Manufacturing method for liquid crystal display devices for watches

Abstract

A method is sought for positioning, in a liquid crystal cell, a polarizer that only partially covers the useful zone / visible zone of the liquid crystal cell.SOLUTION: In order to accurately position the polariser, a target (30a, 30c) is created on the base assembly and a corresponding alignment mark (48a, 48c) is blanked on at least one machined portion of the cover assembly such that the target is visible through the alignment mark when the cover assembly is positioned on the base assembly when the polariser is bonded to the base assembly.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to the field of manufacturing liquid crystal display devices for timepieces (also referred to as "LCD devices"), particularly liquid crystal cells (also referred to as "LCD cells"). The LCD cell defines a display zone only on a part of the visible zone of the LCD cell after the LCD device is placed in the watch case. In particular, such an LCD cell is an electronic display above the dial that partially covers the part of the dial visible to the user of the dial in order to obtain a floating type electronic display, particularly above the analog display device of the watch, and is provided to obtain an electronic display having a transparent zone (a zone of the LCD cell without a polarizer) around the display zone (the zone of the LCD cell having a polarizer and electrodes).

Background Art

[0002] Patent Document 1 describes a timepiece equipped with an electro-optical device having a "floating" electronic display. The transparent zone passing through the electro-optical cell is around the display zone of this electro-optical cell (LCD cell). In this document, the display zone defining the upper electronic display is opaque in contrast to the transparent peripheral zone (the zone without a polarizer), and it is stipulated that the dial and the lower analog display located below the LCD cell are not always visible in the display zone but are visible in the transparent peripheral zone.

[0003] Specifically, the display zone is defined by a rear polarizer and a front polarizer, which overlap and are provided only on a part of the LCD cell area visible to the user in the timepiece. In other words, the polarizer extends over a surface of the LCD cell smaller than the useful surface of this LCD cell (the visible surface of the LCD cell when incorporated in the timepiece), and the LCD cell extends over a surface including the entire window of this timepiece provided so that the analog display and the electronic display can be seen in a general plane, and this window defines the useful zone / visible zone of the liquid crystal cell. One major problem with the aforementioned "floating" electronic displays is that the polarizers are smaller than the dimensions of the window, and the slight misalignment between the front and rear polarizers is clearly visible at the edge of the LCD cell display zone. In fact, the slight misalignment between the two overlapping circular polarizers produces a thin, silvery crescent shape, to varying degrees depending on the misalignment, which is clearly visible to the user. This gives the impression of low-end manufacturing, similar to poor color printing with a series of misaligned (in other words, not precisely aligned) base color prints. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] European Patent No. 3650958 [Overview of the project] [Problems that the invention aims to solve]

[0005] Therefore, there is a need for a manufacturing method for an LCD cell having a "floating" display zone that enables precise alignment of the front and rear polarizers, and precise positioning of these two polarizers relative to the electrodes that define the displayable information. More generally, there is a need for a method to position polarizers in a liquid crystal cell that partially cover the useful / visible zone of the liquid crystal cell. [Means for solving the problem]

[0006] To address key challenges and meet the needs identified in the technical background, the present invention generally relates to a method for manufacturing a liquid crystal display device as described in claim 1. The main embodiments of the manufacturing method are defined in claims 1 and 7. An LCD display device to which this main embodiment is highly advantageous is defined in dependent claim 8. Advantageous modifications are defined in claims 9 and 10.

[0007] The features of the manufacturing method according to the present invention allow for very precise positioning of a polarizer on the transparent plate of a liquid crystal cell. Specifically, a polarizer that partially covers the useful zone / visible zone of the liquid crystal cell can be precisely positioned within this useful zone / visible zone and relative to the electrodes. The manufacturing method according to the present invention can be performed on a front polarizer and repeated for a rear polarizer, so that perfect alignment of these two polarizers can be obtained, especially in the case of a "floating" display. [Brief explanation of the drawing]

[0008] The present invention will be described in detail below with reference to the accompanying drawings, which are provided as non-limiting examples. [Figure 1] This is a plan view of a transparent plate with electrodes formed in the display zone and its periphery, and this transparent plate is designed to form a liquid crystal cell (also called an "LCD cell") used in a method of carrying out the manufacturing method according to the present invention. [Figure 2] This is a cross-sectional view of the base assembly of an LCD cell under manufacturing. [Figure 3] Figure 5 is a cross-sectional view of the initial assembly with a polarizing film along line III-III, where a portion of the polarizing film is designed to form a polarizer that partially covers the useful / visible zone of the LCD cell, and this initial assembly undergoes a specific blanking process. [Figure 4] This schematic diagram illustrates the removal of residual material from the initial assembly so that the remaining portion of the manufacturing process retains a useful portion of the polarizing film. [Figure 5] This is a top view of the intermediate assembly obtained from the original assembly after the residual parts have been removed. [Figure 6] Figure 5 shows a cross-sectional view along line VI-VI, illustrating how the portion of the intermediate assembly, positioned on the rest forming this intermediate assembly, is moved to a further rest to form the final assembly, ready for the placement of the polarizer on the transparent plate of the base assembly. [Figure 7]This shows the precise positioning of the final assembly relative to the base assembly before the polarizer is bonded to the upper transparent plate of the base assembly. [Figure 8] This is a cross-sectional view along line VIII-VIII in Figure 7. [Figure 9] This is a cross-sectional view of a partially formed LCD cell, with the front polarizer bonded to the base assembly. [Figure 10] This is a cross-sectional view of a fully formed LCD cell, where the rear polarizer is positioned in the same manner as the front polarizer on the lower transparent plate of the base assembly. [Modes for carrying out the invention]

[0009] The method for manufacturing liquid crystal cells according to the present invention will be described in detail below.

[0010] After the above-described manufacturing method is carried out, the liquid crystal display device comprises a liquid crystal cell 2 (Figure 10), which is formed by a transparent first plate 4 and a second plate 6, and an adhesive bead 8 that connects the first plate and the second plate and defines a closed space containing liquid crystal 10 together with the first plate and the second plate, the liquid crystal cell defines a useful zone 12 inside the adhesive bead, and comprises a first polarizer 14 and a second polarizer 16 in this useful zone, the useful zone is designed to define the visible zone of this cell in a watch on which the display device is designed, and the first polarizer and the second polarizer are positioned on the outer surface 5 of the first plate 4 and the outer surface 7 of the second plate 6, respectively, using a first adhesive layer 18 and a second adhesive layer 20 to ensure that the first and second polarizers are fixed and held in place. In the field of LCD cells, each of the two transparent plates, on which electrodes are printed or formed on one side and which support polarizers on the other side, is also called a “substrate”. In the advantageous variant described, the first and second polarizers are positioned precisely opposite each other, and the first and second polarizers partially cover the useful zone 12. In this advantageous variant, the LCD display is designed to "float" in a display zone 24 located in the center of the LCD cell 2, and this display zone is defined by the first and second polarizers.

[0011] Electrodes are formed on the inner surfaces of the first plate and the second plate, particularly in zone 26 of the useful zone 12, which includes the display zone 24. Two electrode assemblies 28 and 29, shown in a continuous cross-section considering the dimensions of the drawing, are arranged facing each other in a closed space containing the liquid crystal 10. Generally speaking, in the configuration of the present invention, the first and second polarizers are arranged at least partially facing each other such that at least the first polarizer partially covers the useful zone 12. Thus, in a common implementation, the second polarizer can completely cover the useful zone such that it does not need to be precisely positioned relative to the first polarizer and / or the electrodes of the LCD cell. The LCD cell may have other polarizers arranged on the outer surface of the first plate 4, and it should be noted that these other polarizers define other display zones or decorative zones resulting from the selected polarizers. Preferably, these other polarizers are also arranged by the manufacturing method according to the present invention. It should be noted that the first polarizer 14 and the second polarizer 16 may be the front polarizer and rear polarizer of the LCD cell, respectively, or vice versa.

[0012] The manufacturing method according to the present invention relates to the arrangement of polarizers that partially cover the useful zone 12. Hereinafter, as part of a description of advantageous modifications of the manufacturing method for a “floating” display, the arrangement of the first polarizer 14 will be described in detail. It should be noted that the arrangement of the second polarizer 16 is similar to that of the first polarizer. Therefore, the steps involving the arrangement of the second polarizer will not be repeated in detail.

[0013] The manufacturing process includes the following steps: Step A) Four targets 30a, 30b, 30c, and 30d are created on the first transparent plate 4 for the subsequent placement of the first polarizer 14 (see Figure 1), and on the second transparent plate 6 for the subsequent placement of the second polarizer 16. In detail, the four targets are defined by four relatively thick radial lines printed on the inner surface of the transparent plate and offset by 90°. Generally speaking, at least two targets are created in this Step A). ​​Specific conditions regarding the at least two targets are given in the next step B). Step B) A base assembly 32 (see Figure 2) is formed, comprising a first plate 4, a second plate 6, an adhesive bead 8 defining the closed space, and liquid crystal 10 filling the closed space. Targets 30a to 30d are made such that at least two targets spaced apart in an orthogonal projection on the general plane 22 of the base assembly are visible from the side of the outer surface 5 of the first transparent plate 4 under at least a given light, and the base assembly is formed. Step C) An initial assembly 36 (see Figure 3) is formed, comprising a polarizing film 38, an adhesive film 40 positioned on the inner surface of the polarizing film, and a rest 42 supporting the polarizing film and the adhesive film. A portion of the polarizing film is used to form a first polarizer 14, which is covered by a first portion 18 of the adhesive film. This first portion of the adhesive film is also referred to as the “adhesive layer” in the LCD cell 2 obtained by this manufacturing method. In the particular embodiment shown in the figure, the initial assembly 36 also advantageously includes a protective film 44 provided to protect the polarizer until the LCD cell is mounted in a watch case. Step D) Initially, the assembly 36 (see Figure 3) is blanked from the opposite side of the rest 42, through the polarizing film 38 and the adhesive film 40, while simultaneously defining four processed portions 46a, 46b, 46c, and 46d around the useful portion 50 located on the rest and comprising the first polarizer 14 and the first portion 18 of the adhesive film, but without penetrating the rest 42. It should be noted that in common modifications, at least one processed portion is provided. The four alignment marks 48a, 48b, 48c, and 48d are also blanked in the four processed portions, respectively. The latter blanks may be either blind holes or through holes, meaning they do not penetrate the rest 42. The four alignment marks are blanked such that their relative positions are the same as the relative positions of the four targets 46a-46d printed on the first plate 4 of the base assembly 32. In the case of a particular modification having a protective film 44, it should be noted that the protective film 44 is also blanked in all planned blanks. Thus, the useful portion 50 comprises an upper 45 blanked from the protective film 44. More generally, all of the film located above the rest 42 is blanked during this blanking step. In the illustrated modification, the processed portion comprises a portion of the adhesive film 40, a portion of the polarizing film 38, and a portion of the protective film 44. It should be noted that the processed portion advantageously has portions of the same film that form the useful portion 50, particularly portions of the polarizing film. In a common modification, at least two alignment marks are machined through at least one of the machining portions such that the relative positions between these at least two alignment marks are identical to the relative positions between the at least two targets. Various blanks can be produced using a laser beam, a blade, or any other suitable blanking method. The rest 42 is positioned to maintain the initial relative positions between the useful portion 50 and the machining portions 46a-46d immediately after this blanking step. · Step E) After blanking step D), the residual portion 52 located on the rest 42, which is complementary to the useful portion 50 and the processed portion (more generally, the at least one processed portion), is initially removed from the assembly 36. At the same time, the useful portion and these processed portions (more generally, the at least one processed portion) are left in a predetermined position on the rest. When the rest 42 is located on the opposite side of the polarizing film 38 with respect to the adhesive film 40 (corresponding to the embodiment described with reference to the drawings), an intermediate assembly 56 is obtained (see FIGS. 4 and 5). In other cases, a first final assembly is obtained. If the rest is arranged on the opposite side of the adhesive film with respect to the polarizing film in the initial assembly and step E) results in a first final assembly incorporating the rest, this rest is designed to be transparent at least under the given light or to have openings in at least two zones each overlapping the at least two alignment marks. This situation relates to another method for implementing the manufacturing method of the LCD display device according to the present invention, which is only dealt with in this description when deviating from the embodiment described with reference to the figures. · Step F) (Similar to the illustrated embodiment) When step E) results in an intermediate assembly 56, an additional rest 62 is added to the side of the first polarizer 14 opposite to the first portion 18 of the adhesive film. The first polarizer is transferred from the rest 42 together with the first portion of the adhesive film and the at least one processed portion (particularly the four processed portions in the illustrated variant) to the additional rest 62 to form a second final assembly 66. The additional rest 62 is transparent at least under the given light (variant of FIGS. 6 and 7) or has openings in zones each overlapping the alignment marks 48a - 48d. Next, the additional rest 62 is arranged so as to be able to maintain the initial relative position between the first polarizer 14 and the processed portions 46a - 46d.

[0014] After the aforementioned steps, the following consecutive steps follow. Step G) Depending on the case, the first final assembly or the second final assembly 66 (as illustrated) is added above the first plate 4 of the base assembly 32 using a tool 74 which is transparent under a given light or has an opening in a zone overlapping the alignment marks 48a to 48d (modified in Figure 7), such that a rest or further rest 62 is positioned on the opposite side of the first plate from the processed portion (more generally, the at least one processed portion), and the first portion 18 of the adhesive film 40 is positioned directly facing the first plate (see Figure 7). Depending on the circumstances, a table 70 that can move in a plane parallel to the general plane 22 of the base assembly 32 and an optical device 76 positioned to allow viewing of the target through the alignment marks in a direction perpendicular to the general plane and under a given light (more specifically, collimated blue light) are used to precisely align the targets 30a to 30d (more generally, the at least two targets) with the alignment marks 48a to 48d (more generally, the at least two alignment marks), thereby precisely positioning the first final assembly or the second final assembly 66 relative to the first plate 4 (see Figure 8). The alignment marks are positioned such that the targets can be precisely aligned with the alignment marks in the orthogonal direction. Step H) In a direction perpendicular to the general plane, move the first final assembly or the second final assembly 66 toward the first plate 4 of the base assembly, and use the first portion 18 of the adhesive film to bond the first polarizer 14 to this first plate, and remove the rest or further rest 62. In an advantageous variation of the described method, each processed portion comprises a portion of the adhesive film and is bonded to the first plate 4 simultaneously with the first polarizer. In the first variation, the processed portion is located outside the useful zone 12 and can be left on the first plate 4 in the LCD cell.

[0015] In the second variant, the machining parts are removed after step H), especially when they extend beyond the outer contour of the transparent plate to which they are adhered or are at least partially located within the useful zone 12.

[0016] The manufacturing method is repeated for the placement of the second polarizer 16. The second polarizer 16 only partially covers the useful zone 12 and has the same dimensions as the first polarizer 14 in the advantageous variant shown in the figure and completely overlaps with this first polarizer. Thus, the initial assembly 36 is the first initial assembly, and the manufacturing method, similar to the first initial assembly, further comprises the step of forming a second initial assembly comprising a second polarizing film, a second adhesive film disposed on the inner surface of the second polarizing film, and a second rest supporting the second polarizing film and the second adhesive film. A part of the second polarizing film is designed to form the second polarizer 16 and is covered by a part 20 of the second adhesive film. Generally speaking, at least two targets arranged at intervals in the orthographic projection on the general plane 22 are made so as to be visible from the side of the outer surface of the second transparent plate 6 at least under a given light, and the base assembly 32 is formed. In the specific embodiment shown in the figure, four targets 30a to 30d are printed on the inner surface of the second transparent plate 6. These can be aligned with the four targets printed on the first transparent plate 4 in the orthogonal direction. Steps D) to H) are repeated for the second initial assembly. The final result is the liquid crystal cell 2 shown in FIG. 10.

[0017] According to a particular variant, the first polarizer has a first contour identical to the second contour of the second polarizer at least in a part of the useful zone 12, and the first contour and the second contour are precisely aligned in the orthogonal direction with respect to the general plane 22 in the liquid crystal cell 2.

[0018] In another particular variant, the first polarizer and the second polarizer are completely located inside the useful zone.

[0019] According to the advantageous modification shown in the figure, the first polarizer 14 and the second polarizer 16 form a "floating" display in the watch in which the display device is designed, and the first and second polarizers have the same dimensions and completely overlap each other within the useful zone.

[0020] With respect to step A), in a variation of the method described so that the target can be viewed from outside both sides of the base assembly at least under a given light, the target may be provided only on the first plate 4 or the second plate 6 for arranging the first polarizer 14 and the second polarizer 16. In a common method in which only the first polarizer partially covers the useful zone 12, the target is preferably located on the inner surface of the first plate.

[0021] In a preferred modification, the liquid crystal cell comprises electrodes (electrode assemblies 28 and 29), the electrodes being made of a conductive material that is transparent in the visible region and allows at least its contour to be seen under the given light, and the target 30 is made of the conductive material on the first plate and / or second plate at the same time as forming the transparent electrodes. The target 30 can thus be positioned with great precision relative to the electrode assemblies on the inner surface of the transparent plate. In detail, the conductive material is indium tin oxide (ITO), which is a mixture of indium oxide (InO3) and tin oxide (SnO2).

[0022] In a preferred modification, the target 30 is positioned outside the useful zone 12. This modification is also desirable when the target is printed with ink visible to the user.

[0023] Generally, the adhesive bead 8 connecting the first transparent plate and the second transparent plate is not transparent enough to see the target through the adhesive bead. Therefore, if the target completely overlaps the adhesive bead, the target is generally only useful for positioning a polarizer on the transparent plate on which the target is printed. Similarly, if the target largely overlaps the adhesive bead, the target is advantageously used only for positioning a polarizer on the transparent plate on which the target is printed. Preferably, each target made of ITO has at least one portion that does not overlap the adhesive bead. This is because it is relatively difficult to identify the target under the given light with the adhesive as a background. Also, the portion that does not overlap the adhesive bead is preferably located outside the adhesive bead. In fact, the presence of liquid crystal as a background behind the ITO target reduces the visibility of the target under the light (particularly blue light). Therefore, it is advantageous that at least a portion of the target is located outside the adhesive bead 8 projected onto the general plane 22 of the base assembly 32 (which is also the general plane of the LCD cell 2).

Claims

1. A method for manufacturing a liquid crystal display device comprising a liquid crystal cell (2) formed from a transparent first plate (4) and a transparent second plate (6), and an adhesive bead (8) that connects the first plate and the second plate and defines a closed space containing liquid crystal (10) together with the first plate and the second plate, The liquid crystal cell defines a useful zone (12) inside the adhesive bead, and comprises at least a first polarizer (14) and a second polarizer (16) in the useful zone, the useful zone is designed to define the visible zone of the liquid crystal cell in a watch on which the liquid crystal display device is designed, and the first polarizer and the second polarizer are positioned at least partially opposite each other on the outer surface (5) of the first plate and the outer surface (7) of the second plate, respectively, such that at least the first polarizer covers only a portion of the useful zone. The aforementioned manufacturing method is Step A) creating targets (30a to 30d) on the first plate and / or the second plate, Step B) forming a base assembly (32) comprising the first plate, the second plate, the adhesive bead defining the closed space, and the liquid crystal filling the closed space, wherein the targets are made such that at least two of the targets, which are spaced apart in an orthogonal projection of the base assembly in a general plane, are visible from the outer surface (5) of the first plate under at least a given light, and the base assembly is formed. Step C) forming an initial assembly (36) comprising a polarizing film (38), an adhesive film (40) disposed on the inner surface of the polarizing film, and a rest (42) supporting the polarizing film and the adhesive film, wherein a portion of the polarizing film is used to form the first polarizer (14) and is covered by the first portion (18) of the adhesive film, Step D) blanks the initial assembly (36) from the opposite side of the rest so as to penetrate the polarizing film and the adhesive film, and at the same time blanks at least two alignment marks (48a to 48d) located on the rest (42) that define the edge of a useful portion (50) located on the rest (42) and comprising the first polarizer and the first portion of the adhesive film, and at least one processed portion (46a to 46d) located on the rest, but not penetrating the rest, and passing through at least one processed portion, such that the alignment marks have the same relative position as the relative position of the at least two targets, wherein the rest (42) is positioned from step D) of blanking so as to maintain the initial relative position between the useful portion (50) and the at least one processed portion, and if the rest is located in the initial assembly on the opposite side of the adhesive film relative to the polarizing film, the rest is transparent at least under the given light or has openings in at least two zones overlapping the at least two alignment marks, Step D) of blanking, step E) removes the residual portion (52) located on the rest that is complementary to the useful portion (50) and the at least one processed portion (46a to 46d) from the initial assembly (36), while leaving the useful portion and the at least one processed portion in a predetermined position on the rest, and obtains an intermediate assembly (56) if the rest is located on the opposite side of the polarizing film from the adhesive film, or a first final assembly otherwise. If step E) results in the intermediate assembly (56), step F) adds a further rest (62) on the side of the first polarizer (14) opposite to the first portion (18) of the adhesive film, and moves the first polarizer together with the first portion of the adhesive film and the at least one processed portion from the rest to the further rest to form a second final assembly (66), wherein the further rest is transparent under the given light or has openings in at least two zones that overlap each of the at least two alignment marks, and the further rest is positioned so that the initial relative position between the first polarizer and the at least one processed portion can be maintained. Includes, After these steps, the following sequential steps: The first or second final assembly (66) is added above the base assembly (32) on the side of the first plate (4), with the rest or further rest (62) positioned on the opposite side of the first plate from the at least one processed portion, and the first portion of the adhesive film positioned directly facing the first plate, and the at least two targets (30a to 30d) are precisely aligned with the at least two alignment marks (48a to 48d) using an optical device (76), thereby completing the first or second final assembly. Step G) accurately positioning the final assembly (66) relative to the first plate, wherein the optical device (76) is positioned such that the at least two targets can be seen through the at least two alignment marks (48a-48d) at least under the given light and in a direction perpendicular to the general plane (22) of the liquid crystal cell, and the at least two alignment marks are positioned such that the at least two targets (30a-30d) can each be accurately aligned with the at least two alignment marks in the orthogonal direction, Step H) moves the first final assembly or the second final assembly (66) toward the first plate (4) in a direction perpendicular to the general plane, and adheres the first polarizer (14) to the first plate using the first portion (18) of the adhesive film, and removes the rest or the further rest (62). The manufacturing process continues.

2. The manufacturing method according to claim 1, wherein the liquid crystal cell (2) comprises electrodes (28, 29), the electrodes are formed from a material that is transparent in the visible region and at least its contour can be seen under the given light, and the targets (30a to 30d) are made from the material and are formed on the first plate and / or the second plate at the same time as the electrodes are made.

3. The manufacturing method according to claim 1, characterized in that the target is positioned outside the useful zone (12).

4. The manufacturing method according to any one of claims 1 to 3, characterized in that each of the at least one processed portion (46a to 46d) is covered with at least one corresponding portion of the adhesive film (40) and bonded to the first plate at the same time as the first polarizer.

5. The manufacturing method according to claim 4, characterized in that the at least one processed portion (46a to 46d) is provided outside the useful zone (12) and remains on the first plate in the liquid crystal cell.

6. The manufacturing method according to claim 4, characterized in that the at least one processed portion (46a to 46d) is removed after step H).

7. The initial assembly is a first initial assembly, and the second polarizer (16) partially covers the useful zone (12). The manufacturing method, similar to the first initial assembly, comprises a second polarizing film, a second adhesive film disposed on the inner surface of the second polarizing film, and a second rest supporting the second polarizing film and the second adhesive film, wherein a portion of the second polarizing film is intended to constitute the second polarizer and is covered by a portion of the second adhesive film. The fabrication of the targets and the formation of the base assembly (32) are carried out such that at least two of the targets, which are spaced apart in the orthogonal projection on the general plane, are visible from at least the outer surface (7) of the second plate (6) under the given light. The manufacturing method according to any one of claims 1 to 3, characterized in that steps D) to H) are repeated in the second initial assembly.

8. The manufacturing method according to claim 7, characterized in that the first polarizer (14) has the same first contour as the second contour of the second polarizer (16) in at least a portion of the useful zone, and the first contour and the second contour are precisely aligned in the orthogonal direction in the liquid crystal cell (2).

9. The manufacturing method according to claim 8, characterized in that the first polarizer (14) and the second polarizer (16) are located entirely inside the useful zone (12).

10. The manufacturing method according to claim 9, characterized in that the first polarizer (14) and the second polarizer (16) form a "floating" display zone in the watch on which the liquid crystal display device is designed, and the first polarizer and the second polarizer have the same dimensions and completely overlap each other.

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