阅读说明：本技术 用作瓦楞纸的箱板纸的高效生产 (Efficient production of linerboards for corrugated board ) 是由 弗雷德里克·诺德斯特伦 约翰·库兰德 米凯拉·卡帕萨基斯 于 2020-05-14 设计创作，主要内容包括：提供了生产箱板纸的方法,该箱板纸当根据ISO 9895:2008测量时具有37.0Nm/g至42.0Nm/g的几何SCT指数,该方法包括以下步骤：-提供当根据ISO 5267-1:1999测量时具有15至19的Schopper-Riegler(SR)值的纸浆,其中,纸浆的按干重计的至少70％是NSSC纸浆；-由纸浆形成幅材；-在包括靴式压机的压机部段中对幅材进行压制,其中,靴式压机包括具有不连续凹槽的靴式压机带,以及靴式压机中的线载荷在1400kN/m至2000kN/m的范围内；-在干燥部段中对来自压机部段的幅材进行干燥以获得箱板纸。(There is provided a method of producing linerboard having a geometric SCT index of 37.0Nm/g to 42.0Nm/g when measured according to ISO9895:2008, the method comprising the steps of: -providing a 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; -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 line load in the shoe press is in the range of 1400 to 2000 kN/m; -drying the web coming from the press section in a drying section to obtain a boxboard.)

1. A method of producing linerboard having a geometric SCT index of 37.0Nm/g to 42.0Nm/g when measured according to ISO9895:2008, the method comprising the steps of:

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

-forming a web from the 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 line load in the shoe press is in the range of 1400 to 2000 kN/m;

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

2. A method according to claim 1, wherein the web is subjected to pressure pulses of 105 to 190kPa in the shoe press.

3. A method according to claim 1 or 2, wherein the speed of the web is in the range of 700 to 850m/min, such as 750 to 850 m/min.

4. The method of any preceding claim, wherein the grammage of the liner board is 120g/m when measured according to ISO 536:2012²To 240g/m²In the range of, for example, the grammage of the cardboard paper is 140g/m²To 230g/m²In the range of, for example, 150g/m in grammage of the cardboard paper²To 230g/m²Within the range of (1).

5. Method according to any one of the preceding claims, wherein the line load in the shoe press is in the range of 1500 to 2000kN/m, such as 1600 to 1800 kN/m.

6. The method according to any of the preceding claims, wherein at least 80% of the pulp by dry weight is NSSC pulp.

7. The method according to any of the preceding claims, wherein at least 88% of the pulp by dry weight is NSSC pulp.

8. The method according to any of the preceding claims, wherein the yield of the NSSC pulp is 75% to 85%, such as 79% to 85%.

9. The method according to any one of the preceding claims, wherein the linerboard has a geometric SCT index of 38.0 to 42.0Nm/g, such as 38.5 to 42.0Nm/g, such as 39.0 to 42.0 Nm/g.

10. Method according to any of the preceding claims, wherein at least 70% of the NSSC pulp on dry weight basis is hardwood NSSC pulp, such as birch NSSC pulp.

11. Method according to any of the preceding claims, wherein at least 80% of the NSSC pulp on a dry weight basis is hardwood NSSC pulp, such as birch NSSC pulp.

12. A method according to any of the preceding claims, wherein the steam consumption in the drying section is in the range of 1.20-1.35 tonnes of steam per tonne of paper.

13. A method according to any of the preceding claims, wherein the press section comprises a further press, such as a large press or a shoe press, arranged upstream of the shoe press.

14. The method according to any of the preceding claims, wherein the consistency of the pulp in a headbox used for forming the web is 0.50% to 1.20%.

15. The method according to claim 10 or 11, wherein the consistency of the pulp in the headbox used for forming the web is 0.80-1.20%, 0.90-1.20%, such as 0.90-1.15%.

Technical Field

The invention relates to a method for producing a cardboard used as corrugated cardboard.

Background

Neutral sulfite semi-chemical (NSSC) pulping is an ancient 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 high yield.

In NSSC pulping, the cooking liquor comprises: sulfites, e.g. Na₂SO₃Or (NH)₄)₂SO₃(ii) a And bases, such as NaOH or Na₂CO₃. By "neutral" is meant that the NSSC cooking liquor has a pH value generally 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 relatively large amounts of residual lignin, such as 15% to 20%, which stiffens NSSC pulp. NSSC pulping is "semi-chemical" in that NSSC pulping (after a chemical (cooking step)) includes mechanical treatment/milling.

NSSC pulp is used, for example, to produce linerboard, which is subsequently corrugated to form the fluting of corrugated board.

Examples of plants using the NSSC pulping process are:in Sweden(PM 6) and(PM 4); mondi swieice s.a. plant in boiscie (PM4) poland; mondi's (Powerflute's) at the plant of Koupio, Finland; stora Enso Oyj in Heinola, Finland (Heinola fluidizing Mill); s.c. celrom s.a. plant in romania drosetta; packing Corp. of America in Filer City, USA (PM1, PM2)&PM3),Tomahawk(PM2&PM4) and Wallula (PM 2); factories of Ilim Group in Korjazma, Russia (PM1 and PM 3); permsky Karton, Russian Perm (PM 2); westrock in Longview (PM10) and Stevenson (PM 1) in the United states&PM 2); international Paper, a plant in Mansfield (PM2) and Pine Hill (PM2) of the United states; Georgia-Pacific LLC, at the factories of Big Island (PM1 and PM3) and Cedar Springs, USA; the Cascades Containerboard Packaging works in Trenton, Canada; plant by Tugela in Sappi, south Africa (PM 2); a plant of Lake Utopia Paper, st.george, canada; plant West Monroe, USA, by Graphic Packaging International; greif Bros Corp, Riverville, USA; hood Container Corp, a plant of New Johnsonville, usa; and Sonoco in Hartsville, USA (PM 10).

EP3026173 discloses a method for producing linerboards (used as fluting) with increased SCT strength from a pulp comprising NSSC pulp. According to the method, a web formed from pulp comprising NSSC pulp is pressed in a shoe press, in which shoe press the line load is at least 1200 kN/m.

Furthermore, it is generally accepted in the prior art that the SCT strength of NSSC-based linerboards to be used as fluting increases when the NSSC pulp is subjected to more refining. As an example, the modification of PM4 in swieice in 2015 involved modification of the refining system to allow more refining of NSSC pulp to improve SCT strength. Billerud AB (now called for the same purpose)AB) increased as early as 2005 in swedenThe refining capacity of the NSSC plant of (1).The powerflex NSSC plant and Stora Enso, Heinola-located plants improved their refinery capacity in 2010 and 2011, respectively.

Disclosure of Invention

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

In the context of the present disclosure, the improved efficiency may be an improved energy efficiency (i.e. a reduced energy consumption for producing one ton of paper) and/or a higher productivity (i.e. a higher amount of paper may be produced by the paper machine used for the method).

To meet the above object, there is provided a method of producing linerboards having a geometric SCT index of 37.0Nm/g to 42.0Nm/g when measured according to ISO9895:2008, the method comprising the steps of:

-providing a 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;

-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 line load in the shoe press is in the range of 1400 to 2000 kN/m;

-drying the web coming from the press section in a drying section to obtain a boxboard.

The method can also be described as follows:

a method of producing linerboard having a geometric SCT index of 37.0Nm/g to 42.0Nm/g when measured according to ISO9895:2008, 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 ISO5267-1: 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 line load in the shoe press is in the range of 1400 to 2000 kN/m;

-drying the web coming from the press section in a drying section to obtain a boxboard.

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

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

Thus, the present disclosure may make the production of NSSC-based linerboards more energy efficient, which is of particular interest because the yield of the NSSC pulping process is so high that the remaining biofuel (burned in the recovery boiler) is not sufficient for the papermaking process. NSSC plants therefore 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 fuels as an external energy source. Examples of such non-integrated NSSC plants are the Heinola Fluting Mill and the Powerflute Mill. In addition, the speed of many papermaking processes is limited by the drying capacity of the drying section. This limitation is a particularly great problem when producing cardboard paper of higher grammage. By providing a web requiring less drying energy in the drying section, the present disclosure allows for higher speeds and thus higher production rates in the manufacture of NSSC based linerboards.

Drawings

FIG. 1 is a graph showing the drying during the test of the present invention described belowGraph of the linear load of the shoe press in the drying section and the resulting specific steam consumption (medium pressure steam at about 8 bar). In a first stage (' 1)^st") and a third stage (" 3^rd") the shoe press line load was 1300 kN/m. In the second stage (' 2)^nd") the shoe press line load was 1700 kN/m.

Detailed Description

Accordingly, a method of producing linerboard having a geometric SCT index of 37.0Nm/g to 42.0Nm/g is provided. Linerboards are intended for use as corrugated (i.e., raw) paper in corrugated board. As understood by the person skilled in the art, the method is intended for a full-size paper making machine, i.e. a machine adapted to produce at least 50,000 tonnes per year, typically at least 100,000 tonnes per year. The gram weight of the cardboard paper can be 100g/m²To 240g/m²In the range of (1), such as 110g/m²To 240g/m²E.g. 120g/m²To 240g/m²E.g. 120g/m²To 200g/m²Or 140g/m²To 230g/m²E.g. 150g/m²To 230g/m². Grammage is measured according to ISO 536: 2012.

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

To obtain the geometric SCT index, the compression strength of the cardboard sheet in the Machine Direction (MD) and the Cross Direction (CD) was first measured using a short Span Compression Tester (SCT) measured according to ISO9895: 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 SCT indices in MD and CD:

geometric SCT index ═ v (SCT index (MD) × SCT index (CD)).

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

The method comprises the following steps:

-providing a 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 SR value mentioned above (and in the claims) is the SR value that the pulp has in the headbox (headbox-i.e. the chamber on the wire from which the pulp flows to the wire section). To obtain this SR value, the pulp of the present disclosure may be refined, such as LC refining, between the NSSC pulping process and the headbox.

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

NSSC pulp may comprise hardwood NSSC pulp. Preferably, at least 70% of the NSSC pulp on a dry weight basis is hardwood NSSC pulp, such as birch NSSC pulp. In one example, at least 80% of the NSSC pulp by dry weight 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 large increase in strength. However, the results presented in the example 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 comprise recycled fibre, waste pulp and/or fines (typically of a corrugated box 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, meaning that the cooking liquor of the NSSC cooking comprises Na₂SO₃。

The method further comprises the following steps:

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

In the 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 liner is 140g/m²To 240g/m²E.g. 140g/m²To 240g/m²。

The method further comprises the following steps:

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

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

The shoe press includes a shoe press belt having discontinuous grooves. Such shoe press belts are commercially available. One example is the BlackBelt G DG sold by Valmet. Another example is the 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 line load in the shoe press is in the range 1400kN/m to 2000kN/m, preferably in the range 1500kN/m to 2000kN/m, such as in the range 1600kN/m to 1800 kN/m.

In the shoe press, the web may be subjected to pressure pulses of 105 to 280kPa, such as 105 to 190kPa, such as 105 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 linerboard).

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 100 to 300kN/m, such as 150 to 250kN/m, especially in the case of large presses.

Finally, the method comprises the following steps:

-drying the web coming from the press section in a drying section to obtain the boxboard. As mentioned above, the process of the present disclosure facilitates a reduction of steam consumption in the drying section and/or production at relatively high speeds such as speeds of 700 to 850m/min or even 750 to 850 m/min. When carrying out the method of the invention, the steam consumption in the drying section can be as low as 1.20 to 1.35 tonnes of steam per tonne of paper. Such vapour is typically "medium pressure vapour", by which is meant vapour having a pressure of 6 to 11 bar, such as 6 to 0 bar, typically about 8 bar.

Examples of the invention

First reference test

In the first phase of about three months, SwedenNSSC linerboards (intended for corrugated board) of various grammage are produced in the mill. The production data are presented in table 1. The pulp was 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 press zones; 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 180 kN/m.

In the second phase of about three months, SwedenNSSC linerboards (intended for corrugated board) of the same grammage are produced in the mill. The production data are presented in table 2. Also, the pulp was a mixture of about 90% birch NSSC pulp and about 10% kraft pulp, and the pulp was 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: 1.30 mm;

land (land): 1.80 mm;

depth: 1.30 mm;

open area: 38 percent;

void volume: 460ml/m²。

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

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

Table 2 first reference test, second stage (shoe press belt with discontinuous grooves). "SSC" means specific steam consumption. The SR number is measured online.

Second reference test

Having a density of 140g/m²The grammage of NSSC liner (intended for corrugated board) is in SwedenProduced in a factory. The pulp was 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 press zones; firstly, the methodIs a large press (line load 180kN/m) and then a shoe press with a shoe press belt with blind holes. During the first stage of about 28 hours, the shoe press line load was 1500 kN/m. During the second stage of about 34 hours, the shoe press line load was again 1300 kN/m. The production data are presented in table 3.

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

TABLE 3 second reference test (gram weight 140 g/m)²A shoe press belt with blind holes). "SSC" means specific steam consumption. The SR number is measured online.

Creativity test

Having a density of 160g/m²The grammage of NSSC liner (intended for corrugated board) is in SwedenProduced in a factory. The pulp was 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 press zones; first a large press (line load 180kN/m) and then a shoe press with a shoe press belt with discontinuous grooves having the characteristics described above in the first reference test. During the first stage of about 2.5 hours, the shoe press line load was 1300 kN/m. The shoe press line load was then increased gradually and during a second stage of about two hours the shoe press line load was 1700 kN/m. The shoe press line load was then gradually reduced and during a third phase of approximately one hour, the shoe press line load was again 1300 kN/m. The production data are presented in table 4 (see also fig. 1).

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

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

TABLE 4 creative test (gram weight 160 g/m)²A shoe press belt with discontinuous grooves). "SSC" means specific steam consumption. The SR number is measured online.