RU2814482C2 - Efficient production of containerboard for fluting use - Google Patents

Abstract

FIELD: cardboard.

SUBSTANCE: method for producing containerboard. Cardboard has a geometric SCT index of 37.0 to 42.0 Nm/g when measured according to ISO 9895:2008. The method includes the following steps: providing a mass having a Schopper-Rigler (SR) value from 15 to 19 when measured in accordance with ISO 5267-1:1999; formation of a web from the mass; compressing the web in a press section comprising a shoe press, and drying the web from the press section in a drying section to produce said container board. At least 70% by weight of the dry matter of the mass is the weight of neutral sulphite semi-chemical pulp (NSSP), and the shoe press contains a shoe press belt having intermittent grooves, and the linear load in the shoe press is in the range from 1400 to 2000 kN/m.

EFFECT: increasing the energy efficiency of containerboard production based on NSSP.

15 cl, 4 tbl, 1 dwg

Description

TECHNICAL FIELD

The present invention relates to a method for the production of containerboard intended for use as fluting.

BACKGROUND OF THE ART

Neutral sulphite semi-chemical pulping (NSSP) is an old process well known in the pulp pulping industry and is used in many pulp mills around the world. One of the reasons for using NSPC cooking is the high yield.

When cooking NSPC, the cooking liquid contains a sulfite such as Na ₂ SO ₃ or (NH ₄ ) ₂ SO ₃ and a base such as NaOH or Na ₂ CO ₃ . "Neutral" means that the pH of the cooking liquid for cooking NSPC is usually between 6 and 10. Typically, the cooking time is between 0.5 and 3 hours, and the cooking temperature is between 160 and 185°C. The NSPC mass contains relatively high amounts of residual lignin, for example from 15 to 20%, which imparts rigidity to the specified NSPC mass. Cooking of NSPC is “semi-chemical” in the sense that it involves mechanical processing/grinding (after the chemical (cooking stage)).

NSPC mass is used, for example, for the production of container board, which is subsequently corrugated to form corrugated cardboard fluting.

Examples of plants that use the NSPC cooking method are: plants in Gryvon (RM 6) and Skarblak (RM4), Sweden; Mondi Swiecie SA plant in Swiecie (RM 4), Poland; Mondi (Powerflute) plant in Kuopio, Finland; Stora Enso Oyj's Heinola Fluting Mill, Finland; SC Celrom SA plant in Drobeta, Romania; Packaging Corp. factories of America in Filer City (PM1, PM2 and PM3), Tomahawk (PM2 and PM4) and Wallula (PM2), USA; Ilim Group plants (PM1 and PM3) in Koryazhma, Russia; Perm Cardboard Plant (PM2) in Perm, Russia; WestRock plants in Longview (PM10) and Stevenson (PM1 and PM2), USA; International Paper plants in Mansfield (RM2) and Pine Hill (RM2), USA; Georgia-Pacific LLC plants in Big Island (PM1 and PM3) and Cedar Springs, USA; Cascades Containerboard Packaging plant in Trenton, Canada; Sappi Tugela plant (PM2) in South Africa; Lake Utopia Paper mill in St. George, Canada; Graphic Packaging International plant in West Monroe, USA; Greif Bros Corp plant in Riverville, USA; Hood Container Corp plant in New Johnsonville, USA; and Sonoco plant in Hartsville (PM10), USA.

EP 3026173 discloses a method for the production of containerboard (intended for use as fluting) of increased strength in accordance with the SCT index from a pulp containing NSPC pulp. In accordance with the method, a web formed from a mass containing NSPC mass is compressed in a shoe press in which the linear load is at least 1200 kN/m.

Additionally, it is generally recognized in the art that the SCT strength of NSPC-based containerboard intended for fluting applications is improved by providing greater purity of the NSPC pulp. As an example, the reconstruction of PM4 at Svetse in 2015 included the reconstruction of the cleaning system to enable greater cleaning of the NSPC mass to improve strength in accordance with the SCT index. For the same purpose, Billerud AB (now AB) increased treatment capacity at the NSPC plant in Gryvon, Sweden, in 2005. Powerflute and Stora Enso NSPC plant in Heinola increased treatment capacity in 2010 and 2011, respectively.

DISCLOSURE OF THE INVENTION

The object of the present invention is to improve the efficiency of the method disclosed in EP 3026173, while maintaining a high level of product strength in accordance with the SCT index.

In the context of the present invention, increased efficiency may represent increased energy efficiency (ie, a reduction in the amount of energy consumed to produce one ton of paper) and/or higher productivity (ie, the paper machine used for the method can produce more paper).

To achieve the above objectives, a method is provided for the production of containerboard having a geometric SCT index of 37.0 to 42.0 Nm/g when measured in accordance with ISO 9895:2008, comprising the steps of:

- provide a mass having a Schopper-Rigler (SR) value of between 15 and 19 when measured in accordance with ISO 5267-1:1999, wherein at least 70% of the dry matter weight of the mass is NSPC mass;

- form a canvas from the mass;

- the web is compressed in a press part containing a shoe press, wherein the shoe press contains a shoe press belt having intermittent grooves, and the linear load in the shoe press is in the range from 1400 to 2000 kN/m;

- dry the web from the press part in the drying part to obtain the specified container cardboard.

The method can also be described as follows:

A process for producing containerboard having a geometric SCT index of 37.0 to 42.0 Nm/g when measured in accordance with ISO 9895:2008, comprising the steps of:

- form a web of mass in a forming part containing a headbox, wherein at least 70%, based on the mass of dry matter of the mass, is NSPC mass, and wherein the mass in the headbox has a Schopper-Rigler (SR) value of from 15 to 19 when measured in accordance with ISO 5267-1:1999;

- the web is compressed in a press part containing a shoe press, wherein the shoe press contains a shoe press belt having intermittent grooves, and the linear load in the shoe press is in the range from 1400 to 2000 kN/m;

- dry the web from the press part in the drying part to obtain the specified container cardboard.

The above range for the Schopper-Rigler value for pulp (15-19) reflects a very low degree of purification, which means low energy consumption at this stage of the papermaking process. The inventor has also shown that reducing the energy required for cleaning results in less energy (ie less steam) being required to dry the paper web formed from the pulp in the drying section. Surprisingly, the inventors have found that lower purity is not associated with lower SCT strength when manufactured in accordance with the present invention.

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

Thus, the present invention can improve the energy efficiency of NSPC containerboard production, which is particularly desirable since the yield of the NSPC pulping process is so large that the remaining biofuel (burned in the recovery boiler) is inefficient for the papermaking process. Consequently, NSPC plants depend on external energy. If the NSPC plant does not have an adjacent sulphate plant producing excess biofuel, it may be necessary to use hydrocarbon feedstock as external energy. Examples of such non-integrated NSPC plants are Heinola Fluting Mill and Powerflute Mill. In addition, the speed of many papermaking processes is limited by the drying capacity of the drying section. This limitation is particularly problematic when producing higher gram containerboards. By producing a web that requires less drying energy in the drying section, the present invention enables higher speed and thus higher productivity in the production of NSPC containerboard.

BRIEF DESCRIPTION OF THE DRAWINGS

In fig. 1 is a graph depicting the linear load in the shoe press and the resulting specific steam flow (average pressure steam of approximately 8 bar) in the drying section during the tests of the invention described below. The linear load in the shoe press was 1300 kN/m during the first period (“1st”) and the third period (“3rd”). During the second period (“2nd”) the linear load in the shoe press was 1700 kN/m.

IMPLEMENTATION OF THE INVENTION

Thus, a method for producing containerboard having a geometric SCT index of 37.0 to 42.0 Nm/g is provided. Containerboard is intended for use as fluting (i.e. the corrugated inner layer) in corrugated cardboard. One skilled in the art will appreciate that the method is intended for use in a full size paper machine, that is, a machine configured to produce at least 50,000 ft of containerboard per year, typically at least 100,000 ft of containerboard per year. The grammage of containerboard can be in the range from 100 to 240 g/ ^m2 , for example from 110 to 240 g/ ^m2 , for example from 120 to 240 g/ ^m2 , for example from 120 to 200 g/ ^m2 or from 140 to 230 g/ ^m2 , for example from 150 to 230 g/ ^m2 . Grammage is measured in accordance with ISO 536:2012.

Preferably, the geometric SCT index of the containerboard is from 38.0 to 42.0 Nm/g, for example from 38.0 to 41.0 Nm/g.

To obtain the geometric SCT index, the machine direction (MD) and cross direction (CD) compressive strength of the containerboard is first measured using a short-span compressive tester (SCT). in accordance with ISO 9895:2008 standard. To calculate the compressive strength index, the compressive strength (N/m) is divided by grammage. Thus Nm/g is the unit of measurement for the SCT index. The geometric SCT index is calculated as the square root of the product of the SCT index in the machine direction and the transverse direction:

geometric index SCT=√(SCT index (MD) * SCT index (CD)).

It is believed that compressive strength is more important in the machine direction than in the transverse direction. The SCT index in the transverse direction of the containerboard may be, for example, greater than 28 Nm/g, for example at least 29 Nm/g. The upper limit for the SCT index may, for example, be 32 Nm/g.

The method includes a step in which:

- provide a mass having a Schopper-Riegler (SR) value of between 15 and 19 when measured in accordance with ISO 5267-1:1999, with at least 70% of the dry matter mass being NSPC mass.

In one embodiment, the Shopper-Rigler value is between 16 and 19. In another embodiment, the Shopper-Rigler value is between 15 and 18.

The Schopper-Rigler value mentioned earlier (and in the claims) is the Schopper-Rigler value that the mass has in the headbox (that is, in the chamber from which the mass flows onto the mesh of the mesh part). To obtain this Schopper-Riegler value, between the NSCC pulping process and the headbox, the pulp according to the present invention may be subjected to purification, such as refining and low consistency refining.

Preferably, at least 80% by weight of the dry matter of the mass is NSPC mass. In one example, at least 85% or 88%, on a dry matter basis, of the mass is NSPC mass.

The NSPC mass may contain cellulose NSPC mass made from deciduous wood. Preferably, at least 70%, based on dry matter weight, of the NSPC pulp is a cellulosic NSPC pulp from hardwood, such as birch NSPC pulp. In one example, at least 80%, on a dry matter basis, of the NSPC pulp is a cellulosic NSPC pulp from hardwood, such as birch NSPC pulp.

It has been noted in the prior art that to obtain a large increase in strength, a relatively low yield of NSPC mass is required. However, the results presented in the Examples section were obtained using NSPC pulp in relatively high yield, more specifically approximately 82%. Thus, the yield of the NSPC mass of the present invention can be from 75% to 85%, preferably from 79% to 85%, for example from 80 to 84%.

In addition to NSPC pulp, the pulp may contain recycled fibers, reject pulp and/or trim (usually trim from a corrugated box factory). The previously mentioned cleaning and fine screening may be carried out before or after mixing with such other fibers.

“NSPC mass” is obtained as a result of “NSPC cooking”, which, in turn, is defined in the “State of the art” section. The NSPC mass according to the present invention may be, for example, a sodium-based NSPC mass, which means that the cooking liquid in the NSPC digester contained Na ₂ SO ₃ .

The method further comprises the step of: forming a web from a mass (which has a Schopper-Rigler value of 15 to 19), usually in a mesh part (as is common in papermaking).

In the method, the headbox uniformity may be from 0.50% to 1.20%, for example from 0.80% to 1.20%, for example from 0.90% to 1.15%. Large uniformity values are particularly suitable when the majority (eg, at least 80%) of the NSPC mass is derived from hardwood.

In one embodiment, the headbox uniformity is from 1.05% to 1.20% and the containerboard grammage is from 140 to 240 ^gsm , for example from 140 to 240 ^gsm .

The method further comprises a step in which: - the web is compressed in a press part containing a shoe press.

The length of the clamping zone in a shoe press can, for example, be from 200 to 330 mm, for example from 250 to 300 mm. The shoe press is usually a double felt shoe press.

The shoe press comprises a shoe press belt having intermittent grooves. Such shoe press belt is available in the market. The BlackBelt G DG, marketed by Valmet, is one example. Valmet Black Belt H DG, marketed by Valmet, is another example. The stiffness of the elastomer in the shoe press belt may, for example, be between 93 and 95 Shore A.

The linear load in the shoe press is in the range of 1400 to 2000 kN/m, preferably 1500 to 2000 kN/m, for example 1600 to 2000 kN/m, for example 1600 to 1800 kN/m.

In a shoe press, the web can be subjected to a compression pulse of 105 to 280 kPa*s, for example 105 to 190 kPa*s, for example 105 to 135 kPa*s. The highest baling impulse values are obtained when the linear load is relatively high and the web speed is relatively low (due to the high grams of containerboard being produced).

The press part may contain another press located upstream of the shoe press. The other press is typically a double felt press and may, for example, be a jumbo press or a shoe press. The linear load of another press may be from 100 to 300 kN/m, for example from 150 to 250 kN/m, in particular in the case of a jumbo press.

Finally, the method further comprises the step of: drying the web from the press part in the drying part to obtain said containerboard. As stated previously, the method in accordance with the present invention reduces the steam consumption in the drying section and/or allows production at a relatively high speed, such as 700 to 850 m/min or even 750 to 850 m/min. When implementing the method according to the present invention, the steam consumption in the drying section can reach from 1.20 to 1.35 tons of steam per ton of paper. This steam is typically "medium pressure steam" which refers to steam having a pressure of 6 to 11 bar, for example 6 to 10 bar, typically about 8 bar.

EXAMPLES

First control test

During the first period of approximately three months, NSPC containerboard (intended for fluting) with different grammage values was produced at the plant in Gryvon, Sweden. Production data is presented in Table 1. The mass was a mixture of approximately 90% NSPC birch pulp and approximately 10% kraft pulp. The mass was cleaned. The resulting Schopper-Rigler values are presented in Table 1. The press section had two pressing zones with two felts; first a jumbo press and then a shoe press with a shoe press belt having drilled blind holes. The linear load of the jumbo press was 180 kN/m.

During the second period of approximately three months, NSPC containerboard (intended for fluting) with the same grammage values was produced at the plant in Gryvon, Sweden. Production data is presented in Table 2. Similarly, the pulp was a mixture of approximately 90% NSPC birch pulp and approximately 10% kraft pulp, and was purified. The resulting Schopper-Rigler values are presented in Table 2. The press section was the same as during the first period, except that a different shoe press belt was used. This new shoe press belt had intermittent grooves. The grooves had the following characteristics:

width: 1.30 mm;

platform: 1.80 mm;

depth: 1.30 mm;

open area: 38%;

pore volume: 460 ml/ ^m2 .

From the data in Tables 1 and 2, it does not appear that changing the shoe press belt had any particular effect. It should be noted that the specific steam consumption was not reduced during the second period despite the fact that the average Schopper-Rigler value was slightly lower than during the first period. It should be noted that the geometric mean SCT index was almost the same during the second period as during the first period.

Second control test

NSPC containerboard (intended for fluting), having a grammage of 140 g/m ² , was produced at a plant in Gryvon, Sweden. The mass was a mixture of approximately 90% NSPC birch pulp and approximately 10% kraft pulp. The mass was cleaned. The resulting Schopper-Rigler values are presented in Table 3 along with other production data. The pressing part had two pressing zones with two felts; first a jumbo press (linear load = 180 kN/m) and then a shoe press with a shoe press belt having drilled blind holes. During the first period, which was approximately 28 hours, the linear load in the shoe press was 1500 kN/m. During the second period, which was approximately 34 hours, the linear load in the shoe press was 1300 kN/m. Production data is presented in Table 3.

The data in Table 3 shows that the increased linear load of 1500 kN/m did not reduce the specific steam consumption.

Testing the invention

NSPC containerboard (intended for fluting), having a grammage of 160 g/m ² , was produced at a plant in Gryvon, Sweden. The mass was a mixture of approximately 90% NSPC birch pulp and approximately 10% kraft pulp. The mass was cleaned. The resulting Schopper-Rigler values are presented in Table 4 along with other production data. The pressing part had two pressing zones with two felts; first a jumbo press (linear load = 180 kN/m) and then a shoe press having an intermittent groove shoe press belt having the characteristics previously described under the first proof test. During the first period, which was approximately 2.5 hours, the linear load in the shoe press was 1300 kN/m. The linear load in the shoe press was then gradually increased and during the second period, which lasted approximately two hours, the linear load in the shoe press was 1700 kN/m. The linear load in the shoe press was then gradually reduced and during the third period, which lasted approximately one hour, the linear load in the shoe press was again 1300 kN/m. Production data is presented in Table 4 (also see Fig. 1).

Data in Table 4 and Fig. 1 show that in the case of a shoe press belt with intermittent grooves, increasing the linear load above 1300 kN/m (for example, to 1700 kN/m) significantly reduced the specific steam consumption. On average, the specific steam consumption at 1700 kN/m was 5% lower than at 1300 kN/m.

In addition, the geometric mean SCT index of the containerboard produced during the second period was 38.3 Nm/g. During the same period, the SCT index in the transverse direction was 29.4 Nm/g.

Claims (19)

1. A method for producing containerboard having a geometric SCT index of 37.0 to 42.0 Nm/g when measured in accordance with ISO 9895:2008, comprising the steps of: - provide a mass having a Schopper-Rigler (SR) value of between 15 and 19 when measured in accordance with ISO 5267-1:1999, wherein at least 70% of the dry matter weight of the mass is NSPC mass; - form a canvas from the mass; - the web is compressed in a press part containing a shoe press, wherein the shoe press contains a shoe press belt having intermittent grooves, and the linear load in the shoe press is in the range from 1400 to 2000 kN/m; - dry the web from the press part in the drying part to obtain the specified container cardboard. 2. The method according to claim 1, in which the web is subjected to a compression pulse ranging from 105 to 190 kPa*s in a shoe press. 3. Method according to claim 1 or 2, in which the web speed is in the range from 700 to 850 m/min. 4. The method according to any of the previous claims, wherein the grammage of the containerboard is in the range from 120 to 240 g/m ² when measured in accordance with the ISO 536:2012 standard. 5. The method according to any of the previous paragraphs, in which the linear load in the shoe press is in the range from 1500 to 2000 kN/m. 6. The method according to any of the previous claims, wherein at least 80% by weight of the dry matter of the mass is NSPC mass. 7. The method according to any of the previous claims, wherein at least 88% of the dry matter mass is NSPC mass. 8. The method according to any of the previous paragraphs, in which the yield of NSPC mass is from 75 to 85%. 9. The method according to any of the previous paragraphs, in which the containerboard has a geometric SCT index from 38.0 to 42.0 Nm/g. 10. The method according to any of the previous claims, wherein at least 70%, based on the dry matter weight of the NSPC pulp, is a cellulosic NSPC pulp from hardwood, such as birch NSPC pulp. 11. The method according to any of the previous claims, wherein at least 80% by weight of dry matter of the NSPC mass is cellulosic NSPC pulp from hardwood, such as birch NSPC pulp. 12. The method according to any of the previous paragraphs, in which the steam consumption in the drying part is in the range from 1.20 to 1.35 tons of steam per ton of paper. 13. A method as claimed in any one of the preceding claims, wherein the press portion comprises another press, such as a jumbo press or a shoe press, located upstream of the shoe press. 14. The method as claimed in any one of the preceding claims, wherein the uniformity of the headbox mass used to form the web is from 0.50% to 1.20%. 15. The method according to claim 10 or 11, in which the uniformity of the mass in the headbox used for forming the web is from 0.80% to 1.20%, from 0.90% to 1.20%.

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