Optically transparent pressure sensitive adhesive with low dielectric constant

Abstract

The low dielectric constant adhesive composition is an optically transparent pressure sensitive adhesive having a dielectric constant of 3.1 or less at 25 DEG C and 100 kHz. The adhesive composition is a reaction product of a mixture of a first monomer, a second monomer, and a third monomer with an initiator, the first monomer being a methacrylate, the second monomer being a low Tg (meth) acrylate monomer having an alkyl group having 2-20 carbon atoms and a Tg of-15 DEG C or less, the third monomer is a high Tg monomer of a (meth) acrylate monomer, a (meth) acrylamide monomer or a vinyl functional monomer having a Tg of 70 DEG C or higher.

Description

SUMMARY OF THE INVENTION

[0001] Disclosed herein are optically clear pressure - sensitive adhesive compositions having a low dielectric constant. Also disclosed are adhesive articles prepared from these optically clear pressure - sensitive adhesives.

[0002] In some embodiments, the adhesive composition comprises the reaction product of a mixture comprising: at least one first monomer, the first monomer comprising a methacrylate; at least one second monomer, the second monomer comprising a low Tg (meth)acrylate monomer having a Tg of - 15 °C or lower, the (meth)acrylate monomer having an alkyl group containing 2 - 20 carbon atoms; at least one third monomer, the third monomer comprising a high Tg monomer having a Tg of 70 °C or higher, wherein the high Tg monomer comprises a (meth)acrylate monomer, a (meth)acrylamide monomer, or a vinyl - functional monomer; and at least one initiator. The adhesive is free of acid functional groups; is a pressure - sensitive adhesive; is optically clear, having a visible light transmittance of 90%, a haze value of 1% or less, and a b* color value of 1 or less. The adhesive has a low dielectric constant, wherein the dielectric constant (Dk) is 3.1 or less at 25 °C and 100 kHz.

[0003] The present invention also discloses an adhesive article. In some embodiments, the adhesive article comprises: a first substrate having a first major surface and a second major surface; and an adhesive layer disposed on at least a portion of the second major surface of the first substrate, the adhesive layer comprising the above - described adhesive composition. DETAILED DESCRIPTION

[0004] A variety of optical articles have multiple layers. These multiple layers are typically adhered to each other with an adhesive layer. These adhesive layers have a variety of desired or required properties. In addition to the mechanical properties of adhesion, adhesives typically have other desired properties, such as optical properties or electrical properties. Achieving a range of properties is a very complex process because often conferring one property on the adhesive layer has an adverse effect on other properties.

[0005] An example of a new class of adhesives that has been developed to provide desired properties is optically clear adhesives (OCA). A range of optically clear adhesives have been developed for use in optical articles. These adhesives have a combination of desired adhesive and optical properties and are capable of being used in a variety of optical articles. As the use of these adhesives has increased, it has become apparent that these adhesives have additional properties. However, these new properties cannot be achieved by sacrificing adhesive or optical properties.

[0006] As optically clear adhesives find more widespread use, additional requirements for these adhesives have become apparent. These requirements are modulus (a measure of relative stiffness or softness), high temperature stability (not changing properties when exposed to high temperatures), compatibility with a wide range of electronic or optical components such as wires (since many of these components are sensitive to components commonly used in adhesives, such as acids), and low dielectric constant.

[0007] Care must be taken in modifying OCA to provide additional desired properties, as changing one property may result in an undesired change in other properties. For example, for many optical and electronic devices, it may be desirable to use an adhesive with a low modulus for uses such as a gap filling layer between substrates in a device. However, low modulus adhesives have reduced cohesive strength and thus are more prone to flow or degrade at elevated temperatures. Additionally, long chain hydrocarbon monomers can be used to form adhesive polymers with a low dielectric constant, but these polymers tend to have weak cohesion. To increase cohesive strength, reinforcing monomers are typically used. More common reinforcing monomers are acid functional monomers and aromatic monomers such as styrene. However, aromatic monomers tend to increase the dielectric constant of the resulting polymer, and acid functional monomers tend to corrode wires such as those in electronic devices.

[0008] Accordingly, there is a need for adhesives with multiple desired properties. The adhesives need to have not only practical adhesive properties and optical transparency, but also a suitably low modulus for gap filling properties, high temperature stability, non-corrosiveness to components such as wires, and low dielectric constant.

[0009] Disclosed herein are balanced adhesives having the following properties: desired adhesion, optical transparency, suitable modulus, high temperature stability, non-corrosiveness to wires such as silver nanowires, and low dielectric constant. Also disclosed are articles comprising these adhesives.

[0010] As used herein, the term "adhesive" refers to a polymeric composition that can be used to adhere two adherends together. An example of an adhesive is a pressure sensitive adhesive.

[0011] Those of ordinary skill in the art are familiar with the properties of pressure sensitive adhesive compositions, which include: (1) strong and persistent tack, (2) the ability to adhere by finger pressure, (3) sufficient ability to remain on the adherend, and (4) sufficient cohesive strength to be cleanly removed from the adherend. Materials that are found to function well as pressure sensitive adhesives are polymers that are designed and formulated to exhibit the desired viscoelastic properties such that the tack, peel adhesion, and shear retention are at a desired balance. Achieving the proper balance of properties is not a simple task.

[0012] The term “(meth)acrylate” refers to the monomer acrylate or methacrylate of an alcohol. Acrylate and methacrylate monomers or oligomers are collectively referred to herein as “(meth)acrylate”. Materials referred to as “(meth)acrylate functional” are materials containing one or more (meth)acrylate groups.

[0013] The terms “room temperature” and “ambient temperature” are used interchangeably and mean a temperature in the range of 20 °C to 25 °C.

[0014] The terms “Tg” and “glass transition temperature” are used interchangeably. If measured, unless otherwise specified, the Tg value is determined by differential scanning calorimetry (DSC) at a scan rate of 10 °C / minute. Generally, the Tg value of a copolymer is not measured, but instead the well-known Fox equation is used, and the value is calculated using the homopolymer Tg values provided by the monomer supplier, as understood by those skilled in the art.

[0015] 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 therebetween. They may be in direct contact with each other (e.g., laminated together) or there may be an intervening layer.

[0016] 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 having multiple repeating units. The term “polymer” is used to describe the resulting material formed by a polymerization reaction.

[0017] The term “alkyl” refers to a monovalent group that is an alkane group, where the alkane is a saturated hydrocarbon. The alkyl group can be straight-chain, branched-chain, 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.

[0018] The terms “free-radical polymerizable” and “ethylenically unsaturated” are used interchangeably and refer to a reactive group containing a carbon-carbon double bond that is capable of polymerizing via a free-radical polymerization mechanism.

[0019] Unless otherwise specified, the terms “optically transparent” and “visibly light transmissive” are used interchangeably and refer to an article, film, or adhesive having a high light transmittance over at least a portion of the visible light spectrum (from about 400 nm to about 700 nm). Generally, an optically transparent article has a visible light transmittance of at least 90% and a haze of less than 10%.

[0020] Unless otherwise specified, "optically clear" refers to an adhesive or article having a high light transmittance over at least a portion of the visible light spectrum (from about 400 nm to about 700 nm) and exhibiting a low haze (generally 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 even 0.5% at a thickness of 50 microns. Generally, the optically clear article has a visible light transmittance of at least 90%.

[0021] Disclosed herein is an adhesive composition comprising a reaction product of a reaction mixture that has been polymerized. The reaction mixture comprises: at least one first monomer, the first monomer comprising a methacrylate; at least one second monomer, the second monomer comprising a low Tg (meth)acrylate monomer having a Tg of -15 °C or lower, the (meth)acrylate having an alkyl group containing 2-20 carbon atoms; at least one third monomer, the third monomer comprising a high Tg monomer having a Tg of 70 °C or higher, the high Tg monomer comprising a (meth)acrylate monomer, a (meth)acrylamide monomer, or a vinyl functional monomer; and at least one initiator. Each of these components is described in more detail below.

[0022] The adhesives of the present disclosure are acid-functional group-free pressure-sensitive adhesives and have a variety of desired properties. The pressure-sensitive adhesive is optically clear, having a visible light transmittance of 90%, a haze value of 1% or less, and a b* color value of 1 or less. The adhesive also has a dielectric constant (Dk) of 3.1 or less at 25 °C and 100 kHz. In some embodiments, the adhesive has a storage modulus (G') of 125 kPa or less at 25 °C as measured by dynamic mechanical analysis (DMA). Additionally, in some of these embodiments, the adhesive has desired adhesion properties, such as a 180° peel adhesion to glass of at least 1.65 kg / in at 25 °C and a tensile adhesion to glass of at least 105 kg / in at 25 °C 2 。

[0023] In addition to these desired properties, the adhesive also has silver wire compatibility. Silver wire compatibility can be tested by elevated temperature and humidity aging. The adhesive is compatible with silver nanowires (SNWs) such that when an SNW / adhesive / SNW structure is placed in a 65 °C / 90% RH chamber (where RH is relative humidity) and the anode resistance is tested every 24 hours, the time to reach an anode resistance change of greater than 10% is at least 96 days.

[0024] In some embodiments, the adhesive has a desired elevated temperature stability. There are many techniques available for measuring elevated temperature stability, including measuring the modulus, 180° peel adhesion, and tensile adhesion at elevated temperatures. In some embodiments, the existing adhesive has a storage modulus (G’) of 24 kPa or greater at 65 °C as measured by dynamic mechanical analysis (DMA); a loss tangent value of 0.32 or greater at 65 °C, where the loss tangent value is the calculated ratio (G” / G’) of the measured shear storage modulus (G’) and shear loss modulus (G”). Additionally, in some embodiments, the adhesive has a 180° peel adhesion to glass of at least 0.43 kg / in at 65 °C; and a tensile adhesion to glass of at least 31 kg / in at 65 °C 2 to glass.

[0025] The adhesives of the present disclosure are prepared by polymerization of a reaction mixture that includes at least three monomers and an initiator, and may include additional optional components if desired, provided that these optional components do not interfere with the desired properties of the resulting adhesive.

[0026] The reaction mixture forming the adhesive composition of the present disclosure includes at least one first monomer, which includes a methacrylate. The first monomer is described by Formula 1:

[0027] CH2=C(Me)-(CO)-O-R 2

[0028] Formula 1

[0029] where (CO) is a carbonyl group; Me is a methyl group; and R 2 is a straight-chain or branched-chain alkyl group having 8 to 16 carbon atoms.

[0030] A wide range of methacrylate monomers are suitable as the first monomer. The first monomer can be a single monomer or a combination of monomers. Examples of suitable methacrylate monomers include 2-ethylhexyl methacrylate, n-octyl methacrylate, isooctyl methacrylate, isononyl methacrylate, n-nonyl methacrylate, n-decyl methacrylate, isodecyl methacrylate, stearyl methacrylate, isotridecyl methacrylate, dodecyl methacrylate, isobornyl methacrylate, isostearyl acrylate, and combinations thereof. Particularly suitable methacrylate alkyl ester monomers include monomers of Formula 1 where R2 is a 2-ethylhexyl group, a stearyl group, an isotridecyl group, or a dodecyl group.

[0031] The reaction mixture that forms the adhesive composition of the present disclosure further comprises at least one second monomer, which comprises a low Tg (meth)acrylate monomer. Low Tg means that the homopolymer Tg of the low Tg monomer is -15 °C or lower. The second monomer comprises a (meth)acrylate of Formula 2:

[0032] CH2=CR 1 -(CO)-O-R 3

[0033] Formula 2

[0034] wherein R 1 is H or a methyl group; (CO) is a carbonyl group; and R 3 is a straight-chain or branched alkyl group having 2-20 carbon atoms and optionally contains a hydroxyl group. The second monomer can be a single monomer or a combination of monomers. Since acrylates have a lower Tg than methacrylates, generally speaking, acrylates are more practical monomers to be used as the second monomer. Examples of suitable second monomers include 2-ethylhexyl acrylate, amyl acrylate, n-octyl acrylate, isooctyl acrylate, isononyl acrylate, n-butyl acrylate, isobutyl acrylate, hexyl acrylate, n-nonyl acrylate, n-decyl acrylate, isodecyl acrylate, dodecyl acrylate, isostearyl acrylate, 2-hydroxyethyl acrylate (HEA), 2-propylheptyl acrylate, and combinations thereof.

[0035] In some embodiments, the second monomer is a monomer wherein R 1 is H (i.e., acrylate) and R 3 is a straight-chain or branched alkyl group having 2-18 carbon atoms and optionally contains a hydroxyl group. One class of suitable monomers is monomers wherein R 3 is a 2-alkyl group, which means that the R 3 alkyl group is branched at the 2-position. Such (meth)acrylates are prepared by reacting (meth)acrylic acid with 2-alkanols (also known as Guerbet alkanols). The resulting (meth)acrylates are thus sometimes referred to as Guerbet (meth)acrylates. In Guerbet (meth)acrylates, the group R 3 is described by Formula 3:

[0036] -CH2-CH(R 4 )-CH2-CH2-R 5

[0037] Formula 3

[0038] wherein R4 and R5 are each independently an alkyl group having 4-10 carbon atoms.

[0039] In some particularly suitable embodiments, the second monomer comprises a mixture of acrylate monomers, the mixture comprising at least three monomers (monomer A, monomer B, and monomer C), wherein each of the at least three monomers comprises a monomer of general formula 2:

[0040] CH2=CR 1 -(CO)-O-R 3

[0041] Formula 2

[0042] wherein monomer A comprises a monomer wherein R 1 is H; (CO) is a carbonyl group; and R 3 is a straight-chain alkyl group having 2 carbon atoms and having a hydroxyl group; monomer B is a monomer wherein R 1 is H; (CO) is a carbonyl group; and R 3 is a straight-chain or branched-chain alkyl group having 10 - 14 carbon atoms; and monomer C is a monomer wherein R 1 is H; (CO) is a carbonyl group; and R 3 is a straight-chain or branched-chain alkyl group having 8 - 18 carbon atoms. Examples of suitable branched (meth)acrylate alkyl esters include those disclosed in U.S. Patent Application No. 8,137,807.

[0043] The reaction mixture forming the adhesive composition of the present disclosure further comprises at least one third monomer, the third monomer comprising a high-Tg monomer. A high-Tg monomer means a monomer having a homopolymer Tg of 70 °C or higher. High-Tg monomers can include (meth)acrylate monomers, (meth)acrylamide monomers, vinyl-functional monomers, or combinations thereof. Examples of suitable (meth)acrylate monomers include, but are not limited to, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, stearyl methacrylate, cyclohexyl methacrylate, isobornyl acrylate, isobornyl methacrylate, 3,3,5-trimethylcyclohexyl acrylate, and combinations thereof. Examples of suitable (meth)acrylamide monomers include: N,N-dimethyl(meth)acrylamide. Examples of suitable vinyl-functional monomers include N-vinylpyrrolidone (NVP) and N-vinylcaprolactam (NVC). Particularly suitable third monomers include isobornyl (meth)acrylate, N,N-dimethyl(meth)acrylamide, N-vinylpyrrolidone (NVP), and N-vinylcaprolactam (NVC).

[0044] The reaction mixture that forms the adhesive composition of the present disclosure further comprises at least one initiator. Although thermal polymerization and photopolymerization methods can be used, photopolymerization is typically employed. In a typical photopolymerization method, a monomer mixture can be irradiated with ultraviolet (UV) light in the presence of a photopolymerization initiator (i.e., photoinitiator). Suitable photoinitiators are those available under the trade names IRGACURE and DAROCUR from Ciba Speciality Chemical Corp., Tarrytown, NY, and include 1-hydroxycyclohexyl phenyl ketone (IRGACURE 184), 2,2-dimethoxy-1,2-diphenylethan-1-one (IRGACURE 651), bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide (IRGACURE 819), 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one (IRGACURE 2959), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one (IRGACURE 369), 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (IRGACURE 907), and 2-hydroxy-2-methyl-1-phenylpropan-1-one (DAROCUR 1173). Particularly suitable photoinitiators are IRGACURE 819, 651, 184, and 2959. Based on the total weight of the reactive monomers, the photoinitiator is typically used in an amount of 0.02 wt% - 0.35 wt%.

[0045] The adhesives of the present disclosure may also contain one or more conventional additives. Suitable additives include tackifiers, plasticizers, dyes, antioxidants, and UV stabilizers. Such additives can be used if they do not adversely affect the properties of the adhesive.

[0046] In addition to the wide range of suitable monomers, a wide range of monomer compositions are equally suitable. In some embodiments, the reaction mixture further contains:

[0047] 10 wt% - 20 wt% of a first monomer;

[0048] 70 wt% - 85 wt% of a second monomer; and

[0049] 2 wt% - 17 wt% of a third monomer.

[0050] A wide range of polymerization methods can be used to polymerize the reaction mixtures described in detail above. The polymerization can be carried out using a solvent method or in a solvent-free method. The solvent-free method is generally more desirable. In some embodiments, a coating and curing method is used. In this method, the reactive components are mixed together and a small amount of photoinitiator is added. The initiator is activated to form a slurry having a coatable viscosity. Additional photoinitiator is added to the slurry, and the slurry is coated on a release liner. Generally, a second release liner is placed on top of the coated slurry. The coated slurry is exposed to radiation to activate the photoinitiator, cure the slurry, and form the adhesive layer of the present disclosure.

[0051] Articles containing the adhesives of the present disclosure are also disclosed herein. In some embodiments, the adhesive article comprises: a first substrate having a first major surface and a second major surface; and an adhesive layer disposed on at least a portion of the second major surface of the first substrate. The adhesive layer comprises the above-described adhesive. The adhesive comprises the reaction product of a mixture comprising: at least one first monomer, the first monomer comprising a methacrylate; at least one second monomer, the second monomer comprising a low Tg (meth)acrylate monomer having a Tg of -15 °C or lower, the (meth)acrylate having an alkyl group containing 2-20 carbon atoms; at least one third monomer, the third monomer comprising a high Tg monomer having a Tg of 70 °C or higher, wherein the high Tg monomer comprises a (meth)acrylate monomer, a (meth)acrylamide monomer, or a vinyl functional monomer; and at least one initiator.

[0052] The adhesive is a pressure-sensitive adhesive free of acid functional groups and has a variety of desirable properties. The pressure-sensitive adhesive is optically transparent, having a visible light transmittance of 90%, a haze value of 1% or less, and a b* color value of 1 or less. The adhesive also has a dielectric constant (Dk) of 3.1 or less at 25 °C and 100 kHz. In some embodiments, the adhesive has a storage modulus (G’) of 125 kPa (kilopascals) or less at 25 °C as measured by dynamic mechanical analysis (DMA). Additionally, in some embodiments, the adhesive has desirable adhesion properties, such as a 180° peel adhesion to glass of at least 1.65 kg / in at 25 °C and a tensile adhesion to glass of at least 105 kg / in at 25 °C 2 。

[0053] In addition to these desired properties, the adhesive also has elevated temperature stability and silver nanowire compatibility. There are many techniques available for measuring elevated temperature stability, including measuring modulus, 180° peel adhesion, and tensile adhesion at elevated temperatures. Silver nanowire compatibility can be tested by elevated temperature and humidity aging. In some embodiments, the existing adhesive has a storage modulus (G’) of 24 kPa or greater at 65 °C as measured by dynamic mechanical analysis (DMA); a loss tangent value of 0.32 or greater at 65 °C, where the loss tangent value is the calculated ratio (G” / G’) of the measured shear storage modulus (G’) and shear loss modulus (G”). Additionally, the adhesive has, in some embodiments, a 180° peel adhesion to glass of at least 0.43 kg / in at 65 °C; and a tensile adhesion to glass of at least 31 kg / in at 65 °C 2 The adhesive is compatible with silver nanowires (SNW) such that when an SNW / adhesive / SNW structure is placed in a 65 °C / 90% RH chamber (where RH is relative humidity) and the anode resistance is tested every 24 hours, the time to reach an anode resistance change greater than 10% is at least 96 days.

[0054] A wide range of substrates are suitable for the articles of the present disclosure. In some embodiments, the substrate is a release liner. In the above method, the formed adhesive layer is disposed on the release liner. These articles are also very useful for forming a wide range of other articles because the exposed adhesive layer can be laminated to the surface of a substrate and the release liner can be removed to expose a second adhesive surface.

[0055] In many embodiments, the first substrate is substantially transparent. In many embodiments, the first substrate is optically transparent. The first substrate can be rigid, semi-rigid, or flexible. Examples of rigid substrates include plates such as glass plates, PMMA (polymethyl methacrylate) plates, or PC (polycarbonate) plates or the surfaces of electronic or optical devices. Examples of semi-rigid substrates include, for example, multilayer films where the number or thickness of the layers impedes flexibility such as bendability. Examples of flexible substrates include film substrates such as optical films.

[0056] In some embodiments, the second major surface of the first substrate includes silver nanowires. Silver nanowires are used in a wide range of electronic devices.

[0057] In some embodiments, the article further includes a second substrate, where the second substrate includes a first major surface and a second major surface, and the first major surface of the second substrate is disposed on the adhesive layer. The second substrate can be the same as or different from the first substrate. Like the first substrate, the second substrate can be selected from the substrates described above for the first substrate.

[0058] In some embodiments, the first major surface of the second substrate includes silver nanowires.

[0059] Examples

[0060] 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, the solvents and other reagents used are obtained from Sigma-Aldrich Chemical (Milwaukee, Wisconsin, USA). The following abbreviations are used: cm = centimeter; mm = millimeter; in = inch; kg = kilogram; kgf = kilogram-force; min = minute; hr = hour; PSI = pounds per square inch; mJ = millijoule; Ω = ohm; and RH = relative humidity. The terms "weight %", "% by weight", and "wt %" are used interchangeably.

[0061] Abbreviation Table

[0062]

[0063] Test Method

[0064] Optical Properties

[0065] Haze measurements were performed in transmission mode using a HunterLab (Reston, VA) UltrascanPro spectrophotometer. The component layers were coated between peel-coated carrier liners (liner-1 and liner-2), cut to approximately 5 cm wide by 10 cm long, and their thickness was measured. One of the carrier liners was removed and the sample layer was laminated to a 1 mm thick clear glass. Then the other liner was removed and another 1 mm thick glass was laminated to the component layer. The sample was autoclaved at 50 °C / 45 PSI for 20 minutes to remove entrained air. The sample was then placed in the UltrascanPro spectrophotometer to measure the transmittance and color through the glass / OCA / glass assembly. Additional samples were prepared and aged for 800 hours in a chamber set at 65 °C / 90% relative humidity. After removing the sample from the humidity chamber and allowing it to cool, haze measurements were performed again. Generally, samples acceptable for optical applications have a haze value of less than about 1% and a b* color value of less than about 1.

[0066] Dynamic Mechanical Analysis (DMA)

[0067] The loss tangent value of the sample at 150 °C was evaluated using a rheological dynamic analyzer (ARES-G2 rheometer, purchased from TA Instruments, New Castle, DE, USA). The sample (as described in the Examples section) was laminated to a thickness of approximately 2 mm. Then, the sample was punched out using a circular die with a diameter of 8 mm (0.315 inches) and adhered to the upper parallel plate with a diameter of 8 mm after removing the release liner. The plate with the polymer film was positioned between the clamps, and the polymer film was compressed until the edges of the sample were aligned with the edges of the top plate. Then, at a nominal axial force of 0 g ± 15 g, the temperature was equilibrated for 2 minutes at the test temperature. After two minutes, the axial force controller was deactivated to maintain a fixed gap during the remaining time of the test. The sample was oscillated at 1 Hz and collected from -50 °C to 150 °C at a rate of 3 °C / min. The loss tangent value at 65 °C was recorded.

[0068] Peel Adhesion and Tensile Strength

[0069] The peel adhesion and tensile strength were measured at 74 °F (23 °C) and 50% relative humidity (RH) using an IMASS2100 Slip / Peel Tester equipped with a 25 lb load cell (Instrumentors Incorporated, Strongsville, OH). Peel adhesion samples were prepared by using a 10 mm wide test OCA tape. First, the release liner side was laminated to a 51 µm (2 mil) PET tape, and then its high bond side was laminated to float glass (cleaned with acetone / n-heptane) using a 2 kg roller. Then, the construction was placed in an autoclave at 50 °C / 3 kg for 20 minutes and left to stand at ambient conditions for 24 hours before performing a 180° peel test. The peel rate was 12” / min (30 cm / min). Five specimens were evaluated, and the results were used to obtain the average value in kg / in and convert it to N / mm (Newton / mm).

[0070] Tensile strength samples were prepared by using a 0.5 inch × 0.5 inch (13 mm × 13 mm) test OCA. First, the release liner side of the OCA was laminated to center float glass (cleaned with acetone / n-heptane), and then the top float glass was aligned vertically and its high bond side was laminated on the top float glass. Then, the construction was placed in an autoclave at 50 °C / 3 kg for 20 minutes and left to stand at ambient conditions for 24 hours before performing a tensile strength test. The test speed was 1 in / min (2.54 cm / min). Five specimens were evaluated, and the results were used to obtain the average value in kg / in 2 and convert it to kg / cm2 (kg / cm²).

[0071] SNW Compatibility

[0072] Cut the SNW (silver nanowire) sheet with a multimeter (nominal resistance range: 50 Ω - 200 Ω) into a size of 72 mm * 60 mm. Laminate the conductive side with the OCA (size 60 mm * 60 mm) to form an SNW / OCA / SNW structure, where 6 mm of SNW is exposed for silver wire coating. Coat two parallel silver paint lines on the conductive SNW side, add copper strips to each of the four silver-coated points, and then fold. Autoclave the specimen block samples at 40 °C and 3 kgf / cm 2 for 5 minutes.

[0073] The specimen block tests are carried out in a 65 °C / 90% RH chamber and connected to a 5 V current with "Lo" MΩ on the voltmeter. Measure the anode resistance data every 24 hours, and stop the test when the resistance change > 10% (compared with the T0 resistance).

[0074] Examples E1 - E6 and Comparative Examples CE1 - CE4

[0075] Preparation of Solvent-Free PSA Samples

[0076] Prepare the component layer film according to the formula provided in Table 1. The polymerization / coating process includes preparing a reactive mixture, irradiating to partially polymerize it to form a coatable slurry, coating the slurry on a release liner, and further irradiating the coated layer to fully polymerize. Irradiate the PSA structure with UV-A with a total dose of 1500 mJ / cm 2 . Prepare Examples E1 - E6 and Comparative Examples CE1 - CE4 using the materials and amounts described in Table 1. The thickness of all PSA examples is 150 microns (6 mils).

[0077] Test the modulus of the adhesive samples (by the above DMA test) and the SNW compatibility using the above test methods. The data are shown in Table 2.

[0078] Test the peel adhesion and tensile adhesion of the adhesive samples on glass using the above test methods. The data are shown in Table 3.

[0079] Table 1. PSA Sample Preparation

[0080]

[0081]

[0082] Table 2: Modulus / Loss Tangent Values and SNW Compatibility Results at 25°C and 65°C

[0083]

[0084] Table 3: Peel Adhesion and Tensile Adhesion Results at 25°C and 65°C on Glass

[0085]

Claims

1. An adhesive, the adhesive comprising: The reaction product of a mixture, the mixture comprising: At least one first monomer, the first monomer comprising a methacrylate; At least one second monomer, the second monomer comprising a low Tg (meth)acrylate monomer having a Tg of -15 °C or lower, the (meth)acrylate having an alkyl group containing 2 - 20 carbon atoms; At least one third monomer, the third monomer comprising a high Tg monomer having a Tg of 70 °C or higher, Wherein the high-Tg monomer includes (meth)acrylate monomer, (meth)acrylamide monomer or vinyl functional monomer; and At least one initiator; Wherein the adhesive does not contain acid functional groups; is a pressure - sensitive adhesive; is optically transparent, having a visible light transmittance of 90%, a haze value of 1% or less, and a b* color value of 1 or less; And having a dielectric constant (Dk) of 3.1 or less at 25 °C and 100 kHz.

2. The adhesive according to claim 1, wherein the adhesive has silver nanowire (SNW) compatibility such that when an SNW / adhesive / SNW structure is placed in a 65 °C / 90% RH chamber for testing and the anode resistance is tested every 24 hours, the time to reach an anode resistance change greater than 10% is at least 96 days.

3. The adhesive according to claim 1, wherein the first monomer comprises a methacrylate of general formula 1: CH2=C(Me)-(CO)-O-R 2 Formula 1 Where (CO) is a carbonyl group; Me is a methyl group; and R 2 is a straight-chain or branched alkyl group having 8 to 16 carbon atoms.

4. The adhesive according to claim 1, wherein the first monomer comprises a methacrylate of general formula 1: CH2=C(Me)-(CO)-O-R 2 Formula 1 Where (CO) is a carbonyl group; Me is a methyl group; and R 2 is a 2-ethylhexyl group, a stearyl group, an isotridecyl group or a dodecyl group.

5. The adhesive according to claim 1, wherein the second monomer comprises a (meth)acrylate of general formula 2: CH2=CR 1 -(CO)-O-R 3 Formula 2 wherein R 1 is H or a methyl group; (CO) is a carbonyl group; and R 3 is a straight-chain or branched alkyl group having 2 to 20 carbon atoms and optionally containing a hydroxyl group.

6. The adhesive according to claim 1, wherein the second monomer comprises an acrylate of general formula 2: CH2=CR 1 -(CO)-O-R 3 Formula 2 wherein R 1 is H; (CO) is a carbonyl group; and R 3 is a straight-chain or branched alkyl group having 2 to 18 carbon atoms and optionally containing a hydroxyl group.

7. The adhesive according to claim 1, wherein the second monomer comprises a mixture of acrylate monomers, the mixture comprising at least 3 monomers (monomer A, monomer B, and monomer C), wherein each of the at least 3 monomers comprises a monomer of general formula 2: CH2=CR 1 -(CO)-O-R 3 Formula 2 such that: In monomer A: R 1 is H; (CO) is a carbonyl group; and R 3 is a straight-chain alkyl group having 2 carbon atoms and having a hydroxy group; In monomer B: R 1 is H; (CO) is a carbonyl group; and R 3 is a straight-chain or branched alkyl group having 10 to 14 carbon atoms; and In monomer C: R 1 is H; (CO) is a carbonyl group; and R 3 is a straight-chain or branched-chain alkyl group having 8 to 18 carbon atoms.

8. The adhesive according to claim 1, wherein the third monomer comprises: Selected from isobornyl (meth)acrylate; N,N - dimethyl(meth)acrylamide; N - vinylpyrrolidone (NVP); and at least one of N - vinylcaprolactam (NVC).

9. The adhesive according to claim 1, wherein the reactive components of the reaction mixture comprise: 10 wt% - 20 wt% of the first monomer; 70 wt% - 85 wt% of the second monomer; and 2 wt% - 17 wt% of the third monomer.

10. An adhesive article, the adhesive article comprising: A first substrate, the first substrate having a first major surface and a second major surface; and An adhesive layer, the adhesive layer being disposed on at least a portion of the second major surface of the first substrate, the adhesive layer comprising a reaction product of a mixture, the mixture comprising: At least one first monomer, the first monomer comprising a methacrylate; At least one second monomer, the second monomer comprising a low Tg (meth)acrylate monomer having a Tg of -15 °C or lower, the (meth)acrylate having an alkyl group containing 2 to 20 carbon atoms; At least one third monomer, the third monomer comprising a high Tg monomer having a Tg of 70 °C or higher, wherein the high Tg monomer comprises a (meth)acrylate monomer, (Meth)acrylamide monomer or vinyl functional monomer; And At least one initiator; Wherein the adhesive is free of acid functional groups; is a pressure-sensitive adhesive; is optically transparent, having a visible light transmittance of 90%, a haze value of 1% or less, and a b* color value of 1 or less; Having a dielectric constant (Dk) of 3.1 or less at 25 °C and 100 kHz.

11. The adhesive article according to claim 10, wherein the adhesive has silver wire compatibility such that: The adhesive has silver nanowire (SNW) compatibility such that when an SNW / adhesive / SNW structure is placed in a 65 °C / 90% RH chamber for testing and the anode resistance is tested every 24 hours, the time to reach an anode resistance change greater than 10% is at least 96 days.

12. The adhesive article according to claim 10, wherein the first substrate comprises a release liner.

13. The adhesive article according to claim 10, wherein the second major surface of the first substrate comprises silver nanowires.

14. The adhesive article according to claim 10, wherein the article further comprises a second substrate, wherein the second substrate comprises a first major surface and a second major surface, and wherein the first major surface of the second substrate is disposed on the adhesive layer.

15. The adhesive article according to claim 14, wherein the first major surface of the second substrate comprises silver nanowires.

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