EP4212347A1 - Method for producing a decorative paper - Google Patents

Abstract

The invention relates to a method for producing a decorative paper, in which a decoration is printed onto a paper web, in which method a digital printing system is used, the paper web has a grammage of at least 45 g/m² and at most 65 g/m², a primer in an application quantity of at least 4 g/m² and at most 6 g/m^{2 on the paper web before the decoration is printed on}, preferably 5 g/m², is applied and the decoration is printed with at most 7.5 g/m² printing ink.

Description

The invention relates to a method for producing decorative paper, in which a decoration is printed onto a paper web.

Decorative papers have long been used, for example, to produce laminate panels, for example to produce floor panels or wall and ceiling coverings, but also as furniture panels. A desired decor, for example a real wood decor, is printed onto a paper web or sheet of paper. This is then applied, for example, to a core which is preferably a wood-based panel. For this purpose, the printed paper is often impregnated with a synthetic resin or polyurethane and pressed with the core in a short-cycle press. The manufacture of such panels or plates has long been known to the person skilled in the art from the prior art.

Digital printing systems with which decors can be printed on paper have also been known for a long time. So-called single-pass digital paper printing systems, in which the paper to be printed only has to run through the printing system once, are used, for example, in the packaging industry in order to print packaging materials, such as cardboard boxes. However, the demands on the print and the decoration produced in this way are significantly lower than is the case with the production of decorative paper. This applies both to the quality of the individual print of the decor and to the reproducibility of the decors, which are often produced in large numbers. In addition, decor papers with the same decor often come in different versions Batches are produced with possibly a large time interval, so that even greater demands are placed on reproducibility.

The problem is that a wide variety of parameters influence the print result of the decoration applied to the paper web. This applies to the paper used, the amount and type of printing ink applied, the amount and type of any primer used, which can also be referred to as an undercoat, but also environmental influences such as humidity or temperature. In addition, the parameters cannot be optimized independently of each other, but influence each other.

The invention is therefore based on the object of further developing a method for producing a decorative paper in such a way that the best possible printing result is achieved.

• eine Digitaldruckanlage verwendet wird,
• die Papierbahn eine Grammatur von wenigstens 45 g/m² und höchstens 65 g/m² aufweist,
• auf die Papierbahn vor dem Aufdrucken des Dekors ein Primer in einer Auftragsmenge von wenigstens 4 g/m² und höchstens 6 g/m², bevorzugt 5 g/m², aufgetragen wird und
• das Dekor mit höchstens 7,5 g/m² Drucktinte aufgedruckt wird.

The invention solves the problem set by a method of producing a decorative paper, in which a decoration is printed onto a paper web, with the method

• a digital printing system is used,
• the paper web has a grammage of at least 45 g/m ² and at most 65 g/m ² ,
• a primer is applied to the paper web before the decoration is printed in an application quantity of at least 4 g/m ² and at most 6 g/m ² , preferably 5 g/m ² , and
• the decoration is printed with a maximum of 7.5 g/m ² ink.

The design of the method according to the invention means that the decorative paper can be printed with high quality, quickly and in industrial quantities and requirements. At the same time, high quality is guaranteed at low cost.

The digital printing system preferably has a printing width of at least 2050 mm and/or a web speed of at least 135 m/min and/or at least two rows of print heads for each color used with a resolution of at least 1200 dpi x 1200 dpi at a web speed of 135 m/min and/or a resolution of at least 1200 dpi x 600 dpi at a web speed of 270 m/min. In one embodiment, the digital printing system has a resolution of 1200 dpi×600 dpi at a web speed of 270 m/min. This high speed is particularly advantageous in the case of decorations with little ink consumption, that is to say in particular light and neutral decorations which preferably do not have rather few details and can therefore be described as undemanding.

The digital printing system preferably has an automatic roll changer and/or an automatic paper threader and/or an error monitoring system and/or a color monitoring system. With an automatic roll changer it is possible to change the paper web to be printed, which is supplied on a roll, without having to stop the digital printing system. With an automatic paper threader, the paper to be printed can be changed quickly if necessary. With an error monitoring system and a color monitoring system, each of which has, for example, a camera or a sensor with which the quality and/or the colors of the print can be determined and determined, corrections can be made to the print settings if necessary and faulty or inferior-quality products can be identified and remove from the production line. This reduces the frequency of complaints and the amount of rejects.

The digital printing system particularly preferably has ink circulation, preferably in the print head, so that the ink can be moved in order to prevent the nozzles of the print head from becoming clogged and thus preventing the print head from malfunctioning. In a digital printing system, the ink used to print the decor is applied to the paper web in the form of many small drops. The drops are generated in the print head and then placed on the paper web. The so-called "waveform" with which the drops are generated is preferably adjustable and the digital printing system has a user interface with which this setting can be made. In this way, the generation of the drop can be adapted to the ink and its properties. Fine adjustment options for the density are particularly preferred in order to ensure uniform printing using the software contained in the digital printing system.

The paper web preferably has a titanium dioxide content of less than 40%, preferably less than 35%, particularly preferably less than 32% and more than 20%, preferably more than 23%, particularly preferably more than 28%.

Due to the relatively small grammage of the paper used in the methods according to the present invention, a good ratio of the mass of the paper to its thickness is achieved, which produces good and favorable impregnated properties. The formulation of the paper is chosen in such a way that as many decors as possible can be implemented on this paper, while at the same time the paper is moderately highly filled. More expensive types of paper should only be used for special designs where other advantages prevail. For example, white paper, i.e. paper with a higher proportion of ash and/or titanium dioxide, is used if a very light decoration is to be printed, for which only a small amount of ink has to be used. This saves costs, which often outweigh the increased costs caused by the more expensive paper.

Preferably the primer is an active primer. If less than the specified amount of primer is used, an increased amount of ink must be used for the decoration, which results in increased costs. However, using more than the specified amount of Primer will result in no additional effect being produced, so Primer will be wasted. An active primer, which is preferably matched to the ink system, i.e. the inks of the different colors used, holds the ink pigments in the thin application layer of the primer and prevents or makes it difficult for the pigments to sink into the paper, i.e. to penetrate too deeply. This reduces the amount of ink required for a desired color impression. The primer is preferably applied inline, ie within the printing system during a single run of the paper. Preferably, a Pressure chamber squeegee is used with a ceramic roller with indirect application rubber roller to achieve an even application over the entire printing width. The ceramic anilox roller preferably has an 80 grid. In this way the best possible application quantity of the primer is achieved. A ceramic roller is more durable than, for example, chrome-plated steel bodies, which can also be turned.

The primer is therefore preferably applied by means of a pressure chamber doctor blade and a ceramic roller with an indirect application rubber roller, with the ceramic screen roller preferably having an 80 screen.

The primer is preferably applied using the digital printing system or in the digital printing system.

In a preferred embodiment, the ink has a solvent content of at least 27% and at most 37%, preferably 32% and/or a water content of at least 55% and at most 65%, preferably 60%, and/or a pigment content of 1%. The amount applied is matched to the amount of primer. Inks of the type described here have a solids content and/or a pigment content which results in good impregnability of the paper printed with them. This is advantageous in the production of decorative papers, particularly for laminate panels.

The digital printing system is advantageously operated in a room whose room temperature is at least 22° C. and at most 24° C., preferably 23° C., and/or whose relative humidity is at least 53% and at most 57%, preferably 55%.

An air humidity of 55% in combination with a temperature of 23°C is a particularly advantageous proportion of relative air humidity. As a result, the moisture content of the paper to be printed is also particularly good, i.e. in particular not too dry or too wet too quickly. This leads to less wrinkling in the printing system and thus to better print quality, especially at higher speeds. The risk of the paper to be printed tearing off is then reduced, even at high speeds. It is particularly preferred if the room temperature is kept constant over time. This means that the temperature of the paper, ink and/or primer is also stable, resulting in stable application properties. A temperature that is too low leads to negative drying properties, which can be reflected, for example, in a dirty printed image. The relatively low grammage and/or the small amount of primer and/or ink applied ensures that there are not too many pigments and/or solids in the thin paper after drying. This ensures better resin absorption during later impregnation and thus better adhesion when pressing to the panel.

In a first specific exemplary embodiment, printed decorative paper is produced by a manufacturer of laminate floorboards on a digital paper printing system. The working width of the digital printing system is 2070mm. It has a dual row printhead with a resolution of 1200 dpi x 1200 dpi and ink recirculation in the printhead. The speed of the paper web within the digital printing system is 135 m/min and only one type of decorative paper is printed, but it is used in two different grammages of 50 g/m ² and 65 g/m ² . A water-based ink and the CRYK color system is used for printing. Within the digital printing system, an active primer is applied inline with a ceramic anilox roller in an amount of 5 g/m ² . In the room where the printing is done, the humidity is 55% and the air temperature is 23°C. An average of 4 g/m ² ink application is used for the decorations. Under these conditions, more than 100 million m ² of laminate based on digitally printed decor paper can be produced in one year. This corresponds to more than 6000 t of printed decorative paper. With a width of 2070 mm and 300 working days on which decor papers are printed around the clock, this corresponds to around 120 million m ² . Downtimes are already taken into account. The materials used and their amounts allow for good further processing, for example impregnation or impregnation adhesion on the HDF panel used as the core. This creates in this case a high quality of the end product is created with less than 1% rejects and complaints. The small number of paper types allows, among other things, a low purchase price and fewer downtimes due to changing paper or changing recipes. Due to the high annual volume, the low consumption of production materials, the low rejects and the low proportion of complaints and the production materials bought cheaply in large quantities, a very competitive laminate is created which can be offered more cheaply than with other combinations in digital decor paper printing.

The decorative paper is preferably printed using the single-pass method. The paper to be printed only has to go through the digital printing system once, even if, for example, several colors are printed and/or a primer is applied before printing.

Particularly preferably, at least some, but preferably all of the print heads have an ink recirculation system. This reduces the risk and number of clogs in and/or in front of the printhead and in particular in and/or in front of the nozzles of the printhead through which the ink is applied to the paper.

The printing intensity of print heads is preferably adjustable. Particularly preferably, the printing intensity of the print heads can be adjusted individually and advantageously independently of one another. This is particularly preferably possible for each of the print heads.

As an alternative or in addition to this, the print intensity of groups of print heads can be adjusted. A group of printheads preferably has between 5 and 10 printheads. Each of the print heads preferably belongs to at least one group, particularly preferably to exactly one group in each case.

The easiest way to adjust the print intensity is to adjust the amount of ink that is applied to the paper to be printed by the respective print head. The setting is preferably made using software in the digital printing system, which is preferably also used to control the digital printing system.

Claims (13)

Method for producing a decorative paper, in which a decoration is printed onto a paper web, with the method - a digital printing system is used, - the paper web has a grammage of at least 45 g/m ² and at most 65 g/m ² , - A primer is applied to the paper web before the decoration is printed in an application quantity of at least 4 g/m ² and at most 6 g/m ² , preferably 5 g/m ² , and - the decor is printed with a maximum of 7.5 g/m ² ink. Method according to Claim 1, characterized in that the digital printing system has a printing width of at least 2050 mm and/or a web speed of at least 135 m/min and/or at least two rows of print heads for each color used with a resolution of at least 1200 dpi x 1200 dpi at a web speed of 135 m/min and/or a resolution of at least 1200 dpi x 600 dpi at a web speed of 270 m/min. Method according to Claim 1 or 2, characterized in that the digital printing system has an automatic roll changer and/or an automatic paper threader and/or an error monitoring system and/or a color monitoring system. Method according to one of the preceding claims, characterized in that the paper web preferably has a titanium dioxide content of less than 40% less than 35%, more preferably less than 32% and more than 20%, preferably more than 23%, more preferably more than 28%. Method according to any one of the preceding claims, characterized in that the primer is an active primer. Method according to one of the preceding claims, characterized in that the primer is applied by means of a pressure chamber doctor blade and a ceramic roller with an indirect application rubber roller, the ceramic screen roller preferably having an 80 screen. Method according to one of the preceding claims, characterized in that the primer is applied by means of the digital printing system or in the digital printing system. Method according to one of the preceding claims, characterized in that the ink has a solvent content of at least 27% and at most 37%, preferably 32% and / or a water content of at least 55% and at most 65%, preferably 60%, and / or a has a pigment content of 1%. Method according to one of the preceding claims, characterized in that the digital printing system is operated in a room whose room temperature is at least 22 °C and at most 24 °C, preferably 23 °C and/or whose relative humidity is at least 53% and at most 57%, is preferably 55%. Method according to one of the preceding claims, characterized in that the decorative paper is printed using the single-pass method. Method according to one of Claims 2 to 10, characterized in that at least some of the print heads, preferably all print heads, have an ink recirculation system. Method according to one of the claims, characterized in that a print intensity of individual print heads and/or a print intensity of groups of print heads can be adjusted. Method according to claim 12, characterized in that a group of printheads contains 5 to 10 printheads.