WO2021135881A1

WO2021135881A1 - Method for preparing micro optical glass device

Info

Publication number: WO2021135881A1
Application number: PCT/CN2020/135095
Authority: WO
Inventors: 陈雨叁; 李乾; 刘莹莹
Original assignee: 深圳市绎立锐光科技开发有限公司
Priority date: 2019-12-31
Filing date: 2020-12-10
Publication date: 2021-07-08
Also published as: CN113121093A

Abstract

Disclosed is a method for preparing a micro optical glass device with a low cost and a simple process. The method comprises: obtaining a silica dispersion, adding an acidic solution into the silica dispersion to adjust the pH value of the silica dispersion to a first pH value, and stirring same; adding ethyl orthosilicate into the silica dispersion, and stirring same to obtain a sol, adding a basic solution into the sol to adjust the pH value of the sol to a second pH value, stirring same and leaving same to stand; injecting the sol, which has been left to stand, into a mold, and aging same to obtain a wet gel; demolding the wet gel, washing same, and drying same to obtain a dry gel; and sintering the dry gel to obtain the micro optical glass device, wherein the second pH value is in the range of 3.0-4.0, the shrinkage of the micro optical glass device is more than 88% relative to that of the wet gel, and the molar ratio of the silica to the ethyl orthosilicate contained in the silica dispersion is in the range of 3.8-5.4. The method ensures a good yield at a large shrinkage during the preparation of a sol-gel.

Description

Method for preparing micro-optical glass device

Technical field

The invention relates to the technical field of glass preparation, in particular to a method for preparing a micro-optical glass device.

Background technique

In recent years, with the rapid development of optical design technology in the projection field, large and cumbersome projectors have gradually been replaced by portable projectors with compact and small size, and projection technology has further migrated to smart terminals such as mobile phones and smart glasses. trend. Concomitantly, the reduction of the volume of the optical machine and the reduction of the spot size have put forward higher and higher requirements for the fine shaping and modulation of the beam. Moreover, with the popularization of high-brightness laser light sources, optical components have to withstand higher and higher heat energy under the conditions of the above-mentioned refined light shaping and modulation, and thus have higher requirements for heat resistance. Resin optics Devices can no longer meet the current opto-mechanical design, and glass optical devices have become a must.

When preparing micro-optical devices (such as microlens arrays), the method of processing microstructures (such as grinding) on a whole piece of glass requires high equipment cost and difficult process, which is not conducive to large-scale production, while the sol-gel method is relatively More economical preparation method. The traditional sol-gel process with high solid content and low shrinkage rate is suitable for the preparation of large-sized glass devices. Due to the influence of the mold processing size, it is impossible to directly produce micron-level fine optical structures.

In addition, the inventor applied the traditional low-shrinkage solution sol-gel process to the large-shrinkage solution design, and found that unexpected problems such as excessive gel speed and microstructure deformation would occur, making it difficult to obtain satisfactory products.

Summary of the invention

In view of the high cost, complex process, and low yield of the prior art, the present invention provides a method for preparing a micro-optical glass device, which includes the following steps: Step 1: Obtain a silica dispersion, and add an acid solution to the The silica dispersion liquid to adjust the pH value of the silica dispersion liquid to the first pH value and stir; Step 2: adding ethyl orthosilicate to the silica dispersion liquid and stirring to obtain Sol, adding an alkaline solution to the sol to adjust the pH value of the sol to the second pH value, stirring and standing; Step 3: Injecting the standing sol into a mold, aging, and obtaining wet coagulation Glue; Step 4: demold the wet gel, wash and dry to obtain a dry gel; Step 5: sinter the dry gel to obtain a micro-optical glass device; wherein, the range of the second pH value Is 3.0 to 4.0, the shrinkage rate of the micro-optical glass device relative to the wet gel is greater than 88%, and the molar ratio of the silica contained in the silica dispersion to the ethyl orthosilicate The range is 3.8～5.4.

In one embodiment, in the raw material, the molar ratio of silica contained in the silica dispersion to the ethyl orthosilicate is 3.8 to 4.6.

In one embodiment, the solid content of silicon dioxide in the raw material is not more than 21%, and the solid content means that the silicon dioxide and the ethyl orthosilicate contained in the silicon dioxide dispersion can be hydrolyzed to produce The total amount of silica accounts for the mass percentage of all raw materials.

In one embodiment, the step one includes: obtaining a silica dispersion stock solution with a preset molar volume, and mixing the silica dispersion stock solution with deionized water to obtain the silica dispersion The deionized water is used to adjust the solid content of the silica.

In one embodiment, the second pH value ranges from 3.4 to 4.0.

In one embodiment, in the step 1, the acidic solution is a hydrochloric acid solution, and the first pH value ranges from 1.3 to 2.8.

In one embodiment, the mold is a silicone mold.

In one embodiment, in the fifth step, the sintering temperature is not higher than 1200°C.

In one embodiment, in the step four, the drying includes a first drying stage and a second drying stage, and the temperature of the first drying stage is at least 100° C. lower than the temperature of the second drying stage.

In one embodiment, the smallest microstructure size of the micro-optical glass device is not greater than 1 μm.

Compared with the prior art, the present invention includes the following beneficial effects: a sol-gel with a large shrinkage ratio is used to prepare optical glass devices, a pH value lower than the general process is used in the gel stage, and suitable silica and orthosilicic acid are selected. The ratio of ethyl ester not only ensures easy gelation, but also avoids excessively fast gelation, and optical glass devices with fine structures can be obtained at one time.

Description of the drawings

Figure 1 is a schematic flow chart of the method for preparing the micro-optical glass device of the present invention.

Detailed ways

The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

In the present invention, the main inventive concept is to control the ratio of the two silica sources for preparing glass devices by the sol-gel method and the gel conditions under the ratio, so as to obtain a large shrinkage ratio. The silica dispersion liquid obtained by dispersing fumed silica powder in water has the function of slowing down the gel speed and avoiding the cracking caused by the too fast hydrolysis of the ethyl orthosilicate, and the pH value control during the gel process is very important for the control. The gel speed has a huge impact, and the present invention combines the two to solve the problem of microstructure yield newly encountered in the process of preparing glass devices with large shrinkage rates.

The solid content in the present invention refers to the mass percentage of silicon dioxide in the raw materials (including silicon dioxide after the hydrolysis of ethyl orthosilicate) in the total raw materials.

Please refer to Figure 1, which is a schematic flow chart of the method for preparing the micro-optical glass device of the present invention, including: step one, obtaining a silica dispersion liquid, and adjusting to a first pH; step two, combining the silica dispersion liquid with Ethyl orthosilicate is mixed and adjusted to the second pH value; step three, preparing wet gel; step four, preparing dry gel; step five, sintering, to obtain micro-optical glass device. Each step is described in detail below.

This step includes obtaining a silica dispersion liquid, adding an acidic solution to the silica dispersion liquid to adjust the pH value of the silica dispersion liquid to a first pH value, and stirring, to finally obtain silica with a preset pH value The dispersion is used as the first silica source.

In the present invention, the initial silica dispersion (that is, the pH value is not adjusted) can be obtained by mixing and stirring fumed silica and deionized water, and dispersing by magnetic stirring, homogenizer and/or ultrasonic, so that the gas phase Silica is evenly dispersed in water. Then, the silica dispersion is filtered to remove impurities and undispersed agglomerated particles.

The fumed silica in the present invention selects a particle size with a D50 in the range of 20 nm to 150 nm, and has a larger specific surface area.

Generally, to ensure the uniformity of the silica dispersion liquid, a long time is required for the above-mentioned treatment process, resulting in a long time for each production. Therefore, in one embodiment of the present invention, a large amount of silica dispersion stock solution with a preset molar volume is prepared in advance, and a certain amount of silica dispersion stock solution is obtained during each production, and mixed and diluted with deionized water. Among them, deionized water is used to adjust the solid content of silica, so as to obtain the silica dispersion of the production batch. The technical solution makes the adjustment of the silica solid content simple, reduces the time required for uniform mixing, does not need to filter and remove impurities every time, improves production efficiency, and improves the stability of raw materials in different batches of production.

The acidic solution is added to the silica dispersion and stirred uniformly. The acidic solution can be, for example, a dilute hydrochloric acid solution, so that the silica dispersion is adjusted to a pH value of 1.3-2.8. It can be understood that the acidic solution may also be other acidic solutions for adjusting the pH value.

After the acidic silica dispersion is obtained, ethyl orthosilicate is added to the silica dispersion and stirred, and the ethyl orthosilicate is hydrolyzed to obtain a sol, and an alkaline solution is further added to the sol to adjust the sol PH value to the second pH value, stir and let stand. During the standing process, the sol will gradually form a gel. The process should not be too long, and it only needs to stand for a short time to expel the bubbles during the stirring process.

In the embodiment of the present invention, the alkaline solution may be an aqueous ammonia solution. After the pH value of the sol is adjusted, the pH value increases, and finally is 3.0-4.0. It can be understood that the alkaline solution may also be other alkaline solutions for adjusting the pH value.

In the present invention, since there is a process of standing in the original container (not mold) from step 2 to step 3, and this process is very important to avoid bubbles in the final product, so the gelation process of the sol It should not be too fast, otherwise it will be difficult to transfer it to the mold before the gel is set. After repeated studies, the inventor has concluded that since the second pH value exceeds 4.0, step 3 is obviously affected, and the surface microstructure of the obtained wet gel is not clear.

In a preferred embodiment, the larger the second pH value is within the maximum value, the better, the smaller the second pH value, the greater the difficulty of gelation, and the preferred range is 3.4-4.0.

In the present invention, to prepare a micro-optical glass device with a large shrinkage rate, in order to increase the shrinkage rate, a method of reducing the solid content of silica is adopted so that the solid content of silica in the raw material is not more than 21%. In the previous sol-gel method for preparing glass, a high solid content ratio of raw materials is generally used, usually at least 25% or more. This type of preparation method is difficult to achieve the formation of tiny optical structures.

The static sol is poured into a mold and aged to obtain a wet gel.

In this step, the mold can be of various shapes and sizes as required, so that glass optical devices of various shapes and sizes can be obtained. After aging, the wet gel has a certain strength and can be demolded from the mold. In order to facilitate demolding, the present invention preferably adopts a silicone mold to peel off the wet gel within a certain deformation range of the silicone mold. If a rigid mold is used, on the one hand, it may damage the fine optical surface structure, causing burrs and cracks, and on the other hand, it is not easy to remove the wet gel.

The wet gel is demolded, washed and dried to obtain a dry gel.

After demolding, a wet gel block with transfer fine structure is obtained. There may be certain uneven impurities in the wet gel block, and cleaning it to remove surface impurities is conducive to obtaining a product with higher transparency.

When drying the wet gel block, the temperature should not be too high, otherwise it may cause excessive dehydration and cause the sample to crack.

After drying, a dry gel block with a reduced volume relative to the wet gel block is obtained. This step is the main part of the volume shrinkage in the process of preparing the micro-optical glass device, and the shrinkage rate is very large.

In a preferred embodiment of the present invention, the drying step includes two steps, that is, it includes a first drying stage and a second drying stage. The temperature in the first drying stage is at least 100° C. lower than the temperature in the second drying stage to avoid violent separation of water from the wet gel during the drying process and causing cracking. Specifically, in one embodiment, the first drying stage is carried out in an air atmosphere, and the drying temperature is 30°C to 90°C; the second drying stage is carried out in an oxygen-free and moisture-free atmosphere, and the drying temperature is 150°C to 500°C. ℃.

The dry gel is sintered to obtain a micro-optical glass device. In this step, the sample gets a second volume shrinkage, and changes from opaque to transparent glass device.

Generally, in the prior art technical solution for preparing optical glass by the sol-gel method, sintering needs to be performed at a temperature above 1200°C. The inventor found that sintering at high temperatures will damage the edges and surfaces of optical glass devices, causing them to slightly deform or even deform. Cracked. In traditional larger-sized optical glass devices (such as millimeter-level optical devices), such surface defects have little effect, but in micro-optical glass devices, this will seriously affect the optical performance of the device. In the present invention, the inventor found that by reducing the solid content of silica in the raw material, an optical device with high transparency can be obtained even if the sintering temperature is lowered. In the preferred embodiment of the present invention, the sintering temperature is not higher than 1200°C, which not only protects the micro-optical structure of the glass surface from cracking, but also reduces the risk of internal crystallization and decreased transparency at low solid content, and improves the product yield. . In addition, the reduction of sintering temperature can also reduce energy consumption and production costs.

Above, the preparation steps are described in detail. Please refer to the specific examples below. In order to facilitate the comparison of the effects of various technical solutions, choose different second pH values under the same experimental conditions and different silica dispersions. The molar ratio of silica to tetraethyl orthosilicate.

Example

First, weigh the fumed silica particles and deionized water, mix and stir, use a homogenizer to disperse evenly; add dilute hydrochloric acid, adjust pH=2, after stirring, add ethyl orthosilicate, stir to form a sol solution, and then add ammonia Adjust the sol to the second pH value, stir and then stand still, pour it into a mold with a microstructure, wait for a certain period of time to gel, and then leave it to stand for a preset time before demolding.

Put the above-mentioned wet gel with microstructure in pure deionized water, wash it with circulating water, after washing, put it into a constant temperature and humidity box at 45℃ for the first stage of drying, and then carry out the second stage in a nitrogen atmosphere at 200℃ Staged drying. After the sample is dried, it is sintered at 1100°C for 12 hours to obtain an optical element with a microstructure.

The data table of each example and comparative example is shown in the figure below, in which, the explanation of the solid content is referred to the above description; the ratio is the substance _{of silica (SiO 2) contained in the fumed silica particles or silica dispersion stock solution} The ratio of the amount of TEOS to the amount of _TEOS _{n SiO2} /n TEOS; the shrinkage rate is the volume shrinkage rate of the sintered glass device relative to the gel after demolding, which can be passed through Archimedes Method measurement; Yield rate refers to defective products with cracks, scratches, dirt, bubbles, and extremely low transmittance.

In the present invention, the research on the second pH value and n _SiO2 /n _TEOS is based on the background of large shrinkage rate. The shrinkage rate of the micro-optical glass device prepared by the present invention is greater than 88% relative to the wet gel. The shrinkage will cause problems such as the complete shape of the micro-optical structure molding.

In the present invention, the isoelectric point of the sol particles is pH=2, the surface of the sol particles cannot absorb charges, the polycondensation reaction progresses relatively slowly, the transition state is difficult to form, and the system gel time is longer; when the pH>2, the sol particles The surface can absorb a certain amount of OH-, and through molecular vibration and chemical bond breakage, SiO- will be produced, which can attack the central Si atom of other sol molecules and cause condensation reaction. The condensation reaction mechanism is a nucleophilic reaction mechanism. The inventor found through repeated experiments that when the second pH value is lower than 3.0, the gel time is long, and even if the gel is obtained, the prepared sample is extremely easy to crack; as the pH value increases, the gel time is shortened, The yield rate of the glass device obtained by drying and sintering the sample after the gel is gradually improved; however, when the pH value exceeds 4.0, the gel speed is too fast, which is not conducive to the formation of microstructure. In the present invention, it is preferable that the minimum microstructure size of the micro-optical device is not greater than 1 μm, and it is difficult to form the microstructure if the second pH value exceeds 4.0.

Under the same second pH value, the experimental data shows that the silica dispersion in the principle should not account for too much silica, otherwise the yield will decrease.

Ethyl orthosilicate (TEOS) contributes to the gel process. If only silica dispersion is used as the silica source, the gel formation process is extremely slow and cannot be used in mass production of products. The amount of ethyl orthosilicate, the required gel time is gradually shortened. According to the inventor's research, the molar ratio n _{SiO 2} /n _{TEOS of silicon dioxide to tetraethyl orthosilicate} contained in the silicon dioxide dispersion liquid is below 5.4, which can meet the mass production requirements.

However, too much tetraethyl orthosilicate may cause the gel to crack when it shrinks. Seen from the data in the table, a second at the same pH value, with n _SiO2 / n decrease of _TEOS, good after elevating the lead, when n _SiO2 / n _TEOS as low as 2.8, the yield has decreased to 40%, the smaller the ratio has little economic value.

In the present invention, the solution that does not require a 100% yield rate is adopted. The yield rate and production time need to be considered comprehensively. A higher yield rate often represents a longer gel time, as long as the number of good products per unit time is higher. That's it.

Therefore, in the present invention, the molar ratio of silica to tetraethyl orthosilicate contained in the silica dispersion is 3.8 to 5.4. Preferably, the molar ratio of silica to tetraethyl orthosilicate contained in the silica dispersion is 3.8 to 4.6.

The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referred to each other.

The above are only the embodiments of the present invention, and do not limit the scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the description and drawings of the present invention, or directly or indirectly applied to other related technologies In the same way, all fields are included in the scope of patent protection of the present invention.

Claims

A method for preparing a micro-optical glass device is characterized in that it comprises the following steps:

Step 1: Obtain a silica dispersion liquid, add an acidic solution to the silica dispersion liquid to adjust the pH value of the silica dispersion liquid to the first pH value, and stir;

Step 2: Add ethyl orthosilicate to the silica dispersion liquid and stir to obtain a sol, add an alkaline solution to the sol to adjust the pH value of the sol to the second pH value, stir and stand still Set

Step 3: Inject the static sol into a mold and age to obtain a wet gel;

Step 4: demoulding the wet gel, washing and drying, to obtain a dry gel;

Step 5: Sintering the dry gel to obtain a micro-optical glass device;

Wherein, the second pH value ranges from 3.0 to 4.0, the shrinkage rate of the micro-optical glass device relative to the wet gel is greater than 88%, and the silica contained in the silica dispersion is more than The molar ratio of the ethyl orthosilicate ranges from 3.8 to 5.4.
The method for preparing a micro-optical glass device according to claim 1, wherein, in the raw material, the molar ratio of the silica contained in the silica dispersion to the ethyl orthosilicate is 3.8～4.6.
The method for preparing a micro-optical glass device according to claim 1, wherein the solid content of silicon dioxide in the raw material is not more than 21%, and the solid content refers to the silicon dioxide contained in the silicon dioxide dispersion. The sum of silicon oxide and silicon dioxide produced by the hydrolysis of the ethyl orthosilicate accounts for the mass percentage of all raw materials.
The method for preparing a micro-optical glass device according to claim 3, characterized in that, in the step one, it comprises: obtaining a silica dispersion stock solution of a preset molar volume, and combining the silica dispersion stock solution It is mixed with deionized water to obtain the silica dispersion, and the deionized water is used to adjust the solid content of the silica.
The method for preparing a micro-optical glass device according to any one of claims 1 to 4, wherein the second pH value ranges from 3.4 to 4.0.
The method for preparing a micro-optical glass device according to any one of claims 1 to 4, wherein, in the step 1, the acidic solution is a hydrochloric acid solution, and the first pH value is in the range of 1.3 ~2.8.
The method for preparing a micro-optical glass device according to any one of claims 1 to 4, wherein the mold is a silicone mold.
The method for preparing a micro-optical glass device according to any one of claims 1 to 4, characterized in that, in the fifth step, the sintering temperature is not higher than 1200°C.
The method for preparing a micro-optical glass device according to any one of claims 1 to 4, characterized in that, in the step four, the drying includes a first drying stage and a second drying stage, and the first drying stage The temperature of the drying stage is at least 100°C lower than the temperature of the second drying stage.
The method for manufacturing a micro-optical glass device according to any one of claims 1 to 4, wherein the smallest microstructure size of the micro-optical glass device is not greater than 1 μm.