film 25 μm thick was performed using a gas jet type of vacuum ultraviolet simulator which gives unfixed wavelength from 5 nm to 200 nm.Nanoparticles redeposited on the films were observed and the nanoparticles formed on the surface consist mainly of carbon clusters.Changes in the composition and the chemical characteristics of film surface after radiation were identified by X-ray photoelectron spectroscopy(XPS).Relative O content in the radiated area was found to be higher,while N content was lower than in the pristine area.This indicates that Upilex-S polyimide film releases N atoms as volatile species.And the C1s,O1s envelopes were fitted using Multipak Spectrum software.The surface morphologies on iradiated area were examined by Atomic Force Microscope(AFM).Pieces of radiant products protrude from the eradiated surface,leading to considerable roughness for the iradiated area.And the surface transmittance of Upilex-S film after radiation reduces.

PREPARATION OF POLYIMIDE-BaTiO3 HYBRID FILMS BY A DISPERSION PROCESS AND THEIR MICROSTRUCTURE

Barium titanate (BaTiO3) powders with particle sizes of 30 similar to 50 nm were prepared from barium stearate, titanium alkoxides and stearic acid by stearic acid-gel method. Dispersing the agglomerate of BaTiO3 nanoparticles into poly(amic acid) solution followed by curing led to the formation of polyimide hybrid films. The hybrid films were transparent and well distributed with BaTiO3 nanoparticles when the BaTiO3 content was less than 1 wt%. Highly loaded hybrid film containing 30 wit % BaTiO3 was tough, had a smooth surface and possessed much higher dielectric and piezoelectric constants than the parent polyimide.

Influence of Curing Accelerators on the Imidization of Polyamic Acids and Properties of Polyimide Films

In order to lower the imidization temperature of polyamic acids（PAA）, the catalytic activities of the curing agents p-hydroxybenzoic acid（PHA）, quinoline（QL）, benzimidazole（BI）, benzotriazole（BTA）, triethylamine（Et_3N） and 1, 8-diazabicyclo [5.4.0]undec-7-ene（DBU） were investigated in the process of thermal imidization of PAA. In addition, the effect of these various curing agents on the thermal stabilities and mechanical properties of the resultant polyimide（PI） films was determined. Quinoline was found to be an effective curing accelerator in the use of two-step method for synthesizing PI. Due to its moderate base strength, low steric crowding effect and moderate boiling point, quinoline could not only accelerate PAA to achieve imidization completely at 180 ℃, but also maintain the mechanical properties and thermal stability of the ordinary PI film. Any residual quinoline could be removed from PI films by heating at 250 ℃ for 4 h.

Laser-induced porous graphene on Polyimide/PDMS composites andits kirigami-inspired strain sensor

The laser-induced porous graphene(LIG)prepared in a straightforward fabrication method is presented,and its applications in stretchable strain sensors to detect the applied strain are also explored.The LIGformed on the polyimide/polydimethylsiloxane(PI/PDMS)composite exhibits a naturally high stretchabil-ity(over 30%),bypassing the transfer printing process compared to the one prepared by laser scribing onPI films.The PI/PDMS composite with LIG shows tunable mechanical and electronic performances withdifferent PI particle concentrations in PDMS.The good cyclic stability and almost linear response of theprepared LIG’s resistance with respect to tensile strain provide its access to wearable electronics.To im-prove the PDMS/PI composite stretchability,we designed and optimized a kirigami-inspired strain sensorwith LIG on the top surface,dramatically increasing the maximum strain value that in linear response toapplied strain from 3%to 79%.

Preparation and Properties of Copper Fine Wire on Polyimide Film in Air by Laser Irradiation and Mixed-Copper-Complex Solution Containing Glyoxylic Acid Copper Complex and Methylamine Copper Complex

Formation of copper wiring on a polyimide film by laser irradiation to a stable copper-complex film consisting of glyoxylic acid copper complex and methylamine copper complex in air has been investigated. A stable metallic copper on the polyimide film was precipitated even in air. Since this copper was generated only in the laser-irradiated parts, direct patterning of copper wiring was possible. It was also found that copper was precipitated by electroless copper plating on the laser-deposited copper wiring and it was possible to thicken the copper wiring by this precipitation. The resistivity of the copper wiring was almost the same as that of the bulk of metallic copper. The developed method—combining laser irradiation to a copper-complex-coated film and electroless copper plating—enables the high-speed deposition of fine copper wiring on a polyimide film in air by a printing process, indicating an inexpensive and useful process for fabricating copper wiring without high vacuum facility and heat-treatment under inert gas.

Formation and Characterization of Pd,Pt and Pd-Pt Alloy Films on Polyimide by Catalyst-Enhanced Chemical Vapor Deposition

Platinum, palladium and their alloy films on polyimide were formed by catalyst-enhanced chemical vapor deposition （CVD） in the carrier gas （N2, O2） at 220-300℃ under reduced pressure and normal pressure. The deposition of palladium complexes [ Pd（（η3-allyl）（hfac） and Pd（hfac）2 ] gives pure palladium film, while the deposition of platinum needs the enhancement of palladium complex by mixing precursor platinum complex Pt（COD）Me2 and palladium complex in the same chamber. The co-deposition of Pd and Pt metals was used for the deposition of alloy films. During the CVD of palladium-platinum alloy, the Pd/Pt atomic ratios vary under different co-deposition conditions. These metal films were characterized by XPS and SEM, and show a good adhesive property.

含氟芳香族低介电损耗PI薄膜的制备与性能

聚酰亚胺(PI)薄膜在5G通信场景中具有广阔的使用前景,但5G天线基材对于PI薄膜在高频电场下的介电损耗等性能有十分苛刻的要求。本文制备了含氟共聚PI薄膜,并对其在高频下影响介电性能的部分因素进行探索。采用红外、紫外、热重分析、差示扫描量热等多种测试方法对不同共聚比例PI薄膜样品的热性能、热稳定性和光透过性等进行研究。结果表明,PI薄膜的最高透光率都在90%以上;PI-AD系列PI薄膜最大拉伸强度为112.68 MPa,拉伸模量为3.22 GPa;PI-AE系列PI薄膜的最大拉伸强度为119.32 MPa,拉伸模量为3.52 GPa。PI薄膜受热分解的温度均达到500℃以上,玻璃化转变温度达到270℃以上;含氟共聚PI薄膜在电场为10 GHz的条件下,介电常数都低于3,最低介电损耗为0.00412。

Silicone-coated polyimide films deposited by surface dielectric barrier discharges

Hybrid dielectric barrier discharges are investigated for plasma generated on the surface of a dielectric layer, where two conducting electrodes of high voltage and ground are formulated on the upper and bottom surfaces. Using a flexible thin polyimide-film of a thickness ranging from 25 to 125 μm, a plasma is generated with a voltage of about 1 kV and a frequency of 40 kHz.However, the surface of the dielectric layer was etched through a chemical reaction involving plasma oxygen radical species, and thus the polyimide films failed readily, resulting in dielectric breakdown within short operating time ranging from a few minutes to several tens of minutes,based on the film thicknesses of 25 μm and 125 μm, respectively. These plasma erosions were prevented by coating the polyimide surface with a 25 μm thick silicone paste. The siliconecoated film surface was then reinforced remarkably against plasma erosion as the organic polymer was vulnerable to chemical reaction of the plasma species, while the inorganic silicone exhibited a high chemical resistance against plasma erosion.

EFFECT OF MONTMORILLONITE ADDITION ON MECHANICAL CHARACTERIZATIONS OF POLYIMIDE NANOCOMPOSITE FILMS

Tensile deformation and fracture characteristics of polyimide/montmorillonite nanocomposite films are investigated to enhance the particular mechanical properties and understand the effective factors in dominating the mechanical properties of nanocomposites, such as the nanolayer, matrix and nanolayer/matrix interface. How to contribute to the mechanical properties of nanocomposite film is a very complex problem. In this paper, these factors are analyzed based on the addition amount and fracture mechanics. The results indicate that the specimen at 20 wt% MMT breaks prematurely with a fracture strength （σb = 78 MPa） much lower than that （σb = 128 MPa） at the 1 wt% MMT. However, the Young＇s modulus （3.2 GPa） of the former is higher than that （1.9 GPa） of the latter. Fractography also indicates that the brittle cracking formed in high content addition is the main cause of failure but microscopically ductile fracture morphology still exists locally. And for the trace element addition, the smaller threading slipping veins are evenly distributed on the entire fracture section of these films. Therefore, these characteristics would presumably be associated with both the concentration effects of size of nanocomposite sheets and the increasing deformation harmony in nanolayers.

COMPENSATION EFFECT OF POLYIMIDE THIN FILMS ON NORMALLY WHITE TWISTED NEMATIC LIQUID CRYSTAL DISPLAYS

The disadvantages of Normally White Twisted Nematic Liquid Crystal Display (NW-TN-LCD) were discussed. The reason that the negative birefringent polyimide thin films were used to compensate NW-TN-LCD to decrease off-axis leakage, improve contrast ratios and enlarge viewing angles was explained in this paper. A certain polyimide thin film was taken as an example to show compensation effect on NW-TN-LCD.

Degradation Mechanism of Polyimide Film Under Square Impulse Voltages

Partial discharge (PD) under a sequence of high-repetition-rate square pulses is one of the key factors leading to premature failure of insulation systems of inverter-fed motors. Polyimide (PI) film is an important type of insulating material used in the inverter-fed motors. In this paper, micro-morphology and structure change of PI film aged by bipolar continuous square impulse voltage (BCSIV) with ampli- tude above partial discharge inception voltage (PDIV) are investigated by scanning electron microscope (SEM). The chemical bonds of PI chain are analyzed through Fourier transform infrared spectroscopy (FTIR). The results show that the degradation mechanism of PI film is the fracturing of chemical bonds caused by the erosion from PDs. Three layers are displayed in both 100 HN film and 100 CR film. The de- gradation path of PI film is initiated from surface and then gradually extends to the interior with continuous aging. Nano-fillers can retard the degradation of PI film and prolong its lifetime.

Research of Trap and Electron Density Distributions in the Interface of Polyimide/Al2O3 Nanocomposite Films Based on IDC and SAXS

The distributions of traps and electron density in the interfaces between polyimide （PI） matrix and Al2O3 nanoparticles are researched using the isothermal decay current and the small-angle x-ray scattering （SAXS） tests. According to the electron density distribution for quasi two-phase mixture doped by spherical nanoparticles, the electron densities in the interfaces of PI/Al2O3 nanocomposite films are evaluated. The trap level density and carrier mobility in the interface are studied. The experimental results show that the distribution and the change rate of the electron density in the three layers of interface are different, indicating different trap distributions in the interface layers. There is a maximum trap level density in the second layer, where the maximum trap level density for the nanocomposite film doped by 25 wt% is 1.054 × 10^22 eV·m^-3 at 1.324eV, resulting in the carrier mobility reducing. In addition, both the thickness and the electron density of the nanocomposite film interface increase with the addition of the doped Al2O3 contents. Through the study on the trap level distribution in the interface, it is possible to further analyze the insulation mechanism and to improve the performance of nano-dielectric materials.

太阳电池阵电池基板PI薄膜黏结质量检测技术

航天器太阳电池阵电池基板上PI薄膜的黏结质量直接影响基板工作寿命。为有效、迅速、准确地检测PI薄膜黏结质量,通过热循环和热真空等环境试验,对PI薄膜黏结后微观尺度、非显性化的脱黏、气泡和凸起等典型缺陷进行充分暴露;利用基于偏振成像技术的视觉检测方法,对制备的4组试验样件进行正交试验,准确识别出PI薄膜黏结区域的典型缺陷及其具体尺寸范围。试验结果表明该技术对PI薄膜黏结质量缺陷的检测效果良好。

PI基材磁控溅射法制备柔性覆铜板的结合力优化研究

采用磁控溅射法在聚酰亚胺薄膜表面沉积铜层广泛应用于柔性覆铜板的制备。目前,表面铜膜和聚酰亚胺基材结合强度低是磁控溅射法制备柔性覆铜板所面临的主要问题之一。本文提出通过对聚酰亚胺基材进行等离子体刻蚀处理和引入金属Cr结合层提高表面铜膜结合力,并对比研究不同等离子体刻蚀和金属Cr层对表面铜膜的微观结构、致密性、电阻率和结合力等方面的影响。结果表明,等离子体刻蚀使聚酰亚胺表面粗糙度和表面能增大,有利于铜膜沉积并在界面形成机械互锁和化学键而提高结合力;Cr金属中间层可在薄膜界面处形成固溶体强化结合力,达到最优的5B级别。本研究对解决磁控溅射法制备柔性覆铜板中铜膜和聚酰亚胺基材结合力差的问题具有重要的意义。

一种PI感光干膜的制备与性能

为开发一种分辨率高、力学性能优异的聚酰亚胺(PI)感光干膜,首先采用4,4'-联苯醚二酐(ODPA)与2,2-双(3-氨基-4-羟基苯基)六氟丙烷(BAHF)等合成了碱溶性PI树脂。再将该树脂与交联剂、引发剂、偶联剂等进行复配,制备了光敏性PI胶液,最后将该光敏性PI胶液涂布在载体聚对苯二甲酸乙二酯(PET)薄膜上,经烘干、冷却,覆上聚乙烯膜(PE膜),获得PI感光干膜。利用凝胶渗透色谱、傅里叶变换红外光谱、光学显微镜等对碱溶性PI树脂和感光干膜的性能进行表征。结果表明,成功制备碱溶性PI树脂,亚胺化率为82%,厚度为15μm的PI感光干膜经曝光显影后具有优异的分辨率,为10μm。通过动态热机械分析仪、热重分析等对200℃固化的PI感光干膜的力学性能、耐热性和耐药性进行了研究。结果表明,200℃固化的感光干膜在30℃时的拉伸强度达到101 MPa,断裂伸长率达到7.3%,5%热失重温度为352℃,10%热失重温度为385℃,在590℃的质量保持率为44%,并且在丙酮、N-甲基吡咯烷酮、30%HNO_(3),30%H_(2)SO_(4),1%HF等试剂中的质量变化率均小于1%。综上,PI感光干膜具有优异的分辨率、热稳定性和耐药性。

电晕老化对纳米复合PI薄膜介电性能的影响

高温超导非晶合金变压器作为低温运行设备具有节能降耗的功能。选择耐低温的聚酰亚胺(PI)薄膜为高温超导非晶合金变压器主绝缘材料,改进PI薄膜的制备工艺,搭建电晕老化系统,对PI薄膜进行电晕老化预处理。对经电晕老化预处理后的薄膜的介电特性进行研究,发现液氮环境中电晕老化薄膜的介质损耗角正切值要低于常温环境,在质量分数小于或等于5%时纳米粒子填充PI薄膜的介质损耗角正切值小于处理前薄膜的质损耗角正切值。

柔性聚酰亚胺(PI)衬底上ITO薄膜的生长及其透明导电性能影响机制研究

采用直流磁控溅射法在聚酰亚胺(PI)柔性衬底上生长氧化铟锡(ITO)薄膜,采用XP-2探针台阶仪、X射线衍射(XRD)、霍尔测试仪、紫外-可见分光光度计等对ITO薄膜进行结构和光电性能表征。结果表明溅射功率和沉积气压是影响磁控溅射法生长ITO薄膜透明导电性能的主要因素,实验系统研究了溅射功率和沉积气压对ITO薄膜透明导电性能的影响机制。在优化的工艺条件下(溅射功率100W和沉积气压0.4Pa),制备了在可见光区平均透射率达86%、电阻率为3.1×10-4Ω.cm的光电性能优良的ITO透明导电薄膜。

SolGel法制备PI/SiO_2纳米复合薄膜及结构与性能

采用溶胶 凝胶法 (Sol Gel)制备了二氧化硅不同质量分数的聚酰亚胺 /二氧化硅 (PI/SiO2 )纳米复合薄膜。并用TEM、力学性能、吸水性能及介电性能测试等方法研究了薄膜的结构与性能。结果表明 ,SiO2 微粒均匀分散在PI基体中 ,粒径随着SiO2 含量的增加而增大 ;当SiO2 质量分数在 2 0 %以内时对PI基体有增强作用 ,且在 1 0 %左右拉伸强度达到最大 ,而吸水率逐渐减小 。