Adhesive for flexible OLED (Organic Light Emitting Diode) display panel, adhesive layer, support film and preparation method of support film

Abstract

The invention belongs to the field of adhesives, and relates to an adhesive for a flexible OLED display panel, an adhesive layer, a support film and a preparation method of the support film. The adhesive for the flexible OLED display panel is prepared from the following components in percentage by mass: 5 to 85 weight percent of polyacrylate, 0.5 to 5 weight percent of tackifying resin, 0.5 to 3 weight percent of polyol modified aliphatic isocyanate, 0.01 to 1 weight percent of aromatic isocyanate, 0.002 to 0.01 weight percent of catalyst, 0.2 to 1 weight percent of wetting agent and the balance of organic solvent. The support film prepared from the adhesive can meet the requirements of high stripping force (high viscosity), high mechanical strength, good bonding quality, light transmittance, haze, heat resistance and the like at the same time.

Description

Technical Field

[0001] The invention belongs to the field of adhesives, and relates to an adhesive, an adhesive layer, a support film and a method for preparing the support film for a flexible OLED display panel. Background Art

[0002] OLED (Organic Light-Emitting Diode), also known as organic electric laser display, organic light-emitting semiconductor. OLED is a current-type organic light-emitting device that emits light through the injection and recombination of carriers, and the luminous intensity is proportional to the injected current. Under the action of the electric field, the holes generated by the anode and the electrons generated by the cathode will move, inject into the hole transport layer and the electron transport layer respectively, and migrate to the light-emitting layer. When the two meet in the light-emitting layer, energy excitons are generated, which excite the light-emitting molecules and finally produce visible light.

[0003] Flexible modules used for flexible displays usually include a cover plate, a functional film layer, a backplane film layer, a flexible substrate, and a panel support film (hereinafter referred to as the support film). The support film is mainly used to support and protect the module process after laser peeling, and the support film is usually shipped together with the panel module. Therefore, the support film has high requirements on the mechanical properties of the substrate and the pressure-sensitive adhesive. For example, the substrate has a high elastic modulus, and the peeling force of the support film reaches a certain strength, thereby preventing interlayer peeling of the display module.

[0004] In addition, in the process of display panel manufacturing, in order to prevent the panel support film from affecting the optical recognition positioning, a series of requirements are put forward for the support film and its bonding. For example, the adhesive layer and substrate of the support film have excellent optical properties. In addition, requirements are also put forward for the storage modulus, loss modulus and loss tangent of the pressure-sensitive adhesive at the bonding temperature to avoid bubbles during bonding. In addition, there are certain requirements for the static voltage of the release film when it is torn off, otherwise static electricity is easily accumulated when the release film is torn off, resulting in display abnormalities such as diagonal lines on the display panel.

[0005] The supporting 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 the lamination is completed, the process of binding the chip and the flexible circuit board wiring will also be carried out. Since the process involves the activation of the anisotropic conductive adhesive layer, there will be a hot pressing process, which puts forward requirements on the thermal properties of the substrate and the storage modulus of the pressure-sensitive adhesive at the hot pressing temperature.

[0006] At present, the market is in urgent need of a support film for flexible OLED display panels that simultaneously meets the indicators of high peel force, high mechanical strength, high light transmittance, low static electricity when removing the release film, and good heat resistance. Summary of the invention

[0007] In view of the above problems, the present invention aims to provide an adhesive, a support film and a preparation method thereof for a flexible OLED display panel. The support film prepared by the adhesive can simultaneously meet the requirements of high peeling force (high viscosity), high mechanical strength, good lamination quality, light transmittance, haze, heat resistance, etc.

[0008] In the first aspect, the present invention provides an adhesive for a flexible OLED display panel. The adhesive for a flexible OLED display panel comprises, by mass percentage: 5-85wt% polyacrylate, 0.5-5wt% tackifying resin, 0.5-3wt% polyol-modified aliphatic isocyanate, 0.01-1wt% aromatic isocyanate, 0.002-0.01wt% catalyst, 0.2-1wt% wetting agent, and the balance is an organic solvent; wherein the molecular weight of the polyacrylate is 300,000-1,000,000; the catalyst is an organic tin catalyst; the wetting agent is selected from a mixture of one or more of isopropyl myristate, isopropyl palmitate, and isooctyl palmitate; the organic solvent is selected from a mixture of one or more of butanone, acetylacetone, and toluene.

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

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

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

[0012] Preferably, the polyacrylate is selected from a mixture of one or more of polymethyl acrylate, polymethyl methacrylate, polyethyl acrylate, polybutyl acrylate, and polyacrylate copolymers.

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

[0014] Preferably, the aromatic isocyanate is selected from a mixture of one or more of toluene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate and tetramethyl-meta-xylylene diisocyanate.

[0015] Preferably, the polyol is dissolved in an organic solvent to obtain a polyol dispersion, and aliphatic isocyanate is added to the polyol dispersion under stirring. After the reaction is completed, the polyol-modified aliphatic isocyanate is obtained.

[0016] Preferably, the reaction time is 10 to 40 hours.

[0017] In a second aspect, the present invention provides a glue layer, which is a product obtained by drying and reacting the adhesive film for a flexible OLED display panel according to any one of the above items. The glue layer can be dried by an oven group. The maximum temperature of the oven in the oven group can be 110-150°C, preferably 110-120°C.

[0018] In a third aspect, the present invention provides a support film, comprising a release film, a main film and a protective film arranged in sequence, wherein the main film is formed by laminating the adhesive layer on a substrate, the release film is laminating on another surface of the adhesive layer, and the protective film is laminating on another surface of the substrate.

[0019] In a fourth aspect, the present invention provides a method for preparing a support membrane, comprising the following steps: Laminating the adhesive layer on a substrate to obtain a main body film; Laminating a protective film on 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.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The support film provided by the present invention has excellent properties such as excellent peeling force, high mechanical strength and good surface bonding quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 are bubble effect diagrams of Example 1 (left) and Comparative Example 4 (right) of the present invention; Figure 2 It is a wetting effect diagram of Example 1 (left) of the present invention and Comparative Example 4 (right). DETAILED DESCRIPTION

[0022] The exemplary embodiments are described in more detail below in conjunction with the specific embodiments to make the features and advantages of the embodiments of the present invention more apparent. Please note that the following summary of the invention is not intended to describe every disclosed embodiment of every embodiment of the present invention. It should be understood that those skilled in the art can envision other various embodiments and can modify them according to the teachings of this specification without departing from the scope or spirit of the present invention. Therefore, the following specific embodiments are not intended to be limiting.

[0023] Unless otherwise indicated, all numbers used in the specification and claims to represent feature sizes, quantities and physical properties should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise indicated, the numerical parameters listed in the above specification and the attached claims are approximate values, and those skilled in the art can use the teachings disclosed herein to seek to obtain the desired properties and appropriately change these approximate values. The use of numerical ranges expressed as endpoints includes all numbers within the range and any range within the 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.

[0024] Adhesives for flexible OLED display panels The adhesive for the flexible OLED display panel provided by the present invention can form a high-viscosity adhesive layer. The adhesive for the flexible OLED display panel includes polyacrylate, tackifying resin, polyol-modified aliphatic isocyanate, aromatic isocyanate, catalyst, wetting agent and organic solvent.

[0025] The molecular weight of the polyacrylate may be 300,000 to 1,000,000. The adhesive prepared using the polyacrylate with a molecular weight within this range has a higher viscosity, thereby ensuring that the prepared adhesive layer has a higher viscosity. The molecular weight of the polyacrylate is preferably 500,000 to 700,000, more preferably 550,000 to 650,000.

[0026] The polyacrylate is selected from a mixture of one or more of polymethyl acrylate, polymethyl methacrylate, polyethyl acrylate, polybutyl acrylate, and polyacrylate copolymers. For example, polyacrylate copolymers include but are not limited to copolymers between any two or any three of methyl acrylate, methyl methacrylate, ethyl acrylate, and butyl acrylate. For example, the polyacrylate copolymer is a copolymer of methyl acrylate-butyl acrylate. In some embodiments, in the adhesive for the flexible OLED display panel, the content of polyacrylate may be 5~85wt%, preferably 10~70wt%, more preferably 15~55wt%, and further preferably 15~40wt%.

[0027] A tackifier resin is introduced into the adhesive to further improve the viscosity of the adhesive. The tackifier resin may be selected from a mixture of one or more of a terpene resin, rosin, and a rosin derivative. Preferably, the tackifier resin is a terpene resin. In some embodiments, in the adhesive for the flexible OLED display panel, the content of the tackifier resin is 0.5-5wt%, preferably 1-4wt%, and more preferably 2-4wt%.

[0028] Compared with using commercial (unmodified) aliphatic isocyanates alone or commercial (unmodified) aromatic isocyanates alone, the use of commercial (unmodified) aliphatic isocyanates and commercial (unmodified) aromatic isocyanates in the adhesive for flexible OLED display panels at the same time improves the mechanical strength and peeling force of the adhesive layer to a certain extent, but there is still a problem of poor bonding, and the above mechanical properties cannot be used in high-demand occasions. Based on this, the present invention creatively proposes to develop a polyol-modified aliphatic isocyanate with a special structure. By synergistically using polyol-modified aliphatic isocyanates and aromatic isocyanates in the adhesive for flexible OLED display panels, it can meet the requirements of significantly improving the room temperature peeling force, room temperature storage modulus, and high temperature storage modulus of the support film at the same time, and can also achieve excellent bonding surface quality.

[0029] The polyol-modified aliphatic isocyanate is an aliphatic isocyanate with a surface grafted polyol. 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, the modification effect of the polyol-modified aliphatic isocyanate will be affected, resulting in the inability to simultaneously improve the room temperature peeling force, room temperature storage modulus, and high temperature storage modulus of the support film when the polyol-modified aliphatic isocyanate and aromatic isocyanate are used in conjunction in the adhesive of the flexible OLED display panel.

[0030] As an example but not limited thereto, the polyol is a mixture of one or more of glycerol, butanediol, ethylene glycol, propylene glycol, caprylyl glycol, ethylhexylglycerol, 1,2-hexanediol, and polycaprolactone polyol. The polyol preferably has more than 3 hydroxyl groups. For example, the polycaprolactone polyol includes but is not limited to polycaprolactone diol, polycaprolactone triol, polycaprolactone tetraol, polycaprolactone heptaol, and the like.

[0031] It should be understood that aliphatic isocyanates of any structure are suitable for the present invention. In some embodiments, the aliphatic isocyanate is a mixture of one or more of hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and dicyclohexylmethane-4,4'-diisocyanate (HMDI).

[0032] Any method for preparing polyol-modified aliphatic isocyanate is applicable to the present invention. In some embodiments, a polyol is dissolved in an organic solvent to obtain a polyol dispersion, and an aliphatic isocyanate is added to the polyol dispersion under stirring, and the reaction is carried out for a period of time to obtain the polyol-modified aliphatic isocyanate. The reaction time may be 10 to 40 hours. The organic solvent is, for example, a mixture of one or more selected from butanone, acetylacetone and toluene. The ratio of polyol to organic solvent may be adjusted as needed. For example, the mass ratio of polyol to organic solvent may be 1: (1 to 10). For example, the mass ratio of polyol to organic solvent may be 1: 4. If the polyol is replaced with other small molecules, gelation may occur before the adhesive is coated.

[0033] As an example, a polyol is dissolved in butanone to obtain a butanone dispersion of the polyol, and hexamethylene diisocyanate is added to the butanone dispersion of the polyol under stirring, and the mixture is placed on a homogenizer for shaking reaction for 24 hours to obtain a polyol-modified aliphatic isocyanate, wherein the mass ratio of the polyol to the hexamethylene diisocyanate is 1:0.5.

[0034] In some embodiments, in the adhesive for the flexible OLED display panel, the content of the polyol-modified aliphatic isocyanate is 0.5-3 wt %, preferably 0.8-2.4 wt %.

[0035] It should be understood that aromatic isocyanates of any structure are applicable to the present invention. As an example, the aromatic isocyanate is selected from a mixture of one or more of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), and tetramethyl metaxylylene diisocyanate (TMXDI). In some embodiments, the content of aromatic isocyanate in the adhesive for flexible OLED display panels is 0.01~1wt%, preferably 0.01~0.8wt%. If the content of aromatic isocyanate is too high, the comprehensive performance of the adhesive layer will decrease, such as a significant decrease in peeling force, thereby affecting the bonding ability.

[0036] In the adhesive for the flexible OLED display panel, the solvent may be selected from a mixture of one or more of butanone, acetylacetone, and toluene.

[0037] The catalyst can increase the crosslinking speed and degree of the adhesive for the flexible OLED display panel. The catalyst can be selected from an organic tin catalyst. In some embodiments, the content of the catalyst in the adhesive for the flexible OLED display panel is 0.002-0.01wt%, preferably 0.002-0.008wt%, and more preferably 0.006-0.008wt%.

[0038] The wetting agent can improve the adhesion of the adhesive for the flexible OLED display panel. The wetting agent can be selected from a mixture of one or more of isopropyl myristate, isopropyl palmitate, and isooctyl palmitate. In some embodiments, the content of the wetting agent in the adhesive for the flexible OLED display panel is 0.2-1wt%, preferably 0.2-0.5wt%.

[0039] Adhesive layer The adhesive layer provided by the present invention is a product obtained by coating the adhesive for the flexible OLED display panel, drying and reacting the adhesive, and can be dried by an oven group.

[0040] The drying can be performed by an oven group having different groups of ovens. For example, the highest temperature of the ovens in the oven group is 110-150°C, preferably 110-130°C. Including but not limited to the following settings: as the adhesive passes through the oven group, the temperature of the oven gradually increases, and then the temperature of the oven gradually decreases. After such a drying process, the adhesive layer is obtained. The adhesive layer has good adhesion and mechanical strength. The coating film can also be aged after drying. For example, it can be aged at 45°C for 96 hours.

[0041] Support film The support film provided by the present invention includes a release film, a main film and a protective film, wherein the main film is formed by laminating the adhesive layer on a substrate, the release film is laminating on the other surface of the adhesive layer, and the protective film is laminating on the other surface of the substrate. The substrate has no special requirements, and can be a commonly used substrate, such as a PET film, a COP film, a SRF film, preferably a PET film. The release film also has no special requirements, and can be a commonly used release film, such as a PE film, a PET film, a BOPP film, a PC film, a PMMA film, an EVA film, a PC film, an ABS film, etc., preferably a PET film. The protective film also has no special requirements, and can be a commonly used protective film, such as a PE film, a PET film, a BOPP film, a PC film, a PMMA film, an EVA film, a PC film, an ABS film, etc., preferably a PET film.

[0042] The method for preparing the support film provided by the present invention comprises the following steps: laminating the adhesive layer to the substrate; laminating a protective film on the other surface of the substrate in the main film; and laminating a release film on the other surface of the adhesive layer in the main film.

[0043] The support film obtained by the invention has excellent peeling force, high mechanical properties, good surface wetting quality and other excellent characteristics, and has certain light transmittance, generates little static electricity when the release film is torn off, and has good heat resistance.

[0044] The following examples and comparative examples are provided to help understand the present invention, and these examples and comparative examples should not be construed as limiting the scope of the present invention. Unless otherwise indicated, all parts and percentages are by weight. The raw materials of the following examples and comparative examples are shown in Table 1.

[0045] Table 1 Raw materials

[0046] The preparation method of polyol-modified aliphatic isocyanate is as follows: dissolve polycaprolactone polyol (brand name CAPA 2125a, the main component is polycaprolactone diol) in butanone, add hexamethylene diisocyanate (HDI) under stirring, place it on a homogenizer for shaking reaction for 24 hours before use. Among them, the mass ratio of polycaprolactone polyol to butanone is 1:4, and the mass ratio of polycaprolactone polyol to hexamethylene diisocyanate is 1:0.5.

[0047] Example 1

[0048] Add 70kg of polyacrylate glue (toluene solution of polyacrylate, solid content 36wt%, main component is copolymer of methyl acrylate and butyl acrylate) into the glue barrel; Add 20kg of butanone into the above-mentioned rubber preparation barrel, and insert the mechanical stirring paddle into the liquid preparation barrel to start stirring, maintaining the speed at 500±100 rpm; Put 10 kg of terpene resin into another empty barrel, add 90 kg of butanone thereto, stir at a speed of 500±100 rpm to obtain a terpene resin solution with a concentration of 10 wt%, take 38 kg of the terpene resin solution from it and add it to the above-mentioned glue preparation barrel, and keep stirring; Add 0.3 kg of isopropyl myristic acid into the above-mentioned glue barrel, keep stirring for 30 minutes, and then let it stand for 1 hour to defoam; Add 3.1 kg of polyol-modified aliphatic isocyanate into the above-mentioned rubber mixing barrel, stir for 3 minutes, and then let it stand for 30 minutes before adding the next step; Put 10g of organotin catalyst into an empty beaker, add 990g of butanone, stir at 500±100rpm to obtain a catalyst solution with a concentration of 1 wt%, take 943g of it and add it to the above-mentioned glue barrel, keep stirring; 1 kg of aromatic isocyanate was put into an empty bucket, 1 kg of acetylacetone was added thereto, and the mixture was stirred to be evenly mixed to obtain a solution of aromatic isocyanate with a concentration of 50 wt%. 400 g of the solution was added to the above-mentioned glue barrel, and the adhesive for flexible OLED display panels was obtained after stirring for 40 minutes.

[0049] Example 2

[0050] Add 70kg of polyacrylate glue (toluene solution of polyacrylate, solid content 36wt%, main component is copolymer of methyl acrylate and butyl acrylate) into a 200kg glue barrel; Add 20kg of butanone into the above-mentioned rubber preparation barrel, and insert the mechanical stirring paddle into the liquid preparation barrel to start stirring, maintaining the speed at 500±100 rpm; Put 10 kg of terpene resin into another empty bucket, add 90 kg of butanone, stir at a speed of 500±100 rpm to obtain a terpene resin solution with a concentration of 10 wt%. Take 38.1 kg of the terpene resin solution and add it to the above-mentioned glue preparation bucket, and keep stirring; Add 0.3 kg of isopropyl myristic acid into the above-mentioned glue barrel, keep stirring for 30 minutes, and then let it stand for 1 hour to defoam; Add 2.7 kg of polyol-modified aliphatic isocyanate into the above-mentioned rubber mixing barrel, stir for 3 minutes, let stand for 30 minutes before adding the next step; Put 10g of organotin catalyst into an empty beaker, add 990g of butanone, stir at 500±100rpm to obtain a catalyst solution with a concentration of 1 wt%, take 943g of it and add it to the above-mentioned glue barrel, keep stirring; 1 kg of aromatic isocyanate was put into an empty bucket, 1 kg of acetylacetone was added thereto, and the mixture was stirred to be evenly mixed to obtain a solution of aromatic isocyanate with a concentration of 50 wt%. 0.5 kg of the solution was added to the above-mentioned glue barrel, and the adhesive for flexible OLED display panels was obtained after stirring for 40 minutes.

[0051] Example 3

[0052] Add 70kg of polyacrylate glue (toluene solution of polyacrylate, solid content 36wt%, main component is copolymer of methyl acrylate and butyl acrylate) into a 200kg glue barrel; Add 17.4 kg of butanone into the above-mentioned rubber preparation barrel, and insert the mechanical stirring paddle into the liquid preparation barrel to start stirring, maintaining the speed at 500 ± 100 rpm; Put 10 kg of terpene resin into another empty bucket, add 90 kg of butanone thereto, stir at a speed of 500±100 rpm to obtain a terpene resin solution with a concentration of 10 wt%, take 51.2 kg of the terpene resin solution from it and add it to the above-mentioned glue preparation bucket, keep stirring; Add 0.3 kg of isopropyl myristic acid into the above-mentioned glue barrel, keep stirring for 30 minutes, and then let it stand for 1 hour to defoam; Add 1.3 kg of polyol-modified aliphatic isocyanate into the above-mentioned rubber mixing barrel, stir for 3 minutes, let stand for 30 minutes before adding the next step; Put 10g of organotin catalyst into an empty beaker, add 990g of butanone, stir at 500±100rpm to obtain a catalyst solution with a concentration of 1 wt%, take 823g of it and add it into the above-mentioned glue barrel, keep stirring; 1 kg of aromatic isocyanate was put into an empty bucket, 1 kg of acetylacetone was added thereto, and the mixture was stirred to be evenly mixed to obtain a solution of aromatic isocyanate with a concentration of 50 wt%. 1 kg of the solution was added to the above-mentioned glue barrel, and the adhesive for flexible OLED display panels was obtained after stirring for 40 minutes.

[0053] Comparative Example 1 The method is basically the same as Example 1, except that the adhesive does not contain polyol-modified aliphatic isocyanate and aromatic isocyanate.

[0054] Comparative Example 2 The method is basically the same as Example 1, except that the adhesive contains aromatic isocyanate but does not contain polyol-modified aliphatic isocyanate.

[0055] Comparative Example 3 The method is basically the same as Example 1, except that the adhesive contains polyol-modified aliphatic isocyanate but no aromatic isocyanate.

[0056] The adhesive formulations of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 2.

[0057] Table 2 Adhesive formulations for flexible OLED display panels

[0058] Performance Testing The present invention mainly evaluates the adhesiveness of the adhesive layer by peeling force. On this basis, the coating thickness, transmittance, haze, and storage modulus tests are used to further evaluate the thickness, light transmittance, haze, mechanical strength and other properties of the support film or main film.

[0059] The adhesive is coated on the PET substrate using the micro-concave coating method. After the coating is completed, it enters the 45°C curing room for 96 hours. During the coating process, it is necessary to match the appropriate micro-concave roller according to the required dry weight, and the liquid supply system needs to use a double filter element (5µm+5µm) to eliminate particles and bubbles. After coating, it enters the oven to dry out excess solvent and heat cures in the oven to obtain the main film. The maximum oven temperature is 130°C.

[0060] After leaving the oven, the main film is laminated with the PET release film and finally rolled into a roll, and transferred to a 45°C curing room for curing for 96 hours. After the curing is completed, it can be cut and cut into pieces, and a protective film can be attached to finally obtain a support film product of the required size.

[0061] Peel force test The national standard GB2792-2014 is used to test the viscosity of the main film in the support film. The specific steps are as follows: 1) Cut the support film into test samples with a size of 150 mm in length and 25 mm in width; 2) Set the laminating roller parameters and set the roller weight to 2kg; 3) Measured at 25±5℃, 60±20% RH; 4) Wipe the surface of the glass backplane film with a dust-free cloth dipped in alcohol. After the surface of the glass backplane film is completely dry, tear off the protective film of the test sample, and use a 2kg roller to stick the adhesive layer of the support film of the torn protective film to the surface of the glass backplane 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 tear off the backing film at a speed of 300 mm / min in the 180° direction for a viscosity test. The measured viscosity value is recorded as p1; 6) Repeat the above test 4 times to obtain the viscosity values ​​p2, p3, p4 and p5 respectively, and take the average value to obtain the viscosity value p of the measured main film = (p1 + p2 + p3 + p4 + p5) / 5.

[0062] Film thickness test A thickness gauge model Mitutoyo 547-4001A was used to measure 9 points along the TD (transverse) direction of each sample, and then the average value was recorded to obtain the thickness value of the measured film.

[0063] Transmittance and haze test 1) Cut the prepared support film into test samples with a size of 40 mm in length and 35 mm in width; 2) Use the NDH 2000N test instrument from Japan; 3) After removing the release film from the sample, open the sample pool and stick the sample to completely cover the test window, then close the sample pool for testing and record the transmittance value and haze value 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 get the transmittance and haze value of the test sample.

[0064] Storage modulus test of adhesive layer 1) Use the TA discovery HR-10 test instrument; 2) Turn on the power supply, open the gas source and purge the instrument pipeline for about 30 minutes, and wait until the air pressure valve reading reaches 30psi; 3) Then turn on the mechanical refrigeration power supply and preheat for 1 hour; 4) Turn on the rheometer, install the fixture and perform startup fixture calibration; 5) After loading the sample, set the test parameters on the PC operation terminal according to the calibration test conditions: temperature-modulus curve scanning, using 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 measuring, record the modulus value, repeat the measurement three times and take the average value to get the storage modulus of the measured adhesive layer.

[0065] The supporting membrane performance test results of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 3.

[0066] Table 3 Support membrane performance test results

[0067] It can be seen from Table 3 that the adhesive layer of Comparative Example 1 contains neither polyol-modified aliphatic isocyanate nor aromatic isocyanate, and its room temperature peeling force, 25°C storage modulus and 200°C storage modulus are all low; the adhesive layer of Comparative Example 2 does not contain polyol-modified aliphatic isocyanate but contains aromatic isocyanate, and it has a relatively high room temperature peeling force, but the 25°C storage modulus and 200°C storage modulus still remain 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 peeling force, 25°C storage modulus and 200°C storage modulus are all improved to a certain extent compared with Comparative Example 1, but still need to be further improved. In combination with Examples 1 to 3, the present invention develops a polyol-modified aliphatic isocyanate with a special structure, and synergistically uses polyol-modified aliphatic isocyanate and aromatic isocyanate in the adhesive for the flexible OLED display panel, which can meet the requirements of simultaneously improving the room-temperature peeling force, room-temperature storage modulus, and high-temperature storage modulus of the support film.

[0068] Example 4 The method is basically the same as Example 1, except that the contents of aromatic isocyanate and solvent are adjusted adaptively. The performance test results of Example 4 are shown in Table 4.

[0069] Table 4 Performance test results of Example 4

[0070] It can be seen from Table 4 that when the aromatic isocyanate is excessive (more than 1wt%), the comprehensive performance of the adhesive layer shows a downward trend, among which the room temperature peeling force and 200℃ storage modulus decrease significantly. That is, the improvement of the 200℃ storage modulus did not meet expectations and caused a significant decrease in room temperature peeling force.

[0071] Evaluation of adhesive layer bonding wettability 1) Bond the object with protruding letters (protruding height is about 10μm) and observe the number and size of bubbles at the bonding interface under a microscope. If the number of bubbles generated by bonding is small and the bubble diameter is small, it is qualitatively judged that the wettability is good.

[0072] 2) Place the prepared support film of the same size, remove the release film and place it with the adhesive surface facing the glass plate. After placing it, click the blue point in the figure with your finger to observe the bonding and wetting. In the same time, the larger the bonding area, the faster the bonding and wetting speed.

[0073] Comparative Example 4 The method is basically the same as Example 1, except that the adhesive contains aliphatic isocyanate and aromatic isocyanate, that is, the polyol-modified aliphatic isocyanate is replaced by aliphatic isocyanate.

[0074] Figure 1 The bubble effect diagrams of Example 1 (left) and Comparative Example 4 (right) are shown. It can be seen that the sample of Example 1 has fewer bubbles on the surface, and basically no bubbles, while the sample of Comparative Example 4 has more small bubbles on the surface.

[0075] Figure 2 1 is a diagram showing the wetting effects of Example 1 (left) and Comparative Example 4 (right). It can be seen that the wetting speed and degree of Example 1 are better than those of Comparative Example 4.

[0076] In addition, the room temperature peeling force, 25°C storage modulus and 200°C storage modulus of the adhesive layer of Example 1 are increased by 20% to 30% compared with those of Comparative Example 4.

[0077] Example 5 The method is basically the same as Example 1, except that glycerol is dissolved in butanone, hexamethylene diisocyanate (HDI) is added under stirring, and the mixture is placed on a homogenizer for shaking reaction for 24 hours to obtain a polyol-modified aliphatic isocyanate. The mass ratio of glycerol to butanone is 1:4, and the mass ratio of glycerol to hexamethylene diisocyanate is 1:0.5.

[0078] Example 6 The method is basically the same as Example 1, except that ethylene glycol is dissolved in butanone, hexamethylene diisocyanate (HDI) is added under stirring, and the mixture is placed on a homogenizer for shaking reaction for 24 hours to obtain a polyol-modified aliphatic isocyanate. 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.

[0079] The performance test results of Examples 1, 5-6 are shown in Table 5.

[0080] Table 5 Performance test results of Examples 1, 5-6

[0081] It can be seen from Table 5 that by replacing the polyol from polycaprolactone polyol with glycerol or ethylene glycol, the peeling force of the adhesive layer is significantly reduced.

[0082] Although the above-mentioned specific embodiments contain many specific details for the purpose of illustration, it will be understood by those skilled in the art that many variations, modifications, substitutions and changes of these details are within the scope of the invention protected by the claims. Therefore, the disclosure described in the specific embodiments does not impose any limitation on the invention protected by the claims. The proper scope of the present invention shall be defined by the claims and their appropriate legal equivalents. All cited references are incorporated herein in their entirety by reference.

[0083] In summary, in Examples 1 to 3, products having excellent room-temperature mechanical strength, high-temperature mechanical strength, and room-temperature peeling strength are obtained by using polyol-modified aliphatic isocyanate and aromatic isocyanate.

Claims

1. An adhesive for a flexible OLED display panel, characterized in that: The adhesive for the flexible OLED display panel comprises, by mass percentage, 5-85wt% of polyacrylate, 0.5-5wt% of tackifying resin, 0.5-3wt% of polyol-modified aliphatic isocyanate, 0.01-1wt% of aromatic isocyanate, 0.002-0.01wt% of catalyst, 0.2-1wt% of wetting agent, and the balance is organic solvent; wherein the molecular weight of the polyacrylate is 300,000-1,000,000; the catalyst is an organic tin catalyst; the wetting agent is selected from a mixture of one or more of isopropyl myristate, isopropyl palmitate, and isooctyl palmitate; the organic solvent is selected from a mixture of one or more of butanone, acetylacetone, and toluene.

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

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

4. The adhesive for flexible OLED display panel according to claim 2, characterized in that: The aliphatic isocyanate is a mixture of one or more of hexamethylene diisocyanate, isophorone diisocyanate and dicyclohexylmethane-4,4'-diisocyanate.

5. The adhesive for flexible OLED display panel according to claim 1, characterized in that: The polyacrylate is selected from a mixture of one or more of polymethyl acrylate, polymethyl methacrylate, polyethyl acrylate, polybutyl acrylate, and polyacrylate copolymers.

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

7. The adhesive for flexible OLED display panel according to claim 1, characterized in that: The aromatic isocyanate is selected from a mixture of one or more of toluene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate and tetramethyl-meta-xylylene diisocyanate.

8. The adhesive for flexible OLED display panel according to claim 1, characterized in that: The polyol is dissolved in an organic solvent to obtain a polyol dispersion, and aliphatic isocyanate is added to the polyol dispersion under stirring. After the reaction is completed, the polyol-modified aliphatic isocyanate is obtained.

9. The adhesive for flexible OLED display panel according to claim 8, characterized in that: The reaction time is 10 to 40 hours.

10. A glue layer, wherein the glue layer is a product obtained by coating the adhesive for a flexible OLED display panel according to any one of claims 1 to 9, followed by drying and reaction.

11. A support film, comprising a release film, a main film and a protective film, wherein the main film is formed by laminating the adhesive layer according to claim 10 on a substrate, the release film is laminating on the other surface of the adhesive layer, and the protective film is laminating on the other surface of the substrate.

12. A method for preparing a support membrane, characterized in that: The preparation method comprises the following steps: (1) Laminating the adhesive layer according to claim 10 to a substrate to obtain a main film; (2) affixing a protective film 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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