Foldable optically transparent adhesive film

Abstract

An adhesive article includes a release liner and an adhesive layer disposed on a release surface of the release liner. The adhesive layer is the reaction product of a reaction mixture of: at least two alkyl (meth) acrylate monomers having alkyl groups having at least 4 carbon atoms, being hydroxy-functional alkyl groups or being heteroalkyl groups; at least one multifunctional (meth) acrylate; at least one surface-modified fumed silica; and at least one initiator. The adhesive layer has a variety of desirable characteristics including a Tg of less than-35 DEG C, a storage modulus (G ') of less than 200 kPa at-20 DEG C, 1 Hz as measured by DMA (Dynamic Mechanical Analysis) and is optically transparent.

Description

Summary of the Invention

[0001] Disclosed herein are adhesive compositions for forming adhesive articles and methods for preparing adhesive articles. In some embodiments, the adhesive article comprises: a first release liner having at least one release surface; and an adhesive layer disposed on the release surface of the first release liner. The adhesive layer comprises an adhesive composition that is the reaction product of a reaction mixture comprising at least two (meth)acrylate monomers of Formula 1:

[0002] CH2=CR 1 -(CO)-OR 2

[0003] Formula 1

[0004] where R 1 is hydrogen or a methyl group; -(CO)- is a carbonyl group C=O; and R 2 The adhesive layer comprises an alkyl group, a hydroxyl-functional alkyl group, or a heteroalkyl group containing at least 4 carbon atoms; at least one multifunctional (meth)acrylate; at least one surface-modified fumed silica; and at least one initiator. The adhesive layer has various desirable properties, including a Tg of less than -35°C as measured by DMA (dynamic mechanical analysis), a storage modulus (G') of less than 200 kPa at -20°C and 1 Hz, and is optically transparent.

[0005] Also disclosed is a method for forming an adhesive article, the method comprising: providing a first release liner having at least one release surface; placing a reaction mixture on at least a portion of the release surface of the first release liner; and curing the reaction mixture to form an adhesive layer. The reaction mixture is as described above. DETAILED DESCRIPTION

[0006] Many optical articles have multiple layers. These layers are often adhered to each other using adhesive layers. These adhesive layers possess a variety of desired or required properties. Achieving some of these properties is a very complex process. While adhesive layers are designed to adhere two films or substrates together, they often require additional properties. Many of these properties are difficult to achieve because imparting new properties to the adhesive layer cannot be achieved by sacrificing the adhesive properties.

[0007] A range of optically clear adhesives have been developed for use in optical articles. These adhesives possess adhesive properties while also being optically clear. This combination of properties makes them well-suited for a variety of applications. In some applications, optically clear adhesives are desired to possess additional properties. However, these new properties cannot be achieved by sacrificing either adhesive or optical properties.

[0008] Among the articles that require optically clear adhesives are foldable articles. Examples include flexible OLED displays in foldable phones, tablets, and laptops. Additionally, the trend for such devices is to reduce thickness while desiring a small folding radius. This places many design constraints on the materials used for the display. For example, a thin adhesive layer is expected to reduce the stress generated during display folding while still providing high adhesion to the various substrates of the display. Additionally, OLED displays need to function over a wide temperature range without causing the display to crack or temporarily deform due to material creep when the device is folded, rolled, bent, or flexed. However, it is often observed that when these extreme material properties are employed, peel adhesion generally decreases. Weaker peel adhesion can further increase the risk of delamination during dynamic folding. Therefore, providing an adhesive film that can withstand the mechanical deformation associated with folding and that provides sufficient adhesion to the appropriate device substrate is crucial to overall device performance.

[0009] In many cases, (meth)acrylate based pressure sensitive adhesive is prepared by reaction mixture, and this reaction mixture contains and has polar group (such as acidic group) monomer.In adhesive field, acidic monomer is usually classified as reinforcing monomer, because these monomers tend to increase the cohesive strength of (meth)acrylate based pressure sensitive adhesive.Although widely used, the monomer with acidic group may be problematic, especially in the adhesive for electronic device, because acidic group often has corrosiveness to electronic components.Therefore, preparation retains necessary cohesive strength to be used in electronic application and not comprising (meth)acrylate based pressure sensitive adhesive of acidic reinforcing monomer is a challenge.

[0010] Thus, there is a need for adhesive films that are substantially free of acidic groups and have a desired balance of peel adhesion, low haze, low Tg, low modulus, and a high R / C ratio at both 25°C and 60°C. In some embodiments, the acrylate-based adhesive layer is substantially free of acidic groups. For example, this is desirable to eliminate indium tin oxide (ITO) and metal trace corrosion, which could otherwise damage the touch sensor and its integrated circuit or connector. As used herein, "substantially free" means that the adhesive layer has less than about 2 parts by weight, specifically less than about 0.5 parts, and more specifically less than about 0.1 parts%.

[0011] In the present disclosure, adhesive films comprising a polymer matrix and a small amount of hydrophobically surface-modified fumed silica are described that possess this desirable balance of properties.

[0012] Disclosed herein are adhesive articles. In some embodiments, the adhesive article includes a first release liner having at least one release surface; and an adhesive layer disposed on the release surface of the first release liner. The adhesive layer comprises the reaction product of a reaction mixture comprising: at least two (meth)acrylate monomers of Formula 1:

[0013] CH2=CR 1 -(CO)-OR 2

[0014] Formula 1

[0015] where R 1 is hydrogen or a methyl group; -(CO)- is a carbonyl group C=O; and R 2 An alkyl group, a hydroxyl-functional alkyl group, or a heteroalkyl group containing at least 4 carbon atoms; at least one multifunctional (meth)acrylate; at least one surface-modified fumed silica; and at least one initiator. The adhesive layer has a Tg of less than -35°C, a storage modulus (G') of less than 200 kPa at -20°C and 1 Hz as measured by DMA (dynamic mechanical analysis), and is optically transparent. In some embodiments, the adhesive layer has an R / C (recovery / creep) ratio greater than 2.0. The adhesive article has additional desirable properties, such as a 180° peel adhesion to glass greater than 0.8 kg / inch (31 N / dm), and optical properties, such as a haze value of less than 1.0% or even 0.5% at a film thickness of 100 microns. Also disclosed are methods for preparing adhesive articles and curable compositions for preparing adhesive articles.

[0016] As used herein, the term "adhesive" refers to a polymeric composition that can be used to adhere two adherends together. Examples of adhesives are pressure-sensitive adhesives and heat-activated adhesives.

[0017] Heat activated adhesives are not tacky at room temperature but become tacky and able to bond to substrates at elevated temperatures. g (glass transition temperature) or melting point (T m ) is usually higher than room temperature. When the temperature rises above T g or T m When the storage modulus decreases, the adhesive becomes tacky.

[0018] Pressure sensitive adhesive compositions are well known to those skilled in the art and have the following characteristics: (1) strong and lasting tack, (2) adhesion with no more than finger pressure, (3) sufficient ability to remain on an adherend, and (4) sufficient cohesive strength to enable clean removal from the adherend. It has been found that materials that function well as pressure sensitive adhesives are polymers designed and formulated to exhibit the desired viscoelastic properties, such that tack, peel adhesion, and shear holding power reach a desired balance. Achieving the proper balance of characteristics is not a simple matter.

[0019] The term "(meth)acrylate" refers to monomeric acrylate or methacrylate esters of alcohols. Acrylate and methacrylate monomers or oligomers are collectively referred to herein as "(meth)acrylates." Materials referred to as "(meth)acrylate-functional" are materials that contain one or more (meth)acrylate groups.

[0020] The terms "room temperature" and "ambient temperature" are used interchangeably to refer to temperatures in the range of 20°C to 25°C.

[0021] The terms "Tg" and "glass transition temperature" are used interchangeably. If measured, Tg values ​​are determined by DMA (dynamic mechanical analysis) at a scan rate of 3°C / min unless otherwise indicated. Alternatively, the Tg value of a copolymer is sometimes not measured, but rather calculated using the well-known Fox equation using the homopolymer Tg value provided by the monomer supplier, as understood by those skilled in the art.

[0022] As used herein, the term "adjacent" when referring to two layers means that the two layers are adjacent to each other with no intervening open space between them. They can be in direct contact with each other (eg, laminated together) or there can be intervening layers.

[0023] As used herein, the terms "polymer" and "macromolecule" are consistent with their common usage in chemistry. Polymers and macromolecules are composed of many repeating subunits. As used herein, the term "macromolecule" is used to describe a group attached to a monomer that has multiple repeating units. The term "polymer" is used to describe the resulting material formed by a polymerization reaction.

[0024] The term "alkyl" refers to a monovalent group that is a radical of an alkane, which is a saturated hydrocarbon. The alkyl group can be linear, branched, cyclic, or a combination thereof, and typically has 1 to 20 carbon atoms. In some embodiments, the alkyl group contains 1 to 18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, and ethylhexyl.

[0025] The term "alkylene" refers to a divalent group that is a radical of an alkane. An alkylene group can be linear, branched, cyclic, or a combination thereof. An alkylene group typically has 1 to 20 carbon atoms. In some embodiments, an alkylene group contains 1 to 18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. The radical centers of an alkylene group can be on the same carbon atom (i.e., an alkylidene group) or on different carbon atoms.

[0026] The term "heteroalkyl" refers to a monovalent group comprising at least two alkylene groups linked by sulfur, oxygen, or -NR-, where R is an alkyl group. A heteroalkyl group can be linear, branched, cyclic, substituted with alkyl groups, or a combination thereof. Some heteroalkyl groups are polyoxyalkyl groups, where the heteroatom is oxygen, such as, for example,

[0027] -CH2CH2(OCH2CH2) n OCH2CH3.

[0028] The term "heteroalkylene" refers to a divalent group comprising at least two alkylene groups linked by a thiol, oxy, or -NR- group, where R is an alkyl group. The heteroalkylene group can be linear, branched, cyclic, substituted with alkyl groups, or a combination thereof. Some heteroalkylene groups are polyoxyalkylenes in which the heteroatom is oxygen, such as, for example

[0029] -CH2CH2(OCH2CH2) n OCH2CH2-.

[0030] The terms "free radical polymerizable" and "ethylenically unsaturated" are used interchangeably and refer to reactive groups containing a carbon-carbon double bond capable of polymerizing via a free radical polymerization mechanism.

[0031] Unless otherwise indicated, the terms "optically clear" and "visibly transmissive" are used interchangeably and refer to articles, films, or adhesives that have high light transmittance over at least a portion of the visible light spectrum (about 400 nm to about 700 nm). Typically, an optically clear article has a visible light transmittance of at least 90% and a haze of less than 10%.

[0032] Unless otherwise indicated, "optically clear" refers to an adhesive or article that has high light transmittance over at least a portion of the visible light spectrum (about 400 nm to about 700 nm) and exhibits low haze (typically less than about 5%, or even less than about 2%). In some embodiments, the optically clear article exhibits a haze of less than 1% at a thickness of 50 microns or greater, or even 0.5% at a thickness of 50 microns or greater. Typically, the optically clear article has a visible light transmittance of at least 95%, typically higher, such as 97%, 98%, or even 99% or higher.

[0033] As used herein, the term "flexible device" refers to a device that can undergo repeated flexing or rolling motions with a bending radius as low as 200 mm, 100 mm, 50 mm, 20 mm, 10 mm, 5 mm, or even less than 2 mm.

[0034] Disclosed herein are adhesive articles. In some embodiments, the adhesive article includes a first release liner having at least one release surface; and an adhesive layer disposed on the release surface of the first release liner. The adhesive layer comprises the reaction product of a reaction mixture comprising: at least two (meth)acrylate monomers of Formula 1:

[0035] CH2=CR 1 -(CO)-OR 2

[0036] Formula 1

[0037] where R 1 is hydrogen or a methyl group; -(CO)- is a carbonyl group C=O; and R 2 is an alkyl group, a hydroxyl-functional alkyl group, or a heteroalkyl group containing at least 4 carbon atoms; at least one multifunctional (meth)acrylate; at least one surface-modified fumed silica; and at least one initiator. The adhesive layer has a Tg of less than -35°C, a storage modulus (G') of less than 200 kPa at -20°C and 1 Hz as measured by DMA (dynamic mechanical analysis), and is optically transparent. In some embodiments, the adhesive layer has an R / C (recovery / creep) ratio greater than 2.0. In addition, the adhesive article may have properties such as a 180° peel adhesion to glass greater than 0.8 kg / inch (31 N / dm) and a haze value of less than 1.0%, or even less than 0.5%, at a film thickness of 100 microns. In some embodiments, the multifunctional (meth)acrylate comprises a multifunctional urethane-(meth)acrylate. In some embodiments, the reaction mixture further comprises an adhesion promoter, such as a silane coupling agent, and a Tg modifying monomer, such as a monofunctional urethane-(meth)acrylate.

[0038] In some embodiments, the reaction product is formed by prepolymerizing at least two (meth)acrylate monomers and at least one initiator to form a coatable slurry. To the coatable slurry, a crosslinking agent, such as at least one multifunctional urethane (meth)acrylate, at least one silane coupling agent, at least one surface-modified fumed silica, and at least one initiator are added to form a curable mixture. The curable mixture is placed on the release surface of a release liner and cured to form an adhesive layer. In other embodiments, the reaction product is formed by mixing the components of the reaction mixture, placing the reaction mixture on the release surface of a release liner and curing to form an adhesive layer. Typically, the adhesive layer comprises a pressure-sensitive adhesive.

[0039] Adhesive articles include release liners. In the adhesive field, release liners are fully understood to be films or sheet products with at least one surface to which the adhesive will not adhere securely. Typical release liners include those prepared from paper (e.g., kraft paper) or polymeric materials (e.g., polyolefins such as polyethylene or polypropylene, ethylene vinyl acetate, polyurethanes and polyesters such as polyethylene terephthalate, and combinations thereof). Release liners are coated with a release agent layer, such as silicone, fluorinated silicone-containing materials, or fluorocarbon-containing materials. Exemplary release liners include, but are not limited to, the liner commercially available from CP Film, Martinsville, Va., in Martinsville, Virginia, under the trade name "T-30" and "T-10," which has a silicone release coating on polyethylene terephthalate film. Particularly suitable are silicone-coated PET release liners purchased from SKC Haas with RF12ASW, RF02N, and RF32N.

[0040] In some embodiments, the adhesive article further comprises a second release liner disposed on the adhesive layer. The second release liner may be the same as or different from the first release liner. The use of a second release liner helps protect the adhesive layer so that it can be handled prior to use of the adhesive article.

[0041] The reaction mixture for forming the adhesive layer comprises at least two (meth)acrylate monomers of Formula 1:

[0042] CH2=CR 1 -(CO)-OR 2

[0043] Formula 1

[0044] where R 1 is hydrogen or a methyl group; -(CO)- is a carbonyl group C=O; and R 2is an alkyl group, a hydroxy-functional alkyl group or a heteroalkyl group containing at least 4 carbon atoms.

[0045] At least two (meth)acrylate monomers are different from each other, but may be the same type of monomer (for example, both (meth)acrylate monomers may be alkyl (meth)acrylates having different alkyl groups). 2 Each R in the group 2 Description of the group.

[0046] In some embodiments, at least one of the at least two (meth)acrylate monomers comprises an alkyl (meth)acrylate monomer having an alkyl group comprising at least 4 carbon atoms.A variety of alkyl (meth)acrylate monomers are suitable. Examples of suitable (meth)acrylate monomers include n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, hexyl acrylate, hexyl methacrylate, n-octyl acrylate, n-octyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, isoamyl acrylate, isooctyl acrylate, isononyl acrylate, decyl acrylate, isodecyl acrylate, isodecyl methacrylate, lauryl acrylate, lauryl methacrylate, tridecyl acrylate, tridecyl methacrylate, myristyl acrylate, myristyl methacrylate, hexadecyl acrylate, hexadecyl methacrylate, stearyl acrylate, stearyl methacrylate, isostearyl acrylate, isostearyl methacrylate, eicosyl acrylate, eicosyl methacrylate, hexacosyl acrylate, hexacosyl methacrylate, 2-methylbutyl acrylate, 4-methyl-2-pentyl acrylate, 4-tert-butylcyclohexyl methacrylate, cyclohexyl methacrylate, and isobornyl acrylate. In some embodiments, the alkyl (meth)acrylate monomer has an alkyl group having 4 to 18 carbon atoms. Particularly suitable monomers include n-butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, isooctyl acrylate, and lauryl acrylate.

[0047] In some embodiments, at least one of the at least two (meth)acrylate monomers comprises a monomer having an alkyl group substituted with at least one hydroxyl group. A variety of hydroxy-functional (meth)acrylates are suitable. Examples of suitable hydroxy-functional (meth)acrylate monomers include 4-hydroxybutyl acrylate (4-HBA), 4-hydroxybutyl methacrylate (4-HBMA), 2-hydroxyethyl acrylate (2-HEA), and 2-hydroxyethyl methacrylate (2-HEMA). Particularly suitable hydroxy-functional (meth)acrylate monomers are those having a hydroxy-functional alkyl group with at least 4 carbon atoms, such as 4-hydroxybutyl acrylate (4-HBA).

[0048] In some embodiments, at least one of the at least two (meth)acrylate monomers comprises a monomer having a heteroalkyl group. A heteroalkyl group is an alkyl group that includes at least one heteroatom, such as oxygen, nitrogen, or sulfur. The heteroalkyl group can be linear, branched, cyclic, substituted with an alkyl group, or a combination thereof. Examples of suitable (meth)acrylate monomers having a heteroalkyl group include monomers having -(O-(CH2) n -) m -R type alkylene oxide repeating units, wherein n is 1, 2 or 3, and m is an integer of 2 or greater, and R is an alkyl group. An example is ethoxyethoxyethyl acrylate. Other suitable (meth)acrylate monomers having heteroalkyl groups include those having cyclic groups, such as acryloylmorpholine.

[0049] Some specific combinations of (meth)acrylate monomers are particularly suitable. In some embodiments, the at least two (meth)acrylate monomers of Formula 1 include: at least one wherein R 2 is a (meth)acrylate monomer having a hydroxyl-functional alkyl group of at least 4 carbon atoms; and at least two wherein each R 2 Independently, an alkyl (meth)acrylate monomer having an alkyl group of 4 to 18 carbon atoms.

[0050] In other embodiments, the at least two (meth)acrylate monomers of Formula 1 include: at least one wherein R 2 is a (meth)acrylate monomer having a hydroxyl-functional alkyl group of at least 4 carbon atoms; at least one of which R 2 is an alkyl (meth)acrylate monomer having an alkyl group of 4 to 18 carbon atoms; and at least one wherein R 2 A (meth)acrylate monomer having a heteroalkyl group.

[0051] The reaction mixture forming the adhesive layer also includes at least one multifunctional (meth) acrylate. Multifunctional (meth) acrylate includes tri(meth) acrylate and di(meth) acrylate (i.e., a compound comprising three or two (meth) acrylate groups). Typically, a di(meth) acrylate crosslinking agent (i.e., a compound comprising two (meth) acrylate groups) is used. Available tri(meth) acrylates include, for example, trimethylolpropane tri(meth) acrylate, propoxylated trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, tris(2-hydroxyethyl) isocyanurate triacrylate, and pentaerythritol triacrylate. Useful di(meth)acrylates include, for example, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, alkoxylated 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, cyclohexanedimethanol di(meth)acrylate, alkoxylated cyclohexanedimethanol diacrylate, ethoxylated bisphenol A di(meth)acrylate, neopentyl glycol diacrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, and urethane di(meth)acrylate.

[0052] In some embodiments, the multifunctional (meth)acrylate comprises a urethane-(meth)acrylate of Formula 2:

[0053] CH2=CR 1 -(CO)-OAO-(CO)-CR 1 =CH2

[0054] Formula 2

[0055] where R 1 is hydrogen or a methyl group; -(CO)- is a carbonyl group C=O; and A is a divalent group containing at least one urethane bond.

[0056] In some embodiments, the urethane (meth)acrylate has Formula 2, wherein the divalent group A comprises a group of Formula 3:

[0057] -LO-(CO)-NH-R 3 -NH-(CO)-OL-

[0058] Formula 3

[0059] wherein each L is independently an alkylene group; and R 3 is a divalent alkylene group or a heteroalkylene group.

[0060] Examples of suitable multifunctional urethane-(meth)acrylate monomers include the commercially available urethane diacrylate oligomers EB230 from Allnex, and 61246 and 6127 from Eternal.

[0061] The reaction mixture for forming the adhesive layer further comprises at least one surface-modified hydrophobic fumed silica. In some embodiments, the surface-modified hydrophobic fumed silica comprises disilazane-treated fumed silica, silane-treated fumed silica, or polydimethylsiloxane-treated fumed silica. In some embodiments, the solid fumed silica is added to the curable composition as a solid, while in other embodiments, the hydrophobic fumed silica is dispersed in the curable liquid component of the curable composition, and the dispersion is added to the remainder of the curable composition.

[0062] Examples of suitable surface-modified fumed silica include HMDS (hexamethyldisilazane)-treated fumed silica commercially available as AEROSIL R812 and AEROSIL R812S from Evonik, isooctylsilane-functionalized fumed silica particles, and PDMS-treated fumed silica commercially available as CAB-O-SIL TS-720 from CABOT.

[0063] An unexpected discovery was the observation that low levels of added surface modified fumed silica additive provided improvements to the desired properties of the adhesive layer. In some embodiments, levels of 0.1 to 5 weight percent based on 100 parts by weight of the adhesive base are suitable.

[0064] The reaction mixture also includes at least one initiator. Typically, the one or more initiators include a photoinitiator, which means that the initiator is activated by light, typically ultraviolet (UV) light. Examples of suitable free radical photoinitiators include ESACURE ONE, OMNIRAD 184, OMNIRAD TPO, OMNIRAD 819, OMNIRAD 1173, OMNIRAD 907, OMNIRAD 127, and OMNIRAD BP, all commercially available from IGM Resins, Charlotte, NC.

[0065] The reaction mixture may also contain a property modifier. A particularly suitable property modifier is an adhesion promoter. Among suitable adhesion promoters are silane coupling agents. In some embodiments, the silane coupling agent comprises a compound of Formula 4:

[0066] G-Si-R4 R 5 R 6

[0067] Formula 4

[0068] wherein G is a functional group including an epoxy group or a (meth)acrylate group; each R 4 、R 5 and R 6 is independently an alkyl group or an alkoxy group having 1 to 3 carbon atoms, provided that R 4 、R 5 and R 6 At least one of them is an alkoxy group.

[0069] Examples of suitable silane coupling agents include methacryloxymethyltrimethoxysilane (SIM 6482.0), methacryloxymethyltriethoxysilane (SIM 6483.0), commercially available from Gelest, and 3-glycidoxypropyltrimethoxysilane commercially available from Shin-Etsu as KBM403.

[0070] The reaction mixture may also include one or more additional monomers to modify the properties of the reaction product. These monomers are typically monofunctional, having an average functionality of less than 2. In some embodiments, the reaction mixture also includes at least one Tg-modifying monomer having a homopolymer Tg of less than -35°C. Particularly suitable Tg-modifying monomers are monofunctional urethane-(meth)acrylates. A particularly suitable monofunctional urethane-(meth)acrylate is monomer LD301 (Tg = -69), commercially available from AGC Chemicals.

[0071] The reaction mixture may have a wide composition range. In some embodiments, the reaction mixture further comprises:

[0072] 60 to 99 parts by weight of at least two (meth)acrylate monomers of Formula 1

[0073] 0.1 to 10 parts by weight of at least one multifunctional urethane-(meth)acrylate;

[0074] 0.01 to 1.0 parts by weight of at least one silane coupling agent;

[0075] 0.1 to 5 parts by weight of at least one surface-modified fumed silica; and

[0076] 0.01 to 2 parts by weight of at least one initiator.

[0077] In some embodiments, the reaction mixture further comprises:

[0078] 1 to 30 parts by weight of at least one monofunctional urethane-(meth)acrylate.

[0079] Adhesive layer can have various thicknesses. As mentioned above, usually expect to use thinner and thinner adhesive layer, so current adhesive layer may be as thin as desired. Current adhesive layer can have the thickness of 10 microns to 300 microns.

[0080] In some embodiments, the adhesive article comprises a transfer tape. In these embodiments, as described above, the adhesive article further comprises a second release liner having at least one release surface, wherein the release surface of the second release liner is placed on the adhesive layer. The transfer tape can be used to prepare a variety of articles. The transfer tape can be laminated to a film or tape backing to form an adhesive article that can be adhered to a substrate, or the transfer tape can be laminated to a substrate, the remaining release liner can be removed, and the exposed surface can be laminated to a second substrate.

[0081] As described above, the adhesive articles of the present disclosure have a variety of desirable properties. The adhesive articles are substantially free of acidic groups. These adhesive properties are particularly suitable for foldable devices. Folding creates significant stress on the adhesive layer and can cause the adhesive to fail, can result in the formation of optical defects, and can cause other problems.

[0082] The adhesive layer of the present disclosure has a low Tg of less than -35°C. In contrast, pressure-sensitive adhesives typically have a Tg value less than room temperature (20°C) and typically have a Tg less than 0°C. The low Tg value of the current adhesive tends to increase adhesion to the substrate surface and better reduce the stress generated when folded. Tg can be measured in a variety of ways, and when the homopolymer Tg of the monomer is known, it is usually calculated using the well-known Fox formula. In the current disclosure, the Tg value is measured by DMA (dynamic mechanical analysis).

[0083] The storage modulus of the current adhesives is also low as expected for flexibility. In some embodiments, the storage modulus (G') at -20°C, 1 Hz is less than 200 kPa. In the current disclosure, the storage modulus (such as Tg) is measured by DMA (dynamic mechanical analysis).

[0084] Another desirable adhesive characteristic is 180° peel adhesion to glass. Typically, the 180° peel adhesion to glass is greater than 0.8 kg / inch (31 N / dm) when peeled at a rate of 12 inches / minute.

[0085] Current adhesives also have desirable optical properties. Typically, adhesives are optically clear, meaning they have at least 90% visible light transmittance and less than 5% haze. In some embodiments, the adhesive layer has a low haze value of less than 1.0% or even 0.5% at a film thickness of 100 microns.

[0086] Another desirable characteristic of current adhesive layers is the R / C (recovery / creep) ratio. Current adhesives have an R / C ratio greater than 2.0. The R / C ratio is calculated as described in the Examples section. Recovery % is calculated by applying two strains to a sample of the adhesive using the following formula:

[0087] % Recovery = ((Strain 1 - Strain 2) / Strain 1) x 100%.

[0088] Creep % is measured under stress and constant shear. The ratio is calculated from these values ​​using the following formula:

[0089] R / C ratio = recovery / creep.

[0090] Also disclosed are methods of forming an adhesive article. In some embodiments, the method of forming an adhesive article includes: providing a first release liner having at least one release surface; placing a reaction mixture on at least a portion of the release surface of the first release liner; and curing the reaction mixture to form an adhesive layer. The reaction mixture is as described above and comprises at least two (meth)acrylate monomers of Formula 1:

[0091] CH2=CR 1 -(CO)-OR 2

[0092] Formula 1

[0093] where R 1 is hydrogen or a methyl group; -(CO)- is a carbonyl group C=O; and R 2 is an alkyl group, a hydroxyl-functional alkyl group, or a heteroalkyl group containing at least 4 carbon atoms; at least one multifunctional (meth)acrylate, at least one surface-modified fumed silica, and at least one initiator. As described above, in some embodiments, the multifunctional (meth)acrylate is a multifunctional urethane-(meth)acrylate. In addition, in many embodiments, the reaction mixture also contains an adhesion promoter, typically a silane coupling agent. Each of these components is as described above.

[0094] In some embodiments, a reaction mixture is placed on at least a portion of the release surface of a first release liner, wherein the reaction mixture comprises forming a curable mixture, wherein forming the curable mixture comprises: preparing a mixture comprising at least two (meth)acrylate monomers and at least one initiator, prepolymerizing the at least two (meth)acrylate monomers and the at least one initiator to form a coatable slurry. At least one multifunctional urethane (meth)acrylate, at least one silane coupling agent, at least one surface-modified fumed silica, and at least one initiator are added to the coatable slurry to form a curable mixture. The curable mixture is placed on at least a portion of the release surface of the first release liner and cured to form an adhesive layer.

[0095] In other embodiments, placing the reaction mixture on at least a portion of the release surface includes preparing a reaction mixture comprising mixing at least two (meth)acrylate monomers, at least one multifunctional urethane-(meth)acrylate, at least one silane coupling agent, at least one surface-modified fumed silica, and at least one initiator. The reaction mixture is placed on at least a portion of the release surface of the first release liner and cured to form the adhesive layer.

[0096] The reaction mixture may contain additional components. In some embodiments, the reaction mixture further comprises at least one Tg-modifying monomer having a homopolymer Tg of less than -35°C, as described above.

[0097] In some embodiments, the method further comprises: providing a second release liner having at least one release surface; and positioning the release surface of the second release liner on the adhesive layer before or after curing.

[0098] Example

[0099] These examples are for illustrative purposes only and are not intended to limit the scope of the appended claims. Unless otherwise indicated, all parts, percentages, ratios, etc. in the examples and the remainder of the specification are by weight. Unless otherwise indicated, all solvents and other reagents used were obtained from Sigma-Aldrich Chemical in Milwaukee, Wisconsin. The following abbreviations are used: nm = nanometer; mm = millimeter; cm = centimeter; in = inch; kg = kilogram; Pa = Pascal; kPa = kilopascal; kN = kilonewton; mW = milliwatt; sec = second; min = minute; hr = hour; Hz Hertz; CTH = controlled temperature and humidity, cps = centipoise.

[0100] Abbreviations

[0101]

[0102]

[0103] Synthesis Example: Preparation of SE1 of MFS-1

[0104] To a glass bottle was added 192 g of CAB-O-SPERSE 2017A (available from Cabot Corp., Alpharetta, Ga., USA as an approximately 17% solids silica dispersion in water). With magnetic stirring, 216 g of isopropyl alcohol was slowly added. To this mixture were added 3.55 g of isooctyltrimethoxysilane (available from Wacker Chemical Corp., Adrian, Mich., USA as BS136) and 1.38 g of methyltrimethoxysilane (available from Wacker Chemical Corp., Adrian, Mich., USA as Silane M1-trimethoxysilane). The bottle was tightly sealed with a cap and the combined mixture was heated and stirred in a water bath at 80° C. for 24 hours. After cooling to room temperature, the contents were transferred to a flask using an isopropyl alcohol rinse. To this was added 108.8 g of 2-ethylhexyl acrylate (available from BASF as 2EHA) and 0.011 g of 4-hydroxyTEMPO (available from BASF as Prostab 5198). Water and isopropanol were removed by vacuum distillation on a rotary evaporator, with additional small amounts (15 to 30 g) of isopropanol periodically added as needed to aid water removal. The resulting dispersion of modified silica in 2-ethylhexyl acrylate (MFS-1) was collected at 168.4 g.

[0105] Test Method

[0106] Rheological property measurements

[0107] Tg, storage modulus (G'), tan δ, creep, and recovery values ​​were measured using a TA Dynamic HR-30 in oscillatory shear mode. The test film was stacked to 2 mm thickness without a release liner and placed between parallel plates for Tg, storage modulus (G') and loss modulus (G"), tan δ (8 mm diameter plates and 1 Hz frequency). Tan δ was calculated using the following formula.

[0108] tanδ=loss modulus (G”) / storage modulus (G’)

[0109] After 10 minutes, the creep value is measured at 2000 Pa stress and constant shear force (strain 1 at 600 seconds). Then, all stress is released after another 10 minutes to record the endpoint value (strain 2 at 1200 seconds). Recovery is calculated by the following formula:

[0110] Recovery % = ((Strain 1 - Strain 2) / Strain 1) × 100%

[0111] The recovery / creep ratio is calculated by the following formula:

[0112] R / C ratio = recovery / creep

[0113] Optical properties - haze measurement

[0114] The test film was laminated between two glass substrates using a vacuum laminator, and the haze value was measured using a Hunter Lab instrument.

[0115] 180° peel adhesion measurement

[0116] The test film sample was cut into 10 mm wide strips and one of the release liners was removed, and the adhesive was laminated to a 10 mm wide strip of PET (polyethylene terephthalate). The other release liner was removed and the adhesive surface was laminated to a glass substrate using a 2 kg roller. An autoclave was applied to the prepared sample. (Autoclave conditions -50°C temperature, 3 kg / cm 2 The pressure was maintained for 20 minutes. The samples were then allowed to rest in a CTH chamber (23°C, 50% RH) for 24 hours before testing. 180° peel was performed at 12 inches / minute (30 cm / minute) using an Instron (Model #5965, load cell 2 kN).

[0117] Examples E1 to E10 and Comparative Examples CE1 and CE2

[0118] Preparation of coatable slurries S1 to S10

[0119] Four groups of slurries with different chemical compositions were prepared, for a total of 10 slurries. Group 1 contained slurries S1 to S2, Group 2 contained slurries S3 to S6; Group 3 contained slurries S7 to S8; and Group 4 contained slurries S9 to S10. The compositions are shown in Tables 1A to 1D. The reaction components are expressed in fractions, while the initiator is expressed in pph. The slurry components were mixed in a transparent jar, nitrogen was passed into the jar to create an inert atmosphere, and the jar was sealed. An output wavelength of 365 nm and an intensity of 0.3 mW / cm were used. 2 The mixture in the jar was irradiated with a light source until a viscous slurry solution of about 1000 cps was obtained.

[0120] Table 1A: Group 1 (Slurries S1 to S2)

[0121]

[0122] Table 1B: Group 2 (Slurries S3 to S6)

[0123]

[0124] Table 1C: Group 3 (Slurries S7 to S8)

[0125]

[0126] Table 1D: Group 4 (Slurries S9 to S10)

[0127]

[0128] Preparation of Adhesive Films E1 to E8 and Comparative Films CE1 to CE4

[0129] Four sets of adhesive films with different chemical compositions were prepared, totaling eight films, along with a comparative film for each set. Set 1 consisted of slurries S1 to S2 and included Example E1 and Comparative Example CE1; Set 2 consisted of slurries S3 to S6 and included Examples E2 to E6 and Comparative Example CE2; Set 3 consisted of slurries S7 to S8 and included Example E7 and Comparative Example CE3; and Set 4 consisted of slurries S9 to S10 and included Example E8 and Comparative Example CE4. The compositions are shown in Tables 2A to 2D.

[0130] Each example was prepared by combining the components from Table 2 below, mixing thoroughly and coating between Release Liner-1 and Release Liner-2 to a thickness of 0.05 mm and curing using a 405 nm light source.

[0131] Table 2A: Group 1 (E1 and CE1)

[0132] Components Example E1 Comparative Example CE1 Slurry S1 (parts) 92 ---- Slurry S2 (parts) ---- 100 Initiator-2 (parts) 0.25 0.25 DA-1 (number of copies) ---- 0.75 DA-3 (number of copies) 1.2 ---- Silane (parts) 0.15 0.1 MFS-1 (number of copies) 9 ----

[0133] Table 2B: Group 2 (E2 to E6 and CE2)

[0134] Components E2 E3 E4 E5 E6 CE2 Slurry S3 (parts) 83 ---- ---- ---- ---- ---- Slurry S4 (parts) ---- 96 96 96 ---- ---- Slurry S5 (parts) ---- ---- ---- ---- 83 ---- Slurry S6 (parts) ---- ---- ---- ---- ---- 100 Initiator-3 (parts) 0.25 0.25 0.25 0.25 0.25 0.25 UA-1 (number of copies) 12 12 12 12 12 12 DA-2 (number of copies) 1.5 1.5 1.5 1.5 1.5 1.5 Silane 0.1 0.1 0.1 0.1 0.1 0.1 MFS-1 17 ---- ---- ---- 17 ---- MFS-2 ---- 4 ---- ---- ---- ---- MFS-3 ---- ---- ---- 4 ---- ---- MFS-4 ---- ---- 4 ---- ---- ----

[0135] Table 2C: Group 1 (E7 and CE3)

[0136] Components Example E7 Comparative Example CE3 Slurry S7 (parts) 83 ---- Slurry S8 (parts) ---- 100 Initiator-3 (parts) 0.2 0.25 UA-1 (number of copies) 12 ---- DA-1 (number of copies) ---- 1.25 DA-2 (number of copies) 1.5 ---- Silane (parts) 0.1 0.1 MFS-1 (number of copies) 17 ----

[0137] Table 2D: Group 4 (E8 and CE4)

[0138] Components Example E8 Comparative Example CE4 Slurry S9 (parts) 83 ---- Slurry S10 (parts) ---- 100 Initiator-3 (parts) 0.25 0.2 DA-1 (number of copies) 0.9 ---- DA-2 (number of copies) ---- 1.5 Silane (parts) 0.1 0.1 MFS-1 (number of copies) 17 ----

[0139] Characteristics of Adhesive Films E1 to E8 and Comparative Films CE1 to CE4

[0140] The adhesive films were tested for 180° peel adhesion, creep, recovery, C / R ratio, Tg, modulus, tan δ, and haze according to the test methods and calculations described above. The data for Group 1 are shown in Table 3A, the data for Group 2 are shown in Table 3B, the data for Group 3 are shown in Table 3C, and the data for Group 4 are shown in Table 3D.

[0141] Table 3A: Characteristics of Group 1

[0142] characteristic E1 CE1 Peel Adhesion at 25°C (Kg / in) {N / dm} 1.1{42} 0.8{31} Peel Adhesion at 60°C (Kg / in) {N / dm} 0.6{23} 0.5{19} C1 Creep at 25℃ (%) 28 25 R1 Recovery at 25℃ (%) 89 93 R1 / C1 ratio at 25°C 3.2 3 / 7 C1 Creep at 60℃ (%) 24 28 R1 Recovery at 60℃ (%) 93 94 R1 / C1 ratio at 60°C 3.9 3.4 Tg(℃) -47 -43.6 G' (kPa) at 20℃ 90 128 G' (kPa) at 25°C 40 46 G' (kPa) at 65°C 26 29 G' (kPa) at 85°C 22 25 tanδ at 70℃ 0.31 0.30 Haze (%) 0.1 0.1

[0143] Table 3B: Characteristics of Group 2

[0144]

[0145] Table 3C: Characteristics of Group 3

[0146] characteristic E7 CE3 Peel Adhesion at 25°C (Kg / in) {N / dm} 1.0{39} 0.7{27} Peel Adhesion at 60°C (Kg / in) {N / dm} 0.7{27} 0.5{19} C1 Creep at 25℃ (%) 26 27 R1 Recovery at 25℃ (%) 93 93 R1 / C1 ratio at 25°C 3.6 3.4 C1 Creep at 60℃ (%) 37 27 R1 Recovery at 60℃ (%) 95 94 R1 / C1 ratio at 60°C 2.6 3.5 Tg(℃) -50.1 -46.2 G' (kPa) at 20℃ 58 92 G' (kPa) at 25°C 23 36 G' (kPa) at 65°C 15 23 G' (kPa) at 85°C 13 20 tanδ at 70℃ 0.30 0.30 Haze (%) 0.1 0.1

[0147] Table 3D: Characteristics of Group 4

[0148] characteristic E8 CE4 Peel Adhesion at 25°C (Kg / in) {N / dm} 1.2{46} 1.0{39} Peel Adhesion at 60°C (Kg / in) {N / dm} 0.5{19} 1.0{39} C1 Creep at 25℃ (%) 26 53 R1 Recovery at 25℃ (%) 92 85 R1 / C1 ratio at 25°C 3.5 1.6 C1 Creep at 60℃ (%) 28 89 R1 Recovery at 60℃ (%) 94 86 R1 / C1 ratio at 60°C 3.3 1.0 Tg(℃) -45.8 -47.3 G' (kPa) at 20℃ 92 86 G' (kPa) at 25°C 36 31 G' (kPa) at 65°C 23 18 G' (kPa) at 85°C 19 15 tanδ at 70℃ 0.32 0.38 Haze (%) 0.1 0.1

Claims

1. An adhesive product, comprising: a first release liner having at least one release surface; and an adhesive layer disposed on the release surface of the first release liner, the adhesive layer comprising the reaction product of a reaction mixture comprising: At least two acid-free (meth)acrylate monomers of Formula 1: CH2=CR 1 -(CO)-OR 2 Formula 1 where R 1 is hydrogen or a methyl group; -(CO)- is a carbonyl group C=O; and R 2 is an alkyl group, a hydroxy-functional alkyl group or a heteroalkyl group containing at least 4 carbon atoms; at least one multifunctional (meth)acrylate; at least one surface-modified fumed silica; and at least one initiator, The adhesive layer has a Tg of less than -35°C as measured by DMA (dynamic mechanical analysis), a storage modulus (G') of less than 200 kPa at -20°C and 1 Hz, and is optically clear.

2. The adhesive article of claim 1 , wherein the reaction product is formed by prepolymerizing the at least two (meth)acrylate monomers and at least one initiator to form a coatable syrup, and adding to the coatable syrup: the at least one multifunctional (meth)acrylate; said at least one surface-modified fumed silica; and at least one initiator to form a curable mixture; and placing the curable mixture on the release surface of the release liner and curing to form the adhesive layer.

3. The adhesive article of claim 1, wherein the at least one multifunctional (meth)acrylate comprises a urethane-(meth)acrylate.

4. The adhesive article of claim 1, wherein the reaction mixture further comprises an adhesion promoting additive.

5. The adhesive article of claim 1, wherein the adhesive layer has an R / C (recovery / creep) ratio greater than 2.

0.

6. The adhesive article of claim 1 , wherein the at least two (meth)acrylate monomers of Formula 1 comprise: At least one of R 2 is a (meth)acrylate monomer having a hydroxy-functional alkyl group of at least 4 carbon atoms; and At least two of each R 2 Independently, an alkyl (meth)acrylate monomer having an alkyl group of 4 to 18 carbon atoms.

7. The adhesive article of claim 1, wherein the at least two (meth)acrylate monomers of Formula 1 comprise: At least one of R 2 is a (meth)acrylate monomer having a hydroxy-functional alkyl group of at least 4 carbon atoms; At least one of R 2 is an alkyl (meth)acrylate monomer having an alkyl group of 4 to 18 carbon atoms; and At least one of R 2 A (meth)acrylate monomer having a heteroalkyl group.

8. The adhesive article of claim 3, wherein the at least one multifunctional urethane-(meth)acrylate comprises a compound of Formula 2: CH2=CR 1 -(CO)-OAO-(CO)-CR 1 =CH2 Formula 2 where R 1 is hydrogen or a methyl group; -(CO)- is a carbonyl group C=O; and A is a divalent group containing at least one urethane bond.

9. The adhesive article of claim 6, wherein the divalent group A comprises a group of Formula 3: -LO-(CO)-NH-R 3 -NH-(CO)-OL- Formula 3 wherein each L is independently an alkylene group; and R 3 is a divalent alkylene group or a heteroalkylene group.

10. The adhesive article of claim 4, wherein the at least one adhesion-promoting additive comprises a silane coupling agent of Formula 4: G-Si-R 4 R 5 R 6 Formula 4 wherein G is a functional group comprising an epoxy group or a (meth)acrylate group; Each R 4 、R 5 and R 6 is independently an alkyl group or an alkoxy group having 1 to 3 carbon atoms, provided that R 4 、R 5 and R 6 At least one of them is an alkoxy group.

11. The adhesive article of claim 1 , wherein the at least one surface-modified fumed silica comprises disilazane-treated fumed silica, alkylsilane-treated fumed silica, or polydimethylsiloxane-treated fumed silica.

12. The adhesive article of claim 1 , wherein the reaction mixture further comprises: At least one Tg modifying monomer having a functionality of less than 2, the at least one Tg modifying monomer having a homopolymer Tg of less than -35°C.

13. The adhesive article of claim 10, wherein the at least one Tg-modifying monomer comprises a monofunctional urethane-(meth)acrylate.

14. The adhesive article of claim 1, wherein the reaction mixture comprises: 60 to 99 parts by weight of at least two acid-free (meth)acrylate monomers of Formula 1: CH2=CR 1 -(CO)-OR 2 Formula 1 where R 1 is hydrogen or a methyl group; -(CO)- is a carbonyl group C=O; and R 2 is an alkyl group, a hydroxy-functional alkyl group, or a heteroalkyl group containing at least 4 carbon atoms; 0.1 to 10 parts by weight of at least one multifunctional urethane-(meth)acrylate; 0.01 to 1.0 parts by weight of at least one silane coupling agent; 0.1 to 5 parts by weight of at least one surface-modified fumed silica; and 0.01 to 2 parts by weight of at least one initiator.

15. The adhesive article of claim 12, wherein the reaction mixture further comprises: 1 to 30 parts by weight of at least one monofunctional urethane-(meth)acrylate.

16. The adhesive article of claim 1, wherein the article further comprises a second release liner having at least one release surface, wherein the release surface of the second release liner is disposed on the adhesive layer.

17. A method of forming an adhesive article, the method comprising: providing a first release liner having at least one release surface; placing a reaction mixture on at least a portion of the release surface of the first release liner, wherein the reaction mixture comprises: At least two acid-free (meth)acrylate monomers of Formula 1: CH2=CR 1 -(CO)-OR 2 Formula 1 where R 1 is hydrogen or a methyl group; -(CO)- is a carbonyl group C=O; and R 2 is an alkyl group, a hydroxy-functional alkyl group, or a heteroalkyl group containing at least 4 carbon atoms; at least one multifunctional urethane-(meth)acrylate; at least one silane coupling agent; at least one surface-modified fumed silica; and at least one initiator; and The reaction mixture is cured to form an adhesive layer.

18. The method of claim 17, wherein the reaction mixture is disposed on at least a portion of the release surface of the first release liner, wherein the reaction mixture comprises: forming a curable mixture, wherein forming the curable mixture comprises: preparing a mixture comprising the at least two (meth)acrylate monomers and at least one initiator; prepolymerizing the at least two (meth)acrylate monomers and at least one initiator to form a coatable syrup; To the coatable slurry was added: the at least one multifunctional urethane-(meth)acrylate; said at least one silane coupling agent; said at least one surface-modified fumed silica; and at least one initiator to form a curable mixture, placing the curable mixture on at least a portion of the release surface of the first release liner; and The curable mixture is cured to form the adhesive layer.

19. The method of claim 17, wherein the reaction mixture further comprises: At least one Tg modifying monomer, the at least one Tg modifying monomer having a homopolymer Tg of less than -35°C.

20. The method according to claim 17, wherein the method further comprises: providing a second release liner having at least one release surface; as well as The release surface of the second release liner is placed on the adhesive layer, either before or after curing.

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