Pillow bag body paper and preparation process thereof

Abstract

The invention relates to the technical field of pulp or paper pulp compositions, and discloses pillow wrapping base paper and a preparation process thereof, and the preparation process comprises the following steps: preparing softwood pulp of which the surface is adsorbed with a debonding agent and the Zeta potential is-2mV to + 3mV as a first fiber component; preparing hardwood pulp or microfibrillated cellulose with a surface Zeta potential of-20 mV to-35 mV as a second fiber component; the first fiber component is injected into a flowing second fiber component, Zeta potential difference is utilized to drive the second fiber component to wrap the first fiber component to form a flocculation body, and the flocculation body is conveyed to a net part of a paper machine within 30 seconds to be dehydrated and formed. And a core-shell microstructure with coexistence of skeleton slippage and matrix anchoring is constructed, so that the technical problem that high tensile strength and high folding toughness of the pillow-packing body paper are difficult to consider at the same time is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to a pillow bag base paper and its preparation process, belonging to the technical field of pulp or paper pulp composition. BACKGROUND

[0002] In the current operation of high-speed pillow packaging machines, the shoulder of the original paper former bears instantaneous large-angle folding and high-frequency stretching tension of the longitudinal traction roller. In order to meet the physical strength requirements of high-speed working conditions, the existing mainstream process adopts high beating degree mechanical pulping treatment to increase the degree of fiber fanning to build a dense hydrogen bond network and provide paper page resistance to high-speed traction tensile strength. This homogeneous strengthening mode relying on high-density hydrogen bond combination increases the material shear modulus and bending stiffness exponentially, and the paper page shows a glass-like brittle characteristic. When the high-rigidity paper page passes through the forming machine elephant trunk area and is folded violently, the fiber network lacks micro-slippage freedom and cannot dissipate concentrated shear stress, inducing brittle fracture of the outer fiber layer or generating micro-cracks, resulting in packaging material air tightness failure and dust pollution.

[0003] Simply relying on improving the mechanical precision of the pulping equipment or the conventional programmed control of the flow process cannot touch the essence of microstructure regulation. For example, a Chinese invention patent with publication number CN113389090A discloses a production process of corrugated base paper. This scheme optimizes fiber quality and pulp purity through multi-stage sand removal screening, pressure screening and surface sizing combined control strategy. The technical core stays in the macroscopic physical purification and homogeneous enhancement of mixed pulp. Based on the traditional fluid mechanics process control, it is impossible to realize the directional assembly and ordered distribution of different forms of fibers at the micro level. The internal bonding force of the obtained paper page fiber network shows overall uniform characteristics. When facing large-angle folding shear of the shoulder of the high-speed pillow packaging former, it lacks micro stress dissipation mechanism and induces local rigidity too large brittle fracture, which cannot meet the rigid and flexible engineering requirements of high-speed automatic production line. In order to solve the contradiction between strength and toughness, the existing technology introduces cationic surfactant to adjust the fiber bonding force in the pulping process. Although the step-by-step treatment of long and short fibers tries to build a differentiated microstructure of soft and hard, the pulp system in the wet end papermaking engineering environment is dominated by thermodynamic equilibrium law. The liquid phase mixing of small molecule surfactant is driven by chemical potential energy. The small molecule surfactant is desorbed from the surface of long fibers with low specific surface area and migrates to the surface of small fibers or fillers with high specific surface area and redistributes. The entropy increase drives the mixing and stirring time scale to flatten the preset component difference, and the finished paper shows overall strength decline or overall uniform softening single property.

[0004] Therefore, how to break through the physical limitations of single homogeneous network structure and build a heterogeneous microstructure with stress dissipation function on an industrial scale to solve the contradiction between high tensile strength and high folding toughness in high-speed packaging scenarios has become a technical problem to be solved by the present application. SUMMARY

[0005] To solve the problems presented in the background art, the technical solutions of the present application are as follows: A preparation process of pillow bag base paper, which uses the Zeta potential difference between different fiber components to induce heterogeneous coagulation, to prepare a slurry composition with a core-shell microstructure, and the process comprises the following steps: Step one, preparing a first fiber component, providing coniferous wood pulp with a freeness of 600 mL to 650 mL, adding a cationic surfactant to the coniferous wood pulp, monitoring the filtrate charge density and adjusting the amount of cationic surfactant added, so that the surface Zeta potential of the first fiber component is in the range of -2 mV to +3 mV, forming a hydrophobic layer on the surface of the first fiber component and closing the hydrogen bond sites; Step two, preparing a second fiber component, providing broadleaf wood pulp or microfibrillated cellulose with a freeness of 150 mL to 250 mL, and adjusting the medium pH value through mechanical floc splitting treatment, so that the surface Zeta potential of the second fiber component is in the range of -20 mV to -35 mV; Step three, mixing and forming, injecting the first fiber component into the flowing second fiber component, using the Zeta potential difference between the two to drive the second fiber component to adsorb and wrap around the surface of the first fiber component to form flocculation, and transporting the flocculation to the paper machine wire section within 30 seconds after mixing to dehydrate and form, and limiting the migration of cationic surfactant to the second fiber component through the physical steric hindrance formed.

[0006] Preferably, in step one, the cationic surfactant is a quaternary ammonium salt compound; the cationic group of the quaternary ammonium salt compound adsorbs to the anion sites on the surface of the first fiber component, and its hydrophobic carbon chain extends outward to form an isolation film; the isolation film is used to reduce the interfacial bonding force between the first fiber component and the bonding network formed by the second fiber component in the papermaking process, to allow the fibers to slip axially when deformed under stress.

[0007] Preferably, in step three, the absolute dry mass ratio of the first fiber component to the second fiber component is 6:4 to 8:2; under this ratio, the second fiber component forms a continuous wrapping layer on the surface of the first fiber component, and the mixed slurry system has a dewatering performance suitable for high-speed paper machines.

[0008] Preferably, in step two, while the second fiber component is being subjected to mechanical floc splitting treatment, an amphoteric polyacrylamide is added to the system as a reinforcing agent; the reinforcing agent preferentially adsorbs to the surface of the second fiber component in a potential environment of -20 mV to -35 mV, improving the strength of the bonding network formed between the second fiber components.

[0009] Preferably, in step three, the fluid shear rate when the first fiber component is mixed with the second fiber component is lower than the critical threshold value that destroys the structure of the flocculation; and the pulp temperature at the mixing point is controlled to be 45-55 DEG C, so as to reduce the viscosity of water and increase the rate of heterogeneous coagulation, so as to complete the fixation of the flocculation before the desorption of the cationic surfactant.

[0010] Preferably, in step one, the softwood pulp is unbleached or semi-bleached kraft pulp with an average fiber length of more than 2.0 mm; in step two, the hardwood pulp is bleached kraft pulp with an average fiber length of less than 1.0 mm; the first fiber component forms a skeleton network in the paper, and the second fiber component fills the gaps in the skeleton network.

[0011] Preferably, by adjusting the amount of the cationic surfactant added in step one and the pH value of the medium in step two, the surface potential when the first fiber component is mixed with the second fiber component satisfies the following relationship: , wherein, is the Zeta potential difference, is the surface Zeta potential value of the second fiber component in step two, is the surface Zeta potential value of the first fiber component in step one; the Zeta potential difference is used to overcome the Brownian motion and fluid resistance, and drive the second fiber component to wrap the first fiber component.

[0012] Preferably, in step three, the process of delivering the mixed pulp to the wire section of the paper machine for dewatering and forming includes: spraying the mixed pulp to the forming wire through the headbox, and performing gravity dewatering and vacuum moisture absorption; the dewatering rate of the wire section is controlled so that the dryness of the paper web before entering the press section reaches 18-22%, so as to fix the structure distribution of the flocculation; no fixing agent or retention aid is added in the mixing and delivery process of step three; the formation of the flocculation only depends on the electrostatic attraction between the first fiber component and the second fiber component; in step one, the coverage of the cationic surfactant on the surface of the first fiber component is 30-60%.

[0013] Preferably, in step two, the specific operation of adjusting the pH value of the medium is: detecting the pH value of the second fiber component pulp, if the pH value is lower than 7.0, adding sodium hydroxide solution to adjust the pH value to the range of 7.5-8.5, so as to promote the dissociation of the carboxyl group on the surface of the cellulose and increase the surface negative charge density of the second fiber component.

[0014] A bale wrapper base paper is prepared by a bale wrapper base paper preparation process.

[0015] Compared with the prior art, the bale wrapper base paper has the following advantages: 1. In the preparation of pillow bag base paper, the surface electrochemical potential energy state of different fiber components is respectively controlled, the directional electrostatic heterogeneous condensation mechanism is constructed in the slurry mixing fluid dynamics environment, the strong coulomb attraction between heterogeneous charges is used to drive the high negative electric matrix component to quickly adsorb and densely wrap the micro-positive or electrically neutral skeleton component surface in the contact instant, forming a stable core-shell flocculation structure, the potential potential energy difference dominates the instantaneous physical packaging, the micro diffusion barrier is established before the thermodynamic equilibrium of the wet end system is reached, and the migration path of the adsorbed surfactant on the surface of the skeleton to the surrounding water phase or high-energy surface is blocked. This mechanism overcomes the problem of component homogenization caused by the spontaneous migration of small molecule additives in the conventional pulp preparation process, ensures the independent distribution of the hydrophobic slip phase and the hydrophilic binding phase in the paper, and realizes the stable coexistence of opposite mechanical properties in a single material.

[0016] 2. The paper microstructure is characterized by non-rigid wrapping of low modulus skeleton by high modulus matrix. When the structure difference material is deformed under stress, the modulus mismatch effect is caused. When the base paper bears the longitudinal traction of the high-speed packaging machine, the continuously distributed high-bonding-force matrix network bears the main macroscopic tensile load and maintains the required tensile strength; when the local stress is concentrated sharply due to the folding of the former shoulder, the skeleton fibers with weak interfacial bonding rely on the controlled axial micro-slippage in the matrix pores of the surface lubricating layer, and the interfacial slip behavior converts the crack propagation energy into fiber pull-out friction heat energy dissipation, which eliminates the energy basis for brittle fracture and makes the paper maintain high stiffness while having dynamic toughness suitable for small curvature folding.

[0017] 3. The preparation process is based on the colloidal chemical modification of conventional plant fiber raw materials and papermaking additives in the art, and does not need to introduce elastomer emulsion or subsequent plastic composite treatment to meet the performance requirements of high-speed pillow packaging machinery. Only rely on charge control and assembly in the pulp to realize material modification scheme, avoid adding heterogeneous chemicals to destroy the traditional papermaking water system retention and filtration balance of fiber raw materials, ensure the operability of existing high-speed paper machines, and ensure that the pure cellulose properties of the obtained product can be directly recycled through standard disintegration process after being discarded, eliminate technical barriers in the recycling process of composite packaging material fiber resources, and meet the green manufacturing and resource efficiency requirements of the paper industry. BRIEF DESCRIPTION OF DRAWINGS

[0018] Fig. 1 The pillow bag base paper preparation process based on Zeta potential control of the application is shown in the figure; Fig. 2 The comparison chart of the tensile strength and folding endurance retention rate of the base paper of different test groups of the application is shown in the figure; Fig. 3 The principle block diagram of the two-component heterogeneous condensation preparation system of the pillow bag base paper of the application is shown in the figure. DETAILED DESCRIPTION

[0019] The technical solution 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. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] This invention provides a pillowcase base paper and its preparation process, comprising four key stages: charge-reversal framework preparation, high-negative-electric matrix construction, electrostatically guided assembly, and curing. The charge-reversal framework preparation involves preparing the first fiber component, selecting fibers with an average length greater than [missing information]. Unbleached or semi-bleached softwood sulfate pulp (NBKP) was used as raw material, and dissociated and dispersed using a low-consistency hydraulic pulper. The beatness, i.e., the Canadian Standard Freeness (CSF), was controlled by a disc mill. to To preserve the morphology, stiffness, and length of individual fibers, a closed-loop control system for surface modification based on online current detection (PCD) feedback was established. A cationic surfactant, preferably a quaternary ammonium salt such as distearatedimethylammonium chloride or dialkylimidazoline quaternary ammonium salt, was metered and added to a low-concentration softwood pulp suspension. This cationic surfactant, relying on its positively charged nitrogen atom end, is directionally adsorbed onto the negatively charged carboxyl or hydroxyl sites on the cellulose surface, extending the hydrophobic long carbon chain outward to form a discontinuous molecular lubricating film. The charge density of the pulp filtrate was monitored in real time, and the amount of cationic surfactant added was dynamically adjusted based on feedback data until the surface zeta potential of the first fiber component was reached. Stable to Within a certain range, it reaches an electrically neutral or slightly positively charged state, sealing the hydrogen bond binding sites on the fiber surface and storing positive potential energy.

[0021] Next, a highly negatively charged matrix is ​​constructed, i.e., a second fiber component is prepared, using fibers with an average length of less than [missing information]. Bleached hardwood sulfate pulp (LBKP) or microfibrillated cellulose (MFC) is used as raw material, and high-intensity mechanical pulping is performed to control the freeness (CSF) at a certain level. to This process induces high fiber fibrillation, exposing microfibers and protofibers. A pH adjustment step is introduced into this dispersion system, with the amount of alkali added monitored and controlled using an online pH meter. Sodium hydroxide solution is used to adjust the pH of the medium to the desired level. to To promote the dissociation of carboxyl groups on the cellulose surface, if insufficient negative charge density is detected on the fiber surface, a trace amount of anionic polyacrylamide (APAM) or carboxymethyl cellulose (CMC) is added to increase the surface zeta potential of the second fiber component. Stable and maintained at to In the strong anionic region, amphoteric polyacrylamide is added to the system as a reinforcing agent during or after the pulping process. It is then used to preferentially adsorb onto the surface of the second fiber component by utilizing electrostatic matching to construct a continuous matrix network with high bonding strength.

[0022] Electrostatic guided assembly was performed, in which the prepared first fiber component and second fiber component were combined at an oven-dry mass ratio. to The proportional flow convergence injects the first fiber component into the second fiber component, which is flowing in a turbulent state, establishing a zeta potential difference between the two components. It satisfies the relation (Absolute value), using this greater than The Coulomb attraction generated by the potential difference drives the highly negatively charged second fiber component to adsorb and densely coat the surface of the micro-positive or electrically neutral first fiber component at the moment of contact, forming a soft-core-hard-shell micro-floc. The slurry temperature at the mixing point is controlled to be... to This process reduces water viscosity and increases heterogeneous coagulation rate, while controlling the fluid shear rate below the critical threshold that would disrupt the floc structure, ensuring the physical coating layer effectively blocks the outward diffusion of cationic surfactants. Finally, solidification is performed, allowing the mixed slurry to form flocs. Inside, the flocs are sprayed through the headbox to the forming wire section of the paper machine. Utilizing the water filtration channels within the flocs themselves, combined with gravity dewatering and vacuum desiccant elements in the wire section, the dewatering rate is controlled, allowing the paper web to quickly reach the required dryness before entering the press section. to Rapid dehydration removes free water from the fiber network, causing the matrix layer covering the surface of long fibers to physically shrink and solidify. This spatially locks the relative positions of the sliding skeleton and the anchoring matrix. No fixatives or strong cationic retention aids are added during mixing and transport, ensuring that the formation of flocs depends solely on the pre-set electrostatic attraction between fibers. The resulting pillowcase base paper exhibits modulus mismatch units consisting of low-bonding long fibers wrapped by a high-bonding matrix network, resulting in high tensile strength and energy dissipation and zero brittle fracture characteristics at the crack tip when folded.

[0023] To control the charge stability of the continuous fluid environment between the first and second fiber components, an online feedforward-feedback cascade control strategy based on the correlation between the flow action current potential (SCP) and the Zeta potential is adopted. Before formal pulp preparation, a standard curve for the charge requirement of the current batch of pulp is established through titration testing to determine the basic addition ratio of cationic surfactant and the pH adjustment threshold of the medium required to achieve the target Zeta potential. During the production process, an online particle charge detector installed at the headbox inlet collects the flow action current value of the pulp filtrate in real time. The value is mapped to real-time Zeta potential data through a preset conversion algorithm. When the absolute value of the potential deviation exceeds 0.5mV, the central control unit immediately outputs a correction command to the metering pump frequency converter to adjust the reagent injection rate or acid-base regulator flow rate, so that the electrochemical state of the fiber surface is dynamically locked within the heterogeneous coagulation window defined in the claims, eliminating fluctuations in the conductivity of the raw water or the batch of raw materials. Differences lead to potential drift; and to maintain the morphological integrity of the core-shell structured flocs during transport, the diameter-to-length ratio of the transport pipe is set according to fluid dynamics principles, so that the Reynolds number in the mixed pulp fluid pipe is in the transitional flow and weak turbulence range of 2300 to 4000, ensuring the probability of contact and collision between components and limiting the fluid shear stress to a range less than the binding energy of the flocs; based on the dewatering capacity of the paper machine wire section and the design speed, the frequency of the transport pump is adjusted to precisely control the average residence time of the pulp from the confluence mixing point to the forming wire contact point, ensuring that the time is less than the characteristic diffusion time required for the cationic surfactant to desorb from the surface of the first fiber component and reach thermodynamic equilibrium; the high pressure difference generated by the vacuum moisture absorption element in the wire section removes free water at the moment the pulp contacts the wire, and the second fiber component is rapidly solidified and frozen in physical space to prevent structural rearrangement or component separation in the subsequent pressing process.

[0024] Example 1: At a designed operating speed of In a high-speed pillow packaging production line with a pack / minute capacity, the packaging paper needs to continuously pass through the shoulder area of ​​the forming machine and withstand the high-frequency tension applied by the longitudinal traction rollers. This condition requires the material to simultaneously possess sufficient strength to withstand the tension per meter width. Tensile strength with traction force exceeding Newton and adaptability to minimal curvature of the forming machine shoulder The dynamic toughness of folding resistance is crucial. Traditionally, base paper prepared using high-beating homogeneous pulping processes exhibits glass-like rigidity due to the continuous and dense hydrogen bond network between fibers. When flowing through the "elephant trunk" area of ​​the forming device, it cannot dissipate stress through microscopic deformation, leading to brittle fracture of the outer fiber layer and the generation of fine paper dust, causing packaging airtightness failure. To resolve this engineering contradiction between high tensile strength and high folding toughness within a single homogeneous material, this embodiment employs the electrostatic heterogeneous coagulation process based on Zeta potential regulation to construct a heterogeneous microstructure with stress dissipation capabilities. The process begins with the preparation of the first fiber component, using fibers with an average length of... The free fraction (CSF) of coniferous sulfate pulp was controlled to be [value missing] by low-consistency refining. To maintain the morphological stiffness of the long fiber skeleton, in this slurry system, dioctadecyl dimethyl ammonium chloride is added as a cationic surfactant based on real-time feedback from an online flow current detector, and its addition amount is controlled until the zeta potential of the fiber surface is reached. Stable to In a slightly positive state, the hydrophobic carbon chains of the cationic surfactant form a discontinuous lubricating film on the surface of the long fibers, shielding the hydrogen bonding sites between fibers. The second fiber component is prepared using bleached hardwood sulfate pulp, which undergoes high-energy refining to reduce the Canadian standard free fraction (CSF) to a minimum. This process generates a large number of finely fibrillated fibers, and the pH value of the medium is adjusted to a suitable level using sodium hydroxide solution. This allows the carboxyl groups on the cellulose surface to fully dissociate, increasing the surface zeta potential of the component. Stable to This constructs a continuous matrix phase with high negative charge.

[0025] The two oppositely charged components were compared according to their absolute dry mass ratio. A mixing zone is introduced, in which the slightly positive first fiber component is injected into the flowing strongly negative second fiber component. At this point, a high-pressure zone is established between the two components. Zeta potential difference Driven by this potential energy gradient, the second fiber component, with its high specific surface area, overcomes Brownian motion resistance within milliseconds after contact, adsorbing and densely encapsulating itself on the surface of the first fiber component, forming micro-flocs with a soft core and hard shell. This instantaneous physical encapsulation process, dominated by strong Coulomb attraction, occurs while the temperature of the mixed slurry is maintained at a certain level. The process is further accelerated in this environment, and before the cationic surfactant undergoes thermodynamic desorption and migration, it is locked onto the surface of the long fibers by the physical steric hindrance effect of the external matrix layer. The mixed slurry is then... The paper is conveyed internally to the wire section for dehydration and forming. With the rapid removal of free water, the matrix layer shrinks and solidifies, permanently freezing this heterogeneous core-shell distribution state. The resulting pillowcase base paper exhibits modulus mismatch mechanical behavior on high-speed packaging lines. When the paper web is subjected to longitudinal traction, the continuously distributed, highly cohesive broadleaf matrix network bears the main tensile load and maintains operating strength. When the paper web undergoes abrupt folding at the shoulder of the forming device, the long fiber skeleton located inside the matrix wrapping layer undergoes controlled axial slippage within the micropores, thanks to the pre-placed lubricating layer on the surface and low interfacial bonding energy. This slippage behavior effectively converts the shear stress concentrated at the crack tip into frictional heat energy for dissipation, preventing the stress from exceeding the fiber fracture threshold locally. This achieves the elimination of brittle fracture and dust pollution in the forming and folding area while maintaining the integrity of the macroscopic structure.

[0026] Example 2: at a rate of per minute To objectively verify the actual impact of the core-shell microstructure constructed by the electrostatic heterogeneous condensation process of this invention on the high-speed performance of the base paper on an industrial-grade pillow packaging production line operating at high speeds, this experiment was established. The aim is to quantitatively evaluate its ability to solve the engineering contradiction between high tensile strength and high folding toughness by comparing the key physical indicators of base paper prepared by the traditional homogeneous pulping process and the heterogeneous assembly process of this invention under simulated real packaging conditions. The experimental platform includes a pillow packaging machine simulation table equipped with an online tension monitoring and high-speed camera system, as well as standardized laboratory equipment for microstructure characterization and mechanical property testing.

[0027] The experimental design employed a multi-dimensional control system, setting up three experimental groups: Control group A used a traditional homogeneous process, which involved mixing softwood pulp and hardwood pulp and co-milling them to a Canadian standard free fraction (CSF). No bond-unbonding agent was added; Control group B was a partially missing control group. Although long and short fiber components were prepared separately, Zeta potential regulation was not performed, and the potential difference when the two components were mixed was significant. Only The potential is insufficient to induce strong electrostatic adsorption; experimental group C is the sample group of this invention, and the process parameters of Example 1 are executed, namely the Zeta potential of the first fiber component. for Zeta potential of the second fiber component for Mixed potential difference for All slurries were formed under the same conditions to a quantity of [amount missing]. The base paper was used for microstructure characterization and zeta potential matching verification. The cross-sectional morphology of each group of paper sheets was observed by scanning electron microscopy (SEM). The control group A showed a uniform and dense fiber network with long and short fibers interwoven tightly and no obvious phase separation characteristics. Although there were long and short fibers in the control group B, the interface bonding was relatively loose and no obvious encapsulation structure was observed. The experimental group C clearly showed a core-shell structure in which the long fiber skeleton was tightly wrapped by the fine fiber matrix, and there were micro gaps formed by cationic surfactants at the interface between the long fibers and the matrix, verifying the effectiveness of the electrostatic heterogeneous coagulation mechanism. Key mechanical properties were tested. Under standard constant temperature and humidity conditions, the longitudinal tensile strength and folding endurance retention rate of each group of base paper after simulated folding at the shoulder of the forming device were tested. The test results are shown in Table 1.

[0028] Table 1: Comparison of Mechanical Properties of Base Paper in Each Test Group Data interpretation shows that although control group A has a higher longitudinal tensile strength ( However, its flexural endurance retention rate was only [percentage missing]. In high frequency paper breakage rate ( The performance of control group B was the worst (per 10,000 packs), confirming the brittleness problem caused by the high-density hydrogen bond network. Control group B, lacking effective interfacial bonding, showed a decrease in longitudinal tensile strength. This cannot meet the requirements of high-speed traction. In contrast, experimental group C maintains a high tensile strength comparable to control group A. At the same time, its flexural endurance retention rate jumped to Furthermore, it achieved zero paper breaks during the 10,000-pack operation test. This result is directly attributed to its unique core-shell microstructure: the continuous external matrix network provides traction strength, while the internal lubricated long fiber skeleton dissipates shear stress through micro-slippage in the folded area, thereby effectively inhibiting the initiation and propagation of cracks. Secondly, to verify the rationality of the boundaries of key process parameters, the mixed potential difference in test group C was considered. Conduct gradient experiments and set up They are respectively , and The results showed that in the three subgroups, when Below When the folding endurance retention rate shows a significant inflection point, it indicates that the electrostatic attraction is insufficient to form a dense coating layer, and the unbonding agent migrates and contaminates the matrix; when achieve At and above, the performance indicators tend to be stable and excellent.

[0029] Example 3: This example combines Figs. 1 to 3 A description of a type of pillowcase base paper and its preparation process, such as... Fig. 1 As shown, raw material input A uses softwood pulp. After the first fiber component preparation process, through adsorption of debonding agents and surface modification treatment, the zeta potential is made to be in the range of -2mV to +3mV. In parallel, raw material input B uses hardwood pulp or microfibrillated cellulose (MFC). After the second fiber component preparation process, a flowing fiber pulp is formed, and the zeta potential is made to be in the range of -20mV to -35mV. Entering the fluid injection mixing stage, the first component is injected into the flowing second component. The zeta potential difference drives heterogeneous coagulation, and then enters the microstructure construction stage, so that the second component encapsulates the first component to form a core-shell structured flocculant. In the time-limited conveying and dewatering stage, it is conveyed to the wire section for dewatering within 30s to lock the distribution of debonding agents. Finally, a pillow-wrapped base paper product with coexistence of skeleton slippage and matrix anchoring, achieving high tensile strength and high folding endurance is obtained.

[0030] like Fig. 2As shown in the chart, the left vertical axis represents tensile strength in kN / m, the right vertical axis represents flexural endurance retention rate in %, and the horizontal axis lists three sample groups: control group A, control group B, and experimental group C. Control group A shows a high tensile strength but a very low flexural endurance retention rate; control group B shows a low tensile strength and a moderate flexural endurance retention rate; while experimental group C shows a high tensile strength comparable to control group A, and a significantly higher flexural endurance retention rate than the other two groups. Fig. 3 As shown, the system consists of four main functional blocks: the first station is a softwood pulp processing station, equipped with a low-consistency refiner and a surface modifier metering pump, used to prepare skeletal fibers with a slightly positive potential; the second station is a hardwood pulp processing station, equipped with a high-strength mechanical fiber separator and a pH adjustment system, used to prepare matrix fibers with a strongly negative potential. The injection fluid and matrix flow from the two stations respectively enter the central block, i.e., the fluid convergence and mixing zone. Turbulent mixers and online potential monitoring devices are deployed in this zone. The potential difference drives heterogeneous coagulation. The mixed pulp is transported to the terminal block, i.e., the forming section of the paper machine, within 30 seconds. It is then sprayed through the headbox to the gravity dewatering wire section to complete the rapid solidification of the structure.

[0031] Example 4: Addressing the dynamic heat-sealing adaptability issue of pillowcase base paper during high-speed bag making, this example constructs a targeted repair solution. Conventional processes often only provide static heat-sealing strength data, lacking a transparent explanation of the microscopic evolution mechanism of the heat-sealing interface and the coupling effect of the three-dimensional process parameters of temperature, pressure, and time. Therefore, this solution establishes a calibration procedure for the thermal response characteristics of heat-sealing materials based on differential scanning calorimetry (DSC) combined with thermomechanical analysis (TMA). This is achieved by measuring the melting peak temperature of the heat-sealing coating material. Crystallization temperature and storage modulus at different temperatures The changes were analyzed to plot the thermorheological behavior of the material. Based on this, a gradient heat sealing process window optimization experiment was conducted. The experiment was performed using a precision temperature control system (accuracy...). ) and pressure feedback system (accuracy) The simulation was performed on a heat-sealing workstation, with heat-sealing temperature selected as the core variable, and the parameters set from... to ,by A series of test points for the gradient, while maintaining the heat sealing pressure at [value missing]. Heat sealing time is Under constant conditions, for each temperature point, standard heat-sealed specimens were prepared and heat-sealed strength peel tests were performed according to ASTM F88 standard.

[0032] The experimental results reveal a nonlinear structure-property relationship: when the heat sealing temperature is below... At that time, the heat seal strength was generally lower than Interface microscopic analysis revealed that the coating was not fully melted and contained numerous microscopic voids; when the temperature was... to During the interval, the heat sealing strength shows a rapid increase followed by a plateau period of stabilization, reaching... The above-mentioned excellent level was confirmed by cross-sectional electron microscopy, which showed that the coating molecular chains underwent sufficient interdiffusion and entanglement at the interface, forming a homogeneous and dense sealing layer; and when the temperature exceeded At that time, although the heat-sealing strength remained high, the paper base fibers began to show signs of embrittlement due to thermal degradation, manifested as paper base fracture rather than interfacial separation in the peel test. Based on the above data, this embodiment determined... to The optimal heat-sealing process window for the pillowcase base paper was determined. Secondly, to verify the stability of this process window on an actual high-speed production line, a verification step incorporating disturbance factors was introduced to simulate the actual heat-sealing time caused by production line speed fluctuations. to Variation within the range, and the pressure of the heat sealing roller within to Even with fluctuations within the specified range, as long as the heat-sealing temperature is set within the aforementioned optimal window, the coefficient of variation (CV) of the final product's heat-sealing strength can still be controlled within a certain range, provided the heat-sealing temperature remains within the optimal window. Within.

[0033] Example 5: To address the potential fluctuations in operational stability of pillowcase base paper during the start-up phase of a high-speed production line and during the switching of different batches of raw materials, this example establishes a standardized on-site pre-calibration procedure. In conventional production, due to the differences in the sources of softwood pulp and hardwood pulp and the fluctuations in water conductivity, the preset amount of debonding agent may not accurately match the actual charge requirements, leading to a shift in the zeta potential. Therefore, this procedure introduces a baseline calibration step based on online current titration. Before formal pulp preparation, samples of the first and second fiber components of the current batch are extracted and subjected to charge titration in a laboratory environment simulating the actual wet end (including temperature, pH value, and shear force) to determine the charge requirements and zero charge point (PZC) of each component.

[0034] Based on the above titration data, the optimal amount of cationic surfactant and pH adjuster required to reach the target Zeta potential under the current operating conditions was calculated using a preset electrochemical equilibrium model. This model uses fiber specific surface area, medium ionic strength, and temperature as input variables and outputs precise chemical addition rate setpoints. During the initial startup phase of the production line, this process is executed for a period of time. During the dynamic verification phase lasting several minutes, the system continuously monitors the filtrate charge density of the mixed pulp and the Zeta potential of the paper, comparing the real-time data with a preset model. If the deviation exceeds [a certain threshold], [the system will take action]. The system automatically triggers a fine-tuning feedback loop to correct the frequency of the chemical metering pump until the zeta potential stabilizes within the optimal window defined in the claims. This pre-calibration procedure ensures that the slurry entering the headbox is always in the optimal electrostatic heterogeneous coagulation state, regardless of changes in raw material batches, thereby achieving consistency and reproducibility of product performance. In addition, to address the differences in the dynamic adaptability of different models of high-speed packaging machines to the base paper, this embodiment also constructs an offline adaptability calibration procedure for specific models. Using a simulation test machine with adjustable folding angle and traction tension, the mechanical stress environment of the target packaging machine at its highest operating speed is simulated. The dynamic deformation process of the paper web at the shoulder of the forming device is captured by a high-speed camera, and the real-time tension distribution on the surface of the paper web is measured by strain gauges. During the calibration process, the dryness and surface friction coefficient of the base paper are gradually adjusted until the paper web achieves smooth micro-slippage in the folding area without the generation of macro-cracks. The corresponding rewinding tension and storage temperature and humidity conditions at this time are recorded as the standard operating procedure (SOP) for this model.

[0035] Example 6: To ensure the long-term operational stability and consistency of pillowcase base paper in a high-speed automated production environment, this example constructs a closed-loop parameter calibration and process iteration procedure based on full lifecycle data. This aims to eliminate process deviations that may be introduced by fluctuations in the production environment, equipment aging, and batch differences in raw materials. This procedure defines a standardized baseline establishment process. Using a high-precision online sensor array, key process parameters such as headbox pH value, wire section dewatering rate, drying section temperature distribution, and winding section tension fluctuation under normal production conditions are continuously collected. Combined with offline detection data of finished base paper, such as tensile strength, folding endurance, and zeta potential, a multi-dimensional process parameter baseline database is constructed.

[0036] Secondly, a periodic process deviation self-check and calibration mechanism is implemented, and the system is set to... A self-check window with an hourly cycle is used to perform trend analysis on the real-time acquired process parameters using a statistical process control (SPC) algorithm to identify abnormal fluctuations deviating from the baseline. Once a deviation of a key parameter, such as the headbox zeta potential, is detected, the system will take action. Or the rate of change of the dehydration rate of the mesh section exceeds The system will automatically trigger a graded response calibration process. For minor deviations, online compensation will be performed by fine-tuning the frequency of the chemical addition pump or the opening of the headbox lip plate. For other deviations, the system will prompt operators to perform standardized troubleshooting and parameter reset to ensure that the production process always operates within the preset optimal process window. In order to cope with systemic changes caused by changes in raw material sources or equipment upgrades, this embodiment also establishes a parameter recertification procedure based on engineering tests. When a new batch of wood pulp is introduced or a key papermaking wire is replaced, a scaled-down process optimization test is performed. By setting a series of gradient parameters covering a preset range, such as freeness, debonding agent addition, and drying temperature, the sensitivity of the base paper performance to process parameters under the new conditions is quickly assessed, and the optimal operating point is re-determined. The corrected parameters generated by this recertification process will be updated to the central control system in real time as a new operating benchmark.

[0037] 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 present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A preparation process for pillowcase base paper, characterized in that, This process utilizes the Zeta potential difference between different fiber components to induce heterogeneous aggregation in order to prepare a slurry composition with a core-shell microstructure. The process includes the following steps: Step 1: Prepare the first fiber component by providing softwood pulp with a freeness of 600 mL to 650 mL, adding a cationic surfactant to the softwood pulp, and adjusting the amount of cationic surfactant added by monitoring the charge density of the filtrate to keep the surface zeta potential of the first fiber component in the range of -2 mV to +3 mV, thereby forming a hydrophobic layer on the surface of the first fiber component and blocking hydrogen bond binding sites. Step 2: Prepare the second fiber component by providing 150 mL to 250 mL of hardwood pulp or microfibrillated cellulose with a free degree. Through mechanical fibrillation and adjustment of the pH value of the medium, the surface Zeta potential of the second fiber component is in the range of -20 mV to -35 mV. Step 3, mixing and forming: The first fiber component is injected into the flowing second fiber component. The zeta potential difference between the two drives the second fiber component to adsorb and coat the surface of the first fiber component to form flocs. The flocs are then transported to the wire section of the paper machine for dewatering and forming within 30 seconds after mixing and forming. The physical steric hindrance formed restricts the migration of cationic surfactants to the second fiber component.

2. The preparation process of the pillowcase base paper according to claim 1, characterized in that, In step one, the cationic surfactant is a quaternary ammonium salt compound; the cationic groups of the quaternary ammonium salt compound are adsorbed onto the anionic sites on the surface of the first fiber component, and its hydrophobic carbon chains extend outward to form a separating membrane.

3. The preparation process of the pillowcase base paper according to claim 1, characterized in that, In step three, the oven-dry mass ratio of the first fiber component to the second fiber component is 6:4 to 8:

2.

4. The preparation process of the pillowcase base paper according to claim 1, characterized in that, In step two, while mechanically splitting the second fiber component, amphoteric polyacrylamide is added to the system as a reinforcing agent.

5. The preparation process of the pillowcase base paper according to claim 1, characterized in that, In step three, the fluid shear rate when the first fiber component and the second fiber component are mixed is lower than the critical threshold for destroying the floc structure; at the same time, the slurry temperature at the mixing point is controlled to be between 45°C and 55°C.

6. The preparation process of the pillowcase base paper according to claim 1, characterized in that, In step one, the softwood pulp is unbleached or semi-bleached sulfate pulp with an average fiber length greater than 2.0 mm; In step two, the hardwood pulp is a bleached sulfate pulp with an average fiber length of less than 1.0 mm; the first fiber component forms a skeleton network in the papermaking process, and the second fiber component fills the gaps in the skeleton network.

7. The preparation process of the pillowcase base paper according to claim 1, characterized in that, By adjusting the amount of cationic surfactant added in step one and the pH value of the medium in step two, the surface potential of the first fiber component and the second fiber component when mixed satisfies the following relationship: ,in, The zeta potential difference This refers to the surface Zeta potential value of the second fiber component in step two. The value of the surface Zeta potential of the first fiber component in step one; the Zeta potential difference is used to overcome Brownian motion and fluid resistance, driving the second fiber component to wrap the first fiber component.

8. The preparation process of the pillowcase base paper according to claim 1, characterized in that, In step three, the process of conveying the pulp to the wire section of the paper machine for dewatering and forming includes: spraying the mixed pulp through the headbox onto the forming wire for gravity dewatering and vacuum desiccation; controlling the dewatering rate of the wire section so that the dryness of the paper web reaches 18% to 22% before entering the press section, in order to fix the structural distribution of the flocs. No settling agent or retention aid is added during the mixing and conveying process in step three; the formation of flocs depends only on the electrostatic attraction between the first fiber component and the second fiber component.

9. The preparation process of the pillowcase base paper according to claim 1, characterized in that, In step two, the specific operation of adjusting the pH value of the medium is as follows: detect the pH value of the second fiber component slurry. If the pH value is lower than 7.0, add sodium hydroxide solution to adjust the pH value to the range of 7.5 to 8.5 to promote the dissociation of carboxyl groups on the cellulose surface and increase the surface negative charge density of the second fiber component.

10. A type of pillowcase base paper, characterized in that, The pillowcase base paper is prepared by the preparation process of the pillowcase base paper described in claim 1.

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