FI119112B - Cardboard finishing procedure - Google Patents

Description

j 119112

Method for post-treatment of cardboard

The present invention relates to a method for post-treatment of paperboard.

Patent FI111281 discloses a post-treatment method for paperboard, especially WLC board, where a long nip calendering is performed prior to the actual pigment coating step. The disadvantage of this method is that, especially in WLC grades, the recycled backing layer contains, for example, hot melt adhesives used in the sealing of packages, which adhere to the surface of the soft nip of the long nip calender, which is a major problem. In practice, soiling causes the machine to stop and the belt to be washed by hand. In addition, the cardboard has a soft backing and collapses.

Accordingly, it is an object of the present invention to provide an improved process for post-treatment of 15 cartons, which at least substantially eliminates the above disadvantages, resulting in clearly smoother cartons.

To accomplish this object, the process of the invention is characterized in that the process first comprises at least 20 pigmentation or pigment coating pre-treatments on the backing of the paper web, then the web is passed through a long nip calender and then to the actual coating gun. to form a plurality of coating layers on the surface of the web surface layer (3).

· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · surface sizing, pigmentation and pigment coating. However, it is always necessary to · · · disperse the sticky particles to a suitable particle size, since large sticky particles are not adhered to or adhered by the pigment paste or pigment coating. cover. Further, the efficiency of the process according to FI 111281 can be improved. 30 by treating the surface of the web with a specific chemical, which improves the surface smoothness of the cardboard.

• · · · ··· • *: '·· Surface sizing, pigmentation or pigment coating of the web prior to long nip calendering reduces the web compression on the backing and thus saves the thickness of the 2 119112 board, which is important for one of the board's key features, namely stiffness . The pre-treatment itself increases the rigidity of the paperboard as well as the surface strength and the elastic modulus of the surface layer, which also has a great beneficial effect on the rigidity of the paperboard.

5

The starch adhesive used in surface sizing softens at the high temperature of the long nip heater coil at a typical surface temperature of more than 150 ° C and prevents the flat surface resulting from calendering roll compression from returning to the roughness prior to calendering. The softening of the surface adhesive can be controlled by modified grades of starch which can be cold-soluble instead of the conventional starch dissolution temperature of 90 ° C. Other surface adhesive chemicals may also be used to achieve the same purpose, e.g., CMC or polymer dispersion or emulsion. The surface adhesive on the surface of the paperboard increases the rigidity of the paperboard as well as the surface strength and the elastic modulus of the surface layer, which also has a great advantageous effect on the rigidity of the paperboard.

Pigmentation using a mixture of starch and coating paste or pigment coating (= coating paste) per se improves the smoothness of the surface or contributes to smoothness by filling at least the largest pores of the web before the actual coating portion. Due to the high temperature of the thermal roller, fiber bonds are also formed on the surface of the web, so the amount of coating must be optimized so that the amount of coating on the long nip calender is not too high for heat transfer. naan.

After the pretreatment step, it is preferable to perform at least partial intermediate drying. Ai- ····. * ··. least the back side is good to be close to equilibrium moisture content of cardboard packaging cardboard • V · · · preserve the industry as good as possible. On the surface side, higher moisture content of the web would be advantageous to achieve good smoothness. Therefore, drying is done * ♦. ···. preferably at least mainly from the back of the web.

«·· 30 • ♦ ·

A particularly advantageous process for pre-treating the web before long nip calendering is a film press coating that can perform both sides before: * ·· long nip calendering and where the pre-treatment can also be done with different coating agents on the different sides of the web. The porous coating has a high pore volume of 3,119,112 capable of binding even a large amount of high temperature melt adhesive. The high viscous melt adhesive has a high flow resistance through the pigment coating, which contributes to preventing the adhesive flow to the web surface. whereby the fibers in the direction of plane 5 are always quite close to the surface of the web and the heat conduction through the pre-treatment coating is even. The film press is also advantageous from an investment point of view. s, pigmentation and pigment coating with virtually any solids content and amount of the treatment agent.

10

The process according to the invention can be combined with sub-processes known per se, e.g. to further improve the thickness and smoothness of the web with other calendars before or after the long nip calender or further after the actual coating portion. Still other calendars can be used to enhance the result, for example steam-15 or water treatment.

The invention will now be described in more detail with reference to the accompanying drawing, in which: Figure 1 schematically illustrates the structure of a typical WLC board, and

Figure 2 schematically illustrates an arrangement of a honeycomb according to the invention. to perform the method.

• * * • · · * ·· · • · ·::. ·. Figure 1 is a schematic representation of a multilayer structure of a WLC board, which in the illustrated embodiment includes a bottom layer of a recycled pulp ····. (backing) 1, as well as filler layer 2, recycled pulp layer 3, and pulp layer 4, which may consist of several coating layers.

• ♦ • ♦ ♦ • · · • ·. · ♦ ·. The exemplary embodiment of Figure 2 illustrates a post-treatment of the invention. 30 processing method, wherein the computer board from the board web W is passed first pretreatment • · *; ./ treatment step 11, at least the backside of the web handling, pigmentation • · **; * 'or pigment coating. Preferably, surface pre-coating and background treatment in a single step with a film press prior to long nip calendering. There may also be pre-calendering prior to overwrapping, especially if the overcoating is done on both 4,111,112 sides of the web. The pigment coating is easily calendered and, depending on the binders, improves the surface-hardening effect of the fiber bonds in a controlled manner, e.g. PVA or starch lysse binder, i.e. prevents surface roughness from recovering and thus enhances calendering. The surface finish of the front end I absorbs less water and swells less in subsequent coating steps. The amount of pre-coating in a film press can be very small e.g. 4g / m2 which, for example, carton itself does not improve smoothness but efficiently fills large pores of the surface, i.e. its overall effect is more of a functional layer than of surface smoothing coating itself.

After pre-treatment, the web is preferably passed through an intermediate drying step (not shown) through a long nip calender, for example a shoe calender 12 or a belt calender shown in Figure 2. Following the long nip calender, the web is preferably passed through a machine calender 10, which improves surface smoothness, to the actual coating portion 13, which may be, for example, a spray coating apparatus, a curtain coating apparatus or a blade 15 / rod coating apparatus. In this coating section, one or more coating layers are applied to the surface of the web to achieve the desired coverage. After coating, the web is further subjected to final calendering, for example with a soft calender 14 or a multi roll calender, to improve the smoothness and gloss of the web.

•••••••••••••••••••••••••••••••••••••••••••••••••• ·····•••••••••••••••••••••••••••••••••••••••••••••••••••••• • · • ♦ * «· • ♦ · • ·· • ·

Claims (14)

119112 A method for post-treatment of a paperboard, characterized in that at least the backing (1) of the paper web (W) is first subjected to a pigmentation or pigment coating pre-treatment (11), then the web is passed through a long nip calender (12) and subsequent calender (13) for forming one or more coating layers on the surface of the surface layer (3) of the web. Method according to claim 1, characterized in that in method 10, the cardboard web (W) is pre-treated (11) on both the backing and the surface side. A method according to claim 2, characterized in that the method comprises a surface sizing pretreatment (11) on the surface of the paperboard. Method according to one of Claims 1 to 3, characterized in that the method uses a long nip calender and / or a roll nip calender. Method according to one of Claims 1 to 4, characterized in that the web is dried at least partially after the pretreatment (11) before the long nip calender. 20 6. A method according to claim 5, characterized in that the drying is carried out in such a way that the cardboard surface after drying is more humid than the backing. half. • • • • • • • • t «· Method according to one of Claims 1 to 6, characterized in that on top of 1. there may be a final calendering after the staging station (13). • · ·· ♦ A method according to any one of claims 1 to 7, characterized in that the precursor • ♦ ·. ···. the treatment (s) is performed with a single-sided coating. The process according to any one of claims 1 to 7, characterized in that the pre-treatment (s) are made by a coating which processes both sides at the same time. ·· • · t ♦ · · ♦ · · · · ♦ • · 119112 Method according to one of Claims 1 to 9, characterized in that before and / or after the long nip calender, a hard or soft nip calendar is used, which is optionally preceded by water, glue or steam wetting at least on the surface of the web. 5 11. A method according to any one of claims 1-9, characterized in that the long-nip before and / or after the used hard nip or the soft-nip-s calendar, wherein at least one side of the board top side surface of the roller is optionally provided water or an adhesive film for processing the web of the web superficial least 10 lelta . Method according to one of Claims 1 to 9, characterized in that, before the long nip calender, water, adhesive or steam wetting of the web is carried out at least on the surface side of the web. 15 Method according to one of Claims 1 to 12, characterized in that the surface treatment agent applied to the web surface uses a release agent to prevent the coating from sticking to the roll or belt of the long nip calender. Method according to one of the preceding claims, characterized in that pre-calendering of the web is carried out before the web is pretreated (11). • • • • • • • • • 1 · t «• • • • • • • • • • • • • • • • • • • • • • • • • • •••••••••••••• • • • 1 1 • I 1 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • · 119112