Method for producing a packaging paper web

Abstract

A method for producing a packaging paper web, in particular a testliner paper web, wherein the dry content of the packaging paper web is increased in a pressing section, wherein the pressing section comprises at least one prepress and a main press downstream of the prepress, wherein the main press is single-felted and has an extended pressure nip, wherein the extended pressure nip is formed at least partially by a stationary press shoe and a shoe press jacket moving around the press shoe, wherein the shoe press jacket comprises at least one dewatering groove and / or at least one blind bore and at least one layer made of polyurethane. The polyurethane is selected in such a way that a thickness loss according to a dynamic compression test, in which a 5 mm thick sample of the pure polyurethane is dynamically subjected to a sinusoidal load of 15 MPa at 60°C for 4 hours at a frequency of 10 Hz, is less than 10%.

Description

[0001] Method for producing a packaging paper web

[0002] The present invention relates to a method for producing a packaging paper web, in particular a testliner paper web, wherein the dryness of the packaging paper web is increased in a press section, wherein the press section comprises at least one pre-press and a main press downstream of the pre-press, wherein the main press is simply felted and has an extended press gap, wherein the extended press gap is formed at least partially by a stationary press shoe and a shoe press sleeve moving around the press shoe, wherein the shoe press sleeve has at least one drainage groove and / or at least one blind bore and comprises at least one layer of polyurethane.

[0003] Such a manufacturing process is described, for example, in publication WO2017207475A1, to which reference is hereby made.

[0004] Machines for producing fiber webs typically feature a press assembly in which the fiber web is dewatered or dehumidified by mechanical pressure. The press assembly is usually located between the forming and drying sections. A particularly efficient method of mechanical dewatering can be achieved using a so-called extended press gap. The advantages of an extended press gap are well-known: The press gap is planar and not essentially linear as in conventional roller presses. This means that the pressure exerted on the fiber web to be dewatered in the press gap does not begin abruptly in the direction of travel, but can be gradually increased from a low value to a high value. This reduces the risk of the fiber web being compressed in the press gap.This allows the fiber web to be dewatered very efficiently and with minimal volume loss in an extended press gap. For example, the fiber web can be guided through the extended press gap together with a felt or between two felts. In a so-called shoe press, the extended press gap can be formed between a shoe press roller and a counter roller. Unlike the production of tissue webs, the thickness or bulk is less critical in the production of packaging paper webs. Therefore, and because of the significantly higher basis weight of packaging paper webs, considerably higher line loads can be used in the press.

[0005] The topics of "energy costs" and "CO2 footprint" are playing an increasingly important role in the production of fiber webs. Energy consumption in the drying section, which is almost exclusively gas-heated today, is a particularly significant factor. To save energy and gas, it would be highly advantageous if the fiber web emerging from the upstream press assembly already had the highest possible dryness content. An obvious solution might be to simply increase the line load in the press assembly to achieve a higher dryness content. However, this approach is only practical to a limited extent, as it carries the risk of the fiber web being dewatered being compressed in the press gap, and also leads to premature failure of the familiar shoe press jackets, making operation uneconomical.

[0006] The object of the present invention is to reduce the energy costs and / or the CO2 footprint for the production of a packaging web.

[0007] This problem is solved by the independent claims. The dependent claims relate to advantageous further developments of the present invention.

[0008] Specifically, the problem is solved by the generic manufacturing process described at the beginning, which is particularly distinguished by the fact that the polyurethane, from which at least one layer, preferably all layers of the shoe press shell consists, is selected such that a loss of thickness after a dynamic compression test, in which a 5mm thick sample of pure polyurethane is dynamically subjected to a sinusoidal load of 15MPa at 60°C for 4 hours at a frequency of 10Hz, is less than 10%.

[0009] The inventors have determined that selecting the right polyurethane is crucial—specifically, a particularly pressure-resistant polyurethane—to ensure that the main press can operate under high line loads without the press body failing prematurely. The combination of a pre-press and a simply felted main press also reduces the risk of the fiber web being crushed, even under high line loads in the main press. Achieving a thickness loss of less than 10% in the previously described dynamic compression test is a feat accomplished by very few polyurethanes. This is particularly important in the production of packaging paper webs with a relatively low basis weight of around 70 g / m². 2 and 125g / m² 2In tests using the manufacturing process according to the invention, with the particularly pressure-resistant polyurethane in at least one, preferably exactly one layer of the shoe press jacket of the simply felted main press, significant increases in dryness content were achieved compared to known manufacturing processes when applying correspondingly high line loads, without the fiber web being crushed or the shoe press jacket having a shorter service life than with the known manufacturing processes.

[0010] The simple felted main press can be implemented in various ways. For example, the paper web in the press gap can be in contact with a felt on one side and with a counter roller – usually smooth – on the other.

[0011] In other designs, the paper web in the press gap may be in contact with a felt on one side and with a transfer belt instead of a second felt on the other. A transfer belt differs from a felt, among other things, by its smoother surface and its—at least largely—water impermeability. Such a design can be particularly suitable for lower basis weights between 70 g / m² and above. 2 and 125g / m² 2 This can be very advantageous.

[0012] Preferably, the polyurethane is selected such that the thickness loss after testing remains below 10% even after the sample has been subjected to hydrolysis for 4 days at 110°C. This hydrolysis process weakens the polyurethane.

[0013] In a preferred embodiment of the present invention, the extended press gap of the main press has a length of at least 150 mm, preferably at least 190 mm. In this way, the pressure in the press gap can be continuously increased to a high value over a correspondingly long distance.

[0014] In order to achieve the best possible increase in the dryness content of the packaging paper web, it is advantageous if the packaging paper web is subjected to a line load of more than 1,100 kN / m, preferably more than 1,200 kN / m, and more preferably more than 1,300 kN / m in the main press.

[0015] It is also advantageous if the packaging paper web is subjected to a peak pressure of at least 11 MPa, preferably at least 12 MPa, in the main press. The peak pressure can be at least twice the average pressure in the main press. This has resulted in particularly good increases in dryness. The pressure profile in the main press depends significantly on the geometry of the press shoe.

[0016] A suitable, particularly pressure-resistant polyurethane according to the present invention can be produced by reacting a prepolymer and a crosslinking component, wherein the prepolymer is a reaction product of 1,4-phenylene diisocyanate (PPDI) and a polyol component containing at least polytetramethylene ether glycol (PTMEG) and / or C5-6 polycarbonate diol, and wherein the crosslinking component comprises 1,6-hexanediol. Preferably, the polyol component of the prepolymer comprises polytetramethylene ether glycol (PTMEG) and C5-6 polycarbonate diol in substantially equal weight proportions. More preferably, the polyol component of the prepolymer is formed substantially from 50 wt% polytetramethylene ether glycol (PTMEG) and 50 wt% C5-6 polycarbonate diol.

[0017] Particularly preferably, the prepolymer can be formed from a mixture of two prepolymers, wherein the first prepolymer is a reaction product of 1,4-phenylene diisocyanate (PPDI) and polytetramethylene ether glycol (PTMEG), and wherein the second prepolymer is a reaction product of 1,4-phenylene diisocyanate (PPDI) and Cs-e-polycarbonate diol.

[0018] Furthermore, the crosslinking component may also comprise a polyol, preferably polytetramethylene ether glycol (PTMEG).

[0019] Particularly good increases in dry content were achieved with the manufacturing process according to the invention, especially when the fiber web consists of at least 20 wt.%, preferably at least 50 wt.%, of OCC fibers. OCC is a well-known abbreviation in the trade and stands for "old corrugated containers". In other words, the process according to the invention is particularly well suited for efficiently dewatering fiber webs that contain a significant or even substantial proportion of used fibers, i.e., no virgin fibers. This is due to the high resistance of OCC fibers to high pressures. The remaining fibers of the fiber web to be pressed can be selected, for example, from wood pulp or cellulose, such as TMP, CTMP, and / or PGW.

[0020] The manufacturing process according to the invention is also advantageous because it allows for high production speeds. Speeds of more than 1000 m / min, in particular more than 1200 m / min or even more than 1400 m / min, are possible. The inclusion of at least one pre-press proves advantageous in this context, as it usually allows for an increase in production speed. The at least one pre-press is preferably double-felted.

[0021] As previously described, the advantages in the form of an increased dryness level of the packaging web are particularly noticeable when the packaging paper web has a specific basis weight of 160 g / m². 2 or less, in particular 140 g / m² 2 or less. The expected benefits decrease if the packaging paper web has a specific basis weight below 60 g / m². 2exhibits. In preferred applications, it may therefore be provided that the packaging paper web has a specific basis weight between 70 g / m². 2 and 125g / m² 2 , preferably between 80g / m² 2 and 100g / m² 2 exhibits.

[0022] The invention is explained in more detail below with reference to an exemplary embodiment described by means of schematic figures. These figures show:

[0023] Figure 1: a press arrangement comprising a main press and a

[0024] Prepress, for carrying out the manufacturing process according to the invention;

[0025] Figure 2: an enlarged and detailed representation of the main press of the in

[0026] press arrangement shown in Figure 1,

[0027] Figure 1 schematically shows a press arrangement according to the invention, comprising a main press 1 and a prepress 11 arranged directly upstream of it in the direction of movement BR of a fiber web 8. In this embodiment, both the main press 1 and the prepress 11 are designed as shoe presses and thus each have an extended press gap. Alternatively, however, the prepress 11 could not have an extended press gap and / or the prepress 11 and the main press 1 could share a common central roller. The central roller would then be a press element by means of which both the extended press gap of the prepress 11 and the extended press gap of the main press 1 would be formed. Figure 2 shows an enlarged and detailed view of the main press 1, which is particularly important according to the invention.The extended press gap 7 of the main press 1 is provided by two press elements: a shoe press roller 2 and a counter roller 3. The shoe press roller 2 comprises a press shoe 5, which is supported on a stationary yoke 4, and a shoe press sleeve 6, which is rotatably arranged around the press shoe 5. Unlike the illustration in Figure 2, however, the fiber web 8 is not sandwiched between two press felts 9 through the extended press gap 7; instead, the main press 1 is simply felted. The press shoe 5 has a substantially concave surface over which the shoe press sleeve 6 runs, while the press shoe 5 presses it with a high compressive force F towards the counter roller 3.

[0028] The pressing force F is preferably selected to be large enough that the peak pressure acting on the fiber web 8 in the extended press gap 7 is at least 11 MPa, preferably at least 12 MPa. The length of the extended press gap of the main press 1 is at least 150 mm, preferably at least 190 mm.

[0029] It has proven particularly advantageous at such peak pressures if the shoe press-fit shell 6 consists at least partially of a particularly pressure-resistant polyurethane according to the present invention. This polyurethane can be formed by reacting a prepolymer and a crosslinking component, wherein the prepolymer is a reaction product of 1,4-phenylene diisocyanate (PPDI) and a polyol component containing at least one polyether polyol and / or at least one polycarbonate polyol, and wherein the crosslinking component contains a C2-14 diol. For example, the shoe press-fit shell 6 can have a reinforcing structure of threads embedded in the polyurethane layer, wherein the prepolymer of the polyurethane layer comprises 50 wt.% of a mixture of 1,4-phenylene diisocyanate (PPDI) and C5-6 polycarbonate diol and 50 wt.-% consists of a mixture of 1,4-phenylene diisocyanate (PPDI) and polytetramethylene ether glycol (PTMEG), wherein the crosslinker comprises 1,6-hexanediol or is preferably predominantly formed therefrom. Tests have shown that the polyurethane composition according to the invention is particularly advantageous with regard to its resistance to high peak pressures in the main press of the press arrangement according to the invention. Specifically, various samples with a thickness of 5 mm were cast from pure polyurethane and then subjected over a surface to a dynamically fluctuating pressure load of 15 MPa at peak 15 MPa, fluctuating sinusoidally at 10 Hz, for 4 hours at 60°C. Subsequently, the percentage decrease in thickness compared to the initial thickness was measured. The smaller the decrease, the better the material's resistance to pressure.In some cases, the same experiment was repeated with the same materials, but after hydrolysis. Prior to hydrolysis, the materials were exposed to a temperature of 110°C for four days. Table 1 below shows the results.

[0030] Table 1

[0031] The first two polyurethane compositions in Table 1 are comparative examples not related to the present invention. For these, compaction or settling values ​​of -39% and -65%, respectively, were already very high before hydrolysis, so a repeat of the test after hydrolysis was not performed for these two polyurethane compositions. In comparison, significantly lower values ​​of -8% for compaction before hydrolysis were obtained for polyurethane compositions according to the present invention, i.e., those listed below in Table 1. The compaction values ​​after hydrolysis varied somewhat depending on the composition of the crosslinker. However, in no case was a value of -10% exceeded, which makes the polyurethane compositions according to the invention particularly suitable for use even at high peak pressures.The prepress 11 shown schematically in Figure 1 can and preferably is designed differently from the main press 1. In particular, unlike the main press 1, it can be double-felted. In the press arrangement, the prepress 11 serves, in particular, to sufficiently pre-compact the fiber web 8 for passage through the main press 1, so that it is not excessively compressed despite a relatively high peak pressure in the second press 1.

[0032] The fiber web 8, according to the invention, serves to produce a packaging paper web or is itself such a packaging paper web. The fiber web preferably consists of at least 20 wt.%, and more preferably at least 50 wt.%, of OCC fibers, which are characterized by particularly high resistance even to high peak pressures.

[0033] The manufacturing process according to the invention could theoretically also be carried out with more presses than just the pre-press 11 and the main press 1. However, the main press 1 is preferably the last press in the press arrangement, i.e., the last press before the fiber web 8 is transferred to a drying section downstream of the press arrangement.

[0034] Reference symbol list

[0035] 1 Main Press

[0036] 2 shoe press roller

[0037] 3 Counter roller

[0038] 4 standing yoke

[0039] 5 Press shoe

[0040] 6 shoe press coat

[0041] 7 extended press gap

[0042] 8 Fiber web

[0043] 9 Pressed felt

[0044] 10 press arrangement

[0045] 11 Prepress

[0046] BR Direction of movement

[0047] F Pressure force

Claims

Patent claims 1. A method for producing a packaging paper web, in particular a testliner paper web, wherein the dryness of the packaging paper web is increased in a press section, the press section comprising at least one pre-press and a main press downstream of the pre-press, the main press being simply felted and having an extended press gap, the extended press gap being formed at least partially by a stationary press shoe and a shoe press sleeve moving around the press shoe, the shoe press sleeve having at least one drainage groove and / or at least one blind bore and comprising at least one layer of polyurethane, characterized in that the polyurethane is selected such that a loss of thickness after a dynamic compression test,where a 5mm thick sample of pure polyurethane is dynamically subjected to a sinusoidal load of 15MPa at 60°C for 4 hours at a frequency of 10Hz, the value is less than 10%.

2. Method according to claim 1, characterized in that the polyurethane is selected such that the thickness loss after the test is still less than 10% even if the sample has previously been subjected to a hydrolysis process at 110°C for 4 days.

3. Method according to claim 1 or 2, characterized in that the extended press gap of the main press has a length of at least 150mm, preferably at least 190mm.

4. Method according to one of the preceding claims, characterized in that the packaging paper web in the main press is subjected to a line load of more than 1,100 kN / m, preferably more than 1,200 kN / m, more preferably more than 1,300 kN / m.

5. Method according to one of the preceding claims, characterized in that the packaging paper web is subjected to a peak pressure of at least 11 MPa, preferably at least 12 MPa, in the main press.

6. Method according to one of the preceding claims, characterized in that the packaging paper web is subjected to a peak pressure in the main press which is at least twice as high as the mean pressure in the main press.

7. A method according to any of the preceding claims, characterized in that the polyurethane is formed by reacting a prepolymer and a crosslinking component, wherein the prepolymer is a reaction product of 1,4-phenylene diisocyanate (PPDI) and a polyol component containing at least polytetramethylene ether glycol (PTMEG) and / or C5-6-polycarbonate diol, wherein the crosslinking component comprises 1,6-hexanediol.

8. The method according to claim 7, characterized in that the polyol component of the prepolymer comprises polytetramethylene ether glycol (PTMEG) and Cs-6 polycarbonate diol in substantially equal proportions by weight.

9. The method according to claim 8, characterized in that the polyol component of the prepolymer is formed essentially from 50 wt.% polytetramethylene ether glycol (PTMEG) and from 50 wt.% Cs-e-polycarbonate diol.

10. A method according to any one of claims 7 to 9, characterized in that the prepolymer is formed from a mixture of two prepolymers, wherein the first prepolymer is a reaction product of 1,4-phenylene diisocyanate (PPDI) and polytetramethylene ether glycol (PTMEG), and wherein the second prepolymer is a reaction product of 1,4-phenylene diisocyanate (PPDI) and Cs-6 polycarbonate diol.

11. Method according to one of claims 7 to 10, characterized in that the crosslinking component further comprises a polyol, preferably polytetramethylene ether glycol (PTMEG).

12. Method according to one of the preceding claims, characterized in that the fibrous web consists of at least 20 wt.%, preferably at least 50 wt.%, OCC fibers.

13. Method according to one of the preceding claims, characterized in that the packaging paper web is guided through the main press at a speed of at least 1,000 m / min, in particular at least 1,200 m / min, more preferably at least 1,400 m / min.

14. Method according to one of the preceding claims, characterized in that the at least one pre-press is double felted.

15. Method according to one of the preceding claims, characterized in that the packaging paper web has a specific basis weight between 70g / m²2 and 125g / m² 2 , preferably between 80g / m² 2 and 100g / m² 2 exhibits.

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