A preparation process of a protective film base paper

Abstract

This invention discloses a preparation process for protective film base paper, belonging to the field of papermaking technology. The preparation process includes the following steps: mixing base paper pulp and water, performing pulping treatment, adding caustic soda, and beating; after beating, adding aluminum sulfate and starch in sequence, and after stirring, adding anionic dispersed rosin gum, a release agent, an antioxidant, and phosphorylated cellulose to obtain a mixed pulp; the mixed pulp is then formed, pressed, dried, and calendered to obtain the protective film base paper; the antioxidant is a tea polyphenol-sodium phytate / chitosan-chitosan quaternary ammonium salt composite antioxidant microsphere. This invention provides a preparation process for protective film base paper, which, through the synergistic effect of phosphorylated cellulose and the antioxidant tea polyphenol-sodium phytate / chitosan-chitosan quaternary ammonium salt composite antioxidant microsphere, has significant advantages in terms of dry and wet strength and dry heat aging performance.

Description

Technical Field

[0001] This invention belongs to the field of papermaking technology, specifically relating to a preparation process for a protective film base paper. Background Technology

[0002] In the preparation of protective film base paper, existing technologies generally employ a fiber raw material system using a mixture of hardwood pulp and softwood pulp. The strength and bulk of the paper are balanced by adjusting the ratio of the two types of pulp. Regarding the pulping process, traditional methods rely on disc milling to control the pulp freeness at a relatively high level above 42°SR, promoting full fiber fibrillation and enhancing the interweaving and bonding ability between fibers. The chemical auxiliary agent system encompasses various components such as wet strength agents, sizing agents, reinforcing agents, and fillers. Wet strength agents often use polyamide-epoxychloropropane resins, while sizing agents are mainly alkyl ketene dimers or alkenyl succinic anhydride, aiming to impart water resistance and wet strength to the paper. However, existing technologies have significant shortcomings in each of these stages, and these shortcomings are interconnected and cumulative, hindering the improvement of the overall performance of the protective film base paper.

[0003] First, there is a lack of a balance mechanism between pulping process and fiber properties. While high freeness pulping can improve fiber bonding strength, it can also lead to excessive fiber cutting, reducing the aspect ratio and consequently decreasing the paper's tear resistance and folding endurance. Simultaneously, high-freeness pulp deteriorates water filtration performance, limiting paper machine speed and reducing production efficiency. More importantly, during pulping, fibers are subjected to mechanical shearing and frictional heat, causing thermal and oxidative degradation of cellulose molecular chains, generating chromogenic groups such as carbonyl and carboxyl groups, which can lead to yellowing of the paper later.

[0004] Secondly, the functional singularity and synergistic effect of chemical auxiliaries are insufficient. Existing wet strength agents, reinforcing agents, and sizing agents are mostly added independently, lacking synergistic design at the molecular level. For example, the binding of wet strength agents to fibers mainly relies on electrostatic adsorption and chemical cross-linking, but high charge density easily leads to system flocculation, affecting paper uniformity. While starch-based dry strength agents can improve tensile strength, they are often accompanied by increased brittleness and compete with wet strength agents for adsorption, reducing the efficiency of auxiliaries. More critically, existing auxiliary agent systems generally lack antioxidant design, failing to effectively inhibit free radical chain reactions induced by heat, oxygen, and ultraviolet light. This leads to thermal aging and yellowing of paper during storage and use, increasing color difference and restricting applications requiring high appearance quality, such as optical protective films.

[0005] From the perspective of raw materials, the coupling effect between lignin residue and the yellowing mechanism has not been effectively resolved. When using semi-chemical pulp or mechanical pulp raw materials such as bamboo pulp, 3% to 8% of lignin remains in the pulp. The conjugated double bond structure contained in lignin is oxidized under heat or oxygen, generating quinone and ketone chromophores. Although existing bleaching processes can reduce lignin content, excessive bleaching can easily damage cellulose, and the interaction between residual lignin and bleaching byproducts can actually accelerate photoinduced yellowing.

[0006] Existing processes, while improving paper strength, often sacrifice air permeability and bulk. Improving sizing and water resistance, they reduce interlayer bond strength. This trade-off in performance stems from an unclear regulatory mechanism involving fiber scale, pore structure, and interfacial chemistry, leading to significant fluctuations in the basis weight of the finished paper and poor uniformity of physical properties in the horizontal direction. This makes it difficult to meet the stringent requirements of high-end protective films for thickness accuracy and performance stability. Therefore, there is an urgent need to develop a new process for preparing protective film base paper that can achieve high strength and excellent weather resistance. Summary of the Invention

[0007] The purpose of this invention is to provide a process for preparing protective film base paper to solve the problem of poor strength and weather resistance of protective film base paper.

[0008] The objective of this invention can be achieved through the following technical solutions: This invention provides a process for preparing a protective film base paper, comprising the following steps: The raw paper pulp and water are mixed and pulped. Caustic soda is added and the pulp is beaten. After beating, aluminum sulfate and starch are added in sequence. After stirring, anionic dispersible rosin gum, release agent, antioxidant and phosphorylated cellulose are added to obtain mixed pulp. The mixed pulp is formed, pressed, dried, and calendered to obtain a protective film base paper; the antioxidant is a composite antioxidant microsphere of tea polyphenol-sodium phytate / chitosan-chitosan quaternary ammonium salt. Forming: The mixed pulp is conveyed to the wire section of the paper machine. The water level in the wire box is controlled at 360~450mm and the opening of the screen is 11~15mm. The amplitude of the wire section is adjusted to 12~13mm and the vibration frequency is 70~72 times / min to make the pulp uniformly form a wet paper sheet. The wet paper sheet is dewatered by the vacuum roller. The vacuum degree of the vacuum roller is controlled at 0.01MPa, and the initial forming of the paper sheet is completed. Press drying: The formed wet paper sheet is subjected to a first press and a second press in sequence. The pressure of the first press is controlled at 0.2~0.3MPa and the pressure of the second press is 0.3~0.4MPa. At the same time, the pressure of the first support is 0.4~0.45MPa and the pressure of the second support is 0.4~0.45MPa to assist the press. The pressed wet paper sheet is sent to the drying section, where the total drying air pressure is controlled at 0.4~0.45MPa, the air pressure of the large cylinder is 0.245~0.3MPa, and the speed of the large cylinder is 160~190m / min to complete the drying and shaping of the paper sheet.

[0009] Calendering: After drying, the paper sheet enters the soft calender, the pressure of the soft calender roll is controlled at 0.4~0.45MPa, the speed of the soft calender roll is adjusted to 165~190m / min, and the paper machine speed is matched with 160~185m / min for calendering; after calendering, the paper is slit and wound to obtain the finished paper.

[0010] In some possible implementations, the base pulp comprises 60%–70% hardwood pulp and 30%–40% softwood pulp.

[0011] In some possible implementations, the pulping process controls the pulp concentration to 3%–3.5%; During the pulping process, monitor and adjust the pulp freeness to 31-45°SR. In some possible implementations, the stripping agent is one of white oil, soybean oleic acid, and polydimethylsiloxane; Starch is one of cassava cationic starch and corn oxidized starch.

[0012] In some possible implementations, the amount of caustic soda added per ton of protective film base paper is 10-14 kg, aluminum sulfate is 35-45 kg, starch is 3-5 kg, antioxidant is 0.2-0.3 kg, and phosphorylated cellulose is 10-20 kg.

[0013] In some possible implementations, the phosphorylated cellulose is prepared by the following steps: Wood fibers are ground and pulverized, and water is added to prepare a 0.5%–1% pulp. A phosphate solution is prepared by mixing 12%–20% (by weight of the wood fibers) of disodium hydrogen phosphate and sodium dihydrogen phosphate with water. A treatment solution is then prepared by adding 3%–4% (by weight of the wood fibers) of urea. The pulp and treatment solution are mixed and reacted at 110–120°C for 1.5–2 hours. After the reaction, the mixture is washed with water and dried at 60–80°C to obtain phosphorylated fibers. Cellulose molecules contain a large number of hydroxyl groups, which can undergo esterification with phosphates under heating conditions to form phosphate ester bonds. Modification of the fibers using a mixed salt of disodium hydrogen phosphate and sodium dihydrogen phosphate is based on the synergistic effect and counterion interaction of the buffer system, resulting in high reactivity. When the two are mixed in equal masses, a phosphate buffer system with a pH of approximately 6.0–7.0 is formed, providing a mild reaction condition. Since disodium hydrogen phosphate alone is insufficiently reactive, sodium dihydrogen phosphate is introduced to provide H₂PO₄⁻. - This ensures high phosphate grafting efficiency and reduces the H2PO4 content in the buffer system. - The sodium ion undergoes an esterification reaction with the cellulose hydroxyl groups to form a phosphate ester bond. Simultaneously, the sodium ion, acting as a counterion, exhibits a small ionic radius and high charge density, enabling a strong interaction with the cellulose hydroxyl groups and promoting the reaction. When urea is added as a catalyst, the sodium ion can also alter the pyrolysis pathway of urea through complexation, generating an active intermediate at a lower temperature and thus reducing the reaction temperature.

[0014] In some possible implementations, the wood fiber is either jute fiber or bamboo fiber.

[0015] In some possible implementations, the mass ratio of disodium hydrogen phosphate to sodium dihydrogen phosphate is 1:1.

[0016] In some possible implementations, the antioxidant is prepared through the following steps: Chitosan (CS) and chitosan quaternary ammonium salt (HACC) in a mass ratio of 1:1 were used as a composite carrier, and tea polyphenols and sodium phytate (IP6-Na) were co-loaded. Citric acid (CA) was used as a crosslinking agent, and composite microspheres with pH-responsive slow-release function were prepared by emulsification-chemical crosslinking method.

[0017] Chitosan and chitosan quaternary ammonium salt were added to an aqueous acetic acid solution and stirred to dissolve. Citric acid and water were added and the reaction was continued with stirring to obtain a CS / HACC / CA mixed solution. Weigh out tea polyphenols and sodium phytate, add deionized water, and after they are completely dissolved, slowly add them dropwise to a CS / HACC / CA mixed solution and stir to obtain an aqueous phase. Liquid paraffin and emulsifier Span80 were mixed to obtain an oil phase. An aqueous phase was added dropwise to the oil phase, and emulsification was performed at room temperature to obtain a W / O emulsion. The mixture was heated to 50-60℃ and stirred for 3-4 hours under nitrogen protection. After the reaction, petroleum ether was added to break the emulsion. The mixture was then centrifuged, washed with isopropanol and brine, and finally freeze-dried to obtain an antioxidant, which was a composite antioxidant microsphere consisting of tea polyphenols-sodium phytate / chitosan-chitosan quaternary ammonium salt. Chitosan molecules contain a large number of amino groups. When the pH of the environment is higher than this value (e.g., the initial neutral or weakly alkaline state of paper), the amino groups mainly exist in a deprotonated form. Hydrogen bonds and hydrophobic interactions between molecular chains dominate, causing the microsphere network structure to shrink. This hinders the diffusion of the tea polyphenols loaded inside, resulting in very slow release. When paper experiences prolonged use or aging (dry heat aging causes severe breakage of cellulose glycosidic bonds, leading to increased paper acidity), the local pH drops to acidic levels due to cellulose oxidation and degradation, and adsorption of acidic pollutants. In this process, the amino groups of chitosan undergo protonation, transforming into positively charged ammonium ions. This generates strong electrostatic repulsion between chains, expanding internal pores and allowing tea polyphenols to diffuse and release rapidly, effectively scavenging accumulated free radicals. While the chitosan quaternary ammonium salt itself does not respond to pH changes, its permanent positive charge maintains a certain basic swelling degree in the microspheres, preventing sudden release under extreme acidity and high humidity conditions, resulting in a more stable and controllable release curve. The citric acid crosslinking agent retains some free carboxyl groups after the reaction. These carboxyl groups become negatively charged when the pH increases, attracting the protonated amino groups electrostatically to form reversible ionic crosslinking points, further enhancing the pH response sensitivity.

[0018] In some possible implementations, the mass fraction of the acetic acid aqueous solution is 1%–2%; The mass ratio of chitosan, chitosan quaternary ammonium salt, and citric acid in the CS / HACC / CA mixed solution is 1:1:0.3-0.4. The mass ratio of tea polyphenols, sodium phytate, and deionized water was 0.5g:0.15-0.2g:10mL; the mass ratio of chitosan and tea polyphenols was 2:1.

[0019] Paper pulp fibers typically carry a negative charge in water. This solution employs a 1:1 blend of chitosan and chitosan quaternary ammonium salt. The chitosan quaternary ammonium salt contains permanent quaternary ammonium cationic groups, maintaining a stable positive charge even under the chemical conditions of the wet end of papermaking. After crosslinking with citric acid, the surface of the microspheres still exposes a large number of quaternary ammonium groups and protonated amino groups. When the microspheres are mixed with negatively charged pulp fibers, they rapidly combine through electrostatic attraction. The microspheres are firmly adsorbed onto the fiber surface and even embedded in the pores of the interwoven fibers, reducing loss and waste.

[0020] The beneficial effects of this invention are: This invention provides a process for preparing protective film base paper, which has significant advantages in terms of dry and wet strength and dry heat aging performance through the synergistic effect of phosphorylated fibers and antioxidants (tea polyphenol-sodium phytate / chitosan-chitosan quaternary ammonium salt composite antioxidant microspheres).

[0021] For phosphorylated fibers, phosphate groups were successfully introduced into the modified fiber surface, significantly increasing the charge density and forming a high-density negatively charged surface. This surface can form electrostatic attraction with antioxidants (tea polyphenol-sodium phytate / chitosan-chitosan quaternary ammonium salt composite antioxidant microspheres), improving the retention rate of antioxidants and indirectly improving antioxidant stability.

[0022] Phosphate groups on the surface of phosphorylated fibers can serve as coordination sites. When metal ions are present in the system, they can simultaneously bridge the phosphate groups in the fibers and the sodium phosphate groups in the microspheres, forming a stable three-dimensional ionic cross-linking network. This network can effectively transfer stress in both dry and wet conditions, effectively improving the inter-fiber bonding force and paper density, thereby enhancing dry and wet strength. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] The following is a detailed description of the preparation process of a protective film base paper according to an embodiment of this application.

[0025] The following is a detailed description with reference to specific examples.

[0026] Preparation Example 1 Preparation of antioxidants: Add 1g of chitosan and 1g of chitosan quaternary ammonium salt to 100mL of 1% acetic acid aqueous solution, stir to dissolve, add 0.3g of citric acid and 5mL of water and continue stirring for 10min to obtain a CS / HACC / CA mixed solution. Weigh 0.50g of tea polyphenols and 0.15g of sodium phytate, add 10mL of deionized water, and after they are completely dissolved, slowly add them dropwise to a CS / HACC / CA mixed solution and stir for 20min to obtain the aqueous phase. 250 mL of liquid paraffin and 5 mL of emulsifier Span80 were mixed to obtain the oil phase; the aqueous phase was added dropwise to the oil phase, and emulsified at room temperature for 15 min at a speed of 1000 r / min to obtain a W / O emulsion; the temperature was raised to 50 °C, and the reaction was stirred for 3 h, during which nitrogen gas was introduced for protection; after the reaction was completed, petroleum ether was added to demulsify, and the mixture was separated by centrifugation, washed with isopropanol and brine; finally, the antioxidant, namely tea polyphenol-sodium phytate / chitosan-chitosan quaternary ammonium salt composite antioxidant microspheres, was obtained by freeze drying.

[0027] Preparation Example 2 Preparation of antioxidants: Add 1g of chitosan and 1g of chitosan quaternary ammonium salt to 100mL of 1% acetic acid aqueous solution, stir to dissolve, add 0.4g of citric acid and 5mL of water and continue stirring for 10min to obtain a CS / HACC / CA mixed solution. Weigh 0.50g of tea polyphenols and 0.15g of sodium phytate, add 10mL of deionized water, and after they are completely dissolved, slowly add them dropwise to a CS / HACC / CA mixed solution and stir for 20min to obtain the aqueous phase. 250 mL of liquid paraffin and 5 mL of emulsifier Span80 were mixed to obtain the oil phase; the aqueous phase was added dropwise to the oil phase, and emulsified at room temperature for 15 min at a speed of 1000 r / min to obtain a W / O emulsion; the temperature was raised to 50 °C, and the reaction was stirred for 3 h, during which nitrogen gas was introduced for protection; after the reaction was completed, petroleum ether was added to demulsify, and the mixture was separated by centrifugation, washed with isopropanol and brine; finally, the antioxidant, namely tea polyphenol-sodium phytate / chitosan-chitosan quaternary ammonium salt composite antioxidant microspheres, was obtained by freeze drying.

[0028] Preparation Example 3 Preparation of antioxidants: Add 1g of chitosan and 1g of chitosan quaternary ammonium salt to 100mL of 1% acetic acid aqueous solution, stir to dissolve, add 0.3g of citric acid and 5mL of water and continue stirring for 10min to obtain a CS / HACC / CA mixed solution. Weigh 0.50g of tea polyphenols and 0.2g of sodium phytate, add 10mL of deionized water, and after they are completely dissolved, slowly add them dropwise to a CS / HACC / CA mixed solution and stir for 20min to obtain the aqueous phase. 250 mL of liquid paraffin and 5 mL of emulsifier Span80 were mixed to obtain the oil phase; the aqueous phase was added dropwise to the oil phase, and emulsified at room temperature for 15 min at a speed of 1000 r / min to obtain a W / O emulsion; the temperature was raised to 50 °C, and the reaction was stirred for 3 h, during which nitrogen gas was introduced for protection; after the reaction was completed, petroleum ether was added to demulsify, and the mixture was separated by centrifugation, washed with isopropanol and brine; finally, the antioxidant, namely tea polyphenol-sodium phytate / chitosan-chitosan quaternary ammonium salt composite antioxidant microspheres, was obtained by freeze drying.

[0029] Preparation Example 4 Preparation of phosphorylated cellulose: Wood fibers were ground and pulverized, and water was added to make a 1% pulp. A phosphate solution was prepared by mixing 12% (by weight of the wood fibers) of disodium hydrogen phosphate and sodium dihydrogen phosphate with water. Then, 3% (by weight of the wood fibers) of urea was added to prepare a treatment solution. The pulp and treatment solution were mixed and reacted at 110℃ for 1.5 hours. After the reaction, the mixture was washed with water and dried at 60℃ to obtain phosphorylated fibers. The mass ratio of disodium hydrogen phosphate to sodium dihydrogen phosphate was 1:1. The wood fibers were identified as bamboo fibers.

[0030] Preparation Example 5 Preparation of phosphorylated cellulose: Wood fibers were ground and pulverized, and water was added to make a 1% pulp. A phosphate solution was prepared by mixing 20% ​​(by weight of the wood fibers) of disodium hydrogen phosphate and sodium dihydrogen phosphate with water. A treatment solution was then prepared by adding 3% (by weight of the wood fibers) of urea. The pulp and treatment solution were mixed and reacted at 110°C for 1.5 hours. After the reaction, the mixture was washed with water and dried at 60°C to obtain phosphorylated fibers. The mass ratio of disodium hydrogen phosphate to sodium dihydrogen phosphate was 1:1. The wood fibers were identified as bamboo fibers.

[0031] Example 1 This embodiment provides a process for preparing a protective film base paper, including the following steps: The raw paper pulp and water were mixed and pulped. Caustic soda was added and the pulping was performed. After pulping, aluminum sulfate and starch were added in sequence. After stirring, anionic dispersed rosin gum, a release agent, an antioxidant obtained according to the method and proportion in Preparation Example 1, and phosphorylated cellulose obtained according to the method and proportion in Preparation Example 4 were added to obtain a mixed pulp. The antioxidant was a tea polyphenol-sodium phytate / chitosan-chitosan quaternary ammonium salt composite antioxidant microsphere. The base pulp consists of 70% hardwood pulp and 30% softwood pulp; the pulping process controls the pulp concentration to 3%; the pulp freeness is monitored and adjusted to 40°SR during the beating process; the release agent is white oil; and the starch is cassava cationic starch.

[0032] The amount of caustic soda added per ton of protective film base paper is 14 kg, aluminum sulfate is 45 kg, starch is 4 kg, antioxidant is 0.3 kg, and phosphorylated cellulose is 10 kg.

[0033] Forming: The mixed pulp is conveyed to the wire section of the paper machine, and the wire box water level is controlled at 360mm and the opening of the cover is 11mm. The wire section amplitude is adjusted to 12mm and the vibration frequency is 70 times / min to make the pulp uniformly form a wet paper sheet. The wet paper sheet is dewatered by the vacuum roller, and the vacuum degree of the vacuum roller is controlled at 0.01MPa to complete the initial forming of the paper sheet. Press drying: The formed wet paper sheet is subjected to a first press and a second press in sequence. The pressure of the first press is controlled at 0.2MPa and the pressure of the second press is 0.3MPa. At the same time, the pressure of the first support is 0.4MPa and the pressure of the second support is 0.4MPa to assist the press. The pressed wet paper sheet is sent to the drying section, where the total drying air pressure is controlled at 0.4MPa, the air pressure of the large cylinder is 0.245MPa, and the speed of the large cylinder is 160m / min to complete the drying and shaping of the paper sheet.

[0034] Calendering: After drying, the paper sheet enters the soft calender, the pressure of the soft calender roll is controlled at 0.4MPa, the speed of the soft calender roll is adjusted to 165m / min, and the paper machine speed is matched to 160m / min for calendering; after calendering, the paper is slit and wound to obtain the finished paper.

[0035] Example 2 This embodiment provides a process for preparing a protective film base paper, including the following steps: The raw paper pulp and water were mixed and pulped. Caustic soda was added and the pulping was carried out. After pulping, aluminum sulfate and starch were added in sequence. After stirring, anionic dispersed rosin gum, a release agent, an antioxidant obtained according to the method and proportion in Preparation Example 2, and phosphorylated cellulose obtained according to the method and proportion in Preparation Example 4 were added to obtain a mixed pulp. The antioxidant was a tea polyphenol-sodium phytate / chitosan-chitosan quaternary ammonium salt composite antioxidant microsphere. The base pulp consists of 70% hardwood pulp and 30% softwood pulp; the pulping process controls the pulp concentration to 3%; the pulp freeness is monitored and adjusted to 40°SR during the beating process; the release agent is white oil; and the starch is cassava cationic starch.

[0036] The amount of caustic soda added per ton of protective film base paper is 14 kg, aluminum sulfate is 45 kg, starch is 4 kg, antioxidant is 0.3 kg, and phosphorylated cellulose is 10 kg.

[0037] The remaining raw materials and preparation process are the same as in Example 1.

[0038] Example 3 This embodiment provides a process for preparing a protective film base paper, including the following steps: The raw paper pulp and water were mixed and pulped. Caustic soda was added and the pulping was performed. After pulping, aluminum sulfate and starch were added in sequence. After stirring, anionic dispersed rosin gum, a release agent, an antioxidant obtained according to the method and proportion in Preparation Example 3, and phosphorylated cellulose obtained according to the method and proportion in Preparation Example 4 were added to obtain a mixed pulp. The antioxidant was a tea polyphenol-sodium phytate / chitosan-chitosan quaternary ammonium salt composite antioxidant microsphere. The base pulp consists of 70% hardwood pulp and 30% softwood pulp; the pulping process controls the pulp concentration to 3%; the pulp freeness is monitored and adjusted to 40°SR during the beating process; the release agent is white oil; and the starch is cassava cationic starch.

[0039] The amount of caustic soda added per ton of protective film base paper is 14 kg, aluminum sulfate is 45 kg, starch is 4 kg, antioxidant is 0.3 kg, and phosphorylated cellulose is 10 kg.

[0040] The remaining raw materials and preparation process are the same as in Example 1.

[0041] Example 4 This embodiment provides a process for preparing a protective film base paper, including the following steps: The raw paper pulp and water were mixed and pulped. Caustic soda was added and the pulping was performed. After pulping, aluminum sulfate and starch were added in sequence. After stirring, anionic dispersed rosin gum, a release agent, an antioxidant obtained according to the method and proportion in Preparation Example 1, and phosphorylated cellulose obtained according to the method and proportion in Preparation Example 5 were added to obtain a mixed pulp. The antioxidant was a tea polyphenol-sodium phytate / chitosan-chitosan quaternary ammonium salt composite antioxidant microsphere. The base pulp consists of 70% hardwood pulp and 30% softwood pulp; the pulping process controls the pulp concentration to 3%; the pulp freeness is monitored and adjusted to 40°SR during the beating process; the release agent is white oil; and the starch is cassava cationic starch.

[0042] The amount of caustic soda added per ton of protective film base paper is 14 kg, aluminum sulfate is 45 kg, starch is 4 kg, antioxidant is 0.3 kg, and phosphorylated cellulose is 10 kg.

[0043] The remaining raw materials and preparation process are the same as in Example 1.

[0044] Example 5 The raw paper pulp and water were mixed and pulped. Caustic soda was added and the pulping was performed. After pulping, aluminum sulfate and starch were added in sequence. After stirring, anionic dispersed rosin gum, a release agent, an antioxidant obtained according to the method and proportion in Preparation Example 1, and phosphorylated cellulose obtained according to the method and proportion in Preparation Example 4 were added to obtain a mixed pulp. The antioxidant was a tea polyphenol-sodium phytate / chitosan-chitosan quaternary ammonium salt composite antioxidant microsphere. The base pulp consists of 70% hardwood pulp and 30% softwood pulp; the pulping process controls the pulp concentration to 3%; the pulp freeness is monitored and adjusted to 40°SR during the beating process; the release agent is white oil; and the starch is cassava cationic starch.

[0045] The amount of caustic soda added per ton of protective film base paper is 14 kg, aluminum sulfate is 45 kg, starch is 4 kg, antioxidant is 0.3 kg, and cellulose phosphorylation is 15 kg.

[0046] The remaining raw materials and preparation process are the same as in Example 1.

[0047] Example 6 This embodiment provides a process for preparing a protective film base paper, including the following steps: The raw paper pulp and water were mixed and pulped. Caustic soda was added and the pulping was performed. After pulping, aluminum sulfate and starch were added in sequence. After stirring, anionic dispersed rosin gum, a release agent, an antioxidant obtained according to the method and proportion in Preparation Example 1, and phosphorylated cellulose obtained according to the method and proportion in Preparation Example 4 were added to obtain a mixed pulp. The antioxidant was a tea polyphenol-sodium phytate / chitosan-chitosan quaternary ammonium salt composite antioxidant microsphere. The base pulp consists of 70% hardwood pulp and 30% softwood pulp; the pulping process controls the pulp concentration to 3%; the pulp freeness is monitored and adjusted to 40°SR during the beating process; the release agent is white oil; and the starch is cassava cationic starch.

[0048] The amount of caustic soda added per ton of protective film base paper is 14 kg, aluminum sulfate is 45 kg, starch is 4 kg, antioxidant is 0.3 kg, and phosphorylated cellulose is 18 kg.

[0049] The remaining raw materials and preparation process are the same as in Example 1.

[0050] Example 7 This embodiment provides a process for preparing a protective film base paper, including the following steps: The raw paper pulp and water were mixed and pulped. Caustic soda was added and the pulping was performed. After pulping, aluminum sulfate and starch were added in sequence. After stirring, anionic dispersed rosin gum, a release agent, an antioxidant obtained according to the method and proportion in Preparation Example 1, and phosphorylated cellulose obtained according to the method and proportion in Preparation Example 4 were added to obtain a mixed pulp. The antioxidant was a tea polyphenol-sodium phytate / chitosan-chitosan quaternary ammonium salt composite antioxidant microsphere. The base pulp consists of 70% hardwood pulp and 30% softwood pulp; the pulping process controls the pulp concentration to 3%; the pulp freeness is monitored and adjusted to 40°SR during the beating process; the release agent is white oil; and the starch is cassava cationic starch.

[0051] The amount of caustic soda added per ton of protective film base paper is 14 kg, aluminum sulfate is 45 kg, starch is 4 kg, antioxidant is 0.3 kg, and phosphorylated cellulose is 20 kg.

[0052] The remaining raw materials and preparation process are the same as in Example 1.

[0053] Example 8 The difference between this embodiment and Example 1 is that the conditions for molding, pressing and drying, and calendering of the mixed slurry are different, while the other raw materials and preparation process remain the same as in Example 1.

[0054] Forming: The mixed pulp is conveyed to the wire section of the paper machine, and the wire box water level is controlled at 450mm and the opening of the cover is 15mm. The wire section amplitude is adjusted to 13mm and the vibration frequency is 72 times / min to make the pulp uniformly form a wet paper sheet. The wet paper sheet is dewatered by the vacuum roller, and the vacuum degree of the vacuum roller is controlled at 0.01MPa to complete the initial forming of the paper sheet. Press drying: The formed wet paper sheet is subjected to a first press and a second press in sequence. The pressure of the first press is controlled at 0.3MPa and the pressure of the second press is 0.4MPa. At the same time, the pressure of the first support is 0.45MPa and the pressure of the second support is 0.45MPa to assist the press. The pressed wet paper sheet is sent to the drying section, where the total drying air pressure is controlled at 0.45MPa, the air pressure of the large cylinder is 0.3MPa, and the speed of the large cylinder is 190m / min to complete the drying and shaping of the paper sheet.

[0055] Calendering: After drying, the paper sheet enters the soft calender, the pressure of the soft calender roll is controlled at 0.45MPa, the speed of the soft calender roll is adjusted to 190m / min, and the paper machine speed is matched to 185m / min for calendering; after calendering, the paper is slit and wound to obtain the finished paper.

[0056] The remaining raw materials and preparation process are the same as in Example 1.

[0057] Comparative Example 1 Compared with Example 1, the antioxidant in this comparative example is replaced with tea polyphenols and sodium phytate in a mass ratio of 5:2, while the other raw materials and preparation process remain the same as in Example 1.

[0058] Comparative Example 2 Compared with Example 1, the difference in this comparative example is that the phosphorylated fiber is replaced with untreated bamboo fiber, while the other raw materials and preparation process remain the same as in Example 1.

[0059] Comparative Example 3 Compared with Example 1, the difference in this comparative example is that the antioxidant is replaced with tea polyphenols and sodium phytate in a mass ratio of 5:2, and the phosphorylated fiber is replaced with untreated bamboo fiber. The other raw materials and preparation process are the same as in Example 1.

[0060] Test case Performance tests were conducted on Examples 1-8 and Comparative Examples 1-3; Mechanical property tests: According to the test standards for paper dry strength in GB / T12914-2018 and paper wet strength in GB / T465.2—2008, the paper sample size is 120mm x 15mm. Each sample is tested 10 times, and the average value is taken to obtain the maximum tensile force. Based on the maximum tensile force, paper basis weight, and sample width, the tensile index (T) of the paper is calculated using the formula: T = F / ( W × b Where: F is the maximum tensile force (N); W Paper basis weight (g·m -2 ); b The sample width is in meters (m).

[0061] Yellowing resistance test: According to GB / T464-2008, four experimental paper samples with a size of 23cm×15cm were placed in a constant temperature drying oven at 105℃ to conduct a simulated dry heat aging test, and the decrease rate of dry tensile strength after 30 days of aging was recorded.

[0062] The results are shown in Table 1: Table 1

[0063] Table 1 shows the synergistic effect of phosphorylated fibers and composite antioxidant microspheres in the present invention. Examples 1 to 8 all used phosphorylated fibers and tea polyphenol-sodium phytate / chitosan-chitosan quaternary ammonium salt composite antioxidant microspheres, with their interference tensile strength generally ranging from 24.1 to 26.8 N·m. 2 The wet tensile strength is between 5.0 and 6.1 N·m / g. 2 The strength reduction rate after aging ranged from 10.05% to 12.04% between / g and . Comparative Example 1, which replaced the antioxidant microspheres with tea polyphenols and sodium phytate (while retaining phosphorylated fibers), resulted in a higher loss of antioxidants. Comparative Example 2, which replaced the phosphorylated fibers with ordinary bamboo fibers (while retaining the composite antioxidant microspheres), still showed better aging performance than Comparative Example 3, but its dry and wet strength decreased significantly. The comparison shows that the ionic cross-linking network constructed by phosphorylated fibers significantly improves dry and wet strength, while the slow-release free radical scavenging effect of the composite antioxidant microspheres significantly delays thermal aging degradation. The two work synergistically to protect the overall performance of the film base paper.

[0064] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0065] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for preparing a protective film base paper, characterized in that, Includes the following steps: The raw paper pulp and water are mixed and pulped. Caustic soda is added and the pulp is beaten. After beating, aluminum sulfate and starch are added in sequence. After stirring, anionic dispersible rosin gum, release agent, antioxidant and phosphorylated cellulose are added to obtain mixed pulp. The mixed pulp is formed, pressed, dried, and calendered to obtain the protective film base paper; the antioxidant is a composite antioxidant microsphere of tea polyphenol-sodium phytate / chitosan-chitosan quaternary ammonium salt.

2. The preparation process of the protective film base paper according to claim 1, characterized in that, The base pulp consists of 60%–70% hardwood pulp and 30%–40% softwood pulp.

3. The preparation process of the protective film base paper according to claim 1, characterized in that, The pulp concentration is controlled at 3%–3.5% during pulping; the pulp freeness is monitored and adjusted to 31–45°SR during pulping.

4. The preparation process of the protective film base paper according to claim 1, characterized in that, The stripping agent is one of white oil, soybean oleic acid, and polydimethylsiloxane; Starch is one of cassava cationic starch and corn oxidized starch.

5. The preparation process of a protective film base paper according to claim 1, characterized in that, The amount of caustic soda added per ton of protective film base paper is 10-14 kg, aluminum sulfate is 35-45 kg, starch is 3-5 kg, antioxidant is 0.2-0.3 kg, and phosphorylated cellulose is 10-20 kg.

6. The preparation process of the protective film base paper according to claim 1, characterized in that, The phosphorylated cellulose is prepared by the following steps: Wood fibers are ground and pulverized, and water is added to make a slurry. Sodium hydrogen phosphate and sodium dihydrogen phosphate (12%-20% by weight of wood fibers) are mixed with water to obtain a phosphate solution. Urea (3%-4% by weight of wood fibers) is then added to make a treatment solution. The slurry and treatment solution are mixed and reacted at 110-120℃ for 1.5-2 hours. After the reaction is completed, the mixture is washed with water and dried to obtain phosphorylated fibers.

7. The preparation process of a protective film base paper according to claim 6, characterized in that, Wood fiber is one of jute fiber and bamboo fiber.

8. The preparation process of a protective film base paper according to claim 6, characterized in that, The mass ratio of disodium hydrogen phosphate to sodium dihydrogen phosphate is 1:

1.

9. The preparation process of a protective film base paper according to claim 1, characterized in that, Antioxidants are prepared through the following steps: An antioxidant was prepared by using chitosan and chitosan quaternary ammonium salt as a composite carrier, co-loading tea polyphenols and sodium phytate, and using citric acid as a crosslinking agent via an emulsification-chemical crosslinking method.

10. The preparation process of a protective film base paper according to claim 9, characterized in that, The mass ratio of chitosan to chitosan quaternary ammonium salt is 1:1.

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