STACK

TECHNICAL FIELD

The disclosure relates to a flexible display stack for an electronic apparatus, the flexible display stack comprising a display structure and a cover structure superimposed onto the display structure.

BACKGROUND

The display technology area has evolved immensely since organic light-emitting diodes (OLED) were invented in 1989. The OLEDs are emissive displays that do not require a backlight and are therefore thinner and more efficient than LCD displays. Furthermore, OLEDs facilitated the development of a new technology concept, i.e., bent displays. In the first phase, the display device was a stationary curved display, which became a game-changing product, e.g., due to the new design options which were made available.

True flexible displays were introduced later, allowing the display to be bent and flexed, e.g., in response to folding the electronic apparatus in half. Such true flexible displays required the structure of the display stack to be fundamentally redesigned, one key change being replacing the carrier and cover window glasses of the display stack with flexible substrates made of plastic materials.

Such flexible OLED display stacks require additional layers for durability, user interface, and optical functionality. At least one layer each of a hard coating, a cover window, a touch sensor, and a circular polarizer is generally included, and these must be laminated together with adhesive. The hard coating not only defines the appearance and premium look of the apparatus, but functions as a protection layer for the display stack from mechanical impact, scratches, wear, etc. As its name suggests, the hard coating must be relatively hard, to provide such protection, but must at the same time be sufficiently flexible, to allow bending.

In order to provide those properties, the hard coating material is conventionally made by two components, a hard segment and a soft segment. By controlling the ratio of these segments, it is possible to fine-tune the hardness and flexibility of the hard coating. However, there is always a tradeoff between the mechanical qualities of the two segments - when increasing the hardness, the flexibility decreases and vice versa. Currently, display specifications require the hard coating to pass 200 000 cyclic bending cycles where the strain may exceed up to 3%, and at the same time the hard coating has to be hard enough to pass a nail test or standard steel wool test.

Although there currently exist several different solutions and types of hard coatings, they are mainly suitable for specific applications such as displays that fold around one axis only. These solutions cannot be applied onto other types of bendable displays, such as slidable or Tollable displays, without the hard coating cracking.

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

SUMMARY

It is an object to provide an improved flexible display stack. 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.

According to a first aspect, there is provided a flexible display stack for an electronic apparatus comprising a display structure and a cover structure superimposed onto the display structure. The cover structure comprises a continuous structural element comprising a plurality of voids, and a continuous matrix configured to fill the voids and at least partially enclose the structural element. The structural element comprises a first material and the matrix comprises a second material different from the first material.

This solution allows a cover structure, i.e., a hard coating, which is suitable for displays that fold around one axis as well as other types of bendable displays such as slidable or Tollable displays. The cover structure is sufficiently flexible to bend without cracking, and at the same time hard enough to provide mechanical protection for the display structure.

In a possible implementation form of the first aspect, one of the structural element and the matrix comprises inorganic material and the other of the structural element and the matrix comprises organic material. One of these materials provides hardness while the other of the materials provide flexibility. In a further possible implementation form of the first aspect, the structural element comprises inorganic material and the matrix comprises organic material. The inorganic material provides a relatively harder frame which reinforces the relatively softer, and more flexible, organic matrix. Correspondingly, the relatively flexible, organic matrix provides the relatively harder, inorganic frame with the needed flexibility.

In a further possible implementation form of the first aspect, the cover structure comprises an optically transparent material, allowing the display structure to be visible to the user of the apparatus.

In a further possible implementation form of the first aspect, the structural element and/or the matrix comprises optically transparent material, allowing the display structure to be visible to the user of the apparatus.

In a further possible implementation form of the first aspect, the structural element is a three- dimensional element and the voids are distributed evenly in three dimensions, allowing the cover element to have the same harness and the same flexibility throughout, and to have any suitable thickness.

In a further possible implementation form of the first aspect, the structural element comprises a porous film, allowing simple and efficient manufacture of the cover structure and, hence, the display stack.

In a further possible implementation form of the first aspect, the structural element comprises silicon dioxide, aluminum oxide, silicon nitride, silicon oxynitride, and/or silicon oxycarbide.

In a further possible implementation form of the first aspect, the structural element is a skeleton frame or a grid structure. Such a structure allows any force applied, e.g. due to impact, to be distributed over a large area, as compared to the specific point of impact, hence improving the durability of the cover structure.

In a further possible implementation form of the first aspect, the matrix comprises an organic monomer or polymer. In a further possible implementation form of the first aspect, the matrix comprises thermoplastic polyurethane, silicone-based elastomers, or perylene-based polymers.

In a further possible implementation form of the first aspect, the matrix comprises incompressible material such that force from e.g. impact can be distributed across the cover layer.

In a further possible implementation form of the first aspect, the matrix comprises at least one of a scratch-resistant material and a self-healing material, further improving the durability of the cover structure.

In a further possible implementation form of the first aspect, the scratch-resistant material is a high tensile modulus polymer.

In a further possible implementation form of the first aspect, defects within the matrix have a total volume < 1 % of a total volume of the matrix, such that the main part of the matrix is in direct contact with the structural element. Any contact gaps, i.e. defects in the form of air bubbles, reduce the durability of the cover layer.

In a further possible implementation form of the first aspect, a difference between a reflective index value of the structural element and a reflective index value of the matrix is < 1.2%, such that the display stack is not perceived as being hazy or somehow blurred. A larger difference in reflective index value may lead to the structural element reflecting and diffusively scattering light, which may be perceived as haziness.

In a further possible implementation form of the first aspect, the voids of the structural element have volumes which correspond to /(2xRI), l being a wavelength of radiation and RI being a reflective index value of the cover structure, the radiation being emitted by the display structure or incident radiation from an exterior. Such small void sizes make the scattering of light so insignificant that no hazing can be perceived by the human eye.

In a further possible implementation form of the first aspect, the reflective index value is a reflective index value of the structural element or a reflective index value of the matrix, or wherein the reflective index value is an estimate generated by means of the reflective index value of the structural element and the reflective index value of the matrix.

In a further possible implementation form of the first aspect, the display structure comprises an OLED panel layer, allowing the solution to comprise currently preferred display panels.

In a further possible implementation form of the first aspect, the display structure comprises at least one of a flexible substrate, a polarizing layer, and a touch sensor layer.

According to a second aspect, there is provided an electronic apparatus comprising a housing and a flexible display stack according to the above, wherein the cover structure of the flexible display stack forms a peripheral surface of the electronic apparatus.

Such an apparatus has a cover structure, i.e., a hard coating, which is suitable for different types of bendable displays such as slidable or Tollable displays. The cover structure is sufficiently flexible to bend without cracking, and at the same time hard enough to provide mechanical protection for the display structure.

In a possible implementation form of the second aspect, the flexible display stack is slidable or Tollable relative the housing, allowing the display stack to be used in different dynamic solutions.

According to a third aspect, there is provided a method of manufacturing a flexible display stack, the method comprising the steps of depositing a porous and continuous inorganic structural element, coating the structural element with an organic monomer matrix, and curing the matrix.

The method allows for simple, reliable, and efficient manufacture of a flexible display stack where inorganic material provides a relatively harder frame which reinforces the relatively softer, and more flexible, organic matrix. Correspondingly, the relatively flexible, organic matrix provides the relatively harder, inorganic frame with the needed flexibility. In a possible implementation form of the third aspect, the matrix is configured to shrink < 2% while curing, such that the shape and volume of the cover structure is not affected and/or subjected to inner stress.

In a further possible implementation form of the third aspect, the method further comprises the step of pre-treating the structural element with an adhesion-promoting additive prior to coating the structural element with the organic monomer matrix, improving the penetration of the matrix into the voids of the structural element.

In a further possible implementation form of the third aspect, the adhesion promoting additive is a silane, preferably an aminosilane. The additive improves the wettability of the structural element by forming a nanolayer which enhances the coating and leveling of other polymers.

In a further possible implementation form of the third aspect, the structural element is deposited by means of physical or chemical deposition methods, such methods being cost-effective and simple.

In a further possible implementation form of the third aspect, the physical vapor deposition is one of pulsed laser deposition, electron beam deposition, resistive or arc evaporation, spattering, chemical vapor deposition, sol-gel deposition, or spray pyrolysis.

In a further possible implementation form of the third aspect, the organic monomer matrix is coated onto the structural element by means of spin coating, slit coating, dipping, or infiltration from a gas phase.

These and other aspects will be apparent from the embodiment s) described below.

BRIEF DESCRIPTION OF THE DRAWINGS

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 embodiments shown in the drawings, in which:

Fig. 1 shows a schematic side view of a flexible display stack in accordance with an example of the embodiments of the disclosure; Fig. 2 shows a schematic side view of a cover structure of a flexible display stack in accordance with an example of the embodiments of the disclosure;

Fig. 3a shows a schematic perspective view of a cover structure of a flexible display stack in accordance with an example of the embodiments of the disclosure;

Fig. 3b shows a section of the example shown in Fig. 3a in more detail;

Figs. 4a to 4c show schematic side views of method steps for manufacturing a flexible display stack in accordance with an example of the embodiments of the disclosure.

DETAILED DESCRIPTION

A flexible display stack 1 for an electronic apparatus 2 comprising a display structure 3 and a cover structure 4 superimposed onto the display structure 3. The cover structure 4 comprises a continuous structural element 5 comprising a plurality of voids 6, and a continuous matrix 7, a matrix being a material in which something is enclosed or embedded (as for protection or study). The matrix 7 is configured to fill the voids 6 and at least partially enclose the structural element 5. The structural element 5 comprises a first material and the matrix 7 comprises a second material different from the first material.

As shown in Fig. 1, the electronic apparatus 2 comprises a housing 8 and the flexible display stack 1 described in more detail below. A cover structure 4 of the flexible display stack 1 is configured to form a peripheral surface of the electronic apparatus 2, i.e., an outer surface to be engaged by a user, e.g., by touching. The flexible display stack 1 may be slidable or Tollable relative the housing 8 such that the bent section of the flexible display stack 1 moves in response to the flexible display stack 1 sliding or rolling relative the housing 8. The housing 8 may comprise of two or more interconnected housing sections, the housing sections being interconnected by hinges or one housing section being slidingly arranged relative the other such that one housing section slides into, and out from, the other housing section.

The flexible display stack 1 comprises a display structure 3 and a cover structure 4 superimposed onto the display structure 3. The display structure 3 may comprise a plurality of discrete layers superimposed, i.e., stacked, onto each other. The display structure 3 may comprise an OLED panel layer 3a, and as shown in Fig. 1, the display structure 3 may also comprise at least one of a flexible substrate 3b, a polarizing layer 3c, and a touch sensor layer 3d.

The cover structure 4 comprises a continuous structural element 5 comprising a plurality of voids 6. As shown in Figs 2 to 3b, the structural element 5 may be a skeleton frame or, in other words, a grid structure. The structural element 5 is a three-dimensional element and the voids

6 are distributed evenly in three dimensions and interconnected. The structural element 5 may comprise a porous film.

The cover structure 4 also comprises a continuous matrix 7 configured to fill the voids 6 and at least partially enclose the structural element 5, such not only the voids 6 are filled with matrix

7 but also at least part of the outer surfaces of the structural element 5 are covered with matrix 7. The entire structural element 5 may be covered by the matrix 7. The matrix 7 is continuous such that all matrix material is interconnected as one piece, even though it encloses the structural element 5.

The structural element 5 comprises a first material and the matrix 7 comprises a second material different from the first material. One of the structural element 5 and the matrix 7 may comprise inorganic material and the other of the structural element 5 and the matrix 7 may comprise organic material.

In one example, the structural element 5 comprises inorganic material and the matrix 7 comprises organic material. The structural element 5 may comprise silicon dioxide, aluminum oxide, silicon nitride, silicon oxynitride, and/or silicon oxycarbide.

The matrix 7 may comprise incompressible material, and the matrix 7 may comprise an organic monomer or polymer. The matrix 7 may be a low viscosity solution free of reactive solvents. Furthermore, the matrix 7 may comprise thermoplastic polyurethane, silicone-based elastomers, or perylene-based polymers.

The matrix 7 may comprise at least one of a scratch-resistant material and a self-healing material, configured to recover its initial shape after being scratched or damaged. The scratch- resistant material may be a high tensile modulus polymer. Self-healing materials are conventionally soft and easily scratched, however, combining such a material with a harder structural element 5 can lead to a cover structure 4 having sufficient hardness as well as sufficient flexibility.

The cover structure 4 may comprise an optically transparent material. The structural element 5 and/or the matrix 7 of the cover structure 4 may comprise optically transparent material.

Any defects within the matrix 7 may have a total volume < 1% of the total volume of the matrix 7, such that the main part of the matrix is in direct contact with the structural element. Any contact gaps, i.e., defects in the form of air bubbles, reduce the durability of the cover layer.

The difference between the reflective index value R1 of the structural element 5 and the reflective index value R2 of the matrix 7 may be < 1.2 %.

The voids 6 of the structural element 5 may have volumes which correspond to /2xRI, l being the wavelength of radiation and RI being the reflective index value of the cover structure 4, the radiation being emitted by the display structure 3 or being incident radiation from an exterior such as light from a lamp or sunlight. The width, possibly diameter, of the voids may be, e.g., as small as 200-250 nm.

The reflective index value RI may be equal to either the reflective index value Rl of the structural element 5 or the reflective index value R2 of the matrix 7. The reflective index value RI may also be an estimate, a so-called effective reflective index, generated by means of the reflective index value Rl of the structural element 5 and the reflective index value R2 of the matrix 7. For example, the estimate may be calculated as an average of the reflective index value Rl and the reflective index value R2.

The present invention furthermore relates to a method of manufacturing the flexible display stack 1, as shown in Figs. 4a to 4c. The method comprises the initial step of depositing a porous and continuous inorganic structural element 5, see Fig. 4a. The structural element 5 may be deposited by means of physical or chemical deposition methods. The physical vapor deposition may be one of pulsed laser deposition, electron beam deposition, resistive or arc evaporation, spattering, chemical vapor deposition, sol-gel deposition, or spray pyrolysis. The method furthermore comprises the subsequent step of coating the structural element 5 with the organic monomer matrix 7, see Fig. 4b. The coating may be made by means of spin coating, slit coating, dipping, or infiltration from a gas phase.

The structural element 5 is, in other words, saturated with organic monomer matrix 7, the organic monomer matrix 7 penetrating and filling the voids 6 of the structural element 5 completely. The voids 6 are interconnected such that they form a network of caves and channels, comprising of voids 6 and interconnecting conduits, such that the matrix 7 can fill the entire network and form one integral element. The voids 6 may have spherical or irregular three- dimensional shapes, and the channels may have cylindrical shapes.

Finally, the matrix comprises the step of curing the matrix 7 such that the structural element 5 and matrix 7 together form a cover structure 4, see Fig. 4c. The matrix 7 may be configured to shrink < 2% while curing.

The method may furthermore comprise the intermediate step of pre-treating the structural element 5 with an adhesion-promoting additive prior to coating the structural element 5 with the organic monomer matrix 7, i.e., between the first step shown in Fig. 4a and the second step shown in Fig. 4b. The adhesion-promoting additive improves the penetration of the matrix 7 into the voids 6 of the structural element 5. The adhesion-promoting additive may be a silane, preferably an aminosilane, forming a nanolayer on the structural element 5.

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 measured cannot be used to advantage.

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.