Multilayer structure, contained PVB layer and applied display device

Abstract

The invention provides a multi-layer structure, a PVB (polyvinyl butyral) layer contained in the multi-layer structure, and a display device applying the multi-layer structure. The multi-layer structure comprises an adhesive layer, a polyvinyl butyral (PVB) layer, an adhesive layer, an adhesive layer and an adhesive layer, pVB) layers and an optical layer. The PVB layer is located on the first surface of the adhesive layer, and the optical layer is located on the second surface of the adhesive layer. The PVB layer comprises a PVB composition, the PVB composition comprises, by mass, 40%-70% of a plasticizer and 30%-60% of PVB resin, and the PVB resin is a polyvinyl alcohol copolymer, and the plasticizer is a plasticizer with the mass ratio of 40%-70% and the PVB resin is a polyvinyl alcohol copolymer with the mass ratio of 30%-60%. The content of PVOH is 5%-10% of the mass of the PVB resin.

Description

Technical Field

[0001] This disclosure relates to a multilayer structure, a display device using a multilayer structure, and a polyvinyl butyral (PVB) layer included in the multilayer structure. Background Technology

[0002] In the back-end manufacturing process of self-emissive sub-millimeter light-emitting diode (mini LED) or micro LED display devices, the LEDs are first encapsulated using liquid resins such as epoxy resin or silicone. After the resin has cured, the surface of the cured resin is polished and leveled as needed, and then an optical film layer is applied on top of the resin as required. However, it typically takes several hours for the resin to cure, and the polishing and leveling also require additional time, making the overall back-end process time-consuming and inefficient. Summary of the Invention

[0003] In some embodiments, this disclosure provides a multilayer structure including an adhesive layer having opposing first and second surfaces; a polyvinyl butyral (PVB) layer located on the first surface, the PVB layer comprising a PVB composition comprising 40% to 70% by weight of a plasticizer and 30% to 60% by weight of PVB resin, wherein the polyvinyl alcohol (PVOH) content of the PVB resin is 5% to 10% by weight of the PVB resin; and an optical layer located on the second surface.

[0004] In some embodiments, this disclosure provides a display device including a display panel, including a substrate and a plurality of light-emitting units located on the substrate; and the aforementioned multilayer structure is high-temperature pressed onto the substrate and cured, wherein the aforementioned PVB layer covers the light-emitting units.

[0005] In some embodiments, this disclosure provides a PVB layer comprising a PVB composition comprising 40% to 70% by weight of a plasticizer and 30% to 60% by weight of PVB resin, wherein the PVOH content of the PVB resin is 5% to 10% by weight of the PVB resin. Attached Figure Description

[0006] To make the features and advantages of this disclosure more apparent and understandable, different embodiments are described below in detail with reference to the accompanying drawings. It should be noted that the various features in the drawings are not drawn to scale and are for illustrative purposes only. In fact, the dimensions of the various components in the drawings can be arbitrarily enlarged or reduced according to actual applications to clearly demonstrate the features of the embodiments disclosed herein.

[0007] Figure 1 A cross-sectional view of a multilayer structure according to some embodiments of the present disclosure is shown.

[0008] Figures 2A-2E A schematic diagram illustrating the fabrication process of a multilayer structure according to some embodiments of this disclosure is shown.

[0009] Figure 3A A perspective view of a display device according to some embodiments of the present disclosure is shown.

[0010] Figure 3B Draw along Figure 3A Cross-sectional view of line 3B-3B'.

[0011] Figure 4 A cross-sectional view of a multilayer structure according to some embodiments of the present disclosure is shown.

[0012] Figure 5 A cross-sectional view of a multilayer structure according to some embodiments of the present disclosure is shown.

[0013] Figure 6 A cross-sectional view of a multilayer structure according to some embodiments of the present disclosure is shown. Detailed Implementation

[0014] The following disclosure provides numerous different embodiments or examples to illustrate different components of the embodiments disclosed herein. Specific examples of the components and their arrangements will be disclosed below to simplify the description of this disclosure. Of course, these specific examples are not intended to limit this disclosure. For example, if the following disclosure describes forming a first component on or above a second component, it includes embodiments where the formed first and second components are in direct contact, as well as embodiments where additional components may be formed between the first and second components, in which case the first and second components are not in direct contact. Furthermore, the various examples in this disclosure may use repeated reference numerals and / or words. These repeated numerals or words are intended to simplify and clarify this disclosure and are not intended to limit the various embodiments and / or the relationships between the described configurations.

[0015] Furthermore, to facilitate the description of the relationship between one component or part and another component(s) in a diagram, spatial relative terms such as "below," "under," "lower," "above," "upper," and similar terms can be used. In addition to the orientations shown in the diagram, spatial relative terms also cover different orientations of a structure or device in use or operation. When a structure or device is rotated to a different orientation (e.g., rotated 90 degrees or otherwise), the spatial relative adjectives used therein will also be interpreted according to the orientation after the rotation.

[0016] Here, the terms "about," "approximately," and "roughly" generally mean within 20%, preferably within 10%, and even more preferably within 5%, or within 3%, or within 2%, or within 1%, or within 0.5%, of a given value or range. It should be noted that the quantities provided in the specification are approximate quantities; that is, unless specifically stated otherwise, the meanings of "about," "approximately," and "roughly" are implied. Furthermore, the (meth)acrylic acid copolymer / monomer mentioned herein, as those skilled in the art will know, refers to an acrylic acid copolymer / monomer or a methacrylic acid copolymer / monomer.

[0017] The embodiments disclosed herein provide a multilayer structure, a display device using the multilayer structure, and a polyvinyl butyral (PVB) layer included in the multilayer structure. The multilayer structure of the embodiments is an integrated composite film material, including a modified PVB layer, as an encapsulation material suitable for bonding with a display panel and effectively encapsulating the light-emitting units. Furthermore, when the multilayer structure of the embodiments is bonded to a display panel to form a display device, the downstream processes of the display device can be simplified, significantly improving process efficiency and saving process time.

[0018] Figure 1 A cross-sectional view of a multilayer structure according to some embodiments of the present disclosure is shown. The multilayer structure 10 sequentially includes a PVB layer 102, an adhesive layer 104, and an optical layer 106. The adhesive layer 104 has opposing first surfaces 1041 and second surfaces 1042, the PVB layer 102 is located on the first surface 1041, and the optical layer 106 is located on the second surface 1042.

[0019] According to some embodiments, the adhesive layer 104 is a double-sided adhesive layer, with the optical layer 106 and the PVB layer 102 respectively adhered to its upper and lower sides.

[0020] In some embodiments, the PVB layer 102 comprises a PVB composition, wherein the PVB composition comprises 40% to 70% by weight of a plasticizer and 30% to 60% by weight of PVB resin, and the polyvinyl alcohol (PVOH) content (i.e., hydroxyl content) of the PVB resin is not higher than about 10% by weight of the PVB resin. In some embodiments, the PVOH content of the PVB resin is about 5% to about 10% by weight of the PVB resin.

[0021] Unlike typical PVB resins, which generally contain 70.5%–83% butyraldehyde groups, 16.5%–25% hydroxyl groups, and 0.5%–4.5% acetyl groups in their chemical structure, the PVB layer 102 in this embodiment is a modified PVB material with a reduced hydroxyl group (PVOH) content of no more than 10%. This reduced PVOH content improves the flowability of the PVB layer at high temperatures. When the multilayer structure 10 of this embodiment is integrated into an application product, the PVB layer 102 with its low PVOH content and hydroxyl groups can effectively cover components (e.g., the light-emitting unit of a display device) and fill gaps between components.

[0022] Furthermore, according to some embodiments, the PVB resin of the PVB layer 102 has an appropriate molecular weight to deform at high temperatures, for example, to have a flowability between that of a solid and a liquid. When the multilayer structure 10 of the embodiment is integrated onto an application product, the PVB layer 102 can effectively cover components (e.g., light-emitting units of a display device) on the application product and fill the gaps between components. In some embodiments, the weight-average molecular weight (Mw) of the PVB resin is between about 30,000 and about 60,000.

[0023] Furthermore, according to some embodiments, the PVB layer 102 has a suitable storage modulus (G') to deform at high temperatures, for example, exhibiting fluidity between that of a solid and a liquid. When the multilayer structure 10 of the integrated embodiment is applied to an application product, the PVB layer 102 can effectively cover components (e.g., light-emitting units of a display device) and fill gaps between components. Generally, the higher the storage modulus of a material, the less prone it is to deformation; the lower the storage modulus of a material, the more prone it is to deformation. In some embodiments, the storage modulus of the PVB layer 102 at a temperature of 100°C does not exceed (is less than, or approximately equal to) about 8 × 10⁻⁶. 4 Pa.

[0024] Polyvinyl butyral (PVB) is a common polymer used in glass bonding. While it possesses good mechanical properties and weather resistance, it is not easily bonded to optical film materials. According to the embodiments disclosed herein, the PVB formulation is modified, particularly by reducing its hydrophilicity, to form a PVB layer 102. Furthermore, according to some embodiments, an adhesive layer 104 is used to bond the modified PVB layer 102 and the optical layer 106 together to form a multilayer structure 10. According to some embodiments, the hydroxyl functional groups added to the adhesive layer 104 constitute 30% to 85% of the total mass of the adhesive layer composition, and it bonds well with the modified PVB layer 102, exhibiting good adhesion at room temperature.

[0025] According to some embodiments, the PVB layer 102 comprises polyvinyl butyral (PVB) resin and a plasticizer, wherein the polyvinyl alcohol (PVOH) content of the PVB resin is about 5% to 10% of the mass of the PVB resin. The plasticizer composition contains at least one C9-C... 20 Aliphatic or alicyclic mono- / poly-epoxycarboxylic acid esters, such as (but not limited to) diglycidyl 4,5-epoxycyclohexane-1,2-dicarboxylate, 3,4-epoxycyclohexylcarboxylate 3',4'-epoxycyclohexylmethyl ester, 6-methyl-3',4'-epoxycyclohexylmethyl ester, 3,4-epoxy-1-methyl-6-acetoxymethylcyclohexane carbonate, bis(3,4-epoxycyclohexylmethyl)adipate, glycidyl laurate, and 7,7-dimethyloctanoate ((oxiran-2-yl)methyl 7,7-dimethyloctanoate), glycidyl 2-ethylhexanoate, glycidyl hexanoate, diglycidyl succinate, diglycidyl adipic acid, diglycidyl sebacate; or it can be aliphatic diol diesters and / or aliphatic dicarboxylic acid diesters. For example, C4-C 12 Aliphatic dicarboxylic acids and C4-C 12 diesters or C4-C esters obtained from the reaction of aliphatic monohydric alcohols 12 Diesters obtained from the reaction of aliphatic dicarboxylic acids with aliphatic diols, or diesters, trimers, and tetramers of diols reacting with aliphatic monocarboxylic acids, especially di, trimers, or tetramers of diols reacting with (C6-C) aliphatic monocarboxylic acids. 10 Diesters obtained from the reaction of saturated straight-chain or branched monocarboxylic acids. Examples of typical diesters obtained from the reaction of aliphatic dicarboxylic acids with aliphatic monoalcohols include: dihexyl succinate, diheptyl succinate, di(2-ethylhexyl) succinate, dipentyl adipate, dihexyl adipate, diheptyl adipate, dicyclohexyl adipate, di(diethylene glycol monoethyl ether), di(diethylene glycol monobutyl ether), di(triethylene glycol monobutyl ether), dihexyl sebacate, diheptyl sebacate, and di(2-ethylhexyl) sebacate. Examples of diesters obtained from the reaction of aliphatic diols with aliphatic monocarboxylic acids, or diesters obtained from the reaction of diol dimers, trimers, or tetramers with aliphatic monocarboxylic acids, include (but are not limited to): diethylene glycol di(2-ethylhexanoate), triethylene glycol dihexanoate, triethylene glycol diheptanoate, triethylene glycol di(2-ethylhexanoate), and tetraethylene glycol diheptanoate.

[0026] According to some embodiments disclosed herein, polyvinyl alcohol (PVA) powder can be modified into PVB powder, then uniformly mixed with a plasticizer, melt-coated, and dried to form a film. The following are some embodiments of a PVB modification method.

[0027] First, polyvinyl alcohol (PVA) powder is dissolved in a suitable aqueous solution at 80℃~90℃. After uniform stirring, hydrogen peroxide (H2O2) is added to promote the degradation of PVA. After stirring for a period of time, the temperature is lowered to 40℃, and butyraldehyde and an appropriate amount of acid are added to promote the acetal reaction. Inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid can be selected to promote the acetal reaction. Afterwards, PVB powder is obtained after oven drying.

[0028] According to some embodiments, the content of hydroxyl functional groups (-OH) in PVB powder can be controlled at 5% to 10% of the PVB mass depending on the butyraldehyde addition ratio.

[0029] According to some embodiments, the PVB powder prepared in the embodiments is melted at a temperature of 160°C to 190°C, and after adding a plasticizer and stirring evenly, the molten PVB is coated onto a peelable film substrate using a doctor blade coater. After drying at room temperature, the PVB film material is completed. The material of the plasticizer can refer to (but is not limited to) the materials exemplified above. In some embodiments, the total weight ratio of the plasticizer can be adjusted to account for 40% to 70% of the total solution weight. Furthermore, the predetermined thickness of the PVB layer 102 required for the application of the multilayer structure 10 can be achieved by coating the molten PVB onto the peelable film substrate. In some embodiments, the thickness of the PVB layer 102 is about 20 micrometers to about 3000 micrometers.

[0030] According to some embodiments, the adhesive layer 104 is a double-sided adhesive layer, with the optical layer 106 and the PVB layer 102 adhered to its upper and lower sides, respectively. In some embodiments, the adhesive layer 104 contains hydroxyl functional groups (-OH), and the additives containing hydroxyl functional groups account for 30% to 85% of the total mass of the composition of the overall adhesive layer 104.

[0031] Furthermore, according to some embodiments, the material of the adhesive layer 104 may be a polymer based on acrylic polymers, polysiloxane polymers, polyurethane, polyamide, polyethylene ether, vinyl acetate / vinyl chloride copolymer, epoxy polymers, natural rubber, or synthetic rubber. The following is a method for manufacturing the adhesive layer 104 according to some embodiments.

[0032] First, the (meth)acrylic acid copolymer, isocyanate compound, and silane coupling compound are uniformly dissolved in a suitable organic solvent. Depending on the application requirements, an appropriate amount of black pigment or diffusion particles may be added and uniformly stirred and dispersed. Then, this mixture is uniformly coated onto a peelable film substrate. The organic solvent used may be, for example, toluene, xylene, ethyl acetate, methanol, ethanol, n-butanol, isobutanol, acetone, methyl ethyl ketone, tetrahydrofuran, or other suitable organic solvents, or a combination of one or more of the aforementioned organic solvents. Afterward, the mixture is dried using a suitable high-temperature process, with the temperature at least above the boiling point of the selected solvent. Once the adhesive layer 104 is formed, another peelable film substrate is attached, thus completing the fabrication of the adhesive layer 104, which is covered on both sides with a peelable film substrate.

[0033] In some embodiments, the isocyanate compound may be selected from aliphatic isocyanates, aromatic isocyanates, or similar compounds, depending on performance requirements. The amount of the isocyanate compound added is 0.05% to 1.0% of the mass of the (meth)acrylic acid copolymer.

[0034] In some embodiments, the silane couplings described above may be selected from epoxy silane couplings, vinyl silane couplings, amino silane couplings, (meth)acrylate silane couplings, isocyanate silane couplings, or similar compounds, depending on performance requirements. The amount of the silane couplings added is 0.05% to 1.0% of the mass of the (meth)acrylate copolymer.

[0035] In some embodiments, the above-mentioned (meth)acrylic acid copolymer comprises (meth)acrylic acid monomers or vinyl-containing monomers and hydrophilic monomers, wherein the (meth)acrylic acid monomers or vinyl-containing monomers account for 15% to 70% by mass, and the hydrophilic monomers may be hydroxyl-containing (meth)acrylic acid monomers accounting for 30% to 85% by mass. The above-mentioned (meth)acrylic acid monomers may be selected from methyl methacrylate, butyl methacrylate, n-octyl methacrylate, isooctyl methacrylate, 2-ethylhexyl methacrylate, and isobornyl acrylate. The vinyl-containing monomers may be selected from styrene, acrylonitrile, acryloylmorpholine, or similar substances. The above-mentioned (meth)acrylic acid monomers or vinyl-containing monomers may be used alone or in combination with two or more. The above-mentioned hydroxyl-containing acrylic monomers may be 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, or similar substances.

[0036] Furthermore, according to some embodiments, the optical layer 106 of the multilayer structure 10 may be a single optical film layer or may contain multiple optical film layers. An optical film layer refers to a layer that contributes to functions such as optical gain, alignment, compensation, steering, orthogonality, diffusion, protection, anti-sticking, scratch resistance, anti-glare, reflection suppression, high refractive index, and protection against shattering and splashing. In some embodiments, the optical layer 106 may be any combination of one or more surface treatment layers selected from hard coating (HC) layers, anti-reflective (AR) layers, anti-sticking layers, diffusion layers, anti-glare (AG) layers, anti-glare and anti-reflective (AGAR) layers, low-reflection (LR) layers, anti-glare and low-reflection (AGLR) layers, and explosion-proof layers. Therefore, only a single-layer optical layer 106 is shown in the figures for simplification, but it is not intended to limit the optical layer 106 disclosed herein. Additionally, the surface of the optical layer 106 may be selectively surface-treated to give the surface an uneven shape, thereby achieving effects such as light collection, light diffusion, and anti-glare.

[0037] In some embodiments, the material of the optical layer 106 may be a cellulose-based resin, an acrylic resin, a non-crystalline polyolefin resin, a polyester resin, a polycarbonate resin, or any combination thereof. More specifically, the material of the optical layer 106 may include polymethyl methacrylate (PMMA). Cellulose-based resins refer to resins in which some of the hydroxyl groups in cellulose are esterified with acetate, or mixed esters in which some are esterified with acetate and some are esterified with other esters. The aforementioned cellulose-based resins are preferably cellulose ester resins, and more preferably acetylated cellulose resins, such as triacetylcellulose, diacetylcellulose, cellulose acetate propionate, cellulose acetate butyrate, etc. Fully esterified cellulose is called triacetate cellulose (TAC). Acrylic resin films, polyaryl hydroxyl resin films, polyether resin films, cyclic polyolefin resin films (e.g., polybornene resin films), polycarbonate resins such as polyesters formed from carbonic acid and glycols or bisphenols, such as polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), non-crystalline polyolefin resins such as cycloolefin(co)polymers (COC / COP), composed of ring-opening polymers such as norbornene, cyclopentadiene, dicyclopentadiene, tetracyclododecene, etc., or copolymers with olefins, polycarbonate (PC), and any combination thereof constitute a group.

[0038] Figures 2A-2E A schematic diagram illustrating the fabrication process of a multilayer structure 10 according to some embodiments of the present disclosure is shown.

[0039] like Figure 2A As shown, in some embodiments, an adhesive product 200 is provided, including an adhesive layer 104, a film substrate 210 covering a first surface 1041 of the adhesive layer 104, and a film substrate 220 covering a second surface 1042 of the adhesive layer 104. The adhesive layer 104, with its upper and lower surfaces covered by film substrates 210 and 220, can be fabricated according to the above-described example method. Furthermore, during the subsequent fabrication of the multilayer structure 10 of the embodiment, the film substrates 210 and 220 can be peeled off from the surface of the adhesive layer 104 without damaging the adhesive layer 104. According to some embodiments, the adhesive layer 104 is tacky at room temperature (e.g., room temperature of approximately 20°C-25°C), similar to the properties of double-sided tape.

[0040] In some embodiments, the first surface 1041 of the self-adhesive layer 104 of the thin film substrate 210 is peeled off. For example... Figure 2B As shown, a PVB layer 102 is provided, with the adhesive layer 104 exposed on the first surface 1041 facing the PVB layer 102. The materials and / or fabrication of the optional PVB layer 102 can be described with reference to the examples in the above embodiments.

[0041] After that, as Figure 2C As shown, in some embodiments, the first surface 1041 of the adhesive layer 104 is exposed to adhere the PVB layer 102. After the PVB layer 102 and the adhesive layer 104 are bonded together, the film substrate 220 is peeled off from the second surface 1042 of the adhesive layer 104.

[0042] like Figure 2D As shown, in some embodiments, an optical layer 106 is provided, with the adhesive layer 104 exposing the second surface 1042 facing the optical layer 106. The materials and / or fabrication of the optional optical layer 106 can be described with reference to the examples of the embodiments described above.

[0043] After that, as Figure 2E As shown, in some embodiments, the second surface 1042 of the adhesive layer 104 is exposed to adhere the optical layer 106, thereby forming a multilayer structure 10.

[0044] In some embodiments, the optical layer 106 includes a lower surface 1061 and an upper surface 1062, wherein the lower surface 1061 is adhered (e.g., in direct contact with the entire surface) to the second surface 1042 of the adhesive layer 104. In some embodiments, the upper surface 1062 of the optical layer 106 may be selectively subjected to a surface treatment, such that the upper surface 1062 has an uneven shape, thereby providing optical effects such as light collection, light diffusion, and anti-glare.

[0045] In addition to the above-described manufacturing method, other steps can also be used to complete the fabrication of the multilayer structure 10. For example, in some other embodiments, the dried PVB film material (i.e., the PVB layer 102 described above) and the dried optical film material (i.e., the optical layer 106 described above) of the embodiment are first fabricated separately; then, a composition of the adhesive described above can be uniformly coated on the optical layer 106, and after high-temperature drying, the adhesive layer 104 of the embodiment is formed; then, the adhesive layer 104 (with the optical layer 106 already on one side) is bonded to the PVB layer 102 to form the multilayer structure 10.

[0046] Figure 3A A perspective view of a display device according to some embodiments of the present disclosure is shown. Figure 3B Draw along Figure 3A The cross-sectional view of line 3B-3B'. Please also refer to... Figure 3A and Figure 3B The display device 40 includes a multilayer structure 10 and a display panel 30. In some embodiments, the display panel 30 includes a substrate 310 and a plurality of light-emitting units 330 formed on the substrate 310. For example, the substrate 310 has an upper surface 3102, on which the light-emitting units 330 are formed. The substrate 310 includes an integrated circuit (not shown) for electrical connection with the light-emitting units 330.

[0047] In some embodiments, the light-emitting unit 330 is a light-emitting diode (LED) or a chip composed of multiple LEDs (also referred to as an LED chip). Each LED chip includes LEDs of different colors, such as a red (R) LED, a green (G) LED, and a blue (B) LED. Furthermore, in some embodiments, the display device 40 is a micro LED display, where the LEDs are sub-millimeter LEDs (MiniLEDs) or micro LEDs (Micro LEDs). In some embodiments, such as... Figure 3AAs shown, the light-emitting units 330 are arranged in arrays on the upper surface 3102 of the substrate 310, for example, in multiple rows and columns along direction D1 (e.g., the X-axis direction) and direction D2 (e.g., the Y-axis direction). In some embodiments, the size of the light-emitting unit 330 is, for example, a width w1 in direction D1 (e.g., the X-axis direction) of less than about 500 micrometers, for example, about 100 micrometers. In some embodiments where light-emitting diodes (LEDs) are used as light-emitting units 330, the gap 341 between two adjacent LEDs has a spacing s1 in direction D1 (e.g., the X-axis direction), and the spacing s1 is between 50 micrometers and 500 millimeters. In some embodiments, the spacing s1 is between 1 millimeter and 100 millimeters. Since each light-emitting unit 330 can be used as an individually controllable light source, compared to conventionally larger LEDs (e.g., larger than 500 micrometers), sub-millimeter LEDs or micro LEDs can have more light-emitting units in the same area, and the number of controllable light sources also increases accordingly, resulting in better local dimming effects.

[0048] Furthermore, in some embodiments, the PVB layer 102 of the multilayer structure 10 is disposed above the substrate 310 (e.g., on the upper surface 3102) and covers the light-emitting unit 330, and the PVB layer 102 fills the gaps between the light-emitting units 330. More specifically, in some embodiments, the bottom surface 3301 of the light-emitting unit 330 is in direct contact with the upper surface 3102 of the substrate 310 and is electrically connected to the circuitry of the substrate 310. The top surface 3302 of the light-emitting unit 330 serves as a light-emitting surface. That is, the light generated by the light-emitting unit 330 is emitted from the top surface 3302, passes through the adhesive layer 104 and the optical layer 106, and is then emitted.

[0049] In addition, in some embodiments, the upper surface 1062 of the optical layer 106 may also include a surface treatment structure (not shown), such as giving the upper surface 1062 an uneven shape, so that when the light emitted by the light-emitting unit 330 passes through the optical layer 106, it produces light-collecting, light-diffusing, anti-glare, and / or other optical effects.

[0050] According to some embodiments, the multilayer structure 10 is formed on the substrate 310 by high-temperature bonding. As described above, the PVB layer 102 of the embodiment deforms at high temperatures, exhibiting properties between solid and liquid, and possessing good fluidity. Therefore, during the high-temperature bonding between the multilayer structure 10 and the display panel 30, the PVB layer 102 of the embodiment can not only effectively cover the exposed portion of the upper surface 3102 of the substrate 310, but also effectively cover the exposed surface of the light-emitting unit 330 and fill the gaps between the light-emitting units 330. After the multilayer structure 10 and the display panel 30 are bonded, the temperature returns to room temperature, and the PVB layer 102 between the substrate 310 and the adhesive layer 104 is cured, thus completing the display device 40.

[0051] In some embodiments where a light-emitting diode is used as the light-emitting unit 330, such as Figure 3B As shown, a pixel is composed of light-emitting diodes (LEDs) of different colors (e.g., a red (R) LED, a green (G) LED, and a blue (B) LED). Each LED within a pixel is a sub-pixel. The gap 341 between adjacent sub-pixels has a spacing s1, for example, in direction D1. The gap 342 between adjacent pixels has a spacing s2, for example, in direction D1, and the spacing s2 is greater than the spacing s1. In some embodiments, the PVB layer 102 covers the top surface 3302 and sidewalls 3303 of the light-emitting unit 330, filling the spacing s2 between adjacent pixels and also filling the smaller spacing s1 between adjacent sub-pixels.

[0052] In some embodiments, the multilayer structure 10 can be bonded to the substrate 310 via a vacuum heating and pressing process. In some non-limiting examples, the vacuum level of the heating and pressing process does not exceed about 0.5 atm, such as about 0.5 atm, about 0.45 atm, about 0.4 atm, about 0.35 atm, about 0.3 atm, about 0.25 atm, about 0.2 atm, about 0.15 atm, about 0.1 atm, or other vacuum levels.

[0053] When actually bonding the multilayer structure 10 to the display panel 30, the process temperature of the heating and pressing process in the above embodiment can be selected from any temperature that allows the PVB layer 102 to have good fluidity so as to fully cover the light-emitting unit 330 and fill the gaps between the light-emitting units 330. In some embodiments, the temperature of the heating and pressing process is in the range of about 80°C to about 140°C, or about 85°C to about 135°C, or about 90°C to about 130°C, or about 95°C to about 125°C, or other suitable ranges. In some non-limiting examples, the temperature of the heating and pressing process is about 80°C, about 85°C, about 90°C, about 95°C, about 100°C, about 105°C, about 110°C, about 115°C, about 120°C, about 125°C, about 130°C, about 135°C, about 140°C, or other suitable temperatures.

[0054] If the process temperature is too low, the PVB layer 102 will lack sufficient fluidity, failing to adequately cover the light-emitting unit 330 and fill gaps. Generally, the lower the elastic modulus of a material, the easier it is to deform, and the better the gap-filling effect. According to some embodiments, the elastic modulus of the PVB layer 102 at a temperature of 100°C does not exceed (is less than or equal to) approximately 8 × 10⁻⁶. 4Pa is used to ensure good coverage of the light-emitting unit 330 and filling of the gaps between the light-emitting units 330 at high temperatures. In addition, if the process temperature is too high, although it can make the PVB layer 102 have sufficient fluidity, it may affect the material properties of one or more of the film layers of the optical layer 106.

[0055] In some embodiments, the above-mentioned heating and pressing process is at 3 kg / cm². 2 ~6Kg / cm 2 2.5Kg / cm 2 ~5.5Kg / cm 2 2Kg / cm 2 ~5Kg / cm 2 Pressure, or other suitable pressure, is applied to the three-layer assembly of PVB layer 102, adhesive layer 104, and optical layer 106. In some non-limiting examples, this three-layer assembly is subjected to 2 kg / cm² pressure. 2 2.5Kg / cm 2 3Kg / cm 2 3.5Kg / cm 2 4Kg / cm 2 4.5Kg / cm 2 5Kg / cm 2 5.5Kg / cm 2 6Kg / cm 2 Pressurize using other suitable pressures.

[0056] Furthermore, to ensure smooth bonding of the multilayer structure 10 and the display panel 30 during the aforementioned heating and pressing process, the thickness of the PVB layer 102 must be greater than the thickness (also referred to as the height) of the light-emitting unit 330 in a direction perpendicular to the substrate 310, for example, along direction D3 (e.g., the Z-axis direction). In some embodiments, the PVB layer 102 has a first thickness t1, the light-emitting unit 330 has a second thickness t2, and the first thickness t1 is greater than approximately 1.5 times the second thickness t2, for example, approximately 2 times, 2.5 times, 3 times, 3.5 times, 4 times, 4.5 times, 5 times, 5.5 times, 6 times, 6.5 times, etc. In some embodiments, the ratio of the first thickness t1 to the second thickness t2 is between approximately 1:2 and approximately 1:16.

[0057] According to some embodiments, black pigment is added to the multilayer PVB layer 102 and / or adhesive layer 104 to blacken the applied display device, making the display device appear black when turned off and improving the device's texture. Furthermore, according to some embodiments, diffusing particles may be added to the multilayer PVB layer 102 and / or adhesive layer 104 to enhance optical properties and improve display quality.

[0058] Figure 4A cross-sectional view of a multilayer structure 10A according to some embodiments of this disclosure is shown. See also... Figure 3B and Figure 4 .like Figure 4 As shown, the multilayer structure 10A includes an adhesive layer 104 and a PVB layer 102 and an optical layer 106 respectively located on two opposing surfaces. Depending on the specific requirements, the PVB layer 102 also contains a uniformly dispersed black pigment 410. The multilayer structure 10A is applied to a display panel 30. Figure 3B When forming a display device, the display device can be blackened to enhance its texture.

[0059] According to some embodiments, when fabricating the multilayer structure 10A, the PVB powder prepared according to the above embodiment can be melted at high temperature, and plasticizer and black pigment 410 can be added and stirred evenly. Then, the molten PVB can be coated onto the peelable film substrate using a doctor blade coater. After drying at room temperature, the PVB film containing black pigment 410 can be fabricated.

[0060] Furthermore, in some other embodiments, the PVB layer 102 of the multilayer structure 10A may contain uniformly dispersed diffused particles (not included in the original text). Figure 4 (As shown in the image). Diffused particles can make the light-emitting units 330 of different colors ( Figure 3B The brightness is more uniform, thereby reducing color shift. Furthermore, if the diffused particles have a high refractive index, the light from the light-emitting unit 330 can be further diffused, increasing the emitted brightness. Therefore, adding diffused particles to the PVB layer 102 of the multilayer structure 10A can improve optical properties and thus improve display quality. In some embodiments, the diffused particles are, for example, nano-inorganic powders, the materials of which are selected from the group consisting of titanium dioxide (TiO2), niobium pentoxide (Nb2O5), tantalum oxide (Ta2O5), zirconium dioxide (Zr2O2), silicon (Si), germanium (Ge), gallium phosphide (GaP), indium phosphide (InP), lead sulfide (PbS), and any combination thereof. Furthermore, in some other embodiments, the PVB layer 102 of the multilayer structure 10A may also simultaneously contain black pigment 410 and diffused particles.

[0061] Figure 5 A cross-sectional view of a multilayer structure 10B according to some embodiments of this disclosure is shown. See also... Figure 3B and Figure 5 .like Figure 5 As shown, the multilayer structure 10B includes an adhesive layer 104 and a PVB layer 102 and an optical layer 106 respectively located on two opposite surfaces of the adhesive layer 104. Depending on the specific requirements, the adhesive layer 104 may also contain uniformly dispersed diffusion particles 420. The multilayer structure 10B is applied to a display panel 30. Figure 3BWhen the diffuse particles 420 are used to form a display device, optical properties can be improved and display quality can be enhanced. The materials for which the diffuse particles 420 can be applied can be found in the examples described above, and will not be repeated here.

[0062] According to some embodiments, when fabricating the multilayer structure 10B, when preparing the adhesive layer 104 as described above (e.g., a mixture of (meth)acrylic acid copolymer, isocyanate compound silane coupling agent and organic solvent), an appropriate amount of diffusion particles 420 can be added according to the application requirements, stirred and dispersed evenly, and then uniformly coated onto a peelable film substrate. After high-temperature drying, the adhesive layer 104 containing diffusion particles 420 can be fabricated.

[0063] According to some embodiments, when fabricating the multilayer structure 10B, the adhesive layer 104 may contain a uniformly dispersed black pigment (not included in the original text). Figure 5 (As shown in the diagram), the display device is treated with a black finish to enhance its texture. Furthermore, in some other embodiments, the adhesive layer 104 of the multilayer structure 10B may also simultaneously contain black pigment and diffusion particles 420.

[0064] Based on the above, in some embodiments, such as Figure 4 As shown, the PVB layer 102 of the multilayer structure 10A may have black pigment 410 and / or diffusion particles (not shown) added, while the adhesive layer 104 does not have black pigment and / or diffusion particles added. In some embodiments, such as Figure 5 As shown, the adhesive layer 104 of the multilayer structure 10B may have added diffusion particles 420 and / or black pigment (not shown), while the PVB layer 102 does not have added black pigment and / or diffusion particles. However, this disclosure is not limited thereto, and at least one of the black pigment and diffusion particles mentioned above may be uniformly added and dispersed in the PVB layer 102 and the adhesive layer 104.

[0065] Figure 6 A cross-sectional view of a multilayer structure 10C according to some embodiments of the present disclosure is shown. Figure 6As shown, the multilayer structure 10C includes an adhesive layer 104 and a PVB layer 102 and an optical layer 106 respectively located on two opposite surfaces of the adhesive layer 104. Depending on actual needs, the adhesive layer 104 may contain uniformly dispersed diffusion particles 420 to improve optical properties and enhance display quality; while the PVB layer 102 contains uniformly dispersed black pigment 410 and diffusion particles 430 to simultaneously improve optical properties and blacken the display device, thereby enhancing display quality. However, this disclosure is not limited to this. In some embodiments, the PVB layer 102 and the adhesive layer 104 may both contain uniformly dispersed diffusion particles, or both may contain uniformly dispersed black pigment, or both may contain uniformly dispersed black pigment and diffusion particles. In some other embodiments, one of the PVB layer 102 and the adhesive layer 104 may contain uniformly dispersed black pigment, while the other contains uniformly dispersed diffusion particles. In some other embodiments, one of the PVB layer 102 and the adhesive layer 104 may contain uniformly dispersed black pigment and diffusion particles (i.e., two additives), while the other contains uniformly dispersed black pigment or diffusion particles (one additive).

[0066] In summary, the multilayer structure proposed in the embodiments disclosed herein is an integrated composite film material, comprising at least a PVB layer and an optical layer bonded together by an adhesive layer having double-sided adhesive properties. When the multilayer structure of the embodiments is applied to the back-end manufacturing process of a display device (e.g., a micro LED display device), the PVB layer of the multilayer structure of the embodiments, in addition to having good mechanical properties and weather resistance, can also effectively cover the light-emitting units located on the panel of the display device to complete the encapsulation of the light-emitting units. Furthermore, according to the embodiments, the PVB layer used for encapsulation is first integrated with the optical layer into a multilayer structure by an adhesive layer, and then combined with the display device to encapsulate the light-emitting units. The optical layer is also set up at the same time as the encapsulation is completed, which greatly improves the efficiency of the back-end manufacturing process of the display device and saves process time.

[0067] Furthermore, compared to traditional back-end processes in display devices, encapsulating light-emitting units with liquefied resin involves several steps. First, the resin flows across the panel to fill the gaps between the light-emitting units and cover their top surfaces. Second, excess resin is scraped off, and the resin hardens (generally requiring at least 4 hours). During this hardening process, even slight tilting or airflow disturbances can affect the resin surface or cause it to tilt, resulting in inconsistent resin surface heights at different locations. Subsequent polishing and leveling are then necessary to improve the surface smoothness, making the process time-consuming and inefficient. In contrast, according to this embodiment, the PVB layer used for encapsulation is first formed into a film and then integrated with the adhesive and optical layers to form a multi-layer structure. Therefore, the film thickness and surface smoothness of the PVB layer in this embodiment are controlled before bonding to the display panel. When the multi-layer structure is pressed onto the display device using a vacuum heating and pressing process, the entire PVB layer is subjected to a uniform downward pressure without affecting its film thickness or surface smoothness. Furthermore, the post-encapsulation polishing and leveling process, as required in traditional processes, is unnecessary. Therefore, the multilayer structure proposed in the embodiments can improve process efficiency, and the display device formed by combining it with the display panel also has a packaging layer (PVB layer) with good encapsulation characteristics, uniform film thickness, and high flatness.

[0068] To make the above and other objects, features, and advantages of this disclosure more apparent and understandable, several multilayer structures of embodiments and comparative examples are described below. Several tests, observations, and analyses were conducted on the PVB layer and adhesive layer of these multilayer structures to evaluate the properties of these multilayer structures and related film materials. The experimental results are summarized in Table 1. It is important to note that the embodiments and comparative examples presented below are for illustrative purposes only and should not be construed as limiting the implementation of this disclosure.

[0069] The preparation methods of the multilayer structures in the embodiments and comparative examples can refer to the fabrication of the PVB layer 102, the fabrication of the adhesive layer 104, and as described above. Figures 2A-2E The preparation method of the multilayer structure 10 shown is not repeated here.

[0070] Furthermore, in the multilayer structures of the embodiments and comparative examples, the thickness of the PVB layer is approximately 380 micrometers, and the thickness of the adhesive layer is approximately 25 micrometers.

[0071] Furthermore, the characteristics and / or evaluation methods of the relevant films after the multilayer structures proposed in the embodiments and comparative examples and after lamination onto the substrate provided with the light-emitting diode chip are briefly described below. The testing and evaluation methods will not be repeated when analyzing the experimental test results subsequently.

[0072] [Adhesion Test and Judgment]

[0073] The adhesion test of the adhesive layer to the PVB layer in the multilayer structure of the embodiments and comparative examples is briefly described below.

[0074] According to JIS Z2037 standards, an adhesive layer with a fixed width of 25 mm is adhered to a PVB film with a thickness of 100 micrometers. A 2 kg roller is used to roll the film back and forth twice to ensure a tight bond between the adhesive layer and the PVB film (the substrate). Then, a pressure degassing process is performed, with the temperature set at 50°C and the pressure at 0.5 MPa. After 20 minutes, the PVB film (the substrate) is left to stand for 24 hours at a temperature of 23°C and a humidity of 65%. Next, the adhesion of the 25 mm wide adhesive layer is measured using a universal tensile testing machine manufactured by Shimadzu Corporation, with the tensile speed set at 300 mm / min and the tensile angle at 180 degrees.

[0075] The test results are listed in Table 1. When the adhesive force of the 25 mm wide adhesive layer is equal to or greater than about 10 N (10 N / 25 mm), the adhesive force of the adhesive layer to the PVB layer is judged to be qualified and is indicated by "○"; while when it is less than about 10 N, it is judged to be unqualified and is indicated by "╳".

[0076] [LED filler]

[0077] The height of the light-emitting diode (LED) chip is 100 micrometers, and the distance between adjacent LEDs is 50 micrometers. After the multilayer structures of the embodiments and comparative examples are laminated onto a substrate on which the LED chips are disposed, the PVB, especially the filling of PVB material between the LEDs, is inspected with a 10x magnifying glass.

[0078] After observation, "○" indicates that it is qualified, that is, no tiny bubbles were observed by visual inspection or 10x magnification. PVB material has excellent LED filling properties.

[0079] "╳" indicates non-compliance, meaning it is not easily identifiable by visual inspection, but micro-bubbles can be observed using a 10x magnifying glass; or, micro-bubbles or excess adhesive are visually visible, indicating poor LED filling performance of this PVB material. The test results are listed in Table 1.

[0080] [Reliability Verification]

[0081] The multilayer structure samples of each embodiment and comparative example were bonded between a cellulose triacetate membrane and glass, degassed under pressure, and prepared as test pieces for reliability verification. This included placing the test pieces in an environment of 85°C / 85% humidity for 500 hours. The test pieces were then removed, and the samples were observed for any foaming or peeling.

[0082] After observation, "○" indicates that the sample is qualified, meaning that there is no foaming and no peeling of the film. "╳" indicates that there is foaming or peeling of the film. The test results are listed in Table 1.

[0083] [Comprehensive Judgment]

[0084] According to the test results in Table 1, if the adhesion test, LED filling performance test, and reliability test are all qualified, then "○" indicates that the overall judgment result is qualified. If any one of the adhesion test, LED filling performance test, or reliability test is unqualified, then "╳" indicates that the overall judgment result is unqualified.

[0085] Table 1

[0086]

[0087] (Continued from the previous table) (Continued from the previous table)

[0088]

[0089] (Continued from the previous table) (Continued from the previous table)

[0090]

[0091] Based on the above experiments, as shown in Table 1 for Examples 1-12, the multilayer PVB layer comprises a low hydroxyl content, with PVOH ranging from 5 wt% to 10 wt%; the adhesive layer comprises a double-sided adhesive composition, wherein the hydroxyl functional group additive accounts for 30% to 85% of the total mass of the adhesive layer composition, to ensure good bonding with the PVB layer. For example, the adhesion force of the adhesive layer to the PVB layer in Examples 1-12 is greater than or equal to 10 N / 25 mm. Furthermore, at a temperature of 100°C, the elastic modulus of the PVB layer in some examples is less than or equal to about 8 × 10⁻⁶. 4 Pa. For example, the elastic modulus of the PVB layers in Examples 1-12 is approximately 1.9 × 10⁻⁶. 4 Pa to approximately 8 × 10 4 Pa. The smaller the elastic modulus, the easier it is for the PVB layer to deform. When bonding the display panel at high temperatures, it can effectively encapsulate the LEDs and fill the gaps between them, exhibiting excellent filling properties. After pressing the multilayer structure to bond with the display panel, no small air bubbles appeared. Furthermore, the molecular weight of the PVB layers in Examples 1-12 is approximately 30,000 to approximately 60,000.

[0092] Based on the experiments described above, as illustrated in Comparative Examples 1-11 in Table 1, the hydroxyl functional group additives in the adhesive layer accounted for 50% of the total mass of the adhesive layer composition, and within the range of 30% to 85% in the examples, they could bond well with the PVB layer. According to the tests, the adhesion of the adhesive layer to the PVB layer was greater than 10 N / 25 mm (the critical value for OK adhesion) in the range of 19 N / 25 mm to 27 N / 25 mm.

[0093] Based on the above experiments, as illustrated in Comparative Examples 12-17 in Table 1, the hydroxyl functional group additives in the adhesive layer accounted for less than 1% to 25% of the total mass of the adhesive layer composition. In Comparative Examples 18 and 19, the hydroxyl functional group additives in the adhesive layer accounted for as high as 90% and 95% of the total mass of the adhesive layer composition, respectively. These figures both fall outside the range of 30% to 85% in the examples and cannot bond well with the PVB layer. Therefore, the adhesion of the adhesive layer to the PVB layer was 0.1 N / 25 mm to 7 N / 25 mm, which is less than 10 N / 25 mm (the critical value for determining OK adhesion).

[0094] Furthermore, since Comparative Examples 12-19 were determined to have poor adhesion, reliability verification was not performed, and the overall judgment result was also determined to be unqualified due to insufficient adhesion ("╳").

[0095] Furthermore, according to the above experiments, as illustrated in Comparative Example 1 in Table 1, although the adhesive layer had sufficient adhesion to the PVB layer, and the PVB resin (PVOH content of 4% in the PVB layer) met the requirements for LED coverage and gap filling, foaming and peeling occurred during the reliability test (temperature 85°C / humidity 85% / 500 hours). Therefore, the overall judgment result was also unsatisfactory due to failure in the reliability test, and it was ultimately judged as unqualified ("╳").

[0096] Furthermore, based on the above experiments, as illustrated in Comparative Examples 2-5 and 16-17 in Table 1, the PVOH content of the PVB layer was 11%-20%, higher than the PVOH content of the Examples (5%-10%), indicating a harder PVB resin. As shown in Table 1, the elastic modulus of the PVB layer was approximately 9 × 10⁻⁶. 4 Pa ~ 1.2 × 10 5 Pa, all exceeding the 8×10 of the example. 4 Pa. Therefore, when bonding display panels at high temperatures, the PVB resin does not adequately cover the LEDs or fill the gaps between them, resulting in small air bubbles after lamination.

[0097] Furthermore, based on the above experiments, as illustrated in Comparative Example 6 in Table 1, using 30% plasticizer, the PVB resin with a molecular weight of 60,000 was relatively hard. As shown in Table 1, the elastic modulus of the PVB layer was approximately 1.5 × 10⁻⁶. 5 Pa (exceeding 8 × 10 in the example) 4Therefore, when bonding display panels at high temperatures, the PVB resin does not adequately cover the LEDs or fill the gaps between them, resulting in small air bubbles after lamination.

[0098] Furthermore, as illustrated in Comparative Examples 2 to 6 in Table 1, since they were deemed to have poor filling performance, no reliability verification was performed, and the overall judgment result was also deemed unqualified due to poor filling performance (“╳”).

[0099] Furthermore, according to the above experiments, as illustrated in Comparative Example 7 in Table 1, using 30% plasticizer reduced the molecular weight to 20,000. While the PVB resin's coverage of the LEDs and its ability to fill gaps between LEDs were satisfactory, foaming and peeling occurred during the reliability test (85°C / 85% humidity / 500 hours). Therefore, the overall assessment result was also unsatisfactory due to the failure of the reliability test, and the final determination was "unsatisfactory" ("╳").

[0100] Furthermore, based on the experiments described above, as illustrated in Comparative Examples 8-11 in Table 1, even though the PVB resin's coverage of the LEDs and its ability to fill the gaps between the LEDs were satisfactory, foaming and peeling occurred during the reliability verification. Therefore, the overall assessment result also determined it to be unsatisfactory ("╳").

[0101] Furthermore, based on the above experiments, as shown in Table 1 for Comparative Examples 12-15, 18 and 19, although the coverage of LEDs by PVB resin and the filling of gaps between LEDs were satisfactory, Comparative Examples 12-19 were judged to have poor adhesion, so reliability verification was not performed, and the overall judgment result was also judged to be unqualified due to insufficient adhesion ("╳").

[0102] Furthermore, based on the above experiments, as illustrated in Comparative Examples 16 and 17 in Table 1, the PVOH content of the PVB layer was 20% (higher than the 5% to 10% of the Examples), and the molecular weight of the PVB layer was also as high as 80,000 (greater than 60,000), therefore the PVB resin was relatively hard. As shown in Table 1, the elastic modulus of the PVB layer was approximately 1.2 × 10⁻⁶. 5 Pa (exceeding 8 × 10) 4 Therefore, when bonding display panels at high temperatures, the PVB resin does not adequately cover the LEDs or fill the gaps between them, resulting in small air bubbles after lamination.

[0103] Although this disclosure is based on the foregoing embodiments, it is not intended to limit the scope of this disclosure. Those skilled in the art to which this disclosure pertains can make various modifications and refinements without departing from the spirit and scope of this disclosure. Therefore, the scope of protection of this disclosure shall be determined by the appended claims. Furthermore, each claim constitutes an independent embodiment, and combinations of various claims and embodiments are all within the scope of this disclosure.

[0104] [Symbol Explanation]

[0105] 3B-3B' line

[0106] 30 Display Panel

[0107] 10, 10A, 10B, 10C Multi-layer structure

[0108] 40 Display devices

[0109] 102 PVB layer

[0110] 104 Adhesive Layer

[0111] 106 Optical Layers

[0112] 200 adhesive products

[0113] 310 base plate

[0114] 330 light-emitting units

[0115] 210, 220 Thin film substrates

[0116] 341, 342 gaps

[0117] 410 Black Pigment

[0118] 420,430 Diffused particles

[0119] 1041 First Surface

[0120] 1042 Second Surface

[0121] 1061 Lower surface

[0122] 1062,3102 Upper surface

[0123] 3301 bottom surface

[0124] 3302 Top Surface

[0125] 3303 sidewall

[0126] Directions D1, D2, D3

[0127] Spacing between s1 and s2

[0128] t1 First Thickness

[0129] t2 Second thickness

[0130] w1 width.

Claims

1. A multi-layer structure, comprising: An adhesive layer having opposing first and second surfaces; Polyvinyl butyral; A PVB layer is located on the first surface, the PVB layer comprising a PVB composition comprising 40% to 70% by weight of a plasticizer and 30% to 60% by weight of PVB resin, wherein the polyvinyl alcohol (PVOH) content of the PVB resin is 5% to 10% by weight of the PVB resin; and An optical layer is located on the second surface.

2. The multilayer structure of claim 1, wherein the adhesive layer comprises hydroxyl functional groups, and the additives containing the hydroxyl functional groups account for 30% to 85% of the total mass of the composition of the adhesive layer.

3. The multilayer structure as claimed in claim 1, wherein the storage modulus (G') of the PVB layer is less than or equal to 8 × 10⁻⁶ at a temperature of 100°C. 4 Pa.

4. The multilayer structure of claim 3, wherein at room temperature, the adhesion force of the adhesive layer to the PVB layer is greater than or equal to 25 N / 25 mm.

5. The multilayer structure of claim 1, wherein the molecular weight (Mw) of the polyvinyl butyral (PVB) resin is 30,000 to 60,000.

6. The multilayer structure of claim 1, wherein the PVB layer further comprises uniformly dispersed black pigment or diffused particles.

7. The multilayer structure of claim 1, wherein the adhesive layer is made of a polymer based on acrylic polymers, polysiloxane polymers, polyurethane, polyamide, polyethylene ether, vinyl acetate / vinyl chloride copolymer, epoxy polymers, natural rubber, or synthetic rubber.

8. The multilayer structure of claim 1, wherein the material of the optical layer comprises cellulose triacetate (TAC), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polypropylene (PP), cycloolefin polymer (COP), polycarbonate (PC), or any combination thereof.

9. The multilayer structure of claim 1, wherein the adhesive layer further comprises uniformly dispersed black pigment or diffused particles.

10. A display device, comprising: A display panel includes a substrate and a plurality of light-emitting units located on the substrate; as well as The multilayer structure described in claims 1 to 9 is press-fitted onto the substrate at high temperature and cured, wherein the PVB layer covers the light-emitting unit.

11. The display device of claim 10, wherein the light-emitting unit is a light-emitting diode or a light-emitting diode chip.

12. The display device of claim 10, wherein the light-emitting diode is a sub-millimeter light-emitting diode (Mini LED) or a micro light-emitting diode (Micro LED).

13. The display device of claim 10, wherein the PVB layer has a first thickness in a direction perpendicular to the substrate, the light-emitting unit has a second thickness, and the first thickness is greater than 1.5 times the second thickness.

14. The display device of claim 10, wherein the ratio of the first thickness to the second thickness is between 1:2 and 1:

16.

15. A polyvinyl butyral (PVB) layer comprising a PVB composition, said PVB composition comprising 40% to 70% by weight of a plasticizer and 30% to 60% by weight of polyvinyl butyral (PVB) resin, wherein the polyvinyl alcohol (PVOH) content of the PVB resin is 5% to 10% by weight of the PVB resin.

16. The PVB layer of claim 15, wherein the elastic modulus at a temperature of 100°C is not greater than 8 × 10⁻⁶. 4 Pa.

17. The PVB layer of claim 15, wherein the weight average molecular weight (Mw) of the polyvinyl butyral resin is 30,000 to 60,000.

Images