Patent ID: 8304027

Claim:
A bar coating method for applying a coating liquid to a traveling web, comprising the steps of: applying a coating liquid in a reservoir onto a traveling web by rotating a bar; forming a bead of the coating liquid in a space between the web and a leading end surface provided at a distal end portion of a weir which is arranged at the upstream side of the bar, the leading end surface having an upwardly inclined surface at an angle θ to the horizontal; and supplying the coating liquid to the reservoir and discharging the coating liquid excessively supplied to the reservoir through a liquid discharge passage, wherein an amount of the coating liquid supplied to the reservoir satisfies the following expressions (1) to (4), 0≦Δ P 1−ρ gH≦ΔP 2 (1) Δ P 1=12η qL/δu 3 (2) Δ P 2=(6η U/a )×(1/ h 0 −aX b )−1 /h 0 ) (3) q=Q /(60×ρ× W ) (4) where η designates a viscosity [Pa·s] of the coating liquid, q designates a flow rate per unit width [m 2 /s] of the coating liquid flowing through the liquid discharge passage, Q designates a supply amount [kg/min] of the coating liquid, ρ designates a density [kg/m 3 ] of the coating liquid, L designates a length [m] of the liquid discharge passage, U designates a traveling speed [m/s] of the web, “a” designates a gradient (=tan θ) of the leading end surface of the weir, h0 designates a clearance [m] between a start point of the leading end surface of the weir and the web, X b designates a length [m] of the bead, H designates a height [m] of the weir from the liquid discharge passage to the start point of the leading end surface, W designates a width [m] of the liquid discharge passage, δu designates a clearance [m] of the liquid discharge passage, and “g” designates a gravitational acceleration [m/s 2 ].