Preparation method of cotton-feeling household paper

Abstract

The embodiment of the invention provides a preparation method of cotton-feeling household paper, which comprises the following steps: providing long fibers and short fibers in a specific ratio, and controlling the dry weight ratio of bamboo pulp in mixed pulp to be 20-40%; the pulp is subjected to tandem type two-stage pulp grinding treatment, the specific energy consumption of the first stage is 30-50 kWh / adt, and the specific energy consumption of the second stage is 150-170 kWh / adt; sequentially adding a wet strength agent and a softening agent; and finally, forming, squeezing, drying and carrying out wrinkling treatment with the wrinkling rate of 22-26% to obtain the raw paper, through cooperation of the processes, the problem that high wet strength and high softness of the bamboo-based household paper are difficult to consider at the same time is solved, the wet-to-dry ratio of the prepared product is larger than or equal to 32%, the softness is smaller than or equal to 110 mN, and the product has the wet durability of cotton-like soft towels and the softness of high-end household paper.

Description

Technical Field

[0001] This invention relates to a method for preparing cotton-feel household paper. Background Technology

[0002] In the market, cotton towels made from viscose fiber using a hydroentangling process are widely popular due to their excellent properties of being both strong when wet and soft when dry. However, their production cost is high. Therefore, the industry has developed water-resistant household paper products made from softwood and hardwood pulp using a wet-process papermaking technique. These products, by optimizing fiber ratios and chemical additives, can achieve a higher wet-to-dry ratio and greater softness to a certain extent, thus partially replacing traditional cotton towels.

[0003] However, attempts to replace wood pulp, especially softwood pulp, with more sustainable bamboo pulp to produce similar high-end products have encountered unique technical bottlenecks. Bamboo fibers are characterized by their slender shape, thick walls, small cavities, and high stiffness. This results in bamboo pulp tissue paper produced using traditional processes generally having a stiff feel and difficulty in improving wet strength, making it difficult to simultaneously meet the dual requirements of a high wet-to-dry ratio and high dry softness.

[0004] Existing technologies have attempted to improve bamboo pulp to enhance its overall performance. For example, patent documents CN110904735A and CN110924227A disclose papermaking methods that involve grading, screening, and differentiating bamboo pulp fibers before recombining them. These methods primarily aim to improve the forming properties, uniformity, and basic softness of bamboo pulp, enabling it to adapt to high-speed paper machine production and achieve conventional indicators similar to wood pulp paper. However, these solutions do not fundamentally resolve the contradiction between a high wet-to-dry ratio and high softness. The reason for this is that their process focuses on optimizing the distribution of fiber morphology, rather than aiming to construct a fiber network structure that can simultaneously support high strength and high flexibility. In practice, bamboo pulp tissue paper produced using such existing technologies typically struggles to exceed a wet-to-dry ratio of 25-30%.

[0005] To replace traditional cotton wipes, a qualified cotton-like tissue paper must meet two seemingly contradictory key indicators: on the one hand, it must have a high wet-to-dry ratio, usually ≥32% or even ≥34%, to ensure that repeated wiping in a wet state does not easily cause damage; on the other hand, it must have excellent dry softness, usually ≤110 mN or even ≤100 mN, to provide a comfortable skin-friendly feel.

[0006] Therefore, there is an urgent need for a brand-new technical solution that can specifically target the characteristics of bamboo pulp fiber and, through innovative process design, synergistically resolve the long-standing contradiction between high wet-to-dry ratio and high softness in a high bamboo pulp content system, thereby developing cotton-feel household paper that combines environmental protection attributes with a high-end user experience. Summary of the Invention

[0007] Therefore, the present invention provides a method for preparing cotton-feel household paper to solve the above-mentioned technical problems.

[0008] A method for preparing cotton-feel tissue paper includes the following steps: S10: Provide long fibers with a weighted average length of not less than 1.4 mm and short fibers with a weighted average length of not more than 1.2 mm, and mix the long fibers and the short fibers in a ratio of (20-40):(60-40) based on dry weight to form a mixed pulp, wherein the total dry weight of bamboo pulp accounts for 20-40% of the mixed pulp; S20: The mixed slurry is subjected to a two-stage refining process in series until the freeness is 30-38°, wherein the specific energy consumption of the first refining stage is controlled at 30-50 kWh / adt, and the specific energy consumption of the second refining stage is controlled at 150-170 kWh / adt. S30: Add wet strength agent and softener to the mixed slurry obtained in step S20 in sequence, wherein the amount of wet strength agent added is 60-90 kg / adt oven-dry slurry; and the amount of softener added is 0.5-2.0 kg / adt oven-dry slurry. S40: The mixed pulp treated in step S30 is shaped, pressed, and dried to obtain a paper web, and then creped to obtain a base paper, wherein the creping rate is 22%-26%, the wet-to-dry ratio of the base paper is not less than 32%, and the softness of the hand is not greater than 110 mN.

[0009] In step S10, the long fiber is pure bamboo pulp or a mixture of bamboo pulp and softwood pulp.

[0010] Wherein, when the long fiber is a mixture of bamboo pulp and softwood pulp, the proportion of softwood pulp in the mixture is not greater than 30%.

[0011] The short fibers are all hardwood pulp with an average fiber length between 0.8 and 1.0 mm.

[0012] In step S10, the bamboo pulp has an aspect ratio of ≥80.

[0013] In step S30, the wet strength agent is polyamide epichlorohydrin (PAE) resin. The wet strength agent is added to the slurry tank.

[0014] The mixing and curing time of the wet strength agent is >25 minutes.

[0015] In step S30, the softener is added to the mixing tank, and the time interval between the addition of the wet strength agent and the softener is more than 3 minutes.

[0016] In step S40, the pressing pressure is 20-50 kN / m.

[0017] Beneficial Effects: This invention provides a method for preparing cotton-feel tissue paper, comprising: providing a specific ratio of long fibers and short fibers, controlling the dry weight ratio of bamboo pulp in the mixed pulp to be 20-40%; performing a series two-stage refining process on the pulp, with the first stage having a specific energy consumption of 30-50 kWh / adt and the second stage having a specific energy consumption of 150-170 kWh / adt; subsequently adding a wet strength agent and a softener in sequence; and finally, performing forming, pressing, drying, and creping treatment with a creping rate of 22-26% to obtain the base paper. Through the synergy of the above processes, the problem of achieving both high wet strength and high softness in bamboo-based tissue paper is solved. The resulting product has a wet-to-dry ratio ≥32% and a softness ≤110 mN, combining the wet durability of cotton-like soft towels with the softness of high-end tissue paper. Detailed Implementation

[0018] This invention provides a method for preparing a bamboo-based cotton soft towel, which specifically includes the following steps.

[0019] S10: Provide long fibers with a weighted average length of not less than 1.4 mm and short fibers with a weighted average length of not more than 1.2 mm, and mix the long fibers and the short fibers in a ratio of (20-40):(60-40) based on dry weight to form a mixed pulp, wherein the total dry weight of bamboo pulp in the mixed pulp accounts for 20-40%.

[0020] The long fibers mentioned herein refer to pulp components with a weighted average fiber length (Lw) of not less than 1.4 mm. Specifically, they can be bamboo pulp, coniferous wood, or a combination thereof. The bamboo pulp refers to pulp obtained from bamboo materials such as moso bamboo, nan bamboo, and cizhu bamboo through pulping methods such as sulfate process and caustic soda process. It can be understood that the bamboo pulp can be bamboo pulp that has undergone screening to enrich fiber components of specific lengths. More specifically, the bamboo pulp refers to the long bamboo pulp component after screening to remove fine particles. The average length of the long bamboo pulp component is greater than or equal to 1.4 mm, and the fine particles refer to components with a length less than or equal to 0.4 mm.

[0021] Furthermore, the long fibers are pure bamboo pulp or a mixture of bamboo pulp and softwood pulp.

[0022] Furthermore, when the long fiber is a mixture of bamboo pulp and softwood pulp, the proportion of softwood pulp in the mixture is no more than 30%, preferably, the proportion of softwood pulp in the mixture is 10%-25%.

[0023] The short fibers mentioned above are pulp components with a weighted average fiber length (Lw) of no more than 1.2 mm. Specifically, they may include, but are not limited to, hardwood pulp, such as bleached hardwood sulfate pulp (LBKP) and bamboo pulp with a specific length distribution obtained through screening.

[0024] Furthermore, all of the short fibers are hardwood pulp with an average fiber length between 0.8 and 1.0 mm.

[0025] Understandably, in this embodiment, long fibers form the skeleton structure in the fiber network, giving the paper basic wet strength. At the same time, if the proportion of long fibers is too high, such as >40%, the fiber network will become rigid due to too many long connection points, which is not conducive to softness. Short fibers, as fillers and connection points, fill the large pores formed by the interweaving of long fiber skeletons, increasing network density and the number of connection points. At the same time, their relatively thick and short shape is conducive to slippage and fine adjustment when subjected to pressure or force, thereby absorbing energy and directly contributing to dry softness. By controlling the proportion of long fibers at 20-40% and the proportion of short fibers at 60-80%, it is possible to balance high wet strength and high softness while ensuring sufficient skeleton strength.

[0026] Studies have found that limiting the bamboo pulp content to 20-40% allows bamboo fibers, with their unique morphology of being long, thin, thick-walled, small-cavity, and having a large aspect ratio, to penetrate and entwine more deeply into the matrix composed of relatively short and thick broad-leaved wood pulp. This enables multi-scale filling, effectively reduces ineffective pores in the network, and significantly increases the effective bonding area between fibers, laying the foundation for establishing a high-strength hydrogen bond network in pulping and wet strength agents.

[0027] In addition, it was found that the inherent high stiffness of bamboo fiber is one of the reasons for the stiffness of the paper. If the bamboo pulp content is too high, it will be difficult to achieve a fundamental improvement in the overall softness even after subsequent processing. At the same time, if the content is too low, its reinforcing effect is insufficient and it is difficult to break through the limitation of the wet-to-dry ratio. The bamboo pulp ratio should be controlled at 20-40% to make the best use of the reinforcing effect brought by its slender shape, while its possible negative impact on softness can be overcome through subsequent processes.

[0028] Furthermore, the bamboo pulp has an aspect ratio of ≥80, so that the bamboo pulp fibers can be better interwoven in the fiber network.

[0029] S20: The mixed slurry is subjected to a two-stage refining process in series until the overall freeness is 30-38°SR, wherein the specific energy consumption of the first refining stage is controlled at 30-50 kWh / adt, and the specific energy consumption of the second refining stage is controlled at 150-170 kWh / adt.

[0030] The aforementioned tandem two-stage refining refers to the process where the mixed pulp is sequentially and continuously processed by two independent refining devices, such as disc mills, with their process parameters controlled separately, rather than being processed in stages on the same device or using a circulating refining method. This arrangement ensures that the fibers undergo physical modification with two different intensities and modes of action sequentially and continuously.

[0031] Understandably, when the beating is too low, the fiber fibrillation is insufficient, the effective bonding area between fibers is not enough, and enough hydrogen bond points cannot be formed, resulting in insufficient wet strength. When the beating is too high, although the bonding strength may be further improved, it will lead to excessive fiber cutting and severe fibrillation, making the fiber network dense and rigid. At the same time, excessive fine molecules will block the pores and increase the friction between fibers, seriously damaging the dry softness.

[0032] In this embodiment, the various fibers in the mixed pulp, especially the rigid bamboo fibers, are fully swollen and softened by light grinding with the first stage of grinding energy consumption controlled at 30-50 kWh / adt. This partially breaks down their rigid primary walls, increases the plasticity of the fibers, and at the same time, initially loosens the fiber bundles, allowing them to be evenly dispersed in the pulp. In addition, the light grinding with lower power ensures that the length of the bamboo fibers is preserved to the maximum extent, preventing them from being cut prematurely before they are fully softened, thereby protecting their skeletal function as a long fiber component.

[0033] The second stage of refining, with a specific energy consumption of 150-170 kWh / adt, employs high-intensity mechanical energy, including shearing, compression, and kneading, to act on the softened bamboo fibers. This forces the thick-walled, small-cavity, and rigid bamboo fibers to undergo partial plastic deformation and microfibrillation, reducing their flexural modulus and torsional stiffness. Simultaneously, while the fiber body is softened, the high-energy force further promotes longitudinal splitting of the fibers, including bamboo fibers and softwood pulp long fibers, exposing the filaments. This increases the specific surface area and hydroxyl groups of the fibers, thereby increasing wet strength. Furthermore, after this stage of treatment, the bamboo fibers in the fiber network possess both a flexible mechanical nature and a highly buffed surface morphology. This results in a network structure where the connection points are both strong and easy to bend and slide, thus simultaneously satisfying both wet strength and flexibility.

[0034] S30: Add wet strength agent and softener to the mixed slurry obtained in step S20 in sequence, wherein the amount of wet strength agent added is 60-90 kg / adt oven-dry slurry; and the amount of softener added is 0.5-2.0 kg / adt oven-dry slurry.

[0035] The sequential addition refers to first adding the wet strength agent to the mixed slurry after refining, ensuring that it is fully mixed and adsorbed by the fibers, and then adding the softener.

[0036] Furthermore, the wet strength agent is polyamide epichlorohydrin (PAE) resin.

[0037] Furthermore, the wet strength agent is added to the pulping tank, where the pulp concentration is high, the system volume is large, and the pulp residence time is long. This allows PAE molecules sufficient time to diffuse and migrate during the long residence time in the pulping tank, and to undergo adsorption and preliminary cross-linking reactions with the hydroxyl groups exposed on the surface of the activated bamboo pulp fibers.

[0038] Furthermore, the mixing and curing time of the wet strength agent is >25 minutes.

[0039] Furthermore, the softener is a cationic silicone microemulsion or a quaternary ammonium salt softener. It is understood that the softener should be added after the wet strength agent to avoid the softener occupying the hydroxyl active sites on the fiber surface, forming steric hindrance or shielding effect, interfering with the cross-linking reaction between the wet strength agent and the fiber, and causing a decrease in wet strength.

[0040] Furthermore, the softener is added to the mixing tank, where the slurry concentration is close to the online concentration and the residence time is short. At the same time, the time interval between the addition of wet strength agent and softener is more than 3 minutes.

[0041] S40: The mixed pulp treated in step S30 is shaped, pressed, and dried to obtain a paper web, and then creped to obtain a base paper, wherein the creping rate is 22%-26%, the wet-to-dry ratio of the base paper is not less than 32%, and the softness of the hand is not greater than 110 mN.

[0042] The forming, pressing, drying and creping processes mentioned herein employ high-speed paper machines suitable for tissue paper, such as crescent-shaped formers and their supporting processes.

[0043] Specifically, the forming process involves conveying the mixed pulp processed in step S30 to a headbox, preferably using a single-layer headbox, with the pulp concentration controlled at 0.2%-0.4%. After the pulp is evenly distributed in the headbox, it is dewatered on the forming wire to form a wet paper web.

[0044] The pressing is used to mechanically press and dehydrate the formed wet paper web to further improve its dryness. In this embodiment, the pressing line pressure is controlled in the range of 20-50 kN / m. With moderate line pressure, it can effectively dehydrate and promote closer contact between fibers to facilitate hydrogen bond formation, while avoiding high pressure from completely crushing the fibrillated structure and internal pores created in step S20. Thus, while improving dry strength, it retains a certain amount of bulkiness and potential softness deformation space for the paper.

[0045] The drying process is used to transfer the pressed paper web to a Yankee drying cylinder for drying.

[0046] During the creping process, a creping rate of 22%-26% is used to introduce micro-creases, which forces the paper to bend and deform more easily at the micro level, thereby significantly reducing its macroscopic bending stiffness (rigidity). Studies have found that a creping rate of 22%-26% can achieve an optimal balance point that does not significantly impair the wet strength guaranteed by the wet strength agent and maximizes the softness.

[0047] The present invention will be further illustrated below through specific embodiments.

[0048] Each embodiment and comparative example was carried out according to the following steps: S10: Provide long fibers (weighted average fiber length ≥ 1.4 mm) and short fibers (weighted average fiber length approximately 0.8 mm) according to the proportions shown in Table 1, and mix them evenly in the mixing tank to form a mixed pulp. The concentration of the mixed pulp is 3.5-4.0%.

[0049] S20: The mixed slurry is pumped to two double-disc refiners arranged in series. The energy consumption of the first and second refining stages is controlled according to Table 1, and the final freeness is controlled to be 35±1°SR (Schober degree).

[0050] S30: After grinding, the slurry is transported to the slurry mixing tank. First, add the wet strength agent (polyamide epichlorohydrin resin, solid content 12.5%) and stir for 15 minutes; then add the softener (cationic silicone microemulsion, solid content 20%) and stir for 5 minutes. The amount added is calculated based on the oven-dry slurry.

[0051] S40: After being purified by a pressure screen, the pulp is formed by a crescent-shaped forming machine (speed 1100 m / min) with a pulp concentration of 0.3%. The wet paper web is then pressed by a three-roll compound press (linear pressure 35 kN / m), and dried to 95% dryness in a Yankee drying cylinder (surface temperature 110℃). Then, it is creped using a ceramic doctor blade (angle 78°), and the creping rate is controlled according to Table 1.

[0052] Table 1: project Example 1 Example 2 Comparative Example 1 Comparative Example 2 Long fiber 30% (bamboo pulp, 1.7mm) 30% (bamboo pulp, 1.7mm) + 5% (softwood pulp, 2.0mm) 30% (softwood pulp, 2.5mm) 30% (bamboo pulp, 1.7mm) short fiber 70% (broadleaf wood pulp, 1.0mm) 65% (hardwood pulp, 1.0mm) 70% (broadleaf wood pulp, 1.0mm) 70% (broadleaf wood pulp, 1.0mm) Total proportion of bamboo pulp 30% 30% 0% 30% Pulping process Two-stage grinding (40+160 kWh / adt) Two-stage grinding (40+160kWh / adt) Two-stage grinding (40+160kWh / adt) First stage of pulping (160kWh / adt) Freezing degree (°SR) 35 35 35 35 Wet strength agent (PAE) 75kg / adt 75kg / adt 75kg / adt 75kg / adt softener 1.2kg / adt 1.2kg / adt 1.2kg / adt 1.2kg / adt Adding order Apply wet strength agent first, then softener. Apply wet strength agent first, then softener. Apply wet strength agent first, then softener. Apply wet strength agent first, then softener. Wrinkle rate 24% 24% 20% 18% The test results are shown in the table below: Table 2: Test Project unit Example 1 Example 2 Comparative Example 1 Comparative Example 2 Test methods Quantitative g / m² 17.2 17.4 17.3 17.2 GB / T 451.2-2002 Thickness (10 layers) mm 1.01 1.04 0.97 0.94 GB / T 451.3-2002 Longitudinal tensile index N·m / g 11 11.8 12.5 9.5 GB / T 12914-2018 Lateral tensile index N·m / g 5.5 6 6.3 4.5 GB / T 12914-2018 Longitudinal wet strength N / m 65 73 72 45 GB / T 465.2-2008 wet-to-dry ratio % 34.4 36.3 33.3 28.7 (Longitudinal wet strength / Longitudinal tensile strength) × 100% Softness mN 88 96 135 120 GB / T 8942-2016 (2 layers, average length and width) Lateral suction height mm / 100s 45 43 40 38 GB / T 461.1 As can be seen, both the solutions in Examples 1 and 2 consistently achieved the dual high indicators of wet-to-dry ratio ≥32% and softness ≤110mN. However, Comparative Example 1, using softwood pulp, could not simultaneously achieve both high softness and a high wet-to-dry ratio, proving that the introduction of bamboo pulp is not a simple substitution. Comparative Example 2 used the same bamboo pulp raw material as Example 1, but only employed traditional single-stage pulping, resulting in both the wet-to-dry ratio and softness meeting the requirements. The process of this invention can achieve both high wet strength and high softness.

[0053] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing cotton-feel household paper, characterized in that, Includes the following steps: S10: Provide long fibers with a weighted average length of not less than 1.4 mm and short fibers with a weighted average length of not more than 1.2 mm, and mix the long fibers and the short fibers in a ratio of (20-40):(60-40) based on dry weight to form a mixed pulp, wherein the total dry weight of bamboo pulp accounts for 20-40% of the mixed pulp; S20: The mixed slurry is subjected to a two-stage refining process in series until the freeness is 30-38°, wherein the specific energy consumption of the first refining stage is controlled at 30-50 kWh / adt, and the specific energy consumption of the second refining stage is controlled at 150-170 kWh / adt. S30: Add wet strength agent and softener to the mixed slurry obtained in step S20 in sequence, wherein the amount of wet strength agent added is 60-90 kg / adt oven-dry slurry; and the amount of softener added is 0.5-2.0 kg / adt oven-dry slurry. S40: The mixed pulp treated in step S30 is shaped, pressed, and dried to obtain a paper web, and then creped to obtain a base paper, wherein the creping rate is 22%-26%, the wet-to-dry ratio of the base paper is not less than 32%, and the softness of the hand is not greater than 110 mN.

2. The method for preparing cotton-feel tissue paper as described in claim 1, characterized in that, In step S10, the long fibers are pure bamboo pulp or a mixture of bamboo pulp and softwood pulp.

3. The method for preparing cotton-feel tissue paper as described in claim 2, characterized in that, When the long fiber is a mixture of bamboo pulp and softwood pulp, the proportion of softwood pulp in the mixture is no more than 30%.

4. The method for preparing cotton-feel tissue paper as described in claim 2, characterized in that, The short fibers mentioned are all hardwood pulp with an average fiber length between 0.8 and 1.0 mm.

5. The method for preparing cotton-feel tissue paper as described in claim 1, characterized in that, In step S10, the bamboo pulp has an aspect ratio of ≥80.

6. The method for preparing cotton-feel tissue paper as described in claim 1, characterized in that, In step S30, the wet strength agent is polyamide epichlorohydrin (PAE) resin. The wet strength agent is added to the slurry tank.

7. The method for preparing cotton-feel tissue paper as described in claim 6, characterized in that, The mixing and curing time of the wet strength agent is >25 minutes.

8. The method for preparing cotton-feel tissue paper as described in claim 7, characterized in that, In step S30, the softener is added to the mixing tank, and the time interval between the addition of the wet strength agent and the softener is more than 3 minutes.

9. The method for preparing cotton-feel tissue paper as described in claim 1, characterized in that, In step S40, during pressing, the pressing line pressure is 20-50 kN / m.