Flexible display stack

Abstract

A flexible display stack (1) for an electronic apparatus (2), said display stack (1) comprising a plurality of layers (3) and at least one partially deformable support structure (4). The deformable support structure (4) comprises a reversibly deformable layer (5) configured to change dimension along a first axis (A1) perpendicular to a main plane (P) of said display stack (1), and an actuation layer (6) configured to send an impulse to said deformable layer (5), said deformable layer (5) changing said dimension in response to receiving said impulse. The impulse may comprise thermal energy, electromagnetic radiation, magnetic energy, or electrical energy.

Description

[0001] FLEXIBLE DISPLAY STACK

[0002] TECHNICAL FIELD

[0003] The disclosure relates to a flexible display stack for an electronic apparatus as well as an electronic apparatus comprising a flexible display stack.

[0004] BACKGROUND

[0005] True flexible displays allow the display of an electronic apparatus to be bent and flexed, e.g., in response to folding the electronic apparatus. This means the structure of the display stack has been fundamentally redesigned. In particular, all rigid components such as carrier glass and cover window glass have been replaced by components made of flexible polymeric material.

[0006] When the flexible display stack is bent (rolled), the structural layers of the display stack, usually made of elastomers or polymers, undergo bending strain. The strain in each layer is strongly dependent on the stack design, thickness, and bending radius. The ticker the display, the more the strain increases. The strain may exceed 1-3 %, but even at low strain levels, when the stack is bent for a long time, permanent deformation may be caused by the creep of the polymers which occurs due to the previously mentioned strain.

[0007] This may result in a deformation, a bump, being permanently formed in the bending area of the display stack, which in turn generates a visible crease. Attempts have been made at solving this problem by adding high modulus layers, which have very small deformation in strained conditions, such as ultra-thin glass. These solutions do not prevent a crease from forming since, unexpectedly, the forming of the crease is mainly associated with deformation of the adhesive layers of the display stack, which layers undergo very large shear strain when combined with ultra-thin glass.

[0008] Hence, there is a need for providing an improved flexible display stack that is suitable for foldable electronic apparatuses in general.

[0009] SUMMARY

[0010] It is an object to provide an improved flexible display stack that overcomes or at least reduces the problems above. The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description, and the figures.

[0011] According to a first aspect, there is provided a flexible display stack for an electronic apparatus, the display stack comprising a plurality of layers and at least one partially deformable support structure, the deformable support structure comprising a reversibly deformable layer configured to change dimension along a first axis perpendicular to a main plane of the display stack, and an actuation layer configured to send an impulse to the deformable layer, the deformable layer changing the dimension in response to receiving the impulse.

[0012] This layered arrangement allows a display stack to be folded or rolled while at the same time preventing the forming of a crease or bump in the display stack due to the tensile and compressive stresses induced in the different layers when bending. This ensures image quality of the display stack is not affected negatively by an uneven display surface. Furthermore, the layered arrangement allows the display stack to be as thin as possible, which reduces the strain on the display stack.

[0013] In a possible implementation form of the first aspect, the deformable layer comprises at least one shape memory material, the shape memory material being a shape memory polymer or a shape memory elastomer. The use of such materials allows a reliable, mechanical solution where any bump or cease is pushed or pulled flat by the deformable support structure. Furthermore, these materials have high energy damping performance, wherefore the deformable layer can effectively absorb energy if an apparatus comprising the display stack is subject to impact.

[0014] In a further possible implementation form of the first aspect, the shape memory material comprises liquid crystal polymer, liquid crystal elastomer, norbornene-based polymer, azobenzene-based polymer, shape memory polyurethane, or shape memory polyester. This allows the most suitable material to be selected based on individual prerequisites and objectives.

[0015] In a further possible implementation form of the first aspect, the shape memory material is optically transparent. This allows the deformable support structure to be arranged anywhere within the display stack, e.g. directly underneath the hard top coat layer. In a further possible implementation form of the first aspect, the transmittance of the shape memory material is >85 %, the haze of the shape memory material is <2 %, and the yellowness index of the shape memory material is <2 %, such that the deformable layer has optical properties allowing it to be arranged above the layer comprising the display panel.

[0016] In a further possible implementation form of the first aspect, the actuation layer comprises a thin film heater, the impulse comprising thermal energy. This allows the shape of the shape memory material to be controlled using very thin components.

[0017] In a further possible implementation form of the first aspect, the impulse comprises magnetic energy or electrical energy, allowing use of any suitable components for affecting the shape memory material.

[0018] In a further possible implementation form of the first aspect, the thin film heater comprises electroconductive oxide or electroconductive ink, allowing the shape memory material to be controlled using a very thin layer.

[0019] In a further possible implementation form of the first aspect, the actuation layer comprises a light guide, the impulse comprising electromagnetic radiation. This allows the shape of the shape memory material to be controlled without heat generation.

[0020] In a further possible implementation form of the first aspect, the flexible display stack further comprises a light source configured to emit electromagnetic radiation into the light guide. This allows the shape of the shape memory material to be controlled without heat generation.

[0021] In a further possible implementation form of the first aspect, the light guide comprises an organic transparent polymer or inorganic fiberglass, allowing the material with the most suitable properties to be selected.

[0022] In a further possible implementation form of the first aspect, the display stack comprises a bendable area configured to bend around a second axis, and the reversibly deformable layer is configured to change dimension in an area superimposed with the bendable area. This allows the layers of the display stack to be affected by the deformable layer only in the area where a crease or bump is likely to be formed.

[0023] In a further possible implementation form of the first aspect, the reversibly deformable layer applies a first force onto at least one of the layers of the display stack, in a first direction along the first axis, when the deformable layer receives the impulse, and the reversibly deformable layer applies a second force onto the at least one of the layers of the display stack, in a second direction along the first axis, when the deformable layer does not receive an impulse. The application of force ensures any bump or crease, which may have been formed, is counteracted and the layer maintained planar.

[0024] According to a second aspect, there is provided an electronic apparatus comprising a flexible display stack according to the above, the actuation layer of the deformable support structure being configured to send the impulse to the deformable layer of the deformable support structure when the display stack is being moved from a folded position to an unfolded position.

[0025] This allows an electronic apparatus provided with a display that can be folded or rolled repeatedly without a crease or bump being formed in the bending area. This ensures the image quality of the display is not affected negatively by the bending.

[0026] In a possible implementation form of the second aspect, a deviation of the surface of the display stack from the main plane of the display stack, when in the unfolded position, is less than 0.1 mm along the first axis. This ensures the requirements on the surface smoothness of the display, to avoid image quality deterioration, are fulfilled.

[0027] In a further possible implementation form of the second aspect, the electronic apparatus further comprises an arrangement for manually initiating and / or controlling the impulse, allowing a user to adjust the display as desired.

[0028] These and other aspects will be apparent from the examples and embodiments described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In the following detailed portion of the present disclosure, the aspects, embodiments and implementations will be explained in more detail with reference to the example embodiment shown in the drawings, in which:

[0030] Fig. 1 shows a schematic side view of a flexible display stack in accordance with an example of the embodiments of the disclosure, wherein the display stack is in an unfolded position;

[0031] Fig. 2 shows a schematic side view of the embodiment of Fig. 1, wherein the display stack is in a folded, or closed, position.

[0032] DETAILED DESCRIPTION

[0033] The present invention relates to a flexible display stack 1 for an electronic apparatus 2, the display stack 1 comprising a plurality of layers 3 and at least one partially deformable support structure 4, the deformable support structure 4 comprising a reversibly deformable layer 5 configured to change dimension along a first axis Al perpendicular to a main plane P of the display stack 1, and an actuation layer 6 configured to send an impulse to the deformable layer 5, the deformable layer 5 changing the dimension in response to receiving the impulse.

[0034] Fig. 1 shows a flexible display stack 1 for an electronic apparatus 2. The display stack 1 comprises a plurality of layers 3 and at least one partially deformable support structure 4.

[0035] The plurality of layers 3 may be flexible film layers such as a flexible substrate, window film, a display panel layer for example comprising an OLED material, a polarization layer, and / or a conductive layer. The different film layers may comprise mainly of elastomers and polymers, and the layers may be laminated together using adhesive, e.g., optically clear adhesive.

[0036] The deformable support structure 4 comprises a reversibly deformable layer 5 and an actuation layer 6.

[0037] The reversibly deformable layer 5 is configured to change dimension along a first axis Al perpendicular to a main plane P of the display stack 1. The thickness of the reversibly deformable layer 5 is measured along the first axis Al. The actuation layer 6 is configured to send an impulse to the deformable layer 5, and the deformable layer 5 changes its dimension, along the first axis Al, in response to receiving the impulse.

[0038] The deformable layer 5 may comprise at least one shape memory material, the shape memory material being a shape memory polymer or a shape memory elastomer.

[0039] The shape memory material may comprise liquid crystal polymer, liquid crystal elastomer, norbornene-based polymer, azobenzene-based polymer, shape memory polyurethane, or shape memory polyester.

[0040] The shape memory material may be optically transparent. The shape memory material may be 50-300 pm thick.

[0041] The transmittance of the shape memory material may be >85 %, the haze of the shape memory material may be <2 %, and the yellowness index of the shape memory material may be <2 %.

[0042] The actuation layer 6 may comprise a thin film heater 7, and the impulse may comprise thermal energy. The thin film heater 7 may be 0.1-100 pm thick.

[0043] The thin film heater 7 may comprise electroconductive oxide or electroconductive ink. The thin film heater 7 may be created by R2R (roll-to-roll) technology by depositing electro- conductive film comprising ITO, InZnOSiO / Ag / InZnSiO, AgNW, etc. The thin film heater 7 may optionally be transparent.

[0044] When required, the thin film heater 7 is turned on for short period, e.g. for a few seconds, heating up the deformable layer 5 and forcing it to return its original shape, the original shape being used to flatten any bump or crease formed in the plurality of layers 3.

[0045] The actuation layer 6 may comprise a light guide 8, and the impulse may comprise electromagnetic radiation. The light guide 8 may comprise an organic transparent polymer or inorganic fiberglass. The light guide 8 may be 0.1-120 pm thick. The flexible display stack 1 may further comprise a light source 9 configured to emit electromagnetic radiation into the light guide. The electromagnetic radiation may have wavelengths within the 440-490 nm range or the 620-750 nm range.

[0046] When required, the light source 9 is turned on for short period, e.g. for a few seconds, light propagating uniformly through the light guide 8 and forcing the deformable layer 5 to return its original shape, the original shape being used to flatten any bump or crease formed in the plurality of layers 3.

[0047] The actuation layer 6 may comprise any suitable component, for actuating the deformable layer 5, and the impulse may comprise for example magnetic energy or electrical energy.

[0048] As shown in Fig 2, the display stack 1 may comprise a bendable area la configured to bend around a second axis A2. The reversibly deformable layer 5 is configured to change dimension in an area superimposed with the bendable area la. The reversibly deformable layer 5 may extend across the entire display stack 1 or be limited to the bendable area la only.

[0049] The reversibly deformable layer 5 may apply a first force onto at least one layer 3 of the display stack 1, in a first direction DI along the first axis Al, when the deformable layer 5 receives an impulse.

[0050] The reversibly deformable layer 5 may also apply a second force onto the at least one layer 3 of the display stack 1, in a second direction D2 along the first axis Al, when the deformable layer 5 does not receive an impulse. The second direction D2 is opposite the first direction DI.

[0051] The present invention also relates to an electronic apparatus 2 comprising the above-mentioned flexible display stack 1. The electronic apparatus may be a device such as a tablet, a laptop, or a smartphone.

[0052] The actuation layer 6 of the deformable support structure 4 may be configured to send an impulse to the deformable layer 5 of the deformable support structure 4 when the display stack 1 is being moved from a folded (closed) position to an unfolded (open) position. The impulse, or signal, may in other words be sent when the display of the apparatus is being opened.

[0053] A deviation of the surface of the display stack 1 from the main plane P of the display stack 1, when in the unfolded, or open, position, is less than 0.1 mm along the first axis Al .

[0054] The electronic apparatus 2 may further comprise an arrangement for manually initiating and / or controlling the impulse.

[0055] The various aspects and implementations have been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed subject-matter, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0056] The reference signs used in the claims shall not be construed as limiting the scope. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this disclosure. As used in the description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.

Claims

CLAIMS1. A flexible display stack (1) for an electronic apparatus (2), said display stack (1) comprising a plurality of layers (3) and at least one partially deformable support structure (4), said deformable support structure (4) comprising:- a reversibly deformable layer (5) configured to change dimension along a first axis (Al) perpendicular to a main plane (P) of said display stack (1), and- an actuation layer (6) configured to send an impulse to said deformable layer (5), said deformable layer (5) changing said dimension in response to receiving said impulse.

2. The flexible display stack (1) according to claim 1, wherein said deformable layer (5) comprises at least one shape memory material, said shape memory material being a shape memory polymer or a shape memory elastomer.

3. The flexible display stack (1) according to claim 2, wherein said shape memory material comprises liquid crystal polymer, liquid crystal elastomer, norbornene-based polymer, azobenzene-based polymer, shape memory polyurethane, or shape memory polyester.

4. The flexible display stack (1) according to claim 2 or 3, wherein said shape memory material is optically transparent.

5. The flexible display stack (1) according to any one of claims 2 to 4, wherein the transmittance of said shape memory material is >85 %, the haze of said shape memory material is <2 %, and the yellowness index of said shape memory material is <2 %.

6. The flexible display stack (1) according to any one of the previous claims, wherein said actuation layer (6) comprises a thin film heater (7), said impulse comprising thermal energy.

7. The flexible display stack (1) according to claim 6, wherein said thin film heater (7) comprises electroconductive oxide or electroconductive ink.

8. The flexible display stack (1) according to any one of claims 1 to 5, wherein said actuation layer (6) comprises a light guide (8), said impulse comprising electromagnetic radiation.

9. The flexible display stack (1) according to claim 8, further comprising a light source (9) configured to emit said electromagnetic radiation into said light guide10. The flexible display stack (1) according to claim 8 or 9, wherein said light guide (8) comprises an organic transparent polymer or inorganic fiberglass.

11. The flexible display stack (1) according to any one of the previous claims, wherein said display stack (1) comprises a bendable area (la) configured to bend around a second axis (A2), and said reversibly deformable layer (5) is configured to change dimension in an area superimposed with said bendable area (la).

12. The flexible display stack (1) according to any one of the previous claims, wherein said reversibly deformable layer (5) applies a first force onto at least one of the layers (3) of said display stack (1), in a first direction (DI) along said first axis (Al), when said deformable layer (5) receives said impulse, and wherein said reversibly deformable layer (5) applies a second force onto said at least one of said layers of said display stack (1), in a second direction (D2) along said first axis (Al), when said deformable layer (5) does not receive said impulse.

13. An electronic apparatus (2) comprising a flexible display stack (1) according to any one of claims 1 to 12, the actuation layer (6) of the deformable support structure (4) being configured to send the impulse to the deformable layer (5) of the deformable support structure (4) when said display stack (1) is being moved from a folded position to an unfolded position.

14. The electronic apparatus (2) according to claim 13, wherein a deviation of the surface of the display stack (1) from the main plane (P) of the display stack (1), when in said unfolded position, is less than 0.1 mm along the first axis (Al).

15. The electronic apparatus (2) according to claim 13 or 14, further comprising an arrangement for manually initiating and / or controlling said impulse.

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