Analysis of discoloration mechanisms of polarizer

doi:10.19491/j.issn.1001-9278.2022.05.014

Abstract

Abstract:

The discoloration of the polarizer of liquid crystal displays after solar irradiation was analyzed， and its optical properties， weather resistance， surface elements and of discoloration mechanism were investigated using an intelligent xenon lamp aging tester， a wide?angle/small?angle X?ray scattering applause， an X?ray energy dispersive spectrometer， and a spectrophotometer. The results indicated that the peak intensity of UV absorption for I₃^- was doubled after exposed to 105 oC for 1 h， and its peak intensity increased by a factor of 3 after exposed to 120 oC for 120 h. However， and the peak intensity of UV absorption for PVA?I₅^- decreased， whereas the peak intensity for PVA?I₃^- increased. The discoloration mechanism of the iodine?based polarizer was attributed to the molecular structure conversion from PVA?I₅^- to PVA?I₃^-. With an increase in test time at a high temperature， the color of the polarizer gradually changed to brown as the ratio of I₃^- increased. Meanwhile， the color of the discolored polarizer could recover after a high?temperature and high?humidity treatment. A conversion between the PVA?I₅^- and PVA?I₃^- could be operated mutually in the polarizer. The solar radiation discoloration of the polarizer was mainly affected by the anti?ultraviolet performance and high?temperature resistance of the polarizer. The anti?purple performance of the polarizer could be improved by increasing the content of UV absorber through optimizing the raw materials and manufacturing process， and its high temperature resistance could be improved by increasing the content of PVA?I₅^-. This can solve the problem of discoloration of the iodine?based polari?zers under sunlight.

Key words: iodine, polarizer, xenon lamp test, high temperature, discoloration, sun exposure

CLC Number:

TQ325.9

ZHOU Wenxian. Analysis of discoloration mechanisms of polarizer[J]. China Plastics, 2022, 36(5): 81-88.

Figures/Tables 14

状态	未点亮	点亮
照射前
照射后

Tab.1. Liquid crystal modules before and after sun radiation

样品	380 nm 透过率/%	△E_s /NBS
		直接测试		放置仪表盘中后测试
		500 h	1 000 h	72 h	500 h
1	33	30.25	51.13	22.27	38.9
2	0.2	3.05	3.35	1.99	19.63

Tab.2. Hue change of iodine?type polarizer after xenon lamp aging test

样品	测试前	放置仪表盘中后测试		直接测试
样品	测试前	72 h	500 h	500 h	1 000 h
1
2

Tab.3. Color change of iodine?based polarizer before and after xenon lamp aging test

Fig.1. Basic structure of LCD polarizer

Fig.2. LCD， polarizer and PVA flim after sun exposure

Fig.3. UV transmission spectra of the samples

Fig.4. Color of sample 2 before and after high temperature test under different conditions

Fig.5. Schematic diagram of the discoloration process of iodine?based polarizer

Fig.6. Photos of the polarizers

Fig.7. WAXS curves of the polarizer

Fig.8. Transmittance of the polarizer

Fig.9. UV absorption spectra of PVA films

Fig.10. EDS spectra of PVA film before and after 105 ℃×1 h test

元素	处理前/%	处理后/%
B	9.75	9.66
C	60.57	61.55
O	29.07	27.83
K	0.18	0.27
I	0.42	0.68

Tab.4. Content percentage （mass fraction） of subsurface atoms of PVA film

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