Graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal display screen and preparation method of graphene / silver nanowire composite ultrathin conductive adhesive

Abstract

The invention discloses a graphene / silver nanowire composite ultrathin conductive adhesive for a liquid crystal display screen and a preparation method of the graphene / silver nanowire composite ultrathin conductive adhesive. The graphene / silver nanowire composite ultrathin conductive adhesive is prepared from the following raw materials in parts by mass: 40-60 parts of graphene / silver nanowire composite dispersion liquid, 2.5-4 parts of a binder, 1-2 parts of a silane coupling agent and 40-60 parts of a solvent. The graphene / silver nanowire composite ultrathin conductive adhesive for the liquid crystal display screen provided by the invention is suitable for antistatic grounding connection of the liquid crystal display screen, and can be quickly cured at low temperature, so that the loss of electronic components is avoided; the thickness of the cured adhesive layer is less than 5 microns, the adhesive force to ITO glass is good, and the conductivity is excellent.

Description

Technical Field

[0001] This invention relates to the field of conductive adhesive technology, and in particular to a graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays and its preparation method. Background Technology

[0002] In the manufacturing and application of liquid crystal displays (LCDs), the delicate electronic components inside the LCDs are very fragile and easily damaged by interference currents and static electricity. Therefore, conductive adhesive is needed to connect the components that need protection to the grounding point to effectively guide static electricity and interference currents and prevent them from damaging the delicate electronic components.

[0003] Currently, the conductive adhesives used for grounding on the market are mainly conductive silver pastes, which are composed of silver powder (conductive functional phase), matrix resin (adhesive and support phase), and additives (dispersants, defoamers, and other functional regulators). However, due to the migration of silver in high-temperature and high-humidity environments, and the need for a certain thickness of the adhesive layer to achieve a reliable conductive path, as well as the high conductivity required by silver paste necessitating a high proportion of silver powder, conductive silver pastes suffer from poor adhesion, thick adhesive layers, and poor reliability. With the development of LCD screens towards higher resolution and narrower bezels, higher demands are being placed on the performance of conductive adhesives. They not only need to possess good conductivity but also meet requirements such as thinness, low-temperature rapid curing, and good aging resistance. Conductive silver pastes struggle to simultaneously meet these requirements.

[0004] Therefore, there is an urgent need to provide a novel graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays and its preparation method to solve the above problems. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays, and a method for preparing the same. The method involves preparing a graphene / silver nanowire composite as a conductive filler, and using silver nanowires to connect the sheet-like graphene sheets to form a highly efficient three-dimensional conductive network. It can also have good conductivity at an extremely thin thickness. Therefore, an ultrathin adhesive layer can be used to meet the conductive connection required for grounding.

[0006] To solve the above-mentioned technical problems, one technical solution adopted by the present invention is: to provide a graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays, comprising, by weight: 2.5 to 4 parts adhesive 40-60 parts of graphene / silver nanowire composite dispersion 1-2 parts of silane coupling agent 40-60 parts of solvent In a preferred embodiment of the present invention, the adhesive is one of waterborne polyurethane and waterborne acrylic resin.

[0007] In a preferred embodiment of the present invention, the silane coupling agent is one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, or N-(2-aminoethyl)-3-aminopropyltrimethoxysilane.

[0008] In a preferred embodiment of the present invention, the solvent is a mixture of anhydrous ethanol and deionized water, preferably, the mass ratio of anhydrous ethanol to deionized water is 3:1 to 1.5.

[0009] In a preferred embodiment of the present invention, the preparation method of the graphene / silver nanowire composite dispersion includes the following steps: (1) Mix graphene powder, potassium permanganate and concentrated sulfuric acid with a mass fraction of 98% and place them in an ice water bath and stir for 2-3 hours. Then stir at 35°C for 1-1.5 hours. Then add sufficient deionized water to dilute and add hydrogen peroxide to terminate the reaction. Finally, filter and wash with dilute hydrochloric acid and a large amount of deionized water until the pH test paper shows neutrality to obtain graphene oxide filter cake. (2) The graphene oxide filter cake is ultrasonically dispersed in water, then surfactant PVP is added and fully dispersed until uniform, then silver nanowires are added, then ammonia is added to adjust the pH to 8-9, then hydrazine hydrate is added, and the mixture is heated and stirred at 73-88℃ for 3-5 hours to obtain a reduced graphene / silver nanowire dispersion. The high temperature can completely reduce the graphene oxide, and the surfactant PVP can make the graphene and silver nanowires tightly bonded together. At the same time, the high temperature of 73-88℃ can also decompose the excess hydrazine hydrate into non-toxic and harmless substances. (3) Adjust the pH of the reduced graphene / silver nanowire dispersion to 1-2 with 5% dilute hydrochloric acid, then stir the reaction thoroughly for 0.5-1 hour, filter and wash until neutral, then dry and grind to obtain graphene / silver nanowire composite powder. Finally, mix and disperse the graphene / silver nanowire composite powder, defoamer, dispersant and deionized water evenly to obtain graphene / silver nanowire composite dispersion, wherein the dispersion speed is 500-1000 rpm and the stirring time is 20-30 min.

[0010] Furthermore, the ratio of graphene powder, potassium permanganate, concentrated sulfuric acid, and water is 1.2~1.7g: 2.4~3.3g: 25~35mL: 85~100mL. Preferably, the graphene powder is WJ-GP550 graphene powder independently produced by Hefei Microcrystalline Materials Technology Co., Ltd., with a graphene sheet diameter of 1-6μm and 6-10 layers.

[0011] Furthermore, the ratio of graphene powder in step (1) to silver nanowires, PVP, and hydrazine hydrate in step (2) is 1.2~1.7g: 0.1~0.2g: 2.5~3g: 2.5~3mL.

[0012] Furthermore, the silver nanowires mentioned in step (2) have a diameter of 90~120nm and a length of 15~30μm.

[0013] Furthermore, in step (3), the components of the graphene / silver nanowire composite dispersion are as follows by mass ratio: 1-2g of graphene / silver nanowire composite powder, 0.3-0.5g of defoamer, 0.3-0.5g of dispersant, and 80-100g of deionized water. Preferably, the defoamer is an organosilicon polymer, such as BYK-530, SN-6724, or Deqian 6800, and the dispersant is at least one of sodium dodecylbenzenesulfonate (SDBS) and sodium dodecyl sulfate (SDS).

[0014] To solve the above-mentioned technical problems, another technical solution adopted by the present invention is: to provide a method for preparing a graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays as described in any of the preceding claims, comprising the following steps: 1) Mix the binder, solvent, and silane coupling agent according to the specified ratio, and disperse them at a speed of 500~700 rpm for 5~10 minutes to obtain material A; 2) After material A has cooled to room temperature, add the graphene / silver nanowire composite dispersion and disperse at a low speed of 600~900 rpm for 8~12 minutes. Filter and dispense to obtain the graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays. Store in a sealed container at room temperature.

[0015] The beneficial effects of this invention are: (1) The conductive adhesive of the present invention uses anhydrous ethanol and deionized water as solvents, which can evaporate at a low temperature to cure the conductive adhesive, thus avoiding damage to the electronic components in the liquid crystal screen. At the same time, since the graphene sheet in the system has a submicron thickness, a uniform ultrathin conductive adhesive layer can be obtained after the solvent evaporates, which can meet the requirements of liquid crystal displays for thinner conductive adhesives; (2) The conductive adhesive of the present invention improves conductivity by using a graphene / silver nanowire composite. The introduction of silver nanowires connects two-dimensional graphene sheets to form a three-dimensional conductive network, effectively overcoming the resistance caused by graphene grain boundaries and greatly improving conductivity. Simultaneously, the high mechanical strength of graphene itself provides the adhesive layer with good wear resistance and scratch resistance; its good flexibility ensures high adhesion, preventing a decrease in conductivity due to reduced adhesion after long-term aging; and graphene's good chemical and thermal stability contributes to the conductive adhesive's high reliability. (3) The conductive adhesive prepared by the present invention has excellent resistance to thermal shock and damp heat, and its resistance changes very little after aging for 500 hours. (4) The conductive adhesive of the present invention uses an environmentally friendly solvent that does not contain any substances harmful to the human body and is green and environmentally friendly. Detailed Implementation

[0016] The preferred embodiments of the present invention will now be described in detail so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0017] Example 1: This embodiment first prepares the graphene / silver nanowire composite dispersion according to the following steps: 1) Add 1.5g of graphene powder (Hefei Microcrystalline GP550), 2.8g of potassium permanganate and 30mL of 98% concentrated sulfuric acid to a beaker and mix them. Stir in an ice-water bath for 2.5 hours, then stir at 35℃ for 1 hour. Then add 100mL of deionized water to dilute, and then add hydrogen peroxide to terminate the reaction (until no more bubbles are produced). Then filter and wash with dilute hydrochloric acid and a large amount of deionized water until the pH test paper shows neutrality to obtain graphene oxide filter cake.

[0018] 2) The graphene oxide filter cake was ultrasonically dispersed in 100 mL of water, then 2.5 g of surfactant PVP was added and dispersed until uniform. Then 0.15 g of silver nanowires were added, and ammonia was added to adjust the pH to 8-9. Then 2.8 mL of hydrazine hydrate was added, and the mixture was heated and stirred at 80 °C for 4 hours to obtain a reduced graphene / silver nanowire dispersion.

[0019] 3) Adjust the pH of the above dispersion to 1-2 with 5% dilute hydrochloric acid, then stir and react for 1 hour. Filter and wash until neutral, then dry and grind to obtain graphene / silver nanowire composite powder. Then disperse 1.5g graphene / silver nanowire composite powder, 0.4g defoamer (Shenzhu Chemical SN-6724), 0.3g sodium dodecylbenzenesulfonate and 100ml deionized water at 800rpm for 25min to obtain graphene / silver nanowire composite dispersion.

[0020] Using the graphene / silver nanowire composite dispersion prepared by the above method, this embodiment prepares an ultrathin conductive adhesive for liquid crystal displays using the graphene / silver nanowire composite dispersion according to the following steps: 1) Mix 3g of water-based acrylic resin (Guangdong Keding MR1765W), 40g of anhydrous ethanol, 15g of deionized water, and 1.5g of silane coupling agent (γ-aminopropyltriethoxysilane is used in this example) evenly, and then disperse at a speed of 500~700rpm for 5~10 minutes to obtain material A; 2) After material A has cooled to room temperature, add 50g of graphene / silver nanowire composite dispersion and disperse at a low speed of 600~900rpm for 8~12 minutes. Filter and dispense to obtain graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays. Store in a sealed container at room temperature.

[0021] Example 2: In this embodiment, the conductive adhesive was prepared using the same method as in Example 1, except that the ratio of graphene to silver nanowires was 1g:0.2g when preparing the graphene / silver nanowire composite powder.

[0022] Example 3: In this embodiment, the conductive adhesive is prepared using the same method as in Example 1, except that the amount of graphene / silver nanowire composite powder added in step 3) of preparing the graphene / silver nanowire composite dispersion is 2g.

[0023] Example 4: In this embodiment, the conductive adhesive was prepared using the same method as in Example 1, except that the amount of graphene / silver nanowire composite dispersion added was 60g.

[0024] Comparative Example 1: The conductive adhesive in this comparative example was prepared using the same method as in Example 1, except that the ratio of graphene to silver nanowires was 1g:0.3g when preparing the graphene / silver nanowire composite powder.

[0025] Comparative Example 2: The conductive adhesive in this comparative example was prepared using the same method as in Example 1, except that no silver nanowires were added in step 2) of preparing the graphene / silver nanowire composite dispersion; only the graphene dispersion was prepared.

[0026] Comparative Example 3: The conductive adhesive in this comparative example was prepared using the same method as in Example 1, except that the graphene / silver nanowire composite dispersion was replaced with a 1% by mass dispersion of silver nanowires.

[0027] Comparative Example 4: The conductive adhesive in this comparative example was prepared using the same method as in Example 1, except that the amount of graphene / silver nanowire composite powder added was 0.5g.

[0028] Comparative Example 5: The conductive adhesive in this comparative example was prepared using the same method as in Example 1, except that the amount of graphene / silver nanowire composite powder added was 3g.

[0029] Comparative Example 6: The conductive adhesive in this comparative example was prepared using the same method as in Example 1, except that the amount of graphene / silver nanowire composite dispersion added was 30g.

[0030] Comparative Example 7: The conductive adhesive in this comparative example was prepared using the same method as in Example 1, except that the amount of graphene / silver nanowire composite dispersion added was 70g.

[0031] The following performance tests were performed on the encapsulating adhesives of each embodiment and comparative example: 1. Curing time test Using a dispensing machine, the conductive adhesive prepared in each comparative example and the embodiment was used to connect the upper glass surfaces of two overlapping ITO glass pieces, which were then placed on a heating platform at 50°C to test the curing time.

[0032] 2. Contact resistance test Using a dispensing machine, the conductive adhesive prepared in each comparative example and the embodiment is used to connect the upper glass surfaces of two overlapping ITO glass pieces. The pieces are then placed on a heating platform at 50°C and heated for 10 minutes. The contact resistance is then tested using a multimeter.

[0033] 3. Adhesive layer thickness test Using a dispensing machine, the conductive adhesives prepared in each comparative example and the embodiment were dispensed onto ITO glass to form uniform adhesive layers. The glass was then placed on a heating platform at 50°C and heated for 10 minutes. The thickness was measured using a thickness gauge.

[0034] 4. Adhesion strength test The conductive adhesives prepared in each comparative example and embodiment were applied to ITO glass using a dispensing machine to create uniform adhesive layers. The adhesion strength of the adhesive layers was then tested using the 3M tape test evaluation method.

[0035] 5. Damp heat aging test Using a dispensing machine, the conductive adhesive prepared in each comparative example and the embodiment is used to connect the upper glass surfaces of two overlapping ITO glass pieces. The pieces are placed on a heating platform at 50°C and heated for 10 minutes. Then, they are aged in a constant temperature and humidity chamber for 500 hours. Every 250 hours, the pieces are taken out to test the contact resistance and the adhesion of the adhesive layer.

[0036] The test results of the UV conductive silver paste prepared in the above embodiments and comparative examples are shown in the table below:

[0037] The test results above show that the graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays provided by this invention cures quickly, has low contact resistance, excellent adhesion, and good resistance stability and stable adhesion after 500 hours of humid heat aging (Examples 1, 2, 3, and 4). The two comparative examples that added graphene and silver nanowires alone could not form an efficient three-dimensional conductive network due to the lack of interaction between graphene and silver nanowires, resulting in relatively high contact resistance of the conductive adhesive (Comparative Examples 2 and 3). Adding excessive amounts of silver nanowires or using only silver nanowires would lead to a decrease in the stability of the conductive adhesive, with a large change in resistance after humid heat aging. Furthermore, due to the lack of mechanical strength provided by graphene, the adhesion of the adhesive layer would decrease (Comparative Examples 1 and 3). Adding a small amount of graphene / silver nanowire composite powder would result in an unstable conductive pathway, leading to higher contact resistance and decreased resistance stability. Adding excessive amounts of graphene / silver nanowire composite powder would lead to a thicker adhesive layer (Comparative Examples 4, 5, 6, and 7).

[0038] In summary, this invention provides a graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays: by preparing a graphene / silver nanowire composite, silver nanowires are introduced to connect two-dimensional graphene sheets, building a three-dimensional conductive network, effectively overcoming the resistance caused by graphene grain boundaries, greatly improving conductivity, and significantly reducing the contact resistance of the conductive adhesive. At the same time, the mechanical strength, thermal stability, and chemical stability of graphene also give the adhesive layer good adhesion and aging resistance. The addition of submicron-sized graphene sheets also makes the adhesive layer extremely thin after solvent evaporation.

[0039] This embodiment is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may use the above content as inspiration to make changes or modifications to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications listed in the above embodiments that do not depart from the technical essence of the claims of the present invention shall still fall within the scope of protection of the claims of the present invention.

Claims

1. A graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays, characterized in that, Composed of, by weight, parts including: 2.5 to 4 parts adhesive 40-60 parts of graphene / silver nanowire composite dispersion 1-2 parts of silane coupling agent Solvent 40-60 parts.

2. The graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays according to claim 1, characterized in that, The adhesive is one of waterborne polyurethane or waterborne acrylic resin.

3. The graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays according to claim 1, characterized in that, The silane coupling agent is one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, or N-(2-aminoethyl)-3-aminopropyltrimethoxysilane.

4. The graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays according to claim 1, characterized in that, The solvent is a mixture of anhydrous ethanol and deionized water.

5. The graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays according to claim 1, characterized in that, The preparation method of the graphene / silver nanowire composite dispersion includes the following steps: (1) Mix graphene powder, potassium permanganate and concentrated sulfuric acid with a mass fraction of 98% and place them in an ice water bath and stir for 2-3 hours. Then stir at 35°C for 1-1.5 hours. Then add sufficient deionized water to dilute and add hydrogen peroxide to terminate the reaction. Finally, filter and wash with dilute hydrochloric acid and a large amount of deionized water until the pH test paper shows neutrality to obtain graphene oxide filter cake. (2) The graphene oxide filter cake was ultrasonically dispersed in water, then surfactant PVP was added and fully dispersed until uniform, then silver nanowires were added, then ammonia was added to adjust the pH to 8-9, then hydrazine hydrate was added, and the mixture was heated and stirred at 73-88°C for 3-5 hours to obtain a reduced graphene / silver nanowire dispersion. (3) Adjust the pH of the reduced graphene / silver nanowire dispersion to 1-2 with 5% dilute hydrochloric acid, then stir the reaction thoroughly for 0.5-1 hour, filter and wash until neutral, then dry and grind to obtain graphene / silver nanowire composite powder. Finally, mix and disperse the graphene / silver nanowire composite powder, defoamer, dispersant and deionized water evenly to obtain graphene / silver nanowire composite dispersion.

6. The method for preparing the graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays according to claim 5, characterized in that, The ratio of graphene powder, potassium permanganate, concentrated sulfuric acid and water is 1.2~1.7g: 2.4~3.3g: 25~35mL: 85~100mL.

7. The method for preparing the graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays according to claim 5, characterized in that, The ratio of graphene powder in step (1) to silver nanowires, PVP, and hydrazine hydrate in step (2) is 1.2~1.7g: 0.1~0.2g: 2.5~3g: 2.5~3mL.

8. The method for preparing graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays according to claim 5, characterized in that, The silver nanowires mentioned in step (2) have a diameter of 90~120nm and a length of 15~30μm.

9. The method for preparing the graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays according to claim 5, characterized in that, The graphene / silver nanowire composite dispersion in step (3) consists of the following components in a mass ratio: 1-2g graphene / silver nanowire composite powder, 0.3-0.5g defoamer, 0.3-0.5g dispersant, and 80-100g deionized water.

10. A method for preparing a graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays as described in any one of claims 1 to 9, characterized in that, Includes the following steps: 1) Mix the binder, solvent, and silane coupling agent according to the specified ratio, and disperse them at a speed of 500~700 rpm for 5~10 minutes to obtain material A; 2) After material A has cooled to room temperature, add the graphene / silver nanowire composite dispersion and disperse at a low speed of 600~900 rpm for 8~12 minutes. Filter and dispense to obtain the graphene / silver nanowire composite ultrathin conductive adhesive for liquid crystal displays. Store in a sealed container at room temperature.

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