Paperboard, method and apparatus for its production, and packaging laminate and packaging container produced thereby

Abstract

This invention relates to a paperboard, its preparation method and apparatus, and the resulting composite sheet for packaging and packaging containers made from said composite sheet. The invention uses specific pulp of a specific weight to prepare paperboard with desired properties, and further prepares composite sheets using this paperboard as a carrier layer for manufacturing packaging containers, and packaging containers made from said composite sheet. The composite sheet of this invention possesses improved properties, such as reduced leakage in packaging containers, reduced edge seepage of the paperboard as the carrier layer, a moderate folding factor (FF%) of the composite sheet, moderate Z-axis strength of the paperboard as the carrier layer, and a more favorable delamination position when the paperboard is damaged.

Description

Technical Field

[0001] This invention relates to a paperboard, its preparation method and apparatus, as well as a packaging composite sheet prepared therefrom and a packaging container made from said composite sheet. Background Technology

[0002] Food, especially liquid food, is often packaged in containers to facilitate its production, transportation and carrying, and to extend its shelf life.

[0003] Common packaging containers include bottles and jars made of glass, ceramic, aluminum (which may have coatings or cladding), and tinplate. Such bottles and jars present numerous drawbacks in production, transportation, and use. For example, the cylindrical shape of the containers makes dense stacking difficult; their relative weight increases energy consumption during transport; they typically require separate packaging plant production, leading to cumbersome transportation between the packaging and filling plants; they require considerable force to open, posing a risk of sharp edges and user injury; and information is difficult to print directly on the container surface, among other issues.

[0004] In view of this, packaging containers made of composite sheets are commonly used in the prior art.

[0005] For example, a packaging container can be manufactured by reforming the laminated packaging material web into a tube by welding the innermost and outermost heat-sealable thermoplastic polymer layers together to join the two longitudinal edges of the web together in an overlapping joint; the tube is filled with liquid food and then separated into individual packages by repeating transverse seals spaced a predetermined distance from each other below the level of the contents; the packages are separated from the tube by cuts along the transverse seals and folded along creases prepared in the packaging material to obtain the desired geometry, typically a parallelepiped or cube.

[0006] For example, packaging containers can also be manufactured by starting with a tubular blank of packaging laminate folded into a flat shape, manufacturing the blank into an open tubular container package to produce packaging, wherein one open end is closed by folding and heat-sealing an integral end panel; the already closed container package is filled with liquid food through its open end, and then the open end is closed by further folding and heat-sealing the corresponding integral end panel.

[0007] Examples of packaging containers made from sheet and tubular preforms are the traditional so-called "mountain-top packaging," as well as packaging with molded tops and / or screw caps made of plastic.

[0008] The composite sheet and the method for producing packaging containers using the composite sheet have several advantages. For example, the packaging containers obtained by folding have a cuboid-based shape, making it easy to densely stack the composite sheet and packaging containers; the weight of the packaging containers is much lower than that of the bottles and cans, greatly reducing energy consumption during transportation; the production of packaging containers is easier than that of bottles and cans, avoiding the hassle of transportation between the packaging plant and the filling plant; the packaging containers are easier to open and do not form sharp edges during the opening process; information is also easier to print directly on the surface of the packaging containers, and so on.

[0009] Common composite sheets have a laminated structure that, from the outside to the inside, includes a carrier layer that provides support and structural stability to the packaging container when filled; a barrier layer that isolates the container from substances such as water and oxygen; and a polymer inner layer that provides liquid tightness to the liquid contained within and heat-sealability of the packaging container. The carrier layer is typically a cardboard layer, the barrier layer is typically an aluminum foil layer, and the polymer inner layer is typically a polyolefin layer, particularly a polyethylene layer. The layers of the composite sheet may also contain other layers; for example, an adhesive layer may be present between the polymer inner layer and the barrier layer to improve adhesion between them.

[0010] The paperboard layer, serving as the carrier layer, is typically produced by depositing a suspension of appropriately treated (e.g., pulped) plant fibers, mineral fibers, animal fibers, chemical fibers, or mixtures thereof, preferably plant fibers, onto a forming apparatus and then drying it. This suspension, particularly a suspension of pulped plant fibers in water, is referred to as pulp.

[0011] The plant fiber may be, for example, coniferous wood fiber obtained from coniferous trees such as Masson pine, larch, red pine, and spruce, and broad-leaved wood fiber obtained from broad-leaved trees such as birch, poplar, linden, eucalyptus, and maple, or a combination thereof.

[0012] The properties of pulp vary depending on the type and source of the raw materials used. For example, pulp from softwood trees has long and fine fibers, is relatively pure with few impurities, and produces paperboard with good flexibility, high folding endurance, good tensile strength, and good printability. In contrast, pulp from hardwood trees has shorter fibers, lower lignin content, and often contains more impurities, resulting in paperboard with relatively lower strength, higher bulk, higher stiffness, stronger absorbency, and higher opacity.

[0013] Pulp can be obtained in the form of mechanical pulp, chemical pulp, and mechatronic pulp. Mechanical pulp is made from plant fibers through mechanical pulping methods, such as pressing wood segments lengthwise onto a moist, rough, uniformly rotating millstone to separate the fibers from the wood segments. After screening and concentration, the pulp is made. Chemical pulp is made from plant fibers through chemical pulping methods, such as immersing wood chips in an aqueous solution of chemicals, such as a mixture of sodium hydroxide and sodium sulfide, or a mixture of sodium hydroxide and sodium sulfide, and cooking them under high temperature and pressure to dissolve the lignin in the wood chips, obtaining intact cellulose. Chemimechanical pulp is made from plant fibers through a semi-chemical pulping method that combines chemical and mechanical methods, such as first locally softening or cooking the wood chips with chemicals, and then completing the gelatinization process mechanically.

[0014] Different methods of obtaining pulp result in different pulp properties, leading to variations in the performance of the paperboard made from it. For example, mechanical pulping processes retain almost all the non-cellulose components of the wood in the pulp, resulting in a slightly yellowish pulp. Under sunlight and air exposure, the paper will further yellow, exhibiting lower strength, higher opacity, lower density, higher smoothness, stronger ink absorption, and better printability. In contrast, chemical pulping processes involve chemicals reacting not only with lignin but also with cellulose and hemicellulose, reducing the degree of polymerization of cellulose macromolecules and causing severe degradation or dissolution of hemicellulose. This results in a lower pulp yield but a softer, stronger pulp.

[0015] Those skilled in the art will recognize that not only does the pulp production process affect the properties of the pulp and the paperboard made therefrom, but the conditions during pulp production also affect the properties of the pulp and the paperboard made therefrom.

[0016] Timber sources are widespread and highly regional. Currently, the world's major timber-producing regions include South and North America, such as Brazil, the United States, and Canada; Northern Europe, such as Finland and Sweden; Southeast Asia, such as Indonesia, Vietnam, and Laos; Africa; and Siberia and the Far East of Russia. Coniferous timber is mainly produced in mid- to high-latitude regions, while broadleaf timber is mainly produced in mid- to low-latitude regions. To ensure the availability of raw materials and the consistency and reliability of the performance of finished paperboard, it is necessary to develop methods for producing paperboard with similar or even improved performance from raw materials from various sources (especially from different regions) and from pulp prepared from said raw materials using various methods.

[0017] For the production of composite sheets used in packaging containers, pulp is typically not prepared by means of beating, but rather by purchasing pulp bales directly and then obtaining pulp using methods including pulping, dilution, refining, purification, and deaeration, which is then used to produce paperboard. Therefore, this invention can be embodied as a method for developing paperboard with similar or even improved performance for different pulps. Summary of the Invention

[0018] This invention uses a specific pulp of a specific weight to prepare paperboard with desired properties, and further prepares a composite sheet using the paperboard as a carrier layer for manufacturing packaging containers, as well as a packaging container made from the composite sheet.

[0019] The present invention also prepared the paperboard of the present invention using a preparation method and apparatus under specific conditions.

[0020] Specifically, a first aspect of the present invention relates to a paperboard comprising a printed layer, a core layer, a bottom layer, and an optional coating layer, wherein the core layer comprises 25-35% by weight, preferably about 30% by weight, waste paper, 45-55% by weight, preferably about 51% by weight, BCTMP (bleached chemithermomechanical pulp), and 15-25% by weight, preferably about 19% by weight, BSW (bleached softwood pulp), preferably having a basis weight of 85-100 gsm, preferably about 93 gsm.

[0021] As a supplement, alternative, and / or preferred embodiment, the present invention specifically relates to a paperboard comprising a printed layer, a core layer, and a bottom layer, and optionally a coated layer, wherein the core layer comprises 27-32% by weight, preferably 28-30% by weight, more preferably about 28% by weight, waste paper, 48-52% by weight, preferably 50-51% by weight, more preferably about 50% by weight, BCTMP (bleached chemothermal mechanical pulp), and 17-24% by weight, preferably 19-22% by weight, more preferably about 22% by weight, BSW (bleached softwood pulp), preferably having a basis weight of 90-96 gsm, preferably 90-93 gsm, more preferably about 93 gsm.

[0022] Preferably, in the paperboard of the present invention, the core layer does not contain UBSW (unbleached softwood pulp), that is, UBSW is not added to the pulp used to prepare the core layer. Those skilled in the art will understand that UBSW introduced due to the addition of damaged pulp should not be considered as the addition of UBSW.

[0023] Preferably, in the paperboard of the present invention, the core layer comprises an internal sizing agent, preferably an alkyl ketene dimer.

[0024] Preferably, in the paperboard of the present invention, the printed layer comprises 65-75% by weight, preferably about 70% by weight, of BHW (bleached hardwood pulp) and 25-35% by weight, preferably about 30% by weight, of BSW, preferably with a basis weight of 45-65 gsm, preferably about 55 gsm.

[0025] As a supplement, alternative, and / or preferred embodiment, in the paperboard of the present invention, the printed layer comprises 68-72% by weight, preferably about 70% by weight, of BHW (bleached hardwood pulp) and 28-32% by weight, preferably about 30% by weight, of BSW, with a basis weight preferably 55-53 gsm, more preferably about 53 gsm.

[0026] Preferably, in the paperboard of the present invention, the bottom layer comprises 60-100% by weight of UBSW and 0-40% by weight of BSW, BHW or a mixture of BSW and BHW, more preferably comprising 65-75% by weight of UBSW and 25-35% by weight of BSW, BHW or a mixture of BSW and BHW.

[0027] As a supplement, alternative, and / or preferred, preferably, in the paperboard of the present invention, the bottom layer comprises 65-100% by weight of UBSW and 0-35% by weight of BSW, BHW, or a mixture of BSW and BHW, preferably comprising about 70% by weight of UBSW and about 30% by weight of BSW, BHW, or a mixture of BSW and BHW.

[0028] More preferably, in the paperboard of the present invention, the basis weight of the bottom layer is preferably 30-50 gsm, more preferably about 43 gsm.

[0029] As a supplement, alternative and / or preferred, in the paperboard of the present invention, the basis weight of the bottom layer is preferably 41-45 gsm, more preferably about 43 gsm.

[0030] Preferably, in the paperboard of the present invention, the beating degree of the pulp forming the printing layer, core layer and bottom layer, and the waste pulp are respectively: BHW: 22-37°SR, preferably 28-35°SR;

[0031] BSW: 18-31°SR, preferably 23-27°SR;

[0032] UBSW: 16-29°SR, preferably 21-24°SR;

[0033] BCTMP: 20-35°SR, preferably 21-26°SR;

[0034] Paper damage: 35-60°SR, preferably 37-55°SR.

[0035] As a supplement, alternative, and / or preferred embodiment, in the paperboard of the present invention, the BHW, BSW, UBSW, BCTMP, and freeness of the pulp forming the printing layer and the waste pulp are respectively:

[0036] BHW: 28-35°SR, preferably 33-35°SR;

[0037] BSW: 22-26°SR, preferably 25-26°SR;

[0038] The beating degrees of the pulp forming the bottom layer are as follows:

[0039] BHW: 32-37°SR, preferably 34-35°SR;

[0040] BSW: 22-28°SR, preferably 24-26°SR;

[0041] UBSW: 21-26°SR, preferably 24-26°SR;

[0042] The freeness of the pulp forming the core layer are as follows:

[0043] BSW: 21-27°SR, preferably 21-25°SR;

[0044] BCTMP: 21-24°SR, preferably 23-24°SR;

[0045] Paper damage: 35-50°SR, preferably 35-37°SR.

[0046] Preferably, in the paperboard of the present invention, the fiber thicknesses of the BSW and UBSW are 100-120 μg / m, preferably about 110 μg / m, and 118-138 μg / m, preferably about 128 μg / m, respectively.

[0047] Preferably, the paperboard of the present invention further includes a coating layer comprising pigments, adhesives and additives, wherein the adhesive is preferably SA latex with a basis weight preferably 15-30 gsm, more preferably about 22 gsm.

[0048] As a supplement, alternative, and / or preferred embodiment, the paperboard of the present invention further includes a coating layer comprising pigments, adhesives, and additives, wherein the adhesive is preferably SA latex with a basis weight preferably 20-22 gsm.

[0049] A second aspect of the invention relates to a method for preparing the paperboard of the invention, wherein pulp forming a printing layer, a core layer and a bottom layer is sequentially fed to a wire section, a press section, a drying section, a sizing step, a calendering step, a coating section, a winding step and a rewinding step.

[0050] Preferably, in the method of the present invention, the printed layer, the core layer, and the bottom layer are respectively conveyed from their respective headboxes to the screen section via lip plates, and the openings of the lip plates are respectively:

[0051] Printed layer: 10-17mm, preferably 13-14mm;

[0052] Core layer: 15-30mm, preferably 20-25mm; and

[0053] Bottom layer: 10-17mm, 13-14mm.

[0054] Preferably, in the method of the present invention, when the printed layer, core layer and bottom layer are laminated together in the mesh section, a crosslinking agent is sprayed between the layers, preferably an aqueous starch solution, and the spray nozzle for spraying the crosslinking agent is at an angle of 15-30° to the horizontal plane, preferably about 20°.

[0055] Preferably, in the method of the present invention, the pulp of the printing layer comes from at least two headboxes with the same or different internal pulp compositions, preferably two headboxes with the same internal pulp composition, thereby forming the surface layer and the backing layer.

[0056] A third aspect of the invention relates to an apparatus for preparing the paperboard of the invention, comprising a headbox, a wire section, a press section, and components downstream of the press section.

[0057] Preferably, in the apparatus of the present invention, the pulp of the printing layer, the core layer and the bottom layer is conveyed to the wire section through the lip plate of the headbox, and the opening of the lip plate is 13-14 mm, 20-25 mm and 13-14 mm respectively.

[0058] Preferably, the apparatus of the present invention includes a nozzle for spraying a crosslinking agent between the printed layer, the core layer and the bottom layer when the mesh portion is laminated together, the nozzle being at an angle of 15-30° to the horizontal plane, preferably about 20°.

[0059] A fourth aspect of the invention relates to a composite sheet comprising, in order from the outside to the inside, a carrier layer, a barrier layer and a polymer inner layer, wherein the paperboard of the invention is used as the carrier layer, wherein the bottom layer of the paperboard is adjacent to the barrier layer of the composite sheet.

[0060] The fifth aspect of the invention relates to a packaging container made of the composite sheet of the invention. Detailed Implementation

[0061] In this document, the term "about" used to modify numerical values ​​means that the value should take into account experimental errors and variations that can be expected by those skilled in the art. In particular, "about" can refer to a value that is added to or subtracted from the modified value within the range of 15%, preferably 10%, more preferably 5%, and most preferably 2.5%.

[0062] In this document, "a layer essentially composed of a certain substance" means that the content of said substance in the layer is high enough that the layer exhibits physical and / or chemical properties that a person skilled in the art would consider equivalent to a layer composed solely of that substance. For example, the content of said substance in the layer may be at least 60% by weight, at least 75% by weight, at least 85% by weight, at least 90% by weight, at least 95% by weight, or 100% by weight, based on the weight of the layer. The calculation of the content does not include impurities that are necessarily included.

[0063] In this article, the term "inner side" of a composite sheet or a layer thereof means the side of the composite sheet or layer that is closer to the contents of the packaging container, while the term "outer side" of a composite sheet or a layer thereof means the side of the composite sheet or layer that is closer to the external environment of the packaging container.

[0064] In this article, "layer A 'adjacent' to layer B" means that the surfaces of layers A and B that are opposite each other are in direct contact, or that the surfaces of layers A and B that are opposite each other have only a layer for promoting the bonding of layers A and B, such as an adhesive layer.

[0065] In this document, waste paper refers to paperboard scraps removed during the preparation of the paperboard of the present invention, such as during trimming, which are then added to the pulp raw materials for reuse after being re-shredded.

[0066] In this article, BCTMP refers to bleached chemithermomechanical pulp, such as bleached chemithermomechanical pulp of hardwood, softwood, or combinations thereof. BCTMP is commercially available; for example, long BCTMP fibers may be Glacier products from Pan Pac Forest Products Ltd-Pulp, and short BCTMP fibers may be SAPPI maple products from Sappi Papier Holding GmbH.

[0067] In this article, BSW stands for bleached softwood pulp, sometimes also referred to as bleached long fiber pulp and bleached softwood sulfate pulp. BSW is commercially available, for example, as a Northwood product from Canfor Pulp Ltd.

[0068] In this article, UBSW refers to unbleached softwood pulp. UBSW is commercially available, for example, it can be a Dolphin product from MONDIHINTON INC.

[0069] In this article, BHW refers to bleached hardwood pulp, sometimes also called bleached short fiber pulp and bleached hardwood sulfate pulp. BHW is commercially available, for example, it can be Parrot products from SUZANO INTERNATIONAL TRADE GMBH.

[0070] In this paper, SA and SB refer to styrene-acrylic latex and styrene-butadiene latex, respectively, which can be used to form adhesive layers.

[0071] cardboard

[0072] A first aspect of the present invention relates to a paperboard comprising a printed layer, a core layer, and a bottom layer.

[0073] The core layer of the paperboard of this invention provides most of the paperboard thickness. This core layer comprises, by weight,

[0074] 25-35% by weight, for example, 25% by weight, 27% by weight, 29% by weight, 30% by weight, 31% by weight, 33% by weight or 35% by weight of waste paper;

[0075] 45-55% by weight, for example, 45%, 47%, 49%, 50%, 51%, 53%, or 55% by weight of BCTMP; and 15-25% by weight, for example, 15%, 17%, 19%, 20%, 21%, 23%, or 25% by weight of BSW.

[0076] Preferably, the core layer comprises about 30% by weight of waste paper, about 51% by weight of BCTMP, and about 19% by weight of BSW.

[0077] In one embodiment of the invention, the waste paper is first pulped before use.

[0078] Preferably, the core layer weight of the paperboard of the present invention is 85-100 gsm, such as 85 gsm, 87 gsm, 89 gsm, 91 gsm, 93 gsm, 95 gsm, 97 gsm or 100 gsm.

[0079] More preferably, the core layer of the paperboard of the present invention has a basis weight of about 93 gsm.

[0080] In one embodiment of the present invention, the core layer of the paperboard does not contain UBSW.

[0081] In one embodiment of the invention, the core layer of the paperboard comprises an internal sizing agent to enhance the paperboard's resistance to the penetration and diffusion of liquids (especially water).

[0082] Commonly used sizing agents in the art can be used, such as rosin, alkyl ketene dimers (AKD), alkenyl succinic anhydride (ASA), styrene-acrylate copolymers, styrene-maleic acid copolymers, or combinations thereof. In this invention, the internal sizing agent for the core layer is preferably an alkyl ketene dimer, particularly an alkyl ketene dimer with the following structure:

[0083]

[0084] Those skilled in the art can determine the conditions and amount of sizing agent to be added based on the teachings of the prior art or according to actual needs. Preferably, the amount of sizing agent added in this invention is 15-30 kg / t based on the ton weight of the paperboard.

[0085] In one embodiment of the invention, the printed layer of the paperboard comprises, by weight of the printed layer,

[0086] 65-75% by weight, for example, 65% by weight, 67% by weight, 69% by weight, 70% by weight, 71% by weight, 75% by weight, or 75% by weight of BHW; and

[0087] 25-35% by weight, for example, 25% by weight, 27% by weight, 29% by weight, 30% by weight, 31% by weight, 33% by weight or 35% by weight of BSW.

[0088] Preferably, the printed layer comprises about 70% by weight of BHW and about 30% by weight of BSW based on the weight of the printed layer.

[0089] Preferably, the printing layer weight of the paperboard of the present invention is 45-65 gsm, for example 45 gsm, 47 gsm, 49 gsm, 51 gsm, 53 gsm, 55 gsm, 57 gsm, 59 gsm, 61 gsm, 63 gsm or 65 gsm.

[0090] More preferably, the printed layer of the paperboard of the present invention has a basis weight of about 55 gsm.

[0091] In one embodiment of the invention, the bottom layer of the paperboard comprises 60-100% by weight of UBSW and 0-40% by weight of BSW, BHW, or a mixture of BSW and BHW; preferably 65-75% by weight of UBSW and 25-35% by weight of BSW, BHW, or a mixture of BSW and BHW.

[0092] Preferably, the bottom layer comprises 100% by weight of UBSW, i.e., the bottom layer is composed of UBSW.

[0093] Preferably, the bottom layer of the paperboard of the present invention has a basis weight of 30-50 gsm, such as 30 gsm, 32 gsm, 34 gsm, 36 gsm, 38 gsm, 40 gsm, 42 gsm, 43 gsm, 44 gsm, 46 gsm, 48 gsm or 50 gsm.

[0094] More preferably, the basis weight of the bottom layer of the paperboard of the present invention is about 43 gsm.

[0095] In one embodiment of the present invention, the BHW, BSW, UBSW, BCTMP and freeness of the waste pulp of the printing layer, core layer and bottom layer of the paperboard of the present invention are preferably as follows: BHW: 22-37°SR, for example 22°SR, 24°SR, 26°SR, 28°SR, 30°SR, 31°SR, 32°SR, 34°SR or 36°SR;

[0096] BSW: 18-31°SR, such as 18°SR, 20°SR, 22°SR, 23°SR, 24°SR, 26°SR, 28°SR, 30°SR or 31°SR;

[0097] UBSW: 16-29°SR, such as 16°SR, 18°SR, 20°SR, 21°SR, 23°SR, 24°SR, 25°SR, 27°SR or 29°SR;

[0098] BCTMP: 20-35°SR, such as 23°SR, 25°SR, 27°SR, 28°SR, 30°SR, 32°SR, 34°SR, or 35°SR; and

[0099] Broken paper: 35-60°SR; such as 35°SR, 37°SR, 39°SR, 41°SR, 42°SR, 43°SR, 45°SR, 47°SR, 49°SR, 51°SR, 53°SR, 55°SR, 57°SR, 59°SR or 60°SR.

[0100] Preferably, the beating degrees of the BHW, BSW, UBSW, BCTMP, and waste pulp of the printing layer, core layer, and bottom layer of the paperboard of the present invention are as follows:

[0101] BHW: 22-37°SR, preferably 28-35°SR;

[0102] BSW: 18-31°SR, preferably 23-27°SR;

[0103] UBSW: 16-29°SR, preferably 21-24°SR;

[0104] BCTMP: 20-35°SR, preferably 21-26°SR;

[0105] Paper damage: 37-60°SR, preferably 35-55°SR.

[0106] In one embodiment of the present invention, the fiber thickness of the BSW in the paperboard of the present invention is 100-120 μg / m, for example 100 μg / m, 102 μg / m, 104 μg / m, 106 μg / m, 108 μg / m, 110 μg / m, 112 μg / m, 114 μg / m, 116 μg / m, 118 μg / m or 120 μg / m.

[0107] Preferably, the fiber thickness of the BSW is about 110 μg / m.

[0108] In one embodiment of the present invention, the fiber thickness of the UBSW of the paperboard of the present invention is 118-138 μg / m, for example 118 μg / m, 120 μg / m, 122 μg / m, 124 μg / m, 126 μg / m, 128 μg / m, 130 μg / m, 132 μg / m, 134 μg / m, 136 μg / m or 138 μg / m.

[0109] Preferably, the fiber thickness of the UBSW is about 128 μg / m.

[0110] In this invention, the BSW and BHW in each layer of the cardboard can be the same or different, but preferably the same.

[0111] The paperboard of the present invention, particularly the core layer, may further contain additives, such as performance additives and processing aids, specifically sizing agents, water-resistant agents, whitening agents, dyes, fillers, bactericides, defoamers, flocculants, degassing agents, and biocides, and combinations thereof. The structure, composition, preparation, and usage conditions (e.g., amount, method, and conditions of addition) of the additives are known to those skilled in the art.

[0112] In one embodiment of the invention, the paperboard of the invention includes a coating layer on one or both sides. The coating layer mainly comprises pigments (such as kaolin, titanium dioxide, calcium carbonate), adhesives (SA latex or SB latex, preferably SA latex) and other additives.

[0113] Preferably, the basis weight of the coating layer is 15-30 gsm, such as 15 gsm, 16 gsm, 18 gsm, 20 gsm, 22 gsm, 24 gsm, 26 gsm, 28 gsm or 30 gsm, preferably about 22 gsm.

[0114] Methods and apparatus for preparing paperboard

[0115] The second and third aspects of the present invention relate to a method for preparing the paperboard of the present invention and an apparatus for carrying out the method.

[0116] The paperboard preparation method of this invention is basically consistent with the general methods in the prior art. The paperboard preparation method is described in more detail below. For details not covered herein, such as the specific conditions of each step, those skilled in the art can determine them according to actual needs.

[0117] First, obtain the applicable waste pulp, BCTMP, BSW, UBSW, and BHW.

[0118] The preparation methods and conditions for damaged pulp can be determined by those skilled in the art based on actual needs.

[0119] BCTMP, BSW, UBSW, and BHW can be prepared from their respective raw materials through pulping. Alternatively, they can be prepared by directly purchasing pulp bags and then using methods including pulping, dilution, refining, purification, and deaeration. The preparation methods and conditions described herein can be determined by those skilled in the art based on actual needs.

[0120] According to the formulation of each layer, prepare the mixture of pulps constituting each layer, and after mixing, load them into their respective headboxes. Internal sizing agents, such as the alkyl ketene dimer preferably used for each layer in this invention, should be added to the corresponding mixture and mixed evenly with the pulp.

[0121] The pulp flows from its respective headbox, passes through the gap between the wire mesh and the lip plate, and is stacked together on the wire section in a wet state. It is then dewatered and formed into paperboard. Preferably, the stacking process is carried out in steps, with one layer stacked at a time.

[0122] The width of the gap between the mesh plate and the lip plate is called the lip plate opening.

[0123] It has been found that, preferably, the lip opening of the headbox from which the pulp forms the printing layer, core layer, and bottom layer flows is as follows:

[0124] Printed layer: 10-17mm, preferably 13-14mm;

[0125] Core layer: 15-30mm, preferably 20-25mm; and

[0126] Bottom layer: 10-17mm, preferably 13-14mm.

[0127] In one embodiment of the invention, the printed layer is formed as a two-layer structure, a top layer and a backing layer, wherein the compositions of the top layer and the backing layer may be the same or different, preferably the same. In this case, the top layer and the backing layer flow out from their respective headboxes and are stacked together at the screen to form the printed layer.

[0128] Preferably, a crosslinking agent is sprayed between the layers during the lamination process to strengthen the bonding between them. A preferred crosslinking agent is starch, which is typically used in aqueous solution. The crosslinking agent is sprayed between the layers in a specific amount and manner (e.g., spraying angle). Preferably, the amount of crosslinking agent sprayed between the top layer and the liner is 2.2 kg / t; the amount of crosslinking agent sprayed between the liner and the core layer is 0 kg / t; and the amount of crosslinking agent sprayed between the core layer and the bottom layer is 3 kg / t.

[0129] It has been found that, preferably, the angle between the nozzle used for spraying the crosslinking agent and the horizontal plane is 15-30°, for example 15°, 17°, 19°, 20°, 21°, 23°, 25°, 27°, 30°, and preferably about 20°.

[0130] The applicant discovered that by using the amount of the aforementioned crosslinking agent and the angle between the spray nozzle and the horizontal plane, a more effective bond was achieved between the top layer and the core layer, and between the core layer and the bottom layer.

[0131] The cardboard leaving the wire section is further dehydrated by mechanical pressing with rollers in the press section. Then, it goes through a pre-drying step, a sizing step (in which modified starch is coated on both sides of the cardboard to improve its strength), a post-drying step, a calendering step, a coating step (in which a coating layer is applied to one or both sides of the cardboard), a winding step, and a rewinding step to obtain a cardboard with a printing layer, a core layer, and a bottom layer.

[0132] During the winding and rewinding steps, the scraps removed during the trimming of the cardboard are used as waste paper and then used as waste pulp after beating.

[0133] Composite sheet

[0134] A fourth aspect of the invention relates to a composite sheet that can be used to prepare packaging containers. The composite sheet comprises, in order from the outside to the inside, a carrier layer, a barrier layer, and a polymer inner layer, wherein the paperboard of the present invention is used as the carrier layer, the bottom layer of which is adjacent to the barrier layer of the composite sheet.

[0135] The composite sheet of the present invention first includes a carrier layer. The carrier layer plays a supporting role in the composite sheet, providing structural stability of the packaging container made from the composite sheet in a full state.

[0136] The paperboard of this invention is used as the carrier layer.

[0137] The composite sheet of the present invention further includes a barrier layer. The barrier layer (also referred to as a barrier layer) functions to isolate, for example, water and oxygen in the composite sheet, thereby ensuring the long-term preservation of the contents of the packaging container, especially liquid food.

[0138] The barrier layer commonly used in existing technologies can be used as the barrier layer of this invention.

[0139] In one embodiment of the present invention, the barrier layer may be based on a metal layer, preferably an aluminum foil layer. The aluminum foil layer may be made of aluminum or an aluminum alloy, such as AlFeMn, AlFe... 1.5 Mn, AlFeSi, or AlFeSiMn. The thickness of the aluminum foil layer can be, for example, 3-20 μm, preferably 3.5-12 μm, more preferably 4-10 μm. The aluminum or aluminum alloy suitable for manufacturing the aluminum foil can be commercially available, for example, it can be purchased from Hydro Aluminum Deutschland GmbH or Amcor Flexibles Singen GmbH under the trade names ENAW 1200, ENAW 8079, or ENAW 8111.

[0140] When using aluminum foil layers, to enhance adhesion between the aluminum foil layer and its inner, outer, or side layers, an adhesive layer can be applied to one or both sides of the aluminum foil layer. This adhesive layer can be a polyolefin-based adhesive, i.e., primarily composed of polyolefin monomer units (e.g., polyethylene monomer units). Preferably, it has a melt flow index of 4 to 12 g / 10 min at 190°C and 2.16 kg (measured according to ISO-1133), and a carboxyl functional group content of 3 to 10% by weight. Preferably, the adhesive is an ethylene-(meth)acrylic acid copolymer or graft copolymer, such as EAA or EMAA.

[0141] A deposited metal layer can be used instead of an aluminum foil layer. For this purpose, the metal can be deposited on the surface of the substrate polymer film via physical vapor deposition or chemical vapor deposition. The thickness of the deposited metal layer can be in the nanometer range, for example, from 5 nm to 500 nm. The resulting barrier layer thickness can be further reduced to, for example, even less than 10 μm.

[0142] Aluminum is the preferred metal for deposition. Iron, copper, and other metals can also be used. Other metals or semi-metals, such as silicon, can also be used.

[0143] The substrate polymer film can be made of any polymer suitable for vapor deposition, such as polyolefins, polyethylene terephthalate, or other thermoplastic polymers, preferably polyethylene. The substrate polymer film can be of any thickness, as long as it is suitable for vapor deposition.

[0144] In another embodiment of the invention, the barrier layer may also be based on a metal oxide layer. Useful metal oxide layers include those known to those skilled in the art as suitable for use as barrier layers, preferably layers based on oxides of said metals (such as aluminum, iron, or copper), and metal oxide layers based on titanium oxide or silicon oxide.

[0145] The metal oxide layer can also be fabricated, for example, by vapor deposition of the metal oxide on a substrate polymer film. A preferred method for achieving this is physical vapor deposition.

[0146] The substrate polymer film can be made of any polymer suitable for vapor deposition, such as polyolefins, polyethylene terephthalate, or other thermoplastic polymers, preferably polyethylene. The substrate polymer film can be of any thickness, as long as it is suitable for vapor deposition.

[0147] Obviously, the barrier layer of the present invention may also include any combination of two or more of the metal layer and the metal oxide layer. It should be emphasized that the composition, preparation, and use of the barrier layer of the present invention are not limited to the content disclosed above, but any barrier layer known in the art for composite sheets can be used, and the selection of its composition, structure, and method of use, as well as the adaptive adjustments to the technical solution of the present invention, are known to those skilled in the art.

[0148] The composite sheet of the present invention further includes a polymer inner layer. The polymer inner layer provides the composite sheet with liquid tightness for the liquid contained in the container and heat-sealability of the packaging container.

[0149] The main components of the polymer inner layer of this invention are HDPE, LDPE and mPE.

[0150] Polyethylene is a product of ethylene homopolymerization. Ethylene homopolymerization is usually a free radical polymerization process, and its products are often classified as high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), very low-density polyethylene (VLDPE), and metallocene polyethylene (mPE).

[0151] On the one hand, the classification criteria for polyethylene according to density are known to those skilled in the art. For reference, the densities of completely amorphous and completely crystalline polyethylene are 0.880 and 1.000 g / cm³, respectively. 3 .

[0152] Generally, when high pressure (e.g., 82-276 MPa) is used in ethylene polymerization, the density of the resulting polymer is 0.915-0.940 g / cm³.3 It is classified as LDPE. The reaction is usually carried out at a temperature of 132-332℃, resulting in the formation of a large number of branched structures. Therefore, LDPE has a structure of random long chains with a large number of randomly distributed branched branches. The length of the branched branches is not uniform, but rather has a certain distribution, mainly consisting of 2, 3, or 4 carbon atoms. LDPE is usually a transparent, slightly white, elastic solid.

[0153] According to the definition in ASTM D1248-84, HDPE is a type of polyethylene with a density of 0.940 g / cm³. 3 The above refers to polyethylene. HDPE is obtained through polymerization under low-pressure conditions, such as in the presence of a catalyst, and has a basically linear structure, although a small amount of branching may be intentionally added for specific purposes. The molecular weight distribution of HDPE depends on the catalyst used in the polymerization process and typically has a moderate peak width. HDPE is usually an opaque, white, rigid solid.

[0154] On the other hand, polyethylene includes mPE prepared by polymerization in the presence of a metallocene catalytic system. The metallocene catalytic system comprises a major component of an organometallic compound, typically a Ti or Zr central metal atom positioned between two organic ligands, such as a cyclopentadienyl group, and a minor component of a cocatalyst, typically an organoaluminum compound such as MAO (i.e., methylaluminoxane) or a perfluoroboron aromatic compound. The metallocene catalytic system is a single-active-site catalyst, which, compared to conventional Ziegler-Natta catalysts, can more effectively control the polymer structure, resulting in polyolefins with superior performance. mPE typically has a relatively narrower molecular weight distribution. mPE can be one or more combinations selected from mLDPE (i.e., metallocene low-density polyethylene), mLLDPE (i.e., metallocene linear low-density polyethylene), and mHDPE (i.e., metallocene high-density polyethylene), preferably mLLDPE.

[0155] LDPE, HDPE, and mPE can be prepared by methods known to those skilled in the art. However, more commonly, LDPE, HDPE, and mPE are commercially available. For example, LDPE can be the LDPE series from Dow Chemical (USA), mPE can be the Affinity series from Dow Chemical (USA), and HDPE can be the Rigidex series from Ineos.

[0156] It should be emphasized that the range of HDPE, LDPE, and mPE used in the composite sheets of this invention is known to those skilled in the art and may not be limited to the above description. In other words, given an understanding of the physical / chemical properties and preparation methods of a particular polyethylene, those skilled in the art can easily determine whether it belongs to the HDPE, LDPE, and mPE used in the composite sheets of this invention, without necessarily needing to mechanically refer to the above description.

[0157] The composite sheet of the present invention may optionally include other layers to impart specific properties to the composite sheet. The composition, structure, and preparation of such other layers may be known to those skilled in the art.

[0158] For example, in one embodiment of the invention, the composite sheet of the invention may include a polymer outer layer on its outermost side, which is intended to come into contact with the external environment of the packaging container made from the composite sheet. Preferably, the polymer outer layer is liquid-tight and heat-sealable. The polymer outer layer may, for example, be a layer composed primarily of LDPE.

[0159] For example, in one embodiment of the invention, the composite sheet of the invention may include a laminate between the carrier layer and the barrier layer. This laminate is intended for laminating the carrier layer (such as a cardboard layer) and the barrier layer (such as an aluminum foil layer) together. The laminate may, for example, be a layer substantially composed of LDPE, a layer substantially composed of LDPE and mPE, or a layer substantially composed of HDPE and LDPE.

[0160] The inner side of the laminate may have an adhesive layer to further improve the adhesion between the layers on both sides. The adhesive layer may be a polyolefin-based adhesive, i.e., primarily composed of polyolefin monomer units (e.g., polyethylene monomer units). Preferably, it has a melt flow index of 4 to 12 g / 10 min at 190°C and 2.16 kg (measured according to ISO-1133), and a carboxyl functional group content of 3 to 10% by weight. Preferably, the adhesive is an ethylene-(meth)acrylic acid copolymer or graft copolymer, such as EAA or EMAA.

[0161] For example, in one embodiment of the invention, the composite sheet of the invention may also include an adhesive layer and / or an adhesion promoter layer between any two layers, particularly between the barrier layer and the polymer inner layer, to improve adhesion between the layers on either side. This adhesive layer and / or adhesion promoter layer, for example, comprises a polymer suitable for generating strong bonds by means of functionalization of suitable functional groups, by forming ionic or covalent bonds with the surfaces of their respective adjacent layers. Preferably, these polymers are obtained by copolymerizing ethylene with acrylic monomers, such as acrylic acid, methacrylic acid, crotonic acid, acrylates, methacrylates, other acrylate derivatives, or carboxylic acids with double bonds, such as maleic anhydride, or at least two of these. Among these polymers, polyethylene-maleic anhydride graft polymer (EMAH), ethylene-acrylic acid copolymer (EAA), or ethylene-methacrylic acid copolymer (EMAA) are preferred, examples of which include those from DuPont. and 0609HSA, and from Exxon Mobile Chemical 6000ExCo.

[0162] According to the invention, the adhesion between the carrier layer, barrier layer, and polymer inner layer and their adjacent layers is preferably at least 0.5 N / 15 mm, more preferably at least 0.7 N / 15 mm, and even more preferably at least 0.8 N / 15 mm. In one embodiment of the invention, the adhesion between the carrier layer and the barrier layer is preferably at least 0.3 N / 15 mm, more preferably at least 0.5 N / 15 mm, and even more preferably at least 0.7 N / 15 mm. In another embodiment of the invention, the adhesion between the barrier layer and the polymer inner layer is preferably at least 0.8 N / 15 mm, more preferably at least 1.0 N / 15 mm, and even more preferably at least 1.4 N / 15 mm. If the barrier layer is indirectly connected to the polymer inner layer through an adhesion promoter layer, the adhesion between the barrier layer and the adhesion promoter layer is preferably at least 1.8 N / 15 mm, more preferably at least 2.2 N / 15 mm, and even more preferably at least 2.8 N / 15 mm. In particular, the adhesion between the layers is strong enough that the carrier layer is torn during the adhesion test.

[0163] Those skilled in the art will recognize that if the compatibility between two adjacent layers is good, it may not be necessary to use an adhesive layer or an adhesion promoter layer between the two layers.

[0164] For example, in one embodiment of the invention, the composite sheet of the invention may include an inner surface layer on its innermost side, which is intended to come into contact with the contents, preferably food, contained in a packaging container made of the composite sheet.

[0165] It should be emphasized that the composition, preparation and use of other layers of the present invention are not limited to the contents disclosed above, but any other layer known in the art for composite sheets can be used. The selection of its composition, structure and usage method and the adaptive adjustments to the technical solution of the present invention are known to those skilled in the art.

[0166] The layers of the composite sheet of the present invention may optionally contain other components to impart specific properties to the composite sheet. These other components may be known to those skilled in the art.

[0167] For example, the other components may include colorants. Specifically, according to DIN 55943:2001-10 and Industrial Organic Pigments: Production, Properties, Applications, 3 rd ed.,Willy Herbst et al.,Copyright The colorants mentioned in WILEY-VCH Verlag GmbH & Co. KGaA, ISBN: 3-527-30576-9 are pigments, and more particularly dyes and pigments. Preferred colorants are pigments, and more preferably organic pigments.

[0168] Once the composition and structure of the composite sheet of the present invention are understood, those skilled in the art can easily obtain methods for preparing the composite sheet from the prior art.

[0169] For example, each polymer layer of the composite sheet of the present invention can be applied to the precursor by extrusion coating.

[0170] The extrusion operation can be performed using extrusion tools known to those skilled in the art. The extrusion tools used can be commercially available, such as extruders, extrusion screws, feed blocks, etc. At the end of the extruder, there is preferably an opening through which the polymer melt is extruded. The opening can have any shape that allows the polymer melt to be extruded onto the precursor, such as polygonal, elliptical, or circular. The opening is preferably in the shape of a funnel-shaped channel. In a preferred embodiment of the process, application is achieved through a channel, which preferably has a length of 0.1-100 m, more preferably 0.5-50 m, and particularly preferably 1-10 m. Additionally, the width of the channel is preferably 0.1-20 mm, more preferably 0.3-10 mm, and particularly preferably 0.5-5 mm. During the application of the polymer melt, the channel and the precursor preferably move relative to each other. Preferably, the precursor moves relative to the channel. The temperature of the polymer melt during the extrusion operation is typically set to 210-350°C, measured at the molten polymer film below the extruder die exit.

[0171] In a preferred extrusion operation, the polymer melt is stretched during application, preferably by melt stretching, and very preferably by uniaxial melt stretching. For this purpose, the polymer is applied to the precursor in a molten state using an extruder, and then the layer of polymer, still in a molten state, is stretched along a preferred uniaxial direction to achieve polymer orientation in this direction.

[0172] When the melt layer is applied to the precursor by the stretching process, the melt layer can be cooled to achieve heat setting. This cooling is preferably achieved by quenching through contact with a surface, wherein the surface is preferably maintained in the range of 5 to 50°C, more preferably 10 to 30°C.

[0173] In a further preferred configuration, the region that has appeared is cooled to below the minimum melt temperature of the polymer supplied in that region or its flanks, and then at least the flanks of that region separate from it. Cooling can be performed in any manner known to those skilled in the art. Heat setting, as described above, is also preferred here. Subsequently, at least the flanks separate from the region. This separation can be performed in any manner known to those skilled in the art. Preferably, separation is accomplished by a knife, a laser beam, or a water jet, or a combination of two or more of these, with a knife, particularly scissors, being especially preferred for cutting.

[0174] For example, multiple adjacent polymer layers of the composite sheet of the present invention can be applied together to the precursor by melt co-extrusion coating.

[0175] In a melt co-extrusion coating operation, when materials comprising two or more adjacent polymer layers are transferred to a die using a feed block, the melt exits the die through a die gap (e.g., a die gap 500 mm long and 1 mm wide) and is applied to a precursor that is moving relative to the die gap.

[0176] In one embodiment of the present invention, the composite sheet of the present invention is obtained by a method including the following steps:

[0177] The carrier layer is provided to the composite sheet production line;

[0178] Apply the polymer outer layer to the outer surface of the carrier layer;

[0179] Apply the laminate to the inner surface of the carrier layer;

[0180] Apply the barrier layer to the inner surface of the laminate;

[0181] The second adhesive layer and the inner polymer layer are applied together to the inner surface of the barrier layer, wherein the second adhesive layer and the inner polymer layer are arranged sequentially from the inner surface of the barrier layer inward.

[0182] Obviously, the above description is merely exemplary, and those skilled in the art can also use other methods to obtain the composite sheet of the present invention.

[0183] Packaging containers

[0184] The fifth aspect of the present invention relates to packaging containers manufactured from the composite sheet of the present invention.

[0185] Packaging containers can be manufactured from the composite sheets of the present invention using methods known to those skilled in the art.

[0186] In one embodiment of the present invention, a basic method for manufacturing a packaging container includes the following steps: providing a composite sheet of the present invention, which includes a first longitudinal edge and a second longitudinal edge located on opposite sides of the composite sheet; folding the composite sheet such that the first longitudinal edge contacts and overlaps the second longitudinal edge, thereby obtaining a longitudinal seam.

[0187] In a preferred embodiment of the invention, the packaging container is a cubic container, also known as a "brick-shaped" container. In the manufacture of this cubic container, the composite sheet of the invention, comprising a first longitudinal edge and a second longitudinal edge located on opposite sides of the composite sheet, is first folded as described above, such that the first longitudinal edge contacts and overlaps the second longitudinal edge, thereby obtaining a longitudinal seam, thus producing a jacket-shaped container precursor. This container precursor is then transported to a commercial filling machine, where the bottom region of the container is created by folding and sealed, for example, by blowing with hot air. The contents (e.g., liquid food) are then filled into the container with the bottom region, and the top region of the container is created by further folding. The container is then sealed and closed, for example, by ultrasonic sealing, thereby obtaining a packaging container filled with the contents.

[0188] The steps, conditions, and equipment involved in the method for manufacturing packaging containers from composite sheets of the present invention can be determined by those skilled in the art based on actual needs.

[0189] Evaluation of composite sheets

[0190] This invention uses a specific pulp with a specific weight and a preparation method including specific conditions to prepare paperboard with desired properties, and further prepares composite sheets using the paperboard as a carrier layer for manufacturing packaging containers.

[0191] The composite sheet of the present invention has improved properties, such as reduced leakage of packaging containers, reduced edge leakage of the cardboard as the carrier layer, a moderate folding factor (FF%) of the composite sheet, moderate Z-direction strength of the cardboard as the carrier layer, and a more favorable delamination position when the cardboard is damaged.

[0192] Leakage in packaging containers refers to the phenomenon where liquid containing dye leaks from a pre-formed and sealed packaging container after being left to stand for a period of time. The extent of leakage depends on the composite sheet used to manufacture the packaging container, not the adhesive used to bond it together. The degree of leakage is characterized by the proportion of leakage that occurs.

[0193] Edge seepage in paperboard refers to the phenomenon where liquid seeps into the edges of a composite sheet due to capillary action after both sides of the sheet are sealed with tape. The degree of edge seepage is mainly related to the internal adhesive application of each layer of the composite sheet. The degree of edge seepage is characterized by the change in the weight of the composite sheet before and after seepage.

[0194] The folding factor (FF%) of a composite sheet characterizes the ease with which the composite sheet can be folded. The folding factor is typically related to the thickness, fiber orientation, material, and processing technology of the paperboard. It is determined by first creating indentations on the composite sheet and then folding the sheet along those indentations.

[0195] The Z-direction strength of paperboard, as the carrier layer, refers to its strength perpendicular to its plane. The Z-direction strength of paperboard is determined by taping both sides of the paperboard together and then pulling the tape to break it; the strength at which the paperboard breaks is its Z-direction strength. Paperboard should have moderate Z-direction strength. Too low a Z-direction strength will make the paperboard easily broken, while too high a Z-direction strength will create a burst point (folding point) when the paperboard is folded, causing it to break and resulting in leaks. The Z-direction strength of paperboard is related to the interlacing ability of the fibers. A suitable Z-direction strength can be obtained by adjusting the formulation (such as the beating degree of the pulp forming the paperboard).

[0196] The location of delamination when the cardboard, serving as the carrier layer, is broken refers to the point where the cardboard is torn in a direction perpendicular to its plane. This breakage typically occurs within the core layer (called "core-to-core delamination") or between the core and bottom layers (called "core-to-bottom delamination"). Compared to core-to-bottom delamination, core-to-core delamination results in better folding performance, better shaping, and a lower rate of leaks. The location of delamination when the cardboard breaks depends primarily on the beating degree of the pulp forming each layer, the lip opening when the pulp enters the wire section from the headbox, and the amount and angle of starch sprayed into each layer during the wire lamination process.

[0197] It should be noted that the evaluation of composite sheets should not be limited to a single specific performance, but should be a comprehensive evaluation of various performance characteristics.

[0198] Example

[0199] The technical solutions of the present invention will be described in more detail below with reference to embodiments thereof. Obviously, the following embodiments only relate to some, and not all, of the technical solutions of the present invention. The scope of the present invention should be defined by the appended claims, and not limited to the technical solutions described in the specification, much less limited to the following embodiments.

[0200] raw material

[0201] As a raw material for the production of paperboard,

[0202] BCTMP long fiber is a Glacier product from Pan Pac Forest Products Ltd-Pulp; BCTMP short fiber is a SAPPI maple product from Sappi Papier Holding GmbH; BSW is a Northwood product from Canfor Pulp Ltd.

[0203] UBSW is a dolphin product from MONDI HINTON INC.

[0204] BHW is a parrot product from SUZANO INTERNATIONAL TRADE GMBH.

[0205] As a raw material for preparing composite sheets,

[0206] The aluminum foil used as the barrier layer is 6-micron aluminum foil from Shanghai Shenhuo Aluminum Foil Co., Ltd.

[0207] The LDPE is LDPE 7004 from Dow Chemical in the United States;

[0208] HDPE is a product from Ineos' Rigidex series;

[0209] mPE is a product from Dow Chemical's Affinity series in the United States.

[0210] Test methods

[0211] The leakage rate of packaging containers is determined as follows: D60+ blue dye is added to the water in the packaging container. After the packaging container is sealed, it is left to stand for 24 hours. The percentage of packaging containers from which blue dye is observed to have leaked is the leakage rate.

[0212] The edge seepage of the paperboard shall be determined according to the method in GB / T 31905-2015.

[0213] The Z-direction strength of the paperboard shall be determined according to the method in GB / T 31110-2014.

[0214] The folding factor (FF%) of the composite sheet is determined according to the following method:

[0215] 1) Select the location of the crease sample so that...

[0216] - Only continuous creases are measured;

[0217] - Maintain sufficient distance from adjacent creases;

[0218] - Reserve enough space for a proper uncreased sample.

[0219] L = Vertical (with creases)

[0220] T = Horizontal (with creases)

[0221] U = Sample without creases

[0222] 2) The crease depth data is measured and processed using folding equipment and laboratory drawing software. The folding factor FF% is obtained by (crease signal - no crease signal) / no crease signal * 100%, which represents the crease depth.

[0223] The internal bond strength of the paperboard shall be determined according to the method in GB / T 26203-2010.

[0224] The location of delamination when the cardboard is damaged is determined by observing and measuring the internal bond strength at the location of the damage, i.e., determining whether the damage is core-to-core delamination or core-to-bottom delamination.

[0225] Examples 1-3: The Influence of Pulp Formulation on Performance

[0226] During the paperboard forming process, the paperboard is prepared using the formula and conditions in Table 1. The percentages of each component in Table 1 are by weight and calculated based on the total amount of the layer in which it is located.

[0227] Composite sheets were produced using a German Davis laminating machine at an extrusion temperature of 300°C, according to the descriptions of the layer composition and basis weight in Table 2. Specifically, the following steps were performed sequentially:

[0228] 1. Provide paperboard as a carrier layer;

[0229] 2. The polymer outer layer is applied to the coating layer of the paperboard by extrusion coating;

[0230] 3. Apply the laminate, the first adhesive layer, and the barrier layer sequentially to the bottom layer of the cardboard layer;

[0231] 4. Apply the second adhesive layer and the inner polymer layer to the inner surface of the barrier layer by melt co-extrusion coating.

[0232] The composite sheet is folded and sealed to create a cubic (“brick-shaped”) packaging container using the following method:

[0233] 1. Fold the composite sheet so that its two longitudinal edges come into contact and connect to form a longitudinal seam. Seal the longitudinal seam to create a jacket-shaped packaging container precursor.

[0234] 2. The jacket-shaped packaging container precursor is transported to a commercial filling machine, where the bottom area of ​​the packaging container is created by folding and the bottom is sealed by blowing hot air at a temperature of 300°C.

[0235] 3. Fill the packaging container with water, and then create the top area of ​​the packaging container by further folding it.

[0236] The top area is sealed off using ultrasonic waves.

[0237] The performance of cardboard, composite sheets, and packaging containers was measured, and the results are summarized in Table 3.

[0238]

[0239]

[0240]

[0241] Table 3

[0242]

[0243] As can be seen:

[0244] In Example 1, a "core-bottom" delamination phenomenon occurs, with low internal bonding strength, high Z-axis strength, and excessively high folding factor;

[0245] In Example 2, the internal bonding strength and Z-axis strength were improved, and the delamination position was biased towards "core-core";

[0246] Example 3 further shifts the layering position towards "core-to-core";

[0247] In Example 4, the bottom layer beating degree is easier to control, the process is more stable during production, the internal bonding strength and Z-direction strength are improved, and the folding performance is better.

Claims

1. A paperboard comprising a printed layer, a core layer, a bottom layer, and an optional coated layer, wherein the core layer comprises 25-35% by weight, preferably about 30% by weight, waste paper, 45-55% by weight, preferably about 51% by weight, BCTMP, and 15-25% by weight, preferably about 19% by weight, BSW, preferably having a basis weight of 85-100 gsm, preferably about 93 gsm.

2. The paperboard of claim 1, wherein the core layer does not contain UBSW.

3. The paperboard of claim 1 or 2, wherein the core layer comprises an internal sizing agent, preferably an alkyl ketene dimer.

4. The paperboard according to any one of claims 1 to 3, wherein the printed layer comprises 65-75% by weight, preferably about 70% by weight, of BHW, and 25-35% by weight, preferably about 30% by weight, of BSW, preferably having a basis weight of 45-65 gsm, preferably about 55 gsm.

5. The paperboard according to any one of claims 1 to 4, wherein the bottom layer comprises 60-100% by weight of UBSW and 0-40% by weight of BSW, BHW or a mixture of BSW and BHW; preferably comprising 65-75% by weight of UBSW and 25-35% by weight of BSW, BHW or a mixture of BSW and BHW, wherein the basis weight of the bottom layer is 30-50 gsm, preferably about 43 gsm.

6. The paperboard according to any one of claims 1 to 5, wherein the beating degree of the pulp forming the printed layer, the core layer, and the bottom layer are respectively: BHW: 22-37°SR, preferably 28-35°SR; BSW: 18-31°SR, preferably 23-27°SR; UBSW: 16-29°SR, preferably 21-24°SR; BCTMP: 20-35°SR, preferably 21-26°SR; Paper damage: 35-60°SR, preferably 37-55°SR.

7. The paperboard according to any one of claims 1 to 6, wherein the fiber thickness of the BSW and UBSW is 100-120 μg / m, preferably about 110 μg / m, and 118-138 μg / m, preferably about 128 μg / m, respectively.

8. The paperboard according to any one of claims 1 to 7, further comprising a coating layer comprising pigment, adhesive and additives, wherein the adhesive is preferably SA latex with a basis weight preferably 15-30 gsm, more preferably about 22 gsm.

9. A method for preparing the paperboard according to any one of claims 1-8, wherein the pulp forming the printing layer, the core layer and the bottom layer is sequentially fed to the wire section, the press section, the drying section, the sizing step, the calendering step, the coating section, the winding step and the rewinding step.

10. The method of claim 9, wherein the printed layer, core layer, and underlayer are respectively conveyed from their respective headboxes to the screen section via lip plates, the openings of the lip plates being: Printed layer: 10-17mm, preferably 13-14mm; Core layer: 15-30mm, preferably 20-25mm; and Bottom layer: 10-17mm, 13-14mm.

11. The method of claim 9 or 10, wherein a crosslinking agent, preferably an aqueous starch solution, is sprayed between the printed layer, core layer and bottom layer when the mesh portion is laminated together, and the spray nozzle for spraying the crosslinking agent is at an angle of 15-30° to the horizontal plane, preferably about 20°.

12. The method of any one of claims 9 to 11, wherein the pulp of the printed layer is derived from at least two headboxes with the same or different internal pulp compositions, preferably two headboxes with the same internal pulp composition, thereby forming a surface layer and a backing layer.

13. An apparatus for preparing paperboard according to any one of claims 1-8, comprising a headbox, a wire section, a press section, and a component downstream of the press section.

14. The apparatus of claim 13, wherein the pulp of the printing layer, the core layer and the bottom layer is conveyed to the wire section via the lip plate of the headbox, the lip plate having openings of 13-14 mm, 20-25 mm and 13-14 mm respectively.

15. The apparatus of claim 14, comprising a nozzle for spraying a crosslinking agent, preferably an aqueous starch solution, between the printed layer, the core layer and the bottom layer when the mesh portion is laminated together, the nozzle being at an angle of 15-30° to the horizontal plane, preferably about 20°.

16. A composite sheet comprising, in order from the outside to the inside, a carrier layer, a barrier layer and a polymer inner layer, wherein the paperboard of any one of claims 1-8 is used as the carrier layer, wherein the bottom layer of the paperboard is adjacent to the barrier layer of the composite sheet.

17. A packaging container made of the composite sheet of claim 16.

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