Adhesive composition

Abstract

Provided is an adhesive comprising a cross-linked network of a polyvinyl acetal and an acrylic copolymer obtained by reacting a functionalized polyvinyl acetal with an acrylic monomer. The functionalized polyvinyl acetal is present in a weight fraction of 1% to 20% of the total weight of the adhesive and includes a polyvinyl acetal backbone having side chain functional groups that react with acrylic monomers. The acrylic copolymer is present in a weight fraction of 60% to 99% of the total weight of the adhesive. Advantageously, the adhesive can not only provide deformation resistance to prevent mechanical reading of the polarizer-free display backside component, but also provide a low rebound coefficient to achieve impact damping performance.

Description

Technical Field

[0001] 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 variety of reasons, including high adhesion and cohesion, protective properties, and enhanced touchscreen performance as 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] Conventional organic light-emitting diode (OLED) displays require circular polarizers to prevent total internal reflection from compromising display quality. Recent advances in OLED display technology have made it possible to reduce total internal reflection without circular polarizers, thereby reducing or eliminating the need for polarizers in OLED display components. Eliminating polarizers in OLED displays offers various technical benefits, including reduced overall device thickness and increased efficiency. Increased efficiency, in turn, can improve display brightness, extend battery life, or both. Summary of the Invention

[0004] Eliminating polarizers from displays may present new technical and material challenges. One such challenge involves mechanically reading through components on the back of the display, such as flexible printed circuits, fingerprint sensors, and the texture of the overlay panel. In critical cases, these topological features are visible to the observer and are therefore undesirable.

[0005] The technical requirement remains the adhesive, particularly OCA, which must be strong enough to resist deformation and prevent mechanical readings of these back-end components. However, the adhesive must also be able to protect the display from high-impact events. Impact performance can be characterized by dropping a steel ball onto the display under precisely controlled conditions and examining for damage or malfunction. Furthermore, an adhesive providing good impact performance will also have a relatively low coefficient of rebound (COR). COR is a fundamental property of a given material's kinetic energy absorption and can be correlated with drop ball performance.

[0006] The adhesive presented in this paper achieves the following beneficial properties: both resistance to deformation to prevent mechanical readings of components on the back of a polarizer-less display and low COR for shock damping performance. This is surprising because these performance properties are usually inversely related, with an improvement in one property typically accompanied by a loss in the other. Here, it is found that a single-layer OCA containing a blend of acrylic polymers and polyvinyl acetal polymers such as polyvinyl butyral (PVB), or a multilayer OCA containing at least one layer of a blend of a polyvinyl acetal polymer and an acrylate, can simultaneously achieve both performance properties.

[0007] In a first aspect, an adhesive is provided. The adhesive comprises: a crosslinked network of a polyvinyl acetal and an acrylic copolymer obtained by reacting a functionalized polyvinyl acetal with an acrylic monomer, the functionalized polyvinyl acetal comprising a polyvinyl acetal backbone having side-chain acrylate groups, the side-chain acrylate groups reacting with the acrylic monomer, wherein the functionalized polyvinyl acetal is present in a weight fraction of 1% to 20% of the total weight of the adhesive, and further wherein the acrylic copolymer is present in a weight fraction of 60% to 99% of the total weight of the adhesive.

[0008] In a second aspect, a tape adhesive comprising an adhesive layer is provided.

[0009] In a third aspect, a method for manufacturing an adhesive is provided, the method comprising: functionalizing polyvinyl acetal by reacting polyvinyl acetal with ethyl isocyanate (meth)acrylate and / or allyl isocyanate; and polymerizing acrylic monomers in the presence of the functionalized polyvinyl acetal to form a crosslinked network of polyvinyl acetal and acrylic copolymer. Attached Figure Description

[0010] Figures 1 to 3 A front side view of an adhesive tape according to various exemplary embodiments.

[0011] Reference numerals used repeatedly in the specification and drawings are intended to indicate 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 may not be drawn to scale.

[0012] definition

[0013] 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.

[0014] "Allyl" refers to a functional group with the formula CH2=CH-CH2-.

[0015] "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.

[0016] "Cureable" refers to a composition that can be cured.

[0017] "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.

[0018] "(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-.

[0019] "Oligomers" are molecules that contain at least two repeating units and have a molecular weight smaller than their entanglement molecular weight; unlike polymers, such molecules exhibit significant changes in properties when a single repeating unit is removed or added. Detailed Implementation

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] The adhesives provided are typically based on a crosslinked network of polyvinyl acetal and acrylic acid copolymers obtained by reacting functionalized polyvinyl acetal with acrylic monomers. In some embodiments, the functionalized polyvinyl acetal may be reacted with a mixture of two or more different acrylic monomers.

[0025] 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.

[0026] Polyvinyl acetal is known to be used in the manufacture 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.

[0027] Polyvinyl acetal can be prepared by saponifying polyvinyl acetate to obtain polyvinyl alcohol, followed by acetalization of the polyvinyl alcohol with an aldehyde in the presence of a catalyst. The degree of saponification of polyvinyl alcohol is not particularly limited, but is typically in the range of 70 mol% to 99.9 mol%. Preferably, the degree of saponification is 70 mol% to 99.9 mol%, more preferably 80 mol% to 99.8 mol%.

[0028] The average degree of polymerization of polyvinyl alcohol is not particularly limited. Preferably, the polyvinyl alcohol used has a high average degree of polymerization to improve strength and toughness. The lower limit of the average degree of polymerization of polyvinyl alcohol is preferably 200 repeating units, and the upper limit is preferably 4,000 repeating units. When the average degree of polymerization of polyvinyl alcohol falls within this range, it is beneficial to the reaction during polyvinyl alcohol acetalization, and the resulting polyvinyl alcohol acetal can exhibit high mechanical strength. The lower limit of the average degree of polymerization of polyvinyl alcohol is more preferably 300 repeating units, and the upper limit is more preferably 3,000 repeating units. The lower limit is more preferably 400 repeating units, and the upper limit is preferably 2,000 repeating units.

[0029] As used herein, the average degree of polymerization of polyvinyl alcohol refers to the viscosity-average degree of polymerization obtained based on JIS K6726:1994. When the polyvinyl alcohol resin used is a mixture of two or more types of polyvinyl alcohol resin, the average degree of polymerization of polyvinyl alcohol refers to the apparent viscosity-average degree of polymerization of the entire polyvinyl alcohol resin mixture.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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%.

[0034] If the degree of reactive functionalization of polyvinyl acetal is too high, the adhesive may become highly crosslinked, resulting in a loss of adhesive properties. Conversely, adhesive compositions with too low a degree of polyvinyl acetal may reduce the compatibility between the acrylic polymer and the PVA polymer, potentially producing 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 function as a crosslinking agent to form a crosslinked network, even when reacting with monofunctional acrylic monomers.

[0035] 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.

[0036] 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 alkyl methacrylate monomers are compatible to produce an adhesive with relatively low haze. In some embodiments, these polar monomers may have a glass transition temperature (T0) greater than 0°C. g ), and the T g It can be less than high T g T of monofunctional (meth)acrylate alkyl ester monomers g In a preferred embodiment, the 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 adhesive preferably exhibits at least one glass transition temperature (T0) below 10°C. g ).

[0037] 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.

[0038] In some embodiments, the (meth)acrylate copolymer is substantially free of the acid-functionalized monomers to be polymerized. Hereinafter, the term "substantially free" means that the (meth)acrylate polymer contains less than 1% by weight, less than 0.5% by weight, less than 0.2% by weight, or less than 0.1% by weight of these monomers. In some embodiments, the crosslinkable composition may be substantially free of acid-functionalized monomers to eliminate indium tin oxide (“ITO”) and metal trace corrosion that could otherwise damage the touch sensor and its integrated circuit or connector.

[0039] 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 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.

[0040] 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.

[0041] 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.

[0042] 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 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 adhesive composition.

[0043] 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 monomer has a homopolymer T having a temperature range of -80°C to -5°C, -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.g .

[0044] Low T g A monomer can, for example, have the following formula: , 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.

[0045] 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.

[0046] 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, which is incorporated herein by reference. Further suitable alkyl monomers include secondary alkyl acrylates, such as those described in U.S. Patent No. 9,102,774, which is incorporated herein by reference.

[0047] Based on the total weight of the adhesive, the adhesive may contain at least 20%, 30%, 40%, 50%, 60%, 70%, or 80% by weight of monofunctional (meth)acrylate alkyl esters with low T content. g Monomer (i.e., homopolymer T with a temperature below 0°C) g The polymer units of ) are present. Based on the total weight of the adhesive composition, the adhesive typically contains no more than 60%, 70%, 80%, or 90% by weight of T.g Polymerization unit of monofunctional (meth)acrylate alkyl ester monomers at temperatures below 0°C.

[0048] T of homopolymers of various monomers g This is known and reported in various handbooks. The T of some exemplary monomers... g It is also reported in International Patent Application No. WO 2016 / 094277 (Janoski et al.).

[0049] 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.

[0050] The functionalized polyvinyl acetal may comprise 1% to 20%, 2% to 15%, 3% to 12% of the total weight of the 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.

[0051] 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 adhesive.

[0052] Functionalized polyvinyl acetal and acrylic monomers can be combined with any number of additional additives, including catalysts, crosslinking agents, ultraviolet absorbers, dyes, and pigments.

[0053] Typically, for these blend systems, two or more Ts can be detected for the corresponding phase or domain within the binder. g Values ​​(as defined by the peak tanδ value observed during a DMA temperature scan at 1 Hz). Lowest T g This is typically associated with the cross-linked network of the acrylic copolymer phase. To achieve a low COR, it is generally preferable to maintain a low T in the acrylate phase. g The temperature is typically at least -60°C and at most 10°C, at most 0°C, or at most -10°C.

[0054] To provide resistance to deformation, the adhesive material should possess a relatively high storage modulus at 25°C, which can be measured by dynamic mechanical analysis (DMA) using a temperature scan at a frequency of 1 Hz. A storage modulus at 25°C greater than 200,000 Pascals, greater than 400,000 Pascals, greater than 600,000 Pascals, greater than 800,000 Pascals, or even greater than 1 MPascal may be preferred. Additional heat from heat-assisted lamination and / or autoclave processes (e.g., at temperatures exceeding 60°C, or even exceeding 65°C) may be helpful in achieving good morphological feature coverage (e.g., ink scale coverage) and / or good compliance and adhesion to the substrate.

[0055] In some implementations, the adhesive is considered to be optically transparent and has low haze (less than 4%, 3%, or 2%).

[0056] Figures 1 to 3 An exemplary transfer adhesive incorporating the provided adhesive composition is shown. A tape adhesive according to an exemplary embodiment is... Figure 1 As shown herein, and denoted by the number 100 below, the tape adhesive 100 includes a main layer 102 comprising a polyvinyl acetal-based adhesive composition as described herein and having opposing first main surfaces 104 and second main surfaces 106. Advantageously, the main layer 102 provides mechanical resistance to deformation while maintaining high impact performance.

[0057] Figure 2 A tape adhesive assembly 150 representing an adhesive component is shown. Assembly 150 includes a tape adhesive 100 comprising a main layer 102 characterized as described above. Assembly 150 also includes a pair of release substrates 152, 154 disposed on each of respective opposite main surfaces 104, 106 of the main layer 102. In some embodiments, the main layer 102 directly contacts the two release substrates 152, 154, thereby adhesively bonding these release substrates 152, 154 together. Available release substrates are known in the art and may include, for example, pads made of silicone-coated polyester or silicone-coated paper.

[0058] Figure 3 A tape adhesive 200 according to yet another embodiment is shown, which has a similar construction to tape adhesive 100, except that a pair of secondary layers 252, 254 are interposed between the main layer 202 and the release substrate 252, 254, as shown. The secondary layers 210, 210' can be used as a surface layer made of acrylic OCA, which contains a lower weight fraction of polyvinyl acetal than the main layer 202.

[0059] In a preferred embodiment, one or both of the secondary layers 210, 210' contain zero or substantially zero polyvinyl acetal. A potential advantage of this embodiment is that it maintains high room temperature tack, which may be beneficial for certain applications. Another potential advantage is the ability to introduce greater flowability at the surface, which can improve the adhesive wetting of the substrate or topological features (such as ink scales, if present). Additional advantages may include the ability to isolate certain functions (such as UV blocking) to specific layers.

[0060] The adhesives and adhesive layers described herein can be manufactured using batch or continuous methods. In an exemplary embodiment, the adhesive comprises a plurality of adjacent layers that cannot be delaminated. Each of the layers comprises a photopolymerizable matrix of polymer chains, and at least one of the outer layers is photopolymerized into a pressure-sensitive adhesive state. Details of the method are described, for example, in European Patent No. EP 0305 161 (Zimmerman et al.).

[0061] Uncured compositions can be applied to unstructured or structured release liner using conventional coating techniques. For example, these compositions can be applied by methods such as roll coating, flow coating, dip coating, spin coating, spray coating, blade coating, and mold coating. Coating thickness can vary. Based on the desired viscosity, the composition can have any desired concentration for subsequent coating. Optionally, the coated release liner can be brought into contact with a second backing before curing.

[0062] In some implementations, curing is performed by activating a photoinitiator. Available photoinitiators include benzoin ethers, such as benzoin methyl ether and benzoin isopropyl ether; substituted acetophenones, such as 2,2-dimethoxy-2-phenylacetophenone photoinitiator, which is available under the trade name IRGACURE 651 from Merck KGaA, Darmstadt, Germany, or ESACURE KB-1 photoinitiator from LEHVOSS Group, Hamburg, Germany, and dimethylhydroxyacetophenone; substituted α-keto alcohols, such as 2-methyl-2-hydroxyacetophenone; aromatic sulfonyl chlorides, such as 2-naphthalene-sulfonyl chloride; photooximes, such as 1-phenyl-1,2-propanedione-2-(O-ethoxy-carbonyl)oxime; mono- or bis-acryloylphosphine oxides, such as IRGANOX from BASF SE, Ludwigshafen, Germany. 819 or LUCIRIN TPO from Merck Group.

[0063] Preferred photoinitiators are photoactive compounds that undergo Norrish I cleavage to generate free radicals, which can be initiated by the addition of double bonds to acrylic acids. The photoinitiator can be added to the mixture to be coated after the polymer (e.g., a slurry) has been formed; that is, the photoinitiator can be added. Such polymerizable photoinitiators are described, for example, in U.S. Patents 5,902,836 and 5,506,279 (Gaddam et al.).

[0064] The photoinitiator can be present in amounts ranging from 0.1% to 5% by weight, depending on the total weight of the uncured composition. A relatively thick coating can be achieved when the extinction coefficient of the photoinitiator is low.

[0065] Polymerization can be carried out in the absence of non-polymerizable organic solvents such as ethyl acetate, toluene, and tetrahydrofuran, which do not react with the functional groups of the monomers. Solvents affect the incorporation rate of different monomers into the polymer chain and generally result in lower molecular weights due to polymer gels or precipitates in the solution. Therefore, it may be advantageous for cross-linked network compositions to be free of non-polymerizable organic solvents.

[0066] Uncured compositions containing photoinitiators can be cured by irradiation with photochemical radiation. Photochemical radiation can be, for example, ultraviolet (UV) radiation with a maximum UVA value in the wavelength range of 280 nm to 425 nm, to polymerize the monomer components. There are no particular limitations on the UV light source. Low-intensity light sources such as black lights typically provide 0.1 mW / cm². 2 Or 0.5mW / cm 2 (mW / cm²) to 10mW / cm² 2 Intensity within the range (measured according to procedures approved by the National Institute of Standards and Technology, such as, for example, using a UVIMAP UM 365 LS radiometer manufactured by Electronic Instrumentation & Technology, Inc., Sterling, VA). High-intensity light sources typically provide greater than 10 mW / cm². 2 15mW / cm 2 Or 20mW / cm 2 And at most 450mW / cm 2 The intensity. High-intensity light sources provide up to 500mW / cm². 2 600mW / cm 2 700mW / cm 2 800mW / cm 2 900mW / cm 2 Or 1000mW / cm 2The intensity of the UV light used to polymerize the monomer components can be provided by a variety of light sources, such as light-emitting diodes (LEDs), black lights, medium-pressure mercury lamps, or any combination thereof.

[0067] The UV exposure time used for polymerization and curing typically varies depending on the intensity of the light source used. For example, complete curing using low-intensity light processes can be completed with exposure times ranging from approximately 30 to 300 seconds; while complete curing using high-intensity light sources can be completed with shorter exposure times ranging from approximately 5 to 20 seconds. Partial curing using high-intensity light sources can typically be completed with exposure times ranging from 2 to 10 seconds, or from 2 to 5 seconds.

[0068] The uncured composition optionally includes one or more additives. While not all are suitable for OCA applications, additives may include antioxidants, plasticizers, tackifiers, stabilizers, UV absorbers, lubricants, processing aids, antistatic agents, colorants, impact retardants, fillers, matting agents, flame retardants (e.g., zinc borate), etc. Some examples of fillers or pigments include inorganic oxide materials such as zinc oxide, titanium dioxide, silicon dioxide, carbon black, calcium carbonate, antimony trioxide, metal powders, mica, graphite, talc, ceramic microspheres, glass or polymer beads or bubbles, fibers, starch, etc.

[0069] When present, the additive may be 0.1% to 15%, 0.3% to 10%, 0.5% to 5% by weight of the uncured adhesive composition, or in some embodiments less than, equal to or greater than 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.7%, 1%, 2%, 5%, 7% or 10%, 11%, 12%, 13%, 14% or 15%.

[0070] Example

[0071] The purposes and advantages of this disclosure are further illustrated by the following non-limiting embodiments, but the specific materials and quantities referenced in these embodiments, as well as other conditions and details, should not be construed as undue limitation of this disclosure. Unless otherwise stated, all parts, percentages, and ratios in the embodiments and the remainder of this specification are by weight.

[0072] Material

[0073] Table 1 lists the components used to prepare the examples and comparative examples described herein.

[0074]

[0075] Test methods

[0076] For each of the tests listed below, the examples were coated between peel-coated carrier pads (RF02N and RF22N, SKC Haas, Korea) and cut into pieces approximately 5 cm wide × 10 cm long, and their thicknesses were measured.

[0077] Impact test

[0078] To improve impact test performance in target applications, adhesives that absorb and dissipate more impact energy will exhibit a lower coefficient of rebound (referred to as COR in this paper). OCAs that absorb relatively less impact energy will have a higher COR.

[0079] COR is obtained using known methods, such as those disclosed, for example, in Skórski et al., “Experimental Determination of the Coefficient of Restitution for Selected Modern Hybrid Composites,” Materials, 2021; 14(19): 5638. Samples are tested using a punch equipped with an accelerometer and a mounting plate whose deflection can be monitored by a distance sensor. Assuming that the energy of the punch is dissipated only at the moment of impact with the plate during testing, the height reached by the punch after each impact can be determined based on the time between impacts. The springback coefficient of a given material can then be calculated using the calculated height of the punch after impact and the known initial fall height. Skórski et al. describe this method in more detail.

[0080] Each embodiment for testing COR was prepared by removing the carrier layer and laminating the adhesive onto a 51-micron (2-mil) sheet of polyethylene terephthalate (PET), followed by autoclaving at 65°C with 5 kgf for 5 minutes. This step aimed to prevent adhesion to the dynamic test components of the test system. The adhesive-PET construct was left to stand overnight in a controlled environment maintained at 23 ± 2°C and 50 ± 10% relative humidity, and then directly laminated to the mounting plate of the test system. Therefore, the reported COR values ​​are not direct measurements of the adhesive alone, but rather comparative measurements of the adhesive-PET laminates. The test was repeated three times, and their average values ​​were reported.

[0081] Deformation resistance test

[0082] To measure resistance to deformation, test specimens were prepared by removing the carrier liner and laminating the adhesive onto 51 micrometers (2 mils) of PET, followed by lamination onto 0.7 mm LCD glass. Prior to testing, the samples were allowed to stand overnight in a controlled environment maintained at 23 ± 2 °C and 50 ± 10% relative humidity. The samples were then tested using a TA XT Plus texture analyzer with a 7 mm circular probe. The test specimen was placed on the instrument's base with the PET side facing up, and the probe was applied to the PET surface of the test specimen with a force of 50 g for 60 seconds. The relative penetration depth, in millimeters, was measured as a function of time. The maximum penetration depth was then recorded, referred to in this test as the average (Avg) peak positive (Pos) distance.

[0083] The OCA, which resists mechanical deformation, performed better in this test, showing lower penetration depth results. This mechanical deformation leads to mechanical readings of components on the back of the non-polarized display. As demonstrated by the higher penetration depth results, OCAs that allow for more mechanical deformation will perform worse. It should be noted that for this test, the performance trend observed in the 1-hour test closely matched that observed in the 60-second test. Therefore, a faster test time was chosen to reasonably allocate data collection time for multiple concepts and repetitions. The test was repeated twelve times, and their average values ​​were reported.

[0084] Haze test

[0085] Haze measurements were performed in transmission mode using an UltrascanPro spectrophotometer from HunterLab, Reston, VA. One carrier pad 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 remaining carrier pad was removed, and the sample was placed in the UltrascanPro spectrophotometer to measure transmittance and % haze through the OCA / glass assembly.

[0086] Dynamic mechanical analysis (DMA)

[0087] Dynamic mechanical analysis is used to determine the shear storage modulus (G') as a function of temperature and one or more T values ​​of the material. gValues. An 8 mm diameter × 1 mm thick disk of the laminated component layer was placed between the upper and lower geometry of a DHR parallel plate rheometer (TA Instruments, New Castle, DE). Temperature scans were performed by increasing the temperature from -45 °C to 150 °C at a rate of 3 °C / min. During this increase, the sample oscillated at a frequency of 1 Hz and a strain of approximately 0.4%. During this scan, G', loss modulus (G''), and tanδ were recorded at 25 °C. One or more T values ​​of the material. g The value was also determined to be the temperature at which the tanδ peak was observed.

[0088] Preparation example ( PE )

[0089] Preparation example PVB0

[0090] In a container, 430 g of 30HH grade PVB was mixed with 2050 g of 2EHA using a mixing blade and applied heat. The solution was then mixed at approximately 50°C for 90 minutes until the PVB was fully solubilized by the 2EHA.

[0091] Preparation example: PVB 0.6-IEM

[0092] In a container, 430 g of 30HH grade PVB was mixed with 2050 g of 2EHA using a mixing blade and applied heat. 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.

[0093] Preparation example: PVB5.7-IEM

[0094] In a container, 430 g of 30HH grade PVB was mixed with 2050 g of 2EHA using a mixing blade and applied heat. 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. 25.8 g of IEM was added to the container, and the solution was mixed at approximately 60°C for 20 hours.

[0095] Preparation example: PVB9,1-allyl

[0096] In a container, 420 g of 30HH grade PVB was mixed with 2000 g of 2EHA using a mixing blade and applied heat. 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. 41.9 g of allyl isocyanate was added to the container, and the solution was mixed at approximately 60°C for 20 hours.

[0097] The final compositions of the preparation examples PVB0, PVB0.6-IEM, PVB6-IEM and PVB9.1-allyl are summarized in Table 2 below.

[0098]

[0099] Preparation examples PE1-PE3 were prepared according to the formulations listed in Table 3. Functionalized PVB (PVB0-IEM, PVB0.6-IEM, PVB6-IEM) and acrylate monomers were loaded into a container at the indicated weight % ratios to provide 2000 g of mixture. The weight % values ​​are relative to the overall composition of the preparation examples. HDDA, I819, and BL1B were then added. The container was sealed and mixed on a wide-mouth roller for 16 hours.

[0100]

[0101] Preparation examples PE4-PE6 were prepared according to the formulations listed in Table 4. Functionalized PVB (PVB 0.6-IEM) (if present) and acrylate monomers were loaded into containers at the indicated weight % ratios to provide 2000 g of mixture. Note that PE5 and PE6 do not contain PVB. D1173 was then added to the container. The weight % values ​​are relative to the overall composition of the preparation examples. Then, a strength of 0.3 mW / cm was used. 2 The mixture was irradiated with a 365nm UV LED until it (referred to herein as the prepolymer) reached a viscosity of approximately 100 to 1500 cp as measured by a Brinell viscometer. Then, EB230 or HDDA, I819, BL1B, and KBM403 were added. The container was sealed and mixed on a wide-mouth roller for 16 hours.

[0102]

[0103] Examples and Comparative Examples

[0104] Examples EX1-EX5 and Comparative Example CE1 were prepared according to Table 5 and consist of a single-layer adhesive prepared by blending the preparative adhesive compositions listed in Tables 2 and 3 to provide the overall composition shown. Table 5 also reports DMA test results, including T...g Values ​​and 25°C shear storage modulus, as well as impact and deformation resistance test results, including average COR and average peak positive distance (50g, 60 seconds). Unless otherwise specified, final composition weight % is relative to the total weight of the adhesive composition.

[0105] The examples were applied to 51-micron carrier release liners (RF02N / RF22N from ASICS) using a roll-to-roll coating method, and then polymerized and cured by irradiation with UVV light at a dose of 3380 mJ from a 405 nm UV LED light source. The caliper thickness (i.e., thickness) of all adhesive layers was approximately 150 microns.

[0106]

[0107] Table 6 reports the overall composition of Examples EX6-EX8 and Comparative Examples CE2-CE3, which consist of a single layer of adhesive. Table 6 also reports the corresponding DMA test results (T... g The values ​​and 25°C shear storage modulus), impact resistance and deformation resistance test results, including average COR and average peak positive distance (50g, 60 seconds), and haze test results. These examples were prepared by loading functionalized PVB (preparation examples PVB0-IEM, PVB0.6-IEM, or PVB6-IEM) and acrylate monomers into a container at the indicated weight % ratio to provide 100g of mixture. D1173 was then added to the container. The weight % values ​​are relative to the overall composition of the examples. Then, a strength of 0.3mW / cm was used. 2 The mixture was irradiated with a 365nm UV LED until the prepolymer reached a viscosity of approximately 100 to 1500 cp, as measured by a Brookfield viscometer. HDDA, I819, BL1B, and KBM403 were then added. The container was sealed and mixed on a wide-mouth bottle roller for 16 hours. The sample was coated onto a 51-micron carrier release liner (RF02N / RF22N from ASICS Haas) using a roller-to-roll coating method, and subsequently polymerized and cured with 3380 mJ UVV light from a 405nm UV LED source. The adhesive layer had a caliper thickness of approximately 150 microns.

[0108]

[0109] Table 7 reports the overall composition of Example EX9, which consists of a single-layer adhesive. Table 7 also reports the corresponding 25°C shear storage modulus, impact resistance, and deformation resistance test results, including average COR and average peak positive distance (50 g, 60 s). This example was prepared by loading functionalized PVB (preparation example PVB9.1-allyl) and acrylate monomers into a container at the indicated weight % ratio to provide 100 g of mixture. BL1B, OMNIPOL TP, and BD1 were then added. The container was sealed and mixed on a wide-mouth bottle roller for 16 hours. This example was coated onto a 51-micron carrier release liner (RF02N / RF22N from ASICS) using a roller-to-roll coating method, and subsequently polymerized and cured with 2400 mJ UVV light from a 405 nm UVLED light source. The adhesive had a caliper thickness of approximately 150 microns.

[0110]

[0111] Table 8 reports the compositions of Examples EX10-EX22 and Comparative Example CE4. These are multilayer adhesives prepared using the preparation example compositions shown in Tables 3 and 4, and the corresponding impact and deformation resistance test results are also reported in Table 8. The adhesive was applied to a 51µm carrier release liner (RF02N / RF22N from SK Haas) using a multilayer coating die according to the method described in European Patent No. EP 0 305 161 (Zimmerman et al.), and subsequently polymerized and cured with 2480mJ UVV light from a 405nm UVLED light source.

[0112] The combined adhesive layer has a caliper thickness of approximately 150 micrometers. The layer numbering is defined as follows: "L1" is the layer disposed against the first release liner; "L2" is the layer disposed between L1 and L3; and "L3" is the layer disposed against the second release liner.

[0113]

[0114] 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. An adhesive comprising: A crosslinked network of polyvinyl acetal and acrylic acid copolymer obtained by reacting functionalized polyvinyl acetal with acrylic acid monomer. 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 the acrylic monomer; and Furthermore, the acrylic copolymer is present in a weight fraction of 60% to 99% of the total weight of the adhesive.

2. The adhesive according to claim 1, wherein the polyvinyl acetal backbone is a polyvinyl butyral backbone.

3. The adhesive according to claim 1 or 2, wherein the polyvinyl acetal backbone having side chain functional groups is obtained by reacting polyvinyl acetal with ethyl isocyanate or allyl isocyanate (meth)acrylate.

4. The adhesive according to any one of claims 1 to 3, wherein the acrylic copolymer is a reaction product comprising one or more of a polymeric unit containing a hydroxyl-functional monomer, a nitrogen-containing monomer, and combinations thereof.

5. The adhesive according to claim 4, wherein the polymeric units of one or more of the hydroxyl functional monomers, nitrogen-containing monomers, and combinations thereof are present in a weight fraction of 5% to 55% relative to the total weight of the adhesive.

6. The adhesive according to any one of claims 1 to 5, wherein the functionalized polyvinyl acetal is obtained at least in part by reacting polyvinyl acetal and ethyl isocyanate (meth)acrylate with each other.

7. The adhesive according to any one of claims 1 to 6, wherein the functionalized polyvinyl acetal is obtained at least in part by reacting polyvinyl acetal and allyl isocyanate with each other.

8. The adhesive according to claim 6 or 7, wherein the polyvinyl acetal is present in an amount of 85.0% to 99.9% by weight relative to the total weight of the functionalized polyvinyl acetal.

9. The adhesive according to any one of claims 1 to 8, wherein the adhesive is optically transparent.

10. The adhesive according to any one of claims 1 to 9, wherein the adhesive exhibits a temperature gradient as measured by dynamic mechanical analysis at 1 Hz. g The shear storage modulus at temperatures below 0℃ and above 25℃ is greater than 200 kPa.

11. The adhesive according to any one of claims 1 to 10, wherein the adhesive is derived from a precursor comprising 40% to 90% by weight of homopolymer T. g Alkyl methacrylate monomers at temperatures below 0°C.

12. The adhesive according to any one of claims 1 to 11, wherein the adhesive is substantially free of acid-functional repeating units.

13. A tape adhesive comprising a layer of adhesive according to any one of claims 1 to 12.

14. The tape adhesive of claim 13, wherein the layer is a first layer having a pair of opposite main surfaces, and further comprises a second layer disposed on one of the opposite main surfaces, wherein the second layer contains a lower weight fraction of polyvinyl acetal than the first layer.

15. The tape adhesive of claim 14, wherein the second layer comprises zero content of polyvinyl acetal.

16. A method of manufacturing an adhesive, the method comprising: Polyvinyl acetal is functionalized by reacting it with ethyl isocyanate methacrylate and / or allyl isocyanate. as well as Acrylic acid monomers are polymerized in the presence of functionalized polyvinyl acetal to form a crosslinked network of polyvinyl acetal and acrylic acid copolymer.

17. The method of claim 16, wherein the polyvinyl acetal comprises polyvinyl butyral.

18. The method according to claim 16 or 17, wherein the acrylic copolymer is a reaction product of one or more of hydroxyl-functional monomers, nitrogen-containing monomers, and combinations thereof.

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