Preparation process of environment-friendly film coating

Abstract

The invention provides a preparation process of an environment-friendly film coating, and belongs to the technical field of coatings, the preparation process comprises the following steps: S1, mixing 3-4 parts of epoxy resin, 25-28 parts of polyurethane emulsion, 35-38 parts of water-based acrylic resin emulsion, 0.5-1 part of a curing agent, 0.5-1 part of an accelerant, 2-2.5 parts of a dispersing agent, 0.3-0.5 part of a wetting agent and 6-8 parts of PVA emulsion to obtain a first mixture; s2, adding 4-5 parts of fluorine-doped hexagonal boron nitride and 10-12 parts of nano aluminum oxide into the first mixture, and stirring to obtain a second mixture; adding 2-3 parts of polyoxyethylene, 0.4-0.5 part of citric acid, 2-4 parts of a coalescing agent and 0.5-1 part of a defoaming agent into the second mixture, and stirring to obtain a coating; s3, performing plasma activation on the PET film to obtain a pretreated PET film; and S4, uniformly coating the pretreated PET film with the coating, and curing to obtain the environment-friendly film coating. The ink-jet adhesive force is improved, and meanwhile, the mechanical property of a PET film coated with a coating is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of coatings, and in particular relates to a preparation process of an environmentally friendly thin film coating. Background Art

[0002] PET film has excellent mechanical properties, heat resistance, and high light transmittance, making it widely used as a substrate for protective films, durable labels, and digital printing. However, PET film is used as a consumable in digital inkjet printing. However, due to its low surface energy and chemical inertness, it has poor ink adsorption, which affects the quality of printed graphics.

[0003] Existing techniques typically involve applying a coating to the surface of a PET film and then adding nanoparticles, such as aluminum oxide nanoparticles. These nanoparticles, rich in surface hydroxyl groups and high polarity, can improve surface roughness and chemical activity, enhancing inkjet (ink) adhesion through physical adsorption and chemical bonding. To further enhance ink adsorption, sufficient aluminum oxide nanoparticles must be added. However, excessive aluminum oxide nanoparticles can easily agglomerate due to van der Waals forces and hydrogen bonding, reducing dispersion uniformity and forming localized stress concentration points, which can trigger microcracks in the coating. This ultimately weakens the coating's tensile strength and toughness, resulting in reduced mechanical properties of the coated PET film. Summary of the Invention

[0004] In response to the above problems, the present invention proposes a preparation process for an environmentally friendly thin film coating, which improves the inkjet adhesion while enhancing the mechanical properties of the PET film coated with the coating.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A process for preparing an environmentally friendly thin film coating comprises the following steps:

[0006] S1, 3-4 parts of epoxy resin, 25-28 parts of polyurethane emulsion, 35-38 parts of water-based acrylic resin emulsion, 0.5-1 part of curing agent, 0.5-1 part of accelerator, 2-2.5 parts of dispersant, 0.3-0.5 part of wetting agent and 6-8 parts of PVA emulsion are mixed by ball milling to obtain a first mixture;

[0007] S2. Add 4-5 parts of fluorine-doped hexagonal boron nitride and 10-12 parts of nano-alumina to the first mixture obtained in S1, and stir to obtain a second mixture; then add 2-3 parts of polyethylene oxide, 0.4-0.5 parts of citric acid, 2-4 parts of a film-forming aid, and 0.5-1 part of a defoaming agent to the second mixture, and stir to obtain a coating;

[0008] S3, plasma-activating the PET film to obtain a pretreated PET film;

[0009] S4. Evenly apply the coating obtained in S3 on the pretreated PET film obtained in S4, and solidify the coating to obtain an environmentally friendly thin film coating.

[0010] Furthermore, the preparation method of the fluorine-doped hexagonal boron nitride is as follows:

[0011] A1. Place 1 g of hexagonal boron nitride nanosheets into a round-bottomed biscuit, and add 400-450 mL of fluoroboric acid to a round-bottomed beaker and stir to obtain a first mixed solution.

[0012] A2, magnetically stirring the first mixed solution obtained in A1 at 50±2°C, and then cooling to room temperature to obtain a second mixed solution;

[0013] A3. The second mixed solution obtained in A2 is centrifuged and washed multiple times with deionized water to obtain a solid, which is then dried to obtain fluorine-doped hexagonal boron nitride.

[0014] Furthermore, in A2, the speed of magnetic stirring is 120-150 rpm, and the time of magnetic stirring is 7-8 h.

[0015] Furthermore, in A3, the drying temperature is 55-65° C., and the drying time is 75-90 min.

[0016] Furthermore, in S1, the curing agent is dicyandiamide, the accelerator is 2-methylimidazole, the dispersant is a comb-type polyetheramine dispersant BYK-190, and the wetting agent is an acetylene glycol wetting agent Surfynol 104.

[0017] Furthermore, in S1, the ball milling process uses zirconia balls, and the ball-to-material mass ratio is (4-6):1.

[0018] Furthermore, in S2, the molecular weight of the polyethylene oxide is less than 10,000.

[0019] Furthermore, in S2, the film-forming aid includes dipropylene glycol butyl ether and / or dodecyl alcohol ester (3:1).

[0020] Furthermore, the thickness of the environmentally friendly thin film coating is 5±0.5 μm.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] Fluorine-doped hexagonal boron nitride and nano-aluminum oxide are simultaneously used in the preparation of the environmentally friendly thin film coating of the present invention, and the inkjet adhesion test data is as high as over 99.1%; the tensile strength test data is as high as over 51.0 MPa.

[0023] On the one hand, the two-dimensional lamellar structure of fluorine-doped hexagonal boron nitride forms a "pea pod" interlocking structure with nano-alumina; on the other hand, nano-alumina fills the gaps between the layers of fluorine-doped hexagonal boron nitride, inhibiting lamellar slippage, synergistically improving the tear resistance of the coating, and synergistically improving the tensile strength.

[0024] The surface of nano-alumina is rich in hydroxyl groups and forms hydrophilic areas, which can form hydrogen bonds with aqueous inks to improve adsorption efficiency; the surface of fluorine-doped hexagonal boron nitride forms hydrophobic areas due to fluorine atom doping, which can control the ink spreading speed and avoid blurring; nano-alumina and fluorine-doped hexagonal boron nitride are used together, and the two synergistically form a polarity gradient interface, which retains both hydrophilic areas to accelerate local penetration of ink and hydrophobic areas to prevent excessive penetration of ink, thereby working synergistically to ensure the balanced dispersion of pigment particles in the ink; at the same time, the high specific surface area of nano-alumina provides more physical anchoring points, and synergistically forms a micro-nano rough surface with the layered structure of fluorine-doped hexagonal boron nitride, enhancing the mechanical locking ability of ink components, thereby synergistically improving inkjet adhesion. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a comparative trend chart of inkjet adhesion test data of the environmentally friendly thin film coatings prepared in Examples 1 to 3 and Comparative Examples 1 to 3 in Test Example 1 of the present invention;

[0026] Figure 2 This is a comparative trend chart of the tensile strength test data of the environmentally friendly thin film coatings prepared in Examples 1 to 3 and Comparative Examples 1 to 3 in Test Example 2 of the present invention. DETAILED DESCRIPTION

[0027] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0028] Example 1: (1) The preparation method of fluorine-doped hexagonal boron nitride is as follows: A1. Place 1 g of hexagonal boron nitride nanosheets (particle size 50-200 nm) into a round-bottomed pancake, and add 430 mL of fluoroboric acid (concentration 40 wt%) into a round-bottomed beaker, and mechanically stir at 220 rpm for 10 minutes to obtain a first mixed solution.

[0029] A2. Heat the first mixed solution to about 50°C in an oil bath (temperature control accuracy ±1°C), perform magnetic stirring at a speed of 140 rpm for 7.5 h, and then naturally cool to room temperature (about 25°C) to obtain a second mixed solution.

[0030] A3. The second mixed solution was centrifuged and washed with deionized water at a centrifuge speed of 9000 rpm and a single centrifugation time of 10 min, which was repeated three times to obtain a solid. The solid was then dried in a vacuum drying oven at a pressure of ≤0.1 MPa, a drying temperature of about 60°C, and a drying time of 85 min. After drying, the solid was cooled to room temperature in a nitrogen atmosphere to obtain fluorine-doped hexagonal boron nitride.

[0031] (2) A process for preparing an environmentally friendly thin film coating comprises the following steps: S1, by weight, 3.5 parts of epoxy resin, 26 parts of polyurethane emulsion, 36 parts of waterborne acrylic resin emulsion, 0.7 parts of curing agent dicyandiamide, 0.7 parts of accelerator 2-methylimidazole, 2.3 parts of comb-type polyetheramine dispersant BYK-190, 0.4 parts of acetylene glycol wetting agent Surfynol 104 and 7 parts of PVA emulsion are mixed by ball milling process, the ball milling equipment is a horizontal ball mill, the diameter of the zirconia ball is 2-5 mm (mixed particle size improves efficiency), the ball-to-material mass ratio is 5:1, the ball milling conditions are a rotation speed of 300 rpm, a time of 4 h, and a temperature control of ≤35°C (to avoid emulsion demulsification), and after ball milling, a first mixed material is obtained.

[0032] The epoxy resin was bisphenol A epoxy resin (E-44), purchased from Jining Fangde Chemical Co., Ltd. and preheated to 50°C to reduce viscosity before use. The polyurethane emulsion was a water-based aliphatic polyurethane (anti-yellowing type) (brand name SEAPUR30G30), purchased from Guangdong Xidun New Materials Technology Co., Ltd. The water-based acrylic resin emulsion (H-308) was purchased from Jining Fangyu Chemical Co., Ltd. Dicyandiamide (99% content) was purchased from Zhengzhou Jiafu Chemical Co., Ltd. 2-Methylimidazole was purchased from Jinan Yuansu Chemical Co., Ltd. The comb-type polyetheramine dispersant BYK-190 (Bick, Germany) was purchased from Jining Fangyu Chemical Co., Ltd. The acetylene glycol wetting agent Surfynol 104 (99%) was purchased from Green Alliance (Jining) Chemical Technology Co., Ltd. PVA emulsion (2488) was purchased from Shenzhen Jitian Chemical Co., Ltd.

[0033] S2. Add 4.5 parts of fluorine-doped hexagonal boron nitride and 11 parts of nano-alumina (α-phase, particle size 30-50nm, conventionally modified with 0.5% silane coupling agent KH-550 ethanol solution before use) to the first mixture, stir at 2000rpm for 30min in a high-speed disperser to obtain a second mixture. Then, add 2.5 parts of polyethylene oxide (molecular weight 8000) (which is added by dissolving it in deionized water to make a 5% solution and adding it dropwise), 0.45 parts of citric acid, 3 parts of film-forming aid and 0.8 parts of defoamer (BYK-022) to the second mixture. After addition, stir at 500rpm for 10min to obtain a coating. The film-forming aid includes dipropylene glycol butyl ether and dodecyl alcohol ester, and the mass ratio of dipropylene glycol butyl ether to dodecyl alcohol ester is 3:1. After mixing, let it stand for 1h to eliminate the compatibility difference before adding it for use. Among them, nano-alumina, KH-550, polyethylene oxide, citric acid, dipropylene glycol butyl ether, dodecyl alcohol ester and defoaming agent (BYK-022) were purchased from Jining Fangyu Chemical Co., Ltd.

[0034] S3. Plasma activation of the PET film to obtain a pretreated PET film. Specifically, the plasma activation parameters include: atmospheric pressure plasma jet system, 200W power, 5m / min processing speed, and an argon / oxygen mixture (4:1 volume ratio). After activation, coating must be completed within 2 hours to avoid surface energy degradation.

[0035] S4. The coating obtained in S3 is evenly coated on the pretreated PET film obtained in S4 using micro-gravure coating, an anilox roller with a line count of 200 lines / inch, a coating speed of 10 m / min, a wet film thickness of approximately 15 μm, a leveling temperature of approximately 40°C, a humidity of approximately 50% RH, and a curing time of 5 minutes (to eliminate roller marks). The coating is then cured in stages: the first stage is 80°C for 10 minutes; the second stage is 130°C for 20 minutes; and the third stage is 160°C for 5 minutes. The dry film thickness is 5.4 μm (monitored online using an eddy current thickness gauge). This results in an environmentally friendly thin film coating.

[0036] Example 2: The difference between this example and Example 1 is that: a preparation process for an environmentally friendly thin film coating comprises the following steps: S1, 3 parts of epoxy resin, 25 parts of polyurethane emulsion, 35 parts of water-based acrylic resin emulsion, 0.5 parts of curing agent dicyandiamide, 0.5 parts of accelerator 2-methylimidazole, 2 parts of comb-type polyetheramine dispersant BYK-190, 0.3 parts of acetylene glycol wetting agent Surfynol 104 and 6 parts of PVA emulsion are mixed by ball milling process, the ball milling process uses zirconium oxide balls, and the ball-to-material mass ratio is 4:1 to obtain a first mixture.

[0037] S2. Add 4 parts of fluorine-doped hexagonal boron nitride and 10 parts of nano-alumina to the first mixture and stir to obtain a second mixture; then add 2 parts of polyethylene oxide (molecular weight 8000), 0.4 parts of citric acid, 2 parts of a film-forming aid, and 0.5 parts of a defoamer to the second mixture and stir to obtain a coating. The film-forming aid includes dipropylene glycol butyl ether and dodecyl alcohol ester, and the mass ratio of dipropylene glycol butyl ether to dodecyl alcohol ester is 3:1.

[0038] S3, performing plasma activation on the PET film to obtain a pretreated PET film.

[0039] S4. Evenly apply the coating obtained in S3 on the pretreated PET film obtained in S4, and solidify the coating to obtain an environmentally friendly thin film coating.

[0040] Example 3: The difference between this example and Example 1 is that: a preparation process for an environmentally friendly thin film coating comprises the following steps: S1, 4 parts of epoxy resin, 28 parts of polyurethane emulsion, 38 parts of water-based acrylic resin emulsion, 1 part of curing agent dicyandiamide, 1 part of accelerator 2-methylimidazole, 2.5 parts of comb-type polyetheramine dispersant BYK-190, 0.5 part of acetylene glycol wetting agent Surfynol 104 and 8 parts of PVA emulsion are mixed by ball milling process, the ball milling process uses zirconium oxide balls, and the ball-to-material mass ratio is 6:1 to obtain a first mixture.

[0041] S2. Add 5 parts of fluorine-doped hexagonal boron nitride and 12 parts of nano-alumina to the first mixture and stir to obtain a second mixture; then add 3 parts of polyethylene oxide (molecular weight 8000), 0.5 parts of citric acid, 4 parts of a film-forming aid, and 1 part of a defoamer to the second mixture and stir to obtain a coating. The film-forming aid includes dipropylene glycol butyl ether and dodecyl alcohol ester, and the mass ratio of dipropylene glycol butyl ether to dodecyl alcohol ester is 3:1.

[0042] S3, performing plasma activation on the PET film to obtain a pretreated PET film.

[0043] S4. Evenly apply the coating obtained in S3 on the pretreated PET film obtained in S4, and solidify the coating to obtain an environmentally friendly thin film coating.

[0044] Comparative Example 1: The only difference between this comparative example and Example 1 is that in the preparation of the environmentally friendly thin film coating, fluorine-doped hexagonal boron nitride is replaced by nano-aluminum oxide.

[0045] Comparative Example 2: The only difference between this comparative example and Example 1 is that in the preparation of the environmentally friendly thin film coating, nano-alumina is replaced by fluorine-doped hexagonal boron nitride.

[0046] Comparative Example 3: The only difference between this comparative example and Example 1 is that in the preparation of the environmentally friendly thin film coating, fluorine-doped hexagonal boron nitride is replaced by hexagonal boron nitride nanosheets.

[0047] Test Example 1: Test subjects: Environmentally friendly thin film coatings were prepared using Examples 1-3 and Comparative Examples 1-3. Test items and methods: Inkjet adhesion (%) - Reference ASTM D3359 (cross-hatch method); Calculation formula: Adhesion = (Total number of squares - Number of squares removed) / Total number of squares × 100%. A non-standard expansion solution was used to increase the total number of squares to 1089, with "removed squares" representing squares where the coating was completely peeled off and the substrate exposed. Each sample was tested three times, and the average value was calculated and recorded as the final value. A higher final adhesion (%) value indicates a lower number of squares where the tape peeled (removed), indicating stronger inkjet adhesion. Test results: See Table 1.

[0048] Test Example 2: Test subjects: Environmentally friendly thin film coatings were prepared using Examples 1-3 and Comparative Examples 1-3. Test items and methods: Tensile strength (MPa) - tested according to ASTM D882 (film tensile properties). Test results: See Table 1.

[0049] Table 1. Test results statistics for Test Example 1 and Test Example 2

[0050] Adhesion (%) Tensile strength (MPa) Example 1 99.5 51.0 Example 2 99.1 51.2 Example 3 99.6 51.5 Comparative Example 1 97.7 47.7 Comparative Example 2 93.9 44.4 Comparative Example 3 97.5 51.2

[0051] Result analysis: Analyze Example 1-Example 3 and combine the data in Table 1 and Figure 1-Figure 2 It can be seen that the inkjet adhesion test data of the environmentally friendly thin film coating prepared by the present invention (Example 1-Example 3) is as high as 99.1% or more; the tensile strength test data is as high as 51.0 MPa or more.

[0052] Analyze Example 1 and Comparative Examples 1-3 and combine the data in Table 1 and Figure 1-Figure 2 By comparing Comparative Example 1 and Comparative Example 2, it can be seen that replacing nano-aluminum oxide (Comparative Example 1) with fluorine-doped hexagonal boron nitride (Comparative Example 2) will result in a decrease in the inkjet adhesion and tensile strength of the environmentally friendly thin film coating. This is because the hydrophobic surface properties of fluorine-doped hexagonal boron nitride reduce the interaction between the coating and the polar ink molecules, resulting in poor ink spreadability. The layered structure of fluorine-doped hexagonal boron nitride forms a lubricating interface with low surface energy, further reducing ink penetration, resulting in reduced adhesion. The two-dimensional layered structure of fluorine-doped hexagonal boron nitride introduces a weak interface in the coating, resulting in internal stress concentration in the material. At the same time, its low friction coefficient may also weaken the crosslinking density of the polymer matrix, resulting in a decrease in tensile strength.

[0053] By comparison with Example 1, it can be seen that by partially replacing the nano-alumina with fluorine-doped hexagonal boron nitride, that is, using nano-alumina and fluorine-doped hexagonal boron nitride together, the two can produce a synergistic effect and synergistically improve the inkjet adhesion and tensile strength of the environmentally friendly thin film coating.

[0054] Combined with comparative example 3 for comparison, it can be seen that if the fluorine-doped hexagonal boron nitride in the system of nano-alumina and fluorine-doped hexagonal boron nitride is replaced with hexagonal boron nitride nanosheets, the tensile strength of the obtained environmentally friendly thin film coating does not change significantly, but the inkjet adhesion is significantly reduced. This is because when the hexagonal boron nitride nanosheets are not fluorine-doped, there is a lack of hydrophobic areas to control the spreading speed of the aqueous ink. The aqueous ink is prone to excessive penetration in the coating and blooming. On the one hand, the dispersion balance of the pigment particles in the ink is broken, resulting in local agglomeration and precipitation, forming weak areas; on the other hand, the difference in the drying speed of the ink in the blooming area will lead to uneven internal stress distribution, which is prone to microcracks after drying. It is easier to peel off from the substrate when subjected to external force, resulting in reduced adhesion.

[0055] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A process for preparing an environmentally friendly thin film coating, characterized in that: The following steps are involved: S1, 3-4 parts of epoxy resin, 25-28 parts of polyurethane emulsion, 35-38 parts of water-based acrylic resin emulsion, 0.5-1 part of curing agent, 0.5-1 part of accelerator, 2-2.5 parts of dispersant, 0.3-0.5 part of wetting agent and 6-8 parts of PVA emulsion are mixed by ball milling to obtain a first mixture; S2. Add 4-5 parts of fluorine-doped hexagonal boron nitride and 10-12 parts of nano-alumina to the first mixture obtained in S1, and stir to obtain a second mixture; then add 2-3 parts of polyethylene oxide, 0.4-0.5 parts of citric acid, 2-4 parts of a film-forming aid, and 0.5-1 part of a defoaming agent to the second mixture, and stir to obtain a coating; S3, plasma-activating the PET film to obtain a pretreated PET film; S4. Evenly apply the coating obtained in S3 on the pretreated PET film obtained in S4, and solidify the coating to obtain an environmentally friendly thin film coating.

2. The process for preparing the environmentally friendly thin film coating according to claim 1, characterized in that: The preparation method of the fluorine-doped hexagonal boron nitride is as follows: A1. Place 1 g of hexagonal boron nitride nanosheets into a round-bottomed biscuit, and add 400-450 mL of fluoroboric acid to a round-bottomed beaker and stir to obtain a first mixed solution. A2, magnetically stirring the first mixed solution obtained in A1 at 50±2°C, and then cooling to room temperature to obtain a second mixed solution; A3. The second mixed solution obtained in A2 is centrifuged and washed multiple times with deionized water to obtain a solid, which is then dried to obtain fluorine-doped hexagonal boron nitride.

3. The process for preparing the environmentally friendly thin film coating according to claim 2, characterized in that: In A2, the speed of magnetic stirring is 120-150 rpm, and the time of magnetic stirring is 7-8 h.

4. The process for preparing the environmentally friendly thin film coating according to claim 2, characterized in that: In A3, the drying temperature is 55-65°C and the drying time is 75-90 minutes.

5. The process for preparing the environmentally friendly thin film coating according to claim 1, characterized in that: In S1, the curing agent is dicyandiamide, the accelerator is 2-methylimidazole, the dispersant is a comb-type polyetheramine dispersant BYK-190, and the wetting agent is an acetylene glycol wetting agent Surfynol 104.

6. The process for preparing the environmentally friendly thin film coating according to claim 1, characterized in that: In S1, zirconia balls were used in the ball milling process, and the ball-to-material mass ratio was (4-6):

1.

7. The process for preparing the environmentally friendly thin film coating according to claim 1, characterized in that: In S2, the molecular weight of the polyethylene oxide is less than 10,000.

8. The process for preparing the environmentally friendly thin film coating according to claim 1, characterized in that: In S2, the film-forming aid includes dipropylene glycol butyl ether and / or dodecyl alcohol ester (3:1).

9. The process for preparing the environmentally friendly thin film coating according to claim 1, characterized in that: The thickness of the environmentally friendly thin film coating is 5±0.5 μm.

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