A preparation process of a directional sound folding screen and electronic equipment

Abstract

The present invention discloses a preparation process of a directional sound-emitting folding screen and an electronic device, wherein the preparation process of the directional sound-emitting folding screen comprises preparing a substrate layer and a vibration layer, and then forming a micro-pattern layer on the substrate layer, and then bonding the substrate layer and the vibration layer together through an adhesive layer, and the directional sound-emitting folding screen prepared after bonding comprises a plurality of sound-emitting parts and at least one folding part distributed along a first direction, and each two adjacent sound-emitting parts are connected by a folding part, and the sound-emitting parts are folded in a direction away from or close to a client to the sound-emitting parts adjacent to them and are stacked in a second direction. The present invention adopts UTG as the base layer of the vibration layer and the substrate layer, and is supplemented by the processing technology of other functional structures of the directional sound-emitting screen, to prepare a directional sound-emitting folding screen that can be completely folded in at least one folding direction, and realizes the advantages of a small size and easy to carry while realizing the large-screen sound of the directional sound-emitting screen.

Description

Technical Field

[0001] The present invention relates to the field of screen directional sound technology, and in particular to a preparation process of a directional sound folding screen and electronic equipment. Background Art

[0002] With the development of display technology, consumers are not only concerned about the picture quality and clarity of display devices, but are also gradually paying attention to the sound output effects. They tend to prefer display devices that can achieve the unity of sound and picture and perfectly integrate the display picture with the playback sound.

[0003] There is currently a screen sound technology that achieves the integration of sound and picture in display devices. The principle is to use a vibration element to drive the screen to vibrate and make a sound. For example: a resonant screen sound solution is to attach a device with vibration characteristics to the bottom of the screen or on the middle frame of the whole machine. The device generates vibration when working, and finally drives the screen to vibrate and make a sound; another example: a direct push screen sound solution, the device is mainly composed of two parts, one of which is directly attached to the screen and the other is fixed on the middle frame. When the device is working, the two parts will generate mutual attraction or repulsion, thereby driving the screen to vibrate and make a sound. Compared with the resonant screen sound solution, its conversion efficiency is improved.

[0004] When the display screen on the electronic device is a foldable display screen, the area used for display on the electronic device can be greatly increased, so that the user has a better visual experience. Nowadays, foldable display screens are increasingly used in various types of terminal devices and have good application prospects.

[0005] In other words, the current market demand for foldable screens is becoming more and more clear. Therefore, how to prepare a foldable directional sound screen to better combine it with a foldable display screen is a problem that needs to be solved at present. Summary of the invention

[0006] The purpose of the present invention is to provide a preparation process of a directional sound-emitting folding screen and an electronic device.

[0007] To achieve the above object, on the one hand, the present invention proposes a preparation process of a directional sound folding screen, comprising:

[0008] S1, preparing a substrate layer, said S1 comprising:

[0009] S11, providing a first UFG substrate layer, wherein the first UFG substrate layer comprises at least one first folding region and a plurality of first non-folding regions, the thickness of the first folding region is smaller than the thickness of the first non-folding region, and a first groove opening toward a folding direction is formed between the first folding region and two first non-folding regions on its two adjacent sides;

[0010] S12, forming a first conductive layer at least covering the first non-folded area on the upper end surface of the first UFG substrate layer close to the vibration layer;

[0011] S13, forming a first insulating layer on an upper end surface of the first conductive layer close to the vibration layer, the first insulating layer covering at least the first conductive layer and the first folding region;

[0012] S2, preparing a vibration layer, said S2 comprising:

[0013] S21, providing a second UFG substrate layer, wherein the second UFG substrate layer comprises at least one second folding region corresponding to the position of the first folding region and a plurality of second non-folding regions corresponding to the positions of the first non-folding regions, the thickness of the second folding region is smaller than the thickness of the second non-folding region, and a second groove with an opening facing a folding direction is formed between the second folding region and two second non-folding regions on its two adjacent sides;

[0014] S22, forming a second conductive layer at least covering the second non-folded area on the lower end surface of the second UFG base material layer close to the substrate layer;

[0015] S23, forming a second insulating layer on a lower end surface of the second conductive layer close to the substrate layer, the second insulating layer covering at least the second conductive layer and the second folding region in its entirety;

[0016] S3, forming a micro-pattern layer on the upper end surface of the first insulating layer close to the vibration layer, and then forming an adhesive layer on the micro-pattern layer, and bonding the substrate layer to the vibration layer through the adhesive layer;

[0017] After lamination, an air gap is formed between the vibration layer and the substrate layer through the micro-pattern layer, and the vibration layer vibrates and makes sound in a direction close to or away from the substrate layer under the action of an externally loaded ultrasonic signal;

[0018] The prepared directional sound folding screen includes a plurality of sound emitting parts and at least one folding part distributed along a first direction, and each adjacent two sound emitting parts are connected by a folding part. The sound emitting parts are folded in a direction away from or close to the client to be stacked with the adjacent sound emitting parts in a second direction.

[0019] In a preferred embodiment, in S11 and 21, the first UFG substrate layer and the second UFG substrate layer are both formed by processing UTG raw material; and / or, the preparation process of the first UFG substrate layer and the second UFG substrate layer both include: thinning the UTG raw material as a whole to 30um~100um, and then further thinning the folding area of ​​the thinned UTG raw material; and / or, the process of further thinning the folding area of ​​the thinned UTG raw material includes: covering at least one side of the thinned UTG raw material with a corrosion-resistant protective film and exposing the area to be corroded, immersing the UTG raw material covered with the corrosion-resistant protective film as a whole in a corrosive liquid to corrode and thin the area to be corroded to form a folding area, and then removing the corrosion-resistant protective film.

[0020] In a preferred embodiment, the corrosion-resistant protective film is printed onto the surface of the UTG raw material by non-contact 3D printing, and / or the corrosion-resistant protective film is a laser debonding protective film or a UV debonding protective film.

[0021] In a preferred embodiment, in S12 and S22, a conductive layer is plated on the UFG substrate layer, and the conductive layer corresponding to the folding area is directly etched away or etched into a grid shape, and / or the grid lines of the grid-shaped conductive layer are solid lines or dotted lines, and / or the line width of the grid lines of the grid-shaped conductive layer is 6um~10um, and the line spacing is more than 1mm.

[0022] In a preferred embodiment, between S12 and S13, and between S22 and S23, it also includes: making conductive wiring on the edges of the conductive layer close to the insulating layer, and / or, the preparation process of the conductive wiring includes: using a mask to directly magnetron sputter or evaporate metal in the wiring area of ​​the conductive layer, or first magnetron sputter or evaporate metal on the entire conductive layer, and then etching away the metal except the wiring area.

[0023] In a preferred embodiment, in S13, the first insulating layer is formed on the first conductive layer by printing, silk-screen printing or coating, and / or, S1 also includes: S14, printing, silk-screen printing or coating a first hardened buffer layer on the lower end surface of the first UFG substrate layer away from the vibration layer; in S23, the second insulating layer is formed on the second conductive layer by printing, silk-screen printing or coating, and / or, S2 also includes: S24, printing, silk-screen printing or coating a second hardened buffer layer on the upper end surface of the second UFG substrate layer away from the substrate layer, and forming an optical thin film layer on the upper end surface of the second hardened buffer layer away from the substrate layer.

[0024] In a preferred embodiment, the thickness of the second hardened buffer layer is 15um~25um, and / or the thickness of the optical film layer is less than 5um, and / or the total thickness of the first insulating layer and the second insulating layer is 6um~12um, and / or the thickness of the second conductive layer is less than 100nm; and / or the thickness of the first hardened buffer layer is 2um~4um, and / or the thickness of the first conductive layer is less than 100nm.

[0025] In a preferred embodiment, in S3, the micropattern layer includes a first micropattern layer corresponding to the folding part and a second micropattern layer corresponding to the sound-emitting part, and the pattern of the first micropattern layer is different from the pattern of the second micropattern layer; and / or the micropattern of the first micropattern layer is arranged in a grid shape, and the center point of the micropattern is located at the grid point; and / or, S3 also includes: applying voltage after bonding to expel bubbles between the vibration layer and the substrate layer, and / or, the loaded voltage is a DC bias voltage.

[0026] In a preferred embodiment, the total thickness of the vibration layer is 52um~138um, and / or the total thickness of the substrate layer is 38um~116um, and / or the total thickness of the directional sound folding screen is 90um~254um, and / or the thickness of the first UFG substrate layer and the second UFG substrate layer are both 30um~100um; and / or the thickness of the first folding area is 30um~70um, and / or the thickness of the second folding area is 30um~70um, and / or the thickness of the first folding area folded outward in a direction close to the client is greater than the thickness of the first folding area folded inward in a direction away from the client, and / or the thickness of the second folding area folded outward in a direction close to the client is greater than the thickness of the second folding area folded inward in a direction away from the client, and / or the thickness of the second folding area folded outward in a direction close to the client is greater than the thickness of the first folding area folded outward in a direction close to the client, and / or the thickness of the first folding area folded inward in a direction away from the client is greater than the thickness of the second folding area folded inward in a direction away from the client.

[0027] On the other hand, the present invention proposes a manufacturing process of an electronic device, including laminating a directional sound folding screen with a folding display screen or integrating it inside the folding display screen, and the process of laminating the directional sound folding screen with the folding display screen includes:

[0028] The substrate layer is prepared by adopting step S1 in the preparation process of the directional sound folding screen, and the vibration layer is prepared by adopting step S2 in the preparation process of the directional sound folding screen;

[0029] First, the substrate layer is integrally bonded to the folding display screen, and after bonding, voltage is applied to expel bubbles between the substrate layer and the folding display screen;

[0030] An adhesive layer is formed on the micro-pattern layer, and the substrate layer bonded to the folding display screen is bonded to the vibration layer as a whole through the adhesive layer, and after bonding, a voltage is applied to discharge bubbles between the vibration layer and the substrate layer;

[0031] Alternatively, the process of bonding the directional sound folding screen to the folding display screen includes:

[0032] The substrate layer is prepared by adopting step S1 in the preparation process of the directional sound folding screen, and the vibration layer is prepared by adopting step S2 in the preparation process of the directional sound folding screen;

[0033] First, an adhesive layer is formed on the micro-pattern layer, and the substrate layer bonded to the folding display screen is bonded to the vibration layer through the adhesive layer;

[0034] Then the substrate layer bonded with the vibration layer is bonded to the folding display screen as a whole, and after bonding, voltage is applied to successively discharge the bubbles between the substrate layer and the folding display screen and between the vibration layer and the substrate layer.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The present invention adopts UTG as the base layer of the vibration layer and the substrate layer, and is supplemented by the processing technology of other functional structures of the directional sound screen to prepare a directional sound folding screen that can be completely folded in at least one folding direction. While realizing the large-screen sound of the directional sound screen, it also achieves the advantages of small size and easy to carry.

[0037] 2. The present invention adopts UTG as the base layer of the vibration layer and the substrate layer, which greatly reduces the overall thickness of the directional sound screen and makes it light and thin.

[0038] 3. The present invention improves the flexibility of the folding area by designing the pattern of the conductive layer corresponding to the folding area on the vibration layer and the substrate layer, the pattern of the micro-pattern layer, the thickness of the folding area, etc., so that the folding area is not easy to break when folded under the condition of uneven stress; in addition, the present invention adds a hardened buffer layer and an optical film layer on the base layer of the vibration layer and adds a hardened buffer layer on the base material layer of the substrate layer to prevent the directional sound screen from being easily broken and scratched under the action of external force, and increases the friction resistance of the surface of the sound screen, thereby improving the overall reliability of the directional sound folding screen. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of a folded state of a directional sound folding screen in one embodiment of the present invention;

[0040] Figure 2 It is a schematic diagram of the stacked structure of the directional sound folding screen after folding in one embodiment of the present invention;

[0041] Figure 3 A schematic diagram of the stacked structure of a directional sound-emitting folding screen in one embodiment of the present invention;

[0042] Figure 4 A schematic diagram of stacking of UTG raw materials covered with a corrosion-resistant protective film in one embodiment of the present invention;

[0043] Figure 5a , Figure 5b Schematic diagrams of two grid-shaped patterns of the conductive layer corresponding to the folding area;

[0044] Figure 6a , Figure 6b Schematic diagrams of arrangement of a micro-pattern layer in which square and dot-shaped micro-patterns are arranged in a grid shape;

[0045] Figure 7 is a schematic diagram of a stacked structure of an electronic device in one embodiment of the present invention;

[0046] Figure 8 It is a schematic diagram of the manufacturing process of a directional sound folding screen in one embodiment of the present invention;

[0047] Fig. 9 Schematic diagram of the manufacturing process of an electronic device in one embodiment of the present invention;

[0048] Fig.10 The figure is a schematic diagram of a process flow of manufacturing an electronic device in another embodiment of the present invention.

[0049] The accompanying drawings are marked as follows:

[0050] 1. Directional sound folding screen, 11. Sounding part, 111. First sounding part, 112. Second sounding part, 113. Third sounding part, 12. Folding part, 121. First folding part, 122. Second folding part, 2. Substrate layer, 21. First UFG substrate layer, 211. First folding area, 212. First non-folding area, 213. First groove, 22. First conductive layer, 23. First conductive trace, 24. First insulating layer, 25. First hardened buffer layer, 3. Micro pattern layer, 31. First Second micro-pattern layer, 32, first micro-pattern layer, 4, vibration layer, 41, second UFG substrate layer, 411, second folding area, 412, second non-folding area, 413, second groove, 42, second conductive layer, 43, second conductive trace, 44, second insulating layer, 45, second hardened buffer layer, 46, optical film layer, 5, air gap, 6, thinned UTG raw material, 7, corrosion-resistant protective film, 8, area to be corroded, 10, electronic equipment, 20, display screen, 30, OCA optical glue. DETAILED DESCRIPTION

[0051] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0052] Unless explicitly stated otherwise, throughout the specification and claims, the term “comprise” or variations such as “include” or “comprising”, etc., will be understood to include the stated elements or components but not to exclude other elements or components.

[0053] Combination Figure 1~Figure 3 As shown, a directional sound folding screen 1 disclosed in the present invention includes a plurality of sound emitting parts 11 and at least one folding part 12 distributed along a first direction (such as a horizontal direction), and each adjacent two sound emitting parts 11 are connected by a folding part 12, and the sound emitting parts 11 are folded in a direction away from or close to the client to the adjacent sound emitting parts 11 and are stacked in a second direction (such as a vertical direction). In other words, a directional sound folding screen 1 is divided into a plurality of sound emitting parts 11 for directional sound by at least one folding part 12, and the plurality of sound emitting parts 11 can be folded through the corresponding folding parts 12, and finally folded into a stacked state.

[0054] In a specific embodiment, in combination Figure 1 and Figure 2 As shown, the directional sound folding screen 1 includes three sound parts 11 and two folding parts 12. For the convenience of description, they are defined as the first sound part 111, the first folding part 121, the second sound part 112, the second folding part 122 and the third sound part 113 arranged in sequence along the horizontal direction, wherein the first sound part 111 folds inwards in the direction away from the client, and the third sound part 113 folds outwards in the direction close to the client. After folding, the first sound part 111, the second sound part 112 and the third sound part 113 are stacked in sequence in the longitudinal direction, that is, a three-fold directional sound screen. Of course, in other embodiments, it can also be two folding screens, that is, including two sound parts 11 and one folding part 12, or it can be expanded to more than four folding screens. When folding, the adjacent sound parts 11 can be alternately folded inside and outside. If one of the sound parts 11 is folded inwards, the adjacent sound part 11 is folded outwards, and so on.

[0055] In a specific embodiment, if Figure 3 As shown, the directional sound folding screen 1 as a whole still includes a substrate layer 2, a micro-pattern layer 3 and a vibration layer 4. The micro-pattern layer 3 is located between the substrate layer 2 and the vibration layer 4. The vibration layer 4 and the frame of the substrate layer 2 are in contact with each other, and an air gap 5 is formed between the two through the micro-pattern layer 3. The vibration layer 4 vibrates in a direction close to or away from the substrate layer 2 and makes sound under the action of an externally loaded ultrasonic signal.

[0056] In order to realize the multi-directional folding of the directional sound screen, the structure, material and processing technology of the substrate layer 2, the micro-pattern layer 3 and the vibration layer 4 of the present invention are different from those of the existing directional sound screen. In a specific embodiment, the substrate layer 2 specifically includes a first UFG substrate layer 21, a first conductive layer 22, a first conductive trace 23, a first insulating layer 24 and a first hardened buffer layer 25, wherein the first UFG substrate layer 21 is made of UFG (uneven thickness flexible glass) material, and specifically includes at least one first folding area 211 and a plurality of first non-folding areas 212, wherein the thickness of the first folding area 211 is less than the thickness of the first non-folding area 212, specifically, one side of the first folding area 211 is flush with one side of the first non-folding area 212, and the other side is lower than the other side of the first non-folding area 212. The thin thickness of the first folding area 211 has higher flexibility, and the thickness of the first non-folding area 212 is large by folding, so the strength is high. In a specific embodiment, the thickness of the first non-folding area 212 is 30um~100um, and the thickness of the first folding area 211 is thinned to 30um~70um. The thickness of the first folding area 211 is different according to the different R angle designs of the folding. Generally speaking, the smaller the R angle, the smaller the thickness of the first folding area 211. For example, when the R angle is between 4mm~5mm, the thickness of the first folding area 211 can be between 50um~70um. If the R angle is less than 4mm, the thickness of the first folding area 211 is 30um~50um. In a specific embodiment, when the thickness of the first folding area 211 is 30um, the R angle can be 1.5mm.

[0057] A first groove 213 with an opening facing the folding direction is formed between the first folding area 211 and the two first non-folding areas 212 on its adjacent sides. If it is folded inward (i.e., in the direction away from the client), the opening of the first groove 213 faces inward, that is, the first groove 213 is recessed outward. Conversely, if it is folded outward (i.e., in the direction close to the client), the opening of the first groove 213 faces outward, that is, the first groove 213 is recessed inward. The depth of the first groove 213 is generally the height difference between the first non-folding area 212 and the first folding area 211.

[0058] In addition, preferably, the thickness of the first folding area 211 folded outward in the direction close to the client is greater than the thickness of the first folding area 211 folded inward in the direction away from the client, because when the directional sound-emitting screen is combined with a folding display screen, the first folding area 211 that is generally folded outward has a lower thickness due to the non-folding back panel, folding display screen, etc. wrapped inside, and is easier to fold. Therefore, the thickness of this area after thinning can be kept higher to increase strength, such as 50um; while the first folding area 211 that is generally folded inward has a higher thickness due to the folding back panel and folding display screen wrapped inside, and is more difficult to fold. Therefore, the thickness of this area after thinning can be kept lower, such as 30um, or thinner. Of course, if the thickness of the outer folding and inner folding wrapped parts is the same, the thickness of the first folding areas 211 corresponding to the outer folding and inner folding can also be set to be the same. As in the above-mentioned three-fold embodiment, two first folding areas 211 are formed on the first UFG substrate layer 21, and the opening directions of the two first grooves 213 corresponding to the two first folding areas 211 are opposite, that is, one is facing inward and the other is facing outward, and the thicknesses of the two first folding areas 211 are also different, that is, the thickness of the first folding area 211 folded inward is smaller than the thickness of the first folding area 211 folded outward.

[0059] During implementation, the first UFG substrate layer 21 is formed by processing UTG raw material. During specific preparation, the preparation process of the first UFG substrate layer 21 includes: first thinning the UTG raw material (such as a thickness of 230um) as a whole to 30um~100um, and then further thinning the folding area of ​​the thinned UTG raw material 6. In a specific embodiment, the process of further thinning the folding area of ​​the thinned UTG raw material 6 includes: covering at least one side of the thinned UTG raw material 6 with a corrosion-resistant protective film 7 and exposing the area to be corroded 8, immersing the UTG raw material 6 covered with the corrosion-resistant protective film 7 in the corrosive liquid as a whole, corroding and thinning the area to be corroded 8, and controlling the time of immersion in the corrosive liquid to control the thickness of the first folding area 211 finally formed, and then removing the corrosion-resistant protective film 7. During implementation, the corrosion-resistant protective film 7 here can be a laser debonding protective film or a UV debonding protective film, and the corrosion-resistant protective film 7 is preferably printed on the surface of the UTG raw material 6 by non-contact 3D printing to prevent the UTG raw material 6 from breaking. The etching liquid can be a hydrofluoric acid (HF) etching liquid. In the above-mentioned three-fold screen embodiment, since two first folding areas 211 are formed on the first UFG substrate layer 21, and the opening directions of the two first grooves 213 corresponding to the two first folding areas 211 are opposite, during preparation, it is necessary to cover the upper and lower surfaces of the UTG raw material with the corrosion-resistant protective film 7 and expose the folding area to be thinned, and the two folding areas are staggered left and right, such as Figure 4 shown.

[0060] The first conductive layer 22 is formed on the upper end surface of the first UFG substrate layer 21 close to the vibration layer 4 and at least covers the first non-folding area 212 of the first UFG substrate layer 21. In specific implementation, the thickness of the first conductive layer 22 is generally less than 100 nm. Since the folded portion formed is preferably designed to be silent, the first folding area 211 may be covered with no conductive layer, or the conductive layer of the first folding area 211 may be designed to be in a grid shape. During preparation, a conductive layer (such as an indium tin oxide ITO conductive layer) may be first plated on the entire surface of the first UFG substrate layer 21, and then the conductive layer corresponding to the first folding area 211 may be directly etched away or etched in a grid shape to form the first conductive layer 22. Preferably, in one embodiment, the grid lines of the grid-shaped conductive layer are solid lines or dotted lines, such as Figure 5a and Figure 5b As shown, the line width of the grid lines of the grid-shaped conductive layer is 6um~10um, and the line spacing is more than 1mm. This design can avoid the problem of unstable structure of the folding part caused by the vibration of the vibration layer 4 of the sound-emitting part 11, and can weaken the appearance of etching lines.

[0061] The first conductive trace 23 is formed on the edges of the upper end surface of the first conductive layer 22 close to the vibration layer 4, and is used to increase the conductivity of the first conductive layer 22. During preparation, a mask can be used to directly magnetron sputter or evaporate metal in the trace area of ​​the first conductive layer 22, or the first conductive layer 22 is first magnetron sputtered or evaporated as a whole, and then the metal except the trace area is etched away. During implementation, the first conductive trace 23 can be a copper trace or a silver paste layer, etc., and the thickness is preferably less than 1um, so that the step difference formed is low, and the fragmentation degree of the first UFG substrate layer 21 is low. In a specific implementation case, if the first conductive trace 23 is a copper trace, the thickness is generally less than 0.9um, and the copper trace with a thickness higher than 0.9um has poor adhesion to the first conductive layer 22 on the surface of the first UFG substrate layer 21, but if it is lower than 0.9um, the line resistance of the copper trace will increase again, and the load power of the directional sound folding screen will increase. In another specific implementation case, the first conductive trace 23 can be a composite laminate structure, specifically including a decorative layer (not shown) and a conductive trace layer stacked with the decorative layer (not shown), wherein the conductive trace layer is arranged on the four edges of the upper end surface of the first conductive layer 22 close to the vibration layer 4, and the decorative layer is stacked on the upper end surface of the conductive trace layer close to the vibration layer 4 (that is, the side close to the client). During implementation, the decorative layer can be black ink, which can be conductive or non-conductive, and is used to decorate the first conductive layer 22. It can be used as a cover frame, which can increase the appearance while also achieving a narrow frame or even a frameless design when it is combined with a display screen.

[0062] The first insulating layer 24 is formed on the upper end surface of the first conductive layer 22 close to the vibration layer 4 and covers the first conductive trace 23, the first conductive layer 22 and the first folding area 211. During preparation, the first insulating layer 24 can be formed on the first conductive layer 22 by printing, screen printing or coating. Its thickness is generally preferably designed to be between 6um and 12um, and it is preferably a material with low resistance and low thickness.

[0063] The first hardened buffer layer 25 is formed on the lower end surface of the first UFG substrate layer 21 away from the vibration layer 4. During preparation, like the first insulating layer 24, the first hardened buffer layer 25 can also be formed on the first UFG substrate layer 21 by printing, silk screen printing or coating.

[0064] In a specific embodiment, the vibration layer 4 specifically includes a second UFG substrate layer 41, a second conductive layer 42, a second conductive trace 43, a second insulating layer 44, a second hardened buffer layer 45 and an optical film layer 46, wherein, like the substrate layer of the substrate layer, the substrate layer of the vibration layer 4, i.e., the second UFG substrate layer 41, also adopts UFG (unequal thickness flexible glass) material, which specifically includes at least one second folding area 411 and multiple second non-folding areas 412, wherein the structure, material and preparation process of the second UFG substrate layer 41 are the same as the structure and preparation process of the above-mentioned first UFG substrate layer 21, so the description of the above-mentioned first UFG substrate layer 21 can be referred to and will not be repeated here.

[0065] In addition, preferably, the thickness of the second folding area 411 folded outward in a direction close to the client is greater than the thickness of the first folding area 211 folded outward in a direction close to the client, and / or the thickness of the first folding area 211 folded inward in a direction away from the client is greater than the thickness of the second folding area 411 folded inward in a direction away from the client. The advantage of such a design is that it is conducive to a smaller R-angle design for folding, and is not prone to breakage of the folded portion caused by uneven stress during folding.

[0066] The second conductive layer 42 is formed on the lower end surface of the second UFG substrate layer 41 close to the substrate layer 2 and at least covers the second non-folding area 412 of the second UFG substrate layer 41. The second conductive trace 43 is formed on the edges of the lower end surface of the second conductive layer 42 close to the substrate layer 2 to increase the conductivity of the second conductive layer 42. The second insulating layer 44 is formed on the lower end surface of the second conductive layer 42 close to the substrate layer 2 and covers the second conductive trace 43, the second conductive layer 42 and the second folding area 411 in its entirety. The second hardened buffer layer 45 is formed on the upper end surface of the second UFG substrate layer 41 away from the substrate layer 2. Similarly, the structure, material and preparation process of the second conductive layer 42, the second conductive trace 43, the second insulating layer 44 and the second hardened buffer layer 45 here are the same as the structure and preparation process of the first conductive layer 22, the first conductive trace 23, the first insulating layer 24 and the first hardened buffer layer 25 mentioned above, so the corresponding descriptions mentioned above can be referred to and will not be repeated here.

[0067] Preferably, the thickness of the second hardened buffer layer 45 and the second insulating layer 44 are set differently, because compared with the second insulating layer 44, the main function of the second hardened buffer layer 45 is to prevent splashing when the second UFG substrate layer 41 is broken. At the same time, this layer plays a buffering role when a heavy object hits the screen during a drop test or near the client. Therefore, the thickness of the second hardened buffer layer 45 is set to between 15um and 25um. The higher the thickness, the stronger its impact resistance and the greater the pencil hardness. However, if it is higher than 25um, the folding R angle will be limited. The second insulating layer 44 is the dielectric layer of the parallel plate capacitor, and its main function is insulation. The thickness of this layer of material is generally preferably designed to be between 6um and 12um. If it is lower than 6um, its voltage resistance is weak, which will cause a certain probability of breakdown. However, if the thickness is too thick, the system power will increase and the relative loss energy of the dielectric will increase. In addition, the functions of the second hardened buffer layer 45 and the first hardened buffer layer 25 are also different, because the second hardened buffer layer 45 is close to the client and is a hardened layer, and its function is to prevent scratches and increase the surface friction resistance, while the first hardened buffer layer 25 is far away from the client and is a buffer layer, and its Young's modulus is generally between 100Pa and 1000Pa. The lower the Young's modulus, the better the buffering effect. The first insulating layer 24 and the second insulating layer 44 are both dielectric layers in the dielectric layer, and the total thickness of the two layers is preferably 6um~12um. Preferably, most of the thickness is designed in the second insulating layer 44, such as the thickness of the second insulating layer 44 is 10um and the thickness of the first insulating layer 24 is 2um. The advantages of this design are: the second insulating layer 44 is in the vibration layer 4, and the first insulating layer 24 is in the substrate layer 2. During the sound generation process of the device, the vibration layer 4 has a probability of touching the surface of the substrate layer 2 at the maximum amplitude. As the working time increases, the touched surface of the substrate layer 2 is prone to breakage. Therefore, if the thickness of the second insulating layer 44 is greater than the first insulating layer 24, the probability of the substrate layer 2 surface breaking can be reduced. If the directional sound folding screen 1 is combined with a display screen, since the substrate layer 2 will be attached to the display screen as a whole, the second hardened buffer layer 45 is preferably low in thickness. In one implementation case, the thickness of the second hardened buffer layer 45 is preferably 2um~4um.

[0068] The optical film layer 46 is formed on the upper end surface of the second hardened buffer layer 45 away from the substrate layer 2. In implementation, the optical film layer 46 is specifically an anti-glare (AG) / anti-reflection (AR) anti-fingerprint (AF) layer, and its thickness is less than 5um, generally about 1um. Its thickness is related to the process, and generally the thickness is greater than 5um, which will affect the folding R angle.

[0069] Preferably, there is no optical bonding glue between the second hardened buffer layer 45 and the second UFG substrate layer 41 of the present invention, and the second hardened buffer layer 45 of the present invention is a layer of material, which is integrally formed. After curing, the surface of the second hardened buffer layer 45 has hardening properties, and the surface hardness can reach at least 750g 2H, and can reach up to 750g 7H. In other alternative embodiments, the second hardened buffer layer 45 can also be made of traditional OCA sheets bonded with TPU (thermoplastic polyurethane rubber) or PET (polyethylene terephthalate) or CPI (transparent polyimide film) and other materials with a hard coating.

[0070] In addition, since the first insulating layer 24, the first hardened buffer layer 25, the second insulating layer 44 and the second hardened buffer layer 45 all need to fill the folding area, their refractive index is preferably close to the refractive index of the UFG substrate. The advantage is that there are no reflective marks on the corners of the folding area, and when it is unfolded into the entire screen, no obvious light and shadow will be seen in the originally designed folding area.

[0071] The micro-pattern layer 3 is formed on the upper end surface of the first insulating layer 24 close to the vibration layer 4. The micro-pattern layer 3 specifically includes a first micro-pattern layer 32 corresponding to the folding portion and a second micro-pattern layer 31 corresponding to the sound-generating portion 11. Since the first micro-pattern layer 32 only plays a process role and does not need to be a functional layer for sound generation, the pattern design of the first micro-pattern layer 32 can be different from the pattern design of the second micro-pattern layer 31. In a specific embodiment, the micro-pattern arrangement of the first micro-pattern layer 32 can be in a grid shape, and the center point of the micro-pattern is located at the grid point, and the spacing between two adjacent micro-patterns of the first micro-pattern layer 32 and the spacing between two adjacent micro-patterns of the first micro-pattern layer 32 can be set to be different, which can be set according to the requirements of parameters such as folding flexibility. In other alternative embodiments, the micro-pattern layer 3 can also be formed on the lower end surface of the second insulating layer 44 close to the substrate layer 2. The present invention is not limited to this, as long as the micro-pattern layer 3 is located between the substrate layer 2 and the vibration layer 4 after bonding. During implementation, the micro-pattern layer 3 can be formed by silk screen printing or 3D printing. During implementation, a single micro-pattern of the micro-pattern layer may be, but is not limited to, circular, rectangular, etc., and the grid arrangement is preferably a diamond grid formed by oblique crosses, such as Figure 6a and Figure 6b shown.

[0072] Because the present invention uses UTG as the base layer of the vibration layer 4 and the substrate layer 2, compared with the existing vibration layer 4 using PET or other base film materials, and the substrate layer 2 using PET or tempered glass CG or other base film materials, the present invention greatly reduces the overall thickness of the directional sound screen and achieves its lightness and thinness. Specifically, the thickness of the first UFG substrate layer 21 and the second UFG substrate layer 41 of the present invention are both 30um~100um, the total thickness of the vibration layer 4 is 52um~138um, the total thickness of the substrate layer 2 is 38um~116um, and the total thickness of the formed directional sound folding screen 1 is 90um~254um. Compared with the total thickness of the existing directional sound screen of 375um~525um, the thickness is greatly reduced.

[0073] like Figure 7 As shown, the present invention also discloses an electronic device 10, which at least includes the above-mentioned directional sound folding screen 1, or includes the above-mentioned directional sound folding screen 1 and a foldable display screen 20. When combined with the display screen 20, the directional sound folding screen 1 here can be directly bonded to the display screen 20 as a whole, such as being bonded to the display surface of the display screen 20 through OCA optical glue 30. When bonding, the above-mentioned substrate layer 2 can be bonded to the display screen 20 first, and then the substrate layer 2 can be bonded to the vibration layer 4, or the substrate layer 2 can be bonded to the vibration layer 4 first, and then the substrate layer 2 can be bonded to the display screen 20. The specific bonding method can refer to the description in the preparation process of the electronic device below. Alternatively, in other embodiments, the above-mentioned directional sound folding screen 1 can be integrated into the interior of the display screen 20. The display screen 20 here can be, but not limited to, OLED, LED, LCD display screen, etc., and the electronic device 10 can be, but not limited to, a mobile device such as a computer or a mobile phone.

[0074] like Figure 8 As shown, the present invention also discloses a preparation process of a directional sound-emitting folding screen, which specifically includes the following preparation steps:

[0075] S1, preparing a substrate layer 2, said S1 comprising:

[0076] S11, providing a first UFG substrate layer 21, wherein the first UFG substrate layer 21 includes at least one first folding region 211 and a plurality of first non-folding regions 212, wherein the thickness of the first folding region 211 is less than that of the first non-folding region 212, and a first groove 213 with an opening facing the folding direction is formed between the first folding region 211 and two first non-folding regions 212 adjacent to the first folding region 211;

[0077] S12, forming a first conductive layer 22 covering at least the first non-folding area 212 on the upper end surface of the first UFG substrate layer 21 close to the vibration layer 4;

[0078] S121, making first conductive traces 23 on the edges of the first conductive layer 22 close to the vibration layer 4;

[0079] S13, forming a first insulating layer 24 on the upper end surface of the first conductive layer 22 close to the vibration layer 4, the first insulating layer 24 at least covering the first conductive trace 23, the first conductive layer 22 and the first folding area 211;

[0080] S14 , forming a first hardened buffer layer 25 on the lower end surface of the first UFG base layer 21 away from the vibration layer 4 .

[0081] In a specific implementation, the UTG material with a thickness of 230 um is first thinned as a whole to 30 um to 100 um, and then the folded area of ​​the thinned UTG material 6 is further thinned. Specifically, the upper and lower surfaces of the thinned UTG raw material 6 are covered with a corrosion-resistant protective film 7 and each folding area to be thinned is exposed, and the UTG raw material 6 covered with the corrosion-resistant protective film 7 is immersed in HF etching solution as a whole, and the thickness of the first folding area 211 finally formed is controlled by controlling the immersion time in the etching solution, and then the corrosion-resistant protective film is removed to form a first UFG substrate layer 21; then an ITO conductive layer is plated on the first UFG substrate layer 21, and then the conductive layer corresponding to the first folding area 211 is etched into a grid shape to form a first conductive layer 22; then, a first conductive trace 23 is formed on the edges of the upper end surface of the first conductive layer 22 close to the vibration layer 4 by magnetron sputtering or metal evaporation; finally, a first insulating layer 24 and a first hardened buffer layer 25 are formed on the front and back surfaces of the first UFG substrate layer 21 by printing, silk-screening or coating, respectively, to form a substrate layer 2.

[0082] S2, preparing a vibration layer 4, said S2 comprising:

[0083] S21, providing a second UFG substrate layer 41, wherein the second UFG substrate layer 41 includes at least one second folding region 411 corresponding to the position of the first folding region 211 and a plurality of second non-folding regions 412 corresponding to the positions of the first non-folding regions 212, the thickness of the second folding region 411 is less than the thickness of the second non-folding region 412, and a second groove 413 with an opening facing the folding direction is formed between the second folding region 411 and the two second non-folding regions 412 on its two adjacent sides;

[0084] S22, forming a second conductive layer 42 at least covering the second non-folding area 412 on the lower end surface of the second UFG base material layer 41 close to the substrate layer 2;

[0085] S221, making second conductive traces 43 on the edges of the second conductive layer 42 close to the substrate layer 2;

[0086] S23, forming a second insulating layer 44 on the lower end surface of the second conductive layer 42 close to the substrate layer 2, the second insulating layer 44 at least covering the second conductive trace 43, the second conductive layer 42 and the second folding area 411;

[0087] S24 , forming a second hardened buffer layer 45 on the upper end surface of the second UFG base material layer 41 away from the substrate layer 2 , and forming an optical thin film layer 46 on the upper end surface of the second hardened buffer layer 45 away from the substrate layer 2 .

[0088] Except for the optical film layer 46, the preparation of other structures of the vibration layer 4 can refer to the description of the substrate layer 2 above, which will not be described in detail here.

[0089] S3, forming a micro-pattern layer 3 on the upper end surface of the first insulating layer 24 close to the vibration layer 4, and then forming an adhesive layer (not shown) on the micro-pattern layer 3, and bonding the substrate layer 2 and the vibration layer 4 together through the adhesive layer.

[0090] In a specific embodiment, the micro-pattern layer 3 is screen-printed or 3D-printed on the first insulating layer 24, and then the adhesive layer is screen-printed or 3D-printed on the surface of the micro-pattern layer 3. The substrate layer 2 and the vibration layer 4 are bonded together through the adhesive layer. After bonding, voltage is applied to expel bubbles between the vibration layer 4 and the substrate layer 2. The bubble expelling pressure is generally preferably a DC bias voltage of 300V.

[0091] After bonding, in the formed directional sound folding screen 1, the laminated structure portion corresponding to the folding area is the folding portion 12, and the laminated structure portion corresponding to the non-folding area is the sound portion 11 for directional sound.

[0092] like Fig. 9 As shown, the present invention also discloses a process for preparing an electronic device. In one embodiment, the process specifically includes the following preparation steps:

[0093] The substrate layer 2 is prepared by the above step S1 and the vibration layer 4 is prepared by the above step S2;

[0094] First, the substrate layer 2 is integrally bonded to the folding display screen, and after bonding, voltage is applied to discharge bubbles between the substrate layer 2 and the folding display screen;

[0095] An adhesive layer is formed on the micro-pattern layer 3, and the substrate layer 2 bonded to the folding display screen is bonded to the vibration layer 4 as a whole through the adhesive layer. After bonding, a voltage is applied to discharge the bubbles between the vibration layer 4 and the substrate layer 2.

[0096] Or, if Fig.10 As shown, in another alternative embodiment, the process mainly includes the following steps:

[0097] The substrate layer 2 is prepared by the above step S1 and the vibration layer 4 is prepared by the above step S2;

[0098] First, an adhesive layer is formed on the micro-pattern layer 3, and the substrate layer 2 after being bonded to the folding display screen is bonded to the vibration layer 4 through the adhesive layer, and bubbles are not discharged at this time;

[0099] Then, the substrate layer 2 bonded with the vibration layer is bonded to the folding display screen as a whole, and after bonding, voltage is applied to successively discharge the bubbles between the substrate layer 2 and the folding display screen and between the vibration layer 4 and the substrate layer 2.

[0100] In this embodiment, if the substrate layer 2 and the vibration layer 4 are first defoamed and sealed after being bonded together and then bonded to the display screen 20, if a vacuum bonding machine is used, since the air pressure inside the machine is lower than the air pressure between the substrate layer 2 and the vibration layer 4, it is easy to cause the vibration layer 4 to separate from the adhesive layer, thereby causing the acoustic performance distortion of the formed directional sound screen to increase.

[0101] The advantages of the present invention are as follows: 1. The present invention adopts UTG as the base layer of the vibration layer and the substrate layer, and is supplemented by the processing technology of other functional structures of the directional sound-emitting screen to prepare a directional sound-emitting folding screen that can be completely folded in at least one folding direction, so as to achieve the advantages of large-screen sound emission of the directional sound-emitting screen and small size and easy to carry. 2. The present invention adopts UTG as the base layer of the vibration layer and the substrate layer, which greatly reduces the overall thickness of the directional sound-emitting screen and achieves its lightness and thinness. 3. The present invention improves the flexibility of the folding area by designing the pattern of the conductive layer corresponding to the folding area on the vibration layer and the substrate layer, the pattern of the micro-pattern layer, the thickness of the folding area, etc., so that the folding area is not easy to break when folding under the condition of uneven stress; in addition, the present invention prevents the directional sound-emitting screen from being easily broken and scratched under the action of external force by adding a hardened buffer layer and an optical film layer on the base layer of the vibration layer and adding a hardened buffer layer on the base layer of the substrate layer, and increases the friction resistance of the surface of the sound-emitting screen, thereby improving the overall reliability of the directional sound-emitting folding screen.

[0102] The foregoing description of specific exemplary embodiments of the present invention is for the purpose of illustration and demonstration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is clear that many changes and variations can be made based on the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different selections and changes. The scope of the present invention is intended to be limited by the claims and their equivalents.

Claims

1. A preparation process of a directional sound folding screen, characterized in that: The preparation process comprises: S1, preparing a substrate layer, said S1 comprising: S11, providing a first UFG substrate layer, wherein the first UFG substrate layer comprises at least one first folding region and a plurality of first non-folding regions, the thickness of the first folding region is smaller than the thickness of the first non-folding region, and a first groove opening toward a folding direction is formed between the first folding region and two first non-folding regions on its two adjacent sides; S12, forming a first conductive layer at least covering the first non-folded area on the upper end surface of the first UFG substrate layer close to the vibration layer; S13, forming a first insulating layer on an upper end surface of the first conductive layer close to the vibration layer, the first insulating layer covering at least the first conductive layer and the first folding region; S2, preparing a vibration layer, said S2 comprising: S21, providing a second UFG substrate layer, wherein the second UFG substrate layer comprises at least one second folding region corresponding to the position of the first folding region and a plurality of second non-folding regions corresponding to the positions of the first non-folding regions, the thickness of the second folding region is smaller than the thickness of the second non-folding region, and a second groove with an opening facing a folding direction is formed between the second folding region and two second non-folding regions on its two adjacent sides; S22, forming a second conductive layer at least covering the second non-folded area on the lower end surface of the second UFG base material layer close to the substrate layer; S23, forming a second insulating layer on a lower end surface of the second conductive layer close to the substrate layer, the second insulating layer covering at least the second conductive layer and the second folding region; S3, forming a micro-pattern layer on the upper end surface of the first insulating layer close to the vibration layer, and then forming an adhesive layer on the micro-pattern layer, and bonding the substrate layer to the vibration layer through the adhesive layer; After lamination, an air gap is formed between the vibration layer and the substrate layer through the micro-pattern layer, and the vibration layer vibrates and makes sound in a direction close to or away from the substrate layer under the action of an externally loaded ultrasonic signal; The prepared directional sound folding screen includes a plurality of sound emitting parts and at least one folding part distributed along a first direction, and each adjacent two sound emitting parts are connected by a folding part. The sound emitting parts are folded in a direction away from or close to the client to be stacked with the adjacent sound emitting parts in a second direction.

2. A process for preparing a directional sound folding screen according to claim 1, characterized in that: In S11 and 21, the first UFG substrate layer and the second UFG substrate layer are both formed by processing UTG raw materials; and / or, the preparation processes of the first UFG substrate layer and the second UFG substrate layer both include: thinning the UTG raw material as a whole to 30um~100um, and then further thinning the folding area of ​​the thinned UTG raw material; and / or, the process of further thinning the folding area of ​​the thinned UTG raw material includes: covering at least one side of the thinned UTG raw material with a corrosion-resistant protective film and exposing the area to be corroded, immersing the UTG raw material covered with the corrosion-resistant protective film as a whole in a corrosive solution to corrode and thin the area to be corroded to form a folding area, and then removing the corrosion-resistant protective film.

3. The process for preparing a directional sound folding screen according to claim 2, characterized in that: The corrosion-resistant protective film is printed onto the surface of the UTG raw material by non-contact 3D printing, and / or the corrosion-resistant protective film is a laser debonding protective film or a UV debonding protective film.

4. The process for preparing a directional sound folding screen according to claim 1, characterized in that: In S12 and S22, a conductive layer is plated on the UFG substrate layer, and the conductive layer corresponding to the folding area is directly etched away or etched into a grid shape, and / or the grid lines of the grid-shaped conductive layer are solid lines or dotted lines, and / or the line width of the grid lines of the grid-shaped conductive layer is 6um~10um, and the line spacing is more than 1mm.

5. The process for preparing a directional sound folding screen according to claim 1, characterized in that: Between S12 and S13, and between S22 and S23, it also includes: making conductive wiring on the edges of the conductive layer close to the insulating layer, and / or, the preparation process of the conductive wiring includes: using a mask to directly magnetron sputter or evaporate metal in the wiring area of ​​the conductive layer, or first magnetron sputter or evaporate metal on the entire conductive layer, and then etching away the metal except the wiring area.

6. The process for preparing a directional sound folding screen according to claim 1, characterized in that: In S13, the first insulating layer is formed on the first conductive layer by printing, silk-screen printing or coating, and / or, S1 also includes: S14, printing, silk-screen printing or coating a first hardened buffer layer on the lower end surface of the first UFG substrate layer away from the vibration layer; in S23, the second insulating layer is formed on the second conductive layer by printing, silk-screen printing or coating, and / or, S2 also includes: S24, printing, silk-screen printing or coating a second hardened buffer layer on the upper end surface of the second UFG substrate layer away from the substrate layer, and forming an optical thin film layer on the upper end surface of the second hardened buffer layer away from the substrate layer.

7. The process for preparing a directional sound folding screen according to claim 6, characterized in that: The thickness of the second hardened buffer layer is 15um~25um, and / or the thickness of the optical film layer is less than 5um, and / or the total thickness of the first insulating layer and the second insulating layer is 6um~12um, and / or the thickness of the second conductive layer is less than 100nm; and / or the thickness of the first hardened buffer layer is 2um~4um, and / or the thickness of the first conductive layer is less than 100nm.

8. The process for preparing a directional sound folding screen according to claim 1, characterized in that: In S3, the micro-pattern layer includes a first micro-pattern layer corresponding to the folding portion and a second micro-pattern layer corresponding to the sound-emitting portion, and a pattern of the first micro-pattern layer is different from a pattern of the second micro-pattern layer; and / or the micropatterns of the first micropattern layer are arranged in a grid shape, and the center points of the micropatterns are located at the grid points; And / or, S3 further includes: applying voltage to expel bubbles between the vibration layer and the substrate layer after lamination, and / or, the applied voltage is a DC bias voltage.

9. The process for preparing a directional sound folding screen according to claim 1, characterized in that: The total thickness of the vibration layer is 52um~138um, and / or the total thickness of the substrate layer is 38um~116um, and / or the total thickness of the directional sound folding screen is 90um~254um, and / or the thickness of the first UFG substrate layer and the second UFG substrate layer are both 30um~100um; and / or the thickness of the first folding area is 30um~70um, and / or the thickness of the second folding area is 30um~70um, and / or the thickness of the first folding area folded outward in the direction close to the client is greater than the thickness of the first folding area folded inward in the direction away from the client, and / or the thickness of the second folding area folded outward in the direction close to the client is greater than the thickness of the second folding area folded inward in the direction away from the client, and / or the thickness of the second folding area folded outward in the direction close to the client is greater than the thickness of the first folding area folded outward in the direction close to the client, and / or the thickness of the first folding area folded inward in the direction away from the client is greater than the thickness of the second folding area folded inward in the direction away from the client.

10. A process for preparing an electronic device, characterized in that: The method includes laminating a directional sound folding screen with a folding display screen or integrating the directional sound folding screen into the inside of the folding display screen. The process of laminating the directional sound folding screen with the folding display screen includes: The substrate layer is prepared by adopting step S1 in the preparation process of the directional sound folding screen according to any one of claims 1 to 9, and the vibration layer is prepared by adopting step S2 in the preparation process of the directional sound folding screen according to any one of claims 1 to 9; First, the substrate layer is integrally bonded to the folding display screen, and after bonding, voltage is applied to expel bubbles between the substrate layer and the folding display screen; forming an adhesive layer on the micro-pattern layer, and laminating the substrate layer after laminating the folding display screen to the vibration layer as a whole through the adhesive layer, and applying voltage to discharge bubbles between the vibration layer and the substrate layer after laminating; Alternatively, the process of bonding the directional sound folding screen to the folding display screen includes: The substrate layer is prepared by adopting step S1 in the preparation process of the directional sound folding screen according to any one of claims 1 to 9, and the vibration layer is prepared by adopting step S2 in the preparation process of the directional sound folding screen according to any one of claims 1 to 9; First, an adhesive layer is formed on the micro-pattern layer, and the substrate layer bonded to the folding display screen is bonded to the vibration layer through the adhesive layer; Then the substrate layer bonded with the vibration layer is bonded to the folding display screen as a whole, and after bonding, voltage is applied to successively discharge the bubbles between the substrate layer and the folding display screen and between the vibration layer and the substrate layer.

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