Food-grade high-water-resistance high-stiffness paper cup base paper, preparation method and application thereof

Abstract

The application discloses a food-grade high-water-resistance high-stiffness paper cup base paper and a preparation method and application thereof. The paper cup base paper comprises a paper cup base paper base material and a water-based acrylic resin coating layer coated on at least one surface of the paper cup base paper base material; the water-based acrylic resin coating layer is formed by a coating composition comprising a water-based acrylic resin emulsion and pigments; the water-based acrylic resin emulsion is composed of methyl methacrylate, butyl acrylate, vinyl neodecanoate, an initiator and a curing agent. The preparation method comprises pulp preparation, wire laying, pressing, drying, coating and secondary drying. The obtained food-grade high-water-resistance high-stiffness paper cup base paper has high water barrier effect, high stiffness, can be recycled, is biodegradable and has good environmental protection.

Description

Technical Field

[0001] This invention belongs to the field of special paper-based new materials, and specifically relates to a food-grade high water-resistant and high stiffness paper cup base paper, its preparation method, and its application. Background Technology

[0002] With the improvement of people's living standards and the enhancement of environmental awareness, traditional plastic food packaging materials cause irreversible white pollution to the environment and harm human health, and can no longer meet the needs of green and high-quality economic and social development. Paper-based packaging materials have advantages such as good biocompatibility, biodegradability, and recyclability, making them an ideal alternative to traditional plastic food packaging materials.

[0003] However, paper's main component is cellulose fiber, which contains abundant hydroxyl groups on its surface. Furthermore, paper has a porous structure, resulting in poor barrier properties and strong water absorption. Therefore, a hydrophobic film is typically coated onto the surface of the packaging paper to improve the water resistance of paper cups. A common method to improve the water resistance of paper cup base paper is polyethylene (PE) lamination. However, PE lamination leads to problems such as difficulty in paper-plastic separation, microplastic hazards, white pollution, and the non-biodegradability of the lamination layer. Among these, the potential health hazards of microplastics have received widespread attention in recent years. Additionally, the hydrophilicity and flexibility of cellulose also result in poor stiffness of paper cups, affecting the consumer experience. Therefore, developing new environmentally friendly, biodegradable, food-grade, highly water-resistant, and highly stiff alternative plastic-resistant paper cup base paper has become an urgent problem to be solved by the paper-based packaging industry. Summary of the Invention

[0004] To address the problems of poor water resistance and low stiffness of existing paper cup base paper, or the environmental pollution caused by the use of non-degradable PE coating layers, this paper provides a food-grade high water-resistant and high stiffness paper cup base paper that combines excellent water resistance, high stiffness, biodegradability, and safety and environmental protection, as well as its preparation method and application.

[0005] The first aspect of this invention is to provide a food-grade high water-resistant and high stiffness paper cup base paper, comprising a paper cup base paper substrate and an aqueous acrylic resin coating coated on at least one surface of the base paper substrate; the aqueous acrylic resin coating is formed by a coating composition comprising an aqueous acrylic resin emulsion and pigments, wherein the aqueous acrylic resin emulsion is composed of methyl methacrylate, butyl acrylate, vinyl decanoate, an initiator and a curing agent.

[0006] Further, the coating composition comprises the following components in parts by weight: 60-90 parts of waterborne acrylic resin emulsion, 3-8 parts of nano titanium dioxide, 1.5-2.5 parts of dispersant, 20-40 parts of filler, 4-6 parts of antibacterial agent, and 10-20 parts of deionized water.

[0007] Furthermore, the waterborne acrylic resin emulsion is copolymerized from the following components in parts by weight: 35-45 parts methyl methacrylate, 20-25 parts butyl acrylate, 3-5 parts vinyl decanoate, 0.6-1.5 parts initiator, and 10-24 parts curing agent.

[0008] Furthermore, the initiator is ammonium persulfate, and the curing agent is hexamethylene diisocyanate.

[0009] The preparation process of the waterborne acrylic resin emulsion is as follows: In a reactor equipped with a stirring device, thermometer, reflux condenser, and dropping device, 100 parts of water and 5-8 parts of emulsifier (Tween 80) are added, and the temperature is raised to 80°C. Under stirring conditions, 35-45 parts of methyl methacrylate, 20-25 parts of butyl acrylate, and 3-5 parts of vinyl decanoate are added, and the mixture is kept at this temperature and stirred for 15 minutes to form a pre-emulsion. 0.6-1.5 parts of initiator (ammonium persulfate) are added dropwise to the pre-emulsion. The temperature of the entire process is controlled at around 80°C and carried out under a nitrogen protective atmosphere. The dropwise addition operation is completed within 3-4 hours, and then the mixture is kept at this temperature for 4 hours to complete the polymerization. Finally, 10-24 parts of curing agent (hexamethylene diisocyanate) are added, and the mixture is cooled before being discharged to obtain the waterborne acrylic resin emulsion.

[0010] Furthermore, the paper cup base paper substrate is a plant fiber base paperboard made by blending softwood pulp fiber and hardwood pulp fiber.

[0011] A second aspect of the present invention is to provide a method for preparing food-grade high water-resistant and high stiffness paper cup base paper, comprising the following steps: 1) Pulp preparation: The surface layer, core layer, and bottom layer pulp raw materials (pulp board) are processed by a high-consistency hydraulic pulper (15-18%), screened, and beaten, and then compounded with fillers, additives, and other chemicals to obtain the pulp for each layer. The basis weight of the finished paper is designed to be 200 g / m². 2 ; 2) Netting: The surface layer slurry, core layer slurry and bottom layer slurry obtained in step 1) are compounded after being filtered in the netting section to obtain a composite slurry. The concentration of the surface layer, core layer and bottom layer netting slurry is 0.1-0.25%, and the netting speed is 305m / min. 3) Pressing: The composite slurry obtained in step 2) is first dehydrated by pressing with a vacuum press roller at a pressure of 30-60 kN / m and a vacuum degree of 45-59 kPa, and then pressed with a large-diameter press roller at a pressure of 1500-1700 kN / m. 4) Drying: The composite pulp after pressing and dewatering in step 3) is dried using a combination of double-row, multi-group drying cylinders (e.g., 2-6 groups, each group containing 6-12 drying cylinders). The drying temperature rise curve is as follows: 40-60℃ for 30 minutes, 60-80℃ for about 30 minutes, and 80-120℃ for about 30 minutes. The cylinder surface temperature rises sequentially from 40℃ to 120℃, drying the moisture content in the pulp to 5-10%, thus obtaining the base paper substrate. 5) Coating: Coat at least one surface of the base paper substrate obtained in step 4) with a water-based acrylic resin coating by blade coating. 6) Secondary drying: The base paper substrate coated with water-based acrylic resin in step 5) is dried by a combination of drying cylinder drying and bridge-type wind box drying. The drying cylinder temperature is 120-130℃, the bridge-type wind box temperature is 120-160℃, the wind speed is 20-50 m / s, and the circulating hot air accounts for about 60%, to obtain food-grade high water resistance and high stiffness paper cup base paper.

[0012] Further, in step 1), the surface slurry comprises softwood pulp fiber and hardwood pulp fiber in a mass ratio of 2:1, the core slurry comprises softwood pulp fiber and hardwood pulp fiber in a mass ratio of 1:1, and the bottom slurry comprises softwood pulp fiber and hardwood pulp fiber in a mass ratio of 1:2.

[0013] Furthermore, the surface layer slurry also includes the following raw materials in the following weight proportions: 20-30% calcium carbonate (relative to the oven-dryness of the slurry), 0.05-0.4 wt.% CPAM, 0.5-3.0% cationic starch, and 0.2-0.5% AKD; the core layer slurry and the bottom layer slurry also include the following raw materials in the following weight proportions: 20-30% talc, 0.05-0.4 wt.% CPAM, and 0.5-3.0% cationic starch.

[0014] Further, in step 3), the pressure of the vacuum press roller is 30-60 kN / m, and the vacuum degree is 45-59 kPa; the pressure of the large-diameter press roller is 1500-1700 kN / m; the drying method in step 4) is double-row multi-group drying cylinder drying, and the heating curve of the drying cylinder is: 40-60℃ for 30 min, 60-80℃ for 25-35 min, and 80-120℃ for 25-35 min.

[0015] Furthermore, before step 5) coating, a step of surface sizing of the base paper substrate is included, wherein the surface sizing uses an alkyl ketene dimer sizing solution.

[0016] Furthermore, in step 5), a doctor blade is used for double-sided coating, wherein the coating amount on the front side is 3–5 g / m².2 The coating amount on the back side is 5-10 g / m². 2 .

[0017] A third aspect of the present invention is to provide the application of the above-mentioned food-grade high water-resistant and high stiffness paper cup base paper in the preparation of paper cups or food packaging boxes.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1) Compared with traditional PE coated paperboard, the food-grade high water-resistant and high stiffness paper cup base paper of the present invention is biodegradable, has no white pollution, can be recycled, does not have the problem of difficult paper-plastic separation, and has good environmental performance; 2) The water-based acrylic resin emulsion coating used in this invention has good film-forming properties, so it has excellent density and barrier properties. It can effectively isolate common drinking liquids such as cold water, hot water, and coffee. Moreover, the film has high gloss and good transparency after formation. 3) The food-grade paper cup base paper described in this invention has high stiffness (15.68 mN·m). The high stiffness comes from the synergistic effect of optimized pulp formula, multi-layer papermaking process and surface strengthening treatment (sizing, coating and soft calendering, etc.). After the paper cup is made, it is not easy to bend or collapse when held, thus providing a better comfortable experience in actual use. 4) Compared with traditional PE coated paperboard, the food-grade high water-resistant and high stiffness paper cup base paper waterproof coating of the present invention is a healthy, environmentally friendly and biocompatible water-based acrylic resin emulsion, which contains no or only a very small amount of organic solvents (VOC, volatile organic compounds), and does not pose any health hazards such as microplastic release, and is harmless to human health. 5) Compared with traditional coating processes, which involve papermaking and coating separately and require a dedicated coating machine, the equipment is complex, the production line investment is large, and the energy consumption is relatively high. The production process described in this invention can be completed in one step on the papermaking line, eliminating the transportation, energy consumption, and paper loss of secondary processing. Therefore, the production process is simple, the production efficiency is high, and the production cost is significantly reduced. 6) The water-based acrylic resin emulsion coating of the present invention can be applied by various methods such as spraying, roller coating, brushing, dipping, and scraping, and has a higher tolerance for the construction environment (such as humidity) than other water-based systems (such as water-soluble resins); in addition, the coating tools (brushes, spray guns, coating rollers, scrapers, etc.) only need to be cleaned with water after use, without the need for organic solvents, which saves costs and protects workers' health. 7) The food-grade high water-resistant and high stiffness paper cup base paper described in this invention can effectively replace the use of PE coated paper cup base paper. The prepared high water-resistant acrylic resin coated paper cup base paper can be decomposed and recycled, significantly reducing recycling costs. This represents a technological breakthrough and fills the technological gap in food-grade high water-resistant and high stiffness paper cup base paper both domestically and internationally. Detailed Implementation

[0019] To better understand this technical solution, the present invention will be further described below with reference to specific embodiments.

[0020] Example 1

[0021] Preparation of waterborne acrylic resin emulsion: In a reactor equipped with a stirrer, thermometer, reflux condenser, and dropping device, 100 parts of water and 6 parts of emulsifier Tween 80 were added, and the temperature was raised to 80°C. Under stirring conditions, 35 parts of methyl methacrylate, 20 parts of butyl acrylate, and 4 parts of vinyl neodecanoate were added, and the mixture was kept at this temperature and stirred for 15 min to form a pre-emulsion. 1.0 part of initiator ammonium persulfate was dissolved in a small amount of water and added dropwise to the pre-emulsion. The entire process was carried out at approximately 80°C under a nitrogen atmosphere, and the dropwise addition was completed within 3.5 h. Polymerization was then completed by holding the mixture at this temperature for 4 h. Finally, 16 parts of curing agent hexamethylene diisocyanate were added, and the mixture was stirred for 1 h before cooling and discharging to obtain the waterborne acrylic resin emulsion.

[0022] Preparation of waterborne acrylic resin coating: Take 60 parts of the acrylic resin emulsion prepared above, add 8 parts of nano titanium dioxide, 2.5 parts of dispersant (BYK D-108 from Germany), 40 parts of filler, 6 parts of antibacterial agent (2-methyl-4-isothiazolin-3-one) and 20 parts of deionized water, add water to adjust the coating concentration to about 10% solid content, and place it in a high-speed shear disperser for shearing treatment for 10 min to obtain waterborne acrylic resin coating.

[0023] Preparation of base paper substrate: 1) Pulp preparation: The paper cup substrate is composed of three composite layers: surface layer, core layer, and bottom layer; Surface pulp: Softwood pulp to hardwood pulp in a mass ratio of 2:1, with the addition of 20% calcium carbonate, 0.05 wt.% CPAM, 1.5% cationic starch and 0.3% AKD relative to the oven-dry weight of the pulp; Core pulp: Softwood pulp to hardwood pulp in a 1:1 mass ratio, with the addition of 25% talc, 0.1 wt.% CPAM, and 2.0% cationic starch relative to the oven-dry weight of the pulp.

[0024] The base pulp consists of softwood pulp and hardwood pulp in a mass ratio of 1:2, with the addition of 30% talc, 0.3 wt.% CPAM, and 3.0% cationic starch relative to the oven-dry weight of the pulp.

[0025] The pulp boards of the above layers are broken down by a high-consistency hydraulic pulper (concentration 15-18%), and after screening and pulping, they are compounded with fillers and additives. The basis weight of the finished paper is designed to be 200 g / m².

[0026] 2) Web bonding: The surface layer, core layer and bottom layer pulps are filtered through the wire section. The pulp concentration on the wire is 0.25% and the wire bonding speed is 305 m / min. Then they are laminated to obtain a composite wet paper web.

[0027] 3) Pressing: The composite wet paper web is first pressed by a vacuum press roll at a pressure of 45 kN / m and a vacuum degree of 50 kPa, and then pressed by a large-diameter press roll at a pressure of 1500 kN / m.

[0028] 4) Drying: Four sets of drying cylinders, with 10 cylinders in each set, are used for drying. The drying temperature rise curve is as follows: 50℃ for 30 min, 70℃ for 30 min, and 120℃ for 30 min. The cylinder surface temperature is increased sequentially from 50℃ to 120℃ to dry the paper web moisture content to about 5% to obtain the base paper substrate.

[0029] 5) Surface Sizing: AKD surface sizing is applied to the back of the base paper substrate. AKD sizing solution preparation: Solid AKD is heated to 70–75°C in a reactor and stirred for 2–3 minutes. Cationic starch (15% of the AKD mass) and water are added to another reactor and heated to 80°C with stirring until homogeneous. Under high-speed stirring at 11000 r / min, the molten AKD is added to the cationic starch aqueous solution and stirred for 10–15 minutes. After homogenization, the solution is diluted with cold water to a concentration of 20% to obtain the AKD sizing solution. Sizing is applied using an impregnation roller at a rate of 2.0 g / m².

[0030] 6) Coating: A doctor blade coating method is used to coat the back side (sizing side) of the sizing base paper substrate. The coating amount is 8 g / m², and the front side is not coated.

[0031] 7) Secondary drying: A combination of drying cylinder drying and bridge-type air box drying is used. The drying cylinder temperature is 130℃, and the bridge-type air box drying temperature is 150℃.

[0032] 8) Soft calendering: The dried paper is soft calendered and then wound to obtain food-grade high water resistance and high stiffness paper cup base paper.

[0033] Example 2

[0034] The paper cup base paper and its preparation method in this embodiment are the same as in Example 1, except that: Step 6) In the coating operation, change the single-sided coating to double-sided coating, with a coating amount of 4 g / m² on the front side. 2 The coating amount on the back side is 7 g / m 2 Step 5) The surface sizing process remains unchanged. The final product is food-grade, highly water-resistant, and highly stiff paper cup base paper.

[0035] Example 3

[0036] The paper cup base paper and its preparation method in this embodiment are repeated from Embodiment 2, except that: Step 1) In the preparation of the waterborne acrylic resin emulsion, 35 parts of methyl methacrylate were changed to 38 parts, 20 parts of butyl acrylate were changed to 21 parts, and the dosage and operation of other components were the same as in Example 1.

[0037] The final product is food-grade paper with high water resistance and high stiffness for paper cups.

[0038] Example 4

[0039] The paper cup base paper and its preparation method in this embodiment are repeated from Embodiment 2, except that: In step 1) of preparing the waterborne acrylic resin emulsion, 35 parts of methyl methacrylate were changed to 41 parts, and 20 parts of butyl acrylate were changed to 23 parts. The amounts of other components and the operation were the same as in Example 1. Finally, food-grade high water-resistant and high stiffness paper cup base paper was obtained.

[0040] Example 5

[0041] The paper cup base paper and its preparation method in this embodiment are repeated from Embodiment 2, except that: In step 1) of preparing the waterborne acrylic resin emulsion, 35 parts of methyl methacrylate were changed to 45 parts, and 20 parts of butyl acrylate were changed to 25 parts. The dosage and operation of other components were the same as in Example 1. Finally, food-grade high water-resistant and high stiffness paper cup base paper was obtained.

[0042] Comparative Example 1 The paper cup base paper preparation method of this comparative example is the same as that of Example 1, except that: Replace the water-based acrylic resin coating in step 2) with polyvinyl alcohol (PVA) coating.

[0043] Preparation of PVA coating: 10 parts of PVA (PVA26-99) were added to water, swelled and dispersed at 65°C, and then heated to 90°C and stirred until completely dissolved. After cooling, a 10 wt.% solution was prepared. Then, 8 parts of nano-titanium dioxide, 2.5 parts of dispersant (BYK-163), 40 parts of calcium carbonate, and 6 parts of 2-methyl-4-isothiazolin-3-one were added. Water was added to adjust the solid content to 10%, and the mixture was sheared and dispersed for 10 min to obtain the PVA coating. Other operations were the same as in Example 1, and the final paper cup base paper was obtained.

[0044] Comparative Example 2 The preparation method of the paper cup base paper in this comparative example is a repeat of Example 2 (double-sided coating), except that: in step 1) the preparation of the water-based acrylic resin emulsion, vinyl decanoate monomer is not added, and the amount of methyl methacrylate is increased accordingly to make up the parts. Other components and operations are the same as in Example 1. The final paper cup base paper is obtained.

[0045] Comparative Example 3 The preparation method of the paper cup base paper in this comparative example is the same as that in Comparative Example 2 (without vinyl decanoate, double-sided coating), except that step (5) AKD surface sizing process is omitted. Other operations are the same as in Comparative Example 2, and the paper cup base paper is finally obtained.

[0046] Performance testing The paper cup base paper prepared in Examples 1-5 and Comparative Examples 1-3 was subjected to performance tests, with commercially available PE-coated paper cup base paper used as a control. The test standards are as follows: 1. The waterproof performance (Cobb value) was determined in accordance with the standard GB / T 1540-2002.

[0047] 2. Stiffness was measured in accordance with standard GB / T 22364-2018.

[0048] 3. Tensile strength was determined in accordance with standard GB / T 12914-2008.

[0049] 4. Biodegradability and leakage performance were determined according to standard GB / T 27590-2022. Leakage performance is 0 for failure, + for success, and ++ for excellent results. Test results are shown in Table 1.

[0050] Table 1

[0051] As can be seen from the data in Table 1, the paper cup base paper described in this invention possesses excellent water resistance, stiffness, and biodegradability. The water-based acrylic resin coating significantly improves the water resistance of the paper cup base paper, and the introduction of the neodecanoic acid vinyl ester functional monomer further enhances its water resistance. Table 1 also shows that the paper cup base paper described in this invention exhibits good leak-proof performance against hot water, making it suitable for hot cups.

[0052] Security testing: The paper cup base paper of Example 5 was tested for harmful substance content, and the results are shown in Table 2. The test results show that the content of harmful substances such as lead, arsenic, and formaldehyde in the paper cup base paper of the present invention is far below the national standard limit for food-grade packaging materials, and meets food safety requirements.

[0053] Table 2: Test Report .

Claims

1. A food-grade, high-water-resistant, high-stiffness paper cup base paper, characterized in that, Includes a paper cup base material and an aqueous acrylic resin coating applied to at least one surface of the base material; The waterborne acrylic resin coating is formed from a coating composition comprising a waterborne acrylic resin emulsion and pigments, wherein the waterborne acrylic resin emulsion comprises methyl methacrylate, butyl acrylate, vinyl decanoate, an initiator, and a curing agent.

2. The food-grade high water-resistant and high stiffness paper cup base paper as described in claim 1, characterized in that, The coating composition comprises the following components in parts by weight: 60-90 parts of waterborne acrylic resin emulsion, 3-8 parts of nano titanium dioxide, 1.5-2.5 parts of dispersant, 20-40 parts of filler, 4-6 parts of antibacterial agent, and 10-20 parts of deionized water.

3. The food-grade high water-resistant and high stiffness paper cup base paper as described in claim 2, characterized in that, The waterborne acrylic resin emulsion is copolymerized from the following components in parts by weight: 35-45 parts methyl methacrylate, 20-25 parts butyl acrylate, 3-5 parts vinyl decanoate, 0.6-1.5 parts initiator, and 10-24 parts curing agent.

4. The food-grade high water-resistant and high stiffness paper cup base paper as described in claim 3, characterized in that, The initiator is ammonium persulfate, and the curing agent is hexamethylene diisocyanate.

5. The food-grade high water-resistant and high stiffness paper cup base paper as described in claim 1, characterized in that, The paper cup base material is a plant fiber paperboard made from a blend of softwood pulp fiber and hardwood pulp fiber.

6. The method for preparing food-grade high water-resistant and high stiffness paper cup base paper according to any one of claims 1-5, characterized in that, Includes the following steps: 1) Slurry preparation: The surface layer, core layer and bottom layer slurries are prepared separately to obtain the slurry for each layer; 2) Netting: The surface layer slurry, core layer slurry and bottom layer slurry obtained in step 1) are compounded after being filtered through the net to obtain a composite slurry; 3) Pressing: The composite slurry obtained in step 2) is first pressed and dewatered by vacuum press rollers, and then pressed and dewatered by large-diameter press rollers; 4) Drying: The composite pulp after pressing and dewatering in step 3) is dried to obtain the base paper substrate; 5) Coating: Coat at least one surface of the base paper substrate obtained in step 4) with a water-based acrylic resin coating by blade coating. 6) Secondary drying: The base paper substrate coated with water-based acrylic resin in step 5) is dried to obtain food-grade high water resistance and high stiffness paper cup base paper.

7. The method for preparing food-grade high water-resistant and high stiffness paper cup base paper as described in claim 6, characterized in that, In step 1), the surface slurry comprises softwood pulp fiber and hardwood pulp fiber in a mass ratio of 2:1, the core slurry comprises softwood pulp fiber and hardwood pulp fiber in a mass ratio of 1:1, and the bottom slurry comprises softwood pulp fiber and hardwood pulp fiber in a mass ratio of 1:

2.

8. The method for preparing food-grade high water-resistant and high stiffness paper cup base paper as described in claim 7, characterized in that, The surface slurry further includes the following raw materials in the following weight proportions: 20-30% calcium carbonate (relative to the oven-dryness of the slurry), 0.05-0.4 wt.% CPAM, 0.5-3.0% cationic starch, and 0.2-0.5% AKD; the core slurry and the bottom slurry further include the following raw materials in the following weight proportions: 20-30% talc, 0.05-0.4 wt.% CPAM, and 0.5-3.0% cationic starch.

9. The method for preparing food-grade high water-resistant and high stiffness paper cup base paper as described in claim 6, characterized in that, In step 3), the pressure of the vacuum press roller is 30-60 kN / m and the vacuum degree is 45-59 kPa; the pressure of the large diameter press roller is 1500-1700 kN / m; in step 4), the drying method is double-row multi-group drying cylinder drying, and the heating curve of the drying cylinder is: 40-60℃ for 30 min, 60-80℃ for 25-35 min, and 80-120℃ for 25-35 min.

10. The method for preparing food-grade high water-resistant and high stiffness paper cup base paper as described in claim 6, characterized in that, Step 5) Before coating, the paper substrate is further sizing, wherein the sizing is performed using an alkyl ketene dimer sizing solution.

11. The method for preparing food-grade high water-resistant and high stiffness paper cup base paper as described in claim 6, characterized in that, In step 5), a doctor blade is used for double-sided coating, with the coating amount on the front side being 3–5 g / m². 2 The coating amount on the back side is 5-10 g / m². 2 .

12. The use of the food-grade high water-resistant and high stiffness paper cup base paper according to any one of claims 1-11 in the preparation of paper cups or food packaging boxes.

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