Method and system for manufacturing a coated paperboard and a coated paperboard
The present invention relates to a method for manufacturing coated paperboard suitable for packaging paperboard applications. The method comprises coating a first surface of the paperboard web by applying a) a first coating composition in a precoating unit for forming a precoating layer comprising inorganic mineral pigment particles and least one binder for sealing the first surface of the paperboard web; and b) a second coating composition in a curtain coating unit for forming at least one barrier coating layer on the first surface of the paperboard web; and c) a third coating composition comprising a polymer dispersion in the curtain coating unit for forming at least one heat sealable coating layer on the first surface of the paperboard web. The temperature of the coated paperboard web is controlled and adjusted, and the paperboard web is cooled in at least one cooling unit.
1. A method for manufacturing coated paperboard
by providing a repulpable multilayer coating on a first surface of a paperboard web in a paper manufacturing system comprising a precoating unit, a curtain coating unit, an adjustable heating unit, a cooling unit, and a jumbo reel onto which resulting multilayer coated paperboard is reeled, the method comprising
a) forming a precoating layer directly onto the first surface by applying 4-20 g/m 2 of a first coating composition in a precoater which is a size press or a metering size press, said first coating composition comprising inorganic mineral pigment particles selected from particles of calcium carbonates, and kaolin, and at least one binder selected from synthetic polymer latex, polyvinyl alcohol and starch for sealing the first surface of the paperboard web,
b) forming at least one barrier coating layer directly on the precoating layer by applying a second coating composition in form of an aqueous polymer dispersion in the curtain coating unit, wherein the aqueous polymer dispersion is selected from latex dispersions, polyvinyl alcohol dispersions and polyolefin dispersions and wherein the second coating composition is applied in an amount of less than 20 g/m 2 , and
c) forming at least one heat sealable coating layer directly on the at least one barrier coating layer by applying a third coating composition consisting of a polymer dispersion in the curtain coating unit,
wherein the second and third coating compositions are applied simultaneously as aqueous dispersions without intermediate drying in between application of the coating compositions, and the third coating composition forms the outermost surface of the coated paperboard,
d) allowing the third coating composition to partially or fully melt in the heat sealable coating layer to form a film surface by controlling and adjusting the temperature of the coated paperboard web to a temperature of 90-150° C., and
e) cooling the paperboard web in at least one cooling unit to reduce tackiness of the coated paperboard web before reeling to the jumbo reel.
2. The method according to claim 1 , wherein the temperature of the paperboard web after the temperature adjustment is cooled down to a temperature below 50° C.
3. The method according to claim 1 , wherein the paperboard web is calendered after forming the precoating in step a) and/or after cooling in step e).
4. The method according to claim 1 , wherein the precoating is also formed on a second surface of the paperboard web.
5. The method according to claim 1 , wherein at least the first surface of the paperboard is exposed to electrical surface modification treatment before winding the coated paperboard web onto jumbo reel.
6. The method according to claim 5 , wherein the surface energy of the first surface of the coated paperboard web is charged by the electrical surface modification treatment.
7. The method according to claim 5 , wherein the electrical power used in the electrical surface modification treatment is less than 50 W/m 2 /min.