DEVICE FOR CONTROLLING COATING LIQUID CONCENTRATION

PROBLEM TO BE SOLVED: To control highly accurately the concentration of coating liquid during printing by calculating and indicating the concentration of fluid in terms of a detected ultrasonic speed and temperature of fluid consisting of coating liquid such as printing ink or the like, and controlling the concentration to maintain a predetermined range in accordance with the detection results of the concentration. SOLUTION: A coating liquid control device is installed in contiguity with an ink tank 5 for circulation supply of ink to a printing device by an ink pump 60. Also, an ultrasonic speed measuring device 2 is provided with an ink concentration indication part 21, a setting indication part 22, and an ink temperature indication part 23, and a ultrasonic oscillator 25 is connected thereto by a cable 26. Furthermore, a control part 3 is provided with CPU 31 to obtain a relational expression between a ultrasonic speed and ink concentration of fluid to be an objective for every temperature, thereby calculating a concentration value from the measured ultrasonic speed and ink concentration. The solenoid valve 13 for solvent of a diluted solvent addition part 1 receives a signal from the control part 3 to be controlled in the open and close period of time, and the addition quantity of a solvent is controlled to adjust highly accurately the concentration.