EP2643648B1 - Method and system for impregnating and drying a continuous paper web - Google Patents

Description

The invention relates to a method for impregnating and drying a continuous paper web with a urea resin dissolved in water, wherein the urea resin is applied to the paper web in a metered amount, the paper web is guided in a dryer by heated air and dried to a predetermined residual moisture, wherein at least a portion of the air is circulated, a temperature of the paper web is determined and the drying is controlled by changing drying parameters in a plurality of different drying zones, wherein between the adjacent drying zones in each case a partition wall is arranged.
The invention further relates to a corresponding device for carrying out the method.

Such impregnated paper webs are known per se and are e.g. used as furniture foils or for floor laminate. Here, high demands are placed on the quality. For this reason, predominantly expensive melamine resins have hitherto been used in practice for impregnation.

Here, the decorative papers are impregnated with the melamine resin and dried with warm air. When pressed under heat and pressure with the substrate, e.g. a chipboard, the melamine resin causes the surface to be scratch-resistant and ensures that the decorative paper is securely bonded to the substrate. To save costs, the much cheaper urea resin can be used for a first impregnation. Then the impregnated web must be coated on both sides with melamine resin in order to achieve the required surface properties of the laminate and to ensure the bonding with the flap.

In the usual drying methods, bonding of the pure urea resin-impregnated web to the substrate is not possible.

From the EP 966 641 A1 a method for impregnating and drying a paper web is known in which a target application with melamine resin is controlled by means of measured values of the basis weights. The drying takes place by means of heated air and is regulated by means of a final moisture content of the impregnated paper web.

It is desirable to replace the melamine resin in the impregnation of paper webs largely by much cheaper urea resin.

The WO 2008/134823 A1 describes a process for the production of impregnated paper in which a urea resin is used for impregnation. The drying takes place by means of near-infrared rays, crosslinking of the resin being largely avoided. The low cross-linking allows for the compression of the impregnated with the urea resin film with the substrate, that a secure bonding takes place. A disadvantage of the method is that the required reliability is not given. Furthermore, expensive electrical energy is needed. In the case of colorful decors, spots of different colors are dried differently due to the different absorption and reflection, so that the web as a whole has uneven moisture.

It is therefore a first object of the invention to provide a method which has the required reliability, wherein the crosslinking of the urea resin is largely prevented, and ensures a uniform drying at low energy costs, even in all variants of the decor.

Another object is to provide a device for carrying out the method.

The first object is solved by the features of claim 1. The temperature of the paper web is determined and controlled separately in each of the drying zones, and for each of the drying zones, an amount and / or a temperature of the circulating air are controlled such that the temperature of the paper web is at most 99 ° C, preferably at most 80 ° C to 85 ° C is. In this way, it is certainly achieved that in any of the drying zones, the critical temperature for urea resin exceeded and still the required degree of drying is achieved very evenly. In particular, crosslinking of the urea resin is largely prevented, so that during later lamination, a firm bonding with e.g. a plate is guaranteed. Therefore, contrary to previous practice, the much cheaper urea resin can be used. Decisive for this is the prevention of crosslinking.

Exhaust air is withdrawn from a first of the drying zones and fresh air fed to a last of the drying zones (directional information, positions and the like always refer to a transport direction of the paper web in this application). This has the effect that each of the drying zones is traversed by the largest possible amount of fresh air with as little exhaust air as possible. The control of the amount and / or the temperature of the circulating air as a function of the temperature of the paper web allows a high temperature in a direction of transport of the paper web of the first drying zones at the same time high circulation. In this case, no or only little air can reach the next drying zone, in which a lower temperature prevails. Therefore, the maximum temperature of the paper web can be safely maintained, with high evaporation rates especially in the first drying zone can be achieved. Overall, can be set in the drying zones of high to low graded temperatures without significant mutual interference, so that a total high evaporation rate despite the low temperature of the paper web can be achieved. In particular, it is prevented that air flows from a drying zone with higher temperature and high water content in an adjacent subsequent drying zone at a lower temperature, thus leading to an unacceptably high temperature of the paper web.

The urea resin has the additional advantage that it is fluid and therefore better and faster impregnated into the paper web. Therefore, the impregnation is simplified.

Furthermore, the impregnated with urea resin and then dried paper web is printable, so that a short-term printing decoration can be changed without having to make a change of a supply roll of the paper web. The stockpiling for paper webs is greatly simplified.

The subclaims relate to the advantageous embodiment of the invention.

In a particular embodiment of the method, the fresh air is preheated by means of the exhaust air in a heat exchanger. This reduces the energy consumption of the drying process.

In a further embodiment, an uncontrolled penetration of ambient air into the dryer as far as technically feasible prevented; For this purpose, appropriate barrier locks at the inlet and at the outlet of the paper web are arranged in the dryer, which are e.g. be subjected to blocking air. In this way it is achieved that the fresh air largely enters only the last of the drying zones.

In a further embodiment, the air is heated directly by means of combustible gas, in which case combustion gases produced are mixed with air drawn off from an associated one of the drying stages and then supplied to this drying stage as heating gas. Each drying step is assigned its own burner. The mixing and thus the cooling of the combustion gases with the air from the drying stages causes a strong reduction of the exhaust air of the dryer; less fresh air needs to be heated.

In a further embodiment, the air in the dryer has a relative humidity of at most 10%, preferably at most 5%. This results in a high water absorption capacity of the air and therefore a gentle and rapid drying.

In a further embodiment, the temperature of the air in the first drying step is 120 ° C to 300 ° C, preferably 150 ° C to 200 ° C, and in the last drying step 60 ° C to 100 ° C, preferably 70 ° C to 90 ° C. In the drying stages between the first and the last, the temperature of the air is adjusted to values between that in the first and the last drying stage, wherein the temperature is gradually reduced from one of the drying stages to the next in the transport direction of the paper web. In this way, the highest possible evaporation performance results for each drying stage, without the permissible temperature of the paper web being exceeded.

In a further embodiment, a melamine resin is applied to the paper web after drying. As a result, a higher quality surface of the finished coated paper web is achieved. This largely satisfies the requirements of a solely melamine resin impregnated and / or coated paper web, but with the inventive method, the production costs are significantly reduced.

The second object is solved by the features of claim 8. The same applies to what has been said for the procedure.

• Figur 1 ein Schema einer Vorrichtung zum Imprägnieren und Trocknen einer durchlaufenden Papierbahn und
• Figur 2 ein Schema einer gasbeheizten Trocknungszone.

The invention will be further explained with reference to the schematic drawing. Show it

• FIG. 1 a diagram of an apparatus for impregnating and drying a continuous paper web and
• FIG. 2 a schematic of a gas-heated drying zone.

Like from the FIG. 1 an apparatus for impregnating and drying a continuous paper web 1 comprises a first application device 2 for the metered application of urea resin and a dryer 3. The dryer 3 is preferably followed by a winder 4 for winding up the impregnated paper web 1, whose transport in the direction according to the arrow 5 he follows.

The first application device 2 comprises an application roller 6, guide rollers 7 and not shown means for supplying the urea resin.

The dryer 3 is constructed in a modular manner from here four substantially identically constructed drying zones 3.1, 3.2, 3.3, 3.4 and enclosed by a housing. Between the adjacent drying zones 3.1, 3.2, 3.3, 3.4, a partition wall is arranged in each case.

Each of the drying zones 3.1, 3.2, 3.3, 3.4 comprises, as shown in FIG. 2 is particularly clear, a circulating fan 8, nozzle boxes 9, which are arranged below and above the paper web 1 for inflating air circulated as circulated air to the paper web 1, means for heating the circulating air as well as channels or lines for guiding the circulating air. In each drying zone 3.1, 3.2, 3.3, 3.4, a measuring device 10 is arranged so that a temperature of the paper web 1 in a rear region of the drying zone 3.1, 3.2, 3.3, 3.4 can be determined. The measuring device 10 includes, for example, a non-contact infrared sensor. The circulating air fan 8 is arranged in a suction chamber 11 within the drying zone 3.1, 3.2, 3.3, 3.4 and connected on the pressure side by means of channels to the nozzle boxes 9.

The means for heating the circulating air comprise a gas burner 12 with a burner tube 13 and a burner air fan 14, a mixed air fan 15 and connecting air ducts. The mixed-air fan 15 is connected on the intake side to the suction chamber 11 and on the pressure side to the burner tube 13. An outlet of the burner tube 13 is connected to the suction chamber 11, that in operation a mixing of the sucked from the mixing air fan 15 circulating air is excluded with the introduced from the outlet of the burner tube 13 in the suction chamber 11 heated circulating air.

Alternatively, the means for heating the circulating air comprise a not shown first heat exchanger, which is associated with the suction side of the circulating air fan 8 and can be acted upon by heating medium such as thermal oil or steam.

An inlet of the paper web 1 in the first drying zone 3.1 and an outlet from the last drying zone 3.4 is assigned a barrier lock 16 each. Each of the barrier sluices 16 is separately acted upon with fresh air so that unwanted intrusion of ambient air in and leakage of air from the dryer 3 is largely avoided.

At the first drying zone 3.1. is connected to the housing an exhaust duct 17 which merges behind a second heat exchanger 18 in a fireplace. To the second heat exchanger 18, a fresh air line 19 is further connected, which leads to the last drying zone 3.4. To increase the pressure in the fresh air line 19, a fresh air fan 20 is integrated.

In operation, the paper web 1 is withdrawn from a supply roll 21 and passed through the first application device 2. As is known, the urea resin in aqueous solution is uniformly distributed on the paper web 1 and dosed to a predetermined basis weight of, for example, 50 g of urea resin dry matter per m ² . The urea resin impregnated in the paper web 1 so that it is uniformly saturated.

The impregnated paper web 1 is then fed to the dryer 3, transported therein in a floating manner in the transporting direction and brought to a predetermined residual moisture of e.g. 7% dried. For this purpose, the paper web 1 is acted upon in the drying zones 3.1, 3.2, 3.3, 3.4 with heated circulating air.

In each of the drying zones 3.1, 3.2, 3.3, 3.4, the circulating air is conveyed by means of the associated circulating air fan 8 in the circuit. Here, the circulating air is withdrawn from the suction chamber 11, heated by means of the burner exhaust gases of the gas burner 12, conveyed by the circulating air fan 8 in the nozzle boxes 9 and blown out of these so on the paper web 1, that this is held in suspension. The burner exhaust gases are mixed to cool them with air from the drying zone 3.1, 3.2, 3.3, 3.4, wherein the air is withdrawn by means of the mixed air fan 15 from the associated drying zone 3.1, 3.2, 3.3, 3.4 and introduced into the burner tube 13. The gas mixture thus produced is passed as heated air for heating the circulating air in the suction zone 11 in the immediate suction region of the circulating air fan 8. The heated air is thus supplied directly to the suction side of the circulating air fan 8 so that further mixing with the air withdrawn from the mixed air fan 15 is prevented.

In the drying zones 3.1, 3.2, 3.3, 3.4, the circulating air is adjusted so that it has a low relative humidity of less than 5%. Since in all drying zones 3.1, 3.2, 3.3, 3.4, the temperature of the paper web 1 is controlled at 80 ° C, results in high water evaporation the highest possible temperature of the circulating air and thus for all drying zones 3.1, 3.2, 3.3, 3.4, a low relative humidity , The amount of fresh air is preheated in the second heat exchanger 18 by the exhaust air from the first drying zone 3.1 and passed by means of the fresh air fan 20 and the fresh air line in the last drying zone 3.4.

The exhaust air is discharged by means of the exhaust duct 17 from the first drying zone 3.1, cooled in the heat exchanger 18 and - optionally after a treatment - passed through a chimney into the open air. An amount of the exhaust air and thus also a quantity of fresh air is given and regulated as known according to the process conditions.

At the end of each drying zone 3.1, 3.2, 3.3, 3.4, the temperature of the paper web 1 is determined by means of the measuring device. For each drying zone 3.1, 3.2, 3.3, 3.4, the temperature and / or the amount of air (circulating air) is controlled so that the temperature of the paper web 1 is 80 ° C. The temperature of the air is highest in the first drying zone 3.1 with, for example, 180 ° C and then drops gradually, for example, to 110 ° C in the second 3.2, 90 ° C in the third 3.3 and 80 ° in the last drying zone 3.4. In this way, it is reliably prevented that the urea resin crosslinks too much.

Further probes and control loops can be arranged, wherein the temperature of the paper web 1 is determined as the parent Leitgröße.

After drying, the impregnated paper web 1 is wound in the winder 4 into a roll.
Alternatively, the paper web 1 is cut into sheets by means of a cross cutter.

In an alternative embodiment of the invention, an unillustrated printer is arranged between the dryer 3 and the winder 4, which in operation prints one side of the impregnated paper web 1 with a decor.

In a further alternative embodiment of the invention, a second application device is arranged between the dryer 3 and the winder 4 or between the printer and the winder 4, which applies in operation on the optionally printed page melamine resin in a known manner and dosed. The layer of melamine resin is then dried in a further drying device, wherein a temperature of the paper web of a maximum of 99 ° is maintained. <B> LIST OF REFERENCES </ b> 1 paper web 12 gas burner 2 applicator 13 burner tube 3 dryer 14 Burner air fan 4 winders 15 Mixed air fan 5 Arrow (transport direction) 16 lock lock 6 applicator roll 17 exhaust duct 7 deflecting 18 second heat exchanger 8th circulation fan 19 Fresh air line 9 nozzle box 20 Fresh air fan 10 measuring device 21 supply roll 11 suction

Claims (12)

1. Method for impregnating and drying a continuous paper web (1) with of a urea resin dissolved in water, wherein

   - the urea resin is applied to the paper web (1) in a dosed quantity;

   - the paper web (1) is conveyed in a dryer (3) by heated air while being suspended, and dried to a predetermined residual moisture, wherein at least one part of the air is circulated as recirculated air in a cycle;

   - a temperature of the paper web (1) is determined; and

   - the drying is regulated by changing drying parameters plurality of different drying zones (3.1, 3.2, 3.3 and 3.4),

   - wherein one dividing partition each is placed between the adjoining drying zones (3.1, 3.2, 3.3 and 3.4),

   - wherein the temperature of the paper web (1) in each of the drying zones (3.1, 3.2, 3.3 and 3.4) is determined and regulated separately, characterised in that, for each of the drying zones (3.1, 3.2, 3.3 and 3.4), a quantity and/or a temperature of the recirculated air is regulated in such a way that the temperature of the paper web (1) amounts to a maximum of 99°C, and that exhaust air is exclusively extracted from one of the first drying zones (3.1) and fresh air is exclusively supplied to one of the last drying zones (3.4).
2. Method in accordance with Claim 1, characterised in that the fresh air is pre-heated by means of the exhaust air.
3. Method in accordance with Claim 1 or 2, characterised in that an uncontrolled penetration of ambient air into the dryer (3) is prevented.
4. Method in accordance with one of Claims 1 to 3, characterised in that the recirculated air is directly heated using combustion gas, wherein combustible gases generated here are mixed with air extracted from one of the relevant drying zones (3.1, 3.2, 3.3 or 3.4) and the resulting compound is then supplied to this drying zone (3.1, 3.2, 3.3 or 3.4) as heating gas.
5. Method in accordance with one of Claims 1 to 4, characterised in that the recirculated air in the dryer (3) has a relative humidity up to a maximum of 10%.
6. Method in accordance with one of Claims 1 to 5, characterised in that the temperature of the recirculated air in the initial drying zone (3.1) amounts to 120°C to 300°C, and in the last drying zone (3.4) 60°C to 100°C.
7. Method in accordance with one of Claims 1 to 6, characterised in that a melamine resin is applied to the paper web (1) after drying.
8. Device for impregnating and drying a continuous paper web (1) with a urea resin dissolved in water, comprising

   - a first application device (2) for dosed application of the urea resin to the paper web (1);

   - a dryer with means of suspended conveying whilst blowing heated air that is at least partially recirculated onto the paper web (1), wherein the dryer (3) has a plurality of drying zones (3.1, 3.2, 3.3 and 3.4);

   - wherein one dividing partition each is placed between the adjoining drying zones (3.1, 3.2, 3.3 and 3.4);

   - at least one measuring device (10) for determining a temperature of the paper web (1); and

   - a control loop for changing drying parameters in the drying zones (3.1, 3.2, 3.3 and 3.4);

   - wherein each of the drying zones (3.1, 3.2, 3.3 and 3.4) contains the measuring device (10) for determining the temperature of the paper web (1), characterised in that the control loop influences a temperature and/or a quantity of the recirculated air in each of the drying zones (3.1, 3.2, 3.3 and 3.4) in such a way that the temperature of the paper web amounts to a maximum of 99°C, and that an exhaust duct (17) is exclusively assigned to a first one of the drying zones (3.1) and a fresh air duct (19) is exclusively assigned to last one of the drying zones (3.4).
9. Device in accordance with Claim 8, characterised in that a heat exchanger for heating up fresh air is provided for by means of exhaust air from the dryer (3).
10. Device in accordance with Claim 8 or 9, characterised in that a barrier lock (16) is assigned to both an in-feed of the paper web (1) into the dryer (3) and an outlet respectively.
11. Device in accordance with one of Claims 8 to 10, characterised in that a burner (12) for combustion gas is assigned to each drying zone (3.1, 3.2, 3.3 and 3.4), wherein air from the drying stage (3.1, 3.2, 3.3 or 3.4) can be supplied to combustion gases in a burner pipe (13) by means of a mixed air ventilator (15), and wherein the combustion gases mixed with the air can be conducted into the drying stage (3.1, 3.2, 3.3 or 3.4) as heating gas.
12. Device in accordance with one of Claims 8 to 10, characterised in that a second application device for applying melamine resin is arranged downstream of the dryer (3).

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