EP1664432B1 - Method and device for producing decorative paper and the use thereof - Google Patents

Description

The invention relates to a method for producing a decorative paper with a pigment coating and the advantageous use of such decorative paper for decorative coating purposes.

Previously, when filling the base base paper mainly used titanium white pigments, possibly with pigment blends. The base paper had, for example, a basis weight of about 75 g / m ² . In order to achieve the necessary opacity in view of the various applications in decorative paper, it has been customary to adjust the amount of titanium white pigment to about 40% by weight. Usually short fibers (for example about 80%, for example eucalyptus pulp) and long fibers (for example about 20%, usually softwood pulp) were predominantly used in the production of the base paper. This is usually followed by an equilibrium impregnation, ie, about 75 g / m ^{2 of} impregnating resin were applied. The production of such decorative paper was done in a paper machine, but no coating device was integrated. The impregnation could be done in a variety of ways, for example, on-line or off-line processes by soaking, dipping or coating.

From the above descriptions, it becomes clear that it was difficult to produce lightweight papers. Here, certain limits are set, since the necessary to achieve the required opacity titanium dioxide pigment content due to the low pulp mass was not easy to incorporate. In the method described above, further disadvantages occur. Thus, in the production of the raw paper, a not inconsiderable proportion of the titanium white pigment enters the wastewater. This is economically disadvantageous because titanium white pigments are very expensive. Although the titanium white pigment can be circulated in the case of optimal process control. However, this means an extra effort and often leads to an undesirable circulation load.

The problems addressed are in part solved by a proposal of the prior art, which is known from the publication of the Paper Technology Foundation (PTS), Munich, entitled "The saving of titanium dioxide filler by optimizing the pigment distribution in the paper", ( see ISSN0937-2091, 1st edition, 1998, December 1998 edition). This results in a reduction of the mass of titanium dioxide in the base paper. This reduction is compensated by a coating color with an adjusted content of titanium white pigment. The application of the coating color takes place here after the film pressing process.

The principle of the film press job is to apply a coating of paint film to a roller. There is a predosing with a doctor device, often grooved or smooth rods are used. It is usually applied on both sides. This process has significant disadvantages, especially at high speeds due to high mechanical wear of the application, metering and leveling elements (rollers, doctor blade, metering application) due to the abrasiveness of the pigments. In addition, by opening the nip often paint mist, filament formation (threads or thread pull) and drop formation. This results in unpleasant machine fouling, line defects and unwanted irregularities in the coating surface. It occurs the so-called "orange peel effect". These adverse effects occur especially at high order speed in appearance. Another disadvantage of this method is that the paper web is subjected to so much mechanical stress that it frequently leads to breaks in the film press coating, which has a particularly disadvantageous effect on on-line operation.

The decorative papers produced by the known processes show no satisfactory printability. Desirable high retention of the pigments is achieved only incompletely. The dry application of the coating color is about 3 to 30 g / m ² , preferably 8 to 20 g / m ² .

US 5,820,937 describes a method for producing a wear-resistant paper sheet. A web of cellulosic fibers is produced on a papermaking machine and a gravel-containing slurry is applied to the surface of the web.

EP 1 249 533 A1 describes a process for producing a multi-layered paper. At least two coating liquids are combined and applied to the paper by means of a free-falling curtain.

WO 02/066739 A1 discloses a coating color and method for producing coated paper or board. The coating color is applied in a free-falling curtain on a running paper or board web, wherein initially prepared an aqueous pigment dispersion and subjected to degassing. After degassing, a thickener and a surfactant are admixed as additives with exclusion of air from the pigment dispersion.

The DE 197 16 647 A1 describes a method and apparatus for applying a pigment coating paint to a paper or board web. The coating color is applied to a paper web by means of a slot die in a free-falling curtain.

The state of the art is still on the US-A-5 820 937 , the EP-A-1 349 533 , the WO-A-02/066739 and the DE-A-1 97 16 647 be pointed out, but from which no references to the specific production of decorative paper can be removed.

The object of the invention has been found to remedy the above-mentioned disadvantages of the prior art, in particular to ensure a trouble-free process management and a reduction in the cost of raw material with extensive exclusion of retention problems, in particular, the fastest possible process control is provided.

This object is achieved in that an aqueous coating color is applied to a base paper optionally filled with pigments in a contactless manner by means of the curtain coating or coating method known per se, wherein a base paper weight of optionally filled with pigments is filled with pigments about 28 to 65 g / m ² and an aqueous Spreading a solids content of about 30 to 70 weight% is assumed, and is dried.

After application of the coating color, the paper web is dried in the usual way. This is generally carried out in a temperature range of about 70 to 450 ° C, in particular from about 80 to 250 ° C, wherein in most cases contactless drying units, such as infrared and air dryers are first directed to the freshly coated web surface and then a cylinder Contact drying takes place.

The core idea of the process according to the invention is the curtain application (curtain coating process) with the significant advantage that the aqueous coating color can be applied without contact to the respective base paper, in the present case optionally filled with pigments. The order can be carried out advantageously in a 1: 1 ratio. This means that the amount of coating that is applied will remain on the surface of the paper without being scratched. In this case, no squeegee devices with squeegee elements, such as squeegee blades or squeegee blades, which are heavily subject to wear, need not be used. This and also due to the low circulation amount of coating color can save costs. In addition, the running properties of the manufacturing and / or finishing machines for the decor paper web improve. The curtain application method is particularly advantageous where it depends on a wear-free application of abrasive pigments. The curtain application unit consists essentially of a container having a slot nozzle, from which the spreadable coating or coating color in free fall under the influence of gravity, but also under the influence of electrostatic forces on the respective paper web or their surface to be coated is applied. In particular, the following parameters can be varied: application quantity, web width, nozzle gap opening and selected pressure which acts, curtain fall height and, if necessary, the angle of the running paper web to the horizontal or to the curtain. The curtain delivered by the application unit deposits on the surface of the paper web as a contour line and ensures a surface with high finishing quality.

The aqueous coating color used can be advantageously designed as follows: The solids content of the coating composition is preferably about 40 to 60% by weight. If the value falls below 40 wt .-%, then the order weights to be achieved are too low. A value of more than 60% by weight means that, especially when this amount of the solid is substantially due to the pigment content, the continuity of the curtain film is impaired. In such cases, it can happen that the curtain tears or tears off. Preferably, the drop height of the coating color when performing the curtain coating (curtain coating process) to about 5 to 35 cm, in particular about 8 to 20 cm, adjusted. Compliance with these basic conditions means that the curtain is maintained continuously even at high speeds. The same applies to the following physical information that completes the process of the invention. These include according to the invention a viscosity of about 150 to 1500 mPas (Brookfield, 100 rev / min, 25 ° C), in particular about 250 to 900 mPas and also a surface tension between about 25 and 60 mN / m, in particular from about 27 to 40 mN / m (static ring method according to Du Noüy).

In individual cases, it is expedient if the coating color contains processing aids, in particular surface-active substances, retention aids, surfactants, CMC, calcium stearate and / or (meth) acrylic acid / (meth) acrylamide copolymers. To promote the opacity of the coating color is usually titanium dioxide as a particularly effective, the opacity-increasing white pigment incorporated, in particular in the form of rutile, optionally in admixture with anatase.

To set a desirable high printability of the coating color other additives can be incorporated, such as in particular conventional inorganic extender pigments, such as clays, calcined clays, sodium aluminosilicate, alumina, silicas, diatomaceous earth and / or magnesium silicates, both synthetic and natural origin. In addition, it is advantageous in some cases to incorporate lightfast, age-resistant colorants, in particular color pigments, into the coating color, in particular color pigments in Form of metal oxides, in particular iron oxides, and / or lightfast organic pigments.

It is further preferred if the pigments of the coating color and / or of the coating base paper optionally filled with pigments have a particle size of about 0.1 to 10 μm, in particular of about 0.1 to 2.0 μm. This range guarantees optimum properties, especially with regard to a desirable degree of opacity.

In selecting the coating paper optionally filled with pigments, the invention is not subject to any significant restriction. It has been shown that particularly good results are achieved when the coating color is applied to a paper or board web, in particular a Bekk smoothness measured according to DIN 53101, of about 150 to 2000 s, in particular about 200 to 1000 s, adjust.

The coating color contains, in addition to the mentioned pigments or further additives, a binder, preferably in the form of homo- and / or copolymers. There are no significant restrictions here. It is of advantage if the homopolymers and / or copolymers are based on (meth) acrylic acid, (meth) acrylamide, styrene-acrylamide, melamine resins and / or urea resins. The (meth) acrylic polymers guarantee a high bond strength of the finished pigment coating at a relatively low content, so that it is not torn or damaged by occasional attack forces.

The coating paper used in the context of the invention or provided with a pigment coating by the curtain-coating method may optionally be filled with pigments. With regard to the pigment content, it is advantageous for the décor paper obtained according to the invention if the total content of pigment (in the surface coating and also in the base paper which is optionally filled with pigments) is less than about 60% by weight, in particular less than about 40% by weight. If the content of pigment is too high, then the desirable physical properties, such as wet and dry breaking load and the like, not obtained to the extent required. The minimum content is the requirement for opacity.

In addition to the optional pigments, further materials can be incorporated into the coated base paper according to the invention, such as synthetic fibers for dimensional stabilization in addition to natural fibers. It is preferred if the long fiber content to about 0 to 50%, in particular about 5 to 50%, and the short fiber content is set to about 50 to 100%, in particular about 50 to 95%.

In the composition of the present invention desired white decorative paper, it is particularly advantageous if the main components of the base paper represent a pulp mixture of eucalyptus short fibers and softwood long fibers, the white pigment is titanium dioxide. There may be small amounts of color pigments for shading next to also minor amounts of kaolin. Another component is preferably a wet strength agent, which is to ensure the fiber cohesion in the subsequent impregnation process.

In general, the coating base paper, optionally filled with pigments, is not provided with a pigment coating in a completely dry state by means of the curtain coating method (curtain coating method). Conveniently, the moisture content of the coating base paper to be coated is between about 1 and 15% by weight, in particular about 2 to 8% by weight. Too dry a base paper would disadvantageously in some cases electrostatically charged too high and affect the overall production safety or running safety. Too high a moisture content of the base coating base paper would not have sufficient mechanical strength or dimensional stability.

The coating weight of the coating is not subject to any critical limitation. Preferably, this is at one-sided application to up to about 40 g / m ² , in particular up to about 30 g / m ² , and with two-sided application to each up to about 30 g / m ² , in particular up to about 25 g / m ² , discontinued. Preferably, the order quantity for unilateral application between about 5 and 20 g / m ² and for bilateral application each set to 5 to 12 g / m ² .

After application of a first pigment coat on the basis of the described coating color and subsequent drying, one or more further pigment strokes can be formed. As a result, a thicker pigment coating can be obtained, which would be cumbersome in a single order.

Although the coating unit can be operated both off-line and on-line, it is generally advantageous, in particular in larger production plants, to lead the operation on-line. In smaller installations, the off-line process can be advantageous in individual cases.

A particular advantage of the method according to the invention is that the process is possible at very high speeds. Although the process speed can be easily adjusted to at least about 500 m / min, in particular more than 750 m / min, in particular at least about 1000 m / min. According to the invention, however, the speed is to be set to at least 1500 m / min. This value can be exceeded with appropriate adjustment of coating color, coating weight and base paper, for example, be more than 1750 m / min. In this case, it is also possible without restriction to use pigments having a disadvantageously abrasive effect, since the abrasive coating composition according to the invention is applied contactlessly to the surface of the respective substrate.

With regard to the width of the free-falling or, for example, with electrostatic forces in a certain direction drawn curtain of coating color in the curtain-coating process, there is an advantageous flexibility. Thus, in individual cases, if desired, the width of the curtain can be set to more than the width of the base paper web, in particular a paper or board web. Here, in contrast to known coating methods, the disadvantages associated with the uncoated edge of the coating base paper are remedied (edge relief, corrugation, uneven application weights on the edge and the like). The width of the base paper web can be up to more than 10 m, which is due to the curtain coating process particularly high requirements with regard to the uniformity of the application.

The base paper web is advantageously coated with the curtain if it already has a solids content of about 65%, in particular more than 75% and preferably more than 95%. In this way, a particularly good coverage of the surface of the base paper web is ensured.

The base paper can be used on one side smooth or preinsatinized. Here, the expert can therefore make an advantageous choice.

The application process by means of curtain coating (curtain coating) has already been described in detail above. In addition, the following should also be stated: The clear outlet gap width of the curtain coating head of the coating unit is expediently set to about 0.1 to 1 mm, in particular to about 0.2 to 0.6 mm. It is advantageous according to the invention if the nozzle throughputs for the specific coating color are adjusted to 0.3 to 15.0 cm ³ / (cm working width xs), in particular about 0.5 to 5.0 cm ³ / (cm xs). In principle, the curtain coating head can be set to a single or multiple slit.

• ein fakultativ mit Pigmenten gefülltes Streichrohpapier eines Flächengewichtes von etwa 28 bis 65 g/m²,
• einen Gehalt von weniger als etwa 60 Gew.-% Pigment,
• eine Nassfestigkeit (Nassreißlänge), gemäß nach DIN ISO 3781 von mehr als 4,5 N, bevorzugt mehr als 6,5 N
• eine Trockenbruchlast, gemessen nach DIN ISO 1924-2, von mehr als 25 N, wobei das Dekorpapier einen Pigmentstrich einer Dicke von etwa 1 bis 30 µm mit einem Pigmentgehalt von etwa 50 bis 90 Gew.-% sowie einen Bindemittelgehalt von max. 50 Gew.-%, jeweils bezogen auf den Gesamttrockengehalt der Streichfarbe, aufweist.

The papers or decorative papers with a pigment coating obtained in accordance with the invention can advantageously be used for the decoration of coating materials. Here are the advantages listed below in detail in appearance. It is particularly preferred if the decorative paper used is characterized by:

• a coating base paper optionally filled with pigments having a basis weight of about 28 to 65 g / m ² ,
• a content of less than about 60% by weight pigment,
• a wet strength (wet tear length), according to DIN ISO 3781 of more than 4.5 N, preferably more than 6.5 N
• a dry breaking load, measured according to DIN ISO 1924-2, of more than 25 N, wherein the decorative paper has a pigment coating of a thickness of about 1 to 30 microns with a pigment content of about 50 to 90 wt .-% and a binder content by Max. 50 wt .-%, each based on the total dry content of the coating color having.

A decorative paper particularly preferably used for this purpose is characterized by a dry breaking load of about 30 to 35 N, a pigment coating having a thickness of about 2 to 15 μm, in particular 3 to 10 μm, a pigment content of 70 to 85% by weight and a binder content by Max. 30% by weight.

A particular advantage of the method according to the invention over the prior art, as already mentioned, is that the applied coating color subsequently need not be metered or smoothed with a doctoring element. In individual cases, it is expedient to apply two or more strokes successively on the base paper. It is possible that the following line is applied to the dried pigment coating. But there is also the possibility of the "wet-in-wet" order. In addition, there is the possibility that a simultaneous application takes place, so with a cascade nozzle, with the same or different strokes can be applied.

It is in the aspect of "printability" possible to determine the most suitable amount of binder, which allows easy impregnation with constant product quality and also minimizes the tendency to dust with low binder levels. It is also possible here to influence this by using different binders or binder mixtures. Among other things, the skilled person will consider further aspects as follows: Prevention of a dusty surface, increase of the binder content and prevention of a gluing effect with "mottling" effect (knock-out effect).

As a rule, a base pressure is applied by the customers of the decor paper obtained according to the invention, ie a full-surface coloring of the surface. Such imprinting is costly because at least about 2 to 3 g / m ^{2 of} job is required in a separate printing press. This can according to the invention can be avoided by the desired pigment pigments are already integrated in the applied pigment coating, such as titanium white line, resulting in a homogeneous full-surface coloring.

It is possible to form the pigment coating as a partial impregnation filling. This means that on the one hand the pigment coating fulfills the function of the surface coating and on the other hand comes into play as an impregnation filling for the base paper. By reducing the pigment content in the base paper, which is desirable according to the invention, the decorative paper obtains a higher strength and also has a higher dimensional stability. This decorative paper is particularly well suited for use in the field of furniture decor as well as panels for floor laminates or tile imitations.

The pigment coating obtained according to the invention has a particularly advantageous printability or paintability for aqueous gravure printing systems or ink-jet coating systems. The lacquers are acid-curing or UV-curable lacquers. The printing can be done by various printing methods, in particular based on aqueous and partially solvent-containing gravure printing systems or ink-jet systems.

• Das herangezogene Vorhang- Beschichtungs- Verfahren ist im Hinblick auf verschiedene Eigenschaften, wie bereits teilweise vorstehend angesprochen, vorteilhaft steuerbar, so im Hinblick auf ein angepasstes Viskositätsverhalten, insbesondere Dehnviskositätsverhalten, charakterisiert durch eine ausreichende innere Kohäsion, die sich durch eine ausgeprägte Fadenlänge und Oberflächenspannung der Streichfarbe zeigt. Die übliche Charakterisierung von Streichfarben ist für das Curtain-Coating-Verfahren durch bekannte physikalische Größen, wie Oberflächenspannung, Viskosität und dergl., nicht in ausreichendem Maße beschreibbar. Der sich im Rahmen der Erfindung ausbildende flüssige Vorhang kann durch eine ausreichende innere Kohäsion stabilisiert werden, da er andernfalls abreißen und zumindest eine erhebliche Verfahrensstörung verursachen würde. Diese Eigenschaft, die man als "Dehnviskositätsverhalten" bezeichnen kann, lässt sich in Form der Fadenlänge des aus dem Ford-Becher austretenden Flüssigkeitsfadens steuern bzw. bemessen. Das erfindungsgemäße Verfahren führt dann zu besonders wünschenswerten Eigenschaften des Verfahrenserzeugnisses bzw. lässt die gestellte Aufgabe besonders günstig lösen, wenn die Fadenlänge zwischen 70 und 130 cm, insbesondere zwischen 80 und 120 cm, bevorzugt zwischen 90 und 110 cm liegt.

In addition to the above-mentioned advantages, the invention also offers the following advantages:

• The curtain coating method used is advantageously controllable with regard to various properties, as already partially mentioned above, with regard to an adapted viscosity behavior, in particular extensional viscosity behavior, characterized by a sufficient internal cohesion, which is characterized by a pronounced thread length and surface tension Coating color shows. The usual characterization of coating colors is not sufficiently describable for the curtain coating process by known physical parameters such as surface tension, viscosity and the like. The forming within the scope of the invention, liquid curtain can be stabilized by a sufficient internal cohesion, otherwise he would tear off and at least cause a significant procedural disturbance. This attribute, which can be termed "extensional viscosity behavior" can be controlled or dimensioned in the form of the thread length of the liquid thread emerging from the Ford cup. The process according to the invention then leads to particularly desirable properties of the process product or allows the stated problem to be solved particularly favorably if the thread length is between 70 and 130 cm, in particular between 80 and 120 cm, preferably between 90 and 110 cm.

The invention will be explained in more detail below with reference to various examples:

Examples

The application of an aqueous coating color was carried out by means of the curtain coating method. The clear exit gap width of the curtain coating head was 0.3 mm (single brush). The curtain coating head was operated at a die throughput for the coating color of about 0.5 cm ³ / (cm working width xs). The viscosity of the coating color was adjusted to 400 to 450 mPas (according to Brookfield, 100 rpm, 25 ° C.). The surface tension of the coating color was 35 mN / m (static ring method). The coating was arranged on-line in the production plant. The application of the coating color was carried out on a paper web of a basis weight of 50 g / m ² (free of filler) and a Bekk smoothness, measured according to DIN 5301, of 200 s. The moisture content of the coating base paper was about 3% (ie dry content of 97%). The drop height of the coating color was set to 12 cm, the surface tension to 31 to 36 mN / m (static). The curtain coating process was operated at a speed of 850 m / min.

Furthermore, the coating color was adjusted with respect to the thread length in the Ford cup (nozzle 4) to a range of about 85 to 125 cm. After application of the aqueous coating color, the drying process of the coated paper web takes place in a customary manner.

On the basis of the above information, a decor paper was produced, wherein in each case the following formulations of coating colors were used to form the pigment coating:

Recipe 1:

This is a titanium white or titanium dioxide-containing surface coating whose goal is, in particular, to improve the opacity of the finished product and to reduce the subsequent impregnation requirement. 1% Na polyacrylate (30% aqueous solution, dispersant), 60% Titanium dioxide (white pigment, powder), 15% Magnesium silicate (extender pigment, powder), 10% Plastic pigment (27% aqueous suspension, hollow spheres of polystyrene / extender pigment), 0.5% Calcium stearate (50% aqueous suspension, lubricant), 0.5% Polyethylene wax (30% aqueous suspension, additive), 0.5% Sodium diethylhexyl sulfosuccinate (100% liquid, surfactant), 10% Styrene acrylate copolymer (50% aqueous dispersion, binder) and 2.5% Acrylic Acid / Acrylamide Copolymer (33% Aqueous Dispersion, Thickener / Viscosity Controller)

(Note: All above information refers to otro.- weight% (oven-dry))

The lack of water to adjust to a solids content of 50% by weight was presented in liquid form when preparing the coating. The ingredients mentioned were added in the order given, taking into account the quantitative data with stirring.

Other information: Dry content of the aqueous coating color 50%, pH 8.2; Viscosity (according to Brookfield, 100 rpm, spindle 3, 20 ° C) 400 mPas, surface tension (at 20 ° C) 32.3 mN / m and thread length (in Ford cup with nozzle 4) 95 cm. The application was carried out with 25 g / m ² (otro) on the paper web.

Recipe 2:

This is a titanium white or titanium dioxide-containing surface coating with which, in particular, the opacity of the finished product and the splitting strength should be improved and the subsequent impregnation requirement should be reduced. 1% Na polyacrylate (30% aqueous solution, dispersant), 50% Titanium dioxide (white pigment, powder), 10% Magnesium silicate (extender pigment, powder 5% Plastic pigment (27% aqueous suspension, hollow spheres of polystyrene, extender pigment), 0.5% Calcium stearate (50% aqueous suspension, lubricant), 0.5% Polyethylene wax (30% aqueous suspension, additive), 0.5% Sodium diethylhexyl sulfosuccinate (100% liquid, surfactant), 30% Melamine resin (binder and filling resin) and 2.5% Acrylic acid / acrylamide copolymer (33% aqueous dispersion, thickener / viscosity regulator)

(Note: All the above data are based on otro.% By weight (oven-dried), aqueous fraction analogously to Example 1)

Additional information: Dry content of the aqueous coating color 50%, pH 7.8, viscosity (according to Brookfield, 100 rpm, spindle 3, 20 ° C) 420 mPas, surface tension (at 20 ° C) 33.4 mN / m and thread length (in Ford cup with nozzle 4) 100 cm. The application was carried out with 25 g / m ² (otro) on the paper web.

recipe 3:

Here, a kaolin line was formed on the designated coating base paper based on the above procedure. This is intended to improve the printability and the paint level. It was used as base paper, a standard standard decorative paper, the mass in the titanium dioxide content of about 30%. The composition of the coating color for the surface coating was as follows: 1% Na polyacrylate (30% aqueous solution, dispersant), 60% Aluminum silicate (white pigment, powder), 10% Magnesium silicate (white pigment, powder), 10% Plastic pigment (27% aqueous suspension, hollow spheres of polystyrene, extender pigment), 0.5% Calcium stearate (50% aqueous suspension, lubricant), 0.5% Polyethylene wax (30% aqueous suspension, additive), 0.5% Sodium diethylhexyl sulfosuccinate (100% liquid, surfactant), 15% Styrene acrylate copolymer (50% aqueous dispersion, binder) and 2.5% Acrylic Acid / Acrylamide Copolymer (33% Aqueous Dispersion, Thickener / Viscosity Controller)

(Note: All the above data refer to otro.-wt .-% (oven-dry), aqueous portion as in Example 1).

Additional information: Dry content of aqueous coating color 40%, pH 8.5, viscosity (according to Brookfield) (100 rpm, spindle 3, 20 ° C.) 420 mPas, surface tension (at 20 ° C.) 34.0 mN / m and thread length (in Ford cup with nozzle 4) 115 cm. The order was carried out with 5 g / m ² (otro) on the paper web.

Recipe 4:

Here, a kaolin line was formed on the designated base paper on the basis of the above procedure. This is to improve the printability and the gap strength. The base paper used was a standard standard decorative paper which had a titanium dioxide content of about 20% by mass. The composition of the coating color for the surface coating was as follows: 1% Na polyacrylate (30% aqueous solution, dispersant), 50% Aluminum silicate (white pigment, powder), 7% Magnesium silicate (white pigment, powder), 8th% Plastic pigment (27% aqueous suspension, hollow spheres of polystyrene, extender pigment), 0.5% Calcium stearate (50% aqueous suspension, lubricant), 0.5% Polyethylene wax (30% aqueous suspension, additive), 0.5% Sodium diethylhexyl sulfosuccinate (100% liquid, surfactant), 30% Melamine resin (binder and filling resin) and 2.5% Acrylic Acid / Acrylamide Copolymer (33% Aqueous Dispersion, Thickener / Viscosity Controller)

(Note: All the above data are based on otro.% By weight (oven-dried), aqueous fraction analogously to Example 1)

Additional information: Dry content of aqueous coating color 40%, pH 7.6, viscosity (according to Brookfield, 100 rpm, spindle 3, 20 ° C) 450 mPas, surface tension (at 20 ° C) 34.5 mN / m and thread length (in Ford cup with nozzle 4) 115 cm. The job was carried out with 21 g / m ² (otro) on the paper web.

The invention will be further explained with reference to an exemplary embodiment.

• Figur 1 : eine Prinzipdarstellung eines erfindungsgemäßen Verfahrens, mit dem innerhalb einer Papiermaschine eine Dekorpapierbahn hergestellt werden soll.
• Figur 2 : eine Prinzipdarstellung der Vorrichtung zur Durchführung des erfindungsgemäßen Verfahrens mit einem Vorhang- Auftragswerk

Show it:

• FIG. 1 : A schematic representation of a method according to the invention with which a decorative paper web is to be produced within a paper machine.
• FIG. 2 : A schematic diagram of the device for carrying out the method according to the invention with a curtain applicator

In both figures, the same reference numerals are chosen for the same components.

In FIG. 1 is first a Stoffbütte B recognizable, which contains a mixed for producing a wood-free raw paper web 1 with water pulp. The pulp consists in the example of 25% to 50% long fibers and accordingly 75% to 50% short fibers on. No pigments and opacifying substances have yet been added to this fiber mixture in the fabric chest B outside the paper machine. The mixture of substances is thus fed to the paper machine P in a quasi-simple manner, the mixture of substances initially arriving in a headbox 2 and then being formed on screens 3 as a web. Thereafter, the dewatering takes place within the press section 4, which is followed by the consisting of einreireihigen drying cylinders drying section 5a. After reaching a dry content of at least 65%, in particular of at least 75%, preferably of more than 92%, the paper web 1 is deleted. Thus, this paper web is suitable as decorative paper web and therefore should not be translucent, now opacitätsfördernde and whitening pigments and fillers are applied to the paper web 1. This is done with formulations that have been described in the previous examples. Since the opacifying and whitening additives have an extremely abrasive effect, a contactless curtain applicator 7 is integrated into the paper machine as a commissioned work. (Also possible as an offline coater).

With this commissioned work 7, it is possible that this amount of ink produced by the curtain 7a in the specified size can also remain on the paper without having to be stripped off.
The job, which is referred to as a 1: 1 job, takes place without pressing pulses and without suction on the paper web 1. As a result, the coating film sets on the paper surface, without penetrating into the paper web and affect their further path within the paper machine P. , The binders contained in the application medium ensure good anchoring to the paper web. Depending on the setting of the chemical and physical properties of the application medium, targeted penetration of the application medium into the paper can also be effected in order, for example, to increase the gap strength.

Thereafter, the coated paper web 1 is dried contactless and / or via contactless acting web guide elements, such as a so-called Air turn 8, further dried with suspended dryers 9 and passed to subsequent (here double row) drying cylinders, where in the night section 5b the finished drying Paper web 1 is done. Finally, the paper web Rolled up in a winding machine 10 and is available for further processing, such as printing available.

Alternatively, it is possible to smooth the paper web prior to its winding with calenders 11.

The decorative paper web thus produced is characterized by high strength, a constant and homogeneous coating and is almost opaque to light.

It should be mentioned that both sides of the web can be painted one or more times with the given parameters. That depends on the particular intended use of decorative paper.

In FIG. 2 the coating head 7.1 of the curtain applicator 7 is shown schematically and in section. The spreading head extends essentially over the entire machine width or width of the paper web 1 running in the running direction L. A slit nozzle or an exit slit 7.3 branches off from an inner ink chamber 7.2, which is adjusted by adjusting one or both of the lips 7, 4 and 7 forming the exit slit 7.5 in its gap width s, also seen in zones across the width of the entire curtain application unit 7, is adjustable. This adjustability is indicated by the two force arrows F.
The gap width s is between 0.1 and 0.6 mm, whereby nozzle throughputs for the coating color to about 0.3 to 15 cm ³ / cm working width and second can be achieved.
From the nip, the coating color in the desired coating composition according to the examples described above emerges in the form of a curtain 8 running in the direction of gravity and deposits in a contour line 7b as a cover layer on the base paper web 1.

Claims (24)

1. A method for producing a decorative paper with a pigment coating, wherein an aqueous coating slip is applied in contactless manner to a coating base paper by means of the curtain coating method and is dried, wherein the starting point is a coating base paper of a basis weight of 28 to 65 g/m² and the coating slip has a solids content of 30 to 70% by weight, a viscosity of 150 to 1500 mPas (measured according to Brookfield, 100 rpm, 25°C), characterised in that the coating slip has a surface tension of between 25 and 60 mN/m (measured using the Du Noüy static ring method), the curtain coating method being operated at a rate of at least 1500 m/min and throughputs of a curtain nozzle of a curtain coating head for the coating slip which nozzle is used are set to 0.3 to 15.0 cm³/(cm operating width x s).
2. A method according to Claim 1,
   characterised in that the solids content of the coating slip is between 40 and 60% by weight.
3. A method according to Claim 1 or 2,
   characterised in that the height of fall of the coating slip when implementing the curtain coating method is set in the range between 5 and 35 cm, in particular between 8 and 20 cm.
4. A method according to one of Claims 1 to 3,
   characterised in that the coating slip has a viscosity (measured according to Brookfield, 100 rpm, 25°C) of 250 to 900 mPas.
5. A method according to one of Claims 1 to 4,
   characterised in that the surface tension of the coating slip is set to between 27 and 40 mN/m (Du Noüy static ring method).
6. A method according to one of Claims 1 to 5,
   characterised in that the coating slip is applied to a web of paper or board, in order to set in particular a Bekk smoothness, measured to DIN 53101, of 150 to 2000 s.
7. A method according to at least one of the preceding claims,
   characterised in that processing aids are incorporated in the coating slip, in particular for example surface-active substances, retention aids, surfactants, CMC, starch, calcium stearate, (meth)acrylic acid/(meth)acrylamide copolymers.
8. A method according to at least one of the preceding claims, characterised in that titanium dioxide, in particular in the form of rutile, optionally in an admixture with anatase, is used in the coating slip to promote opacity.
9. A method according to Claim 8,
   characterised in that inorganic extender pigments are added to the coating slip in order to set high printability of the finished product, in particular in the form of clays, calcined clays, sodium aluminosilicate, aluminium oxide, silicas, diatomaceous earth and/or magnesium silicates, of both synthetic and natural origin.
10. A method according to at least one of the preceding claims,
    characterised in that the pigments of the coating slip and/or of the coating base paper have a particle size of 0.1 to 10 µm, in particular of 0.1 to 2.0 µm.
11. A method according to at least one of the preceding claims,
    characterised in that light-stable, ageing-resistant colorants, in particular coloured pigments, are incorporated in the coating slip.
12. A method according to Claim 11,
    characterised in that the coloured pigments are present in the form of metal oxides, in particular iron oxides, and/or in the form of light-fast organic pigments.
13. A method according to at least one of the preceding claims,
    characterised in that a binding agent in the form of homopolymers and/or copolymers based on (meth)acrylic acid, (meth)acrylamide, styrene acrylamide, melamine resins and/or urea resins, is incorporated in the coating slip.
14. A method according to at least one of the preceding claims,
    characterised in that the coating base paper contains synthetic fibres in addition to natural fibres for dimensional stabilisation.
15. A method according to Claim 14,
    characterised in that the long-fibre fraction of the coating base paper is set to 0 to 50%, in particular 5 to 50%, and the short-fibre fraction of the coating base paper to 50 to 100%, in particular to 50 to 95%.
16. A method according to at least one of the preceding claims,
    characterised in that the coating weight of the coating slip for one-sided application is set to up to 40 g/m², in particular to up to 30 g/m², and for both-sided application to up to 30 g/m², in particular to up to 25 g/m², in each case.
17. A method according to Claim 16,
    characterised in that the coating amount of the coating slip for one-sided application is set to 5 to 20 g/m² and for both-sided application is set to 5 to 12 g/m² in each case.
18. A method according to at least one of the preceding claims,
    characterised in that once a first pigment coating has been formed one or more further pigment coating(s) are formed.
19. A method according to at least one of the preceding claims,
    characterised in that the coating base paper has a moisture content of 1 to 25% by weight, in particular of 2 to 8% by weight.
20. A method according to at least one of the preceding claims,
    characterised in that the coating apparatus is operated online.
21. A method according to at least one of the preceding claims,
    characterised in that the width of the curtain in the curtain coating method is set to more than the width of the web of coating base paper, in particular a web of paper or board.
22. A method according to Claim 21,
    characterised in that the slot length of the curtain coating head upon coating is set to 15 to 25 cm beyond the respective substrate web edge.
23. A method according to at least one of the preceding claims,
    characterised in that the coating base paper is used smooth or pre-glazed on one side.
24. A method according to at least one of the preceding claims,
    characterised in that the exit slot width of a curtain nozzle of a curtain coating head which is used in the curtain coating method is set to 0.1 to 1 mm, in particular to 0.2 to 0.6 mm, and/or throughputs of the curtain nozzle for the coating slip are set to 0.5 to 5.0 cm³/(cm x s), the curtain coating head being able to be set to a single or multiple slot.

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