Low-refractive-index coating material and preparation method thereof

Abstract

The application relates to a low-refractive-index coating material and a preparation method thereof, and relates to the field of optical coating materials. The coating material comprises the following raw materials: magnesium fluoride, nano-silicon dioxide, aluminum oxide, yttrium fluoride, neodymium fluoride, praseodymium neodymium fluoride. The application adds neodymium fluoride, praseodymium neodymium fluoride and yttrium fluoride to the coating material, the neodymium fluoride and the praseodymium neodymium fluoride are evaporated and deposited on the surface of a substrate at the same time as the magnesium fluoride and the nano-silicon dioxide during the coating process, the directional growth problem of the magnesium fluoride in the deposition process can be inhibited through the joint action of the neodymium fluoride and the praseodymium neodymium fluoride, and a more uniform optical film layer is formed, and the adhesion effect of the film layer on the substrate is improved. The yttrium fluoride can form a denser film layer during the coating process, and the film layer is uniform, the uniformity of the film layer is improved, and the adhesion is enhanced. In addition, the addition of the yttrium fluoride can also improve the moisture absorption problem of the neodymium fluoride and the praseodymium neodymium fluoride, and the stability of the coating material is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical coating materials, in particular to a low refractive index coating material and a preparation method thereof. BACKGROUND

[0002] Optical coating refers to the process of coating one or more layers of metal or dielectric thin film on the surface of an optical part, which can achieve the purpose of reducing or increasing the reflection, beam splitting, color separation, light filtering, polarization and other characteristics of light by coating on the surface of the optical part.

[0003] Low refractive index optical coating material, as the name implies, has a relatively low refractive index and can be used for the coating of antireflection film to improve the light transmittance of optical parts. Magnesium fluoride, as a commonly used low refractive index coating material, is widely used in the field of optical coating. However, magnesium fluoride has certain molecular bonds in the process of film formation, and the bonding force of the molecular bonds is relatively weak. In addition, the magnesium fluoride film layer is relatively soft due to the single charge effect of fluorine ions, and the mechanical strength is poor, so it is easy to cause the formed film layer to be uneven, which can easily cause the film layer to be broken during the coating process and affect the performance of the optical device. SUMMARY

[0004] In view of the above technical problems, the present application provides a low refractive index coating material and a preparation method thereof to enhance the film forming performance of the coating material and the mechanical strength of the film layer.

[0005] In a first aspect, the present application provides a low refractive index coating material, which adopts the following technical solution:

[0006] A low refractive index coating material, comprising the following raw materials in weight percentage: magnesium fluoride 65-90%, nano-silicon dioxide 1-15%, aluminum oxide 1-10%, yttrium fluoride 1-5%, neodymium fluoride 0.5-5%, praseodymium-neodymium fluoride 0.1-2%.

[0007] Further preferably, the low refractive index coating material comprises the following raw materials in weight percentage: magnesium fluoride 74.4%, nano-silicon dioxide 12.2%, aluminum oxide 6.5%, yttrium fluoride 3.2%, neodymium fluoride 2.5%, praseodymium-neodymium fluoride 1.2%.

[0008] By adopting the technical scheme, the low-refractive-index coating material takes magnesium fluoride as a main raw material, and a certain amount of nano-silicon dioxide and aluminum oxide is added therein, the silicon dioxide is a coating material with good film performance among oxides and has a low refractive index, the silicon dioxide film has good adhesion on a quartz substrate and is stable and not easy to decompose, the neodymium fluoride and praseodymium neodymium fluoride are evaporated and deposited on the substrate surface at the same time as the magnesium fluoride and nano-silicon dioxide during the coating process, and the directional growth problem of the magnesium fluoride during the deposition process can be inhibited through the joint action of the neodymium fluoride and praseodymium neodymium fluoride, thereby forming a more uniform optical film layer and improving the adhesion of the film layer on the substrate. The yttrium fluoride can form a denser film layer during the coating process, and the film is uniform, which improves the uniformity of the film layer and enhances the adhesion. In addition, the addition of the yttrium fluoride can also improve the moisture absorption problem of the neodymium fluoride and praseodymium neodymium fluoride and improve the stability of the coating material.

[0009] Optionally, the purity of the praseodymium neodymium fluoride is 99.9%, and the particle size is 100-300 nm.

[0010] Optionally, the purity of the neodymium fluoride is 99.9%, and the particle size is 200-500 nm.

[0011] By adopting the technical scheme, the praseodymium neodymium fluoride and the neodymium fluoride contain a certain amount of other rare earth metal elements and impurities, and too much impurity content will cause changes in the light transmittance, color, and other properties of the optical film layer, affecting the use performance of the optical device. Therefore, the purity of the neodymium fluoride and praseodymium neodymium fluoride is limited within the above range, which can effectively avoid the influence of impurities on the performance of the coating material,

[0012] In a second aspect, the application provides a preparation method of a low-refractive-index coating material, which adopts the following technical scheme:

[0013] The preparation method of the low-refractive-index coating material comprises the following steps:

[0014] S1, after the quartz substrate is cleaned, it is dried at 150-300℃ for 1-2h;

[0015] S2, the praseodymium neodymium fluoride and the neodymium fluoride are baked at 120-150℃ for 2-5h, then the yttrium fluoride is sintered at 1500-1600℃ for 5-8h to obtain a first mixture;

[0016] S3, the magnesium fluoride, nano-silicon dioxide, and aluminum oxide are mixed and sintered at 1700-2000℃ for 3-5h to obtain a second mixture;

[0017] S4, the first mixture and the second mixture are mixed and smelted at 1700-1900℃ for 8-10h to obtain a coating material;

[0018] S5, placing the coating material on a coating machine, coating the quartz substrate surface in a vacuum environment to obtain a coating material blank;

[0019] S6, calcining the coating material blank at 1800-2000℃ for 1-2h to obtain a low refractive index coating material.

[0020] By adopting the above technical scheme, the praseodymium fluoride, neodymium fluoride and yttrium fluoride are sintered separately from other raw materials, the influence of the neodymium fluoride and praseodymium fluoride on other raw materials due to moisture absorption is avoided in the early stage of sintering, and the moisture absorption of the neodymium fluoride and praseodymium fluoride is also inhibited to a certain extent during and after sintering due to the presence of yttrium fluoride, thereby improving the stability of the coating material. The praseodymium fluoride and praseodymium fluoride are baked before sintering to remove moisture. In addition, since the melting points of the neodymium fluoride, praseodymium fluoride and other raw materials have a large difference, separate sintering in the early stage can also reduce energy consumption and improve sintering efficiency. The first mixture and the second mixture are mixed after separate sintering is completed, then melted, and the composite material is plated on the quartz substrate by a coating process for subsequent coating of optical devices.

[0021] Optionally, in step S1, the cleaning of the quartz substrate comprises sequentially cleaning with a sodium hydroxide solution, dilute sulfuric acid, ethanol and deionized water.

[0022] Optionally, each cleaning agent is cleaned 1-5 times, and each cleaning time is 1-10 minutes.

[0023] Optionally, the concentration of the dilute sulfuric acid is 8-15%.

[0024] Optionally, the concentration of the sodium hydroxide solution is 5-8%.

[0025] By adopting the above technical scheme, the quartz substrate is sequentially cleaned by the alkali solution, the acid solution, the ethanol and the deionized water to remove some strongly adsorbed impurities and grease substances on the surface, thereby improving the adhesion of the coating material on the quartz substrate. The sodium hydroxide solution has a certain corrosion effect on the quartz surface, and through the treatment of the sodium hydroxide solution, the quartz substrate surface is micro-etched while the grease on the quartz substrate surface is removed, thereby improving the surface roughness of the quartz substrate and further improving the adhesion stability of the coating material on the quartz substrate surface. The reagent residues on the quartz substrate surface are removed through the sequential cleaning of the acid washing, the ethanol and the deionized water, thereby reducing the influence on the purity of the coating material. The sodium hydroxide solution is selected to be a low-concentration sodium hydroxide solution to avoid excessive corrosion of the quartz substrate surface and affect the surface state and adhesion performance of the coating material.

[0026] In summary, the present application includes at least one of the following beneficial technical effects:

[0027] 1. In the technical solution of the application, neodymium fluoride, praseodymium neodymium fluoride and yttrium fluoride are added to the coating material. After the addition of neodymium fluoride and praseodymium neodymium fluoride, they are evaporated and deposited on the surface of the substrate at the same time as magnesium fluoride and nano silicon dioxide, etc. during the coating process. Through the joint action of neodymium fluoride and praseodymium neodymium fluoride, the problem of directional growth of magnesium fluoride during deposition can be inhibited, thereby forming a more uniform optical film layer and improving the adhesion of the film layer on the substrate. Yttrium fluoride can form a denser film layer during the coating process, and the film is uniform, which improves the uniformity of the film layer and enhances the adhesion. In addition, the addition of yttrium fluoride can also improve the moisture absorption problem of neodymium fluoride and praseodymium neodymium fluoride, and improve the stability of the coating material.

[0028] 2. In the process of preparing the coating material, praseodymium neodymium fluoride, neodymium fluoride and yttrium fluoride are sintered separately with other raw materials. In the early stage of sintering, the influence of neodymium fluoride and praseodymium neodymium fluoride on other raw materials due to moisture absorption is avoided. The presence of yttrium fluoride during and after sintering also inhibits the moisture absorption of neodymium fluoride and praseodymium neodymium fluoride to some extent, thereby improving the stability of the coating material.

[0029] 3. The quartz substrate is sequentially cleaned with lye, acid, ethanol and deionized water to remove some strongly adsorbed impurities and grease substances on the surface, thereby improving the adhesion of the coating material on the quartz substrate. Sodium hydroxide solution has a certain corrosion effect on the surface of quartz. Through the treatment of sodium hydroxide solution, the surface of the quartz substrate is etched to some extent while removing the grease on the surface of the quartz substrate, thereby improving the surface roughness of the quartz substrate and the adhesion stability of the coating material on the surface of the quartz substrate. DETAILED DESCRIPTION

[0030] The application will be further described in detail below in conjunction with specific examples. It should be noted that in the following examples, if not specified, the conditions are in accordance with the conventional conditions or the conditions recommended by the manufacturer; the raw materials used in the following examples can be obtained from ordinary market sources unless otherwise specified.

[0031] Example 1

[0032] A low refractive index coating material, comprising: magnesium fluoride 65wt%, nano silicon dioxide 15wt%, aluminum oxide 10wt%, yttrium fluoride 3wt%, neodymium fluoride 5wt%, praseodymium neodymium fluoride 2wt%, and the total amount of each component is 10kg; wherein the purity of praseodymium neodymium fluoride and aluminum fluoride is 99.9%, the particle size of praseodymium neodymium fluoride is 200nm, and the particle size of neodymium fluoride is 300nm.

[0033] The specific preparation method of the coating material is as follows:

[0034] S1, take quartz substrate, first wash the surface of the quartz substrate with a 6.5wt% sodium hydroxide solution for 2 minutes, then wash twice with an 8% sulfuric acid solution, each time for 1 minute, then wash the quartz substrate twice with an ethanol solution, each time for 5 minutes, and finally wash the quartz substrate 5 times with deionized water, each time for 10 minutes; after washing, place it in an oven at 180°C for 2 hours;

[0035] S2, take praseodymium neodymium fluoride and neodymium fluoride in the ratio, mix evenly, first bake at 120°C for 3 hours, then add yttrium fluoride and mix, heat to 1600°C and sinter for 8 hours to obtain a first mixture;

[0036] S3, take magnesium fluoride, nano-silicon dioxide, and aluminum oxide in the ratio, mix evenly, and sinter at 1800°C for 3 hours to obtain a second mixture;

[0037] S4, mix the first mixture and the second mixture evenly, and melt at a temperature of 1850°C for 10 hours to obtain a coating material;

[0038] S5, place the coating material on a coating machine to perform vacuum coating, and coat the coating material onto the surface of the quartz substrate to obtain a coating material blank;

[0039] S6, calcine the coating material blank at 1800°C for 2 hours to obtain a coating material.

[0040] Examples 2-4

[0041] Examples 2-4 differ from Example 1 in that the component ratios of the coating material are different, and for specific reference to Table 1, the rest are consistent with Example 1.

[0042] Table 1: Raw material component ratios (wt%) of Examples 2-4

[0043]

[0044] Comparative Example 1

[0045] This comparative example differs from Example 1 in that an equal amount of magnesium fluoride is used to replace neodymium fluoride and praseodymium neodymium fluoride, and the rest is consistent with Example 1.

[0046] Comparative Example 2

[0047] This comparative example differs from Example 1 in that an equal amount of magnesium fluoride is used to replace yttrium fluoride, and the rest is consistent with Example 1.

[0048] Comparative Example 3

[0049] This comparative example differs from Example 1 in that an equal amount of praseodymium neodymium fluoride is used to replace neodymium fluoride, and the rest is consistent with Example 1.

[0050] Comparative Example 4

[0051] The difference between this comparative example and Example 1 is that the same amount of neodymium fluoride is used instead of praseodymium neodymium fluoride, and the rest is consistent with Example 1.

[0052] Performance detection test

[0053] The film-coated material prepared in the above examples and comparative examples is subjected to film coating test to detect its performance. The film coating conditions are: the diameter of the film coating machine is 1100 mm, the evaporation speed is 10 A / S, and the glass substrate temperature is 200°C. °

[0054] Adhesion performance of the film layer: the bonding strength of the film layer on the substrate surface is tested according to GB / T 28786-2012 "Vacuum Technology - Measurement Method for Vacuum Coating Layer Bonding Strength - Adhesive Tape Method".

[0055] The performance detection results of Examples 1-4 and Comparative Examples 1-4 are shown in Table 2 below.

[0056] Table 2: Performance detection results of Examples 1-4 and Comparative Examples 1-4

[0057] Bond strength rating Film layer rupture Transmittance Refractive index / 500 nm Example 1 1 No 96.8％ 1.58 Example 2 1 No 96.5％ 1.62 Example 3 0 No 97.2％ 1.59 Example 4 0 No 97.8％ 1.52 Comparative Example 1 3 Yes 97.2％ 1.48 Comparative Example 2 2 Yes 96.8％ 1.56 Comparative Example 3 3 No 96.2％ 1.50 Comparative Example 4 3 No 96.6％ 1.52

[0058] As can be seen from the data in Table 1, the addition of neodymium fluoride, praseodymium neodymium fluoride and yttrium fluoride can effectively improve the adhesion of the film-coated material on the glass substrate, obtain a film layer with good adhesion strength, and through the cooperation of neodymium fluoride, praseodymium neodymium fluoride and yttrium fluoride, the strength of the film layer is also obviously improved, which can effectively reduce the rupture of the film layer.

[0059] As can be seen from the data of Examples 1 and Comparative Examples 1-4, the addition of yttrium fluoride can well improve the strength of the film layer, and the anti-cracking performance of the film layer is obviously improved. Further comparison of the data of Comparative Example 3 and Comparative Example 4 shows that although the addition of single praseodymium fluoride or praseodymium neodymium fluoride can also improve the strength of the film layer, the adhesion strength of the film layer on the substrate is weak, and the film layer is prone to falling off.

[0060] Example 5

[0061] The difference between this example and Example 1 is that the particle size of neodymium fluoride is 800 nm, and the rest is consistent with Example 1.

[0062] Example 6

[0063] The difference between this example and Example 1 is that the particle size of praseodymium neodymium fluoride is 500 nm, and the rest is consistent with Example 1.

[0064] Example 7 ​

[0065] The difference between the embodiment and embodiment 1 is that various raw materials are sintered synchronously during preparation, and the specific preparation method is as follows:

[0066] S1, take the quartz substrate, first wash the surface of the quartz substrate with a sodium hydroxide solution with a concentration of 6.5wt% for 2min, then wash it with a sulfuric acid solution with a concentration of 8% twice, each time for 1min, then wash the quartz substrate with an ethanol solution twice, each time for 5min, and finally wash the quartz substrate with deionized water 5 times, each time for 10min; after washing, place it in an oven and bake at 180℃ for 2h;

[0067] S2, take praseodymium neodymium fluoride and neodymium fluoride according to the proportion and mix them evenly, first bake at 120℃ for 3h, then add yttrium fluoride, magnesium fluoride, nanosilica, and aluminum oxide and mix them evenly, and sinter at 1600℃ for 8h to obtain a mixed material;

[0068] S3, mix the mixed material evenly, and melt it at a temperature of 1850℃ for 10h to obtain a coating material;

[0069] S4, place the coating material on a coating machine to perform vacuum coating, and coat the coating material onto the surface of the quartz substrate to obtain a coating material blank;

[0070] S5, calcine the coating material blank at 1900℃ for 2h to obtain a coating material.

[0071] The rest is consistent with embodiment 1.

[0072] Example 8

[0073] The difference between the embodiment and embodiment 1 is that the quartz substrate is not washed with a sodium hydroxide solution, and the rest is consistent with embodiment 1.

[0074] Performance test of examples 5-8 is shown in table 3 below.

[0075] Table 3: performance test results of examples 5-8

[0076] Bond strength rating Film layer rupture Transmittance Refractive index / 500 nm Example 5 2 No 96.1％ 1.55 Example 6 2 No 95.6％ 1.56 Example 7 1 Yes 96.2％ 1.58 Example 8 2 No 96.8％ 1.54

[0077] As can be seen from the data in table 3, the particle size of neodymium fluoride and praseodymium neodymium fluoride should be within the range defined in the application, otherwise the performance of the coating material will be poor. As can be seen from the data of example 7, when preparing the coating material, sintering neodymium fluoride and praseodymium neodymium fluoride together with other raw materials, although the bonding strength of the prepared coating layer changes little, the coating layer is easy to break, which may be because the directional growth inhibition effect of praseodymium neodymium fluoride and neodymium fluoride on magnesium fluoride is limited during sintering, resulting in poor crack resistance of the coating layer.

[0078] The above are all preferred embodiments of the present application, and are not intended to limit the protection scope of the present application, and thus: any equivalent changes made according to the structure, shape, principle of the present application should be covered within the protection scope of the present application.

Claims

1. A low refractive index coating material, characterized by, The raw materials include the following weight percentages: magnesium fluoride 65-90%, nano-silicon dioxide 1-15%, aluminum oxide 1-10%, yttrium fluoride 1-5%, neodymium fluoride 0.5-5%, praseodymium neodymium fluoride 0.1-2%.

2. The low refractive index coating material of claim 1, wherein, The low-refractive-index coating material includes the following weight percentages of raw materials: magnesium fluoride 74.4%, nano-silicon dioxide 12.2%, aluminum oxide 6.5%, yttrium fluoride 3.2%, neodymium fluoride 2.5%, praseodymium neodymium fluoride 1.2%.

3. The low refractive index coating material of claim 1, wherein the low refractive index coating material is a material having a refractive index of 1.3 or less. The praseodymium neodymium fluoride has a purity of 99.9% and a particle size of 100-300 nm.

4. The low refractive index coating material of claim 1, wherein, The neodymium fluoride has a purity of 99.9% and a particle size of 200-500 nm.

5. A method for preparing a low refractive index coating material according to any one of claims 1-4, characterized in that, The method includes the following steps: S1. After cleaning the quartz substrate, dry it at 150-300℃ for 1-2h; S2. Bake the praseodymium neodymium fluoride and the neodymium fluoride at 120-150℃ for 2-5h, then add the yttrium fluoride and sinter it at 1500-1600℃ for 5-8h to obtain a first mixture; S3. Mix the magnesium fluoride, nano-silicon dioxide, and aluminum oxide, then sinter them at 1700-2000℃ for 3-5h to obtain a second mixture; S4. Mix the first mixture and the second mixture, then smelt them at 1700-1900℃ for 8-10h to obtain a coating material; S5. Place the coating material on a coating machine and coat it onto the surface of the quartz substrate in a vacuum environment to obtain a coating material blank; S6. Calcine the coating material blank at 1800-2000℃ for 1-2h to obtain the low-refractive-index coating material.

6. The method for preparing a low refractive index coating material according to claim 5, characterized in that, In step S1, the cleaning of the quartz substrate includes sequentially cleaning with a sodium hydroxide solution, dilute sulfuric acid, ethanol, and deionized water.

7. The method for preparing a low refractive index coating material according to claim 5, characterized in that, Each cleaning agent is used for 1-5 times, and each cleaning time is 1-10 min.

8. The method for preparing a low refractive index coating material according to claim 5, characterized in that, The concentration of the dilute sulfuric acid is 8-15%.

9. The method for preparing a low refractive index coating material according to claim 5, characterized in that, The concentration of the sodium hydroxide solution is 5-8%.

Images