Black adhesive film for foldable display device

Abstract

Provided is a black adhesive film for a foldable display device. The black adhesive film comprises a pressure-sensitive adhesive and a black paste. The pressure-sensitive adhesive comprises an acrylic copolymer, an organic solvent, and a cross-linker. The black adhesive film is characterized by an optical density of greater than 3.5, thereby ensuring enhanced visual quality and performance of a foldable display.

Description

[0001] BLACK ADHESIVE FILM FOR FOLDABLE DISPLAY DEVICE

[0002] TECHNICAL FIELD

[0003] The present disclosure generally relates to a black adhesive fdm for a foldable display device, and a related composition and method for preparing said black adhesive fdm.

[0004] BACKGROUND ART

[0005] In recent years, foldable devices have rapidly become popular, driven by the increasing demand for portable multi-functional electronic devices such as smartphones, tablets, and laptop computers. One key component of these devices is a foldable display, which must maintain high performance and reliability amid repeated folding and unfolding. Typical foldable panel designs involve laminating various layers, including transparent foldable adhesive (PSA), black polyimide (PI) fdm, and amorphous super PET (polyethylene terephthalate), to ensure durability and flexibility.

[0006] To meet the changing demands of foldable devices, innovative adhesive solutions are needed, that provide not only robust mechanical performance, but also superior optical performance. Specifically, there is a need for black adhesives to enhance the optical appearance by minimizing light leakage and improving contrast. Traditionally, achieving a desired black optical density in an adhesive involves the incorporation of carbon black. However, said means typically results in reduced adhesion of the adhesive, which presents significant challenges in maintaining both optical performance and mechanical integrity of the foldable display.

[0007] Therefore, there is a need to provide a black adhesive that combines optimal optical density with high adhesive strength and excellent mechanical performance without compromising adhesive performance, thereby enhancing the durability and visual quality of foldable devices.

[0008] SUMMARY

[0009] In a first aspect, the present disclosure provides a black adhesive film for a foldable display device, the black adhesive film having an optical density of greater than 3.5.

[0010] In a second aspect, the present disclosure provides a black adhesive film comprising a pressure-sensitive adhesive and a black paste. In a third aspect, a method for preparing a black adhesive fdm having an optical density of greater than 3.5 is provided, comprising: mixing a pressure -sensitive adhesive, comprising an acrylic copolymer, an organic solvent and a cross-linker, with a black paste.

[0011] In a fourth aspect, the present invention provides a method for coating a black adhesive fdm between two polyethylene terephthalate (PET) liners.

[0012] The details of one or more embodiments of the present disclosure are illustrated in the drawings and the detailed description below. Other features, objects, and advantages of the present disclosure will be apparent from the specification and drawings, and from the claims.

[0013] BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The exemplary embodiments disclosed herein can be more fully understood by considering the following detailed description in conjunction with the following drawings. The drawings are not necessarily drawn to scale. The same numbers used in the drawings refer to the same components. However, it will be understood that the use of one number to refer to a component in a given drawing is not intended to limit the use of the same number to refer to the component in another drawing.

[0015] FIG. 1 is a flowchart of a method for forming a black adhesive film according to one embodiment of the present disclosure.

[0016] FIG. 2 is a cross-sectional view of a black adhesive film according to various exemplary embodiments.

[0017] FIG. 3 is a photograph showing the appearance of a black foldable PSA 1-1 prepared in an example of the present application.

[0018] FIG. 4 is a photograph showing the appearance of a black foldable PSA 1-2 prepared in an example of the present application.

[0019] FIG. 5 is a photograph showing the appearance of a black foldable PSA 1-3 prepared in an example of the present application.

[0020] FIG. 6 is a photograph showing the appearance of a black foldable PSA 1-4 prepared in an example of the present application.

[0021] FIG. 7 is a photograph showing the appearance of a black foldable PSA 2-1 prepared in an example of the present application. FIG. 8 is a photograph showing the appearance of a black foldable PSA 2-2 prepared in an example of the present application.

[0022] FIG. 9 is a photograph showing the appearance of a black foldable PSA 3 prepared in an example of the present application.

[0023] DETAILED DESCRIPTION

[0024] Described herein in more detail is a black adhesive fdm for a foldable display device, and a related composition and method for preparing said black adhesive film.

[0025] In the following description, reference is made to the drawings that form a part thereof, and in which various embodiments are shown by way of illustration. It is to be understood that other embodiments may be conceived of and made without departing from the scope or spirit of the present disclosure. The following detailed description is, therefore, not to be taken in a limiting sense.

[0026] In the following disclosure, the following definitions are employed.

[0027] As used herein, all numbers are to be considered to be modified by the term “about”. As used herein, “a”, “an”, “the”, “at least one” and “one or more” are used interchangeably.

[0028] The term “foldable display” may refer to a flexible display that is designed to be repeatedly folded and unfolded like paper and has a folding portion having a curvature radius within 5 mm.

[0029] The words “preferred” and “preferably” refer to embodiments described herein that can provide particular benefits under particular circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are unavailable, and is not intended to exclude other embodiments from the scope of the present invention.

[0030] Reference throughout the present specification to “one embodiment”, “certain embodiments”, “one or more embodiments”, or “an embodiment” means that particular features, structures, materials, or characteristics described with respect to the embodiment(s) are included in at least one embodiment of the present invention. Thus, phrases such as “in one or more embodiments”, “in certain embodiments”, “in one embodiment”, or “in an embodiment” occurring at various places throughout the present specification do not necessarily refer to the same embodiment of the present invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.

[0031] Hereinafter, the black adhesive film will be described in detail.

[0032] The black adhesive film according to one exemplary embodiment of the present invention comprises a pressure-sensitive adhesive layer and a black paste. The pressuresensitive adhesive layer is obtained from a composition comprising an acrylic copolymer, an organic solvent and a cross-linker.

[0033] In one embodiment, the acrylic copolymer is formed by the polymerization of at least one C4-C 18 acrylate monomer and a carboxylic acid functional comonomer, and has a glass transition temperature (Tg) of -50°C to -20°C.

[0034] In one embodiment, the weight ratio of the C4-C 18 acrylate monomer to the carboxylic acid functional comonomer ranges from 1 to 40.

[0035] In another embodiment, the weight ratio of the C4-C18 acrylate monomer to the carboxylic acid functional comonomer ranges from 3 to 30.

[0036] In one preferred embodiment, the weight ratio of the C4-C 18 acrylate monomer to the carboxylic acid functional comonomer ranges from 5 to 20.

[0037] In one embodiment, the C4-C18 acrylate monomer is selected from: n-octyl acrylate, butyl acrylate, methyl acrylate and acrylic acid, or a combination thereof.

[0038] In yet another embodiment, the carboxylic acid functional comonomer includes - carboxy ethyl acrylate.

[0039] In addition, the pressure-sensitive adhesive may further comprise athermal initiator in addition to the acrylic copolymer. The thermal initiator decomposes upon heating, to generate free radicals that initiate polymerization of the acrylate monomer to form a long polymer chain, thereby producing the acrylic copolymer in the pressure-sensitive adhesive layer.

[0040] Depending on the polymerization method, a water-soluble or water-insoluble (i.e., oilsoluble) thermal initiator may be selectively used. As the water-soluble initiator, it is possible to use: persulfates, such as potassium persulfate, ammonium persulfate, sodium persulfate and mixtures thereof; redox initiators, such as reaction products of reducing agents such as pyrosulfites (e.g. sodium pyrosulfite) or bisulfates (e.g. sodium bisulfate) and persulfates; or 4,4’ -azobis(4-cyanoval eric acid) and soluble salts thereof (e.g., sodium salt, potassium salt), and the like. As the water-insoluble initiator, 2,2’-azobis(2,4-dimethylvaleronitrile), 2,2’- azobis(isobutyronitrile), 2,2’-azobis(methylbutyronitrile), 1,1’- azobis(cyclohexanecarbonitrile), dibenzoyl peroxide, and the like may be used.

[0041] The content of the initiator may be 0.05 parts by weight to 0.3 parts by weight, based on 100 parts by weight of copolymer. The content of the initiator may be 0.05 to 0.25 parts by weight, 0.07 to 0.2 parts by weight, 0.07 to 0.18 parts by weight, or 0.07 to 0.14 parts by weight, based on 100 parts by weight of copolymer.

[0042] In addition, the pressure-sensitive adhesive layer comprises an organic solvent.

[0043] The organic solvent may include a non-polar solvent, a weakly polar solvent, a moderately polar solvent, or a combination thereof. It may include toluene, xylene, methyl isobutyl ketone, methyl ethyl ketone, methyl propyl ketone, isoamyl methyl ketone, or a combination thereof.

[0044] In addition, according to an exemplary embodiment of the present invention, the pressure-sensitive adhesive layer may comprise a cross-linker.

[0045] The cross-linker may react with the copolymer to form a fdm or layer, etc.

[0046] The cross-linker may contain a functional group that can react with the functional group of the copolymer.

[0047] For example, the cross-linker may have one or at least two functional groups selected from the group consisting of: an epoxy group, an isocyanate group, a carboxyl group, a hydroxyl group, an acryloyl group, a methacryloyl group, an acetate group, and a vinyl group.

[0048] As a specific example, the cross-linker may have an epoxy or an isocyanate group.

[0049] The cross-linker may be a thermal cross-linker.

[0050] For example, the cross-linker may be at least one selected from the group consisting of: bisamides, isocyanates, epoxides, aziridines, organosilanes and carbodiimides.

[0051] The content of the cross-linker in the composition may be 0.01 to 0.5 parts by weight, based on 100 parts by weight of copolymer. Specifically, the content of the cross-linker in the composition may be 0.05 to 0.25 parts by weight, preferably 0.07 to 0.2 parts by weight, or more preferably 0.08 to 0.2 parts by weight or 0.08 to 0.15 parts by weight, based on 100 parts by weight of copolymer. In addition, the contents of the initiator and the cross-linker in the composition may be 0.05 to 0.3 parts by weight and 0.01 to 0.5 parts by weight, respectively, based on 100 parts by weight of copolymer.

[0052] The black adhesive fdm comprises a black paste consisting of finely dispersed carbon black pigment particles. These particles are uniformly dispersed within an organic solvent to produce a consistent and homogeneous mixture. In addition, the dispersion of the carbon black ensures that the adhesive film achieves a desired black optical density while maintaining the homogeneity of appearance and performance, and the use of the organic solvent facilitates homogeneous dispersion and stability of the carbon black particles in the adhesive composition.

[0053] In one embodiment, the black adhesive film comprises a black paste, wherein the particle size (D90) of the carbon black pigment particles is less than 20 pm, preferably less than 15 pm, and more preferably less than 10 pm.

[0054] In one embodiment, the organic solvent is selected from: isopropanol, ethyl acetate, toluene, xylene, methyl isobutyl ketone, methyl ethyl ketone, methyl propyl ketone, isoamyl methyl ketone, or a combination thereof.

[0055] The adhesive composition according to an exemplary embodiment may further comprise other additives as necessary.

[0056] Specific examples of additives include: tackifiers (e.g., rosin esters, terpenes, phenols, and aliphatic synthetic hydrocarbon resins, aromatic synthetic hydrocarbon resins, or mixtures of aliphatic and aromatic synthetic hydrocarbon resins), surfactants, plasticizers (other than physical foaming agents), nucleating agents (e.g., talc, silica, or TiCf). fillers (e.g., inorganic and organic fillers), fibers, aging inhibitors, antioxidants, UV absorbers, antistatic agents, lubricants, pigments, dyes, reinforcing agents, hydrophobic or hydrophilic silicas, calcium carbonate, tougheners, flame retardants, finely ground polymer particles (e.g., polyester, nylon, or polypropylene), stabilizers (e.g., UV stabilizers), and combinations thereof.

[0057] The content of the additive is not particularly limited as long as it is an appropriate amount to obtain desired performance of the composition, but may be, for example, 0.1 to 10 parts by weight or 0. 1 to 5 parts by weight, based on 100 parts by weight of copolymer.

[0058] As shown in FIG. 1, a method for preparing the black adhesive film according to one embodiment of the present invention may comprise: a pressure -sensitive adhesive is prepared by means of mixing an acrylic copolymer, an organic solvent, and a cross-linker. In addition, a black paste is prepared by means of finely dispersing carbon black pigment particles in an organic solvent. The prepared pressure-sensitive adhesive composition is gradually mixed with the black paste. Thorough mixing is performed, to obtain a homogeneous adhesive mixture which maintains the desired optical density and adhesive performance.

[0059] In addition, the black adhesive fdm may be prepared by means of adjusting the viscosity using a solvent in each mixing step, as necessary. The content of each component is controlled to ensure optimal performance and a desired optical density of greater than 3.5.

[0060] However, there is no particular limitation on the preparation method for the adhesive composition, and the process conditions may be appropriately changed as needed to meet specific requirements or to optimize the film performance for specific applications.

[0061] The black adhesive film according to an exemplary embodiment of the present invention exhibits an optical density of greater than 3.5, which is particularly useful for a foldable display device.

[0062] The black adhesive film according to an exemplary embodiment of the present invention has a thickness of 5-50 micrometers. Specifically, the black adhesive film has a thickness of 10-40 micrometers. More specifically, the black adhesive film has a thickness of 5-35 micrometers.

[0063] The black adhesive film prepared according to an embodiment of the present invention has a 180° peel adhesion of 500-2000 gf / inch at room temperature after thermal curing. Specifically, the adhesive film has a 180° peel adhesion of 700 to 1900 gf / inch at room temperature after thermal curing. More specifically, the adhesive film has a 180° peel adhesion of 800 to 1800 gf / inch at room temperature after thermal curing.

[0064] The 180° peel adhesion may be measured by means of: cutting an adhesive film having a width of 1 inch, removing the release film, attaching the adhesive film to a stainless steel (SS) substrate at room temperature for 1 hour, and then peeling the adhesive film at an angle of 180° at a peel rate of 305 mm / min at room temperature or 70°C.

[0065] The adhesive film according to an exemplary embodiment of the present invention may have a creep strain of 38% or less at 60°C after thermal curing. Specifically, the adhesive film may have a creep strain of 35% or less, 30% or less, 28% or less, 26% or less, 25% or less, or 24% or less at 60°C after thermal curing. More specifically, the adhesive film may have a creep strain of 20% to 38%, 20% to 35%, 20% to 30%, 20% to 28%, or 20% to 25% at 60°C after thermal curing. Creep strain indicates deformation of a material that continues over time in a state where a constant load is applied. Therefore, this indicates that the lower the creep strain, the better the creep resistance. That is, when the creep strain is low, the occurrence of defects such as deformation or cracks and delamination may be reduced.

[0066] In the creep strain, the test may be performed after folding a 25 pm -thick adhesive layer 32 times to reach a thickness of 800 pm, using a DHR-2 rheometer TA instrument at 60°C under measurement conditions of a static stress of 2000 Pa, a creep time of 600 seconds, and a recovery time of 600 seconds.

[0067] In another aspect, the adhesive film according to an exemplary embodiment of the present invention may have a shear modulus of 0.01-0.5 MPa at -20°C after thermal curing. Specifically, the adhesive film may have a shear modulus of 0.02 to 0.2 MPa at -20°C after thermal curing, and more specifically, the adhesive film may have a shear modulus of 0.05-0.3 MPa at -20°C after thermal curing.

[0068] The shear modulus is assessed as a modulus value at -20°C measured under conditions of a strain of 0.02 to 15%, an axial force of 1 N, and a vibration frequency of 10 rad / sec after increasing the temperature from -50°C to 150°C at a rate of 5°C / min using an ARES-G2 rheometer TA instrument.

[0069] The adhesive film according to the embodiment of the present invention may be coated on at least one layer, or may be laminated between a first layer and a second layer.

[0070] The first layer and the second layer may comprise at least one selected from the group consisting of: for example, polyethylene terephthalate (PET) film, polyethylene (PE) film, polypropylene (PP) film, stainless steel, and paper.

[0071] In one preferred embodiment, each layer may be a polyethylene terephthalate (PET) film liner.

[0072] As shown in FIG. 2, the adhesive film may be laminated between a first layer and a second layer, wherein the first layer and the second layer both comprise a polyethylene terephthalate (PET) film liner.

[0073] The black adhesive-coated layer is heated in an oven at a suitable temperature, i.e. 120°C, for 5 minutes. This step evaporates the solvent and activates the cross-linker, thereby forming a durable adhesive film.

[0074] Examples Objects and advantages of the present disclosure are further illustrated by means of the following non-limiting examples, but the particular materials and amounts thereof set forth in these examples, as well as other conditions and details, should not be construed to unduly limit the present disclosure.

[0075] 5 Abbreviations of materials and reagents used in the examples are as follows: a) CSA1001 (50% solids): commercially available transparent foldable PSA obtained from FMRD, an internal 3M supplier, b) RD1054 (5% solids% in toluene): commercially available cross-linker obtained from 3M

[0076] 10 c) B01 (Isoversal Black Lm-20473 / 9174): black paste obtained from Bomex, particle size (D90 < 10 pm) d) B02 (16B2330 Black): black paste obtained from Penn Color, particle size (DOO- ISO nm to 170 nm) e) B03 (JS49313): black paste obtained from ColorSaint, particle size (D90 -<=40

[0077] 15 pm)

[0078] Preparation of Cross-Linked PSA Adhesive Films for Rheology and Peel Analysis

[0079] A transparent adhesive having specific weight parts of acrylic copolymer CSA1001 (solid content 50%) and RD1054 (solid content, 0.195 wt% with respect to the dry weight of the acrylate copolymer) was used as a basis, and mixed with different types and amounts of

[0080] 20 black paste to prepare a black PSA solution having a solid content of 35%. The PSA solution was then coated onto a 50 pm -thick PET liner having a thickness of about 25 pm after drying at 120°C for 5 min, and the adhesive film was then folded to 1 to 2 mm thick for rheology testing.

[0081] Table 1. Composition of adhesive film examples:

[0082] Test methods:

[0083] 180° Peel Force Test (23 °C, 55 rh% Humidity)

[0084] The peel force of the samples was tested on stainless steel (SS) plates or PET laminated 5 stainless steel liners according to ASTM D3330 / D3330M. The test was performed on an Instron at a peel rate of 12 inch / minute. The SS plates and PET film liners were brand new and the protective film was peeled away, to expose a fresh surface for testing. The test samples were prepared by rolling a 1 inch x 8 inch strip of adhesive tape twice on a test plate using a 1 kg rubber roller. The test samples were allowed to dwell for 20 min at 23 °C, 50 rh% humidity o before the peel test.

[0085] Optical Test

[0086] The light transmittance (T%) was tested by means of BYK 4775. The optical density was calculated by means of OD = LOGio(l / T%).

[0087] All references, patents, and patent applications cited in the above patent certificate 5 application are incorporated herein by reference in their entirety in a consistent manner. If any inconsistency or conflict arises between portions of the incorporated references and the present application, the information in the foregoing description shall control. The foregoing description, which is provided to enable a person of ordinary skill in the art to implement the claimed disclosure, is not to be construed as limiting the scope of the present disclosure, which 0 is defined by the claims and all equivalent solutions thereof.

Claims

CLAIMS1. A black adhesive film for a foldable display device, comprising: a pressure-sensitive adhesive and a black paste; wherein the pressure-sensitive adhesive comprises an acrylic copolymer, an organic solvent, and a cross-linker, and wherein the black adhesive film has an optical density of greater than 3.5.

2. The black adhesive film according to claim 1, wherein the black adhesive film has a 180° peel adhesion of 800-1800 gf / inch at room temperature afterthermal curing.

3. The black adhesive film according to claim 1, wherein the black adhesive film has a shear modulus of 0.05-0.3 MPa at -20°C.

4. The black adhesive film according to claim 1, wherein the black adhesive film has a thickness of 15-35 micrometers.

5. The black adhesive film according to claim 1, wherein the black paste comprises carbon black pigment particles finely dispersed in an organic solvent.

6. The black adhesive film according to claim 5, wherein the carbon black pigment particles have a particle size (D90) of less than 10 pm.

7. The black adhesive film according to claim 5, wherein the organic solvent is selected from: isopropanol, ethyl acetate, toluene, xylene, methyl isobutyl ketone, methyl ethyl ketone, methyl propyl ketone, isoamyl methyl ketone, or a combination thereof.

8. The black adhesive film according to claim 1, wherein the pressure-sensitive adhesive further comprises an initiator.

9. The black adhesive film according to claim 8, wherein the initiator is selected from: 2,2’-azobis(2,4-dimethylvaleronitrile), 2,2’-azobis(isobutyronitrile), 2,2’- azobis(methylbutyronitrile), l,r-azobis(cyclohexanecarbonitrile), dibenzoyl peroxide, or a combination thereof.

10. The black adhesive film according to claim 1, wherein the acrylic copolymer has a glass transition temperature (Tg) of -50°C to -20°C.

11. The black adhesive film according to claim 1, wherein the acrylic copolymer is formed by polymerization of at least one C4-C 18 acrylate monomer with a carboxylic acid functional comonomer.

12. The black adhesive film according to claim 11, wherein the weight ratio of the C4- C18 acrylate monomer to the carboxylic acid functional comonomer ranges from 5 to 20.

13. The black adhesive film according to claim 11, wherein the C4-C18 acrylate monomer is selected from: n-octyl acrylate, butyl acrylate, methyl acrylate and acrylic acid, or a combination thereof.

14. The black adhesive film according to claim 11, wherein the carboxylic acid functional comonomer comprises -carboxyethyl acrylate.

15. The black adhesive film according to claim 1, wherein the cross-linker is selected from: bisamides, isocyanates, epoxides, aziridines, organosilanes and carbodiimides.

16. The black adhesive film according to claim 1, wherein the contents of the initiator and the cross-linker are 0.05 to 0.3 parts by weight and 0.01 to 0.5 parts by weight, respectively, based on 100 parts by weight of copolymer.

17. The black adhesive film according to claim 1, wherein the black adhesive film can be coated on a PET liner.

18. A method for preparing a black adhesive film having an optical density of greater than 3.5, comprising: mixing a pressure-sensitive adhesive, comprising an acrylic copolymer, an organic solvent and a cross-linker, with a black paste.

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