Adhesive, adhesive layer, support film and support film preparation method for flexible OLED display panel

Abstract

The present application belongs to the field of adhesive, and relates to an adhesive for flexible OLED display panel, a glue layer, a supporting film and a supporting film preparation method.The adhesive for flexible OLED display panel comprises, in mass percentage, 5wt%-85wt% of polyacrylate with hydroxyl, 0.5wt%-5wt% of tackifying resin, 0.5wt%-3wt% of polyol modified aliphatic isocyanate, 0.01wt%-1wt% of aromatic isocyanate, 0.002wt%-0.01wt% of catalyst, 0.2wt%-1wt% of wetting agent, and the rest is organic solvent.The supporting film prepared from the adhesive can meet the requirements of high peeling force (high adhesion), high mechanical strength, good bonding quality, light transmittance, haze, heat resistance and the like.

Description

Technical Field

[0001] This invention belongs to the field of adhesives and relates to an adhesive, adhesive layer, support film and support film preparation method for flexible OLED display panels. Background Technology

[0002] OLED (Organic Light-Emitting Diode), also known as organic electroluminescent display or organic light-emitting semiconductor, is a current-driven organic light-emitting device. It emits light through the injection and recombination of charge carriers, and the luminous intensity is directly proportional to the injected current. Under the influence of an electric field, holes generated at the anode and electrons generated at the cathode move and are injected into the hole transport layer and electron transport layer, respectively, migrating to the light-emitting layer. When these two elements meet in the light-emitting layer, they generate excitons, which excite the light-emitting molecules to ultimately produce visible light.

[0003] Flexible modules used in flexible displays typically include a cover plate, functional film layers, a backplate film layer, a flexible substrate, and a panel support film (hereinafter referred to as the support film). The support film mainly serves to support and protect the module after laser peeling, and it is usually shipped together with the panel module. Therefore, the support film has high requirements for the mechanical properties of the substrate and pressure-sensitive adhesive. For example, the substrate must have a high elastic modulus, and the peel force of the support film must reach a certain strength to prevent interlayer delamination of the display module.

[0004] Furthermore, in the manufacturing process of display panels, a series of requirements are imposed on the support film and its bonding to avoid affecting optical recognition and positioning during panel bonding. For example, the adhesive layer and substrate of the support film must possess excellent optical properties. In addition, requirements are set for the storage modulus, loss modulus, and loss tangent of the pressure-sensitive adhesive at the bonding temperature to prevent air bubbles from forming during bonding. Moreover, certain requirements are placed on the static voltage of the release film during removal; otherwise, static electricity accumulation can easily occur when the release film is removed, leading to display abnormalities such as diagonal lines on the display panel.

[0005] The support film structure is divided into a display area (Active Area, AA area) and a non-display area (Non-AA area). For the Non-AA area, after lamination, a process is performed to bond the chip and flexible circuit board wiring. Since this process involves the activation of the anisotropic conductive adhesive layer, a hot-pressing process is involved, which places requirements on the thermal properties of the substrate and the energy storage modulus of the pressure-sensitive adhesive at the hot-pressing temperature.

[0006] Currently, there is an urgent need in the market for a support film for flexible OLED display panels that simultaneously meets the requirements of high peel strength, high mechanical strength, high light transmittance, low static electricity generation when removing the release film, and good heat resistance. Summary of the Invention

[0007] To address the aforementioned problems, this invention aims to provide an adhesive, a support film, and a method for preparing the same for flexible OLED display panels. The support film prepared from the adhesive can simultaneously meet requirements such as high peel strength (high adhesion), high mechanical strength, good bonding quality, light transmittance, haze, and heat resistance.

[0008] In a first aspect, the present invention provides an adhesive for flexible OLED display panels. The adhesive for flexible OLED display panels comprises, by weight percentage: 5 wt% to 85 wt% polyacrylate, 0.5 wt% to 5 wt% tackifying resin, 0.5 wt% to 3 wt% polyol-modified aliphatic isocyanate, 0.01 wt% to 1 wt% aromatic isocyanate, 0.002 wt% to 0.01 wt% catalyst, 0.2 wt% to 1 wt% wetting agent, and the balance being an organic solvent. In a preferred embodiment, the polyacrylate is a polyacrylate having hydroxyl functional groups.

[0009] Preferably, the polyol-modified aliphatic isocyanate is an aliphatic isocyanate with surface-grafted polyol, wherein the mass ratio of the polyol to the aliphatic isocyanate is 0.5~5:0.5~5.

[0010] Preferably, the polyol is one or a mixture of glycerol, butanediol, ethylene glycol, propylene glycol, octyl glycol, ethylhexylglycerol, 1,2-hexanediol, and polycaprolactone polyol.

[0011] Preferably, the aliphatic isocyanate is one or a mixture of hexamethylene diisocyanate, isoflurane diisocyanate, and dicyclohexylmethane-4,4'-diisocyanate.

[0012] Preferably, the polyacrylate having hydroxyl functional groups is selected from one or more mixtures of polymethyl acrylate, polyethyl acrylate, polypropyl acrylate, polybutyl acrylate, polymethyl methacrylate, polyethyl methacrylate, polyhydroxypropyl methacrylate, polyethylene glycol diacrylate, polypropylene glycol polyacrylate, bifunctional hydroxyl-containing alkyl acrylates, and hydroxyl-containing polyacrylate copolymers.

[0013] Preferably, the tackifying resin is selected from one or more of terpene resins, rosin, and rosin derivatives, or a mixture thereof.

[0014] Preferably, the aromatic isocyanate is selected from one or more of toluene diisocyanate, diphenylmethane diisocyanate, phenylmethylene diisocyanate, and tetramethyl isophthalimethylene diisocyanate, or a mixture thereof.

[0015] Preferably, the wetting agent is selected from one or more of isopropyl myristate, isopropyl palmitate, and isooctyl palmitate, or a mixture thereof.

[0016] Preferably, the solvent is selected from one or more of butanone, acetylacetone, and toluene.

[0017] Preferably, a polyol is dissolved in an organic solvent to obtain a polyol dispersion. Under stirring, an aliphatic isocyanate is added to the polyol dispersion. After the reaction is complete, the polyol-modified aliphatic isocyanate is obtained.

[0018] Preferably, the reaction time is 10 to 40 hours.

[0019] Preferably, the molecular weight of the polyacrylate is 300,000 to 1,000,000.

[0020] Secondly, the present invention provides an adhesive layer, which is a product obtained by coating a flexible OLED display panel with any of the above-mentioned adhesives, followed by drying and reaction. It can be dried using an oven assembly. The maximum temperature of the oven in the oven assembly can be 110~150℃, preferably 110~120℃.

[0021] Thirdly, the present invention provides a support film comprising a release film, a main film, and a protective film arranged in sequence. The main film is formed by bonding the adhesive layer to a substrate, the release film is bonded to another surface of the adhesive layer, and the protective film is bonded to another surface of the substrate.

[0022] Fourthly, the present invention provides a method for preparing a support membrane, comprising the following steps: The adhesive layer is bonded to the substrate to obtain the main film; A protective film is attached to the other surface of the substrate in the main film; A release film is attached to the other surface of the adhesive layer in the main film.

[0023] Compared with the prior art, the present invention has the following beneficial effects: The support film provided by this invention has excellent properties such as superior peel strength, high mechanical strength, and good surface adhesion quality. Attached Figure Description

[0024] Figure 1 These are bubble effect diagrams of Embodiment 1 (left) and Comparative Example 4 (right) of the present invention; Figure 2 These are wetting effect diagrams of Embodiment 1 (left) and Comparative Example 4 (right) of the present invention. Detailed Implementation

[0025] The following detailed description of exemplary embodiments, with reference to specific implementation details, will make the features and advantages of the present invention more apparent. Please note that the following description is not intended to depict every disclosed embodiment of every implementation of the invention. It should be understood that those skilled in the art can conceive of various other embodiments and modifications thereof based on the teachings of this specification without departing from the scope or spirit of the invention. Therefore, the following detailed description is not intended to be limiting.

[0026] Unless otherwise specified, all figures used in this specification and claims to indicate feature dimensions, quantities, and physical properties should be understood to be modified by the term "about" in all cases. Therefore, unless stated to the contrary, the numerical parameters listed in the foregoing specification and appended claims are approximations, and those skilled in the art can appropriately modify these approximations to obtain the desired properties using the teachings disclosed herein. The use of numerical ranges indicated by endpoints includes all numbers within that range and any range within that range; for example, 1, 2, 3, 4, and 5 include 1, 1.1, 1.3, 1.5, 2, 2.75, 3, 3.80, 4, and 5, etc.

[0027] Adhesives for flexible OLED display panels The adhesive for flexible OLED display panels provided by this invention can form a highly viscous adhesive layer. The adhesive for flexible OLED display panels includes hydroxyl-containing polyacrylates, tackifying resins, polyol-modified aliphatic isocyanates, aromatic isocyanates, catalysts, wetting agents, and organic solvents.

[0028] For example, the molecular weight of the hydroxyl-containing polyacrylate can be between 300,000 and 1,000,000. Adhesives prepared using polyacrylates with molecular weights within this range have high tack, thus ensuring that the prepared adhesive layer has high adhesion.

[0029] The hydroxyl-containing polyacrylate is selected from one or more mixtures of polymethyl acrylate, polyethyl acrylate (PHEA), polypropyl acrylate (PHPA), polyhydroxybutyl acrylate, polymethyl methacrylate, polyethyl methacrylate (PHEMA), polypropyl methacrylate (PHPMA), polyethylene glycol diacrylate (PEGDA), polypropylene glycol polyacrylate (PPGDA), bifunctional hydroxyl-containing alkyl acrylates, and hydroxyl-containing polyacrylate copolymers. For example, polyacrylate copolymers include, but are not limited to, copolymers of any two or any three of methyl acrylate, methyl methacrylate, hydroxyethyl acrylate, and hydroxybutyl acrylate. In some embodiments, the content of polyacrylate in the adhesive for flexible OLED display panels may be 5 wt% to 85 wt%, preferably 10 wt% to 70 wt%, more preferably 15 wt% to 55 wt%, and even more preferably 15 wt% to 40 wt%.

[0030] A tackifying resin is introduced into the adhesive to further improve its tackiness. The tackifying resin may be selected from one or more mixtures of terpene resins, rosin, and rosin derivatives. Preferably, the tackifying resin is a terpene resin. In some embodiments, the content of the tackifying resin in the adhesive for flexible OLED display panels is 0.5 wt% to 5 wt%, preferably 1 wt% to 4 wt%, and more preferably 2 wt% to 4 wt%.

[0031] In adhesives used for flexible OLED display panels, the simultaneous use of commercially available (unmodified) aliphatic isocyanates and commercially available (unmodified) aromatic isocyanates, compared to using either alone, while improving the mechanical strength and peel strength of the adhesive layer to some extent, still results in poor adhesion, and the aforementioned mechanical properties are unsuitable for demanding applications. Therefore, this invention creatively proposes the development of a polyol-modified aliphatic isocyanate with a special structure. By synergistically using polyol-modified aliphatic isocyanates and aromatic isocyanates in the adhesives for flexible OLED display panels, the requirements for significantly improving the room-temperature peel strength, room-temperature energy storage modulus, and high-temperature energy storage modulus of the support film can be met simultaneously, while also achieving excellent bonding surface quality.

[0032] The polyol-modified aliphatic isocyanate is an aliphatic isocyanate with polyol grafted onto its surface. The mass ratio of the polyol to the aliphatic isocyanate is 0.5~5:0.5~5. If the mass ratio of the polyol is too high or too low, it will affect the modification effect of the polyol-modified aliphatic isocyanate. This will prevent the simultaneous improvement of the room-temperature peel strength, room-temperature energy storage modulus, and high-temperature energy storage modulus of the support film when using polyol-modified aliphatic isocyanate and aromatic isocyanate synergistically in the adhesive of flexible OLED display panels.

[0033] As an example, but not limited to, the polyol is one or more of glycerol, butanediol, ethylene glycol, propylene glycol, octyl glycol, ethylhexylglycerol, 1,2-hexanediol, and polycaprolactone polyol. The polyol preferably has three or more hydroxyl groups. For example, the polycaprolactone polyol includes, but is not limited to, polycaprolactone diol, polycaprolactone triol, polycaprolactone tetraol, and polycaprolactone heptaol.

[0034] It should be understood that aliphatic isocyanates of any structure are applicable to this invention. In some embodiments, the aliphatic isocyanate is one or more of hexamethylene diisocyanate (HDI), isoflurane diisocyanate (IPDI), and dicyclohexylmethane-4,4'-diisocyanate (HMDI).

[0035] Any method for preparing polyol-modified aliphatic isocyanates is applicable to this invention. In some embodiments, a polyol is dissolved in an organic solvent to obtain a polyol dispersion. While stirring, an aliphatic isocyanate is added to the polyol dispersion, and the reaction is carried out for a period of time to obtain the polyol-modified aliphatic isocyanate. The reaction time can be 10-40 hours. The organic solvent is, for example, selected from one or more mixtures of butanone, acetylacetone, and toluene. The ratio of polyol to organic solvent can be adjusted as needed. For example, the mass ratio of polyol to organic solvent can be 1:(1-10). For example, the mass ratio of polyol to organic solvent can be 1:4. If the polyol is replaced with other small molecules, gelation may occur before the adhesive is fully coated.

[0036] As an example, a polyol is dissolved in butanone to obtain a butanone dispersion of the polyol. Hexamethylene diisocyanate is then added to the butanone dispersion under stirring, and the mixture is homogenized and reacted for 24 hours to obtain aliphatic isocyanates modified with polyol. The mass ratio of polyol to hexamethylene diisocyanate is 1:0.5.

[0037] In some embodiments, the adhesive for flexible OLED display panels contains 0.5 wt% to 3 wt% polyol-modified aliphatic isocyanate, preferably 0.8 wt% to 2.4 wt%.

[0038] It should be understood that aromatic isocyanates of any structure are applicable to this invention. As an example, the aromatic isocyanate is selected from one or more mixtures of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), phenylenediamine diisocyanate (XDI), and tetramethyl-methylene diisocyanate (TMXDI). In some embodiments, the content of aromatic isocyanate in the adhesive for flexible OLED display panels is 0.01 wt% to 1 wt%, preferably 0.01 wt% to 0.8 wt%. Excessive content of aromatic isocyanate can lead to a decrease in the overall performance of the adhesive layer, such as a significant reduction in peel strength, thereby affecting bonding ability.

[0039] In the adhesive used for flexible OLED display panels, the solvent may be selected from one or more mixtures of methyl ethyl ketone (MEK), acetylacetone (AES), and toluene.

[0040] The catalyst can improve the crosslinking speed and degree of crosslinking of the adhesive for flexible OLED display panels. The catalyst may be selected from organotin catalysts. In some embodiments, the catalyst content in the adhesive for flexible OLED display panels is 0.002wt%~0.01wt%, preferably 0.002wt%~0.008wt%, more preferably 0.006wt%~0.008wt%.

[0041] A wetting agent can improve the adhesion of the adhesive used in the flexible OLED display panel. The wetting agent may be selected from one or more mixtures of isopropyl myristate, isopropyl palmitate, and isooctyl palmitate. In some embodiments, the wetting agent content in the adhesive for the flexible OLED display panel is 0.2wt% to 1wt%, preferably 0.2wt% to 0.5wt%.

[0042] adhesive layer The adhesive layer provided by this invention is a product obtained by coating the adhesive used in flexible OLED display panels with the aforementioned adhesive film, followed by drying and reaction. It can be dried using an oven assembly.

[0043] Drying can be performed using an oven group with different sets of ovens. For example, the highest temperature of the ovens in the oven group is 110~150°C, preferably 110~130°C. This includes, but is not limited to, the following setup: as the adhesive passes through the oven group, the oven temperature gradually increases, and then the oven temperature gradually decreases. After such a drying process, the adhesive layer is obtained. This adhesive layer has good adhesion and mechanical strength. The coating can also be cured after drying. For example, it can be cured at 45°C for 96 hours.

[0044] Support membrane The support film provided by this invention includes a release film, a main film, and a protective film. The main film is formed by adhering the adhesive layer to a substrate. The release film is adhered to another surface of the adhesive layer, and the protective film is adhered to another surface of the substrate. The substrate has no particular requirements and can be any commonly used substrate, such as PET film, COP film, or SRF film, with PET film being preferred. The release film also has no particular requirements and can be any commonly used release film, such as PE film, PET film, BOPP film, PC film, PMMA film, EVA film, PC film, or ABS film, with PET film being preferred. The protective film also has no particular requirements and can be any commonly used protective film, such as PE film, PET film, BOPP film, PC film, PMMA film, EVA film, PC film, or ABS film, with PET film being preferred.

[0045] The method for preparing the support film provided by the present invention includes the following steps: attaching the adhesive layer to the substrate; attaching a protective film to another surface of the substrate in the main film; and attaching a release film to another surface of the adhesive layer in the main film.

[0046] The support film obtained by this invention has excellent peel strength, high mechanical properties, good surface wetting quality, and good light transmittance. It also generates little static electricity when the release film is removed and has good heat resistance.

[0047] The examples and comparative examples provided below are intended to aid in understanding the invention, and should not be construed as limiting the scope of the invention. Unless otherwise specified, all parts and percentages are by weight. The raw materials for the following examples and comparative examples are shown in Table 1.

[0048] Table 1 Raw Materials

[0049] The preparation method of polyol-modified aliphatic isocyanate is as follows: Polycaprolactone polyol (Pastol PCL Capa® 2125A, France) is dissolved in methyl ethyl ketone (MEK). Hexamethylene diisocyanate (HDI) is added under stirring, and the mixture is homogenized and reacted for 24 hours before use. The mass ratio of polycaprolactone polyol to MEK is 1:4, and the mass ratio of polycaprolactone polyol to HDI is 1:0.5.

[0050] Example 1

[0051] Add 70 kg of polyacrylate adhesive to the mixing tank; Add 20 kg of methyl ethyl ketone to the above-mentioned mixing tank, and insert the mechanical stirring paddle into the mixing tank to start stirring, maintaining a speed of 500 ± 100 rpm; 10 kg of terpene resin was placed in another empty bucket, and 90 kg of butanone was added to it. The mixture was stirred at 500 ± 100 rpm to obtain a terpene resin solution with a concentration of 10 wt%. 38 kg of the terpene resin solution was then added to the above-mentioned mixing tank and stirred. Add 0.3 kg of isopropyl myristate to the above mixing tank, stir for 30 min, and then let stand for 1 h to defoam. Add 3.1 kg of polyol-modified aliphatic isocyanate to the above mixing tank, stir for 3 minutes, let stand for 30 minutes, and then add it to the next step. Place 10g of organotin catalyst into an empty beaker, add 990g of butanone, and stir at 500±100rpm to obtain a catalyst solution with a concentration of 1 wt%. Take 943g of the solution and add it to the above-mentioned mixing tank, while keeping it stirred. 1 kg of aromatic isocyanate was placed in an empty bucket, and 1 kg of acetylacetone was added to it. The mixture was stirred until homogeneous, resulting in a 50 wt% aromatic isocyanate solution. 400 g of the solution was then added to the above-mentioned adhesive mixing bucket and stirred for 40 minutes to obtain the adhesive for flexible OLED display panels.

[0052] Example 2

[0053] Add 70 kg of polyacrylate adhesive to a 200 kg mixing tank; Add 20 kg of methyl ethyl ketone to the above-mentioned mixing tank, and insert the mechanical stirring paddle into the mixing tank to start stirring, maintaining a speed of 500 ± 100 rpm; 10 kg of terpene resin was placed in another empty bucket, and 90 kg of butanone was added to it. The mixture was stirred at 500 ± 100 rpm to obtain a terpene resin solution with a concentration of 10 wt%. 38.1 kg of the terpene resin solution was then added to the above mixing bucket and stirred. Add 0.3 kg of isopropyl myristate to the above mixing tank, stir for 30 min, and then let stand for 1 h to defoam. Add 2.7 kg of polyol-modified aliphatic isocyanate to the above mixing tank, stir for 3 minutes, let stand for 30 minutes, and then proceed to the next step. Place 10g of organotin catalyst into an empty beaker, add 990g of butanone, and stir at 500±100rpm to obtain a catalyst solution with a concentration of 1 wt%. Take 943g of the solution and add it to the above-mentioned mixing tank, while keeping the mixture stirred. 1 kg of aromatic isocyanate was placed in an empty bucket, and 1 kg of acetylacetone was added to it. The mixture was stirred until homogeneous, resulting in a 50 wt% aromatic isocyanate solution. 0.5 kg of this solution was then added to the above-mentioned adhesive mixing bucket and stirred for 40 minutes to obtain the adhesive for flexible OLED display panels.

[0054] Example 3

[0055] Add 70 kg of polyacrylate adhesive to a 200 kg mixing tank; Add 17.4 kg of methyl ethyl ketone to the above-mentioned mixing tank, and insert the mechanical stirring paddle into the mixing tank to start stirring, maintaining a speed of 500±100 rpm; 10 kg of terpene resin was placed in another empty bucket, and 90 kg of butanone was added to it. The mixture was stirred at 500 ± 100 rpm to obtain a terpene resin solution with a concentration of 10 wt%. 51.2 kg of the terpene resin solution was then added to the above-mentioned mixing tank and stirred. Add 0.3 kg of isopropyl myristate to the above mixing tank, stir for 30 min, and then let stand for 1 h to defoam. Add 1.3 kg of polyol-modified aliphatic isocyanate to the above mixing tank, stir for 3 minutes, let stand for 30 minutes, and then proceed to the next step. Place 10g of organotin catalyst into an empty beaker, add 990g of butanone, and stir at 500±100rpm to obtain a catalyst solution with a concentration of 1 wt%. Take 823g of the solution and add it to the above-mentioned mixing tank, while keeping the mixture stirred. 1 kg of aromatic isocyanate was placed in an empty bucket, and 1 kg of acetylacetone was added to it. The mixture was stirred until homogeneous, resulting in a 50 wt% aromatic isocyanate solution. 1 kg of this solution was then added to the above-mentioned mixing bucket and stirred for 40 minutes to obtain the adhesive for flexible OLED display panels.

[0056] Comparative Example 1 It is basically the same as Example 1, except that the adhesive does not contain polyol-modified aliphatic isocyanates or aromatic isocyanates.

[0057] Comparative Example 2 The adhesive is essentially the same as in Example 1, except that it contains aromatic isocyanates but not polyol-modified aliphatic isocyanates.

[0058] Comparative Example 3 The results are basically the same as in Example 1, except that the adhesive contains polyol-modified aliphatic isocyanates but not aromatic isocyanates.

[0059] The adhesive formulations for Examples 1-3 and Comparative Examples 1-3 are shown in Table 2.

[0060] Table 2 Adhesive formulations for flexible OLED display panels

[0061] Performance testing This invention primarily evaluates the adhesiveness of the adhesive layer through peel force. Based on this, it further evaluates the thickness, light transmittance, haze, and mechanical strength of components such as the support film or main film through coating thickness, transmittance, haze, and storage modulus tests.

[0062] The obtained adhesive was coated onto a PET substrate using a microgravure coating method. After coating, the substrate was cured in a 45°C curing chamber for 96 hours. During the coating process, appropriate microgravure rollers were matched according to the required dryness, and the liquid supply system used a dual-filter system (5µm + 5µm) to eliminate particles and air bubbles. After coating, the substrate was dried in an oven to remove excess solvent while undergoing thermal curing to obtain the main film. The maximum oven temperature was 130°C.

[0063] After exiting the oven, the main film is laminated with the PET release film and finally rolled up. It is then transferred to a 45°C curing chamber for 96 hours of curing. After curing, it can be slit, cut into pieces, and have protective films applied to obtain the final support film product of the required size.

[0064] Peel force test The viscosity of the main membrane in the support membrane was tested according to the national standard GB2792-2014. The specific steps are as follows: 1) Cut the support membrane into test samples with dimensions of 150mm in length and 25mm in width; 2) Set the parameters for the bonding roller, and set the roller weight to 2kg; 3) Measured at 25±5℃ and 60±20% RH; 4) Wipe the surface of the glass backing film clean with a lint-free cloth dampened with alcohol. After the surface of the glass backing film is completely dry, peel off the protective film of the test sample. Use a 2kg roller to attach the adhesive side of the support film with the protective film removed to the surface of the glass backing film. Roll the roller back and forth once. 5) Place the pasted sample at room temperature for 30 minutes, and then use a tensile testing machine to peel off the backing film along the 180° direction at a speed of 300 mm / min to conduct an adhesion test. Record the measured adhesion value as p1. 6) Repeat the above test 4 times to obtain viscosity values ​​p2, p3, p4 and p5 respectively. Take the average value to obtain the viscosity value of the measured main membrane p = (p1 + p2 + p3 + p4 + p5) / 5.

[0065] Membrane thickness test Using a Mitutoyo 547-4001A thickness gauge, nine points were measured along the TD (lateral) direction of each sample, and the average value was recorded to obtain the thickness value of the film.

[0066] Transmittance and haze tests 1) Cut the prepared support membrane into test samples with a length of 40 mm and a width of 35 mm; 2) The testing instrument selected is the Japanese NDH 2000N electrochromic turbidimeter; 3) After removing the release film from the sample, open the sample cell, attach the sample to completely cover the test window, close the sample cell, and perform the test. Record the transmittance and haze values ​​respectively. 4) Test two more test samples according to the above test method, and record the transmittance and haze values ​​obtained from the test; 5) Calculate the average value of the three test data to obtain the transmittance and haze value of the test sample.

[0067] Energy storage modulus test of adhesive layer 1) Select the TA discovery HR-10 testing instrument; 2) Connect the power supply and turn on the air source to purge the instrument tubing for about 30 minutes until the air pressure valve reading reaches 30 psi; 3) Then turn on the mechanical refrigeration power supply and preheat for 1 hour; 4) Turn on the rheometer, install the fixture, and perform a power-on fixture calibration; 5) After loading the sample, set the test parameters on the PC operation terminal according to the test conditions: temperature-modulus curve scanning, using an 8mm stainless steel fixture, temperature scanning range 0~200℃, sample thickness 0.9±0.1mm, gap monitoring mode using axial force 0.5N, strain 0.5%, frequency 1Hz. 6) Start the measurement, record the modulus value, repeat the measurement three times and take the average value to obtain the energy storage modulus of the measured adhesive layer.

[0068] The performance test results of the support membranes in Examples 1-3 and Comparative Examples 1-3 are shown in Table 3.

[0069] Table 3. Test results of support membrane performance

[0070] As shown in Table 3, the adhesive layer of Comparative Example 1 contains neither polyol-modified aliphatic isocyanate nor aromatic isocyanate, and its room temperature peel strength, storage modulus at 25℃, and storage modulus at 200℃ are all low. The adhesive layer of Comparative Example 2 does not contain polyol-modified aliphatic isocyanate but contains aromatic isocyanate, and it has relatively high room temperature peel strength, but its storage modulus at 25℃ and 200℃ remains at a low level. The adhesive layer of Comparative Example 3 contains polyol-modified aliphatic isocyanate but does not contain aromatic isocyanate, and its room temperature peel strength, storage modulus at 25℃, and storage modulus at 200℃ are all improved to some extent compared with Comparative Example 1, but there is still room for improvement. In conjunction with Examples 1-3, this invention develops a polyol-modified aliphatic isocyanate with a special structure. By synergistically using the polyol-modified aliphatic isocyanate and aromatic isocyanate in the adhesive for flexible OLED display panels, the requirements for simultaneously improving the room temperature peel strength, room temperature energy storage modulus, and high temperature energy storage modulus of the support film can be met.

[0071] Example 4

[0072] The results were essentially the same as in Example 1, except that the content of aromatic isocyanate and solvent was adjusted accordingly. The performance test results for Example 4 are shown in Table 4.

[0073] Table 4 Performance test results of Example 4

[0074] As shown in Table 4, when aromatic isocyanates are in excess (above 1 wt%), the overall performance of the adhesive layer shows a downward trend, with significant decreases in room temperature peel strength and storage modulus at 200℃. This means that the improvement in storage modulus at 200℃ did not meet expectations and resulted in a significant decrease in room temperature peel strength.

[0075] Evaluation of adhesive layer bonding wettability 1) Adhere the bonded object to the raised lettering (approximately 10 μm in height) and observe the number and size of air bubbles at the bonding interface using a microscope. If the number of air bubbles produced during bonding is small and the bubble diameter is small, it is qualitatively judged as having good wettability.

[0076] 2) Place the prepared support film of the same size, with the adhesive side facing the glass plate after removing the release film. After placement, tap the blue dot in the diagram with your finger to observe the adhesion and wetting. A larger adhesion area within the same time frame indicates a faster adhesion and wetting speed.

[0077] Comparative Example 4 This is essentially the same as Example 1, except that the adhesive contains both aliphatic and aromatic isocyanates. Specifically, the polyol-modified aliphatic isocyanate is replaced with an aliphatic isocyanate.

[0078] Figure 1 These are bubble effect diagrams of Example 1 (left) and Comparative Example 4 (right). It can be seen that the sample surface of Example 1 has fewer bubbles, or almost no bubbles, while the sample surface of Comparative Example 4 has more small bubbles.

[0079] Figure 2 These are wetting effect diagrams of Example 1 (left) and Comparative Example 4 (right). It can be seen that the wetting speed and degree of wetting in Example 1 are better than those in Comparative Example 4.

[0080] In addition, the room temperature peel strength, 25°C storage modulus and 200°C storage modulus of the adhesive layer in Example 1 are increased by 20% to 30% compared with Comparative Example 4.

[0081] Example 5

[0082] The process is essentially the same as in Example 1, except that: glycerol is dissolved in butanone, and hexamethylene diisocyanate (HDI) is added while stirring. After reacting with the mixture in a homogenizer for 24 hours, polyol-modified aliphatic isocyanate is obtained. The mass ratio of glycerol to butanone is 1:4, and the mass ratio of glycerol to hexamethylene diisocyanate is 1:0.5.

[0083] Example 6

[0084] The process is essentially the same as in Example 1, except that: ethylene glycol is dissolved in butanone, and hexamethylene diisocyanate (HDI) is added under stirring. After reacting with the mixture in a homogenizer for 24 hours, polyol-modified aliphatic isocyanate is obtained. The mass ratio of ethylene glycol to butanone is 1:4, and the mass ratio of ethylene glycol to hexamethylene diisocyanate is 1:0.5.

[0085] The performance test results of Examples 1, 5-6 are shown in Table 5.

[0086] Table 5 Performance test results of Examples 1, 5-6

[0087] As can be seen from Table 5, by replacing the polyol with polycaprolactone polyol or glycerol, the peel strength of the adhesive layer decreased significantly.

[0088] While the above detailed description contains numerous specific details for illustrative purposes, it will be understood by those skilled in the art that many variations, alterations, substitutions, and modifications of these details are within the scope of the invention protected by the claims. Therefore, the disclosure described in the detailed description does not impose any limitation on the invention protected by the claims. The appropriate scope of the invention should be defined by the claims and their appropriate legal equivalents. All cited references are incorporated herein by reference in their entirety.

[0089] In summary, Examples 1-3 obtained products with excellent room temperature mechanical strength, high temperature mechanical strength, and room temperature peel strength by using polyol-modified aliphatic isocyanates and aromatic isocyanates.

Claims

1. An adhesive for flexible OLED display panels, characterized in that, The adhesive for the flexible OLED display panel comprises, by weight percentage: 5wt%~85wt% polyacrylate, 0.5wt%~5wt% tackifying resin, 0.5wt%~3wt% polyol-modified aliphatic isocyanate, 0.01wt%~1wt% aromatic isocyanate, 0.002wt%~0.01wt% catalyst, 0.2wt%~1wt% wetting agent, and the balance being organic solvent.

2. The adhesive for flexible OLED display panels according to claim 1, characterized in that, The polyacrylate is a polyacrylate having hydroxyl functional groups.

3. The adhesive for flexible OLED display panels according to claim 1, characterized in that, The polyol-modified aliphatic isocyanate is an aliphatic isocyanate with surface-grafted polyol, wherein the mass ratio of the polyol to the aliphatic isocyanate is 0.5~5:0.5~5.

4. The adhesive for flexible OLED display panels according to claim 3, characterized in that, The polyol is one or a mixture of glycerol, butanediol, ethylene glycol, propylene glycol, caprylyl glycol, ethylhexylglycerol, 1,2-hexanediol, and polycaprolactone polyol.

5. The adhesive for flexible OLED display panels according to claim 3, characterized in that, The aliphatic isocyanate is one or a mixture of hexamethylene diisocyanate, isoflurane diisocyanate, and dicyclohexylmethane-4,4'-diisocyanate.

6. The adhesive for flexible OLED display panels according to claim 2, characterized in that, The polyacrylate having hydroxyl functional groups is selected from one or more of the following: polymethyl methacrylate, polyethyl methacrylate, polypropyl methacrylate, polybutyl methacrylate, polymethyl methacrylate, polyethyl methacrylate, polypropyl methacrylate, polyethylene glycol diacrylate, polypropylene glycol polyacrylate, bifunctional hydroxyl-containing alkyl acrylates, and hydroxyl-containing polyacrylate copolymers.

7. The adhesive for flexible OLED display panels according to claim 1, characterized in that, The tackifying resin is selected from one or more of terpene resins, rosin, and rosin derivatives, or a mixture thereof.

8. The adhesive for flexible OLED display panels according to claim 1, characterized in that, The aromatic isocyanate is selected from one or more of toluene diisocyanate, diphenylmethane diisocyanate, phenylmethylene diisocyanate, and tetramethyl isophthalimethylene diisocyanate, or a mixture thereof.

9. The adhesive for flexible OLED display panels according to claim 1, characterized in that, The wetting agent is selected from one or more of isopropyl myristate, isopropyl palmitate, and isooctyl palmitate, or a mixture thereof.

10. The adhesive for flexible OLED display panels according to claim 1, characterized in that, The organic solvent is selected from one or more of butanone, acetylacetone, and toluene, or a mixture thereof.

11. The adhesive for flexible OLED display panels according to claim 1, characterized in that, A polyol is dissolved in an organic solvent to obtain a polyol dispersion. Under stirring, an aliphatic isocyanate is added to the polyol dispersion. After the reaction is complete, the polyol-modified aliphatic isocyanate is obtained.

12. The adhesive for flexible OLED display panels according to claim 11, characterized in that, The reaction time is 10 to 40 hours.

13. The adhesive for flexible OLED display panels according to claim 1, characterized in that, The molecular weight of the polyacrylate is 300,000 to 1,000,000.

14. An adhesive layer, said adhesive layer being a product obtained by coating an adhesive for a flexible OLED display panel according to any one of claims 1 to 13, followed by drying and reaction.

15. A support film comprising a release film, a body film, and a protective film, wherein the body film is formed by bonding an adhesive layer according to claim 14 onto a substrate, the release film is bonded to another surface of the adhesive layer, and the protective film is bonded to another surface of the substrate.

16. A method for preparing a support membrane, characterized in that, The preparation method includes the following steps: (1) The adhesive layer according to claim 15 is bonded to the substrate to obtain the main film; (2) A protective film is attached to the other surface of the substrate in the main film; (3) A release film is attached to the other surface of the adhesive layer in the main film.

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