New conductive ink process analysis

Conductive ink refers to an ink printed on a non-conductive substrate so that it has the ability to conduct electrical current and eliminate the accumulation of electrostatic charge. It is generally printed on non-conductive substrates such as plastics, glass, ceramics or paperboard. There are many printing methods, such as screen printing, letterpress printing, flexographic printing, gravure printing, and offset printing. Different printing methods may be selected according to the film thickness requirements. The resistance, solder resistance, and abrasion resistance of the film are also different depending on the film thickness. Conductive inks can be divided into structure type and filling type according to their structure. The conductive inks currently used in the electronics industry are mainly composite conductive inks. The conductive fillers used are generally inorganic fillers such as gold, silver, copper, nickel, Carbon black, graphite, carbon fiber, etc., and the binder resin is usually selected from phenolic resin, epoxy resin, polyurethane and so on.

Among them, epoxy resins are widely used in conductive polymers because of their excellent performance and cheap raw materials. However, they also have disadvantages such as large viscosity, large brittleness, low elasticity, and poor impact resistance, so it is necessary to modify and toughen them. Interpenetrating polymer networks (IPNs) are a new field of polymer modification. Polyurethanes and epoxy resins are compounded and blended to form an IPN system, which has been the subject of much research in recent years. The IPN structure can combine the high elasticity of polyurethane with the good heat resistance and adhesiveness of epoxy resin by forcing mutual compatibility and synergistic effect to achieve good toughening effect. I used isocyanate polyurethane as a toughening agent, reacted with a secondary hydroxyl group on the epoxy resin by an isocyanate group, and introduced a flexible ether bond on the epoxy resin, thereby improving the toughness of the epoxy resin, and using the modified ring Oxygen resin is added with conductive filler to make conductive ink.

In terms of its application, it can be applied to flexible circuits and RFID. Flexible circuits are key components for realizing the multifunctionality, integration, miniaturization and low cost of electronic information products. With the development of electronic products and devices in the direction of lightness, thinness, low cost, multi-function, and high reliability, the amount of flexible circuits is increasing, and the use of conductive ink or conductive ink through printing or printing is flexible. The formation of conductive lines on an insulating substrate has attracted widespread attention. The test shows that the modified epoxy resin-based conductive ink has good adhesion, and the printed circuit has a flexural resistance of 10,000 times, which meets 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 uneconomical technology, and low-cost tag antennas printed with new conductive inks are low. Cost packaging technology will promote the large-scale production of RFID tags and become one of the key factors that determine the speed of development of the industry in the future. I modified the epoxy resin as a binder, conductive carbon black, conductive graphite as a conductive filler, plus an appropriate amount of curing agent, solvent and dispersant, prepared a modified epoxy-based conductive ink, and its performance Research, applied to RFID, the advantages of the antenna will be more and more prominent.

First, the preparation of materials and inks. 1.Preparation of polyurethane prepolymers: First add polyethylene glycol to a three-necked flask, and then heat and vacuum dehydrate for 1 hour. After cooling, recharge with nitrogen. Maintain the internal temperature at 80°C and add stoichiometric TDI as soon as possible. The molar ratio of TDI to polyethylene glycol is 1.2:1. After 4 hours of stirring, the reaction is stopped to obtain an isocyanate-terminated polyurethane prepolymer, which is cooled to room temperature and used. The n-butylamine method was used to measure the NCO content of 5%.

The polyurethane modified epoxy resin IPN was synthesized by adding an epoxy resin to a three-necked flask, stirring, and adding ethylene glycol ether acetate (CAC) while stirring until the epoxy resin completely dissolved, and then maintaining the internal temperature 70 °C, a stoichiometric polyurethane prepolymer was added, the mass ratio of epoxy resin to prepolymer was 9:1, reaction time was 2 hours, and polyurethane modified epoxy resin IPN was finally obtained.

Preparation of modified epoxy resin-based conductive inks, first mix conductive carbon black with a mass ratio of 3:2 and conductive graphite, and then add polyurethane modified epoxy resin IPN (mass ratio to the mixture is 6:25). A small amount of a curing agent (urethane resin), a solvent (cyclohexanone) and a dispersant (FA-196) were added and the mixture was 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 resin-based conductive inks. Differential scanning thermal analysis (DSC) was performed using a PerkinElmer DSC-7 thermal analyzer. The atmosphere was static air, and the temperature was increased. The DSC heating rate was 10°C/min. The temperature range is 35 to 180°C. 2. The flexible circuit board is resistant to bending, and TOS-817 rocking tester is used to test the bending resistance of the modified epoxy resin-based conductive ink printed circuit. The length of the conductive lines was 2.4 cm, width 0.9 mm, and thickness 3 μm. Five parallel values ​​were measured and averaged. The experimental parameters are as follows: swing angle: 180°; swing speed: 60 times·min-1; swing number: 10000 times; temperature: 28°C, relative humidity: 80%.

Modified epoxy resin-based conductive ink printed circuit line adhesion, 3M600# adhesive tape stuck on the cured printed sample line, conductive lines length 10cm, width 0.9mm, thickness 3μm, to ensure the long side of the adhesive tape Parallel to the direction of the conductive lines, rub it flat with a high-level drawing eraser, place it for 1 minute, and then pull the tape quickly and forcefully to observe whether the tape and the sample line are pulled off, and measure the change in line resistance before and after adhesion. Conductive lines measured 5 parallel values, averaged.

Third, the conclusion. An isocyanate-terminated polyurethane prepolymer synthesized by the reaction of 2,4-toluene diisocyanate and polyethylene glycol, which is used in the modification of epoxy resin, and modified epoxy resin as a binder, conductive carbon black and conductive graphite As a conductive filler, an appropriate amount of a curing agent, a solvent, and a dispersant are added to prepare a modified epoxy-based conductive ink. The test shows that the modified epoxy-based conductive ink has good adhesion, and printed conductive line resistance Flexibility reached 10,000 times.