Preparation of new conductive ink
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Conductive ink refers to an ink printed on a non-conductive substrate that has the ability to conduct current and eliminate static charge. It is usually printed on non-conductive substrates such as plastic, glass, ceramic or cardboard. There are many printing methods, such as screen printing, letterpress printing, flexographic printing, gravure printing and lithography. Different printing methods can be selected according to the film thickness requirements, and the resistance, solder resistance and abrasion resistance are also different depending on the film thickness. Conductive inks can be divided into structural and filled types according to their different structures. Currently, conductive inks used in the electronics industry are mainly composite conductive inks. The conductive fillers used are generally inorganic fillers such as gold, silver, copper and nickel. Carbon black, graphite, carbon fiber, etc., and the binder resin is usually selected from phenol resin, epoxy resin, polyurethane, and the like. Among them, epoxy resin is widely used in conductive polymers because of its excellent performance and easy availability of raw materials, but it also has disadvantages such as high viscosity, large brittleness, small elasticity, and poor impact resistance, so it is necessary to modify and toughen it. Interpenetrating polymer networks (IPN) are a new field of polymer modification. The combination of polyurethane and epoxy resin to form an IPN system is a subject of research in recent years. The IPN structure can combine the high elasticity of polyurethane with the good heat resistance and adhesion of epoxy resin by forcing mutual compatibility and synergistic effect to achieve good toughening effect. I used a terminal isocyanate polyurethane as a toughening agent to react with a secondary hydroxyl group on an epoxy resin to introduce a flexible ether bond onto the epoxy resin to improve the toughness of the epoxy resin and to use the modified ring. The conductive resin is prepared by adding an oxygen resin to the conductive filler.
In terms of its application, it can be applied to flexible circuits and RFID. Flexible circuits are key components for the realization of multi-functionality, integration, miniaturization and low cost of electronic information products. With the development of electronic products and equipment in the direction of light, thin, small, low cost, multi-function, high reliability, etc., the amount of flexible circuits is increasing, and conductive or ink is used to print or print. The formation of conductive lines on an insulating substrate has attracted wide attention. The test shows that the modified epoxy-based conductive ink has good adhesion, and the printed conductive circuit has a bending resistance of 10,000 times, which satisfies the requirements of the flexible printed circuit. RFID is an electronic tag that is expected to replace bar codes. It consists of an antenna and a microchip. However, in the promotion process, development is hindered due to its lack of technology, and low-cost tag antennas printed with new conductive inks are low. Cost packaging technology will promote the mass production of RFID tags and become one of the key factors determining the speed of the industry in the future. I prepared modified epoxy resin-based conductive ink with modified epoxy resin as binder, conductive carbon black and conductive graphite as conductive filler, plus appropriate amount of curing agent, solvent and dispersant. Research, and apply it to RFID, the advantages of antennas will become more and more prominent.
First, the preparation of the binder and ink
1. Preparation of polyurethane prepolymer
First, add polyethylene glycol to the three-necked flask, then heat and dehydrate for 1 hour. After cooling, then refill with nitrogen to maintain the internal temperature of 80 ° C. Add stoichiometric TDI, TDI and polyethylene glycol as soon as possible. The amount ratio was 1.2:1, and the reaction was stopped after stirring for 4 hours to obtain a terminal isocyanate polyurethane prepolymer, which was cooled to room temperature for use. The NCO content was measured by the di-n-butylamine method to be 5%.
2. Synthesis of polyurethane modified epoxy resin IPN
Add epoxy resin to the three-necked flask, stir, and add ethylene glycol ethyl ether acetate (CAC) while stirring until the epoxy resin is completely dissolved, then keep the internal temperature at 70 °C, and add the stoichiometric polyurethane prepolymer. Epoxy resin: The prepolymer has a mass ratio of 9:1 and a reaction time of 2 h. Finally, a polyurethane modified epoxy resin IPN is obtained.
3. Preparation of modified epoxy resin based conductive ink
First, the conductive carbon black and conductive graphite with a mass ratio of 3:2 are mixed together, and then the polyurethane modified epoxy resin IPN (mass ratio of the mixture is 6:25) is added, and a small amount of curing agent (polyurethane resin) and solvent are added. (cyclohexanone) and a dispersing agent (FA-196) were ground in a grinder for 30 minutes to obtain a modified epoxy-based conductive ink.
Second, the detection of conductive ink
1. Curing behavior of modified epoxy-based conductive ink
Differential Scanning Thermal Analysis (DSC) was performed using a Perkin Elmer DSC-7 type thermal analyzer. The atmosphere was static air, and the temperature was solidified. The DSC was heated at a rate of 10 ° C/min and the temperature range was 35 to 180 ° C.
DSC curve of conductive ink
Figure 1
It can be seen from the curve a of Fig. 1 that the conductive ink has a distinct exothermic peak at about 140 ° C, which is related to the curing of the modified epoxy resin. As can be seen from the curve b in the figure, after the conductive ink was heated at 140 ° C for 15 minutes, the conductive ink was substantially completely cured.
2. Flexible circuit board bending resistance
The bending resistance of the modified epoxy-based conductive ink printed circuit was tested by a Tusta TOS-817 swing tester. The conductive lines were measured to be 2.4 cm long, 0.9 mm wide, and 3 μm thick. Five parallel values were measured and averaged. The experimental parameters are as follows: rocking angle: 180°; rocking speed: 60 times·min-1; number of swings: 10,000 times; temperature: 28°C, relative humidity: 80%.
Table 1 Resistance value of bending resistance test of modified epoxy resin-based conductive ink printing circuit × 106Ω
Can be seen from the table. Conductive carbon paste made of polyurethane modified epoxy resin as binder is printed on the conductive circuit by screen printing. After 10000 times of 180° bending, the resistivity increases to 0.57%, indicating polyurethane modified epoxy resin. The flexibility of E-51 has been improved to meet the requirements of printed circuits as a binder for conductive inks.
3. Modified epoxy resin based conductive ink printed circuit line adhesion
The 3M600# adhesive tape is adhered to the line of the cured printing sample. The conductive line is 10cm long, 0.9mm wide and 3μm thick. The long side of the adhesive tape is parallel to the direction of the conductive line, and is polished with a high-level drawing eraser. After standing for 1 minute, pull the tape vertically and forcefully to observe whether the tape and the sample line are pulled off, and measure the resistance change of the line before and after the adhesion. Five parallel values of each conductive line are measured and averaged.
Table 2 Resistance value of the epoxy resin-based conductive ink printed circuit adhesion test × 106Ω
After the 3M600# adhesive tape pull-off experiment, the modified epoxy-based conductive ink printed lines were pulled off without a film layer. It can be seen from the table that the resistance of the conductive line resistance after the adhesion test is 29.95%. It is indicated that the conductive ink using the modified epoxy resin as a binder has good adhesion.
Third, the conclusion
A terminal isocyanate polyurethane prepolymer synthesized by reacting 2,4-toluene diisocyanate with polyethylene glycol, which is used for modification of epoxy resin, modified epoxy resin as binder, conductive carbon black, conductive graphite As a conductive filler, plus a suitable amount of curing agent, solvent and dispersant, the modified epoxy resin-based conductive ink prepared by the test shows that the modified epoxy-based conductive ink has good adhesion, and the printed conductive line resistance The bending property reached 10,000 times.