Flexible displays having stiff layers for neutral plane adjustment

At least some aspects of the present disclosure feature a flexible display including a plurality of functional layers, a plurality of bonding layers, and a stiff layer. Each of the plurality of bonding layers is disposed between two adjacent functional layers. The stiff layer having an elastic modulus greater than elastic modulus of the plurality of functional layers to adjust a position of a neutral plane of the flexible display within the display layer.

TECHNICAL FIELD

At least some aspects of the present disclosure relate to displays with interlocking devices. At least some aspects of the present disclosure relate to displays having stiff layers for neutral plane adjustment.

SUMMARY

At least some aspects of the present disclosure feature a flexible display, comprising: a plurality of functional layers comprising a display layer having a display component, a plurality of bonding layers comprising a bonding component, and a stiff layer. Each of the plurality of bonding layers is disposed between two adjacent functional layers. The stiff layer having an elastic modulus greater than an elastic modulus of each of the plurality of functional layers to adjust a position of a neutral plane of the flexible display within the display layer.

In the drawings, like reference numerals indicate like elements. While the above-identified drawings, which may not be drawn to scale, set forth various embodiments of the present disclosure, other embodiments are also contemplated, as noted in the Detailed Description. In all cases, this disclosure describes the presently disclosed disclosure by way of representation of exemplary embodiments and not by express limitations. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of this disclosure.

DETAILED DESCRIPTION

As used herein, when an element, component or layer for example is described as forming a “coincident interface” with, or being “on” “connected to,” “coupled to” or “in contact with” another element, component or layer, it can be directly on, directly connected to, directly coupled with, in direct contact with, or intervening elements, components or layers may be on, connected, coupled or in contact with the particular element, component or layer, for example. When an element, component or layer for example is referred to as being “directly on,” “directly connected to,” “directly coupled to,” or “directly in contact with” another element, there are no intervening elements, components or layers for example. As used herein, “powered” means a device receiving operational power.

Some aspects of the present disclosure are directed to a display, in some cases, a flexible display, using an interlocking device to provide adequate bonding strength and shear mobility. The interlocking device can be disposed between adjacent functional layers of a flexible display, for example, a support layer, a display layer, a protection layer, a touch device, or the like. Each functional layer can include one or more components. For example, the display layer can include an organic light-emitting device or other display device. As another example, the protection layer can include a touch sensitive device, a protection film, a light enhancement film, or the like. As yet another example, the support layer can include a supporting substrate, batteries, electrical circuit layer, or the like. In some embodiments, the interlocking device can be used with optical clear gel, adhesive, or liquid to improve bonding property and/or optical property.

Some aspects of the present disclosure are directed to a display, in some cases, a flexible display, having a stiff layer to configure the position of the neutral plane of the display. A neutral plane refers to a conceptual plane within a structure subjected to bending, where it is not under stress, neither compression nor tension. A stiff layer refers to a layer having a relative high elastic modulus, for example, greater than at least one layer or greater than other layers in a display. It is often desirable to position the neutral plane at, within, or proximate to the display layer where the display components are disposed.

FIG. 1illustrates a close-up conceptual view of a portion of a display100using an interlocking device110. The display100, as illustrated, includes a first layer120and a second layer130and a bonding layer150disposed between the two layers (120,130). The bonding layer150includes the interlocking device110. The display may include other layers besides layers120and130. The interlocking device110includes a first interlocking component102attached to or integrated with the layer120and a second interlocking component104attached to or integrated with the layer130. The second interlocking component104is configured to engage with the first interlocking component102. In some embodiments, the engagement prevents the separation of the first layer120from the second layer130along the direction Z perpendicular to the surface of the second layer. In some embodiments, the engagement between the first and second interlocking components provides little or no restriction of the first layer120sliding with respect to the second layer in the direction X along the surface of the second layer130. In some cases, the first interlocking component120and/or the second interlocking component130have channels that can facilitate or guide sliding between the two components. For example, the first interlocking component120and/or the second interlocking component130have rails or generally aligned elements forming channels.

In some embodiments, the interlocking device110can use materials that are optically clear, for example, material with visible light transmission at least 90% and haze less than 2%. In some cases, the interlocking device110can be disposed outside viewing area. In such cases, the interlocking device110can use materials that are not optically clear. In some implementations, the interlocking device110can include air gap between interlocking components. In some other cases, at least part of the interlocking device110can be disposed within viewing area. In such cases, the part of the interlocking device110disposed in the viewing area using an optically clear material, for example, optically clear polymer, or the like. In some embodiments, the optically clear polymer may be a selected polymer with a refractive index between 1.50 and 1.60, for example, polyester, polymethylmethacrylate, polycarbonate, cyclic olefin copolymer, or the like.

In some implementations, the bonding layer150can include bonding materials140can be disposed proximate to the first layer120and the second layer130together with the interlocking device110. In some cases, the bonding material140can include an optically clear material, for example, optically clear adhesive, optically clear gel, optically clear liquid, or the like. With the interlocking device, the bonding material140can use materials that have relative low viscosity, for example, a low viscosity liquid, to reduce resistance to bending. In some embodiments, the bonding material140can use a material that has a refractive index closely matching the refractive index of the interlocking device110. For example, the bonding material140can have an overall refractive index that has an absolute difference less than or equal to 0.05 from the refractive index of the part of interlocking device110, more particularly the interlocking components102and104, within the viewing area. For example, the bonding material140can include materials, for example, acrylates, urethanes, silicones, polyolefins, or the like.

In some embodiments, the interlocking device110has a height no more than 10 mm. In some cases, the interlocking device110has a height no more than 1 mm. In some cases, the interlocking device110has a height no more than 200 micrometers. In some cases, the interlocking device110has a height no more than 100 micrometers. In some cases, the interlocking device110has a height no less than 5 micrometers. In some embodiments, the interlocking device110further comprises an optical coupler106disposed proximate to the first interlocking component102and the second interlocking component104. In some cases, the optical coupler106includes materials that have relatively low elastic modulus, low creep, and a high degree of shear strain under shear load to facilitate the repeated bending, for example, liquid, adhesive, gel, or the like. As an example, the optical coupler106can include a low viscosity liquid to reduce frictional drag between interlocking components and reduce resistance to bending.

In some embodiments, the optical coupler106can use a material that has a refractive index closely matching the refractive index of the interlocking device110, more particular the interlocking components102and104. In such cases, the optical clarity of the interlocking device110can be restored by eliminating the air gaps between the interlocking components102and104. In some cases, the optical coupler106can have an overall refractive index that has an absolute difference less than or equal to 0.05 from the refractive index of the part of interlocking device110, more particularly the interlocking components102and104, within the viewing area. For example, the optical coupler106can include materials such as, for example liquids containing phenyl and phosphorus groups such as Santicizer 141 (available from Ferro, USA), or gels formulated using such liquids in combination with acrylate polymers using monomers containing higher refractive index contributing functional groups such as aromatic groups like phenyl, naphtyl, anthracyl, sulfur groups, bromine groups, or the like, to control and adjust the optical index of the gel. If a closely matching adhesive is used as optical coupling element106it cannot restrict the relative movement (i.e. relative sliding) of the interlocking device110. In some cases, the optical coupler106can use the same material as the bonding material140.

In some embodiments, the first interlocking component102or the second interlocking component104comprises a plurality of engagement elements. At least some of the engagement elements have a cross-sectional shape having a stem and a cap wider than the stem, as illustrated inFIG. 1, such that the engagement between the engagement elements prevents separation or displacement along the Z axis. In some cases, the first or the second interlocking component includes a plurality of engagement rails allowing sliding along the X axis. In some implementations, at least some of the engagement rails has a cross-sectional shape having a post and a cap. In some embodiments, each of the plurality of engagement elements or engagement rails has a height no more than 10 mm. In some cases, each of the plurality of engagement elements or engagement rails has a height no more than 1 mm. In some cases, each of the plurality of engagement elements or engagement rails has a height no more than 200 micrometers. In some cases, each of the plurality of engagement elements or engagement rails has a height no more than 100 micrometers. In some cases, each of the plurality of engagement elements or engagement rails has a height no less than 5 micrometers.

In some cases, the first interlocking component102includes a set of first engagement elements and the second interlocking component104includes a set of second engagement elements. In some cases, the first engagement elements have generally same shapes as the second engagement elements.

In some cases, the flexible display100has an X axis and a Y axis generally perpendicular to the X axis, where the flexible display100is configured to bend about the Y axis. In some embodiments, the interlocking device110is disposed along the X axis. In some cases, the interlocking device110is disposed proximate to two opposing edges of the flexible display100along the X axis. In some configurations, the flexible display100may include more than two functional layers, where every two adjacent functional layers have a bonding layer in between and the bonding layer includes an interlocking device.

FIGS. 2A-2Fillustrate some examples of interlocking devices. Referring toFIG. 2A, an interlocking device200A includes a first interlocking component210A and a second interlocking component220A configured to engage with the first interlocking component210A. The first interlocking component210A can include a substrate211and one or more engagement rails215A. The second interlocking component220A can include a substrate221and one or more engagement rails225A. The engagement rail215A includes a stem212and a cap214A that is wider than the stem212. The cross section of the engagement rail215A is in a mushroom-like shape. Similarly, the engagement rail225A includes a stem222and a cap224A that is wider than the stem222. This design may have a little gap between the two interlocking components.

FIG. 2Billustrates a similar design of an interlocking device200B as the interlocking device200A. The first interlocking component210B can include a substrate211and one or more engagement rails215B. The second interlocking component220B can include a substrate221and one or more engagement rails225B. The engagement rail215B includes a stem212and a cap214B that is wider than the stem212. The cross section of the engagement rail215B is in a mushroom-like shape. Similarly, the engagement rail225B includes a stem222and a cap224B that is wider than the stem222. With this configuration, the two interlocking components (210B,220B) have more overlaps between the caps (214B,224B) that may provide higher through thickness bonding strength than the configuration illustrated inFIG. 2A.

FIG. 2Cillustrates an example of an interlocking device200C. The interlocking device200C includes a first interlocking component210C and a second interlocking component220C configured to engage with the first interlocking component210C. The first interlocking component210C can include a substrate211and one or more engagement rails215C. The second interlocking component220C can include a substrate221and one or more engagement rails225C. The engagement rail215C includes a stem212and a cap214C that is wider than the stem212. The cross section of the engagement rail215C is in a mushroom-like shape. Similarly, the engagement rail225C includes a stem222and a cap224C that is wider than the stem222. The caps214C and224C are generally flat. With this design, the two interlocking components (210C,220C) having more gaps in between, which may reduce friction and improve bending flexibility. More configurations and relative spacing and materials of engagement rails are described in U.S. Pat. Nos. 6,357,128, 6,546,604, and 6,588,074, which are incorporated by reference in their entirety.

FIGS. 2D and 2Eillustrate some examples of engagement rails (200D,200E) with similar shapes. The engagement rail200D, supported by a substrate210, has a stem212and a cap214D, similar to the ones illustrated inFIG. 2B. The engagement rail200E has a similar shape as the engagement rail200D but one or more slits216along a direction generally perpendicular to the longitudinal direction of the engagement rail200E. In some cases, the slit216may have a small angle, for example, 5°, from the direction perpendicular to the general surface of the engagement rail200E. In some embodiments, the distance between two adjacent slits216is within a range between ¼ of a height of the engagement rail200E and 50 times of the height. In some cases, the slits216can be an opening through a portion of the engagement rail200E, for example, the entirety of the cap214E, stem212, and/or substrate210. As another example, the slits216can be an opening through a portion of the cap214D, stem212, and/or substrate210. In some cases, the slits216can have a predefined width, which may allow bending along both directions (i.e., inward and outward) that are generally perpendicular to the surface of the substrate210. The slits216can be disposed along the entire length of the engagement rail, or proximate to selected location(s). The slit216can improve bending flexibility of the engagement rails and the interlocking device formed thereof.

FIG. 2Fillustrates another example of an interlocking device200F. The interlocking device200F includes a first interlocking component210F and a second interlocking component220F configured to engage with the first interlocking component210F. The first interlocking component210F can include a substrate211and one or more engagement elements215F. The second interlocking component220F can include a substrate221and one or more engagement elements225F. The engagement element215F includes a stem212and a cap214F that is wider than the stem212. The cross section of the engagement element215F is in a mushroom-like shape. Similarly, the engagement element225F includes a stem222and a cap224F that is wider than the stem222. In some embodiments as illustrated inFIG. 2F, the engagement elements215F and225F are disposed with regular spacing. In some cases, the engagement elements215F and/or225F form rows to allow or guide sliding. The spacing of the rows of stems and the size of the caps can be selected to provide a desired degree of mechanical engagement along the direction generally perpendicular to the substrate (211or221), while still allowing easy sliding along the direction of the rows. The caps, on the stems of the interlocking components, on one or both of the interlocking components, can have a shape other than generally round or mushroom shaped. For example the caps on one or more engagement elements can be oblong or oval shaped. Suitable materials for this include those taught in U.S. Pat. Nos. 5,077,870 and 5,845,375 for round or mushroom shaped caps, and as taught in U.S. Pat. No. 5,868,987 for oval or oblong shaped caps, which are incorporated by reference in their entireties.

FIG. 2Gillustrates a cross-section view of a conceptual example of interlocking device200G that can be provided in a tape form or a sheet form; andFIG. 2Hillustrates a prospective view of the interlocking device200G. The interlocking device200G includes a first interlocking component210G, a second interlocking component220G, a first adhesive layer230, a first release liner240, a second adhesive layer250, and a second release liner260. The first interlocking component210G includes a substrate211and one or more engagement rails215G and the second interlocking component220G includes a substrate221and one or more engagement rails225G. The engagement rails (215G,225G) allow relative sliding along longitudinal direction of the rail between the interlocking components and prevent separation along Z direction that is generally perpendicular to the surface of the substrate211or221. The interlocking components (210G,220G) may use any configuration of interlocking components described herein, for example, including slits.

In some embodiments, an interlocking device may include a plurality of interlocking segments. Each of the interlocking segments can include two interlocking components, where each interlocking component may use any configuration of interlocking components described herein. The plurality of interlocking segments may be disposed in a geometry pattern.FIGS. 3A-3Fillustrate some example of disposition of the interlocking segments.FIG. 3Aillustrates an interlocking device300A disposed on a functional layer305of a display. The interlocking device300A includes a plurality of interlocking segments310A disposed generally perpendicular to the bending direction Y. In some embodiments, at least two of the plurality of interlocking segments310A are generally parallel to each other. In one embodiment, every two adjacent interlocking segments310A have a generally equal spacing along Y axis.

FIG. 3Billustrates another example of an interlocking device300B disposed on a functional layer305of a display. The interlocking device300B includes a first set of interlocking segments310B generally parallel to each other, a second set of interlocking segments314B generally parallel to each other, and a third set of interlocking segments312B disposed between the first and second sets of interlocking segments. The third set of interlocking segments312B can be disposed in a bending area providing adequate bending flexibility.FIG. 3Cillustrates an example of an interlocking device300C disposed on a functional layer305of a display. The interlocking device300C includes a plurality of short interlocking segments or individual interlocking elements310C dispersed on the surface of the functional layer305, which may allow adequate bonding property and bending flexibility.

FIG. 3Dillustrates an example of an interlocking device300D disposed on a functional layer305of a display. The interlocking device300D comprises a first set of interlocking segments310D and a second set of interlocking segments320D. The first set of interlocking segments310D are disposed approximate to a first edge along X axis of the functional layer305and the second set of interlocking segments320D are disposed approximate to a second edge along X axis of the functional layer305. The first set of interlocking segments310D includes two generally parallel interlocking segments312D. The second set of interlocking segments320D includes two generally parallel interlocking segments322D.

FIG. 3Eillustrates another example of an interlocking device300E disposed on a functional layer305of a display. The interlocking device comprises a first set of interlocking segments310E and a second set of interlocking segments320E. The first set of interlocking segments310E are disposed approximate to a first edge along X axis of the functional layer305and the second set of interlocking segments320E are disposed approximate to a second edge along X axis of the functional layer305. The first set of interlocking segments310E includes two generally parallel interlocking segments312E disposed on a first side, two generally parallel interlocking segments314E disposed on a second side, and a set of short interlocking segments316E disposed between the first side and the second side. The second set of interlocking segments320E includes two generally parallel interlocking segments322E disposed on a first side, two generally parallel interlocking segments324E disposed on a second side, and a set of short interlocking segments or individual interlocking elements326E disposed between the first side and the second side.

FIG. 3Fillustrates yet another example of an interlocking device300F disposed on a functional layer305of a display. The interlocking device comprises a first set of interlocking segments310F and a second set of interlocking segments320F. The first set of interlocking segments310F are disposed approximate to a first edge along X axis of the functional layer305and the second set of interlocking segments320F are disposed approximate to a second edge along X axis of the functional layer305. The first set of interlocking segments310F includes a set of short interlocking segments or individual interlocking elements312F. The second set of interlocking segments320F includes a set of short interlocking segments or individual interlocking elements322F.

In some embodiments, it is desirable to adjust the position of the neutral plane of a flexible display to a location that requires low tension and/or compression, for example, the display layer including components sensitive to stress (e.g., indium tin oxide (ITO) driving electrode, thin film transistor, etc.). A flexible display may have a plurality of functional layers including the display layer and a plurality of bonding layers, where the neutral plane is located outside the display layer. At least some aspects of the present disclosure direct to adding a stiff layer to the display to adjust the neutral plane.FIG. 4illustrates a cross-sectional view of one example of a display400having a stiff layer410. The display has a first layer420, a first bonding layer430, a display layer440, a second bonding layer450, and a second layer460. As an example, the first layer420has an elastic modulus of 1 GPa and a thickness of 25 μm; the first bonding layer430has an elastic modulus of 100 KPa and a thickness of 25 μm; the display layer440has an elastic modulus of 10 GPa and a thickness of 15 μm; the second bonding layer450has an elastic modulus of 100 KPa and a thickness of 25 μm; and the second layer460has an elastic modulus of 10 GPa and a thickness of 75 μm. The position of neutral plane can be calculated using Equation (1):

yNP=∑i=1n⁢y_i⁢Ei⁢Ai∑i=1n⁢Ei⁢Ai(1)
where yNPis the position of the neutral plane measured from a reference plane, such as the bottom surface of the second layer,yiis the distance from the reference plane to the centroid of the ithlayer where i identifies the layer from 1 to n where n is defined as the number of layers in film stack or flexible display, Eiis the elastic modulus of the ithlayer, and Aiis the cross sectional area of the ithlayer.

In some embodiments, the stiff layer is selected to use materials with elastic modulus greater than the lowest elastic modulus of the functional layer. Using the above example, the stiff layer has an elastic modulus greater than 1 GPa. The stiff layer410can be disposed above or below any layer. For example, the stiff layer410can be disposed above or below the first layer, or above or below the second layer. The stiff layer can use materials such as, for example, flexible glass, metal foil, fiber reinforced plastic, or the like. In some embodiments, a thickness of the stiff layer is selected at least in part based on at least one of the plurality of functional layers' elastic modulus. In some cases, a thickness of the stiff layer is selected at least in part based on at least one of the plurality of functional layers' thickness. In some cases, a thickness of the stiff layer selected at least in part based on at least one of the plurality of bonding layers' elastic modulus. In some cases, a thickness of the stiff layer is selected at least in part based on at least one of the plurality of bonding layers' thickness.

FIG. 5Aillustrates the position of a neutral plane versus the thickness of the stiff layer for the stiff layer having an elastic modulus of 10 GPa, where the stiff layer410is placed on the top surface of the first layer420. The dotted lines indicate the position of the upper and lower surfaces of the display layer440. As illustrated, the stiff layer410having a thickness between 10-15 μm will adjust the neutral plane position proximate to the display layer.FIG. 5Billustrates the position of a neutral plane versus the thickness of the stiff layer for the stiff layer having an elastic modulus of 70 GPa, where the stiff layer410is placed on the top surface of the first layer420. The dotted lines indicate the position of the upper and lower surfaces of the display layer440. As illustrated, the stiff layer410having a thickness less than 5 μm will adjust the neutral plane position at the display layer. In some implementations, having a material with greater elastic modulus, the stiff layer can reduce its thickness, which may be desirable for some flexible display configurations.

FIG. 5Cillustrates the position of a neutral plane versus the thickness of the stiff layer for the stiff layer having an elastic modulus of 70 GPa, where the stiff layer410is placed on the bottom surface of the first layer420. The dotted lines indicate the position of the upper and lower surfaces of the display layer440.FIG. 5Dillustrates the position of a neutral plane versus the thickness of the stiff layer for the stiff layer having an elastic modulus of 70 GPa, where the stiff layer410is placed on the top surface of the display layer440. The dotted lines indicate the position of the upper and lower surfaces of the display layer440.

In some embodiments, one of the plurality of the bonding layers of the flexible display400may have an interlocking device. The interlocking device can use any one of the configurations described herein. Such embodiments may reduce stress in the display layer and improve bending flexibility of the display. In some embodiments, the stiff layer410includes an interlocking device, using any one of the configurations described herein. The stiff layer410may also include materials, for example, flexible glass, metal foil, fiber reinforced plastic, or the like.

In some embodiments, a display may include a functional layer that is nonplanar in an unstrained state. For example, the display layer may be in a bent shape at an unstrained state. In one embodiment, a flexible or foldable display includes a plurality of functional layers comprising a display layer having a display component and a plurality of bonding layers, as illustrated inFIG. 4with or without a stiff layer. Each of the plurality of bonding layers is disposed between two adjacent functional layers. As illustrated inFIG. 6A, one of the plurality of functional layers610A is nonplanar in an unstrained state. In one embodiment, the functional layer610A has a first part612A and a second part614A forming an angle616A with the first part612A when the functional layer610A is in the unstrained state. In some cases, the angle616A is less than 150°. In some cases, the angle616A is greater than 45°. In some cases, the angle616A is approximately 90°. In some cases, the angle616A is in the range of 80°-100°. In some implementations, a bonding layer620A is disposed on the functional layer610A in the unstrained state. As an example, the bonding layer620A includes optically clear adhesive. The bonding layer may use any embodiment of bonding layer described herein.

In some implementations, a flexible or foldable display includes one or more functional layers having a nonplanar substrate in an unstrained state. In some cases, none of the nonplanar functional layers is a protective layer. A finite element analysis is performed on four samples, where a two (2) mm sample of polyethylene terephthalate (PET) is originally formed flat, or formed with a radius of 1R, 2R, or 4R in unstrained state. The samples are then bent to a radius of R and also forced to lay flat. The analysis utilized linear elastic material behaviors to describe all functional layers of the display to create the prescribed motions. The analysis was considered static in nature and ignored thermal effects. The maximum stress and the minimum and maximum strain are then recorded for those four scenarios. The results are summarized in Table 1. The results show that the maximum stress experienced at the extreme conditions (held flat and bent to radius R) can be greatly reduced by using layers that have a nonplanar unstrained state.

FIG. 6Cillustrates another example of a functional layer610C having a nonplanar shape in an unstrained state. As illustrated, the functional layer610C has a wavy shape when the functional layer610C is in the unstrained state. As illustrated inFIG. 6D, a bonding layer620C can be disposed on the functional layer in the unstrained state.

EXAMPLES

Flexible Display with Interlocking Sheets Assembly

A film stack was assembled using two 2.60E1 cm (1.02E1 inches)×1.88E1 cm (7.40 inches)×2.54E-2 cm (1.0E-2 inches) Lexan™ 9034 polycarbonate sheets obtained from United States Plastic Corp. of Lima, Ohio as the first layer120and second layer130represented inFIG. 1. Both sides of two interlocking 2.60E1 cm (1.02E1 inches)×1.0E0 cm (3.93E-1 inches)×2.00E-1 (7.87E-2 inches) devices110obtained from 3M Company of St. Paul, Minn. and described in U.S. Pat. No. 6,367,128, entitled “Self-mating Reclosable Mechanical Fastener,” which is incorporated herein by reference in entirety, were secured to the polycarbonate sheets by applying a layer of 2.54E-2 cm (1.00E-2 inch) thick CEF 2210 optically clear adhesive (OCA) obtained from 3M Company of St. Paul, Minn. The interlocking devices110were positioned lengthwise, perpendicular to the bending direction, on the polycarbonate sheets a distance of 4.00E-1 cm (1.57E-1 inches) from each edge as represented inFIG. 3F.

Flexible Display with Adjustable Stiff Layers—Assembly

As represented inFIG. 4, a film stack was assembled using a 2.60E1 cm (1.02E1 inches)×1.88E1 cm (7.40 inches)×7.5E-3 cm (2.9E-3 inches) Lexan™ 9034 polycarbonate sheet obtained from United States Plastic Corp. of Lima, Ohio as the second layer460. The second layer460had an elastic modulus of 2.5 GPa. A 2.60E1 cm (1.02E1 inches)×1.88E1 cm (7.40 inches)×2.5E-3 cm (9.8E-4 inch) layer450of CEF 2210 optically clear adhesive (OCA) obtained from 3M Company of St. Paul, Minn. was placed on top of the second layer. A 2.60E1 cm (1.02E1 inches)×1.88E1 cm (7.40 inches)×1.5E-3 cm (5.9.E-4 inches) ECOVYLOPET® EMC2330 display layer440obtained from Toyobo America of Osaka, Japan was positioned on top of the layer of OCA450. The elastic modulus of the display layer was 10 GPa. A 2.60E1 cm (1.02E1 inches)×1.88E1 cm (7.40 inches)×2.5E-3 cm (9.8E-4 inch) layer430of CEF 2210 optically clear adhesive (OCA) obtained from 3M Company of St. Paul, Minn. was placed on top of the display layer440. The two layers of CEF 2210 OCA each had an elastic modulus of 1.00E-4 GPa. A first layer420of 2.60E1 cm (1.02E1 inches)×1.88E1 cm (7.40 inches)×2.5E-3 cm (9.8E-4 inches) Alathon H5112 HDPE display layer obtained from LyondellBasell of Rotterdam, South Holland was placed on top of the OCA layer430. The elastic modulus of the first layer420was 1 GPa.

Flexible Display with Adjustable Stiff Layers—Neutral Plane Shift

A stiff adjusting layer was added to the top surface of the film stack second layer described in Example 2. Movement of the neutral plane position relative to a reference plane was calculated based upon the thickness of the stiff layer applied. The relationship used to calculate the shifting of the neutral plane position was described as:

yNP=∑i=1n⁢y_i⁢Ei⁢Ai∑i=1n⁢Ei⁢Ai
where yNPwas the position of the neutral plane measured from the reference plane such as the lower portion of the second layer,yiwas the distance from the reference plane to the centroid of the ithlayer where i identifies the layer from 1 to n where n was defined as the number of layers in film stack, Eiwas the elastic modulus of the ithlayer, and Aiwas the cross sectional area of the ithlayer.

Table 2 provides a summary of the results andFIG. 5Aprovides a visual representation when the stiff layer added had an elastic modulus of 10 GPa. The reference plane was designated as the bottom surface of the second layer460.

TABLE 2Stiff Layer Thickness (cm)Position of Neutral Plane (cm)5.0E−49.08E−31.0E−31.01E−21.5E−31.11E−22.0E−31.19E−22.5E−31.27E−23.0E−31.34E−2

Table 3 provides a summary of the results andFIG. 5Bprovides a visual representation when the stiff layer added had an elastic modulus of 70 GPa.

TABLE 3Stiff Layer Thickness (cm)Position of Neutral Plane (cm)1.0E−49.41E−32.0E−41.05E−23.0E−41.13E−25.0E−41.26E−21.0E−31.44E−21.5E−31.56E−2

Flexible Display with Adjustable Stiff Layers—Neutral Plane Shift

A stiff adjusting layer was added to the bottom surface of the first layer420described in Example 2. Movement of the neutral plane position relative to a reference plane was calculated based upon the thickness of the stiff layer applied. The relationship used to calculate the shifting of the neutral plane position was described as:

yNP=∑i=1n⁢y_i⁢Ei⁢Ai∑i=1n⁢Ei⁢Ai
where yNPwas the position of the neutral plane measured from the reference plane such as the lower portion of the second layer,yiwas the distance from the reference plane to the centroid of the ithlayer where i identifies the layer from 1 to n where n was defined as the number of layers in film stack, Eiwas the elastic modulus of the ithlayer, and Aiwas the cross sectional area of the ithlayer.

Table 4 provides a summary of the results andFIG. 5Cprovides a visual representation when the stiff layer added had an elastic modulus of 70 GPa.

TABLE 4Stiff Layer Thickness (cm)Position of Neutral Plane (cm)1.0E−49.04E−32.0E−49.82E−33.0E−41.04E−25.0E−41.12E−21.0E−31.24E−21.5E−31.31E−2

A stiff neutral plane adjusting layer was added to the top surface of the display layer described in Example 2. Movement of the neutral plane position relative to a reference plane was calculated based upon thickness of the stiff layer applied. The relationship used to calculate the shifting of the neutral plane position was described as:

yNP=∑i=1n⁢y_i⁢Ei⁢Ai∑i=1n⁢Ei⁢Ai
where yNPwas the position of the neutral plane measured from the reference plane such as the lower portion of the second layer460,yiwas the distance from the reference plane to the centroid of the ithlayer where i identifies the layer from 1 to n where n was defined as the number of layers in the film stack, Eiwas the Young's modulus of the ithlayer, and Aiwas the cross sectional area of the ithlayer.

Table 5 provides a summary of the results andFIG. 5Dprovides a visual representation when the stiff layer added had an elastic modulus of 70 GPa.

TABLE 5Stiff Layer Thickness (cm)Position of Neutral Plane (cm)1.0E−48.60E−32.0E−49.07E−33.0E−49.42E−35.0E−49.94E−31.0E−31.07E−21.5E−31.13E−2

Exemplary Embodiments

Embodiment A1. A flexible display, comprising: a plurality of functional layers comprising a display layer having a display component, a plurality of bonding layers comprising a bonding component, each of the plurality of bonding layers is disposed between two adjacent functional layers, and a stiff layer having an elastic modulus greater than an elastic modulus of each of the plurality of functional layers to adjust a position of a neutral plane of the flexible display within the display layer.

Embodiment A2. The flexible display of Embodiment A1, wherein the stiff layer is disposed below a first layer of the plurality of functional layers, the first layer above the display layer.

Embodiment A3. The flexible display of Embodiment A1 or 2, wherein the stiff layer is disposed above a second layer of the plurality of functional layers, the second layer below the display layer.

Embodiment A4. The flexible display of any one of Embodiments A1-A3, wherein the stiff layer is disposed below a second layer of the plurality of functional layers, the second layer below the display layer.

Embodiment A5. The flexible display of any one of Embodiments A1-A4, wherein a thickness of the stiff layer is selected at least in part based on at least one of the plurality of functional layers' elastic modulus.

Embodiment A6.The flexible display of any one of Embodiments A1-A5, wherein a thickness of the stiff layer is selected at least in part based on at least one of the plurality of functional layers' thickness.

Embodiment A7. The flexible display of any one of Embodiments A1-A6, wherein a thickness of the stiff layer is selected at least in part based on at least one of the plurality of bonding layers' elastic modulus.

Embodiment A8. The flexible display of any one of Embodiments A1-A7, wherein a thickness of the stiff layer is selected at least in part based on at least one of the plurality of bonding layers' thickness.

Embodiment A9. The flexible display of any one of Embodiments A1-A8, wherein the display component comprises an organic light-emitting device.

Embodiment A10. The flexible display of any one of Embodiments A1-A9, wherein the bonding component comprises at least one of acrylate, urethane, silicone, and polyolefin.

Embodiment A11. The flexible display of any one of Embodiments A1-A10, wherein at least one of the bonding layers comprising an interlocking device comprising a first interlocking component and a second interlocking component engaging with the first interlocking component.

Embodiment A12. The flexible display of Embodiment A11, wherein the interlocking device has a height no more than 10 mm.

Embodiment A13. The flexible display of Embodiment A11 or A12, wherein the interlocking device further comprises an optical coupler between the first interlocking component and the second interlocking component.

Embodiment A14. The flexible display of Embodiment A13, wherein the optical coupler is liquid, adhesive, gel, or a combination thereof.

Embodiment A15. The flexible display of Embodiment A13, wherein the optical coupler has a refractive index having an absolute different less than or equal to 0.05 from a refractive index of the interlocking device.

Embodiment A16. The flexible display of any one of Embodiments A11-A15, wherein the interlocking device is optically clear.

Embodiment A17. The flexible display of any one of Embodiments A11-A16, wherein the first or the second interlocking component comprises a plurality of engagement elements.

Embodiment A18. The flexible display of Embodiment A17, wherein at least some of the engagement elements has a cross-sectional shape having a stem and a cap wider than the stem.

Embodiment A19. The flexible display of any one of Embodiments A11-A18, wherein the first or the second interlocking component comprises a plurality of engagement rails.

Embodiment A20. The flexible display of Embodiment A19, wherein at least some of the engagement rails has a cross-sectional shape having a stem and a cap.

Embodiment A21. The flexible display of Embodiment A19, wherein at least some of the engagement rails has one or more slits.

Embodiment A22. The flexible display of any one of Embodiments A11-A21, wherein the first fastener comprises a set of first engagement elements and the second fastener comprises a set of second engagement elements.

Embodiment A23. The flexible display of Embodiment A15, wherein the first engagement elements have generally same shapes as the second engagement elements.

Embodiment A24. The flexible display of any one of Embodiments A11-A23, wherein the flexible display has an X axis and a Y axis generally perpendicular to the X axis, wherein the flexible display is configured to bend about the Y axis.

Embodiment A25. The flexible display of Embodiment A24, wherein the interlocking device is disposed along the X axis.

Embodiment A26. The flexible display of Embodiment A24, wherein the interlocking device comprises a first interlocking segment and a second interlocking segment, wherein the first interlocking segment is disposed approximate to a first edge along X axis of the flexible display and the second interlocking segment is disposed approximate to a second edge along X axis of the flexible display.

Embodiment A27. The flexible display of Embodiment A24, wherein the interlocking device comprises a plurality of interlocking segments.

Embodiment A28. The flexible display of Embodiment A26, wherein the plurality of interlocking segments are disposed in a pattern.

Embodiment A29. The flexible display of Embodiment A26, wherein at least two of the plurality of interlocking segments are generally parallel to each other.

Embodiment A30. The flexible display of Embodiment A26, wherein the plurality of interlocking segments are disposed with generally equal spacing along X axis and Y axis.

Embodiment A31. The flexible display of any one of Embodiments A1-A30, wherein at least one of the functional layers comprises at least one of a touch sensitive device, an electrical circuit, a battery, and a protection film.

Embodiment A32. The flexible display of any one of Embodiments A1-A31, wherein at least one of the bonding layers comprises an optical clear material.

Embodiment A33. The flexible display of Embodiment A31, wherein the optical clear material includes an optical clear adhesive, optical clear gel, or optical clear liquid.

Embodiment A34. The flexible display of any one of Embodiments A11-33, wherein the interlocking device is disposed outside viewing area.

Embodiment A35. The flexible display of Embodiment A32, wherein at least part of the interlocking device is disposed within viewing area.

Embodiment A36. The flexible display of Embodiment A35, wherein the at least part of the interlocking device disposed within viewing area is optically clear.

Embodiment A37. The flexible display of Embodiment A36, wherein the optical clear material has a refractive index having an absolute different less than or equal to 0.05 from a refractive index of the interlocking device.

Embodiment B1. A flexible display, comprising: a plurality of functional layers comprising a display layer having a display component, a plurality of bonding layers comprising a bonding component, each of the plurality of bonding layers is disposed between two adjacent functional layers, wherein at least one of the plurality of functional layers is nonplanar in an unstrained state.

Embodiment B2. The flexible display of Embodiment B1, wherein the at least one of the plurality of functional layers has a first part and a second part forming an angle with the first part when the at least one of the plurality of functional layers is in the unstrained state.

Embodiment B3. The flexible display of Embodiment B2, wherein the angle is less than 150°.

Embodiment B4. The flexible display of Embodiment B1, wherein the at least one of the plurality of functional layers has a wavy shape when the at least one of the plurality of functional layers is in the unstrained state.

Embodiment B5. The flexible display of any one of Embodiments B1-B4, wherein the at least one of the plurality of functional layers comprises a nonplanar substrate in an unstrained state.

Embodiment B6. The flexible display of any one of Embodiments B1-B5, wherein the at least one of the plurality of functional layers is not a protective layer.

Embodiment C1. A flexible display, comprising: a first layer and a second layer, a bonding layer disposed between the first layer and the second layer, wherein the bonding layer comprises an interlocking device, wherein the interlocking device comprises a first interlocking component attached to or integrated with the first layer and a second interlocking component attached to or integrated with the second layer configured to engage with the first interlocking component such that the engagement prevent the separation of the first layer from the second layer along a direction generally perpendicular to a surface of the second layer.

Embodiment C2. The flexible display of Embodiment C1, wherein the interlocking device has a height no more than 10 mm.

Embodiment C3. The flexible display of Embodiment C1 or C2, wherein the interlocking device further comprises an optical coupler between the first interlocking component and the second interlocking component.

Embodiment C4. The flexible display of Embodiment C3, wherein the optical coupler is liquid, adhesive, gel, or a combination thereof.

Embodiment C5. The flexible display of Embodiment C4, wherein the optical coupler has a refractive index having an absolute different less than or equal to 0.05 from a refractive index of the interlocking device.

Embodiment C6. The flexible display of any one of Embodiments C1-05, wherein the interlocking device is optically clear.

Embodiment C7. The flexible display of any one of Embodiments C1-C6, wherein the first or the second interlocking component comprises a plurality of engagement elements.

Embodiment C8. The flexible display of Embodiment C7, wherein at least some of the engagement elements form a sliding channel.

Embodiment C9. The flexible display of Embodiment C7, wherein at least some of the engagement elements has a cross-sectional shape having a stem and a cap wider than the stem.

Embodiment C10. The flexible display of any one of Embodiments C1-C9, wherein the first or the second interlocking component comprises a plurality of engagement rails.

The flexible display of Embodiment C10, wherein at least some of the engagement rails has a cross-sectional shape having a stem and a cap.

Embodiment C12. The flexible display of Embodiment C10, wherein at least some of the engagement rails has one or more slits.

Embodiment C13. The flexible display of any one of Embodiments C1-C12, wherein the first fastener comprises a set of first engagement elements and the second fastener comprises a set of second engagement elements.

Embodiment C14. The flexible display of Embodiment C13, wherein the first engagement elements have generally same shapes as the second engagement elements.

Embodiment C15. The flexible display of any one of Embodiments C1-C14, wherein the flexible display has a X axis and a Y axis generally perpendicular to the X axis, wherein the flexible display is configured to bend about the Y axis.

Embodiment C16. The flexible display of Embodiment C15, wherein the interlocking device is disposed along the X axis.

Embodiment C17. The flexible display of Embodiment C15, wherein the interlocking device comprises a first interlocking segment and a second interlocking segment, wherein the first interlocking segment is disposed approximate to a first edge along X axis of the flexible display and the second interlocking segment is disposed approximate to a second edge along X axis of the flexible display.

Embodiment C18. The flexible display of Embodiment C15, wherein the interlocking device comprises a plurality of interlocking segments.

Embodiment C19. The flexible display of Embodiment C18, wherein the plurality of interlocking segments are disposed in a pattern.

Embodiment C20. The flexible display of Embodiment C18, wherein at least two of the plurality of interlocking segments are generally parallel to each other.

Embodiment C21. The flexible display of Embodiment C18, wherein the plurality of interlocking segments are disposed with generally equal spacing along X axis and Y axis.

Embodiment C22. The flexible display of any one of Embodiments C1-C21, wherein at least one of the first layer and the second layer comprises at least one of a touch sensitive device, an electrical circuit, a battery, and a protection film.

Embodiment C23. The flexible display of any one of Embodiments C1-C22, wherein at least one of the first layer and the second layer comprises an organic light-emitting device.

Embodiment C24. The flexible display of any one of Embodiments C1-C23, wherein the bonding layer comprises an optical clear material.

Embodiment C25. The flexible display of Embodiment C24, wherein the optical clear material includes an optical clear adhesive, optical clear gel, optical clear elastomer, or optical clear liquid.

Embodiment C26. The flexible display of any one of Embodiments C1-C25, wherein the interlocking device is disposed outside viewing area.

Embodiment C27. The flexible display of Embodiment C24, wherein at least part of the interlocking device is disposed within viewing area.

Embodiment C28. The flexible display of Embodiment C27, wherein the at least part of the interlocking device disposed within viewing area is optically clear.

Embodiment C29. The flexible display of Embodiment C28, wherein the optical clear material in the bonding layer has a refractive index having an absolute different less than or equal to 0.05 from a refractive index of the interlocking device.

The present invention should not be considered limited to the particular examples and embodiments described above, as such embodiments are described in detail to facilitate explanation of various aspects of the invention. Rather the present invention should be understood to cover all aspects of the invention, including various modifications, equivalent processes, and alternative devices falling within the spirit and scope of the invention as defined by the appended claims and their equivalents.