KR102444641B1 - adhesive film using foldable display - Google Patents

Abstract

The present invention relates to an adhesive film for a foldable display, and more particularly, to an adhesive film for a foldable display which has excellent bending recovery properties without fold marks or gaps between adherents when repeatedly bent and minimizes the generation of air bubbles between the adherents.

Description

Adhesive film for foldable display {adhesive film using foldable display}

The present invention relates to an adhesive film for a foldable display, and more particularly, a folder capable of minimizing the generation of air bubbles between the adherends as well as having excellent flex recovery properties without traces of folds or gaps between adherends during repeated bending. It relates to an adhesive film for a display screen.

A pressure sensitive adhesive is a material that uses a material capable of maintaining a permanently sticky property as long as the surface is not contaminated, and easily adheres to an adherend in a short time by a very small pressure such as acupressure at room temperature.

Such pressure-sensitive adhesives are used in a wide variety of fields such as household goods, automobiles, aviation, and IT industries, and in the IT industry, semiconductors, mobile phones, displays, precision products, etc. are transported, and materials are fixed and protected.

Recently, with the development of display-related technologies, display devices that can be deformed in the use stage, such as folding, rolling in a roll shape, or stretching like a rubber band, are being researched and developed. Since these displays can be deformed into various shapes, it is possible to satisfy both the demand for enlargement of the display in the use stage and the demand for miniaturization of the display for portability. The deformable display device may not only be transformed into a preset shape, but may also be transformed into various shapes according to a user's request or a situation in which the display device is used. Accordingly, it is necessary to recognize the deformed shape of the display and control the display device in response to the recognized shape.

On the other hand, since the deformable display device has a problem in that each configuration of the display device is damaged according to the deformation, each configuration of the display device must satisfy folding reliability and stability.

Therefore, the adhesive used in the deformable display device must also satisfy the aforementioned folding reliability and stability, and the adhesive used in the deformable display device currently on the market, in addition to satisfying the folding characteristics, , there was a problem in that all physical properties such as adhesion, heat resistance and recovery rate were not satisfied.

Korean Patent Publication No. 2015-0011230 (published on: January 30, 2015)

The present invention was devised in consideration of the above points, and has excellent flex recovery properties without any traces of folds or gaps between adherends during repeated bending, as well as an adhesive for a foldable display that can minimize the generation of air bubbles between adherends An object of the present invention is to provide a film.

In order to solve the above problems, the adhesive film for a foldable display of the present invention includes an adhesive layer formed by curing the adhesive composition for a foldable display.

As a preferred embodiment of the present invention, the pressure-sensitive adhesive composition for a foldable display may include an acrylic polymer and a curing agent.

As a preferred embodiment of the present invention, the adhesive film for a foldable display of the present invention may have a creep rate of 30 to 60% at 25° C. measured by the following Relational Equation 1.

[Relational Expression 1]

In Relation 1, σ is stress, E is elastic modulus, t is creep deformation time, λ is η/E, and η is viscosity rate.

As a preferred embodiment of the present invention, the adhesive film for a foldable display of the present invention may have a recovery rate of 60% or more at 25° C. measured by the following Relational Equation 2.

[Relational Expression 2]

In Relation 2, σ is the stress, E is the elastic modulus, t is the creep strain time, tr is the creep recovery time after creep deformation, λ is η/E, and η is the viscosity rate).

As a preferred embodiment of the present invention, the adhesive film for a foldable display of the present invention may have a loss coefficient (tan δ) of 1.0 to 2.0 at -20°C.

As a preferred embodiment of the present invention, the adhesive film for a foldable display of the present invention may have a creep rate of 20 to 50% at 60° C. measured by Relation 1 above.

As a preferred embodiment of the present invention, the adhesive film for a foldable display of the present invention may have a recovery rate of 80% or more at 60°C as measured by the above relation (2).

As a preferred embodiment of the present invention, the adhesive film for a foldable display of the present invention may have a loss factor (tan δ) of 0.4 to 1.0 at 25°C.

As a preferred embodiment of the present invention, the adhesive film for a foldable display of the present invention may have a loss coefficient (tan δ) of 0.05 to 0.5 at 60°C.

As a preferred embodiment of the present invention, the adhesive film for a foldable display of the present invention may have a loss coefficient (tan δ) of 0.1 to 0.8 at 100°C.

As a preferred embodiment of the present invention, the acrylic polymer is a monomer represented by Formula 1 below, a monomer represented by Formula 2 below, a monomer represented by Formula 3 below, a monomer represented by Formula 4 below, and a monomer represented by Formula 5 below. A monomer comprising at least three selected from a monomer, an isobornyl acrylate monomer, a 2-hydroxypropyl acrylate monomer, an acrylic acid monomer, and an acrylonitrile monomer It may be a polymer obtained by polymerization including a mixture.

[Formula 1]

In Formula 1, B ₁ is -CH ₂ -, -CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ CH ₂ - or -CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ -, and R ₁ and R ₂ are each independently a C1-C12 straight-chain alkyl group, a C3-C12 pulverized alkyl group, a phenyl group, or an alkylphenyl group.

[Formula 2]

In Formula 2, B ₂ is -CH ₂ -, -CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ CH ₂ - or -CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ -, and R ₃ is a C1 to C12 linear alkyl group, a C3 to C12 pulverized alkyl group, a phenyl group, or an alkylphenyl group.

[Formula 3]

In Formula 3, R ₄ is a C1-C12 straight-chain alkyl group, a C3-C12 pulverized alkyl group, a phenyl group, or an alkylphenyl group.

[Formula 4]

In Formula 4, B ₂ is -CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ - or - CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ —.

[Formula 5]

In Formula 5, R ₅ and R ₆ are each independently a C1-C12 straight-chain alkyl group, a C3-C12 pulverized alkyl group, a phenyl group, or an alkylphenyl group.

As a preferred embodiment of the present invention, the acrylic polymer may include a compound represented by the following Chemical Formula 1-1 as the main resin.

[Formula 1-1]

In Formula 1-1, B ₁ is -CH ₂ -, R ₁ is an ethyl group, and R ₂ is a butyl group.

As a preferred embodiment of the present invention, the acrylic polymer may contain 3 to 25 parts by weight of the compound represented by the following Chemical Formula 3-1 based on 100 parts by weight of the main resin.

[Formula 3-1]

In Formula 3-1, R ₄ is a methyl group.

As a preferred embodiment of the present invention, the acrylic polymer may have a glass transition temperature (Tg) of -70 ~ -90 ℃.

As a preferred embodiment of the present invention, the acrylic polymer may have a weight average molecular weight of 100,000 to 2,000,000.

As a preferred embodiment of the present invention, the curing agent may include at least one selected from an isocyanate-based curing agent and an epoxy-based curing agent.

As a preferred embodiment of the present invention, the pressure-sensitive adhesive layer may have a thickness of 20 ~ 200㎛.

The adhesive film for a foldable display of the present invention not only has excellent bending recovery characteristics without any traces of folds or gaps between adherends during repeated bending, but also minimizes the occurrence of bubbles between adherends.

Hereinafter, with reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. In order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and the same reference numerals are added to the same or similar components throughout the specification.

The adhesive film for a foldable display of the present invention is an adhesive film including an adhesive layer formed by curing the adhesive composition for a foldable display, and the adhesive layer is included in the adhesive film for a foldable display to form a display panel and a cover glass. It can be used for purposes such as attachment.

In addition, the term "foldable display" as defined in the present invention may refer to a flexible display in which a folded portion has a radius of curvature of 5 mm or less because it is designed to be repeatedly folded and unfolded like paper.

In addition, the adhesive film for a foldable display of the present invention applied to a foldable display has to implement a folding characteristic, unlike the conventional adhesive for other uses, so that a creep rate and a recovery rate in a specific range and loss coefficient (tan δ, loss tangent) may be satisfied.

In addition, other specific configurations of the foldable display are known, for example, by Korean Patent Publication No. 2015-0138450, etc., and the pressure-sensitive adhesive composition for a foldable display of the present invention is not limited to the configuration of the known foldable display. may include

The pressure-sensitive adhesive composition for a foldable display of the present invention may include an acrylic polymer and a curing agent.

The acrylic polymers of the present invention can be prepared in a variety of ways. As an example, the acrylic polymer of the present invention is obtained by selecting the following monomers necessary for preparing the acrylic polymer, and mixing the selected monomers in a desired ratio with a mixture of monomers through solution polymerization, bulk polymerization, It may be prepared by applying a method such as suspension polymerization or emulsion polymerization, and may be suitably prepared by solution polymerization. A method for preparing the polymer through solution polymerization is not particularly limited.

In addition, in the solution polymerization method, a radical polymerization initiator and a solvent are mixed in a state in which the monomer components selected for preparing the acrylic polymer of the present invention are mixed in an appropriate weight ratio, and the polymerization temperature is 30° C. to 140° C. for 3 to 15 hours. can be performed while

The radical polymerization initiator used for preparing the acrylic polymer of the present invention may be a known material, and as an example, an azo-based polymerization initiator such as azobisisobutyronitrile or azobiscyclohexanecarbonitrile or benzoyl peroxide or peroxide oxides such as acetyl and the like; etc. can be used.

In addition, the radical polymerization initiator may be used alone or in mixture of two or more, and 0.01 to 1 part by weight may be used with respect to 100 parts by weight of the acrylic polymer.

In addition, the solvent used for preparing the acrylic polymer of the present invention may be a known material, and as an example, ethyl acetate or toluene may be used, but is not limited thereto.

The acrylic polymer of the present invention is a monomer represented by the following formula (1), a monomer represented by the following formula (2), a monomer represented by the following formula (3), a monomer represented by the following formula (4), a monomer represented by the following formula (5), isobornyl acrylate (Isobornyl acrylate) monomer, 2-hydroxypropyl acrylate (2-hydroxypropyl acrylate) monomer, acrylic acid (Acrylic acid) monomer and acrylonitrile (acrylonitrile) monomer mixture containing at least 3 selected from the group consisting of polymerization It may be a polymer. If the acrylic polymer of the present invention is a polymer obtained by polymerization including less than three kinds of the above-listed monomers, there may be a problem in that the physical properties required by the present invention are not satisfied.

[Formula 1]

In Formula 1, B ₁ is -CH ₂ -, -CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ CH ₂ - or -CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ -, preferably -CH ₂ -, -CH ₂ CH ₂ - or -CH ₂ CH ₂ CH ₂ -.

In Formula 1, R ₁ and R ₂ are each independently a C1-C12 straight-chain alkyl group, a C3-C12 pulverized alkyl group, a phenyl group or an alkylphenyl group, preferably a C1-C5 straight-chain alkyl group, More preferably, R ₁ is a C1-C3 straight-chain alkyl group, and R ₂ is a C3-C5 straight-chain alkyl group.

[Formula 2]

In Formula 2, B ₂ is -CH ₂ -, -CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ CH ₂ - or -CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ -, preferably CH ₂ -, -CH ₂ CH ₂ - or -CH ₂ CH ₂ CH ₂ -.

In Formula 2, R ₃ is a C1-C12 straight-chain alkyl group, a C3-C12 pulverized alkyl group, a phenyl group or an alkylphenyl group, preferably a C1-C5 straight-chain alkyl group, more preferably a C1-C3 of a straight-chain alkyl group.

[Formula 3]

In Formula 3, R ₄ is a C1-C12 straight-chain alkyl group, a C3-C12 pulverized alkyl group, a phenyl group or an alkylphenyl group, preferably a C1-C5 straight-chain alkyl group, more preferably a C1-C3 of a straight-chain alkyl group.

[Formula 4]

In Formula 4, B ₃ is -CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ - or - CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ —, preferably —CH ₂ CH ₂ CH ₂ CH ₂ —, —CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ — or —CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ -.

[Formula 5]

In Formula 5, R ₅ and R ₆ are each independently a C1-C12 straight-chain alkyl group, a C3-C12 pulverized alkyl group, a phenyl group, or an alkylphenyl group, preferably a C1-C5 straight-chain alkyl group.

Specifically, the acrylic polymer of the present invention may include a compound represented by the following Chemical Formula 1-1 as the main resin.

[Formula 1-1]

In Formula 1-1, B ₁ is -CH ₂ -, R ₁ is an ethyl group, and R ₂ is a butyl group.

The main resin is a monomer that accounts for 50% by weight or more of the monomer based on the total weight% of the monomers used in preparing the acrylic polymer. By including 50% or more with respect to the total weight% of the monomer used in the preparation, it has excellent flex recovery properties without any traces of folds or gaps between adherends during repeated bending, and an adhesive film that can minimize the generation of bubbles between adherends that can be manufactured.

Furthermore, the acrylic polymer of the present invention may contain 3 to 25 parts by weight, preferably 4 to 10 parts by weight of the compound represented by the following Chemical Formula 3-1, based on 100 parts by weight of the main resin.

[Formula 3-1]

In Formula 3-1, R ₄ is a methyl group.

On the other hand, the acrylic polymer of the present invention may have a glass transition temperature (Tg) of -70 ~ -90 ℃, preferably -72 ~ -80 ℃, more preferably -74 ~ -76 ℃, if such If the glass transition temperature is out of the range, there may be a problem that the physical properties required of the present invention cannot be satisfied.

As a preferred embodiment of the present invention, the acrylic polymer may have a weight average molecular weight of 100,000 to 2,000,000, preferably 100,000 to 1,000,000, more preferably 200,000 to 800,000, even more preferably 300,000 to 600,000, and if such If the weight average molecular weight is out of the range, there may be a problem in that the required physical properties of the present invention cannot be satisfied.

The curing agent of the present invention may include at least one selected from an isocyanate-based curing agent and an epoxy-based curing agent, preferably an isocyanate-based curing agent.

In addition, the pressure-sensitive adhesive composition for a foldable display may include 0.01 to 1 parts by weight of a curing agent, preferably 0.1 to 0.4 parts by weight, based on 100 parts by weight of the acrylic polymer.

In addition, the pressure-sensitive adhesive layer may have a thickness of 20 to 200 μm, preferably a thickness of 20 to 50 μm, and more preferably a thickness of 25 to 45 μm.

On the other hand, the adhesive film for a foldable display of the present invention has a creep rate at 25° C. measured by the following relation 1 of 30 to 60%, preferably 30 to 55%, more preferably 30 to 40 It can be %. If the creep rate at 25° C. is less than 30%, there may be a problem in that fold traces occur during repeated bending, and if it exceeds 60%, there may be a problem in that gaps between the adherends occur during repeated bending.

[Relational Expression 1]

In Relation 1, σ is stress, E is elastic modulus, t is creep deformation time, λ is η/E, and η is viscosity rate.

Creep refers to a phenomenon in which deformation of a material continues over time while a constant load is applied to the material, and t is a phenomenon in which creep deformation occurs when a constant load is applied to the adhesive film for a foldable display of the present invention. indicates time.

In addition, the adhesive film for a foldable display of the present invention has a creep rate at 60° C. measured by the above relation 1 of 20 to 50%, preferably 20 to 40%, more preferably 20 to 30 It can be %. If the creep rate at 60° C. is less than 20%, there may be a problem in that fold traces occur during repeated bending, and if it exceeds 50%, there may be a problem in that gaps between the adherends occur during repeated bending.

Furthermore, the adhesive film for a foldable display of the present invention has a recovery rate at 25° C. measured by the following Relation 2 of 60% or more, preferably 80% or more, more preferably 90% or more, even more preferably For example, it may be 95 to 99.9%. If the recovery rate at 25° C. is less than 60%, there may be a problem in that gaps between the adherends occur during repeated bending.

[Relational Expression 2]

In Relation 2, σ is the stress, E is the elastic modulus, t is the creep strain time, tr is the creep recovery time after creep deformation, λ is η/E, and η is the viscosity rate).

Creep refers to a phenomenon in which deformation of a material continues over time while a constant load is applied to the material, and t is a phenomenon in which creep deformation occurs when a constant load is applied to the adhesive film for a foldable display of the present invention. represents the time, and tr represents the time at which a certain portion of the deformation is recovered after the creep deformation occurs in the adhesive film for a foldable display of the present invention.

In addition, the adhesive film for a foldable display of the present invention has a recovery rate at 60° C. measured by the above relation 2 of 80% or more, preferably 90% or more, more preferably 95% or more, even more preferably It may be 95 to 99%. If the recovery rate at 60° C. is less than 80%, there may be a problem in that gaps between the adherends occur during repeated bending.

Meanwhile, the adhesive film for a foldable display of the present invention may have a loss coefficient (tan δ, loss tangent) at -20°C of 1.0 to 2.0, preferably 1.4 to 2.0, and more preferably 1.7 to 1.95. The loss modulus refers to the ratio of the storage modulus to the loss modulus. If the loss modulus at -20°C is less than 1.0, there may be a problem of folding marks during repeated bending, and it exceeds 2.0. If this is done, there may be a problem in that gaps between the adherends occur during repeated bending.

In addition, the adhesive film for a foldable display of the present invention may have a loss factor of 0.4 to 1.0, preferably 0.5 to 1.5, and more preferably 0.6 to 0.8 at 25°C, and if the loss factor at 25°C is 0.4 If it is less than, there may be a problem that fold traces occur during repeated bending, and if it exceeds 1.0, there may be a problem that gapping between the adherends occurs during repeated bending.

In addition, the adhesive film for a foldable display of the present invention may have a loss coefficient of 0.05 to 0.5, preferably 0.1 to 0.3, and more preferably 0.1 to 0.2 at 60°C, and if the loss coefficient at 25°C is 0.05 If it is less than, there may be a problem that fold traces occur during repeated bending, and if it exceeds 0.5, there may be a problem that gaps between the adherends occur during repeated bending.

In addition, the adhesive film for a foldable display of the present invention may have a loss factor of 0.1 to 0.8, preferably 0.1 to 0.6, more preferably 0.2 to 0.4 at 100° C., and if the loss factor at 25° C. is 0.1 If it is less than, there may be a problem in that fold traces occur during repeated bending, and if it exceeds 0.8, there may be a problem in that gaps between the adherends occur during repeated bending.

Furthermore, when the adhesive film for a foldable display of the present invention is attached to an alkali-free glass plate (Non Alkali Glass) and peeled off at 180° at a rate of 300 mm per minute, the measured adhesive force is 600 gf/inch or more, preferably 650 It may be ~ 1200 gf / inch, more preferably 680 ~ 1000 gf / inch.

On the other hand, in the adhesive film for a foldable display of the present invention, after attaching the adhesive film to the PET film, and folding evaluation up to 200,000 times with a radius of curvature of 1.5 mm, cracks do not occur, and the adhesive film and PET There is no gap between the films.

Furthermore, the adhesive film for a foldable display of the present invention is prepared by attaching the adhesive film to the polyimide film, and then autoclaving using an autoclave for 5 to 20 minutes, preferably 6 to 10 minutes, after autoclaving, After holding for 5 to 20 minutes, preferably 6 to 10 minutes, the number of bubbles generated in an area of 50 mm × 50 mm (width × length) using a microscope is less than 5, preferably 1 to 3 may be. In addition, the cell size may be less than 200 μm, preferably 80 to 120 μm. In addition, the penetration distance may be less than 400 μm, preferably 300 to 380 μm.

In the above, the present invention has been mainly described with respect to the embodiment, but this is only an example and does not limit the embodiment of the present invention. It can be seen that various modifications and applications not exemplified above are possible without departing from the scope. For example, each component specifically shown in the embodiment of the present invention can be implemented by modification. And the differences related to these modifications and applications should be construed as being included in the scope of the present invention defined in the appended claims.

Example 1: Preparation of adhesive composition for foldable display

A pressure-sensitive adhesive composition for a foldable display was prepared by mixing an acrylic polymer having a weight average molecular weight of 450,000 and a glass transition temperature of -74.9°C and an isocyanate-based curing agent. At this time, 0.2 parts by weight of an isocyanate-based curing agent was mixed with respect to 100 parts by weight of the acrylic polymer.

In addition, based on 100 parts by weight of the monomer represented by the following Chemical Formula 1-1 as an acrylic polymer, 20 parts by weight of the monomer represented by the following Chemical Formula 2-1, 6.67 parts by weight of the monomer represented by the following Chemical Formula 3-1, and the following Chemical Formula 4- A polymer obtained by polymerizing 6.67 parts by weight of the monomer represented by 1 was used.

[Formula 1-1]

In Formula 1-1, B ₁ is -CH ₂ -, R ₁ is an ethyl group, and R ₂ is a butyl group.

[Formula 2-1]

In Formula 2-1, B ₂ is —CH ₂ CH ₂ —, and R ₃ is a methyl group.

[Formula 3-1]

In Formula 3-1, R ₄ is a methyl group.

[Formula 4-1]

In Formula 4-1, B ₃ is —CH ₂ CH ₂ CH ₂ CH ₂ —.

Example 2: Preparation of adhesive composition for foldable display

A pressure-sensitive adhesive composition for a foldable display was prepared in the same manner as in Example 1. However, unlike Example 1, an acrylic polymer having a weight average molecular weight of 1,600,000 and a glass transition temperature of -73.7° C. was used, and as the acrylic polymer, with respect to 100 parts by weight of the monomer represented by Formula 1-1, the following Formula 3- A polymer obtained by polymerizing 23.08 parts by weight of a monomer represented by 2, 7.69 parts by weight of a monomer represented by Formula 5-1, 23.08 parts by weight of a monomer represented by Formula 3-1, and 7.69 parts by weight of a monomer represented by Formula 4-2 was used.

[Formula 3-2]

In Formula 3-2, R ₄ is a butyl group.

[Formula 5-1]

In Formula 5-1, R ₅ is an ethyl group, and R ₆ is a methyl group.

[Formula 4-2]

In Formula 4-2, B ₂ is —CH ₂ CH ₂ —.

Comparative Example 1: Preparation of adhesive composition for foldable display

A pressure-sensitive adhesive composition for a foldable display was prepared in the same manner as in Example 1. However, unlike Example 1, an acrylic polymer having a weight average molecular weight of 1,200,000 and a glass transition temperature of -64.0° C. was used, and isobornyl acrylate based on 100 parts by weight of the monomer represented by Formula 1-1 as the acrylic polymer. (Isobornyl acrylate) A polymer obtained by polymerizing 20 parts by weight of a monomer and 13.33 parts by weight of a monomer represented by Formula 4-2 was used.

Comparative Example 2: Preparation of adhesive composition for foldable display

A pressure-sensitive adhesive composition for a foldable display was prepared in the same manner as in Example 1. However, unlike Example 1, an acrylic polymer having a weight average molecular weight of 1,700,000 and a glass transition temperature of -65.8° C. was used, and as the acrylic polymer, based on 100 parts by weight of the monomer represented by Formula 1-1, Formula 3- A polymer obtained by polymerizing 23.08 parts by weight of the monomer represented by 2, 15.38 parts by weight of the monomer represented by Formula 5-1, and 15.38 parts by weight of the monomer represented by Formula 4-2 was used.

Comparative Example 3: Preparation of adhesive composition for foldable display

A pressure-sensitive adhesive composition for a foldable display was prepared in the same manner as in Example 1. However, unlike Example 1, an acrylic polymer having a weight average molecular weight of 870,000 and a glass transition temperature of -53.0°C was used, and 95% by weight of the monomer represented by Formula 3-2 with respect to the total weight% of the monomer as the acrylic polymer. and a polymer obtained by polymerizing 5 wt % of the monomer represented by Formula 4-1 was used.

Comparative Example 4: Preparation of adhesive composition for foldable display

(1) A pressure-sensitive adhesive composition for a foldable display was prepared by mixing an acrylic polymer having a weight average molecular weight of 760,000 and a glass transition temperature of -34.5° C. and an epoxy-based curing agent. At this time, 0.5 parts by weight of an epoxy curing agent was mixed with respect to 100 parts by weight of the acrylic polymer.

In addition, based on 100 parts by weight of the monomer represented by Formula 3-2 as the acrylic polymer, 12.5 parts by weight of the monomer represented by the following Formula 5-2, 6.25 parts by weight of an isobornyl acrylate monomer, and acrylic acid (Acrylic acid) ) A polymer obtained by polymerizing 6.25 parts by weight of a monomer was used.

[Formula 5-2]

In Formula 5-2, R ₅ and R ₆ are methyl groups.

Experimental Example 1

The pressure-sensitive adhesive compositions prepared in Examples 1 to 2 and Comparative Examples 1 to 4 were evaluated based on the following physical property evaluation methods, respectively, and the results are shown in Table 1.

(1) Adhesive force measurement

After curing the pressure-sensitive adhesive compositions prepared in Examples 1 to 2 and Comparative Examples 1 to 4 to a thickness of 35 μm, respectively, a sample was prepared by transfer lamination to a polyimide film (SKC Kolon, GF200) having a thickness of 50 μm. . The prepared sample was cut to a size of 25 mm in width × 150 mm in length. Washed 3 times with MEK (Methyl Ethyl Ketone) to prepare Non Alkali Glass with no stain on the surface, and the cured adhesive composition side of the sample cut using a 2 kg hand roller was laminated on the prepared Non Alkali Glass. After lamination, it was left at room temperature (25° C.) for 24 hours, peeled at 180° at a rate of 300 mm per minute, and the adhesive force was measured using UTM (WL2100) (the adhesive force was calculated as an average value in the stabilizing section).

(2) Determination of the occurrence of air bubbles

After curing the pressure-sensitive adhesive composition prepared in Examples 1 to 2 and Comparative Examples 1 to 4 to a thickness of 150 μm, respectively, it was placed between a polyimide film (SKC Kolon, GF200) having a thickness of 50 μm and a glass plate. A sample was prepared by laminating. The prepared sample was cut to a size of 25mm in width × 150mm in length, and the cut sample was autoclaved for 8 minutes using an autoclave (autoclave conditions: using 15 psi of autoclaved steam at 121℃). After proceeding, after maintaining for 7 minutes and 30 seconds, the pressure was reduced again for 8 minutes, and then the number of bubbles, bubble size, and penetration distance included in an area of 50 mm × 50 mm (width × length) at 5x magnification under the microscope were measured.

(3) Folding Test

Between a PET film (TORAY U48) having a thickness of 50 µm and a release film having a thickness of 50 µm, the pressure-sensitive adhesive compositions prepared in Examples 1 to 2 and Comparative Examples 1 to 4 were laminated to a thickness of 35 µm, respectively, and 50 mm × Samples were prepared by cutting to 100 mm (width × length). The prepared sample was subjected to bending evaluation up to 200,000 times with a radius of curvature of 1.5 mm using bending evaluation equipment (F1_2SV, ForeHu Co., Ltd).

After bending evaluation in 10,000 cycles, destructive and non-destructive testing was performed, and it was checked whether cracks occurred and whether the laminated surface was open. In the case of no change, it was evaluated as OK, and in the case of deformation such as peeling, cracking, or thickness change, it was evaluated as NG.

(4) creep rate and recovery rate measurement

The pressure-sensitive adhesive compositions prepared in Examples 1 to 2 and Comparative Examples 1 to 4 were respectively laminated to a thickness of 35 μm between a polyimide film having a thickness of 50 μm (SKC Kolon, GF200), and cured to prepare a sample. . The data required to calculate the creep rate and recovery rate were measured through the following measuring instrument and measurement conditions for the prepared sample, and the creep rate at 25°C and 60°C measured by the following relation 1, measured by the following relation 2 The recovery rates at 25°C and 60°C were calculated.

* Measuring instruments and measuring conditions

① Measuring device: ARES-G2, TA Instruments Inc.

② Measurement temperature range: 20 ~ 70℃

③ Temperature increase rate: 10℃/min

④ Axial Force: 0.5N

⑤ Stress: 2kPa

⑥ Creep deformation time (t): 10 minutes

⑦ Creep recovery time after creep deformation (tr): 10 minutes

[Relational Expression 1]

In Relation 1, Stress, E denotes an elastic modulus, t denotes a creep deformation time, λ denotes η/E, and η denotes a viscosity rate.

[Relational Expression 2]

In Relation 2, σ is the stress, E is the elastic modulus, t is the creep strain time, tr is the creep recovery time after creep deformation, λ is η/E, and η is the viscosity rate).

(5) Measurement of loss factor (tan δ)

The pressure-sensitive adhesive compositions prepared in Examples 1 to 2 and Comparative Examples 1 to 4 were laminated to a thickness of 35 μm and cured to prepare a sample so as not to generate bubbles between the release films. The prepared sample is placed on one side of a parallel plate, the gap is adjusted, the zero point of the torque is adjusted, and after confirming the stabilization of the force, -20 with the following measuring device and measurement conditions The storage modulus at ℃, 25℃, 60℃, 100℃ and the loss modulus at -20℃, 25℃, 60℃, 100℃ were measured, and the loss coefficient ( Tan δ) was calculated.

[Relational Expression 3]

Loss modulus (Tan δ) = loss modulus / storage modulus

* Measuring instruments and measuring conditions

① Measuring device: ARES-G2, TA Instruments Inc.

② Strain: 1%

③ Measurement temperature range: -55 ~ 250℃

④ Temperature increase rate: 10℃/min

⑤ Measurement frequency: 6.28 rad/s

As can be seen in Table 1, the pressure-sensitive adhesive composition prepared in Example 1 has excellent flex recovery properties without any traces of folds or gaps between adherends during repeated bending, and it can be confirmed that it is possible to minimize the generation of air bubbles between adherends. can

Simple modifications or changes of the present invention can be easily carried out by those skilled in the art, and all such modifications or changes can be considered to be included in the scope of the present invention.

Claims (10)

An adhesive film comprising a pressure-sensitive adhesive layer formed by curing the pressure-sensitive adhesive composition for a foldable display,
The pressure-sensitive adhesive composition for a foldable display may include an acrylic polymer; and a curing agent; and
The pressure-sensitive adhesive film has a creep rate of 30 to 60% at 25° C. measured by the following Relational Equation 1, and a creep rate of 20 to 50% at 60° C. measured by the following Relational Equation 1, measured by the following Relation 2 The recovery rate at 25°C is 60% or more, the recovery rate at 60°C measured by the following relation 2 is 80% or more, and the loss coefficient (tan δ) at -20°C is 1.0 to 2.0. Adhesive film for foldable display;
[Relational Expression 1]

[Relational Expression 2]

In Relation 1, σ is stress, E is elastic modulus, t is creep deformation time, λ is η/E, η is viscosity rate,
In Relation 2, σ is the stress, E is the elastic modulus, t is the creep strain time, tr is the creep recovery time after creep deformation, λ is η/E, and η is the viscosity rate).
delete According to claim 1, wherein the adhesive film
The loss factor (tan δ) at 25°C is 0.4 to 1.0,
The loss factor (tan δ) at 60°C is 0.05 to 0.5,
An adhesive film for a foldable display, characterized in that the loss coefficient (tan δ) at 100° C. is 0.1 to 0.8.
According to claim 1,
The acrylic polymer is a monomer represented by Formula 1 below, a monomer represented by Formula 2 below, a monomer represented by Formula 3 below, a monomer represented by Formula 4 below, a monomer represented by Formula 5 below, and isobornyl acrylate (Isobornyl acrylate) monomer, 2-hydroxypropyl acrylate monomer, acrylic acid (Acrylic acid) monomer, and acrylonitrile (acrylonitrile) monomer is a polymer obtained by polymerization including a monomer mixture comprising at least three selected from the group consisting of Adhesive film for foldable display, characterized in that.
[Formula 1]

[Formula 2]

[Formula 3]

[Formula 4]

[Formula 5]

In Formula 1, B ₁ is -CH ₂ -, -CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ CH ₂ - or -CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ -, and R ₁ and R ₂ are each independently a C1 ~ C12 linear alkyl group, C3 ~ C12 pulverized alkyl group, phenyl group or alkylphenyl group,
In Formula 2, B ₂ is -CH ₂ -, -CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ CH ₂ - or -CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ -, R ₃ is a C1 ~ C12 linear alkyl group, C3 ~ C12 pulverized alkyl group, a phenyl group or an alkylphenyl group,
In Formula 3, R ₄ is a C1-C12 straight-chain alkyl group, a C3-C12 pulverized alkyl group, a phenyl group, or an alkylphenyl group,
In Formula 4, B ₃ is -CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ CH ₂ -, -CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ - or - CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ -,
In Formula 5, R ₅ and R ₆ are each independently a C1-C12 straight-chain alkyl group, a C3-C12 pulverized alkyl group, a phenyl group, or an alkylphenyl group.
According to claim 1,
The acrylic polymer is an adhesive film for a foldable display, characterized in that it comprises a compound represented by the following Chemical Formula 1-1 as a main resin.
[Formula 1-1]

In Formula 1-1, B ₁ is -CH ₂ -, R ₁ is an ethyl group, and R ₂ is a butyl group.
6. The method of claim 5,
The acrylic polymer is an adhesive film for a foldable display, characterized in that it contains 3 to 25 parts by weight of the compound represented by the following Chemical Formula 3-1 based on 100 parts by weight of the main resin.
[Formula 3-1]

In Formula 3-1, R ₄ is a methyl group.
According to claim 1,
The acrylic polymer is an adhesive film for a foldable display, characterized in that it has a glass transition temperature (Tg) of -70 ~ -90 ℃.
8. The method of claim 7,
The acrylic polymer is an adhesive film for a foldable display, characterized in that it has a weight average molecular weight of 100,000 to 2,000,000.
According to claim 1,
The curing agent is an adhesive film for a foldable display, characterized in that it comprises at least one selected from an isocyanate-based curing agent and an epoxy-based curing agent.
According to claim 1,
The adhesive layer is an adhesive film for a foldable display, characterized in that it has a thickness of 20 ~ 200㎛.