Method for manufacturing a liquid crystal display device for a timepiece

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 (also referred to as "LCD devices") for watches, in particular liquid crystal cells (also referred to as "LCD cells"), which define a display zone in only a portion of the visible zone of the LCD cell after the LCD device is placed in a watch case. In particular, such LCD cells are provided for obtaining floating electronic displays above a watch face, in which the display zone partially covers the portion of the watch face visible to the user, in particular for electronic displays located above an analog display device of a watch, with a transparent zone (a zone of the LCD cell without a polarizer) surrounding the display zone (a zone of the LCD cell with a polarizer and electrodes). [Background technology]

[0002] Patent document 1 describes a watch equipped with an electro-optical device having a "floating" electronic display, in which a transparent zone through the electro-optical cell is located around the display zone of this electro-optical cell (LCD cell). This document specifies that the display zone defining the upper electronic display is opaque in contrast to the transparent peripheral zone (zone without polarizer), so that the dial and lower analog display located below the LCD cell are always invisible in the display zone but visible in the transparent peripheral zone.

[0003] In particular, the display zone is defined by a rear polarizer and a front polarizer, which overlap and are provided only over a portion of the LCD cell area visible to the user in the watch. In other words, the polarizers extend over a surface of the LCD cell that is smaller than the useful surface of the LCD cell (the visible surface of the LCD cell when incorporated into a watch), which in its general plane extends over a surface that includes the entire window of the watch through which the analog display and the electronic display are visible, and which window defines the useful / visible zone of the liquid crystal cell. One major problem with "floating" electronic displays as described above is that the polarizers have dimensions smaller than the dimensions of the windows, and any slight misalignment between the front and rear polarizers is clearly visible at the edge of the LCD cell display zone. In fact, a slight misalignment between two overlapping circular polarizers produces a thin silver crescent shape, more or less visible to the user, depending on the misalignment. This gives the impression of low-end manufacturing, similar to poor color printing, for example, due to a series of misaligned (i.e., not precisely aligned) base color prints. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] European Patent No. 3650958 Summary of the Invention [Problem to be solved by the invention]

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

[0006] To address the main problems 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 set forth in claim 1. Main implementations of the manufacturing method are defined in claims 1 and 7. An LCD display device for which this main implementation is highly advantageous is defined in dependent claim 8. Advantageous variations are defined in claims 9 and 10.

[0007] The features of the manufacturing method according to the present invention allow polarizers to be positioned very precisely on the transparent plates of a liquid crystal cell. In particular, polarizers that only partially cover the useful / visible zone of the liquid crystal cell can be precisely positioned in this useful / visible zone and relative to the electrodes. The manufacturing method according to the present invention can be performed on the front polarizer and repeated on the rear polarizer, thereby obtaining perfect alignment of these two polarizers, especially in the case of "floating" displays. [Brief explanation of the drawings]

[0008] The invention will now be described in more detail with reference to the accompanying drawings, which are provided as non-limiting examples. [Figure 1] FIG. 1 is a plan view of a transparent plate having a display zone and electrodes formed around its periphery, the transparent plate being designed to form a liquid crystal cell (also called an "LCD cell") for use in carrying out a manufacturing method according to the present invention. [Figure 2] 1 is a cross-sectional view of a base assembly of an LCD cell during manufacture. [Figure 3] 5 along line III-III of FIG. 5, an initial assembly with polarizing films, some of which are designed to form a polarizer that only partially covers the useful / visible zone of the LCD cell, this initial assembly undergoing a specific blanking operation. [Figure 4] 10A and 10B show diagrammatically the removal of residual portions from the initial assembly, leaving portions of the polarizing film useful for the remainder of the manufacturing process. [Figure 5] FIG. 10 is a top view of an intermediate assembly obtained from the initial assembly after residual portions have been removed. [Figure 6] 6 shows a cross-sectional view along line VI-VI in FIG. 5 , illustrating how the portion of the intermediate assembly placed on the rest forming this intermediate assembly is transferred to a further rest to form the final assembly ready for placing the polarizer on the transparent plate of the base assembly. [Figure 7]1 shows the correct positioning of the final assembly relative to the base assembly before the polarizer is glued to the top transparent plate of the base assembly. [Figure 8] FIG. 8 is a cross-sectional view taken along line VIII-VIII in FIG. 7. [Figure 9] FIG. 1 is a cross-sectional view of a partially formed LCD cell with a front polarizer adhered to a base assembly. [Figure 10] 1 is a cross-sectional view of a fully formed LCD cell in which the rear polarizer is positioned in the same manner as the front polarizer on the bottom transparent plate of the base assembly. DETAILED DESCRIPTION OF THE INVENTION

[0009] The method for carrying out the method for manufacturing a liquid crystal cell / LCD cell according to the present invention will be described in detail below.

[0010] After the manufacturing method is performed, the liquid crystal display device comprises a liquid crystal cell 2 (FIG. 10) formed by transparent first and second plates 4 and 6 and an adhesive bead 8 connecting the first and second plates and defining, together with the first and second plates, a closed space containing liquid crystal 10; 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 being designed to define the visible zone of the cell in a watch for which the display device is designed; the first and second polarizers are disposed 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 that ensure the first and second polarizers are fixed and held in place. In the field of LCD cells, each of the two transparent plates, with electrodes printed or formed on one side and supporting a polarizer on the other side, is also called a "substrate." In the advantageous variant described, the first and second polarizers are positioned exactly opposite each other, and the first and second polarizers only 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, which display zone is defined by the first and second polarizers.

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

[0012] The manufacturing method according to the invention involves the placement of a polarizer that only partially covers the useful zone 12. Below, the placement of the first polarizer 14 will be described in detail as part of the description of an advantageous variant of the manufacturing method for a "floating" display. It should be noted that the placement of the second polarizer 16 is similar to that of the first polarizer. Therefore, the steps involved in placing the second polarizer will not be repeated in detail.

[0013] The manufacturing method includes the following steps: Step A) Four targets 30a, 30b, 30c and 30d are produced on the first transparent plate 4 (see FIG. 1) for the subsequent placement of the first polarizer 14 and on the second transparent plate 6 for the subsequent placement of the second polarizer 16. In particular, the four targets are defined by four relatively thick radial lines printed on the inner surface of the transparent plates and offset by 90°. Generally speaking, at least two targets are produced in this step A). ​​The specific conditions for the at least two targets are given in the following step B). Step B) A base assembly 32 (see FIG. 2) is formed, comprising a first plate 4, a second plate 6, an adhesive bead 8 defining the closed space, and a liquid crystal 10 filling the closed space. The targets 30a-30d are fabricated and the base assembly is formed such that at least two spaced apart targets are visible from the outer surface 5 of the first transparent plate 4 in at least a given light in orthogonal projection on the general plane 22 of the base assembly. Step C) An initial assembly 36 (see FIG. 3) is formed, 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. A portion of the polarizing film is used to form the first polarizer 14 and 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 figures, the initial assembly 36 also advantageously comprises a protective film 44 provided to protect the polarizer until the LCD cell is attached to the watch case. Step D) The initial assembly 36 (see FIG. 3) is blanked from the side opposite the rest 42, penetrating the polarizing film 38 and the adhesive film 40, thereby defining the periphery of the useful portion 50, which is located on the rest and includes the first polarizer 14 and the first portion 18 of the adhesive film, and four processed portions 46a, 46b, 46c, and 46d, but not penetrating the rest 42. It should be noted that in a typical variant, at least one processed portion is provided. Four alignment marks 48a, 48b, 48c, and 48d are also blanked in the four processed portions, respectively. The latter blanks can be either blind holes or through holes, meaning they do not penetrate the rest 42. The four alignment marks are blanked so that their relative positions are identical to the relative positions of the four targets 46a-46d printed on the first plate 4 of the base assembly 32. It should be noted that in the particular variant having a protective film 44, the protective film 44 is also blanked out in all planned blanks. The useful part 50 therefore comprises an upper part 45 blanked out from the protective film 44. More generally, all of the films located above the rest 42 are blanked out during this blanking step. In the variant shown, the processed part comprises a part of the adhesive film 40, a part of the polarizing film 38 and a part of the protective film 44. It should be noted that the processed part advantageously comprises parts of the same films that form the useful part 50, in particular respective parts of the polarizing film. In a typical variant, at least two alignment marks are machined through at least one of the workpieces such that the relative positions between these at least two alignment marks are identical to the relative positions of the at least two targets. The various blanks can be made using a laser beam, a blade, or any other suitable blanking method. The rest 42 is positioned so as to maintain the initial relative positions between the useful portion 50 and the workpieces 46a-46d immediately after this blanking step. Step E) Blanking: After step D), the remaining portions 52 located on the rest 42, which are complementary to the useful portion 50 and the processed portion (more generally, the at least one processed portion), are removed from the initial assembly 36, while the useful portion and these processed portions (more generally, the at least one processed portion) remain in their predetermined positions on the rest, so that an intermediate assembly 56 is obtained (see Figures 4 and 5) 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 implementation method described with reference to the drawings), and in other cases a first final assembly is obtained. If a rest is placed on the polarizing film in the initial assembly opposite the adhesive film, 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 that respectively overlap the at least two alignment marks. This situation relates to another method for implementing the method for manufacturing an LCD display device according to the present invention, and it will be addressed in the present description only if it deviates from the implementation method described with reference to the figures. Step F) (as in the illustrated implementation) if step E) results in an intermediate assembly 56, then a further rest 62 is added to the side of the first polarizer 14 opposite the first portion of the adhesive film 18, and the first polarizer together with the first portion of the adhesive film and the at least one processed portion (in particular, four processed portions in the illustrated variant) is transferred from the rest 42 to the further rest 62 to form a second final assembly 66. The further rest 62 is either transparent at least under the given light (in the variants of FIGS. 6 and 7) or has openings in the zones overlapping the alignment marks 48a-48d, respectively. The further rest 62 is then positioned so as to maintain the initial relative positions between the first polarizer 14 and the processed portions 46a-46d.

[0014] The above steps are followed by the following successive steps: Step G) Adding, as the case may be, the first or second final assembly 66 (embodiment shown) above the first plate 4 of the base assembly 32 using a tool 74 that is transparent at least under the given light or has openings in the zones that overlap the alignment marks 48a-48d (variant of FIG. 7), with a rest or a further rest 62 arranged on the opposite side of the processed part (more generally, the at least one processed part) from the first plate and with the first part 18 of the adhesive film 40 arranged directly facing the first plate (see FIG. 7). In some cases, the first or second final assembly 66 is accurately positioned with respect to the first plate 4 by accurately aligning the targets 30a-30d (more generally, the at least two targets) with the alignment marks 48a-48d (more generally, the at least two alignment marks) using 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 that is positioned so that the targets can be viewed through the alignment marks at least under the given light (particularly collimated blue light) and in a direction orthogonal to the general plane (see FIG. 8 ). The alignment marks are positioned so that the targets can be accurately aligned with the alignment marks in the orthogonal direction. Step H) In a direction orthogonal to the general plane, the first or second final assembly 66 is moved towards the first plate 4 of the base assembly, the first polarizer 14 is adhered to this first plate using the first part 18 of the adhesive film, and the rest or further rest 62 is removed. In an advantageous variant of the described method, the processed parts each comprise a part of the adhesive film and are adhered to the first plate 4 at the same time as the first polarizer. In a first variant, the processed parts are arranged outside the useful zone 12 and can remain on the first plate 4 in the LCD cell.

[0015] In a second variant, the processed parts are removed after step H), in particular if they extend beyond the outer contour of the transparent plate to which they are glued or are located at least partially within the useful zone 12.

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

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

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

[0019] According to an advantageous variant shown in the figure, the first polarizer 14 and the second polarizer 16 form a "floating" display in the watch for which the display device is designed, the first and second polarizers having the same dimensions and completely overlapping each other inside the useful zone.

[0020] In a variant of the implementation described for step A) so that the targets are visible from the outside on both sides of the base assembly, at least under given light, the targets can be provided only on the first plate 4 or on the second plate 6 for positioning the first polarizer 14 and the second polarizer 16. In the general implementation where only the first polarizer only partially covers the useful zone 12, the targets are preferably placed on the inner surface of the first plate.

[0021] In a preferred variant, the liquid crystal cell comprises electrodes (electrode assemblies 28 and 29) made of a conductive material that is transparent in the visible range and allows at least its outline to be seen under the given light, and target 30 is made of said conductive material on the first plate and / or the second plate at the same time as constructing the transparent electrodes. In this way, target 30 can be positioned very accurately with respect to the electrode assemblies on the inner surface of the transparent plates. In particular, the conductive material is indium tin oxide (ITO), which is a mixture of indium oxide InO3 and tin oxide SnO2.

[0022] In a preferred variation, the target 30 is located outside the useful zone 12. This variation is also desirable if the target is printed with ink that is visible to the user.

[0023] Generally, the adhesive bead 8 connecting the first and second transparent plates is not transparent enough to allow the target to be seen through it. Therefore, if the target completely overlaps the adhesive bead, it is generally only useful for placing a polarizer on the transparent plate on which it is printed. Similarly, if the target largely overlaps the adhesive bead, it is advantageously only used for placing a polarizer on the transparent plate on which it is printed. Preferably, each ITO target 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 against the adhesive background. Furthermore, the portion that does not overlap the adhesive bead is preferably located outside the adhesive bead. In fact, the presence of a liquid crystal background behind the ITO target reduces the visibility of the target under the given light (especially blue light). Therefore, it is advantageous for at least a portion of the target to be 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. 1. A method for manufacturing a liquid crystal display device comprising a liquid crystal cell (2) formed from transparent first and second plates (4, 6) and an adhesive bead (8) connecting said first and second plates and defining together therewith an enclosed space containing liquid crystal (10), comprising: The liquid crystal cell defines a useful zone (12) inside the adhesive bead and is provided with at least a first polarizer (14) and a second polarizer (16) in the useful zone, the useful zone being designed to define a visible zone of the cell in a watch for which the display device is designed, the first polarizer and the second polarizer being arranged at least partially opposite each other on the outer surface (5) of the first plate and on the outer surface (7) of the second plate, respectively, so that at least the first polarizer covers only a part of the useful zone; The manufacturing method includes: A) creating targets (30a-30d) on the first plate and / or the second plate; B) forming a base assembly (32) comprising the first plate, the second plate, an adhesive bead defining the closed space, and a liquid crystal filling the closed space, wherein the targets are fabricated and the base assembly is formed such that at least two of the spaced apart targets are visible from the side of the outer surface (5) of the first plate in at least a given light in an orthogonal projection on the general plane of the base assembly; C) forming an initial assembly (36) comprising a polarizing film (38), an adhesive film (40) disposed on an 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 a first portion (18) of the adhesive film; D) blanking the initial assembly (36) from the side opposite the rest so as to penetrate the polarizing film and the adhesive film, and at the same time blanking at least two alignment marks (48a-48d) that are located on the rest (42) and define an edge of a useful portion (50) comprising the first polarizer and a first portion of the adhesive film and at least one processed portion (46a-46d) located on the rest, but do not penetrate the rest, and that at least pass through the at least one processed portion, so as to have the same relative positions as the relative positions of the at least two targets, wherein the rest (42) is positioned so as to maintain the initial relative positions between the useful portion (50) and the at least one processed portion from the blanking step, and when the rest is located on the side opposite the adhesive film in the initial assembly with respect to the polarizing film, the rest is transparent at least under the given light or has openings in at least two zones that overlap the at least two alignment marks; After the blanking step D), a step E) of removing from the initial assembly 36 a residual portion (52) located on the rest, complementary to the useful portion (50) and the at least one processed portion (46a-46d), while leaving the useful portion and the at least one processed portion in place on the rest, to obtain an intermediate assembly (56) if the rest is located on the opposite side of the adhesive film from the polarizing film, or a first final assembly otherwise; If step E) results in the intermediate assembly (56), step F) of adding a further rest (62) to a side of the first polarizer (14) opposite the first portion (18) of the adhesive film and transferring 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, wherein the further rest is transparent at least under the given light or has openings in at least two zones respectively overlapping the at least two alignment marks, and the further rest is positioned so as to be able to maintain the initial relative position between the first polarizer and the at least one processed portion; Including, These steps are followed by the following successive steps: optionally adding the first final assembly or the second final assembly (66) above the base assembly (32) on the side of the first plate (4) with the rest or the further rest (62) arranged on the opposite side of the first plate with respect to the at least one processed portion and with the first portion of the adhesive film arranged directly facing the first plate, and optionally using an optical device (76) to accurately align the at least two targets (30a-30d) with the at least two alignment marks (48a-48d), respectively, thereby forming the first final assembly. and (G) precisely positioning the first or second final assembly (66) relative to the first plate, wherein the optical device (76) is arranged so that the at least two targets are visible 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 arranged so that the at least two targets (30a-30d) can be precisely aligned with the at least two alignment marks, respectively, in the orthogonal direction. H) moving the first final assembly or the second final assembly (66) towards the first plate (4) in a direction perpendicular to the general plane, adhering the first polarizer (14) to the first plate using the first part (18) of the adhesive film, and removing the rest or the further rest (62); Next comes the manufacturing method.

2. 2. The method according to claim 1, wherein the liquid crystal cell (2) comprises electrodes (28, 29), the electrodes being made of a material that is transparent in the visible range and allows at least the outlines of the electrodes to be seen under the given light, and the targets (30a-30d) are made of the material and are formed on the first plate and / or the second plate simultaneously when the transparent electrodes are made.

3. 2. The method of claim 1, wherein the target is located outside the useful zone (12).

4. 4. The method according to claim 1, wherein the at least one processed portion (46a-46d) is covered with at least one corresponding portion of the adhesive film (40) and is bonded to the first plate simultaneously with the first polarizer.

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

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

7. the initial assembly is a first initial assembly, and the second polarizer (16) only partially covers the useful zone (12); The method includes forming a second initial assembly, similar to the first initial assembly, including a second polarizing film, a second adhesive film disposed on an 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 targets are fabricated and the base assembly (32) is formed such that at least two of the targets spaced apart in orthogonal projection on the general plane are visible from the outer surface (7) of the second plate (6) at least 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 with the second initial assembly.

8. 8. The method of claim 7, wherein the first polarizer (14) has a first contour that is identical to 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 of the liquid crystal cell (2).

9. 9. The method of claim 8, wherein the first polarizer (14) and the second polarizer (16) are located entirely inside the useful zone (12).

10. 10. The manufacturing method according to claim 9, characterized in that the first polarizer (14) and the second polarizer (16) are located entirely inside the useful zone (12) and form a "floating" display zone in the watch for which the 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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