Method and device for single-or double-sided application

A method for the application of liquid through viscid medium onto the surface of a pre-dried material web including the steps of applying a viscid medium to at least one side of the material web, routing the material web through a press nip and supporting the material web substantially without free draw.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method and device for the application of a liquid medium onto a material web, and, more particularly, to a method and device for the application of liquid through viscid mediums onto a pre-dried material web.

2. Description of the Related Art

In the direct application process a liquid or viscid medium is applied directly by an applicator device to the surface of a moving material web, which is supported during the application process by a rotating support surface, such as a backing roll or a continuous belt. The liquid or viscid medium is initially applied to a carrier surface, such as the surface of a roll serving as an applicator roll, or the surface of one side of a flexible belt, and is transferred therefrom to the material web.

Indirect application is normally accomplished by a so-called film press implemented by two rolls, which together form a nip, and which transfer the medium successively or simultaneously to both sides of the material web or to only one side of the web.

Reference is made to U.S. Pat. No. 5,683,509 which discloses a flexible continuous belt, together with a transfer roll, which form the press nip through which the web travels. A press shoe is located on the inside of the continuous belt, thereby extending the nip and pressing the coating medium, that is applied by this unit, into the web. This improves the coating result, specifically by avoiding film splitting.

Reference is also made to DE 198 23 739 A1, according to which, a material web is coated in the wet section or immediately following the wet section, of a paper machine.

Film or size presses have been in operation for years. They have some significant disadvantages when utilized with today's high-speed machines, and depending upon the type of fiber web and coating medium, they do not always provide sufficient coating quality.

The raw material quality of paper or cardboard is continuously degrading. This is particularly true of the production of corrugated board base paper, which is largely manufactured from recovered paper. There is also an ever increasing demand for a lower mass per unit area (also referred to as basis weight). The result of using poor raw material quality and lower basis weight is that the tensile strength of the web, following the film press coating application, is very low, resulting in frequent web breaks after the coating of the web. This results in enormous production down times and associated high costs.

Film Presses, variously known as Speedsizer, Speedcoater, Optisizer or metering size press, frequently cause nip flattening and crushing in the nip. These effects are particularly negative in corrugated board production.

In the field, web breaks, particularly in the production of corrugated board base paper, are reduced by using modified starches, that have a low viscosity and a high solids content, as a coating medium. The low viscosity provides effective penetration and the high solids content produce low remoistening, thereby rendering possible only a low drop in tensile strength following the film press. However, modified starches are more expensive as compared to crystal starches.

Even these measures do not always lead to satisfactory results.

SUMMARY OF THE INVENTION

The present invention provides a method and a device for the production of corrugated board base paper, whereby a deep penetration of coating medium containing starch into the material web, independent of the basis weight, and by utilizing the starch characteristics, is accomplished and web breaks are largely avoided.

The inventors recognized that the hitherto used starches, whose viscosity and solids contents were modified, produced only an insignificant increase in strength of the coated and impregnated material web, as compared to crystal starches.

The positive effects of the starch in the coating medium increase since the pre-dried corrugated board base paper web travels through a press nip only after coating, and because the web is dried a considerable distance after the nip, essentially the distance to the first dryer cylinder, being supported without free draw.

An advantage of the present invention is that a penetration through to the “sheet center” can be achieved, even at low basis weights, resulting in an increase of the web's tensile strength.

Another advantage is that it is now possible to use crystal starches in spite of intensive remoistening. Crushing during corrugated board base paper production is reliably avoided.

A further advantage of the present invention is that fewer web breaks occur following the coating process.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly toFIG. 1, there is illustrated a pre-dried corrugated board base paper web B that has a dry content of approximately 85 to 95%, following a last dryer cylinder2of pre-dryer group3, in a machine for the production of corrugated board base paper, running onto a first applicator roll4. Applicator roll4has an applicator device5assigned to it, with which web B is coated on it's top side Bo. All known coating devices, such as a Short Dwell Time Applicator (SDTA), Long Dwell-Time Applicator (LDTA), open jet nozzle applicators or a curtain coating nozzles are suitable. A pre-penetration of the coating medium is achieved with this one- or two-sided application.

In order to support web B, a transfer belt, that is a flexible continuous synthetic or rubber belt, is routed around additional roll16, a support or backing roll7and around several guide or turning rollers8. A tension roll21, which is located on the paper machine floor PMB, reacts on belt6from the outside, thereby tensioning it.

Whereas a two-sided application is illustrated, applicator5ais assigned to support roller7. The coating medium is transferred from continuous belt6to underside BUof web B, as soon as belt6makes contact with web B. The application by applicators5and5amay occur simultaneously, or successively in an offset time sequence. If only a one-sided application is to occur, on either the topside or the underside of the web, one of the idle applicator devices are pivoted down. As can be seen inFIG. 1, rolls4and7together do not form a press nip. This is intentional, so that no crushing of the web is caused and no web breaks occur.

The embodiment illustrated inFIG. 1, includes a long pre-penetration segment Pg,that ought to be considerably longer than 100 mm, thereby providing good penetration due to the capillary effect during the extended reaction time. This long distance is particularly advantageous in achieving the desired through-penetration.

Now additionally referring toFIG. 2, which essentially uses the identical references for the identical components asFIG. 1, there is shown another embodiment of the invention. In this embodiment there is no roll4; only applicator device5is present for direct application of coating onto the topside of web Bo. Alternatively, an additional continuous belt, in place of the roll4, may be utilized with which web B is supported, and indirect coating of the material web is achieved.

After passing penetration segment Pgweb B runs together with belt6, which can be used as an applicator and support belt, through press zone9. Press zone9may be realized in various ways. In order to allow a long dwell time and avoid crushing, as well as to be able to adjust variable line pressures across the entire width of web B, a shoe press is utilized. In press zone9the pre-penetrated starch can after-penetrate, thereby anchoring itself solidly in web B.

Alternatively, press zone9may include an additional flexible continuous belt10running over guide rollers11,12and13. Belt10runs with it's inside surface over a slide face of press shoe14, whereby the slide face, together with roll15, which could for example be a suction roll, forms a press nip N. Press shoe14is shown in only as a simplified depiction and may extend over a large area of belt10. Press zone9can also include rolls15and16which form a press nip N. InFIGS. 1 and 2, roll15is illustrated in a dash-dot configuration and embodies a so-called flexonip roll. This construction is already known from DE 198 20 516 A1, which is incorporated herein and made a part hereof, however there are no statements therein regarding supporting of the web after squeezing in the coating.

Roll15is one of those rolls, around which continuous belt6travels, forming the aforementioned backing surface to roll16and/or the belt acting as a press, support or applicator belt10. Continuous belt10, as well as continuous belt6, each form a support surface therebetween for web B that is penetrated through after Nip N. Support surface SFextends essentially to first dryer cylinder18, in the following dryer section19, of the paper machine.

As indicated by the dashed lines, inFIG. 2, continuous belt10can be extended, to a desired extent, by adjustment of guide roller13. Likewise belt6can also extend its support surface, to a desired extent, by adjusting upper guide roller8. As is also shown inFIG. 2, an extended support surface provides for a blow box, suction roll or suction box20, or for another type of transfer aid, to facilitate transfer of web B, or of a transfer strip, to dryer cylinder18.

InFIG. 1the possibility of supporting web B in the direction of the location of application is shown as a dotted line. For this purpose belt10, or a separate belt10a, is routed around roll4, or around an adequately positioned guide roller. Belt10amay also be additionally supported by roll11. Alternatively, continuous belt10acan replace roll4, thereby providing the aforementioned support of web B, as well as indirect coating, at the same location as is being done with roll4.

Belts6and10are equipped with a drive and rolls4,7and15are driven. Relative to belt6this drive is located at nip N, in order to ensure sufficient pull of web B. In addition, tensioning devices, such as tensioning roller21and tension control devices, for the belts are provided, as well as belt adjustments which are indicated by double arrows at guide rolls8and13.

In order to facilitate a flawless transfer of web B to dryer section19, a suction roll22, with or without foil23, is provided after press zone9or continuous belt10. This arrangement allows for a transfer of the web without ropes.

For the sake of completeness it must be mentioned that in order to facilitate a flawless transfer of web B, one or more showers (not depicted in the drawings) are provided prior to the point where belt6runs onto applicator roll4. These provide a targeted liquid application onto belt6or web B, in order to ensure adhesion of the transfer strip or web B. In order to avoid lifting of web B at press roll16, additional support belts, so-called fibron belts or other known transfer aids, can be provided. The paper machine section illustrated inFIGS. 1 and 2is essentially consistent with a “closed transfer” into dryer section19.

It is also feasible to include an additional applicator device5cto continuous belt10, thereby providing for a double application onto topside Boof web B. This may occur with or without intermediate drying. Additional support belts10a. . .10nor6a. . .6n, on one or both sides of web B, may be provided, which have associated applicator devices5a. . .5n, being of the same type or acting independently from each other. An advantage of this type of arrangement is that only a fraction of the starch is applied by each applicator device. This reduces the re-moistening of web B immediately after the application. Web B does not loose consistency, thereby increasing runability.

Overall, it has been determined in tests that the consistency gain of the paper and cardboard web is not approximately 20N/% starch as was the case previously, but 40N/% starch. This means that, while maintaining the same quality the starch amount can be reduced by 30%. Alternatively the quality is increased when the same amount of starch is used. This is especially important considering the drop in quality of raw materials used in the production of corrugated board base paper.

Furthermore crystal starches can now also be used.