Multi-ply liner using washed NSSC pulp

Abstract

The present invention relates to a multi-ply liner for use as a packaging material for food or beverages, the multi-ply liner comprising a first ply and a second ply, wherein the first ply comprises at least 70 wt% unbleached kraft pulp and less than 30 wt% neutral sulfite semi-chemical (NSSC) pulp based on dry weight, and the second ply comprises at least 50 wt% NSSC pulp and less than 50 wt% unbleached kraft pulp based on dry weight, and the NSSC pulp in the second ply is a washed NSSC pulp having an ash content of less than 1.8 wt% determined in accordance with ISO standard 1762:2019. The present invention further relates to a method for manufacturing the multi-ply liner.

Description

Technical Field

[0001] The present invention relates to a multi-ply liner using NSSC pulp. The multi-ply liner can be used directly as a packaging material or as a component of cardboard.

Background Art

[0002] A liner or linerboard is a type of thin cardboard that can be used directly as a packaging material, for example, as paper for packaging paperboard or as a base material for paperboard, but is more commonly used as a component of cardboard.

[0003] Cardboard (sometimes called cardboard paper or cardboard fiber paper) is a packaging material that can be converted into various types of packaging solutions. Cardboard is a fiber-based material made from cellulose fibers. The fibers can be virgin cellulose fibers or recycled cellulose fibers such as those from used cardboard paper or other materials.

[0004] Cardboard includes at least one core paper (fluting) and at least one non-core paper (liner or linerboard) adhered to the surface of the core paper. For example, cardboard can consist of a layer of fluting adhered between two layers of liner to form a sandwich structure. The sandwich structure can be formed in various ways, such as single-wall, double-wall, triple-wall, as described, for example, in Kirwan M., J., Paper and Paperboard. Packaging Technology, Blackwell Publishing 2005.

[0005] There are various types of corrugated board quality, which may include various types of liners and medium base papers. Examples of liners include kraft liner and test liner. Kraft liner is usually made from kraft pulp, which can be bleached or unbleached, and can contain one or more layers / plys. The top layer / ply is optimized to provide a good printing surface and good moisture resistance. Test liner is mainly made from recycled corrugated board and is usually made of two layers / plys. Due to the presence of recycled cellulose fibers, test liner may typically have lower mechanical strength, especially lower bursting strength, than kraft liner. Kraft liner is often used for packaging boxes with high requirements for strength characteristics.

[0006] Two-ply liners such as test liner, having a top ply made from unbleached kraft pulp and a back ply containing recycled cellulose fiber pulp, typically have poor mechanical properties and a high potential for contamination levels of recycled cellulose fiber content, so their use in food packaging applications is usually limited. Papers or boards for food packaging applications preferably comply with the BfR XXXVI recommendations regarding papers and boards for food contact as of April 1, 2021.

[0007] Replacing the recycled cellulose fiber content with unbleached kraft pulp is not feasible due to increased costs. The strength and mechanical properties of the liner can be improved by adding a small amount of chemical pulp and unbleached kraft pulp to the mechanical pulp. Typically, 5 - 15% of chemical pulp is added. Of course, this increases costs, but it also leads to a decrease in the dehydration rate and may affect operability and machine performance. Another solution is to wash the recycled cellulose fibers, but this also increases costs and may affect, for example, the bursting strength characteristics of the liner.

[0008] The combination of new machine concepts, improved machine speeds, and the increasing demand for source reduction has further heightened the need to improve pulp properties.

[0009] There is still a need for new and improved liner materials useful as paper or paperboard substrates for liquid packaging board (LPB) or food service board (FSB) that combine strength, low basis weight, water resistance / wet strength, low chemical consumption, low cost, and / or high recyclability, or as liners for corrugated board. SUMMARY OF THE INVENTION

[0010] An object of the present disclosure is to provide an improved multi-ply liner for use, for example, in corrugated board that solves or ameliorates at least some of the above problems.

[0011] A further object of the present disclosure is to provide a method for manufacturing a multi-ply liner that can reduce the consumption of unbleached kraft pulp (UBKP) in the liner without losing the mechanical properties of the UBKP liner when used in corrugated board.

[0012] The above-described objects, as well as other objects that will be realized by those skilled in the art in light of the present disclosure, are achieved by various aspects of the present disclosure.

[0013] NSSC pulp is generally used for the fluting of corrugated board, but due to its optical and mechanical properties, it is not used to the same extent in linerboard. The problem with NSSC pulp is that its process is mainly designed for high-yield and high-efficiency processes. The main goal is to provide fibers or fiber suspensions that meet the requirements of corrugated board / paperboard, such as for use in fluting or medium. Furthermore, NSSC pulp often contains contaminants as well as organic and inorganic residues, so the pulp is not very suitable for food packaging applications. In addition, the use of such NSSC pulp containing a large amount of contaminants and / or impurities requires an increase in the dosage of, for example, slime control agents, preservatives, dehydration accelerators, and / or retention agents, which may affect the wet-end chemistry. Adding NSSC pulp to the production of liner has been known to have a significant adverse effect on wet-end chemistry and cause problems with web breakage.

[0014] Normally, NSSC pulp made from hardwood species is known for its exceptional stiffness and high rigidity. Neutral sulfite semi-chemical (NSSC) pulping is an old process well known in the field of papermaking. One of the reasons for using NSSC pulping is the high yield, usually exceeding 60%. In NSSC pulping, the cooking liquor contains a sulfite such as Na2SO3 or (NH4)2SO3 and a base such as NaOH or Na2CO3. "Neutral" means that the pH of the NSSC cooking liquor is usually between 6 and 10. The pulp can be cooked in a batch or continuous cooker. Usually, the cooking time is between 5 minutes and 3 hours, and the cooking temperature is 160 - 200 °C. NSSC pulp contains a relatively large amount of residual lignin, such as 15 - 20%, which makes the NSSC pulp hard. The kappa number of NSSC pulp typically exceeds 70. NSSC pulping is "semi-chemical" in the sense that it also includes mechanical refining of the pulp. Refining can be done, for example, using a disk refiner at digester pressure or atmospheric pressure.

[0015] The multi-ply liner typically includes a first ply intended as an upper or printing ply mainly composed of unbleached kraft pulp (UBKP), and a second ply intended as a back ply facing the fluting of the corrugated board, which contains recycled cellulose fiber pulp and has a low UBKP content.

[0016] The present invention is based on the recognition that washed NSSC pulp having a low ash content of less than 1.8% by weight, determined in accordance with ISO standard 1762:2019, can be advantageously used in large amounts in the back ply of the multi-ply liner. It has been found that washing the NSSC pulp reduces the adverse effects on wet-end chemistry and the problem of web breakage associated with unwashed NSSC pulp. The washed NSSC pulp of the second ply, especially in liners (e.g., test liners) where washed NSSC pulp is used instead of recycled cellulose fibers, can improve the strength of the liner. The washed NSSC pulp of the second ply also reduces the consumption of the more expensive UBKP, thereby reducing the cost of the liner. By using washed NSSC pulp in the second ply, large amounts of NSSC can be used, such as more than 50% of the total fiber content of the second ply.

Embodiments for Carrying Out the Invention

[0017] According to a first aspect shown herein, a multi-ply liner for use as a packaging material for food or beverages, a first ply, and a second ply comprising, wherein the first ply comprises at least 70% by weight of unbleached kraft pulp and less than 30% by weight of neutral sulfite semi-chemical (NSSC) pulp based on dry weight, the second ply comprises at least 50% by weight of NSSC pulp and less than 50% by weight of unbleached kraft pulp based on dry weight, and The washed NSSC pulp, in the second ply, has an ash content of less than 1.8% by weight as determined in accordance with ISO standard 1762:2019. A multi-ply liner is provided.

[0018] “NSSC pulp” is obtained from “NSSC pulping” as defined in the Background section. The NSSC pulp can be hardwood pulp, softwood pulp, or a mixture thereof. The NSSC pulp is preferably hardwood pulp or a hardwood / softwood pulp mixture containing less than 15% by weight of softwood, preferably less than 10% by weight of softwood, more preferably less than 5% by weight of softwood. Hardwoods can be, for example, aspen, birch, poplar, eucalyptus, oak, acacia, or beech. The NSSC pulp is preferably prepared by cooking using a cooking liquor containing sulfite, preferably Na2SO3 or (NH4)2SO3, and a base, preferably NaOH or Na2CO3. In some embodiments, the yield from NSSC pulping is greater than 60%, preferably greater than 65%, preferably greater than 70%, more preferably greater than 75%. The term “neutral” means that the pH of the NSSC cooking liquor is in the range of 6 to 10. The cooking time is preferably in the range of 5 minutes to 3 hours. The cooking temperature is preferably in the range of 160 to 200 °C. The NSSC pulp can contain a relatively large amount of residual lignin, such as 15 to 20%. The kappa number of the NSSC pulp is typically greater than 70, preferably greater than 80, preferably greater than 95, more preferably greater than 100 according to ISO 3260. NSSC pulping is “semichemical” in the sense that it also includes mechanical refining of the pulp. The refining can be carried out using a disk refiner, for example, at digester pressure or atmospheric pressure. The refining can be carried out in one or more steps at the same or different pulp concentrations. The first refining step is preferably carried out at a high concentration, such as 5 to 35%, and the second refining step is preferably carried out at a low concentration of less than 5%.

[0019] The low ash content of the washed NSSC pulp can be achieved by washing the pulp. The ash content can also be reduced by more efficiently removing the bark before the pulping process.

[0020] In some embodiments, the NSSC pulp is subjected to washing to reduce its ash content. The purpose of washing is to separate the pulp from the black liquor, wash away residual substances such as alkali lignin produced in the cooking process, and purify the pulp. In some embodiments, the washing of the NSSC pulp includes diluting the NSSC pulp with more than 10 m 3 per ton of dry NSSC pulp, preferably more than 12 m 3 per ton of dry NSSC pulp, more preferably more than 15 m 3 per ton of dry NSSC pulp of clean water, and then subjecting the pulp to dewatering until the solid content exceeds 40% by weight. In some embodiments, the washing of the NSSC pulp includes diluting the NSSC pulp with 10 - 50 m 3 per ton of dry NSSC pulp, preferably 12 - 50 m 3 per ton of dry NSSC pulp, more preferably 15 - 50 m 3 per ton of dry NSSC pulp of clean water, and then subjecting the pulp to dewatering until the solid content exceeds 40% by weight. The washing can be carried out in one or more washing steps, and each washing step includes diluting the NSSC pulp and then subjecting the pulp to dewatering. The washing can be performed using one or more conventional pulp washing methods and washing equipment including, but not limited to, rotary vacuum washers, rotary pressure washers, pressure and atmospheric diffusion washers, horizontal belt washers, and / or dilution / extraction equipment. The washing typically includes diluting the NSSC pulp with water and then removing the water together with the diluted colloidal substances, salts, impurities, and fines through a wire. A preferred washing procedure uses at least one twin-wire, drum replacement washer, twin-roll press, rotary vacuum drum washer, rotary pressure drum, horizontal belt press, atmospheric or pressure diffuser, or extraction press, and then uses at least one pulp screw press.

[0021] In some embodiments, at least one washing step, preferably the last washing step, is carried out with hot water. The temperature of the hot water is preferably above 50 °C, more preferably above 60 °C or above 70 °C. In some embodiments, the temperature of the hot water is in the range of 50 - 100 °C, 60 - 100 °C, or 70 - 100 °C. In some embodiments, the pulp temperature in the washing step carried out with hot water is in the range of 40 - 90 °C or 45 - 80 °C.

[0022] The washing of NSSC pulp can be characterized by the Norden efficiency coefficient (E), preferably the Norden efficiency coefficient (E 10 ) normalized to a 10% discharge concentration. E 10 can be calculated by the following formula: TIFF2025522869000001.tif23170where, L0 = pulp inlet liquor, lb / lb pulp L1 = pulp outlet liquor, lb / lb pulp x0 = pulp inlet solids concentration, wt% x1 = pulp outlet solids concentration, wt% y1 = wash liquor outlet solids concentration, wt% y2 = wash liquor inlet solids concentration, wt% DF = dilution factor = V2 - L1 V2 = shower water flow rate, lb / lb pulp

[0023] In some embodiments, the Norden efficiency coefficient (E 10 ) of the washing step normalized to a 10% discharge concentration is greater than 2, preferably greater than 2.2, more preferably greater than 2.5.

[0024] In some embodiments, the Norden efficiency coefficient (E 10 ) of the washing step normalized to a 10% discharge concentration is in the range of 2 - 6, preferably 2.2 - 5, more preferably 2.5 - 4.

[0025] When washing is carried out continuously in two or more washing steps, the E 10 values are added. That is, E 10The first washing step with a value of 2 and E 10 In the washing sequence consisting of the second washing step with a value of 1, the total E 10 The value becomes 3.

[0026] In some embodiments, the NSSC pulp is prepared from wood containing less than 3 wt%, less than 2.5 wt%, less than 2 wt%, or preferably less than 1 wt% or less than 0.8 wt% bark.

[0027] The washed NSSC pulp of the present invention has an ash content of less than 1.8 wt%. The ash content can be measured in accordance with ISO standard 1762:2019. In some embodiments, the NSSC pulp has an ash content of less than 1.6 wt%, preferably less than 1.4 wt%, more preferably less than 1.2 wt%, or less than 1.0 wt%, or less than 0.9 wt% as determined in accordance with ISO standard 1762:2019.

[0028] The ash content representing the washing efficiency and purity of the NSSC pulp can also be measured by measuring the hot water extraction conductivity of the NSSC pulp in accordance with ISO 6587. In some embodiments, the washed NSSC pulp has a hot water extraction conductivity of less than 30 mS / cm, preferably less than 20 mS / cm, more preferably less than 15 mS / cm as determined in accordance with ISO 6587.

[0029] In some embodiments, the conductivity of the washed NSSC pulp is less than 1200 mS / m, less than 1000 mS / m, less than 800 mS / m, or less than 600 mS / m, more preferably less than 500 mS / m, less than 450 mS / m, less than 400 mS / m, less than 350 mS / m, or less than 300 mS / m when decomposed at 3.5 wt% in distilled water.

[0030] In some embodiments, the washed NSSC pulp contains less than 2%, preferably less than 1.8%, more preferably less than 1.6% Pulmac shives (slot size 0.1 mm).

[0031] In addition to reducing the ash content, washing can also reduce the content of cellulose fines in the washed NSSC pulp. As used herein, the term cellulose fines generally refers to cellulose particles that are significantly smaller in size than cellulose fibers. In some embodiments, the term fines as used herein refers to fine cellulose particles that can pass through a 200-mesh screen (corresponding hole diameter 76 μm) of a conventional laboratory fractionation device (SCAN-CM 66:05). The reduction of fines in the washed NSSC pulp can be, for example, in the range of 0.1 to 10 wt% or in the range of 0.5 to 7 wt%.

[0032] During the preparation of semi-chemical pulps such as NSSC, soluble organic substances are formed. These soluble organic substances are usually measured as the chemical oxygen demand (COD) in accordance with NF standard T90-101 (referred to herein as COD / t 90 ). Typically, after the preparation of the semi-chemical pulp, a COD / t 90 value of at least 120 kg is obtained, and in some cases, COD / t 90 values exceeding 150 or 180 kg are also obtained. Furthermore, during further defibrillation and purification of the pulp, a significant amount of soluble organic substances may be formed. Depending on the purification conditions, an additional 10 to 100 kg or more of COD / t 90 may be formed. To reduce the COD / t 90 , it is necessary to optimize the washing of semi-chemical pulps such as NSSC. Preferably, the washed NSSC pulp contains less than 30 kg of COD / t 90 , more preferably less than 20 kg of COD / t 90 , and most preferably less than 10 kg of COD / t 90 .

[0033] The first ply of the multi-ply liner contains at least 70% by weight of unbleached kraft pulp (UBKP). In some embodiments, the first ply contains at least 75% by weight, preferably at least 80% by weight of unbleached kraft pulp based on the dry weight. The first ply can contain 100% by weight of UBKPs, but more generally, the ply can also contain other components such that the first ply contains 95% by weight or less, 90% by weight or less, or 85% by weight or less based on the dry weight of the UBKPs. The multi-ply liner preferably contains 70 - 95% by weight, preferably 80 - 90% by weight of unbleached kraft pulp based on the dry weight.

[0034] Unbleached kraft pulp or UBKP generally refers to unbleached sulfate pulp based on pine and / or spruce. The main raw material of UBKP is preferably pine, but can also contain up to 45% by weight of spruce. In some embodiments, the UBKP has a kappa number of greater than 55, preferably greater than 60, more preferably greater than 70 as determined according to SCAN ISO C-1.

[0035] The first ply can further contain NSSC pulp, but its content is lower than that of the second ply. The first ply contains less than 30% by weight of NSSC pulp based on the dry weight. Preferably, the first ply contains less than 20% by weight, or less than 10% by weight of NSSC pulp based on the dry weight. The first ply preferably contains between 5 - 30% by weight, preferably between 5 - 20% by weight, and even more preferably between 5 - 10% by weight of NSSC pulp based on the dry weight. In some embodiments, the first ply does not contain NSSC pulp.

[0036] The first ply portion that is not UBKP or NSSC pulp can include any type of fibers such as hardwood and / or softwood fibers, and can include, for example, chemical pulp, mechanical pulp, thermomechanical pulp, or chemithermomechanical pulp (CTMP). In some embodiments, the liner is a kraft liner and the first ply portion that is not UBKP is made entirely from virgin fibers. The first ply portion that is not UBKP can also include, for example, recycled cellulose fibers. For example, the first ply of the present disclosure can consist essentially of UBKP or a mixture of UBKP and recycled cellulose fibers. "Recycled cellulose fibers" refers to fiber materials that have previously been incorporated into some paper or paperboard product. The recycled fibers are preferably pre-consumer recycled fibers or broke obtained from the paperboard manufacturing process. Alternatively, or in addition, the pulp portion that is not UBKP can include, for example, reject pulp. For example, the pulp of the present disclosure can consist essentially of UBKP and reject pulp. "Reject pulp" refers to pulp prepared by purifying screen rejects from another process.

[0037] In some embodiments, the first ply of the multi-ply liner is optimized to provide a good printing surface and good moisture resistance. In some embodiments, the optimization to provide a good printing surface and good moisture resistance includes surface sizing. In some embodiments, the multi-ply liner is surface sized. In some embodiments, the multi-ply liner is surface sized with starch. In some embodiments, the multi-ply liner is surface sized with a combination of starch and at least one other functional component preferably selected from the group consisting of a crosslinking agent, a strengthening agent, and a hydrophobizing sizing agent. The crosslinking agent can be selected from the group consisting of metal salts such as zirconium carbonate, glyoxal or modified glyoxal, aminoplast resin, formaldehyde, melamine, and modified melamine. In some embodiments, the crosslinking agent is citric acid. The strengthening agent can be, for example, microfibrillated cellulose (MFC). The hydrophobizing sizing agent can be, for example, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), SMA (styrene maleic anhydride), rosin size, or a mixture thereof.

[0038] The second ply contains at least 50 wt% of washed NSSC pulp based on the dry weight. The second ply contains a significantly higher content of NSSC pulp than the first ply. In some embodiments, the second ply contains at least 60 wt%, preferably at least 70 wt%, more preferably at least 80 wt% of washed NSSC pulp based on the dry weight. The second ply may consist of only washed NSSC pulp, but more generally, the second ply can also contain other components such that the second ply contains 95 wt% or less, 90 wt% or less, 85 wt% or less, 80 wt% or less, or 75 wt% or less of washed NSSC pulp based on the dry weight.

[0039] The second ply may also include UBKP, but the second ply includes a significantly lower content of UBKP than the first ply. The second ply includes less than 50 wt% UBKP, based on dry weight. Preferably, the second ply includes less than 40 wt%, less than 30 wt%, or less than 20 wt% UBKP, based on dry weight. The second ply preferably includes between 5 and 50 wt%, more preferably between 5 and 40 wt%, or between 5 and 30 wt% UBKP, based on dry weight.

[0040] The washed NSSC pulp or the portion of the second ply that is not UBKP can include any type of fiber such as hardwood and / or softwood fibers, for example, chemical pulp, mechanical pulp, thermomechanical pulp, or chemithermomechanical pulp (CTMP). In some embodiments, the liner is a kraft liner and the portion of the second ply that is not washed NSSC pulp is made entirely from virgin fibers. Thus, in some embodiments, the second ply does not include recycled fibers.

[0041] In some embodiments, the portion of the second ply that is not washed NSSC pulp can include recycled cellulose fibers. For example, the second ply of the present disclosure can consist essentially of washed NSSC pulp, or a mixture of washed NSSC pulp and recycled cellulose fibers. "Recycled cellulose fibers" refers to fiber materials that were previously incorporated into some paper or paperboard product. The recycled fibers are preferably pre-consumer recycled fibers or broke obtained from the paperboard manufacturing process. Alternatively, or in addition, the portion of the pulp that is not washed NSSC pulp can include, for example, reject pulp. For example, the pulp of the present disclosure can consist essentially of washed NSSC pulp and reject pulp. "Reject pulp" refers to pulp prepared by purifying screen rejects from another process.

[0042] Adding washed NSSC pulp to the second ply can improve the strength of the liner, especially in multi-ply liners where washed NSSC pulp is used instead of recycled fibers. In some embodiments, less than 30% by weight of the second ply is composed of broken cellulose fibers or recycled cellulose fibers.

[0043] The liner of the present disclosure is a multi-ply liner having a first ply (also called the top ply) and a second ply (also called the back ply). The outer surfaces of the multi-ply liner, i.e., the surfaces of the top ply and the back ply facing away from the other ply, are called the upper side and the back side, respectively.

[0044] The liner can be manufactured on a paper machine or a board machine suitable for manufacturing multi-ply liners. Paper machines or board machines for manufacturing multi-ply liners are well known in the art. Typically, the machine layout includes a stock preparation section, a wet end section, a press and drying section, and a calendar and / or coating section. In the wet end section, the plies of the multi-ply liner can be individually formed using different head boxes and laminated in the wet state or formed together using a multi-ply head box. When formed individually, the plies are usually laminated or overlaid together before the press and drying sections of the paper machine.

[0045] In some embodiments, the basis weight of each of the first ply and the second ply of the multi-ply liner is in the range of 20 - 150 g / m 2 preferably in the range of 30 - 100 g / m 2 The total basis weight of the multi-ply liner is preferably in the range of 40 - 300 g / m 2

[0046] ​In some embodiments, the multi-ply liner further includes a strengthening agent or an adhesive applied to the interface between the first ply and the second ply. Preferably, this strengthening agent or adhesive includes steamed or gelatinized or unsteamed starch, or a mixture of steamed or gelatinized or unsteamed starch and microfibrillated cellulose (MFC). A preferred strengthening agent or adhesive is steamed natural starch, or steamed natural starch mixed with microfibrillated cellulose. In some embodiments, the strengthening agent or adhesive further includes a cross-linking agent. The cross-linking agent can be selected from the group consisting of, for example, metal salts such as zirconium carbonate, glyoxal or modified glyoxal, aminoplast resins, formaldehyde, melamine, and modified melamine. In some embodiments, the cross-linking agent is citric acid. In some embodiments, the strengthening agent or adhesive further includes an insolubilizing agent. The insolubilizing agent can be, for example, an amino resin, glyoxal, or a zirconium salt insolubilizing agent. The amount of the strengthening agent or adhesive applied to the interface between the second ply and the second ply is preferably in the range of 0.1 to 5 g / m 2 based on the dry weight, more preferably in the range of 0.5 to 3 g / m 2 of.

[0047] Due to the high content of the washed NSSC pulp in the second ply, the entire multi-ply liner has a high content of the washed NSSC pulp. In some embodiments, the amount of the washed NSSC pulp in the multi-ply liner is at least 10% by weight, preferably at least 20% by weight, more preferably at least 30% by weight based on the dry weight. In some embodiments, the amount of the washed NSSC pulp in the multi-ply liner is at least 40% by weight, preferably at least 50% by weight, more preferably at least 60% by weight based on the dry weight.

[0048] In some embodiments, the washed NSSC pulp used in the multi - ply liner is fractionated and is washed NSSC pulp. The fractionated and washed NSSC pulp is obtained by size - fractionating a washed NSSC pulp starting material into a fine - fiber fraction and a coarse - fiber fraction. Compared to the starting material, the fine - fiber fraction contains a large amount of shorter and finer fibers. In other words, the average particle size of the washed NSSC pulp in the fine - fiber fraction is smaller than the average particle size of the washed NSSC pulp in the coarse - fiber fraction. The fine - fiber fraction can be obtained, for example, by separating the washed NSSC pulp starting material with a pressure screen to achieve a fraction containing shorter and finer fibers.

[0049] The fine - fiber fraction obtained by size - fractionating the washed NSSC pulp is particularly advantageous for use in the first ply of a multi - ply liner intended for use as a top layer or a printing layer because it has less impact on the optical properties of the liner compared to the unfractionated fiber fraction or the coarse - fiber fraction of the washed NSSC pulp. The coarse - fiber fraction may be advantageously used in a second ply that does not affect the optical properties of the liner. In a preferred embodiment, the washed NSSC pulp used in the first ply is the fractionated fine - fiber fraction of the NSSC. The first ply preferably does not contain NSSC shives. In a preferred embodiment, the washed NSSC pulp used in the second ply is the fractionated and washed coarse fraction of the NSSC pulp. In some embodiments, the average particle size of the washed NSSC pulp used in the first ply is smaller than the average particle size of the washed NSSC pulp used in the second ply. In some embodiments, the average particle size is the length - weighted average fiber measured in accordance with ISO standard 16065 - 2 using a FS5 optical fiber analyzer (Valmet).

[0050] In some embodiments, the multiprinterliner further comprises an internal sizing agent. The internal sizing agent is preferably a hydrophobic sizing agent. In some embodiments, the internal sizing agent is selected from the group consisting of alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), rosin size, and mixtures thereof. In some embodiments, the amount of the internal sizing agent in the multiprinterliner ranges from 0.5 to 6 kg / tn, preferably from 0.8 to 4 kg / tn, more preferably from 1 to 3 kg / tn, based on the dry weight.

[0051] In some embodiments, at least one surface of the multiprinterliner, preferably the upper surface, has a Cobb 30 s value of less than 40, preferably less than 25, more preferably less than 22, as determined in accordance with ISO standard 535.

[0052] In some embodiments, the multiprinterliner has an equilibrium moisture content (EMC) of less than 10 wt%, preferably less than 8 wt% at a relative humidity of 50%, as determined in accordance with ISO standard 287.

[0053] The multiprinterliner may further contain additives such as natural starch or starch derivatives, cellulose derivatives such as sodium carboxymethyl cellulose, fillers, chemicals for retention and / or drainage, flocculation additives, deflocculation additives, dry strength additives, softeners, crosslinking aids, sizing chemicals, dyes and colorants, resins for wet strength, fixing agents, antifoaming agents, microbial and slime control aids, or mixtures thereof.

[0054] In some embodiments, all the pulp used for the multiprinterliner is formed from FSC-certified wood.

[0055] In some embodiments, the multiprinterliner complies with the BfR XXXVI recommendations regarding paper and board in contact with food as of April 1, 2021.

[0056] The multi-ply liner can further include a third ply, where the third ply includes at least 70% by dry weight of unbleached kraft pulp and between 5% and 30% by weight, preferably between 5% and 20% by weight, and even more preferably between 5% and 10% by weight of neutral sulfite semi-chemical (NSSC) pulp. The third ply preferably has the same composition as the first ply. It is preferred that the first ply and the third ply of the multi-ply liner form the outer plies, and the second ply forms the intermediate ply of the multi-ply liner. The NSSC pulp of the third ply is also preferably washed.

[0057] In some embodiments, the multi-ply liner is preferably a two-ply liner. The two-ply liner includes only two cellulose-based plies, namely, only the first ply and the second ply.

[0058] According to a second aspect shown herein, a method for manufacturing a multi-ply liner for use as a packaging material for food or beverage, a) forming a first web layer from a first pulp suspension and dewatering the first web layer to obtain a first ply; b) forming a second web layer from a second pulp suspension and dewatering the second web layer to obtain a second ply on the first ply; each step of the first pulp suspension includes at least 70% by dry weight of unbleached kraft pulp and less than 30% by weight of neutral sulfite semi-chemical (NSSC) pulp, the second pulp suspension includes at least 50% by dry weight of NSSC pulp and less than 50% by dry weight of unbleached kraft pulp, and the NSSC pulp in the second pulp suspension is washed NSSC pulp having an ash content of less than 1.8% by weight determined in accordance with ISO standard 1762:2019, A method is provided.

[0059] In some embodiments, to obtain a washed neutral sulfite semi-chemical (NSSC) pulp of the second pulp suspension, step b) comprises b1) providing a raw NSSC pulp having an ash content of at least 2 wt% as determined in accordance with ISO standard 1762:2019, b2) washing the raw NSSC pulp and obtaining a washed NSSC pulp having an ash content of less than 1.8 wt% as determined in accordance with ISO standard 1762:2019, and b3) optionally, mixing the washed NSSC pulp with at least one internal sizing agent each step of.

[0060] The purpose of washing is to separate the pulp from the black liquor, wash away residual substances such as alkali lignin produced in the cooking process, and purify the pulp.

[0061] In some embodiments, step b2) comprises diluting the raw NSSC pulp with water and then removing the water through a wire together with the diluted colloidal substances, salts, impurities, and fines.

[0062] In some embodiments, the washing of the NSSC pulp is carried out at more than 10 m 3 per ton of dry NSSC pulp, preferably more than 12 m 3 per ton of dry NSSC pulp, more preferably more than 15 m 3 per ton of dry NSSC pulp, of clean water to dilute the NSSC pulp, and then subjecting the pulp to dewatering until the solid content exceeds 40 wt%. In some embodiments, the washing of the NSSC pulp is carried out at 10 - 50 m 3 per ton of dry NSSC pulp, preferably 12 - 50 m 3 per ton of dry NSSC pulp, more preferably 15 - 50 m 3This includes diluting the NSSC pulp using clean water and then subjecting the pulp to dewatering until the solids content exceeds 40% by weight. Washing can be carried out in one or more washing steps, and each washing step includes diluting the NSSC pulp and then subjecting the pulp to dewatering. Washing can be carried out using one or more conventional pulp washing methods and washing equipment including, but not limited to, rotary vacuum washers, rotary pressure washers, pressure and atmospheric diffusion washers, horizontal belt washers, and / or dilution / extraction equipment. Washing typically includes diluting the NSSC pulp with water and then removing the water together with the diluted colloidal substances, salts, impurities, and fines through a wire. Preferred washing procedures use at least one twin wire, drum replacement washer, twin roll press, rotary vacuum drum washer, rotary pressure drum, horizontal belt press, atmospheric or pressure diffuser, or extraction press, and then use at least one pulp screw press.

[0063] In some embodiments, at least one washing step, preferably the last washing step, is carried out with hot water. The temperature of the hot water is preferably above 50 °C, more preferably above 60 °C, or above 70 °C. In some embodiments, the temperature of the hot water is in the range of 50 - 100 °C, 60 - 100 °C, or 70 - 100 °C. In some embodiments, the pulp temperature in the washing step carried out with hot water is in the range of 40 - 90 °C or 45 - 80 °C.

[0064] In some embodiments, step b2) includes washing the raw NSSC pulp to obtain a washed NSSC pulp having an ash content of less than 1.6% by weight, preferably less than 1.4% by weight, more preferably less than 1.2% by weight, or less than 1.0% by weight, or less than 0.9% by weight as determined in accordance with ISO standard 1762:2019.

[0065] The washing of the NSSC pulp can be characterized by the Norden efficiency coefficient (E), preferably the Norden efficiency coefficient (E 10 ) normalized to a 10% discharge concentration. E10 can be calculated by the following formula: TIFF2025522869000002.tif23170where L0 = pulp inlet liquor, lb / lb pulp L1 = pulp outlet liquor, lb / lb pulp x0 = pulp inlet solids concentration, wt% x1 = pulp outlet solids concentration, wt% y1 = solids concentration of the wash liquor outlet, wt% y2 = solids concentration of the wash liquor inlet, wt% DF = dilution factor = V2 - L1 V2 = shower water flow rate, lb / lb pulp

[0066] In some embodiments, the Norden efficiency coefficient (E 10 ) of the washing step normalized to a 10% discharge concentration is greater than 2, preferably greater than 2.2, more preferably greater than 2.5.

[0067] In some embodiments, the Norden efficiency coefficient (E 10 ) of the washing step normalized to a 10% discharge concentration is in the range of 2 - 6, preferably 2.2 - 5, more preferably 2.5 - 4.

[0068] When washing is carried out continuously in two or more washing steps, the E 10 values are added. That is, in a washing sequence consisting of a first washing step with an E 10 value of 2 and a second washing step with an E 10 value of 1, the total E 10 value is 3.

[0069] In some embodiments, step b2) comprises washing the raw NSSC pulp to obtain a washed NSSC pulp having a hot water extraction conductivity of less than 30 mS / cm, preferably less than 20 mS / cm, more preferably less than 15 mS / cm, as determined in accordance with ISO 6587.

[0070] The terms "first and second web layers" do not necessarily indicate the order in which the web layers are formed. The web layers can be formed simultaneously or individually in any order.

[0071] In some embodiments, the first and second web layers are formed individually using different head boxes and one or more wires, partially dewatered, and then laminated while wet.

[0072] In some embodiments, the first and second web layers are formed together using a multi-ply head box and a single wire and partially dewatered.

[0073] For example, the first web layer is formed individually, partially dewatered, and then laminated with the second web layer while wet to obtain a second ply on the first ply. Alternatively, the second web layer may be formed and dewatered together with the first web layer.

[0074] In some embodiments, the first pulp suspension comprises at least 75 wt%, preferably at least 80 wt% unbleached kraft pulp based on dry weight.

[0075] In some embodiments, the first pulp suspension comprises less than 20 wt%, preferably less than 10 wt% washed NSSC pulp based on dry weight. Preferably, the first pulp suspension comprises between 5 - 20 wt%, even more preferably between 5 - 10 wt% washed NSSC pulp based on dry weight.

[0076] In some embodiments, the second pulp suspension comprises at least 60 wt%, preferably at least 70 wt%, more preferably at least 80 wt% washed NSSC pulp based on dry weight.

[0077] In some embodiments, at least 30% of the pulp in the second pulp suspension is composed of recycled cellulose fibers.

[0078] In some embodiments, the basis weight of each of the first ply and the second ply is in the range of 20 to 150 g / m 2 , preferably in the range of 30 to 100 g / m 2 .

[0079] In some embodiments, the amount of the washed NSSC pulp in the multi-ply liner is at least 10 wt%, preferably at least 20 wt%, more preferably at least 30 wt% based on the dry weight.

[0080] In some embodiments, the average particle size of the washed NSSC pulp used in the first pulp suspension is smaller than the average particle size of the washed NSSC pulp used in the second pulp suspension.

[0081] The method includes forming and dewatering a number of webs from the pulp suspension. Methods of forming and dewatering a web having multiple layers are well known in the art. The liner can be manufactured on a paper machine or a board machine suitable for the production of multi-ply liners. Paper machines or board machines for manufacturing multi-ply liners are well known in the art. Typically, the machine layout includes a stock preparation section, a wet end section, a press and drying section, and a calender and / or coating section.

[0082] The web is generally formed and dewatered in a wet end section including one or more wires conventional in this field. The plies can be formed individually using different head boxes and laminated in the wet state or formed together in a multi-ply head box. The web is usually formed with a gap former, but can also be formed with a fourdrinier type former. When formed individually, the wet plies are usually laminated or overlaid together before the press and drying sections of the paper machine.

[0083] Before lamination, a strengthening agent or an adhesive can be applied between the first ply and the second ply. Preferably, this strengthening agent or adhesive comprises steamed or gelatinized or unsteamed starch, or a mixture of steamed or gelatinized or unsteamed starch and microfibrillated cellulose (MFC). A preferred strengthening agent or adhesive is steamed natural starch, or steamed natural starch mixed with microfibrillated cellulose. In some embodiments, the strengthening agent or adhesive further comprises a crosslinking agent. The crosslinking agent can be, for example, citric acid. In some embodiments, the strengthening agent or adhesive further comprises an insolubilizing agent. The insolubilizing agent can be, for example, an amino resin, glyoxal, or a zirconium salt insolubilizing agent. The strengthening agent or adhesive is preferably added as a paste or an aqueous dispersion using a non-contact deposition technique such as spraying or foaming or curtain application. Preferably, the solids content of the aqueous dispersion is in the range of 0.5 to 50 wt%, more preferably in the range of 1 to 30 wt%. The amount of the strengthening agent or adhesive applied is preferably in the range of 0.1 to 5 g / m 2 , more preferably in the range of 0.5 to 3 g / m 2 based on the dry weight.

[0084] The web is typically subjected to further dewatering. This includes, for example, passing the formed multi-layer web through the press section of a paper machine, where the web passes between large rolls loaded under high pressure to squeeze out as much water as possible. The press section can be composed of conventional nip press units and press fabric felts, and / or one or more shoe presses or extended dewatering nips. These can be carried out with various nip or press loads, including different positions, temperatures, and dwell times. The press section may be provided with one or more shoe presses to maximize productivity. When using one or more shoe presses, these can be carried out at a press level exceeding 800 kN / m, for example, exceeding 1000 kN / m, exceeding 1200 kN / m, or exceeding 1450 kN / m. The removed water is typically received by the fabric or felt.

[0085] After the press section, the multi-layer web is subjected to drying in a drying section. Drying can include, for example, drying the multi-layer web by passing it around a series of heated drying cylinders. Drying can typically remove the moisture content to a level of about 1 - 15 wt%, preferably about 2 - 10 wt%.

[0086] According to a third aspect shown herein, there is provided a packaging material for food or beverage, comprising a multi-ply liner as described in the first aspect, or a multi-ply liner obtained according to the method described in the second aspect, wherein the first ply faces the printing surface of the packaging material and the second ply faces the inside of the packaging material.

[0087] In some embodiments, the packaging material for food or beverage is liquid packaging board, food supply board, or cardboard.

[0088] In some embodiments, the packaging material for food or beverage is cardboard. The cardboard includes at least one layer of a non-corrugated liner adhered to at least one layer of fluting. For example, the cardboard can consist of a layer of fluting sandwiched between two layers of liner. In a preferred embodiment, the fluting is adhered to the second ply of a multi-ply liner.

[0089] The multi-ply liner can also be used as a self-supporting substrate, i.e., paperboard or cardboard that does not form part of the cardboard. The self-supporting substrate can be used, for example, as a paper or cardboard substrate for liquid packaging board (LPB) or food service board (FSB). Thus, in some embodiments, the packaging material for food or beverage is liquid packaging board or food service board. The multi-ply liner for use as liquid packaging board (LPB) or food service board (FSB) may be further coated with additional functional layers such as a print-receptive layer barrier or a barrier layer, or laminated using additional paper or plastic films.

[0090] In some embodiments, the packaging material for food or beverage complies with the BfR XXXVI recommendations regarding paper and cardboard for food contact as of April 1, 2021.

[0091] According to a fourth aspect shown herein, there is provided a packaging container for food or beverage comprising the multi-ply liner described in the first aspect, or the multi-ply liner obtained according to the method described in the second aspect, wherein the first ply faces the printed surface of the packaging container and the second ply faces the inside of the packaging container.

[0092] The present invention has been described with reference to various exemplary embodiments, and it will be understood by those of ordinary skill in the art that various changes can be made without departing from the scope of the invention and that elements of the invention can be replaced with equivalents. Further, many modifications can be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Accordingly, the invention is not intended to be limited to the particular embodiments disclosed as the best mode contemplated for carrying out the invention, but rather the invention is intended to cover all embodiments within the scope of the appended claims.

Examples

[0093] These examples show that a large amount of washed NSSC pulp can be used in the two-ply liner without adversely affecting the mechanical or optical properties of the liner. Three samples of 135 g / m 2 two-ply liners were prepared and analyzed, each containing UBKP for the top ply and RCF, NSSC, and washed NSSC for the back ply.

[0094] The washing of the NSSC pulp used was carried out by diluting the NSSC pulp with more than 10 m 3 of clean water per ton of dry NSSC pulp. The pulp was then subjected to dewatering with a dewatering cloth so that the solid content exceeded 40% by weight.

[0095] Qualitative and quantitative analysis of volatile organic compounds (VOCs) in the samples was performed using a headspace gas chromatography unit equipped with a flame ionization detector (HS GC / FID or HS GC / MS).

[0096] The sample (2.0 g) was heated to 90 °C for 40 minutes in a closed sample vial, and the evaporated (gaseous) compounds in the air space above the sample were analyzed.

[0097] The amounts of total volatile compounds and hexanal were calculated. The compounds were identified by comparison with a spectral library.

[0098] Method for preparing two-ply liner A two-ply linerboard with a top ply (corresponding to the first ply of the present invention) and a back ply (corresponding to the second ply of the present invention) was prepared on a pilot machine equipped with two head boxes, two wires, a press section, and a drying section. The target final moisture content of the two-ply structure was 8% by weight, and the target basis weight was 135 g / m 2 It was.

[0099] Example 1 (comparative example) - During back ply, 100% RCF According to the method for preparing the two-ply liner described above, as shown in Table 1, 100% unbleached kraft pulp (UBKP) was used for the top ply and 100% recycled cellulose fiber pulp (RCF) was used for the back ply to prepare a two-ply, 135 g / m 2 linerboard. The liner was analyzed and the results are shown in Table 1. Ash content 1.3% by weight, SR is 32, conductivity, pH 6.6. The quantitative and qualitative determination of VOCs showed that the total amount of volatile substances was 16100 ppb and the amount of hexanal was 4060 ppb.

[0100] Example 2 (comparative example) - During back ply, 100% NSSC pulp A two-ply, 135 g / m 2 linerboard was prepared according to the method for preparing the two-ply liner described above. In this example, the back ply contained 100% unwashed NSSC pulp (1), as shown in Table 1. The liner was analyzed and the results are shown in Table 1.

[0101] Example 3 - During back ply, 100% washed NSSC pulp A two-ply, 135 g / m 2The linerboard was prepared according to the method for preparing a 2-ply liner described above. In this example, the back ply contained 100% washed NSSC pulp (2) as shown in Table 1. The liner was analyzed and the results are shown in Table 1. The ash content was 0 wt%, the SR of NSSC was 25, the conductivity was 1.32 mS / cm, and the pH was 6.2. The quantitative and qualitative determination of VOCs showed that the total amount of volatile substances was 9790 ppb and the amount of hexanal was 3110 ppb. This indicates that the washed NSSC pulp can provide a significant reduction in the amount of total VOC and hexanal. TIFF2025522869000003.tif74170

[0102] Unless otherwise specified, the physical properties discussed in this disclosure are determined according to the following criteria: Grammage ISO 536 Roughness ISO 8791-2:2013 Cobb 30 s ISO 535 Water content at 50% relative humidity ISO 287 Scott bond TAPPI T569 SCT ISO 9895 Burst index ISO 2759 Burst strength ISO 2759

[0103] Unless otherwise specified, the standard methods can be applied to the measurement of physical and mechanical properties in both the cross direction (cd) and the machine direction (md).

Claims

1. A multiply liner for use in food or beverage packaging materials, The first ply, and Second Pride Includes, The first ply comprises, based on dry weight, at least 70% by weight of unbleached kraft pulp and less than 30% by weight of neutral sulfite semi-chemical (NSSC) pulp. The second ply comprises, based on dry weight, at least 50% by weight of NSSC pulp and less than 50% by weight of unbleached kraft pulp, The NSSC pulp in the second ply is a washed NSSC pulp having an ash content of less than 1.8% by weight, as determined in accordance with ISO standard 1762:2019. Multiply liner.

2. The multiply liner according to claim 1, wherein the washed NSSC pulp has an ash content of less than 1.6% by weight, preferably less than 1.4% by weight, more preferably less than 1.2% by weight, or less than 1.0% by weight, or less than 0.9% by weight, as determined in accordance with ISO standard 1762:2019.

3. The multiply liner according to claim 1, wherein the washed NSSC pulp has a hot water extraction conductivity of less than 30 mS / cm, preferably less than 20 mS / cm, and more preferably less than 15 mS / cm, as determined in accordance with ISO 6587.

4. The multiply liner according to claim 1, wherein the first ply comprises at least 75% by weight, preferably at least 80% by weight, of unbleached kraft pulp, based on dry weight.

5. The multiply liner according to claim 1, wherein the first ply comprises less than 20% by weight, preferably less than 10% by weight, of NSSC pulp based on dry weight.

6. The multiply liner according to claim 1, wherein the second ply comprises at least 60% by weight, preferably at least 70% by weight, and more preferably at least 80% by weight of NSSC pulp, based on dry weight.

7. The basis weight of the first ply and the second ply is 20 to 150 g / m². ２ The range is preferably 30 to 100 g / m². ２ A multiply liner according to claim 1, which is within the range of.

8. The multiply liner according to claim 1, wherein the average particle size of the washed NSSC pulp used in the first ply is smaller than the average particle size of the washed NSSC pulp used in the second ply.

9. The multiply liner according to claim 1, wherein at least one surface of the multiply liner has a Cobb value (30 seconds) of less than 40, preferably less than 25, and more preferably less than 22, as determined in accordance with ISO standard 535.

10. The multiply liner according to claim 1, wherein the multiply liner has an equilibrium moisture content (EMC) of less than 10% by weight, preferably less than 8% by weight, at a relative humidity of 50%, as determined in accordance with ISO standard 287.

11. A method for manufacturing a multiply liner for use in packaging materials for food or beverages, a) Forming a first web layer from a first pulp suspension, and dewatering the first web layer to obtain a first ply, b) Form a second web layer from the second pulp suspension, and dehydrate the second web layer to obtain a second ply on the first ply. Each step includes, The first pulp suspension comprises, based on dry weight, at least 70% by weight of unbleached kraft pulp and less than 30% by weight of neutral sulfite semi-chemical (NSSC) pulp. The second pulp suspension comprises, based on dry weight, at least 50% by weight of NSSC pulp and less than 50% by weight of unbleached kraft pulp, The NSSC pulp in the second pulp suspension is a washed NSSC pulp having an ash content of less than 1.8% by weight, as determined in accordance with ISO standard 1762:2019. method.

12. To obtain the washed neutral sulfite semi-chemical (NSSC) pulp from the second pulp suspension, step b) is performed. b1) To provide raw NSSC pulp having an ash content of at least 2% by weight, as determined in accordance with ISO standard 1762:2019. b2) Wash the raw NSSC pulp to obtain washed NSSC pulp having an ash content of less than 1.8% by weight, as determined in accordance with ISO standard 1762:2019, and b3) Optionally, the washed NSSC pulp is mixed with at least one internal sizing agent. Each step further includes, A method for manufacturing the multiply liner described in claim 11.

13. A method for producing a multiply liner according to claim 12, wherein step b2 comprises diluting the NSSC pulp with water, and then removing the water along with the diluted colloidal substance, salts, impurities, and fine particles by passing it through a wire.

14. A method for producing a multiply liner according to claim 12, wherein step b2 comprises washing the raw NSSC pulp to obtain washed NSSC pulp having an ash content of less than 1.6% by weight, preferably less than 1.4% by weight, more preferably less than 1.2% by weight, or less than 1.0% by weight, or less than 0.9% by weight, as determined in accordance with ISO standard 1762:2019.

15. A method for producing a multiply liner according to claim 12, wherein step b2 comprises washing the raw NSSC pulp to obtain washed NSSC pulp having a hot water extract conductivity of less than 30 mS / cm, preferably less than 20 mS / cm, and more preferably less than 15 mS / cm, as determined in accordance with ISO 6587.