Paper with good stiffness and texture and manufacturing process thereof

Abstract

The invention provides paper with good stiffness and texture and a manufacturing process thereof, the paper comprises a surface layer, a core layer and a bottom layer, the surface layer is formed by compounding hardwood pulp and nano cellulose, the core layer is formed by high-yield pulp, and the bottom layer is formed by softwood pulp. The paper is divided into three layers, and the surface texture, stiffness and strength of the paper are improved under the condition that the gram weight of the paper is not greatly increased. According to the paper manufacturing process, adjacent fibers are interlocked, the fiber binding force is improved, the strength and stiffness are improved, fiber flocculation is eliminated, and the paper smoothness is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of papermaking, and in particular relates to paper with good stiffness and texture and a manufacturing process thereof. Background Art

[0002] With the rapid development of e-commerce and the logistics industry, the demand for paper as a packaging material has increased significantly. High-strength paper can better protect products, reduce damage during transportation, and lower logistics costs. As part of promotional materials and packaging design, paper's unique texture can attract consumers' attention and enhance product competitiveness.

[0003] The stiffness of traditional paper mainly depends on the interweaving density of wood fibers and reinforcing agents (such as starch). The strength of natural wood fibers is limited, and its stiffness needs to be improved by increasing the fiber interweaving density or increasing the grammage. High-grammage paper is prone to brittle cracking and increases the cost.

[0004] Therefore, the above problems need to be solved urgently. Summary of the Invention

[0005] Purpose of the invention: In order to overcome the above shortcomings, the present invention provides a paper with good stiffness and texture and its production process, which improves the strength and stiffness of the paper without significantly increasing the grammage of the paper, so that the surface of the paper has a good texture.

[0006] Technical solution: In order to achieve the above-mentioned purpose, the present invention provides a paper with good stiffness and texture, comprising a surface layer, a core layer and a bottom layer, wherein the surface layer is composed of a composite of hardwood pulp and nanocellulose, the core layer is composed of high-yield pulp, and the bottom layer is composed of softwood pulp. The present invention divides the paper into a surface layer, a core layer and a bottom layer, wherein the surface layer is composed of a composite of hardwood pulp and nanocellulose. The hardwood pulp has a low lignin content and short fibers, and the surface flatness of the paper produced is good and the printing adaptability is excellent. The addition of nanocellulose composite enhances the density of the paper surface and improves the touch and texture of the paper. The core layer is composed of high-yield pulp, which has long fibers and low cost, and can provide paper stiffness and reduce paper cost. The bottom layer is composed of softwood pulp, which has long fibers, so that the paper has higher tensile strength, bursting resistance and folding resistance. The present invention sets the paper as three layers, which improves the surface texture, stiffness and strength of the paper without significantly increasing the grammage of the paper.

[0007] Furthermore, in the aforementioned paper having excellent stiffness and texture, the hardwood pulp is set at 30 parts, the high-yield pulp is set at 40 parts, and the softwood pulp is set at 30 parts. The top layer, core layer, and bottom layer are arranged in a balanced manner to achieve a balanced dehydration rate among the three layers, thus avoiding delamination or breakage of the wet paper sheets, while maintaining the paper's lightness, stiffness, and texture, and reducing pulp costs.

[0008] Furthermore, in the aforementioned paper with excellent stiffness and texture, the high-yield pulp is BCTMP. BCTMP is bleached chemical thermomechanical pulp. BCTMP fibers retain a large portion of lignin, resulting in a coarse, hard fiber morphology and resistance to swelling, which imparts greater bulk to the paper and improves its stiffness.

[0009] Furthermore, in the above-mentioned paper with good stiffness and texture, carboxylated nanocellulose is added to the high-yield pulp, and the amount of carboxylated nanocellulose added is 0.3% of the high-yield pulp. The addition of carboxylated nanocellulose improves the tensile index and burst index of the paper.

[0010] Furthermore, in the aforementioned paper with excellent stiffness and texture, the nanocellulose content is set at 0.05% of the hardwood pulp, and the nanocellulose particles have a diameter of 10-50 nm and a length of 500-2000 nm. The nanocellulose is embedded in the interstices between the fibers, improving the paper's surface smoothness and texture, increasing hydrogen bonding sites, locking the surface and core layers, and strengthening the fiber network, thereby increasing the paper's strength and stiffness. The nanofibers fill the pores, blocking moisture penetration and improving weather resistance.

[0011] A process for preparing the above-mentioned paper is characterized in that it comprises the following steps: S1: Pulp preparation: hardwood pulp, softwood pulp and high-yield pulp are pretreated with enzymes and then beaten separately; S2: Slurry mixing: adding carboxylated nanocellulose to high-yield slurry, and uniformly mixing the high-yield slurry and carboxylated nanocellulose; S3: Forming on the net: Spray softwood pulp, high-yield pulp, and hardwood pulp onto the forming net in proportion, control the amount of pulp on each layer, and form a multi-layer stacked net structure; S4: Electric field forming: Parallel electrode plates are set behind the forming net and a DC electric field is applied for 10-30 seconds to guide the fibers vertically. S5: Pressing and drying: After the paper sheet is formed on the wire, it enters a multi-pass press to squeeze the fibers into overlapping arrangements, followed by gradient temperature drying; S6: Surface treatment: The dried paper is coated with nanocellulose and then calendered; S7: Winding and Cutting: The paper in step S6 is wound and then cut.

[0012] Furthermore, in the above production process: in step S1, the biological enzyme is set to Green Microcon beating enzyme, and the conditions for the biological enzyme pretreatment are: in step S1, the pulp concentration of the coniferous pulp, high-yield pulp, and broad-leaved pulp is 3.5-4.5%, the pH value is 6-7, the temperature is 45-50°C, and the time is 1.5-2 hours; the conditions for the segmented beating are: the beating degree of the surface layer pulp is 35-40°SR, the beating degree of the core layer pulp is 45-50°SR, and the beating degree of the bottom layer pulp is 35-40°SR.

[0013] Furthermore, in the above manufacturing process: in step S4, the electric field strength is set to 15-25 kV.

[0014] Furthermore, in the above-mentioned production process: in step S5: the conditions of the multi-pass pressing are: the first pressing pressure is 90-110 kN / m, the second pressing pressure is 150-180 kN / m, the third pressing pressure is 60-80 kN / m, and the fourth pressing pressure is 80-100 kN / m; the conditions of the gradient temperature drying are: the wire section temperature is 80-90°C, the drying cylinder zone temperature is 110-120°C, and the calendering section temperature is 90-100°C.

[0015] Furthermore, in the above production process: the nanocellulose dispersion method is a high-pressure homogenization treatment.

[0016] As can be seen from the above technical solution, the present invention has the following beneficial effects: The present invention provides paper with excellent stiffness and texture. The paper is arranged into three layers, utilizing different fiber properties to improve the surface texture, stiffness, and strength of the paper without significantly increasing the paper weight. The present invention utilizes a bio-enzyme pretreatment process to remove impurities from the fiber surface while retaining fiber length, preventing damage to the fibers by strong acids and alkalis. The bio-enzyme pretreatment can break fiber bonds and reduce beating energy consumption. Different beating degrees are designed based on the different fibers and functions of the surface, core, and bottom layers, improving the paper's delicate surface and excellent texture, and enhancing its bonding strength and tear resistance. Simultaneously, the core layer is beating to form a dense hydrogen bond network with the carboxylated nanocellulose, enhancing interlayer bonding, and improving the paper's strength and stiffness. Passing the paper through a high-voltage electric field polarizes the cellulose fibers, causing them to align perpendicular to the plane of the paper along the electric field, reducing fiber interweaving, improving fiber bonding, and increasing the paper's stiffness. The vertical fibers of the surface, core, and bottom layers interpenetrate each other, forming a physical anchor and improving interlayer bonding. After electric field forming, the paper undergoes a gradient pressing process. Initially, light pressure is applied to prevent vertical fiber collapse and remove free water. Then, higher pressure is applied to squeeze out fiber-bound water and activate hydrogen bonding. A third pressing pass releases resilience, and a fourth press balances water distribution and reduces warping. During the pressing process, vertical fibers are bent and interlocked with adjacent fibers, enhancing fiber bonding, strength, and stiffness. After the electric field and four pressing passes, fiber flocculation is eliminated, improving paper smoothness. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a cross-sectional view of the paper with good stiffness and texture according to the present invention; Figure 2 Flowchart of the manufacturing process of the present invention. DETAILED DESCRIPTION

[0018] Example 1 like Figure 1 The present invention discloses a paper with excellent stiffness and texture, and its production process. The paper comprises a surface layer, a core layer, and a bottom layer. The surface layer is composed of a composite of hardwood pulp and nanocellulose, the core layer is composed of high-yield pulp, and the bottom layer is composed of softwood pulp. The surface layer is composed of a composite of hardwood pulp and nanocellulose. Hardwood pulp has a low lignin content and short fibers, resulting in a smooth surface and excellent printability. The addition of nanocellulose enhances the surface density and improves the feel and texture of the paper. The core layer is composed of high-yield pulp, which has long fibers and is low-cost, providing stiffness and reducing paper costs. The bottom layer is composed of softwood pulp, which has long fibers, resulting in high tensile strength, burst resistance, and folding resistance.

[0019] In this embodiment, the broadleaf pulp is set to 30 parts, the high-yield pulp is set to 40 parts, and the coniferous pulp is set to 30 parts.

[0020] In this embodiment, the high-yield pulp is BCTMP. BCTMP is bleached chemical thermomechanical pulp. BCTMP fibers retain a large portion of lignin, resulting in a coarse, hard fiber shape that is less susceptible to swelling, giving the paper a higher bulk and, in turn, improving the paper's stiffness.

[0021] In this embodiment, carboxylated nanocellulose is added to the high-yield pulp in an amount of 0.3% of the high-yield pulp. Adding carboxylated nanocellulose improves the tensile index and burst index of the paper.

[0022] In this embodiment, the nanocellulose content is set to 0.05% of the hardwood pulp, and the nanocellulose particle size is 10-50 nm and the length is 500-2000 nm.

[0023] In this example, the hardwood pulp used is 30 parts of bleached eucalyptus kraft pulp, with a whiteness ≥ 88% ISO, a degree of polymerization of 1200-1500, and an average fiber length of approximately 0.8-1.2 mm. This short fiber material facilitates a smooth surface, meeting printing requirements. Eucalyptus pulp is chosen because its fiber cell walls are thin, allowing for easy fibrillation during beating, which allows for better bonding with nanocellulose, enhancing the strength and smoothness of the surface layer. In this example, a high-yield pulp (BCTMP) of spruce (Picea abies) was used, with a freeness of 250-300 ml CSF and an average fiber length of approximately 2.0-2.5 mm. During BCTMP preparation, the cooking temperature was 130-140°C, the pressure was 0.5-0.7 MPa, the cooking time was 60-90 min, the refining consistency was 25-30%, and the grinding disc gap was 0.1-0.2 mm. These conditions retain a high amount of lignin, resulting in coarse and stiff fibers, which improves the paper's bulk and stiffness. These cooking conditions moderately soften the fibers for refining while retaining sufficient lignin to maintain fiber rigidity. In this example, softwood pulp is set at 30 parts. Bleached pine kraft pulp is used, with a brightness ≥ 85% ISO, a degree of polymerization of 1500-1800, and an average fiber length of approximately 2.5-3.0 mm. Long fibers enhance the physical strength of the paper. The long fibers of pine pulp form a stable skeleton in the bottom layer, supporting the upper pulp layer and improving the overall strength of the paper. In this embodiment, carboxylated nanocellulose is added to the high-yield pulp in an amount of 0.3% of the high-yield pulp. The carboxylated nanocellulose is prepared by acid hydrolysis combined with oxidation, with a carboxyl content of 1.2-1.5 mmol / g, which can effectively improve the tensile strength index and burst resistance index of the paper. Experimental verification has shown that when the carboxylated nanocellulose is added at a level of 0.3%, it forms the strongest hydrogen bonds and electrostatic interactions with the carboxyl and hydroxyl groups of the high-yield pulp fibers, resulting in the best reinforcement effect. At the same time, the nanocellulose dosage is 0.05% of the hardwood pulp, with a particle size of 30 nm and a length of 1200 nm. It can be embedded in the gaps between the fibers, improving the smoothness of the paper surface, strengthening the fiber network, and also blocking moisture and improving weather resistance.

[0024] like Figure 2 The paper making process shown is characterized by comprising the following steps: S1: Pulp preparation: hardwood pulp, softwood pulp and high-yield pulp are pretreated with enzymes and then beaten separately; S2: Slurry Mixing: Add carboxylated nanocellulose to high-yield pulp and mix thoroughly. Stir the carboxylated nanocellulose with the high-yield pulp using a stirrer at 300-500 rpm for 15-20 minutes. The high-yield pulp has a loose fiber structure and a large surface area, which facilitates uniform dispersion and adsorption of the nanocellulose, enhancing its reinforcing properties. Rheological testing indicates that this speed and time result in optimal viscosity uniformity in the mixture.

[0025] S3: Forming on the net: Spray softwood pulp, high-yield pulp, and hardwood pulp onto the forming net in proportion, control the amount of pulp on each layer, and form a multi-layer stacked net structure; S4: Electric field forming: Parallel electrode plates are set behind the forming net and a DC electric field is applied for 10-30 seconds to guide the fibers vertically. S5: Pressing and drying: After the paper sheet is formed on the wire, it enters a multi-pass press to squeeze the fibers into overlapping arrangements, followed by gradient temperature drying; S6: Surface treatment: The dried paper is coated with nanocellulose and then calendered; S7: The paper in step S6 is wound and cut using a rewinder for winding and a paper cutter for cutting according to specifications.

[0026] In this embodiment, in step S1, the biological enzyme is set to Green Microcon beating enzyme, and the conditions for the biological enzyme pretreatment are: in step S1, the pulp concentration of the coniferous pulp, high-yield pulp, and broad-leaved pulp is 3.5-4.5%, the pH value is 6-7, the temperature is 45-50°C, and the time is 1.5-2 hours; the conditions for the segmented beating are: the beating degree of the surface layer pulp is 35-40°SR, the beating degree of the core layer pulp is 45-50°SR, and the beating degree of the bottom layer pulp is 35-40°SR.

[0027] The three pulps were pretreated with enzymes before beating. Green Microcon beating enzyme (Model: LM-100) was used, and treatment was carried out for 1.8 hours at a pulp concentration of 4%, a pH of 6.5, and a temperature of 48°C. Under these conditions, the cellulases and hemicellulases in the beating enzymes gently decompose the hemicellulose on the fiber surface, reducing interfiber bonding, facilitating subsequent beating and fiber refinement, while also minimizing fiber damage. At a pulp concentration of 4%, the enzymes were in full contact with the fibers, while a pH of 6.5 and a temperature of 48°C were within the optimal range for enzyme activity. Beating was performed in sections using a pulping machine. The surface pulp had a beating degree of 38°SR to ensure both surface fiber bonding and smoothness; the core pulp had a beating degree of 48°SR to achieve a higher degree of fiber fibrillation and enhance internal structural strength; and the bottom pulp had a beating degree of 38°SR to balance strength and formability.

[0028] In step S4, the electric field strength is set to 15-25 kV. Parallel electrode plates are placed behind the forming screen, and a 20 kV electric field is applied using a DC power supply for 20 seconds. This step is performed after the paper is initially formed, when the fibers are in a semi-suspended state and not yet fully fixed. The electric field guides the fibers into vertical alignment, increasing interfiber interlacing points and significantly improving paper stiffness. Simulations show that at a 20 kV electric field strength, fiber orientation can be increased to over 85%, resulting in a 15-20% improvement in stiffness compared to traditional processes.

[0029] In step S5: the conditions of the multi-pass pressing are: the first pressing pressure is 90-110 kN / m, the second pressing pressure is 150-180 kN / m, the third pressing pressure is 60-80 kN / m, and the fourth pressing pressure is 80-100 kN / m; the conditions of the gradient temperature drying are: the wire section temperature is 80-90°C, the drying cylinder zone temperature is 110-120°C, and the calendering section temperature is 90-100°C.

[0030] The paper undergoes multiple pressing stages. The first stage, at 100kN / m, pre-presses and dehydrates the paper, giving it an initial shape. The second stage, at 160kN / m, further compacts the fibers and increases the paper's density. The third stage, at 70kN / m, releases the pressure to prevent damage. The fourth stage, at 90kN / m, stabilizes the paper's structure. The dryer uses a gradient drying process. The wire section, at 85°C, rapidly evaporates surface moisture to prevent deformation. The dryer section, at 115°C, deep-dries the paper to remove internal moisture. The calendering section, at 95°C, balances moisture and softens the fibers, facilitating subsequent calendering.

[0031] In step S6, the nanocellulose dispersion method is high-pressure homogenization.

[0032] Performance test data Performance indicators Paper in this embodiment Traditional craft paper Non-electric field forming paper Tensile strength (N / m) 60 45 55 Burst strength (kPa) 350 280 320 Folding endurance (times) 300 200 250 Smoothness (s) 120 80 100 Basis weight (g / m²) 60 60 60 Stiffness (mN・m) 2.8 2.2 2.5 The above embodiments are illustrative and are intended to illustrate the technical concepts and features of the present invention so that those skilled in the art can understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made based on the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A paper with good stiffness and texture, characterized by: The invention comprises a surface layer, a core layer and a bottom layer. The surface layer is composited from broadleaf wood pulp and nano cellulose, the core layer is composed of high-yield pulp, and the bottom layer is composed of softwood pulp.

2. The paper with good stiffness and texture according to claim 1, characterized in that: The broadleaf pulp is set to 30 parts, the high-yield pulp is set to 40 parts, and the coniferous pulp is set to 30 parts.

3. The paper with good stiffness and texture according to claim 1, characterized in that: The high-yield pulp is set as BCTMP.

4. The paper with good stiffness and texture according to claim 1, characterized in that: Carboxylated nanocellulose is added to the high-yield pulp, and the added amount of carboxylated nanocellulose is 0.3% of the high-yield pulp.

5. The paper having good stiffness and texture according to claim 1, characterized in that: The nanocellulose content is set at 0.05% of the hardwood pulp, and the nanocellulose particle size is 10-50 nm and the length is 500-2000 nm.

6. A process for preparing the paper according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1: Pulp preparation: hardwood pulp, softwood pulp and high-yield pulp are pretreated with enzymes and then beaten separately; S2: Slurry mixing: adding carboxylated nanocellulose to high-yield slurry, and uniformly mixing the high-yield slurry and carboxylated nanocellulose; S3: Forming on the net: Spray softwood pulp, high-yield pulp, and hardwood pulp onto the forming net in proportion, control the amount of pulp on each layer, and form a multi-layer stacked net structure; S4: Electric field forming: Parallel electrode plates are set behind the forming net and a DC electric field is applied for 10-30 seconds to guide the fibers vertically. S5: Pressing and drying: After the paper sheet is formed on the wire, it enters a multi-pass press to squeeze the fibers into overlapping arrangements, followed by gradient temperature drying; S6: Surface treatment: The dried paper is coated with nanocellulose and then calendered; S7: Winding and Cutting: The paper in step S6 is wound and then cut.

7. The manufacturing process according to claim 6, characterized in that: In step S1, the biological enzyme is set to Green Microcon beating enzyme, and the conditions for the biological enzyme pretreatment are: in step S1, the pulp concentration of the coniferous pulp, high-yield pulp, and broad-leaved pulp is 3.5-4.5%, the pH value is 6-7, the temperature is 45-50°C, and the time is 1.5-2 hours; the conditions for the segmented beating are: the beating degree of the surface layer pulp is 35-40°SR, the beating degree of the core layer pulp is 45-50°SR, and the beating degree of the bottom layer pulp is 35-40°SR.

8. The manufacturing process according to claim 6, characterized in that: In step S4, the electric field strength is set to 15-25 kV.

9. The production process according to claim 6: in step S5: the conditions of the multi-pass pressing are: the first pressing pressure is 90-110 kN / m, the second pressing pressure is 150-180 kN / m, the third pressing pressure is 60-80 kN / m, and the fourth pressing pressure is 80-100 kN / m; the conditions of the gradient temperature drying are: the wire section temperature is 80-90°C, the drying cylinder section temperature is 110-120°C, and the calendering section temperature is 90-100°C.

10. The manufacturing process according to claim 6, characterized in that: In step S6, the nanocellulose dispersion method is high-pressure homogenization.

Images