KR102672208B1 - Adhesive sheet and display device including the same - Google Patents

Abstract

Embodiments of the present invention provide an adhesive sheet and a display device including the same. The adhesive sheet is formed from an adhesive composition containing a polymer of a (meth)acrylic monomer and a polar functional group-containing monomer, and a plasticizer with a refractive index of 1.57 or more, and may have an average dielectric constant and refractive index within a predetermined range. Accordingly, a pressure-sensitive adhesive sheet having excellent optical and dielectric properties and improved adhesive strength can be provided.

Description

Adhesive sheet and display device including same {ADHESIVE SHEET AND DISPLAY DEVICE INCLUDING THE SAME}

The present invention relates to an adhesive sheet and a display device including the same. More specifically, it relates to an adhesive sheet formed of an adhesive composition containing an acrylic polymer and a display device including the same.

Recently, various information processing functions have been combined with image display devices combined with communication functions, such as smart phones. Accordingly, one image display device may include structures such as a touch panel and an antenna along with an optical layer (eg, a polarizer, a retardation plate, etc.) for image implementation.

Accordingly, an adhesive layer or adhesive sheet is used to laminate the above-described optical layer and structures on the display panel. For example, an adhesive sheet can be used to attach an antenna or a touch panel to the display panel.

Therefore, electrical signals and radiation characteristics can be easily disturbed by dielectric characteristics around electrode patterns included in a display panel, touch panel, or antenna. For example, the dielectric constant of the adhesive sheet may reduce the touch sensitivity and sensing sensitivity of the touch electrode layer or pixel electrode.

Additionally, as adhesive sheets are applied within image display devices, a high refractive index is required. For example, if the adhesive has a low refractive index, light reflection and loss may increase due to a difference in refractive index between structures bonded to the adhesive sheet, and image quality of the image display device may deteriorate. Therefore, there is a need to design an adhesive or adhesive sheet that has a high refractive index and excellent adhesion to various structures.

For example, Korean Patent Publication No. 10-2010-0039274 discloses an adhesive for a polarizer applied to an image display device.

Korean Patent Publication No. 10-2010-0039274

One object of the present invention is to provide an adhesive sheet with improved dielectric properties and a high refractive index.

One object of the present invention is to provide a display device to which the adhesive sheet is applied.

1. It includes a cured product of an adhesive composition containing a copolymer of a polar functional group-containing monomer and a (meth)acrylic monomer, and a plasticizer with a refractive index of 1.57 or more at 25°C,

An adhesive sheet having a dielectric constant average value (E _avg ) of 4.0 or less and a refractive index at 25° C. of 1.60 or more, expressed by the following formula 1:

[Equation 1]

E _avg = (E _max +E _min )/2

(In Equation 1, E _max is the maximum value of the dielectric constants measured in the range of 10 ³ Hz to 10 ⁶ Hz, and E _min is the minimum value of the dielectric constants measured in the range of 10 ³ Hz to 10 ⁶ Hz).

2. The adhesive sheet of 1 above, wherein the plasticizer contains a thiol-based compound.

3. The adhesive sheet according to 2 above, wherein the thiol-based compound contains three or more thiol groups.

4. The adhesive sheet of 3 above, wherein the thiol-based compound includes a compound represented by the following Chemical Formula 1 or Chemical Formula 2:

[Formula 1]

[Formula 2]

.

5. The adhesive sheet of 1 above, wherein the content of the plasticizer is 0.1 to 20 parts by weight based on 100 parts by weight of the copolymer.

6. The adhesive sheet according to 1 above, wherein the (meth)acrylic monomer has a refractive index of 1.50 or more at 25°C.

7. The adhesive sheet according to 1 above, wherein the glass transition temperature of the polar functional group-containing monomer is 0°C or lower.

8. The adhesive sheet of 1 above, wherein the content of the polar functional group-containing monomer is 2 to 20 parts by weight based on 100 parts by weight of the (meth)acrylic monomer.

9. The adhesive sheet of 1 above, wherein the dielectric constant average value (E _avg ) is 2.0 to 4.0.

10. The adhesive sheet according to 1 above, comprising an adhesive layer containing the cured product, and a protective film disposed on at least one surface of the adhesive layer.

11. The adhesive sheet of item 10 above, wherein the haze value measured at a thickness of 25㎛ of the adhesive layer is less than 2%.

12. A display device comprising the adhesive sheet according to 1 above.

13. The display device according to 12 above, comprising a display panel, a touch screen disposed on the display panel, and an adhesive sheet attached to the touch screen.

The adhesive sheet according to example embodiments may have an average dielectric constant of less than a predetermined value and a refractive index of more than a predetermined value. In this case, the adhesive sheet may have improved dielectric properties, and for example, the sensitivity of the display panel or touch panel to electrical signals can be prevented from being reduced by the adhesive sheet. Additionally, signal disturbance and interference between electrodes bonded by the adhesive sheet can be suppressed, thereby providing excellent sensitivity.

Additionally, the adhesive sheet has a high refractive index, so it can have low reflectance and high light transmittance. Therefore, when the adhesive sheet is applied to a display device, the visibility and resolution of the display device can be improved by minimizing the difference in refractive index between various substrates.

Additionally, the adhesive sheet may include a cured product of an adhesive composition containing an acrylic copolymer and a plasticizer. The acrylic copolymer may include a (meth)acrylic monomer and a polar monomer. Accordingly, the internal cohesion and adhesion of the adhesive sheet can be improved, and high refractive index and flexibility can be provided. The plasticizer may have a refractive index greater than a predetermined value. Therefore, the plasticizer can provide the adhesive sheet with a high refractive index while having a low storage modulus.

1 and 2 are schematic cross-sectional views showing adhesive sheets according to example embodiments, respectively.
Figure 3 is a schematic cross-sectional view showing a display device according to example embodiments.

The adhesive sheet according to embodiments of the present invention may include a cured product of an adhesive composition containing a copolymer of a polar functional group-containing monomer and a (meth)acrylic monomer, and a plasticizer having a refractive index of 1.57 or more. In addition, the adhesive sheet may have an average dielectric constant (E _avg ) expressed by a specific formula of 4.0 or less and a refractive index at 25°C of 1.60 or more.

Additionally, display devices according to embodiments of the present invention include the adhesive sheet.

Hereinafter, the present invention will be described in detail. If there are isomers of the compound or resin represented by the chemical formula used in this application, the compound or resin represented by the chemical formula means the representative chemical formula including the isomers.

<Adhesive sheet>

1 is a schematic cross-sectional view showing an adhesive sheet according to example embodiments.

Referring to FIG. 1, the adhesive sheet 100 may include an adhesive layer 110.

The adhesive layer 110 may include a cured product of an adhesive composition containing an acrylic copolymer and a plasticizer. The acrylic copolymer may be a copolymer of a polar functional group-containing monomer and a (meth)acrylic monomer.

For example, the adhesive layer 110 may be formed by applying an adhesive composition on the protective film 120 and drying and/or curing the adhesive composition. For example, the adhesive layer 110 can be formed by applying the adhesive composition on the protective film 120 using a coating method such as roll coating, gravure coating, reverse coating, spray coating, air knife coating, or die coater. .

The adhesive sheet 100 may have an average dielectric constant value (E _avg ) expressed by Equation 1 below of 4.0 or less.

[Equation 1]

E _avg = (E _max +E _min )/2

In Equation 1, E _max may be the maximum value of permittivity measured in the range of 10 ³ Hz to 10 ⁶ Hz. E _min may be the minimum value of the dielectric constant measured in the range of 10 ³ Hz to 10 ⁶ Hz.

Specifically, the dielectric constant of the adhesive sheet 100 is measured while increasing the frequency in the frequency range of 10 ³ Hz to 10 ⁶ Hz, and the highest value of the measured dielectric constants is taken as Emax, and the lowest value is taken as Emin. Thus, the average dielectric constant value (E _avg ) can be measured.

In this case, because the adhesive sheet 100 has an average dielectric constant of 4.0 or less, signal disturbance and interference caused by the adhesive sheet 100 can be suppressed when applied to a display device, for example. Accordingly, a decrease in sensitivity to electrical signals such as a display panel or touch panel can be prevented, and excellent signal characteristics or sensing sensitivity can be provided.

Additionally, since the adhesive sheet 100 has a low dielectric constant in a wide frequency band, it can be applied to various display devices, touch screens, antenna structures, etc. Accordingly, electronic devices with excellent resolution, touch sensitivity, or signal transmission/reception characteristics can be provided.

In some embodiments, the average dielectric constant of the adhesive sheet 100 may be 2.0 to 4.0.

The refractive index of the adhesive sheet 100 at 25°C may be 1.60 or more. For example, the refractive index of the adhesive sheet 100 can be measured by irradiating sodium D line to the 25㎛ thick adhesive layer 110 using an Abbe refractometer at a temperature of 25°C.

As the adhesive sheet 100 has a high refractive index of 1.60 or more, it can have low reflectance and high light transmittance. In this case, the difference in refractive index between various structures (eg, electrode patterns) bonded to the adhesive sheet 100 can be minimized. Therefore, light reflection due to refractive index deviation at the interface can be prevented, for example, visibility of various structures can be prevented.

Preferably, the refractive index of the adhesive sheet 100 at 25°C may be 1.60 to 1.80, for example, 1.61 to 1.80. In this case, the hiding power of the adhesive sheet 100 and the structures bonded to the adhesive sheet 100 can be improved, and for example, the visibility and image quality of the display device can be further improved.

According to exemplary embodiments, the adhesive layer 110 may include a cured product of an adhesive composition containing an acrylic copolymer and a plasticizer.

The acrylic copolymer may be a polymer of a (meth)acrylic monomer and a polar functional group-containing monomer. For example, the acrylic copolymer may be prepared from a monomer blend or monomer syrup containing a (meth)acrylic monomer and a polar functional group-containing monomer. The term “(meth)acryl-” used in this application is used to encompass both “acryl-” and “methacryl-“.

The storage modulus of the acrylic copolymer can be maintained low and flexibility can be improved by the (meth)acrylic monomer. Accordingly, the brittleness of the acrylic copolymer may be reduced, and the mechanical properties and applicability of the adhesive sheet 100 may be improved.

In one embodiment, the refractive index of the (meth)acrylic monomer may be higher than the refractive index of the crosslinkable monomer having the polar functional group.

In some embodiments, the refractive index of the (meth)acrylic monomer at 25°C may be 1.50 or more. The refractive index of the (meth)acrylic monomer can be measured by the refractive index of the homopolymer formed from the monomer at 25°C. For example, the refractive index can be measured by irradiating sodium D line using an Abbe refractometer at a temperature of 25°C.

As the (meth)acrylic monomer has a high refractive index, the refractive index of the acrylic copolymer formed therefrom can be maintained low.

Preferably, the refractive index of the (meth)acrylic monomer at 25°C may be 1.51 or more, and more preferably 1.55 or more.

For example, as a (meth)acrylic monomer having a refractive index of 1.51 or more, pentabromophenyl (meth)acrylate, 2-(naphthalen-2-yloxy)ethyl (meth)acrylate ( 2-(Naphthalen-2-yloxy)ethyl (meth)acrylate), 2-(Naphthalen-2-ylthio)ethyl (meth)acrylate), 1 -Ethoxylated phenol acrylate (1-ethoxylatephenol(meth)acrylate), Biphenyl methyl (meth)acrylate and 1-Pyrene methyl (meth)acrylate (meth)acrylate), etc. These may be used alone or in combination of two or more.

As the acrylic copolymer is formed from a (meth)acrylic monomer having a high refractive index, the storage modulus of the acrylic copolymer can be maintained low while the refractive index can be increased. Accordingly, the adhesive layer 110 can have low reflectivity and high transparency, and when applied to, for example, a display panel, external visibility and resolution reduction due to the adhesive layer 110 can be prevented.

The polar functional group-containing monomer may be a polymerizable monomer capable of copolymerization with a (meth)acrylic monomer. For example, the polar group-containing monomer may be a crosslinkable monomer having a polar functional group and a crosslinkable functional group capable of polymerizing with a (meth)acrylic monomer.

The polar functional group-containing monomer may form an additional crosslinking network when the adhesive composition is cured. Accordingly, the adhesive sheet 100 can have high cohesion and adhesive strength due to the chemical bonding of the polar functional groups, and it is possible to prevent the cohesion of the adhesive layer 110 from being broken and the adhesion from being reduced even under harsh conditions of high temperature and high humidity.

For example, the polar functional group-containing monomer includes a sulfonic acid group-containing monomer, a phosphoric acid group-containing monomer, a cyano group-containing monomer, vinyl esters, a carboxyl group-containing monomer, an acid anhydride group-containing monomer, a hydroxy group-containing monomer, an amide group-containing monomer, and an amino group-containing monomer. , it may include at least one of an imide group-containing monomer, an epoxy group-containing monomer, and an ether group-containing monomer.

Examples of the sulfonic acid group-containing monomer include styrenesulfonic acid, allylsulfonic acid, 2-(meth)acrylamido-2-methylpropanesulfonic acid, (meth)acrylamidopropanesulfonic acid, sulfopropyl (meth)acrylate, ( Meta)acryloyloxynaphthalenesulfonic acid, sodium vinylsulfonate, etc. are mentioned.

Examples of the phosphoric acid group-containing monomer include 2-hydroxyethyl acryloyl phosphate.

Examples of the cyano group-containing monomer include (meth)acrylonitrile.

Examples of the vinyl ester monomers include vinyl acetate, vinyl propionate, and vinyl laurate.

Examples of the acid anhydride-containing monomer include maleic anhydride, itaconic anhydride, and acid anhydrides thereof.

Examples of the hydroxy group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate. Rate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, (4-hydroxymethylcyclohexyl)methyl acrylate, N -Methylol (meth)acrylamide, vinyl alcohol, allyl alcohol, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, diethylene glycol monovinyl ether, etc.

Examples of the carboxyl group-containing monomer include monobasic acids such as (meth)acrylic acid and crotonic acid; Dibasic acids such as maleic acid, itaconic acid, and fumaric acid, and their monoalkyl esters; 3-(meth)acryloylpropionic acid; Succinic anhydride ring-opening adduct of 2-hydroxyalkyl (meth)acrylate with an alkyl group having 2-3 carbon atoms, succinic anhydride ring-opening adduct of hydroxyalkylene glycol (meth)acrylate with an alkylene group having 2-4 carbon atoms , compounds obtained by ring-opening addition of succinic anhydride to a caprolactone adduct of 2-hydroxyalkyl (meth)acrylate having 2-3 carbon atoms in the alkyl group. Preferably, the carboxyl group-containing monomer may include (meth)acrylic acid.

Examples of the amino group-containing monomer include aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, (meth)acryloylmorpholine. etc. can be mentioned.

Examples of the imide group-containing monomer include cyclohexylmaleimide, isopropylmaleimide, N-cyclohexylmaleimide, and itaconimide.

Examples of the epoxy group-containing monomer include glycidyl (meth)acrylate, methylglycidyl (meth)acrylate, and allyl glycidyl ether.

Examples of the ether group-containing monomers include 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, phenoxyethyl (meth)acrylate, and acrylic. Royl morpholine, etc. can be mentioned.

Preferably, the polar functional group-containing monomer may include a carboxyl group-containing monomer, an amide group-containing monomer, an amino group-containing monomer, or a hydroxy group-containing monomer, and more preferably, a hydroxy group-containing monomer.

In this case, high internal cohesion and adhesion can be imparted to the adhesive sheet 100 by the polar functional group (for example, a hydroxy group) present in the acrylic copolymer, and the dielectric constant of the adhesive sheet 100 can be appropriately adjusted. there is. For example, the polar functional group can increase the polarization characteristics of the adhesive layer 110, and the minimum dielectric constant value (E _min ) and the maximum dielectric constant value (E _max ) can be adjusted to a predetermined range.

In some embodiments, the content of the polar functional group-containing monomer may be 2 to 20 parts by weight, preferably 5 to 15 parts by weight, based on 100 parts by weight of the (meth)acrylic monomer.

If the content of the polar functional group-containing monomer is less than 2 parts by weight, the cohesive force of the adhesive composition may be reduced, and the durability and adhesive strength of the adhesive sheet 100 may be reduced. When the content of the polar functional group-containing monomer exceeds 20 parts by weight, the gel fraction of the adhesive composition increases excessively, and thus adhesion and adhesive reliability may decrease.

In one embodiment, the glass transition temperature (Tg) of the polar functional group-containing monomer may be lower than the glass transition temperature of the (meth)acrylic monomer. For example, the glass transition temperature can be measured using a differential scanning calorimeter for a homopolymer of the corresponding monomer.

The polar functional group-containing monomer may provide a low glass transition temperature to the adhesive layer 110. For example, the glass transition temperature of the acrylic copolymer can be lowered by the polar functional group-containing monomer, and the adhesive sheet 100 with low elastic modulus, excellent flexibility, and step filling ability can be provided.

In some embodiments, the polar functional group-containing monomer may have a glass transition temperature of less than 0°C, and preferably may have a glass transition temperature of less than -20°C.

For example, as the acrylic copolymer is formed from a (meth)acrylic monomer with a high refractive index and a polar functional group-containing monomer with a low glass transition temperature, it may have high refractive index and low elasticity characteristics. Accordingly, the flexibility of the adhesive sheet 100 can be improved, and the bending characteristics and bending durability of the adhesive sheet 100 can be improved.

Therefore, by adjusting the ratio and content ratio of the (meth)acrylic monomer and the polar functional group-containing monomer, the adhesive sheet 100 having a high refractive index and a low glass transition temperature can be formed.

In addition, in addition to the (meth)acrylic monomer and the polar functional group-containing monomer, other polymerizable monomers known in the art are used in a range that does not reduce adhesive strength, dielectric properties, and refractive index, for example, 10% by weight of the total weight of the acrylic copolymer. Additional information may be included below.

The method for producing the acrylic copolymer is not particularly limited, and may be produced using methods commonly used in the art, such as bulk polymerization, solution polymerization, emulsion polymerization, or suspension polymerization, preferably using the solution polymerization method. It can be manufactured. Additionally, commonly used solvents, polymerization initiators, and chain transfer agents for molecular weight control can be used during polymerization.

In some embodiments, the acrylic copolymer may have a weight average molecular weight (polystyrene conversion, Mw) of 50,000 to 2,000,000 g/mol as measured by gel permeation chromatography (GPC). Preferably, the weight average molecular weight of the acrylic copolymer may be 500,000 to 1,500,000 g/mol.

If the weight average molecular weight of the acrylic copolymer is less than 50,000 g/mol, adhesive durability may be reduced due to insufficient cohesion between the copolymers. If the weight average molecular weight of the acrylic copolymer is more than 2,000,000 g/mol, a large amount of diluting solvent may be required to ensure fairness during coating.

The plasticizer can reduce the storage modulus of the adhesive sheet 100 and increase the refractive index. The refractive index of the plasticizer measured at 25°C may be 1.57 or higher.

According to exemplary embodiments, the plasticizer may include a thiol-based compound. As the thiol-based compound contains a thiol group with excellent reactivity and a high refractive index, the storage modulus of the adhesive sheet 100 can be efficiently lowered, and an adhesive layer 110 with low reflection characteristics and excellent light transmittance can be formed. there is.

In some embodiments, the thiol-based compound may be a monofunctional, difunctional, or trifunctional or more multifunctional compound, and preferably may be a trifunctional or more multifunctional compound. For example, the thiol-based compound may be a polyfunctional thiol compound having three or more thiol groups, and more preferably, it may be a tri- or tetra-functional thiol compound.

As the thiol-based compound has three or more thiol groups, the crosslinking reactivity of the pressure-sensitive adhesive composition can be improved, and the pressure-sensitive adhesive layer 110 with a high refractive index and low elastic modulus can be formed. In addition, as the thiol-based compound has four or less thiol groups, the amount of thiol groups remaining after the curing reaction may be reduced, and the internal cohesion and stability over time of the adhesive layer 110 may be improved.

For example, the thiol-based compound may include a compound represented by Formula 1 or Formula 2 below.

[Formula 1]

[Formula 2]

In some embodiments, the refractive index of the thiol-based compound at 25°C may be 1.57 or more, and preferably 1.6 or more. Specifically, the refractive index of the thiol-based compound at 25°C may be 1.6 to 1.8. Within the above range, a decrease in the refractive index of the adhesive layer 110 can be prevented, and an adhesive sheet 100 with high transparency and low reflectance can be provided.

In some embodiments, the molecular weight of the thiol-based compound may be 250 g/mol or more. Specifically, the molecular weight of the thiol-based compound may be 250 to 400 g/mol. Within the above range, the crosslinking reactivity of the thiol-based compound may be excellent, and the applicability and step absorption of the adhesive composition may be improved.

In some embodiments, the content of the thiol-based compound may be 0.1 to 20 parts by weight, preferably 5 to 15 parts by weight, based on 100 parts by weight of the acrylic copolymer.

When the content of the thiol-based compound is less than 0.1 part by weight, the elastic modulus of the adhesive layer 110 may increase and the refractive index may decrease. If the content of the thiol-based compound exceeds 20 parts by weight, the stability over time of the adhesive composition may be reduced due to the high reactivity of the thiol group. Additionally, additional reactions may occur within the adhesive layer 110 due to the thiol groups remaining after the curing reaction, and the storage stability and reliability of the adhesive sheet 100 may be reduced.

In some embodiments, the adhesive composition may further include a photopolymerization initiator or a thermal curing agent to improve crosslinkability or curability.

The photopolymerization initiator is, for example, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-butyl ether, benzoin isobutyl ether, acetophenone, 1-hydroxycyclohexyl. -1-phenylmethanone, hydroxydimethylacetophenone, dimethylaminoacetophenone, dimethoxy-2-phenylacetophenone, 3-methylacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2- Diethoxy-2-phenylacetophenone, 4-chronolocetophenone, 4,4-dimethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 4-hydroxycyclophenyl ketone , 1-hydroxycyclohexylphenylketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one, oligo[2-hydroxy-2-methyl-1 -(4-(1-methylvinyl)phenyl)propanone], 4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl)ketone, benzophenone, p-phenylbenzophenone, 4 ,4-diaminobenzophenone, 4,4'-diethylaminobenzophenone, dichlorobenzophenone, anthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-t-butylanthraquinone, 2-aminoanthra Quinone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, benzyldimethylketal, diphenylketonebenzyl Dimethyl ketal, acetophenone dimethyl ketal, p-dimethylaminobenzoic acid ester, 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO), fluorene, triphenylamine, carbazole, azobisisobutyronitrile (AIBN) ), etc. may be included. These can be used individually or in combination of two or more types.

In some embodiments, the content of the photopolymerization initiator may be 0.01 to 3 parts by weight, preferably 0.2 to 2 parts by weight, based on 100 parts by weight of the acrylic copolymer.

The heat curing agent may strengthen the cohesion of the adhesive composition by appropriately crosslinking the acrylic copolymer, and may include, for example, an isocyanate crosslinking agent.

The isocyanate-based crosslinking agent is, for example, tolylene diisocyanate, xylene diisocyanate, hexamethylene diisocyanate, 2,4-diphenylmethane diisocyanate, 4,4-diphenylmethane diisocyanate, isophorone diisocyanate, tetra Methylxylene diisocyanate, naphthalene diisocyanate, isocyanurate trimer, etc. are mentioned.

The content of the heat curing agent may be 0.1 to 1 part by weight, preferably 0.1 to 0.5 parts by weight, based on 100 parts by weight of the acrylic copolymer.

In some embodiments, the adhesive composition may further include a silane coupling agent. In this case, durability and reworkability of the adhesive layer 110 may be improved.

The silane coupling agent is, for example, vinylchlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethyl Toxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropyl Triethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-acryloxypropyltrimethoxysilane, N- 2-(Aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyltriene Toxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-amino Propyltrimethoxysilane, 3-chloropropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, 3-isocyanate propyl It may include triethoxysilane, silane containing a substituted acetamide group, etc. These can be used alone or in combination of two or more types.

The content of the silane coupling agent may be 0.01 to 5 parts by weight, preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the acrylic copolymer.

The adhesive composition contains antioxidants, corrosion inhibitors, leveling agents, surface lubricants, anti-foaming agents, fillers, light stabilizers, reaction initiators, solvents, etc. within the range that does not impair the adhesion, high refraction, and low elasticity characteristics of the acrylic copolymer and plasticizer described above. It may further contain additives.

According to example embodiments, the adhesive sheet 100 may further include a protective film formed on the surface of the adhesive layer 110.

For example, the adhesive sheet 100 may include a first protective film 120 and a second protective film 130 formed on the bottom and top surfaces of the adhesive layer 110, respectively.

The first protective film 120 may be provided as a base film for forming the adhesive layer 110. The second protective film 130 may be provided as a release film for attaching the adhesive layer 110 to an object.

In some embodiments, the first protective film 120 may also be provided as a release film. In this case, the adhesive sheet 100 may be provided as a double-sided adhesive sheet.

The first protective film 120 and the second protective film 130 are, for example, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate; polyimide resin; Acrylic resin; Styrene-based resins such as polystyrene and acrylonitrile-styrene; Polycarbonate resin; Polylactic acid resin; Polyurethane resin; Polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymer; Vinyl-based resins such as polyvinyl chloride and polyvinylidene chloride; polyamide resin; Sulfone-based resin; Polyether-etherketone-based resin; It may include allylate-based resins, etc.

According to exemplary embodiments, the haze value of the adhesive layer 110 may be less than 2%. For example, the haze value of the adhesive layer 110 can be measured using a haze transmittance reflectometer under the conditions of a thickness of 25 μm and a temperature of 25°C.

Preferably, the haze value of the adhesive layer 110 may be 1% or less, and more preferably 0.5% or less.

Within the above range, the transparency of the adhesive layer 110 can be improved, and for example, the adhesive sheet 100 and the structure bonded to the adhesive sheet 100 can be prevented from being visible. Therefore, it is possible to prevent deterioration of image quality and resolution of the display device due to the adhesive sheet 100 and improve visibility.

Figure 2 is a schematic cross-sectional view showing an adhesive sheet according to example embodiments.

Referring to FIG. 2, the adhesive sheet 100 includes a base film 130, an adhesive layer 110 disposed on one side of the base film 130, and an optical function layer disposed on the adhesive layer 110 ( 140) may be included. For example, the adhesive sheet 100 may be provided as an optical film.

For example, the adhesive sheet 100 is formed by applying and curing the above-described adhesive composition on one side of the base film 130 to form an adhesive layer 110, and then forming an optical functional layer ( 140) can be formed by attaching it.

For example, the adhesive sheet 100 may be formed by removing the first protective film 120 from the adhesive sheet described above and then attaching the optical function layer 140 to one surface of the exposed adhesive layer 110.

In one embodiment, the base film 130 may be provided as a release film. In this case, after removing the release film, the exposed surface of the adhesive layer 110 may be attached to an object, for example, a display panel.

In some embodiments, the optical functional layer 140 may include a touch sensor layer, an anti-reflection layer, a hard coating layer, a retardation layer, a window layer, or a polarizer. For example, the adhesive sheet 100 may be provided as a touch panel, anti-reflection film, hard coating film, window film, retardation film, or polarizing plate, depending on the type of optical functional layer.

<Display device>

FIG. 3 is a schematic cross-sectional view illustrating a display device according to example embodiments.

Referring to FIG. 3 , the display device may include a display panel 200, a polarizing layer 270 disposed on the display panel, and an adhesive sheet 100 according to the above-described exemplary embodiments.

The display panel 200 may include a pixel electrode 210, a pixel defining film 220, a display layer 230, an opposing electrode 240, and an encapsulation layer 250 disposed on a panel substrate 205. You can.

A pixel circuit including a thin film transistor (TFT) may be formed on the panel substrate 205, and an insulating film may be formed to cover the pixel circuit. The pixel electrode 210 may be electrically connected to, for example, a drain electrode of a TFT on the insulating film.

The pixel defining layer 220 may be formed on the insulating layer to expose the pixel electrode 210 to define the pixel area. A display layer 230 is formed on the pixel electrode 210, and the display layer 230 may include, for example, a liquid crystal layer or an organic light-emitting layer.

An opposing electrode 240 may be disposed on the pixel defining layer 220 and the display layer 230. The counter electrode 240 may be provided as a common electrode or cathode of an image display device, for example. An encapsulation layer 250 for protecting the display panel 200 may be stacked on the counter electrode 240 .

A polarizing layer 270 may be stacked on the display panel 200. For example, the polarizing layer 270 may be laminated on the display panel 200 through the adhesive sheet 100.

For example, the adhesive sheet 100 may be attached to the bottom of the polarizing layer 270 by removing the second protective film 130. Accordingly, the adhesive layer 100 may directly contact the bottom surface of the polarization layer 270.

The polarizing layer 270 may be attached to the display panel 200 through the adhesive sheet 100. For example, after removing the first protective film 120, the polarizing layer 270 may be attached to the display panel 200 through the adhesive layer 110.

In some embodiments, the touch sensor layer 260 may be stacked on the display panel 200. For example, the touch sensor layer 260 may be attached to the encapsulation layer 250 of the display panel 200 through the first point adhesive layer 50 . In this case, the polarization layer 270 may be laminated on the touch sensor layer 260 through the adhesive sheet 100.

As described above, as the adhesive sheet 100 has a low average dielectric constant of 4.0 or less, signal disturbance and interference of the electrode pattern within the touch sensor layer 260 can be suppressed. Accordingly, the electrical sensitivity and touch sensitivity of the touch sensor layer 260 may be improved.

In addition, since the adhesive sheet 100 has a high refractive index of 1.60 or more, for example, the difference in refractive index between the polarizing layer 270 and the adhesive sheet and the difference in refractive index between the touch sensor layer 260 and the adhesive sheet 100 It can be minimized. Accordingly, reflection and loss of light due to differences in refractive index can be suppressed, and deterioration of image quality of the display device can be prevented.

In some embodiments, an image display device may include an antenna structure 300. The antenna structure 300 may include an antenna electrode layer 160, an antenna dielectric layer 150, and a second point adhesive layer 60.

The antenna structure 300 may be stacked on the polarization layer 270. For example, the antenna structure 300 may be attached to the polarization layer 270 through the second point adhesive layer 60.

A cover window 280 may be stacked on the antenna structure 300. For example, the cover window 280 may be attached to the antenna structure 300 through the third point adhesive layer 70.

As described above, the antenna structure 300, the polarization layer 270, and the touch sensor layer 260 may be sequentially arranged from the user's viewing side. Alternatively, the antenna structure 300 may be disposed under the touch sensor layer 260 or between the polarization layer 270 and the touch sensor layer 260.

As described above, as the adhesive sheet 100 has low reflectance and high light transmittance, resolution degradation and visibility of the display device can be improved. Additionally, since the adhesive sheet 100 has an average dielectric constant of 4.0 or less, excellent electrical sensitivity and sensing sensitivity can be secured within the display device. In addition, it can have a low storage modulus, and can prevent separation, peeling, and breakage between structures within the image display device even under harsh conditions such as physical external force such as repeated folding/bending or high temperature/high humidity, and adhesion can be maintained for a long period of time. there is. Therefore, the adhesive sheet 100 can be usefully applied for bonding structures within a display device.

Hereinafter, experimental examples including preferred examples and comparative examples are presented to aid understanding of the present invention. However, these examples are only illustrative of the present invention and do not limit the scope of the appended claims, and do not limit the scope of the present invention. It is obvious to those skilled in the art that various changes and modifications to the embodiments are possible within the scope and technical spirit, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

Examples and Comparative Examples

(1) Preparation of adhesive composition

Example 1

A monomer mixture consisting of 70 parts by weight of phenoxybenzyl acrylate, 20 parts by weight of benzyl acrylate, and 10 parts by weight of caprolactone acrylate was added to a 1L reactor equipped with a cooling device to reflux nitrogen gas and facilitate temperature control, and then dissolved in solvent. 300 parts by weight of methyl ethyl ketone was added. Oxygen was removed by purging nitrogen gas for 1 hour, and the temperature was maintained at 70°C. After stirring the monomer mixture uniformly, 0.07 parts by weight of azobisisobutyronitrile (AIBN) based on 100 parts by weight of the monomer mixture was added as a reaction initiator and reacted for 8 hours to prepare an acrylic copolymer with a weight average molecular weight of 1.46 million. .

Afterwards, 10 parts by weight of the thiol-based compound represented by Formula 1, 0.2 parts by weight of the isocyanate-based crosslinking agent (AK75), and 1.0 parts by weight of the silane agent (KBM-403) were added to prepare an adhesive composition.

Examples 2 to 8 and Comparative Examples

An adhesive composition was prepared using the same method as Example 1 with the ingredients and contents shown in Table 1 below.

division Example Comparative example One 2 3 4 5 6 7 8 One 2 3 Acrylic copolymer A-1 70 70 70 70 70 70 70 70 A-2 70 70 70 A-3 20 20 20 20 20 29 30 20 A-4 10 10 B-1 10 10 20 10 One 30 10 B-2 20 10 10 plasticizer C-1 10 10 10 10 10 10 10 10 10 C-2 10 Silane coupling agent D One One One One One One One One One One One crosslinking agent E 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 A-1: Phenoxybenzyl acrylate (refractive index: 1.565, Tg: 22℃)
A-2: Biphenylmethyl acrylate (refractive index: 1.600, Tg: 20℃)
A-3: Benzyl acrylate (refractive index: 1.516, Tg: 11℃)
A-4: Phenoxyethyl acrylate (refractive index: 1.517, Tg: 7℃)
B-1: Caprolactone acrylate (refractive index: 1.465, Tg: -40℃)
B-2: 4-hydroxybutylacrylate (refractive index: 1.452, Tg: -32℃)
C-1: Thiol-based compound represented by Formula 1 (molecular weight: 366.7 g/mol, refractive index: 1.647)
C-2: Thiol-based compound represented by Formula 2 (molecular weight: 260.5 g/mol, refractive index: 1.647)
D: KBM-403 (Shin-Etsu)
E: Isocyanate-based crosslinking agent (AK75) (Aekyung Chemical)

(2) Manufacturing of adhesive sheet

The adhesive composition was coated on a 75㎛ thick polyethylene terephthalate (PET) film that had been treated with a release coating solution using a bar coater. Afterwards, it was dried at 100°C for 2 minutes and cured at room temperature for 7 days to prepare an adhesive sheet with an adhesive layer thickness of 25㎛.

Experiment example

(1) Transparency evaluation

The adhesive layer of the examples and comparative examples was peeled from the release film and bonded to a slide glass (S1111, manufactured by Matsunami Glass Co., Ltd.). Thereafter, the haze value (%) was measured in accordance with JISK-7136 using a haze transmittance reflectometer (HR-100 type, manufactured by Murakami Shiki Saikijutsu Kenkyu Shosha Co., Ltd.) at a temperature of 25°C. The value obtained by subtracting the haze value (0.2%) of the glass slide from the measured value was taken as the haze value of the adhesive layer.

The evaluation criteria are as follows.

<Evaluation criteria>

○: Haze value less than 2%

×: Haze value 2% or more

(2) Refractive index evaluation

The adhesive layers of the examples and comparative examples were irradiated with sodium D-rays at a temperature of 25°C, and the refractive index was measured with an Abbe refractometer (DMM4, manufactured by ATAGO).

The evaluation criteria are as follows.

<Evaluation criteria>

◎: 1.61 or higher

○: Above 1.60 and below 1.61

△: greater than 1.55 and less than 1.60

×: less than 1.55

(3) Evaluation of step absorbency

A step pattern with a step height of 25 ㎛ was formed on the outside using printing ink on a flat glass plate. The size of the glass is 5cm x 10cm x 0.7cm. A laminate was manufactured by attaching the adhesive layer of the adhesive sheet of Examples and Comparative Examples to the surface of the glass plate on which the step pattern was formed. Afterwards, the laminate was left at 85°C, 40°C, and room temperature (23°C) for 24 hours, respectively, and then the surface to which the adhesive layer was bonded was observed for lifting.

The evaluation criteria are as follows.

<Evaluation criteria>

◎: No heaving at 85°C.

○: No heaving at 40°C.

△: No heaving at room temperature.

X: There is excitation at room temperature.

(4) High temperature reliability evaluation

The adhesive layers of the adhesive sheets of Examples and Comparative Examples were attached to the polarizing plate and then laminated to produce a laminate (polarizing plate/adhesive layer/PET). The laminate was stored at a temperature of 85°C and a relative humidity of 85% for 10 days, and then visually observed to determine whether bubbles were generated.

The evaluation criteria are as follows.

<Evaluation criteria>

ⓞ: No bubbles or peeling.

○: Bubbles or peeling < 5

△: 5 ≤ bubbles or peeling < 10

×: 10 ≤ Bubble or peeling

(5) Measurement of dielectric constant average value

The ^adhesive sheets of Examples and Comparative Examples were cut into 4cm x 6cm x ^1mm (width Measure the dielectric constant while increasing . The average dielectric constant value (E _avg ) is measured according to Equation 1 below.

[Equation 1]

E _avg = (E _max +E _min )/2

E _max is the maximum value of dielectric constants measured in the range of 10 ³ Hz to 10 ⁶ Hz, and E _min is the minimum value of dielectric constants measured in the range of 10 ³ Hz to 10 ⁶ Hz.

division Example Comparative example One 2 3 4 5 6 7 8 One 2 3 transparency ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ refractive index ○ ⓞ ⓞ ⓞ ⓞ ⓞ ○ ○ × ○ × step absorbency ○ ⓞ ○ ○ ○ ○ ○ △ ○ ○ × high temperature reliability ⓞ ○ ⓞ ⓞ ○ ○ ⓞ ○ ○ × ○ Dielectric constant average value 3.2 3.3 3.5 3.6 3.8 3.8 3.3 2.9 4.2 2.8 3.2

Referring to Tables 1 and 2, it can be seen that the adhesive sheets formed from the adhesive compositions according to the examples have an average dielectric constant of 4.0 or less and a refractive index of 1.60 or more. In addition, it can be confirmed that it has a low haze value, so it can have high light transmission characteristics, and has excellent step absorption due to a low storage modulus. In addition, it can be confirmed that it provides excellent reliability and stability over time even under harsh conditions of high temperature and high humidity.

However, it can be confirmed that the adhesive sheets according to the comparative examples have deteriorated optical properties such as dielectric properties, transparency, and refractive index, or have deteriorated storage properties such as high-temperature reliability and stability over time. For example, in the case of Comparative Example 1 in which the average dielectric constant of the adhesive sheet was 4.2, sensing sensitivity and electrical signals may be deteriorated when applied to a display panel or touch panel.

100: Adhesive sheet 110: Adhesive layer
120: first protective film 130: second protective film
160: antenna dielectric layer 170: antenna electrode layer
200: display panel 260: touch sensor layer
270: Polarizing layer 280: Cover window
300: antenna structure 400: display device

Claims (13)

It includes a cured product of an adhesive composition containing a copolymer of a (meth)acrylic monomer and a monomer containing a polar functional group, and a plasticizer with a refractive index of 1.57 or more at 25°C,
An adhesive sheet having an average dielectric constant value (E _avg ) of 4.0 or less and a refractive index of 1.61 to 1.80 at 25° C. expressed by the following formula 1:
[Equation 1]
E _avg = (E _max +E _min )/2
(In Equation 1, E _max is the maximum value of the dielectric constants measured in the range of 10 ³ Hz to 10 ⁶ Hz, and E _min is the minimum value of the dielectric constants measured in the range of 10 ³ Hz to 10 ⁶ Hz).
The adhesive sheet of claim 1, wherein the plasticizer includes a thiol-based compound.
The adhesive sheet according to claim 2, wherein the thiol-based compound contains three or more thiol groups.
The adhesive sheet of claim 3, wherein the thiol-based compound includes a compound represented by Formula 1 or Formula 2:
[Formula 1]

[Formula 2]
.
The adhesive sheet of claim 1, wherein the content of the plasticizer is 0.1 to 20 parts by weight based on 100 parts by weight of the copolymer.
The adhesive sheet according to claim 1, wherein the (meth)acrylic monomer has a refractive index of 1.50 or more at 25°C.
The adhesive sheet according to claim 1, wherein the polar functional group-containing monomer has a glass transition temperature of 0° C. or lower.
The adhesive sheet of claim 1, wherein the content of the polar functional group-containing monomer is 2 to 20 parts by weight based on 100 parts by weight of the (meth)acrylic monomer.
The adhesive sheet of claim 1, wherein the dielectric constant average value (E _avg ) is 2.0 to 4.0.
The adhesive sheet of claim 1, comprising an adhesive layer containing the cured product, and a protective film disposed on at least one surface of the adhesive layer.
The adhesive sheet of claim 10, wherein the haze value measured at a thickness of 25㎛ of the adhesive layer is less than 2%.
A display device comprising the adhesive sheet according to claim 1.
In claim 12,
display panel;
a touch screen disposed on the display panel; and
A display device comprising an adhesive sheet attached to the touch screen.