Paper-based material for liquid packaging box as well as preparation method and application of paper-based material

Abstract

The invention belongs to the technical field of packaging materials, and provides a paper-based material for a liquid packaging box as well as a preparation method and application of the paper-based material. The pulp of the surface layer, the pulp of the core layer and the pulp of the bottom layer are prepared respectively, then papermaking is performed, the pulp proportion of each layer, the use amount of a reactive sizing agent, the beating degree of the surface layer and the pulp-net speed ratio in the papermaking process are optimized, meanwhile, the lactic acid edge seepage resistance, the telescopic performance and the impact resistance of the paper-based material for the liquid packaging box are improved, and the performance of a dart falling test is excellent; under some extreme conditions, it can be guaranteed that package leakage, damage and expansion are avoided, the packaging box can be stacked together, enough strength supporting can be provided, and the printing requirement can be met.

Description

Technical Field

[0001] The present invention relates to the technical field of packaging materials, and more specifically, to a paper-based material for a liquid packaging box, a preparation method thereof, and an application thereof. Background Art

[0002] Liquid packaging boxes are a kind of packaging material specially used for low-temperature fresh milk, yogurt, juice and other liquid beverages. For example, the commonly used roof-type packaging boxes have a unique shape and are named because the top is similar to a "roof". They are a kind of uncoated base paper, and the pulp is generally bleached pulp. Since liquid packaging boxes are often used for the packaging of fresh milk, yogurt and other dairy products, and are required to be able to be stored under refrigeration for at least 7-21 days, the requirements for 24h lactic acid edge permeability, scalability and impact resistance of roof-type packaging boxes are relatively high. However, liquid packaging boxes cannot fully meet the requirements at present, as follows:

[0003] 1. 24h lactic acid osmosis (requires 24 hours, lactic acid osmosis ≤ 4.0kg / m 3 ): Roof-type prefabricated packaging paper usually adopts AKD sizing process (sizing process using alkyl ketene dimer sizing agent), that is, heavy sizing is carried out on the base paper, which is prone to AKD false sizing and precipitation problems, resulting in bright spots on the paper surface, poor flatness of the paper surface, and crushing of the paper surface, resulting in paper breaks, especially in the production of high-weight paper. The probability of paper breaks is greatly increased, resulting in leakage problems during the filling test;

[0004] 2. Scalability: As the capacity of the packaging box continues to expand, when it exceeds 1L, the problem of bulging will occur (the base paper has insufficient scalability, resulting in lateral expansion of the paper box, which manifests as bulging), which directly affects the packaging and transportation of the paper box. In addition, roof-type liquid packaging paper usually requires cold chain transportation, which aggravates the bulging problem. If the bulging is serious, it is easy to leak (i.e. liquid leakage);

[0005] 3. Impact resistance: The roof-type prefabricated packaging box has insufficient impact resistance. During transportation and handling, it may fall or collide violently, resulting in deformation. In severe cases, cracks may even appear, causing leakage of contents.

[0006] In addition, while adjusting the 24h lactic acid edge penetration, scalability and impact resistance of the paper, the flatness of the paper surface will be affected. The roof-type prefabricated packaging paper is printed after the base paper is coated, so the flatness of the paper surface is high, and most of them are dark-colored printings. If the paper flatness is poor, the printing performance will be poor, and problems such as white printing and missing dots will easily occur.

[0007] Therefore, there is an urgent need to develop a paper-based material that can simultaneously meet the requirements of resistance to lactic acid edge seepage, scalability, and impact resistance, and further be used to prepare packaging boxes to meet liquid packaging, transportation, and storage needs, while ensuring normal printing needs. Summary of the invention

[0008] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides a paper-based material for liquid packaging boxes and a preparation method and application thereof. The paper-based material for liquid packaging boxes provided by the present invention has excellent resistance to lactic acid edge seepage, scalability and impact resistance by adjusting the pulp ratio of each layer, the beating degree of the surface layer, the amount of reactive sizing agent, and the pulp-to-net speed ratio. The 24h lactic acid edge seepage is only 2.0-2.8kg / m 3 , internal bonding strength can reach 247-282J / m 2 The Z-axis strength can reach 392-425kPa, the wet-to-dry tensile strength ratio (longitudinal) is 7.9-8.3, the wet-to-dry tensile strength ratio (transverse) is 8.7-9.7, the dart breakage rate (front) is 12-19%, the dart breakage rate (back) is 7-17%, and the flatness is good, the flatness reaches 1.0-1.4 level, the base paper uniformity index is 74-79, and the uniformity index after ink spreading is 56-60, which can meet the printing needs, broaden the application range of paper-based materials, and can be used to prepare liquid packaging boxes (such as roof-type packaging boxes), and meet the packaging, transportation and storage needs of liquids.

[0009] A first aspect of the present invention provides a method for preparing a paper-based material for a liquid packaging box.

[0010] Specifically, a method for preparing a paper-based material for a liquid packaging box, wherein the paper-based material for a liquid packaging box comprises a surface layer, a core layer and a bottom layer stacked in sequence; the preparation method comprises the following steps:

[0011] The slurries of the surface layer, the core layer and the bottom layer are prepared respectively, and then paper-made to obtain the paper-based material for the liquid packaging box; wherein the paper-making step comprises: after the slurry is drained, compounding, pressing, drying, surface sizing, drying again, calendering and rolling into paper in sequence to obtain the paper-based material for the liquid packaging box;

[0012] The pulp of the surface layer includes 60-80% long fiber wood pulp and 20-40% short fiber wood pulp in terms of mass percentage;

[0013] The pulp of the core layer comprises, by mass percentage, 40-60% bleached chemical mechanical pulp, 20-45% long fiber wood pulp and 10-20% short fiber wood pulp;

[0014] The bottom layer pulp comprises 30-50% short fiber wood pulp and 50-70% long fiber wood pulp in terms of mass percentage;

[0015] The beating degree of the surface layer is 14-18°SR;

[0016] The slurries of the surface, core and bottom layers all contain sizing agent, and the sizing agent is a reactive sizing agent. The contents of the sizing agent in the surface, core and bottom layers are 15-25, 25-40 and 10-30 kg / ton of slurry respectively.

[0017] During the compounding process, when the gram weight of the paper-based material for the liquid packaging box is ≤300 g / m2, the pulp-to-web speed ratios of the surface, core, and bottom layers are 0.978-0.982, 0.958-0.962, and 0.923-0.927, respectively, and / or, when the gram weight of the paper-based material for the liquid packaging box is >300 g / m2, the pulp-to-web speed ratios of the surface, core, and bottom layers are 0.983-0.987, 0.963-0.967, and 0.928-0.932, respectively.

[0018] First, the present invention controls the pulp ratio of the surface, core and bottom layers, wherein the long fiber ratio of the surface layer is increased, the beating degree of the surface layer pulp is increased, the beating performance is optimized, the lateral pressure bearing capacity is increased, and the internal bonding strength of the paperboard is enhanced (up to 247-282 J / m 2 ) and Z-direction strength (i.e., the strength perpendicular to the plane of the paperboard, which can be increased to 392-425kPa), thereby improving the overall rigidity and impact resistance of the paperboard. Even if it is used to prepare large-volume (such as ≥1L) packaging boxes, it can meet its impact resistance requirements. However, in general, the improvement of impact resistance is generally accompanied by a decrease in flatness. This is because the increase in the proportion of long fibers, although it improves the strength, the higher rigidity it brings also causes the paperboard to deform uncontrollably during the manufacturing and processing process, affecting the flatness and aesthetics of the final product. The present invention, by reasonably proportioning the long fiber ratio of the surface layer, makes the impact resistance and flatness in a balanced state, and both the impact resistance and flatness can meet the requirements. Secondly, the present invention adopts a reactive sizing agent, and by reducing the amount of reactive sizing agent added to the surface, core, and bottom layers, it can not only avoid the precipitation of the reactive sizing agent, but also improve the resistance to lactic acid edge seepage (24h lactic acid seepage ≤3.0kg / m 3) at the same time, the flatness of the paper is ensured to meet the requirements of printing. Furthermore, by controlling the pulp-to-web speed ratio during the papermaking process of the surface, core, and bottom layers, the longitudinal and transverse stiffness ratio of the paperboard is effectively improved, so that the paperboard exhibits excellent rigidity and stability in different directions, thereby improving the scalability and ensuring the flatness of the paper. In addition, by adjusting the beating degree of the surface layer to 14-18°SR, the tightness and strength of the paper are effectively improved, the burrs and powdering on the surface of the paper are reduced, the flatness is improved while taking into account the lactic acid resistance, scalability, and impact resistance, and the ink absorption performance of the paper is improved, the printing quality is improved, and it is also helpful to improve the water filtration performance of the pulp, making the paper easier to form and dry during the production process, thereby improving production efficiency. The consequences of excessive surface beating: 1. Fiber shortening: excessive beating will cause excessive fiber damage in the pulp, shortening the fiber length, thus affecting the strength and durability of the paper; 2. Reduced paper quality: excessive beating will increase the burrs and powdering on the paper surface, reduce the smoothness and glossiness of the paper, thus affecting the printing quality and aesthetics. 3. Increased energy consumption and cost: excessive beating will increase the energy consumption and production cost of the paper machine, because more energy is required to destroy the fibers and achieve the required beating degree. The consequences of too little surface beating: 1. Insufficient fiber destruction: too little beating will cause the pulp to still contain more long fibers and unbroken impurities, affecting the uniformity and strength of the paper; 2. Impact on paper performance: pulp with too little beating will lead to insufficient paper density, low strength, easy breakage, etc., reducing the performance and life of the paper; 3. Reduced production efficiency: too little beating will affect the production efficiency of the paper machine, because the pulp is not easy to form and dry, and it takes longer to complete the production process. In summary, the present invention simultaneously regulates the pulp ratio of each layer, the surface layer beating degree, the reactive type dosage, and the pulp-to-net speed ratio, so that the packaging box made thereby has excellent resistance to lactic acid edge seepage and is not easy to leak; at the same time, it also has good scalability, can avoid the problem of bulging, can meet the transportation needs of packaging boxes of various sizes and specifications, and avoid leaking; it also has excellent impact resistance and excellent dart drop performance (the dart drop performance refers to the damage of the paper box after the paper roll is dropped from a certain height and subjected to a vibration test under certain quality conditions after filling), during the transportation of the packaging box, it is ensured that the product can be guaranteed not to leak under some extreme conditions, and during the cold chain transportation of the packaging box after containing liquid, even if the packaging boxes are stacked together, it can provide sufficient strength support to ensure that the paper box will not be damaged during transportation.

[0019] Preferably, the long fiber wood pulp includes at least one of bleached coniferous wood kraft pulp, unbleached coniferous wood kraft pulp and semi-bleached coniferous wood kraft pulp.

[0020] Preferably, the short fiber wood pulp includes at least one of bleached hardwood kraft pulp, bleached chemical thermomechanical pulp, unbleached hardwood kraft pulp and semi-bleached hardwood kraft pulp.

[0021] Preferably, the pulp of the surface layer comprises, by mass percentage, 60-80% bleached coniferous wood sulfate pulp and 20-40% bleached hardwood sulfate pulp; and / or, by mass percentage, the pulp of the core layer comprises, by mass percentage, 40-60% bleached chemical mechanical pulp, 20-45% bleached coniferous wood sulfate pulp and 10-20% bleached hardwood sulfate pulp; and / or, by mass percentage, the pulp of the bottom layer comprises, by mass percentage, 30-50% bleached hardwood sulfate pulp and 50-70% bleached coniferous wood sulfate pulp.

[0022] Further preferably, the pulp of the surface layer comprises, by mass percentage, 70-80% bleached coniferous wood sulfate pulp and 20-30% bleached hardwood sulfate pulp; and / or, by mass percentage, the pulp of the core layer comprises 50-60% bleached chemical mechanical pulp, 20-30% bleached coniferous wood sulfate pulp and 14-20% bleached hardwood sulfate pulp; and / or, by mass percentage, the pulp of the bottom layer comprises 40-50% bleached hardwood sulfate pulp and 50-60% bleached coniferous wood sulfate pulp.

[0023] Preferably, the contents of the sizing agent in the surface, core and bottom layers are 18-23, 32-37 and 19-25 kg / ton of pulp respectively.

[0024] Preferably, the reactive sizing agent is an alkyl ketene dimer (AKD sizing agent), and / or the sizing agent is a high temperature resistant sizing agent, and the high temperature resistant temperature of the high temperature resistant sizing agent is 55-60° C. The high temperature resistant AKD sizing agent solves the problem that AKD is easily precipitated in a high temperature environment.

[0025] Preferably, the beating degree of the core layer is 16-20° SR.

[0026] Preferably, the beating degree of the bottom layer is 24-32°SR. Further preferably, the beating degree of the bottom layer is 26-32°SR. More preferably, the beating degree of the bottom layer is 28°SR. Optimizing the beating degrees of the surface, core and bottom layer is beneficial to ensuring the flatness of the paper.

[0027] Preferably, the slurry of the surface, core and bottom layer also contains a wet strength agent. When the gram weight of the paper base material for the liquid packaging box is ≤300 g / m2, the flow rate of the wet strength agent added to the slurry of the surface, core and bottom layer is 60-80, 160-180, 30-50 L / h respectively. When the gram weight of the paper base material for the liquid packaging box is greater than 300 g / m2, the flow rate of the wet strength agent added to the slurry of the surface, core and bottom layer is 55-75, 275-295, 13-23 L / h respectively. The wet strength agent of the surface, core and bottom layer improves the wet tensile strength of the paper and improves the retractable performance. However, excessive wet strength agent of the bottom layer will cause wrinkles on the back of the paper.

[0028] Preferably, the wet strength agent is a polymer of adipic acid with N-(-2-aminoethyl), 1,2-ethylenediamine and (chloromethyl)ethylene oxide.

[0029] Preferably, the papermaking is carried out on a paper machine.

[0030] Preferably, the paper machine has a speed of 280-380 m / min.

[0031] Preferably, the pressing pressure is 20-80 KN / m.

[0032] Preferably, the drying temperature is 100-180°C, and / or the secondary drying temperature is 100-180°C.

[0033] The invention ensures that the paperboard reaches the best state during the forming, dehydration and drying processes by strictly regulating the key process parameters of the paper machine speed (280-380m / min), pressing pressure (20-80KN / m) and drying temperature (100-180°C).

[0034] Preferably, when the gram weight of the paper-based material for the liquid packaging box is ≤300 g / m2, the pulp-to-web speed ratios of the surface, core and bottom layers are 0.980-0.982, 0.960-0.962 and 0.925-0.927, respectively, and / or, when the gram weight of the paper-based material for the liquid packaging box is >300 g / m2, the pulp-to-web speed ratios of the surface, core and bottom layers are 0.985-0.987, 0.965-0.967 and 0.930-0.932, respectively.

[0035] Further preferably, when the gram weight of the paper-based material for the liquid packaging box is ≤300 g / m2 (low gram weight), the pulp-to-web speed ratios of the surface, core and bottom layers are 0.980-0.981, 0.960-0.961, 0.925-0.926, respectively, and / or, when the gram weight of the paper-based material for the liquid packaging box is >300 g / m2 (high gram weight), the pulp-to-web speed ratios of the surface, core and bottom layers are 0.985-0.986, 0.965-0.966, 0.930-0.931, respectively.

[0036] More preferably, when the gram weight of the paper-based material for the liquid packaging box is ≤300 g / m2 (low gram weight), the pulp-to-web speed ratios of the surface, core and bottom layers are 0.980, 0.960 and 0.925, respectively, and / or, when the gram weight of the paper-based material for the liquid packaging box is >300 g / m2 (high gram weight), the pulp-to-web speed ratios of the surface, core and bottom layers are 0.985, 0.965 and 0.930, respectively.

[0037] Preferably, the slurry temperature of the headbox is 30-50°C, and / or the slurry pH value of the headbox is 7.0-9.0, and / or the spray device is enabled on the four-press upper roller. The headbox and the four-press are both in the paper machine section, where the headbox is at the end of the pulping section and the beginning of the paper machine section. Its main function is to evenly and stably sprinkle and spray the slurry onto the forming net, which is crucial for paper web forming. The limiting temperature and pH value are to ensure that the sizing performance of AKD is not affected, while minimizing the problem of AKD hydrolysis or wax powder precipitation. AKD is a substance that is easily hydrolyzed. During the production process, it will be affected by the production environment and other factors, and milky white waxy flakes, i.e., hydrolysis products, will appear. Wax powder is a substance that appears after hydrolysis.

[0038] A second aspect of the present invention provides a paper-based material for a liquid packaging box.

[0039] A paper-based material for a liquid packaging box, wherein the paper-based material for a liquid packaging box is prepared by the above-mentioned preparation method, and the basis weight of the paper-based material for a liquid packaging box is 250-350g / m 2 , and / or, the 24h lactic acid permeability of the paper-based material for the liquid packaging box is ≤3.5kg / m 3 .

[0040] Preferably, the longitudinal wet-to-dry tensile strength ratio of the paper-based material for liquid packaging boxes is 8.1-9.5, and / or the transverse wet-to-dry tensile strength ratio of the paper-based material for liquid packaging boxes is 7.9-9.3, and / or the front dart breakage rate of the paper-based material for liquid packaging boxes is ≤20%, and / or the back dart breakage rate of the paper-based material for liquid packaging boxes is ≤17%.

[0041] A third aspect of the present invention provides an application of a paper-based material for a liquid packaging box.

[0042] The invention discloses an application of a paper-based material for a liquid packaging box in preparing a dairy product packaging box, a juice packaging box, a tea packaging box, a carbonated beverage packaging box, a coffee packaging box, a water packaging box or a liquid medicine packaging box.

[0043] Preferably, the shape of the liquid packaging box is one of a roof shape, a cube shape, a rectangular parallelepiped shape, a cylinder shape or an irregular shape.

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] The invention prepares slurries for a surface layer, a core layer and a bottom layer respectively, and then performs papermaking. The papermaking process includes the following steps: after the slurry is filtered, it is compounded, pressed, dried, sizing on the surface, dried again, calendered and rolled into paper in sequence, so as to obtain a paper-based material for a liquid packaging box having a surface layer, a core layer and a bottom layer stacked in sequence, wherein the slurry ratio of each layer, the amount of a reactive sizing agent, the beating degree of the surface layer and the pulp-to-net speed ratio during the papermaking process are optimized, thereby improving the overall rigidity and impact resistance of the paperboard, and at the same time making the paperboard exhibit excellent rigidity and stability in different directions (internal bonding strength 247-282 J / m 2 , Z-axis strength 392-425kPa), thereby improving the scalability and avoiding the problem of bulging (wet-to-dry tensile strength ratio (longitudinal) is 7.9-8.3, wet-to-dry tensile strength ratio (transverse) is 8.7-9.7), and the dart drop test performance is excellent (dart drop breakage rate (front) is 12-19%, dart drop breakage rate (back) is 7-17%), which can meet the transportation needs of packaging boxes of various sizes (even for the preparation of packaging boxes with a volume of ≥1L). During the transportation of the packaging box, it ensures that the product will not leak under some extreme conditions (24h lactic acid side permeability is only 2.0-2.8kg / m 3 ), so during the cold chain transportation of the packaging boxes filled with liquids, even if the packaging boxes are stacked together, they can provide sufficient strength support to ensure that the paper boxes will not be damaged during transportation, and can meet the requirements of its impact resistance. At the same time, the impact resistance and flatness are in a balanced state (flatness reaches 1.0-1.4 level, base paper uniformity index 74-79, uniformity index after ink spreading 56-60), the flatness can meet the needs of printing, the raw materials are green and environmentally friendly, and meet the requirements of food preservation and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a schematic diagram of the structure of the paper-based material of Example 1 of the present invention and a diagram of its main raw materials;

[0047] Figure 2 This is a diagram showing the precipitation of AKD in the pressing section of a paper machine in Comparative Example 2;

[0048] Figure 3 This is the WIS test (paper disease test) result of comparative example 2 (bright spots appear). DETAILED DESCRIPTION

[0049] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0050] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0051] The raw materials involved in the present invention are:

[0052] NBKP: Bleached softwood kraft pulp (long fiber pulp), manufacturer Celulosa Arauco Y Constitucion S.A. Chile, brand Silver Star.

[0053] LBKP: bleached hardwood kraft pulp (short fiber pulp), manufacturer SUZANO INTERNATIONAL TRADE GMBH., brand Parrot.

[0054] BCTMP: bleached chemical thermomechanical pulp (BCM), a mixture of wood pulp A (manufacturer Rayonier A.M. Canada GP, brand Tempura maple) and wood pulp B (manufacturer Millar Western Forest Products Ltd. Canada, brand Crystal needle) in a mass ratio of 1:1.

[0055] Example 1

[0056] A method for preparing a paper-based material for a liquid packaging box comprises the following steps:

[0057] 1. Pulping section

[0058] The surface layer, core layer and bottom layer pulp boards are crushed by hydraulic pulper, screened, pulped, mixed and finally fed to paper machine for papermaking. In the pulping process, cationic starch, wet strength agent, AKD sizing agent, retention agent and spray starch are added in sequence. Cationic starch and wet strength agent are added before sizing pump, AKD is added before flushing pump, retention agent is added before and after pressure screen, and spray starch is added in the net part. The addition amount is as follows:

[0059] (1) The addition amount of AKD sizing agent (alkyl ketene dimer) for the surface, core and bottom layers (diluted to a mass concentration of 5% before use) is: 7.5 kg / ton pulp for the surface layer, 24 kg / ton pulp for the core layer, 7.5 kg / ton pulp for the bottom layer, and 23 kg / ton paper;

[0060] (2) Liquid caustic soda (NaOH): The diluted liquid caustic soda (sodium hydroxide solution, mass concentration 4%) is added to the white water tank outside the machine to control the pH value of the headbox to 8.0; the total alkalinity of the flow is controlled to be ≥150ppm;

[0061] (3) Retention aid: mass concentration 0.5%, addition coefficient: the addition coefficients of retention aid 1 (polyacrylamide anionic retention aid, Solenis SP4715) for the surface, core, and bottom layers are 1.5, 1.5, and 1.5, respectively; the addition coefficients of retention aid 2 (polymer retention aid, Solenis PC9912) for the surface, core, and bottom layers are 1.5, 1.5, and 1.5, respectively;

[0062] (4) Wet strength agent (polymer of adipic acid with N-(-2-aminoethyl), 1,2-ethylenediamine and (chloromethyl)ethylene oxide): the addition flow rates for the top, core and bottom layers were 65, 285 and 18 L / h respectively;

[0063] (5) Cationic starch: mass concentration: 4.0%, the addition coefficients of the surface, core and bottom are 1.0, 0.8 and 1.2 respectively;

[0064] (6) Spraying starch (native cassava starch): mass concentration: 3.0%, the spraying starch is sprayed between the surface layer and the core layer, and between the core layer and the bottom layer;

[0065] The slurry proportions of each layer are as follows:

[0066] Surface slurry ratio (mass percentage): 70% NBKP + 30% LBKP;

[0067] Core layer slurry ratio (mass percentage): 59% BCTMP + 27% NBKP + 14% LBKP;

[0068] Bottom slurry ratio (mass percentage): 40% LBKP + 60% NBKP;

[0069] The beating degree of the surface layer is 16°SR, the beating degree of the core layer is 16°SR, and the beating degree of the bottom layer is 29°SR.

[0070] 2. Paper machine section

[0071] (1) Wire mesh: The slurry temperature of the headbox is 45°C, the pH value is 8.0, and the wire mesh concentrations of the top, core, and bottom layers are 0.35%, 0.8%, and 0.35%, respectively. After the three layers of slurry are filtered (the dehydration rate of the top wire is controlled at 2500 L / min), they are compounded, and the slurry-to-wire speed ratios of the top, core, and bottom layers are controlled to be 0.980, 0.960, and 0.925, respectively;

[0072] (2) Pressing: The four upper rollers use a spray device;

[0073] (3) Drying: temperature 168°C;

[0074] (4) Surface sizing: The upper roller is coated with starch, and the lower roller is a barrier agent (using a special metering rod). The amount of surface sizing is 3g / m 2 ;

[0075] (5) Drying: temperature 124°C;

[0076] (6) Calendering: Soft calendering pressure 75 kN / m, belt calendering pressure 20 kN / m;

[0077] (7) Winding, rewinding (rewinding tension 1600N / M), packaging and storage, gram weight 260g / m 2 , thickness 370μm, moisture content 7.0wt%.

[0078] The structure of the paper-based material for liquid packaging box prepared in Example 1 is as follows: Figure 1 As shown, it includes a stacked surface layer (mainly made of chemical long fibers and chemical short fibers), a core layer (mainly made of chemical long fibers, chemical short fibers and bleached chemical mechanical pulp), and a bottom layer (mainly made of chemical long fibers and chemical short fibers).

[0079] Embodiment 2 (increasing AKD dosage)

[0080] A method for preparing a paper-based material, which differs from Example 1 in that, in step (1), the amounts of AKD sizing agent (diluted to a mass concentration of 5% before use) added to the surface, core and bottom layers are: 18 kg / ton pulp for the surface layer, 32 kg / ton pulp for the core layer, 19 kg / ton pulp for the bottom layer, and 27 kg / ton paper.

[0081] Example 3 (reducing the amount of wet strength agent)

[0082] A method for preparing a paper-based material, which differs from Example 1 in that, in step (4), the amount of wet strength agent is adjusted: the addition flow rates of the surface, core, and bottom layers are 55, 275, and 13 L / h, respectively.

[0083] Example 4 (Increasing the pulp-to-wire speed ratio of each layer)

[0084] A method for preparing a paper-based material, which differs from Example 1 in that the pulp-to-web speed ratios of the surface, core, and bottom layers are adjusted to 0.982, 0.963, and 0.928, respectively.

[0085] Example 5 (Adjusting the ratio of long fibers in the surface layer)

[0086] A method for preparing a paper-based material, which is different from Example 1 in that the surface layer pulp is adjusted to: 20% LBKP (bleached hardwood kraft pulp) + 80% NBKP (bleached softwood kraft pulp).

[0087] Example 6 (reducing the amount of wet strength agent)

[0088] A method for preparing a paper-based material, which differs from Example 1 in that the addition flow rates of the wet strength agent for the surface, core, and bottom layers are reduced to 55, 275, and 13 L / h, respectively.

[0089] Comparative Example 1 (reducing the beating degree of the surface layer)

[0090] A method for preparing a paper-based material, which is different from Example 1 in that the beating degree of the surface layer is reduced to 12°SR.

[0091] Comparative Example 2 (Increasing AKD dosage)

[0092] A method for preparing a paper-based material, which differs from Example 1 in that the contents of AKD sizing agent in the surface, core and bottom layers are adjusted to 30, 45 and 35 kg / ton pulp, respectively.

[0093] Comparative Example 3 (Reducing the three-layer pulp wire speed ratio)

[0094] A method for preparing a paper-based material, which differs from Example 1 in that the pulp-to-web speed ratios of the surface, core, and bottom layers are adjusted to 0.975, 0.960, and 0.915, respectively.

[0095] Comparative Example 4 (reducing the amount of long fibers in the surface layer)

[0096] A method for preparing a paper-based material, which differs from Example 1 in that the surface layer slurry ratio is adjusted to (mass percentage): 50% NBKP+50% LBKP.

[0097] Product effect testing

[0098] 1. Test methods

[0099] Wet-to-dry tensile strength ratio: The higher the ratio, the better the strength of the paper is maintained in a wet state, which usually means that the fibers of the paper are more tightly bound and are not easily expanded or contracted due to changes in moisture content. On the contrary, if the wet-to-dry tensile strength is relatively low, it means that the paper is prone to lose strength in a wet state, and may be accompanied by greater expansion and contraction changes.

[0100] Dart impact test: The test was conducted using a dart impact tester (GBD-L2). The device simulates the reaction of packaging materials when subjected to a certain mass of falling impact, and records the proportion of packaging damage (i.e., breakage rate), which is used as a quantitative indicator for evaluating the impact resistance of the material. First, set the impact height to 66cm, use a plastic dart head with a diameter of 38mm, and a total combined weight of 90g. Use the single-piece method for testing, place the sample in the middle of the sample clamp, release the dart head, and record whether the sample is "broken" or "not broken". Repeat the above steps 10 times, and calculate the dart breakage rate according to the number of broken pieces, i.e., dart breakage rate = number of broken pieces / total number × 100%.

[0101] Flatness: Evaluation is performed with the naked eye. The specific evaluation steps are as follows: (1) Lay the paper to be tested flat on the inspection table or desktop to ensure that the paper is in a relaxed state without tension or external force; (2) Choose an environment with soft and uniform light for evaluation, avoiding strong light or direct sunlight to reduce the interference of light on the evaluation results; (3) Reflected light horizontal inspection: Observe the flatness and smoothness of the paper with the naked eye at a distance of about 30 cm from the paper surface; (4) Light perspective inspection: Look at the paper facing the light source, let the light pass through the paper, and observe the uniformity and opacity of the paper fiber structure; check whether the paper has "cloud flowers", transparent spots, dirty spots, holes, and uneven light transmission streaks; (5) Oblique inspection: Some minor defects on the surface of the paper, such as glossy or matte streaks, wool marks, roller shadow marks, etc., are not easy to detect by flat viewing. At this time, oblique inspection can be used. It takes a certain amount of experience and skills to evaluate the flatness of paper with the naked eye. Therefore, the on-site inspection is carried out by three experienced and professionally trained inspectors. The surface flatness of the paper to be tested is judged by the above method, using a 1.0-2.0 rating scale, with 1.0 representing the best flatness, 2.0 representing the worst flatness, and 0.2 as one level, for a total of 6 levels. The average of the rating results of all inspectors is taken as the final flatness grade.

[0102] Evenness index of base paper and after ink spreading: tested with a uniformity meter. The higher the value, the better the flatness of the paper. The evenness index will decrease as the gram weight increases.

[0103] Gram weight: "Determination of grammage of paper and paperboard (GB / T 451.2-2002)".

[0104] Thickness: "Determination of thickness of paper and paperboard (GB / T 451.3-2002)".

[0105] Moisture content: GB / T 462-2023 Determination of moisture content of paper, paperboard and pulp analysis samples.

[0106] Internal bonding strength: GBT 26203-2023 Determination of internal bonding strength of paper and paperboard (Scott type).

[0107] Z-direction strength: "ISO 15754 Paper and paperboard - Determination of tensile strength in the z-direction".

[0108] Lactic acid edge penetration: "GB / T 31905-2015 Determination of edge penetration of paper and paperboard".

[0109] Wet-dry tensile strength ratio: "GB / T 12914 Determination of tensile strength of paper and paperboard".

[0110] 2. Test results

[0111] Table 1 Performance test results of paper-based materials in various embodiments

[0112]

[0113]

[0114] As can be seen from the above table, the internal bonding strength of the paper-based material provided by the present invention can reach 232-282 J / m 2 , Z-axis strength 374-425kPa, 1h lactic acid edge permeability does not exceed 0.49-0.64kg / m 3 24h lactic acid osmotic pressure should not exceed 2.0-2.8kg / m 3 , wet-to-dry tensile strength ratio (longitudinal direction) is 7.6-8.3, wet-to-dry tensile strength ratio (transverse direction) is 8.2-9.7, dart breakage rate (front side) is 12-32%, dart breakage rate (reverse side) is 7-23%, flatness reaches 1.0-1.6 level, base paper uniformity index is 73-79, and uniformity index after ink spreading is 55-60. It shows that the paper-based material provided by the present invention has excellent resistance to lactic acid edge seepage, scalability and impact resistance, and can still maintain a high strength even in a wet state, meeting the packaging, transportation and storage requirements of liquids, so that it can be used to prepare liquid packaging boxes (such as roof-type packaging boxes), and has good flatness and can be printed normally.

[0115] Compared with Example 1, since Example 6 reduces the amount of the wet strength agent used in each layer, the strength, wet-dry tensile strength, and flatness of the paper base material are reduced, and the dart breakage rate is increased. This is because Example 1 increases the content of the wet strength agent in the surface, core, and bottom layers, which helps to improve the wet tensile strength and retractable properties of the paper.

[0116] Compared with Example 1, Example 2 increases the amount of AKD in each layer, and has excellent resistance to lactic acid edge seepage, but the flatness is slightly reduced. Compared with Example 1, the amount of wet strength agent in Example 3 is reduced, and the wet-to-dry tensile strength ratio is reduced, but it is within the qualified range. Compared with Example 1, the wet-to-dry tensile strength ratio of Example 4 is reduced, but it is within the qualified range. Compared with Example 5 (20% LBKP + 80% NBKP), the dart test breakage rate (front and back) of Example 1 is controlled in the range of 7-12%, and the flatness is good, indicating that the surface layer slurry ratio of Example 1 (the surface layer long and short fiber ratio is: 70% NBKP + 30% LBKP) is more conducive to simultaneously obtaining excellent impact resistance and flatness.

[0117] Comparison between Example 1 and Comparative Example 1 shows that, after adjusting the beating degree of the surface layer, the dart test breakage rate (front and back) of the paperboard of the present invention is greatly reduced from 45-52% to 7-12%, which indicates that the strength of the paperboard is significantly improved, and the protective ability of the packaging box is effectively enhanced.

[0118] Compared with Example 1, Comparative Example 2 increases the amount of AKD. Although the ability of the paper-based material to resist lactic acid edge seepage is slightly improved, the dart breakage rate increases, the flatness decreases, and AKD precipitates during the paper machine pressing process ( Figure 2 ), the prepared paper-based material has bright spots ( Figure 3 ), this is because: 1. Although excessive AKD dosage can improve the water resistance of paper, excessive dosage will lead to instability of the internal structure of paper, reduced flatness and precipitation of AKD. 2. The uneven distribution of AKD on the fiber surface is one of the main reasons for the decline in paper performance and the formation of bright spots.

[0119] Compared with Example 1, Comparative Example 3 reduces the pulp-to-web speed ratio of the three layers, resulting in a decrease in the internal bonding strength and Z-direction strength of the paper base material, an increase in the dart breakage rate, and a decrease in flatness. This is because: 1. The reduction in the pulp-to-web speed ratio weakens the degree of interweaving of fibers in the paper sheet, which reduces the bonding force between fibers, thereby affecting the internal bonding strength and Z-direction strength. 2. The reduction in the pulp-to-web speed ratio may increase the unevenness of the internal structure of the paper, making the paper more easily damaged when subjected to external forces, and increasing the dart breakage rate of the paper. 3. The adjustment of the pulp-to-web speed ratio will affect the dehydration uniformity of the paper during the pressing and drying process, thereby affecting the flatness of the paper.

[0120] Compared with Example 1, Comparative Example 4 reduces the amount of long fibers in the surface layer, resulting in a significant decrease in the internal bonding strength and Z-direction strength of the paper-based material, and a significant increase in the dart breakage rate. This is because: 1. The reduction in the amount of long fibers in the surface layer leads to a weakening of the stability of the fiber network structure and a decrease in the degree of fiber interweaving in the Z direction, which reduces the internal bonding strength and Z-direction strength. 2. When the amount of long fibers is reduced, the stability of the fiber network structure is weakened, the bonding force between fibers is weakened, and the toughness of the paper is reduced, resulting in a decrease in the overall strength of the paper. The paper is more likely to be damaged when subjected to external forces, resulting in a significant increase in the dart breakage rate of the paper.

Claims

1. A method for preparing a paper-based material for a liquid packaging box, characterized in that: The paper-based material for liquid packaging box comprises a surface layer, a core layer and a bottom layer which are stacked in sequence; and the preparation method comprises the following steps: The slurries of the surface layer, the core layer and the bottom layer are prepared respectively, and then paper-made to obtain the paper-based material for the liquid packaging box; wherein the paper-making step comprises: after the slurry is drained, compounding, pressing, drying, surface sizing, drying again, calendering and rolling into paper in sequence to obtain the paper-based material for the liquid packaging box; The pulp of the surface layer includes 60-80% long fiber wood pulp and 20-40% short fiber wood pulp in terms of mass percentage; The pulp of the core layer comprises, by mass percentage, 40-60% bleached chemical mechanical pulp, 20-45% long fiber wood pulp and 10-20% short fiber wood pulp; The bottom layer pulp comprises 30-50% short fiber wood pulp and 50-70% long fiber wood pulp in terms of mass percentage; The beating degree of the surface layer is 14-18°SR; The slurries of the surface, core and bottom layers all contain sizing agent, and the sizing agent is a reactive sizing agent. The contents of the sizing agent in the surface, core and bottom layers are 15-25, 25-40 and 10-30 kg / ton of slurry respectively. During the compounding process, when the gram weight of the paper-based material for the liquid packaging box is ≤300 g / m2, the pulp-to-web speed ratios of the surface, core, and bottom layers are 0.978-0.982, 0.958-0.962, and 0.923-0.927, respectively, and / or, when the gram weight of the paper-based material for the liquid packaging box is >300 g / m2, the pulp-to-web speed ratios of the surface, core, and bottom layers are 0.983-0.987, 0.963-0.967, and 0.928-0.932, respectively.

2. The preparation method according to claim 1, characterized in that: The long fiber wood pulp includes at least one of bleached coniferous wood kraft pulp, unbleached coniferous wood kraft pulp and semi-bleached coniferous wood kraft pulp.

3. The preparation method according to claim 1, characterized in that: The short fiber wood pulp includes at least one of bleached hardwood kraft pulp, bleached chemical thermomechanical pulp, unbleached hardwood kraft pulp and semi-bleached hardwood kraft pulp.

4. The preparation method according to claim 2 or 3, characterized in that: The pulp of the surface layer comprises, by mass percentage, 60-80% bleached coniferous wood sulfate pulp and 20-40% bleached broadleaf wood sulfate pulp; and / or, by mass percentage, the pulp of the core layer comprises, by mass percentage, 40-60% bleached chemical mechanical pulp, 20-45% bleached coniferous wood sulfate pulp and 10-20% bleached broadleaf wood sulfate pulp; and / or, by mass percentage, the pulp of the bottom layer comprises, by mass percentage, 30-50% bleached broadleaf wood sulfate pulp and 50-70% bleached coniferous wood sulfate pulp.

5. The preparation method according to claim 1, characterized in that: The contents of the sizing agent in the surface, core and bottom layers are 18-23, 32-37 and 19-25 kg / ton of pulp respectively.

6. The preparation method according to claim 1, characterized in that: The slurries of the surface, core and bottom layers also contain a wet strength agent. When the gram weight of the paper-based material for the liquid packaging box is ≤300 g / m2, the flow rate of adding the wet strength agent to the slurries of the surface, core and bottom layers is 60-80, 160-180 and 30-50 L / h respectively; when the gram weight of the paper-based material for the liquid packaging box is >300 g / m2, the flow rate of adding the wet strength agent to the slurries of the surface, core and bottom layers is 55-75, 275-295 and 13-23 L / h respectively.

7. The preparation method according to claim 1, characterized in that: When the gram weight of the paper-based material for the liquid packaging box is ≤300 g / m2, the pulp-to-web speed ratios of the surface, core and bottom layers are 0.980-0.982, 0.960-0.962 and 0.925-0.927, respectively, and / or, when the gram weight of the paper-based material for the liquid packaging box is >300 g / m2, the pulp-to-web speed ratios of the surface, core and bottom layers are 0.985-0.987, 0.965-0.967 and 0.930-0.932, respectively.

8. The preparation method according to claim 1, characterized in that: The reactive sizing agent is an alkyl ketene dimer sizing agent, and / or the sizing agent is a high temperature resistant sizing agent, and the high temperature resistant temperature of the high temperature resistant sizing agent is 55-60°C.

9. A paper-based material for liquid packaging, characterized in that: The paper-based material for liquid packaging boxes is prepared by the preparation method according to any one of claims 1 to 8, and the gram weight of the paper-based material for liquid packaging boxes is 250-350 g / m 2 , and / or, the 24h lactic acid edge permeability of the paper-based material for the liquid packaging box is ≤3.5kg / m 3 .

10. The paper-based material for liquid packaging box according to claim 9, characterized in that: The longitudinal wet-to-dry tensile strength ratio of the paper-based material for liquid packaging boxes is 8.1-9.5, and / or the transverse wet-to-dry tensile strength ratio of the paper-based material for liquid packaging boxes is 7.9-9.3, and / or the front dart breakage rate of the paper-based material for liquid packaging boxes is ≤20%, and / or the back dart breakage rate of the paper-based material for liquid packaging boxes is ≤17%.

11. Use of the paper-based material for liquid packaging boxes according to claim 9 or 10 in preparing dairy product packaging boxes, juice packaging boxes, tea packaging boxes, carbonated beverage packaging boxes, coffee packaging boxes, water packaging boxes or liquid medicine packaging boxes.

12. The use according to claim 11, characterized in that: The shape of the liquid packaging box is one of a roof shape, a cube shape, a rectangular parallelepiped shape, a cylinder shape or an irregular shape.

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