阅读说明：本技术 用nssc浆制成的高强度瓦楞芯纸 (High strength corrugated medium paper made of NSSC pulp ) 是由 弗雷德里克·诺德斯特伦 于 2015-11-20 设计创作，主要内容包括：提供了一种包括衬纸和瓦楞芯纸的瓦楞纸板,其中瓦楞芯纸由包含NSSC浆的纸浆制成,瓦楞芯纸的密度为725kg/m<Sup>3</Sup>以上,并且瓦楞芯纸的几何SCT指数(ISO 9895)为37Nm/g以上。还提供了一种包括上述瓦楞纸板构成的壁的用于水果或蔬菜的箱或托盘。(There is provided a corrugated cardboard comprising a liner paper and a corrugated medium, wherein the corrugated medium is made of pulp containing NSSC pulp and has a density of 725kg/m 3 And the geometric SCT index (ISO 9895) of the medium is 37Nm/g or more. There is also provided a box or tray for fruit or vegetables comprising a wall of corrugated board as described above.)

1. Corrugated board comprising a liner and a fluting, wherein the fluting is made from a pulp comprising NSSC pulp and the fluting has a density according to ISO 534 of 725kg/m³-the geometric SCT-index of the fluting according to ISO9895 is 37Nm/g or more and-the SCT-index of the fluting in the Cross Direction (CD) according to ISO9895 is 28Nm/g or more and wherein at least 70% by dry weight of the pulp is NSSC pulp.

2. Corrugated board according to claim 1, wherein the density of the corrugated medium according to ISO 534 is at least 740kg/m³。

3. Corrugated board according to claim 1 or 2, wherein the geometric SCT-index of the fluting is at least 38 Nm/g.

4. Corrugated board according to claim 3, wherein the geometric SCT index of the fluting is at least 39 Nm/g.

5. Corrugated board according to claim 4, wherein the geometric SCT index of the fluting is at least 40 Nm/g.

6. Corrugated board according to any one of claims 1 to 5, wherein the CCT index according to SCAN P-42 of the fluting is at least 25 Nm/g.

7. Corrugated board according to claim 6, wherein the CCT index according to SCAN P-42 of the fluting is at least 26 Nm/g.

8. Corrugated board according to claim 7, wherein the CCT index according to SCAN P-42 of the fluting is at least 27 Nm/g.

9. Corrugated board according to any one of claims 1 to 8, wherein at least 80% of the pulp by dry weight is NSSC pulp.

10. Corrugated board according to claim 9, wherein at least 85% of the pulp by dry weight is NSSC pulp.

11. Corrugated board according to any one of claims 1 to 10, wherein the grammage of the corrugated medium paper is 100 to 200g/m when measured according to ISO 536²。

12. Corrugated board according to any one of claims 1 to 11, wherein the SCT index according to ISO9895 in the Cross Direction (CD) of the fluting is 29Nm/g or more.

13. A box or tray for fruits or vegetables comprising walls constructed from the corrugated board according to any one of claims 1 to 12.

Technical Field

The present invention relates to a method of producing linerboards for use as corrugating medium (fluting).

Background

Neutral sulfite semi-chemical (NSSC) pulping is an old process well known in the art of papermaking pulping and 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 sulfite (such as Na)₂SO₃Or (NH)₄)₂SO₃) And bases (such as NaOH or Na)₂CO₃). By "neutral" is meant that the pH of the NSSC cooking liquor is typically between 6 and 10. Typically, the cooking time is 0.5 to 3 hours and the cooking temperature is 160-185 ℃. NSSC pulp contains higher amounts (such as 15-20%) of residual lignin, which stiffens the NSSC pulp (stiff). NSSC pulping is "semi-chemical" in the sense that NSSC pulping includes mechanical treatment/grinding.

NSSC pulp is used, for example, to produce linerboards, which are subsequently corrugated to form the corrugated core of corrugated board.

Examples of plants using the NSSC pulping process are: factory of Mondi swieicie s.a. of polish schivit (PM 4); a plant of Savon Sellu Oy (Powerflute) of Koupio, Finland; a plant of Stora Enso Oyj (Straunay corporation) of Heinola, Finland (Heinola Flutter Mill); factories of Packaging corp. of philir tinti and tomahok, usa; factories of Ilim Group of Russian Korjazma (PM1 and PM3) (KotlasMill); plant JSC Arkhangelsk Pulp & Paper, Russian New Dewenskk (PM 2); factory of Rock-Tenn Co. of Stachtshenson, America; factories of International paper by Mansfield, Pingshan and Wallent, USA; the American island, the Georgia Pacific LLC of Stapplins and Toledo (Georgia Pacific Co., Georgia Pacific) and the Norampac Inc of Canada Carbamo and Telenton.

Disclosure of Invention

One way to increase the strength of corrugated board is to increase the compressive strength of the linerboards used to form the corrugated medium (i.e., the corrugating medium) of the corrugated board.

It is an object of one aspect of the present disclosure to provide a method of producing enhanced strength linerboard from pulp comprising NSSC pulp.

It is an object of another aspect of the present disclosure to provide a corrugated board having a corrugated base paper with improved strength, in which a linerboard of the corrugated base paper is formed using a pulp containing NSSC pulp.

It is generally desirable to reduce the density (i.e., increase the volume) of the paperboard because lower densities are associated with lower fiber/raw material consumption. However, the present inventors have recognized that one way to increase the compressive strength of a linerboard is to increase its density. Furthermore, the inventors have realized that the density can be increased by wet pressing. However, due to the stiffness of NSSC fibers, it is difficult to press a web made with NSSC pulp to a higher density.

The shoe press can be used to dewater a paper web. Many times, shoe presses are used to dewater a web without reducing the bulk too much. The shoe press design allows the nip (nip) to be longer than other types of presses. The pressure pulse in the shoe press is thus longer. Longer pressure pulses mean that adequate dewatering can be achieved in the shoe press at a lower maximum nip pressure than in other types of presses. Traditionally, this reduction in maximum nip pressure has been used to save bulk on the web.

The solution of the above-mentioned problem of the present inventors for pressing a web made of NSSC pulp to high density is to use a shoe press at very high line loads. When a shoe press with such a high line load is used on the web from NSSC pulp, a high density linerboard with high compressive strength is obtained.

Another benefit of the present invention is also that increased compressive strength can be achieved at sustained or even increased machine speeds.

Accordingly, the present disclosure provides a method of producing a linerboard comprising the step of pressing a web made of pulp comprising NSSC pulp in an extended nip press (such as a shoe press), wherein the line load in the extended nip press is 1200kN/m or more. Linerboards are used as the medium paper in corrugated board.

Further, the present disclosure provides a corrugated cardboard comprising a liner paper and a corrugated medium, wherein the corrugated medium is made of pulp containing NSSC pulp, and the density of the corrugated medium is 725kg/m³And the geometric SCT index of the corrugated medium paper is more than 37 Nm/g.

Drawings

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

figure 1 is a schematic view of a wire section used for small scale productivity tests.

Figure 2 is a schematic of a press section used for small scale productivity tests.

FIGS. 3-11 relate to results obtained in small scale productivity tests.

Fig. 3 shows the nip pressure curve in a shoe press at different line loads and an inclination of 1.3.

Figure 4 shows the nip pressure curve in a shoe press at different inclinations and a line load of 1400 kN/m. Also shown is a nip pressure curve with a slope of 1.3 and a line load of 1500 kN/m.

Figure 5 shows the density obtained when the shoe press is used at different inclinations at a line load of 1400 kN/m.

Fig. 6 shows the densities obtained when the shoe press is used at a constant inclination (1.3) at different line loads (306 to 1500kN/m, resulting in different total pressure pulses). The figure also shows the density obtained at a line load of 1500kN/m when steam is added (point 3017).

Fig. 7 shows the geometric SCT index values obtained when the shoe press is used at a constant inclination (1.3) at different line loads (30 to 1500kN/m, resulting in different total pressure impulses). The figure also shows the geometric SCT index obtained at a line load of 1500kN/m when steam was added (point 3017).

Fig. 8 shows SCT index values in Cross Direction (CD) obtained when the shoe press was used at a constant inclination (1.3) at different line loads (306 to 1500kN/m, resulting in different total pressure impulses). The figure also shows the geometric SCT index obtained at a line load of 1500kN/m when steam was added (point 3017).

Fig. 9 shows the geometric SCT index values obtained when using the shoe press at different inclinations at a line load of 1400 kN/m.

Fig. 10 shows the measured air resistance (air resistance, air permeability) according to the golley method (ISO 5635-5) for paper obtained when using a shoe press at a constant inclination (1.3) at different line loads (306 to 1500kN/m, resulting in different total pressure impulses). The graph also shows the gurley barrier properties obtained at a line load of 1500kN/m when steam is added (point 3017).

Fig. 11 shows CCT index values obtained when the shoe press is used at a constant inclination (1.3) at different line loads (306 to 1500kN/m, resulting in different total pressure impulses). The figure also shows the CCT index obtained at a line load of 1500kN/m when steam is added (point 3017). The CCT index is measured in the transverse direction.

Detailed Description

As a first aspect of the present disclosure, a method of producing a linerboard is provided.

Linerboards are intended for use as the medium (i.e., the body) of corrugated paper in corrugated board. The corrugated board comprises at least one layer of lining paper and at least one layer of corrugated medium paper, wherein the lining paper is non-corrugated. In the normal production of corrugated cardboard, the linerboard is corrugated and then glued to the liner board. For example, corrugated board may be comprised of a corrugated medium layer sandwiched between two liner sheets.

The method comprises the step of pressing a web made from a pulp comprising NSSC pulp. As is conventional in the art, a paper web is typically formed in the wire section.

In a headbox, i.e. a head section (chamber) on a wire from which the pulp flows to the wire section, the pulp of the present disclosure may for example have a schopper riegler (° SR) (ISO5267-1) value of 20 to 25 and a Water Retention Value (WRV) (ISO 23714: 2007) of 1.7 to 2.1. After the NSSC pulping process, the SR value may be, for example, 13 to 19, and the WRV may be, for example, 1.3 to 1.7. This means that the pulp of the present disclosure may be subjected to beating, e.g. LC beating, between the NSSC pulping process and the headbox.

For example, at least 50% (dry weight) of the pulp of the present disclosure may be NSSC pulp. In other examples, at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95% (by dry weight) of the pulp is NSSC pulp. The non-NSSC pulp fraction of the pulp may, for example, comprise recycled fibers. For example, the pulp of the present disclosure may consist essentially of NSSC pulp or of a mixture of NSSC pulp and recycled fibers. "recycled fiber" refers to a fibrous material that has been previously incorporated into certain paper or paperboard products. Alternatively or additionally, the non-NSSC pulp fraction of the pulp may comprise, for example, a pulp slurry. For example, the pulp of the present disclosure may consist essentially of NSSC pulp and bagasse pulp. "reject" refers to pulp prepared by beating reject discarded from another process.

"NSSC pulp" is obtained from "NSSC pulping", which is also defined in the background section. The NSSC pulp of the present disclosure may be, for example, a sodium-based NSSC pulp, meaning that the cooking liquor of NSSC cooking contains Na₂SO₃。

The pressing of the first aspect is performed in an extended nip press, such as a shoe press. Shoe presses are sold by several suppliers of the pulp and paper industry, such as fueit, vimard and anderwitz. An extended nip press is arranged in the press section of a paper machine. A dryer section is arranged downstream of the press section.

An extended nip press differs from a conventional roll press in that a longer nip is obtained.

In the process of the first aspect, the line load in the extended nip press is 1200kN/m or more. "line load" means the applied force divided by the width of the nip. For example, the line load may be 1300kN/m or more, such as 1400kN/m or more, such as at least 1500 kN/m.

The shoe press is not normally designed for such high linear loads, but when the inventors specifically require that the linear load should be as high as possible and at least 1500kN/m, the fuite provides a shoe press of 1700kN/m size.

The pressure pulsation in the nip of the press is obtained by dividing the line load by the machine speed. The total pressure pulsation of the press section is obtained by summing the pressure pulsations of the nips used in the press section.

The web of the first aspect may, for example, be subjected to a pressure pulse of at least 102kPa, such as at least 110kPa, such as at least 115kPa, such as at least 120kPa, in an extended nip press. Such pressure pulsations can be obtained in shoe presses with high line loads (see for example table 1 below).

The web of the first aspect may, for example, be subjected to a total pressure pulse of at least 122kPa, such as at least 130kPa, such as at least 135kPa, such as at least 140kPa, in the press section. Such pressure pulsations can be obtained in the press section comprising a shoe press used at high linear loads (see for example table 1 below).

Further, the web of the first aspect may, for example, be subjected to a peak nip pressure of at least 60 bar, such as at least 70 bar, such as at least 80 bar, such as at least 90 bar, in an extended nip press (e.g., a shoe press). As shown in fig. 3-4, such peak nip pressures can be obtained in shoe presses with high line loads. To further increase the peak pressure, the inclination of the shoe press may be increased, as shown in fig. 4. The "peak nip pressure" is sometimes referred to as specific pressure.

A particular benefit of using a shoe press at high line loads is the ability to achieve a combination of high peak nip pressure and high pressure impulse. This combination is particularly beneficial in the production of linerboards with high compressive strength from NSSC pulp.

The inventors have found that the compressive strength of the produced linerboards is significantly improved if the temperature of the web is increased before and/or in the extended nip press. For example, the web in the extended nip press may be at least 45 ℃, such as at least 50 ℃, such as at least 55 ℃, such as at least 60 ℃, such as at least 65 ℃. The temperature may be measured, for example, with an infrared thermometer, such as a hand-held infrared thermometer ("infrared thermometer"). To increase the temperature of the web, steam may be applied to the web just before and/or in the shoe press. The steam box may for example be arranged just before the nip of the extended nip press, below or above the web.

The nip length in an extended nip press may be at least 150mm, such as at least 200mm, such as at least 230mm, for example. In conventional roll presses, such nip lengths are not available.

In one embodiment of the first aspect, the web of the first aspect is further pressed in a second extended nip press (such as a second shoe press). The conditions in the second extended nip press may be the same as in the (first) extended nip press discussed above.

The press section used in the first aspect may also comprise one or more roll presses (not shoe presses). Alternatively, the press section may consist of only one or more shoe presses. The press section of the first aspect is typically followed by a dryer section, as is conventional in the art.

As shown in fig. 5 and 6, the pressing according to the first aspect increases the density of the resulting linerboard, and the increase in density causes an increase in the compressive strength value. The density (SCAN-P88: 01) of the linerboard of the first aspect may be, for example, 725kg/m³Above, such as at least 740kg/m³Such as at least 750kg/m³Such as at least 760kg/m³。

The compressive strength of linerboards in the Machine Direction (MD) and Cross Direction (CD) can be measured using a short Span Compression Tester (SCT). The SCT compressive strength (N/m) can be measured according to ISO 9895. To calculate the compressive strength index, the compressive strength (N/m) is divided by the grammage (g/m)²). The unit of SCT index is therefore Nm/g. The grammage of the linerboard may be, for example, 100 to 200g/m²Such as 100 to 190g/m²Such as 110 to 180g/m²。

The geometric SCT index is calculated as the square root of the product of the SCT indices in the longitudinal and lateral directions:

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

The geometric SCT index of the linerboard of the first aspect may be, for example, 37Nm/g or more, such as at least 38Nm/g, such as at least 39Nm/g, such as at least 40Nm/g, such as at least 41Nm/g, such as at least 42Nm/g, such as at least 43Nm/g, such as at least 44 Nm/g.

The compressive strength in the transverse direction is considered to be more important than in the longitudinal direction. The SCT index in the transverse direction of the linerboard of the first aspect may be, for example, 28Nm/g or more, such as at least 29 Nm/g.

As a second aspect of the present disclosure, there is provided a corrugated cardboard including a liner sheet and a corrugated medium sheet. Corrugated medium is made from pulp comprising NSSC pulp. Various examples of such pulp are given above in connection with the first aspect.

The linerboard for making the corrugated medium paper of the second aspect may be obtained, for example, using the method of the first aspect.

The density (SCAN-P88: 01) of the medium paper of the corrugated cardboard of the second aspect is 725kg/m³The above. Higher density is generally associated with higher compressive strength. Accordingly, the density of the corrugated medium paper is preferably at least 740kg/m³Such as at least 750kg/m³Such as at least 760kg/m³。

The geometric SCT index (ISO 9895) of the medium of the second aspect may be 37Nm/g or more, for example. The index is preferably at least 38Nm/g, such as at least 39Nm/g, such as at least 40Nm/g, such as at least 41Nm/g, such as at least 42Nm/g, such as at least 43Nm/g, such as at least 44 Nm/g.

As described above, the compressive strength in the transverse direction is considered to be more important than that in the longitudinal direction. The SCT index in the transverse direction of the corrugating medium of the second aspect may be, for example, 28Nm/g or more, such as at least 29 Nm/g.

CCT values can also be used to quantify compressive strength. In the CCT measurement according to SCAN P-42, the sample was corrugated, and then the compressive strength was measured in the transverse direction. To obtain the CCT index, the CCT value is divided by the grammage. The CCT index of the corrugating medium of the second aspect may be, for example, at least 25Nm/g, such as at least 26Nm/g, such as at least 27 Nm/g. The linerboards of the first aspect may also have such a CCT index as measured in accordance with SCAN P-42.

The grammage (ISO 536) of the corrugated medium paper may be, for example, 100 to 240g/m²Such as 100 to 200g/m²Such as 100 to 190g/m²Such as 110 to 180g/m²。

The gurley barrier properties (ISO 5636-5) of the corrugated medium may for example be at least 150s, such as at least 200 s.

There is also provided a three-dimensional article, for example a box or tray comprising walls constructed from corrugated board according to the second aspect. Such a bin or tray may be suitable for use with fruits or vegetables, for example.

Examples of the invention

Small scale productivity tests were performed in Packaging Greenhouse (carlstade, sweden). For small scale productivity tests, beaten NSSC pulp was run fromTaken out of the machine chest on the paper machine 6(PM6) of a paper mill (grumes, sweden).

Figure 1 shows a schematic view of a wire section 10 for small scale productivity tests. A headbox 11 is arranged upstream of the wire section 10. A press section 12 is arranged downstream of the wire section 10. The temperature at various points in the wire section measured by the infrared temperature gun is shown when the steam box 13 is used. The steam box 13 is arranged so that the temperature of the paper web can be raised from 50 c to 70 c just before the press section. However, as explained below, the temperature drops below 70 ℃ in the press section.

Figure 2 shows a schematic of a press section for small scale productivity tests. After the pick-up roll 21, a large-scale double-felted press (first press) 22 is arranged, followed by a shoe-type double-felted press (second press) 23. After the second press nip 24 the web is transported through a third press (not shown). In test 3012 (see below) which did not involve steaming, the temperatures measured with the infrared thermometer were as follows: before and after the couch roll (couch)25 is about 47 deg.c, after the first press 22 is 44 deg.c, after the second press 23 is 40 deg.c and on the reel 26 is 38 deg.c. In test 3017 (see below) involving the passage of steam, the temperatures were as follows: before and after the couch roll 25 is about 52 ℃, 53 ℃ after the first press 22, 49 ℃ after the second press 23, and 47 ℃ on the reel 26.

Tables 1 and 2 below show different small-scale productivity tests. The machine speed (web) was 730m/min (higher than the machine speed on PM6), and the target grammage was 140g/m². The vertical slice lip (slice lip) is 16.1 mm. Samples from the small scale productivity tests of tables 1 and 2 were dried off-line in a single cylinder dryer.

A first reference test (3001) was performed with a higher line load before the test, and a second reference test (3012) was performed with a higher line load after the test. In these reference experiments, the same pressure impulse currently obtained on PM6 was used to simulate the process conditions on PM 6.

Table 1. test with varying line load. The inclination was 1.3 in all tests. Except for test 3017, the steam box was closed for all tests.

Table 1 shows that by increasing the line load in the shoe press to 1250kN/m, the density is increased by 9% compared to the most reliable reference point (3012). When the line load in the shoe press was increased to 1500kN/m, the density increased by 11% compared to the most reliable reference point. When the line load was 1500kN/m and steam was added, the density increased by 15% compared to the most reliable reference point.

In commercial production using a full-scale dryer section (such as production on PM6), the density obtained is typically lower than in small-scale productivity tests using a single-cylinder off-line dryer. However, it is expected that the relative increase in density in commercial production will be about the same as in small scale productivity tests when the shoe press is used at high line loads. The density of the linerboards produced on PM6 was about 670kg/m³. Thus, it is contemplated that when the shoe press is at least 1When used under a line load of 200kN/m, a commercial linerboard will have a weight of at least 725kg/m³The density of (c).

TABLE 2 tests with varying inclinations on shoe presses

Fig. 3 shows the nip pressure curve for a second press (shoe press) at different line loads and an inclination of 1.3, which is the default value. In the reference test (3001), the maximum nip pressure was 20 bar or less. The maximum nip pressure was about 40 bar when a line load of 750kN/m (trial 3003) was used. When using a line load of 1250kN/m and 1500kN/m, the maximum nip pressure is about 65 bar and about 75 bar, respectively.

Fig. 4 shows that the maximum nip pressure can be increased by increasing the inclination. At a line load of 1400kN/m, the maximum nip pressure is above 100 bar for a slope of 1.9.

Fig. 5 shows that the density increases with increasing inclination.

Fig. 6 shows that the density increases with increasing pressure impulse (kPa × s). The pressure impulse in turn increases with increasing line load. The second reference trial (3012) produces a higher density than the first reference trial (3001). The cause of such differences may be due to start-up imbalances, such as insufficient fines balancing and/or other effects related to, for example, temperature, press felt performance, and the like. Therefore, the second reference trial (3012) is considered to give more representative value.

Figure 6 further shows that steam (trial 3017) gives an additional increase in density.

The compressive strength is considered to be the most important property of the corrugated base paper. Fig. 7 shows the geometric SCT-indices obtained at different pressure impulses. In general, the geometric SCT index increases with increasing pressure pulsations. The pressure pulsations generated by the line loads 1400kN/m and 1500kN/m (i.e. trials 3006, 3007 and 3017) show a particular effect on the compressive strength. Figure 7 further shows that steaming (trial 3017) gives a significant additional increase in the geometric SCT index value.

The compressive strength in the transverse direction is particularly important. Fig. 8 shows that the SCT index in the lateral direction increases as the pressure pulsation increases.

Fig. 9 shows that not only the density increases with increasing inclination, but also the geometric SCT index increases with increasing inclination. Thus, as the maximum nip pressure increases, the geometric SCT index increases.

The density of the linerboard may also be quantified by measuring the air resistance according to the gurley test. Fig. 10 shows that the gas barrier property increases significantly when the pressure impulse increases.

Fig. 11 shows the CCT index at different pressure impulses. The pressure pulsations generated at line loads of at least 1000kN/m (i.e. trials 3004, 3005, 3003, 3007 and 3017) result in CCT index values above 25 Nm/g. The line load of 1000kN/m or less is such that the CCT index value is 25Nm/g or less. Figure 11 further shows that steaming (trial 3017) gave a significant additional increase in the CCT index value.