A hydrophilic microstructured pla anti-fog coating and method of forming the same

Abstract

The application discloses a hydrophilic microstructure PLA anti-fog coating and relates to the technical field of degradable materials, and comprises the following components in parts by mass: tween 20 10-15 parts; sucrose laurate 3-5 parts; polyethylene glycol 15-20 parts; polyvinyl alcohol 8-12 parts; glycerol 3-5 parts; crosslinking agent 1-2 parts; wetting agent 0.1-0.5 parts; and deionized water 35-45 parts. The application further discloses a film forming method of the hydrophilic microstructure PLA anti-fog coating. Compared with the prior art, the application solves the problem that the surface of a packaging box made of a degradable PLA sheet is prone to condensing water drops due to the temperature difference between the inside and the outside.

Description

Technical Field

[0001] This invention relates to the field of biodegradable materials technology, and in particular to a hydrophilic microstructure PLA anti-fog coating and its film formation method. Background Technology

[0002] Polylactic acid (PLA), as a bio-based biodegradable material, is widely used in the processing of disposable food containers. PLA packaging boxes can be completely decomposed into carbon dioxide and water by microorganisms in the natural environment within 6-12 months, without environmental pollution.

[0003] Packaging boxes made from biodegradable PLA transparent blister sheets are safe, hygienic, and offer good display when used for food packaging. However, PLA transparent packaging boxes are prone to condensation in refrigerated or frozen environments due to temperature differences between the inside and outside, which scatters light and obscures the contents, hindering observation of the food inside the packaging. Summary of the Invention

[0004] The purpose of this invention is to provide a hydrophilic microstructure PLA anti-fog coating and its film-forming method to solve the problem that water droplets easily condense on the surface of packaging boxes made of biodegradable PLA sheets due to temperature differences between the inside and outside.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In one aspect, the present invention discloses a hydrophilic microstructure PLA anti-fog coating, comprising the following components in parts by mass:

[0006] Tween 20 10-15 servings;

[0007] 3-5 parts of sucrose laurate;

[0008] 15-20 parts of polyethylene glycol;

[0009] 8-12 parts of polyvinyl alcohol;

[0010] 3-5 parts glycerin;

[0011] 1-2 parts of crosslinking agent;

[0012] Wetting agent 0.1-0.5 parts;

[0013] 35-45 parts deionized water.

[0014] On the other hand, the present invention discloses a method for forming a PLA anti-fog coating with the above-described hydrophilic microstructure, comprising the following steps:

[0015] S1. Coating preparation: Prepare the raw materials for PLA anti-fog coating according to the above ratio, and mix the raw materials to obtain anti-fog coating;

[0016] S2, A-side spraying: After cleaning the first side of the PLA sheet, the first side of the PLA sheet is treated with low-temperature atmospheric pressure plasma. The anti-fog coating is applied to the first side of the PLA sheet by wire bar scraping to form the first wet film. Then, it is dried at a low temperature of 40℃ for 20-40 minutes to achieve the pre-curing of the first wet film.

[0017] S3, B-side spraying: The second side of the PLA sheet is cleaned, and the second side of the PLA sheet is treated with low-temperature atmospheric pressure plasma. The anti-fog coating is applied to the second side of the PLA sheet to form a second wet film by wire bar scraping.

[0018] S4. Double-sided total curing: PLA sheets are placed in an oven and dried at 50°C for 1-1.5 hours, so that both the first wet film and the second wet film are cured to form a dry film of 5-10μm.

[0019] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0020] 1. In this invention, the anti-fog coating alters the surface energy of the PLA sheet, causing condensate to spread evenly into a transparent water film rather than droplets, ensuring display clarity. Tween 20, as a nonionic surfactant, reduces surface tension, adsorbs water molecules, lowers the contact angle, and provides rapid anti-fog properties. Sucrose laurate, as a synergistic surfactant, enhances hydrophilicity and improves coating uniformity. Polyethylene glycol, as a hydrophilic core, forms hydrogen bonds with water molecules through hydroxyl groups and inhibits the dissolution of hydrophilic components through a PEG crosslinking network, achieving long-lasting anti-fog performance.

[0021] 2. In this invention, polyvinyl alcohol serves as a film-forming substance in the coating components, improving the coating adhesion and mechanical strength. The crosslinking agent promotes the formation of the coating network structure, subsequently forming a microporous hydrophilic network microstructure on the surface of the PLA sheet.

[0022] 3. In this invention, when the anti-fog coating is formed on the surface of PLA sheet, the surface of the PLA sheet is subjected to plasma treatment before the coating is applied to ensure the adhesion quality of the coating. Then, the thickness and uniformity of the wet film are precisely controlled by wire bar coating, so that a dry film of 5-10 μm is obtained after the wet film is cured. This not only effectively ensures the transparency of the coating, but also makes it easy to degrade and avoids affecting the degradation rate of the PLA sheet. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a flowchart illustrating the film formation method for a hydrophilic microstructure PLA anti-fog coating. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0026] Example 1

[0027] Please see Figure 1 On one hand, the present invention discloses a hydrophilic microstructure PLA anti-fog coating, comprising the following components in parts by weight:

[0028] Tween 20 10-15 servings;

[0029] 3-5 parts of sucrose laurate;

[0030] Polyethylene glycol (PEG-400) 15-20 parts;

[0031] 8-12 parts of polyvinyl alcohol;

[0032] 3-5 parts glycerin;

[0033] 1-2 parts of crosslinking agent;

[0034] Wetting agent 0.1-0.5 parts;

[0035] 35-45 parts deionized water.

[0036] On the other hand, the present invention discloses a method for forming a PLA anti-fog coating with the above-described hydrophilic microstructure, comprising the following steps:

[0037] S1. Coating preparation: Prepare the raw materials for PLA anti-fog coating according to the above ratio, and mix the raw materials to obtain anti-fog coating;

[0038] S2, A-side spraying: After cleaning the first side of the PLA sheet, the first side of the PLA sheet is treated with low-temperature atmospheric pressure plasma to improve the surface energy of the PLA sheet and ensure the adhesion of the anti-fog coating. Within 3 minutes after plasma treatment, the anti-fog coating is applied to the first side of the PLA sheet by wire bar scraping to form the first wet film. Then, it is dried at a low temperature of 40℃ for 20-40 minutes to achieve the pre-curing of the first wet film.

[0039] S3, B-side spraying: The second side of the PLA sheet is cleaned, and the second side of the PLA sheet is treated with low-temperature atmospheric pressure plasma. The anti-fog coating is applied to the second side of the PLA sheet to form a second wet film by wire bar scraping.

[0040] S4. Double-sided total curing: PLA sheets are placed in an oven and dried at 50°C for 1-1.5 hours, so that both the first wet film and the second wet film are cured to form a dry film of 5-10μm.

[0041] In step S1, the preparation of the anti-fog coating includes the following steps:

[0042] S11. Add deionized water to the reaction vessel, slowly add polyvinyl alcohol (PVA 1788) while stirring, heat to 80-85℃, and keep stirring for 30-40 minutes until the polyvinyl alcohol is completely dissolved and a transparent viscous solution is formed. Then cool down to below 40℃, add glycerol, and stir for 2-8 minutes to obtain the basic solution.

[0043] S12. Add polyethylene glycol, Tween 20 and sucrose laurate to the base solution in sequence. Stir for 10-20 minutes after each component is added to ensure that the three hydrophilic substances are fully mixed and form a stable hydrophilic system.

[0044] S13. Add crosslinking agent and stir for 10-20 minutes. Then add wetting agent to promote network structure formation. Next, adjust the pH value of the solution to 7-8 with pH adjuster to improve the stability of coating performance. Then stir at high speed of 800-1000 r / min for 20-30 min to ensure uniform and stable coating to obtain anti-fog coating. Before spraying anti-fog coating, filter through 180-250 mesh filter to remove impurities and let stand at room temperature for 12-24 hours to eliminate bubbles and improve film quality.

[0045] In step S2, the first side of the PLA sheet is cleaned by wiping with ethanol and then air-drying to remove surface dust and oil. During plasma treatment, the spray gun speed is 3–5 cm / s, and the spray gun is repeatedly sprayed across the PLA sheet surface 1–2 times. The cleaning and plasma treatment of side B are performed similarly. The sheet surface temperature is monitored during plasma treatment using a temperature monitoring device to ensure it does not exceed 45°C, preventing yellowing and deformation. Plasma treatment is stopped if the temperature exceeds the set threshold.

[0046] After applying an anti-fog coating to the PLA sheet surface, performance tests were conducted. These tests included anti-fog effectiveness, adhesion, and transparency. Based on the anti-fog and adhesion test results, the coating component ratios were adjusted. For example, the proportion of PEG (polyethylene glycol) or Tween 20 was increased to improve anti-fog effectiveness, and the proportion of polyvinyl alcohol was adjusted based on adhesion test results.

[0047] Working principle: The anti-fog coating changes the surface energy of PLA sheets, causing condensate to spread evenly into a transparent water film instead of fog droplets, ensuring display clarity. The coating uses deionized water as a solvent, ensuring its fluidity. Tween 20, or polyoxyethylene (20) sorbitan monolaurate, acts as a nonionic surfactant, reducing surface tension, adsorbing water molecules, reducing the contact angle, and providing rapid anti-fog properties. Sucrose laurate acts as a synergistic surfactant, enhancing hydrophilicity and improving coating uniformity. Polyethylene glycol acts as a hydrophilic core, forming hydrogen bonds with water molecules through hydroxyl groups, and inhibiting the dissolution of hydrophilic components through the PEG crosslinking network, achieving long-lasting anti-fog properties. In the coating components, polyvinyl alcohol acts as a film-forming substance, improving coating adhesion and mechanical strength. Glycerin acts as a plasticizer, preventing coating cracking and improving flexibility. The crosslinking agent promotes the formation of the coating network structure, subsequently forming a microporous hydrophilic network microstructure on the PLA sheet surface. The wetting agent improves the wettability of the coating on the PLA surface.

[0048] When anti-fog coating is applied to the surface of PLA sheet, the PLA sheet surface is subjected to plasma treatment before coating to ensure coating adhesion quality. Then, the thickness and uniformity of the wet film are precisely controlled by wire bar coating. The thickness of the wet film is determined by the film thickness and the solid content of the anti-fog coating, so that a dry film of 5-10 μm is obtained after the wet film is cured. This not only effectively ensures the transparency of the coating, but also makes it easy to degrade and avoids affecting the degradation rate of the PLA sheet.

[0049] Example 2

[0050] Based on the above embodiments, this embodiment further improves upon the following technical solution: the crosslinking agent is a composite crosslinking agent, and the components of the composite crosslinking agent include citric acid and sodium citrate, with an addition ratio of 3:2 for citric acid and sodium citrate.

[0051] The crosslinking agent is a mild crosslinking hydroxyl compound crosslinking agent, with citric acid as the main crosslinking agent and sodium citrate as the auxiliary crosslinking agent. It also plays a role in stabilizing foam and plasticizing the coating. The food-grade compound crosslinking agent formula is non-toxic and does not affect PLA degradation.

[0052] Example 3

[0053] Based on the above embodiments, this embodiment further improves upon the following technical solution: the wetting agent is a composite wetting agent, the components of which include polyglycerol fatty acid ester and lecithin, and the addition ratio of polyglycerol fatty acid ester and lecithin is 2:1.

[0054] The wetting agent is also a food-grade, biodegradable composite wetting agent to avoid the anti-fog coating affecting the degradation performance of PLA sheets. Polyglycerol fatty acid ester is used as the main wetting agent, which has strong wetting and transparency. The lecithin is made of natural bio-based soybean lecithin or sunflower lecithin that can be decomposed by microorganisms. This not only ensures food safety, but also further ensures that the anti-fog coating forms a biodegradable film on the surface of PLA sheets.

[0055] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A hydrophilic microstructure PLA anti-fog coating, characterized in that, Includes the following components in parts by weight: Tween 20 10-15 servings; 3-5 parts of sucrose laurate; 15-20 parts of polyethylene glycol; 8-12 parts of polyvinyl alcohol; 3-5 parts glycerin; 1-2 parts of crosslinking agent; Wetting agent 0.1-0.5 parts; 35-45 parts deionized water.

2. The PLA anti-fog coating with a hydrophilic microstructure according to claim 1, characterized in that, The crosslinking agent is a composite crosslinking agent, and the components of the composite crosslinking agent include citric acid and sodium citrate, with an addition ratio of 3:2 for citric acid and sodium citrate.

3. The PLA anti-fog coating with a hydrophilic microstructure according to claim 1, characterized in that, The wetting agent is a composite wetting agent, and the components of the composite wetting agent include polyglycerol fatty acid ester and lecithin, with the addition ratio of polyglycerol fatty acid ester and lecithin being 2:

1.

4. A method for forming a PLA anti-fog coating with a hydrophilic microstructure as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Coating preparation: Prepare the raw materials for PLA anti-fog coating according to the above ratio, and mix the raw materials to obtain anti-fog coating; S2, A-side spraying: After cleaning the first side of the PLA sheet, the first side of the PLA sheet is treated with low-temperature atmospheric pressure plasma. The anti-fog coating is applied to the first side of the PLA sheet by wire bar scraping to form the first wet film. Then, it is dried at 40℃ for 20-40 minutes to achieve the pre-curing of the first wet film. S3, B-side spraying: The second side of the PLA sheet is cleaned, and the second side of the PLA sheet is treated with low-temperature atmospheric pressure plasma. The anti-fog coating is applied to the second side of the PLA sheet to form a second wet film by wire bar scraping. S4. Double-sided total curing: PLA sheets are placed in an oven and dried at 50°C for 1-1.5 hours, so that both the first wet film and the second wet film are cured to form a dry film of 5-10μm.

5. The method for forming a PLA anti-fog coating with a hydrophilic microstructure according to claim 4, characterized in that, In step S1, the preparation of the anti-fog coating includes the following steps: S11. Add deionized water to the reaction vessel, slowly add polyvinyl alcohol while stirring, heat to 80-85℃, and keep warm and stir for 30-40 minutes until the polyvinyl alcohol is completely dissolved and a transparent viscous solution is formed. Then cool down to below 40℃, add glycerin, and stir for 2-8 minutes to obtain the basic solution. S12. Add polyethylene glycol, Tween 20 and sucrose laurate to the base solution in sequence, stirring for 10-20 min after each component is added. S13. Add crosslinking agent, stir for 10-20 minutes, then add wetting agent, and stir at high speed of 800-1000 r / min for 20-30 minutes to obtain anti-fog coating.

6. The method for forming a PLA anti-fog coating with a hydrophilic microstructure according to claim 5, characterized in that, In step S13, before high-speed stirring, the pH of the solution is adjusted to 7-8 using a pH adjuster.

7. The method for forming a PLA anti-fog coating with a hydrophilic microstructure according to claim 5, characterized in that, In step S13, the anti-fog coating obtained by stirring is filtered through a 180-250 mesh filter and left to stand at room temperature for 12-24 hours.

8. The method for forming a PLA anti-fog coating with a hydrophilic microstructure according to claim 4, characterized in that, In step S2, when the PLA sheet is subjected to plasma treatment, the spray gun speed is 3-5 cm / s, and the spray gun is repeatedly sprayed on the surface of the PLA sheet 1-2 times.

9. The method for forming a PLA anti-fog coating with a hydrophilic microstructure according to claim 4, characterized in that, In step S2, when cleaning the PLA sheet, it is first wiped with ethanol and then air-dried.

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