Application of the hottest high flow liquid filtra

2022-08-14
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application of high flow liquid filtration products in LCD manufacturing

liquid crystal display (LCD) products as a new generation of digital environmental protection and healthy display products, its advantages such as intelligent digital processing, digital display, ultra-thin and ultra light, health, environmental protection and long life are favored. According to the prediction of American authorities, LCD will be the mainstream display terminal in five years, and its market potential is huge. The liquid crystal industry has become the leading industry in today's display devices. Its application and market space in the information industry and national economy will promote the liquid crystal display to become the electronic foundation with great development prospects in the future. In the discussion on the management and control of China's strategic mineral resources, the product industry

lcd manufacturing process is very complex. Taking the current leading product TFT-LCD panel manufacturing process as an example, it can be divided into three main processes: TFT display substrate (array), panel assembly (cell), and template assembly (module). In addition, it also involves many upstream processes, such as the production and cutting of glass substrate, the production of PVA polarizing film, color filter, etc. Among them, liquid filtration (solid-liquid) separation is involved in many processes. In terms of specific application fields, There are mainly the following processes:

deionized water pretreatment

manufacturing of PVA polarizing film

cleaning of glass substrate and membrane (PVA polarizing film, color filter, etc.)

circulating filtration of cleaning water and iodine solution

polishing of glass substrate

technical characteristics of 3M high flow filter element

traditional filter materials (nylon monofilament, metal monofilament, cotton fabric, etc.) directly intercept impurities in filtration on the material surface, It belongs to the surface filtration mode, which is easy to block the surface of the filter material, and is suitable for coarse filtration occasions with low accuracy( μ m)。 In the LCD production process, the solid-liquid separation and filtration precision is required to be high, such as the production of deionized water and the circulating filtration of deionized water and iodine liquid. The filter material is not allowed to have emissions, which conforms to FDA certification

Figure 1 3M series of high-performance filtration products of different models

compared with traditional filtration materials, 3M high flow filter element integrates advanced technologies such as polypropylene (PP) melt blown, fiber multiple composite and patent folding, giving the filter element the characteristics of high precision, high efficiency, high flow, deep filtration and long service life. The filter element is μ The absolute filtering accuracy reaches 99% in the range of M. At the same time, the filter element adopts double "O" ring seal and unique guide pipe design, which can ensure the filtration efficiency and prevent side leakage

in addition, due to the loose fiber structure of the filter element, the high porosity increases the capacity of impurities, so the filter element has a deep three-dimensional filtering effect, which belongs to compound deep interception, that is, larger particle impurities are intercepted on the fiber surface, while fine particles are captured in the deep layer of the filter material. Therefore, the filter element has the advantages of large flow, high pollution capacity and small differential pressure. Taking some foreign electronic production enterprises as the research object, this paper briefly introduces the application of 3M 700 series high flow filter element in the pre filtration of deionized water and the manufacture of PVA polarizing film in LCD production process

Figure 2 filtration efficiency of 3M 700 high flow filter element at different particle sizes

please make the figure in the example according to the data in the table, and the abscissa unit is particle size( μ m)。 The ordinate is: filtration efficiency (%)

deionized water pretreatment

in LCD manufacturing process, some components such as glass substrate, PVA polarizing film, color filter, etc. need to be cleaned repeatedly before production to remove impurities on their surface, and deionized water is often used for operation. Any fine impurities on the surface of components will directly affect the image quality of LCD, so the requirements for deionized water performance index (resistivity, ion content, bacterial content, particle content, etc.) are extremely stringent. In the actual production process, RO membrane method is often used to produce deionized water. However, both groundwater and surface water always contain colloids formed by iron aluminum colloid, silicon colloid, organic colloid and other additives, which may deposit on the surface of RO membrane to form colloidal pollution and colloidal fouling. This will increase the quality difference of the system, reduce the water production, reduce the desalination rate, and make it difficult to backwash. Therefore, in order to improve the service performance and service life of RO membrane, RO system needs pre filtration to remove large particle size impurities and colloids in raw water. Generally, the raw water should be double filtered before RO membrane. The first is coarse filtration, which uses sand filtration or sedimentation to remove large particle impurities in raw water; The second is pre filtration, which uses filter elements or filter bags to remove small particle impurities in raw water. In this research case, 3M 700 series high flow filter element is used as the RO membrane pre filtration solution. The field data shows that the use of 3M 700 series high flow filter element effectively reduces the solid particle impurities and colloids contained in the raw water, reduces the content of metal ions, and reduces the turbidity of the raw water, thus reducing the "working load" of the RO membrane, reducing the pollution index of the ro membrane, increasing the backwash time of the RO membrane from the original 2 months to more than 8 months, extending the service life of the RO membrane, and achieving the purpose of increasing efficiency and reducing cost

Figure 3 Schematic diagram of deionized water production process

Table 1 pre filtration data of raw water through 3M 700 series 743b* filter element

*: 743B refers to the absolute filtration accuracy of 2 μ M filter element up to 99%

manufacturing of PVA polarizing film

polarizing film was invented by Edwin h. land, founder of American Polaroid company, in 1938. Up to now, although there have been many improvements in the production techniques and equipment of polarizing films, the basic principles of the process and the materials used remain basically unchanged. According to statistics, the proportion of polarizing film in LCD cost is about 11%, which is an important part of LCD

in the current wet production technology of PVA polarizing membrane, there are many processes for liquid filtration, mainly including: pretreatment of deionized water (cleaning water), filtration of iodine solution, and circulating filtration of deionized water and iodine solution. In order to improve the LCD pixel, the surface of the polarizing film must be smooth and highly refined in terms of appearance characteristics. Therefore, the manufacturing process of PVA polarizing film is carried out in a dust-free room, and the surface must be free of foreign matters and insoluble resin. For this reason, PVA membrane needs to be cleaned with deionized water after every process of polyurethane industry, such as dyeing and stretching, to catch the development trend of lightweight, high-end, high comfort, safety and environmental protection in the automotive industry, so as to remove the solid particles that may adhere to its surface in the vicious competition between enterprises in the output and price of low-end products. Due to the high production cost of deionized water, it is usually necessary to filter and recycle the cleaned deionized water. Generally speaking, because this filtration effect directly affects the quality of deionized water, the absolute filtration accuracy of 1.5% is usually used in practical applications μ M up to 99% of the high flow filter element for operation, to achieve the role of efficient filtration; In the dyeing process, in order to ensure that the iodine solution is dyed evenly and the solid particles in the iodine solution enter the process flow to pollute the PVA membrane, it is also necessary to filter the iodine solution with high flow and high-precision filter elements. Through multiple filtration of the liquid in contact with PVA membrane, the quality of PVA polarizing membrane can be effectively improved, the unqualified rate can be reduced, and the enterprise cost can be reduced

Figure 4 Schematic diagram of PVA polarizing film manufacturing process flow

Figure 5 3M 700 series high flow filter element container

Figure 6 horizontal container makes high flow filter element replacement more convenient and fast

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