A plastic substrate surface hydrophilic anti-fog transparent coating and a preparation method thereof

Abstract

This invention relates to the field of coatings, and discloses a hydrophilic anti-fog transparent coating for a plastic substrate and its preparation method. The hydrophilic anti-fog transparent coating comprises the following raw materials: 40-80% linear acrylic copolymer, 0.1-2% active monomer, 0.05-0.2% photoinitiator, 0-0.5% defoamer, 0-0.5% leveling agent, and 20-60% solvent. The linear acrylic copolymer is copolymerized from acrylate soft monomers, hard monomers containing olefin bonds, and functional monomers; the functional monomers contain olefin bonds and hydrophilic groups; the active monomer is one or more of ethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol diacrylate, and butanediol diacrylate. The hydrophilic anti-fog coating of this invention not only has excellent anti-fog effect, but also good adhesion to the plastic substrate, and exhibits long-lasting water resistance, high temperature and humidity resistance, and high transparency.

Description

Technical Field

[0001] This invention relates to the field of coatings, and more particularly to a hydrophilic anti-fog transparent coating for the surface of a plastic substrate and its preparation method. Background Technology

[0002] Coatings are widely used in industries such as construction, machinery, electronics, and security. Once cured, the coating primarily protects and decorates the substrate. However, with advancements in technology, market demands for coating performance are increasing, including requirements for resistance to light aging, high and low temperatures, solvent resistance, moisture resistance, and scratch resistance. This has led to the emergence of specialized functional coatings, such as hardening, anti-corrosion, anti-fog, anti-fogging, fireproof, and heat-insulating coatings, with demand becoming increasingly strong.

[0003] Fogging is a natural phenomenon. When the temperature and humidity of the environment change, water vapor in the air condenses on solid surfaces, forming small water droplets. This causes light refraction and affects light transmission, resulting in a whitening or even condensation phenomenon, which can cause inconvenience to production and daily life, and even pose safety hazards. For example, fogging of a camera lens can cause the imaging system to malfunction; fogging of a car's windshield can affect the driver's normal driving.

[0004] To prevent fogging, a layer of hydrophilic coating is applied to the substrate surface, making the static contact angle of water droplets <30°. This prevents water vapor from condensing and agglomerating into small droplets, allowing it to spread evenly on the coating surface and form a uniform water film. This significantly reduces the decrease in light transmittance caused by light refraction, thus achieving an anti-fogging effect.

[0005] However, due to limitations in manufacturing processes, current anti-fog coatings on plastic substrates (such as PC substrates) generally suffer from poor water resistance. Under prolonged high temperature and humidity conditions, or after immersion in water, their anti-fog lifespan is short, rendering them impractical. Furthermore, some coatings with good anti-fog performance lack sufficient transparency, failing to meet the requirements of specialized applications such as cameras. Therefore, developing long-lasting, water-resistant, high-temperature and high-humidity resistant, and highly transparent hydrophilic anti-fog coatings is of significant importance. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a hydrophilic anti-fog transparent coating for a plastic substrate and its preparation method. The hydrophilic anti-fog coating of this invention not only possesses excellent anti-fog properties but also exhibits good adhesion to the plastic substrate, long-lasting water resistance, high temperature and humidity resistance, and high transparency.

[0007] The specific technical solution of this invention is as follows:

[0008] In a first aspect, the present invention provides a hydrophilic anti-fog transparent coating for the surface of a plastic substrate, comprising the following raw materials in weight percentages: 40-80% linear acrylic copolymer, 0.1-2% active monomer, 0.05-0.2% photoinitiator, 0-0.5% defoamer, 0-0.5% leveling agent, and 20-60% solvent.

[0009] The linear acrylic copolymer is copolymerized from acrylate soft monomers, olefin-containing hard monomers, and functional monomers in a mass ratio of (20-40%):(50-70%):(1-8%); the functional monomers contain olefin bonds and hydrophilic groups. The active monomers are one or more of ethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol diacrylate, and butanediol diacrylate.

[0010] This invention provides a hydrophilic anti-fogging coating using a linear acrylic copolymer as the main film-forming material. This linear acrylic copolymer is obtained by copolymerizing acrylate soft monomers, olefin-containing hard monomers, and functional monomers in a specific ratio. Because its molecular chain contains hydrophilic functional monomers, it is a linear thermoplastic hydrophilic polymer, exhibiting good anti-fogging effects as a coating film-forming material. However, this invention found that the linear acrylic copolymer exhibits poor adhesion to the plastic substrate after curing, and its anti-fogging effect is unsatisfactory in high-temperature, high-humidity, or water-immersion environments. Therefore, this invention combines the linear acrylic copolymer with active monomers during coating preparation. Before coating curing, the active monomers are uniformly dispersed in the linear acrylic copolymer. After UV curing, cross-linking reactions occur between the active monomers, thereby forming a semi-interpenetrating polymer network with the linear acrylic copolymer. Figure 1 As shown in the figure, this can significantly enhance the adhesion between the coating and the plastic substrate, and at the same time greatly improve the anti-fogging effect of the coating in high temperature and high humidity or water immersion environments.

[0011] Furthermore, this invention also discovered that the content of reactive monomers has a significant impact on the performance of the coating: at a certain reactive monomer content, the adhesion of the coating gradually increases with the increase of the amount of reactive monomers, indicating that increasing the reactive monomers increases the crosslinking density and cohesion of the coating, improves the bonding ability between the coating and the PC substrate, and simultaneously enhances the anti-fogging performance after high temperature and humidity resistance and water resistance. However, when the reactive monomer content reaches a certain level, if its content continues to increase, the anti-fogging level begins to decrease. This is because the continued increase in crosslinking density leads to a decrease in the hydrophilicity of the coating, affecting the anti-fogging effect.

[0012] Preferably, the plastic substrate is a PC substrate, a PET substrate, or a PMMA substrate.

[0013] Preferably, the acrylate soft monomer is one or more of ethyl acrylate, butyl acrylate, isooctyl acrylate, lauryl acrylate, and n-octyl methacrylate.

[0014] Preferably, the hard monomer is one or more of styrene, methyl methacrylate, acrylonitrile, and ethyl methacrylate.

[0015] Preferably, the functional monomer is one or more of acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, acrylamide, N-hydroxymethylacrylamide, N,N-dimethylacrylamide, glycidyl methacrylate, and vinylpyrrolidone.

[0016] Preferably, the photoinitiator is one or more of 2,4,6-trimethylbenzoyl)diphenylphosphine oxide, 2-methyl-1-[4-methylthiophenyl]-2-morpholino-1-propanone, 2-isopropylthioxanthone, and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide.

[0017] Preferably, the solvent is one or more of ethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol methyl ether acetate, isopropanol, and n-butanol.

[0018] Preferably, the defoamer is one or more of BYK066N, BYK028, and Tego901.

[0019] Preferably, the leveling agent is one or more of BYK333, BYK375, and Tego410.

[0020] Preferably, the method for preparing the linear acrylic copolymer includes:

[0021] S1: The initiator is mixed with acrylate soft monomers, hard monomers and functional monomers to obtain a premix.

[0022] S2: Add solvent to the reaction vessel and heat and stir.

[0023] S3: Add a premix to the solvent.

[0024] S4: Cool after heat preservation reaction.

[0025] Preferably, in step S2, the amount of solvent used is 105-110 wt% of the total monomer, and the heating temperature is 70-75°C.

[0026] Preferably, in step S3, the premix is ​​added within 2-3 hours.

[0027] Preferably, in step S4, the heat preservation reaction time is 2.5-3.5 hours.

[0028] Preferably, in S1: the initiator is one or more of benzoyl peroxide, azobisisobutyronitrile, ammonium persulfate, tert-butyl hydroperoxide and dicyclohexyl percarbonate; in S2: the solvent is one or more of isopropanol, isobutanol and methanol.

[0029] Preferably, the coating has an adhesion rating of 0, an anti-fog rating of ≤3, an anti-fog rating of ≤3 after high temperature and humidity aging, an anti-fog rating of ≤3 after water resistance test, and a transmittance of ≥88%.

[0030] Secondly, the present invention provides a method for preparing the above-mentioned hydrophilic anti-fog transparent coating on the surface of a plastic substrate, specifically including the following steps:

[0031] 1) Add linear acrylic copolymer, solvent, active monomer, photoinitiator, defoamer and leveling agent to the reaction vessel and stir evenly to obtain hydrophilic anti-fog transparent coating.

[0032] 2) Spray the hydrophilic anti-fog transparent coating onto the surface of the plastic substrate.

[0033] 3) Curing by heating only once.

[0034] 4) Apply a second coat of hydrophilic anti-fog transparent coating.

[0035] 5) Reheat to cure.

[0036] 6) UV curing.

[0037] After heat curing and UV curing, a semi-interpenetrating polymer network structure is formed in the coating. Figure 1 (As shown). Heating and curing promote the penetration of the coating into the PC substrate, aiding in the formation of a bonding layer, while UV curing enhances the coating's cohesion. Furthermore, this invention reveals that during the post-spray curing process, the coating surface cures first, causing solvent from the underlying layer to migrate to the surface, generating Bénard vortices. This affects the coating's microscopic smoothness and consequently its transparency. Using a "one-time spraying + one-time heating and curing" process results in a thick wet film thickness for each coat, making it prone to Bénard vortices. However, using the "two-time spraying + two-time heating and curing" process of this invention results in a thinner wet film thickness for each coat, reducing the formation of Bénard vortices and ultimately achieving a higher coating transparency.

[0038] Preferably, in step 1), the stirring is performed at 600-800 rpm for 20-40 minutes.

[0039] Preferably, in step 2), the plastic substrate is pre-cleaned until the surface is free of water and oil.

[0040] Preferably, in steps 2) and 4), the first spraying uses a 1.0-1.5mm nozzle spray gun, a spray pressure of 0.4-0.6MPa, a plastic substrate conveying speed of 15-25mm / s, and a spray gun moving speed of 0.5-1.5m / s; the second spraying uses a 1.0-1.5mm nozzle spray gun, a spray pressure of 0.2-0.3MPa, a plastic substrate conveying speed of 15-25mm / s, and a spray gun moving speed of 0.5-1.5m / s.

[0041] Preferably, in steps 3) and 5), the temperature for the first heating and curing is 40-60℃ and the time is 5-10 min; the temperature for the second heating and curing is 70-80℃ and the time is 5-10 min.

[0042] To further improve the transparency of the coating, this invention employs a "two-stage spraying + two-stage heat curing" process with differentiated parameters. Specifically: During the first spraying, the spray pressure is 0.4-0.6 MPa. Higher pressure results in a smaller spray flow rate and a thinner coating film. Combined with curing conditions of 40-60℃, this achieves rapid solvent evaporation and a quick effect. During the second spraying, the spray pressure is 0.2-0.3 MPa. Lower pressure results in a larger spray flow rate and a thicker coating film. Combined with curing conditions of 70-80℃, this allows for rapid co-curing with the first sprayed coating, achieving good leveling and higher coating transparency.

[0043] Preferably, in step 6), the energy of the UV-curing mercury lamp is 3000-5000 mJ / cm². 2 Curing time < 5s.

[0044] Compared with the prior art, the beneficial effects of the present invention are:

[0045] (1) The hydrophilic anti-fog transparent coating of this invention uses linear acrylic copolymer as the main film-forming material. It is obtained by copolymerizing acrylate soft monomers, hard monomers containing olefin bonds, and functional monomers in a specific ratio. The functional monomers are hydrophilic, so the linear acrylic copolymer film has a good anti-fog effect. Based on this, this invention combines the linear acrylic copolymer with active monomers. The active monomers are uniformly dispersed in the linear acrylic copolymer. After UV curing, the active monomers crosslink and form a semi-interpenetrating polymer network with the linear acrylic copolymer. This can significantly enhance the adhesion between the coating and the plastic substrate, and at the same time greatly improve the anti-fog effect of the coating in high temperature and high humidity or water immersion environments.

[0046] (2) The hydrophilic anti-fog transparent coating of this invention, applied to a PC substrate, maintains its anti-fog effect even after exposure to high temperature and humidity (85℃ / 85% relative humidity for 720 hours) and immersion in water (40℃ for 240 hours). It can be used on plastic substrate surfaces that frequently operate in high humidity or immersion environments, such as PC dome covers for security cameras.

[0047] (3) The present invention adopts a “secondary spraying + secondary curing” process, which can build a highly transparent hydrophilic anti-fog transparent coating on the surface of a plastic substrate; furthermore, if the “secondary spraying + secondary curing” process with specific parameter differentiation settings of the present invention is adopted, the coating transparency is even better. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the coating curing principle of the present invention; wherein: a represents a linear acrylic copolymer; b represents the addition of active monomers to the linear acrylic copolymer after the coating is compounded; c represents the formation of cross-linked polymers by the active monomers after curing, which in turn form a semi-interpenetrating polymer network with the linear acrylic copolymer. Detailed Implementation

[0049] The present invention will be further described below with reference to embodiments.

[0050] General Implementation Examples

[0051] A hydrophilic, anti-fog, transparent coating for a plastic substrate comprises the following raw materials in weight percentages: 40-80% linear acrylic copolymer, 0.1-2% active monomer, 0.05-0.2% photoinitiator, 0-0.5% defoamer, 0-0.5% leveling agent, and 20-60% solvent.

[0052] The linear acrylic copolymer is copolymerized from acrylate soft monomers, olefin-containing hard monomers, and functional monomers in a mass ratio of (20-40%):(50-70%):(1-8%); the functional monomers contain olefin bonds and hydrophilic groups. The active monomers are one or more of ethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol diacrylate, and butanediol diacrylate.

[0053] In some preferred embodiments, the plastic substrate is a PC substrate, a PET substrate, or a PMMA substrate.

[0054] In some preferred embodiments, the acrylate soft monomer is one or more of ethyl acrylate, butyl acrylate, isooctyl acrylate, lauryl acrylate, and n-octyl methacrylate.

[0055] In some preferred embodiments, the hard monomer is one or more of styrene, methyl methacrylate, acrylonitrile, and ethyl methacrylate.

[0056] In some preferred embodiments, the functional monomer is one or more of acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, acrylamide, N-hydroxymethylacrylamide, N,N-dimethylacrylamide, glycidyl methacrylate, and vinylpyrrolidone.

[0057] In some preferred embodiments, the photoinitiator is one or more of 2,4,6-trimethylbenzoyl)diphenylphosphine oxide, 2-methyl-1-[4-methylthiophenyl]-2-morpholino-1-propanone, 2-isopropylthioxanthone, and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide.

[0058] In some preferred embodiments, the solvent is one or more of ethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol methyl ether acetate, isopropanol, and n-butanol.

[0059] In some preferred embodiments, the defoamer is one or more of BYK066N, BYK028, and Tego901.

[0060] In some preferred embodiments, the leveling agent is one or more of BYK333, BYK375, and Tego410.

[0061] In some preferred embodiments, the method for preparing the linear acrylic copolymer includes:

[0062] S1: The initiator is mixed with acrylate soft monomers, hard monomers and functional monomers to obtain a premix.

[0063] In some preferred embodiments, in S1: the initiator is one or more of benzoyl peroxide, azobisisobutyronitrile, ammonium persulfate, tert-butyl hydroperoxide, and dicyclohexyl percarbonate.

[0064] S2: Add solvent to the reaction vessel and heat and stir.

[0065] In some more specific implementations, in S2, the amount of solvent used is 105-110 wt% of the total monomer, and the heating temperature is 70-75°C.

[0066] In some more preferred embodiments, in S2: the solvent is one or more of isopropanol, isobutanol and methanol.

[0067] S3: Add a premix to the solvent.

[0068] In some more specific implementations, in S3, the premix is ​​added within 2-3 hours.

[0069] S4: Cool after heat preservation reaction.

[0070] In some more specific implementation examples, in S4, the heat preservation reaction time is 2.5-3.5 hours.

[0071] In some preferred embodiments, the coating has an adhesion rating of 0, an anti-fog rating of ≤3, an anti-fog rating of ≤3 after high temperature and humidity aging, an anti-fog rating of ≤3 after water resistance test, and a transmittance of ≥88%.

[0072] A method for preparing a hydrophilic anti-fog transparent coating on the surface of the above-mentioned plastic substrate specifically includes the following steps:

[0073] 1) Add linear acrylic copolymer, solvent, active monomer, photoinitiator, defoamer and leveling agent to the reaction vessel and stir evenly to obtain hydrophilic anti-fog transparent coating.

[0074] In some more specific implementations, in step 1), the stirring is performed at 600-800 rpm for 20-40 minutes.

[0075] 2) Spray the hydrophilic anti-fog transparent coating onto the surface of the plastic substrate.

[0076] In some more specific implementations, in step 2), the plastic substrate is pre-cleaned until the surface is free of water and oil.

[0077] In some more specific implementation cases, in step 2), the hydrophilic anti-fog transparent coating is sprayed with a 1.0-1.5mm nozzle spray gun, the spray pressure is 0.4-0.6MPa, the plastic substrate transmission speed is 15-25mm / s, and the spray gun movement speed is 0.5-1.5m / s.

[0078] 3) Curing by heating only once.

[0079] In some more specific implementation cases, in step 3), the temperature of the first heating and curing is 40-60℃ and the time is 5-10min.

[0080] 4) Apply a second coat of hydrophilic anti-fog transparent coating.

[0081] In some more specific implementation cases, in step 4), the hydrophilic anti-fog transparent coating is sprayed with a 1.0-1.5mm nozzle spray gun, the spray pressure is 0.2-0.3MPa, the plastic substrate transmission speed is 15-25mm / s, and the spray gun movement speed is 0.5-1.5m / s.

[0082] 5) Reheat to cure.

[0083] In some more specific implementation cases, in step 3), the reheating and curing temperature is 70-80℃ and the time is 5-10 minutes.

[0084] 6) UV curing.

[0085] In some more specific implementation cases, in step 6), the mercury lamp energy is 3000-5000 mJ / cm².2 Curing time < 5 seconds.

[0086] Specific embodiments and comparative examples

[0087] The coating performance testing method is as follows:

[0088]

[0089] Anti-fog rating comparison table

[0090] Level / Class Judgment basis 1 A uniform water film, completely transparent, without water droplets. 2 A localized, uneven water film covering less than 5% of the area exhibits good transparency and forms a small number of water droplets. 3 A localized, uneven water film covering less than 30% of the area results in the formation of numerous water droplets. 4 Uneven water film covering more than 30% of the area.

[0091] (I) Effect of different amounts of active monomers

[0092] S1: Take 300g of soft acrylate monomer (isooctyl acrylate), 650g of hard monomer (methyl methacrylate), 50g of functional monomer (N,N-dimethylacrylamide), and 3g of initiator (benzoyl peroxide), mix them to obtain a premix; take 1050g of solvent one (isobutanol) and add it to the reactor, heat it to 72℃ under water bath heating and stirring; after the temperature stabilizes, add the premix to the reactor at a uniform rate through a peristaltic pump over 2.5h, keep it at the temperature for another 3h and then cool it to room temperature to obtain a linear acrylic copolymer.

[0093] S2: Add 600g of linear acrylic copolymer, active monomer (polyethylene glycol diacrylate, Average Mn750) (addition amount shown in Table 1), 0.5g of photoinitiator (2,4,6-(trimethylbenzoyl)diphenylphosphine oxide), 1g of defoamer (BYK028), 2g of leveling agent (BKY333) and solvent di(propylene glycol methyl ether) (to a total of 1000g) to another reactor, disperse at 700 rpm for 30 min to obtain a hydrophilic anti-fog transparent coating.

[0094] S3: Clean the PC substrate until the surface is free of water and oil. Transport the plastic substrate via a conveyor belt. Above the conveyor belt, there is a spray gun that moves laterally (perpendicular to the conveying direction). Apply the hydrophilic anti-fog transparent coating using a 1.2mm nozzle spray gun. The spray pressure is 0.5MPa, the plastic substrate conveying speed is 20mm / s, and the spray gun moving speed is 1m / s. Bake in a 55℃ oven for 8 minutes to form a coating with a thickness of about 4 micrometers.

[0095] S4: Apply the hydrophilic anti-fog transparent coating again using a 1.2mm nozzle spray gun, with the following settings: spray pressure 0.3MPa, plastic substrate transport speed 20mm / s, and spray gun movement speed 1m / s; bake in a 75℃ oven for 8 minutes; finally, apply an energy of 4000mJ / cm³. 2 It is cured under a mercury lamp for 4 seconds to form a coating with a total thickness of about 12 micrometers.

[0096] The performance test results of the obtained coating are shown in Table 1:

[0097] Table 1

[0098]

[0099] The data comparison in the table above shows that:

[0100] (1) The test results show that from Comparative Example 1, Example 1 to Example 2, as the amount of active monomer increases, the adhesion of the coating increases from level 2 to level 0. This indicates that after adding active monomer, the crosslinking density of the coating increases, the cohesive force is enhanced, the bonding ability of the coating with the PC substrate is improved, and the anti-fogging performance after high temperature and high humidity and water resistance is improved. The optimal state is reached at the addition amount (1%) in Example 2.

[0101] (2) The test results show that as the amount of active monomer continued to increase from Example 2 and Example 3 to Comparative Example 2, the anti-fogging level began to decrease, indicating that further increases in crosslinking density would lead to a decrease in the hydrophilicity of the coating and affect the anti-fogging effect.

[0102] (II) The Influence of Different Types of Active Monomers

[0103] S1: Take 300g of soft acrylate monomer (isooctyl acrylate), 650g of hard monomer (methyl methacrylate), 50g of functional monomer (N,N-dimethylacrylamide), and 3g of initiator (benzoyl peroxide), mix them to obtain a premix; take 1050g of solvent one (isobutanol) and add it to the reactor, heat it to 72℃ under water bath heating and stirring; after the temperature stabilizes, add the premix to the reactor at a uniform rate through a peristaltic pump over 2.5h, keep it at the temperature for another 3h and then cool it to room temperature to obtain a linear acrylic copolymer.

[0104] S2: Add 600g of linear acrylic copolymer, 10g of active monomer (see Table 2 for types), 0.5g of photoinitiator (2,4,6-trimethylbenzoyl)diphenylphosphine oxide), 1g of defoamer (BYK028), 2g of leveling agent (BKY333), and solvent di(propylene glycol methyl ether) (to a total of 1000g) to another reactor. Disperse at 700 rpm for 30 min to obtain a hydrophilic anti-fog transparent coating.

[0105] S3: Clean the PC substrate until the surface is free of water and oil. Transport the plastic substrate via a conveyor belt. Above the conveyor belt, there is a spray gun that moves laterally (perpendicular to the conveying direction). Apply the hydrophilic anti-fog transparent coating using a 1.2mm nozzle spray gun. The spray pressure is 0.5MPa, the plastic substrate conveying speed is 20mm / s, and the spray gun moving speed is 1m / s. Bake in a 55℃ oven for 8 minutes to form a coating with a thickness of about 4 micrometers.

[0106] S4: Apply the hydrophilic anti-fog transparent coating again using a 1.2mm nozzle spray gun, with the following settings: spray pressure 0.3MPa, plastic substrate transport speed 20mm / s, and spray gun movement speed 1m / s; bake in a 75℃ oven for 8 minutes; finally, apply an energy of 4000mJ / cm³. 2 It is cured under a mercury lamp for 4 seconds to form a coating with a total thickness of about 12 micrometers.

[0107] The performance test results of the obtained coating are shown in Table 2:

[0108] Table 2

[0109]

[0110] The data comparison in the table above shows that in Examples 2 and 4-5, as the polyether segments in the active monomers increase, the molecular weight of the monomers increases. Under the same content, with the increase of molecular weight, the anti-fogging effect of the coating improves from level 2 to level 1; however, the water resistance and high temperature and humidity resistance of the coating are also affected. Considering the results of various performance indicators, the optimal average molecular weight (Average Mn) of polyethylene glycol diacrylate is 750.

[0111] (III) The Influence of Different Spraying Processes on Coating Transparency

[0112] Comparative Example 3 (using a single spraying and single heat curing process)

[0113] S1: Take 300g of soft acrylate monomer (isooctyl acrylate), 650g of hard monomer (methyl methacrylate), 50g of functional monomer (N,N-dimethylacrylamide), and 3g of initiator (benzoyl peroxide), mix them to obtain a premix; take 1050g of solvent one (isobutanol) and add it to the reactor, heat it to 72℃ under water bath heating and stirring; after the temperature stabilizes, add the premix to the reactor at a uniform rate through a peristaltic pump over 2.5h, keep it at the temperature for another 3h and then cool it to room temperature to obtain a linear acrylic copolymer.

[0114] S2: Add 600g of linear acrylic copolymer, 10g of active monomer (polyethylene glycol diacrylate, Average Mn750), 0.5g of photoinitiator (2,4,6-trimethylbenzoyl)diphenylphosphine oxide), 1g of defoamer (BYK028), 2g of leveling agent (BKY333), and solvent di(propylene glycol methyl ether) (to a total of 1000g) to another reactor. Disperse at 700 rpm for 30 min to obtain a hydrophilic anti-fog transparent coating.

[0115] S3: Clean the PC substrate until the surface is free of water and oil. Transport the plastic substrate via a conveyor belt. Above the conveyor belt, a spray gun with a transverse reciprocating motion (perpendicular to the conveying direction) is installed. Apply the hydrophilic anti-fog transparent coating using a 1.2mm nozzle spray gun. The spray pressure is 0.2MPa, the plastic substrate transport speed is 15mm / s, and the spray gun movement speed is 1m / s. Bake in a 75℃ oven for 16 minutes, and finally, apply the coating at an energy level of 4000mJ / cm³. 2 It is cured under a mercury lamp for 4 seconds to form a coating with a total thickness of about 12 micrometers.

[0116] Example 6 (The parameters for secondary spraying and heat curing are the opposite of those in Example 1)

[0117] S1: Take 300g of soft acrylate monomer (isooctyl acrylate), 650g of hard monomer (methyl methacrylate), 50g of functional monomer (N,N-dimethylacrylamide), and 3g of initiator (benzoyl peroxide), mix them to obtain a premix; take 1050g of solvent one (isobutanol) and add it to the reactor, heat it to 72℃ under water bath heating and stirring; after the temperature stabilizes, add the premix to the reactor at a uniform rate through a peristaltic pump over 2.5h, keep it at the temperature for another 3h and then cool it to room temperature to obtain a linear acrylic copolymer.

[0118] S2: Add 600g of linear acrylic copolymer, 10g of active monomer (polyethylene glycol diacrylate, Average Mn750), 0.5g of photoinitiator (2,4,6-trimethylbenzoyl)diphenylphosphine oxide), 1g of defoamer (BYK028), 2g of leveling agent (BKY333), and solvent di(propylene glycol methyl ether) (to a total of 1000g) to another reactor. Disperse at 700 rpm for 30 min to obtain a hydrophilic anti-fog transparent coating.

[0119] S3: Clean the PC substrate until the surface is free of water and oil. Transport the plastic substrate via a conveyor belt. Above the conveyor belt, there is a spray gun that moves laterally (perpendicular to the conveying direction). Apply the hydrophilic anti-fog transparent coating using a 1.2mm nozzle spray gun. The spray pressure is 0.3MPa, the plastic substrate conveying speed is 20mm / s, and the spray gun moving speed is 1m / s. Bake in a 75℃ oven for 8 minutes to form a coating with a thickness of about 8 micrometers.

[0120] S4: Apply the hydrophilic anti-fog transparent coating again using a 1.2mm nozzle spray gun, with a spray pressure of 0.5MPa, a plastic substrate transport speed of 20mm / s, and a spray gun movement speed of 1m / s; bake in a 55℃ oven for 8 minutes; finally, apply the coating at an energy level of 4000mJ / cm³. 2 It is cured under a mercury lamp for 4 seconds to form a coating with a total thickness of about 12 micrometers.

[0121] The performance test results of the obtained coating are shown in Table 3:

[0122] Table 3

[0123]

[0124] The data comparison in the table above shows that:

[0125] (1) Comparative Example 3 adopted a spraying process of "one-time spraying + one-time curing", while Example 6 and Example 2 adopted a spraying process of "one-time spraying + one-time curing + two-time spraying + two-time curing". The results showed that the transmittance of the coatings formed by Example 6 and Example 2, which adopted the spraying process of "one-time spraying + one-time curing + two-time spraying + two-time curing", was significantly higher than that of Comparative Example 3.

[0126] (2) Further, the difference between Example 2 and Example 6 is that the spraying parameters and heating curing parameters in Example 6 are reversed compared to Example 2. The results show that the coating obtained by the two-step differentiated spraying-curing process in Example 2 has a higher transmittance. The reason is that in the differentiated spraying-curing process in Example 2, the spray pressure of the first spray is increased, while the pressure of the second spray is decreased, resulting in a lower coating thickness in the first spray and a higher thickness in the second spray. Combined with an appropriate curing temperature, the coating achieves a mirror-like leveling effect to the greatest extent while reducing Bénard vortices during the curing process.

[0127] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0128] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a hydrophilic, anti-fog, transparent coating on the surface of a plastic substrate, characterized in that... include: 1) Mix 40-80wt% linear acrylic copolymer, 20-60wt% solvent, 0.1-2wt% reactive monomer, 0.05-0.2wt% photoinitiator, 0-0.5wt% defoamer, and 0-0.5wt% leveling agent until the total amount is 100wt%; 2) Spray the obtained hydrophilic anti-fog transparent coating onto the surface of the plastic substrate; 3) Curing by heating only once; 4) Apply a second coat of hydrophilic, anti-fog, transparent coating; 5) Reheat to cure; 6) UV curing; The linear acrylic copolymer is copolymerized from acrylate soft monomers, olefin-containing hard monomers and functional monomers in a mass ratio of 20-40:50-70:1-8. The functional monomer contains olefinic bonds and hydrophilic groups; The active monomer is one or more of ethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol diacrylate, and butanediol diacrylate.

2. The preparation method according to claim 1, characterized in that: The plastic substrate is a PC substrate, a PET substrate, or a PMMA substrate.

3. The preparation method according to claim 1, characterized in that: The acrylate soft monomer is one or more of ethyl acrylate, butyl acrylate, isooctyl acrylate, lauryl acrylate and n-octyl methacrylate; The hard monomer is one or more of styrene, methyl methacrylate, acrylonitrile, and ethyl methacrylate; The functional monomer is one or more of acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, acrylamide, N-hydroxymethylacrylamide, N,N-dimethylacrylamide, glycidyl methacrylate, and vinylpyrrolidone.

4. The preparation method according to claim 1, characterized in that: The photoinitiator is one or more of 2,4,6-trimethylbenzoyl)diphenylphosphine oxide, 2-methyl-1-[4-methylthiophenyl]-2-morpholino-1-propanone, 2-isopropylthioxanthone, and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide; The solvent is one or more of ethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol methyl ether acetate, isopropanol, and n-butanol; The defoamer is one or more of BYK066N, BYK028 and Tego901; The leveling agent is one or more of BYK333, BYK375, and Tego410.

5. The preparation method according to claim 1, characterized in that: The method for preparing the linear acrylic copolymer includes: S1: The initiator is mixed with acrylate soft monomers, hard monomers and functional monomers to obtain a premix; S2: Heat and stir the solvent; S3: Add a premix to the solvent; S4: Cool after heat preservation reaction.

6. The preparation method according to claim 5, characterized in that: In S2, the amount of solvent used is 105-110 wt% of the total amount of monomers, and the heating temperature is 70-75℃; In S3, the premix is ​​added within 2-3 hours; In S4, the heat preservation reaction time is 2.5-3.5h.

7. The preparation method according to claim 5, characterized in that: In S2 and S3, the solvent is one or more of isopropanol, isobutanol and methanol; In S1, the initiator is one or more of benzoyl peroxide, azobisisobutyronitrile, ammonium persulfate, tert-butyl hydroperoxide, and dicyclohexyl percarbonate.

8. The preparation method according to claim 1, characterized in that: In steps 2) and 4), the initial spraying uses a 1.0-1.5mm nozzle spray gun, a spray pressure of 0.4-0.6MPa, a plastic substrate conveying speed of 15-25mm / s, and a spray gun moving speed of 0.5-1.5m / s; For the second coat, use a 1.0-1.5mm nozzle spray gun, spray air pressure of 0.2-0.3MPa, plastic substrate conveying speed of 15-25mm / s, and spray gun movement speed of 0.5-1.5m / s; In steps 3) and 5), the temperature for the first heating and curing is 40-60℃, and the time is 5-10 min; the temperature for the second heating and curing is 70-80℃, and the time is 5-10 min. In step 6), the UV-curing mercury lamp has an energy of 3000-5000 mJ / cm². 2 Curing time < 5s.

9. A hydrophilic, anti-fog, transparent coating on the surface of a plastic substrate obtained by the preparation method according to any one of claims 1-8.

10. The hydrophilic anti-fog transparent coating on the surface of the plastic substrate according to claim 9, characterized in that: Adhesion rating = 0, anti-fog rating ≤ 3, anti-fog rating after high temperature and humidity aging ≤ 3, anti-fog rating after water resistance test ≤ 3, transmittance ≥ 88%.

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