DE102004041537A1 - Method and apparatus for producing a coated LWC paper web - Google Patents

Abstract

The invention relates to a method for producing a coated, gravure-capable LWC paper web.
According to the invention, the following method steps are provided:
In a first step (A), the surface of a running web (1) made of raw paper is pre-smoothed and its thickness profile is made uniform;
in a second step (B), a precoat (2) in the form of a contour line is applied to one or both sides of the web (1);
in a third step (C), the web (1) is dried a first time;
in a fourth step (D), the web (1) is subjected to intermediate smoothing;
in a fifth step (E), a top coat in the form of a contour line is applied to one or both sides of the web (1);
in a sixth step (F), the web (1) is dried a second time;
in a seventh step (G), the web (1) is finally smoothed.

Description

The The invention relates to a method for producing a coated, deep printable LWC paper web, by brushing a base paper with a liquid until pasty Coating medium.

At the Refining or coating, i. making the paper suitable for the latter desired Printing process of the paper, one knows the direct procedure, at which coating medium on the moving paper web over the entire width is applied. To apply are different Facilities known, for example, nozzle applicators, in which a shallow jet or individual sprays of the coating medium be applied to the paper web. Downstream of the impact point of the Application medium is a surplus by means of a doctor device scraped off the applied line, with a leveling at the same time is achieved. Also, the indirect application is known, the Coating medium first on a circumferential surface is applied, for example, on the lateral surface of a Cylinder from which the medium delivered to the moving paper web becomes. A paper web can be both single-sided and two-sided be painted in a so-called film press.

Coated papers are widely used, for example as writing and printing paper or as magazine paper. Magazine paper is made of LWC (light-weightcoated) paper, which has a basis weight of between 70 and 100 g / m ² and is later to be printed by gravure printing.

at Magazine papers therefore require particularly high surface smoothness. Therefore, not only a single stroke is applied to the base paper, but a top coat with intervening drying process.

Around to produce such paper, one currently uses offline methods, So where the refining process outside the paper machine takes place. An online procedure with coating machine integrated into the paper machine is indeed more economical, but so far only supplies offset-suitable LWC paper, because for applying the top layer with so-called blade coaters (Blade coaters worked with coating blade (Blade) becomes. However, such coating blades are subject to wear, so that she after a few hours thoroughly are useless and need to be replaced. But also after a relatively short time Operating time and thus before the replacement is an impairment the working edge of the blade, resulting in nonuniformities the stroke surface and thus to quality impairments leads. Also, a damaged blade can break even before the final wear the wet and thus less tear-resistant paper web lead. It also worsens at higher Running speed of the machine whose runnability.

Of the Invention is based on the object of specifying an online method, where the mentioned disadvantages do not occur. The surface of the Stroke is about it out as possible flat and smooth, especially with regard to later printing, preferably in the gravure printing process. In addition, should tears of the paper web be avoided.

These The object is solved by the features of claim 1.

One The essential idea is the application of a multiple stroke. The precoat is done with a so-called film press, that is one Roll press. The top coat can also be used with the film press be applied. However, one or two are also suitable Curtain coater arranged one behind the other for the Top coat. Of particular importance in the invention is the step of the pre-smoothing before the precoat and the step of intermediate smoothing after the application of the Pre-painting and before applying the top coat. Something for everyone Case is a prank blade with their above mentioned Disadvantages as cause for Tears and as a wear element.

Further advantageous embodiment variants emerge from the dependent claims.

With The invention makes it possible for the first time, LWC paper in the online process and also also produce low pressure.

The The invention is explained in more detail with reference to the drawing. There are five essentials in it Process steps or treatment stations reproduced.

The 1 to 5 show in each case a paper web in cross section transverse to the running direction of the paper web, optionally with one or two layers of a line.

6 shows: the entire process flow in a schematic representation

Out 1 you recognize the raw paper 1 , It was manufactured on a paper machine which has at least three presses in its wet part. If less than three presses are present, at least one shoe press is present.

The raw paper shown here 1 has a basis weight of 35 to 50 g / m ² . Deviations are possible, especially upwards. The paper according to 1 is initially untreated, which can be recognized by the different surface topography O. Accordingly, it has a different sheet thickness, seen transversely to the direction, as shown here in dashed lines. It can be seen in the central region of the sectional view of a bottleneck, that is, a particularly small thickness d, while the two outer regions have a greater thickness D. The area boundary lines are similar to sinusoids.

2 shows the same base paper after performing the first treatment step, namely after passing through a smoother. The smoothing device is used for pre-smoothing and at the same time calibrating the thickness. As you can see, the thickness is now largely unified (d = D), seen over the web width. The sinusoids are relatively uniform. The pre-smoothing is carried out in a calender. This consists in the present case of two steel rollers, that is rollers in which at least coats are made of steel and are very smooth. In addition, the calender has a device for sectionally adjusting the line force. The average line pressure in the calender during pre-smoothing is between 30 and 40 kN / m. It can also be between 20 and 60 kN / m.

The next step is in 3 illustrated. You can see the train again 1 , This now has a primer on both sides 2 The contour line is characterized by a uniform layer thickness and is applied with a film press.The line can be applied simultaneously on both sides or consecutively on each side of the web.For the film press, also under "Speedcoater or Speedsizer" The hardness of the rubber covering is between 30 and 80 P & J, preferably between 50 and 70 P & J when using a polyurethane cover, the hardness is between 20 to 50 P & J, preferably between 30 and 40 P & J. Roll diameters of at least 1250 mm are possible.

A liquid film of coating medium, generally called "coating color", is first applied to the rollers, and from there to the relevant side of the paper web 1 issued. The solids concentration of the coating color is between 50 and 70%, preferably 60 to 68% by mass. The coating color is composed of mineral pigments and synthetic binders. Calcium carbonate pigments with an average particle size of less than one micron are preferably used. The calcium carbonate can be added to other mineral constituents such as kaolin or titanium dioxide. However, the proportion of calcium carbonate is at least 50%.

The coating weight is an amount of 5 to 15 g / m ² per side, preferably between 6 and 10 g / m ² (dry wt.) In question.

at the dosage of the liquid Coating color slowly rotating doctor blades are used. It has been shown that the required coating weights are best set with squeegee rods of diameter 10-25 mm, preferably 14-18mm can be. The circular cylindrical smooth or grooved doctor rod runs along a speed of 100 to 5000 / min, preferably 150 to 300 U / min.

When painting with a film press, a so-called film splitting occurs. A part of the coating medium remains on the lateral surface of the transferred roller, while another part is delivered to the paper web. This creates a micro-roughness on the surface of the still liquid coating layer. This micro-roughness is important for the printability of the finished paper. In offset printing, it is still acceptable, but not in gravure printing. If the micro-roughness M _{R is} too large, in 3 should be indicated by the serrated stroke surface, namely, defects in the printed image, so-called "missing dots".

By the invention avoids such phenomena as below yet to be explained should.

How to get out 3 detects, is the primer 2 on both sides of the paper web 1 , This will be discussed later.

On The pre-coat is followed by a drying process.

The paper web 1 with the very moist layer on top 2 is first pre-dried without contact by means of infrared radiators. In this case, temperatures of at least 50 ° C are reached. This is followed by a drying process by means of non-contact hot air dryers. The paper web is generally held in suspension on a levitation route by means of air jets and dried at the same time. This is not shown here.

According to 4 now takes place an intermediate smoothing. The intermediate smoothing serves to largely reduce the said micro-roughness M _R , which has arisen during film splitting. Here, a calender is used, which may include a roller combination. So is a Hartnip combination consisting of two hard rolls, one of which is a hot roll, or two soft rolls, or a combination consisting of a hard / hot roll and a soft roll, or in the reverse case consisting of an upper soft roll possible with an engaged hard / hot roller. Both rolls may have a plastic cover, with a hardness between 85 and 96 ShD, preferably between 90 and 92 ShD. The line pressure of the rollers of the calender stands between 100 and 600 kN / m, preferably between 100 and 300 kN / m.

Instead of such a calender can also be provided a shoe calender. The with the pressure shoe set gap length can be between 20 and 250 mm. It is preferably between 40 and 70 mm.

The heated smoothing roll can be up to 300 ° C For one even smoothing on Both web pages, it is advantageous if a second Schuhkalander with the hot smoothing roll acting on the other side of the track.

The step of intermediate smoothing is again carried out by applying a cover layer. The result is in 5 shown. The paper web 1 now carries the precursor 2 , as well as the top coat 3 , The two layers - top coat and primer - are of uniform thickness and of great uniformity and smoothness of the surfaces. The top coat according to 5 is again applied with a film press. The same roll covers are used as for the precoat. The diameter of the film press roll is also at least 1250 mm, as with larger diameters, the film splitting is less abrupt.

The weight of the top coat is per page of the paper web 1 between 5 and 15 g / m ² , preferably 6 to 10 g / m ² .

At the application of the top coat 3 This is followed in turn by pre-drying by means of IR radiation, followed by drying with hot-air dryers, whereby the treatment in the on-line coater is shot down. The water content of the finished paper web is between 4 and 8%, preferably between 4 and 6% (absolute humidity).

• A- Vorglätten der Rohpapierbahn mit einem Glättwerk, wie es unter 2 beschrieben ist. Die beiden vorzugsweise einen harten Glättnip bildenden Walzen dienen dem Herstellen eines einheitlichen Dickenprofils des Rohpapieres, wobei sich eine Makro-Rauhigkeit von größer 1 mm ergibt;
• B- Vorstreichen mittels einer Filmpresse (siehe auch 3), also mit indirektem Auftrag; hierbei erfolgt vorzugsweise ein Simultanauftrag des Streichmediums auf beide Seiten der Papierbahn und eine Konturabdeckung der Oberfläche;
• C- Umlenken der Bahn mit einem sogenannten Airturn und Trocknen der Strichschicht zunächst kontaktlos mit Infrarot- und Lufttrocknern und anschließender Zylindertrocknung
• D- Zwischenglätten zwischen Glättwalzen, deren Kombinationsmöglichkeiten in 4 erläutert sind, wobei eine Mikro-Rauhigkeit M_R von unter 1 mm erzielt wird;
• E- Auftragen eines Deckstrichs (siehe 5) mit einer Filmpresse, vorzugsweise simultan auf beide Seiten, alternativ kann der Auftrag auch mit jeweils einem kontaktlos arbeitenden, sogenanntem Vorhang-Streichaggregat (Curtain coatern), der beispielhaft in gestrichelter Form eingezeichnet ist erfolgen. Der Auftrag kann pro Seite auch unmittelbar nacheinander und ohne Zwischentrocknung der Beschichtung vorzunehmen, erfolgen. Mit den besagten Vorhangstreichaggregaten ist ein sogenannter 1:1-Auftrag möglich. Das heißt, ohne Abrakelelement wird nur die Menge an Auftragsmedium aufgetragen, die auf der Bahn auch verbleiben soll.
• F- Trocknen des Deckstriches, zunächst erfolgt ein erneutes Umlenkung mit einem Airturn, anschließend wird die Bahn bzw. der Deckstrich kontaktlos mit Infrarot- und Lufttrocknern und anschließenden Trockenzylindern getrocknet.
• G- Endglättung, bzw. abschließendes Finishing des doppelt gestrichenen und getrockneten Papieres, vorzugsweise mit einem Januskalander, d.h. Mehrwalzensoftkalander – wie in 6 dargestellt – oder mit wenigstens zwei Schuhkalandern, die jeweils eine beheizte Gegenwalze für jede Bahnseite aufweisen. Die Endglättung kann aber auch wie herkömmlich mit einem sogenannten Superkalander erfolgen. Selbstverständlich ist es auch möglich die Endglättung in mehreren, mindestens zwei Walzenspalten zu glätten. Dabei werden Kombinationen aus beheizten Gußstahlwalzen und Kunststoff beschichteten Walzen benutzt. Die Oberflächentemperatur der Gußstahlwalzen beträgt zwischen 80 und 200°C, vorzugsweise 120 bis 160°C. Die Linienkraft in den einzelnen Walzenspalten beträgt 200 bis 450 N/mm, vorzugsweise 300 bis 400 N/mm. Diese abschließende Glättung erfolgt, wie dargestellt, entweder online direkt im Anschluß an die Trocknung des Deckstriches. Alternativ kann die abschließende Glättung auch in einem separaten, nicht mit der Papiermaschine verbundenem Glättwerk erfolgen (offline), wozu allerdings eine zusätzliche Auf- und Abrollung der Bahn notwendig ist. Besonders vorteilhaft für die abschließende Glättung der Oberfläche ist eine Papiertemperatur größer als 50°C, vorzugsweise 60-80° C sowie eine Feuchte der Bahn von 5-10%, vorzugsweise 6-8%. Von Vorteil ist hierbei, dass jede gestrichene Papierseite mindestens einmal eine beheizte Gußstahlwalze berührt.
• H- Aufrollung der fertigen LWC-Bahn. Sie ist nun geeignet für das Bedrucken im Tiefdruckverfahren.

By the invention, the above object is solved in a perfect way. Decisive for this is the intelligent selection of process steps or processing stations, which is again summarized as follows and summarized in 6 should be shown:
The process steps take place in the following order:

• A- Vorglatten the base paper web with a calender, as it is under 2 is described. The two rolls, preferably forming a hard smooth nip, serve to produce a uniform thickness profile of the raw paper, with a macro-roughness of greater than 1 mm;
• B- prime by means of a film press (see also 3 ), so with indirect order; In this case, preferably, a simultaneous application of the coating medium on both sides of the paper web and a contour coverage of the surface;
• C- deflecting the web with a so-called Airturn and drying the coating layer initially contactless with infrared and air dryers and subsequent drying cylinder
• D- Between smoothing between smoothing rollers, their possible combinations in 4 are explained, wherein a micro-roughness M _R of less than 1 mm is achieved;
• E- Apply a top coat (see 5 ) with a film press, preferably simultaneously on both sides, alternatively, the order can also be carried out with a non-contact, so-called curtain coating unit (curtain coatern), which is shown by way of example in dashed form. The order can be made per side also immediately after one another and without intermediate drying of the coating. With the said Vorhangstreichaggregaten a so-called 1: 1 order is possible. That is, without Abrakelelement only the amount of application medium is applied, which should also remain on the web.
• F- drying of the cover coat, first a new deflection with an Airturn, then the web or the top coat is dried contactless with infrared and air dryers and subsequent drying cylinders.
• G finish smoothing or final finishing of the double-coated and dried paper, preferably with a Janus calender, ie multi-roll soft calender - as in 6 shown - or with at least two shoe calenders, each having a heated counter-roller for each web page. However, the final smoothing can also be carried out as conventionally with a so-called supercalender. Of course, it is also possible to smooth the final smoothing in several, at least two nips. Combinations of heated cast steel rolls and plastic coated rolls are used. The surface temperature of the cast steel rolls is between 80 and 200 ° C, preferably 120 to 160 ° C. The line force in the individual nips is 200 to 450 N / mm, preferably 300 to 400 N / mm. This final smoothing is done, as shown, either online immediately following the drying of the top coat. Alternatively, the final smoothing in a separate, not connected to the paper machine smoothing done (offline), including, however, an additional winding and unwinding of the web is necessary. Particularly advantageous for the final smoothing of the surface is a paper temperature greater than 50 ° C, preferably 60-80 ° C and a moisture content of the web of 5-10%, preferably 6-8%. The advantage here is that each coated paper page touches at least once a heated cast steel roller.
• H winding of the finished LWC track. It is now suitable for gravure printing.

It should be mentioned be that in principle it is conceivable to apply not only two layers to the web, but also three or more. Again this is usually one intermediate smoothing each be provided.

Also in the 1 to 6 illustrated process steps or processing stations do not necessarily follow each other directly. It can be interposed further action steps, for example. An intermediate humidification or an intermediate heating.

1

paper web

2

layer of the primer

3

layer of the top coat

d

thickness minimal

D

thickness maximum

O

surface topography

M _R

microroughness

Claims (11)

A process for producing a coated, gravure-capable LWC paper web, characterized by the following process steps: 1.1 in a first step (A) the surface of a moving web ( 1 ) pre-smoothed from raw paper and equalized its thickness profile; 1.2 in a second step (B), one or both sides of the track ( 1 ) a primer ( 2 ) applied in the form of a contour line; 1.3 in a third step (C) the train ( 1 ) dried for a first time; 1.4 in a fourth step (D) the web ( 1 ) is subjected to intermediate smoothing; 1.5 in a fifth step (E) is placed on one or both sides of the track ( 1 ) applied a top coat in the form of a contour line; 1.6 in a sixth step (F) the web ( 1 ) dried a second time; 1.7 in a seventh step (G), the train ( 1 ) finally smoothed. Method according to Claim 1, characterized in that at least the first to sixth steps (A to F) are carried out online within a machine for producing the paper web ( 1 ) is carried out. Method according to Claims 1 and 2, characterized that in the first step (A) of pre-smoothing a smoothing device consisting of a two-roller combination is applied, in which Line pressure of 20 to 60 kN / m, preferably between 30 and 40 kN / m is set. Method according to Claims 1 and 2, characterized in the fourth step (D) of intermediate smoothing, a smoothing device consisting of a two-roller combination is applied, in which Line pressure between 100 and 600 kN / m, preferably between 100 and 300kN / m is set. A method according to claim 1 and 2, characterized in that for the application of the precoat ( 2 ) in the second step (B) a known film press is used. Method according to one of claims 1 and 2, characterized in that for the application of the top coat ( 3 ) in the fifth step (E) at least one curtain coater is used for at least one web page. A method according to claim 5 and 6, characterized in that per side of the sheet precursor ( 2 ) and the top coat ( 3 ) is applied with a weight of 5 to 15 grams of absolutely dry coating color per square meter, preferably 6 to 10 g / m ² . Process according to Claims 5 to 8, characterized in that the solids concentration of the precoat ( 2 ) and the top coat ( 3 ) is between 50 and 70%, preferably 60 to 68%. Method according to one of claims 1 to 8, characterized in that at least one of the drying operations in the third (C) and / or sixth step (F) is preceded by a preheater, preferably an infrared heater to the web ( 1 ) to at least 50 ° C preheat. A method according to claim 1 and 2, characterized in that in the fourth step (D) of the intermediate smoothing a smoothing device in the form of a Shoe calender is applied, set with a pressure shoe gap length 20 to 250mm, preferably 40 to 70 mm. Method according to claim 1, characterized in that at the seventh step (G) for the final smoothing of the web ( 1 ) a Janus calender or supercalender or combinations of heated cast steel rolls and plastic coated rolls is used.