Acidic uncoated food casing paper and method for its production

Abstract

The application provides an acid uncoated food carton paper and a preparation method thereof. The preparation method comprises the following steps: preparing a slurry, wherein the slurry comprises paper pulp, a filler and an auxiliary agent, the filler is porcelain clay with a fluorine content of less than 50 mg / kg; papermaking under an acid condition; and product detection. The preparation method of the acid uncoated food carton paper provided in the application controls the introduction of fluorine-containing substances from the source, and then a safe and reliable acid uncoated food carton paper meeting the national standard is prepared.

Description

Technical Field

[0001] This application relates to the technical field of papermaking, specifically to an acidic uncoated food-grade cardboard and its preparation method. Background Technology

[0002] Due to its good stiffness, excellent printability, and moderate production cost, acid-coated uncoated food-grade cardboard has extremely wide applications in food packaging, baking containers, and catering utensils—packaging materials that come into direct contact with food. However, with the continuous upgrading of global food safety standards in recent years, the environmental and health risks of fluoride residues, especially per- and polyfluoroalkyl substances (PFAS), in food contact paper products have become a focus of international concern. Therefore, domestic and international regulatory agencies have introduced very strict restrictions, and acid-coated uncoated food-grade cardboard produced using traditional processes can no longer meet these standards.

[0003] The problem of PFAS in paper is most prominent in the recycling chain. The concentration of PFAS in post-consumer paper products is significantly higher than that in pre-consumer samples. Waste collection and recycling agreements have a direct and significant impact on the spread and accumulation of PFAS in the papermaking system. Therefore, simply replacing raw materials cannot solve the problem of internal circulation and accumulation.

[0004] As global restrictions on fluorides and PFAS in food contact paper products become increasingly stringent, the main compliance requirements can be summarized as follows: Domestic standards: Since the National Food Safety Standard for Food Contact Paper and Paperboard Materials and Products (GB4806.8-2024) and GB31604.1-2025 explicitly prohibit the use of additives containing PFAS, the industry association standard T / CNFIA 189-2024 sets the total fluoride content ≤50mg / kg as the safety threshold for food-grade cardboard.

[0005] International Standards: The EU 2022 / 204 regulation sets clear limits on single PFAS (≤ 25 ppb), total PFAS (≤ 250 ppb), and total fluoride (≤ 50 mg / kg), while the US FDA 21 CFR 176.170 and other regulations directly and strictly prohibit the use of persistent and bioaccumulative fluorides in food packaging. Therefore, there is a very clear difference between the two.

[0006] Traditional processes typically produce acidic uncoated food-grade cardboard with residual fluoride levels ranging from 80 to 150 mg / kg, and it is difficult to prove that PFAS are undetectable, thus failing to meet the aforementioned mandatory safety standards. Therefore, developing a papermaking process that can meet the compliance requirements of major global markets and consistently reduce residual fluoride levels to extremely low levels is a necessary prerequisite for achieving the high-end and internationalization of food-grade cardboard. Summary of the Invention

[0007] The first aspect of this application provides a method for preparing acidic uncoated food-grade cardboard, the method comprising: Prepare a pulp, wherein the pulp comprises paper pulp, filler and additives, and the filler is kaolin with a fluorine content of <50mg / kg; Papermaking under acidic conditions; Finished product inspection.

[0008] In some optional embodiments, the pulp is LBKP pulp or a mixture of LBKP pulp and waste pulp, wherein the fluorine content of the waste pulp is ≤15mg / kg.

[0009] In some optional embodiments, the pulping freeness of LBKP pulp is 350~400 mL.

[0010] In some optional embodiments, the additives include fluorine-free sizing agents, fluorine-free retention aids, and fluorine-free defoamers.

[0011] In some optional embodiments, the amount of the fluorine-free sizing agent added is 30~50 kg / t slurry, the fluorine-free retention aid includes 0~100 g / t slurry dry powder and 2~5 kg / t slurry silica, and the amount of the fluorine-free defoamer added is 700~900 mL / min.

[0012] In some optional embodiments, the amount of kaolin added is 85~150 kg / t paper.

[0013] In some optional embodiments, the preparation method further includes the step of setting up a sampling point at at least one of the white water pan, white water pool, and circulating water tower to monitor the fluoride content in the white water in real time.

[0014] In some optional embodiments, the preparation method further includes the step of: when the fluoride content in the white water reaches the warning threshold, increasing the white water discharge by 5% to 10% and simultaneously replenishing an equal amount of clean water.

[0015] In some optional embodiments, the preparation method further includes the steps of: when the fluoride content in the white water reaches the warning threshold, stopping the white water circulation and reflux, discharging the contaminated white water to the set lower limit of the liquid level, then replenishing clean water to the normal liquid level, and continuously and reliably measuring the fluoride concentration until it drops to a safe range; Wherein, the fluoride content of the warning threshold is ≥10mg / L, and the fluoride content of the alert threshold is ≥15mg / L.

[0016] Secondly, this application provides an acidic uncoated food cardboard, which is prepared using the preparation method described in the above embodiments.

[0017] The method for preparing acidic uncoated food-grade cardboard provided in this application controls the introduction of fluorine-containing substances from the source, thereby preparing safe and reliable acidic uncoated food-grade cardboard that meets national standards. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic flowchart of an embodiment of the method for preparing acidic uncoated food-grade cardboard according to this application; Figure 2 This is a schematic flowchart of another embodiment of the method for preparing acidic uncoated food-grade cardboard according to this application; Figure 3 This is a schematic diagram of the process flow nodes of the preparation method of this application. Detailed Implementation

[0020] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be particularly noted that the following embodiments are for illustrative purposes only and do not limit the scope of the application. Similarly, the following embodiments are only some, not all, embodiments of the present application, and all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present application.

[0021] The terms "first," "second," and "third" used in the embodiments of this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. All directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationships and movement of components in a specific posture (as shown in the figures). If the specific posture changes, the directional indication will also change accordingly. The terms "comprising" and "having," and any variations thereof, in the embodiments of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or components inherent to these processes, methods, products, or devices.

[0022] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0023] In conventional technical solutions, the introduction of fluorine mainly involves the following aspects: 1. The filler is mainly talc, and its mineral source is associated with fluorine-containing minerals. The measured total fluorine content generally reaches more than 100 mg / kg, which is the main source of residual fluorine in paper. 2. The flaky structure of talc powder easily adsorbs free fluorides in the system, and the continuous accumulation of fluorides occurs as waste paper is recycled and reused. 3. Chemicals such as wet-end additives and sizing agents often contain fluorine components, continuously introducing exogenous fluorine into the system; 4. Closed-loop white water circulation exacerbates fluoride accumulation, and conventional processes lack effective removal methods; 5. Existing methods for reducing fluoride levels mostly involve replacing a single additive or localized treatment, without forming a complete chain control system, resulting in unstable and fluctuating fluoride reduction effects.

[0024] The purpose of this invention is to overcome the shortcomings of conventional technologies and provide a papermaking process to improve the residual fluoride content of acidic uncoated food-grade cardboard, achieving a stable residual fluoride content of ≤10mg / kg and undetectable PFAS, while maintaining the stability of the acidic papermaking system and ensuring that the paper strength, uniformity, printability, and other indicators do not decline. This process does not require modification of existing equipment, is suitable for continuous industrial production, and completely solves the industry problems of fluoride cycling and accumulation and unstable fluoride reduction effects, enabling products to meet stringent domestic and international food contact safety standards.

[0025] Please see Figure 1 , Figure 1 This is a schematic flowchart of an embodiment of the preparation method of acidic uncoated food cardboard of this application, which includes, but is not limited to, the following steps.

[0026] Step S100: Prepare slurry.

[0027] In this step, the pulp includes paper pulp, fillers, and additives. The paper pulp can be 100% fresh LBKP pulp with a beating freeness of 350~400mL, and the specific beating freeness can be 350mL, 355mL, 360mL, 380mL, 390mL, 400mL, etc.

[0028] Alternatively, the pulp can be a mixture of LBKP (bleached softwood pulp) pulp and waste pulp, wherein the proportion of waste pulp does not exceed 30%. In this embodiment, the fluoride content of the waste pulp is ≤15mg / kg.

[0029] Completely discontinue the use of recycled waste paper containing talc. During the initial stage of production and when changing product types, completely remove all original waste paper pulp from the surface, core, and bottom layers from the system. Establish an independent clean waste paper collection system to collect only waste paper produced from fluorine-free raw materials for graded, targeted, and pollution-free reuse. Define the criteria for clean waste paper: ① It originates from this process; ② It is not mixed with waste paper containing talc; ③ The total fluorine content is ≤15mg / kg after random sampling. Waste paper that does not meet the above standards shall be downgraded or sold externally and shall not be reused.

[0030] The filling material system is replaced with a low-fluoride alternative, ceasing the use of high-fluoride talc filler and replacing it with low-fluoride kaolin clay. The core requirements for the kaolin clay are: total fluoride content <50mg / kg, high chemical stability, and no adsorption of free fluorides within the system. This completely eliminates fluoride input from talc at the mineral source, solving the core problem of fluoride input in traditional processes. The amount of kaolin clay added is 85~150kg / t paper, specifically 85kg / t paper, 90kg / t paper, 100kg / t paper, 110kg / t paper, 120kg / t paper, and 150kg / t paper.

[0031] Optionally, the additives used in this embodiment are fluorine-free additives, free of PFOA, PFOS and their salts, and without the addition of any fluorinated surfactants. All papermaking chemicals, such as sizing agents, surface sizing agents, retention and filtration aids, and defoamers, are all fluorine-free environmentally friendly additives.

[0032] Establish an access system for testing the fluorine content of additives. All additives must be tested for fluorine and PFAS content before use, and only those that pass the test can be put into use, thus eliminating external fluorine pollution at the source.

[0033] In this embodiment, the additives may specifically include a fluorine-free sizing agent, a fluorine-free retention aid, and a fluorine-free defoamer. The addition amount of the fluorine-free sizing agent is 30~50 kg / t of slurry, specifically 30 kg / t, 35 kg / t, 38 kg / t, 40 kg / t, 45 kg / t, 50 kg / t, etc. The fluorine-free retention aid includes 0~100 g / t of dry powder and 2~5 kg / t of silica. The addition amount of the fluorine-free defoamer is 700~900 mL / min, specifically 700 mL / min, 750 mL / min, 780 mL / min, 800 mL / min, 850 mL / min, and 900 mL / min, etc.

[0034] Please continue reading. Figure 1The preparation method of acidic uncoated food cardboard in this embodiment further includes step S200, papermaking under acidic conditions; and step S300, finished product testing.

[0035] In the finished product testing step, it is required that the total fluoride content be ≤10mg / kg and that the acidic uncoated food-grade cardboard be free of PFAS. The preparation method in this embodiment is applied in the preparation of food contact paper products that meet the standards of GB 4806.8-2024 and EU 2022 / 204.

[0036] The method for preparing acidic uncoated food-grade cardboard provided in this application controls the introduction of fluorine-containing substances from the source, thereby preparing safe and reliable acidic uncoated food-grade cardboard that meets national standards.

[0037] Please refer to the following: Figure 2 and Figure 3 , Figure 2 This is a schematic flowchart of another embodiment of the method for preparing acidic uncoated food-grade cardboard according to this application. Figure 3 This is a schematic diagram of the process flow nodes of the preparation method of this application. Figure 3 In the process, the main nodes include the core layer flow system (low-fluoride kaolin + fluoride-free additives + cleaning pulp) → flow system → wire section → press section → drying cylinder → fluoride-free sizing → calendering → finished paper rolls → cleaning waste paper classification, collection and reuse, etc.

[0038] The preparation method includes, but is not limited to, the following steps.

[0039] Step S100: Prepare slurry.

[0040] In this step, the pulp includes paper pulp, fillers, and additives. The paper pulp can be 100% fresh LBKP pulp with a beating freeness of 350~400mL, and the specific beating freeness can be 350mL, 355mL, 360mL, 380mL, 390mL, 400mL, etc.

[0041] Alternatively, the pulp can be a mixture of LBKP (bleached softwood pulp) pulp and waste pulp, wherein the proportion of waste pulp does not exceed 30%. In this embodiment, the fluoride content of the waste pulp is ≤15mg / kg.

[0042] Completely discontinue the use of recycled waste paper containing talc. During the initial stage of production and when changing product types, completely remove all original waste paper pulp from the surface, core, and bottom layers from the system. Establish an independent clean waste paper collection system to collect only waste paper produced from fluorine-free raw materials for graded, targeted, and pollution-free reuse. Define the criteria for clean waste paper: ① It originates from this process; ② It is not mixed with waste paper containing talc; ③ The total fluorine content is ≤15mg / kg after random sampling. Waste paper that does not meet the above standards shall be downgraded or sold externally and shall not be reused.

[0043] The filling material system is replaced with a low-fluoride alternative, ceasing the use of high-fluoride talc filler and replacing it with low-fluoride kaolin clay. The core requirements for the kaolin clay are: total fluoride content <50mg / kg, high chemical stability, and no adsorption of free fluorides within the system. This completely eliminates fluoride input from talc at the mineral source, solving the core problem of fluoride input in traditional processes. The amount of kaolin clay added is 85~150kg / t paper, specifically 85kg / t paper, 90kg / t paper, 100kg / t paper, 110kg / t paper, 120kg / t paper, and 150kg / t paper.

[0044] Optionally, the additives used in this embodiment are fluorine-free additives, free of PFOA, PFOS and their salts, and without the addition of any fluorinated surfactants. All papermaking chemicals, such as sizing agents, surface sizing agents, retention and filtration aids, and defoamers, are all fluorine-free environmentally friendly additives.

[0045] Establish an access system for testing the fluorine content of additives. All additives must be tested for fluorine and PFAS content before use, and only those that pass the test can be put into use, thus eliminating external fluorine pollution at the source.

[0046] In this embodiment, the additives may specifically include a fluorine-free sizing agent, a fluorine-free retention aid, and a fluorine-free defoamer. The addition amount of the fluorine-free sizing agent is 30~50 kg / t of slurry, specifically 30 kg / t, 35 kg / t, 38 kg / t, 40 kg / t, 45 kg / t, 50 kg / t, etc. The fluorine-free retention aid includes 0~100 g / t of dry powder and 2~5 kg / t of silica. The addition amount of the fluorine-free defoamer is 700~900 mL / min, specifically 700 mL / min, 750 mL / min, 780 mL / min, 800 mL / min, 850 mL / min, and 900 mL / min, etc.

[0047] Please continue reading. Figure 2 The preparation method of acidic uncoated food cardboard in this embodiment further includes step S200, papermaking under acidic conditions; and step S300, finished product testing.

[0048] In the finished product testing step, it is required that the total fluoride content be ≤10mg / kg and that the acidic uncoated food-grade cardboard be free of PFAS. The preparation method in this embodiment is applied in the preparation of food contact paper products that meet the standards of GB 4806.8-2024 and EU 2022 / 204.

[0049] Unlike the previous embodiments, the preparation method of acidic uncoated food cardboard in this embodiment further includes step S400, which involves setting a sampling point at at least one of the white water pan, white water pool, and circulating water tower to monitor the fluoride content in the white water in real time. Step S400 can be performed concurrently with step S200.

[0050] In step S400 of this embodiment, a dynamic control mechanism integrating monitoring, early warning, and graded replacement is established to address the fluoride accumulation problem caused by closed-loop white water circulation, as detailed below.

[0051] Total fluoride concentration should be monitored periodically using offline or online detection methods. A warning threshold of ≥10 mg / L and a warning threshold of ≥15 mg / L should be set for fluoride content. When the fluoride content in the white water reaches the warning threshold, increase the white water discharge rate by 5%–10%, and simultaneously add an equal amount of clean water to prevent further increases in fluoride content. When the fluoride content in the white water reaches the warning threshold, stop the white water circulation and backflow, discharge the contaminated white water to the set lower limit (the discharge rate should not be less than 30% of the total system capacity), then add clean water to the normal level, and continuously and reliably measure the fluoride concentration until it drops to a safe range. The safe range is a fluoride content ≤8 mg / L.

[0052] The following will describe several specific embodiments.

[0053] Implementation Case Description: This invention was implemented on a closed-loop paper machine with a speed of 1400~1500m / min and a basis weight of 210~350g / m² for producing acidic uncoated white cardboard. The following examples further verify the effectiveness of this process. All process parameters are based on the specific limitations of the claims. Example 1 Validation of fluoride reduction in a 100% fresh pulp system 1.1. Pulp system: 100% fresh LBKP pulp, with a pulping freeness of 350~400mL; 2.2. Filler: Low-fluoride kaolin, fluoride content <20mg / kg, addition amount 85~150kg / t paper; 3.3. Additives: Fluorine-free sizing agent (30~50kg / t slurry), fluorine-free retention aid (0~100g / t dry powder + 2~5kg / t silica), fluorine-free defoamer (700~900mL / min). 4.4. Waste Paper: Do not reuse waste paper containing talcum powder; only reuse clean waste paper that meets the defined standards. 5.5. Plain water: Test the fluoride content every 4 hours, and control it to <10mg / L. If it exceeds the standard, immediately start the corresponding replacement procedure; 6.6. Papermaking: Papermaking under acidic conditions, quantitative amount 250g / m²; 7.7. Finished product testing: Total fluorine content 6.2 mg / kg, PFAS not detected.

[0054] Implementation Case 2 10% Clean Paper Reuse and Fluoride Reduction Verification 1. Pulp: LBKP + clean waste paper (ratio 90:10), total fluoride content of clean waste paper ≤15mg / kg; 2. Filler: Low-fluoride kaolin, fluoride content <50mg / kg; 3. Additives: A fluorine-free additive system consistent with that in Example 1; 4. Plain water: Online real-time monitoring, warning value 10mg / L, alert value 15mg / L, tiered replacement initiated if the standard is exceeded; 5. Copying: The process is consistent with traditional techniques, without changing the machine speed or procedures; 6. Finished product testing: Total fluorine content 7.5 mg / kg, PFAS not detected.

[0055] Example 3 Stability verification of 30% high-proportion clean paper recycling 1.1. Pulp: LBKP + clean waste paper (ratio 70:30), total fluoride content of clean waste paper ≤15mg / kg; 2.2. Filler: Low-fluoride kaolin, fluoride content <30mg / kg, addition amount 100-120kg / t paper; 3.3. Additives: A fluorine-free additive system consistent with that of Example 1; 4.4. White water: Online monitoring showed 0 emergency replacement triggers after 30 days of continuous operation; 5.5. Copying: Vehicle speed 1450m / min, quantitative quantity 280g / m²; 6.6. Finished product testing: Total fluorine content was 8.1 mg / kg (5 consecutive samples, with a maximum value of 9.3 mg / kg and a minimum value of 7.2 mg / kg), and PFAS was not detected.

[0056] Comparative Example 1: Traditional Craftsmanship Using talc filler (fluorine content 144ppm), fluorine-containing additives, conventional waste paper recycling, and no monitoring or replacement of white water, the total fluorine content of the finished product was 86-132mg / kg, and PFAS was found to be excessive.

[0057] Comparative Example 2: Localized defluorination process by replacing only the packing material Simply replacing talc with low-fluoride kaolin, while still reusing fluoride-containing waste paper and using unmonitored white water, resulted in a total fluoride content of 32–45 mg / kg in the finished product, which still falls short of the industry's 50 mg / kg threshold. This demonstrates that a single process cannot effectively reduce fluoride levels.

[0058] It should be noted that the specific implementation methods of the present invention are as described in the above specific technical solutions and embodiments. The scope of protection of the present invention is not limited to the above embodiments. Any slight adjustments to the process parameters based on the technical solutions of the present invention (such as the amount of kaolin added, the amount of white water replacement discharge, the proportion of waste paper reuse, etc.) that do not deviate from the core process of the four-in-one integration of filler replacement, waste paper cleaning, fluoride-free additives, and dynamic monitoring of white water are all within the scope of protection of the present invention.

[0059] The method for preparing acidic uncoated food-grade cardboard in this embodiment accurately identifies and eliminates the mineral-source fluoride input from talc, achieving low-fluoride replacement of the filler system; it cuts off the fluoride cycle enrichment path caused by the recycling of fluoride-containing waste paper, establishes a clean fiber supply system, and clearly defines standards; it achieves fluoride-free auxiliaries throughout the papermaking process, eliminating the introduction of exogenous organic and inorganic fluoride; it establishes a dynamic monitoring and dual-threshold graded replacement mechanism for white water fluoride content to accurately prevent fluoride accumulation in the system; and it maintains the stability of the acidic papermaking system while reducing fluoride, ensuring that the core physical indicators and printability of the finished paper do not decline. This invention achieves a highly efficient and stable reduction of residual fluoride content in acidic uncoated food-grade cardboard through a four-in-one synergistic control process of source substitution, cycle blocking, complete fluoride-free production, and dynamic monitoring.

[0060] Compared with existing technologies, this preparation method has significant technological advancements and beneficial effects, with the following core advantages: 1. Significant and stable fluoride reduction effect: The residual fluoride content of finished paper is consistently ≤10mg / kg. Even with a 30% recycling rate of clean waste paper, there is still no risk of exceeding the standard, which is far superior to the domestic access standard of 50mg / kg and the EU 2022 / 204 limit requirements. PFAS is undetectable. 2. Complete control of fluoride at the source: Low-fluoride kaolin with a fluoride content of ≤50mg / kg is used to replace high-fluoride talc powder, eliminating the largest source of fluoride input in traditional processes, and reducing fluoride is fundamental and irreversible; 3. Completely block fluoride cycling and enrichment: By defining clean paper waste standards and using a graded collection system, the cyclic accumulation path of fluorides in the pulp-white water system is cut off, solving the industry problem of "PFAS propagation and enrichment during the recycling process" revealed by existing research. Long-term operation shows no rebound in fluoride reduction effect. 4. Safer by being fluorine-free throughout the entire process: The entire production line uses fluorine-free additives and has established a testing and access system. The system has no PFAS source, eliminating the introduction of exogenous fluorine from the chemical end, and greatly improving the safety of the finished product. 5. Global Compliance Coverage: Products manufactured using this process perfectly comply with all major domestic and international food contact safety standards, including China's GB 4806.8-2024, the European Union's EU2022 / 204, and the US FDA 21 CFR176.170, greatly enhancing product market competitiveness and compliance risk defense capabilities. 6. Strong industrial applicability: It does not change the original acid papermaking process, does not affect core indicators such as machine speed, paper strength / uniformity / printability, does not require equipment modification, does not increase production costs, is suitable for industrial continuous production, and is easy to promote in the industry; 7. Balancing resource recycling and fluoride reduction: Since a graded recycling system for clean waste paper is established while achieving efficient fluoride reduction, up to 30% of clean waste paper can be recycled. This effectively balances resource utilization and production economy, and naturally avoids raw material waste.

[0061] In summary, because the process of this invention can be directly applied to all closed-loop paper machines producing acidic uncoated food-grade cardboard, and only requires appropriate adjustments to the filler, additives, waste paper recycling, and white water monitoring processes according to the requirements of this invention, it can reliably and stably reduce residual fluoride content, thus showing excellent prospects for industrial application. More importantly, rigorous verification on actual production lines shows that the total fluoride content of the finished product produced by this process can be stably controlled within the range of 15–28 mg / kg, a reduction of over 37%, fully meeting the requirements of the latest food contact material safety standards. Simultaneously, the stability of paper machine operation is improved, and the paper breakage rate decreases by over 22%.

[0062] The above description is only a part of the embodiments of this application and does not limit the scope of protection of this application. Any equivalent device or equivalent process transformation made based on the content of this application specification and drawings, or direct or indirect application in other related technical fields, are similarly included in the patent protection scope of this application.

Claims

1. A method for preparing acidic uncoated food-grade cardboard, characterized in that, The preparation method includes: Prepare a pulp, wherein the pulp comprises paper pulp, filler and additives, and the filler is kaolin with a fluorine content of <50mg / kg; Papermaking under acidic conditions; Finished product inspection.

2. The preparation method according to claim 1, characterized in that, The pulp is LBKP pulp or a mixture of LBKP pulp and waste pulp, wherein the fluorine content of the waste pulp is ≤15mg / kg.

3. The preparation method according to claim 2, characterized in that, The freeness of LBKP pulp is 350~400mL.

4. The preparation method according to claim 1, characterized in that, The additives include fluorine-free sizing agents, fluorine-free retention aids, and fluorine-free defoamers.

5. The preparation method according to claim 4, characterized in that, The amount of the fluorine-free sizing agent added is 30~50kg / t slurry, the fluorine-free retention aid includes 0~100g / t slurry dry powder and 2~5kg / t slurry silica, and the amount of the fluorine-free defoamer added is 700~900mL / min.

6. The preparation method according to claim 1, characterized in that, The amount of kaolin added is 85~150 kg / t paper.

7. The preparation method according to claim 1, characterized in that, The preparation method further includes the step of setting up a sampling point at at least one of the white water pan, white water pool, and circulating water tower to monitor the fluoride content in the white water in real time.

8. The preparation method according to claim 7, characterized in that, The preparation method also includes the following steps: when the fluoride content in the white water reaches the warning threshold, increase the white water discharge by 5% to 10% and simultaneously replenish an equal amount of clean water.

9. The preparation method according to claim 8, characterized in that, The preparation method further includes the following steps: when the fluoride content in the white water reaches the warning threshold, stop the white water circulation and backflow, discharge the contaminated white water to the set lower limit of the liquid level, then add clean water to the normal liquid level, and continuously and reliably measure the fluoride concentration until it drops to a safe range. Wherein, the fluoride content of the warning threshold is ≥10mg / L, and the fluoride content of the alert threshold is ≥15mg / L.

10. An acidic uncoated food-grade cardboard, characterized in that, The acidic uncoated food cardboard is prepared using the preparation method described in any one of claims 1-9.

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