Chemical solution spraying method

A chemical solution spraying method for spraying a chemical solution onto a canvas having a continuous canvas loop while reciprocating a nozzle device along a rail extending in a width direction of the canvas with respect to the canvas in a dry part of a paper-making machine, wherein

• the canvas is guided by a dryer roll with the canvas contacting wet paper, and is then guided by a canvas roll with the canvas separating from the wet paper,
• a time period Tc during which the canvas is in contact with the wet paper is 0.03 seconds or more,
• a distance of the canvas travels during the time period Tc is 0.5 to 16 m,
• a time period Tn required for the nozzle device to one-way move is 1 to 20 minutes,
• a traveling speed Vp of the canvas is 500 m/min or more,
• a length K of the canvas is 20 to 80 m,
• a number of times of contact N of any point on a surface of the canvas with the wet paper during the time period Tn, the time period Tn, the traveling speed Vp, and the length K satisfy a relationship of N=(Tn·Vp)/K, and the number of times of contact Nis 50 to 150, and
• a spray amount of the chemical solution is 0.1 to 500 mg/m2 as a total amount of components other than water in the chemical solution,
• an air permeability of the canvas is 2000 to 50000 cm3/cm2·min,
• the canvas roll includes an outside canvas roll positioned outside the canvas and an inside canvas roll positioned inside the canvas, and
• the nozzle device sprays the chemical solution onto the canvas in a time period elapsed until the canvas contacts the outside canvas roll after separating from the wet paper.