Method of producing a coated substrate

#This invention relates to a method of producing coated substrates. In a further embodiment the present invention relates to a method of producing coated paper or paperboard.

#In the manufacturing of coated substrates usually coating compositions are applied to said substrate, for example, by blade type, bar type, or reverse roll type coating methods. The line speed may exceed 1,000 m/min. Any or all of these methods are commonly employed to sequentially apply coatings to the moving substrates.

#However, each of these application methods inherently has its own set of problems that can result in an inferior coated surface quality. In the case of the blade type coating method, the lodgment of particles under the blade can result in streaks in the coating layer, which lowers the quality of the coated paper or paperboard. In addition, the high pressure that must be applied to the blade to achieve the desired coating weight places a very high stress on the substrate and can result in breakage of the substrate web, resulting in lowered production efficiency. Moreover, since the pigmented coatings are highly abrasive, the blade must be replaced regularly in order to maintain the evenness of the coated surface. Also, the distribution of the coating on the surface of the paper or paperboard substrate is affected by the surface irregularities of the substrate. An uneven distribution of coating across the paper or paperboard surface can result in a dappled or mottled surface appearance that can lead to an inferior printing result.

#FIG. 1 is an explanatory cross-sectional view of a curtain coating unit 1 with a slide nozzle arrangement 2 for delivering multiple streams 3 of curtain layer to form a continuous, multilayer curtain 4. When a dynamic equilibrium state is reached, the flow amount of the curtain layers flowing into the slide nozzle arrangement 2 is completely balanced with the flow amount flowing out of the slide nozzle arrangement. The free falling multilayer curtain 4 comes into contact with web 5 which is running continuously and thus the web 5 is coated with multiple layers of the respective curtain layers. The running direction of the web 5 is changed immediately before the coating area by means of a roller 6 to minimize the effect of air flow accompanying the fast moving web 5.

#An advantage of the process of the present invention over the prior art is that a coated substrate having specific properties can be obtained by applying a curtain comprising at least two reactive compounds to a substrate. Said method allows one to prepare a coated substrate having specific layers imparting, due to the reaction of said reactive compounds, specific properties. As the methods known in the prior art apply an excess of coating color, they cannot effectively apply coatings comprising reactive compounds to substrates. Preferably, the coated substrates can be printed with any printing method customarily employed by persons skilled in the art.

#The present invention is exemplified by the following examples. All parts and percentages are by weight unless otherwise specified.

#The following materials were used to make the layers in the reactive coating structure:

#Carbonate: dispersion of calcium carbonate with particle size of 90%<2 μm in water (Hydrocarb® 90 ME available from Pluess-Stauffer), 77% solids.