Production process of high folding resistance corrugated paper

Abstract

This invention discloses a production process for high-fold-resistance corrugated base paper, specifically relating to the field of corrugated paper production technology. The process includes mixing different types of waste paper raw materials through hydraulching to obtain raw waste paper pulp with a concentration of 2.5-2.8%; passing the raw waste paper pulp through high-consistency desanding, coarse screening, and low-consistency desanding before entering a grading screen to separate the fibers in the waste paper pulp into long fibers and short fibers; mixing the long fiber pulp and short fiber pulp in a certain proportion for papermaking and surface sizing; wherein, papermaking includes wire forming, pressing and dewatering, and pre-drying to obtain initial corrugated base paper with a dryness of 90-92%; then, surface sizing is performed on the initial corrugated base paper with boiled sizing solution, followed by drying at 60-100℃ to a dryness of 85-92%, and finally curling and slitting to obtain high-fold-resistance corrugated base paper. This invention achieves stable production of high-fold-resistance corrugated base paper through diversified raw materials, refined fiber processing, flexible control of the papermaking process, and precise preparation of the sizing solution.

Description

Technical Field

[0001] This invention relates to the field of corrugated paper production technology, specifically to a production process for high-fold-resistance corrugated base paper. Background Technology

[0002] Waste paper, also known as secondary fiber, is a raw material for papermaking. It refers to used paper that has been processed and reused as a raw material for papermaking. Large-scale recycling of waste paper by the papermaking industry reduces waste generation and potential environmental harm, while also generating economic benefits through resource recovery. This approach aims to protect the ecological environment and conserve resources from the source.

[0003] Corrugated boxes are made of corrugated cardboard. Due to their multi-layered structure and high strength, they are widely used in packaging and transportation, especially for heavy goods. During the loading process, the corrugated cardboard needs to be folded multiple times to form a specific shape. However, because the existing corrugated cardboard has low strength, it is easy for it to break or be damaged during the folding process, thus making it unusable.

[0004] Chinese patent CN111021130A uses waste paper and further processes it through pulping, papermaking, and slag removal to obtain corrugated paper. However, the corrugated paper obtained by this patent has poor folding endurance and cannot be considered a high-folding-endurance corrugated base paper, thus lacking competitiveness. Therefore, how to improve the folding endurance of corrugated paper is a problem that urgently needs to be solved.

[0005] While some existing patents and technologies have improved the folding resistance of corrugated paper to some extent, these mainly involve adding large amounts of cellulose or cellulose-like components to the pulp. For example, Chinese patent CN114808522A adds a large amount of cellulose nanocrystals, which are then covalently bonded to the active groups on dopamine to form a porous cellulose nanocrystal network, thereby increasing the folding resistance of corrugated paper. Chinese patent CN115262283A uses plant fiber pulp as raw material and adds resin, modified nano-silica, etc., and adds different raw materials and additives to different layers to achieve the requirement of increasing the folding resistance of corrugated paper. However, these patents require the addition of a large number of other additives, the process is complex, the production cost is high, and these patents cannot be directly prepared using waste paper, resulting in a low waste paper recycling rate. Summary of the Invention

[0006] Therefore, the present invention provides a production process for high-bending-resistance corrugated base paper to solve the problems in the prior art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] According to the present invention, a production process for high-fold-resistance corrugated base paper is provided, the process comprising:

[0009] Step 1: Different types of waste paper raw materials are mixed and hydrated to obtain raw waste paper pulp with a concentration of 2.5-2.8%.

[0010] Step two: After passing through high-consistency desanding, coarse screening, and low-consistency desanding, the raw waste paper pulp enters a grading screen to separate the fibers in the waste paper pulp into long fibers and short fibers. The long fiber segment includes fine screening and long fiber concentration. The fine screening uses a double fiber fine screening, and 0.2-0.3% of cellulase is added during the fine screening process. After concentration, the concentration of long fibers is 8-10%. After concentration, a wet strength agent is added to obtain long fiber pulp. The short fiber segment includes short fiber concentration, and the concentration after concentration is 6-8%. After concentration, 0.3-0.5% of fiber strengthening agent is added to obtain short fiber pulp.

[0011] Step 3: Mix long fiber pulp and short fiber pulp in a certain proportion, and perform papermaking and surface sizing treatment. The papermaking process includes wire forming, pressing and dewatering, and drying in the pre-drying section to obtain an initial corrugated base paper with a dryness of 90-92%. Then, apply the boiled sizing solution to the surface of the initial corrugated base paper, dry it at 60-100℃ to a dryness of 85-92%, and then roll and slit it to obtain a high-folding-resistance corrugated base paper.

[0012] Furthermore, in step one, the waste paper raw materials include the following weight percentages: 35-40% premium waste paper, 24-28% corrugated cardboard from cardboard factories, 4-8% mixed market waste paper, 8-12% dry pulp bales, and 18-22% industrial cardboard waste paper.

[0013] This invention controls the concentration of raw waste paper pulp to reduce inter-fiber collision and shearing.

[0014] Furthermore, 0.5-1% of a fiber protectant is added to the hydration pulp, preferably polyvinyl alcohol (PVA), to coat the fiber surface during pulping and reduce frictional damage; 0.1-0.3% NaOH is added to adjust the pH to 8.5-9.0, softening the fiber surface and reducing excessive hydrogen bonding between fibers (to avoid difficulty in separating fibers during subsequent pulping).

[0015] Furthermore, the parameters for hydraulic pulping are to control the pulping time at 15-20 minutes and the rotation speed at 3000-3500 rpm; the beating degree is 30-45°SR, to avoid excessive dissociation that would cause the fibers to break down. Excessive beating will reduce the flexibility and elasticity of the fibers and affect their folding endurance.

[0016] Furthermore, in step two, the compound fiber sieving includes a pressure screen and a centrifugal screen. As an example, preferably, the pressure screen has a sieve opening of 0.18-0.22 mm, and the centrifugal screen rotates at 1500-1800 rpm to remove fiber bundles and impurities while retaining intact long fibers. Preferably, the cellulase is an endoglucanase, which mildly hydrolyzes the fiber surface, promotes hydrogen bonding, and enhances the interfiber bonding force.

[0017] Furthermore, in step two, the wet strength agent is PAE resin, and the addition amount is 0.5-1%, which forms a cross-linked network on the fiber surface to enhance the folding resistance.

[0018] As an example, a drum vacuum concentrator is preferred for long fiber concentration to control the shear force (linear speed of 12-15 m / min) during the concentration process and avoid excessive compression damage to the fibers.

[0019] Furthermore, a plate and frame thickener is preferred for short fiber thickening, and starch derivatives are preferred for fiber reinforcing agents to fill the gaps between short fibers and improve the density of the paper structure.

[0020] Furthermore, in step three, the ratio of long fibers to short fibers is 6:4-8:2; the proportion of long fibers is controlled at 60%-80%, providing skeletal support; the proportion of short fibers is 20%-40%, used to fill gaps and improve uniformity and surface smoothness. Generally, long fibers are defined as those greater than 1.8 mm, and those less than or equal to 1.8 mm are defined as short fibers. In this invention, long fibers greater than 2.2 mm refer to a proportion of over 90% of the fibers being greater than 2.2 mm.

[0021] Web forming: Optimize fiber orientation and distribution. Low vacuum dewatering: Vacuum level from the breast roll to the vacuum couch roll section is -25 to -30 kPa, extending the fiber residence time on the web (0.8-1.0 seconds) and promoting transverse fiber dispersion (reducing stress concentration during folding caused by longitudinal orientation). Polyester web selection: Use a long web of 80-100 mesh / inch (fineer than the traditional 60 mesh), reducing fiber loss while improving the smoothness of the wet paper sheet (reducing fiber deformation during subsequent pressing).

[0022] Pressing and dehydration: Balancing dryness and fiber binding force. Pressing pressure gradient control: Employing a three-roll press (diameter increasing sequentially), the linear pressure is gradually increased from 90 kN / m on the first roll to 300 kN / m on the third roll, avoiding fiber breakage caused by a single high pressure (dryness increases from 30% to 45-50%). Temperature-assisted dehydration: 60-70℃ steam is introduced onto the surface of the press rolls to soften the fiber surface (reducing the binding resistance of free water between fibers) and simultaneously improving dehydration efficiency (reducing the amount of chemical auxiliaries used).

[0023] Pre-drying: Controlling moisture and internal stress. Segmented drying curve: The pre-drying section adopts a "low-temperature slow drying" mode (first drying cylinder 80-90℃, second cylinder 90-100℃), increasing the dryness from 45-50% to 90-92% (rather than directly >90%), avoiding the accumulation of internal stress (increased paper brittleness) caused by rapid drying. Tension control: Applying a longitudinal tension of 0.1-0.2 N / m during the drying process (through speed adjustment between transmission groups) to suppress paper shrinkage (reducing elastic recovery stress during folding).

[0024] Furthermore, the adhesive solution contains 10-14% starch adhesive solution with a viscosity of 20-30 mPa·s, 100-150g of amylase per ton of paper, and 3-4kg of styrene-acrylic sizing agent per ton of paper.

[0025] Furthermore, the adhesive solution is prepared by precisely controlling starch gelatinization and enzymatic hydrolysis through segmented heating, followed by vacuum degassing and static curing for stabilization.

[0026] As an example, the preferred option is:

[0027] 1. Low-temperature pre-dissolution (40-50℃, 15-20 minutes): Slowly add starch to deionized water (solid-liquid ratio 1:8), start low-speed stirring (100rpm), and heat to 40-50℃ to obtain starch mixture; dilute styrene-acrylic sizing agent (3-4kg / ton) with deionized water in advance (solid-liquid ratio 1:5) to form a uniform styrene-acrylic sizing agent emulsion;

[0028] 2. Enzymatic hydrolysis and temperature-controlled gelatinization (55-65℃, 30-40 minutes): Add amylase and sizing agent emulsion to the starch mixture, increase the stirring speed to 200 rpm, and slowly heat to 55-65℃ for enzymatic hydrolysis and mixing;

[0029] 3. High-temperature curing (65-75℃, 15-20 minutes): Continue heating to 85-90℃ (the temperature at which starch is completely gelatinized), maintain for 15-20 minutes, and keep warm to ensure complete gelatinization of the starch. After cooking, transfer the glue solution to a vacuum degassing tank and maintain at -0.08 to -0.09 MPa for 10 minutes to degas under vacuum, avoiding residual air bubbles during sizing that could cause defects on the paper surface. After degassing, let the glue solution stand in a sealed container for 2 hours, stirring continuously (at low speed, 50 rpm) to obtain a glue solution with a viscosity of 20-30 mPa·s.

[0030] The drying method after sizing is low-temperature segmented drying: After sizing, the paper enters the drying section. The temperature of the first drying cylinder is 60-70℃ (low-temperature slow drying), the second cylinder is 80-90℃ (medium-temperature curing), and the third cylinder is ≤100℃ (high-temperature setting). The final dryness is controlled at 85-92% (retaining some moisture).

[0031] The present invention has the following advantages:

[0032] This invention uses a mixture of different types of waste paper, covering the main types of packaging waste paper. Compared to traditional processes that rely on only a single type of waste paper (such as OCC) or require the addition of external waste paper, this invention makes full use of domestically recycled waste paper resources through a multi-material waste paper blend. The addition of dry pulp bags, rich in long fibers (such as unbleached chemical pulp fibers), compensates for the fiber breakage issues caused by repeated recycling of other waste papers (such as industrial cardboard box waste paper and paper scraps), improving the overall fiber length and strength of the raw materials and providing a high-quality foundation for the subsequent preparation of long-fiber pulp.

[0033] This invention adds 0.5-1% polyvinyl alcohol (PVA) as a fiber protectant during hydration pulping to coat the fiber surface and reduce frictional damage; simultaneously, it adds 0.1-0.3% NaOH to adjust the pH to 8.5-9.0, softening the fiber surface and reducing excessive hydrogen bonding. These measures effectively reduce fiber breakage during pulping, preserving more of the original fiber length and softness, thus laying a raw material foundation for high folding resistance.

[0034] This invention provides differentiated treatment for long and short fibers. The long fibers are subjected to pressure sieving and centrifugal sieving to achieve high purity. Different stabilizers are added to the long / short fiber pulp after pulping. Through a special long / short fiber ratio adjustment, the tensile strength and folding support of the paper are significantly improved.

[0035] The adhesive of this invention does not require the addition of complex additives such as cellulose nanocrystals and modified nano-silica, and the process is simple and has a high waste paper utilization rate.

[0036] This invention provides precise control over the preparation of the adhesive solution, resulting in a suitable viscosity that is more suitable for high-fold-resistance corrugated base paper.

[0037] This invention achieves stable production of high-fold-resistance corrugated base paper by diversifying raw materials (dry pulping to supplement long fibers), refining fiber treatment (enzymatic hydrolysis + wet strength agent / reinforcing agent), flexibly controlling the papermaking process (low shear + low temperature drying), and precisely preparing the glue solution (segmented cooking + vacuum degassing). Detailed Implementation

[0038] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Premium waste paper is divided into premium waste cardboard boxes (X0) and premium mixed waste paper (HHO). Premium waste cardboard boxes (X0) refer to composite packaging boxes made entirely of virgin wood pulp, with each layer having a basically uniform color and no obvious color difference, and containing no recycled pulp or other pulp components. Premium mixed waste paper (HHO) mainly consists of unbound, unlaminated, and unprinted white paper cuts from printing plants, unprinted office waste paper, and pure white offset paper, etc.

[0040] Corrugated cardboard factory cardboard: Corrugated cardboard generally refers to corrugated paperboard, while factory cardboard usually refers to scraps or waste generated during the production process of cardboard boxes. Corrugated cardboard factory cardboard is mainly composed of corrugated paperboard scraps, waste cardboard boxes, etc., and is usually yellowish in color, containing a certain proportion of recycled fibers.

[0041] Mixed waste paper from shopping malls: This mainly refers to waste paper generated by shopping malls, supermarkets, and other similar venues. Its composition is relatively complex and may include various packaging papers, brochures, labels, etc. It usually contains a certain amount of colored paper and laminated paper.

[0042] Dry pulp bales: These are waste paper pulp bales produced during the papermaking process, formed after drying. They are mainly composed of pulp fibers and are usually relatively pure, but may contain small amounts of additives or residues. Shenzhen Dacheng New Energy Technology Co., Ltd. imports dry pulp bales from Vietnam.

[0043] Industrial waste paper: mainly comes from packaging cartons in industrial production processes. It is usually made of kraft paper, has high strength and good fiber quality, and is generally brown or light yellow in color.

[0044] Polyvinyl alcohol (PVA): CAS 9002-89-5;

[0045] Endoglucanase: CAS 9012-54-8;

[0046] PAE resin: CB92126242;

[0047] Amylase: CAS 9001-11-0;

[0048] Styrene-acrylic sizing agent: Top-760, manufactured by Top-760 New Materials Co., Ltd.

[0049] Starch: CAS 9005-25-8;

[0050] Fiber reinforcing agent: B.BRAUN, hydroxyethyl starch, product number L6511.

[0051] Example 1

[0052] This embodiment provides a production process for high-bending-resistance corrugated base paper:

[0053] Waste paper raw materials: 38% premium waste paper, 26% corrugated cardboard from cardboard factories, 6% mixed market waste paper, 10% dry pulp bales, and 20% industrial cardboard box waste paper;

[0054] Process:

[0055] Step 1: After mixing and hydrating different types of waste paper raw materials, add 0.5% polyvinyl alcohol (PVA) and use NaOH solution to adjust the pH to 8.5 to obtain the original waste paper pulp with a concentration of 2.5%.

[0056] The parameters for hydraulic pulping are: pulping time of 15-20 minutes and rotation speed of 3000-3500 rpm; and a freeness of 30-45°SR.

[0057] Step 2: After passing through high-consistency desanding, coarse screening, and low-consistency desanding, the raw waste paper pulp enters a grading screen to separate the fibers in the waste paper pulp into long fibers and short fibers. The long fiber segment includes fine screening and long fiber concentration. The fine screening uses a double fiber fine screening (pressure screen + centrifugal screen). The pressure screen has a screen gap of 0.22mm, and the centrifugal screen rotates at 1800rpm to remove fiber bundles and impurities while retaining intact long fibers. During the fine screening process, 0.2% cellulase is added, and the concentration of long fibers after concentration is 8%. After concentration, 1% wet strength agent PAE resin is added to obtain long fiber pulp. The short fiber segment includes short fiber concentration, and the concentration after concentration is 6%. After concentration, 0.3% fiber reinforcing agent is added to obtain short fiber pulp. The long fibers are larger than 2.2mm, and the short fibers are smaller than 1.8mm.

[0058] For long fiber concentration, a drum vacuum concentrator is preferred; for short fiber concentration, a plate and frame concentrator is preferred.

[0059] Step 3: Long fibers and short fibers are mixed in an 8:2 ratio and then subjected to papermaking and surface sizing. The papermaking process includes wire forming, pressing and dewatering, and drying in the pre-drying section to obtain an initial corrugated base paper with a dryness of 90-92%. Then, the initial corrugated base paper is surface-sized with a boiled sizing solution (containing a 12% concentration, 25 mPa·s starch sizing solution, 120g of amylase per ton of paper, and 3kg of styrene-acrylic sizing agent per ton of paper). The paper is then dried at 60-100℃ to a dryness of 85-92%, and finally rolled and slit to obtain a high-folding-resistance corrugated base paper.

[0060] Web forming: Vacuum degree of -60kPa from the breast roller to the vacuum couch roller section, extending the fiber residence time on the web (1.0 second). Polyester web selection: Use 80 mesh / inch long web.

[0061] Pressing pressure gradient control: A three-roll press (diameter increasing sequentially) is used, with the linear pressure gradually increased from 90 kN / m on the first roll to 300 kN / m on the third roll, avoiding fiber breakage caused by one-time high pressure (dryness increases from 30% to 45-50%). Temperature-assisted dewatering: Hot water (or steam) at 60-70℃ is introduced onto the surface of the press rolls to soften the fiber surface (reducing the resistance between fibers) and simultaneously improving dewatering efficiency (reducing the amount of chemical auxiliaries used).

[0062] Pre-drying segmented drying curve: The pre-drying section adopts a "low temperature slow drying" mode (first drying cylinder 80-90℃, second drying cylinder 90-100℃), which increases the dryness from 45-50% to 90-92% (instead of directly >90%), avoiding the accumulation of internal stress (increased paper brittleness) caused by rapid drying.

[0063] Tension control: Apply a longitudinal tension of 0.1 N / m during the drying process.

[0064] Boiling the glue solution:

[0065] 1. Low-temperature pre-dissolution (40-50℃, 15-20 minutes): Slowly add starch to deionized water (solid-liquid ratio 1:8), start low-speed stirring (100rpm), and heat to 40-50℃ to obtain starch mixture; dilute styrene-acrylic sizing agent (3-4kg / ton) with deionized water in advance (solid-liquid ratio 1:5) to form a uniform styrene-acrylic sizing agent emulsion;

[0066] 2. Enzymatic hydrolysis and temperature-controlled gelatinization (55-65℃, 30-40 minutes): Add amylase and sizing agent emulsion to the starch mixture, increase the stirring speed to 200 rpm, and slowly heat to 55-65℃ for enzymatic hydrolysis and mixing;

[0067] 3. High-temperature curing (85-90℃, 15-20 minutes): Continue heating to 85-90℃ (the temperature at which starch is completely gelatinized) and maintain for 15-20 minutes. After cooking, transfer the glue solution to a vacuum degassing tank and maintain it at -0.08 to -0.09 MPa for 10 minutes to degas it under vacuum. This prevents residual air bubbles from causing defects on the paper surface during sizing. After degassing, let the glue solution stand in a sealed container for 2 hours, stirring for 5 minutes every 30 minutes (at low speed, 50 rpm) to obtain a glue solution with a viscosity of 20-30 mPa·s.

[0068] The drying method after sizing is segmented drying: after sizing, the paper enters the drying section. The temperature of the first drying cylinder is 60-70℃ (low temperature slow drying), the second is 80-90℃ (medium temperature curing), and the third is ≤100℃ (high temperature setting). The final dryness is controlled at 85-92% (retaining some moisture).

[0069] All the slag discharge methods involved in this invention do not have any innovative aspects, and therefore will not be limited or described one by one.

[0070] Example 2

[0071] This embodiment provides a production process for high-bending-resistance corrugated base paper:

[0072] Waste paper raw materials: 35% premium waste paper, 28% corrugated cardboard from cardboard factories, 6% mixed market waste paper, 12% dry pulp bales, and 19% industrial cardboard box waste paper;

[0073] Process:

[0074] Step 1: After mixing and hydrating different types of waste paper raw materials, add 1% polyvinyl alcohol (PVA) and use NaOH solution to adjust the pH to 9 to obtain the original waste paper pulp with a concentration of 2.8%.

[0075] Step two: After passing through high-consistency desanding, coarse screening, and low-consistency desanding, the raw waste paper pulp enters a grading screen to separate the fibers in the waste paper pulp into long fibers and short fibers. The long fiber segment includes fine screening and long fiber concentration. The fine screening uses a dual fiber fine screening (pressure screen + centrifugal screen). The pressure screen has a screen gap of 0.18 mm, and the centrifugal screen rotates at 1500 rpm to remove fiber bundles and impurities, retaining intact long fibers with a purity of 90% (a separate fine screening method was tried during the experiment, but the highest long fiber purity was only 70%, which did not meet the expectations). During the fine screening process, 0.3% cellulase is added, and the concentration of long fibers after concentration is 10%. After concentration, 1% wet strength agent PAE resin is added to obtain long fiber pulp. The short fiber segment includes short fiber concentration, with a concentration of 8% after concentration. After concentration, 0.5% fiber reinforcing agent is added to obtain short fiber pulp. The long fibers are larger than 2.2 mm, and the short fibers are smaller than 1.8 mm.

[0076] Step 3: Long fibers and short fibers are mixed in a 6:4 ratio and subjected to papermaking and surface sizing. The papermaking process includes wire forming, pressing and dewatering, and drying in the pre-drying section to obtain an initial corrugated base paper with a dryness of 90-92%. Then, the initial corrugated base paper is surface-sized with a boiled sizing solution (containing 10% starch sizing solution with a viscosity of 20 mPa·s, 100g of amylase per ton of paper, and 4kg of styrene-acrylic sizing agent per ton of paper). The paper is then dried at 60-100℃ to a dryness of 85-92%, and finally rolled and slit to obtain a high-folding-endurance corrugated base paper.

[0077] All other parameters are exactly the same as in Example 1.

[0078] Example 3

[0079] This embodiment provides a production process for high-bending-resistance corrugated base paper:

[0080] Waste paper raw materials: 35% premium waste paper, 28% corrugated cardboard from cardboard factories, 6% mixed market waste paper, 12% dry pulp bales, and 19% industrial cardboard box waste paper;

[0081] Process:

[0082] Step 1: After mixing and hydrating different types of waste paper raw materials, add 0.5% polyvinyl alcohol (PVA) and use NaOH solution to adjust the pH to 8.5 to obtain the original waste paper pulp with a concentration of 2.5%.

[0083] Step 2: After passing through high-consistency desanding, coarse screening, and low-consistency desanding, the raw waste paper pulp enters a grading screen to separate the fibers in the waste paper pulp into long fibers and short fibers. The long fiber segment includes fine screening and long fiber concentration. The fine screening uses a double fiber fine screening (pressure screen + centrifugal screen). The pressure screen has a screen gap of 0.22mm, and the centrifugal screen rotates at 1800rpm to remove fiber bundles and impurities while retaining intact long fibers. During the fine screening process, 0.2% cellulase is added, and the concentration of long fibers after concentration is 8%. After concentration, 1% wet strength agent PAE resin is added to obtain long fiber pulp. The short fiber segment includes short fiber concentration, and the concentration after concentration is 6%. After concentration, 0.3% fiber reinforcing agent is added to obtain short fiber pulp. The long fibers are larger than 2.2mm, and the short fibers are smaller than 1.8mm.

[0084] Step 3: Long fibers and short fibers are mixed in a 7:3 ratio and subjected to papermaking and surface sizing. Papermaking includes wire forming, pressing and dewatering, and drying in the pre-drying section to obtain an initial corrugated base paper with a dryness of 90-92%. Then, a boiled sizing solution (containing 12% starch sizing solution with a viscosity of 25 mPa·s, 120 g of amylase per ton of paper, and 3 kg of styrene-acrylic sizing agent per ton of paper) is used to surface-size the initial corrugated base paper. The paper is then dried at 60-100°C to a dryness of 85-92%, and finally rolled and slit to obtain a high-folding-endurance corrugated base paper. Other parameters are completely consistent with Example 1.

[0085] Comparative Example 1

[0086] This comparative example provides a production process for high-fold-resistance corrugated base paper:

[0087] Waste paper raw materials: 48% premium waste paper, 26% corrugated cardboard factory paper, 6% mixed market waste paper, and 20% industrial cardboard box waste paper; among which, long fibers are greater than 1.9mm, and 1.9-2.0mm account for more than 90%, and short fibers are less than 1.8mm.

[0088] Everything else is completely consistent with Example 1.

[0089] Comparative Example 2

[0090] This comparative example provides a production process for high-fold-resistance corrugated base paper:

[0091] Waste paper raw material: Same as in Example 1.

[0092] In this comparative example, no fiber protectant or NaOH was added during the hydraulic pulping process to adjust the pH; otherwise, it was completely consistent with Example 1.

[0093] Comparative Example 3

[0094] This comparative example provides a production process for high-fold-resistance corrugated base paper:

[0095] Waste paper raw material: Same as in Example 1.

[0096] In this comparative example, no cellulase or wet strength agent was added to the long fiber treatment; no fiber reinforcing agent was added to the short fiber treatment; otherwise, it was completely consistent with Example 1.

[0097] Comparative Example 4

[0098] This comparative example provides a production process for high-fold-resistance corrugated base paper:

[0099] Waste paper raw material: Same as in Example 1.

[0100] The long / short fiber ratio in this comparative example is 5:5, and everything else is completely consistent with Example 1.

[0101] Comparative Example 5

[0102] This comparative example provides a production process for high-fold-resistance corrugated base paper:

[0103] Waste paper raw material: Same as in Example 1.

[0104] The method for cooking the adhesive solution is as follows: mix starch and water, add amylase, heat to 65°C for enzymatic hydrolysis, then mix with styrene-acrylic sizing agent emulsion and stir evenly before use.

[0105] Everything else is completely consistent with Example 1.

[0106] Comparative Example 6

[0107] This comparative example provides a production process for high-fold-resistance corrugated base paper:

[0108] Waste paper raw material: Same as in Example 1.

[0109] Adhesive solution: Mix cationic starch, solid sizing agent, ADK, styrene-acrylic gum, potassium aluminum sulfate, cationic rosin emulsion, chitosan, polyethylene glycol, polyethylene oxide and deionized water evenly and set aside.

[0110] Everything else is completely consistent with Example 1.

[0111] Comparative Example 7

[0112] This comparative example provides a production process for high-fold-resistance corrugated base paper:

[0113] Waste paper raw material: Same as in Example 1.

[0114] The long / short fiber ratio in this comparative example is 9:1, and everything else is completely consistent with Example 1.

[0115] Experimental Example 1

[0116] The corrugated base paper obtained in Examples 1-3 and Comparative Examples 1-7 was subjected to folding endurance tests, and the results are shown in Tables 1 and 2.

[0117] Basis weight: GB / T 451.2, Thickness: GB / T 451.3, Density = Basis weight / Thickness, Water absorption: GB / T1540, Ring crush strength: GB / T 2679.8, Breaking length: GB / T 13023, Moisture content: GB / T 462, Flexural endurance: GB / T 457.

[0118] Table 1

[0119] Flexural endurance test Ring pressure index (N·m / g) Fracture length (longitudinal) km Example 1 70 10.1 5.8 Example 2 68 10.3 6.0 Example 3 72 10.5 6.1 Comparative Example 1 55 9.3 5.0 Comparative Example 2 45 8.5 4.5 Comparative Example 3 38 8.0 4.0 Comparative Example 4 52 9.0 4.9 Comparative Example 5 65 9.7 5.3 Comparative Example 6 62 9.9 5.6 Comparative Example 7 48 7.8 4.0

[0120] Table 2

[0121] Quantitative g / m2 <![CDATA[Bulk density g / cm 3 > Water absorption g / m2 Example 1 145 0.652 30 Example 2 142 0.648 32 Example 3 143 0.650 33 Comparative Example 1 132 0.621 35 Comparative Example 2 138 0.625 38 Comparative Example 3 132 0.633 42 Comparative Example 4 135 0.621 36 Comparative Example 5 137 0.636 35 Comparative Example 6 133 0.638 33 Comparative Example 7 138 0.623 38

[0122] As shown in Tables 1 and 2, the absence of a dry pulping bag (Comparative Example 1) results in an insufficient proportion of long fibers (long fibers in a dry pulping bag can typically reach over 2.2 mm, but long fibers in waste paper are usually only between 1.9-2.0 mm, indicating a low fiber length). During the fine screening process, fiber damage is significant, the concentration of long fibers is low, fiber bonding strength is reduced, and both folding endurance and edge crush strength decrease. PVA coating reduces frictional damage, and NaOH softens the fiber cell walls, improving flexibility. The absence of a protective agent (Comparative Example 2) leads to an increased fiber cutting rate during pulping, increasing paper brittleness. Adding a protective agent during the pulping stage can significantly improve fiber integrity and is a key process for improving folding endurance.

[0123] Cellulase optimizes hydrogen bonds on the fiber surface, PAE forms a cross-linked network, and reinforcing agents fill the gaps in short fibers. The lack of auxiliaries (Comparative Example 3) leads to weak inter-fiber bonding and easy breakage during folding. The auxiliary system is the core of improving folding resistance, and its absence will lead to a significant decrease in performance.

[0124] Long fibers provide skeletal support, while short fibers fill the pores. A 5:5 ratio results in insufficient long fiber skeleton, making it prone to cracking during folding. A long fiber content of ≥70% is necessary for high folding endurance; reducing it to 50% (Comparative Example 4) significantly weakens mechanical properties. However, excessive increases, with a content of ≥90% (Comparative Example 7), lead to decreased paper flexibility (increased rigidity), making it difficult for fibers to bend and absorb stress during folding, and causing them to easily break from the skeleton layer. A reduction in short fibers (only 10%) fails to effectively fill the gaps between long fibers, exacerbating localized stress concentrations during folding (such as at the junction of corrugated core and face paper). Interlayer bonding strength decreases due to the reduction in short fibers (weakening the role of short fibers as "interface bridges"), making them prone to peeling from the layers during folding. The reduction in short fibers (reduced filling capacity) slightly increases the internal porosity of the paper (loose structure), further weakening ring crush performance.

[0125] Segmented cooking allows for more thorough starch gelatinization, while vacuum degassing prevents air bubbles. Simple cooking (Comparative Example 5) results in coarse glue particles and uneven sizing. Complex glue (Comparative Example 6) not only increases costs but also provides limited improvement to the folding resistance of corrugated paper.

[0126] In summary, the diversified raw materials (dry pulping to supplement long fibers), refined fiber treatment (enzymatic hydrolysis + wet strength agent / reinforcing agent), flexible control of the papermaking process (low shear + low temperature drying), and precise preparation of the sizing solution (segmented cooking + vacuum degassing) of this invention enable the stable production of high-fold-endurance corrugated base paper. In contrast, the comparative examples suffer from deficiencies in key parameters (such as insufficient dry pulping, simplified fiber treatment, and defects in the sizing solution process), leading to a decline in fiber length, bonding strength, surface quality, and ultimately a significant reduction in folding endurance and other physical properties (edge ​​crush, ring crush, etc.).

[0127] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A production process of high folding endurance corrugating medium, characterized by, The process includes: Step 1: Different types of waste paper raw materials are mixed and hydrated to obtain raw waste paper pulp with a concentration of 2.5-2.8%; Step two: After passing through high-consistency desanding, coarse screening, and low-consistency desanding, the raw waste paper pulp enters a grading screen to separate the fibers in the waste paper pulp into long fibers and short fibers. The long fiber segment includes fine screening and long fiber concentration. The fine screening uses a double fiber fine screening, and 0.2-0.3% of cellulase is added during the fine screening process. After concentration, the concentration of long fibers is 8-10%. After concentration, a wet strength agent is added to obtain long fiber pulp. The short fiber segment includes short fiber concentration, and the concentration after concentration is 6-8%. After concentration, 0.3-0.5% of fiber strengthening agent is added to obtain short fiber pulp. Step 3: Mix long fiber pulp and short fiber pulp in a certain proportion, and carry out papermaking and surface sizing treatment; among which, papermaking includes wire forming, pressing and dewatering, and drying in the pre-drying section to obtain initial corrugated base paper with a dryness of 90-92%; then, apply the boiled sizing solution to the surface of the initial corrugated base paper, dry it at 60-100℃ to a dryness of 85-92%, and then roll and slit it to obtain high folding endurance corrugated base paper; In step one, the waste paper raw materials include the following weight percentages: 35-40% premium waste paper, 24-28% corrugated cardboard from cardboard factories, 4-8% mixed commercial waste paper, 8-12% dry pulp bales, and 18-22% industrial cardboard waste paper. In step one, 0.5-1% fiber protectant and 0.1-0.3% NaOH are added to the hydraulic pulping to adjust the pH to 8.5-9.0; In step three, the ratio of long fiber pulp to short fiber pulp is 6:4-8:2; In step three, the adhesive solution contains 10-14% starch adhesive solution with a viscosity of 20-30 mPa·s, 100-150g of amylase per ton of paper, and 3-4kg of styrene-acrylic sizing agent per ton of paper. The adhesive solution is prepared by precisely controlling starch gelatinization and enzymatic hydrolysis through segmented heating, followed by vacuum degassing and static curing for stabilization.

2. The production process of high folding endurance corrugating medium according to claim 1, characterized in that, In step one, the parameters for hydraulic pulping are: pulping time of 15-20 minutes and rotation speed of 3000-3500 rpm; and beating degree of 30-45°SR.

3. The production process of high folding endurance corrugating medium according to claim 1, characterized in that, In step two, the compound fiber sieve includes a pressure sieve and a centrifugal sieve.

4. The production process of high folding endurance corrugating medium according to claim 1, characterized in that, In step two, the wet strength agent is PAE resin, and the amount added is 0.5-1%.

5. The production process of high-fold-resistance corrugated base paper according to claim 1, characterized in that, In step three, the drying temperature of the pre-drying section is 40-90℃.