Patterned adhesive

Abstract

A patterned adhesive useful for foldable electronic display applications is provided. The patterned adhesive includes a center adhesive layer and a pair of edge adhesive layers. The pair of edge adhesive layers extends along and adjacent opposite sides of the central adhesive layer in an alternating stripe pattern. Optionally, the ratio of shear moduli between the center adhesive layer and each edge adhesive layer is from 2: 1 to 10: 1, or vice versa, measured by dynamic mechanical analysis at a frequency of 1 Hz and a temperature of 25 DEG C. Further, the center adhesive layer exhibits a difference between a refractive index of the center adhesive layer and a refractive index of the edge adhesive layer of within 0.015 as measured at a wavelength of light of 532 nm, and the center adhesive layer and the edge adhesive layer each exhibit a glass transition temperature of at most-30 DEG C.

Description

Technical Field

[0001] Patterned adhesive compositions and articles are provided. These adhesive compositions and articles can be used to bond optical films in electronic display applications. Background Technology

[0002] Optically clear adhesives (OCAs) have diverse applications in consumer, industrial, and automotive display technologies. These adhesives have become the preferred bonding solution for a number of reasons, including high adhesion and cohesion, protective properties, and enhanced touchscreen performance when devices transition from resistive to capacitive touch technologies. Desired properties of OCAs may include optical transparency and high interfacial adhesion over a wide temperature range.

[0003] Foldable touchscreen displays typically have a multi-layered configuration, with some layers providing protection against impacts and mechanical forces during bending. Some layers have more than one function—for example, such layers may include polarizers, structural films, thin glass, and metal layers. The properties of these functional films during repeated bending can lead to highly specialized mechanical property requirements unique to the display industry.

[0004] When a membrane bends, the inner surface experiences compression, while the outer surface is under tension. The point within the membrane where these forces are in equilibrium (where strain is neutral) is called the neutral plane. Typically, the neutral plane will be located at the midpoint of the membrane thickness, but in a multilayer system, one or more precise locations can be controlled using an OCA (Optical Coefficient of Motion). Summary of the Invention

[0005] Certain layers in displays, such as OLED packages, transistor control planes, polarizers, or touch panels, can withstand a limited range of bending strain before yielding or breaking. OCAs with low modulus undergo large shear displacements during bending, rather than applying shear and bending stresses to the harder layers bonded together by the adhesive. In this way, OCAs with low modulus can create multiple neutral planes in the lamination system, allowing the harder layers (e.g., functional films) to bend more independently, while the OCA shears around them. Therefore, OCAs with appropriate stiffness can be used to adjust the position of the neutral planes closest to these sensitive layers. Minimizing bending strain on the sensitive layers improves the durability and reliability of the entire laminate (e.g., an electronic display) during folding.

[0006] To meet these technical requirements, foldable OCAs tend to have more extreme properties than traditional requirements, such as low haze and high adhesion. For example, the OCA should have high elasticity to avoid deformation. It must also exhibit a low shear modulus. In particular, it should be able to bend over a wide temperature range while mechanically decoupling the adhesive layers from each other, which also indicates the need for materials with low glass transition temperatures. The adhesive's T... gThis limits the range of modulus and therefore the range of flexural stiffness that increases sharply with cooling. Slightly opposite to the above, the adhesive must also maintain high interfacial adhesion over a wide temperature range, even for low T... g Low-modulus pressure-sensitive adhesives are often very challenging. Furthermore, stiffer OCAs can benefit from improved folding performance by resisting buckling and cavitation. Therefore, the challenge of achieving neutral-plane equilibrium for folding involves minimizing the difference in adhesive modulus over the operating temperature range without reducing the modulus to a level where buckling and cavitation could induce other failure modes.

[0007] These design constraints can be balanced by using multi-material constructions. One such construction would be the patterning of different materials or the different mechanical properties within a single material, to better address the material challenges of a dynamically folding device. However, designing and pairing material groups with complementary mechanical properties required to achieve the desired behavior within the device, as well as handling and positioning the materials, makes the spatial pattern invisible to the naked eye when observing the device, both extremely difficult.

[0008] The provided adhesive articles utilize different adhesive compositions within spatially patterned adhesive articles to offer surprising technical benefits for the construction of foldable electronic displays. Patterned arrays with different mechanical properties within a single adhesive layer are practical in balancing the properties required for complex foldable display elements. In some cases, the degree of elasticity or stiffness / modulus of the material is manipulated through a patterned exposure curing step. In others, different materials are coated or treated together in a manner that produces the desired patterned effect. The provided adhesives emphasize that it is insufficient to have different moduli only in the target areas of the foldable stack; rather, it is important to maintain a low TT even within materials of different moduli. g This allows the device to exhibit good folding performance over a wide range of operating temperatures.

[0009] In T g When the change is very small, especially when T g Manipulating the general modulus of polymer materials at temperatures far below ambient temperature is technically challenging. Furthermore, designing where the modulus of patterned material groups can be systematically varied while maintaining a relatively consistent and matched refractive index (except for T) g Other solutions (beyond which) may be even more difficult. The provided adhesive articles utilize a group of materials in which multiphase and single-phase adhesive compositions are integrated to achieve a wide range of moduli while enabling other properties (such as T...) gThe variation in refractive index is minimized. Ultimately, this enables high levels of folding performance over a wide range of operating temperatures, while minimizing haze and optical defects. The deployment of these material groups in the patterned adhesive is unique and highly practical in addressing some of the challenging design constraints of adhesives used in the construction of foldable displays.

[0010] In a first aspect, a patterned adhesive is provided, comprising: a central adhesive layer; a pair of edge adhesive layers extending along opposite sides of the central adhesive layer in an alternating stripe pattern and adjacent to opposite sides of the central adhesive layer; optionally, wherein the ratio of the shear modulus between the central adhesive layer and each edge adhesive layer is from 2:1 to 10:1, or vice versa, the shear modulus being measured by dynamic mechanical analysis at a frequency of 1 Hz and a temperature of 25 °C; wherein, if measured at a light wavelength of 532 nm, the difference between the refractive index of the central adhesive layer and the refractive index of the edge adhesive layer is within 0.015; and further wherein the glass transition temperature of each of the central adhesive layer and the edge adhesive layer is at most -30 °C.

[0011] In a second aspect, a patterned adhesive is provided, comprising: a central adhesive layer; a pair of intermediate adhesive layers, the pair of edge adhesive layers extending along and adjacent to opposite sides of the central adhesive layer; and a pair of edge adhesive layers extending along and adjacent to opposite sides of the intermediate adhesive layers in an ABCBA stripe pattern; optionally, wherein the ratio of the shear modulus between the central adhesive layer and each edge adhesive layer is from 2:1 to 10:1, or vice versa, the shear modulus being measured by dynamic mechanical analysis at a frequency of 1 Hz and a temperature of 25 °C; wherein, if measured at a light wavelength of 532 nm, the difference between the refractive index of the central adhesive layer and the refractive index of the edge adhesive layer is within 0.015; wherein each of the intermediate adhesive layers exhibits a refractive index between the refractive indices of the adjacent central adhesive layer and the edge adhesive layer; and further wherein each of the central adhesive layer, intermediate adhesive layer, and edge adhesive layer exhibits a glass transition temperature of at most -30 °C. Attached Figure Description

[0012] Figure 1 This is a plan view of an adhesive article according to an exemplary embodiment.

[0013] Figure 2 It shows a folded configuration. Figure 1 A perspective view of the components of the product.

[0014] Figure 3 and Figure 4This is a perspective view showing components of corresponding adhesive articles in a folded configuration according to various embodiments.

[0015] Figure 5 It is used for manufacturing Figures 1 to 4 A schematic diagram of the method for producing the product.

[0016] Figure 6 This is a perspective view showing the components of an adhesive article according to another exemplary embodiment.

[0017] Figure 7 It shows a folded configuration. Figure 6 A side view of the components of the product.

[0018] Figure 8 It is used for manufacturing Figure 7 A schematic diagram of the methods of the component.

[0019] Figure 9 It is a side view of an adhesive article component showing both its folded and unfolded configurations.

[0020] Figure 10 yes Figure 9 An enlarged side view of the component, which identifies certain dimensions related to the adhesive layer therein.

[0021] Figures 11A to 11C The equivalent strain and hydrostatic stress distributions of three different components with the same geometry but different only in their respective adhesive compositions are shown.

[0022] Reference numerals used repeatedly in the specification and drawings are intended to denote the same or similar features or elements of this disclosure. It should be understood that those skilled in the art can devise many other modifications and embodiments that fall within the scope and spirit of the principles of this disclosure. The drawings are not to scale.

[0023] definition

[0024] As used in this article: "alkyl" refers to a monovalent group that is a free radical of an alkane and includes straight-chain, branched, cyclic, and bicyclic alkyl groups, as well as combinations thereof, including both unsubstituted and substituted alkyl groups. Unless otherwise specified, alkyl groups typically contain 1 to 30 carbon atoms. In some embodiments, alkyl groups contain 1 to 20 carbon atoms, 1 to 10 carbon atoms, 1 to 6 carbon atoms, 1 to 4 carbon atoms, or 1 to 3 carbon atoms. Cyclic groups can be monocyclic or polycyclic and typically have 3 to 10 cyclic carbon atoms. Examples of "alkyl" groups include methyl, ethyl, n-propyl, n-butyl, n-pentyl, isobutyl, tert-butyl, isopropyl, n-octyl, n-heptyl, ethylhexyl, cyclopentyl, cyclohexyl, cycloheptyl, adamantyl, and norbornyl.

[0025] "Allyl" refers to a functional group with the formula CH2=CH-CH2-.

[0026] "Environmental conditions" refers to a temperature of 23°C and a pressure of 103.4 kPa.

[0027] "Ambient temperature" means 23℃.

[0028] "Cure" refers to linking polymers together through covalent chemical bonds (usually via crosslinking molecules or groups) to form a network polymer. Therefore, in this disclosure, the terms "cured" and "crosslinked" are used interchangeably. Cured or crosslinked polymers are typically characterized by insolubility, but can be swollen in the presence of a suitable solvent.

[0029] "Cureable" refers to a composition that can be cured.

[0030] "Glass transition temperature" (or "T") g The temperature at which an amorphous polymer changes from a hard / glassy state to a more flexible rubbery state, or vice versa, is determined by performing a dynamic mechanical analysis (or "DMA") temperature scan at a given frequency. According to this technique, T... g It can be defined as tan The temperature at which the peak value is reached.

[0031] "(Meth)acrylate" refers to a functional group of acrylate group with the formula CH2=CH-C(O)O- or methacrylate group with the formula CH2=C(CH3)-C(O)O-. Detailed Implementation

[0032] As used herein, the terms "preferred" and "ideally" refer to embodiments described herein that provide certain benefits in certain circumstances. However, other embodiments may also be preferred in the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of the invention.

[0033] As used herein and in the appended claims, unless the context clearly indicates otherwise, the singular forms “a” and “the” include plural objects. Thus, by way of example, references to “a” or “the” component may include one or more components known to those skilled in the art and their equivalents. Additionally, the term “and / or” means one or all of the listed elements or a combination of any two or more of the listed elements.

[0034] It is important to note that when the term "comprising" and its variations appear in the appended specification, these terms are not intended to be limiting. Furthermore, "a," "an," "the," "at least one," and "one or more" are used interchangeably herein. Relative terms such as left, right, forward, backward, top, bottom, side, upper, lower, horizontal, vertical, etc., may be used herein, and if so, they are derived from the perspective observed in the specific drawings. However, these terms are used only for simplicity of description and are not intended to limit the scope of the invention in any way.

[0035] Throughout this specification, references to "one embodiment," "some embodiments," "one or more embodiments," or "implementation" are intended to indicate that a specific feature, structure, material, or characteristic described with respect to that embodiment is included in at least one embodiment of the invention. Therefore, phrases appearing in various places throughout this specification, such as "in one or more embodiments," "in some embodiments," "in one embodiment," or "in an embodiment," do not necessarily refer to the same embodiment of the invention.

[0036] Layered structure

[0037] Exemplary adhesive articles incorporated into the provided adhesive composition Figure 1As shown in the figure, and hereinafter referred to by the numeral 100, the article 100 includes a composite layer 101 consisting of three spatially separated layers with an alternating stripe pattern. These layers include a central adhesive layer 102 and a pair of edge adhesive layers 104, forming the central stripe and the outer stripe, respectively. Each of the edge adhesive layers 104 extends along a common edge 106 along the central adhesive layer 102 and directly contacts the central adhesive layer. The article 100 is optically transparent, with a haze value equal to or less than 0.5% for an adhesive 50 micrometers thick.

[0038] In the depicted embodiments, the adhesive article 100 is intended for use in foldable electronic displays or other foldable components, and is therefore characterized by a folding axis 108. Optionally and as shown, the central adhesive layer 104 and the edge adhesive layers 102, 104 are arranged symmetrically around the folding axis 108.

[0039] In the provided striped configuration, the shear modulus differs significantly between the central adhesive layer and each edge adhesive layer. In some embodiments, the ratio of the shear modulus between the central adhesive layer and each edge adhesive layer is in the range of 2:1 to 10:1, or alternatively, the ratio of the shear modulus between each edge adhesive layer and the central adhesive layer is in the range of 2:1 to 10:1. As mentioned above, the shear modulus is measured by dynamic mechanical analysis at a frequency of 1 Hz and a temperature of 25 °C.

[0040] Preferably, as measured at a light wavelength of 532 nm, the difference in refractive index between the central adhesive layer and the edge adhesive layer is within 0.015, more preferably within 0.010, and most preferably within 0.005. The provided composition also enables the central adhesive layer and the edge adhesive layer to achieve the aforementioned difference in shear modulus, wherein each layer exhibits a low Ti. g In various embodiments, the T1 of the center adhesive layer and the edge adhesive layer are respectively... g It can be up to -30℃, up to -35℃ or up to -40℃.

[0041] A surprising technical benefit of this configuration is the ability to tailor the properties of the OCA in the foldable device to optimize the mechanical properties of both the folded and unfolded areas of the electronic display without causing observable visual defects. For example, the folded area can be provided with a multiphase adhesive with a relatively low shear modulus, creating multiple neutral planes along the thickness dimension, while the unfolded area can be provided with a higher shear modulus and have only a single neutral plane.

[0042] Multiple neutral planes allow the multilayer film within a region to bend almost independently, thereby minimizing strain on the mechanically sensitive layer. At the same time, a single neutral plane can benefit the non-bending areas of the display by resisting deformation from buckling, cavitation, and projectile impacts.

[0043] The strip represented by the central adhesive layer 104 and the edge adhesive layer 102 can have any lateral width suitable for the current application. To accommodate the bending of the adhesive when the device is folded, the central adhesive layer 102 can have a lateral width of 2 mm to 100 mm, 4 mm to 50 mm, 6 mm to 30 mm, or in some embodiments, less than, equal to, or greater than 2 mm, 3 mm, 4 mm, 5 mm, 7 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, 65 mm, 70 mm, 75 mm, 80 mm, 85 mm, 90 mm, 95 mm, or 100 mm. The size of the edge adhesive layer 104 is typically set based on the overall dimensions of the display.

[0044] The relative sizes of the center adhesive layer 104 and the edge adhesive layer 102 are not particularly limited. Relative to each other, the center adhesive layer 102 may have a lateral width of 1% to 99%, 10% to 50%, 10% to 20% of the total composite layer 101, or in some embodiments, less than, equal to, or greater than 1%, 2%, 3%, 5%, 7%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 60%, 70%, 80%, 90%, 95%, 97%, or 99%, where the remainder is constituted by the edge adhesive layer 104. As used above, the term "lateral width" refers to the stripe width and is therefore measured in a plan view perpendicular to the fold axis 108.

[0045] For display applications, it is generally desirable that the adhesive layers 102 and 104 have consistent thicknesses to ensure a uniform thickness of the composite layer over its entire area. In various embodiments, these layers may have thicknesses ranging from 5 micrometers to 200 micrometers, 15 micrometers to 150 micrometers, 25 micrometers to 75 micrometers, or in some embodiments, thicknesses less than, equal to, or greater than 5 micrometers, 10 micrometers, 15 micrometers, 20 micrometers, 25 micrometers, 30 micrometers, 35 micrometers, 40 micrometers, 45 micrometers, 50 micrometers, 75 micrometers, 100 micrometers, 150 micrometers, or 200 micrometers.

[0046] Figure 2A partial view of the adhesive article 100 is shown, in which the composite layer 101 is partially peeled off and folded back onto itself at a 180° angle. In this illustration, the composite layer 101 is part of component 150, wherein the composite layer 101 is disposed between an upper release liner 110 and a lower release liner 112. The upper release liner 110 and the lower release liner 112 have direct contact with the main surface of the composite layer 101 to facilitate the handling and storage of the adhesive.

[0047] Figure 3 An assembly 250 including an adhesive article 200 is shown. The adhesive article 200 includes two layers: a composite layer 201 laminated together and a monolithic layer 203. The composite layer 201 has a configuration similar to that of the composite layer 101 and includes a central adhesive layer 202 side-attached by an edge adhesive layer 204. The monolithic layer 203 extends co-existing with the composite layer 201 and has a uniform composition throughout the layer. In a preferred embodiment, the composition of the monolithic layer is equivalent to that of the edge adhesive layer 204, such that the composition does not change along the thickness dimension along the area corresponding to the edge adhesive layer 204.

[0048] As shown in the figure, the upper release liner 210 is retained along the top main surface of the adhesive layer 200, but the lower release liner has been removed and the adhesive article 200 has been adhesively bonded to the substrate 214. The substrate 214 can be any of many suitable adhesives, such as a glass layer or a functional film. Available functional films can be made of polyethylene terephthalate, polyimide, cyclic olefin polymer (COP), multilayer optical film (MOF), or polarizing film.

[0049] Figure 4 Component 350 is shown, and this component is Figure 3 A variation of the component provided differs in that the order of the composite layer 301 and the monolithic layer 303 within the adhesive article 300 is reversed. While the composite layer 201 contacts the substrate 214 in component 250, the monolithic layer 303 contacts the substrate 314 in component 350. Other aspects of component 350 are similar to those already described and need not be repeated. In these embodiments, the monolithic carrier layer can increase the stability of the composite coating of different formulations or fluids, particularly in the area between the die exit and the web.

[0050] Figure 5An exemplary apparatus 160 is shown capable of manufacturing the composite layer as described above using a continuous process. In this process, polymer coating solutions 170, 172, corresponding to the central adhesive layer 102 and the edge adhesive layer 104, respectively, are guided into a feed block and then discharged through an extrusion die 162 onto a moving release liner 112 wrapped around a casting roller 166, as shown. The coated web is then conveyed to a curing station 168, which exposes the coated web to ultraviolet light or other photochemical radiation to functionally cure the polymer coating solution. As previously described, the polymer coating solution itself may include components that are partially or fully cured to adjust viscosity and facilitate the casting of a uniform film onto the release liner 112.

[0051] Figure 6 A variation of the existing component is shown. In this figure, component 450 of composite layer 400, where the adhesive layer is disposed on release liner 412, is shown. While composite layer 400 has a striped pattern (with a center layer 402 situated between a pair of edge layers 404), it also includes an additional pair of stripes. These additional stripes are represented by an intermediate layer 420 situated between the center layer 402 and the edge layers 404, as shown, to provide an ABCBA striped pattern. It may be advantageous for the intermediate layer 420 to have a blended composition obtained by mixing the compositions used to manufacture the center layer 402 and the edge layers 404 prior to curing.

[0052] It is expected that some degree of mixing of the coating composition will occur at the stripe boundaries after casting and before curing. However, where even minute differences in refractive index are visually perceptible, the inclusion of the intermediate layer 420 can facilitate a smoother transition in optical and / or mechanical properties between the central layer 402 and the edge layer 404.

[0053] Alternative embodiments are also possible. These embodiments may use a set of adhesive materials that utilizes a reinforcing adhesive composition in the transition zone represented by the intermediate layer 420. Surprisingly, it has been found that using a higher modulus reinforcing adhesive in this transition zone, while using a central and outer region comprising a relatively lower modulus adhesive, provides an enhanced decoupling effect between layers along the area most needed, while still enhancing resistance to buckling or deflection in a direction perpendicular to the composite thickness. This will be discussed later in the references. Figures 11A to 11C The effects of this technique will be illustrated with examples in upcoming chapters.

[0054] Figure 7Component 550 is shown, wherein the adhesive article represented by composite layer 400 is sandwiched between release liner pads 410, 412 and folded over itself at a 180° folding angle. As shown, the folded area is entirely within the central layer 402, wherein both the intermediate layer 420 and the edge layer 404 extend approximately along the planar region of component 550 when in their folded configuration.

[0055] Figure 8 An apparatus and process 560 for manufacturing component 550 are shown. In an exemplary method, polymer coating solutions are provided in reservoirs 570, 572, and 574 corresponding to the center layer 402, edge layer 404, and intermediate layer 420, respectively. As shown, these polymer coating solutions are then conveyed using a pump 575 to a feed block and die 562, which divides the flow into a predetermined stripe pattern. The die 562 dispenses the solution onto a release liner 564 backed by a casting roller 566, as shown, to provide a coated web 567. Optionally and as shown, the upper release liner 510 may be applied to the exposed top surface of the coated web 567 using a roller 576 before the coated web cures through photochemical radiation via the upper release liner 510 as it passes under a curing station 568. The pressure applied by the roll 576 to the casting roll 566 can be appropriately adjusted to obtain the desired thickness of the adhesive article.

[0056] Figure 9 An adhesive assembly 950 in folded and unfolded configurations is shown. As shown, assembly 950 includes an adhesive article 900 bonded to a pair of fixing plates 914. The fixing plates 914 are bonded along the end regions of the adhesive article 900, while they are not bonded along the central region. In its folded configuration, the folded region of assembly 950 has a teardrop shape, characterized by a half-gap thickness “d”. It was found that the bonding interface between the adhesive and the adherend experiences maximum hydrostatic tension near the inflection point of assembly 950, which is defined as the point where the layer transitions from concave to convex. Furthermore, it was found that using an adhesive with a relatively high modulus (relative to those in the central and outer regions) along these regions provides a reinforcing effect, enabling enhanced resistance to cavitation and bubbling defects through repeated folding and unfolding of assembly 950.

[0057] Figure 10 A partial view of component 950 is shown, defining three spatial regions along component 950—“A”, “B”, and “C”—corresponding to the central region, intermediate region, and outer region, respectively. Component 950 includes an adhesive article 900 bonded to a fixing plate 914, which extends only a portion of the length of article 900. In this figure, “W” represents the lateral dimension of the intermediate adhesive layer, and “d” represents the degree of overlap between the intermediate adhesive layer and the fixing plate.

[0058] In a preferred embodiment, as measured by dynamic mechanical analysis under environmental conditions and at 1 Hz, the shear modulus of the central adhesive layer and the edge adhesive layer are each between 10 kPa and 100 kPa, or in some embodiments, less than, equal to, or greater than 10 kPa, 15 kPa, 20 kPa, 25 kPa, 30 kPa, 35 kPa, 40 kPa, 45 kPa, 50 kPa, 55 kPa, 60 kPa, 65 kPa, 70 kPa, 75 kPa, 80 kPa, 85 kPa, 90 kPa, 95 kPa, or 100 kPa.

[0059] In a preferred embodiment, as measured by dynamic mechanical analysis under environmental conditions and at 1 Hz, each intermediate adhesive layer may exhibit a shear modulus that is 2 to 500 times, 5 to 100 times, and 10 to 50 times greater than the shear modulus of the center adhesive layer and the edge adhesive layer, respectively; or in some embodiments, less than, equal to, or greater than 2, 3, 5, 7, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 120, 150, 170, 200, 250, 300, 350, 400, 450, or 500 times.

[0060] When bent, the composite adhesive assembly exhibits a neutral plane, which is the location where the axial strain along the thickness is zero. At this location, the shear strain is typically at its maximum. When a low-modulus layer is added, an additional neutral plane can be formed when the structure bends, which partially decouples the regions above and below the low-modulus layer. Advantageously, this allows for shear decoupling between the layers.

[0061] Figures 11A to 11C Three columns of diagrams are shown representing three corresponding adhesive assemblies. Each assembly comprises four adhesive layers laminated alternately onto five adhesive layers. The three assemblies differ in the composition of their adhesive layers but are identical in all other respects. Each column shows three vertically arranged diagrams, with the top diagram showing the equivalent strain distribution along the layers, the middle diagram showing the hydrostatic stress distribution along the layers, and the bottom diagram showing the flexural strain as a function of distance from the bottom main surface of the adhesive assembly.

[0062] Equivalent strain distribution, hydrostatic stress distribution, and bending strain are calculated using a two-dimensional planar finite element analysis (FEA) model simulating a folded panel configuration. The adhesive modulus is fitted to a finite strain viscoelastic model, a model that captures both viscoelastic (relaxation) and hyperelastic (nonlinear large strain) properties. A simplified polynomial hyperelastic function is used to represent the instantaneous modulus function as a function of strain. Figure 10 As defined in the documentation, in this FEA model, W is 5 mm and d is 1 mm.

[0063] Figure 11A An adhesive assembly (i.e., an unpatterned adhesive) with a uniform adhesive composition on the entire main surface of each adhesive layer is shown, the adhesive having a given baseline modulus. Figure 11B An adhesive assembly is shown that includes an intermediate adhesive along region B (region 916), which is 5 mm wide and has a modulus that is 10 times higher (i.e., harder) than the baseline modulus of the adjacent central adhesive layer and outer adhesive layer along regions A and C, respectively. Figure 11C An adhesive assembly is shown, wherein the modulus of the overall adhesive extending along regions A and B (collectively referred to as region 918) is 10 times greater than the baseline modulus of the outer adhesive along region C.

[0064] like Figures 11A to 11C The distribution reveals that for the overall configuration ( Figure 11A ) and configurations with reinforced transition regions ( Figure 11B The degree of strain and hydrostatic stress in the transition zone is much greater than in configurations with reinforced centers and transition zones. Figure 11C The superior properties offered by the first two adhesives are also evident in the flexural strain chart, which shows the smaller negative flexural strain of these compositions. The differences are particularly significant in regions far from the bottom surface of the component (e.g., region 920). These data distributions indicate... Figure 11A and Figure 11B The strong decoupling effect between layers in the configuration. Figure 11B The configuration is superior Figure 11A A significant benefit of this configuration is the enhanced modulus in the transition zone, which enables stronger adhesive bonding.

[0065] Adhesive composition

[0066] The center adhesive layer and the edge adhesive layer can be made from any number of various adhesive compositions known in the art.

[0067] In some embodiments, the central adhesive layer has a multiphase composition, while each of the edge adhesive layers has a single-phase composition. Alternatively, each edge adhesive layer has a multiphase composition, while the central adhesive layer has a single-phase composition. The multiphase and single-phase compositions are typically derived from acrylic polymers with optional alternative polymer additives to act as a second phase.

[0068] Useful multiphase compositions include biphase compositions. A biphase composition may have a primary phase and a secondary phase, wherein the secondary phase has a size scale in the micrometer range. For example, the secondary phase may exist in a discrete domain uniformly dispersed within a continuous primary phase. The median lateral size of the discrete domain may range from 0.1 μm to 25 μm, 0.5 μm to 10 μm, 1 μm to 5 μm, or in some embodiments, less than, equal to, or greater than 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.7 μm, 1 μm, 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, or 25 μm. Although less common, the secondary phase may also be bicontinuous with the primary phase.

[0069] The minor phase may comprise 0.5% to 40% by weight, 1% to 30% by weight, 2% to 15% by weight, or in some embodiments, less than, equal to or greater than 0.5% by weight, 1% by weight, 2% by weight, 5% by weight, 10% by weight, 15% by weight, 20% by weight, 25% by weight or 30% by weight, relative to the total weight of the biphase composition.

[0070] During folding or unfolding events, the composite layer is expected to undergo significant deformation and generate stress. The resistance to these stresses will be determined in part by the modulus and thickness of the layers (including the composite layer) of the foldable display.

[0071] To ensure low resistance to folding during bending events and sufficient performance to generate minimal stress and good stress dissipation, the composite layer has a sufficiently low storage modulus or elastic modulus, typically characterized as the shear storage modulus (G'). To further ensure consistent behavior over the intended operating temperature range of such devices, minimal variation in G' exists over a wide and relevant temperature range. In one embodiment, the relevant temperature range is between about -30°C and about 90°C. In one embodiment, the shear modulus is less than about 2 MPa, particularly less than about 1 MPa, and more particularly less than about 0.5 MPa, within the relevant temperature range. Therefore, it is preferable to use T... g (The temperature at which the material transitions to the glassy state, where G' correspondingly changes to a value typically greater than about 10⁷ Pa) is outside and below the relevant operating range. In one embodiment, the T of the composite layer in the flexible display... gLess than about -20°C, especially less than about -30°C, and even more especially less than about -35°C.

[0072] In one embodiment, the composite layer also exhibits relatively low creep to avoid persistent deformation in the multilayer composite material displayed after repeated folding or bending events. Material creep can be determined by a simple creep test in which a constant shear stress is applied to the material for a given amount of time. Once the stress is removed, the recovery of the induced strain is observed. In one embodiment, the shear strain recovers to at least about 50%, particularly at least about 60%, about 70%, and about 80%, and more particularly at least about 90%, of the peak strain observed when the shear stress was applied within 1 minute after the applied stress is removed at room temperature. This test is typically performed at room temperature, but can also be performed at any temperature associated with the use of the flexible device.

[0073] Multiphase adhesive composition

[0074] In some embodiments, the multiphase composition is based on a crosslinked network of polyvinyl acetal and acrylic acid copolymer obtained by reacting functionalized polyvinyl acetal with acrylic acid monomers. In some embodiments, the functionalized polyvinyl acetal may be reacted with a mixture of two or more different acrylic acid monomers.

[0075] Polyvinyl acetal is a class of useful polymers derived from the condensation reaction between polyvinyl alcohol and an aldehyde (usually formaldehyde). The resulting material exhibits excellent chemical resistance, good mechanical properties, and excellent thermal stability, making it suitable for various technical applications.

[0076] Polyvinyl acetal is known to be used in the production of various engineering plastics. Its excellent thermal stability allows it to withstand high temperatures without significant degradation, making it suitable for applications where heat resistance is critical. Furthermore, it exhibits good mechanical strength and dimensional stability, making it valuable in the production of components and parts for various industries, including automotive, electrical, and consumer goods.

[0077] Polyvinyl acetal can be prepared by saponifying polyvinyl acetate to obtain polyvinyl alcohol, followed by acetalizing the polyvinyl alcohol with an aldehyde in the presence of a catalyst. The degree of saponification of polyvinyl alcohol is not particularly limited and is generally in the range of 70 mol% to 99.9 mol%. Preferably, the degree of saponification is 70 mol% to 99.9 mol%, and more preferably 80 mol% to 99.8 mol%.

[0078] When acetalizing polyvinyl alcohol with aldehyde in the presence of a catalyst, a solution containing polyvinyl alcohol can be used. An exemplary solvent for using a solution containing polyvinyl alcohol is water.

[0079] Aldehydes are not particularly limited. Generally, C1-C10 aldehydes are advantageously used. C1-C10 aldehydes are not particularly limited and can be linear or branched aldehydes. Examples include n-butyraldehyde, isobutyraldehyde, n-pentanaldehyde, 2-ethylbutyraldehyde, n-hexanaldehyde, n-octanaldehyde, n-nonanaldehyde, n-decanaldehyde, formaldehyde, acetaldehyde, and benzaldehyde. Aldehydes can be used alone or in combination of two or more of them. Preferred among these are n-butyraldehyde, n-hexanaldehyde, and n-pentanaldehyde, with n-butyraldehyde being more preferred.

[0080] In some embodiments, polyvinyl acetal includes polyvinyl butyral (where the aldehyde is n-butyral, and the polyvinyl acetal is referred to as polyvinyl butyral). The use of polyvinyl butyral allows for adequate adhesion to glass, resulting in better lightfastness and weather resistance. Two or more types of polyvinyl acetal may optionally be used in combination.

[0081] In some embodiments, polyvinyl acetal can be functionalized by reacting it with ethyl isocyanate or allyl isocyanate in the presence of a suitable catalyst and acrylic monomers. This reaction provides a polyvinyl acetal backbone having side-chain (meth)acrylate or allyl groups. These side-chain functional groups can then be copolymerized with any number of other acrylic monomers. Based on the total weight of the polyvinyl acetal, ethyl isocyanate or allyl isocyanate can be present in any weight percentage to appropriately produce the desired functionality. For example, relative to the amount of polyvinyl acetal, ethyl isocyanate or allyl isocyanate can be present in amounts from 0.1 wt% to 15 wt%, 0.3 wt% to 13 wt%, 0.5 wt% to 10 wt%, or in some embodiments, in amounts less than, equal to, or greater than 0.1 wt%, 0.3 wt%, 0.5 wt%, 1 wt%, 3 wt%, 6 wt%, 10 wt%, 13 wt%, or 15 wt%.

[0082] If the degree of reactive functionalization of polyvinyl acetal is too high, the multiphase adhesive may become highly crosslinked, resulting in a loss of adhesive properties. However, adhesive compositions with too low a degree of polyvinyl acetal can reduce the compatibility between the acrylic polymer and the PVA polymer, which may produce undesirable haze. Additional hydroxyl reactive compounds containing copolymerizable or crosslinkable functional groups can be used. A sufficient degree of side-chain crosslinkable functional groups allows the functionalized polyvinyl acetal to act as a crosslinking agent to form a crosslinked network even when reacting with monofunctional acrylic monomers.

[0083] Once functionalized, polyvinyl acetal can then react with one or more acrylic monomers to form a crosslinked network comprising the functionalized polyvinyl acetal and an acrylic copolymer. The acrylic copolymer is typically a random copolymer, but suitable copolymers may also include acrylic block copolymers and graded block copolymers.

[0084] Useful acrylic monomers include alkyl and polar monomers. Such polar monomers include acid-functionalized monomers, hydroxyl-functionalized monomers, nitrogen-containing monomers, and combinations thereof. Hydroxyl-functionalized monomers include, for example, 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. Advantageously, polar monomers can facilitate the polymerization of polyvinyl acetal (e.g., butyral) polymers with high glass transition temperatures (high Tg). g ) and low glass transition temperature (low T g The monomers are compatible with alkyl methacrylate monomers to produce multiphase binders with relatively low haze. In some embodiments, these polar monomers may have a To greater than 0°C. g And T g It can be less than high T g T of monofunctional (meth)acrylate alkyl ester monomers g In a preferred embodiment, the multiphase adhesive is derived from a precursor comprising 40% to 90% by weight of homopolymer T. g Alkyl (meth)acrylate monomers with a temperature below 0°C. When characterized using DMA, the multiphase adhesive preferably exhibits at least one T value below 10°C. g .

[0085] Acid-functionalized monomers include, but are not limited to, those selected from: olefinically unsaturated carboxylic acids, olefinically unsaturated sulfonic acids, olefinically unsaturated phosphonic acids, and mixtures thereof. Examples of such compounds include those selected from acrylic acid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid, citrate, maleic acid, oleic acid, β-carboxyethyl methacrylate, 2-sulfoethyl methacrylate, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, vinylphosphonic acid, and mixtures thereof.

[0086] Nitrogen-containing monomers include, but are not limited to, N-vinylpyrrolidone; N-vinylcaprolactam; acrylamide; mono- or di-N-alkyl-substituted acrylamides, such as N,N-dimethylacrylamide; tert-butylacrylamide; dimethylaminoethylacrylamide; acryloylmorpholine; and N-octylacrylamide. In some embodiments, the crosslinking network of the polyvinyl acetal and acrylic copolymer comprises, relative to the total weight of the multiphase adhesive composition, 0% to 20% by weight, 0.5% to 10% by weight, 1% to 5% by weight, or in some embodiments equal to or greater than 0% by weight, or less than, equal to or greater than 0.1% by weight, 0.5% by weight, 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, 7% by weight, 10% by weight, 12% by weight, 15% by weight, or 20% by weight of polymeric units of nitrogen-containing monomers.

[0087] Other polar monomers include alkoxy-functionalized (meth)acrylate monomers. Representative examples include 2-(2-ethoxyethoxy)ethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-(methoxyethoxy)ethyl acrylate, 2-methoxyethyl methacrylate, and polyethylene glycol mono(meth)acrylate.

[0088] In some embodiments, the crosslinking network of the polyvinyl acetal and acrylic copolymer comprises, relative to the total weight of the crosslinking network, 0.5 wt% to 45 wt%, 1 wt% to 30 wt%, or in some embodiments, less than, equal to, or greater than 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 7 wt%, 10 wt%, 12 wt%, 15 wt%, 17 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, and 45 wt% of alkoxy-functional (meth)acrylate monomer polymeric units. In other embodiments, the crosslinking network comprises less than 20 wt%, less than 15 wt%, or less than 10 wt% of alkoxy-functional (meth)acrylate monomer polymeric units, or polymeric units without alkoxy-functional (meth)acrylate monomers. When the polyvinyl acetal (e.g., butyral) polymer exhibits low crosslinkability functionality, a higher amount of polar monomers may be required to provide a compatible mixture. Conversely, when the polyvinyl acetal has relatively high functionality, a lower amount of polar monomers may be required for compatibilization.

[0089] In some embodiments, the crosslinking network comprises polymeric units of one or more polar monomers, such as 2-hydroxyethyl (meth)acrylate or N,N-dimethylacrylamide. The multiphase adhesive may contain 5% to 55%, 7% to 45%, 10% to 35%, or in some embodiments, less than, equal to, or greater than 5%, 7%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or 55% of polymeric units of one or more of these monomers, relative to the total weight of the multiphase adhesive composition.

[0090] In some implementations, the crosslinked network comprises one or more low-T g The polymerization unit of (meth)acrylate monomers, that is, when the reaction forms a homopolymer, it has a T value not greater than 0°C. g (Meth)acrylate monomers. In some embodiments, low T g The homopolymer T of the monomer g The temperature ranges from -80°C to -5°C, from -70°C to -10°C, or in some embodiments, less than, equal to, or greater than -80°C, -70°C, -60°C, -50°C, -40°C, -30°C, -20°C, -10°C, or 5°C.

[0091] Low T g A monomer can, for example, have the following formula: H2C=CR 1 C(O)OR 8 , where R 1 It is H or methyl, and R 8 It is an alkyl group having 1 to 22 carbons or a heteroalkyl group having 2 to 20 carbons and 1 to 6 heteroatoms selected from oxygen or sulfur. The alkyl or heteroalkyl group can be straight-chain, branched, cyclic, or a combination thereof.

[0092] Low T g Examples of monomers include, but are not limited to, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, isopentyl acrylate, n-hexyl acrylate, 2-methylbutyl acrylate, 2-ethylhexyl acrylate, 4-methyl-2-pentyl acrylate, n-octyl acrylate, 2-octyl acrylate, isooctyl acrylate, isononyl acrylate, decyl acrylate, isodecyl acrylate, lauryl acrylate, isotriadecyl acrylate, octadecyl acrylate, and dodecyl acrylate.

[0093] In some embodiments, the crosslinked network comprises at least one low-T... g The polymerization unit of the monomer. In some implementations, low T g The monomer has an alkyl group containing 7 or 8 carbon atoms. Exemplary monomers include, but are not limited to, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-octyl (meth)acrylate, 2-octyl (meth)acrylate, isodecanyl (meth)acrylate, and lauryl (meth)acrylate. In some embodiments, the monomer is an ester of (meth)acrylate with an alcohol derived from a renewable source, such as 2-octyl (meth)acrylate. Other suitable monomers include branched long-chain acrylates, such as those described in U.S. Patent No. 8,137,807 (Clapper et al.). Additional suitable alkyl monomers include secondary alkyl acrylates, such as those described in U.S. Patent No. 9,102,774 (Clapper et al.).

[0094] Based on the total weight of the multiphase adhesive, the multiphase adhesive may contain at least 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, or 80 wt% of monofunctional (meth)acrylate alkyl esters with low T g Monomer (i.e., homopolymer T with a temperature below 0°C) gThe polymer units of ) are present. Based on the total weight of the multiphase adhesive composition, the multiphase adhesive typically contains no more than 60 wt%, 70 wt%, 80 wt%, or 90 wt% of T. g Polymerization unit of monofunctional (meth)acrylate alkyl ester monomers at temperatures below 0°C.

[0095] T of homopolymers of various monomers g It is known and reported in various manuals. Some illustrative monomers' T... g It is also reported in international patent application WO2016 / 094277 (Janoski et al.).

[0096] The polyvinyl acetal may be present in amounts of 85.0% to 99.9% by weight, 87.0% to 99.7% by weight, 90.0% to 99.5% by weight, or in some embodiments less than, equal to or greater than 85.0% by weight, 87.0% by weight, 90.0% by weight, 91.0% by weight, 92.0% by weight, 94.0% by weight, 96.0% by weight, 97.0% by weight, 98.0% by weight, 99.0% by weight, 99.5% by weight, 99.7% by weight or 99.9% by weight, relative to the total weight of the functionalized polyvinyl acetal.

[0097] The functionalized polyvinyl acetal may comprise 1% to 20%, 2% to 15%, 3% to 12% by weight relative to the total weight of the multiphase adhesive, or in some embodiments, less than, equal to, or greater than 1%, 2%, 3%, 4%, 5%, 8%, 10%, 12%, 15%, or 20% by weight.

[0098] The acrylic copolymer may be present in a weight fraction of 60% to 99%, 70% to 98%, 80% to 97%, or in some embodiments, less than, equal to, or greater than 60%, 70%, 80%, 85%, 90%, 93%, 95%, 97%, 98%, or 99% relative to the total weight of the multiphase adhesive.

[0099] Functionalized polyvinyl acetal and acrylic monomers can be combined with any number of additional additives, including catalysts, crosslinking agents, ultraviolet absorbers, dyes, and pigments.

[0100] Typically, for these blend systems, two or more Ts can be detected for the corresponding phase or domain within the multiphase binder. g Values ​​(e.g., defined by the peak loss tangent observed during a DMA temperature scan at 1 Hz). The lowest T g This is usually associated with acrylic copolymer phases with cross-linked networks.

[0101] Other aspects of multiphase adhesives are described in a co-pending patent application filed under U.S. Patent Application No. 63 / 531,032 (Beagi et al.).

[0102] Single-phase adhesive composition

[0103] This single-phase adhesive composition can be obtained by directly polymerizing any number of selected acrylic monomer mixtures. These compositions can be crosslinked at different levels to provide a range of elastic properties while generally still meeting optical transparency requirements. In one embodiment, the single-phase adhesive composition is derived from a reactive precursor comprising at least one (meth)acrylate having between about 1 and about 24 carbon atoms in an alkyl group and containing a radical generation initiator.

[0104] Examples of suitable alkyl acrylates (i.e., alkyl acrylate monomers) include, but are not limited to, straight-chain or branched monofunctional acrylates or methacrylates of non-tertiary alkyl alcohols, wherein the alkyl group has 1 to 24 carbon atoms. Examples of suitable monomers include, but are not limited to: 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, amyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, hexyl (meth)acrylate, n-nonyl (meth)acrylate, isoamyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, dodecyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, isostearylacrylate, and 2-methylbutyl (meth)acrylate, as well as combinations thereof. Other suitable monomers include branched long-chain acrylates, such as those described in U.S. Patent No. 8,137,807 (Clapper et al.). Additional suitable alkyl monomers include secondary alkyl acrylates, such as those described in U.S. Patent No. 9,102,774 (Clapper et al.).

[0105] To modulate the optical properties of a single-phase adhesive composition relative to the optical properties of a multiphase adhesive composition, monomers with higher refractive index (RI) can be added to the acrylic monomer mixture. For example, methyl biphenyl acrylate, with a relatively high RI, can be added to improve the overall RI of the single-phase adhesive composition. Advantageously, small amounts of various monomers can be added to help match the RI between the multiphase and single-phase adhesive compositions, while also maintaining the low shear modulus and low Tg of the single-phase adhesive. g nature.

[0106] In some embodiments, the monomer composition contains only alkyl (meth)acrylate monomers or styrene monomers having optional vinyl esters. In such cases, the modulus and T of the composition... g By selecting low T g Producing monomers and high T g The monomer composition is modified by producing a combination of monomers. In another embodiment, the monomer composition comprises an alkyl (meth)acrylate having between about 1 and about 24 carbon atoms in an alkyl group, between about 60 parts by weight and about 99 parts by weight, particularly between about 65 parts by weight and about 95 parts by weight, and even more particularly between about 70 parts by weight and about 95 parts by weight.

[0107] In some embodiments, the precursor composition comprises a polar copolymerizable monomer. Examples of suitable polar copolymerizable monomers include, but are not limited to: acrylic acid (AA), methacrylic acid, itaconic acid, fumaric acid, methacrylamide, N-alkyl-substituted and N,N-dialkyl-substituted acrylamides or methacrylamides (wherein the alkyl group has up to 3 carbons), and N-vinyl lactam. Examples of suitable monomers include, but are not limited to: (meth)acrylamide, N-morpholino(meth)acrylate, N-vinylpyrrolidone, and N-vinylcaprolactam. Other suitable polar monomers may include hydroxyl-containing monomers such as 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate; and ether-containing monomers such as 2-ethoxyethoxyethyl (meth)acrylate, and 2-methoxyethoxyethyl (meth)acrylate and ethoxylated 2-ethylhexyl acrylate (e.g., M1086, Miwon Specialty Chemicals (KR)). In some embodiments, the monomer composition comprises a polar copolymerizable monomer between about 1 part by weight and about 40 parts by weight, particularly between about 5 parts by weight and about 35 parts by weight, and even more particularly between about 5 parts by weight and about 30 parts by weight.

[0108] The monomer composition may also include vinyl esters, such as C1 to C10 vinyl esters. Examples of commercially available suitable vinyl esters include, but are not limited to, vinyl acetate, VeOVA 9, or VeOVA 10, available from Momentive Specialty Chemicals, New Smyrna Beach, FL. Vinyl esters may be added to the monomer mixture in amounts between about 1 part by weight and about 20 parts by weight, particularly between about 1 part by weight and about 15 parts by weight, and even more particularly between about 1 part by weight and about 10 parts by weight. Other monomers, such as styrene monomers, may also be used.

[0109] Examples of free radical generation initiators include, but are not limited to, thermal initiators or photoinitiators. Examples of thermal initiators include, but are not limited to, peroxides, such as benzoyl peroxide and its derivatives, or azo compounds. Examples of commercially available azo compounds include VAZO 67, 2,2'-azobis-(2-methylbutyronitrile), available from DuPont, Wilmington, Delaware. A variety of peroxides or azo compounds are available for initiating thermal polymerization at a range of temperatures. Photoinitiators may also be used, either in place of thermal initiators or in combination with thermal initiators. Particularly available photoinitiators include IRGACURE 651 and DAROCUR 1173, both available from BASF, Tarrytown, NY. The initiator is typically added to the precursor mixture in an amount between about 0.01 parts by weight and about 2 parts by weight, particularly between about 0.02 parts by weight and about 1 part by weight, and even more particularly between about 0.02 parts by weight and about 0.5 parts by weight.

[0110] In some embodiments, the monomer mixture comprises a multifunctional crosslinking agent. For example, the precursor mixture may include a thermally crosslinking agent activated during the drying step of preparing the solvent-coated adhesive and a crosslinking agent copolymerized during the polymerization step. Such thermally crosslinking agents may include, but are not limited to, multifunctional isocyanates, multifunctional aziridines, and epoxy compounds. Exemplary copolymerizable crosslinking agents include difunctional acrylates, such as 1,6-hexanediol diacrylate; or multifunctional acrylates, such as those known to those skilled in the art. Available isocyanate crosslinking agents include, for example, aromatic triisocyanates that may be obtained from Bayer AG, Cologne, Germany, such as DESMODUR 3300. Ultraviolet or “UV” activated crosslinking agents may also be used to crosslink the precursor of the single-phase adhesive composition. Such UV crosslinking agents may include non-copolymerizable photocrosslinking agents, such as benzophenone; and copolymerizable photocrosslinking agents, such as acrylated benzophenone or methacrylate benzophenone (e.g., 4-acryloyloxybenzophenone). Typically, the crosslinking agent (if present) is added to the monomer mixture in an amount between about 0.01 parts by weight and about 5 parts by weight, particularly between about 0.01 parts by weight and about 4 parts by weight, and even more particularly between about 0.01 parts by weight and about 3 parts by weight. Other crosslinking methods may also be used, such as ionic crosslinking, acid-base crosslinking, or physical crosslinking methods, such as by copolymerizing high-T g Macromonomers, such as, for example, polymethyl methacrylate macromonomers or polystyrene macromonomers. The macromonomers may be used in amounts of about 1 part by weight to about 20 parts by weight of the total monomer components.

[0111] The monomer composition may be inherently tacky. If desired, a tackifier may be added to the precursor mixture prior to the formation of the monomer composition. Available tackifiers include, for example, rosin ester resins, aromatic hydrocarbon resins, aliphatic hydrocarbon resins, terpenes, and terpene phenolic resins. Generally, light-colored tackifiers selected from hydrogenated rosin esters, terpenes, or aromatic hydrocarbon resins are preferred. When a tackifier is included, it is added to the precursor mixture in an amount between about 1 part by weight and about 50 parts by weight, more particularly between about 5 parts by weight and about 45 parts by weight, and most particularly between about 10 parts by weight and about 30 parts by weight.

[0112] Other materials can be added to the monomer mixture for specific purposes, including, for example, molecular weight control agents, coupling agents, oils, plasticizers, antioxidants, UV stabilizers, UV absorbers, pigments, curing agents, polymer additives, nanoparticles, and other additives. When optical transparency is required in the monomer composition, other materials can be added to the monomer mixture, provided that they do not significantly reduce the optical transparency of the single-phase adhesive composition after polymerization and coating.

[0113] Monomer components can be blended into a precursor mixture, which can then be prepolymerized by exposure to heat or photochemical radiation (to decompose the initiator in the mixture). This can be done before the addition of crosslinking agents and other components to form a coatable slurry, followed by the addition of one or more crosslinking agents, other additives, and additional initiators. The blended slurry is then coated onto a backing or directly onto a substrate and fully polymerized in an inert atmosphere by additional exposure to UV. Alternatively, crosslinking agents, optional additives, and initiators can be added to the monomers, and the mixture can be polymerized and cured in a single step (e.g., as liquid OCA). The desired coating method and viscosity will determine which step is used.

[0114] In another process, the monomer component can be blended with a solvent to form a mixture. The mixture can be polymerized by exposure to heat or photochemical radiation (to decompose the initiator in the mixture). Crosslinking agents and additional additives (such as tackifiers and plasticizers) can be added to the solvated polymer, which can then be coated onto a pad and dried in an oven to remove the solvent to produce a coated adhesive film. Solvent-free polymerization methods, such as the continuous free radical polymerization methods described in U.S. Patents 4,619,979 and 4,843,134 (Kotnour et al.); the substantially adiabatic polymerization method using a batch reactor described in U.S. Patent 5,637,646 (Ellis); and the method described in U.S. Patent 5,804,610 (Hamer et al.) for polymerizing pre-adhesive compositions for packaging, can also be used.

[0115] Additional options and advantages associated with these adhesive compositions are described in U.S. Patent 10,640,689 (Behling et al.).

[0116] Example

[0117] The purposes and advantages of this disclosure are further illustrated by the following non-limiting examples, but the specific materials and quantities referenced in these examples, as well as other conditions and details, should not be considered as unduly limiting the disclosure. Unless otherwise stated, all parts, percentages, and ratios in the embodiments and the remainder of this specification are by weight.

[0118] Material

[0119] Table 1 lists the components used to prepare the examples and comparative examples described herein.

[0120] Table 1 .

[0121] Test methods

[0122] Haze test

[0123] Haze measurements were performed in transmission mode using an UltrascanPro spectrophotometer from HunterLab (Reston, VA). One carrier liner was removed, and the sample was laminated onto a sheet of clear 0.7 mm thick LCD glass (Swift Glass, Elmira Heights, New York). The sample was placed in the UltrascanPro spectrophotometer to measure transmittance and % haze through the OCA / glass assembly. The instrument's aperture diameter was approximately 30 mm. To approximate the haze measurement of the stripe adhesive, the stripes were positioned such that they were centered in front of the aperture of the HunterLab instrument.

[0124] Dynamic mechanical analysis (DMA)

[0125] Dynamic mechanical analysis is used to probe the modulus as a function of temperature and to determine the temperature T of the material. g An 8 mm diameter × approximately 1 mm thick disk of the laminated component layers was placed between the probes of a DHR parallel plate rheometer (TA Instruments, New Castle, DE, Newcastle, Dlaiv). Temperature scans were performed by increasing the temperature from -50 °C to 150 °C at a rate of 3 °C / min. During this temperature increase, the sample was oscillated at a frequency of 1 Hz and a strain of approximately 0.4%. During this scan, the shear storage modulus (G'), loss modulus (G"), and loss tangent were recorded at selected temperatures. The material's T... g It was also determined to be the peak value of the loss tangent relative to the temperature distribution.

[0126] Refractive index analysis

[0127] The refractive index was measured using a Metricon 2010 prism coupler equipped with a 532nm laser. Measurements were performed by applying adhesive directly to the prism. All refractive index measurements were conducted at room temperature.

[0128] Peel test : Peel tests were performed on the air side of float borosilicate glass. Prior to testing, the glass surface was cleaned with an isopropyl alcohol-moistened wiping agent, followed by a dry wipe. One peeling pad was removed from the OCA sample, and the OCA sample was manually laminated onto a 2-mil thick, primer-coated PET backing film (Skyrol SH81, SKC, South Korea), with the primer facing the OCA. The peeling pads on the opposite adhesive side were then removed, and the OCA sample was placed on a glass slide under slight tension. The OCA was manually laminated onto the glass using rollers, and stripes 1 cm or 1 inch wide were cut, extending beyond the glass substrate. The free end of the sample was attached to the clamp of the peeling arm of the IMASS-SP2100 peel tester. The peeling arm was then carefully positioned on the appropriate location on the IMASS force sensor. The test began with the IMASS platen moving at 12 inches / minute, and the arm peeling the OCA at an angle close to 180 degrees. When recording peel force data from IMASS, the first two seconds of each peel were excluded as instantaneous initiating force. Then, the average of each peel over the following 10 seconds was used to provide the values ​​in the table.

[0129] Folding test -20℃ and 25℃

[0130] OCA samples were cut to 6cm × 15cm sizes. The central OCA stripe was aligned to extend parallel to the short axis of each part, and the stripe was positioned at the midpoint of the long axis of each part. After removing the release liner from the OCA and treating both sides with air plasma to optimize adhesion, the OCA samples were laminated onto a 50mm polyimide film (GL30, SKC-Kolon, South Korea) and a 30mm glass film (Joongwoo M-tech, South Korea).

[0131] The laminated sample is adhered to the folding platform of a Covotech bending machine with a 3mm bending radius using double-sided tape. The laminate is then aligned with the center stripe of the machine's bending axis area. After the temperature in the ambient chamber surrounding the bending machine has equilibrated to -20°C or 25°C, the machine begins folding the laminate at a continuous rate of 30 cycles per minute, without pauses in the open or closed position.

[0132] Sample preparation

[0133] Preparation example: PVB 0.6-IEM

[0134] 430 g of 30HH grade PVB was mixed with 2050 g of 2EHA in a container using a mixing blade and heat was applied. The solution was mixed at approximately 50 °C for 90 minutes until the PVB was fully solvated by the 2EHA. 2.5 g of bismuth catalyst (BICAT 8108) was added and mixed for 10 minutes. 2.57 g of IEM was added to the container, and the solution was mixed at approximately 60 °C for 20 hours.

[0135] Preparation of prepolymer coating solution

[0136] Prepare the polymer coating solution (PCS) according to the following steps and the amounts provided in Table 2. First, fill the components listed in the premix section of Table 2 into a clear wide-mouth bottle and mix for 30 minutes. Then, expose PCS-1 to PCS-7 to UV irradiation at approximately 350 nm until a viscous solution is obtained. Next, add the additional components listed in the compounding section of Table 2 to the wide-mouth bottle and mix on a roller in the wide-mouth bottle for more than 4 hours. PCS samples 8 and 9 are mixed simultaneously with the premix and compounding components in one step for more than 4 hours without the UV irradiation step that increases viscosity.

[0137] The compositions of polymer coating solutions PCS-1 to PCS-9 are provided in Table 2 below. Amounts shown are in weight percent (%).

[0138] Table 2 .

[0139] A polymer solution for both the inner and outer stripes is simultaneously delivered to the slit coating die by a pump. The position and width of the center stripe are determined by a shim within the slit die. In the embodiments included herein, the stripe is 16 mm wide.

[0140] Upon exiting the die head, a patterned polymer solution is coated onto a silicone-modified PET release liner (RF02N SKC Hass, KR, Korea). A second silicone-modified PET release liner is laminated on top of the structure, and the laminated structure is exposed to an output wavelength centered at approximately 365 nm and a total dose of approximately 2,500 mJ / cm². 2 UV radiation.

[0141] The physical properties of the patterned structures represented by Examples 1 to 6 and Comparative Examples CE1 and CE2 are provided in Table 3 below.

[0142] Table 3 .

[0143] For Examples 1 to 3 in Table 3 above, the outer striations of the adhesive remain at a constant low modulus and low T. g The configuration is such that the central fringe is designed to have a high modulus. A unique material scheme is used to systematically increase the modulus of the central fringe while maintaining T0. g Below -35°C, and the refractive index of the material did not increase significantly. By keeping the increase in refractive index to a minimum, the difference in RI between the central and outer stripes was also minimized, so as to also reduce the visual appearance of the stripe pattern. Example 4 shows the opposite design, in which the higher modulus formulation is located in the outer stripe, while the lower modulus material group is located in the central stripe. In Examples 4, 5, and 6, the matching T between the central and outer stripes was maintained. g and RI. Examples 5 and 6 show that by adding a biphenyl monomer to the outer stripe formulation, an even greater reduction in the RI difference from the outer stripe to the central stripe can be achieved.

[0144] CE1 indicates that the center stripe with higher modulus has an increased T along the fold axis. g The configuration of the formulation. Not only is there a T between the two regions of the adhesive. g Significant mismatch exists, and there is also a large difference in refractive index between the material pairs, as indicated in Table 4 below. Finally, CE2 shows a case where there is no modulus difference between the central and outer fringe regions, similar to more conventional coated unpatterned materials.

[0145] Performance data for Examples 1 to 6 and Comparative Examples CE1 and CE2 are provided in Table 4 below. The table provides the number of folding cycles and failure modes (e.g., delamination or cracking, if present), RI difference, % haze, and peel performance at two different temperatures.

[0146] Table 4 .

[0147] Considering the number of folding cycles passed, the type of failure mode observed, the expectation of low differences in RI between materials, and the combined analysis of low haze and adhesion, Examples 1 to 6 in Table 4 generally show better performance than either Comparative Example CE1 or Comparative Example CE2.

[0148] All references, patents, and patent applications cited in the above-mentioned patent-certified applications are incorporated herein by reference in their entirety. In the event of any inconsistency or contradiction between the incorporated references and this application, the information in the foregoing description shall prevail. The foregoing description, given to enable those skilled in the art to practice this disclosure protected by the claims, should not be construed as a limitation on the scope of this disclosure, which is defined by the claims and all their equivalents.

Claims

1. A patterned adhesive, the patterned adhesive comprising: Central adhesive layer; A pair of edge adhesive layers, the pair of edge adhesive layers extending along opposite sides of the center adhesive layer in an alternating stripe pattern and adjacent to opposite sides of the center adhesive layer; Optionally, the ratio of the shear modulus between the central adhesive layer and each edge adhesive layer is 2:1 to 10:1, or vice versa, wherein the shear modulus is measured by dynamic mechanical analysis at a frequency of 1 Hz and a temperature of 25 °C. When measured at a light wavelength of 532 nm, the difference between the refractive index of the central adhesive layer and the refractive index of the edge adhesive layer is within 0.015; and Furthermore, the glass transition temperature of the central adhesive layer and the edge adhesive layer is at most -30°C.

2. The patterned adhesive of claim 1, wherein, when measured at a light wavelength of 532 nm, the difference between the refractive index of the central adhesive layer and the refractive index of the edge adhesive layer is within 0.

010.

3. The patterned adhesive of claim 2, wherein, when measured at a light wavelength of 532 nm, the difference between the refractive index of the central adhesive layer and the refractive index of the edge adhesive layer is within 0.

005.

4. The patterned adhesive according to any one of claims 1 to 3, wherein the glass transition temperature of the center adhesive layer and the edge adhesive layer is at most -35°C.

5. The patterned adhesive of claim 4, wherein the glass transition temperature of the center adhesive layer and the edge adhesive layer is at most -40°C.

6. The patterned adhesive according to any one of claims 1 to 5, wherein the central adhesive layer comprises a multiphase composition and each edge adhesive layer comprises a single-phase composition.

7. The patterned adhesive according to any one of claims 1 to 5, wherein the central adhesive layer comprises a single-phase composition and each edge adhesive layer comprises a multi-phase composition.

8. The patterned adhesive according to 6 or 7, wherein the multiphase composition comprises a primary phase and a secondary phase uniformly dispersed in the primary phase, the secondary phase existing in a discrete domain with a median lateral dimension of 0.1 micrometer to 5 micrometer.

9. The patterned adhesive according to any one of claims 6 to 8, wherein the single-phase composition is derived from an alkyl (meth)acrylate having 1 to 24 carbon atoms in the alkyl group and from a free radical generation initiator.

10. The patterned adhesive according to any one of claims 6 to 9, wherein the multiphase composition comprises a crosslinked network of polyvinyl acetal and acrylic copolymer.

11. The patterned adhesive of claim 10, wherein the functionalized polyvinyl acetal is present in a weight fraction of 1% to 20% of the total weight of the adhesive, and comprises a polyvinyl acetal backbone having side-chain functional groups that react with acrylic monomers; and further wherein the acrylic copolymer is present in a weight fraction of 60% to 99% of the total weight of the adhesive.

12. The patterned adhesive according to claim 11, wherein the polyvinyl acetal backbone is a polyvinyl butyral backbone.

13. The patterned adhesive according to claim 11 or 12, wherein the polyvinyl acetal backbone having side chain functional groups is obtained by reacting polyvinyl acetal with ethyl isocyanate (meth)acrylate or allyl isocyanate.

14. A patterned adhesive, said patterned adhesive comprising: Central adhesive layer; A pair of intermediate adhesive layers, the pair of edge adhesive layers extending along and adjacent to the opposite sides of the central adhesive layer; A pair of edge adhesive layers, the pair of edge adhesive layers extending along the opposite sides of the middle adhesive layer in an ABCBA stripe pattern and adjacent to the opposite sides of the middle adhesive layer; Optionally, the ratio of the shear modulus between the central adhesive layer and each edge adhesive layer is 2:1 to 10:1, or vice versa, wherein the shear modulus is measured by dynamic mechanical analysis at a frequency of 1 Hz and a temperature of 25 °C. If measured at a light wavelength of 532 nm, the difference between the refractive index of the central adhesive layer and the refractive index of the edge adhesive layer is within 0.

015. Each of the intermediate adhesive layers exhibits a refractive index between that of the adjacent central adhesive layer and the edge adhesive layer; and Furthermore, the glass transition temperature of each of the central adhesive layer, the intermediate adhesive layer, and the edge adhesive layer is at most -30°C.

15. A patterned adhesive, said patterned adhesive comprising: Central adhesive layer; A pair of intermediate adhesive layers, the pair of edge adhesive layers extending along and adjacent to the opposite sides of the central adhesive layer; and A pair of edge adhesive layers, the pair of edge adhesive layers extending along the opposite sides of the middle adhesive layer in an ABCBA stripe pattern and adjacent to the opposite sides of the middle adhesive layer; When measured under environmental conditions and at 1 Hz, the shear modulus of the central adhesive layer and the edge adhesive layer are each between 10 kPa and 100 kPa. When measured under environmental conditions and at 1 Hz, each intermediate adhesive layer exhibits a shear modulus that is 2 to 500 times greater than that of the central adhesive layer and the edge adhesive layer, respectively. When measured at a light wavelength of 532 nm, the difference between the refractive index of the intermediate adhesive layer and the refractive index of the edge adhesive layer and the refractive index of the central adhesive layer is within 0.015; and Furthermore, the glass transition temperature of each of the central adhesive layer, the intermediate adhesive layer, and the edge adhesive layer is at most -30°C.

16. The patterned adhesive of claim 15, wherein, as measured under ambient conditions and at 1 Hz, each intermediate adhesive layer exhibits a shear modulus exceeding 5 to 100 times the shear modulus of the central adhesive layer and the edge adhesive layer, respectively.

17. The patterned adhesive of claim 16, wherein, as measured under ambient conditions and at 1 Hz, each intermediate adhesive layer exhibits a shear modulus exceeding 10 to 50 times the shear modulus of the central adhesive layer and the edge adhesive layer, respectively.

18. The patterned adhesive according to any one of claims 15 to 17, wherein the center adhesive layer and the edge adhesive layer have the same composition.

19. The patterned adhesive according to any one of claims 1 to 18, wherein for an adhesive 50 micrometers thick, the patterned adhesive is optically transparent and has a haze value equal to or less than 0.5%.

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