Slide-bead coating method and apparatus with coating liquid containing polyvinyl alcohol

A slide-bead coating method where a slide-hopper coating apparatus makes a plurality of coating liquids containing polyvinyl alcohol flow down along a slide surface and coats a running web with the coating liquids through a bead part formed between an end of the slide surface and the running web to simultaneously form a plurality of layers on a surface of the running web, wherein:

• an inclining angle of the slide surface with respect to a horizontal plane is within a range between 5° and 30°;
• a total thickness T [mm] of the coating liquids on the running web is smaller than a total thickness S [mm] of the coating liquids flowing down along the slide surface;
• a bead clearance CL [mm] between the end of the slide surface and the running web at the bead part is determined in accordance with the total thickness T [mm] of the coating liquids on the running web in an inequality (1),
• T+0.05<CL<2T+0.1;
• and
• a bead back pressure P [mmH2O] reduced at a bottom of the bead part with respect to an atmospheric pressure is determined in accordance with the bead clearance CL [mm] in an inequality (2),
• 2/CL+20<P<10/CL+20.

A slide-bead coating apparatus, comprising:

• a slide hopper having a slide surface of which an inclining angle with respect to a horizontal plane is within a range between 5° and 30°, a coating liquid containing polyvinyl alcohol flowing down along the slide surface, the coating liquid being applied on a surface of a running web through a bead part formed between an end of the slide surface and the running web, a thickness T [mm] of the coating liquid on the running web being smaller than a thickness S [mm] of the coating liquid flowing down along the slide surface;
• a backing roller which supports the running web, the backing roller being arranged with respect to the slide hopper to form a bead clearance CL [mm] between the end of the slide surface and the running web at the bead part satisfying an inequality (1),
• T+0.05<CL<2T+0.1;
• and
• a pressure reduction device which reduces a bead back pressure P [mmH2O] at a bottom of the bead part with respect to an atmospheric pressure satisfying an inequality (2),
• 2/CL+20<P<10/CL+20.

A slide-bead coating apparatus, comprising:

• a slide hopper having a slide surface of which an inclining angle with respect to a horizontal plane is within a range between 5° and 30°, a plurality of coating liquids containing polyvinyl alcohol flowing down along the slide surface, the coating liquids being applied on a surface of a running web through a bead part formed between an end of the slide surface and the running web, a total thickness T [mm] of the coating liquids on the running web being smaller than a total thickness S [mm] of the coating liquids flowing down along the slide surface;
• a backing roller which supports the running web, the backing roller being arranged with respect to the slide hopper to form a bead clearance CL [mm] between the end of the slide surface and the running web at the bead part satisfying an inequality (1),
• T+0.05<CL<2T+0.1;
• and
• a pressure reduction device which reduces a bead back pressure P [mmH2O] at a bottom of the bead part with respect to an atmospheric pressure satisfying an inequality (2),
• 2/CL+20<P<10/CL+20.