CN113825876B

CN113825876B - Method for producing cardboard paper

Info

Publication number: CN113825876B
Application number: CN202080035389.7A
Authority: CN
Inventors: 弗雷德里克·诺德斯特伦; 约翰·库兰德; 米凯拉·卡帕萨基斯
Original assignee: Billerudkorsnas AB
Current assignee: Billerudkorsnas AB
Priority date: 2019-05-14
Filing date: 2020-05-14
Publication date: 2024-06-18
Anticipated expiration: 2040-05-14
Also published as: EP3739114A1; PL3889345T3; CN113825876A; FI3889345T3; PL3739114T3; EP3739115A1; ES2882002T3; CA3137795A1; EP3739115B1; EP3739114B1; WO2020229611A1; EP3969658A1; EP3885490A1; ES2877201T3; PL3739115T3; EP3889345B1; EP3889345A1; US20220213649A1

Abstract

There is provided a method of producing a cardboard paper having a geometric SCT index of 37.0Nm/g to 42.0Nm/g when measured according to ISO 9895:2008, the method comprising the steps of: -providing pulp having a Schopper-Riegler (SR) value of 15 to 19 when measured according to ISO 5267-1:1999, wherein at least 70% by dry weight of the pulp is NSSC pulp; -forming a web from pulp; -pressing the web in a press section comprising a shoe press, wherein the shoe press comprises a shoe press belt with discontinuous grooves, and the wire load in the shoe press is in the range of 1400kN/m to 2000 kN/m; -drying the web from the press section in a drying section to obtain a board paper.

Description

Method for producing cardboard paper

Technical Field

The present invention relates to a method for producing cardboard paper for corrugated paper.

Background

Neutral sulfite semi-chemical (NSSC) pulping is an old process that is well known in the pulp art and is being used in many pulp mills around the world. One of the reasons for using NSSC pulping is the high yield.

In NSSC pulping, the cooking liquor comprises: sulfite, such as Na ₂SO₃ or (NH ₄)₂SO₃; and alkali, such as NaOH or Na ₂CO₃), "neutral" means that the pH of the NSSC cooking liquor is typically between 6 and 10, typically, the cooking time is between 0.5 and 3 hours and the cooking temperature is 160 ℃ to 185 ℃. NSSC pulp comprises a relatively large amount of residual lignin, such as 15% to 20%, which stiffens the NSSC pulp.

NSSC pulp is used, for example, to produce board paper which is subsequently corrugated to form corrugated board.

Examples of factories that use NSSC pulping methods are: In Swedish/> (PM 6)A plant of (PM 4); mondi Swiecie s.a. at the factory of poland Swiecie (PM 4); mondi's (Powerflute's) in Finnish Koupio; stora Enso Oyj at Finland Heinola factory (Heinola Fluting Mill); c.celrom s.a. at the factory of roman Drobeta; factories of Packaging corp. Of America in usa FILER CITY (PM 1, PM2& PM 3), tomahawk (PM 2& PM 4) and Wallula (PM 2); ilim Group in Russian Korjazma plant (PM 1 and PM 3); permsky Karton at the Russian Perm plant (PM 2); westRock factories in U.S. Longview (PM 10) and Stevenson (PM 1& PM 2); international Paper in Mansfield (PM 2) and Pin Hill (PM 2) factories; georgia-PACIFIC LLC is a factory in Big Island (PM 1 and PM 3) and CEDAR SPRINGS, U.S.A.; cascades Containerboard Packaging in the factory of Trenton, canada; plant of Sappi in south africa Tugela (PM 2); lake Utopia Paper at the factory of st. GRAPHIC PACKAGING International in West Monroe, U.S.A.; greif Bros Corp at the factory in the united states RIVERVILLE; hood Container Corp at the factory in the united states New Johnsonville; and Sonoco in the factory of U.S. HARTSVILLE (PM 10).

EP3026173 discloses a method for producing board paper (used as corrugated paper) with increased SCT strength from pulp comprising NSSC pulp. According to the method, a web formed from pulp including NSSC pulp is pressed in a shoe press where the wire load is at least 1200kN/m.

Furthermore, it is widely acknowledged in the prior art that the SCT strength of NSSC-based board paper to be used as corrugated paper increases when the NSSC pulp is subjected to more refining. As an example, the modification of PM4 at Swiecie in 2015 involves modification of the refining system to allow more refining of NSSC pulp to increase SCT strength. For the same purpose Billerud AB (nowAB) was elevated in sweden/>, as early as 2005Is the refining capacity of the NSSC plant. The NSSC plant of Powerflute and the plant of Stora Enso at Heinola improved their refining capacity in 2010 and 2011, respectively.

Disclosure of Invention

The object of the present disclosure is to increase the efficiency of the process disclosed in EP3026173 while maintaining the SCT strength of the product at a high level.

In the context of the present disclosure, the increased efficiency may be increased energy efficiency (i.e., reduced energy consumed to produce one ton of paper) and/or higher productivity (i.e., higher amounts of paper may be produced by the paper machine used in the process).

To meet the above object, a method of producing a cardboard paper having a geometric SCT index of 37.0Nm/g-42.0Nm/g when measured according to ISO 9895:2008 is provided, comprising the steps of:

-providing pulp having a Schopper-Riegler (SR) value of 15 to 19 when measured according to ISO 5267-1:1999, wherein at least 70% by dry weight of the pulp is NSSC pulp;

-forming a web from pulp;

-pressing the web in a press section comprising a shoe press, wherein the shoe press comprises a shoe press belt with discontinuous grooves, and wherein the wire load in the shoe press is in the range of 1400kN/m to 2000 kN/m;

-drying the web from the press section in a drying section to obtain a board paper.

The method can also be described as follows:

a method of producing a linerboard having a geometric SCT index of from 37.0Nm/g to 42.0Nm/g when measured according to ISO 9895:2008, the method comprising the steps of:

-forming a web from pulp in a forming section comprising a headbox, wherein at least 70% by dry weight of the pulp is NSSC pulp, and wherein the pulp in the headbox has a Schopper-Riegler (SR) value of 15 to 19 when measured according to ISO 5267-1:1999;

-pressing the web in a press section comprising a shoe press, wherein the shoe press comprises a shoe press belt with discontinuous grooves, and the wire load in the shoe press is in the range of 1400kN/m to 2000 kN/m;

The range of Schopper-Riegler values (15-19) for the above-mentioned pulps reflects a very low refining degree, which means that the energy consumption is low at this stage of the papermaking process. The inventors have also shown that a reduction in refining energy results in less energy (i.e. less steam) being required to dry a paper web formed from pulp in the drying section. Surprisingly, the inventors have found that low refining is independent of compromised SCT strength when produced according to the present disclosure.

Regarding pressing of the web in a shoe press, the inventors have found that increasing the wire load to 1400kN/m or higher generally does not increase dewatering of the web unless the correct type of shoe press belt is selected. However, when the correct belt is selected, this increase in wire load effectively reduces the amount of steam required to dry the web in the downstream drying section.

Thus, the present disclosure may make NSSC based board paper production more energy efficient, which is of particular interest, as the yield of NSSC pulping processes is so high that the remaining biofuel (burned in the recovery boiler) is insufficient for the papermaking process. Thus, NSSC plants rely on external energy sources. If the NSSC plant is not integrated with an adjacent sulfate plant that produces excess biofuel, it may be desirable to use fossil fuel as an external energy source. Examples of such non-integrated NSSC plants are Heinola Fluting Mill and Powerflute Mill. Furthermore, the speed of many papermaking processes is limited by the drying capacity of the drying section. This limitation is particularly problematic when producing higher grammage linerboards. By providing a web in the drying section that requires less drying energy, the present disclosure allows for higher speeds and thus higher productivity in NSSC based box board paper manufacture.

Drawings

Fig. 1 is a graph showing the shoe press line load and the resulting specific vapor consumption (medium pressure vapor at about 8 bar) in the drying section during the inventive test described below. During the first stage ("1 ^st") and the third stage ("3 ^rd"), the shoe press line load was 1300kN/m. During the second stage ("2 ^nd"), the shoe press line load was 1700kN/m.

Detailed Description

Thus, a method of producing a linerboard having a geometric SCT index of 37.0Nm/g to 42.0Nm/g is provided. The linerboard is intended for use as corrugated paper (i.e., corrugated base paper) in corrugated board. As will be appreciated by those skilled in the art, the method is intended for use with full-scale papermaking machines, i.e., machines adapted to produce at least 50,000 tons of cardboard per year, and typically at least 100,000 tons of cardboard per year. The grammage of the cardboard paper may be in the range of 100g/m ² to 240g/m ², such as 110g/m ² to 240g/m ², such as 120g/m ² to 240g/m ², such as 120g/m ² to 200g/m ² or 140g/m ² to 230g/m ², such as 150g/m ² to 230g/m ². The grammage is measured according to ISO 536:2012.

Preferably, the geometric SCT index of the cardboard paper is 38.0Nm/g to 42.0Nm/g, such as 38.0Nm/g to 41.0Nm/g.

To obtain the geometric SCT index, the compressive strength of the linerboard in the Machine Direction (MD) and Cross Direction (CD) was first measured using a short Span Compression Tester (SCT) measured according to ISO 9895:2008. To calculate the compressive strength index, the compressive strength (N/m) is divided by the grammage. Thus, the unit of SCT index is Nm/g. The geometric SCT index is calculated as the square root of the product of the SCT index in MD and CD:

geometric SCT index= v (SCT index (MD) ×sct index (CD)).

Compressive strength is considered to be more important in CD than MD. The SCT index on the CD of the board paper may for example be higher than 28Nm/g, such as at least 29Nm/g. The upper limit of the SCT index may be, for example, 32Nm/g.

The method comprises the following steps:

-providing pulp having a Schopper-Riegler (SR) value of 15 to 19 when measured according to ISO5267-1:1999, wherein at least 70% by dry weight of the pulp is NSSC pulp.

In one embodiment, the SR value is 16 to 19. In another embodiment, the SR value is 15 to 18.

The above mentioned SR value is the SR value that the pulp has in the headbox (the headbox even though the pulp flows from the headbox to the chambers on the wire of the wire section). To obtain this SR value, the pulp of the present disclosure may be refined, such as LC refined, between the NSSC pulping process and the headbox.

Preferably, at least 80% by dry weight of the pulp is NSSC pulp. In one example, at least 85% or 88% by dry weight of the pulp is NSSC pulp.

The NSSC pulp may comprise hardwood NSSC pulp. Preferably, at least 70% by dry weight of the NSSC pulp is a hardwood NSSC pulp, such as a birch NSSC pulp. In one example, at least 80% by dry weight of the NSSC pulp is hardwood NSSC pulp, such as birch NSSC pulp.

It has been reported in the prior art that a relatively low NSSC pulp yield is required to obtain a substantial increase in strength. However, the results presented in the examples section are obtained using a relatively high yield of NSSC pulp, more precisely about 82% yield. The yield of NSSC pulp of the present disclosure may thus be 75% to 85%, preferably 79% to 85%, such as 80% to 84%.

The pulp may include recycled fiber, waste pulp and/or chips (typically chips of a corrugated board mill) in addition to NSSC pulp. The LC refining described above may be performed before or after mixing with such other fibers.

"NSSC pulp" is obtained from "NSSC pulping", which is defined in the background section. The NSSC pulp of the present disclosure may for example be a sodium-based NSSC pulp, which means that the cooking liquor of NSSC cooking comprises Na ₂SO₃.

The method further comprises the steps of:

typically in the wire section, a web (as is conventional in papermaking) is formed from pulp having an SR value of 15 to 19.

In this method, the headbox consistency may be, for example, 0.50% to 1.20%, such as 0.80% to 1.20%, such as 0.90% to 1.15%. Higher consistency is particularly important when a significant proportion (e.g. at least 80%) of the NSSC pulp is derived from hardwood.

In one embodiment, the headbox consistency is 1.05% to 1.20% and the grammage of the board is 140g/m ² to 240g/m ², such as 140g/m ² to 240g/m ².

The method further comprises the steps of:

-pressing the web in a press section comprising a shoe press.

The nip length in a shoe press may be, for example, 200mm to 330mm, such as 250mm to 300mm. The shoe press is typically a twin felt boots press.

The shoe press includes a shoe press belt having a discontinuous groove. Such shoe press belts are commercially available. One example is BlackBelt G DG sold by Valmet. Another example is Valmet Black Belt H DG sold by Valmet. The hardness of the elastomer in the shoe press belt may be, for example, 93Shore a to 95Shore a.

The wire load in the shoe press is in the range of 1400 to 2000kN/m, preferably 1500 to 2000kN/m, such as 1600 to 1800 kN/m.

In a shoe press, the web may be subjected to pressure pulses of 105kpa to 280kpa, such as 105kpa to 190kpa, such as 105kpa to 135 kpa. The highest pressure pulse is obtained when the line load is relatively high and the web speed is relatively low (due to the high grammage of the produced box board).

The press section may comprise a further press arranged upstream of the shoe press. The other press is typically a double felt press and may be, for example, a large press or a shoe press. The line load of the other press may be 100kN/m to 300kN/m, such as 150kN/m to 250kN/m, especially in the case of large presses.

Finally, the method further comprises the steps of:

-drying the web from the press section in a drying section to obtain the board paper. As described above, the methods of the present disclosure facilitate reducing vapor consumption in the drying section and/or production at relatively high speeds, such as 700m/min to 850m/min or even 750m/min to 850 m/min. When carrying out the process of the invention, the steam consumption in the drying section may be as low as 1.20 to 1.35 tons of steam per ton of paper. Such vapor is typically "medium pressure vapor" which refers to vapor having a pressure of from 6 bar to 11 bar, such as from 6 bar to 0bar, typically about 8 bar.

Example

First reference test

In a first phase of about three months, swedenNSSC cardboard papers of various grammage (intended for corrugated paper) were produced in factories. The production data are presented in table 1. The pulp is a mixture of about 90% birch NSSC pulp and about 10% kraft pulp. The pulp is refined. The resulting SR numbers are presented in table 1. The press section has two double felt nips; first a large press and then a shoe press with a shoe press belt with blind holes. The line load of the large press was 180kN/m.

In a second phase of about three months, swedenNSSC cardboard papers of the same grammage (intended for corrugated paper) were produced in the factory. The production data are presented in table 2. Likewise, the pulp is a mixture of about 90% birch NSSC pulp and about 10% kraft pulp, and the pulp is refined. The resulting SR numbers are presented in table 2. The press section is the same as during the first stage except that another shoe press belt is used. The new shoe press belt has discontinuous grooves. The groove is characterized in that:

Width: 1.30mm;

Land (land): 1.80mm;

depth: 1.30mm;

Open area: 38%;

Void volume: 460ml/m ².

From the data of tables 1 and 2, the shoe press belt changes appear to have no particular effect. It is worth noting that, although the average SR number is slightly lower than in the first stage, the specific vapor consumption is not reduced during the second stage. It is also worth noting that during the second phase, the average geometric SCT index is almost the same as during the first phase.

Table 1. First reference test, first stage (shoe press belt with blind holes). "SSC" refers to specific vapor consumption. The SR number is measured online.

Table 2. First reference test, second stage (shoe press belt with discontinuous grooves). "SSC" refers to specific vapor consumption. The SR number is measured online.

Second reference test

NSSC cardboard paper (intended for corrugated paper) with a grammage of 140g/m ² is in SwedenProduced in a factory. The pulp is a mixture of about 90% birch NSSC pulp and about 10% kraft pulp. The pulp is refined. The resulting SR numbers are presented in table 3 along with other production data. The press section has two double felt nips; first a large press (line load = 180 kN/m) and then a shoe press with a shoe press belt with blind holes. During the first phase of about 28 hours, the shoe press line load was 1500kN/m. During the second phase of about 34 hours, the shoe press line load was again 1300kN/m. The production data are presented in table 3.

The data in Table 3 shows that the increased line load of 1500kN/m does not reduce specific vapor consumption.

Table 3. Second reference test (grammage=140 g/m ², shoe press belt with blind holes). "SSC" refers to specific vapor consumption. The SR number is measured online.

Creative test

NSSC cardboard paper (intended for corrugated paper) with a grammage of 160g/m ² is in SwedenProduced in a factory. The pulp is a mixture of about 90% birch NSSC pulp and about 10% kraft pulp. The pulp is refined. The resulting SR numbers are presented in table 4 along with other production data. The press section has two double felt nips; first a large press (line load = 180 kN/m) and then a shoe press with a shoe press belt with discontinuous grooves having the features of the first reference test described above. During the first phase of approximately 2.5 hours, the shoe press line load was 1300kN/m. The shoe press line load was then gradually increased and during the second stage of about two hours, the shoe press line load was 1700kN/m. The shoe press line load was then gradually lowered and during a third stage of about one hour, the shoe press line load was again 1300kN/m. The production data are presented in table 4 (see also fig. 1).

The data in Table 4 and FIG. 1 show that increasing the line load above 1300kN/m (e.g., up to 1700 kN/m) significantly reduces specific steam consumption in the case of shoe press belts with discontinuous grooves. On average, 1700kN/m is less than 5% less than 1300 kN/m.

Furthermore, the average geometric SCT index of the cardboard paper produced during the second stage was 38.3Nm/g. Meanwhile, the SCT index in the transverse direction was 29.4Nm/g.

Table 4. Inventive test (grammage=160 g/m ², shoe press belt with discontinuous grooves). "SSC" refers to specific vapor consumption. The SR number is measured online.

Claims

1. A method of producing a cardboard paper having a geometric SCT index of 37.0Nm/g to 42.0Nm/g when measured according to ISO 9895:2008, the method comprising the steps of:

-providing pulp having a Schopper-Riegler value of 15 to 19 in a headbox when measured according to ISO 5267-1:1999, wherein at least 70% by dry weight of the pulp is NSSC pulp, and the pulp is refined between a NSSC pulping process and the headbox to obtain the Schopper-Riegler value;

-forming a web from the pulp;

-drying the web from the press section in a drying section to obtain the box board paper.

2. The method of claim 1, wherein in the shoe press, the web is subjected to pressure pulses of 105kpa x to 190kpa x.

3. The method according to claim 1 or 2, wherein the web has a speed in the range of 700m/min to 850 m/min.

4. The method of claim 1 or 2, wherein the web has a speed in the range of 750m/min to 850 m/min.

5. The method according to claim 1 or 2, wherein the grammage of the linerboard is in the range of 120g/m ² to 240g/m ² when measured according to ISO 536:2012.

6. The method according to claim 1 or 2, wherein the grammage of the linerboard is in the range of 140g/m ² to 230g/m ² when measured according to ISO 536:2012.

7. The method according to claim 1 or 2, wherein the grammage of the linerboard is in the range of 150g/m ² to 230g/m ² when measured according to ISO 536:2012.

8. The method according to claim 1 or 2, wherein the wire load in the shoe press is in the range of 1500kN/m to 2000 kN/m.

9. The method according to claim 1 or 2, wherein the wire load in the shoe press is in the range of 1600kN/m to 2000 kN/m.

10. The method according to claim 1 or 2, wherein the wire load in the shoe press is in the range of 1600kN/m to 1800 kN/m.

11. The method according to claim 1 or 2, wherein at least 80% by dry weight of the pulp is NSSC pulp.

12. The method according to claim 1 or 2, wherein at least 88% by dry weight of the pulp is NSSC pulp.

13. The method according to claim 1 or 2, wherein the NSSC pulp yield is 75% to 85%.

14. The method according to claim 1 or 2, wherein the NSSC pulp yield is 79% to 85%.

15. The method of claim 1 or 2, wherein the linerboard has a geometric SCT index of 38.0Nm/g to 42.0 Nm/g.

16. The method of claim 1 or 2, wherein the linerboard has a geometric SCT index of 38.5Nm/g to 42.0 Nm/g.

17. The method according to claim 1 or 2, wherein the cardboard paper has a geometric SCT index of 39.0Nm/g to 42.0 Nm/g.

18. The method of claim 1 or 2, wherein at least 70% by dry weight of the NSSC pulp is hardwood NSSC pulp, which is birch NSSC pulp.

19. The method of claim 1 or 2, wherein at least 80% by dry weight of the NSSC pulp is hardwood NSSC pulp, which is birch NSSC pulp.

20. The method of claim 1 or 2, wherein the amount of steam consumption in the drying section is in the range of between 1.20 tons and 1.35 tons of steam per ton of paper.

21. The method of claim 1 or 2, wherein the press section comprises another press arranged upstream of the shoe press.

22. The method of claim 21, wherein the other press is a large press.

23. The method according to claim 1 or 2, wherein the consistency of the pulp in the headbox used for forming the web is 0.50 to 1.20%.

24. The method of claim 18, wherein the consistency of the pulp in the headbox used to form the web is 0.80% to 1.20%.

25. The method of claim 18, wherein the consistency of the pulp in the headbox used to form the web is 0.90% to 1.20%.

26. The method of claim 18, wherein the consistency of the pulp in the headbox used to form the web is 0.90% to 1.15%.

27. The method of claim 21, wherein the other press is a shoe press.