Multilayer liner for use in corrugated board

Abstract

The present invention relates to a multi-layer liner for use in corrugated board, the multi-layer liner comprising: a first ply, and a second ply, the first ply comprising at least 70 wt.% unbleached kraft pulp and 5-30 wt.% neutral sulfite semi-chemical (NSSC) pulp on a dry weight basis, and the second ply comprising at least 50 wt.% NSSC pulp and 5-50 wt.% unbleached kraft pulp on a dry weight basis.

Description

[Technical Field]

[0001] The present invention relates to a multi-layer liner for use in corrugated board, said multi-layer liner comprising NSSC pulp. [Background technology]

[0002] Corrugated cardboard (sometimes called corrugated cardboard or corrugated fiberboard) is a packaging material that can be converted into various types of packaging solutions. Corrugated cardboard is a fibrous substrate made from cellulose fibers. The fibers can be virgin or recycled, such as fibers derived from post-consumer cardboard or other materials.

[0003] Corrugated board contains at least one medium (fluting) and at least one flat base paper (liner or linerboard) bonded to the surface of the medium. For example, corrugated board may consist of a layer of fluting bonded between two layers of liner to form a sandwich structure. Sandwich structures can be formed in various formats, such as single-, double-, and triple-wall, as described, for example, in Kirwan M., J., Paper and Paperboard. Packaging Technology, Blackwell Publishing 2005.

[0004] One challenge when producing corrugated board is the adhesion between the liner and the fluting. Too little adhesion can cause delamination, and adding too much adhesive to ensure sufficient adhesion can cause washboarding and curling of the board. It is important that the adhesive added has optimal absorption into the liner and / or corrugating medium. If the adhesive does not absorb into the fluting / liner, delamination will occur, and if too much adhesive absorbs into the fluting / liner, the same can happen.

[0005] There are various qualities of corrugated board, which may contain different types of liner and medium. Container board (also known as CCM or corrugated case stock) is a type of paperboard manufactured specifically for the production of corrugated board and contains both linerboard and medium (or fluting), the two types of paper that make up corrugated board. Container board is generally brown in color because it is made primarily from natural, unbleached wood fiber, although its color can vary depending on the wood species, pulping process, recycling rate, and impurity content.

[0006] Examples of different types of liners are kraft liners and test liners. Kraft liners are typically produced from kraft pulp, which can be bleached or unbleached, and can contain one or more layers / plies, where the top layer / ply is often optimized to provide a good print surface and good moisture resistance. Test liners are primarily produced from recycled cardboard and are usually made with two layers / plies. Due to the presence of recycled fibers, test liners can typically have lower mechanical strength than kraft liners, especially lower burst strength. Kraft liners are often used for packaging boxes with higher demands on strength properties.

[0007] Fluting is formed from paper or paperboard that has been corrugated using a corrugator with the aid of heat, moisture and pressure.

[0008] Fluting is often prepared from neutral sulfite semi-chemical (NSSC) pulp. NSSC pulp, usually made from hardwood species, is noted for its exceptional stiffness and high stiffness, making it suitable for use in fluting. Neutral sulfite semi-chemical (NSSC) pulping is an old process well known in the paper pulping field. One of the reasons for using NSSC pulping is its high yield, typically exceeding 60%. In NSSC pulping, the cooking liquor contains a sulfite salt 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 generally between 6 and 10. Pulp can be cooked in either batch or continuous cookers. Cooking times typically range from 5 minutes to 3 hours, and cooking temperatures range from 160 to 200°C. NSSC pulp contains a relatively high amount of residual lignin, such as 15-20%, which makes it hard. The Kappa number of NSSC pulp is typically above 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 disc refiner at digester pressure or atmospheric pressure.

[0009] Currently, the strength and mechanical properties of fluting and medium are improved by adding small amounts of chemical pulp to mechanical pulp. Typically, 5-15% chemical pulp is added, which naturally increases costs but also reduces dewatering rates. One possible approach is to blend a semi-chemical pulp, such as NSSC, with unbleached kraft pulp, but this can result in undesirable light mottling and color shifts, as well as changes in sensory properties.

[0010] The fluting and liner are attached to one another by placing an adhesive between the core and the liner. The liner is attached to at least one surface of the core with the adhesive. The adhesive is preferably applied to at least one surface of the fluted core, after which the liner is attached to said surface. Any adhesive conventional in the art can be used. The adhesive can be, for example, a starch-based glue that can be extracted from a wide variety of plants. Some of the most common plants are corn, wheat, barley, rice, potato, tapioca, and pea. The starch is preferably natural, i.e., the starch is not modified. The adhesive can also contain water, sodium hydroxide, and boric acid. Other additives, such as additives to improve wet strength or adhesive bond strength, can also be added. Other functional chemicals, such as borax, glyoxal, or mixtures thereof, can also be added, for example, to improve moisture resistance or gelling behavior.

[0011] One significant challenge when creating corrugating board and board is resistance to moisture. When corrugated board is exposed to moisture, water and water vapor can diffuse through the liner and soften the board. Common solutions to this problem include fluting and / or increasing the basis weight of the liner, but this conflicts with environmental imperatives that require lower basis weight materials that consume less raw material.

[0012] Another solution is to provide a barrier layer in the liner to reduce water and water vapor transmission. However, this is only an incomplete solution, since moisture diffusion can still occur on the other side or through the edges, thereby affecting the mechanical stability of the board. Barrier layers also increase costs and usually reduce the recyclability of the material.

[0013] The fluting or medium may also be treated or coated with hydrophobizing agents, but this generally increases cost and may also negatively affect the mechanical properties of the fluting. High levels of hydrophobizing agents may also impair the adhesion between the fluting and the liner. NSSC pulp, in particular, requires high levels of hydrophobizing agents to achieve the required level of water resistance in the finished fluting.

[0014] New machine concepts and increased machine speeds, combined with an increased desire to conserve resources, have further increased the need for pulps with improved properties.

[0015] There remains a need for new and improved liner materials that combine strength, low basis weight, water / moisture resistance, low chemical consumption, low cost, and / or high recyclability. Summary of the Invention

[0016] It is an object of the present disclosure to provide an improved liner for use in corrugated board that solves or ameliorates at least some of the problems mentioned above.

[0017] A further object of the present disclosure is to provide a liner for use in corrugated board that contains a high amount of NSSC pulp yet exhibits good appearance and optical properties.

[0018] It is a further object of the present disclosure to provide a method for producing a liner for use in corrugated board that can reduce consumption of unbleached kraft pulp (UBKP) without losing the mechanical and / or optical properties of the UBKP liner when used in corrugated board.

[0019] The above objectives, as well as other objectives that will be appreciated by those skilled in the art in light of this disclosure, are achieved by various aspects of the present disclosure.

[0020] NSSC pulp is commonly used for fluting for corrugated board, but is not used to the same extent for linerboard due to its optical and mechanical properties.

[0021] The present invention is based on the inventive realization that a liner with a high content of NSSC pulp for use in corrugated board can be embodied in the form of a multi-layer liner in which a first ply intended as a top or printing layer consists primarily of unbleached kraft pulp (UBKP), and a second ply intended as a back ply facing the flutes within the corrugated board contains a high content of NSSC pulp. The addition of NSSC to the second ply can improve the strength of liners, particularly liners containing a high amount of recycled fiber (e.g., test liners). The NSSC in the second ply also reduces the consumption of the more expensive UBKP, thereby lowering the cost of the liner. The use of NSSC in the second ply allows for the use of a high amount of NSSC, even low-grade or inferior NSSC, without causing unwanted light spots and color changes in the liner. This is because the second layer is hidden by the UBKP-based first ply. Placing NSSC pulp in the second ply allows for a much higher total NSSC content in the liner than when NSSC is mixed with UBKP in a single ply liner or in all plies of a multi-ply liner. DETAILED DESCRIPTION OF THE INVENTION

[0022] According to a first embodiment shown herein, for use in corrugated board, the multi-layer liner comprising: a first ply, and Second Ply Including, the first ply comprises, on a dry weight basis, at least 70 wt. % unbleached kraft pulp and 5 to 30 wt. % neutral sulfite semi-chemical (NSSC) pulp; A multi-layer liner is provided, wherein the second ply comprises at least 50 wt% NSSC pulp and 5-50 wt% unbleached kraft pulp on a dry weight basis.

[0023] The liner of the present disclosure is a multi-layer liner including a first ply (also referred to as the top ply) and a second ply (also referred to as the back ply). The outer surfaces of the multi-layer liner, i.e., the surfaces of the top and back plies away from the other plies, are referred to as the upper and lower surfaces, respectively.

[0024] The liner can be manufactured on a paper or paperboard machine adapted to manufacture multi-layer liners. Paper or paperboard machine tools for making multi-layer liners are well known in the art. Typically, the machine layout includes a stock processing section, a wet-end section, a press and dryer section, and a calender and / or coating section. In the wet-end section, the plies of the multi-layer liner can be formed individually using different headboxes and laminated wet, or they can be formed together using a multi-layer headbox. If formed individually, the plies are typically laminated or couched together before the press and dryer sections of the paper machine.

[0025] In some embodiments, the basis weight of each of the first ply and the second ply is between 20 and 150 g / m 2 in the range of 30 to 100 g / m 2 The total basis weight of the multi-layer liner is preferably in the range of 40 to 300 g / m 2 The range is.

[0026] The first ply of the multi-layer liner comprises at least 70 wt% unbleached kraft pulp (UBKP). In some embodiments, the first ply comprises at least 75 wt%, preferably at least 80 wt%, unbleached kraft pulp on a dry weight basis. The first ply comprises no more than 95 wt%, no more than 90 wt%, or no more than 85 wt% UBKP on a dry weight basis.

[0027] Unbleached kraft pulp, or UBKP, generally refers to unbleached sulfate pulp primarily composed of pine and / or spruce. The primary raw material for UBKP is preferably pine, but it may also contain up to 45 wt.% spruce. In some embodiments, the UBKP has a Kappa number greater than 55, preferably greater than 60, and more preferably greater than 70, as determined according to SCAN ISO C-1.

[0028] The first ply may further contain NSSC pulp, but at a lower content than the second ply. The first ply contains 5 to 30 wt% NSSC pulp on a dry weight basis. Preferably, the first ply contains 5 to 20 wt% or 5 to 10 wt% NSSC pulp on a dry weight basis.

[0029] The non-UBKP or NSSC pulp portion of the first ply can include any type of fiber, such as hardwood and / or softwood fibers, including, for example, chemical pulp, mechanical pulp, thermomechanical pulp, or chemi-thermomechanical pulp (CTMP). In some embodiments, the liner is a kraft liner, and the non-UBKP portion of the first ply is made entirely from virgin fibers. The non-UBKP portion of the first ply can also include, for example, recycled fibers. For example, the first ply of the present disclosure can consist essentially of UBKP or a mixture of UBKP and recycled fibers. "Recycled fibers" refers to fibrous materials previously incorporated into some type of paper or board product. Alternatively, or as a complement, the non-UBKP portion of the pulp 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 refining screen rejects from another process.

[0030] In some embodiments, the first ply of the multi-layer liner is optimized to provide a good print surface and good moisture resistance. In some embodiments, the optimization to provide a good print surface and good moisture resistance includes surface sizing. In some embodiments, the multi-layer liner is surface sized. In some embodiments, the multi-layer liner is surface sized with starch. In some embodiments, the multi-layer liner is surface sized with a combination of starch and at least one other functional ingredient, preferably selected from the group consisting of a cross-linking agent, a reinforcing agent, and a hydrophobizing sizing agent. The cross-linking agent can be, for example, citric acid. The reinforcing 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.

[0031] The second ply contains a significantly higher content of NSSC pulp than the first ply. The second ply contains at least 50 wt% NSSC pulp on a dry weight basis. In some embodiments, the second ply contains at least 60 wt%, preferably at least 70 wt%, and more preferably at least 80 wt% NSSC pulp on a dry weight basis. The second ply may contain up to 95 wt%, up to 90 wt%, up to 85 wt%, up to 80 wt%, or up to 75 wt% NSSC pulp on a dry weight basis.

[0032] "NSSC pulp" is obtained by "NSSC pulping," as defined in the Background Art section. NSSC pulp can be hardwood pulp or softwood pulp, or a mixture thereof. NSSC pulp is preferably hardwood pulp or a hardwood / softwood pulp mixture containing less than 15 wt% softwood, preferably less than 10 wt% softwood, and more preferably less than 5 wt% softwood. Hardwood can be, for example, aspen, alder, poplar, eucalyptus, birch, acacia, or beech. 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%, and 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 160-200°C. NSSC pulp may contain a relatively high amount of residual lignin, such as 15-20%. NSSC pulp typically has a Kappa number greater than 70, preferably greater than 80, preferably greater than 95, and more preferably greater than 100, according to ISO 3260. NSSC pulping is "semi-chemical" in the sense that it also includes mechanical refining of the pulp. Refining can be carried out, for example, using a disc refiner at digester pressure or atmospheric pressure. Refining can be carried out in one or more steps at the same or different pulp consistencies. The first refining step can be preferably carried out at a higher consistency, such as 5-35%, and the second refining step can be preferably carried out at a lower consistency, <5%.

[0033] The second ply may also contain UBKP, but at a significantly lower content than the first ply. The second ply contains 5 to 50 wt% UBKP on a dry weight basis. Preferably, the second ply contains 5 to 40 wt%, 5 to 30 wt%, or 5 to 20 wt% UBKP on a dry weight basis.

[0034] The non-NSSC pulp or non-UBKP portion of the second ply can include any type of fiber, such as hardwood and / or softwood fibers, e.g., chemical pulp, mechanical pulp, thermomechanical pulp, or chemi-thermomechanical pulp (CTMP). In some embodiments, the liner is a kraft liner, and the non-NSSC pulp portion of the second ply is made entirely from virgin fibers. The non-NSSC pulp portion of the second ply can also include, e.g., recycled fibers. For example, the second ply of the present disclosure can consist essentially of NSSC pulp or a mixture of NSSC pulp and recycled fibers. "Recycled fibers" refers to fibrous materials that have previously been incorporated into some type of paper or board product. Alternatively, or as a complement, the non-NSSC pulp portion of the pulp can include, e.g., rejected pulp. For example, the pulp of the present disclosure can consist essentially of NSSC pulp and rejected pulp. "Reject pulp" refers to pulp prepared by refining screen rejects from another process.

[0035] The addition of NSSC in the second ply can improve the strength of liners, especially multi-layer liners containing a high amount of recycled fibers (e.g., test liners). In some embodiments, at least 30% of the second ply is made of regenerated cellulose fibers.

[0036] In some embodiments, the multi-layer liner further comprises a reinforcing or adhesive applied to the interface between the first and second plies. Preferably, the reinforcing or adhesive comprises cooked or gelatinized or uncooked starch, or a mixture of cooked or gelatinized or uncooked starch and microfibrillated cellulose (MFC). Preferred reinforcing or adhesives are cooked native starch or cooked native starch mixed with microfibrillated cellulose. In some embodiments, the reinforcing or adhesive further comprises a cross-linking agent. The cross-linking agent may be, for example, citric acid. In some embodiments, the reinforcing or adhesive further comprises an insolubilizer. The insolubilizer may be, for example, an amino resin, glyoxal, or a zirconium salt insolubilizer. The amount of reinforcing or adhesive applied to the interface between the first and second plies is preferably 0.1 to 5 g / m2 on a dry weight basis. 2 range, more preferably 0.5 to 3 g / m 2 The range is.

[0037] Due to the high NSSC pulp content in the second ply, the multi-layer liner as a whole has a high NSSC pulp content. In some embodiments, the amount of NSSC pulp in the multi-layer liner is at least 10 wt%, preferably at least 20 wt%, and more preferably at least 30 wt% on a dry weight basis. In some embodiments, the amount of NSSC pulp in the multi-layer liner is at least 40 wt%, preferably at least 50 wt%, and more preferably at least 60 wt% on a dry weight basis.

[0038] In some embodiments, the NSSC pulp used in the multilayer liner is fractionated NSSC pulp. Fractionated NSSC pulp is obtained by size fractionation of the NSSC pulp starting material into a fine fiber fraction and a coarse fiber fraction. Compared to the starting material, the fine fiber fraction has a higher amount of shorter, finer fibers. In other words, the average particle size of the NSSC pulp in the fine fiber fraction is lower than the average particle size of the NSSC pulp in the coarse fiber fraction. The fine fiber fraction can be obtained, for example, by separating the NSSC pulp starting material with a pressure screen to obtain the fraction of shorter, finer fibers.

[0039] The fine fiber fraction obtained by size fractionation of NSSC pulp is particularly advantageous for use in the first ply of a multi-layer liner intended as an upper or printing layer because it has less impact on the optical properties of the liner compared to unfractionated or coarse fiber fractions of NSSC pulp. The coarse fiber fraction may be advantageously used in the second ply without affecting the optical properties of the liner. In preferred embodiments, the NSSC pulp used in the first ply is a fine fiber fraction of fractionated NSSC pulp. In preferred embodiments, the NSSC pulp used in the second ply is a coarse fraction of fractionated NSSC pulp. In some embodiments, the average particle size of the NSSC pulp used in the first ply is lower than the average particle size of the NSSC pulp used in the second ply.

[0040] In some embodiments, the multi-layer liner 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 internal sizing agent in the multi-layer liner is in the range of 0.5 to 6 kg / tn, preferably 0.8 to 4 kg / tn, and more preferably 1 to 3 kg / tn, on a dry weight basis.

[0041] In some embodiments, at least one surface of the multi-layer liner, preferably the top surface, has a Cobb 30s value of less than 30, preferably less than 25, and more preferably less than 22, as determined according to ISO Standard 535.

[0042] In some embodiments, the multi-layer liner has an equilibrium moisture content (EMC) of less than 10 wt. %, preferably less than 8 wt. %, at 50% RH as determined according to ISO Standard 287.

[0043] The multi-layer liner may further exhibit one or more of the following physical properties: The tensile index GEOM (ISO 1924-3) is preferably higher than 65 Nm / g, preferably higher than 66 Nm / g, more preferably higher than 67 Nm / g. The tensile stiffness index GEOM (ISO 1924-3) is preferably higher than 5.9 kNm / g, preferably higher than 6.0 kNm / g, more preferably higher than 6.2 kNm / g. The fracture toughness index GEOM (ISO / TS 17958) is preferably higher than 8 Jm / kg, preferably higher than 8.5 Jm / kg, more preferably higher than 9 Jm / kg. The SCT index GEOM (ISO 9895) is preferably higher than 25 Nm / g, more preferably higher than 26 Nm / g. Burst index (ISO 2759) preferably at least 3 kPa 2 / g, more preferably at least 3.2 kPa 2 / g.

[0044] The multi-layer liner may further contain additives such as natural starch or starch derivatives, cellulose derivatives such as sodium carboxymethyl cellulose, fillers, retention and / or drainage aids, flocculating additives, deflocculating additives, dry strength additives, softeners, crosslinking aids, sizing agents, dyes and colorants, wet strength resins, solidifying agents, defoaming aids, microbial and slime control aids, or mixtures thereof.

[0045] The multi-layer liner may further include a third ply, wherein the third ply comprises, on a dry weight basis, at least 70 wt.% unbleached kraft pulp and 5-30 wt.%, preferably 5-20 wt.%, or even more preferably 5-10 wt.% neutral sulfite semi-chemical (NSSC) pulp. Preferably, the third ply has the same composition as the first ply. Preferably, the first and third plies of the multi-layer liner form outer plies, and the second ply forms a central ply of the multi-layer liner.

[0046] In some embodiments, it is preferred that the multi-layer liner is a two-ply liner, which includes only two cellulose-based plies, namely the first and second plies.

[0047] The multi-layer liner is intended for use in corrugated board. The corrugated board includes at least one layer of liner, which is not corrugated, and is bonded to at least one layer of fluting. For example, the corrugated board may consist of a layer of fluting sandwiched between two layers of liner. According to a second aspect shown herein, there is provided corrugated board including the multi-layer liner and fluting according to the first aspect. In a preferred embodiment, the fluting is bonded to the second ply of the multi-layer liner.

[0048] According to a third aspect presented herein, there is provided a method of making a multi-layer liner for use in corrugated board, comprising: 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 said second web layer to obtain a second ply on the first ply; Includes; the first pulp suspension comprising, on a dry weight basis, at least 70 wt. % unbleached kraft pulp and 5 to 30 wt. % neutral sulfite semi-chemical (NSSC) pulp; A method is provided wherein the second pulp suspension comprises, on a dry weight basis, at least 50 wt% NSSC pulp and 5-50 wt% unbleached kraft pulp.

[0049] The terms first and second web layer do not necessarily refer to the order in which the web layers are formed. The web layers can be formed simultaneously or separately in any order.

[0050] In some embodiments, the first and second web layers are formed separately using different headboxes and one or more wires, partially dewatered, and then wet laminated.

[0051] In some embodiments, the first and second web layers are formed and partially dewatered together using a multi-layer headbox and a single wire.

[0052] For example, a first web layer may be formed separately and partially dewatered, and then laminated wet with a second web layer to obtain a second ply on the first ply, or the second web layer may be formed together with the first web layer and dewatered.

[0053] In some embodiments, the first pulp suspension comprises at least 75 wt.%, preferably at least 80 wt.%, unbleached kraft pulp on a dry weight basis.

[0054] In some embodiments, the first pulp suspension comprises 5 to 20 wt %, preferably 5 to 10 wt %, NSSC pulp on a dry weight basis.

[0055] In some embodiments, the second pulp suspension comprises at least 60 wt%, preferably at least 70 wt%, more preferably at least 80 wt% NSSC pulp on a dry weight basis.

[0056] In some embodiments, at least 30% of the pulp in the second pulp suspension consists of regenerated cellulose fibers.

[0057] In some embodiments, the basis weight of each of the first ply and the second ply is between 20 and 150 g / m 2 in the range of 30 to 100 g / m 2 The range is.

[0058] In some embodiments, the amount of NSSC pulp in the multi-layer liner is at least 10 wt%, preferably at least 20 wt%, more preferably at least 30 wt%, on a dry weight basis.

[0059] In some embodiments, the average particle size of the NSSC pulp used in the first pulp suspension is lower than the average particle size of the NSSC pulp used in the second pulp suspension.

[0060] The method includes forming and dewatering a multi-ply web from a pulp suspension. Methods for forming and dewatering webs having multiple layers are well known in the art. The liner can be made on a paper or board machine adapted to make multi-layer liners. Paper or board machines for making multi-layer liners are well known in the art. Typically, the machine layout includes a stock processing section, a wet end section, a press and drying section, and a calender and / or coating section.

[0061] The web is generally formed and dewatered in a wet end section containing one or more wires as is conventional in the art. The plies may be formed separately and wet-laminate using different headboxes, or they may be formed together in a multi-layer headbox. The web is typically formed on a gap former, but may also be formed on a Fourdrinier-type former. If formed separately, the wet plies are typically laminated or couched together prior to the press and dryer sections of the paper machine.

[0062] Prior to lamination, a reinforcing or adhesive agent can be applied between the first and second plies. Preferably, the reinforcing or adhesive agent comprises cooked, gelatinized, or uncooked starch, or a mixture of cooked, gelatinized, or uncooked starch and microfibrillated cellulose (MFC). Preferred reinforcing or adhesive agents are cooked native starch or cooked native starch mixed with microfibrillated cellulose. In some embodiments, the reinforcing or adhesive agent further comprises a crosslinking agent. The crosslinking agent can be, for example, citric acid. In some embodiments, the reinforcing or adhesive agent further comprises an insolubilizer. The insolubilizer can be, for example, an amino resin, glyoxal, or a zirconium salt insolubilizer. The reinforcing or adhesive agent is preferably applied as a paste or as an aqueous dispersion using a non-contact deposition technique such as spray, foam, or curtain coating. Preferably, the solids content of the aqueous dispersion is in the range of 0.5 to 50 wt %, more preferably 1 to 30 wt %. The amount of reinforcing or adhesive agent applied is preferably 0.1 to 5 g / m on a dry weight basis. 2 range, more preferably 0.5 to 3 g / m 2 The range is.

[0063] The web is typically subjected to further dewatering, for example, by passing the formed multilayer web through the press section of a papermaking machine, where the web passes between large rolls under high pressure to squeeze out as much water as possible. The press section may consist of a traditional nip press unit and a press woven felt, and / or may further comprise one or several shoe presses or extended dewatering nips. These may operate at various nip or press loads, including various positions, temperatures, and delay times. The press section may comprise one or more shoe presses to maximize production. If one or several shoe presses are used, they may operate at pressure levels greater than 800 kN / m, e.g., greater than 1000 kN / m, e.g., greater than 1200 kN / m, or e.g., greater than 1450 kN / m. The removed water is typically received by a woven fabric or felt.

[0064] After the press section, the multi-layer web may be subjected to drying in a drying section. Drying may include, for example, drying the multi-layer web by passing the multi-layer web around a series of heated drying cylinders. Drying may typically remove the water content to a level of about 1 to 15 wt %, preferably about 2 to 10 wt %.

[0065] While the present invention has been described with reference to various exemplary embodiments, it will be apparent to those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is not intended that the invention be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but the invention is intended to include all embodiments falling within the scope of the appended claims. [Example]

[0066] These examples demonstrate that high amounts of NSSC pulp can be used in two-ply liners without negatively affecting the mechanical or optical properties of the liner.

[0067] 2-Ply Liner Preparation Method Two-ply linerboards, including a front ply (corresponding to the first ply of the present invention) and a back ply (corresponding to the second ply of the present invention), were prepared on a pilot machine equipped with two headboxes and two wires, a press section, and a dryer section. The target final moisture content for the two-ply construction was 8.5 wt %, and the target basis weight was 120 g / m 2 The web was calendered online using a mechanical calender at 100° C. and a nip load of 45 kN / m.

[0068] The NSSC pulp had an Lc(w) fiber length of 1.14 mm as determined by the FS5 ISO method. The FS5 curl was 2% and the FS5 fibrillation was 1.55%. The FS5 Fines A content was 20.3%.

[0069] Unbleached kraft pulp was refined to SR30. The corresponding fiber properties were: Lc(w) fiber length 2.32 mm, FS5 curl 6.8%, FS5 fibrillation 1.78%. FS5 Fines A content was 18.8%.

[0070] All pulp suspensions contained the same amounts of retention and drainage aids and strength and internal size agents (AKD).

[0071] The pH of the pulp suspension was approximately 7.0 (±0.5).

[0072] When starch is applied between the top and center plies, the application rate is approximately 2 g / m2 on a dry weight basis. 2 It was.

[0073] Examples 1A and 1B (Comparative Examples) 2-ply 120g / m 2 Linerboard was prepared according to the two-ply liner preparation method described above using 100% UBKP in both the top and back plies as shown in Table 1. Two-ply constructions were made with (1A) starch between the plies and without (1B) starch between the plies. The liners were analyzed, and the results are shown in Table 2.

[0074] Examples 2A and 2B In this example, the back ply contained 90% NSSC pulp as shown in Table 1. Two-ply constructions were made with starch between the plies (2A) and without starch between the plies (2B). The liners were analyzed, and the results are shown in Table 2. Testing indicates that many mechanical properties can be maintained or improved, especially the Scott Bond and SCT index GEOM.

[0075] Examples 3A and 3B In this case, the NSSC content of the top ply was increased to 25% and the NSSC content of the back ply was increased to 95%, as shown in Table 1. Two-ply constructions were made with starch between the plies (3A) and without starch between the plies (3B). The liners were analyzed, and the results are shown in Table 2.

[0076] Examples 4A and 4B (Comparative) In this example, a two-ply construction was prepared with a high content of NSSC (50%) in the first ply, while the back ply contained 95% NSSC, as shown in Table 1. Two-ply constructions were made with starch between the plies (4A) and without starch between the plies (4B). The liners were analyzed, and the results are shown in Table 2. TIFF0007824978000001.tif63170TIFF0007824978000002.tif255170TIFF0007824978000003.tif44170

[0077] Unless otherwise specified, the physical properties discussed in this disclosure are determined according to the following standards: Whiteness C / 2°+UV ISO 2470-1 L* C / 2°+UV ISO 5631-1 a* C / 2°+UV ISO 5631-1 b* C / 2°+UV ISO 5631-1 Basis weight ISO 536 Thickness, single sheet ISO 534 Umbrella, single sheet ISO 534 Air permeability GH ISO 5636-5 Cobb 30s ISO 535 Moisture content 50%rh ISO 287 Scott-Bond TAPPI T569 Tensile strength ISO 1924-3 Tensile Index ISO 1924-3 Tensile strength md / cd ISO 1924-3 Elongation ISO 1924-3 Tensile stiffness ISO 1924-3 Tensile stiffness index ISO 1924-3 E-Module ISO 1924-3 TEA ISO 1924-3 TEA index ISO 1924-3 TEA index ISO 1924-3 Fracture toughness ISO / TS 17958 Fracture toughness index ISO / TS 17958 Tear resistance ISO 1974 Tear index ISO 1974 SCT ISO 9895 SCT index ISO 9895 RCT ISO 12192 RCT index ISO 12192 Rupture Index ISO 2759 Bursting strength ISO 2759

[0078] Unless otherwise specified, standard methods are applicable for determining physical and mechanical properties in both the cross direction (cd) and machine direction (md).

Claims

1. 1. A multi-layer liner for use in corrugated board, said multi-layer liner comprising: a first ply; and Second Ply Including, the first ply comprising, on a dry weight basis, at least 70 wt. % unbleached kraft pulp and 5 to 30 wt. % neutral sulfite semi-chemical (NSSC) pulp; The second ply comprises, on a dry weight basis, at least 50 wt. % NSSC pulp and 5-50 wt. % unbleached kraft pulp.

2. 10. The multi-layer liner of claim 1, wherein the first ply comprises at least 75 wt%, preferably at least 80 wt%, unbleached kraft pulp on a dry weight basis.

3. 3. The multi-layer liner of claim 1 or 2, wherein the first ply comprises 5 to 20 wt %, preferably 5 to 10 wt %, NSSC pulp on a dry weight basis.

4. 3. The multi-layer liner of claim 1 or 2, wherein the second ply comprises at least 60 wt%, preferably at least 70 wt%, more preferably at least 80 wt% NSSC pulp on a dry weight basis.

5. 3. The multi-layer liner of claim 1 or 2, wherein at least 30% of the second ply is made of regenerated cellulose fibers.

6. The basis weight of each of the first ply and the second ply is 20 to 150 g / m ２ in the range of 30 to 100 g / m ２ 3. The multilayer liner of claim 1, wherein the thickness of the multilayer liner is in the range of

7. 3. A multi-layer liner according to claim 1 or 2, wherein the amount of NSSC pulp in the multi-layer liner is at least 10 wt%, preferably at least 20 wt%, more preferably at least 30 wt%, based on dry weight.

8. 3. The multi-layer liner of claim 1 or 2, wherein the average particle size of the NSSC pulp used in the first ply is lower than the average particle size of the NSSC pulp used in the second ply.

9. The multi-layer liner of claim 1 or 2, wherein the multi-layer liner further comprises an internal sizing agent.

10. 3. The multi-layer liner of claim 1 or 2, wherein at least one surface of the multi-layer liner has a Cobb 30s value of less than 30, preferably less than 25, more preferably less than 22, as determined according to ISO Standard 535.

11. 3. A multilayer liner according to claim 1 or 2, wherein the multilayer liner has an equilibrium moisture content (EMC) at 50% RH determined according to ISO standard 287 of less than 10 wt%, preferably less than 8 wt%.

12. 3. The multi-layer liner of claim 1 or 2, wherein the multi-layer liner comprises a third ply, the third ply comprising, on a dry weight basis, at least 70 wt. % unbleached kraft pulp and 5 to 30 wt. % neutral sulfite semi-chemical (NSSC) pulp.

13. The multi-layer liner of claim 1 or 2, wherein the multi-layer liner is a two-ply liner.

14. 3. A corrugated board comprising the multi-layer liner and fluting of claim 1 or 2.

15. 1. A method of making a multi-layer liner for use in corrugated board, comprising: 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 said second web layer to obtain a second ply on the first ply; The process includes the steps of: the first pulp suspension comprising, on a dry weight basis, at least 70 wt. % unbleached kraft pulp and 5 to 30 wt. % neutral sulfite semi-chemical (NSSC) pulp; The method wherein the second pulp suspension comprises, on a dry weight basis, at least 50 wt. % NSSC pulp and 5 to 50 wt. % unbleached kraft pulp.

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