CN115035787A - Back plate film for flexible display and flexible display comprising same - Google Patents
Back plate film for flexible display and flexible display comprising same Download PDFInfo
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- CN115035787A CN115035787A CN202110441478.8A CN202110441478A CN115035787A CN 115035787 A CN115035787 A CN 115035787A CN 202110441478 A CN202110441478 A CN 202110441478A CN 115035787 A CN115035787 A CN 115035787A
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
- G09F9/00—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements
- G09F9/30—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements
- G09F9/301—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements flexible foldable or roll-able electronic displays, e.g. thin LCD, OLED
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/549—Organic PV cells
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Abstract
The invention provides a back plate film for a flexible display and a flexible display comprising the same. Specifically, the present invention relates to a backsheet film comprising: a matrix membrane; and an adhesive layer disposed on one or both sides of the substrate film, wherein the back sheet film has a light transmittance of 85% or more and an a value derived from the following formula 1(a ═ α 1- α 2 |) of 7 or less.
Description
Technical Field
The present invention relates to a flexible display, and more particularly, to a backplane film for a flexible display capable of preventing damage occurring during folding and unfolding of the flexible display, and a flexible display including the same.
Background
In recent years, with the development of technology, various studies have been made on display devices that can be deformed in various ways such as bending, folding, and stretching.
In the foldable, slidable, rollable, stretchable display device, each structure of the display device must satisfy reliability and stability against deformation such as bending (bending), bending (curling), folding (folding), twisting (twisting), rolling (rolling), etc., so as not to damage each structure of the display device even if morphological deformation such as folding, winding, stretching, etc. is repeated.
The back sheet film is a film that protects and supports the lower portion of the display panel, and is composed of a substrate film and an adhesive. Such a back sheet film has a function of supporting a panel while requiring reliability against deformation. In particular, when bending deformation is repeatedly applied to a flexible display, the back sheet film is not restored to its original state, and external deformation such as wave buckling (wave buckling) which remains in a bent state is prevented, and adhesion reliability should be ensured by preventing peeling and air bubbles at the bent or deformed portion.
In addition, in recent years, in order to manufacture a front fingerprint recognition and udc (under display camera) panel, an optical sensor is attached to the rear of a backsheet film, and a backsheet film having high light transmittance is required. In the past, polyimide films have been mostly used as substrate films of the back sheet films, but in this case, there is a problem that the optical sensor has a low recognition rate due to low light transmittance. On the other hand, the polyester film has not only high light transmittance but also high toughness as compared with the polyimide film, and thus has excellent characteristics in terms of impact resistance, and has excellent characteristics as a film for supporting the back surface of the panel.
In addition, the back sheet film is attached to the lower surface of the OLED display panel through an adhesive layer, and it is necessary for the adhesive to disperse stress by high strain of the adhesive layer adjacent to the panel when bending deformation is applied to the flexible display, to prevent peeling and air bubbles from being generated at the bent portion, and to have high restoring force and restoring force. That is, the stress applied to the panel is dispersed by the deformation of the adhesive layer, thereby preventing the occurrence of peeling and air bubbles at the bent portion of the display and satisfying excellent restoring force and restoring force. However, the conventional adhesive composition for flexible displays has a problem that it cannot satisfy deformation reliability and stability because of its low adhesive force and strain under severe conditions.
Disclosure of Invention
In order to solve the above-described conventional problems, an object of an embodiment of the present invention is to provide a backsheet film having high light transmittance, which is excellent in deformation and adhesion reliability and durability and impact resistance because deformation, peeling, bubbles, and the like do not occur at a bent portion even under various environmental conditions.
Another embodiment of the present invention is directed to a flexible display having excellent durability and deformation reliability.
An embodiment of the present invention provides a backsheet film, including: a matrix membrane; and an adhesive layer provided on one or both surfaces of the substrate film, wherein the back sheet film has a light transmittance of 85% or more and an A value of 7 or less as derived from the following formula 1,
formula 1: a ═ α 1- α 2 |,
in formula 1, α 1 and α 2 are calculated by the following formulas 2 and 3, respectively,
formula 2: α 1 ═ 1/L 0 )*(△L/△T)，
Formula 3: α 2 ═ 1/W 0 )*(△W/△T)，
In the above formulas 2 and 3, Δ L is a dimensional change in the longitudinal direction of the backsheet film caused by a temperature change from-40 ℃ to 100 ℃, Δ W is a dimensional change in the width direction of the backsheet film caused by a temperature change from-40 ℃ to 100 ℃, Δ T is a temperature change from-40 ℃ to 100 ℃, L is a dimensional change in the width direction of the backsheet film caused by a temperature change from-40 ℃ to 100 ℃, [ delta ] L 0 Is the initial dimension in the length direction of the backsheet film at a temperature of-40 ℃, W 0 Is the initial dimension in the width direction of the backsheet film at a temperature of-40 ℃.
In one embodiment of the present invention, α 1 and α 2 may be 57 or less.
In one embodiment of the present invention, the matrix film may be a polyester (polyester) resin.
In an embodiment of the present invention, the polyester resin may include one or more resins selected from the group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polycyclohexylenedimethylene terephthalate (PCT), and polytrimethylene terephthalate (PTT).
In one embodiment of the present invention, the light transmittance of the matrix film may be 83% or more, and the initial haze may be less than 5%.
In one embodiment of the present invention, the adhesive layer may have a strain of more than 10% when a stress of 10000Pa is applied at-10 ℃ for 10 minutes, and may have a strain of more than 35% when a stress of 10000Pa is applied at 80 ℃ for 10 minutes.
In one embodiment of the present invention, the crosslinking degree of the adhesive layer may be 40% or more, and the crosslinking swelling degree may be 11 or more.
In an embodiment of the present invention, the light transmittance of the adhesive layer may be 92% or more, and the haze may be less than 3%.
In one embodiment of the present invention, the adhesive force of the adhesive layer to the substrate of the display panel may be 400gf/in or more at normal temperature.
In one embodiment of the present invention, a protective release film may be further included on one side of the adhesive layer.
Other embodiments of the present invention provide a flexible display, including: the above-mentioned back sheet film; and a display panel.
In an embodiment of the present invention, the display panel may be a foldable display panel, a rollable display panel, a stretchable display panel, or a slidable display panel.
Effects of the invention
In one embodiment of the present invention, since the backplane film has a high light transmittance, it is possible to provide high-quality photographs and images and a high fingerprint recognition rate by sufficiently absorbing light by an optical sensor such as a display camera sensor or a fingerprint sensor.
Other embodiments of the present invention provide a flexible display having excellent durability and deformation reliability including the backplane film.
Drawings
Fig. 1 shows the change in the length of the back sheet film according to the temperature.
Fig. 2 shows the variation of the width of the back sheet film according to temperature.
Detailed Description
In this specification, a "foldable (foldable) display" refers to a display device that can be repeatedly folded and unfolded like paper, a "rollable (rollable) display" refers to a display device that can be bent, a "stretchable (stretchable) display" refers to a display device in which a screen can be elastically stretched, and a "sliding display" refers to a display device in which a display screen is expanded in a specific direction.
In the present invention, the "flexible display" is a display that can be deformed in a form, can be bent, and has a bent or folded shape, and includes a foldable display, a rollable display, a stretchable display, a sliding display, and the like.
In the present specification, the term "crosslinking" refers to a process of inducing a physical or chemical action to a composition by irradiating light or maintaining the adhesive composition at a predetermined temperature or applying moisture, etc., thereby expressing adhesive characteristics to the adhesive composition.
In the present specification, the term "deformation" means that the inherent form of the flexible display device or its structure is deformed into a plurality of forms such as bending (bending), folding (creasing), folding (folding), twisting (twisting), rolling (rolling) and the like when an external force is applied, and the terms "deformation reliability" and "deformation stability" mean that the function and appearance of the device are not damaged despite the above-mentioned "deformation", and the original form of the flexible display can be restored, and further, the device can be continuously and repeatedly performed.
In the present specification, the term "bending property" refers to "deformation reliability" and "deformation stability" with respect to a bending formation portion (curved edge) or a bending formation portion (curved section) when a portion of a display device is deformed by a form such as bending (bending), bending (curving), folding (folding), twisting (twisting), or rolling.
In the present specification, the crosslinked adhesive composition may be used in the same meaning as the adhesive or the adhesive layer, as the case may be.
In the present specification, the term "normal temperature" means 25 ℃.
The present specification will be described in more detail below.
The present invention relates to a backplane 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.
< Back sheet film >
An embodiment of the present invention provides a backsheet film, including: a matrix membrane; and an adhesive layer provided on one or both surfaces of the substrate film, wherein the back sheet film has a light transmittance of 85% or more and an A value of 7 or less as derived from the following formula 1.
Formula 1: a ═ alpha 1-alpha 2-alpha
Here, α 1 represents a dimensional change rate (ppm/° c) in the longitudinal direction of the backsheet film (the longitudinal direction (MD) of the substrate film), and more specifically, α 1 may be calculated from formula 2 representing an average slope of dimensional change (ppm/° c) in a temperature range of-40 ℃ to 100 ℃.
Formula 2: α 1 ═ 1/L 0 )*(△L/△T)
α 2 represents a dimensional change rate (ppm/° c) in the width direction of the backsheet film (width direction (TD) of the substrate film), and more specifically, α 2 can be calculated from formula 3 representing an average slope of dimensional change (ppm/° c) in a temperature range of-40 ℃ to 100 ℃.
Formula 3: α 2 ═ 1/W 0 )*(△W/△T)
In the above-mentioned formula, the compound of formula,
DeltaL and DeltaW are respectively the size change of the backboard film in the length direction and the width direction caused by the temperature change from-40 ℃ to 100 ℃, DeltaT is the temperature change from-40 ℃ to 100 ℃, and L is 0 And W 0 The initial dimensions in the length direction and width direction of the backsheet film at a temperature of-40 c, respectively.
The a value calculated by the above formula 1 is 7 or less, preferably, may be 5 or less. When the value a is small, it means that the difference between the change rates in the longitudinal direction and the width direction of the backsheet film is small, and that the backsheet film is free from the bending and twisting phenomenon even under severe environments as the value a is small. The back sheet film of the present invention can prevent deformation, peeling, bubbles, and the like of the appearance even if repeatedly bent or deformed, and thus can provide excellent deformation characteristics of a flexible display.
In one embodiment of the present invention, α 1 represents a dimensional change rate (ppm/° c) in the longitudinal direction of the backsheet film, the longitudinal direction of the backsheet film is the same as the longitudinal direction of the substrate film, and the longitudinal direction of the substrate film is the Machine Direction (MD) at the time of production. The value of α 1 is 57 to 2, and more preferably, may be 50 to 5. As shown in fig. 1, it can be calculated from the average slope of the dimensional change (ppm/° c) over the temperature range of-40 ℃ to 100 ℃.
In one embodiment of the present invention, α 2 represents a dimensional change rate (ppm/° c) in the width direction of the backsheet film, the width direction of the backsheet film is the same as the width direction of the substrate film, and the width direction of the substrate film is the Transverse Direction (TD) during production. The value of α 2 is 57 to 2, more preferably 50 to 7. As shown in fig. 2, it can be calculated from the average slope of the dimensional change (ppm/° c) at a temperature range of-40 ℃ to 100 ℃. α 1 and α 2 represent dimensional change rates (ppm/° c) in the longitudinal direction and the width direction of the back sheet film due to temperature changes, respectively, and can be obtained by suspending a sample of the back sheet film on a probe of TMA and measuring dimensional changes in the longitudinal direction and the width direction of the back sheet film under temperature change conditions of-40 ℃ to 100, as a specific example.
The smaller the α 1 and α 2, the smaller the deformation of the length and width of the backsheet film, and the smaller the difference between α 1 and α 2, the less the phenomenon of distortion or bending deformation of the backsheet film.
In one embodiment of the present invention, the light transmittance of the back sheet film is 85% or more, preferably 87% or more. Since the back sheet film has high light transmittance, it sufficiently absorbs light from an optical sensor such as a display camera sensor or a fingerprint sensor, and thus, it is possible to take high-quality pictures and images and provide a high fingerprint recognition rate.
In one embodiment of the present invention, a backsheet film includes a substrate film having high light transmittance and an adhesive layer.
< matrix film >
The matrix film has light transmittance of more than 83% and haze of less than 5%, preferably, the light transmittance is more than 85% and the haze is less than 4%.
The substrate film has excellent mechanical properties such as high strength, and supports the rear surface of the display panel by excellent impact resistance.
The matrix film includes a polyester (polyester) resin. The polyester resin includes polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polycyclohexylenedimethylene terephthalate (PCT), polytrimethylene terephthalate (PTT), and the like.
Specifically, the polyester resin may be a homopolymer resin or a copolymer resin obtained by polycondensation of dicarboxylic acid and diol. In addition, the polyester resin may be a blend resin in which the homopolymer resin or the copolymer resin is mixed.
Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic 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-cyclohexanedicarboxylic acid, 1, 4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3-diethylsuccinic acid, glutaric acid, 2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid, sebacic acid, suberic acid, and dodecanedicarboxylic acid.
Examples of the diol include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1, 2-cyclohexanedimethanol, 1, 4-cyclohexanedimethanol, decanediol, 1, 3-propanediol, 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, 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, and for example, a polyethylene terephthalate (PET) resin may be used as a main component.
As an example, the matrix film may include a polyester resin, specifically, may include about 85 wt% or more of a PET resin, and more specifically, may include 90 wt% or more, 95 wt% or more, or 99 wt% or more. As another example, the substrate film may further include a polyester resin other than the PET resin. Specifically, the matrix film may further include polyethylene naphthalate (PEN) resin of about 15 wt% or less. More specifically, the matrix film may further include about 0.1 to 10 wt% or about 0.1 to 5 wt% of a PEN resin.
The matrix membrane can be prepared by: that is, a composition comprising a polyester resin is extruded, stretched in a longitudinal direction and a width direction, and then the stretched film is heat-set, and the thickness of the matrix film is 200 to 10 μm, preferably, may be 150 to 20 μm.
< adhesive layer >
In one embodiment of the present invention, there is provided an adhesive composition, wherein the adhesive layer has a strain (stress) of more than 10% when a stress (stress) of 10000Pa is applied at-10 ℃ for 10 minutes, and the adhesive layer has a strain of more than 35% when a stress (stress) of 10000Pa is applied at 80 ℃ for 10 minutes. Preferably, the strain at-10 ℃ is 20% or more and 500% or less, and the strain at 80 ℃ is 40% or more and 3500% or less. More preferably, the strain at-10 ℃ is 25% or more and 400% or less, and the strain at 80 ℃ is 50% or more and 3000% or less.
In an embodiment of the present invention, the light transmittance of the adhesive layer is 92% or more, and the haze is less than 3%, and preferably, the light transmittance is 95% or more, and the haze is less than 2%.
In one embodiment of the present invention, the adhesive layer may be prepared from the following adhesive composition.
The adhesive composition has a high strain in the above range even under severe environmental conditions, and therefore, stress generated when bending deformation is applied to an optical member in a display device is sufficiently dispersed, thereby preventing the display panel from being broken or warped. In addition, the adhesive composition for a flexible display, after being crosslinked, can provide a flexible display excellent in folding characteristics due to high strain. In the present invention, the adhesive composition has endurance reliability and high strain by satisfying a specific range of crosslinking degree.
In one embodiment of the present invention, the adhesive composition may have a crosslinking degree of 40% or more and a crosslinking swelling degree of 11 or more after crosslinking. Preferably, the degree of crosslinking is 42% or more and 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 degree of crosslinking and the degree of swelling in crosslinking are calculated by the following formulae:
degree of crosslinking (%) [ (d-b)/a ] × 100,
the degree of swelling by crosslinking is [ (c-b)/(d-b) ].
Wherein, a: the weight of the initial adhesive composition; b: the weight of the wire mesh; c: the sum of the weights of the adhesive composition and the wire mesh swollen after being immersed in the ethyl acetate solvent; d: the sum of the weight of the crosslinked adhesive and the wire mesh.
More specifically, the adhesive composition (initial weight a) and an ethyl acetate solvent were added to a cylindrical container having a diameter of 65mm, and then, after being left at a temperature of 50 ℃ for 20 hours, the adhesive composition was filtered using a 200 mesh (mesh) wire mesh (weight b), and after 20 minutes, the sum of the weights of the wire mesh and the adhesive composition swollen in the solvent (weight c) was measured, and after being dried in an oven at 100 ℃ for one hour, the sum of the weights of the crosslinked adhesive and the wire mesh (weight d) was measured, whereby the crosslinking degree and the crosslinking swelling degree could be calculated.
In one embodiment of the present invention, the adhesive composition may have a crosslinking degree of 40% to 87%. When the crosslinking degree is less than 40%, the cohesiveness is insufficient, and the durability reliability is poor, whereas when the crosslinking degree exceeds 87%, the cohesiveness is too high, and the strain is small, and the deformation and bending characteristics are weak.
The degree of crosslinking swelling depends on the crosslinking density of the adhesive composition. When the crosslinking density is high, it is difficult for a solvent to penetrate into the crosslinked polymer chains included in the adhesive composition, and thus, a decrease in the crosslinking swelling degree is caused. On the other hand, when the crosslinking density is low, since a solvent easily penetrates into a polymer chain, the crosslinking swelling degree becomes high. That is, the difficulty in penetration of a solvent means that the crosslink density between polymer chains is high and deformation is difficult when stress is applied, and conversely, the ease in penetration of a solvent means that the crosslink density between polymer chains is low and deformation is easy when stress is applied.
The crosslinking swelling degree is calculated as a ratio of weight of the adhesive composition when it absorbs a solvent to weight after drying, and the crosslinking swelling degree of the adhesive composition for the flexible display may be 11 to 300. When the crosslinking swelling degree is less than 11, a problem of weak deformation characteristics occurs due to small strain, and conversely, when the crosslinking swelling degree exceeds 300, a problem of weak durability reliability occurs due to a loose crosslinked structure.
In one embodiment of the present invention, the adhesive force of the adhesive layer to the substrate of the display panel is 400gf/in or more, preferably 450gf/in or more at normal temperature. The adhesive force is a value obtained by measuring 180 ° peel (peel) adhesive force, and may be measured after leaving the adhesive layer laminated on the adhesive face for one day. The adhesive layer has high adhesive force, so that the adhesive layer has the characteristic that the interface of the adhesive layer and the flexible display device does not generate a tilting phenomenon when the flexible display is deformed. The display panel may be selected from the group consisting of polyimide (polyimide), polyether ether ketone (peek), polyether sulfone (polyethersulfone), polyether imide (polyetherimide), and Polycarbonate (Polycarbonate), but is not limited thereto, and may be a known thin film layer.
In one embodiment of the invention, the adhesive layer has a rate of change of adhesion C at-20 ℃ of-90% < C < 300%, preferably-85% < C < 280%, more preferably-80% < C < 270%. The rate of change C is calculated by the following formula:
c (%) { [ (-20 ℃ adhesive force) - (ambient temperature adhesive force) ]/(ambient temperature adhesive force) } × 100.
In the case where the rate of change C satisfies the above range, when the flexible display is deformed, the occurrence of interface peeling can be prevented. On the contrary, when the change rate C is out of the above range, for example, the adhesive force at low temperature is drastically reduced although the adhesive force at normal temperature is high, and thus, when the change rate C is-90% or more, the interface peeling occurs when the flexible display is deformed at low temperature.
In one embodiment of the present invention, the 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 acrylic, rubber, urethane, silicone polymers and a mixture thereof, but is not limited thereto. Preferably, the polymer including the crosslinkable functional group may use an acrylic polymer.
The acrylic polymer may be a polymer including a (meth) acrylate-based monomer as a polymerization unit. As the (meth) acrylate-based monomer, for example, an alkyl (meth) acrylate having an alkyl group of a carbon number of 1 to 14 may be used in consideration of cohesive force, glass transition temperature, or adhesiveness of the adhesive. 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, sec-butyl (meth) acrylate, pentyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, 2-ethylbutyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, lauryl (meth) acrylate, and tetradecyl (meth) acrylate, and one or a mixture of two or more of the above monomers can be used, but the monomers are not limited thereto.
The monomer having a crosslinkable functional group of the acrylic polymer imparts a crosslinkable functional group to the acrylic polymer, thereby forming a crosslinked structure by a reaction with a crosslinking agent. The monomer having such a crosslinkable functional group may be one or two or more 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, but are not limited to, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 8-hydroxyoctyl (meth) acrylate, and 10-hydroxydecyl (meth) acrylate. Examples of the carboxyl group-containing monomer include, but are not limited to, (meth) acrylic acid, carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.
As other polymerizable monomers for the acrylic polymer, vinyl monomers, N-vinylpyrrolidone, N-vinylcaprolactam, styrene, α -methylstyrene, etc.; (meth) acrylamide; amide group-containing monomer, 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-dimethyl (meth) acrylamide, N-diethyl (meth) acrylamide, N-dipropyl (meth) acrylamide, N-diisopropyl (meth) acrylamide, N-di (N-butyl) (meth) acrylamide, N-di (tert-butyl) (meth) acrylamide, N-dialkyl (meth) acrylamide, N-methylol (meth) acrylamide, N-hydroxyethyl (meth) acrylamide and the like; alkoxy group-containing monomers such as ethoxy glycol (meth) acrylate, ethoxy propylene glycol (meth) acrylate, ethoxy diethylene glycol (meth) acrylate or ethoxy dipropylene glycol (meth) acrylate, methoxy propylene glycol (meth) acrylate, methoxy diethylene glycol (meth) acrylate or methoxy dipropylene glycol (meth) acrylate, phenoxy glycol (meth) acrylate or phenoxy propylene glycol (meth) acrylate, phenoxy diethylene glycol (meth) acrylate, phenoxy dipropylene glycol (meth) acrylate, and the like.
In the present invention, the crosslinking agent reacts with the polymer including the crosslinkable functional group to form a crosslinked structure, thereby imparting cohesive force and simultaneously exerting an adhesive force-reinforcing effect. In the present invention, the crosslinking agent may use a thermal crosslinking agent or a photocrosslinking agent generally used in the art to which the present invention pertains. The crosslinking agent reacts with the acrylic copolymer to form a crosslinked structure, thereby further improving the durability of the pressure-sensitive adhesive layer, and for example, an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, or the like can be used. As the crosslinking agent, a conventional crosslinking agent known in the art may be used, and an isocyanate-based compound may be used. Examples of the isocyanate-based compound include at least one compound selected from the group consisting of tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, and a reaction product with one of the above-mentioned polyhydric alcohols (trimethylolpropane); examples of the epoxy compound include, but are not limited to, one or more selected from the group consisting of ethylene glycol diglycidyl ether, triglycidyl ether, trimethylolpropane triglycidyl ether, N' -tetraglycidyl ethylenediamine, and glycerol diglycidyl ether.
The adhesive composition may include a silane coupling agent, an antistatic agent, a plasticizer, a tackifying resin, an ultraviolet stabilizer, an antioxidant, and the like, in addition to the polymer having a crosslinkable functional group and the crosslinking agent.
The adhesive layer may further include a protective release film on one side thereof.
At this time, the thickness of the adhesive layer may be 200 to 2 μm, and preferably may be 150 to 5 μm.
In the present invention, the method for producing the back sheet film is not particularly limited, and the following methods can be applied; that is, a method of directly applying the pressure-sensitive adhesive layer to the surface of the substrate film using a bar coater or the like and then drying the pressure-sensitive adhesive layer, or a method of applying the pressure-sensitive adhesive layer to the surface of the substrate of the releasable release film and then drying the pressure-sensitive adhesive layer, and then transferring the pressure-sensitive adhesive layer formed on the surface of the releasable substrate to the surface of the substrate film. Preferably, by the method of directly applying the adhesive to the surface of the substrate film and then drying, the interfacial adhesion force to the substrate film and the adhesive is excellent, and the effect of reducing the dimensional transformation ratio in the length and width directions of the backsheet film can be improved.
Other embodiments of the present invention provide a back sheet film and a flexible display including a display panel of the display.
Detailed description of the preferred embodiments
Hereinafter, the present invention is described in more detail by 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 to the following examples.
Manufacture of backsheet films
Example 1
A polyethylene terephthalate (PET) composition was extruded by an extruder and stretched in a length direction (MD) and a width direction (TD). Then, the stretched sheet was heat-set, annealed and cooled to prepare a polyester film. At this time, relaxation was performed in two steps while lowering the temperature in the annealing step to manufacture a matrix film having a thickness of 50 μm.
An acrylic copolymer composed of 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 was charged with 0.3 part by weight of a crosslinking agent (hexamethylene diisocyanate adduct (HDI) of isocyanate trimethylolpropane) with respect to 100 parts by weight of the acrylic copolymer, and diluted with ethyl acetate until the solid content became 25% by weight, thereby manufacturing an adhesive composition.
The adhesive composition prepared above was coated on a substrate film, dried in an oven at 120 ℃ for 3 minutes until the thickness of the adhesive layer became 25 μm, then a release film was laminated to protect the coated adhesive surface, and then aged at 60 ℃ for 2 days to form a crosslinked structure, to prepare a backsheet film.
As a result of measurement by the method described in the following test example, the light transmittance of the backsheet film produced in this example was 92% or more, and the dimensional change rates α 1 and α 2 in the length direction and the width direction of the backsheet film were 21ppm/° c and 19ppm/° c, respectively.
Example 2
A composition consisting of polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) was extruded with an extruder and stretched in the length direction (MD) and width direction (TD). Then, the stretched sheet was heat-set, annealed and cooled to prepare a polyester film. At this time, relaxation was performed in two steps while lowering the temperature in the annealing step to manufacture a substrate film having a thickness of 50 μm.
An acrylic copolymer composed of 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 was charged with 0.3 part by weight of a crosslinking agent (hexamethylene diisocyanate adduct (HDI) of isocyanate trimethylolpropane) with respect to 100 parts by weight of the acrylic copolymer, and diluted with ethyl acetate until the solid content became 25% by weight, thereby manufacturing an adhesive composition.
The adhesive composition prepared above was coated on a substrate film, dried in an oven at 120 ℃ for 3 minutes until the thickness of the adhesive layer became 25 μm, then a release film was laminated to protect the coated adhesive surface, and then aged at 60 ℃ for 2 days to form a crosslinked structure, to prepare a backsheet film.
As a result of measurement by the method described in the following test example, the light transmittance of the backsheet film produced in this example was 90% or more, and the dimensional change rates α 1 and α 2 in the length direction and the width direction of the backsheet film were 35ppm/° c and 32ppm/° c, respectively.
Example 3
A composition consisting of polyethylene terephthalate (PET) was extruded with an extruder and stretched in a length direction (MD) and a width direction (TD). Then, the stretched sheet was heat-set, annealed and cooled to prepare a polyester film. At this time, relaxation was performed in two steps while lowering the temperature in the annealing step to manufacture a matrix film having a thickness of 50 μm.
An acrylic copolymer composed of 90 parts by weight of 2-ethylhexyl acrylate (2-EHA), 7 parts by weight of N, N-diethylacrylamide and 3 parts by weight of hydroxybutyl acrylate (2-HBA) as a crosslinkable monomer was charged with 0.15 parts by weight of a crosslinking agent (hexamethylene diisocyanate adduct (HDI) of isocyanate trimethylolpropane) with respect to 100 parts by weight of the acrylic copolymer and diluted with ethyl acetate until the solid content became 25% by weight, thereby manufacturing an adhesive composition.
The adhesive composition prepared above was coated on a substrate film, dried in an oven at 120 ℃ for 3 minutes until the thickness of the adhesive layer became 25 μm, then a release film was laminated to protect the coated adhesive surface, and then aged at 60 ℃ for 2 days to form a crosslinked structure, to prepare a backsheet film.
As a result of measurement by the method described in the following test example, the light transmittance of the backsheet film produced in this example was 88% or more, and the dimensional change rates α 1 and α 2 in the length direction and the width direction of the backsheet film were 14ppm/° c and 8ppm/° c, respectively.
Comparative example 1
A polyethylene terephthalate (PET) composition was extruded by an extruder and stretched in the length direction (MD) and width direction (TD). Then, the stretched sheet was heat-set, annealed and cooled to prepare a polyester film. At this time, relaxation was performed in two steps while lowering the temperature in the annealing step to manufacture a substrate film having a thickness of 50 μm.
An acrylic copolymer was composed of 11 parts by weight of N-Butyl Acrylate (BA), 79 parts by weight of 2-ethylhexyl acrylate (2-EHA), 7 parts by weight of N, N-diethylacrylamide, and 3 parts by weight of hydroxybutylacrylate (2-HBA) as a crosslinkable monomer, and 0.3 parts by weight of a crosslinking agent (hexamethylene diisocyanate adduct (HDI) of isocyanate trimethylolpropane) was charged with respect to 100 parts by weight of the acrylic copolymer, and diluted with ethyl acetate until the solid content became 25% by weight, thereby manufacturing an adhesive composition.
The adhesive composition prepared above was coated on a release film, dried in an oven at 120 ℃ for 3 minutes until the thickness of the adhesive layer became 25 μm, and then the coated adhesive surface was laminated to a substrate film, and after transferring the adhesive to the substrate film, the substrate film was aged at 60 ℃ for 2 days to form a crosslinked structure, to prepare a back sheet film.
As a result of measurement by the method described in the following test example, the light transmittance of the backsheet film manufactured in this comparative example was 91% or more, and the dimensional change rates α 1 and α 2 in the length direction and the width direction of the backsheet film were 28ppm/° c and 14ppm/° c, respectively.
Comparative example 2
A polyethylene terephthalate (PET) composition was extruded by an extruder and stretched in the length direction (MD) and width direction (TD). Then, the stretched sheet was heat-set, annealed and cooled to prepare a polyester film. At this time, relaxation was performed in two steps while lowering the temperature in the annealing step to manufacture a substrate film having a thickness of 50 μm.
An acrylic copolymer composed of 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 was charged with 0.7 parts by weight of a crosslinking agent (hexamethylene diisocyanate adduct (HDI) of isocyanate trimethylolpropane) with respect to 100 parts by weight of the acrylic copolymer, and diluted with ethyl acetate until the solid content became 25% by weight, to thereby manufacture an adhesive composition.
The adhesive composition prepared above was coated on a substrate film, dried in an oven at 120 ℃ for 3 minutes until the thickness of the adhesive layer became 25 μm, then a release film was laminated to protect the coated adhesive surface, and then aged at 60 ℃ for 2 days to form a crosslinked structure, to prepare a backsheet film.
As a result of measurement by the method described in the following test example, the light transmittance of the backsheet film produced in this comparative example was 92% or more, and the dimensional change rates α 1 and α 2 in the longitudinal direction and the width direction of the backsheet film were 21ppm/° c and 19ppm/° c, respectively.
Comparative example 3
After coating the polyamic acid solution on the carrier film, the polyimide film having a thickness of 50 μm was prepared by drying and curing.
An acrylic copolymer composed of 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 was charged with 0.3 part by weight of a crosslinking agent (hexamethylene diisocyanate adduct (HDI) of isocyanate trimethylolpropane) with respect to 100 parts by weight of the acrylic copolymer, and diluted with ethyl acetate until the solid content became 25% by weight, thereby manufacturing an adhesive composition.
The adhesive composition prepared above was coated on a substrate film, dried in an oven at 120 ℃ for 3 minutes until the thickness of the adhesive layer became 25 μm, then a release film was laminated to protect the coated adhesive surface, and then aged at 60 ℃ for 2 days to form a crosslinked structure, to prepare a backsheet film.
As a result of measurement by the method described in the following test example, the light transmittance of the backsheet film produced in this comparative example was 65% or more, and the dimensional change rates α 1 and α 2 in the longitudinal direction and the width direction of the backsheet film were 34ppm/° c and 37ppm/° c, respectively.
Test example 1: measurement of light transmittance of a backsheet film
For the prepared backsheet film, after peeling the release type film from the adhesive layer, with the adhesive face as the upper face, the total light transmittance (380 to 760nm) was measured under JIS K7105 standard using NDH-7000 (Nippon Denshoku corporation).
Test example 2: measurement of dimensional Change Rate of Back sheet film
After preparing measurement samples with the longitudinal direction (the longitudinal direction of the substrate, the MD direction) and the width direction (the width direction of the substrate, the TD direction) of the prepared backsheet film as described above as measurement directions, the dimensional change with temperature of the backsheet film (the substrate film and the adhesive structure) remaining after removing the release film was measured by TMA (TA Instruments, Q400). The measurement conditions were as follows.
And (3) measuring a sample: length 8mm x width 4.4mm (length direction is the measuring direction respectively)
Measuring a temperature interval: -60 ℃ to 110 DEG C
Temperature rise rate: 5 ℃/min
Initial Force (Force): 0.05N
α 1: dimension change rate in the longitudinal direction of the back sheet film in a temperature range of-40 ℃ to 100 ℃ (ppm/. degree.C.)
α 2: dimensional change rate in width direction of back sheet film in temperature range from-40 ℃ to 100 ℃ (ppm/. degree.C.)
Test example 3: measuring strain of adhesive layer
After the release film was coated or transferred with the adhesive composition manufactured in examples and comparative examples instead of the matrix film, the release film was laminated to a thickness of 700 μm to prevent generation of bubbles, and a sample was manufactured after crosslinking. The measurement was performed using an ARES-G2(TA Instruments Inc.) apparatus, the manufactured sample was cut into a circular shape having a diameter of 8mm, the release films attached to both sides of the sample were removed, the sample was placed on an 8mm flat plate (parallell plate), the gap was adjusted so that the axial force (axial force) became 1N, and then the strain was measured while applying stress in the shear direction (shear mode).
A: strain at 10 minutes of 10000Pa of stress applied to a sample of the crosslinked adhesive composition under an environmental condition of-10 ℃
B: a sample of the cross-linked adhesive composition was subjected to a stress of 10000Pa for 10 minutes at an ambient condition of 80 ℃.
Test example 4: measurement of adhesion
The adhesive force of the OLED display panel substrate (polyimide film) of the above-fabricated back sheet film was measured by the following method. After the produced backsheet film was cut into a width of 25mm and a length of 200mm, the release film was peeled from the adhesive layer, attached to the polyimide surface using a 2kg roller, and then left to stand at room temperature for one day. The measuring apparatus used a Texture Analyzer (Stable Micro Systems) and measured the 180 ℃ adhesive force at a peeling speed of 300mm/min at normal temperature.
Test example 5: measurement of the degree of crosslinking and the degree of swelling
0.2g of the adhesive composition (weight a) for the above-produced backsheet film and 90g of ethyl acetate as a solvent were put into a cylindrical container having a diameter of 65mm, sealed, and left at a temperature of 50 ℃ for 20 hours. Then, the adhesive composition was filtered through a 200-mesh wire net (weight b), and after 20 minutes, the weight (weight c) of the wire net and the adhesive swollen after being immersed in an ethyl acetate solvent was measured. And the weight (weight d) of the wire mesh and the crosslinked adhesive was measured after drying in an oven at 100 ℃ for 1 hour.
The degree of crosslinking (%) ([ (d-b)/a ] × 100,
the degree of swelling in crosslinking is [ (c-b)/(d-b) ].
Wherein, a: the weight of the initial adhesive composition;
b: the weight of the wire mesh;
c: the sum of the weights of the adhesive composition and the wire mesh swollen after immersion in the ethyl acetate solvent;
d: the sum of the weight of the crosslinked adhesive and the wire mesh.
Test example 6: strain testing
For the backsheet film manufactured above, the release film was removed from the adhesive layer and then laminated to a polyimide film of 50 μm. The laminated sample was cut into a width of 70mm and a length of 150mm, and left at ordinary temperature for 1 day. Using a dynamic strain device (Flexigo corporation, Foldy-200), deformation was performed at a rate of once per second for 20 ten thousand times under a temperature environment of-20 ℃ with a radius of curvature of 1.2mm, and then appearance was observed as follows after performing a dynamic strain test at-20 ℃. In the case of the 70 ℃ dynamic strain test, the same method as that of the-20 ℃ dynamic strain test was used except that the temperature environment was set to 70 ℃.
O: no wavy deformation of the back sheet film, no interfacial peeling, bubbling, or lifting between the adhesive layer and the substrate film or the polyimide film, and good adhesion
And (delta): without the wavy deformation of the back sheet film, interfacial peeling, bubbling, and lifting of the adhesive layer and the substrate film or the polyimide film occur
X: the back sheet film had wavy deformation, but was free from interfacial peeling, bubbling, and lifting between the adhesive layer and the substrate film or the polyimide film, and was satisfactory
Test example 7: evaluating fingerprint recognition rate
For the backsheet film manufactured above, after peeling the release type film from the adhesive layer, it was applied to the lower surface of the display panel of the display to manufacture a display device to which the pattern film and the fingerprint recognition sensor were attached, and then the fingerprint recognition rate of the user who contacted the front of the display device was evaluated as follows.
O: the recognition rate is good
X: poor recognition rate
The overall results measured by the above-described methods are described in table 1 below.
TABLE 1
The backsheet films of examples 1 to 3 of table 1 described above have an a value of 6 or less, prevent peeling and bubbles from occurring at the folded portion of the flexible display, and disperse stress applied due to a high strain rate of the adhesive layer, thereby providing excellent deformation and adhesion reliability of the flexible display. In addition, the adhesive layers of examples 1 to 3 have excellent adhesive force to the OLED display panel substrate (polyimide film), and the back sheet films of examples 1 to 3 have excellent fingerprint recognition rate due to high light transmittance.
However, although the backsheet films of comparative examples 1 to 3 have high adhesive force, the a value of comparative example 1 exceeds 7, and in comparative example 2, the lifting of the deformed portion of the flexible display and the breaking of the optical member cannot be prevented due to the low strain of the adhesive layer. Also, it can be seen that the fingerprint recognition rate is lowered due to the low light transmittance in comparative example 3.
Claims (12)
1. A backsheet film, comprising:
a matrix membrane; and
an adhesive layer provided on one or both surfaces of the substrate film,
the light transmittance of the back plate film is more than 85%,
the value of A derived from the following formula 1 is 7 or less,
formula 1: a ═ α 1- α 2 |,
here, α 1 and α 2 are calculated by the following formulas 2 and 3, respectively,
formula 2: α 1 ═ 1/L 0 )*(△L/△T)，
Formula 3: α 2 ═ 1/W 0 )*(△W/△T)，
In the case of the formulas 2 and 3,
Δ L is a dimensional change in the longitudinal direction of the backsheet film caused by a temperature change from-40 ℃ to 100 ℃,
Δ W is a dimensional change in the width direction of the backsheet film caused by a temperature change from-40 ℃ to 100 ℃,
Δ T is the temperature change from-40 ℃ to 100 ℃,
L 0 is the initial dimension in the length direction of the backsheet film at a temperature of-40 c,
W 0 is the initial dimension in the width direction of the backsheet film at a temperature of-40 ℃.
2. The backsheet film of claim 1, wherein α 1 and α 2 are 57 or less.
3. The backsheet film of claim 1 wherein the matrix film is a polyester resin.
4. The backsheet film of claim 3, wherein the polyester resin comprises one or more selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polycyclohexylenedimethylene terephthalate, and polytrimethylene terephthalate.
5. The backsheet film of claim 1, wherein the matrix film has a light transmittance of 83% or more and an initial haze of less than 5%.
6. The backsheet film of claim 1, wherein the adhesive layer has a strain of more than 10% when a stress of 10000Pa is applied for 10 minutes at-10 ℃ and more than 35% when a stress of 10000Pa is applied for 10 minutes at 80 ℃.
7. The backsheet film according to claim 1, wherein the adhesive layer has a crosslinking degree of 40% or more and a crosslinking swelling degree of 11 or more.
8. The backsheet film of claim 1, wherein the adhesive layer has a light transmittance of 92% or more and a haze of less than 3%.
9. The backsheet film according to claim 1, wherein an adhesive force of the adhesive layer to a substrate of the display panel at normal temperature is 400gf/in or more.
10. The backsheet film of claim 1, further comprising a protective release film on one side of the adhesive layer.
11. A flexible display, comprising:
the backsheet film of any one of claims 1 to 10; and
the display displays a panel.
12. The flexible display of claim 11, wherein the display panel is a foldable display panel, a rollable display panel, a stretchable display panel, or a slidable display panel.
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