阅读说明：本技术 淀粉涂布方法和装置 (Starch coating method and apparatus ) 是由 C.亨宁格 M.德曼 于 2019-07-09 设计创作，主要内容包括：用于在移动的纤维网、尤其是包装纸网(例如强韧箱纸板或瓦楞原纸网)上涂布淀粉的方法和装置,其中第一种淀粉被涂布到第一辊和/或第二辊上,并且纤维网通过由第一辊和第二辊形成的处理辊隙,其特征在于,第一辊或第二辊中的至少一个(优选两个辊)的硬度为15P&J(赵氏硬度)以下,优选为5P&J以下,最优选为1P&J以下,并且淀粉经由狭缝式模具和/或滑动式模具涂布到第一辊和/或第二辊上,然后转移到处理辊隙内的纤维网上。(Method and device for coating starch on a moving web, in particular a packaging web, such as a strong box board or corrugated base web, wherein a first starch is coated onto a first roll and/or a second roll and the web is passed through a treatment nip formed by the first roll and the second roll, characterized in that at least one, preferably both, of the first roll or the second roll has a hardness of below 15P & J (jones hardness), preferably below 5P & J, most preferably below 1P & J, and that the starch is coated onto the first roll and/or the second roll via a slot die and/or a slide die and then transferred onto the web in the treatment nip.)

1. Method for coating starch on a moving web of fibers (5), in particular a packaging web (5), such as a strong box board (5) or a corrugated base web (5), wherein a first starch is applied to the first roll (1) and/or the second roll (2), and the web (5) is passed through a treatment nip (6) formed by the first roll (1) and the second roll (2), characterized in that at least one of the first or second rolls (1, 2), preferably both rolls (1, 2), has a hardness of 15P & J (Zhao hardness) or less, preferably 5P & J or less, most preferably 1P & J or less, and starch is applied to the first roll (1) and/or the second roll (2) by means of a slot die (3) and/or a slide die (3a) and then transferred to the web (5) in the process nip (6).

2. The method according to claim 1, characterized in that the starch is applied to the first roll (1) and/or the second roll (2) in the form of a free-falling curtain and/or a free-jet coating.

3. A method as claimed in any one of the preceding claims, characterized in that the hardness of the first roll (1) and the second roll (2) is 15P & J or less, preferably 5P & J or less, most preferably 1P & J or less.

4. A method as claimed in any one of the preceding claims, characterized in that the line load of the treatment nip (6) is between 30 and 140 kn/m, preferably between 60 and 100 kn/m.

5. A method as claimed in any one of the preceding claims, characterized in that the web (5) is passed through the nip at a speed of more than 800 m/min, preferably 1000 m/min to 1900 m/min.

6. Method according to one of the preceding claims, characterized in that the applied starch has a solids content of 6 to 25%, preferably 8 to 18%, and/or a viscosity of 5 to 60mPas, preferably 10 to 40 mPas.

7. The method according to one of the preceding claims, characterized in that the starch content of the fibre web (5) at the winder is 2.5 to 6% by weight on a basis.

8. Device for coating starch on a moving web (5), comprising a first roll (1) and a second roll (2) arranged to form a treatment nip (6) of the web (5), and a coating device (3, 3a) for coating starch on at least one of the rolls (1, 2), characterized in that at least one, preferably both rolls (1, 2) of the first roll (1) or the second roll (2) has a hardness of 15P & J (pusey hardness) or less, preferably 5P & J or less, most preferably 1P & J or less, said coating device (3, 3a) comprising a slot die (3) and/or a sliding die (3 a).

9. An apparatus according to claim 8, characterized in that the apparatus further comprises means (10) for removing a boundary layer of air from at least one of the first roll (1) or the second roll (2).

10. The device according to claim 9, characterized in that the means (10) for removing the boundary layer of air comprise at least one of a doctor blade, an air jet, a brush or a foil.

11. A device according to any one of claims 8 to 10, characterised in that the first roll (1) and the second roll (2) have the same diameter or differ by less than 10%.

12. The apparatus as claimed in one of claims 8 or 11, characterized in that the diameter of the first roll (1) and/or the second roll (2) is 0.25 to 2 meters, in particular 0.7 to 1.8 meters.

13. The device according to one of claims 8 to 12, characterized in that the first roll (1) has a coating (6) consisting of metal or ceramic, the layer thickness of the coating (6) being less than 1 mm, preferably 50 to 150 μm; and/or the second roller has a coating (6) made of one of rubber, polyurethane or a composite material, the layer thickness of the coating (6) being 10 mm to 20 mm.

14. An apparatus according to any one of claims 8 to 13, characterized in that at least one of the first roll (1) or the second roll (2) comprises sensor means (11) for measuring the nip load.

Technical Field

The present invention relates to a method and apparatus for treating a web. In particular, the invention relates to a starch coating method according to the preamble of claim 1 and a starch coating apparatus according to the preamble of claim 6.

Background

For the production of paper, board and packaging webs, waste paper is being used more and more for its economic and environmental benefits. Especially for grades such as strong linerboard (TL) or Corrugated Medium (CM), waste paper is often the only fiber source used. But over the past years, the quality of waste paper used for these grades has deteriorated due to the increasing number of recycles. The accumulation of fillers and the reduction in fiber quality due to mechanical and chemical damage to the fibers causes a reduction in various strength properties of the produced paperboard and wrapper.

The addition of fillers such as mineral pigments (e.g., calcium carbonate, titanium dioxide, sand … …) can reduce the wet web strength of the paper sheet. This results in an increased amount of sheet breaks during the production process.

The degraded fiber quality (e.g., reduction in fiber length) can be partially compensated for by treating the web with a synthetic binder (e.g., a polymer latex). Alternatively, the web may be treated with a natural binder (e.g., starch). The use of starch is generally preferred because the cost of polymer latex is generally expensive.

Starch coating has long been a standard practice. The starch may be applied directly to the pulp stock or may be sprayed onto a wet wire in the forming section of a paper machine. But it is also possible to coat the starch after the press section and the pre-dryer section in a more efficient manner. Here, the starch can also be sprayed onto the fibrous web, but is usually applied using a film press or size press. For example, DE 102011076718 describes a method of using a size press in the production of strong linerboards in the case of low-quality recycled fibers.

Due to the above mentioned degradation of the quality of the fibrous material and the increased production speed of most grades of paper, including TL and CM, there is a need in the industry for an efficient method of further improving the strength properties of paper webs.

In application FI 20170013, the applicant has already discussed some relevant aspects.

Disclosure of Invention

The object of the invention is to provide a method for increasing the strength of a fibre web which is technically and economically very efficient.

It is another object of the present invention to provide an efficient method of coating starch onto a moving web.

It is another object of the present invention to provide a method for stably producing strong linerboards (TL) and Corrugating Mediums (CM) even in the case of low raw material quality.

The above objects and those that will become apparent from the following description are achieved by a method having the features of claim 1 and by an apparatus having the features of claim 8.

In terms of method, the object is achieved by a method for coating starch on a moving web, in particular on a packaging web, such as a strong boxboard or corrugated base web, wherein a first starch is coated onto a first roll and/or a second roll, and the web is then passed through a treatment nip formed by the first roll and the second roll, characterized in that at least one, preferably both, of the first or second rolls has a hardness of 15P & J (jones hardness) or less. In addition, starch is first coated onto the first roll and/or the second roll by a slot die and/or a slide die and then transferred to the web in the process nip.

P & J hardness is a common measure of roll hardness. This index can be determined by a commercially available device (e.g., a Zwick 3108P & J durometer) that meets the requirements of the ASTM D531-89 standard.

The term "hardness of the roll" is to be understood as the hardness of the outer or cover layer of the respective roll, except as otherwise indicated, even though the inner layer (i.e., the layer not in contact with the web) may have a different hardness.

The inventors have surprisingly found that by using one or even two rolls with higher hardness in the treatment nip, starch can be transferred to the web more efficiently. Currently, rolls in standard size presses or film presses have a hardness of 20P & J or more, which means that current rolls are significantly softer than rolls in the present invention. Such stiffer rolls have been found to improve the transfer of starch to the web.

The starch coating of the present invention is accomplished by first coating the starch onto the first roll and/or the second roll via a slot die and/or a slide die and then transferring to the web in the process nip.

Slot dies and slide dies are well known per se in the paper coating art.

The starch may be applied from a slot die in the form of a curtain or a jet. In the use of a slide-type mold, the starch is first slid on an inclined surface for a certain length and then falls as a curtain onto a moving web.

Here, the starch may be coated onto one or two rolls, which results in the starch being coated onto one or both sides of the web.

The correct amount of starch applied to the roll is important to the performance of the process.

Standard film presses with soft rollers typically use a system that applies an excess of starch to the rollers. Accurate dosing is achieved by removing excess starch from the roll with a rod or blade.

Tests conducted by the applicant have shown that these contact bars or blades are not suitable for use in the hard rolls of the present invention. They are prone to severe wear and process stability is difficult to guarantee.

Therefore, it is desirable to coat the starch on the roll in a non-contact manner. Spraying starch onto the rolls with a set of nozzles involves a number of problems, including the problem of uniform distribution of starch across the width of the web. Moreover, these nozzles must also be cleaned frequently. This can lead to coater downtime, which reduces the efficiency of the process.

Thus, the present invention uses a slot die or a slide die to apply starch to a roll. These dies meter the amount of starch required in a non-contact manner, thus avoiding the disadvantages of bars or blades. On the other hand, they ensure a uniform starch distribution and are less prone to soiling than nozzles.

Advantageous features of the method of the invention are set out in the dependent claims.

The width of the curtain or jet may be at least as wide as the web.

The starch may be applied from the slot die as a free falling curtain under the influence of gravity.

Alternatively, the slot die may be used to apply the starch in the form of a jet stream, with the starch solution in the slot die under pressure.

In a preferred embodiment, the starch is applied to the first roll and/or the second roll in the form of a free-falling curtain. Since the curtain falls under the influence of gravity, it will contact the upper half of the roller, in many cases at or near the 12 o' clock position. While a 12 o' clock position may be advantageous, different placement positions of the mold are possible. Depending on the geometry of the rollers and the travel of the web, the point of impact of the curtain may be at or near 10 o 'clock, 11 o' clock, 1 o 'clock, 2 o' clock, or other suitable point in time therebetween.

If the starch is applied from the slot die in the form of a jet, the jet nozzle can be placed at any position around the roll. Such jets may also contact the lower half of the roll.

It may be advantageous to use a stiffer roll. In some applications, at least one of the first or second rolls (preferably both rolls) has a hardness of 5P & J or less, preferably 1P & J or less. Even a hardness of 0P & J may be beneficial. This can be achieved, for example, by a hard ceramic or metal surface of the roller.

In an advantageous variant, the treatment nip can be formed by two hard rolls having a hardness of 15P & J or less. This combination further improves the transfer of starch to the web.

In another advantageous variant, the process nip may be formed by a hard roll and a softer roll having a hardness of 15P & J or less. The softer roll may have a hardness greater than 15P & J, particularly greater than 20P & J.

The web of the present invention may be a single layer or a multi-layer web. The layers of the multi-layer web may be produced in two, three or more forming sections and are typically bonded together prior to the starch coating of the present invention. Such multilayer webs are common for TL and CM coatings.

As previously described, the web may be produced from fibers produced from waste paper. The strength-producing effect of the invention is particularly advantageous here.

To further improve starch transfer, the line load of the treatment nip may be selected to be from 30 to 140 kN/m, preferably from 60 to 120 kN/m, more preferably from 80 to 100 kN/m.

The TL and CM production speeds on modern machines are very high, at least exceeding 800 meters/minute. The standard value is more than 1000 m/min, reaching 1500 m/min or even 1900 m/min. At such high speeds, efficient starch transfer is particularly important because they typically operate at the upper strength limit of the web, and the increase in speed may be limited by insufficient web strength.

In certain applications, it may be beneficial to adjust the properties of the starch used. The solids content of the starch can be selected from 6% and 25%, preferably from 8% and 18%.

The viscosity of the starch may be chosen to be from 5 to 60mPas, preferably from 10 to 40 mPas.

It has been found that the combination of the above solids content and viscosity is particularly beneficial.

Unless otherwise indicated, viscosity values in this application are always understood to be Brookfield viscosities measured at 50 ℃ and 100 rpm.

The starch may be coated at a temperature of 50 ℃ to 80 ℃.

Typically, after starch coating and further drying, the web is wound up at a winder. In some preferred applications (e.g., for TL and CM), the basis weight of the web at the winder can be from 60 to 250 grams per square meter, more typically from 90 to 170 grams per square meter.

In a preferred embodiment of the method, the starch coating in the step of the invention is adjusted so that the starch content of the web at the winder is 2.5 to 6% by weight of the basis. This amount of starch is generally sufficient to achieve the desired strength characteristics.

In another preferred implementation of the method, the crown of the roll can be adjusted to achieve a consistent process nip length across the cross-machine width of the roll.

In terms of apparatus, the object is achieved by an apparatus for coating starch on a moving web, comprising a first roll and a second roll arranged to form a treatment nip of the web, and coating means for coating starch onto at least one of the rolls, characterized in that at least one, preferably both, of the first or second rolls has a hardness below 15P & J (zhao hardness). The device further comprises a slot die and/or a slide die for applying the starch to the roll.

Advantageous features are also described in the dependent claims.

It may be advantageous to use a stiffer roll. In some applications, at least one of the first or second rolls (preferably both rolls) has a hardness of 5P & J or less, preferably 1P & J or less.

In an advantageous embodiment, the process nip may be formed by hard and softer rolls having a hardness of 15P & J or less. The softer roll may have a hardness greater than 15P & J, particularly greater than 20P & J. This combination further improves the transfer of starch to the web.

It is advantageous if the apparatus further comprises means for removing a boundary layer of air from at least one of the first or second rolls.

These means for removing the air boundary layer may comprise at least one of a doctor blade, an air jet, a foil or a brush.

In most applications, these devices will be placed before the point of impact of the curtain on the roller (seen in the direction of rotation of the roller).

In a preferred embodiment of the coating apparatus, the first and second rolls are the same diameter or differ by less than 10%.

Depending on the web and the production speed, the use of such a harder nip in sizing may generate detrimental vibrations. If the two rolls are of the same or approximately the same size, this tendency to generate vibrations can be reduced, thereby improving the stable running capability of the machine.

In general, it is advantageous for the first roll and/or the second roll to have a diameter of 0.25 to 2 meters, in particular 0.7 to 1.8 meters.

In a further preferred embodiment of the device, the first roller has a coating of metal or ceramic, the layer thickness of which can be up to 800 microns or even 1000 microns, preferably between 50 microns and 150 microns; and/or the second roller has a coating of one of rubber, polyurethane or composite material, the layer thickness of which is between 10 mm and 20 mm.

Depending on the specific application, the first and second rollers may also have a coating of metal or ceramic as described above, or the first and second rollers may have a coating of one of rubber, polyurethane or a composite material.

In selecting a layer, several aspects should be considered. First, the desired hardness of the present invention must be achieved. In addition, thicker layers may increase the run time of the roll. On the other hand, for example, rollers having thicker finishes are more likely to produce harmful vibrations. The values given above represent the best compromise for many applications.

It should be noted that the rollers in the device may in principle be of any type used in the art. In some embodiments, it may be beneficial, for example, if at least one of the rollers is a shoe roller or a controlled deflection roller.

The arrangement position of the rollers can be freely selected. The first and second rolls may be arranged side by side with the web moving vertically and through the nip.

Alternatively, the rolls may be arranged one above the other with the web passing horizontally through the nip. But any inclined arrangement is possible.

In the case of first and second rollers having different hardnesses, the higher position is preferably selected for the softer roller, although in general they may be arranged in any manner.

In another preferred embodiment at least one of the first or second rollers comprises sensor means to measure the nip load. In a more preferred embodiment, the sensor means are means for measuring the cross direction profile of the nip load. Such means may include a fiber optic sensor, one or more piezoelectric element-based sensors, or a thin film sensor, among others.

In case the first and second rollers have different hardness, it may be beneficial to arrange the sensor device at or in the softer roller. In a more preferred embodiment, these sensor means are also capable of determining the length (e.g. machine direction length) of the process nip, especially over the entire cross direction width of the process nip.

For example, roll crown and/or nip load may be adjusted based on measurements from such sensor devices to adjust conditions within the processing nip and optimize starch transfer to the web based on characteristics of the product being produced (e.g., web thickness, basis weight or mass of fibrous material used).

Drawings

The invention will be explained in more detail below with reference to the accompanying drawings, in which:

fig. 1 shows a schematic view of an apparatus of an aspect of the invention.

Figures 2 and 2a show schematic views of an apparatus according to another aspect of the invention.

Fig. 3 shows a schematic view of an apparatus according to another aspect of the invention.

Fig. 4a and 4b show different embodiments of a roll with a sensing device according to another aspect of the invention.

Detailed Description

In fig. 1, the apparatus of one aspect of the invention comprises a first roll 1 and a second roll 2, forming a process nip 6. A web 5, which may be a strong linerboard (TL) or a Corrugated Medium (CM) web 5, for example, passes through the nip 6. Since the rollers are placed in an inclined position, the paper web 5 is also moved in an inclined direction, which is preferably at an angle of about 45 ° to the horizontal.

Here, starch is applied in the form of jets to the surfaces of the rolls 1, 2 via two slot dies 3 and from there transferred to the paper web 5 in the nip. In order to improve the transfer of starch to the paper web, the hardness of one roll 1, 2 or even both rolls 1, 2 is below 15P & J (zhao hardness). In particular, the hardness of at least one of the rolls may be less than 5P & J, or even less than 1P & J.

In the example of fig. 1, the diameters of the rollers 1, 2 are chosen to be equal to each other, in the range of 0.7 to 1.8 meters, but larger or smaller diameters may also be chosen depending on the specific application.

The starch used may have a solids content of from 6% to 25%, preferably from 8% to 18%.

Furthermore, the viscosity of the starch can be selected to be from 5 to 60mPas, preferably from 10 to 40 mPas.

The nip load of the nip 6 may be set in the range of 30 to 140 kn/m, preferably 60 to 100 kn/m. For example, one roller 1, 2 may alternatively comprise a ceramic or metal layer, while the other roller may comprise a rubber, polyurethane or composite layer.

Typical amounts of starch transferred using the apparatus of the invention are typically 2.5% to 6% by weight of the basis.

Fig. 2 shows an embodiment of another aspect of the invention.

Although the apparatus shown in fig. 2 may include rolls 1, 2 similar to the apparatus in fig. 1, the rolls are arranged side-by-side and the web 5 moves vertically through the nip. In this example, starch is applied to each roll 1, 2 by a slot die 3. Unlike fig. 1, the starch is coated in the form of a free-falling curtain. Thus, the slot die 3 is located in the upper half of the rolls 1, 2, preferably at or near the 12 o' clock position. The apparatus of fig. 2 further comprises means 9 for removing a boundary layer of air from the first and second rolls 1, 2. This arrangement is advantageous in avoiding disturbance of the curtain by air in the boundary layer, thereby forming a stable curtain and a uniform starch coating. Although the device 9 in fig. 2 is in the form of an air nozzle 9 generating an air jet, there are many possible alternatives, such as a scraper, a brush or a foil.

All of the features mentioned with respect to the size, hardness or composition of the rolls, nip load and starch characteristics for the embodiment of fig. 1 are also valid for the embodiment of fig. 2.

Figure 2b shows a very similar arrangement to that of figure 2. The main difference is the direction of rotation of the roll. Although the point of impact of the curtain is closer to the process nip 6 in fig. 2, this is not the case in fig. 2 b. It is very well possible to apply starch to the rolls 1, 2 and then to transport the starch over a longer distance on the surface of the rolls. Fig. 2b shows an embodiment in which starch is coated on the first roll 1 near the 12 o 'clock position and then transported on the roll surface in a counter-clockwise rotation to the process nip 6, which process nip 6 is at about the 3 o' clock position. To show a possible alternative, the means 9 for removing the boundary layer of air are shown here as foils or flexible wipers.

The embodiment of fig. 3 is very similar to the embodiment of fig. 2. The only difference is the way in which the starch is applied to the rolls 1, 2 by means of the slide mould 3 a. The starch is also coated in the form of a curtain. Although the embodiment in fig. 3 does not explicitly show means 9 for removing the air boundary layer from the roller, such means 9 are also advantageous for stabilizing the curtain in this embodiment.

Devices similar to the embodiments shown in the figures can be used to perform the method of the invention.

Fig. 4a and 4b show the first or second roll 1, 2 comprising a set of sensor means 11 for measuring the nip load. The sensor device 11 can be integrated into the cover 20 of the roll. The sensor devices 11 in these examples are connected by a signal carrier 10. The signal carrier may carry an electrical or optical signal depending on the nature of the sensing device.

In fig. 4a, the sensing devices are all arranged along a line in the cross-machine direction. In the embodiment of fig. 4b, the sensor devices are arranged helically around the circumference of the rolls 1, 2.

The sensor means 11 may for example be included in the cover 6 or cladding of the rolls 1, 2 or be located between the cover and the next layer.