Preparation method of environment-friendly paper product waterproof coating

Abstract

The invention relates to a preparation method of an environment-friendly paper product waterproof coating, and belongs to the technical field of waterproof materials, and the preparation method comprises the following operation steps: 1, making backing paper, selecting moso bamboo fibers as paper pulp fibers, adding polylactic acid fibers into the paper pulp fibers, and fully mixing to prepare paper; 2, preparing a film spraying solution to obtain a film spraying solution I; and 3, obtaining a film spraying liquid II. And 4, obtaining a film spraying solution III. And 5, carrying out film spraying treatment. And 6, carrying out drying treatment. (7) carrying out curing treatment; a preheating stage, a hot melting and laminating stage and a cooling stage are adopted in the curing treatment process. The coating is made of bio-based materials and degradable components, so that plastic pollution and VOC emission are reduced. The coating has excellent water resistance, hydrolysis resistance and mechanical strength, and meets various packaging requirements. The coating is degradable, and the paper can be recycled, so that the resource waste is reduced. The technological process is optimized, the production cost is reduced, and meanwhile the production efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of waterproof materials, and in particular to a method for preparing an environmentally friendly waterproof coating on paper products. Background Art

[0002] The research and development background of environmentally friendly paper product waterproof coating is mainly based on the following factors: Environmental protection needs: With the increasing global awareness of environmental protection, traditional plastic coatings are gradually being eliminated due to their difficulty in degradation, and environmentally friendly coatings have become the mainstream direction of industry development.

[0003] Material innovation: The introduction of new environmentally friendly materials (such as bio-based polyester and nanoparticles) not only improves the performance of waterproof coatings but also reduces environmental impact.

[0004] Policy support: National environmental protection policies (such as restricting the use of disposable plastic products) and green packaging industry planning have promoted the research and development and application of environmentally friendly coating technologies.

[0005] Research on environmentally friendly waterproof coatings for paper products is of great significance. This technology replaces traditional plastic coatings with biodegradable materials, effectively addressing white pollution while avoiding the environmental risks of fluorinated compounds. Its waterproof properties meet the needs of food packaging, logistics, and transportation, while also providing a greener and more efficient production process. This innovation aligns with the global trend toward plastic reduction and promotes sustainable development in the packaging industry, achieving both environmental and economic benefits.

[0006] Traditional paper product waterproof coatings mainly rely on polyethylene (PE) lamination or fluorinated compound treatment, which has significant defects: (1) PE coated paper causes white pollution due to its non-degradability. The global annual waste volume exceeds 20 million tons, and it takes more than 200 years to decompose after landfill. (2) Fluorine-containing waterproofing agents (such as PFAS) are bioaccumulative and toxic and have been restricted by the EU REACH regulation.

[0007] (3) The paraffin coating has poor temperature resistance (<60°C) and insufficient oil resistance (contact angle <90°).

[0008] (4) Existing bio-based coatings (such as PLA films) have poor flexibility due to their high crystallinity and are difficult to meet the requirements of carton folding.

[0009] (5) Solvent-based polyurethane coatings require high-temperature curing (>120°C), which consumes a lot of energy and can easily cause paper deformation.

[0010] (6) Nanomaterial modification technology has not yet solved the problem of coating defects caused by uneven dispersion. Summary of the Invention

[0011] The present invention primarily addresses the deficiencies in the prior art and provides a method for preparing an environmentally friendly waterproof coating for paper products, which offers the advantages of environmental friendliness, high performance, repulpability, and cost-effectiveness. The coating utilizes bio-based materials and degradable components, reducing plastic pollution and VOC emissions. The coating exhibits excellent water resistance, hydrolysis resistance, and mechanical strength, meeting a variety of packaging requirements. The coating is biodegradable, allowing the paper to be recycled, reducing resource waste. The optimized process reduces production costs while improving production efficiency. The introduction of nanoparticles and UV curing technology further enhances the coating's water resistance and mechanical strength.

[0012] The above technical problems of the present invention are mainly solved by the following technical solutions: A method for preparing an environmentally friendly waterproof coating for paper products comprises the following steps: The first step is to make the base paper. The pulp fiber is selected as bamboo fiber, and polylactic acid fiber is added into it. After sufficient mixing, it is prepared into paper. After the paper is rolled, it does not need to be dried for use.

[0013] Step 2: Prepare the coating solution to obtain coating solution I. Polyurethane resin is used as the film-forming substance to enhance the water and oil repellency of the coating layer. A mixture of ethanol and water is used as the diluent to adjust the viscosity of the coating solution and ensure uniform coating. The surfactant used is a bio-based surfactant, alkyl glycoside, with a concentration of 0.5-0.8 wt%. Epoxy resin is used as the curing agent to accelerate the resin cross-linking reaction and enhance the mechanical strength and heat resistance of the film layer. Isotridecyl alcohol ether is used as the defoaming agent to eliminate bubbles generated during the coating process and prevent pinhole defects after film formation.

[0014] Step 3: Add biodegradable polyester and hexamethylene diisocyanate to the coating solution I and mix thoroughly. The ratio of PBAT-based polyester and hexamethylene diisocyanate is 1:1 to 1:2. Add a certain amount of trimethylolpropane to obtain coating solution II.

[0015] Step 4: Add nano-carbonate particles and plastic powder to the coating solution II, and mix them thoroughly under magnetic stirring for 30 minutes to obtain the coating solution III.

[0016] By controlling the powder particle size and distribution, the uniformity and adhesion of the coating layer are optimized, giving paper products waterproof and oil-resistant properties. Nano calcium carbonate is low-cost and provides a certain degree of adhesion.

[0017] Step 5: Carry out laminating treatment, preheat the base paper to 60-80℃, and then use a shower to spray laminating liquid III. The amount of laminating liquid III used is 20-30g per square meter of paper.

[0018] Step 6: Drying treatment: Place the coated base paper in a drying oven and dry it at a temperature of 50-80℃.

[0019] Step 7: Curing treatment is carried out. The dried base paper is sent to the ultraviolet curing room to cross-link and cure the cross-linked substances in the coating liquid. The curing process includes a preheating stage, a hot melt bonding stage and a cooling stage.

[0020] Preferably, the plastic fibers are smaller than 10mm and made of ultra-short polylactic acid. Their maximum diameter is less than 1.5 times that of the pulp fibers, ensuring uniform fiber distribution within the pulp while enhancing the paper's flexibility and water resistance. The ratio of pulp fiber to plastic fiber is 8:1 to 10:1, balancing the paper's strength and environmental friendliness.

[0021] Preferably, the mixed solution in the coating solution preparation is heated to 60-80° C. in a magnetic stirrer, fully mixed for 5-6 hours, and naturally cooled to obtain coating solution I. This ensures that the components are fully reacted, thereby improving the stability and film-forming properties of the coating.

[0022] Preferably, a polyurethane backbone is formed by reacting a biodegradable polyester with hexamethylene diisocyanate. This long-chain structure improves the hardness, elastic modulus, and hydrolysis resistance of the coating, resisting the penetration of water, oil, and organic solvents. Biodegradable polyester improves degradability, contributing to environmental benefits. Hexamethylene diisocyanate also enhances the coating's flexibility and impact resistance. Biodegradable polyester is also known as PBAT-based polyester, and hexamethylene diisocyanate is also known as HDI.

[0023] Preferably, the nano-carbonate particles are nano-calcium carbonate, the particle diameter of the plastic powder is less than 0.1 μm, and the amount of plastic powder added is 5-6 wt% of the coating solution II.

[0024] Preferably, infrared radiation heating is used in the preheating stage at a temperature of 120°C to 150°C, replacing the first-stage hot rolling process to evenly increase the surface temperature of the paper and soften the fiber structure.

[0025] During the hot-melt lamination stage, high-frequency induction heating is used at temperatures between 180°C and 250°C. During the cooling stage, a pressure roller is used to rapidly melt and bond the laminating solution to the paper, reducing the risk of deformation caused by thermal stress.

[0026] The temperature is lowered to 100-120°C through a mixed air and water cooling system. This prevents cracking of the coating caused by sudden cooling while maintaining the dimensional stability of the paper.

[0027] The present invention can achieve the following effects: The present invention provides a method for preparing an environmentally friendly waterproof coating for paper products. Compared with the existing technology, the base paper is prepared using bamboo fiber and polylactic acid fiber, which enhances the mechanical strength and environmental performance of the paper. Coating liquid I is based on polyurethane resin and combines bio-based surfactants and epoxy resin to improve the adhesion and environmental performance of the coating. Coating liquid II optimizes the hardness and hydrolysis resistance of the coating by adding biodegradable polyester and hexamethylene diisocyanate. Coating liquid III introduces nano-calcium carbonate and plastic powder to enhance the waterproof performance and mechanical strength of the coating. Ultraviolet curing technology ensures rapid curing of the coating while reducing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a table of the ratios of different pulp fibers and plastic fibers of the present invention.

[0029] Figure 2 This is a table of surface tension values ​​corresponding to the addition of bio-based surfactant alkyl glycoside in the present invention.

[0030] Figure 3 This is the ISO standard table of adhesion corresponding to the nano-calcium carbonate added in the present invention. DETAILED DESCRIPTION

[0031] The technical solution of the invention is further described in detail below through embodiments and in conjunction with the accompanying drawings.

[0032] Example: Figure 1-3 As shown, a method for preparing an environmentally friendly waterproof coating for paper products includes the following steps: The first step is to make the base paper. The pulp fiber is selected as bamboo fiber, and polylactic acid fiber is added into it. After sufficient mixing, it is prepared into paper. After the paper is rolled, it does not need to be dried for use.

[0033] The plastic fiber is smaller than 10 mm and is made of ultra-short polylactic acid. Its maximum diameter is less than 1.5 times that of pulp fiber, and the ratio of pulp fiber to plastic fiber is 8:1 to 10:1.

[0034] Step 2: Prepare a coating solution to obtain coating solution I. Polyurethane resin is used as the film-forming material, a mixture of ethanol and water is used as the diluent, and a bio-based surfactant, alkyl glycoside, is used as the surfactant at a concentration of 0.5-0.8 wt%. Epoxy resin is used as the curing agent, and isomeric tridecanol ether is used as the defoaming agent. The mixture is heated to 60-80°C in a magnetic stirrer, thoroughly mixed for 5-6 hours, and then cooled naturally to obtain coating solution I.

[0035] Step 3: Add biodegradable polyester and hexamethylene diisocyanate to the coating solution I and mix thoroughly. The ratio of PBAT-based polyester and hexamethylene diisocyanate is 1:1 to 1:2. Add a certain amount of trimethylolpropane to obtain coating solution II.

[0036] The polyurethane main chain is formed by the reaction of biodegradable polyester and hexamethylene diisocyanate. This long-chain structure improves the hardness, elastic modulus and hydrolysis resistance of the coating layer.

[0037] Step 4: Add nano-carbonate particles and plastic powder to the coating solution II, and mix them thoroughly under magnetic stirring for 30 minutes to obtain the coating solution III.

[0038] The nano carbonate particles are nano calcium carbonate, the particle diameter of the plastic powder is less than 0.1 μm, and the amount of plastic powder added is 5-6 wt % of the leaching solution II.

[0039] Step 5: Carry out laminating treatment, preheat the base paper to 60-80℃, and then use a shower to spray laminating liquid III. The amount of laminating liquid III used is 20-30g per square meter of paper.

[0040] Step 6: Drying treatment: Place the coated base paper in a drying oven and dry it at a temperature of 50-80℃.

[0041] Step 7: Curing treatment is carried out. The dried base paper is sent to the ultraviolet curing room to cross-link and cure the cross-linked substances in the coating liquid. The curing process includes a preheating stage, a hot melt bonding stage and a cooling stage.

[0042] The preheating stage uses infrared radiation heating at a temperature of 120°C to 150°C; the hot melt bonding stage uses high-frequency induction heating at a temperature of 180°C to 250°C; the cooling stage uses a mixed air and water cooling system to reduce the temperature to 100°C to 120°C.

[0043] Figure 1 The adhesion test results of waterproof coatings on paper products at different pulp fiber to plastic fiber ratios are presented. The results show that the ratio of pulp fiber to plastic fiber has a significant impact on the adhesion of the coating. The performance is optimal when the ratio of pulp fiber to plastic fiber is 8:1 to 10:1.

[0044] Figure 2Experimental results on the surface tension of waterproof coatings for paper products in the presence of different bio-based surfactants, alkyl glycosides, are presented. The results show that the addition of bio-based surfactants, alkyl glycosides, can increase the surface tension of the coating. When the alkyl glycoside content is increased to 0.5%, the difference in surface tension of the coating is minimal. Therefore, for economic reasons, the alkyl glycoside addition range is 0.5-0.8t%, but this does not limit the alkyl glycoside content to above 0.8%.

[0045] Figure 3 The adhesion test results of waterproof coating on paper products with different nano-calcium carbonate contents are given. According to the experimental test results, the optimal nano-calcium carbonate content is 5~6 wt%.

[0046] In summary, the preparation method of the environmentally friendly paper product waterproof coating has the following advantages: (1) Surfactant: Bio-based surfactant alkyl glycoside reduces the surface tension of the liquid, enhances the wettability and leveling of the coating liquid on the paper surface, has strong hard water tolerance, and is renewable and biodegradable. It has good environmental protection effect.

[0047] (2) The polyurethane backbone can be formed by reacting biodegradable polyester (PBAT-based polyester) with hexamethylene diisocyanate (HDI). This long-chain structure can improve the hardness, elastic modulus, and hydrolysis resistance of the coating layer. It can resist the penetration of water, oil, and organic solvents. Biodegradable polyester can improve degradability and is beneficial to the environment. At the same time, hexamethylene diisocyanate (HDI) improves the flexibility and impact resistance of the coating.

[0048] (3) Compared with traditional polylactic acid fibers, the polylactic acid fibers added to pulp are completely biodegradable and can be easily decomposed into CO2 and water in the natural environment, making them environmentally friendly.

[0049] The above description is only a specific embodiment of the present invention, but the structural features of the present invention are not limited thereto. Any changes or modifications made by any technician in this field within the scope of the present invention are included in the patent scope of the present invention.

Claims

1. A method for preparing an environmentally friendly waterproof coating for paper products, characterized in that The steps are as follows: The first step is to make the base paper. The pulp fiber is selected from bamboo fiber, and polylactic acid fiber is added thereto. After being fully mixed, the paper is prepared. After the paper is rolled, it does not need to be dried for use. Step 2: Prepare a coating solution to obtain coating solution I, using polyurethane resin as the film-forming material, a mixture of ethanol and water as the diluent, a bio-based surfactant alkyl glycoside as the surfactant, the concentration of the bio-based surfactant alkyl glycoside being 0.5-0.8 wt%, an epoxy resin as the curing agent, and isomeric tridecyl alcohol ether as the defoaming agent; Step 3: Add biodegradable polyester and hexamethylene diisocyanate to the coating solution I and mix thoroughly. The ratio of PBAT-based polyester and hexamethylene diisocyanate is 1:1 to 1:

2. A certain amount of trimethylolpropane is added to obtain coating solution II. Step 4: Add nanocarbonate particles and plastic powder to the coating solution II, and mix them thoroughly under magnetic stirring for 30 minutes to obtain the coating solution III; Step 5: Preheat the base paper to 60-80℃, then use a shower to spray the coating liquid III. The amount of coating liquid III is 20-30g per square meter of paper. Step 6: Drying treatment: Place the coated base paper in a drying oven and dry it at a temperature of 50-80°C. Step 7: Curing treatment is carried out. The dried base paper is sent to the ultraviolet curing room to cross-link and cure the cross-linked substances in the coating liquid. The curing process includes a preheating stage, a hot melt bonding stage and a cooling stage.

2. The method for preparing an environmentally friendly waterproof coating for paper products according to claim 1, characterized in that: The size of the plastic fiber is less than 10 mm, and it is ultra-short polylactic acid; its maximum diameter is less than 1.5 times that of the pulp fiber, and the ratio of the pulp fiber to the plastic fiber is 8:1 to 10:

1.

3. The method for preparing an environmentally friendly waterproof coating for paper products according to claim 1, characterized in that: The mixed solution in the coating solution preparation was heated to 60-80° C. in a magnetic stirrer, fully mixed for 5-6 h, and naturally cooled to obtain coating solution I.

4. The method for preparing an environmentally friendly waterproof coating for paper products according to claim 1, wherein: The polyurethane main chain is formed by the reaction of biodegradable polyester and hexamethylene diisocyanate. This long-chain structure improves the hardness, elastic modulus and hydrolysis resistance of the coating layer.

5. The method for preparing an environmentally friendly waterproof coating for paper products according to claim 1, wherein: The nano carbonate particles are nano calcium carbonate, the particle diameter of the plastic powder is less than 0.1 μm, and the amount of plastic powder added is 5-6 wt % of the leaching solution II.

6. The method for preparing an environmentally friendly waterproof coating for paper products according to claim 1, characterized in that: The preheating stage uses infrared radiation heating at a temperature of 120°C to 150°C; the hot melt bonding stage uses high-frequency induction heating at a temperature of 180°C to 250°C; the cooling stage uses a mixed air and water cooling system to reduce the temperature to 100°C to 120°C.

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