Coating method of coating solution
View Patent ↗In an aspect of the coating method according to the present invention, the lower limit decompression degree P S1 at which a seam trouble occurs is obtained from the formula of the viscocapillary model. According to the aspect of the present invention, coating is performed by setting the P b so as to satisfy P S1 <P 0 −P b ≦P S1 +0.2, and therefore, stepped unevenness can be effectively suppressed so that a seam trouble does not occur. It goes without saying that the aspect of the present invention can be applied to high viscosity/thick film coating, but it is effective especially in the case where a coating solution with low viscosity (for example, 0.005 Pa·s or lower) is coated to be an ultra-thin film (for example, 10 μm or less in the wet film thickness) where stepped unevenness easily occurs.
1. A coating method for discharging a coating solution from a slot tip end of a slot die, to which a lip land is closely disposed, to a web surface which continuously travels while being supported by a backup roller to form a bead between the slot tip end and the web, and coating the coating solution on the web surface while decompressing a web upstream side of the bead, comprising the steps of:
setting P b so that a decompression degree P 0 −P b (kPa) at the web upstream side with respect to a web downstream side of the bead satisfies the following formula:
P S1 <P 0 −P b ≦P S1 +0.2
where
P
S
1
=
1.34
(
μ
v
/
σ
1
)
2
/
3
(
σ
1
/
h
)
-
σ
4
(
1
+
cos
θ
)
d
+
12
μ
vl
1
{
(
d
/
2
)
-
h
}
d
3
P 0 : pressure at the web downstream side of the bead
P b : pressure at the web upstream side of the bead
μ: viscosity of the coating solution (Pa·s)
v: coating speed (m/min)
σ 1 : surface tension of a downstream side bead (N/m)
σ 4 : surface tension of an upstream side bead (N/m)
h: wet film thickness of the coating solution coated on the web (m)
d: a coating gap between the lip land and the web (m)
l 1 : length in a web traveling direction of a downstream side lip land (m), and
θ: a contact angle of the web and the bead; and
performing coating while suppressing a stepped unevenness of the film thickness of the coating solution,
wherein the viscosity of the coating solution (μ) is 0.005 Pa·s or lower,
wherein the wet film thickness of the coating solution coated on the web (h) is 10 μm or less, and
wherein a coating gap d of the lip land and the web is set so as to satisfy the following formula:
d= (2 h/ 1.34)(μ v/σ 1 ) −2/3 ×α
0.25≦α<1.
2. A coating method for discharging a coating solution from a slot tip end of a slot die, to which a lip land is closely disposed, to a web surface which continuously travels while being supported by a backup roller to form a bead between the slot tip end and the web, and coating the coating solution on the web surface while decompressing a web upstream side of the bead, comprising the steps of:
firstly obtaining a lower limit decompression degree P S1 (kPa) at which a seam trouble begins to occur to a coating solution film surface coated on the web when the decompression degree P b (kPa) at the web upstream side of the bead is made smaller by a preliminary operation;
after said obtaining step, setting P b so that a decompression degree P 0 −P b (kPa) at the web upstream side with respect to a web downstream side of the bead satisfies the following formula in a full-scale operation:
P S1 <P 0 −P b ≦P S1 +0.2
where
P 0 : pressure at the web downstream side of the bead, and
P b : pressure at the web upstream side of the bead; and
after said setting step, performing coating,
wherein a viscosity of the coating solution (μ) is 0.005 Pa·s or lower,
wherein a wet film thickness of the coating solution coated on the web (h) is 10 μm or less,
wherein a stepped unevenness of the film thickness of the coating solution is suppressed during said coating step, and
wherein a coating gap d of the lip land and the web is set so as to satisfy the following formula:
d= (2 h/ 1.34)(μ v/σ 1 ) −2/3 ×α
0.25≦α<1.