International Paper Company

K Krishna Mohan

Alexander A Koukoulas

Michael J Smith

A paperboard product having at least one layer of bleached or semi-bleached pulp and having improved smoothness and reduced bulk loss. For paperboard having sizing without pigment, the smoothness on the printed side, measured by the Parker test is better (lower) than 6.5 when measured using a pressure of 10 kgf/cm while the smoothness measured by the Hagerty/Sheffield test is not below 280 Sheffield units. For paperboard having sizing with pigment, the Parker smoothness is less than 5.0 and the Hagerty/Sheffield smoothness is not less than 180 Sheffield units. The web is finished by applying temperature and moisture gradients, then smoothing the web surface using extended nip calendering. The surface temperature of the calendering roll is maintained at 250-400&deg; F. Prior to entering the extended nip, the web surface is moisturized using steam showers. The nipload applied in the heated extended nip is preferably between 300 to 2,500 pli.

Paperboard of improved smoothness and bulk

A paperboard product having at least one layer of bleached or semi-bleached pulp and having improved smoothness and reduced bulk loss. For paperboard having sizing without pigment, the smoothness on the printed side as measured by the Parker test is better (lower) than 6.5 when measured using a pressure of 10 kgf/cm,while the smoothness measured by the Hagerty/Sheffield test is not below 280 Sheffield units. For paperboard having sizing with pigment, the Parker smoothness is less than 5.0 and the Hagerty/Sheffield smoothness is not less than 180 Sheffield units. The web is finished by applying temperature and moisture gradients to the web and then smoothing the web surface using extended nip calendering. The surface of the calendering roll is maintained at a temperature of 250-400&deg; F. Prior to entering the extended nip, the web surface is moisturized using steam showers. The nipload applied in the heated extended nip is preferably in the range of 300 to 2,500 pli.

Method for finishing paperboard to achieve improved smoothness

A calendering method which enhances the smoothness of surface sized paper/paperboard by a combination of temperature and moisture gradient calendering processes without the fiber sticking/picking problems that affect runnability and without using waterboxes. The moisture gradient calendering is performed so that the cross direction moisture profile can be corrected and high smoothness levels can be obtained. Heated calender rolls form a hot pressure nip having a temperature greater than the temperature of the moisturized web. Lubricant is applied to both sides of the web to prevent fiber sticking/picking in the hot nip. The lubricant may be applied by the size press, by the moisturizing showers or by separate lubricant showers. The smoothness developed by moisturizing and hot nip calendering is substantially irreversible.

Method for calendering surface sized paper/paperboard to improve smoothness

A multilayer linerboard product having a top layer made up of bleached/unbleached virgin or recycled pulp and at least one bottom layer made up of unbleached pulp. The external surface of the top layer has reduced gloss mottle and improved printing properties. In particular, the top surface of the multilayer linerboard has a Parker smoothness less than 6.5 and a Hagerty/Sheffield smoothness in the range of 240 to 280. Print voids on a flexo printed product are less than 0.20% (by area) as measured by image analysis. These improvements are achieved in an extended nip calender section having a heated calender roll, a backing roll or shoe and a conformable belt. Preferably, the nip width is 1 to 25 cm. The temperature of the surface of the heated calender roll is preferably maintained in the range of 300 to 500&deg; F. The nipload between the heated calender roll and the conformable belt is preferably maintained in the range of 500 to 2,500 pli.

Growing community of inventors

Staten Island, NY, United States of America

K Krishna Mohan