WO2025169036A1

WO2025169036A1 - Low dielectric constant curable ink compositions

Info

Publication number: WO2025169036A1
Application number: PCT/IB2025/050815
Authority: WO
Inventors: Jonathan A. ANIM-ADDO; Evan L. Schwartz; Tabitha A. SILLIMAN; Claire Hartmann-Thompson; Sihan Xie; Saswata CHAKRABORTY
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2024-02-05
Filing date: 2025-01-24
Publication date: 2025-08-14
Anticipated expiration: 2026-08-05

Abstract

Curable ink compositions include at least one first monomer that is a branched alkyl (meth)acrylate monomer with at least 2 branches having 10 or more carbon atoms, at least one crosslinking monomer, and at least one initiator. The curable ink composition is solvent free and inkjet printable, having a viscosity of less than 35 centipoise at a temperature of from room temperature to less than 60°C. Upon curing the ink forms a non-crystalline, optically clear layer with a dielectric constant of less than or equal to 2.6 at 100 kiloHertz. In some embodiments, the Tg of the cured optically clear layer is 80°C or greater as measured by the peak of tan(delta) in a DMA (Dynamic Mechanical Analysis).

Description

LOW DIELECTRIC CONSTANT CURABLE INK COMPOSITIONS

Summary

Disclosed herein are curable ink compositions that have a low dielectric constant, optical articles that include the cured ink compositions, and methods of making the optical articles.

Curable ink compositions of the current disclosure comprise at least one first monomer comprising a branched alkyl (meth)acrylate monomer comprising at least 2 branches wherein each branch comprises 10 or more carbon atoms, at least one crosslinking monomer, and at least one initiator. The curable ink composition is solvent free and inkjet printable, having a viscosity of less than 35 centipoise at a temperature of from room temperature to less than 60°C, and upon curing forms a non-crystalline, optically clear layer with a dielectric constant of less than or equal to 2.6 at 100 kiloHertz. In some embodiments, the Tg of the cured optically clear layer is 80°C or greater as measured by the peak of tan(delta) in a DMA (Dynamic Mechanical Analysis).

Also disclosed are optical articles. In some embodiments, the articles comprise a substrate with a first major surface and a second major surface, and a cured organic layer with a first major surface and a second major surface, where the first major surface of the cured organic layer is adjacent to at least a portion of the second major surface of the substrate. The cured organic layer comprises a crosslinked (meth)acrylate-based layer and has a thickness of from 1-50 micrometers, has a dielectric constant of 2.6 or less at 100 kiloHertz, a Tg of 80°C or greater as measured by the peak of tan(delta) in a DMA (Dynamic Mechanical Analysis), and is non-crystalline and optically clear. The cured organic layer comprises a layer comprising a curable ink composition that has been printed and cured on at least a portion of the second major surface of the substrate. The curable ink composition is described above.

Also disclosed are methods of preparing optical articles. In some embodiments, the method comprises providing an optical substrate with a surface, preparing a curable ink composition, disposing the curable ink composition on at least a portion of the surface of the optical substrate, and curing the curable ink composition to form a cured layer. The curable ink composition has been described above.

Brief Description of the Drawings

The present application may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying drawings.

Figure 1 shows a cross sectional view of an embodiment of an article of this disclosure.

Figure 2 shows a cross-sectional view of an embodiment of another article of this disclosure.

In the following description of the illustrated embodiments, reference is made to the accompanying drawings, in which is shown by way of illustration, various embodiments in which the disclosure may be practiced. It is to be understood that the embodiments may be utilized and structural changes may be made without departing from the scope of the present disclosure. The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number.

Detailed Description

The increased complexity of optical devices places increasingly difficult requirements upon the materials used in them. In particular, organic polymeric materials have found widespread use in optical devices, but increasingly stringent requirements are being placed upon these polymeric materials.

For example, thin organic polymeric films are desirable for a wide range of uses in optical devices, as adhesives, protective layers, spacer layers, and the like. As articles have become more complex, the physical demands upon these layers have increased. For example, as optical devices have become more compact, and at the same time often include more layers, there has been an increasing need for thinner layers. At the same time, since the layers are thinner, the layers also need to be more precise. For example, a thin spacer layer (of 1 micrometer thickness) needs to be level and free of gaps and holes in order to provide the proper spacing function. This requires deposition of the organic layer in a precise and consistent manner.

One function that thin spacer layers are called upon to fulfill in multilayer optical and electronic devices is electrical insulation, in order to electrically isolate a layer or series of layers from other nearby layers. Therefore, it is desirable to have thin layers of organic polymeric materials that have a low dielectric constant. In this context, a low dielectric constant material is one which has a dielectric constant of less than or equal to 2.6 at 100 kiloHertz. This function also requires precision in the formation of the layers as the presence of gaps or pinholes can destroy the insulating ability of the layer.

Additionally, not only do these layers have to fulfdl their physical role (adhesion, protection, spacing, and the like) they must also provide the requisite optical properties. Among the properties that are becoming increasingly important is optical clarity.

For example, thin fdm encapsulation (TFE) layers are used to prevent air and moisture ingress into the OLED device. The TFE is typically composed of alternating layers of inorganic and organic materials (Chwang, Applied Physics Letters 83, 413 (2003)). The function of the inorganic layers is to block the ingress of air and moisture into the OLED device. The functions of the organic layers are twofold: 1) to planarize the substrate and present a smooth interface for the deposition of the inorganic layer; and 2) to decouple any defects (pinholes, micro-cracks) that may occur in the inorganic layers on either side of the organic layer. The organic layer can be thought of as a buffer layer that is critical for the success of the inorganic layer barrier function.

Among the methods that have been developed to provide a precise and consistent deposition of organic polymeric material are printing techniques. In printing techniques, a polymer or a curable composition that upon curing forms a polymer, is printed onto a substrate surface to form a layer. In the case of printable polymers, typically solvents are added to make the polymer a solution or dispersion capable of being printed. When polymers are used, typically a drying step is necessary after printing to produce the desired polymeric layer. In the case of curable compositions that upon curing form polymers, the curable compositions may or may not include a solvent. The curable composition is then cured, typically either with the application of heat or radiation (such as UV light) and if a solvent is used the layer may also be dried. A wide variety of printing techniques can be used, with inkjet printing being particularly desirable because of the excellent precision of inkjet printing.

As was mentioned above, an example of an optical device that utilizes thin fdm layers are OLED (organic light-emitting diode) devices. In particular, organic lightemitting devices are susceptible to degradation from the permeation of certain liquids and gases, such as water vapor and oxygen. To reduce permeability to these liquids and gases, barrier coatings are applied to the OLED device. Typically, these barrier coatings are not used alone, rather a barrier stack is used which can include multiple dyads. Dyads are two layer structures that include a barrier layer and decoupling layer. The decoupling layer provides a planarized and/or smooth surface for the deposition of the inorganic barrier layer.

In this disclosure, curable inks that are capable of being printed are described which have a number of traits that make them suitable for the formation of layers within multilayer optical devices. Many of these traits are contradictory to each other, and therefore it is unexpected that an ink composition can have these contradictory traits. For example, the formulations, when cured have a dielectric constant of less than or equal to 2.6 at 100 kiloHertz and have a Tg of at least 80°C as measured by the peak of tan(delta) in a DMA (Dynamic Mechanical Analysis). Meeting both of these requirements simultaneously is desirable or required for curable layers in many optical devices and optical uses.

In order to achieve this low dielectric constant, monomers that are branched hydrocarbons, often highly branched hydrocarbons, with relatively long chains are used, and these branched, long chain monomers have a relatively high viscosity. However, in order to be printable, especially inkjet printable, the viscosity cannot be too high. Often this viscosity problem can be overcome through the use of solvents to dilute the monomer mixtures and thus reduce their viscosity. The use of solvents is not suitable for the inks of the present disclosure because it is undesirable to have to dry the prepared coatings, and drying is known to affect coatings by decreasing the thickness and drying can also adversely affect the surface smoothness and may also create defects in the coating. In many applications for optical devices, it is desired that the coatings be precise, that is to say that they do not lose thickness or smoothness upon drying. Therefore, the inks of the present disclosure are “100% solids”, meaning that they do not contain any intentionally added volatile solvents and that most of the mass that is deposited on a surface remains. In other words, no volatile mass is lost from the coating. Another technique that can be used to decrease the viscosity of inks is to raise the temperature of the ink at the inkjet printhead. However, this is also not desirable for the inks of the present disclosure because the inks are often applied to substrates that are either thermally sensitive or are kept at ambient temperature and therefore coating a hot ink onto the room temperature substrate can cause defects in the coating. These defects can come about either from a lack of proper wetting on the substrate surface or from other inconsistencies that form a non-uniform coating. A higher printhead temperature also reduces the useful lifetime of an inkjet printhead, which is not desirable for mass manufacturing.

Therefore, the curable compositions of the present disclosure are useful as inks, meaning that they are capable of being printed by for example inkjet printing techniques without the use of solvents at a temperature of from room temperature to about 60°C, or even room temperature to 35°C. Typically, the printable curable composition has a viscosity at these temperatures of 35 centipoise or less.

The curable ink composition, when coated and cured to form a cured organic layer, produces a cured organic layer that has a dielectric constant of 2.6 at 100 kiloHertz and is optically clear. In some embodiments, the cured organic layer has a Tg of at least 80°C as measured by the peak of tan(delta) in a DMA (Dynamic Mechanical Analysis). In some embodiments, the cured organic layer has a dielectric constant of 2.5 or less at 100 kiloHertz, or even 2.3 or less at 100 kiloHertz.

The cured organic layer typically has a thickness of from 1-50 micrometers, in some embodiments 2-10 micrometers, and a surface roughness of less than 10 nanometers, in some embodiments less than 5 nanometers. Surface roughness in this context refers to the arithmetic mean deviation Ra as defined by the equation: where the roughness trace includes n ordered equally spaced data points along the trace, and yi is vertical distance from the mean line to the i^th point. In this way, the cured organic layer is suitable for use as a decoupling layer as described above.

The curable ink compositions of this disclosure are reactive mixtures that comprise at least one first monomer comprising a branched alkyl (meth)acrylate monomer comprising at least 2 branches wherein each branch comprises 10 or more carbon atoms, at least one crosslinking monomer, and at least one initiator. The term monomer as used herein may include oligomeric species. The curable ink composition is solvent free and inkjet printable, having a viscosity of less than 35 centipoise at a temperature of from room temperature to less than 60°C, and upon curing forms a non-crystalline, optically clear layer with a dielectric constant of less than or equal to 2.6 at 100 kiloHertz and has a Tg of at least 80°C as measured by the peak of tan(delta) in a DMA (Dynamic Mechanical Analysis).

Also disclosed herein are articles and methods of preparing articles, especially optical articles that comprise multiple layers of fdms, substrates and coatings. Among the articles of this disclosure are articles comprising a substrate, a cured organic layer adjacent to the substrate. The cured organic layer comprises a crosslinked (meth)acrylate-based layer that has a thickness of from 1-50 micrometers and has a dielectric constant of less than or equal to 2.6 at 100 kiloHertz, has a Tg of at least 80°C as measured by the peak of tan(delta) in a DMA (Dynamic Mechanical Analysis), and is optically clear.

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

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

The terms “Tg” and “glass transition temperature” are used interchangeably. If measured, Tg values are determined by the peak of tan(delta) in a Dynamic Mechanical Analysis (DMA) unless otherwise indicated. Typically, Tg values for copolymers are not measured but are calculated using the well-known Fox Equation, using the homopolymer Tg values provided by the monomer supplier, as is understood by one of skill in the art.

The term “adjacent” as used herein when referring to two layers means that the two layers are in proximity with one another with no intervening open space between them. They may be in direct contact with one another (e.g. laminated together) or there may be intervening layers.

The curable ink compositions are “substantially solvent free” or “solvent free”. As used herein, “substantially solvent free” refers to the curable ink compositions having less than 5 wt-%, 4 wt-%, 3 wt-%, 2 wt-%, 1 wt-% and 0.5 wt-% of non-polymerizable (e.g. organic) solvent. The concentration of solvent can be determined by known methods, such as gas chromatography (as described in ASTM D5403). The term “solvent free” is used as the term implies, that no solvent is present in the composition. It should be noted that whether the curable ink composition is substantially solvent free or solvent free, no solvent is deliberately added.

Typically, the curable ink compositions are described as “100% solids”. As used herein, “100% solids” refers to curable ink compositions that do not contain volatile solvents and that all of the mass that is deposited on a surface remains there, no volatile mass is lost from the coating.

The terms “polymer” and “macromolecule” are used herein consistent with their common usage in chemistry. Polymers and macromolecules are composed of many repeated 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 resultant material formed from a polymerization reaction.

The term “organic” as used herein to refer to a cured layer, means that the layer is prepared from organic materials and is free of inorganic materials.

The term “alkyl” refers to a monovalent group that is a radical of an alkane, which is a saturated hydrocarbon. The alkyl can be linear, branched, cyclic, or combinations 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.

The term “aryl” refers to a monovalent group that is aromatic and carbocyclic. The aryl can have one to five rings that are connected to or fused to the aromatic ring. The other ring structures can be aromatic, non-aromatic, or combinations thereof. Examples of aryl groups include, but are not limited to, phenyl, biphenyl, terphenyl, anthryl, naphthyl, acenaphthyl, anthraquinonyl, phenanthryl, anthracenyl, pyrenyl, perylenyl, and fluorenyl.

The term “alkylene” refers to a divalent group that is a radical of an alkane. The alkylene can be straight-chained, branched, cyclic, or combinations thereof. The alkylene often has 1 to 20 carbon atoms. In some embodiments, the alkylene 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 the alkylene can be on the same carbon atom (i.e., an alkylidene) or on different carbon atoms.

The terms “free radically polymerizable” and “ethylenically unsaturated” are used interchangeably and refer to a reactive group which contains a carbon-carbon double bond which is able to be polymerized via a free radical polymerization mechanism.

Unless otherwise indicated, the terms “optically transparent”, and “visible light transmissive” are used interchangeably, and refer to an article, fdm or adhesive that has a high light transmittance over at least a portion of the visible light spectrum (about 400 to about 700 nm). Typically, optically transparent articles have a visible light transmittance of at least 90% and a haze of less than 10%.

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

Disclosed herein are curable compositions that are printable, and thus are described as inks. The curable compositions need not be used as inks, that is to say that they need not be printed and then cured, the curable compositions can be delivered to substrate surfaces in a wide variety of ways, but they are capable of being printed. In particular, the printable compositions of this disclosure are typically capable of being inkjet printed, which means that they have the proper viscosity and other attributes required to be inkjet printed. The term “inkjet printable” is not a process description or limitation, but rather is a material description, meaning that the curable compositions are capable of being inkjet printed, and not that the compositions necessarily have been inkjet printed. This is akin to the expression hot melt processable, which means that a composition is capable of being hot melt processed but does not mean that the composition has been hot melt processed.

The curable ink compositions of this disclosure are reactive mixtures that comprise at least one first monomer comprising a branched alkyl (meth)acrylate monomer comprising at least 2 branches wherein each branch comprises 10 or more carbon atoms, at least one crosslinking monomer, and at least one initiator. The term monomer as used herein may include oligomeric species. The curable ink composition is solvent free and inkjet printable, having a viscosity of less than 35 centipoise at a temperature of from room temperature to less than 60°C, and upon curing forms a non-crystalline, optically clear layer with a dielectric constant of less than or equal to 2.6 at 100 kiloHertz. In some embodiments, the optically clear layer has a Tg of at least 80°C as measured by the peak of tan(delta) in a DMA (Dynamic Mechanical Analysis). The ink compositions are inkjet printable and are free from solvents. By free from solvents it is meant that no solvents are added to the curable ink composition, and that no solvents are detectable in the curable composition. The term “solvents” is used herein consistent with the generally understood term of art and encompassing volatile organic and non-organic materials that are liquids at room temperature.

A wide variety of monomeric species are suitable for use as the first monomer of the curable ink composition. The first monomer comprises a branched alkyl (meth)acrylate monomer. The alkyl group is a long chain hydrocarbon group. Hydrocarbon chains that contain 12 or greater carbon atoms are frequently referred to as “long chain hydrocarbons”. The hydrocarbons of the present disclosure are branched long chain hydrocarbons, meaning that they have at least one branch point along the hydrocarbon chain. The current first monomers comprise at least 2 branches wherein each branch comprises 10 or more carbon atoms. In some embodiments, the branched long chain hydrocarbons have more than one branch point and are sometimes referred to as “highly branched hydrocarbons”. In these embodiments, at least one of the branches of the hydrocarbon group has at least one further branch point.

Branched and highly branched long chain hydrocarbon monomers are desirable for use in the present curable compositions for many reasons. Long chain hydrocarbon monomers are desirable, because they contain a higher ratio of non-polarizable content (that is to say C-C and C-H bonds) relative to the polarizable content (from the carbonyl groups on the (meth)acrylate). It is desirable that the long chain hydrocarbon monomers be branched or even highly branched so that the curable and cured compositions are noncrystalline. In the curable state, crystallinity is not desirable, especially when the curable composition is to be inkjet printed, as crystalline compositions can clog the inkjet nozzles. In the cured state, crystallinity can adversely affect the optical properties of the cured composition as is well known in the art. It is also well known in the chemical arts that “likes attract likes” meaning that similar chemical compositions tend to associate. A commonly used analogy is to view the hydrocarbon chains as strands of spaghetti, which when placed next to each other can agglomerate and form an associated mass. In the case of long chain hydrocarbon chains, especially when the hydrocarbon chains are 12 carbon atoms or larger, the hydrocarbon chains tend to associate and form crystallites. The formation of these crystallites can be prevented through the use of monomers with branched hydrocarbon chains, as the branching tends to disrupt the association of the hydrocarbon chains.

In some embodiments, the first monomer comprises general Structure 1 :

CH₂=CR¹(CO)-O-R²

Structure 1 where R¹ is H or methyl; (CO) is a carbonyl group C=O; and R² is branched alkyl group with general Structure 2:

-CH₂-CHR³R⁴

Structure 2 where R³ is a alkyl, alkylidene or alkyl group substituted with ethylene groups comprising at least 10 carbon atoms, and R⁴ is a alkyl, alkylidene or alkyl group substituted with ethylene groups comprising at least 10 carbon atoms.

In some embodiments, the R³ and R⁴ are different. Each of R³ and R⁴ may be a straight chain alkyl group, or it may be a branched alkyl group. Each straight chain or branched alkyl group can independently have the same number of carbon atoms, or a different number of carbon atoms.

In some embodiments, R³ and R⁴ are straight chain alkyl groups. In some embodiments, R³ comprises an alkyl group with 14 carbon atoms, and R⁴ comprises an alkyl group with 16 carbon atoms.

The curable ink compositions include at least one crosslinking monomer. In this disclosure, the terms “crosslinker” and “crosslinking monomer” are used interchangeably. Crosslinkers are well understood in the polymer arts as polyfimctional molecules that link polymer chains together. In the present curable ink compositions, the crosslinker typically is a multifunctional (meth)acrylate. In some embodiments, the crosslinking monomer comprises at least one di(meth)acrylate of the general Structure 3

CH₂=CR¹-(CO)-O-A-O-(CO)-R¹C=CH₂

Structure 3 wherein R¹ is H or methyl; (CO) is a carbonyl group C=O; and A is an alkylene group comprising 4-12 carbon atoms, or an alicyclic group with 8-12 carbon atoms.

In some embodiments, the crosslinking monomer comprises a mixture of at least 2 di(meth)acrylates of Structure 3 :

CH₂=CR¹-(CO)-O-A-O-(CO)-R¹C=CH₂

Structure 3 where in the first crosslinking monomer: R¹ is H or methyl; (CO) is a carbonyl group C=O; and A is an alkylene group comprising 6-8 carbon atoms; and where in the second crosslinking monomer: R¹ is H or methyl; (CO) is a carbonyl group C=O; and A is an alicyclic group with 10 carbon atoms. A particularly suitable crosslinking monomer is tricyclodecane dimethanol dimethacrylate.

In some embodiments, the curable ink composition further comprises at least one additional (meth)acrylate monomer. Examples of suitable (meth)acrylates include 2,2- (diethoxy)ethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, caprolactone (meth)acrylate, 3 -hydroxypropyl (meth)acrylate, methyl (meth)acrylate, isobomyl (meth)acrylate, 2-(phenoxy)ethyl (meth)acrylate, biphenyl methyl (meth)acrylate, t- butylcyclohexyl (meth)acrylate, cyclohexyl (meth)acrylate, dimethyladamantyl (meth)acrylate, 2-naphthyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, tetrahydrofurfiiryl (meth)acrylate, t-butyl (meth)acrylate, 2, 3, 3 -trimethyl buten-2yl-acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, n-hexyl (meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, 3,3,5-trimethyl cyclohexyl (meth)acrylate, isopropyl (meth)acrylate, and ethylhexyl (meth)acrylate. In some embodiments, the additional monomer is an aryl monomer. A particularly suitable monomer is phenyl (meth)acrylate.

The curable ink composition also comprises at least one initiator. Typically, the initiator is a photoinitiator, meaning that the initiator is activated by light, generally ultraviolet (UV) light, although other light sources could be used with the appropriate choice of initiator, such a visible light initiators, infrared light initiators, and the like. Thus, the curable ink compositions are generally curable by UV or visible light, typically UV light. Therefore, typically, UV photoinitiators are used as the initiator. Photoinitiators are well understood by one of skill in the art of (meth)acrylate polymerization. Examples of suitable free radical photoinitiators include OMNIRAD 4265, OMNIRAD 184, OMNIRAD 651, OMNIRAD 1173, OMNIRAD 819, OMNIRAD TPO, OMNIRAD TPO-L, commercially available from BASF, Charlotte, NC. Particularly suitable photoinitiators include those that feature high absorbance above 365 nm wavelength. These include the acylphosphine oxide family of photoinitiators such as OMNIRAD TPO, OMNIRAD TPO-L, and OMNIRAD 819.

Generally, the photoinitiator is used in amounts of 0.01 to 10 parts by weight, more typically 0.1 to 4.0, parts by weight relative to 100 parts by weight of total reactive components.

A particularly suitable embodiment of the curable ink composition comprises: 40-50% by weight of at least one first monomer; 10-20% by weight of a first crosslinking monomer comprising a di(meth)acrylate of Structure 3 :

CH₂=CR¹-(CO)-O-A-O-(CO)-R¹C=CH₂

Structure 3 where in the first crosslinking monomer: R¹ is H or methyl; (CO) is a carbonyl group C=O; and A is an alkylene group comprising 6-8 carbon atoms; 30-40% by weight of a second crosslinking monomer comprising a di(meth)acrylate of Structure 3 :

CH₂=CR¹-(CO)-O-A-O-(CO)-R¹C=CH₂

Structure 3 where in the first crosslinking monomer: R¹ is H or methyl; (CO) is a carbonyl group C=O; and A is an alicyclic group with 10 carbon atoms;

0-10% by weight of at least one additional (meth)acrylate monomer; and

0.1 to 2.0, parts by weight relative to 100 parts by weight of total reactive components of at least one initiator.

Also disclosed herein are method for preparing optical articles. In some embodiments, the method comprises providing an optical substrate with a surface, preparing a curable ink composition, disposing the curable ink composition on at least a portion of the surface of the optical substrate, and curing the curable ink composition to form a cured layer that is a non-crystalline, optically clear layer with a dielectric constant of less than or equal to 2.6 at 100 kiloHertz and has a Tg of at least 80°C as measured by the peak of tan(delta) in a DMA (Dynamic Mechanical Analysis). Preparing a curable ink composition comprises preparing a curable reaction mixture comprising a first monomer comprising a branched alkyl (meth)acrylate monomer comprising at least 2 branches wherein each branch comprises 10 or more carbon atoms, a crosslinking monomer, and at least one initiator, and mixing the components of the curable reaction mixture to form a curable ink composition that is solvent free and inkjet printable, having a viscosity of less than 35 centipoise at a temperature of from room temperature to less than 60°C.

Examples of first monomers, crosslinking monomers, optional additional monomers, and initiators are described in detail above. In some embodiments, the first monomer comprises general Structure 1 :

CH₂=CR'(CO)-O-R²

-CH₂-CHR³R⁴

Structure 2 where R³ is a alkyl, alkylidene or alkyl group substituted with ethylene groups comprising at least 10 carbon atoms; where R⁴ is a alkyl, alkylidene or alkyl group substituted with ethylene groups comprising at least 10 carbon atoms.

The first monomer of general Structure 1 can be prepared by either the reaction of an alcohol with an (meth)acrylic anhydride or the reaction of an alcohol with a (meth)acrylic chloride.

In some embodiments, the first monomer of general Structure 1 is prepared from a reaction mixture of Reaction Scheme 1 :

HO-CH₂-CHR³R⁴ + CH₂=CR¹(CO)-O-(CO)-CR¹=CH₂ Reaction Scheme 1 where the reaction mixture further comprises at least one solvent and at least one base catalyst; and where R¹ is H or methyl; (CO) is a carbonyl group C=O; R³ is a alkyl, alkylidene or alkyl group substituted with ethylene groups comprising at least 10 carbon atoms; and R⁴ is a alkyl, alkylidene or alkyl group substituted with ethylene groups comprising at least 10 carbon atoms. In some particularly suitable embodiments, R³ comprises a straight chain alkyl group with 14 carbon atoms, and R⁴ comprises an alkyl group with 16 carbon atoms. In other particularly suitable embodiments, R³ comprises a branched alkyl group with 10 carbon atoms, and R⁴ comprises a branched alkyl group with 13 carbon atoms.

In other embodiments the first monomer of general Structure 1 is prepared from a reaction mixture of Reaction Scheme 2:

HO-CH₂-CHR³R⁴ + CH₂=CR¹(CO)-C1

Reaction Scheme 2 where the reaction mixture further comprises at least one solvent and at least one base catalyst; and wherein R¹ is H or methyl; (CO) is a carbonyl group C=O; R³ is a alkyl, alkylidene or alkyl group substituted with ethylene groups comprising at least 10 carbon atoms; and R⁴ is a alkyl, alkylidene or alkyl group substituted with ethylene groups comprising at least 10 carbon atoms.

In some embodiments, the crosslinking monomer comprises at least one the crosslinking monomer comprises at least one di(meth)acrylate of the general Structure 3

CH₂=CR¹-(CO)-O-A-O-(CO)-R¹C=CH₂

Structure 3 where R¹ is H or methyl; (CO) is a carbonyl group C=O; and A is an alkylene group comprising 4-12 carbon atoms, or an alicyclic group with 8-12 carbon atoms.

CH₂=CR¹-(CO)-O-A-O-(CO)-R¹C=CH₂ Structure 3 where in the first crosslinking monomer: R¹ is H or methyl; (CO) is a carbonyl group C=O; and A is an alkylene group comprising 6-8 carbon atoms; 30-40% by weight of a second crosslinking monomer comprising a di(meth)acrylate of Structure 3 :

CH₂=CR¹-(CO)-O-A-O-(CO)-R¹C=CH₂

0-10% by weight of at least one additional (meth)acrylate monomer; and

Also disclosed herein are articles. These articles are prepared by the methods described above. In some embodiments, the articles comprise a substrate with a first major surface and a second major surface, a cured organic layer with a first major surface and a second major surface, where the first major surface of the cured organic layer is adjacent to at least a portion of the second major surface of the substrate, where the cured organic layer comprises a crosslinked (meth)acrylate-based layer having a thickness of from 1-50 micrometers, has a dielectric constant of 2.6 or less at 100 kiloHertz, a Tg of 80°C or greater as measured by the peak of tan(delta) in a DMA (Dynamic Mechanical Analysis), and is non-crystalline and optically clear. The cured organic layer comprises a layer comprising a curable ink composition that has been printed and cured on at least a portion of the second major surface of the substrate. The curable ink composition is described in detail above and comprises a first monomer comprising a branched alkyl (meth)acrylate monomer comprising at least 2 branches where each branch comprises 10 or more carbon atoms, a crosslinking monomer, and at least one initiator. The curable ink composition is solvent free and inkjet printable, having a viscosity of less than 35 centipoise at a temperature of from room temperature to less than 60°C.

In some embodiments, the article further comprises a device disposed on the second major surface of the substrate, and adjacent to the first major surface of the cured organic layer. A wide range of devices are suitable. In some embodiments the device comprises an OLED (organic light-emitting diode). The device may comprise additional layers.

An example of a simple article is shown in Figure 1, where article 100 comprises substrate 120 with cured organic layer 110 disposed on the substrate.

Substrate 120 includes a wide array of flexible and non-flexible substrates. For example substrate 120 may be glass or a relatively thick layer of a polymeric material such as PMMA (polymethyl methacrylate) or PC (polycarbonate). Alternatively, substrate 120 may be flexible polymeric fdm such as fdms of PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PC (polycarbonate), polyimide, PEEK (polyetherether ketone), and the like.

Cured organic layer 110 is a (meth)acrylate-based cured layer of the curable ink compositions described above. Again, it is important to note that while the curable composition is described as an “ink”, this just means that the composition is printable and not necessarily that the cured organic layer 110 has been printed, since as described above, other coating methods can also be used. In many embodiments, however, the cured organic layer 110 has been coated by printing, especially inkjet printing, and then has been cured. Cured organic layer 110 has all of the properties described above, namely the layer has a thickness of from 1-50 micrometers, in some embodiments from 5-30 micrometers, the layer has a dielectric constant of 2.6 or less at 100 kiloHertz, and is optically clear.

Figure 2 shows a device that includes a multilayer article of the present disclosure. Figure 2 shows article 200 comprising substrate 230 with device 240 disposed on substrate 230. Inorganic barrier layer 250 is in contact with device 240, and cured organic layer 210 is in contact with the inorganic barrier layer 250. Figure 2 also includes optional inorganic layer 260 that is in contact with cured organic layer 210. Optional layer 270 is in contact with optional inorganic layer 260 and also with substrate 280. Additionally, between optional layer 260 and optional layer 270, there may be optional alternating pairs of layers of cured organic (210) and inorganic (260). For clarity these optional layers are not shown, but one can readily envision a stack of layers in the sequence 250/210/260/210/260, or 250/210/260/210/260/210/260, and so on.

The inorganic layer barrier layer 250 in contact with cured organic layer 210 can be prepared from a variety of materials including metals, metal oxides, metal nitrides, metal oxynitrides, metal carbides, metal oxyborides, and combinations thereof. A wide range of metals are suitable use in the metal oxides, metal nitrides, and metal oxynitrides, particularly suitable metals include Al, Zr, Si, Zn, Sn, and Ti. One particularly suitable inorganic barrier layer material is silicon nitride.

The thickness of the inorganic barrier layer 250 is not particularly limited, generally it is between 20 nanometers and 1 micrometer (1000 nanometers). More typically the thickness is from 20 nanometers to 100 nanometers.

The inorganic barrier layer can be deposited in a variety of ways. In general, any suitable deposition method can be utilized. Examples of suitable methods include vacuum processes such as sputtering, chemical vapor deposition, ALD (atomic layer deposition), metal-organic chemical vapor deposition, plasma enhanced chemical vapor deposition, evaporation, sublimation, electron cyclotron resonance-plasma enhanced chemical vapor deposition, and combinations thereof.

Optional inorganic barrier layer 260 is of a similar thickness as inorganic barrier layer 250 and may comprise the same inorganic material, or it may be a different inorganic material.

Examples

These examples are merely for illustrative purposes only and are not meant to be limiting on the scope of the appended claims. All parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight, unless noted otherwise. The following abbreviations are used: mm = millimeters; cm = centimeters; nm = nanometers; in = inch; mL = milliliters; g = grams; cPs = centipoise; M = Molar; Hz = Hertz; kHz = kiloHertz; MHz = megaHertz; W = Watts; J = Joules; s = seconds; min = minutes; MPa = megaPascals; rpm = revolutions per minute.

Table of Abbreviations

Test Methods

Dk Measurements

The dielectric measurements were performed with a Novocontrol Impedance Spectrometer paired with a contact wedge PicoProbe by GGH. The picoprobe has a <10 micrometer tip and allows for a high-input impedance measurement with sensitivity at MHz frequencies. When performing an impedance measurement, an AC bias was applied across the sample. The current response typically has a phase shift from the applied voltage, yielding a complex impedance. The dielectric constant, capacitance, and loss tangent is determined from the real, imaginary, and ratio of components of complex impedance, Z*. Frequencies from 100Hz to 1MHz were tested. The effective electrode area is the overlap cross-section of two electrodes. For the e-beam masks used for this project, this corresponds to a circle with diameter, d, of 10mm. In the case of electrode offset by some distance a, the effective electrode area can be calculated from overlap area, A, of two circles of diameter d, offset by a distance a. (here a is necessarily less than d)

Dk thin film sample preparation

10 nm of Ti was evaporated onto a cleaned glass substrate, followed by 100 nm of Al, to form the patterned bottom electrode. Ink formulation was then spin coated and cured only on the center active areas. This was achieved by applying two semiconductor protection tapes (Semiconductor Equipment Corp. 18733-1.25 Blue Eow Tack) to mask off the electrode areas. The ink was cured according to the procedure below. The low- tack tape was peeled off after curing the ink, and 100 nm of Al was deposited as top electrode to complete the sample preparation.

Viscosity

A Brookfield DV2T viscometer was used to measure the viscosity of sample inks. The measuring cylinder and spindle were first cleaned with acetone and isopropyl alcohol (IP A), then blow dried with N2. About 17 mE of ink formulation was filtered with a 1 micrometer filter and loaded in the cylinder. The shear rate was set to 10 Hz and the temperature was to set to 25°C. Viscosity measurement was repeated multiple times, and an average and standard deviation of all data points was taken, in units of centipoise.

Curing

Unless noted otherwise, ink samples were all cured using a 395 nm UV lamp (FireJet FJ801, Phoseon Technology) at 0.24 W/cm² power for 30 s (equal to 7.2 J/cm² in dose) in a custom-made box filled with N2.

Glass Transition Temperature (Tg) and Modulus

Dynamic Mechanical Analysis (DMA) was used to measure ink’s Tg and modulus. Ink formulations were UV cured inside a silicon mold (2 in by 3 in (5 cm by 8 cm) mold with 5 mm by 2 in (5 cm) cut-out in center). A caliper was used to measure and record the width and thickness of the resulting ink sample strip before it was loaded into the TA Instruments Q800 DMA. The sample was ramped from 25°C to 150°C at 2°C/min with a strain of 0. 1%. Tg and modulus were extracted from the peak of the Tan Delta curve in °C and storage modulus at 25°C in MPa, respectively.

Cure Ratio

Cleaned 50 x 50 x 1 mm glasses (Coming Eagle XG from Swift Glass) were treated with UV-Ozone (NOVASCAN PSD Pro Series) for 15 min. To prepare cured thin film samples, ink formulations were first filtered using a 0.2 micrometer filter before spin coated (Laurell WS-650Mz-23NPPB) at 500 rpm for 15 s then 2000 rpm for 15 s onto glass substrate, then UV cured under N2. A Nicolet iZIO FT-IR Spectrometer equipped with a diamond crystal was used to measure liquid and cured thin film samples at room temperature. Each spectrum was acquired by averaging 32 scans at a spectral range of 400 to 4000 cm"¹. The spectra peak at 810 cm"¹ was noted and the peak area was extracted to calculate cure ratio by using the equation below, where Ai and A2 are the peak areas at 810 cm"¹ of liquid and thin film samples, respectively.

Cure Ratio (%) = (1 - A1/A2) x 100

Examples

Synthesis Examples

Synthesis Example SE-1: Tetradecyloctadecyl methacrylate (I32MA)

In a 2-neck flask was added 55g of Alcohol- 1 and 200g of Ethyl Acetate the mixture was stirred with a magnetic stirrer till Alcohol- 1 was completely dissolves and a clear homogeneous solution was attained. 0 ,43g of DMAP was added prior to adding Anhydride- 1 via a dropping funnel. The flask was heated to 60°C for 17 hours. After 17 hours the temperature was raised to 90°C for 7 hours, and then cooled to room temperature.

100g of ethyl acetate was added to flask, and contents transferred into a separation funnel. A IM solution of Hydrogen Chloride was added to wash reaction solution, followed by super saturated solution of Sodium Bicarbonate solution was used to wash reaction solution (twice), succeeded by a solution of Sodium Chloride solution. An amount of anhydrous Magnesium sulphate was added to organic solvent phase and swirled to mix and allowed to sit for about 2 hours prior to vacuum fdtration. The residual solution was processed with a rotatory evaporator to obtain a clear oil of I32MA.

Synthesis Example SE-2: Tetradecyloctadecyl acrylate (I32A)

The same procedure was followed, except acryloyl chloride was used in place of Anhydride- 1.

Ink Examples

Examples El -Ex and Comparative Examples CE1-CE8

A series of ink compositions were prepared with the components described in Table 1 (Examples E1-E5) and Tables 2 and 3 (Comparative Examples CE1-CE5 and CE6-CE8). The components are in parts by weight. The ink samples were tested for viscosity using the method described above and cured using the method described above and tested for Dk, Tg, and modulus using the method described above. These data are presented in Tables 1-3.

Table 1

Table 2

Table 3

Claims

What is claimed is:

1. A curable ink composition comprising: at least one first monomer comprising a branched alkyl (meth)acrylate monomer comprising at least 2 branches wherein each branch comprises 10 or more carbon atoms; at least one crosslinking monomer; and at least one initiator, wherein the curable ink composition is solvent free and inkjet printable, having a viscosity of less than 35 centipoise at a temperature of from room temperature to less than 60°C, and upon curing forms a non-crystalline, optically clear layer with a dielectric constant of less than or equal to 2.6 at 100 kiloHertz.

2. The curable ink composition of claim 1, wherein the ink composition upon curing has a Tg of at least 80°C as measured by the peak of tan(delta) in a DMA (Dynamic Mechanical Analysis).

3. The curable ink composition of claim 1, wherein the first monomer comprises general

Structure 1:

CH₂=CR¹(CO)-O-R²

Structure 1 wherein R¹ is H or methyl;

(CO) is a carbonyl group C=O; and

R² is branched alkyl group with general Structure 2:

-CH₂-CHR³R⁴

Structure 2 wherein R³ is a alkyl, alkylidene or alkyl group substituted with ethylene groups comprising at least 10 carbon atoms; wherein R⁴ is a alkyl, alkylidene or alkyl group substituted with ethylene groups comprising at least 10 carbon atoms;

4. The curable ink composition of claim 3, wherein the R³ and R⁴ are different.

5. The curable ink composition of claim 3, wherein R³ comprises an alkyl group with 14 carbon atoms, and R⁴ comprises an alkyl group with 16 carbon atoms.

6. The curable ink composition of claim 5, wherein R³ and R⁴ comprise straight chain alkyl groups.

7. The curable ink composition of claim 3, wherein R³ comprises an alkyl group with 10 carbon atoms, and R⁴ comprises an alkyl group with 13 carbon atoms.

8. The curable ink composition of claim 7, wherein R³ and R⁴ comprise branched alkyl groups.

9. The curable ink composition of claim 1, wherein the crosslinking monomer comprises at least one di(meth)acrylate of the general Structure 3

CH₂=CR¹-(CO)-O-A-O-(CO)-R¹C=CH₂

Structure 3 wherein R¹ is H or methyl;

(CO) is a carbonyl group C=O; and

A is an alkylene group comprising 4-12 carbon atoms, or a alicyclic group with 8-12 carbon atoms.

10. The curable ink composition of claim 9, wherein the crosslinking monomer comprises a mixture of at least 2 di(meth)acrylates of Structure 3 :

CH₂=CR¹-(CO)-O-A-O-(CO)-R¹C=CH₂

Structure 3 wherein in the first crosslinking monomer:

R¹ is H or methyl;

(CO) is a carbonyl group C=O; and A is an alkylene group comprising 6-8 carbon atoms; and wherein in the second crosslinking monomer:

R¹ is H or methyl;

(CO) is a carbonyl group C=O; and

A is an alicyclic group with 10 carbon atoms.

11. The curable ink composition of claim 1, further comprising at least one additional (meth)acrylate monomer.

12. The curable ink composition of claim 10 comprising:

40-50% by weight of at least one first monomer comprising a branched alkyl (meth)acrylate monomer comprising at least 2 branches wherein each branch comprises 10 or more carbon atoms;

10-20% by weight of a first crosslinking monomer comprising a di(meth)acrylate of Structure 3 :

CH₂=CR¹-(CO)-O-A-O-(CO)-R¹C=CH₂

Structure 3 wherein in the first crosslinking monomer:

R¹ is H or methyl;

(CO) is a carbonyl group C=O; and

A is an alkylene group comprising 6-8 carbon atoms;

30-40% by weight of a first crosslinking monomer comprising a di(meth)acrylate of Structure 3 :

CH₂=CR¹-(CO)-O-A-O-(CO)-R¹C=CH₂

Structure 3 wherein in the first crosslinking monomer:

R¹ is H or methyl;

(CO) is a carbonyl group C=O; and

A is an alicyclic group with 10 carbon atoms;

0-10% by weight of at least one additional (meth)acrylate monomer; and at least one initiator.

13. A method of preparing an optical article comprising: providing an optical substrate with a surface; preparing a curable ink composition comprising, wherein preparing a curable ink composition comprises: preparing a curable reaction mixture comprising a first monomer comprising a branched alkyl (meth)acrylate monomer comprising at least 2 branches wherein each branch comprises 10 or more carbon atoms; a crosslinking monomer; and at least one initiator, and mixing the components of the curable reaction mixture to form a curable ink composition that is solvent free and inkjet printable, having a viscosity of less than 35 centipoise at a temperature of from room temperature to less than 60°C, disposing the curable ink composition on at least a portion of the surface of the optical substrate; and curing the curable ink composition to form a cured layer that is a non-crystalline, optically clear layer with a dielectric constant of less than or equal to 2.6 at 100 kiloHertz and has a Tg of at least 80°C as measured by the peak of tan(delta) in a DMA (Dynamic Mechanical Analysis).

14. The method of claim 13, wherein the first monomer comprises general Structure 1:

OfcCR^COj-O-R²

Structure 1 wherein R¹ is H or methyl;

(CO) is a carbonyl group C=O; and

R² is branched alkyl group with general Structure 2:

-CH₂-CHR³R⁴ Structure 2 wherein R³ is a alkyl, alkylidene or alkyl group substituted with ethylene groups comprising at least 10 carbon atoms; wherein R⁴ is a alkyl, alkylidene or alkyl group substituted with ethylene groups comprising at least 10 carbon atoms.

15. The method of claim 14, wherein the first monomer of general Structure 1 is prepared by either the reaction of an alcohol with an (meth)acrylic anhydride or the reaction of an alcohol with a (meth)acrylic chloride.

16. The method of claim 14, wherein the first monomer of general Structure 1 is prepared from a reaction mixture of Reaction Scheme 1:

HO-CH₂-CHR³R⁴ + CH₂=CR¹(CO)-O-(CO)-CR¹=CH₂

Reaction Scheme 1 wherein the reaction mixture further comprises at least one catalyst; and wherein R¹ is H or methyl;

(CO) is a carbonyl group C=O;

R³ is a alkyl, alkylidene or alkyl group substituted with ethylene groups comprising at least 10 carbon atoms; and

R⁴ is a alkyl, alkylidene or alkyl group substituted with ethylene groups comprising at least 10 carbon atoms.

17. The method of claim 16, wherein R³ comprises a straight chain alkyl group with 14 carbon atoms, and R⁴ comprises an alkyl group with 16 carbon atoms.

18. The method of claim 14, wherein the first monomer of general Structure 1 is prepared from a reaction mixture of Reaction Scheme 2:

HO-CH₂-CHR³R⁴ + CH₂=CR¹(CO)-C1

Reaction Scheme 2 wherein the reaction mixture further comprises at least one solvent and at least one base catalyst; and wherein R¹ is H or methyl;

(CO) is a carbonyl group C=O;

19. The method of claim 13, wherein the crosslinking monomer comprises at least one the crosslinking monomer comprises at least one di(meth)acrylate of the general Structure 3

CH₂=CR¹-(CO)-O-A-O-(CO)-R¹C=CH₂

Structure 3 wherein R¹ is H or methyl;

(CO) is a carbonyl group C=O; and

A is an alkylene group comprising 4-12 carbon atoms, or an alicyclic group with 8-12 carbon atoms.

20. An article comprising: a substrate with a first major surface and a second major surface; a cured organic layer with a first major surface and a second major surface, where the first major surface of the cured organic layer is adjacent to at least a portion of the second major surface of the substrate, wherein the cured organic layer comprises a crosslinked (meth)acrylate-based layer and has a thickness of from 1-50 micrometers, and has a dielectric constant of 2.6 or less at 100 kiloHertz, a Tg of 80°C or greater as measured by the peak of tan(delta) in a DMA (Dynamic Mechanical Analysis), and is noncrystalline and optically clear, wherein the cured organic layer comprises a layer comprises a curable ink composition that has been printed and cured on at least a portion of the second major surface of the substrate, wherein the curable ink composition comprises: a first monomer comprising a branched alkyl (meth)acrylate monomer comprising at least 2 branches wherein each branch comprises 10 or more carbon atoms; a crosslinking monomer; and at least one initiator, wherein the curable ink composition is solvent free and inkjet printable, having a viscosity of less than 35 centipoise at a temperature of from room temperature to less than 60°C.