Method for coating a paper web

Abstract

The invention relates to a method for coating a paper web (1), comprising the steps in the following sequence: applying a first layer (20) made of a predetermined quantity of melamine resin to a first side of the paper web (1), first drying of the thus coated paper web (1) at a web temperature of at least 120 C., applying a second layer (21) made of a predetermined quantity of urea resin to a second side of the paper web (1), and second drying of the paper web (1) at a web temperature below 100 C.

Claims

1. A method of coating a paper web, the method comprising the steps of sequentially: applying a first layer composed of a predetermined quantity of only melamine resin to a first face of the paper web; first drying the paper web immediately after the application of the first layer at a web temperature of between 110 and 140 C.; applying a second layer composed of a predetermined quantity of only urea resin to a second face of the paper web; and second drying the paper web to which the second layer is applied at a web temperature of between 90 and 110 C.

2. The method according to claim 1, wherein the paper web is a decor paper.

3. The method according to claim 1, further comprising the step of: adding hard particles to the melamine resin prior to application to the first face of the paper web.

4. The method according to claim 1, further comprising the step of: conveying the web at a web speed is at least 15 m/min during application of the first and second layers and drying.

5. The method according to claim 1, wherein the application of the first layer is effected in a gap.

6. The method according to claim 5, wherein the gap is defined between a catch element and a deflecting roller.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention is described below in more detail with reference to the attached schematic drawing. Therein:

(2) FIG. 1 is a side view of an apparatus for carrying out the method, and

(3) FIG. 2 is a section through a coated paper web.

SPECIFIC DESCRIPTION OF THE INVENTION

(4) As shown in FIG. 1, an apparatus for carrying out the method comprises an unwinder 2 for a paper web 1, a first applicator 3, a first drier 4, a second applicator 5, and a the second drier 6. An unillustrated take-up roller or a cross-cutter including a stacker are provided downstream of the second drier 6.

(5) The paper web 1 is composed of a printed or unprinted paper weighing between 20 and 250 g/m.sup.2. In the case of a printed paper web 1, the paper's first face is the printed face.

(6) The first applicator 3 used to apply a first coating compound to the first face of the web 1 comprises a deflecting roller 7 to redirect the web 1 and a feed roller 8. The deflecting roller 7 and the feed roller 8 are offset from each other both vertically and but have parallel rotational axes.

(7) A catch element 9 associated with the deflecting roller 7 is formed by an essentially planar plate extending parallel the axial length of the deflecting roller 7. The element 9 is below the feed roller 8 and forms a gap 10 with the deflecting roller 7. This element extends at an acute angle to the vertical in the wrap-around zone of the web 1 on the deflecting roller 7, and approaches at a lower end region so close to the roller's outer surface that it almost touches the web 1 tangentially and seals the gap 10 at the bottom. The axial ends of the gap 10 are open. A manifold 11 introduces the first coating compound into the gap 10 and is connected to a supply line. A drip tray 12 below the deflecting roller 7 collects any overflow of the first coating compound. The drip tray 12 is a connected to a recirculation system for the first coating compound.

(8) The feed roller 8 and the deflecting roller 7 form a narrow adjustable feed gap.

(9) The first drier 4 is downstream in the transport direction (arrow P) of the first applicator 3 and is a circulating-air, flotation drier. A spacing between the first applicator 3 and the first drier 4 is kept as small as possible, measuring less than 2 m. Combined with a high web speed, a first drying is effected in terms of time and space immediately following an application of a first layer 20 so as to essentially prevent saturation of the web 1.

(10) The second applicator 5 for applying a second coating compound to a second face of the web 1 is downstream of the first drier 4, and comprises an anilox roller 13 and two pressure rollers 14 that provide a predetermined wrap angle of the web 1 on the anilox roller 13. Urea resin can be applied using conventional means as the second coating compound and the supply can be regulated, for example by a doctor blade.

(11) The second drier 6 is downstream of the second applicator 5 and essentially corresponds to the first drier 4.

(12) In a so-called breathing section is provided between the second applicator 5 and the second drier 6 the web 1 passes through multiple loops so as to extend the travel distance, thereby achieving the greatest possible saturation of the web 1.

(13) When operating, the web 1 is pulled off a supply roll that is mounted in the unwinder 2 and moved to the first applicator 3. Here the web 1 is moved around the deflecting roller 7 and through the feed gap.

(14) The speed of the web 1 is at least 15 m/min.

(15) Any excess amount of the first coating compound is pumped from a supply tank through the manifold 11 into the gap 10. A portion of the first coating compound, which is essentially composed of melamine resin in aqueous solution and optional hard particles, is entrained as the first layer 20 by the first face of the web 1 and fed at a predetermined grammage in the feed gap. Excess amounts of the first coating compound flow out the open ends of the gap 10 into the drip tray 12. From here the excess first coating compound is recirculated back into the supply tank.

(16) The web 1 including the first wet layer 20 then enters the first drier 4 and is dried here to a predetermined residual moisture level at relatively high temperatures at which the web temperature reaches between approximately 110 and 140 C.

(17) Since very little time elapses between the application of first layer 20 and the first drying, the first coating compound only incompletely saturates the web 1. This is intentional so that the first layer 20 gets as much as possible as the wear-resistant layer.

(18) Following the first drying, the second coating compound composed of urea resin in aqueous solution is applied in a predetermined quantity in the second applicator 5 to a second face of the web 1 as the second layer 21.

(19) The web 1 including the layers 20 and 21 then passes through a dwell section in which the second coating compound penetrates into the web 1 such that the web is partially infused with the first coating compound and otherwise infused with the second coating compound.

(20) Downstream of the dwell section, the coated web 1 is dried in the second drier 6 to a predetermined final moisture level such that a web temperature measures 90 to a maximum of 110 C.

(21) Following the second drying, the finished coated web 1 is either cut into sheets that are stacked, or wound up into a roll.

(22) A layer structure for the finished coated and dried web 1 is shown in FIG. 2. The first layer 20 is formed on the first printed top face here of the web 1. This layer penetrates only partially through the web 1, as indicated by a dotted line 22. The second layer 21 is applied to the second face of the web 1 that is opposite the first and is contiguous with first layer 20 inside the paper.

(23) The invention is described based on one embodiment in which the first layer 20 is applied in the gap 10 and the second layer 21 is applied with an anilox roller 13. Other known coating apparatuses can also be used instead of these application methods.