KR102305521B1 - Backplate film for flexible display and flexible display comprising the same - Google Patents

Abstract

The present invention relates to a backplate film comprising: a base film; and an adhesive layer provided on one or both sides of the base film. The light transmittance of the backplate film is 85% or more, and the A value derived from the following equation 1 (A = │α1 - &α│) is 7 or less.

Description

Backplate film for flexible display and flexible display including same

The present invention relates to a flexible display, and more particularly, to a backplate film for a flexible display capable of preventing damage occurring in the process of folding and unfolding the flexible display, and a flexible display including the same.

Recently, with the development of technology, various studies on display devices capable of various modifications, such as bending, folding, or stretching the display, are being conducted.

In the foldable, slide, rollable, and stretchable display device, in order not to damage each configuration of the display device despite repetition of shape deformation such as folding, rolling, or stretching, each configuration of the display device is bent, Reliability and stability against deformation such as crooking, folding, twisting, and rolling must be satisfied.

The backplate film is a film that protects and supports the lower part of the display panel, and is composed of a base film and an adhesive. Such a backplate film needs to support the panel and at the same time have reliability against deformation. In particular, when bending deformation is repeatedly applied to the flexible display, the backplate film does not recover to its original state and prevents appearance deformation such as wave buckling that maintains a bent state, and peels and bubbles at the bent or deformed area. It should be possible to secure adhesion reliability by preventing

In addition, as an optical sensor is attached to the back of the backplate film for front fingerprint recognition and UDC (Under display camera) panel manufacture, a backplate film having high light transmittance is required. Currently, most polyimide films are used as the base film of the back plate film, but in this case, there is a problem in that the light transmittance is low and the recognition rate of the optical sensor is lowered. On the other hand, the polyester film not only has high light transmittance, but also has high toughness compared to the polyimide film, so it has excellent characteristics in terms of impact resistance.

On the other hand, the backplate film is attached to the lower surface of the OLED display panel through an adhesive layer. Even in the case of this adhesive, when bending deformation is applied to the flexible display, peeling and air bubbles in the bent portion are prevented, and high restoring force and recovery power are provided. In order to have it, it is necessary to distribute the stress through the high strain of the adhesive layer adjacent to the panel. That is, by dispersing the stress applied to the panel through the deformation of the pressure-sensitive adhesive layer, it is necessary to prevent peeling and bubble generation in the curved portion of the display, and to satisfy excellent restoring force and recovery force. However, the conventional pressure-sensitive adhesive composition for a flexible display has a problem in that deformation reliability and stability are not satisfied due to low adhesion and deformation rate under severe conditions.

In order to solve the above-mentioned conventional problems, one embodiment of the present invention has high light transmittance, and has excellent deformation and adhesion reliability because deformation and peeling and air bubbles do not occur in bent portions even in various environmental conditions, and thus has excellent durability and durability. and to provide a backplate film having excellent impact resistance.

Another embodiment of the present invention is to provide a flexible display having excellent durability and deformation reliability.

One embodiment of the present invention is a base film; and a back plate film comprising an adhesive layer provided on one or both sides of the base film, wherein the light transmittance of the back plate film is 85% or more, and the A value derived from the following formula 1 is 7 or less. do.

Equation 1: A= │α1 - α2│

In Equation 2, α1 and α2 are calculated from Equations 2 and 3, respectively.

Equation 2: α1=(1/L ₀ )*(ΔL /ΔT)

Equation 3: α2=(1/W ₀ )*(ΔW /ΔT)

In Equations 2 and 3, ΔL is the dimensional change in the longitudinal direction of the backplate film according to the temperature change from -40°C to 100°C, and ΔW is the backplate according to the temperature change from -40°C to 100°C is the dimensional change in the width direction of the film, ΔT is the temperature change from -40°C to 100°C, L ₀ is the initial dimension in the longitudinal direction of the backplate film _{at -40°C, and W 0} is the temperature change from -40°C to -40°C The initial dimension with respect to the width direction of a backplate film is shown.

In one embodiment of the present invention, α1 and α2 may be 57 or less.

In one embodiment of the present invention, the base film may be a polyester resin.

In one embodiment of the present invention, the polyester resin is polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), poly(cyclohexylenedimethylene terephthalate (PCT), polytri It may include one or more resins selected from the group consisting of methylene terephthalate (PTT).

In one embodiment of the present invention, the light transmittance of the base film may be 83% or more, and the initial haze may be less than 5%.

In one embodiment of the present invention, the pressure-sensitive adhesive layer has a strain greater than 10% when a stress of 10000 Pa is applied for 10 minutes at a -10°C condition, and a stress at 80°C for 10 minutes ) when 10000 Pa is applied, the strain may be greater than 35%.

In one embodiment of the present invention, the crosslinking degree of the pressure-sensitive adhesive layer may be 40% or more, and the crosslinking swelling degree may be 11 or more.

In one embodiment of the present invention, the light transmittance of the pressure-sensitive adhesive layer may be 92% or more, and the haze may be less than 3%.

In one embodiment of the present invention, the adhesive strength of the pressure-sensitive adhesive layer to the substrate of the display panel at room temperature may be 400 gf/in or more.

In one embodiment of the present invention, a protective release film may be further included on one surface of the pressure-sensitive adhesive layer.

Another embodiment of the present invention provides a flexible display including the above-described back plate film and a display display panel.

In one embodiment of the present invention, the display display panel may be a foldable display display panel, a rollable display display panel, a stretchable display display panel, or a slide display display panel.

In one embodiment of the present invention, since the backplate film has a high light transmittance, it is possible to provide high-quality photo/image taking and a high fingerprint recognition rate by allowing an optical sensor such as a display camera sensor and a fingerprint sensor to absorb sufficient light.

Another embodiment of the present invention provides a flexible display having excellent durability and deformation reliability, including the back plate film.

As used herein, “foldable display” refers to a display device that can be folded and unfolded like paper, “rollable display” refers to a display device that can be bent, and “ A “stretchable display” refers to a display device in which a screen is elastically stretched, and a “slide display” refers to a display device in which a display screen is expanded in a specific direction.

In the present invention, a “flexible display” is a display that can be deformed in shape, and may have a curved, curved, or folded portion, and the “flexible display” includes a foldable display, a rollable display, a stretchable display, a slide display, etc. All of this is included.

As used herein, the term "crosslinking" induces a physical action or chemical reaction in the composition by irradiating light, maintaining the pressure-sensitive adhesive composition at a predetermined temperature, or applying moisture, etc., and thus provides adhesive properties to the pressure-sensitive adhesive composition It means the process of manifestation.

As used herein, the term “deformation” refers to a flexible display in various forms such as bending, bending, crooking, folding, twisting, or rolling when an external force is applied. It means that the intrinsic shape of the device or its configuration is changed, and the terms “deformation reliability” and “deformation stability” mean that the function and appearance of the device are not damaged despite the “deformation”, and the flexible display returns to its original shape. It means that recovery is possible and further, continuous and repetitive device working (working) is possible.

As used herein, the term “bending characteristic” refers to a portion of the display device that is curved (bending), bent (crooking), folded (folding), twisted (twisting), or part of the display device by shape deformation such as rolling (rolling). When it has a curved edge) or a curved portion, it means “deformation reliability” and “deformation stability” for the curved portion.

In the present specification, the cross-linked pressure-sensitive adhesive composition may be used in the same sense as the pressure-sensitive adhesive or the pressure-sensitive adhesive layer in some cases.

As used herein, the term “room temperature” means 25°C.

Hereinafter, the present specification will be described in more detail.

The present invention relates to a backplate film for a flexible display capable of preventing damage occurring in the process of folding and unfolding the flexible display, and a flexible display including the same.

<Backplate Film>

One embodiment of the present invention is a base film; and a backplate film comprising an adhesive layer provided on one or both sides of the base film, wherein the light transmittance of the backplate film is 85% or more, and the A value derived from the following formula 1 is 7 or less. do.

Equation 1: A= │α1 - α2│

Here, α1 represents the dimensional change rate (ppm/°C) in the longitudinal direction of the backplate film (the longitudinal direction (MD) of the base film), and more specifically, α1 is the average slope of the dimensional change in the range from -40°C to 100°C. (ppm/°C) can be calculated from the formula (2).

Equation 2: (1/L ₀ )*(ΔL /ΔT)

α2 represents the rate of dimensional change (ppm/°C) in the width direction of the backplate film (width   direction   (TD) of the base film), and more specifically, α2 is the average slope of dimensional change (ppm/ ℃) can be calculated from Equation 3.

Equation 3: (1/W ₀ )*(ΔW /ΔT)

In the above formula, ΔL and ΔW are the dimensional changes for the backplate film with a temperature change from -40°C to 100°C, ΔT is the temperature change from -40°C to 100°C, and L ₀ and W ₀ are These are the initial dimensions for the longitudinal direction and the width direction of the backplate film at -40°C, respectively.

A value calculated from Equation 1 may be 7 or less, preferably 5 or less. When the value of A is small, it means that the difference in the rate of change in the longitudinal direction and the width direction of the backplate film is reduced, and the smaller the A value, the less warping and distortion of the backplate film even in a harsh environment. The backplate film of the present invention can provide excellent deformability characteristics of a flexible display by preventing deformation, peeling, and air bubbles in appearance despite repeated bending or deformation.

In one embodiment of the present invention, α1 represents the rate of dimensional change (ppm/℃) with respect to the longitudinal direction of the backplate film, the longitudinal direction of the backplate film is the same as the longitudinal direction of the base film, and the longitudinal direction of the base film is manufactured It means machine direction (MD). The value of α1 may be 57 to 2, more preferably 50 to 5. As shown in Figure 1 below, it can be calculated from the average slope of the dimensional change (ppm/℃) in the section from -40℃ to 100℃.

In one embodiment of the present invention, α2 represents the dimensional change rate (ppm/℃) with respect to the width direction of the back plate film, the width direction of the back plate film is the same as the width direction of the base film, and the width direction of the base film is manufactured It means transverse direction (TD). The value of α2 is 57 to 2, more preferably 50 to 7. As shown in Figure 2 below, it can be calculated from the average slope (ppm/℃) of dimensional change in the range from -40℃ to 100℃. Equations α1 and α2 respectively represent the dimensional change rate (ppm/°C) in the longitudinal direction and the width direction of the backplate film according to the temperature change. It can be obtained by measuring the dimensional change of the longitudinal direction and the width direction of a backplate film under the temperature change condition of up to degreeC.

The smaller the α1 and α2, the less deformation of the length and width of the backplate film, and the smaller the difference between α1 and α2, the less warping or bending deformation of the backplate film.

In one embodiment of the present invention, the light transmittance of the backplate film is 85% or more, preferably 87% or more. Since the backplate film has a high light transmittance, it is possible to provide high-quality photo/image taking and a high fingerprint recognition rate by allowing an optical sensor such as a display camera sensor and a fingerprint sensor to absorb sufficient light.

In one embodiment of the present invention, the back plate film includes a base film and a pressure-sensitive adhesive layer having a high light transmittance.

<Base film >

The base film has a light transmittance of 83% or more, a haze of less than 5%, and preferably a light transmittance of 85% or more, and a haze of less than 4%.

The base film has excellent mechanical properties such as high strength, and supports the rear surface of the display panel with excellent impact resistance.

The base film includes a polyester resin. Polyester resins include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), poly(cyclohexylenedimethylene terephthalate (PCT), polytrimethylene terephthalate (PTT), etc. include

Specifically, the polyester resin may be a homopolymer resin or a copolymer resin in which dicarboxylic acid and diol are polycondensed. In addition, the polyester resin may be a blend resin in which the homopolymer resin or copolymer resin is mixed.

Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5- Naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonecarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclo Hexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2 ,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid trimethyladipic acid, pimelic acid, azelaic acid, sebacic acid, suberic acid, dodecadicarboxylic acid, and the like.

In addition, examples of the diol include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)sulfone, and the like.

Preferably, the polyester resin may be an aromatic polyester resin having excellent crystallinity, for example, a polyethylene terephthalate (PET) resin may be a main component.

As an example, the base film may include about 85% by weight or more of a polyester resin, specifically, a PET resin, and more specifically, 90% by weight or more, 95% by weight or more, or 99% by weight or more. As another example, the base film may further include another polyester resin in addition to the PET resin. Specifically, the base film may further include a polyethylene naphthalate (PEN) resin in an amount of about 15% by weight or less. More specifically, the base film may further include about 0.1 wt% to 10 wt%, or about 0.1 wt% to 5 wt% of the PEN resin.

The base film may be prepared by extruding a composition containing a polyester resin, stretching it in the longitudinal direction and in the width direction, and then thermally fixing the stretched film, and the thickness of the base film is 200 μm to 10 μm, preferably 150 μm to 20 μm.

<Adhesive layer>

In one embodiment of the present invention, the pressure-sensitive adhesive layer has a strain greater than 10% when a stress of 10000 Pa is applied for 10 minutes at a -10°C condition, and a stress at 80°C for 10 minutes ) when 10000 Pa is applied, a pressure-sensitive adhesive composition having a strain rate of more than 35% is provided. Preferably, the strain at -10°C is 20% or more and 500% or less, and the strain at 80°C condition is 40% or more and 3500% or less. More preferably, the strain at -10°C is 25% or more and 400% or less, and the strain at 80°C is 50% or more and 3000% or less.

In one embodiment of the present invention, the light transmittance of the pressure-sensitive adhesive layer is 92% or more, the haze is less than 3%, preferably the light transmittance is 95% or more, and the haze is less than 2%.

In one embodiment of the present invention, the pressure-sensitive adhesive layer may be prepared from the following pressure-sensitive adhesive composition.

The pressure-sensitive adhesive composition has a high strain rate in the above range even under severe environmental conditions, thereby sufficiently dispersing the stress generated when bending deformation is applied to the optical member in the display device to prevent the display panel from breaking or lifting. On the other hand, the pressure-sensitive adhesive composition for a flexible display can provide a flexible display excellent in flexural properties due to a high strain rate after crosslinking. In the present invention, the pressure-sensitive adhesive composition satisfies a degree of crosslinking in a specific range, and thus has durability reliability and high deformation rate.

In one embodiment of the present invention, the pressure-sensitive adhesive composition may have a degree of crosslinking after crosslinking of 40% or more and a degree of crosslinking swelling of 11 or more. Preferably, the degree of crosslinking is 42% or more, the degree of crosslinking swelling is 15 or more, more preferably, the degree of crosslinking is 45% or more, and the degree of crosslinking swelling is 18 or more. Here, the crosslinking degree and the crosslinking swelling degree are calculated by the following formula.

Crosslinking degree (%) = [(d-b)/a ] x 100

delete

Crosslinking swelling degree = [(c-b)/(d-b)]

(a: weight of the initial pressure-sensitive adhesive composition

b: weight of mesh wire mesh

c: the sum of the weights of the pressure-sensitive adhesive composition and the mesh wire mesh swollen after immersion in ethyl acetate solvent

d: the sum of the weights of the crosslinked adhesive and the mesh wire mesh)

More specifically, the pressure-sensitive adhesive composition (initial weight a) and the ethyl acetate solvent were put into a cylindrical container having a diameter of 65 mm, left at 50 ° C. for 20 hours, and the pressure-sensitive adhesive composition was filtered through a 200 mesh wire mesh (weight b). After 20 minutes, measure the total weight (weight c) of the mesh wire mesh and the pressure-sensitive adhesive composition swollen in the solvent, and then dry in an oven at 100° C. for 1 hour, and then measure the weight sum (weight d) of the crosslinked pressure-sensitive adhesive and the mesh wire mesh By doing so, the degree of crosslinking and degree of crosslinking swelling can be calculated.

In one embodiment of the present invention, the crosslinking degree of the pressure-sensitive adhesive composition may be 40% to 87%. If the degree of crosslinking is less than 40%, there may be a problem that the durability reliability is weakened due to insufficient cohesiveness. Conversely, if it exceeds 87%, the deformation and flexural properties are weak due to a small deformation rate due to too high cohesiveness.

The degree of crosslinking swelling depends on the adhesive and the crosslinking density of the composition. When the crosslinking 　 density is high, it is difficult for the solvent to penetrate into the crosslinked polymer chain included in the pressure-sensitive adhesive composition and the crosslinking swelling degree is lowered. On the other hand, when the crosslinking density is low, the solvent easily permeates into the polymer chain, so that the crosslinking swelling degree is increased. In other words, when the solvent is difficult to penetrate, the crosslinking density between polymer chains is high, which means that it is difficult to deform when stress is applied. On the other hand, when the solvent is easy to penetrate, the crosslinking density between the polymer chains is low and it is easy to deform when stress is applied. Means that.

The degree of crosslinking swelling is calculated by calculating the weight ratio of the pressure-sensitive adhesive composition when the solvent is absorbed to the weight after drying, and the crosslinking swelling degree of the pressure-sensitive adhesive composition for a flexible display may be 11 to 300. If the crosslinking swelling degree is less than 11, the deformation rate is small and there may be a problem in that the deformability is weak. On the contrary, if it exceeds 300, the crosslink structure is very loose and the durability reliability is weak.

In one embodiment of the present invention, the adhesive layer has an adhesive strength of 400 gf/in or more, preferably 450 gf/in or more, of the display panel to the substrate at room temperature. The adhesive force is a value obtained by measuring 180° peel adhesive force, and may be measured after laminating the adhesive to the adherend and leaving it for one day. Since the pressure-sensitive adhesive layer has a high adhesive strength, when the flexible display is deformed, a lifting phenomenon at the interface between the pressure-sensitive adhesive layer and the flexible display device does not occur. The substrate of the display panel may be selected from the group consisting of polyimide, polyetheretherketone, polyethersulfone, polyetherimide, and polycarbonate. It may be a known film layer without limitation.

In one embodiment of the present invention, the pressure-sensitive adhesive layer has an adhesive force change rate C of -90% < C < 300% at -20°C, preferably -85% < C < 280%, and more preferably -80% < C < 270%. The rate of change C is calculated by the following formula.

C = { [ (-20℃ adhesion) - (room temperature adhesion) ] / (room temperature adhesion) } x 100

When the change rate C satisfies the above range, the occurrence of interfacial peeling during deformation of the flexible display may be prevented. On the other hand, when the rate of change C is out of the above range, for example, although the adhesion at room temperature is high, when the rate of change C is -90% or less due to a sharp decrease in adhesion at low temperature, interfacial peeling may occur when the flexible display is deformed under low temperature conditions. can

In one embodiment of the present invention, the pressure-sensitive adhesive composition may include a polymer including a crosslinkable functional group and a crosslinking agent.

In one embodiment of the present invention, the polymer including the crosslinkable functional group may be an acryl-based, rubber-based, urethane-based, silicone-based polymer, and mixtures thereof, but is not limited thereto. Preferably, the polymer including a crosslinkable functional group may be an acrylic polymer.

The acrylic polymer may be a polymer including a (meth)acrylic acid ester-based monomer as a polymerization unit. As the (meth)acrylic acid ester-based monomer, for example, alkyl (meth)acrylate may be used, and in consideration of the cohesive force, glass transition temperature or adhesiveness of the pressure-sensitive adhesive, alkyl (meth) having an alkyl group having 1 to 14 carbon atoms ) acrylates can be used. Examples of such monomers include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate ) acrylate, sec-butyl (meth)acrylate, pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-ethylbutyl (meth)acrylate, n-octyl (meth)acrylate, iso octyl (meth) acrylate, isononyl (meth) acrylate, lauryl (meth) acrylate, and tetradecyl (meth) acrylate, and one or a mixture of two or more of the above may be used, but is limited thereto it is not

The monomer having a crosslinkable functional group of the acrylic polymer forms a crosslinked structure through reaction with a crosslinking agent by imparting a crosslinkable functional group to the acrylic polymer. As the monomer having such a crosslinkable functional group, one or more than one type may be selected from the group consisting of a hydroxyl group-containing monomer, a carboxyl group-containing monomer, and the like. Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl ( meth) acrylate, 8-hydroxyoctyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate, and the like, but is not limited thereto. In addition, the carboxyl group-containing monomer may include, for example, (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, and the like. However, the present invention is not limited thereto.

Examples of other polymerizable monomers to the acrylic polymer include vinyl monomers such as N-vinylpyrrolidone, N-vinylcaprolactam, styrene and α-methylstyrene; (meth)acrylamide; N-ethyl (meth)acrylamide, N-butyl (meth)acrylamide, N-isopropyl (meth)acrylamide, N-methylol (meth)acrylamide, N-methylolpropane (meth)acrylamide, N -Methoxymethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N,N-dipropyl (meth)acrylamide, N,N-diisopropyl (meth)acrylamide, N,N-di(n-butyl)(meth)acrylamide, N,N-di(t-butyl)(meth)acrylamide , amide group-containing monomers such as N,N-dialkyl (meth)acrylamide, N-methylol (meth)acrylamide, and N-ethylol (meth)acrylamide; Ethoxy ethylene glycol (meth) acrylate, ethoxy propylene glycol (meth) acrylate, ethoxy diethylene glycol (meth) acrylate or ethoxy dipropylene glycol (meth) acrylate, methoxy ethylene glycol (meth) acrylic rate, methoxy propylene glycol (meth) acrylate, methoxy diethylene glycol (meth) acrylate or methoxy dipropylene glycol (meth) acrylate, phenoxy ethylene glycol (meth) acrylate or phenoxy propylene glycol (meth) ) acrylate, phenoxy diethylene glycol (meth) acrylate, and alkoxy-containing monomers such as phenoxy dipropylene glycol (meth) acrylate may be included.

In the present invention, the cross-linking agent reacts with the polymer including the cross-linkable functional group to form a cross-linked structure, thereby providing cohesive force and strengthening adhesive force. In the present invention, the crosslinking agent may be a thermal crosslinking agent or a photocrosslinking agent commonly used in the technical field to which the present invention belongs. The crosslinking agent is to further improve the durability of the adhesive layer by reacting with the acrylic copolymer to form a crosslinked structure, and for example, an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, and the like may be used. As the crosslinking agent, a conventional one known in the art may be used, and an isocyanate-based compound may be used. Examples of the isocyanate-based compound include toluene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isoform diisocyanate, tetramethylxylene diisocyanate, naphthalene diisocyanate, and any one of the above polyols (trimethylol propane ) and at least one selected from the group consisting of reactants; Examples of the epoxy compound include ethylene glycol diglycidyl ether, triglycidyl ether, trimethylolpropane triglycidyl ether, N,N,N',N'-tetraglycidyl ethylenediamine and glycerin diglycidyl ether It may include one or more selected from the group consisting of, but is not limited thereto.

The pressure-sensitive adhesive composition may include a silane coupling agent, an antistatic agent, a plasticizer, a tackifying resin, a UV stabilizer, an antioxidant, and the like, in addition to a polymer and a crosslinking agent including a crosslinkable functional group.

A protective release film may be further included on one surface of the pressure-sensitive adhesive layer.

In this case, the thickness of the pressure-sensitive adhesive layer may be 200 μm to 2 μm, preferably 150 μm to 5 μm.

There is no particular limitation on the method of manufacturing the backplate film in the present invention, and a method of applying the pressure-sensitive adhesive layer directly to the surface of the base film using a bar coater, etc. A method of transferring the pressure-sensitive adhesive layer formed on the surface of the releasable substrate to the surface of the substrate film after application to and drying may be applied. Preferably, the adhesive is applied directly to the surface of the base film and then dried. The interfacial adhesion between the base film and the adhesive is excellent, and the effect of reducing the dimensional change rate in the length and width directions of the back plate film can be increased. .

Another embodiment of the present invention provides a flexible display including the back plate film and a display display panel.

Hereinafter, the present invention will be described in more detail through Examples according to the present invention and Comparative Examples not according to the present invention, but the scope of the present invention is not limited by the Examples presented below.

<Production of Backplate Film>

Example 1

A polyethylene terephthalate (PET) composition was extruded in an extruder and stretched in the longitudinal direction (MD) and the transverse direction (TD). Thereafter, the stretched sheet was heat-set, annealed and cooled to prepare a polyester film. At this time, in the annealing step, while lowering the temperature, relaxation was performed in two stages to prepare a base film having a thickness of 50 μm.

81 parts by weight of 2-ethylhexyl acrylate (2-EHA), 4 parts by weight of N-vinylpyrrolidone, and 15 parts by weight of hydroxyethyl acrylate (2-HEA) as a crosslinkable monomer in 100 parts by weight of an acrylic copolymer In contrast, 0.3 parts by weight of a crosslinking agent (a hexamethylene diisocyanate adduct (HDI) of isocyanate-based trimethylolpropane) was added and diluted with ethyl acetate so that the solid content was 25% by weight to prepare a pressure-sensitive adhesive composition.

The pressure-sensitive adhesive composition prepared above is applied on the base film, dried in an oven at 120° C. for 3 minutes, coated so that the thickness of the pressure-sensitive adhesive layer becomes 25 μm, and the release film is laminated to protect the coated surface of the pressure-sensitive adhesive. After laminating the cross-linked structure To form, it was aged at 60° C. for 2 days to prepare a back plate 　 film.

As a result of measuring by the method described in the following test examples, the light transmittance of the backlate film prepared in this example was 92% or more, and the dimensional changes in the longitudinal and width directions of the backplate film, α1 and α2, were 21 ppm, respectively. /°C and 19 ppm/°C.

Example 2

A composition composed of polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) was extruded in an extruder and stretched in the longitudinal direction (MD) and the width direction (TD). Thereafter, the stretched sheet was heat-set, annealed and cooled to prepare a polyester film. At this time, while lowering the temperature in the annealing step, relaxation was performed in two stages to prepare a base film having a thickness of 50 μm.

81 parts by weight of 2-ethylhexyl acrylate (2-EHA), 4 parts by weight of N-vinylpyrrolidone, and 15 parts by weight of hydroxyethyl acrylate (2-HEA) as a crosslinkable monomer in 100 parts by weight of an acrylic copolymer In contrast, 0.3 parts by weight of a crosslinking agent (a hexamethylene diisocyanate adduct (HDI) of isocyanate-based trimethylolpropane) was added and diluted with ethyl acetate so that the solid content was 25% by weight to prepare a pressure-sensitive adhesive composition.

The pressure-sensitive adhesive composition prepared above is applied on the base film, dried in an oven at 120° C. for 3 minutes, coated so that the thickness of the pressure-sensitive adhesive layer becomes 25 μm, and the release film is laminated to protect the coated surface of the pressure-sensitive adhesive. After laminating the cross-linked structure To form, it was aged at 60° C. for 2 days to prepare a back plate 　 film.

As a result of measuring by the method described in the following test example, the light transmittance of the backlate film prepared in this example was 90% or more, and α1 and α2, which are the dimensional changes in the longitudinal and width directions of the backplate film, were 35 ppm, respectively. /°C and 32 ppm/°C.

Example 3

A composition made of polyethylene terephthalate (PET) was extruded in an extruder and stretched in the longitudinal direction (MD) and the transverse direction (TD). Thereafter, the stretched sheet was heat-set, annealed and cooled to prepare a polyester film. At this time, while lowering the temperature in the annealing step, relaxation was performed in two stages to prepare a base film having a thickness of 50 μm.

An acrylic copolymer comprising 90 parts by weight of 2-ethylhexyl acrylate (2-EHA), 7 parts by weight of N,N-diethyl acrylamide, and 3 parts by weight of hydroxybutyl acrylate (2-HBA) as a crosslinkable monomer. With respect to 100 parts by weight, 0.15 parts by weight of a crosslinking agent (hexamethylene diisocyanate adduct (HDI) of isocyanate-based trimethylolpropane) was added and diluted with ethyl acetate so that the solid content was 25% by weight to prepare a pressure-sensitive adhesive composition.

The pressure-sensitive adhesive composition prepared above is applied on the base film, dried in an oven at 120° C. for 3 minutes, coated so that the thickness of the pressure-sensitive adhesive layer becomes 25 μm, and the release film is laminated to protect the coated surface of the pressure-sensitive adhesive. After laminating the cross-linked structure To form, it was aged at 60° C. for 2 days to prepare a back plate 　 film.

As a result of measuring by the method described in the following test example, the light transmittance of the backlate film prepared in this Example was 88% or more, and α1 and α2, which are the dimensional changes in the longitudinal and width directions of the backplate film, were 14 ppm, respectively. /°C and 8 ppm/°C.

Comparative Example 1

A polyethylene terephthalate (PET) composition was extruded in an extruder and stretched in the longitudinal direction (MD) and the transverse direction (TD). Thereafter, the stretched sheet was heat-set, annealed and cooled to prepare a polyester film. At this time, in the annealing step, while lowering the temperature, relaxation was performed in two stages to prepare a base film having a thickness of 50 μm.

11 parts by weight of n-butyl acrylate (BA), 79 parts by weight of 2-ethyl hexyl acrylate (2-EHA), 7 parts by weight of N,N-diethyl acrylamide, and hydroxybutyl acrylate as a crosslinkable monomer (2-HBA) With respect to 100 parts by weight of the acrylic copolymer consisting of 3 parts by weight, 0.3 parts by weight of a crosslinking agent (hexamethylene diisocyanate adduct (HDI) of isocyanate-based trimethylolpropane) was added, and the solid content was 25% by weight with ethyl acetate. The pressure-sensitive adhesive composition was prepared by diluting it so that

The pressure-sensitive adhesive composition prepared above was applied to the release film, dried in an oven at 120° C. for 3 minutes, coated so that the thickness of the pressure-sensitive adhesive layer became 25 μm, and the coated surface was laminated on the base film to transfer the pressure-sensitive adhesive to the base film. Then, to form a crosslinked structure, the film was aged at 60° C. for 2 days to prepare a backplate 　 film.

As a result of measuring by the method described in the following test examples, the light transmittance of the backlate film prepared in this comparative example was 91% or more, and α1 and α2, which are the dimensional changes in the longitudinal and width directions of the backplate film, were 28 ppm, respectively. /°C and 14 ppm/°C.

Comparative Example 2

A polyethylene terephthalate (PET) composition was extruded in an extruder and stretched in the longitudinal direction (MD) and the transverse direction (TD). Thereafter, the stretched sheet was heat-set, annealed and cooled to prepare a polyester film. At this time, in the annealing step, while lowering the temperature, relaxation was performed in two stages to prepare a base film having a thickness of 50 μm.

100 parts by weight of an acrylic copolymer comprising 32 parts by weight of n-butyl acrylate (BA), 53 parts by weight of 2-ethylhexyl acrylate (2-EHA), and 15 parts by weight of hydroxyethyl acrylate (2-HEA) as a crosslinkable monomer. With respect to the part, 0.7 parts by weight of a crosslinking agent (hexamethylene diisocyanate adduct (HDI) of isocyanate-based trimethylolpropane) was added and diluted with ethyl acetate so that the solid content was 25% by weight to prepare a pressure-sensitive adhesive composition.

The pressure-sensitive adhesive composition prepared above is applied on the base film, dried in an oven at 120° C. for 3 minutes, coated so that the thickness of the pressure-sensitive adhesive layer becomes 25 μm, and the release film is laminated to protect the coated surface of the pressure-sensitive adhesive. After laminating the cross-linked structure To form, it was aged at 60° C. for 2 days to prepare a back plate 　 film.

As a result of measuring by the method described in the following test examples, the light transmittance of the backlate film prepared in this comparative example was 92% or more, and the dimensional change rates of the backplate film in the longitudinal and width directions α1 and α2 were 21 ppm, respectively. /°C and 19 ppm/°C.

Comparative Example 3

The polyamic acid solution was coated on a carrier film, dried and cured to prepare a polyimide film having a thickness of 50 μm.

81 parts by weight of 2-ethylhexyl acrylate (2-EHA), 4 parts by weight of N-vinylpyrrolidone, and 15 parts by weight of hydroxyethyl acrylate (2-HEA) as a crosslinkable monomer in 100 parts by weight of an acrylic copolymer In contrast, 0.3 parts by weight of a crosslinking agent (a hexamethylene diisocyanate adduct (HDI) of isocyanate-based trimethylolpropane) was added and diluted with ethyl acetate so that the solid content was 25% by weight to prepare a pressure-sensitive adhesive composition.

The pressure-sensitive adhesive composition prepared above is applied on the base film, dried in an oven at 120° C. for 3 minutes, coated so that the thickness of the pressure-sensitive adhesive layer becomes 25 μm, and the release film is laminated to protect the coated surface of the pressure-sensitive adhesive. After laminating the cross-linked structure To form, it was aged at 60° C. for 2 days to prepare a back plate 　 film.

As a result of measuring by the method described in the following test example, the light transmittance of the backlate film prepared in this comparative example was 65% or more, and α1 and α2, which are dimensional changes in the longitudinal and width directions of the backplate film, were 34 ppm, respectively. /°C and 37 ppm/°C.

Test Example 1: Measurement of light transmittance of the backplate film

After removing the release film from the pressure-sensitive adhesive layer for the prepared back plate film, the total light (380 to 760 nm) light transmittance according to JIS K 7105 standard with the pressure-sensitive adhesive side facing up was measured using NDH-7000 (Nippon Denshoku).

Test Example 2: Measurement of dimensional change rate of backplate film

After preparing a measurement sample by using the prepared backplate film in the longitudinal direction (longitudinal direction of the substrate, MD direction) and the width direction (the width direction of the substrate, TD direction) as the measurement directions, the release film is removed and the remaining bag The plate film (base film and pressure-sensitive adhesive structure) sample was measured for dimensional change according to temperature using TMA (TA instruments, Q400). Measurement conditions are as follows.

Measurement sample: length 8mm x width 4.4mm (longitudinal direction is each measurement direction)

Measurement temperature range: -60℃ ~110℃

Temperature increase rate: 5℃/min

Initial Force: 0.05 N

α1: Dimensional change rate in the longitudinal direction of the backplate peel in the range from -40℃ to 100℃ (ppm/℃)

α2: Dimensional change rate in the width direction of the backplate film in the section from -40℃ to 100℃ (ppm/℃)

Test Example 3: Determination of the pressure-sensitive adhesive layer

Using the pressure-sensitive adhesive composition prepared in Examples and Comparative Examples, it was prepared by coating or transferring to a release film instead of a base film, and then laminated to a thickness of 700 μm so as not to generate bubbles, and cross-linked, and then a sample was prepared. Measured using ARES-G2 (TA Instruments Inc.) equipment, cut the prepared sample into a circle with a diameter of 8mm, remove both release films attached to the sample, and place the sample on an 8mm parallel plate. After adjusting the gap so that the force becomes 1N, the strain was measured while applying stress in the shear mode.

A: Strain when 10000 Pa of stress is applied to the sample of the cross-linked pressure-sensitive adhesive composition at -10°C environmental condition for 10 minutes

B: Strain when 10000 Pa of stress is applied to the sample of the cross-linked pressure-sensitive adhesive composition at 80° C. for 10 minutes

Test Example 4: Adhesion Measurement

The adhesive force of the prepared backplate film to the OLED display panel substrate (polyimide film) was measured by the following method. After cutting the prepared back plate film to have a width of 25 mm and a length of 200 mm, the release film was peeled off from the pressure-sensitive adhesive layer, attached to the polyimide surface using a 2 kg roller, and left at room temperature for one day. Texture Analyzer (Stable Micro Systems) was used as a measuring device, and 180° adhesion was measured at a peeling rate of 300 mm/min at room temperature.

Test Example 5: Measurement of crosslinking degree and crosslinking swelling degree

0.2 g (weight a) of the pressure-sensitive adhesive composition used in the backplate film prepared above and 90 g of the solvent ethyl acetate were put into a cylindrical container having a diameter of 65 mm, sealed, and left at 50° C. for 20 hours. After 20 minutes after filtering the pressure-sensitive adhesive composition on a 200 mesh wire mesh (weight b), the weight (weight c) of the swollen pressure-sensitive adhesive after immersion in the mesh wire mesh and ethyl acetate solvent is measured. After drying in an oven at 100° C. for 1 hour, the weight (weight d) of the mesh wire mesh and the cross-linked pressure-sensitive adhesive was measured.

Crosslinking degree (%) = [(d-b)/a] x 100

Crosslinking swelling degree = [(c-b)/(d-b)]

a: weight of the initial pressure-sensitive adhesive composition

b: weight of mesh wire mesh

c: the sum of the weights of the pressure-sensitive adhesive composition and the mesh wire mesh swollen after immersion in ethyl acetate solvent

d: the sum of the weights of the crosslinked adhesive and the mesh wire mesh

Test Example 6: Deformation test

After removing the release film from the pressure-sensitive adhesive layer for the back plate film prepared above, it was laminated on a 50 μm polyimide film. The laminated sample was cut to a width of 70 mm and a length of 150 mm, and left at room temperature for 1 day. Using dynamic deformation equipment (Flexigo, Foldy-200), under a temperature of -20 ° C, a radius of curvature of 1.2 mm, deforming 200,000 times at a rate of once per second, and performing a -20 ° C dynamic deformation test, the appearance is as follows was observed. In addition, in the case of the 70°C dynamic strain test, the same method as the -20°C dynamic strain test was performed except that the temperature environment was 70°C.

○: There is no wave deformation of the back plate film, and there is no interfacial peeling, bubbles, or floating between the adhesive layer and the base film or polyimide film.

△: There is no wave deformation of the backplate film, but interfacial peeling, bubbles, and lifting between the adhesive layer and the base film or polyimide film

X: Wave deformation of the backplate film occurred. Interfacial peeling, bubbles, and lifting between the adhesive layer and the base film or polyimide film

Test Example 7: Fingerprint recognition rate evaluation

After peeling the release film from the pressure-sensitive adhesive layer with respect to the manufactured backplate film, it is applied to the lower surface of the display panel to manufacture a display device with a pattern film and a fingerprint recognition sensor attached thereto, and then the user's fingerprint in contact with the front of the display device The recognition rate was evaluated as follows.

○: Good recognition rate

X: Poor recognition rate

The results measured by the above method are all shown in Table 1 below.

Light transmittance of backplate film (%) α1 value α2 value A value Strain rate of the pressure-sensitive adhesive layer at -10°C
(%) of the adhesive layer at 80°C
strain rate
(%) adhesiveness
(gf/in) Degree of crosslinking (%) / Degree of crosslinking swelling -20℃ dynamic strain test 70℃ dynamic strain test Fingerprint recognition rate evaluation Example 1 92 21 19 2 37 289 2874 67/33 ○ ○ ○ Example 2 90 35 32 3 37 289 2691 67/33 ○ ○ ○ Example 3 88 14 8 6 81 148 1057 76/18 ○ ○ ○ Comparative Example 1 91 28 14 10 28 64 2278 57/42 X X ○ Comparative Example 2 92 21 19 2 2 21 3587 93/8 △ △ ○ Comparative Example 3 65 34 37 3 37 289 2467 67/33 ○ ○ X

The backplate films of Examples 1 to 3 of Table 1 have an A value of 5 or less, prevent peeling and air bubbles in the folded portion of the flexible display, and disperse the stress applied at a high strain rate of the pressure-sensitive adhesive layer This provided excellent deformation and adhesion reliability of the flexible display. In addition, the pressure-sensitive adhesive layer of Examples 1 to 3 had excellent adhesion to the OLED display panel substrate (polyimide film), and the backplate films of Examples 1 to 3 exhibited excellent fingerprint recognition rate due to high light transmittance.

However, although the backplate films of Comparative Examples 1 to 3 had high adhesive strength, Comparative Example 1 had an A value of more than 7, and Comparative Example 2 had a floating portion of the flexible display due to the low strain rate of the pressure-sensitive adhesive layer and the optical member breakage could not be prevented. In addition, it can be seen that Comparative Example 3 has a low fingerprint recognition rate due to low light transmittance.

Claims (12)

base film; and
A back plate film comprising an adhesive layer provided on one or both sides of the base film,
The light transmittance of the back plate film is 85% or more and less than 100%,
A value derived from the following formula 1 is 7 or less,
Equation 1: A= │α1 - α2│
(Here, α1 and α2 are calculated from Equations 2 and 3, respectively,
Equation 2: α1=(1/L ₀ )*(ΔL /ΔT)
Equation 3: α2=(1/W ₀ )*(ΔW /ΔT)
In the above formula,
ΔL is the dimensional change in the longitudinal direction of the backplate film according to the temperature change from -40°C to 100°C,
ΔW is the dimensional change in the width direction of the backplate film according to the temperature change from -40°C to 100°C,
ΔT is the temperature change from -40°C to 100°C,
L ₀ is the initial dimension with respect to the longitudinal direction of the backplate film at -40 ℃,
W ₀ is the initial dimension with respect to the width direction of the backplate film at -40°C.)
The pressure-sensitive adhesive layer has a strain greater than 10% and less than or equal to 500% when a stress of 10,000 Pa is applied for 10 minutes at -10°C,
A backplate film having a strain greater than 35% and less than or equal to 3500% when a stress of 10,000 Pa was applied at 80° C. for 10 minutes. According to claim 1,
A backplate film wherein α1 and α2 are greater than 0 and not greater than 57. According to claim 1,
The base film is a back plate film comprising a polyester resin. 4. The method of claim 3,
The polyester resin is made of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), poly(cyclohexylenedimethylene terephthalate (PCT), and polytrimethylene terephthalate (PTT). A backplate film comprising at least one resin selected from the group. According to claim 1,
A backplate film having a light transmittance of 83% or more and less than 100% of the base film, and an initial haze of more than 0% and less than 5%. delete According to claim 1,
A backplate film having a degree of crosslinking of the pressure-sensitive adhesive layer of 40% or more and 87% or less, and a crosslinking swelling degree of 11 or more and 300 or less. According to claim 1,
A backplate film having a light transmittance of 92% or more and less than 100% of the pressure-sensitive adhesive layer, and a haze of more than 0% and less than 3%. According to claim 1,
A backplate film having an adhesive strength of 400 gf/in or more of the pressure-sensitive adhesive layer to a substrate of a display panel at room temperature. According to claim 1,
A backplate film further comprising a protective release film on one surface of the pressure-sensitive adhesive layer. A flexible display comprising the back plate film and the display panel according to any one of claims 1 to 5 and 7 to 10. 12. The method of claim 11,
The display display panel is a foldable display display panel, a rollable display display panel, a stretchable display display panel, or a slide display display panel.