RU2090472C1 - Method of filling of display pack with liquid-crystalline substance - Google Patents

Abstract

FIELD: fabrication of products of optoelectronics, applicable in video devices, in which liquid crystal serves as optical medium and member, in particular, at filling of the display pack with liquid crystal. SUBSTANCE: method consists in successive arrangement of liquid crystal and display pack in a pressurized chamber, degassing of the pack and liquid crystal in the process of chamber vacuum treatment, submersion of the pack with the filling hole in liquid-crystalline substance, filling of the pack with liquid crystal by depressurization of the chamber, pressurization of the pack filling hole; degassing of liquid - crystalline substance and filling of the pack are accomplished at a temperature exceeding the temperature of isotropic state of liquid-crystalline substance in vacuum, and vacuum treatment of the chamber and display pack is conducted at a temperature not exceeding the solidification temperature of liquid-crystalline substance. EFFECT: facilitated procedure. 1 tbl

Description

 The invention relates to the production of optoelectronic products (video equipment) and can be used to produce video devices whose optical medium and structural element is liquid crystal (LCD), in particular when filling in an LCD display package.

 For highly informative large-format liquid crystal displays (LCDs), the main way to introduce LCDs into a display package is the vacuum method that is widely used in serial production.

There is a method of filling the cell of the indicator device LCD with a pressure difference, according to which an indicator cell and a cell with an LCD are placed in a sealed chamber, then a vacuum of 1.33 0.133 Pa (10 ^-2 - 10 ^-3 mm Hg) is created in the chamber and the cell is immersed filling hole in the cell with the LCD, let air into the chamber and the LCD fills the cavity of the cell [1]
The reasons that impede the achievement of the required technical result when using the known method include the fact that the known method, when filling packages of indicators of large sizes, does not allow the separation of impurity ions over the entire area, which leads to a significant spread of electro-optical parameters.

 Similar methods for filling the LCD indicator package are known from foreign patents. For example, in [2] a filling method is described, according to which gas is pumped out of the cavity of the bag and the LC substance is introduced into the gas through the filling hole under reduced pressure.

The closest method of the same purpose to the claimed object by the totality of signs is the vacuum filling method, which consists in the fact that the LCD materials and indicator packages having one filling hole in the end are placed in a sealed chamber from which air is pumped out, the end of the indicator is immersed air or other gas is introduced into the liquid crystal layer and into the chamber, which “presses” the liquid crystal into the indicator packages, the filling hole is sealed [3]
In the process of pumping air from the chamber and the package, the degassing process of the liquid crystal simultaneously occurs, accompanied by the release of gas bubbles from the liquid crystal mixture and their removal from the working area. Degassing the LCD eliminates the possibility of gas cavities in the filled bag, reducing the optical characteristics of the indicator.

 The reasons that impede the achievement of the required technical result when using the known method adopted for the prototype include the fact that in it during degassing in a vacuum, the gas components of the mixture are removed, which are formed during the evaporation of molecules from the LC surface and which are in the form of saturated air bubbles in the volume vapor. This leads to a depletion of the mixture, a decrease in the concentration of components, and a change in the initial composition of the LC mixture, which violates the homogeneity of the optical medium, degrades the electro-optical characteristics of the indicator and increases the defectiveness (reject rate) of products at the final stage of the technological route when the LCD is introduced into the indicator package.

The negative consequences of this method are exacerbated by a number of factors that take place in modern LCD manufacturing practice, namely
1) the use of multicomponent mixtures of LC, which allows you to change the parameters of the optical medium within the required limits (see Grebenkin NF Ivaschenko AV Liquid crystal materials. M. Chemistry, 1989, 288 pp.), But leads to different quantitative losses of each the component during evaporation is proportional to its volatility or the value of the partial pressure;
2) using wide-temperature LC mixtures and increasing the filling temperature, which allows to reduce the operation time by reducing the viscosity of the mixture, but leads to an increase in the disproportionate losses of each of the LC components, due to the temperature dependence of the saturated vapor pressure P according to the ratio
P e ^{A-B / T} ,
where A and B are constants for a given temperature range ΔT (see the Handbook of a chemist. T.1. M.-L. Goskhimizdat, 1963, 1072 pp.);
3) an increase in losses due to the need to use temperature conditions for filling the packet above the temperature of the phase transition to the isotropic state (T≥T _J ) for displays based on LC smectic A and C ^* mesophases that are in a paste-like state under normal conditions and have an anomalously high viscosity at temperatures below the phase transition temperature, the nematic smectic T ₁ ≅ T _{N → S.}

 The invention consists in the following. The problem to which the invention is directed, is to increase the yield of products, reducing the time of filling the package and reducing the loss of the LCD.

 This problem is solved by eliminating defects in the optical medium due to a change in the initial concentration of the components during evaporation at the stage of degassing of the liquid crystal and the effect of chromatographic separation of the liquid crystal mixture in a flat capillary of the packet.

 The specified technical result in the implementation of the invention is achieved by the fact that in the known method of filling the display package with a liquid crystal substance, comprising sequentially placing a liquid crystal substance and a display package in a sealed chamber, degassing the package and liquid crystal substance in the process of evacuating the chamber, immersing the package with a filling hole in the liquid crystal substance, filling a package of liquid crystal material by depressurizing the chamber and sealing the filling about the openings of the package, the degassing of the liquid crystal substance is carried out at a temperature above the temperature of the isotropic state of the liquid crystal substance in vacuum, and the chamber and the display package are evacuated at a temperature not higher than the crystallization temperature of the liquid crystal substance.

Thus, the differences of the proposed method of filling the LCD display package in that LCD degassing and package evacuation are carried out in different temperature conditions, namely, the package and chamber are evacuated at temperatures below the crystallization temperature T _{to the} liquid crystal, and gas inclusions are removed from the LCD mixture and filling the packet at temperatures above the temperature of the existence of the isotropic phase of the LC T _J

 The method is applicable to all classes of LC compounds and is based on the principle of reversibility of mesomorphic states of LC.

The proposed method for introducing a liquid crystal optical element into the display structure is as follows: a cuvette with an LCD is placed in a chamber on a stove equipped with a thermostating system and providing change, installation and automatic control of temperature constancy in the range ΔT 50 ^o C 150 ^o C. Above the cuvette on the manipulator lever that allows at least vertical movement, a bag is fixed, facing the filling end with a slit to the cuvette parallel to the LCD surface, after which the package and cuvette are hermetically closed They are covered with a transparent cover with a cap having air outlet and a vacuum pump.

 The method involves the following sequential operations.

1. The system (board, cuvette, LCD, package) is cooled and thermostated at a temperature not higher than the crystallization temperature of the LCD (T ₁ <T _to ).

2. By turning on the vacuum pump, air is pumped out of the chamber and the package to a predetermined pressure level P _k .

 3. The chamber is isolated from the vacuum pump.

4. The system heats up and thermostats at T ₂ ≥T _J.

5. The pressure difference inside the chamber and gas inclusions in the volume of the liquid crystal provides gas evolution in the form of rising and falling bubbles on the surface of the liquid crystal and is fixed by a change in pressure ΔP = P - P _k > 0.
6. The system is cooled again to T _{1 to} ≅T, which leads to vapor condensation and the LCD cessation evaporation processes, etc.

7. The sequence of operations for PP. 1 5 is repeated until the gas evolution is completely stopped and stops when, after heating the LC, in accordance with 4,5 increase in pressure P _to does not occur ΔP = 0 and P P _to .

 8. The mechanical manipulator, the control of which is outside the camera, the package moves until the end gap is immersed (contact) with the surface of the LCD.

 9. The camera is connected to the atmosphere, the filling process is visually monitored by the movement of the LCD front along the height of the package. The process stops after the package is completely filled, and the operation time is fixed.

 10. The system is cooled to room temperature, the cap of the chamber rises, the filled bag is removed from the chamber, and the filling gap is sealed.

The temperature separation of LC degassing and air removal from the chamber and LC volume, carried out at Т ₂ ≥Т _J and Т ₁ <Т _к, respectively, implements a physical mechanism, according to which the smallest possible number of LC components present above the surface of the LC are aspirated as saturated steam, the bulk of which condenses at T ₁ ≅T _k .

и закону Пуазейля

где
η динамическая вязкость;
С эмпирическая константа;
V, l, d объем, длина и толщина (зазор) внутренней полости пакета (плоского капилляра) соответственно;
S площадь щели заполнения;
DP = P_к- P_атм перепад давления внутри и вне полости пакета при заполнении.Thus, the proposed method of introducing an LCD optical element into the display structure has the following advantages compared to the known method:
a) the loss of LC due to evaporation and gas evolution processes is minimized, since the system is evacuated at a temperature below the crystallization temperature, and LC degasses into an enclosed space at a temperature above the temperature of transition to an isotropic state, followed by cooling to T ₁ ≅ T _{to a} corresponding decrease in pressure saturated vapors and their condensation into liquid and crystalline phases;
b) decreasing defective products and increase the yield of the process cycle by maintaining the starting mixture composition LCD and a uniform optical display medium neutralization and evaporation processes increasing the proportion of condensed vapor LC mixture components with different values of the partial pressures of the pumping down to the temperature T _{1 to} ≅T;
c) the unevenness of contrast in the information field of the display is reduced, due to the depletion of the LCD mixture as a result of the deposition of individual components of the LCD on the inner surface of the flat capillary of the bag (the effect of chromatographic separation of the LCD mixture in the bag), due to an increase in the speed of movement of the LCD and a reduction in the time of filling the packet with a decrease viscosity of the mixture with increasing temperature according to the equation

and Poiseuille's law

Where
η dynamic viscosity;
C is an empirical constant;
V, l, d volume, length and thickness (gap) of the internal cavity of the package (flat capillary), respectively;
S is the area of the filling gap;
DP = P _to - P _atm differential pressure inside and outside the cavity of the package when filling.

 The application of the proposed method for introducing an LCD optical element into a display package is illustrated by the following examples.

 Example 1

 The package of the LCD P-662 used as the personal computer PC-300 screen has dimensions of 246x124x3 mm, information capacity of 640x200 display elements, the gap of the internal cavity is 8.0 0.1 μm and three symmetrically located openings (slots) of length 7 2 mm at the end of the bag.

 The optical medium of the display package is a wide-temperature LCD material Z41-1565 f. "Merck", which is a mixture of 6 components of the following composition, wt.

с температурами фазовых переходов Т_к 20^oC и Т_J 85^oC.

with temperatures of phase transitions T _to 20 ^o C and T _J 85 ^o C.

A boat cuvette with an amount of LC mixture of at least twice the volume of the bag cavity (2 mm ³ ) is placed on the plate of the filling device (for example, type УВР-3) equipped with a thermostatic system that allows changing, setting and automatic temperature control in the range 50 - 150 ^o C (for example, circulating refrigerant like ammonia, liquid nitrogen, etc., by electric or thermal radiation heating using KGM-150 type IR lamps, relays, and T control piezoelectric sensors).

 Above the boat, on the arm of the manipulator, controlled from the outside of the camera and allowing at least vertical movement, a bag is fixed facing down with its holes to fill parallel to the surface of the LCD, after which the package and boat are closed with a sealed transparent hemispherical cap (camera lid) with an outlet to the atmosphere and vacuum pumps (for example, 16NVRND forevacuum type and TNM-150 type turbomolecular type).

The chamber and everything in it (board, boat, LCD) are cooled and thermostated at T ₁ 25 ^o C (T ₁ <T _to - 20 ^o C), after which air is pumped out of the chamber and package to a pressure of P _to 10 ^-4 mmHg Then the chamber is isolated from the atmosphere, heated and thermostated at T ₂ 120 ^o C (T ₂ > T _J 85 ^o C). The visually observed gas evolution from the LC volume in the form of rising and falling bubbles on the LC surface is fixed by an increase in pressure P (P _to <P <P _atm ). After establishing a constant pressure value P, the chamber is again cooled, thermostated at T ₁ 25 ^o C and pumped out. The process is repeated until after another temperature increase to 110 ^o C the pressure in the chamber does not change (ΔP = P - P _к = 0) For the case described in example 1, the process takes 2 3 cycles: cooling pumping heating .

 With a mechanical manipulator, the package moves vertically downward until the end slots are in contact with or contact the LCD surface. The chamber is connected in the atmosphere and the packet is filled, which is observed by the motion of the LC front in the flat capillary of the packet. The process stops after the bag is completely filled for ≈240 ± 15 s, then the heating is turned off, the hood of the chamber is lifted, and after reaching temperature equilibrium with the environment, the packet is removed from the chamber and the filling holes are sealed (for example, with epoxy resin).

 Example 2

 In the display package in example 1, the LC optical element SZHK-160 is introduced with a range of operating temperatures in the region of the existence of smectic A mesophase and which is a five-component mixture of the following composition, wt.

с температурами фазовых переходов
К.-5^oC.S_A.53^oC.N.60^oC.J.

with phase transition temperatures
K.-5 ^o CS _A .53 ^o CN60 ^o CJ

The operation of introducing the LCD into the package is carried out similarly to that described in example 1 with the following parameters of the pumping and degassing modes: cooling temperature T ₁ = -10 ^o C, pressure level after pumping and degassing P 10 ^-4 mm RT. Art. gas evolution temperature T ₂ 85 ^o C, number of cycles (n): cooling; pumping-out heating equals two; filling time (t) 230 ± 20 s.

 Example 3

The LCD optical element ZhKS-43 with a range of operating temperatures in the region of existence of the smectic C ^* mesophase and representing a four-component mixture of the following composition, wt.

с температурами фазовых переходов
К.5^oC.С^*.47^oC.S_A.60^oC.N.66^oC.J
Процесс проводится аналогично описанному в примере 1 со следующими параметрами режимов откачки и дегазации: Т₁ 0^oC, Т₂ 91^oC, Р 10^-4 мм рт.ст. n 3, t 160±20 с.

with phase transition temperatures
K.5 ^o C.S _{^{* .47 o CS A .60 o CN66}} o CJ
The process is carried out similarly to that described in example 1 with the following parameters of the pumping and degassing modes: T ₁ 0 ^o C, T ₂ 91 ^o C, P 10 ^-4 mm Hg n 3, t 160 ± 20 s.

In all cases, the most preferred values of T ₁ at 5 ^o C below T _to and T ₂ at 25 ^o C above T _J are taken. From the experimental data on the identification of the optimal regime, it follows that the excess of T ₂ over T _J over 25 ^o C does not significantly affect the dynamics of the process, and the accepted difference ΔT = T _to - T _{1 is} sufficient to take into account the variance of T for the LC mixture.

 The table shows the comparative results of the introduction of the LCD optical element in the design of the display according to the known, serial and proposed methods.

 It follows from the table that, in comparison with the prototype and serial methods, the proposed method improves the optical uniformity of the display information field, increases the yield of products at this stage of the technological process, reduces the time of the package filling operation and reduces the consumption of an expensive liquid crystal display design element.

Claims (1)

 A method for filling a display package with a liquid crystal substance, including sequentially placing a liquid crystal substance and a display package in a sealed chamber, degassing the package and liquid crystal substance during the chamber evacuation, immersing the package with a filling hole in the liquid crystal substance, filling the package with a liquid crystal substance by depressurizing the chamber, and sealing the filling hole of the package, characterized in that the degassing of the liquid crystal substance and filling chum is carried out at a temperature above the liquid crystal isotropic state in a vacuum and evacuating the chamber, and the display package is conducted at a temperature not higher than the crystallization temperature of the liquid crystal material.

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