A low-reflection coating, its preparation method and application

Abstract

The present invention relates to the field of materials. A low-reflection coating, a preparation method thereof, and an application thereof are disclosed. The low-reflection coating comprises: 10-30 wt% of a hydroxyl acrylic resin, 5-35 wt% of a blocked polyurethane black powder, 2-25 wt% of a carbon black paste, 0.5-5 wt% of an additive, and 20-80 wt% of a solvent. The blocked polyurethane black powder is a blocked polyurethane loaded with carbon black and having a fluorine-containing segment. The low-reflection coating of the present invention contains the blocked polyurethane black powder, which can generate -NCO after heating and form a crosslinked structure after crosslinking with the -OH of the hydroxyl acrylic resin, enabling the coating to have strong mechanical properties and durability. Coupled with the carbon black paste in the coating, an extremely low reflectivity can be finally achieved. In addition, the blocked polyurethane black powder of the present invention has a fluorine-containing segment, which can make the surface of the coating have sufficient micro-roughness and further reduce the gloss of the coating.

Description

Technical Field

[0001] The present invention relates to the field of materials, and particularly to a low-reflection coating and its preparation method and application. Background Art

[0002] Stray light is unwanted noise light in an imaging system, which will directly affect the imaging of optical components; non-imaging stray light irradiates the focal plane after scattering to form ghost images, which will cause the imaging of the observed target to be blurred and affect the recognition ability. To eliminate the adverse effects of stray light, the currently common solution is to modify the surface of the housing material of optical components with a coating to shield stray light.

[0003] Currently, the low-reflection coatings for industrial applications mainly use carbon black as the light-absorbing material, and are combined with matting agents (wax powder, fumed silica) to reduce the gloss of the coating, so as to achieve the effect of reducing the reflectivity. However, to achieve a lower reflectivity, the amounts of carbon black and matting agents required are usually large, which easily leads to a decline in the mechanical properties of the coating; increasing the resin content in the coating can improve the mechanical properties, but at the same time it will increase the reflectivity of the coating to a certain extent. Therefore, the reflectivity of the current low-reflection coatings can basically only be controlled at about 2%, which cannot meet the application scenarios with extremely low reflectivity requirements. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a low-reflection coating and its preparation method and application. The low-reflection coating of the present invention contains blocked polyurethane black powder, which can generate -NCO at the open end under heating conditions, and further crosslink with -OH in the hydroxyl acrylic resin in the coating to form a crosslinked structure, which can endow the coating with strong mechanical properties and durability. On this basis, combined with the carbon black paste in the coating, an extremely low reflectivity (≤0.08%) can be finally achieved. In addition, the blocked polyurethane black powder of the present invention has a fluorine-containing chain segment, which can make the surface of the coating have sufficient micro-roughness after drying, and further reduce the gloss of the coating.

[0005] The specific technical solution of the present invention is as follows:

[0006] In the first aspect, the present invention provides a low-reflection coating, which comprises raw materials in the following mass percentages: 10-30 wt% of hydroxyl acrylic resin, 5-35 wt% of blocked polyurethane black powder, 2-25 wt% of carbon black paste, 0.5-5 wt% of additives, and 20-80 wt% of solvent. Among them, the blocked polyurethane black powder is a blocked polyurethane loaded with carbon black and having a fluorine-containing chain segment.

[0007] The coating of the present invention uses a special capped polyurethane black powder loaded with carbon black as an active filler, which can generate -NCO groups under heating conditions and undergo a cross-linking reaction with -OH in the hydroxy acrylic resin in the formulation, ultimately forming a cross-linked structure. Therefore, this active filler can not only effectively reduce the gloss of the coating (reduce the reflectivity), but also ensure that the coating still has strong mechanical properties and durability with less resin usage. On this basis, combined with the carbon black paste in the formulation to absorb light, an extremely low reflectivity (≤0.08%) can be ultimately achieved.

[0008] In addition, in the molecular structure of the capped polyurethane in the capped polyurethane black powder of the present invention, a fluorine-containing chain segment is introduced, which can endow the capped polyurethane black powder with extremely low surface tension, making the black powder easily migrate to the surface of the coating during the drying process of the coating, so that the surface of the coating has sufficient micro-roughness instead of forming a smooth coating surface, which can further reduce the coating gloss.

[0009] The present invention controls the content of the capped polyurethane black powder at 5-35 wt%, because if the content is too low, the effect of reducing the coating gloss and reflectivity is not obvious enough; on the contrary, if the content is too high, too much black powder will lead to a decrease in the aging resistance of the coating and easy powdering.

[0010] Preferably, the NCO content of the capped polyurethane black powder is 10±0.3%, and the deblocking temperature is 105-120°C.

[0011] Preferably, the preparation method of the capped polyurethane black powder includes the following steps:

[0012] S1: Dehydrate aliphatic diisocyanate, perfluoropolyethylene glycol, chain extender, capping agent, carbon black and part of the reaction solvent.

[0013] S2: Add aliphatic diisocyanate to the reaction vessel, heat it, add perfluoropolyethylene glycol and react; add the chain extender and the reaction solvent, and continue to react to generate a polyurethane prepolymer.

[0014] S3: Heat the mixture of carbon black and the remaining reaction solvent, add it to the prepolymer and react; cool down, add the capping agent and continue to react; add a neutralizing agent to adjust the pH of the system to 7-9.

[0015] S4: Cool down, vacuum dry, crush and screen the obtained black solid product to obtain the capped polyurethane black powder.

[0016] Through the grafting reaction in the above preparation process, the present invention introduces fluorinated segments into the diisocyanate, and extends the chain to increase the molecular weight to form a polyurethane prepolymer. The -NCO groups in the polyurethane prepolymer react with -COOH in the carbon black, binding the polyurethane segments and the carbon black through chemical bonds. After capping, a capped polyurethane black powder is obtained. When it is added to the coating to prepare a low reflectivity coating, after the coating is heated to a temperature higher than the deblocking temperature, the blocked isocyanate is deblocked, and the generated free -NCO groups react with -OH in the hydroxy acrylic resin, which can ensure that the coating has sufficient mechanical properties and durability.

[0017] Preferably, the aliphatic diisocyanate is selected from one or two of hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI); the molecular weight of the perfluoropolyethylene glycol is 100 - 1000; the chain extender is selected from one or several of trimethylolpropane (TMP), dimethylolpropionic acid (DMPA), and dimethylolbutyric acid (DMBA); the capping agent is selected from one or two of methyl ethyl ketoxime and sodium bisulfite; the neutralizing agent is selected from one or several of triethanolamine, ammonia water, and 2 - amino - 2 - methyl - 1 - propanol; the carbon black is high - blackness furnace - process carbon black with a pH of 2.5 - 4; the reaction solvent is selected from one or several of acetone, butanone, and methyl isobutyl ketone.

[0018] Preferably, in the preparation process of the capped polyurethane black powder, the weight parts of each raw material are as follows: 100 parts of aliphatic diisocyanate, 50 - 150 parts of perfluoropolyethylene glycol, 1 - 10 parts of chain extender, 1 - 10 parts of capping agent, 5 - 15 parts of carbon black, and 200 - 400 parts of reaction solvent.

[0019] Preferably, S1 specifically includes: vacuum - drying the aliphatic diisocyanate, perfluoropolyethylene glycol, chain extender, capping agent, and carbon black at 110 - 130 °C for more than 12 h; adding molecular sieves to the reaction solvent to remove water.

[0020] Preferably, in S2, the temperature of the heat treatment is 45 - 55 °C, and after adding the perfluoropolyethylene glycol, the reaction is carried out for 20 - 40 min; the time for the subsequent reaction is 80 - 100 min.

[0021] Preferably, in S3, the temperature of the heat treatment is 45 - 55 °C, and it is added to the polyurethane prepolymer for reaction for 110 - 130 min: the temperature is lowered to 35 - 45 °C, and after adding the capping agent, the reaction is continued for 20 - 40 min.

[0022] Preferably, in S4, the particle size of the sieved capped polyurethane black powder is 1 - 10 microns.

[0023] Preferably, the hydroxyl acrylic resin has a solid content of 49-51 wt% and a hydroxyl value of 60-70 mgKOH / g; the carbon black paste is a high-blackness pyrogenic carbon black paste with a solid content of 39-41 wt%; the additives are selected from one or more of a dispersant, a wetting agent, an antifoaming agent, a leveling agent, a silane coupling agent, a sediment prevention agent, and a rheology aid; the solvent is selected from one or more of xylene, n-butyl acetate, ethyl acetate, ethylene glycol monobutyl ether, and propylene glycol methyl ether acetate.

[0024] Preferably, the 85° gloss of the coating formed after curing the low-reflection coating is ≤0.5, and the reflectivity is ≤0.2%.

[0025] In a second aspect, the present invention provides a method for preparing the above low-reflection coating, comprising the following steps: successively adding a hydroxyl acrylic resin, an additive, a part of the solvent, and a blocked polyurethane black powder in a container, grinding to a fineness of ≤35 μm, adding the carbon black paste and the remaining solvent, and dispersing for 20-30 min until uniform, and controlling the system temperature below 70 °C during the whole preparation process.

[0026] In a third aspect, the present invention provides an application of the above low-reflection coating in suppressing stray light in the visible light and near-infrared bands.

[0027] Compared with the prior art, the present invention has the following technical effects:

[0028] (1) The coating of the present invention uses a blocked polyurethane black powder loaded with carbon black as an active filler, which can generate -NCO groups at the open end under heating conditions and undergo a cross-linking reaction with -OH in the hydroxyl acrylic resin to finally form a cross-linked structure. Therefore, the coating formed after curing the coating can not only effectively reduce the gloss of the coating (reduce the reflectivity), but also ensure that the coating still has strong mechanical properties and durability with less resin usage. On this basis, combined with the absorption of light by the carbon black paste in the formula, a very low reflectivity (≤0.08%) can be finally achieved.

[0029] (2) A fluorine-containing chain segment is introduced into the molecular structure of the blocked polyurethane in the blocked polyurethane black powder of the present invention, which can endow the blocked polyurethane black powder with an extremely low surface tension, making it easy for the black powder to migrate to the coating surface during the coating drying process, so that the coating surface has sufficient micro-roughness instead of forming a smooth coating surface, which can further reduce the coating gloss.

[0030] (3) During the preparation process of the blocked polyurethane black powder of the present invention, -NCO in the polyurethane prepolymer reacts with -COOH in the carbon black to bond the polyurethane chain segment and the carbon black through chemical bonds, with high bonding strength and good compatibility. Detailed embodiments

[0031] The present invention will be further described below in conjunction with embodiments.

[0032] General Embodiment

[0033] A low-reflection coating, comprising raw materials in the following mass percentages:

[0034] Hydroxy acrylic resin (solid content 49 - 51 wt%, hydroxyl value 60 - 70 mgKOH / g) 10 - 30 wt%;

[0035] Blocked polyurethane black powder (blocked polyurethane loaded with carbon black and having a fluorinated segment, NCO content 10 ± 0.3%, deblocking temperature 105 - 120 °C) 5 - 35 wt%;

[0036] Carbon black paste (high-blackness fumed carbon black paste, solid content 39 - 41 wt%) 2 - 25 wt%;

[0037] Auxiliaries (selected from dispersants, wetting agents, defoamers, leveling agents, silane coupling agents, anti-settling agents and rheological aids) 0.5 - 5 wt%; Solvents (selected from xylene, n-butyl acetate, ethyl acetate, ethylene glycol monobutyl ether and propylene glycol methyl ether acetate) 20 - 80 wt%.

[0038] Preferably, the preparation method of the blocked polyurethane black powder comprises the following steps:

[0039] S1: Dehydrate aliphatic diisocyanate (selected from hexamethylene diisocyanate, isophorone diisocyanate), perfluoropolyethylene glycol (molecular weight 100 - 1000), chain extender (trimethylolpropane, dimethylolpropionic acid and dimethylolbutyric acid), blocking agent (selected from methyl ethyl ketoxime, sodium bisulfite), carbon black (high-blackness furnace carbon black, pH = 2.5 - 4) and reaction solvent (selected from acetone, butanone and methyl isobutyl ketone); specifically including: vacuum drying aliphatic diisocyanate, perfluoropolyethylene glycol, chain extender, blocking agent and carbon black at 110 - 130 °C for more than 12 h; adding molecular sieve to the reaction solvent for water removal.

[0040] S2: Under stirring conditions, add 100 parts by weight of aliphatic diisocyanate to the reaction vessel, heat to 45 - 55 °C, add 50 - 150 parts by weight of perfluoropolyethylene glycol and react for 20 - 40 min; add 1 - 10 parts by weight of chain extender and 100 - 350 parts by weight of reaction solvent, and continue to react for 80 - 100 min to form a polyurethane prepolymer.

[0041] S3: Heat the mixture of 5 - 15 parts by weight of carbon black and 50 - 100 parts by weight of reaction solvent to 45 - 55 °C, add it to the polyurethane prepolymer and react for 110 - 130 min; cool down to 35 - 45 °C, add 1 - 10 parts by weight of capping agent and continue to react for 20 - 40 min; add a neutralizing agent (selected from triethanolamine, ammonia water and 2 - amino - 2 - methyl - 1 - propanol) to adjust the pH of the system to 7 - 9.

[0042] S4: Cool down, conduct vacuum drying, crush and sieve the obtained black solid product to obtain a capped polyurethane black powder with a particle size of 1 - 10 microns.

[0043] A preparation method of a low - reflection coating, comprising the following steps: sequentially add hydroxyl acrylic resin, additives, part of the solvent, and capped polyurethane black powder into a container, grind to a fineness of ≤35 μm, add carbon black paste and the remaining solvent, disperse for 20 - 30 min until uniform, and control the system temperature below 70 °C during the whole preparation process.

[0044] Example 1

[0045] A low - reflection coating has the following formulation shown in the table below:

[0046]

[0047]

[0048] The preparation method of the above - mentioned low - reflection coating is as follows:

[0049] (1) Preparation of capped polyurethane black powder:

[0050] S1: Vacuum - dry aliphatic diisocyanate (hexamethylene diisocyanate), perfluoropolyethylene glycol (molecular weight about 1000), chain extender (trimethylolpropane), capping agent (methyl ethyl ketoxime), and carbon black (high - blackness furnace - method carbon black, pH = 2.5 - 4) at 120 °C for 12.5 h; add molecular sieve to the reaction solvent (acetone) to remove water.

[0051] S2: In a container equipped with a condensing water reflux device and a stirrer, add 1000 g of aliphatic diisocyanate to the reaction container under stirring conditions, heat to 50 °C, add 1000 g of perfluoropolyethylene glycol and react for 30 min; add 50 g of chain extender and 3000 g of reaction solvent, and continue to react for 90 min to generate a polyurethane prepolymer.

[0052] S3: Heat the mixture of 100 g of carbon black and 1000 g of reaction solvent to 50 °C, add it to the polyurethane prepolymer and react for 120 min; cool down to 40 °C, add 50 g of capping agent and continue to react for 30 min; add a neutralizing agent (triethanolamine) to adjust the pH of the system to 8.

[0053] S4: Cooling, vacuum drying, crushing and sieving the obtained black solid product to obtain a capped polyurethane black powder with an average particle size of 5 microns.

[0054] (2) Preparation of the coating: In a container, successively add hydroxy acrylic resin, additives, 2 / 3 of the solvent, and the capped polyurethane black powder, grind to a fineness of ≤ 35 μm, add carbon black paste and the remaining solvent, and disperse for 25 min until uniform. During the entire preparation process, control the system temperature below 70 °C.

[0055] Examples 2 - 5 and Comparative Examples 1 - 4

[0056] The differences between Examples 2 - 5 and Comparative Examples 1 - 4 and Example 1 are shown in the following table:

[0057]

[0058] The preparation method of the capped polyurethane black powder without fluorinated chain segments in the formulation of Comparative Example 4 is as follows: (1) Preparation of the capped polyurethane black powder:

[0059] S1: Vacuum dry aliphatic diisocyanate (hexamethylene diisocyanate), polyethylene glycol (molecular weight about 1000), chain extender (trimethylolpropane), capping agent (methyl ethyl ketoxime), carbon black (high blackness furnace carbon black, pH = 2.5 - 4) at 120 °C for 12.5 h; dehydrate the reaction solvent (acetone) with molecular sieve.

[0060] S2: In a container equipped with a condensing water reflux device and a stirrer, add 1000 g of aliphatic diisocyanate to the reaction container under stirring conditions, heat to 50 °C, add 1000 g of polyethylene glycol and react for 30 min; add 50 g of chain extender and 3000 g of reaction solvent, and continue to react for 90 min to form a polyurethane prepolymer.

[0061] S3: Heat the mixture of 100 g of carbon black and 1000 g of reaction solvent to 50 °C, add it to the polyurethane prepolymer and react for 120 min; cool to 40 °C, add 50 g of capping agent and continue to react for 30 min; add a neutralizing agent (triethanolamine) to adjust the system pH to 8.

[0062] S4: Cooling, vacuum drying, crushing and sieving the obtained black solid product to obtain a capped polyurethane black powder with an average particle size of 5 microns.

[0063] Performance testing

[0064] Take the coatings prepared in each example and comparative example, spray them onto a PC / ABS substrate with an air spray gun, heat and cure at 130 °C for 60 min, and the dry film thickness is 30 ± 5 μm. Conduct performance testing.

[0065] The test methods are shown in the following table:

[0066]

[0067] The test results of each example are shown in Table 1:

[0068] Table 1

[0069]

[0070]

[0071] The test results of each comparative example are shown in Table 2:

[0072] Table 2

[0073]

[0074] From the data comparison in Tables 1-2 above, it can be seen that:

[0075] Through Table 1, it can be found that as the content of the blocked polyurethane black powder in Examples 1-5 increases (5%, 10%, 15%, 25%, 35%), the glossiness and reflectivity of the obtained coating gradually decrease, indicating that the presence of the blocked polyurethane black powder can effectively reduce the glossiness of the coating and thus reduce the reflectivity. When the content of the blocked polyurethane black powder reaches 25%, continuing to increase its content, the glossiness and reflectivity reach a bottleneck and the decline is no longer obvious. In addition, from Table 1, it can also be found that as the content of the blocked polyurethane black powder in Examples 1-5 increases, the hardness and high-temperature heat aging resistance of the obtained coating are also improved to a certain extent.

[0076] Through Table 2, it can be found that since the coating of Comparative Example 1 does not contain blocked polyurethane black powder and the content of blocked polyurethane black powder in Comparative Example 2 is too small, the glossiness and reflectivity of their coatings are significantly inferior to those of Example 1. On the contrary, the content of blocked polyurethane black powder in the coating of Comparative Example 3 is too high. Although the obtained coating still has extremely low glossiness and reflectivity, there is a decline in terms of hardness and light aging resistance. The difference between Comparative Example 4 and Example 1 lies in that there is no fluorine-containing chain segment in the blocked polyurethane black powder. Therefore, the surface tension of the blocked polyurethane black powder is relatively high, resulting in that the black powder is not easy to migrate to the coating surface during the drying process of the coating, so the surface micro-roughness of the coating is insufficient and it is smoother. Therefore, the glossiness and reflectivity of the coating are higher.

[0077] The raw materials and equipment used in the present invention are all common raw materials and equipment in the art without special instructions; the methods used in the present invention are all conventional methods in the art without special instructions.

[0078] The above are only the preferred embodiments of the present invention, and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent transformations made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A low-reflection coating, characterized in that: It includes the following raw materials: Hydroxyl acrylic resin: 10 - 30 wt%, Blocked polyurethane black powder: 5 - 35 wt%, Carbon black paste: 2 - 25 wt%, Auxiliary agent: 0.5 - 5 wt%, Solvent: 20 - 80 wt%; The blocked polyurethane black powder is a blocked polyurethane loaded with carbon black and having a fluorinated segment. The weight parts of each raw material in its preparation process are as follows: aliphatic diisocyanate 100 parts, perfluoropolyethylene glycol 50 - 150 parts, chain extender 1 - 10 parts, blocking agent 1 - 10 parts, carbon black 5 - 15 parts, reaction solvent 200 - 400 parts.

2. The low-reflection coating according to claim 1, wherein: The NCO content of the blocked polyurethane black powder is 10 ± 0.3%, and the deblocking temperature is 105 - 120 °C.

3. The low-reflection coating according to claim 1 or 2, characterized in that: The preparation method of the blocked polyurethane black powder includes the following steps: S1: Dehydrate the aliphatic diisocyanate, perfluoropolyethylene glycol, chain extender, blocking agent, carbon black and reaction solvent. S2: Add the aliphatic diisocyanate into a reaction vessel, heat it, add perfluoropolyethylene glycol and react; add the chain extender and part of the reaction solvent, and continue to react to form a polyurethane prepolymer. S3: Heat the mixture of carbon black and the remaining reaction solvent, add it to the polyurethane prepolymer and react; cool down, add the blocking agent and continue to react; add a neutralizing agent to adjust the pH of the system to 7 - 9. S4: Cool down, dry under vacuum, crush and sieve the obtained black solid product to obtain the blocked polyurethane black powder.

4. The low - reflection coating according to claim 3, wherein: The aliphatic diisocyanate is selected from one or two of hexamethylene diisocyanate and isophorone diisocyanate; The molecular weight of the perfluoropolyethylene glycol is 100 - 1000; The chain extender is selected from one or several of trimethylolpropane, dimethylolpropionic acid and dimethylolbutyric acid; The blocking agent is selected from one or two of methyl ethyl ketoxime and sodium bisulfite; The neutralizing agent is selected from one or several of triethanolamine, ammonia water and 2 - amino - 2 - methyl - 1 - propanol; The pH of the carbon black is 2.5 - 4; The reaction solvent is selected from one or several of acetone, butanone and methyl isobutyl ketone.

5. The low - reflection coating according to claim 3, wherein: In S2, the temperature of the heat treatment is 45 - 55 °C, and the reaction time after adding perfluoropolyethylene glycol is 20 - 40 min; the time of the continued reaction is 80 - 100 min; In S3, the temperature of the heat treatment is 45 - 55 °C, the reaction time after adding it to the prepolymer is 110 - 130 min; cool down to 35 - 45 °C, and continue to react for 20 - 40 min after adding the blocking agent; In S4, the particle size of the sieved blocked polyurethane black powder is 1 - 10 microns.

6. The low - reflection coating according to claim 1, wherein: The solid content of the hydroxyl acrylic resin is 49 - 51 wt%, and the hydroxyl value is 60 - 70 mgKOH / g; The solid content of the carbon black paste is 39 - 41 wt%.

7. The low - reflection coating according to claim 1, wherein: The auxiliary agent is selected from one or more of a dispersant, a wetting agent, an antifoaming agent, a leveling agent, a silane coupling agent, an anti-settling agent, and a rheology aid; The solvent is selected from one or more of xylene, n-butyl acetate, ethyl acetate, ethylene glycol monobutyl ether, and propylene glycol methyl ether acetate.

8. The low-reflection coating according to any one of claims 1 to 7, characterized in that: The 85° gloss of the cured coating is ≤0.5, and the reflectivity is ≤0.2%.

9. A preparation method of the low-reflection coating according to any one of claims 1-8, characterized in that It includes the following steps: successively add hydroxyl acrylic resin, auxiliary agent, part of the solvent, and blocked polyurethane black powder into a container, grind, add carbon black paste and the remaining solvent, and disperse evenly. During the whole preparation process, control the system temperature below 70°C.

10. Application of the low-reflection coating according to any one of claims 1-8 or the low-reflection coating obtained by the preparation method according to claim 9 in suppressing stray light in the visible light and near-infrared bands.

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