Preparation method and application of fluoride-free oil-proof coating film for food

Abstract

The invention relates to the technical field of oil-proof materials, in particular to a preparation method and application of a fluoride-free oil-proof coating film for food. Comprising the following steps: uniformly mixing a fluorine-free acrylate combined solution, an initiator, an emulsifier and a polyvinyl alcohol aqueous solution under an anaerobic condition, and carrying out emulsion polymerization on the acrylate combined solution to obtain the fluorine-free oil-proof agent, and coating the surface of tableware with the fluoride-free oil-proof agent, and drying to obtain the fluoride-free oil-proof coating film. The fluoride-free oil-proof coating film for the food has the advantages of being fluoride-free, oil-proof, good in film-forming property, heat-stable, good in acid resistance and the like, paper pulp tableware obtained through coating has the advantages of being environmentally friendly, degradable, oil-proof, acid-resistant, heat-resistant and the like, and the fluoride-free oil-proof coating film has a good application prospect in the field of disposable food tableware.

Description

Technical Field

[0001] The invention relates to the technical field of oil-proof materials, and in particular to a preparation method and application of a fluorine-free oil-proof coating for food. Background Art

[0002] Pulp molding uses sugarcane bagasse, corn stalks, wheat straw, reeds, straw and other herbaceous plants as raw materials, using the waste parts of crops, fully improving the utilization rate of plant resources, with simple production process, and the finished product has a certain mechanical strength, which has great application prospects in the field of environmentally friendly tableware. However, paper materials have a high porosity, and the fiber itself has hydroxyl groups, which leads to its biggest characteristic of not being oil-proof and waterproof. When used for food tableware packaging, its effect is obviously unsatisfactory.

[0003] In order to improve this characteristic, during the pulping process of pulp molded products, waterproofing agents, oil-proof agents, and other functional additives such as adhesives, brighteners, plasticizers, and antioxidants are added to the pulp in order to achieve good effects. However, the added additives will migrate into the food during the contact between the tableware and the food, and then be ingested into the human body, causing certain harm to human health. This requires effective modification of the pulp molded tableware, by surface treatment of the pulp molded tableware, and by coating the surface coating with an oil-proof agent to give it excellent properties such as direct contact with food, waterproofness, and oil resistance. In addition, since the tableware is inevitably in contact with acidic substances, the coating also needs to have a certain acid resistance effect.

[0004] Oil repellents are widely used in the industrial field, such as the fluorine-containing polymer and the protective coating agent containing the fluorine-containing polymer disclosed in patent 201911177507.3. The protective coating agent of the fluorine-containing polymer of this technical solution has strong adhesion and high hardness, and also has excellent waterproof and oil-proof properties and acid and alkali resistance. However, the use of fluorine-containing materials in tableware may pose a food safety risk, so there is an urgent need for a food-contactable fluorine-free oil repellent coating with excellent oil resistance and acid resistance. Summary of the invention

[0005] The present invention aims to overcome the defects in the prior art that fluorine-containing oil-proof coatings cannot be used in the food field and the production cost of bio-based fluorine-free oil-proof agents is high. A preparation method and application of fluorine-free oil-proof coatings for food are proposed to overcome the above defects.

[0006] In order to achieve the above-mentioned invention object, the present invention adopts the following technical solutions: A method for preparing a fluorine-free oil-proof coating for food, comprising the following steps: S1. Under anaerobic conditions, uniformly mixing a fluorine-free acrylate combination liquid, an initiator, an emulsifier and a polyvinyl alcohol (PVA) aqueous solution, so that the acrylate combination liquid undergoes emulsion polymerization to obtain a fluorine-free oil repellent; S2. Applying a fluorine-free oil-proof agent on the surface of tableware and drying the same to obtain a fluorine-free oil-proof coating.

[0007] Whether the oil repellent contains fluorine will affect its performance. Fluorine-containing oil repellent refers to fluorine-containing surfactants, commonly perfluorinated compounds, which are fully fluorinated anionic polymers with hydrophobic and oleophobic properties. Since the fluorine-carbon bond is very stable, this stability allows fluorinated compounds to maintain their performance in a variety of environments, including chemical resistance and heat resistance. Due to the presence of the fluoride layer, non-polar substances such as water and oil will be repelled by the surface fluoride molecules when they contact the coating surface. This repulsive force prevents water and oil droplets from maintaining stable contact on the coating surface, but instead forms spherical water droplets or oil droplets that are easy to roll off the surface.

[0008] However, fluorine-free bio-based oil repellents have high raw material and production costs, and usually need to be compounded with other oil repellents to obtain excellent water and oil resistance. In addition, additional production equipment needs to be purchased and production lines need to be built, which increases process costs and labor costs. Silicone oil repellents are similar to them and are difficult to achieve large-scale commercial production. Therefore, the present invention optimizes the process flow and verifies through experiments that the prepared oil-proof coating has good heat resistance, oil resistance, and acid resistance.

[0009] Preferably, the fluorine-free acrylic ester composition liquid in step S1 consists of butyl acrylate (BA), hydroxyethyl methacrylate (HEMA) and ethyl methacrylate (EMA).

[0010] As a further preference, the oil-water ratio of the fluorine-free oil repellent obtained by emulsion polymerization in step S1 is ≥1:2.

[0011] Preferably, the initiator in step S1 is water-soluble azobisisobutylamidine hydrochloride (V-50).

[0012] Preferably, the emulsifier in step S1 is a combination of one or more of polysorbate 80 (Tween 80) and sodium oleate.

[0013] Preferably, the fluorine-free oil repellent obtained in step S1 has a solid content of 35% to 45%.

[0014] Preferably, in step S2, the fluorine-free oil repellent is applied by spin coating, and a drying operation is performed while coating.

[0015] As a further preference, the drying operation temperature is 70-100° C. and the time is 2-3 hours.

[0016] On the other hand, the present invention discloses a fluorine-free oil-proof coating prepared based on the above method, and its application in coating the surface of pulp molded tableware.

[0017] Therefore, the present invention has the following beneficial effects: (1) The present invention conducts emulsion polymerization of acrylic ester monomers BA, HEMA and EMA in an oxygen-free environment to synthesize a fluorine-free oil repellent having good stability and being safe and non-toxic.

[0018] (2) The present invention directly applies the fluorine-free oil-proof agent on the surface of tableware, and forms an oil-proof film through a drying operation, which has good oil-proofing, temperature resistance and acid resistance.

[0019] (3) The fluorine-free oil-proof coating for food prepared by the present invention has a simple preparation process, low cost, safety and non-toxicity, and good stability, and has good application prospects in the field of disposable food tableware. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a SEM size morphology image of the fluorine-free oil repellent in Example 1 of the present invention.

[0021] Figure 2 This is a comparison chart of the oil and high temperature resistance of coated tableware and uncoated tableware.

[0022] Figure 3 This is a comparison chart of the acid resistance of coated tableware and uncoated tableware. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further clearly and completely described below through specific examples and in combination with the accompanying drawings. It should be noted that the embodiments described in the present invention are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating processes are given, but they are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. The experimental methods used in the following embodiments are conventional methods unless otherwise specified, and the materials, reagents, etc. used in the embodiments, unless otherwise specified, can be obtained from commercial channels.

[0024] The present invention provides a method for preparing a food-contactable fluorine-free oil-proofing agent coating, comprising the following steps: (1) Preparation of dispersant: 1.0-3.0 parts of polyvinyl alcohol is added to 100 ml of aqueous solution and stirred with a magnetic stirrer to fully dissolve and mix the mixture to obtain a PVA aqueous solution with a concentration of 1.0-3.0%.

[0025] (2) System construction and deoxygenation: 0.3-0.4 parts of V-50 initiator are placed in a three-necked flask reaction bottle, fixed on a mechanical stirring device, the three-necked flask is immersed in a water bath, and the reaction system is evacuated and nitrogen is circulated to ensure that the reaction system is in an oxygen-free environment; (3) Oil phase pretreatment: Use a balance to accurately weigh 30-40 parts of BA, HEMA, and EMA monomers into a monomer tube to obtain an oil phase solution, and then pass nitrogen through the oil phase solution for more than 20 minutes to remove oxygen from the solution.

[0026] (3) Pretreatment of the aqueous phase: Use a balance to accurately weigh 2.0-4.0 parts of an emulsifier and 50-70 parts of a PVA aqueous solution in a conical flask. Shake the flask thoroughly to dissolve the emulsifier completely to obtain an aqueous solution. Pass nitrogen through the solution for more than 20 minutes to remove oxygen from the solution.

[0027] (4) Feeding reaction: Under nitrogen protection, use a syringe to extract the oil phase and the water phase into a three-necked flask respectively, and seal the injection port with wax to prevent oxygen from entering the reaction process; (5) Reaction: Set the reaction temperature to 25-40°C, the reaction time to 5-8h, and the reaction speed to 100-400r to start the emulsion polymerization reaction; (6) Stopping the reaction: When the polymerization reaction reaches the desired state, stop stirring, remove the three-necked flask, cool to room temperature, transfer the emulsion to a clean sample bottle, and obtain a fluorine-free oil repellent emulsion. Determine its solid content and conversion rate.

[0028] (7) Coating: Fix the bagasse pulp molded tableware on a rotating device, spray the above-prepared fluorine-free oil-proofing agent, adjust the rotation speed so that the oil-proofing agent is evenly coated on the surface of the tableware, and bake at 70-100°C for 2-3 hours to obtain a food-contactable fluorine-free oil-proofing agent coating film. The oil-proofing test is then performed.

[0029] The characterization test method in the embodiment of the present invention is as follows: Determination of reaction conversion rate (Conv.%): Conv.%=(S2 / S1)*100%. In the above formula, S1 is the solid content of the solution before the reaction, and S2 is the solid content of the emulsion after the polymerization reaction.

[0030] SEM determination of fluorine-free oil repellent: Take 5 μL of the above-mentioned fluorine-free oil repellent emulsion, dilute it to 1 mL with deionized water, take a drop of the diluted emulsion on a clean silicon wafer of 0.5 cm × 0.5 cm, dry it naturally at room temperature, perform gold spray coating, and after cooling, use SEM to characterize it.

[0031] Oil-proof and heat-resistant test: Spin-coat the fluorine-free oil-proof agent on the surface of pulp tableware and dry it. Then add a certain amount of hot oil at 95±5 ℃ at room temperature. Let it stand for 6 hours at room temperature to observe whether there is wrinkling or leakage. The oil-proof property can reach 6 hours without penetration after testing.

[0032] Example 1 The raw material composition of the fluorine-free oil repellent reaction agent is as follows: monomer BA: HEMA: EMA = 13mL: 2mL: 20mL, Tween 80: sodium oleate: 2.5% PVA solution = 2.0g: 0.5g: 50mL, V-50: 0.35g, and the oil-water ratio is 35:50.

[0033] Take 0.35g of initiator V-50 into a clean three-necked flask, seal the flask mouth with a rubber stopper, fix it on a stirring device, and perform vacuum + nitrogen blowing cycles for 6 times to ensure that the system is in an anaerobic state. During the cycle, weigh BA:HEMA:EMA=13mL:2mL:20mL in a monomer tube to obtain the oil phase, accurately weigh Tween 80: sodium oleate: 2.5% PVA aqueous solution=2.0g:0.5g:50mL in a conical flask to obtain the water phase, and blow nitrogen through the water phase and oil phase for more than 20min to deoxygenate them. After the cycle, under nitrogen protection, use a syringe to pump the water phase and oil phase into a three-necked reaction bottle, seal the sample inlet with wax, turn on the agitator, set the stirring speed to 300r, the reaction temperature to 30℃, and react for 6h. After the reaction is completed, the three-necked flask is removed, air is introduced, and the mixture is cooled to room temperature. The emulsion is transferred to the sample to obtain a fluorine-free oil-proofing agent. The obtained fluorine-free oil-proofing agent is spin-coated onto the surface of pulp molded tableware, and dried at 80°C for 2 hours to obtain a food-contactable fluorine-free oil-proofing agent coating.

[0034] Take a small amount of emulsion for SEM characterization to obtain the emulsion size morphology, such as Figure 1 The test results show that the solid content of the emulsion is 40.5%, the conversion rate of the polymerization reaction is 98.7%, and the average particle size of the obtained fluorine-free oil repellent is 118nm.

[0035] Example 2 The oil-water ratio is 33:60, and the raw material composition of the fluorine-free oil repellent is as follows: monomer BA: HEMA: EMA = 12.2mL: 1.9mL: 18.8mL, Tween 80: sodium oleate: 2.5% PVA solution = 2.4g: 0.6g: 60mL, V-50: 0.35g, reaction temperature 30°C, reaction time 6h, reaction speed 300r, and the specific preparation steps are the same as those in Example 1. The test results show that the solid content of the emulsion is 35.3%, the conversion rate of the polymerization reaction is 99.0%, and the average particle size of the obtained fluorine-free oil repellent is 120nm.

[0036] Comparative Example 1 The oil-water ratio is 30:65, and the raw material composition of the fluorine-free oil repellent is as follows: monomer BA: HEMA: EMA = 11.1 mL: 1.7 mL: 17.1 mL, Tween 80: sodium oleate: 2.5% PVA solution = 2.4 g: 0.65 g: 65 mL, reaction temperature is 30°C, reaction time is 6 h, reaction speed is 300 r, and the specific preparation steps are the same as those in Example 1. The test results show that the solid content of the emulsion is 31.3%, the conversion rate of the polymerization reaction is 95.7%, and the average particle size of the obtained fluorine-free oil repellent is 147 nm.

[0037] Comparative Example 2 The oil-water ratio is 25:70, and the raw material composition of the fluorine-free oil repellent is as follows: monomer BA: HEMA: EMA = 9.3mL: 1.4mL: 14.3mL, Tween 80: sodium oleate: 2.5% PVA solution = 2.8g: 0.7g: 70mL, reaction temperature is 30°C, reaction time is 6h, reaction speed is 300r, and the specific preparation steps are the same as those in Example 1. The test results show that the solid content of the emulsion is 24.57%, the conversion rate of the polymerization reaction is 95.3%, and the average particle size of the obtained fluorine-free oil repellent is 143nm.

[0038] Comparative Example 3 The oil-water ratio is 20:80, and the raw material composition of the fluorine-free oil repellent is as follows: monomer BA: HEMA: EMA = 7.4 mL: 1.1 mL: 11.4 mL, Tween 80: sodium oleate: 2.5% PVA solution = 3.2 g: 0.8 g: 80 mL, reaction temperature is 30°C, reaction time is 6 h, reaction speed is 300 r, and the specific preparation steps are the same as those in Example 1. The test results show that the solid content of the emulsion is 21.9%, the conversion rate of the polymerization reaction is 91.3%, and the average particle size of the obtained fluorine-free oil repellent is 189 nm.

[0039] The above tableware was tested by adding 95±5℃ hot oil and leaving it at room temperature for 6 hours to observe whether the surface of the tableware was wrinkled or deformed, whether there were stains on the back of the tableware, and whether there was liquid leakage. Figure 2 As shown, the tableware without coating has been completely soaked in oil, while the tableware coated with the oil-proof coating of Example 1 and Example 2 has almost no oil stains. By comparing with Comparative Examples 1-3, the emulsion synthesized with an oil-water ratio greater than 1:2 and a solid content of more than 35% has a better oil-proof effect, and its oil-proof effect can last for more than 6 hours without penetration.

[0040] Then conduct acid resistance test: Spin-coat the polyacrylate oil-proofing agent evenly on the inner surface of pulp molded tableware, dry the tableware, add 95±5℃ hot acetic acid to the tableware coated with the oil-proofing agent at room temperature (20℃) to test the acid resistance, and let it stand at room temperature for 6 hours. The test results are as follows: Figure 3As shown, a is tableware having the fluorine-free oil-proof coating of the present invention, and b is tableware not coated with the fluorine-free oil-proof coating.

[0041] The results show that after the tableware with the fluorine-free oil-proof coating of the present invention is filled with hot acetic acid, it still has no deformation, no peeling, no wrinkling, and no leakage; while the tableware without the fluorine-free oil-proof coating of the present invention has a larger area of ​​penetration and obvious discoloration on the bottom. The results show that the pulp molded tableware coated with the polyacrylate oil-proof agent is acid-resistant.

[0042] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, according to the technical essence of the present invention, any simple modification, equivalent replacement and improvement made to the above embodiment still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a fluorine-free oil-proof coating for food, characterized in that: The steps include: S1. Under anaerobic conditions, uniformly mixing a fluorine-free acrylate composition liquid, an initiator, an emulsifier and a polyvinyl alcohol aqueous solution, so that the acrylate composition liquid is subjected to emulsion polymerization to obtain a fluorine-free oil repellent; S2. Applying a fluorine-free oil-proof agent on the surface of tableware and drying the same to obtain a fluorine-free oil-proof coating.

2. The method for preparing a fluorine-free oil-proof coating for food according to claim 1, characterized in that: In step S1, the fluorine-free acrylate composition liquid is composed of butyl acrylate, hydroxyethyl methacrylate and ethyl methacrylate.

3. The method for preparing a fluorine-free oil-proof coating for food according to claim 1, characterized in that: The oil-water ratio of the fluorine-free oil repellent obtained by emulsion polymerization in step S1 is ≥1:

2.

4. The method for preparing a fluorine-free oil-proof coating for food according to claim 1, characterized in that: The initiator in step S1 is water-soluble azobisisobutylamidine hydrochloride.

5. The method for preparing a fluorine-free oil-proof coating for food according to claim 1, characterized in that: The emulsifier in step S1 is a combination of one or more of polysorbate 80 and sodium oleate.

6. The method for preparing a fluorine-free oil-proof coating for food according to claim 1, characterized in that: The fluorine-free oil-proofing agent obtained in step S1 has a solid content of 35% to 45%.

7. The method for preparing a fluorine-free oil-proof coating for food according to claim 1, characterized in that: In step S2, the fluorine-free oil-proofing agent is applied by spin coating, and a drying operation is performed while the coating is being performed.

8. The method for preparing a fluorine-free oil-proof coating for food according to claim 7, characterized in that: The drying operation temperature is 70-100°C and the time is 2-3h.

9. Use of the fluorine-free oil-proof coating prepared according to any one of claims 1 to 8 in coating the surface of pulp molded tableware.

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