TWI886885B - Liquid crystal electronic paper - Google Patents

Abstract

A liquid crystal electronic paper is provided to solve the problems of weak brightness and low contrast of the display screen of conventional liquid crystal electronic paper. The liquid crystal electronic paper includes two substrates and a liquid crystal layer. Two alignment layers are respectively located on the opposite inner surfaces of the two substrates. A tilt angle of the two alignment layers ranges from 0 degrees to 10 degrees. An anchoring force of the two alignment layers is less than 10 joules per square meter. The alignment layer away from a light source has a directivity. The liquid crystal layer is a liquid crystal material located between the two substrates. The crystal material contacts the two alignment layers respectively. Applying a first electric field to the liquid crystal layer and then removing the electric field to switch the liquid crystal layer to a dark state. Applying a second electric field to the liquid crystal layer and then removing the electric field to switch the liquid crystal layer to a bright state. The second electric field is greater than the first electric field. The liquid crystal electronic paper provides the effects of improving the brightness and contrast of images.

Description

LCD electronic paper

The present invention relates to an optoelectronic technology product, in particular to a liquid crystal electronic paper that increases light reflectivity and improves display contrast.

It is known that electronic paper uses reflective display technology to present images by reflecting ambient light. Electronic paper does not require an active backlight module. It only needs to be powered on to switch the bright and dark distribution on the display screen when switching images. No electricity is required when continuously displaying a fixed image. Therefore, electronic paper is suitable for use in electronic billboards, electronic shelf labels, electronic books and other devices that do not require frequent image switching. In addition, electronic paper technology is divided into electrophoretic and cholesteric liquid crystal. Electrophoretic electronic paper uses different electric fields to control the movement of colloid particles of different colors and different charging characteristics to switch the color and brightness of the image. However, electrophoretic electronic paper must use a variety of colloid particles or color filters to present a variety of colors, and requires more precise electric field control to perform switching, and the number of colors that can be presented is limited; while cholesteric liquid crystal electronic paper can include three liquid crystal layers for reflecting red, green and blue light respectively, and by adjusting the reflectivity of each liquid crystal layer, it can produce color levels with different brightness. The number of color levels of the three colors of light multiplied together is the number of colors that the liquid crystal electronic paper can present. The conventional liquid crystal electronic paper has the advantages of rich colors and easy adjustment.

The actual measurement of the specular component exclusion (SCE) of the known liquid crystal electronic paper products shows that the reflectivity in the visible light band is only about 30%, and the screen contrast is 10~11. This causes the known liquid crystal electronic paper to only present low-brightness images when the ambient light is insufficient, and the weaker the ambient light, the worse the gray level and clarity of the screen.

In view of this, the known LCD electronic paper still needs to be improved.

To solve the above problems, the purpose of the present invention is to provide a liquid crystal electronic paper that can enhance the image brightness.

The second purpose of the present invention is to provide a liquid crystal electronic paper that can make the displayed image clear.

The directions or similar terms described in the present invention, such as "upper (top)", "lower (bottom)", "inner", "outer", "side", etc., are mainly with reference to the directions of the attached drawings. Each direction or similar terms are only used to assist in the description and understanding of the various embodiments of the present invention, and are not used to limit the present invention.

The quantifiers "one" or "a" used in the components and parts described throughout the present invention are only for the convenience of use and to provide a general meaning of the scope of the present invention; in the present invention, they should be interpreted as including one or at least one, and the single concept also includes the plural case, unless it is obvious that it means otherwise.

The liquid crystal electronic paper of the present invention comprises: two substrates, which are parallel to each other, wherein the outer surface of one of the substrates faces an ambient light source, a first alignment layer and a second alignment layer are respectively located on the inner surfaces of the two substrates, the first alignment layer is close to the ambient light source, the tilt angle of the first alignment layer and the second alignment layer ranges from 0 degrees to 10 degrees, and the anchoring force of the first alignment layer and the second alignment layer is less than 10 ^-4 joules per square meter, the second alignment layer has a directivity; and a liquid crystal layer, which is filled with a liquid crystal material between the two substrates, the liquid crystal material is in contact with the first alignment layer and the second alignment layer respectively, the liquid crystal material includes a positive liquid crystal and a chiral molecule, the two substrates apply a first electric field to the liquid crystal layer and then remove the electric field to switch the liquid crystal layer to a dark state, and apply a second electric field and then remove the electric field to switch the liquid crystal layer to a bright state, the second electric field is greater than the first electric field.

Accordingly, the liquid crystal electronic paper of the present invention can adjust the boundary characteristics of the first alignment layer and the second alignment layer to low tilt angle and low anchoring force, so that the liquid crystal molecules of the liquid crystal layer can be arranged neatly in the bright state to improve the light reflectivity, and the liquid crystal molecules in the dark state can maintain the chaotic degree of focal cone arrangement to achieve low reflectivity. In addition, by forming directivity only in the second alignment layer, the mirror reflection ratio of the reflection surface of the liquid crystal layer can be reduced, which has the effect of improving image brightness, picture contrast and image clarity.

Among them, a back plate is bonded to the outer surface of the substrate away from the ambient light source. In this way, after the incident light penetrates the liquid crystal layer in the dark state, it can be absorbed by the back plate to avoid interfering with the reflected light image, which has the effect of maintaining low reflectivity in the dark state and improving image contrast.

The two substrates are transparent composite materials, including sealed materials such as glass, acrylic, plastic, and conductive materials such as indium tin oxide, nanosilver wires, and nanometal particles. In this way, the two substrates can seal the liquid crystal material, switch the applied electric field, and allow light to pass through, which has the functions of protecting the liquid crystal, transmitting light, and conducting electricity.

The reflected light band of the liquid crystal layer is in the visible light range. In this way, the electronic paper can reflect visible light with the highest reflectivity, which has the effect of enhancing the brightness of the image.

The directivity is achieved by brushing the second alignment layer in a contact manner. In this way, the brushing process can quickly and stably form the directivity, which has the effect of reducing production costs.

Among them, the directivity is to perform light directing, ion beam directing or evaporation treatment on the second alignment layer in a non-contact manner. In this way, the non-contact directing treatment can perform fine processing on the alignment film, and can also avoid the generation of debris and electrostatic residue, which has the effect of improving the quality and precision of the alignment film.

1:Substrate

1a: Inner surface

1b: External surface

11: First alignment layer

12: Second alignment layer

2: Liquid crystal layer

S: Ambient light source

B: Back panel

E1: The first electric field

E2: Second electric field

P: Bright state

F: dark state

[Figure 1] A three-dimensional diagram of a preferred embodiment of the present invention.

[Figure 2] A diagram showing the switching between the bright state and the dark state of a preferred embodiment of the present invention.

[Figure 3] Relationship between light reflectivity and light wavelength of liquid crystal electronic paper with different boundary characteristics in bright and dark states

In order to make the above and other purposes, features and advantages of the present invention more clearly understood, the following specifically cites the preferred embodiments of the present invention and provides a detailed description in conjunction with the attached drawings; in addition, the same symbols in different drawings are considered the same and their descriptions will be omitted.

Please refer to Figure 1, which is a preferred embodiment of the liquid crystal electronic paper of the present invention, comprising two substrates 1 and a liquid crystal layer 2. The two substrates 1 are spaced and parallel to each other, and the liquid crystal layer 2 is located between the two substrates 1. The inner surface 1a of each substrate 1 faces the liquid crystal layer 2, and the outer surface 1b of one substrate 1 faces an ambient light source S, while the outer surface 1b of the other substrate 1 can be attached to a backplane B.

Please refer to Figures 1 and 2. The two substrates 1 can be transparent composite materials so that light can penetrate the two substrates 1. The composite material of each substrate 1 can include a sealed material, such as glass, acrylic, plastic, etc. The sealed material is used to seal the fluid between the two substrates 1. Each substrate 1 can also include a transparent conductive material, such as indium tin oxide (ITO), nanosilver wires, nanometal particles, etc. The two substrates 1 are electrically connected to a voltage source (not shown) through the conductive material, and the voltage source can switch between the two substrates 1 to apply a first electric field E1 and a second electric field E2. In addition, a first alignment layer 11 and a second alignment layer 12 are respectively located on the inner surface 1a of the two substrates 1, and the first alignment layer 11 is close to the ambient light source S, and the second alignment layer 12 is close to the backplane B (far away from the ambient light source S).

The liquid crystal layer 2 is formed by filling a liquid crystal material between the two substrates 1, and the upper and lower surfaces of the liquid crystal layer 2 are in contact with the first alignment layer 11 and the second alignment layer 12 respectively. In this embodiment, the liquid crystal material includes positive liquid crystal and chiral molecules, wherein the positive liquid crystal is a nematic liquid crystal with a dielectric anisotropy greater than zero (△ε>0), so that the molecular arrangement direction of the liquid crystal material is parallel to the direction of the external electric field; the concentration of the chiral molecules in the liquid crystal material is preferably adjusted to the reflected light band of the liquid crystal layer 2 in the visible light range, and the chiral molecules can be left-handed or right-handed, and the present invention is not limited thereto.

The addition of chiral molecules makes the liquid crystal material cholesteric liquid crystal and has bi-stable characteristics. The liquid crystal layer 2 can be switched into two stable states, namely the bright state P in which the liquid crystal molecules are arranged in a planar structure and the dark state F in which the liquid crystal molecules are arranged in a focal conic structure. As shown in Figure 2, when the liquid crystal molecules are arranged in a planar structure, the light incident on the liquid crystal layer 2 from the ambient light source S tends to be reflected and presents the luminous bright state P; when the liquid crystal molecules are arranged in a focal conic structure, the incident light tends to penetrate the liquid crystal layer 2 and then be absorbed by the backplane B to present the dark state F. The liquid crystal electronic paper of the present invention forms an image screen through the arrangement of the bright state P or dark state F of numerous pixels of the liquid crystal layer 2.

Please refer to Figure 2. When the liquid crystal layer 2 is acted upon by the first electric field E1 between the two substrates 1, the liquid crystal molecules are disturbed by the electric field and form a focal cone structure. After removing the first electric field E1, the liquid crystal molecules in the liquid crystal layer 2 still maintain the dark state F of the stable focal cone structure. Furthermore, when the liquid crystal layer 2 is acted upon by the second electric field E2, wherein the second electric field E2 is greater than the first electric field E1 and is sufficient to arrange the liquid crystal molecules of the positive liquid crystal in a direction parallel to the second electric field E2. After removing the second electric field E2, the liquid crystal molecules in the liquid crystal layer 2 return to the bright state P of the stable planar structure.

，ε₀為真空介電常數(≒8.854x10^-12F/m)，△ε為液晶材料介電異向性，K為液晶材料彈性係數，d為液晶細胞間隙，V_s為液晶面板的飽和電壓。 Please refer to Figures 1 and 2. In addition to switching the dark state F and the bright state P of the liquid crystal layer 2 by the strength of the first electric field E1 and the second electric field E2, several boundary characteristics between the first alignment layer 11 and the second alignment layer 12 of the two substrates 1 and the liquid crystal layer 2 will also change the arrangement of the liquid crystal molecules and thus affect the performance of the dark state F and the bright state P. The several boundary characteristics include: the tilt angle of the liquid crystal molecules, the liquid crystal molecules near the alignment interface and the alignment interface The boundary directivity is whether the boundary liquid crystal molecules on the plane are uniformly directed in a specific direction. The boundary directivity can be achieved by contact rubbing (Rubbing) in which the bristles are rubbed in a fixed direction on the alignment interface, or by non-contact methods such as light pointing, ion beam pointing and evaporation methods, but the present invention is not limited thereto; and anchoring is the strength and depth of the alignment interface affecting the arrangement of liquid crystal molecules. The formula for the anchoring force W is

, ε ₀ is the vacuum dielectric constant (≒8.854x10 ^-12 F/m), △ε is the dielectric anisotropy of the liquid crystal material, K is the elastic coefficient of the liquid crystal material, d is the liquid crystal cell gap, and V _s is the saturation voltage of the liquid crystal panel.

Among them, the saturation voltage applied to the liquid crystal panel can rotate the unpolarized light passing through the liquid crystal panel. In detail, the saturation voltage of a liquid crystal panel can be measured by placing two polarizers with polarization axes perpendicular to each other on both sides of the liquid crystal panel. When the voltage applied to the liquid crystal panel is gradually increased, the transmittance of the light after passing through the two polarizers and the liquid crystal panel is measured synchronously. The voltage value when the transmittance is less than 5% is the saturation voltage. Therefore, in addition to being related to the composition characteristics of the liquid crystal material, the anchoring force is also positively correlated with the interaction force of the liquid crystal boundary.

In this embodiment, the tilt angle range of the first alignment layer 11 and the second alignment layer 12 is 0-10 degrees, which is a low tilt angle; the anchoring force of the first alignment layer 11 and the second alignment layer 12 on the liquid crystal layer 2 is less than 10 ^-4 joule per square meter (Jm ^-2 ); and only the second alignment layer 12 has directivity.

Please refer to FIG. 3, which is a graph measuring the variation of light reflectivity in the visible light wavelength range of liquid crystal electronic paper in the bright state P and dark state F with different boundary characteristics, including: boundary characteristics with high tilt angle, boundary characteristics with low tilt angle, boundary characteristics with low tilt angle and anchoring force less than ^10-4 joules per square meter, and boundary characteristics with low tilt angle and anchoring force less than ^10-4 joules per square meter and the second alignment layer 12 having directivity. As shown in FIG. 3, the reflectivity variation curve in the bright state can achieve the maximum reflectivity peak and a wider wavelength range under the conditions of low tilt angle, low anchoring force and unilateral directivity, which can improve the screen brightness and color range.

The peak values of the curves in Figure 3 are sorted into Table 1, as follows:

As shown in Table 1, the reflectivity of liquid crystal electronic paper with different boundary characteristics in the dark state F is between 2.3% and 3.2%, and the difference is only within 1%. However, the reflectivity of liquid crystal electronic paper with boundary characteristics of low tilt angle, low anchoring force and unilateral directivity in the bright state P can reach a relatively high 35.2%. Therefore, the first alignment layer 11 and the second alignment layer 12 of the present invention can increase the reflectivity of the bright state P while maintaining the low reflectivity of the dark state F, which has the effect of enhancing the brightness and clarity of the image.

In summary, the liquid crystal electronic paper of the present invention can adjust the boundary characteristics of the first alignment layer and the second alignment layer to low tilt angle and low anchoring force, so that the liquid crystal molecules of the liquid crystal layer can be arranged neatly in the bright state to improve the light reflectivity, and the liquid crystal molecules in the dark state can maintain the chaotic degree of focal cone arrangement to achieve low reflectivity. In addition, by forming directivity only in the second alignment layer, the mirror reflection ratio of the reflection surface of the liquid crystal layer can be reduced, which has the effect of improving image brightness, picture contrast and image clarity.

Although the present invention has been disclosed using the above preferred embodiments, they are not intended to limit the present invention. Any person skilled in the art may make various changes and modifications to the above embodiments without departing from the spirit and scope of the present invention, and these changes and modifications are still within the technical scope protected by the present invention. Therefore, the protection scope of the present invention shall include all changes within the meaning and equivalent scope recorded in the attached patent application scope.

1:Substrate

1a: Inner surface

1b: External surface

11: First alignment layer

12: Second alignment layer

2: Liquid crystal layer

S: Ambient light source

B: Back panel

Claims (6)

A liquid crystal electronic paper comprises: two substrates, which are parallel to each other, wherein the outer surface of one of the substrates faces an ambient light source, a first alignment layer and a second alignment layer are respectively located on the inner surfaces of the two substrates, the first alignment layer is close to the ambient light source, a tilt angle of the first alignment layer and the second alignment layer ranges from 0 degrees to 10 degrees, and an anchoring force of the first alignment layer and the second alignment layer is less than 10 ^-4 joules per square meter, the second alignment layer has a directivity; and a liquid crystal layer, which is filled with a liquid crystal material between the two substrates, the liquid crystal material is in contact with the first alignment layer and the second alignment layer respectively, the liquid crystal material includes a positive liquid crystal and a chiral molecule, the two substrates apply a first electric field to the liquid crystal layer and then remove the electric field to switch the liquid crystal layer to a dark state, and apply a second electric field and then remove the electric field to switch the liquid crystal layer to a bright state, the second electric field is greater than the first electric field. As for the liquid crystal electronic paper of claim 1, a back plate is bonded to the outer surface of the substrate away from the ambient light source. As in claim 1, the two substrates are transparent composite materials, including a sealed material such as glass, acrylic, plastic, and a conductive material such as indium tin oxide, nanosilver wires, and nanometal particles. As in claim 1, the liquid crystal electronic paper, wherein the reflection light band of the liquid crystal layer is in the visible light range. As in the liquid crystal electronic paper of claim 1, wherein the directivity is achieved by brushing the second alignment layer in a contact manner. As in claim 1, the directivity is achieved by non-contact light directing, ion beam directing or evaporation treatment of the second alignment layer.

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