High-strength paper corner protection core paper and preparation method thereof

Abstract

The invention discloses high-strength paper angle bead core paper and a preparation method thereof, and relates to the technical field of papermaking, the high-strength paper angle bead core paper comprises a surface paper layer, a lining paper layer, a core paper layer and a bottom paper layer, the surface paper layer comprises, by weight, 50-70% of mineral fibers, 15-59% of waste paper pulp and 1-5% of starch; the lining paper layer is positioned below the surface paper layer and comprises the following components in percentage by weight: 50-70% of starch, 20-30% of mineral fiber and 5-30% of pulp residue; the core paper layer is positioned below the lining paper layer and comprises the following components in percentage by weight: 10-20% of papermaking sludge, 40-70% of pulp residue and 5-20% of starch; the bottom paper layer is positioned below the core paper layer and comprises the following components in percentage by weight: 50-70% of mineral fibers, 15-59% of waste paper pulp and 1-5% of starch. According to the invention, dialdehyde cross-linked starch prepared through periodate oxidation is adopted as a core binding phase in the lining paper layer, so that the problem of difficult balance among interlayer binding force, overall strength and water resistance of traditional paper corner protection core paper is solved.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, specifically to a high-strength paper corner protector core paper and its preparation method. Background Technology

[0002] In packaging, warehousing, and logistics, high-strength paper corner protectors are a crucial edge protection material, and the performance of their core paper directly determines the product's compression resistance, bending resistance, and cushioning capabilities. Currently, most mainstream products on the market rely on multi-layer composite or reinforced filler processes, which, while improving mechanical properties to some extent, still face challenges in terms of interlayer bonding strength, moisture resistance, and long-term stability.

[0003] In existing technologies, chemically modified starches, such as formaldehyde, glutaraldehyde, and epichlorohydrin, are commonly used for cross-linking modification as a means of interlayer bonding and reinforcement. However, while these materials improve bonding strength, there is often a balance problem between toughness, water resistance, and environmental friendliness. For example, excessive cross-linking in pursuit of high water resistance can lead to brittleness and decreased toughness; while using milder reagents in pursuit of environmental friendliness may sacrifice water resistance and strength. Furthermore, on heterogeneous interfaces composed of multiple layers of different materials, traditional cross-linking agents are difficult to form a strong and stable bonding network, easily leading to delamination, moisture absorption, and softening at the interlayer interface.

[0004] Therefore, it is essential to design a high-strength paper corner protector core paper and its preparation method that significantly improves interlayer bonding strength, overall strength and water resistance. Summary of the Invention

[0005] The purpose of this invention is to provide a high-strength paper corner protector core paper and its preparation method, so as to solve the problems mentioned in the background art. To solve the above technical problems, this invention provides the following technical solution: a high-strength paper corner protector core paper, comprising a face paper layer, a liner paper layer, a core paper layer, and a bottom paper layer: The face paper layer comprises, by weight, 50-70% mineral fiber, 15-59% waste paper pulp, and 1-5% starch; The liner paper layer, located below the face paper layer, comprises, by weight fraction, 50-70% dialdehyde crosslinked modified starch, 20-30% mineral fiber, and 5-30% pulp residue; The core paper layer, located below the liner paper layer, comprises, by weight fraction, 10-20% papermaking sludge, 40-70% pulp residue, and 5-20% starch; The bottom paper layer, located below the core paper layer, comprises, by weight, 50-70% mineral fiber, 15-59% waste paper pulp, and 1-5% starch.

[0006] According to the above technical solution, the preparation method of the dialdehyde crosslinked modified starch is as follows: Using corn starch as raw material and sodium periodate (NaIO4) as oxidant, the starch was dissolved in water at a mass ratio of 1:0.1 to 1:0.5. The mixture was then fed into the solution and mechanically stirred for 24 hours at room temperature in the dark. After the reaction was completed, ethylene glycol was added to quench the reaction. The mixture was then centrifuged, washed three times, dried, and ground to obtain 40-mesh dialdehyde starch powder. The dialdehyde starch and the prepared branched hexaamine were added to a container, deionized water was added and stirred evenly, and then placed in an oil bath. The mixture was stirred at 70°C for 3-5 hours. After the reaction was completed, the mixture was placed in a cold water bath and cooled to 25°C with continuous stirring to obtain the dialdehyde crosslinked starch prepolymer solution for later use. The mass ratio of the dialdehyde starch to the branched hexaamine is 1:0.3 - 1:0.8.

[0007] According to the above technical solution, the basis weight of the face paper layer is 80-120 g / m². 2 The thickness is 0.10 - 0.15mm.

[0008] According to the above technical solution, the basis weight of the lining paper layer is 80-120 g / m². 2 The thickness is 0.08 - 0.12 mm.

[0009] According to the above technical solution, the basis weight of the core paper layer is 90-140 g / m². 2 The thickness is 0.25 - 0.40 mm.

[0010] According to the above technical solution, the basis weight of the base paper layer is 100-160 g / m². 2 The thickness is 0.15 - 0.25 mm.

[0011] A method for preparing high-strength paper corner protector core paper includes the following steps: Step 1: Waste paper pulp boards are broken down by a hydrapulper, purified and impurity removed by a high-consistency separator and pressure screen, and then pumped into a fiber grading screen to separate the mixed pulp into components with fiber lengths greater than 1.1 mm, which are retained as waste paper pulp, and components with fiber lengths less than or equal to 1.1 mm, which are separated into pulp residue pulp; papermaking sludge is dried, crushed, and premixed in a special mixing tank for later use; mineral fibers are dispersed separately in a pulping tank for later use. Step 2: Take the waste paper pulp, pulp residue, papermaking fiber, mineral fiber and starch, mix them in the mixing tank according to the weight ratio of each layer, and stir thoroughly to form the pulp for each layer; Step 3: The pulp for the face paper layer, the pulp for the liner paper layer, the pulp for the core paper layer, and the pulp for the bottom paper layer prepared in Step 2 are pumped to the paper machine and filtered and interwoven on the forming wire in sequence to form a wet paper sheet. The face paper layer, the liner paper layer, the core paper layer, and the bottom paper layer are then stacked and pressed together layer by layer in a wet state through the composite device of the wire section to obtain a four-layer composite wet paper web. Step 4: The four-layer composite wet paper web obtained in Step 3 is sequentially subjected to vacuum suction and mechanical pressing for dehydration to ensure that the fibers are tightly bound, and then it is put into a drying cylinder for drying. Step 5: After the dried paper web is calendered, it is wound by a paper winding machine and slit by a rewinding and slitting machine to obtain the finished paper corner protector core paper.

[0012] According to the above technical solution, step two further includes: (1) Preparation of pulp for face paper layer: Take the waste paper pulp, mineral fiber and starch obtained in step one respectively, mix them in the mixing tank according to the weight ratio of face paper layer, add pulp sizing agent and reinforcing agent, and stir evenly to form; (2) Preparation of pulp for lining layer: Take the pulp residue obtained in step one, mineral fiber and dialdehyde cross-linked starch prepolymer solution, and mix them slowly and evenly under stirring according to the weight ratio of the lining layer. Adjust the ratio of the mixed pulp to 5.5-6.5 with dilute hydrochloric acid.

[0013] According to the above technical solution, the sizing agent and reinforcing agent are respectively alkyl ketene dimer and polyamide epichlorohydrin resin.

[0014] According to the above technical solution, step four involves drying the drying cylinder at a temperature of 120-160℃.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) The present invention effectively improves the overall strength of the paper corner core by using mineral fibers in the face paper layer and the back paper layer and combining them with waste paper pulp in each layer. By introducing pulp residue into the liner paper layer and filling the gaps in the network skeleton formed by mineral fibers and starch glue, the density and flatness of the liner paper layer are increased, and the stress transmission path is optimized, making the stress distribution more uniform.

[0016] (2) The present invention obtains dialdehyde starch by oxidizing starch with periodate, and forms a cross-linked starch-based adhesive network by reacting the aldehyde group of the dialdehyde starch with the amino group of the branched hexaamine through a Schiff base reaction, thereby forming a large number of covalent bond networks in the core paper structure, thereby improving the strength, stiffness and moisture resistance of the paper corner protector core paper.

[0017] (3) The present invention also provides a weakly acidic environment during the hot pressing process, so that the aldehyde groups remaining in the double aldehyde cross-linked starch can not only react with the epoxy and amino groups in the upper layer of the paper, but also react with the organic components contained in the papermaking sludge in the core paper layer. At the same time, it forms strong hydrogen bonds with the fibers of the upper and lower adjacent layers, and constructs a synergistic reinforcement structure of chemical cross-linking and physical interlocking between the multi-layer interfaces, thereby improving the strength, stiffness and moisture resistance of the paper corner protector core paper. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1 This invention provides a technical solution: a high-strength paper corner protector core paper and its preparation method, comprising a face paper layer, a liner paper layer, a core paper layer, and a bottom paper layer: the face paper layer, by weight, comprises 50% mineral fiber, 47% waste paper pulp, and 3% starch; the liner paper layer, located below the face paper layer, by weight, comprises 50% aldehyde crosslinked modified starch, 30% mineral fiber, and 20% pulp residue; the core paper layer, located below the liner paper layer, by weight, comprises 20% papermaking sludge, 70% pulp residue, and 10% starch; and the bottom paper layer, located below the core paper layer, by weight, comprises 50% mineral fiber, 47% waste paper pulp, and 3% starch.

[0020] The preparation method of dialdehyde cross-linked starch is as follows: Using corn starch as raw material and sodium periodate (NaIO4) as oxidant, the starch was dissolved in water at a mass ratio of 1:0.1 to oxidant. The mixture was then fed into the solution and mechanically stirred for 24 hours at room temperature in the dark. After the reaction was completed, ethylene glycol was added to quench the reaction. The mixture was then centrifuged, washed three times, dried, and ground to obtain 40-mesh dialdehyde starch powder. The dialdehyde starch and the prepared branched hexaamine were added to a container, deionized water was added, and the mixture was stirred until homogeneous. The container was then placed in an oil bath and stirred at 70°C for 3-5 hours. After the reaction was complete, the container was placed in a cold water bath and cooled to 25°C with continuous stirring to obtain a dialdehyde crosslinked starch prepolymer solution for later use in the preparation of the subsequent paper liner slurry. The mass ratio of dialdehyde starch to branched hexaamine was 1:0.5. The preparation steps of the branched hexaamine were obtained according to patent CN202210271661.2.

[0021] The preparation method of corner protector core paper includes the following steps: Step 1: The waste paper pulp board is broken down in a hydraulic pulper until the degree of dissociation reaches 90%. After purification and impurity removal by a high-consistency separator and a pressure screen, it is pumped into a fiber classifier screen to separate the mixed pulp into components with fiber length greater than 1.1 mm, which are retained as waste paper pulp, and components with fiber length less than or equal to 1.1 mm, which are separated into pulp residue pulp. After drying and crushing, the papermaking sludge is premixed in a special mixing tank for later use. The fineness of the crushed particles is 200 mesh. Mineral fibers are dispersed separately in the pulping tank for later use. The mineral fibers purchased are silicified mineral fibers with a particle size of 400 mesh.

[0022] Step 2: (1) Preparation of pulp for the face paper layer: Take the waste paper pulp, mineral fiber and starch obtained in Step 1 respectively, mix them in the mixing tank according to the weight ratio of the face paper layer, and add the sizing agent alkyl ketene dimer and the reinforcing agent polyamide epichlorohydrin resin. Stir evenly to form the face paper pulp. The mass of alkyl ketene dimer is 0.5% of the waste paper pulp and the mass of polyamide epichlorohydrin resin is 1.2%. (2) Preparation of pulp for lining layer: Take the pulp residue obtained in step one, mineral fiber and double aldehyde cross-linked starch prepolymer solution, and mix them slowly and evenly under stirring according to the weight ratio of the lining layer. Adjust the ratio of the mixed pulp to 6.5 with dilute hydrochloric acid. (3) Preparation of pulp for core paper / liner paper: Take the pulp residue obtained in step one, papermaking sludge and starch, and mix them evenly in the third batching tank according to the weight ratio of the core paper layer; the preparation process of pulp for liner paper is similar, and it is prepared in the fourth batching tank.

[0023] Step 3: The pulp for the face paper layer, the liner paper layer, the core paper layer, and the bottom paper layer prepared in Step 2 are pumped to the paper machine and filtered and interwoven on the forming wire in sequence to form a wet paper sheet. The face paper layer, the liner paper layer, the core paper layer, and the bottom paper layer are then stacked and pressed together layer by layer in a wet state through the composite device of the wire section to obtain a four-layer composite wet paper web.

[0024] Step 4: The four-layer composite wet paper web obtained in Step 3 is sequentially subjected to vacuum suction and mechanical pressing to dehydrate the fibers, and then placed into a drying cylinder for drying at a temperature of 140℃.

[0025] Step 5: After the dried paper web is calendered, it is wound by a paper winding machine and slit by a rewinding and slitting machine to obtain the finished high-strength paper corner protector core paper.

[0026] Example 2 This invention provides a technical solution: a high-strength paper corner protector core paper and its preparation method, comprising a face paper layer, a liner paper layer, a core paper layer, and a bottom paper layer. The face paper layer, by weight, comprises 50% mineral fiber, 47% waste paper pulp, and 3% starch; the liner paper layer, located below the face paper layer, comprises 50% aldehyde cross-linked modified starch, 30% mineral fiber, and 20% pulp residue by weight; the core paper layer, located below the liner paper layer, comprises 20% papermaking sludge, 70% pulp residue, and 10% starch by weight; and the bottom paper layer, located below the core paper layer, comprises 50% mineral fiber, 47% waste paper pulp, and 3% starch by weight.

[0027] The preparation method of dialdehyde cross-linked starch is as follows: Using corn starch as raw material and sodium periodate (NaIO4) as oxidant, the starch was dissolved in water at a mass ratio of 1:0.5 to oxidant. The mixture was then fed into the solution and mechanically stirred for 24 hours at room temperature in the dark. After the reaction was completed, ethylene glycol was added to quench the reaction. The mixture was then centrifuged, washed three times, dried, and ground to obtain 40-mesh dialdehyde starch powder. The dialdehyde starch and the prepared branched hexaamine were added to a container, deionized water was added, and the mixture was stirred until homogeneous. The container was then placed in an oil bath and stirred at 70°C for 3-5 hours. After the reaction was complete, the container was placed in a cold water bath and cooled to 25°C with continuous stirring to obtain a dialdehyde crosslinked starch prepolymer solution for later use in the preparation of the subsequent paper liner slurry. The mass ratio of dialdehyde starch to branched hexaamine was 1:0.5. The preparation steps of the branched hexaamine were obtained according to patent CN202210271661.2.

[0028] The preparation method of the corner protector core paper is the same as in Example 1.

[0029] Example 3 This invention provides a technical solution: a high-strength paper corner protector core paper and its preparation method, comprising a face paper layer, a liner paper layer, a core paper layer, and a bottom paper layer: the face paper layer, by weight, comprises 50% mineral fiber, 47% waste paper pulp, and 3% starch; the liner paper layer, located below the face paper layer, by weight, comprises 50% aldehyde crosslinked modified starch, 30% mineral fiber, and 20% pulp residue; the core paper layer, located below the liner paper layer, by weight, comprises 20% papermaking sludge, 70% pulp residue, and 10% starch; and the bottom paper layer, located below the core paper layer, by weight, comprises 50% mineral fiber, 47% waste paper pulp, and 3% starch.

[0030] The preparation method of dialdehyde cross-linked starch is as follows: Using corn starch as raw material and sodium periodate (NaIO4) as oxidant, the starch was dissolved in water at a mass ratio of 1:0.5 to oxidant. The mixture was then fed into the solution and mechanically stirred for 24 hours at room temperature in the dark. After the reaction was completed, ethylene glycol was added to quench the reaction. The mixture was then centrifuged, washed three times, dried, and ground to obtain 40-mesh dialdehyde starch powder. The dialdehyde starch and the prepared branched hexaamine were added to a container, deionized water was added, and the mixture was stirred until homogeneous. The container was then placed in an oil bath and stirred at 70°C for 3-5 hours. After the reaction was complete, the container was placed in a cold water bath and cooled to 25°C with continuous stirring to obtain a dialdehyde crosslinked starch prepolymer solution for use in the subsequent preparation of the lining paper pulp. The mass ratio of dialdehyde starch to branched hexaamine was 1:2. The preparation steps of the branched hexaamine were described in accordance with patent CN202210271661.2.

[0031] The preparation method of the corner protector core paper is the same as in Example 1.

[0032] Example 4 This invention provides a technical solution: a high-strength paper corner protector core paper and its preparation method, comprising a face paper layer, a liner paper layer, a core paper layer, and a bottom paper layer. The face paper layer, by weight, comprises 50% mineral fiber, 47% waste paper pulp, and 3% starch; the liner paper layer, located below the face paper layer, comprises 60% aldehyde cross-linked modified starch, 30% mineral fiber, and 10% pulp residue by weight; the core paper layer, located below the liner paper layer, comprises 20% papermaking sludge, 70% pulp residue, and 10% starch by weight; and the bottom paper layer, located below the core paper layer, comprises 50% mineral fiber, 47% waste paper pulp, and 3% starch by weight.

[0033] The preparation steps are the same as in Example 1.

[0034] Comparative Example 1 This invention provides a technical solution: a high-strength paper corner protector core paper and its preparation method, comprising a face paper layer, a liner paper layer, a core paper layer, and a bottom paper layer. The face paper layer, by weight, comprises 50% mineral fiber, 47% waste paper pulp, and 3% starch; the liner paper layer, located below the face paper layer, comprises 50% starch, 30% mineral fiber, and 20% pulp residue by weight; the core paper layer, located below the liner paper layer, comprises 20% papermaking sludge, 70% pulp residue, and 10% starch by weight; and the bottom paper layer, located below the core paper layer, comprises 50% mineral fiber, 47% waste paper pulp, and 3% starch by weight.

[0035] The preparation steps are the same as in Example 1.

[0036] Comparative Example 2 This invention provides a technical solution: a high-strength paper corner protector core paper and its preparation method, comprising a face paper layer, a liner paper layer, a core paper layer, and a bottom paper layer. The face paper layer, by weight, comprises 50% mineral fiber, 47% waste paper pulp, and 3% starch; the liner paper layer, located below the face paper layer, comprises 62.5% aldehyde cross-linked modified starch and 37.5% mineral fiber by weight; the core paper layer, located below the liner paper layer, comprises 20% papermaking sludge, 70% pulp residue, and 10% starch by weight; and the bottom paper layer, located below the core paper layer, comprises 50% mineral fiber, 47% waste paper pulp, and 3% starch by weight.

[0037] The preparation steps are the same as in Example 1.

[0038] Comparative Example 3 This invention provides a technical solution: a high-strength paper corner protector core paper and its preparation method, comprising a face paper layer, a liner paper layer, a core paper layer, and a bottom paper layer. The face paper layer, by weight, comprises 50% mineral fiber, 47% waste paper pulp, and 3% starch; the liner paper layer, located below the face paper layer, comprises 50% aldehyde cross-linked modified starch, 30% mineral fiber, and 20% pulp residue by weight; the core paper layer, located below the liner paper layer, comprises 87.5% pulp residue and 12.5% ​​starch by weight; and the bottom paper layer, located below the core paper layer, comprises 50% mineral fiber, 47% waste paper pulp, and 3% starch by weight.

[0039] The preparation steps are the same as in Example 1.

[0040] Comparative Example 4 This invention provides a technical solution: a high-strength paper corner protector core paper and its preparation method, comprising a face paper layer, a liner paper layer, a core paper layer, and a bottom paper layer: the face paper layer, by weight, comprises 50% mineral fiber, 47% waste paper pulp, and 3% starch; the liner paper layer, located below the face paper layer, by weight, comprises 50% aldehyde crosslinked modified starch, 30% mineral fiber, and 20% pulp residue; the core paper layer, located below the liner paper layer, by weight, comprises 20% papermaking sludge, 70% pulp residue, and 10% starch; and the bottom paper layer, located below the core paper layer, by weight, comprises 50% mineral fiber, 47% waste paper pulp, and 3% starch.

[0041] In the preparation method of corner protector core paper, in step two, when preparing the pulp for the face paper layer, polyamide epichlorohydrin resin is not added, and the remaining steps are the same as in Example 1.

[0042] The following performance tests were performed on Examples 1 to 4 and Comparative Examples 1 to 4 respectively: (1) The ring crush strength was tested according to standard GB / T 2679.8. The ring crush tester was used to roll the sample into a standard cylinder (152mm×12.7mm) and place it between two pressure plates. The pressure was applied at a constant speed (12.7±3mm / min) until crushed, and the maximum pressure value was recorded.

[0043] (2) Referring to GB / T 454, the bursting strength index is tested using an electronic tensile testing machine. A 15mm wide specimen is clamped at a specified clamping distance of 180mm and stretched at a constant tensile speed (20±5mm / min) until fracture. The maximum tensile force and elongation are recorded. Using a bursting strength tester, the specimen is clamped onto a rubber diaphragm, and the hydraulic pressure is increased uniformly until the specimen ruptures. The maximum pressure is recorded, i.e., the bursting strength. The bursting strength index is calculated by dividing the bursting strength by the weight of the specimen.

[0044] (3) Refer to GB / T 26203 to test the interlayer bond strength. Use a Z-direction tensile tester to bond the two sides of the sample to the upper and lower metal blocks respectively with a fast-curing two-component epoxy resin adhesive. After curing, peel it vertically at a constant speed (25±5mm / min) and record the average force per unit area required to separate the sample.

[0045] (4) Refer to GB / T 465.2 to test the wet strength retention rate. Use a tensile strength tester to immerse the sample in distilled water at (23±1)℃ for one hour, take it out and wipe it dry, test the ring crush strength, and calculate the retention rate relative to the dry state.

[0046] The performance test results are shown in the table below.

[0047] Table 1 In summary, compared with Example 1, Example 2, by increasing the proportion of sodium periodate oxidant, provides more aldehyde groups, thereby forming a denser liner paper layer and interlayer crosslinking network, significantly increasing interlayer bonding strength, enhancing hydrophobicity, and significantly improving wet strength retention. Compared with Example 2, Example 3, by reducing the mass ratio of dialdehyde starch to branched hexaamine from 1:0.5 to 1:2, resulted in a lower crosslinking density, interlayer bonding strength, and wet strength retention compared to Example 2. Example 4, based on Example 2, increased the proportion of dialdehyde crosslinked modified starch, resulting in enhanced ring crush index, bursting strength, and interlayer bonding strength. Compared with Example 1, Comparative Example 1, by replacing the dialdehyde crosslinked modified starch in the liner paper layer with the same proportion of ordinary starch, significantly decreased all properties of the corner protector core paper. Compared with Example 1, Comparative Example 2, by removing pulp residue from the liner paper layer and keeping the other components unchanged, resulted in a slight decrease in bursting strength and interlayer bonding strength. Compared to Example 1, Comparative Example 3 shows that the absence of papermaking sludge in the core paper layer leads to a significant decrease in the bonding strength between the core paper layer and the liner paper layer due to reduced chemical bonding, resulting in a lower wet strength retention rate. Comparative Example 4 shows that the absence of reinforcing agents in the preparation of the face paper layer prevents the formation of a tight chemical covalent cross-linked network between the face paper layer and the liner paper layer through the Schiff base reaction, resulting in a significant decrease in both interlayer bonding strength and wet strength.

[0048] This invention designs a four-layer composite structure consisting of a face paper layer, a liner paper layer, a core paper layer, and a bottom paper layer. A high proportion of mineral fibers and waste paper pulp are combined in the face paper and bottom paper layers to enhance overall rigidity, while pulp residue is introduced into the liner paper layer to optimize stress transfer. Simultaneously, dialdehyde starch is prepared by oxidizing starch with periodate, which then crosslinks with amines to form a network adhesive with active aldehyde groups. Under the weakly acidic environment of hot pressing, the residual aldehyde groups undergo a Schiff base reaction with adjacent layers to form hydrogen bonds, thereby constructing a stable interface between the layers that is synergistically enhanced by chemical crosslinking and physical interlocking. This scheme synergistically improves the strength, stiffness, moisture resistance, and interlayer bonding of the paper corner protector core paper.

[0049] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A high-strength paper corner protector core paper, comprising a face paper layer, a liner paper layer, a core paper layer, and a bottom paper layer, characterized in that: The face paper layer comprises, by weight, 50-70% mineral fiber, 15-59% waste paper pulp, and 1-5% starch; The liner paper layer, located below the face paper layer, comprises, by weight fraction, 50-70% dialdehyde crosslinked modified starch, 20-30% mineral fiber, and 5-30% pulp residue; The core paper layer, located below the liner paper layer, comprises, by weight fraction, 10-20% papermaking sludge, 40-70% pulp residue, and 5-20% starch; The bottom paper layer, located below the core paper layer, comprises, by weight, 50-70% mineral fiber, 15-59% waste paper pulp, and 1-5% starch.

2. The high-strength paper corner protector core paper according to claim 1, characterized in that, The preparation method of the dialdehyde crosslinked modified starch is as follows: Using corn starch as raw material and sodium periodate (NaIO4) as oxidant, the starch was dissolved in water at a mass ratio of 1:0.1 to 1:0.

5. The mixture was then fed into the solution and mechanically stirred for 24 hours at room temperature in the dark. After the reaction was completed, ethylene glycol was added to quench the reaction. The mixture was then centrifuged, washed three times, dried, and ground to obtain 40-mesh dialdehyde starch powder. The dialdehyde starch and the prepared branched hexaamine were added to a container, deionized water was added and stirred evenly, and then placed in an oil bath. The mixture was stirred at 70°C for 3-5 hours. After the reaction was completed, the mixture was placed in a cold water bath and cooled to 25°C with continuous stirring to obtain the dialdehyde crosslinked starch prepolymer solution for later use. The mass ratio of the dialdehyde starch to the branched hexaamine is 1:0.3 - 1:0.

8.

3. The high-strength paper corner protector core paper according to claim 2, characterized in that: The basis weight of the face paper layer is 80-120 g / m². 2 The thickness is 0.10 - 0.15mm.

4. The high-strength paper corner protector core paper according to claim 3, characterized in that: The basis weight of the liner paper layer is 80-120 g / m². 2 The thickness is 0.08 - 0.12 mm.

5. The high-strength paper corner protector core paper according to claim 4, characterized in that: The basis weight of the core paper layer is 90-140 g / m². 2 The thickness is 0.25 - 0.40 mm.

6. The high-strength paper corner protector core paper according to claim 5, characterized in that: The basis weight of the base paper layer is 100-160 g / m². 2 The thickness is 0.15 - 0.25 mm.

7. A method for preparing a high-strength paper corner protector core paper according to any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Waste paper pulp boards are broken down by a hydrapulper, purified and impurity removed by a high-consistency separator and pressure screen, and then pumped into a fiber grading screen to separate the mixed pulp into components with fiber lengths greater than 1.1 mm, which are retained as waste paper pulp, and components with fiber lengths less than or equal to 1.1 mm, which are separated into pulp residue pulp; papermaking sludge is dried, crushed, and premixed in a special mixing tank for later use; mineral fibers are dispersed separately in a pulping tank for later use. Step 2: Take the waste paper pulp, pulp residue, papermaking fiber, mineral fiber and starch, mix them in the mixing tank according to the weight ratio of each layer, and stir thoroughly to form the pulp for each layer; Step 3: The pulp for the face paper layer, the pulp for the liner paper layer, the pulp for the core paper layer, and the pulp for the bottom paper layer prepared in Step 2 are pumped to the paper machine and filtered and interwoven on the forming wire in sequence to form a wet paper sheet. The face paper layer, the liner paper layer, the core paper layer, and the bottom paper layer are then stacked and pressed together layer by layer in a wet state through the composite device of the wire section to obtain a four-layer composite wet paper web. Step 4: The four-layer composite wet paper web obtained in Step 3 is sequentially subjected to vacuum suction and mechanical pressing for dehydration to ensure that the fibers are tightly bound, and then it is put into a drying cylinder for drying. Step 5: After the dried paper web is calendered, it is wound by a paper winding machine and slit by a rewinding and slitting machine to obtain the finished paper corner protector core paper.

8. The method for preparing a high-strength paper corner protector core paper according to claim 7, characterized in that, Step two further includes: (1) Preparation of pulp for face paper layer: Take the waste paper pulp, mineral fiber and starch obtained in step one respectively, mix them in the mixing tank according to the weight ratio of face paper layer, add pulp sizing agent and reinforcing agent, and stir evenly to form; (2) Preparation of pulp for lining layer: Take the pulp residue obtained in step one, mineral fiber and dialdehyde cross-linked starch prepolymer solution, and mix them slowly and evenly under stirring according to the weight ratio of the lining layer. Adjust the ratio of the mixed pulp to 5.5-6.5 with dilute hydrochloric acid.

9. The method for preparing a high-strength paper corner protector core paper according to claim 8, characterized in that: The sizing agent and reinforcing agent are alkyl ketene dimer and polyamide epichlorohydrin resin, respectively.

10. The method for preparing a high-strength paper corner protector core paper according to claim 7, characterized in that: Step four involves drying the drying cylinder at a temperature of 120-160℃.

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