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Newton ring, also known as "Newton Circle." Optically, the Newton ring is a thin film interference phenomenon. An interference pattern of light is a concentric ring of light and dark. For example, a convex surface of a convex lens having a large radius of curvature is in contact with a flat glass. When exposed to sunlight or white light, the contact point is a dark point surrounded by a number of bright and dark colored rings; When the color light is illuminated, it appears as a number of solid circles of light and dark. The distances of these circles are unequal and gradually narrow as the distance from the center point increases. They are interference fringes formed by the interference of light reflected on the spherical surface and the plane.
In the schematic diagram of the Newton's ring, the lower part is a flat glass (planar crystal), A is a plano-convex lens, and its center of curvature is O, and the air gap between the plane glass and the convex lens is around the contact point of the middle part. When parallel monochromatic light is incident perpendicularly on the flat surface of the convex lens. The reflected light caused by the upper and lower surfaces of the air gap forms coherent light. Light is reflected on the upper and lower surfaces of the air gap (one is reflected on the light-dissipating surface, and the other is reflected on the light-tight medium).
We know that whether it is a resistive touch screen or a liquid crystal display, the support body is two pieces of ITO glass or one piece of ITO glass, one piece of ITOFILM. If one side of the material is deformed, the inner surface of the material ITO produces a curved surface with a radius of curvature, with ordinary physics. The convex lens that produces the Newton's ring in optics has the same effect as the inner surface of the mirror. The Newton's ring also reflects the relationship between the optical path difference and the wavelength of the reflected light and the incident light on the opposite surfaces. It is also the same, because the optical path difference increases, that is, the distance between the two surfaces increases, and the spacing of Newton's rings also increases. 5FI"T=QF In the actual production process, regardless of the resistive touch screen, the liquid crystal display is good, the gap distance at the outer frame support will be slightly larger than the middle, if the parameters in the process are slightly different, Then the distance difference cannot be eliminated, so that the two surfaces are inwardly recessed inward, so that the optical path difference between the two surfaces is different, and the incident light and the reflected light are mutually different. During the interference process, different wavelengths are selected according to different optical path difference regions, and the colors of the corresponding wavelengths are displayed.
Third, the actual production of the Newton ring where and whyIn the LCD module, there are three places that are most likely to generate Newton's rings:
1. Rainbow generated inside the LCD monitorThe thickness of the liquid crystal display is generally less than 10 microns. If the number of spatial particles in the space is insufficient or unevenly distributed, or the spatial particle diameter of the outer frame and the inner support are not suitable for the process of the factory design, rainbow defects will occur. Another major cause is that during the process of boxing, the inside of the box is contaminated by foreign objects that exceed the diameter of the space particles. This is also the reason why the liquid crystal display factory is very strict in controlling the clean environment.
The distance between the plano-convex lens and the planar lens is e, and the plano-convex lens has a radius of curvature R.
2. Water ripple between the liquid crystal display and the resistive touch screen (also called water pattern)This water ripple is also one of the Newton rings. Especially when the resistive touch screen is operated, the external pressure applied to the resistive touch screen causes the lower surface of the resistive touch screen to bend and deform, and the Newton ring changes with the force. The color radius will also move, generate or disappear, just like the water ripple generated by the water surface, so this Newton ring is also called water ripple or water ripple, which is manifested by the change of action location and action pressure. .
3. The Newton ring (also called rainbow pattern) resistive touch screen inside the resistive touch screen. In the production process, in order to generate the deformation amount of the touch area, the height of the outer frame is generally much higher than the support point inside, if printed. If the water-based adhesive is used as a frame, the height is generally about 50~70 microns. If the double-sided tape of PET substrate is used, it is generally more than 50 microns, and the support point inside is generally less than 25 microns. If diameter 30 is used. ~45 micron DOT, the final forming height of the support point is only about 15 ~ 25 microns. In addition, the operating surface of the resistive touch screen is also used to generate a deformation amount of the touch area, which is generally ITOFILM, and the material is flexible. In this way, if the process parameters in the production process are not precisely controlled and there is no action operation, the ITOFILM in the middle part of the product will collapse and stick to the support point, causing the surface deformation, so that the incident light and the opposite surface of the two ITO inner surfaces When the light interferes, a Newton's ring is formed.
In actual production, how to effectively prevent the generation of Newton's ring can also be prevented according to the optical law of Newton's ring.
At the beginning of designing the product, we can calculate the height of the inner and outer frames according to the product's external dimensions. The inner ring radius of the Newton ring will fall outside the product size, so that we can optimize our own design parameters. . (How to calculate and principle formula, please refer to the attached "equal thickness interference experiment")
Of course, the above method is only a theoretical verification. In fact, if we really follow the calculation data, we can't make the product that the customer needs, but this calculation can guide us how to be as close as possible to the theoretical value in production. . Some people will say that the calculation is not necessarily accurate, and there is no better way to avoid it in production. Yes, or refer to the attached method of "equal thickness interference experiment". When using a microscope or a micrometer to measure the deflection of your upper film, the Newton's ring appears. Then calculate the smallest middle of your Newton's ring. The thickness of the space particles or support points, if combined with the pressure gauge, can also measure the pressure experienced by the product when the Newton ring appears. Therefore, the emergence of the problem, first from the test method, then from the experimental data, and then from the process parameters.
Rainbow defects can be quickly found by microscopy. If it is point-like, three cases can be seen under the microscope: the number of spatial particles is small, the spatial particles gather, and the foreign objects in the box. Such defects, according to the observed phenomenon, can be immediately prevented from adjusting the parameters of the front space particle spreader, the space particle spreading section and the environmental clean maintenance of the combined section.
If the entire LCD display is a rainbow, then either the outer frame and the inner space of the box are mismatched, or the number of particles in the box is not enough or not. Such defects may check the process material parameters of the particle scattering in the front space, and adjust the parameters on the particle detection data for prevention.
2. Water ripple between resistive touch screen and liquid crystal displayTo prevent the generation of water ripples, first increase the strength of the resistive touch screen. For example, it is replaced by a PC substrate that is subjected to a larger force or glass material, or is replaced by a thin substrate. Thick substrate. This is one of the reasons why 2 MM thick glass or tempered glass is required for a resistive touch screen product with a certain size. All the design parameter changes are justified. They can't be copied from the outside. If you don't know the principle, you will waste your material and quality costs, or you can't avoid your potential quality defects and good products. The second is that the assembled double-sided tape between the resistive touch screen and the liquid crystal display can be thicker than the customer's requirements, so that the dark ring of the Newton ring can be moved outside the product size. Or the support point is printed on the assembly surface of the resistive touch screen and the liquid crystal display, and the external pressure is transferred to the liquid crystal display and the main board casing through the support point, thereby reducing the deformation of the resistive touch screen and preventing the Newton ring, that is, the water ripple. produce. If it can meet the display requirements of the product, the polarizer on the combination of the resistive touch screen and the liquid crystal display can be replaced with the anti-glare polarizer under the condition that the display effect can be accepted. Note that the close-up display effect of the anti-glare polarizer is much worse than that of the ordinary polarizer. Especially for the QVGA or higher liquid crystal display, if the display is fine, the fineness, reaction speed and contrast of the display will be significantly reduced, so it must be The final customer can determine the display effect before replacing
3. Newton ring of resistive touch screenThe Newton ring of the resistive touch screen is indeed more troublesome to prevent, because the operating surface of most resistive touch screens uses a flexible ITOFILM substrate.
To prevent the Newton ring of resistive touch screen, firstly, in the process of ITOFILM quenching and tempering, select the tempering and processing parameters suitable for your tooling fixture and equipment, so that all parts of ITOFILM can shrink synchronously without generating unevenness due to uneven shrinkage. Leveling or transferring the unevenness on the loading fixture to ITOFILM. This Newton ring, which is produced by ITOFILM quenching and tempering treatment, has a very obvious feature. If it is a combination of re-divided products, the Newton ring can not be seen after the combination, but about 48 hours after the product is divided. Will appear
The height control of the support point is also the main way to prevent the Newton's ring. From the above calculations, it can be seen that the height of the brace point exceeds a certain value, it will be difficult to form, or the distance is large, and is diluted. , so we must ensure a certain height of the support point
The height of the support point must have a certain relationship with the attachment area of ​​the support point. Under the same conditions, the higher the height, the larger the attachment area of ​​the support point. For some fine-quality liquid crystal displays, the pixel size may be only 60 to 90 microns, if a support point size exceeds half of the pixel size, then this pixel will produce display distortion, observed at a certain distance, can show the entire support point layout from the display. In order to solve this problem, Japanese manufacturers use a mold or a combination of gaskets in a small-sized product designed with a narrow side to fill the air and artificially increase the distance between the inner surfaces of the product, that is, to avoid the appearance of Newton's rings. It is also not necessary to design a very complicated and difficult to make ventilation passage for the outer frame, and it is also possible to design a support point with a small attachment area. The defect of the inflation method is that it cannot be used in an environment where the temperature difference changes drastically or in a large-sized product. In particular, the product of printing water-based adhesives is difficult to handle due to the narrow-edge design and insufficient adhesion. After the temperature changes drastically, it is easy to cause air leakage. After the air leaks, the effect of avoiding the Newton's ring is gone. Many manufacturers' products are placed in their own constant temperature warehouse before leaving the factory. There is no problem in the customer's ordinary warehouse, or just after the car is transported, the Newton ring phenomenon appears in the product. This is the reason. Therefore, inflation is not an ancestral recipe for dealing with Newton's ring. If you do not consider the conditions and environment of the product, plus other auxiliary techniques, it will not play a real role. The Newton's ring in the sensitive area of ​​the resistive touch screen is also the combination of the thickness of each process material and the FPC hot pressing temperature and pressure parameters. It can basically solve the FPC material thickness and hot pressing parameters.
As for some large-size display products with a long viewing distance, because the pixel size is relatively large, it is possible to use support points of 50 to 60 micrometers in size, unless the support points are unevenly printed or the support points are highly collapsed, and Newton is generally not present. The ring phenomenon.
Sixth, the application of Newton ringJudging the surface of the lens, accurately checking the surface quality of the optical element, measuring the radius of curvature of the lens surface, and the refractive index of the liquid.
When machining optical components, the principle of Newton's rings is widely used to check the surface accuracy of planes or surfaces.
It is applied to a spectrometer to separate the composite light into a monochromatic light.
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