Document RagNB9MeLEK2VwZXm8E1EOGvk

Classification: Public Date Division/Dept. Author 10.08.2023 EL-SC-QRGD EL Product Compliance PFAS in Liquid Crystal Displays Contents Summary ................................................................................................................................................. 2 Abbreviations .......................................................................................................................................... 3 Flat panel displays in electronic devices ................................................................................................. 4 Nematic Liquid Crystals for Active-Matrix Displays................................................................................. 4 Relevant Physical Parameters ................................................................................................................. 6 Early Research with Cyano-groups containing Liquid Crystals................................................................ 6 Modern Displays - emerging of fluorinated Liquid Crystals .................................................................... 7 High-end LC modes and display technologies ......................................................................................... 8 Conditions during LC production in the EU ............................................................................................. 9 Mixture preparation and device manufacturing in non-EU .................................................................... 9 Further processing, production of displays and end of life of electric and electronic devices............. 10 Impact of PFAS Restriction on Liquid Crystal display use...................................................................... 10 Derogation for PFAS in LC displays........................................................................................................ 10 References............................................................................................................................................. 11 PFAS IN LIQUID CRYSTAL DISPLAYS - MERCK ELECTRONICS 1 Classification: Public Summary Flat panel displays are essential components of electric and electronic devices. Their invention has triggered a boom in IT and consumer electronics leading to the substitution of the huge and heavy CRT displays with lightweight and high-resolution displays. New areas of display applications appeared, that were not possible with CRT (e.g., automotive). As the usage of the flat panel display is widespread, each display must have specific properties which are finely tuned in a multidimensional development process. The decisive component of the Liquid Crystal (LC) display is the liquid crystal substance. These molecules are formulated into LC mixtures, each mixture with its own individual properties. Currently available technical modes are VA, TN and IPS with its own right to exist due to their advantages for the intended use of the display. All modes use highly fluorinated alkyl and fluorinated aromatic substances having a high dipole moment which is relevant for the functionality of LC displays. Out of these modes, only the IPS mode contains some LC substances with structural moieties in scope of the draft of the universal PFAS restriction in the EU and thus might be banned by end of 2025. The IPS displays possess unique properties and are used in mobile applications, computer monitors and automotive applications without alternative due to requirements regarding usability in a broad temperature range, high image quality and color gamut. IPS displays are used in medical device monitors due to high color gamut and stability from different viewing angles. This property reduces misdiagnosis in the respective medicinal application. In the explanations presented below, we can show that we minimize the exposition towards the environment and workers during production. As the LC is encapsulated in the display, we can exclude exposition during the normal use of the display. At their end of life, electric and electronic devices are regulated by the WEEE directive and are collected. The display needs to be dismantled and is thermally recycled at temperatures which lead to PFAS decomposition to HF and CO2. OLED as successor technology is not yet capable to fully substitute all applications. The reliability of LC displays is still unattained. Furthermore, the production capacity is not yet available to fully switch from IPS to OLED. In this regard, we apply for a 5-year derogation for the use of PFAS LC substances in IPS displays. A derogation is necessary because we are currently working on alternatives to the essential LC substances which are in scope of the universal PFAS restriction. From our experience, this time is needed to find alternative substances usable in IPS LC mixtures to obtain the desired properties in the final display and the subsequent ramp up to mass production. PFAS IN LIQUID CRYSTAL DISPLAYS - MERCK ELECTRONICS 2 Classification: Public Abbreviations CRT cathode ray tube EU european union IPS in plane switching IT information technology ITO indium tin oxide LC liquid crystal OLED organic light-emitting diode PFAS per- and polyfluoroalkyl substances PS-VA polymer stabilized vertical alignment R&D research and development RoHS restriction of hazardous substances SR specific resistivity TFT thin film transistor TN twisted nematic UB-FFS ultra-bright fringe field switching VA vertical alignment VHR voltage holding ratio WEEE Waste of electric and electronic equipment PFAS IN LIQUID CRYSTAL DISPLAYS - MERCK ELECTRONICS 3 Classification: Public Flat panel displays in electronic devices Flat panel displays are widely used and led to a development leap of electronics in the early 2000s. Compared to the huge and heavy formerly used cathode ray tubes (CRT), flat panel displays are thin and lightweight. Additionally, flat panel displays can display images in high resolutions. These characteristics are relevant for the use in portable devices such as laptops, mobile phones and tablets where the flat panel display is combined with a touch screen as well as TVs or computer monitors where the high resolution and high image quality is a key factor. In the automotive industry, flat panel displays have superseded analog displays with the increasing use of sensors and electronic equipment in cars. It is expected that the use of displays in cars will gain further speed with further electrification of cars. The key component of modern flat panel displays is the liquid crystal (LC). After more than 20 years of intensive research, highly sophisticated LCs are fluorinated substances.[1] Some of them having structural moieties which are in scope of the published draft for a universal PFAS restriction. As the flat panel display is used in a wide range of applications with specific requirements, LC displays are still state of the art in several applications. The established display modes twisted nematic (TN), vertical alignment (VA) and in plane switching (IPS) still have individual advantages in special fields of application and compared to emerging competitive technologies like OLED. Only IPS displays strongly depend on LCs which are in scope of the published draft for a universal PFAS restriction. Therefore, Merck Electronics wants to provide evidence that the LC use is considered for a 5-year derogation for automotive, mobile and monitor application until suitable alternatives are found and ramped up to mass production. Nematic liquid crystals for active-matrix displays Modern high-end Liquid Crystal (LC) in plane switching (IPS) displays are based on active-matrix technology. Each pixel is controlled separately by a thin film transistor (TFT) and a separated electrode layer on the same side of the glass substrate. The layer of LC is usually 3 m thick and acts as light modulator. Liquid crystals have properties in between liquids and solids and can occur in different states: the smectic and the nematic state and the isotropic state in which the LC behavior is not present. In the smectic state the LC is periodically oriented in layers, in the nematic phase the LC is oriented towards a director and in the isotropic phase, the LC is oriented randomly towards all directions. Relevant for the application in LC Displays is the nematic state only. In the nematic state the LCs can be oriented parallel or perpendicular towards the orientation layers. If LC substances with a dielectric anisotropy due to strongly electronegative groups are used, the predetermined orientation can be switched along a field vector by application of an external electric field. This orientation change is the main principle behind the LC Display technique (figure 1).[1] PFAS IN LIQUID CRYSTAL DISPLAYS - MERCK ELECTRONICS 4 Classification: Public Figure 1: Structure of a IPS LC subpixel.[2] Left side (voltage off): the light passes the polarizer and does not pass the perpendicular analyzer. Right side (voltage on): The light passes the polarizer and changes the orientation while passing the LC layer. The perpendicular second polarizer lets the light pass. Modern TVs in 4K resolution have 8.3 megapixels. Each pixel consists of three subpixels with red, green, and blue color filters. The LC layer of the single subpixel acts as a valve for light that is passing through the color filter of the display by applying a voltage (figure 2). If the color of the individual pixel is adjusted, large images can be shown on the screen. Figure 2: Exemplary voltage/transmittance diagram showing that applied voltage is changing the transmittance of the LC layer. The LC substance aligns with its dipole moment along the electrical field. PFAS IN LIQUID CRYSTAL DISPLAYS - MERCK ELECTRONICS 5 Classification: Public Relevant physical parameters Relevant for the image quality and performance of the display is the nematic phase temperature range, dielectric anisotropy () depending on the dipole moment, birefringence (n) rotational viscosity () and elastic constants.[3] Depending on the field of application these parameters need to be carefully adjusted by combining the necessary LC substances in a mixture with the desired properties. LC substances and LC mixtures need to be stable if different temperatures are applied. E.g., in LC displays for automotive application the nematic phase must be stable between -40 and +110 C. Furthermore, the LC mixture needs to be photostable towards the used backlight.[3] The specific resistivity (SR), the ion density and especially the voltage holding ratio (VHR) are the most important reliability parameters. A low VHR related to a voltage drop caused by a power leak through the LC decreases the image quality of the display or leads to flickering (figure 3).[3] Figure 3: a) High voltage holding ration leads to an almost constant transmittance. b) Low voltage holding ratio leads to a permanent transmittance drop which is perceived by the eye as flickering.[4] To manufacture displays for specific applications a tedious multidimensional optimization process is necessary, so that LC mixtures contain normally 15 or even more compounds. These LC mixtures are composed for the special needs of our downstream users for each type of application. Early research with cyano-groups containing liquid crystals In the initial development phase of active-matrix liquid crystal displays, cyano-based materials were tested and could not meet the requirements regarding the specific resistivity and the VHR for active matrix displays. Remaining ions in the liquid crystal mixture influence the VHR especially of cyanogroups containing substances negatively. This leads to a high leakage current responsible for a poor image quality and thus a low production yield of the panel.[3] Responsible for the low VHR is the ability of cyano-groups to solvate the ions present in the LC layer and from adjacent materials like polyimide films via ion-dipole and ion-induced dipole interactions. Even after intensive purification of cyanogroup containing substances the VHR could not be raised to a level sufficient for the requirements of PFAS IN LIQUID CRYSTAL DISPLAYS - MERCK ELECTRONICS 6 Classification: Public modern high-quality devices.[3] So more than 20 years of research have proven that cyano-groups other than stated in the Annex XV report[5] are not suitable alternatives for the usage in active matrix displays. Modern Displays - emerging of fluorinated liquid crystals Modern active matrix displays emerged with the availability of highly fluorinated LCs. These materials possess a wide nematic range and fulfill the reliability requirements for active matrix displays: high polarity due to the high electronegativity of fluorine, high reliability, high stability due to the strong carbon-fluorine bond and a high VHR. Individual substances of this group of chemicals are not able to fulfill all necessary properties for the different applications, and so a variety of LCs are used to create tailored mixtures of LCs with the desired properties.[1,3] Especially for energy-saving mobile devices a low driving voltage is crucial. LC substance groups having terminal and bridging alkyl perfluoro groups (-CF2- and -CF3) are increasing the dielectric anisotropy which leads to a low threshold voltage necessary to switch the liquid crystals in the direction of an external electric field. Furthermore, these substances can increase the clearing point which is beneficial as well.[3] Within our portfolio LC substances with the following structures, currently falling under the proposed PFAS restriction are crucial compounds used in the LC mixture of in plane switching (IPS) displays (figure 4:) Figure 4: Essential compounds for high quality, low energy IPS displays in scope of the PFAS restriction. These substances are used in LC mixtures for IPS displays in typical concentrations from 1% up to 30%. The mixtures are used in high quality displays with a high color gamut and a large viewing angle usable within a high temperature range. In the final electric and electronic device, LC mixtures are completely sealed inside the panel and amount to 0.008 g for 7.6-inch smartphones, 0.025 g for 13-inch tablets, 0.035 g for 15-inch notebooks and 3.8 g for 65-inch TVs. Nevertheless, the threshold as suggested in the restriction draft will be exceeded. PFAS IN LIQUID CRYSTAL DISPLAYS - MERCK ELECTRONICS 7 Classification: Public High-end LC modes and display technologies IPS displays are used in mobile applications because of the large viewing angle and the touch resistivity. Additionally, high-end computer monitors are using IPS displays as well because of the accurate color reproduction and the high color gamut of this technology. The automotive industry is using IPS displays without alternatives, as on the one hand these displays can be used in a temperature range from -40C to 110 C and on the other hand safety is ensured due to good readability from driver, co-driver and backseats. The average use period of a car lasts 18 years[6] and therefore, the built-in display needs to last at least as long, so that the lifetime of the display is essential to avoid early replacements which produces additional electronic waste. Regarding the megatrends connected cars and autonomous driving, display sizes in cars are expected to grow. The display used as control panel for the radio, or for the air conditioner becomes more and more the central interface in the car for the safety features of modern cars. E.g., via the display, air pressure of the tires can be checked and during navigation track information like the maximum allowed speed are shown. IPS displays are also essential for the use in medical monitors. The high color quality and the large viewing angle combined with the high brightness are important to facilitate the diagnosis. IPS monitors are capable to correctly reproduce grayscales from different viewing angles (figure 5). Figure 5:a) IPS display in medical monitors. The image shows the monitors with different viewing angles, so the stable contrast ratio at large viewing angle of IPS displays is crucial. b) TN-type display showing gray scales. c) VA-type display showing gray scales. d) IPS display showing grayscales. The IPS display clearly possesses the best image quality. Technologically different modes are the twisted nematic (TN), the polymer-stabilized vertical alignment (PS-VA) and the IPS related ultra-bright fringe field switching (UB-FFS) mode. TN displays are usually used in gaming monitors. The biggest advantage is the quick response times, but the color and contrast quality and the viewing angle is lower compared to the other modes. The main application of PS-VA is the TV display. There, a high viewing angle is not as relevant as in mobile devices, but the higher contrast of PS-VA is beneficial. Typically, UB-FFS-displays are used in mobile applications but have longer response times leading to worse moving picture quality compared to IPSdisplays. PFAS IN LIQUID CRYSTAL DISPLAYS - MERCK ELECTRONICS 8 Classification: Public In conclusion, the IPS mode cannot be fully substituted by technologically different modes, as each mode provides its own advantages depending on the specific use scenario of the display. OLED is not yet capable of replacing the LC display technology. Although contrast and color quality are superior, the lifetime of the molecules is inferior compared to LC displays. Especially blue emitters have a low lifetime as the high energy emission leads to degradation of the molecule.[7] Typically the luminescence of blue OLED emitters drop to 95% (LT95) after 700 h and to 50% (LT50) after 20000 h of operation.[8] In automotive application where the display is exposed to temperatures >80 C the LT95 is a factor of 10 lower than at room temperature. So, in this environment, the OLED display does not have the lifetime needed to accompany the car from production to its end of life. In contrast, LC displays are quite long-lived with unchanged image quality during the time of use. Additionally, the brightness of OLED is not yet comparable to the high brightness of LC displays and the current demand of displays for automotive applications is mostly covered by LC technology. Conditions during liquid crystal production in the EU The manufacturing of the LC substances in Europe is carried out in Darmstadt in a poly production plant. The synthesis of LC intermediates takes place in closed and defined processes during production. Containment is achieved by technical design, i.e., process connections, cask covers, docking fittings. being capable of ensuring adherence to the respective exposure limits. The exposition to workers is minimized via usage of closed barrel lances entries and intermediate bulk containers. The target LC substances of the synthesis are dried in paddle dryers and filled into stainless steel barrels. Residual LC substance is dissolved with a solvent mixture and transferred back into the next production/reaction batch. A management system is in place which ensures that the containment remains effective. This management system defines the appropriate training of the personnel, maintenance, and integrity checks. Detailed risk-based safety assessments are carried out (according to German GefStoffVO). These safety assessments cover normal operation, as well as ramp-up and shut-down of the systems, cleaning, maintenance, and interruptions to operation. Exhaust air is passed through K2/K3 scrubber and oil scrubber systems with catalytic afterburners. Stripping steam as well as used organic solvents and wastewater are fed into the disposal system. In conclusion the exposition is minimized according to state-of-the-art measures, and we expect no significant exposition towards workers and environment. Mixture preparation and device manufacturing in non-EU The LC substances are exported to Asia where the formulation step takes place at different Merck Electronics subsidiaries. Our customers are using the LC mixtures to manufacture display panels or final displays in controlled and closed clean room processes. Subsequently, displays are built in electric and electronic devices and the LC mixtures are enclosed in the final device. The displays or the final devices are imported in the EU. PFAS IN LIQUID CRYSTAL DISPLAYS - MERCK ELECTRONICS 9 Classification: Public Further processing, production of displays and end of life of electric and electronic devices During the use of the LC mixture, we do not expect any significant release of PFAS into the environment because adhesive forces prevent LC mixtures from leaking even if the display brakes. Electric and electronic devices are regulated under the RoHS (Restriction of Hazardous Substances) directive in the EU (European Union). For disposal, the devices are collected. According to the WEEE (Waste Electrical and Electronic Equipment) directive, each LC panels need to be removed from the device and be collected separately. Merck holds a patent for display disposal.[9] The display is treated thermally in industrial waste facilities. Organic substances and foils in the display provide enough energy to melt the glass of the display whereas the waste display is heated >1200 C. This is above the heat of 600-1000 C that has to be applied to destroy the PFAS compounds[10] and the LC substance of the LC mixture will decompose. Thus, we do not expect significant emissions of PFAS at the end of life. Impact of PFAS restriction on liquid crystal display use The published draft for the universal PFAS restriction will affect displays using the IPS technology. For four essential LC substances a suitable alternative is not yet available. As explained above, LC mixture development is a multidimensional task where different parameters must be adjusted. New LC substances possess new properties, which influence the behavior of the mixture. Finding a working replacement is a two-step approach. First, a new LC substance with the desired properties needs to be synthesized. Second, the mixture needs to be designed accordingly to the substitute LC substance and needs to be optimized to fulfill the requirements desired by the customer. Derogation for PFAS in liquid crystal displays IPS is the only LC mode fulfilling the requirements of the automotive industry and for medicinal devices. Merck Electronics has the experience and know how to successfully manage the process for development of new LC substances and mixtures. We therefore ask for a 5-year derogation for the use of PFAS in IPS displays for automotive, mobile and monitor application until suitable alternatives are found. PFAS IN LIQUID CRYSTAL DISPLAYS - MERCK ELECTRONICS 10 Classification: Public References [1] T. Geelhaar, K. Griesar, B. Reckmann Angew. Chem. Int. Ed. 2013, 52, 8798 - 8809 [2] https://cc-special.merck.de/lcd_explorer_EN/#topic=tn;scene=tn_chap1;lang=en [3] P. Kirsch, M. Bremer, Angew. Chem. 2000, 112, 4384-4405. [4] Ko, Jeong-Hoon & Choi, Jun-Chan & Lee, Dong-Jin & Lee, Jae-Won & Kim, Hak-Rin. (2021). Photocontrollable Resistivity Change in Nanoparticle-Doped Liquid Crystal Alignment Layer: Voltage Holding and Discharging Properties of Fringe-Field Switching Liquid Crystal Modes. Crystals. 11. 268. 10.3390/cryst11030268. [5] Annex XV Restriction Report: Proposal for a Restriction: Per- and polyfluoroalkyl substances (PFASs) https://echa.europa.eu/documents/10162/1c480180-ece9-1bdd-1eb8-0f3f8e7c0c49 [6] WirtschaftsWoche. (28. Juli, 2014). Typische Lebensdauer von Autos in Deutschland nach Automarken (Stand: 2014*; in Jahren) [Graph]. In Statista. Zugriff am 20. Juli 2023, von https://de.statista.com/statistik/daten/studie/316498/umfrage/lebensdauer-von-autosdeutschland/ [7] https://cordis.europa.eu/article/id/244889-durable-blue-emitters-boost-oled-lifetime [8] Forrest, S. (2021) Waiting for Act 2: what lies beyond organic light-emitting diode (OLED) displays for organic electronics? Nanophotonics, Vol. 10 (Issue 1), pp. 31-40. https://doi.org/10.1515/nanoph2020-0322 [9] https://patents.google.com/patent/EP2082817B1/en EP2082817B1 European Patent Office [10] S. Verma, T. Lee, E. Sahle Demessie, M. Ateia, M. N. Nadagouda, Chemical Engineering Journal Advances 13 (2023) 100421 PFAS IN LIQUID CRYSTAL DISPLAYS - MERCK ELECTRONICS 11