TWI886886B - 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. The ratio of inclination angle between the alignment layer away from a light source and the alignment layer close to the light source is greater than 8. The liquid crystal layer is a liquid crystal material located between the two substrates. The crystal material contacts the two alignment layers respectively. The crystal material contains a positive nematic liquid crystal and a chirality molecule. 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.

Conventional liquid crystal electronic paper utilizes reflective display technology to present images by reflecting ambient light. Electronic paper does not require an active backlight module and only needs to be powered on to switch the distribution of light and dark states on the display screen when switching images. No electricity is required when a fixed image is continuously displayed. 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; 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 known 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 less than 30%, which 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 image.

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, and the ratio of the tilt angle of the second alignment layer to the tilt angle of the first alignment layer is greater than 8; and a liquid crystal layer, which is filled between the two substrates with a liquid crystal material, the liquid crystal material is in contact with the first alignment layer and the second alignment layer, the liquid crystal material comprises 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, by selecting an asymmetric alignment structure with a relatively low tilt angle for the reflective surface (close to the ambient light source) and a relatively high tilt angle for the backlight surface (far away from the ambient light source), can gradually achieve a stable and neatly arranged planar structure for the liquid crystal molecules after switching to the bright state and removing the electric field, thereby improving the light reflectivity and providing a stable bright state, and has the effect of improving image brightness, screen 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 tilt angle of the first alignment layer is 0 to 10 degrees, and the tilt angle of the second alignment layer is 80 to 90 degrees. In this way, the liquid crystal molecules close to the first alignment layer are almost parallel to the alignment interface, while the liquid crystal molecules close to the second alignment layer are almost perpendicular to the alignment interface. The liquid crystal layer can form an asymmetric liquid crystal arrangement, so that when the liquid crystal molecules return to the planar structure, they are arranged more neatly due to the flow, which has the effect of improving the reflectivity of the bright state.

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 dark state of a preferred embodiment of the present invention.

[Figure 3] A diagram showing the switching bright state of a preferred embodiment of the present invention.

[Figure 4] A diagram showing the change in light reflectivity during the bright state switching process of the preferred embodiment of the present invention.

[Figure 5] The relationship between the light reflectivity and light wavelength of liquid crystal electronic paper with different boundary characteristics in the red light range.

[Figure 6] The relationship between the light reflectivity and light wavelength of liquid crystal electronic paper with different boundary characteristics in the green light range.

[Figure 7] Relationship between light reflectivity and light wavelength in the blue light range of liquid crystal electronic paper with different boundary characteristics.

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 to 3. The two substrates 1 may be transparent composite materials, so that light can penetrate the two substrates 1. The composite materials of each substrate 1 may 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 may also include a transparent conductive material, such as indium tin oxide (ITO), nano silver wires, nano metal 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.

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, but 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 FIG. 2, when the liquid crystal molecules are arranged in a focal conic structure, the incident light tends to penetrate the liquid crystal layer 2 and is then absorbed by the backplane B to present the dark state F; and as shown in FIG. 3, when the liquid crystal molecules are arranged in a planar structure, the light from the ambient light source S incident on the liquid crystal layer 2 tends to be reflected to present the luminous bright state P. The liquid crystal electronic paper of the present invention can form an image screen by controlling the numerous pixels of the liquid crystal layer 2 to be in the bright state P or the dark state F.

The 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 affect the arrangement of the liquid crystal molecules and thus affect the performance of the dark state F and the bright state P. For example, the tilt angle of the liquid crystal molecules is the angle formed between the liquid crystal molecules near the alignment interface and the alignment interface through the selection of the alignment. The two substrates 1 of the present invention can form a low tilt angle by the first alignment layer 11 near the ambient light source S. , the low tilt angle is close to 0 degrees, that is, the liquid crystal molecules and the alignment interface are almost parallel; and the second alignment layer 12 close to the back plate B forms a high tilt angle, The high tilt angle is close to 90 degrees, that is, the liquid crystal molecules and the alignment interface are almost perpendicular, and the angle ratio of the high tilt angle to the low tilt angle is preferably greater than 8. In this embodiment, the low tilt angle ranges from 0 degrees to 10 degrees, and the high tilt angle ranges from 80 degrees to 90 degrees.

Please refer to Figure 2. The liquid crystal layer 2 is affected by the first electric field E1 between the two substrates 1, which causes the liquid crystal molecules to be 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.

Please refer to FIG. 3 , in which 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 cause the liquid crystal molecules of the positive liquid crystal to be arranged neatly in a direction parallel to the second electric field E2. After the second electric field E2 is removed, the liquid crystal molecules not only rebound due to the sudden disappearance of the force forcing the arrangement by the electric field, but are also affected by the asymmetric orientation characteristics of the low tilt angle of the upper layer and the high tilt angle of the lower layer, generating a temporary flow force in the liquid crystal layer 2. Specifically, when the electric field just disappears, the liquid crystal molecules are arranged into an irregular planar structure. After being acted upon by the flow force for a period of time, the liquid crystal molecules can be arranged more neatly and stably, thereby improving the reflectivity of the bright state P. Please refer to Figure 4 again, which shows the light reflectivity change of the liquid crystal electronic paper of the present invention after the second electric field E2 is removed from 1 second to 15 seconds. The peak value of the reflectivity is only 22% at 1 second, and the reflectivity increases to 27.5% at 3 seconds, and reaches 29.3% at 5 seconds. After 7 seconds, the light reflectivity remains at about 30% and no longer changes significantly. The liquid crystal molecules of the liquid crystal layer 2 have reached the bright state P of the stable planar structure.

Please refer to Figures 1 and 5 to 7, which are graphs showing the variation of light reflectance of liquid crystal electronic paper with different tilt alignment selections in the ranges of blue light, green light and red light, respectively, and include four tilt alignment combinations: the first alignment layer 11 and the second alignment layer 12 are both high tilt angles, the first alignment layer 11 and the second alignment layer 12 are both low tilt angles, the first alignment layer 11 (close to the reflective surface of the ambient light source S) is high tilt angle and the second alignment layer 12 (close to the back plate B) is low tilt angle, the first alignment layer 11 is low tilt angle and the second alignment layer 12 is high tilt angle. As can be seen from Figures 5 to 7, the liquid crystal electronic paper with asymmetric upper and lower tilt angles and a low tilt angle on the side close to the reflective surface can achieve relatively high reflectivity peaks in the red, green and blue light ranges.

In summary, the liquid crystal electronic paper of the present invention, by selecting an asymmetric alignment structure with a relatively low tilt angle on the reflective surface (close to the ambient light source) and a relatively high tilt angle on the backlight surface (far away from the ambient light source), can gradually achieve a stable and neatly arranged planar structure of liquid crystal molecules after switching to the bright state and removing the electric field, thereby improving light reflectivity and providing a stable bright state, and has the effect of improving image brightness, screen 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 within the spirit and scope of the present invention, and the 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 (5)

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, and the ratio of the tilt angle of the second alignment layer to the tilt angle of the first alignment layer is greater than 8; and A liquid crystal layer, which is filled between the two substrates with a liquid crystal material, the liquid crystal material contacts the first alignment layer and the second alignment layer respectively, the liquid crystal material comprises 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 claim 1, the liquid crystal electronic paper, wherein the tilt angle of the first alignment layer is 0 degrees to 10 degrees, and the tilt angle of the second alignment layer is 80 degrees to 90 degrees.