Hydrophobic composite coating, preparation method of hydrophobic composite coating and paper-based product applying hydrophobic composite coating

Abstract

The invention relates to a hydrophobic composite coating, a preparation method thereof and a paper-based product applying the coating. The preparation method comprises the following steps: S1, uniformly mixing boehmite of 1-10 [mu] m, ZIF-8 of 0.2-2 [mu] m, stearic acid and a first organic solvent to obtain a first hydrophobic coating; s2, uniformly mixing polydimethylsiloxane, a matched curing agent and a second organic solvent to obtain a second hydrophobic coating; s3, spraying a first hydrophobic coating on the base material, and drying at room temperature for 5-20 minutes; and S4, spraying a second hydrophobic coating on the first hydrophobic layer of the base material, curing for 60-180 minutes at the temperature of 60-90 DEG C, and repeating twice to form the hydrophobic composite coating on the surface of the base material. Different from the prior art, according to the technical scheme, two kinds of nanoparticles boehmite and ZIF-8 which are complementary in function and structure are combined with a fluorine-free binder with low surface energy, a hydrophobic coating with a micro-nano rough structure and low surface energy is constructed on a base plane, and therefore efficient waterproof modification of the paper-based material is achieved.

Description

Technical Field

[0001] The invention relates to the field of hydrophobic materials, and in particular to a hydrophobic composite coating and a preparation method thereof, and a paper-based product using the coating. Background Art

[0002] Traditional hydrophobic interface construction technology mainly relies on fluorine-containing substances (such as perfluoroalkyl compounds PFASs). Studies have shown that PFASs are closely related to a variety of health problems such as immune system suppression, endocrine disruption, and increased cancer risk. At the same time, these substances are difficult to degrade in the environment, tend to remain in soil and water for a long time, and accumulate in organisms through the food chain, posing a serious threat to ecosystems and human health. Therefore, the development of fluorine-free, environmentally friendly hydrophobic interface construction technology is of great practical significance.

[0003] Traditional plastic packaging has caused serious environmental pollution problems due to its difficult-to-degrade properties. With the increasing global environmental awareness, seeking alternative new environmentally friendly packaging materials has become an important research direction in the industry. Paper-based packaging materials have received widespread attention due to their low cost, good recyclability, environmental friendliness and certain mechanical strength. However, the main component of paper-based materials is cellulose, which contains a large number of hydrophilic hydroxyl groups on its surface, causing the material to be easily affected by moisture when in contact with water or moisture, affecting the normal packaging function. Therefore, improving the waterproof performance of paper-based packaging materials has become a research focus.

[0004] In the prior art, the water resistance and moisture resistance of paper-based materials are usually improved by coating a layer of plastic film on the surface of the paper-based material. However, this method does not fundamentally solve the problem that plastics are difficult to degrade, and it is difficult to promote and apply in many countries and regions due to restrictions on environmental protection laws and regulations. In addition, in recent years, the research on superhydrophobic surfaces has provided new ideas for the design and preparation of functional food packaging materials. Superhydrophobic surfaces not only have excellent waterproof properties, but also show broad application prospects in the fields of self-cleaning, anti-fog, antibacterial adhesion, and liquid food packaging. However, how to achieve efficient superhydrophobic modification of paper-based materials without using fluorine-containing materials is still a major challenge in the current technical field. Summary of the invention

[0005] In view of the above problems, the present application provides a hydrophobic composite coating and a preparation method thereof and a paper-based product using the coating. The method combines two nanoparticles with complementary structures and functions with a fluorine-free binder with low surface energy to construct a super-hydrophobic coating with a micro-nano rough structure and low surface energy on the surface of a substrate, thereby achieving efficient waterproof modification of the coating and the substrate.

[0006] The first aspect of the present application provides a method for preparing a hydrophobic composite coating, comprising the following steps:

[0007] S1: mixing 1-10 μm boehmite, 0.2-2 μm ZIF-8, stearic acid and a first organic solvent to obtain a first hydrophobic coating;

[0008] S2: uniformly mixing polydimethylsiloxane, polydimethylsiloxane supporting curing agent and a second organic solvent to obtain a second hydrophobic coating;

[0009] S3: spraying the first hydrophobic coating on the substrate and drying it at room temperature for 5 to 20 minutes; forming a first hydrophobic coating on the surface of the substrate;

[0010] S4: spraying the second hydrophobic coating onto the first hydrophobic layer of the substrate, curing at 60-90° C. for 60-180 min, repeating twice, and forming the hydrophobic composite coating on the surface of the substrate.

[0011] ZIF-8 is a new type of imidazolate zeolite framework with a zeolite topological structure. In addition to its high stability, its surface also has low surface energy and good hydrophobic properties.

[0012] The surface of the nanoparticle boehmite has a micro-nano structure to provide the necessary surface roughness. ZIF-8 has nanoparticles with low surface energy, which can reduce the surface energy of the coating. The hydrophobic performance is optimized through the synergistic effect of the two nanoparticles.

[0013] The spraying process is adopted to better combine the two nanoparticles in a coating solution through the surface modification effect of the non-polar alkyl chain of stearic acid. The composite coating solution is evenly applied to the surface of the paper-based material through the spraying process to control the thickness and uniformity of the coating and ensure the stability and consistency of the hydrophobic performance. The paper-based material after spraying is dried and cured to form a hydrophobic surface with excellent waterproof, antifouling and corrosion resistance.

[0014] Different from the existing technology, this technical solution combines two nanoparticles with complementary functions and structures, boehmite and ZIF-8, with a low surface energy fluorine-free binder to construct a hydrophobic coating with a micro-nano rough structure and low surface energy on the surface of the paper-based material, thereby achieving efficient waterproof modification of the paper-based material.

[0015] In some embodiments, the feed ratio of the solid material composed of boehmite, ZIF-8 and stearic acid to the first organic solvent is 1g:10-25mL; the mass ratio of boehmite, ZIF-8 and stearic acid is 20-35:1-20:8-15.

[0016] In some embodiments, the mass ratio of boehmite to ZIF-8 is 15:8.

[0017] In some embodiments, the first organic solvent is ethyl acetate or n-hexane.

[0018] In some embodiments, the mass ratio of the polydimethylsiloxane to the curing agent is 1:0.1; the feed ratio of the polydimethylsiloxane to the second organic solvent is 1 g: 15-30 mL.

[0019] In some embodiments, the second organic solvent is ethyl acetate or n-hexane.

[0020] In some embodiments, the boehmite is prepared by a hydrothermal method using urea and sodium aluminate.

[0021] In some embodiments, the ZIF-8 is prepared by a solvent method using Zn(NO3)2·6H2O and 2-methylimidazole, wherein the solvent is anhydrous methanol.

[0022] The second aspect of the present application provides a hydrophobic composite coating, which is prepared using the preparation method described in the first aspect of the present application.

[0023] A third aspect of the present application provides a hydrophobic paper, wherein the coating in the hydrophobic paper adopts the hydrophobic composite coating of the second aspect of the present application.

[0024] The above-mentioned records related to the invention content are only an overview of the technical solution of the present application. In order to enable ordinary technicians in the field to more clearly understand the technical solution of the present application, and then implement it according to the written contents of the specification, and to make the above-mentioned purpose and other purposes, features and advantages of the present application easier to understand, the specific implementation mode and drawings of the present application are explained below. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings are only used to illustrate the principles, implementation methods, applications, characteristics and effects of the specific embodiments of the present application and other related contents, and shall not be considered as limitations of the present application.

[0026] In the drawings of the specification:

[0027] Figure 1 The contact angle diagrams of the prepared hydrophobic papers of the embodiments and comparative examples;

[0028] Figure 2 is a surface scanning electron microscope image of the hydrophobic paper prepared in Example 3;

[0029] Figure 3 The XRD pattern of the coating layer in the hydrophobic paper prepared in Example 3;

[0030] Figure 4 This is a hydrophobic test diagram of the hydrophobic paper prepared in Example 3; wherein Figure 4(A) is an optical image of paper floating on the water surface; (B) is a picture of the silver mirror phenomenon when the paper surface is immersed in water under the action of external force; (C) is an image of droplets of different liquid foods on the hydrophobic paper surface;

[0031] Figure 5 This is a diagram of the anti-fouling test of the hydrophobic paper prepared in Example 5; Figure 5 (A)-(C) are diagrams showing the anti-fouling test process of hydrophobic paper in muddy water; (D)-(F) are diagrams showing the anti-fouling test process of super-hydrophobic paper in methyl orange-dyed water. DETAILED DESCRIPTION

[0032] In order to explain in detail the possible application scenarios, technical principles, specific schemes that can be implemented, and the purposes and effects that can be achieved, the following is a detailed description of the specific embodiments listed in conjunction with the accompanying drawings. The embodiments described herein are only used to more clearly illustrate the technical solutions of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0033] Reference to "embodiment" herein means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The term "embodiment" appearing in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or association with other embodiments. In principle, in the present application, as long as there is no technical contradiction or conflict, the various technical features mentioned in the embodiments can be combined in any way to form a corresponding implementable technical solution.

[0034] Unless otherwise defined, the technical terms used in this document have the same meanings as those generally understood by those skilled in the art to which this application belongs; the use of relevant terms in this document is only for describing specific embodiments and is not intended to limit this application.

[0035] In the description of this application, the term "and / or" is an expression used to describe the logical relationship between objects, indicating that three relationships may exist, for example, A and / or B, which means: A exists, B exists, and A and B exist at the same time. In addition, the character " / " in this article generally indicates that the objects before and after are in an "or" logical relationship.

[0036] In the present application, terms such as “first” and “second” are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship of quantity, priority or sequence between these entities or operations.

[0037] Without further limitations, in this application, the words "include", "comprises", "has" or other similar expressions used in the sentences are intended to cover non-exclusive inclusion. These expressions do not exclude the presence of additional elements in the process, method or product including the elements, so that the process, method or product including a series of elements may include not only those limited elements, but also other elements not explicitly listed, or also include elements inherent to such process, method or product.

[0038] Similar to the understanding in the Examination Guidelines, in this application, expressions such as "greater than", "less than", "exceed" and the like are understood to exclude the number itself; expressions such as "above", "below", "within" and the like are understood to include the number itself. In addition, in the description of the embodiments of this application, "multiple" means more than two (including two), and similar expressions related to "multiple" are also understood in this way, such as "multiple groups", "multiple times", etc., unless otherwise clearly and specifically limited.

[0039] The first aspect of the present application provides a method for preparing a hydrophobic composite coating, comprising the following steps:

[0040] S1: mixing 1-10 μm boehmite, 0.2-2 μm ZIF-8, stearic acid and a first organic solvent to obtain a first hydrophobic coating;

[0041] S2: uniformly mixing polydimethylsiloxane, polydimethylsiloxane supporting curing agent and a second organic solvent to obtain a second hydrophobic coating;

[0042] S3: spraying the first hydrophobic coating on the substrate and drying it at room temperature for 5 to 20 minutes; forming a first hydrophobic coating on the surface of the substrate;

[0043] S4: spraying the second hydrophobic coating onto the first hydrophobic layer of the substrate, curing at 60-90° C. for 60-180 min, repeating twice, and forming the hydrophobic composite coating on the surface of the substrate.

[0044] ZIF-8 is a new type of imidazolate zeolite framework with a zeolite topological structure. In addition to its high stability, its surface also has low surface energy and good hydrophobic properties.

[0045] The surface of the nanoparticle boehmite has a micro-nano structure to provide the necessary surface roughness. ZIF-8 has nanoparticles with low surface energy, which can reduce the surface energy of the coating. The hydrophobic performance is optimized through the synergistic effect of the two nanoparticles.

[0046] The spraying process is adopted to better combine the two nanoparticles in a coating solution through the surface modification effect of the non-polar alkyl chain of stearic acid. The composite coating solution is evenly applied to the surface of the paper-based material through the spraying process to control the thickness and uniformity of the coating and ensure the stability and consistency of the hydrophobic performance. The paper-based material after spraying is dried and cured to form a hydrophobic surface with excellent waterproof, antifouling and corrosion resistance.

[0047] Different from the existing technology, this technical solution combines two nanoparticles with complementary functions and structures, boehmite and ZIF-8, with a low surface energy fluorine-free binder to construct a hydrophobic coating with a micro-nano rough structure and low surface energy on the surface of the paper-based material, thereby achieving efficient waterproof modification of the paper-based material.

[0048] In some embodiments, the feed ratio of the solid material composed of boehmite, ZIF-8 and stearic acid to the first organic solvent is 1g:10-25mL; the mass ratio of boehmite, ZIF-8 and stearic acid is 20-35:1-20:8-15.

[0049] In some embodiments, the mass ratio of boehmite to ZIF-8 is 15:8.

[0050] In some embodiments, the first organic solvent is ethyl acetate or n-hexane.

[0051] In some embodiments, the mass ratio of the polydimethylsiloxane to the curing agent is 1:0.1; the feed ratio of the polydimethylsiloxane to the second organic solvent is 1 g: 15-30 mL.

[0052] In some embodiments, the second organic solvent is ethyl acetate or n-hexane;

[0053] In some embodiments, the boehmite is prepared by a hydrothermal method using urea and sodium aluminate.

[0054] In some embodiments, the ZIF-8 is prepared by a solvent method using Zn(NO3)2·6H2O and 2-methylimidazole, wherein the solvent is anhydrous methanol.

[0055] The second aspect of the present application provides a hydrophobic composite coating, which is prepared using the preparation method described in the first aspect of the present application.

[0056] A third aspect of the present application provides a hydrophobic paper, wherein the coating in the hydrophobic paper adopts the hydrophobic composite coating of the second aspect of the present application.

[0057] The boehmite and ZIF-8 in this embodiment are prepared in the following manner:

[0058] Preparation of Boehmite (BMPs)

[0059] Dissolve 8.67g urea and 1.02g sodium aluminate in 15ml deionized water, mix and stir vigorously for 20min, transfer to a hydrothermal reactor and react at 140℃ for 10h. After the reaction, wash with deionized water until the filtrate is clear and neutral, dry in a vacuum oven at 60℃ for 6h, take out and grind to obtain 1-10μm BMPs particles.

[0060] Preparation of ZIF-8

[0061] Take 0.90g Zn(NO3)2·6H2O and dissolve it in 30ml anhydrous methanol. Take 1.090g 2-methylimidazole and dissolve it in 30ml anhydrous methanol. Then pour the 2-methylimidazole solution into the Zn(NO3)2·6H2O solution and continue stirring for 24h. Then, centrifuge, wash and dry to obtain 0.2-2μm ZIF-8 particles.

[0062] In this embodiment, the polydimethylsiloxane and the matching curing agent are polydimethylsiloxane prepolymer of Dow Corning Sylgard 184 and the matching curing agent.

[0063] Implementation Case 1:

[0064] 1. Preparation of hydrophobic coating

[0065] (1) 1.5 g of boehmite powder, 0.4 g of ZIF-8 powder and 0.6 g of stearic acid were added to 40 ml of ethyl acetate at a ratio of 1 g of solid to 13.7 mL of organic solvent, and ultrasonically mixed to obtain a first hydrophobic coating.

[0066] (2) 2 g of polydimethylsiloxane (PDMS) was added to 40 ml of ethyl acetate, and 0.2 g of curing agent was added according to the mass ratio of polydimethylsiloxane to curing agent being 1:0.1, and ultrasonic mixing was performed to obtain a second hydrophobic coating.

[0067] 2. Preparation of hydrophobic paper

[0068] The first hydrophobic coating A was sprayed on a 30 cm x 30 cm paper substrate and dried at room temperature for 20 min. The second hydrophobic coating was then sprayed on the paper substrate and cured at 80 ° C for 120 min. This was repeated twice to obtain a super hydrophobic composite coating on the paper substrate surface. The sample was labeled ZIF-8 / SA / BMPs@PDMS@paper-0.04.

[0069] Implementation Case 2:

[0070] 1. Preparation of hydrophobic coating

[0071] (1) In a ratio of solid to organic solvent of 1 g:13.7 mL, 1.5 g of boehmite powder, 0.6 g of ZIF-8 powder and 0.6 g of stearic acid were added to 40 ml of ethyl acetate and ultrasonically mixed to obtain a first hydrophobic coating.

[0072] (2) 2 g of polydimethylsiloxane (PDMS) was added to 40 ml of ethyl acetate, and 0.2 g of curing agent was added according to the mass ratio of polydimethylsiloxane to curing agent being 1:0.1, and ultrasonic mixing was performed to obtain a second hydrophobic coating.

[0073] 2. Preparation of hydrophobic paper

[0074] The first hydrophobic coating was sprayed on a 30cm x 30cm paper substrate and dried at room temperature for 20 minutes; the second hydrophobic coating was sprayed on the paper substrate and cured at 80°C for 120 minutes. The spraying and curing were repeated twice to obtain a super hydrophobic composite coating on the paper substrate surface. The sample was labeled as ZIF-8 / SA / BMPs@PDMS@paper-0.06. Implementation Case 3:

[0075] 1. Preparation of hydrophobic coating

[0076] (1) In a ratio of solid to organic solvent of 1 g:13.7 mL, 1.5 g of boehmite powder, 0.8 g of ZIF-8 powder and 0.6 g of stearic acid were added to 40 ml of ethyl acetate and ultrasonically mixed to obtain a first hydrophobic coating.

[0077] (2) 2 g of polydimethylsiloxane (PDMS) was added to 40 ml of ethyl acetate, and 0.2 g of curing agent was added according to the mass ratio of polydimethylsiloxane to curing agent being 1:0.1, and ultrasonic mixing was performed to obtain a second hydrophobic coating.

[0078] 2. Preparation of hydrophobic paper

[0079] The first hydrophobic coating was sprayed on a 30 cm x 30 cm paper substrate and dried at room temperature for 20 min. The second hydrophobic coating was then sprayed on the paper substrate and cured at 80 ° C for 120 min. This process was repeated twice to obtain a super hydrophobic composite coating on the paper substrate surface. The sample was labeled ZIF-8 / SA / BMPs@PDMS@paper-0.08.

[0080] Comparative case 1:

[0081] 1. Preparation of hydrophobic coating

[0082] 2 g of polydimethylsiloxane (PDMS) was added to 40 ml of ethyl acetate, and 0.2 g of curing agent was added according to the mass ratio of polydimethylsiloxane to curing agent being 1:0.1, and 0.6 g of stearic acid was added, and ultrasonic mixing was performed to obtain a hydrophobic coating.

[0083] 2. Preparation of hydrophobic paper

[0084] The hydrophobic coating was sprayed on a 30 cm x 30 cm paper substrate and cured at 80°C for 60 to 180 min, and repeated twice to obtain a super hydrophobic composite coating on the paper substrate surface. The sample was labeled PDMS@paper.

[0085] Comparative Case 2:

[0086] 1. Preparation of hydrophobic coating

[0087] (1) 1.5 g of boehmite powder and 0.6 g of stearic acid were added to 40 ml of ethyl acetate at a ratio of 1 g of solid to 13.7 mL of organic solvent, and the mixture was ultrasonically mixed to obtain a hydrophobic coating A.

[0088] (2) 2 g of polydimethylsiloxane (PDMS) was added to 40 ml of ethyl acetate, and 0.2 g of curing agent was added according to the mass ratio of polydimethylsiloxane to curing agent being 1:0.1. The mixture was ultrasonically mixed to obtain a hydrophobic coating B.

[0089] 2. Preparation of hydrophobic paper

[0090] The hydrophobic coating A was sprayed on a 30cm x 30cm paper substrate and dried at room temperature for 20 minutes; the hydrophobic coating B was then sprayed on the paper substrate and cured at 80°C for 120 minutes, and the process was repeated twice to obtain a super-hydrophobic composite coating on the paper substrate surface. The sample was labeled as SA / BMPs@PDMS@paper.

[0091] Performance testing:

[0092] 1. Contact angle detection:

[0093] The hydrophobic paper obtained in the examples and comparative examples was tested for contact angle. The results are as follows: Figure 1 As shown. Figure 1 It can be seen from the figure that after spraying a fluorine-free binder with certain hydrophobic properties, polydimethylsiloxane (PDMS), on the paper base, the hydrophobicity of the paper is significantly enhanced, and the contact angle reaches more than 130°. After adding BMPs, the hydrophobicity of the paper surface is further improved. This is because there are many nano-fine structures on the spherical structure BMPs, which can greatly increase the roughness of the paper base surface, thereby improving the hydrophobicity. However, even after adding BMPs, the average contact angle of the paper is less than 150°, which has not yet reached super hydrophobic properties.

[0094] In Examples 1 to 3, the content of ZIF-8 added increases. In the coating, polydimethylsiloxane is used as a binder to improve mechanical properties. ZIF-8 is a substance with lower surface energy, which can improve super-hydrophobic performance. In theory, the ratio of ZIF-8 is large, the super-hydrophobic performance of the material surface will be improved, and the contact angle of the paper-based hydrophobic coating will be larger. However, the content of ZIF-8 in Examples 1 and 2 is not enough, the distribution is not uniform enough, and the deficiency plays a role. When the mass ratio of the added ZIF-8 to BMPs is less than 8:15, the contact angle of the paper-based hydrophobic coating is maintained below 150°, which is not much different from the result without adding ZIF-8. However, when the mass ratio of ZIF-8 to BMPs reaches 8:15, the contact angle of the paper-based hydrophobic coating is greatly improved, and the average contact angle reaches 156°, achieving a super-hydrophobic effect. The 8:15 of ZIF-8 and BMPs is the optimal ratio of the hydrophobic coating, and the contact angle is greater than 150°, reaching super-hydrophobic performance.

[0095] The study found that if the ZIF-8 content is too high, the surface energy of the coating will be too low, making it difficult to adhere to the paper base, causing the coating surface to fall off and destroying the surface microstructure.

[0096] 2. Morphology detection:

[0097] Figure 2 This is a surface scanning electron microscope image of the paper-based super-hydrophobic coating in Example 3. It can be seen that the coating surface has a large roughness, which is composed of the spherical needle-like structure of BMPs and the cubic ZIF-8. The BMPs in the coating provide a three-dimensional structure with roughness, and ZIF-8 has good hydrophobic properties and can structurally fill the uneven blank positions of BMPs, thereby better achieving the effect of increasing the roughness and reducing the surface energy.

[0098] The spraying process applies these micro-nanoparticles to the surface of the paper-based material more evenly and bonds them together through the binder polydimethylsiloxane (PDMS), so that the coating is uniform and the stability and consistency of the superhydrophobic performance are ensured.

[0099] Figure 3 : is the XRD pattern of the hydrophobic coating prepared in Examples 1 to 3 and the comparative example.

[0100] For pure BMPs particles, the characteristic peak at 18.2° is attributed to the (002) crystal plane, and the diffraction peaks at 20.3°, 20.5°, 36.6°, 37.7°, 44.1° and 63.8° are respectively attributed to the (110), (200), (021), (311), (313) and (324) planes, which are consistent with the standard card PDF#33-0018. For pure ZIF-8 particles, strong characteristic diffraction peaks appear at 2θ=7.3°, 10.3°, 12.7°, 14.7°, 16.4° and 17.9°, which are respectively attributed to the (011), (002), (112), (022), (013) and (222) crystal planes, which is also consistent with the standard card PDF#62-1030.

[0101] The paper as the base surface is mainly composed of cellulose, so the peaks of the paper base at 11.2°, 22.5° and 31.0° belong to the peaks of the (002), (004) and (040) crystal planes of cellulose, respectively. When there is only polydimethylsiloxane on the paper base, the XRD peak of the sample does not change basically, indicating that the crystalline structure of the paper base is not affected. When the hydrophobic layer is sprayed on the paper base, its XRD pattern is the same as the pattern of BMPs and ZIF-8 superimposed on the paper base, indicating that ZIF-8 and BMPs are introduced into the super hydrophobic layer.

[0102] 3. Paper hydrophobicity test:

[0103] The hydrophobic paper obtained in Example 3 was (A) placed in water, (B) immersed in the water surface by external force, and (C) some common liquid foods (such as honey, milk, orange juice, etc.) were dropped on the surface of the hydrophobic paper. The results are as follows: Figure 4 shown.

[0104] Figure 4 (A) It can be seen that the hydrophobic paper obtained in Example 3 has super hydrophobic properties, so the paper can float freely and stably on the water surface. Figure 4 (B) It can be seen that when the super-hydrophobic paper is immersed in water under the action of external force, its surface shows a mirror reflection phenomenon. This is mainly caused by the reflection of the residual air between the super-hydrophobic paper and the water. Figure 4 (C) shows some common liquid foods (such as honey, milk, orange juice, etc.) droplets on the surface of super-hydrophobic paper. Figure 4 As can be seen in (C), the droplets do not spread out on the paper, but maintain their original droplet shape.

[0105] The above results show that the super-hydrophobic paper in Example 3 has excellent water-repellent properties and can keep its surface dry even when in direct contact with water or various liquid foods. Therefore, it has potential application prospects in food packaging.

[0106] 5. Paper anti-fouling performance test:

[0107] Antifouling performance is crucial to the practical application of super-hydrophobic surfaces. Therefore, the super-hydrophobic paper prepared in Example 3 was immersed in muddy water or methyl orange dyed water for 10 minutes and then taken out. It was found that the surface of the paper sample was very clean without any residual mud or dye. The test process and results are shown in Figure 2. Figure 5 shown.

[0108] The above phenomenon shows that the hydrophobic paper prepared in Example 3 has excellent waterproof and antifouling properties, which further confirms its feasibility in practical application in food packaging.

[0109] In summary, this technical solution combines two nanoparticles, boehmite and ZIF-8, with complementary functions and structures, with a fluorine-free binder with low surface energy to construct a superhydrophobic coating with a micro-nano rough structure and low surface energy on the surface of the paper-based material, thereby achieving efficient waterproof modification of the paper-based material.

[0110] The surface of the paper-based material prepared by this technical solution can achieve super-hydrophobic properties with a contact angle greater than 150°, showing excellent waterproof performance. The use of fluorine-free binders avoids harm to the environment and human health; at the same time, it has anti-fouling and corrosion-resistant properties, expanding the application range of paper-based packaging materials. The spraying process used in this technical solution is easy to operate and suitable for large-scale industrial production.

[0111] Finally, it should be noted that although the above embodiments have been described in the specification and drawings of this application, this does not limit the scope of patent protection of this application. All technical solutions generated by replacing or modifying equivalent structures or equivalent processes based on the essential concept of this application using the contents recorded in the specification and drawings of this application, as well as directly or indirectly implementing the technical solutions of the above embodiments in other related technical fields, are included in the scope of patent protection of this application.

Claims

1. A method for preparing a hydrophobic composite coating, characterized in that: The following steps are included S1: mixing 1-10 μm boehmite, 0.2-2 μm ZIF-8, stearic acid and a first organic solvent to obtain a first hydrophobic coating; S2: uniformly mixing polydimethylsiloxane, polydimethylsiloxane supporting curing agent and a second organic solvent to obtain a second hydrophobic coating; S3: spraying the first hydrophobic coating on the substrate and drying it at room temperature for 5 to 20 minutes; forming a first hydrophobic coating on the surface of the substrate; S4: spraying the second hydrophobic coating onto the first hydrophobic layer of the substrate, curing at 60-90° C. for 60-180 min, repeating twice, and forming the hydrophobic composite coating on the surface of the substrate.

2. The method for preparing the hydrophobic composite coating according to claim 1, characterized in that: The feed ratio of the solid material composed of boehmite, ZIF-8 and stearic acid to the first organic solvent is 1g:10-25mL; the mass ratio of the boehmite, ZIF-8 and stearic acid is 20-35:1-20:8-15.

3. The method for preparing the hydrophobic composite coating according to claim 1, characterized in that: The mass ratio of the boehmite to ZIF-8 is 15:

8.

4. The method for preparing the hydrophobic composite coating according to claim 1, characterized in that: The first organic solvent is ethyl acetate or n-hexane.

5. The method for preparing the hydrophobic composite coating according to claim 1, characterized in that: The mass ratio of the polydimethylsiloxane to the polydimethylsiloxane supporting curing agent is 1:0.1; the feeding ratio of the polydimethylsiloxane to the second organic solvent is 1g:15-30mL.

6. The method for preparing the hydrophobic composite coating according to claim 1, characterized in that: The second organic solvent is ethyl acetate or n-hexane.

7. The method for preparing the hydrophobic composite coating according to claim 1, characterized in that: The boehmite is prepared by a hydrothermal method using urea and sodium aluminate.

8. The method for preparing the hydrophobic composite coating according to claim 1, characterized in that: The ZIF-8 is prepared by using Zn(NO3)2·6H2O and 2-methylimidazole using a solvent method.

9. A hydrophobic composite coating, characterized in that: The hydrophobic coating is prepared by the preparation method according to any one of claims 1 to 8.

10. A hydrophobic paper, characterized in that: The coating in the hydrophobic paper adopts the hydrophobic composite coating described in claim 9.

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