Environment-friendly bacteriostatic waterproof colored paper and preparation method thereof

Abstract

The application discloses an environment-friendly bacteriostatic waterproof colored paper and a preparation method thereof. The modified paper with improved performance is obtained by adding persimmon paint and a natural colorant in paper pulp and spraying the persimmon paint and the natural colorant on the surface of the paper. The composite treatment mode of the combination of the pulp adding and the surface spraying can significantly improve the mechanical strength, the hydrophobic waterproof performance and the bacteriostatic activity of the paper. The raw materials used in the application are all derived from nature, and the product can be biodegraded after being discarded, so that the pollution problem caused by synthetic chemicals is fundamentally solved.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, specifically to a colored paper with antibacterial and waterproof functions and its environmentally friendly preparation method. Background Technology

[0002] As an indispensable material in daily production and life, paper's applications are constantly expanding, and the functional requirements for paper are becoming increasingly stringent. For example, in the food packaging industry, paper needs to be waterproof to prevent grease penetration and moisture erosion; in the medical, book, and handicraft fields, paper is required to have certain antibacterial and antiseptic capabilities to extend its service life.

[0003] Currently, the mainstream technologies for imparting water resistance to paper rely primarily on fluorinated compounds (such as PFAS) or polyethylene (PE) coating. However, fluorinated compounds are bioaccumulative and potentially toxic, and their use has been restricted in many countries; while PE coating is difficult to recycle and degrade, causing "white pollution." Regarding antibacterial properties, synthetic antibacterial agents are often added, which may pose migration and safety issues. In terms of coloring, the use of synthetic dyes may also bring environmental burdens and health risks.

[0004] Existing technologies struggle to simultaneously achieve waterproofing, antibacterial properties, and colorfastness. Furthermore, functional papers often sacrifice mechanical strength, leading to a decline in key mechanical properties such as tear resistance, folding endurance, and bursting strength, failing to meet the demands of high-end applications. With increasingly stringent global environmental policies and heightened consumer health awareness, the market urgently needs paper that combines environmental friendliness, multifunctionality (such as antibacterial, waterproofing, and stable colorfastness), and high mechanical strength. Current technologies cannot simultaneously achieve excellent antibacterial, waterproof, and colorfast effects, along with high mechanical strength, under environmentally friendly production conditions, making it difficult to meet the needs of high-end applications across multiple fields.

[0005] Therefore, developing an environmentally friendly, harmless, antibacterial, waterproof, and safe colored paper and its preparation method to solve the problem of balancing environmental friendliness, safety, functionality, and mechanical strength has significant market value and environmental significance. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a natural, biodegradable, antibacterial, waterproof and colorful environmentally friendly paper and its preparation method.

[0007] On the one hand, the present invention provides a method for preparing environmentally friendly, antibacterial, and waterproof colored paper, the method comprising the following steps: (1) Pulp preparation: The plant fiber raw materials are crushed and loosened into pulp, and the pulp concentration is adjusted to 3%-6% (wt%). (2) Persimmon lacquer modification: The original persimmon lacquer is finely filtered to remove impurities, and then concentrated at low temperature or treated with bio-enzymes to obtain refined persimmon lacquer. (3) Mixing and dyeing: Add the auxiliaries and refined persimmon lacquer to the sizing in sequence, stir thoroughly to make the components evenly distributed and bonded to the fibers; (4) Papermaking and forming: The uniformly mixed pulp is formed by papermaking through a paper forming device to form a wet paper sheet; (5) Dehydration and drying: The wet paper sheets are pressed to dehydrate, and then dried in stages at a temperature range of 50-90℃ to the finished product moisture content; (6) Post-processing: The dry paper is post-processed as needed to obtain colored paper products.

[0008] In a preferred embodiment, in step (1), the pulp is one or more of wood pulp, bamboo pulp, straw pulp, cotton pulp, or waste paper pulp.

[0009] In a preferred embodiment, in step (2), the condensed tannin content of the refined persimmon lacquer is 2-10% (w / w), i.e., the content is a mass fraction. More preferably, the condensed tannin content of the refined persimmon lacquer is 3-7%; for example, the condensed tannin content can be 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, etc.

[0010] In a preferred embodiment, in step (3), the additive is a natural flocculant and / or a pH adjuster.

[0011] More preferably, the concentration of the natural flocculant or pH adjuster in the slurry is 0.5%-5% (w / v); more preferably, the concentration in the slurry is 1%-4% (w / v).

[0012] More preferably, the flocculant is chitosan or cationic starch; More preferably, the pH adjuster is alum or acetic acid.

[0013] In the preferred embodiment, the ratio of oven-dried fiber to added refined persimmon lacquer in the slurry is 1g:(4-16)ml; more preferably, the ratio is 1g:(8-12)ml.

[0014] In a preferred embodiment, the thorough mixing is carried out at 40-60°C for 20-60 minutes to ensure that the components are evenly distributed and bonded to the fibers.

[0015] In the preferred embodiment, in step (5), when the paper is dried to a moisture content of 8%-10%, the refined persimmon lacquer is sprayed onto the surface of the paper, and then the paper is dried to the finished product moisture content.

[0016] In the preferred embodiment, in step (3), a natural colorant is first added to the slurry containing the additives, and the mixture is stirred, followed by the addition of refined persimmon lacquer.

[0017] More preferably, the natural colorant is one or more of the following: plant carbon black, gardenia yellow, indigo, sappanwood red, tea polyphenol oxidation products, safflower red, and smoke tree yellow. These colorants can combine with persimmon tannins to enhance color fastness and improve functional effects.

[0018] Persimmon lacquer can be combined with different natural colorants to be called persimmon red (persimmon lacquer + safflower red), persimmon gardenia (persimmon lacquer + gardenia yellow), persimmon yellow (persimmon lacquer + smoke tree yellow), and persimmon sage (persimmon lacquer + sappanwood red).

[0019] In a further preferred embodiment, in step (5), the paper is surface-sprayed with a mixture of the natural colorant and the refined persimmon lacquer.

[0020] In a further preferred embodiment, the volume ratio of the natural colorant to the refined persimmon lacquer is 1:(1-3); for example, the volume ratio can be 1:1.0, 1:1.3, 1:1.7, 1:2.0, 1:2.4, 1:2.5, 1:2.8, 1:3.0, etc.

[0021] In a further optimized scheme, the amount of spraying liquid used is 150 mL / m, depending on the paper characteristics. 2 ~640mL / m 2 .

[0022] In a further preferred embodiment, the natural colorant is safflower red dye, gardenia yellow dye, sappanwood red dye, or smoke tree yellow dye.

[0023] The inventors unexpectedly discovered during their research that when persimmon lacquer (or persimmon red, persimmon gardenia, persimmon yellow, persimmon perilla) was added to the pulp and sprayed onto the surface, the resulting colored paper exhibited extremely excellent antibacterial properties, with its color difference at a moderate level.

[0024] Further analysis revealed that colored paper prepared by adding persimmon lacquer to the pulp and spraying it onto the surface had the best bursting strength, folding endurance, and tear resistance, while its tensile strength and water resistance were at the second-best levels.

[0025] Colored paper prepared by adding persimmon red to the pulp and spraying it onto the surface exhibits extremely excellent water resistance: its Cobb value is the lowest among all 16 treatment groups, and its water contact angle is the highest, indicating that the paper surface is strongly hydrophobic. Its water resistance is significantly better than that of other color combination composite processes. Other indicators are at a suboptimal or moderate level.

[0026] When persimmon sucrose is added to the pulp and sprayed onto the surface, the antibacterial and Cobb values ​​are optimal, while other indicators are second or third.

[0027] The inventors also unexpectedly discovered during their research that when only persimmon lacquer was added to the pulp, the prepared colored paper exhibited extremely excellent tensile strength, while other properties were mostly at a suboptimal or moderate level.

[0028] Those skilled in the art can flexibly select the type and combination of colorants based on the above research results, according to the target performance requirements of colored paper in one or more dimensions such as mechanical strength, water resistance, and antibacterial properties.

[0029] In this invention, the segmented drying in step (5) can be carried out in existing paper drying equipment such as multi-segment drying cylinders and multi-zone hot air drying boxes. The drying process can be divided into multiple segments, and the temperature of each segment can be independently adjusted according to the actual moisture content of the paper, so that the temperature increases gradually or is flexibly set within the range of 50°C to 90°C until the paper reaches the predetermined dryness.

[0030] In the preferred embodiment, the moisture content of the finished product in step (5) can be selected as 5%-9%.

[0031] In the preferred embodiment, the post-processing in step (6) is calendering, winding or slitting, etc.

[0032] On the other hand, the present invention provides an environmentally friendly, antibacterial, and waterproof colored paper, which is prepared by the aforementioned method.

[0033] On the other hand, the present invention provides the application of the aforementioned preparation method in the preparation of multifunctional colored paper. According to the target performance of the colored paper, it is selected whether to add natural colorants during the preparation process and the type of natural colorants added. The target performance is selected from at least two of mechanical strength, water resistance, appearance characteristics and antibacterial properties.

[0034] In the preferred embodiment, when colored paper requires high strength, water resistance, and antibacterial properties, no natural colorant is added during the preparation process; when colored paper requires high water resistance, antibacterial properties, and paper strength, a natural colorant is added during the preparation process, and the natural colorant is safflower red.

[0035] Preferably, colored paper prepared by adding persimmon lacquer to the pulp and spraying it onto the surface has the best antibacterial, burst-resistant, fold-resistant and tear-resistant properties, while also taking into account tensile strength, water resistance and low color difference.

[0036] Another preferred option is to prepare colored paper by adding persimmon red to the pulp and spraying it with the surface. This paper has the best antibacterial and waterproof properties, while also having good tensile strength, burst strength, folding strength, tear resistance and low color difference.

[0037] Another preferred method is to add persimmon sap to the slurry and spray it onto the surface, which provides optimal antibacterial properties while also ensuring waterproof, tensile, burst-resistant, fold-resistant, tear-resistant, and low color difference properties.

[0038] Another preferred option is that when persimmon lacquer is added only to the slurry, it has the best tensile properties, while also taking into account antibacterial, waterproof, tensile, burst-resistant, fold-resistant and tear-resistant properties.

[0039] The beneficial effects of this invention are: 1. All key functional ingredients of this invention, such as persimmon lacquer, plant pigments, and natural additives, are derived from nature. The product is biodegradable after disposal, fundamentally solving the pollution problem caused by synthetic chemicals.

[0040] 2. Compared with the existing technology that only sprays persimmon lacquer on the paper surface, the present invention combines adding persimmon lacquer into the pulp and spraying persimmon lacquer on the surface during the papermaking process. This composite process can significantly improve the tear index, folding endurance, tensile index and bursting index of the paper, while significantly reducing the Cobb value, increasing the water contact angle and enhancing the antibacterial rate.

[0041] 3. This invention further incorporates natural plant colorants during the papermaking process, resulting in a synergistic effect between persimmon lacquer and natural pigments. The prepared paper not only exhibits high strength, strong hydrophobicity, and excellent antibacterial properties, but also boasts richer colors. Compared to traditional single-dyeing processes, the composite process of this invention offers significant advantages in terms of mechanics, hydrophobicity, antibacterial properties, and color, demonstrating high practical value and promising industrialization prospects.

[0042] 4. The colored paper prepared by this invention has excellent properties: The tannins in persimmon lacquer have a significant inhibitory effect on a variety of bacteria and molds, thus exhibiting superior antibacterial properties.

[0043] Persimmon lacquer cross-links to form a film on the fiber surface, creating a dense layer with low surface energy that effectively resists the penetration of oils and water. Tests show that its Cobb value can be below 50 g / m², its hydrophobic angle can reach 100°, its resistance to vegetable oils can reach level 6, and its antibacterial rate (against E. coli) is greater than 99.5%.

[0044] Natural pigments are firmly bonded to tannins and fibers through hydrogen bonds, complexation, and other interactions, making them resistant to fading and resulting in paper with excellent colorfastness.

[0045] The colored paper of this invention is safe and environmentally friendly, with rich colors, and can be widely used in food packaging bags, lunch box liners, environmentally friendly cups and bowls, high-grade book covers, handicrafts and other fields. Attached Figure Description

[0046] Figure 1 Phenotypes of the papers prepared in Examples 1-5 and Comparative Examples 1-11.

[0047] Figure 2 The tensile index is the tensile index of the paper prepared in Examples 1-5 and Comparative Examples 1-11.

[0048] Figure 3 Bursting index is the bursting strength index of the paper prepared in Examples 1-5 and Comparative Examples 1-11.

[0049] Figure 4 The folding endurance of the paper prepared in Examples 1-5 and Comparative Examples 1-11.

[0050] Figure 5 The tear index is the tear index of the paper prepared in Examples 1-5 and Comparative Examples 1-11.

[0051] Figure 6 Cobb values ​​of the papers prepared in Examples 1-5 and Comparative Examples 1-11.

[0052] Figure 7 The water contact angle is for the paper prepared in Examples 1-5 and Comparative Examples 1-11.

[0053] Figure 8 The antibacterial rate of the paper prepared in Examples 1-5 and Comparative Examples 1-11.

[0054] Figure 9 The color difference is the color difference of the paper prepared in Examples 1-5 and Comparative Examples 1-11.

[0055] It should be noted that, Figures 2-9 Different lowercase letters indicate significant differences between groups (p<0.05), while the same letter indicates no significant difference. Detailed Implementation

[0056] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0058] The persimmon lacquer used in this invention refers to lacquer mainly composed of persimmon (Diospyros kaki), a plant belonging to the genus Diospyros of the family Ebenaceae. Diospyros kaki (Linn.) is a plant dye produced by juicing and fermenting unripe fruit.

[0059] The safflower red, gardenia yellow, smoke tree yellow, and sappanwood red dyes used in this invention are all water-extracted dyes, namely, safflower petal water extract, gardenia fruit water extract, smoke tree wood water extract, and sappanwood heartwood water extract.

[0060] All of the above dyes can be purchased commercially or prepared using conventional extraction methods in this field. For example, they can be prepared using the following methods: Persimmon lacquer: Take fresh astringent persimmons, squeeze out the juice, filter it, cover it with gauze and place it in a fermentation tank. Ferment aerobically for one month, boil it, seal it and place it in a cool place to ferment for 2 years.

[0061] Gardenia Yellow Dye Solution: Chop the gardenia fruit, add water at a ratio of 1:20, heat to 100℃ and keep warm for 30 minutes. Then filter the dye residue through 200-mesh gauze to obtain the dye solution.

[0062] Smoke Tree Yellow Dye Solution: Crush smoke tree wood, add water at a ratio of 1:20, heat to 100℃ and keep warm for 30 minutes, then filter the dye residue through 200-mesh gauze to obtain the dye solution.

[0063] Sappanwood Red Dye Solution: Crush sappanwood heartwood, add water at a ratio of 1:20, heat to 100℃ and keep warm for 30 minutes, then filter the dye residue through 200-mesh gauze to obtain the dye solution.

[0064] Safflower red dye solution: (1) First, wash a certain amount of safflower petals and add them to water. The ratio of material to liquid is 1:15. You can add a small amount of acetic acid. Soak for 2-3 hours, filter and gently squeeze out the flower residue, and discard the yellow filtrate.

[0065] (2) Add the yellowed flower residue to a certain amount of 35℃ warm water, with a material-to-liquid ratio of 1:15. Adjust the pH of the system to 9.0-9.5 with sodium carbonate solution. Knead the safflower repeatedly, filter after 30 minutes, slowly add glacial acetic acid to the filtrate, stir thoroughly, and adjust the pH to 4.0-5.0 to obtain safflower red dye solution.

[0066] Tests have shown that the dyes produced by the above-mentioned self-made method can achieve the technical effects of this invention.

[0067] In this invention, spraying on the paper surface refers to uniformly spraying the front side of the paper.

[0068] Example Example 1 A method for preparing environmentally friendly, antibacterial, and waterproof colored paper includes the following steps: 5g (based on oven-dry fiber) of bleached wood pulp is loosened and diluted to a concentration of 4% (wt%). Persimmon lacquer is filtered through a 200-mesh sieve to remove particulate residue and then concentrated to a condensed tannin concentration of 5% (w / w) for later use, thus obtaining refined persimmon lacquer. 2% (w / v) alum is added to the diluted pulp and stirred for 10 minutes. 40mL of refined persimmon lacquer is added, and the mixture is stirred continuously at 50℃ for 30 minutes. The mixed pulp is poured into a hand-made paper machine for forming, and after pressing and dewatering, it is dried in a drying cylinder at 90℃ to a moisture content of 8%, obtaining paper.

[0069] A layer of refined persimmon lacquer solution with a condensed tannin concentration of 5% (w / w) was uniformly sprayed onto the surface of the paper using a spray method, and then dried at 60°C until the finished product moisture content (moisture content of about 8%) was obtained. The paper prepared in this example is referred to as persimmon lacquer 3.

[0070] Example 2 A method for preparing environmentally friendly, antibacterial, and waterproof colored paper includes the following steps: 5g (based on oven-dry fiber) of bleached wood pulp is loosened and diluted to a concentration of 4% (wt%). Persimmon lacquer is filtered through a 200-mesh sieve to remove particulate residue and then concentrated to a condensed tannin concentration of 5% (w / w) for later use, thus obtaining refined persimmon lacquer. 2% (w / v) alum is added to the diluted pulp and stirred for 10 minutes. 20mL of safflower red dye solution is added and stirred for 15 minutes. 40mL of refined persimmon lacquer is slowly added, and the mixture is continuously stirred at 50℃ for 30 minutes. The mixed pulp is poured into a hand-made paper machine for forming, and after pressing and dehydration, it is dried in a drying cylinder at 90℃ to a moisture content of 8%, obtaining paper.

[0071] A layer of a mixture of safflower red dye and refined persimmon lacquer in a volume ratio of 1:2 was uniformly sprayed onto the surface of the paper. The paper was then dried at 60°C until the moisture content of the finished product was reduced to approximately 8%. The paper prepared in this example is designated as Persimmon Red 3.

[0072] Example 3 A method for preparing environmentally friendly, antibacterial, and waterproof colored paper includes the following steps: 5g (based on oven-dry fiber) of bleached wood pulp is loosened and diluted to a concentration of 4% (wt%). Persimmon lacquer is filtered through a 200-mesh sieve to remove particulate residue, and then concentrated to a condensed tannin concentration of 5% (w / w) for later use, thus obtaining refined persimmon lacquer. 2% (w / v) alum is added to the diluted pulp and stirred for 10 minutes. 20mL of gardenia yellow dye is added and stirred for 15 minutes. 40mL of refined persimmon lacquer is slowly added, and the mixture is continuously stirred at 50°C for 30 minutes. The mixed pulp is poured into a hand-made paper machine for forming, and after pressing and dehydration, it is dried in a drying cylinder at 90°C to a moisture content of 8%, obtaining paper.

[0073] A mixture of gardenia yellow dye and refined persimmon lacquer in a 1:2 ratio (volume ratio) was uniformly sprayed onto the surface of the paper using a spray method. The paper was then dried at 60°C until the moisture content of the finished product (approximately 8%) was reached, and the resulting paper was labeled as Persimmon Gardenia 3.

[0074] Example 4 A method for preparing environmentally friendly, antibacterial, and waterproof colored paper includes the following steps: 5g (based on oven-dry fiber) of bleached wood pulp is loosened and diluted to a concentration of 4% (wt%). Persimmon lacquer is filtered through a 200-mesh sieve to remove particulate residue, and then concentrated to a condensed tannin concentration of 5% (w / w) for later use, thus obtaining refined persimmon lacquer. 2% (w / v) alum is added to the diluted pulp and stirred for 10 minutes. 20mL of smoke tree yellow dye is added and stirred for 15 minutes. 40mL of refined persimmon lacquer is slowly added, and the mixture is continuously stirred at 50℃ for 30 minutes. The mixed pulp is poured into a hand-made paper machine for forming, and after pressing and dehydration, it is dried in a drying cylinder at 90℃ to a moisture content of 8%, obtaining paper.

[0075] A layer of a mixture of smoke tree yellow dye and refined persimmon lacquer in a volume ratio of 1:2 was uniformly sprayed onto the surface of the paper. The paper was then dried at 60°C until the moisture content of the finished product was reduced to approximately 8%. The paper prepared in this example was designated as Persimmon Yellow 3.

[0076] Example 5 A method for preparing environmentally friendly, antibacterial, and waterproof colored paper includes the following steps: 5g (based on oven-dry fiber) of bleached wood pulp is loosened and diluted to a concentration of 4% (wt%). Persimmon lacquer is filtered through a 200-mesh sieve to remove particulate residue, and then concentrated to a condensed tannin concentration of 5% (w / w) for later use, thus obtaining refined persimmon lacquer. 2% (w / v) alum is added to the diluted pulp and stirred for 10 minutes. 20mL of hematoxylin red dye solution is added and stirred for 15 minutes. 40mL of refined persimmon lacquer is slowly added, and stirring is continued at 50℃ for 30 minutes. The mixed pulp is poured into a hand-made paper machine for forming, and after pressing and dehydration, it is dried in a drying cylinder at 90℃ to a moisture content of 8%, obtaining paper.

[0077] A layer of a mixture of sappanwood red dye and refined persimmon lacquer in a volume ratio of 1:2 was uniformly sprayed onto the surface of the paper. The paper was then dried at 60°C until the moisture content of the finished product was reduced to approximately 8%. The paper prepared in this example is designated as Persimmon-Sappanwood 3.

[0078] To highlight the technical advantages of this invention, comparative examples are provided below.

[0079] Comparative Example Comparative Example 1 5g (based on oven-dry fiber) of bleached wood pulp was loosened and diluted to a concentration of 4% (wt%). 2% (w / v) alum was added to the diluted pulp, and the mixture was stirred for 10 minutes. The pulp was then poured into a hand paper machine for papermaking. After pressing and dehydration, the pulp was dried in a drying cylinder at 90°C to a moisture content of 8% to obtain paper. The paper prepared in this comparative example is referred to as the base paper.

[0080] The only difference between Comparative Example 2 and Example 1 is that Comparative Example 2 only sprays persimmon lacquer onto the surface of the paper, without adding persimmon lacquer to the pulp. All other process steps, parameters, and conditions are the same as in Example 1. The paper prepared in this comparative example is referred to as Persimmon Lacquer 1.

[0081] The only difference between Comparative Example 3 and Example 1 is that Comparative Example 3 only adds persimmon lacquer to the pulp, without spraying persimmon lacquer onto the paper surface. All other process steps, parameters, and conditions are the same as in Example 1. The paper prepared in this comparative example is designated as Persimmon Lacquer 2.

[0082] The only difference between Comparative Example 4 and Example 2 is that Comparative Example 4 only sprays a mixed solution of safflower red and persimmon lacquer onto the paper surface, without adding safflower red and persimmon lacquer to the pulp. The remaining process steps, parameters, and conditions are the same as in Example 2. The paper prepared in this comparative example is designated as Persimmon Red 1.

[0083] The only difference between Comparative Example 5 and Example 2 is that Comparative Example 5 only adds safflower red and persimmon lacquer to the pulp, without spraying a mixed solution of safflower red and persimmon lacquer onto the paper surface. All other process steps, parameters, and conditions are the same as in Example 2. The paper prepared in this comparative example is designated as Persimmon Red 2.

[0084] The only difference between Comparative Example 6 and Example 3 is that Comparative Example 6 only sprays a mixed solution of gardenia yellow and persimmon lacquer onto the paper surface, without adding gardenia yellow and persimmon lacquer to the pulp. All other process steps, parameters, and conditions are the same as in Example 3. The paper prepared in this comparative example is designated as Persimmon-Gardenia 1.

[0085] The only difference between Comparative Example 7 and Example 3 is that Comparative Example 7 only adds gardenia yellow and persimmon lacquer to the pulp, without spraying a mixed solution of gardenia yellow and persimmon lacquer onto the paper surface. All other process steps, parameters, and conditions are the same as in Example 3. The paper prepared in this comparative example is designated as Persimmon Gardenia 2.

[0086] The only difference between Comparative Example 8 and Example 4 is that Comparative Example 8 only sprays a mixed solution of smoke yellow and persimmon lacquer onto the paper surface, without adding smoke yellow and persimmon lacquer to the pulp. The remaining process steps, parameters, and conditions are the same as in Example 4. The paper prepared in this comparative example is designated as Persimmon Yellow 1.

[0087] The only difference between Comparative Example 9 and Example 4 is that Comparative Example 9 only adds smoke yellow and persimmon lacquer to the pulp, without spraying a mixed solution of smoke yellow and persimmon lacquer onto the paper surface. All other process steps, parameters, and conditions are the same as in Example 4. The paper prepared in this comparative example is designated as Persimmon Yellow 2.

[0088] The only difference between Comparative Example 10 and Example 5 is that Comparative Example 10 only sprays a mixed solution of sappanwood and persimmon lacquer onto the paper surface, without adding sappanwood and persimmon lacquer to the pulp. All other process steps, parameters, and conditions are the same as in Example 5. The paper prepared in this comparative example is designated as Persimmon-Sappanwood 1.

[0089] The only difference between Comparative Example 11 and Example 5 is that Comparative Example 11 only adds sappanwood and persimmon lacquer to the pulp, without spraying a mixed solution of sappanwood and persimmon lacquer onto the paper surface. All other process steps, parameters, and conditions are the same as in Example 5. The paper prepared in this comparative example is designated as Persimmon-Sappanwood 2.

[0090] The technical solutions in Comparative Examples 2-11 above, which involve spraying only onto the paper surface without adding it to the pulp, are as follows: 5g (based on oven-dry fiber) of bleached wood pulp was loosened and diluted to a concentration of 4% (wt%). Persimmon lacquer was filtered through a 200-mesh sieve to remove particulate residue, and then concentrated to a condensed tannin concentration of 5% (w / w) for later use, thus obtaining refined persimmon lacquer. 2% (w / v) alum was added to the diluted pulp, and the mixture was stirred for 10 minutes. The pulp was then poured into a hand-made paper machine for forming. After pressing and dehydration, the paper was dried in a 90℃ drying cylinder to a moisture content of 8%, yielding paper. A layer of refined persimmon lacquer or a mixture of safflower red / gardenia yellow / smoke yellow / sappanwood red dye and refined persimmon lacquer in a 1:2 (volume ratio) was then evenly sprayed onto the paper surface using a spray method. The paper was then dried further at 60℃ until the final moisture content (approximately 8%) was reached, yielding the final paper.

[0091] The technical solutions in Comparative Examples 2-11 above, which only add the material to the pulp and do not spray it onto the paper surface, are as follows: 5g (based on oven-dry fiber) of bleached wood pulp was loosened and diluted to a concentration of 4% (wt%). Persimmon lacquer was filtered through a 200-mesh sieve to remove particulate residue, and then concentrated to a condensed tannin concentration of 5% (w / w) for later use, thus obtaining refined persimmon lacquer. 2% (w / v) alum was added to the diluted pulp, and the mixture was stirred for 10 minutes. 40mL of refined persimmon lacquer was added (or 20mL of safflower red / gardenia yellow / smoke yellow / sappanwood red dye solution was added, stirred for 15 minutes, and then 40mL of refined persimmon lacquer was slowly added), and the mixture was stirred continuously at 50℃ for 30 minutes. The mixed pulp was poured into a hand-made paper machine for forming, and after pressing and dehydration, it was dried in a drying cylinder at 90℃ to a moisture content of 8%, yielding paper.

[0092] The paper samples obtained in Examples 1-5 and Comparative Examples 1-11 were subjected to performance tests, including tear index, folding endurance, tensile index, bursting index, Cobb value, hydrophobic angle, antibacterial rate, and color. The testing methods for each indicator are as follows: Tear index: According to GB / T 455.1-2023, the force required to tear a pre-cut specimen is measured using an Elmendorf tear tester, and then the index is calculated.

[0093] Flexural endurance: According to GB / T 2679.5-2021, the MIT flexural endurance tester was used to fold the sample back and forth under constant tension until it broke.

[0094] Tensile index: According to GB / T 12914-2018, the tensile test specimen is stretched at a constant speed until fracture using a tensile testing machine, the tensile strength is determined, and the index is obtained by dividing by the quantitative value.

[0095] Bursting strength index: According to GB / T 454-2020, a bursting strength tester is used to burst the sample by uniformly increasing the hydraulic pressure through the rubber membrane, and the bursting strength is measured. The index is obtained by dividing by the quantitative value.

[0096] Cobb value: According to GB / T 1540-2002, using a Cobb tester, allow one side of the sample to be in contact with water for a specified time (60 seconds) and measure the water absorption per unit area.

[0097] Hydrophobic angle: The contact angle of a water droplet on a surface is determined using the static contact angle method and a contact angle measuring instrument.

[0098] Inhibition rate: According to GB / T 20944.3-2023, the sample was shaken and contacted with Escherichia coli bacterial solution for a certain period of time, and the percentage of viable bacteria reduction was calculated.

[0099] Color difference (ΔE): Measured using a spectrophotometer under D65 light source conditions according to GB / T 7975-2005, and calculated using the following formula: .

[0100] Experimental results: Paper samples from each treatment are as follows Figure 1 As shown. The performance test results for each process are as follows. Figure 2-9 As shown in Table 1.

[0101] Table 1. Color difference of paper obtained from each treatment ( ) The results showed that the method of adding persimmon lacquer had a significant impact on the overall performance of paper. The composite treatment of adding persimmon lacquer into the pulp and spraying persimmon lacquer on the surface showed the best performance in terms of physical and mechanical properties, hydrophobic and moisture-proof properties, and antibacterial properties, which were significantly better than single surface spraying or pulp addition treatments. In particular, the composite method showed a synergistic effect of 1+1>2 in key indicators such as bursting index, folding endurance, tear index, and Cobb value.

[0102] The composite treatment of adding pigments within the pulp and then spraying them onto the surface demonstrates superior performance in physical and mechanical properties, hydrophobic and waterproof properties, and antibacterial properties compared to single treatments. This approach is also applicable to compound systems of persimmon lacquer and natural colorants. Furthermore, the effects of different natural pigments combined with persimmon lacquer on paper properties exhibit distinct characteristics: for example, the persimmon lacquer-safflower red compound treatment exhibits excellent hydrophobic and waterproof properties, while the persimmon lacquer-gardenia yellow compound treatment shows strong hydrophilicity. The composite treatment of adding pigments within the pulp and then spraying them onto the surface is also effective for the persimmon lacquer-smokewort yellow and persimmon lacquer-sappanwood red systems, improving all properties and outperforming single treatment methods. Therefore, in practical applications, the type of colorant added can be flexibly selected based on the specific application scenario of the paper.

[0103] Furthermore, the above experiments also show that the antibacterial rate of the paper in Examples 1-5 against E. coli is close to 100%, and generally greater than 99%. The paper prepared by this invention is particularly suitable for scenarios with high requirements for hygiene and safety, such as: antibacterial food packaging paper, disposable tableware lining, medical care paper, infant product packaging, and antibacterial book covers, etc., and has broad application prospects.

[0104] To further illustrate the broad applicability of the method of the present invention in preparing papers of different colors and for different purposes, several application examples are provided below. Comparative examples are also provided to contrast the performance advantages of the paper of the present invention. It should be noted that the following application examples are only some specific embodiments of the present invention and do not constitute a limitation on the scope of protection.

[0105] Application Example 1: Preparation of Khaki-colored Packaging Paper 5g (based on oven-dry fiber) of bleached softwood fiber pulp was loosened and diluted to a concentration of 4% (wt%). Persimmon lacquer was filtered through a 200-mesh sieve and then concentrated or enzymatically treated to prepare persimmon lacquer with a condensed tannin content of 5%. 2% (w / v) alum was added to the diluted pulp and stirred for 10 minutes. 40mL of persimmon lacquer was slowly added, and the mixture was stirred continuously at 50°C for 30 minutes. The mixed pulp was poured into a hand-made paper machine for forming, and after pressing and dehydration, it was dried in a drying cylinder at 90°C to a moisture content of 8%, yielding khaki-colored paper.

[0106] Application Example 2: Preparation of Reddish-Brown Antibacterial Placemat Paper 5g (based on oven-dry fiber) of bleached coniferous fiber pulp was loosened and diluted to a concentration of 4% (wt%). Persimmon lacquer was filtered through a 200-mesh sieve and then concentrated or enzymatically treated to prepare refined persimmon lacquer with a condensed tannin content of 5%. 2% (w / v) alum was added to the diluted pulp and stirred for 10 minutes. 20mL of safflower red dye solution was added and stirred for 15 minutes. 40mL of refined persimmon lacquer was slowly added, and the mixture was stirred continuously at 50℃ for 30 minutes. The mixed pulp was poured into a hand-made paper machine for forming, and after pressing and dehydration, it was dried in a drying cylinder at 90℃ to a moisture content of 8%, yielding light red paper.

[0107] A mixture of refined persimmon lacquer and safflower red dye in a volume ratio of 2:1 was uniformly sprayed onto the paper surface using a spraying method, covering an area of ​​approximately 0.0314 m². 2 The paper sheets require a total volume of approximately 20 mL of mixed solution, which is then dried at 60°C until the final moisture content (approximately 8%) is reached, resulting in reddish-brown placemats with a higher surface gloss.

[0108] Comparative Example The only difference between this comparative example and Application Example 1 is that no persimmon lacquer was added to the pulp in the comparative example. Everything else was the same as in Application Example 1, and ordinary paper was prepared.

[0109] Performance tests were conducted on the paper prepared for corresponding use cases 1-2 and the comparative example. The results are shown in Table 2. Table 2 Paper properties obtained by each treatment Test results show that the paper prepared by this invention has excellent mechanical, waterproof and antibacterial properties, which are far superior to ordinary paper without added persimmon lacquer.

[0110] Traditional persimmon lacquer paper is typically prepared by surface spraying with persimmon lacquer solution. Experiments in this invention demonstrate that, compared to surface spraying, paper made by adding persimmon lacquer to the pulp exhibits superior physical and mechanical properties and a higher antibacterial rate. When a composite process combining internal addition of persimmon lacquer to the pulp and surface spraying is employed, the paper's physical and mechanical properties, water resistance, and antibacterial properties are further enhanced, with the antibacterial rate approaching 100%. By adding natural colorants to this composite process, the paper retains its core properties while achieving stable and rich natural colors, meeting the diverse color requirements of various applications.

[0111] Based on the above experimental results, the resulting paper can be adapted to appropriate application scenarios according to its performance characteristics. For example: Paper with persimmon lacquer 2 has good basic mechanical properties and moderate water resistance. It has no surface coating, and writing and printing are smooth. It is suitable for daily paper such as office printing paper and student notebooks. Its basic antibacterial and anti-mildew capabilities can extend the storage life of the paper.

[0112] Persimmon Lacquer 3 possesses outstanding mechanical properties, with a bursting strength index approaching 12.5 kPa·m² / g, folding endurance exceeding 4500 cycles, and a tear index greater than 30 mN·m² / g. It also exhibits excellent water resistance, with a Cobb value less than 50 g / m², a water contact angle greater than 100°, and an antibacterial rate approaching 100%. This paper is suitable for foldable paper products such as archives, maps, and drawings, as well as medical-grade aseptic packaging and waterproof packaging.

[0113] Persimmon Red 3 also possesses excellent mechanical properties and outstanding waterproof and antibacterial properties, making it suitable for use in red waterproof / moisture-proof paper, gift wrapping paper, antibacterial and preservation packaging paper for fresh fruits and vegetables, and high-strength colored waterproof packaging paper. Persimmon Gardenia 3, Persimmon Yellow 3, and Persimmon Perilla 3 each exhibit different natural warm colors. While maintaining excellent physical and mechanical properties, hydrophobic and moisture-proof properties, and high antibacterial rates, they are suitable for various application scenarios with comprehensive requirements for color recognition, hygiene, and protection, such as antibacterial children's picture book covers, children's book paper, and cultural paper. Of course, the above application scenarios are just examples, and the scope of application of this invention is not limited to these.

[0114] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make appropriate changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A method for preparing environmentally friendly, antibacterial, and waterproof colored paper, characterized in that, The preparation method includes the following steps: (1) Pulp preparation: The plant fiber raw materials are crushed and loosened into pulp, and the pulp concentration is adjusted to 3%-6% (wt%). (2) Persimmon lacquer modification: The original persimmon lacquer is finely filtered to remove impurities, and then concentrated at low temperature or treated with bio-enzymes to obtain refined persimmon lacquer. (3) Mixing and dyeing: Add the auxiliaries and refined persimmon lacquer to the sizing in sequence, stir thoroughly to make the components evenly distributed and bonded to the fibers; (4) Papermaking and forming: The uniformly mixed pulp is formed by papermaking through a paper forming device to form a wet paper sheet; (5) Dehydration and drying: The wet paper sheets are pressed to dehydrate, and then dried in stages at a temperature range of 50-90℃ to the finished product moisture content; (6) Post-processing: The dry paper is post-processed as needed to obtain colored paper products.

2. The preparation method according to claim 1, characterized in that, In step (1), the pulp is one or more of wood pulp, bamboo pulp, straw pulp, cotton pulp or waste paper pulp.

3. The preparation method according to claim 1, characterized in that, In step (2), the mass fraction of condensed tannins in the refined persimmon lacquer is 2-10%.

4. The preparation method according to claim 1, characterized in that, In step (3), the auxiliary agent is a natural flocculant and / or a pH adjuster; Preferably, the flocculant is chitosan or cationic starch, and the concentration of the flocculant in the slurry is 0.5%-5% (w / v); More preferably, the pH adjuster is alum or acetic acid, and the concentration of the pH adjuster in the slurry is 0.5%-5% (w / v).

5. The preparation method according to claim 1, characterized in that, In step (5), when the paper is dried to a moisture content of 8%-10%, the refined persimmon lacquer is sprayed onto the surface of the paper, and then the paper is dried to the finished product moisture content.

6. The preparation method according to claim 1, characterized in that, In step (3), natural colorant is first added to the slurry containing additives and stirred, and then refined persimmon lacquer is added; More preferably, the natural colorant is one or more of the following: plant carbon black, gardenia yellow, indigo, sappanwood red, tea polyphenol oxidation products, safflower red, and smoke yellow; More preferably, the volume ratio of the natural colorant to the refined persimmon lacquer is 1:(1-3).

7. The preparation method according to claim 6, characterized in that, In step (5), the paper is sprayed with a mixed solution of the natural colorant and the refined persimmon lacquer, wherein the volume ratio of the natural colorant to the refined persimmon lacquer is 1:(1-3).

8. An environmentally friendly, antibacterial, and waterproof colored paper, prepared by the method described in any one of claims 1-7.

9. The application of the preparation method according to any one of claims 1-7 in the preparation of multifunctional colored paper, characterized in that, Based on the target properties of the colored paper, it is selected whether to add natural colorants during the preparation process and the types of natural colorants added, wherein the target properties are selected from at least two of mechanical strength, water resistance, appearance characteristics and antibacterial properties.

10. The application according to claim 9, characterized in that, When colored paper requires high strength, water resistance, and antibacterial properties, no natural colorants are added during the preparation process; When colored paper requires high water resistance, antibacterial properties, and paper strength, a natural colorant is added during the preparation process, and the natural colorant is safflower red dye solution.

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