A kind of bending-resistant waterproof and oil-proof coating and its preparation method and application

Abstract

The invention discloses a kind of anti-bending waterproof and oil-proof coating, belong to the field of food packaging technology, including that the mass ratio shared by PLA is 5 20%, the mass ratio shared by film-forming aid is 0.1 3%, the mass ratio shared by flexible film component is 0.5 5%, the mass ratio shared by wetting and leveling agent is 0.5 2%, the mass ratio shared by dispersant is 0.5 2%, and surplus is water. PLA is processed into tiny particles by the present invention, and by being combined with flexible film-forming material, PLA particles are made to be evenly distributed on the film of paper surface, after paper bends, membrane material can withstand tensile force and will not cause PLA as a whole to crack, and is solidified on paper surface by film, thus paper will not affect waterproof and oil-proof effect after bending. Simultaneously, the consumption of PLA can be greatly reduced, the degradation rate of paper is made faster, and the raw material used is food contact material, will not cause harm to food and environment, meet food packaging demand, and can also ensure the sustainable development of consumer's health and environment.

Description

Technical Field

[0001] The present invention relates to the technical field of food packaging, and in particular to a bending-resistant, waterproof and oil-proof coating, and a preparation method and application thereof. Background Art

[0002] Food packaging paper is primarily made from pulp and paperboard. It must be non-toxic, oil-resistant, waterproof, moisture-proof, and airtight, as well as meet food safety requirements. With the promulgation and implementation of my country's "plastic ban," the trend of replacing plastic packaging with paper is unstoppable. Because food packaging paper comes into direct contact with food, and most of the packaging it contains is food that is directly ingested, the most fundamental requirement for food packaging paper is that it must comply with food hygiene requirements. Furthermore, depending on the specific application requirements, the paper must also meet relevant technical standards.

[0003] Food contact paper refers to various paper products and food processing and cooking paper that are intended to come into contact with food under normal or foreseeable conditions of use. Because food packaging must be water- and oil-resistant to prevent water and oil from the food from penetrating the paper and causing leakage or rupture, various additives are added during processing. Chemical residues such as additives, monomers, oligomers, and degradation products contained in these additives can migrate into food through absorption, dissolution, and diffusion, contaminating it and posing a food safety risk.

[0004] Currently, there are three common methods for producing waterproof and greaseproof paper that meets food packaging requirements. The first is to coat the paper surface with a plastic film, typically PE, PP, or PET. With the introduction of plastic bans and the promotion of biodegradable plastics, PLA or PBAT-coated paper is the predominant material. This is paper, with a PLA, PBAT, or other material film applied to one or both sides, to create a coated paper suitable for food packaging. The second method involves using a fluorinated treatment agent to bond fluorinated compounds to the paper surface to reduce surface tension. The third method involves using a film-forming polymer to form a dense film on the paper surface.

[0005] To achieve oil-proofing, coated paper has traditionally been made from plastic containers or films such as polyethylene, polypropylene, and polyvinyl chloride. While these materials offer resistance to oil and grease penetration, they are still essentially plastics. Synthetic polymers are generally difficult to degrade or degrade very slowly in nature. Consequently, the use of these materials causes significant environmental pollution.

[0006] Although PLA is a biodegradable plastic, and paper coated with PLA can degrade in soil, its degradation in soil requires certain conditions. PLA production requires extracting starch from plants, fermenting it to produce lactic acid, and then chemically synthesizing it. This currently results in high production costs. Furthermore, due to PLA's high melting point, the raw materials must be melted at high temperatures before coating, further increasing production costs, degradation difficulties, and the environmental burden.

[0007] While PLA coated paper exhibits excellent water and oil resistance, the film itself is inherently hard and brittle. Bends can easily cause cracks in the film, compromising its water and oil resistance. Conventional approaches to addressing PLA film brittleness typically involve grafting to improve its flexibility, but this process is complex, production control is difficult, and can alter the readily interpretable properties of PLA. Summary of the Invention

[0008] To address the problems existing in the prior art, the present invention provides a flex-resistant, waterproof, and oil-proof coating, its preparation method, and application. This coating eliminates the need to melt PLA at high temperatures to form a film, or to induce a reaction through graft copolymerization. Instead, PLA is processed into fine particles and combined with a flexible film-forming material, so that the PLA particles are evenly distributed on the film on the paper surface. After the paper is bent, the film material can withstand tensile tension without causing cracks in the PLA as a whole. Furthermore, the film solidifies on the paper surface, thus maintaining its waterproof and oil-proof properties even after bending. Furthermore, the amount of PLA used can be significantly reduced, accelerating the degradation of the paper. Furthermore, the raw materials used are all food-contact materials, thus posing no harm to food or the environment. This meets food packaging requirements while also ensuring consumer health and environmental sustainability.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] A bending-resistant, waterproof and oil-proof coating comprises PLA, a flexible film emulsion, a film-forming aid, a wetting and leveling agent, a dispersant and water; wherein the mass ratio of PLA is 5-20%, the mass ratio of the film-forming aid is 0.1-3%, the mass ratio of the flexible film component is 0.5-5%, the mass ratio of the wetting and leveling agent is 0.5-2%, the mass ratio of the dispersant is 0.5-2%, and the balance is water.

[0011] Preferably, the particle size D90 of the bending-resistant, waterproof and oil-proof coating is less than 8 μm, and the viscosity is 70-150 cps.

[0012] Preferably, the flexible film emulsion is a pullulan-grafted butyl acrylate copolymer emulsion.

[0013] Preferably, the flexible film emulsion preparation method comprises the following steps: adding sodium dodecylbenzenesulfonate as an emulsifier to a certain amount of water, adding pullulan and stirring to dissolve it completely, using cerium nitrate as an initiator, adding butyl acrylate under nitrogen protection, heating to 60° C. to react for 3 hours, and then adding a hydroquinone aqueous solution to terminate the reaction, thereby obtaining the flexible film emulsion.

[0014] Preferably, the concentration of the sodium dodecylbenzenesulfonate is 2-10%; the concentration of the pullulan is 5-10%; the stirring speed during the dissolution of the pullulan is 500-1000 r / min; and the concentration of the hydroquinone aqueous solution is 0.05-0.5%.

[0015] Preferably, the film-forming aid is any one of PVA, PVP, cationic starch, acrylic emulsion, hydroxy silicone oil emulsion, chitosan hydroxyethyl cellulose or other starch or cellulose derivatives.

[0016] Preferably, the wetting and leveling agent is polyether-modified polysiloxane or polyether-modified acetylene glycol.

[0017] Preferably, the dispersant is white carbon black or diatomaceous earth.

[0018] A method for preparing a bending-resistant, waterproof and oil-proof coating comprises the following steps:

[0019] Step A: Preliminary crushing of PLA particles in a crusher to obtain PLA powder with a particle size of less than 300 mesh;

[0020] Step B, according to the mass composition of the above-mentioned coating, the preliminarily crushed PLA powder, flexible film emulsion, film-forming aid, wetting and leveling agent, dispersant and water are added in proportion, stirred at 500-1000 r / min for 10-20 minutes, and then sheared at 2000-4000 r / min for 5-10 minutes using a high shear emulsifier to mix evenly;

[0021] Step C: adding the mixed raw materials into a sand mill and sand milling them at 1400 r / min, and testing the median particle size of the PLA solid particles after sand milling to make sure that it is ≤3 μm, thereby obtaining the waterproof and oil-proof coating.

[0022] The invention discloses an application of a bending-resistant, waterproof and oil-proof coating. The obtained coating is sprayed or coated on paper, and then dried at 140-170°C for 4-6 minutes to obtain bending-resistant, waterproof and oil-proof food packaging paper. Alternatively, the obtained coating is added to paper pulp to prepare bending-resistant, waterproof and oil-repellent food packaging paper.

[0023] The beneficial effects of this technical solution are as follows:

[0024] 1. The present invention provides a bending-resistant waterproof and oil-proof coating. The PLA usage of the prepared coating is only one-fifth to one-tenth of that of directly using a PLA coating, which can greatly reduce the amount of PLA used, reduce production costs and environmental pressure, and does not require high-temperature heating and melting during use. It can be directly sprayed or coated, which is more convenient and quicker, and saves energy. The produced paper can not only meet the waterproof and oil-proof requirements, but also has the same waterproof and oil-proof performance after the paper is bent, which makes up for the disadvantage that the use of PLA alone easily causes the film to break and thus affects the waterproof and oil-proof effect. At the same time, the present invention also meets the contact requirements of food packaging and can be used for food packaging.

[0025] Second, the present invention provides a flex-resistant, waterproof, and oil-resistant coating. A pullulan-grafted butyl acrylate copolymer emulsion acts as a flexible film-forming aid in the coating. Pullulan possesses two important properties: structural elasticity and high solubility. It also exhibits strong film-forming properties, gas barrier properties, plasticity, and viscosity, and is readily soluble in water, non-toxic, harmless, colorless, and odorless. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a scanning electron microscope image of the coated paper of the present invention after bending;

[0027] Figure 2 This is the PLA coating picture after bending. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited thereto.

[0029] Example 1

[0030] A bending-resistant, waterproof and oil-proof coating comprises 5% PLA (polylactic acid), 3% flexible film-forming agent, 24882% polyvinyl alcohol, 0.5% polyether-modified polysiloxane, 2% white carbon black and 90.5% deionized water.

[0031] Preparation of a flexible film-forming agent: Weigh 74.8% aqueous solution and 5% sodium dodecylbenzenesulfonate, add 10% pullulan, and stir until completely dissolved. The stirring speed is 1000 rpm during the dissolution of the pullulan. Under nitrogen protection, 0.1% cerium nitrate is added as an initiator, followed by 10% butyl acrylate. The temperature is raised to 60°C and stirred for 3 hours. Finally, 0.1% hydroquinone solution is added and the reaction temperature is allowed to cool naturally to room temperature to obtain a flexible film emulsion.

[0032] A method for preparing a bending-resistant, waterproof and oil-proof coating comprises the following steps:

[0033] Step A: Put a certain amount of PLA particles into a grinder and grind them for multiple short periods of time to obtain polylactic acid powder with a particle size of 300 mesh.

[0034] Step B, then take a flexible film emulsion (3% of the total mass of the coating) of mass 1, 2% of polyvinyl alcohol and 90.5% of water, add them to a stirring tank, heat to 60 ° C and stir for 1 hour to obtain a film-forming liquid, then take 5% of the initially crushed polylactic acid powder, the prepared film-forming liquid, 0.5% of polyether-modified polysiloxane, and 2% of white carbon black, add them to a stirring tank and stir at 500 r / min for 20 minutes, and then shear for 10 minutes at 2000 r / min through a high shear emulsifier;

[0035] Step C: Finally, add the mixture into a sand mill and perform sand milling at 1400 r / min. After sand milling for 3 hours, filter the material to obtain the degradable waterproof and oil-proof coating.

[0036] The preparation process of Examples 2-12 is roughly the same as the above steps, except that the addition amount of each component of the bending-resistant waterproof and oil-proof coating, some process parameters for the preparation of the flexible film-forming aid, and some process parameters for the preparation of the bending-resistant waterproof and oil-proof coating are different. The types and addition amounts of each component of the bending-resistant waterproof and oil-proof coating are shown in Table 1, some process parameters for the preparation of the flexible film-forming aid are shown in Table 2, and some process parameters for the preparation of the bending-resistant waterproof and oil-proof coating are shown in Table 3.

[0037] Table 1 Preparation formula of bending-resistant waterproof and oil-proof coatings in various embodiments

[0038]

[0039] Table 2 Process parameters in the preparation method of flexible film-forming aids in various examples

[0040]

[0041] Table 3 Process parameters in the preparation method of the bending-resistant waterproof and oil-proof coating of each embodiment

[0042]

[0043] The particle size of the coatings prepared in Examples 1-12 was measured using a laser particle size analyzer, with the PLA refractive index set to 1.485 and the added sample opacity within the range of 5-10%. The test results are shown in Table 4.

[0044] The samples were tested for viscosity using a rotational viscometer. A suitable rotor connected to the instrument was rotated, immersed in the sample, and the viscosity of the sample was measured. The test results are shown in Table 4. The particle size (D90) of the flex-resistant, waterproof, and oil-resistant coatings prepared in Examples 1-12 all fell within the 4-8 μm range, and the viscosity fell within the 70-150 cps range.

[0045] Table 4 Test results of the bending-resistant, waterproof and oil-proof coatings obtained in various embodiments

[0046]

[0047] (1) Scanning electron microscope test

[0048] The surface structure of the coated paper of the present invention, the surface structure of the PLA coated paper, and the surface structure of the coated paper of the present invention after bending and the surface structure of the PLA coated paper after bending were observed using a scanning electron microscope.

[0049] Depend on Figure 1 、 Figure 2 It can be seen that after coating with the present invention, the PLA particles form a dense protective layer on the paper surface, which does not show obvious horizontal lines even after bending. In contrast, although the PLA coating forms a protective layer on the paper surface, cracks appear in the PLA after bending, which may affect the water and oil repellency.

[0050] (2) Water and oil resistance test

[0051] Referring to the American Association of the Pulp and Paper Industry's (TAPPI) oil repellency test method TAPPI-UM-557, paper's oil repellency is tested by mixing toluene, castor oil, and n-heptane in varying volume ratios. The mixtures are divided into 12 grades based on the different ratios (see Table 5). To test, after spraying the oil repellent material onto the paperboard, the paperboard is folded in two perpendicular directions, with the test surface facing upward. A drop of a test solution with a known Kit number is placed 25 mm above the intersection of the folds. After 15 seconds, the remaining test solution is removed with clean toilet paper. The back of the droplet is immediately observed for discoloration due to penetration. The test is repeated until the paper surface with the test solution of the specified Kit number is no longer discolored. The oil repellency of the paper sample is then determined by the Kit number.

[0052] Table 5 Kit standard test solution formula

[0053]

[0054] The waterproofness test refers to the national standard GB / T 36787-2018. During the test, after applying the oil-proof coating on the paper, fold it in two perpendicular directions with the test surface facing up. Add 0.5ml of 95℃±5℃ water at a height of 25mm at the intersection of the fold lines. After standing for 30 minutes, observe whether there is any seepage or leakage.

[0055] In this experiment, the coatings prepared in Examples 1-12 were sprayed or applied to paper and then dried at 140-170°C for 4-6 minutes to produce fold-resistant, waterproof, and oil-repellent food packaging paper. Alternatively, the resulting coatings were added to paper pulp to produce fold-resistant, waterproof, and oil-repellent food packaging paper. After folding the paper according to the above method, the water- and oil-repellent properties of the paper were measured. The water- and oil-repellent properties of the PLA-coated paper and the folded PLA-coated paper were also measured. The results are shown in Table 6.

[0056] Table 6 Test results of water and oil resistance of paper with different treatments

[0057]

[0058] In summary, the degradable bending-resistant waterproof and oil-proof coating prepared by the present invention has good waterproof and oil-proof properties and bending resistance, and can significantly reduce the amount of PLA used, while reducing production energy consumption, and can meet market needs.

[0059] Finally, it should be noted that the above embodiments are only for illustration, not for limitation of the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A bending-resistant, waterproof and oil-proof coating, characterized by: The invention comprises PLA solid particles, a flexible film emulsion, a film-forming agent, a wetting and leveling agent, a dispersant and water; wherein the mass ratio of PLA solid particles is 5-20%, the mass ratio of film-forming agent is 0.1-3%, the mass ratio of flexible film components is 0.5-5%, the mass ratio of wetting and leveling agent is 0.5-2%, the mass ratio of dispersant is 0.5-2%, and the balance is water; the median particle size of the PLA solid particles is ≤3 μm; the flexible film emulsion adopts pullulan polysaccharide grafted butyl acrylate copolymer emulsion; the flexible film emulsion is prepared The method comprises the following steps: adding an emulsifier, sodium dodecylbenzenesulfonate, and then adding pullulan to a certain amount of water, stirring and dissolving the emulsifier completely; using cerium nitrate as an initiator, adding butyl acrylate under nitrogen protection, heating to 60° C. for reaction for 3 hours, and then adding a hydroquinone aqueous solution to terminate the reaction, thereby obtaining a flexible membrane emulsion; the concentration of the sodium dodecylbenzenesulfonate is 2-10%; the concentration of the pullulan is 5-10%; the stirring speed during the dissolution of the pullulan is 500-1000 r / min; and the concentration of the hydroquinone aqueous solution is 0.05-0.5%.

2. The bending-resistant, waterproof and oil-proof coating according to claim 1, characterized in that: The bending-resistant, waterproof and oil-proof coating has a particle size D90 of less than 8 μm and a viscosity of 70-150 cps.

3. The bending-resistant, waterproof and oil-proof coating according to claim 1, characterized in that: The film-forming aid is any one of PVA, PVP, cationic starch, acrylic emulsion, hydroxy silicone oil emulsion, chitosan, hydroxyethyl cellulose or other starch or cellulose derivatives.

4. The bending-resistant, waterproof and oil-proof coating according to claim 1, characterized in that: The wetting and leveling agent is polyether-modified polysiloxane or polyether-modified acetylene glycol.

5. The bending-resistant, waterproof and oil-proof coating according to claim 1, characterized in that: The dispersant is white carbon black or diatomaceous earth.

6. A method for preparing a bending-resistant, waterproof and oil-proof coating according to any one of claims 1 to 5, comprising the following steps: Step A: Preliminary crushing of PLA particles in a crusher to obtain PLA powder with a particle size of less than 300 mesh; Step B, according to the mass composition of the above-mentioned coating, the preliminarily crushed PLA powder, flexible film emulsion, film-forming aid, wetting and leveling agent, dispersant and water are added in proportion, stirred at 500-1000 r / min for 10-20 minutes, and then sheared at 2000-4000 r / min for 5-10 minutes using a high shear emulsifier to mix evenly; Step C: adding the mixed raw materials into a sand mill and sand milling them at 1400 r / min, and testing the median particle size of the PLA solid particles after sand milling to make sure that it is ≤3 μm, thereby obtaining the waterproof and oil-proof coating.

7. Use of the flexural-resistant, waterproof, and oil-proof coating according to any one of claims 1 to 5, comprising spraying or coating the obtained coating on paper, and drying the obtained coating at 140-170° C. for 4-6 minutes to obtain flexural-resistant, waterproof, and oil-proof food packaging paper; or adding the obtained coating to paper pulp to prepare flexural-resistant, waterproof, and oil-repellent food packaging paper.

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