High refractive index glass microbeads and method for making same

Abstract

The application discloses a preparation method of high-refractive glass microbeads, which comprises the following steps: mixing, mixing SiO2, TiO2, BaO, CaO, BaSO4 and ZrO2 raw materials in proportion to obtain a mixture; sieving, sieving the mixture to ensure uniform mixing; electrothermal melting, placing the sieved mixture in an electric furnace to melt, clarify and homogenize, forming a homogenized glass liquid; centrifugal bead throwing, forming glass microbead rudiments through a centrifugal bead throwing device and collecting the glass microbead rudiments; annealing, annealing the collected glass microbead rudiments to eliminate internal stress; and flame polishing, adopting a group of flame spray guns to perform flame exposure treatment on the annealed glass microbeads to obtain high-refractive glass microbeads with smooth surfaces. Through improvement of the melting and clarifying process and the polishing process, crystallization inhibition of the interior and surface of the glass microbeads is realized, and the high-refractive glass microbeads with the characteristics of high refractive index, low crystallization rate and high retroreflective coefficient are obtained.

Description

Technical Field

[0001] This invention belongs to the field of glass microsphere technology, and in particular relates to a high refractive index glass microsphere and its preparation method. Background Technology

[0002] Glass microspheres are spherical or near-spherical glass particles with diameters ranging from a few micrometers to several hundred micrometers. They possess characteristics such as transparency, adjustable refractive index, directional retroreflection, smooth surface, good flowability, electrical insulation, chemical stability, heat resistance, and high mechanical strength. Glass microspheres are generally divided into solid and hollow types. Solid glass microspheres are commonly used in abrasive media, road markings, and reflective pavement signs. When solid glass microspheres are used in reflective pavement signs and road markings, their reflective performance, as a crucial reflective element, directly determines the reflectivity of the signs and markings. However, not all solid glass microspheres possess good reflective performance (i.e., high retroreflection performance). Geometric optics research shows that within a considerable range of incident angles from 0 to 50°, when the refractive index of the glass microsphere is around 1.93, the incident light, after being deflected by the glass microsphere, will still return roughly in the opposite direction along the optical axis, achieving optimal retroreflection. Ordinary glass microspheres typically have a refractive index of around 1.5, while glass microspheres with a refractive index between 1.9 and 2.0 are generally referred to as high-refractive-index glass microspheres.

[0003] There are numerous methods for preparing high-refractive-index glass microspheres, but they can be broadly categorized into three types: melt processing, powder processing, and sol-gel processing. The sol-gel process involves the hydrolysis and condensation of metal alkoxide or inorganic salt precursors to form amorphous oxide colloids. These oxide colloids can transform into a glassy state at relatively low temperatures, and generally require titration to form microspheres. Patent 201510777606.0 describes the process of preparing glass microspheres using the sol-gel method, which offers advantages such as high product purity, low energy consumption, and simple equipment. However, due to poor sol stability and low production efficiency, it has not been widely adopted in actual production. The powder processing method involves recycling waste glass, crushing it into powder, and then producing glass microspheres using spraying or flame flotation methods. Patent 201711064579.8 describes a method and apparatus for preparing glass microspheres using recycled waste glass powder. This method is low-cost and highly efficient, and is therefore widely adopted in actual production. However, since the raw material used is still ordinary glass (with a low refractive index), a secondary coating is required to obtain glass microspheres with a high refractive index. However, secondary coating has always suffered from problems such as poor film uniformity and stability, and limited improvement in the refractive index of the microspheres, which significantly reduces the performance and lifespan of the high-refractive-index glass microspheres. The melt method involves mixing various oxides (containing high-refractive-index components), melting them into a glass melt, and then directly forming high-refractive-index glass microspheres through methods such as blowing or centrifugal spinning. The most classic raw material system for the melt method is BaO-SiO2-TiO2, where SiO2 forms a stable glass network, and BaO and TiO2 help to improve the glass refractive index. Patent 202411825986.6 describes a typical melt-process method for preparing high-refractive-index glass microspheres. This method produces glass microspheres with high refractive index and high yield, and its high production efficiency makes it suitable for large-scale production and promotion. However, the melt-process also has some problems. Because heavy metal oxides such as BaO and TiO2 are introduced into the raw material system, while these components lower the glass melting temperature and increase the refractive index, they also reduce the chemical stability of the glass and increase the tendency for crystallization. Crystallization can adversely affect the optical uniformity and light transmittance of glass microspheres, introduce stress leading to breakage risk, and alter surface morphology and optical properties, causing problems such as turbidity, decreased mechanical strength, and surface diffuse reflection. Depending on the location, crystallization can be divided into surface crystallization and internal crystallization, and different methods are needed to suppress crystallization at different locations. How to comprehensively suppress crystallization has become a major challenge in the melt-process preparation of high-refractive-index glass microspheres. Summary of the Invention

[0004] To address the technical challenges in preparing high-refractive-index glass microspheres using the melt method, this invention provides a method for preparing high-refractive-index glass microspheres. By improving the melt clarification process and the polishing process, crystallization suppression is achieved inside and on the surface of the glass microspheres, resulting in a high-refractive-index glass microsphere with characteristics such as high refractive index, low crystallization rate, and high retroreflection coefficient.

[0005] In a first aspect, the present invention provides a method for preparing high refractive index glass microspheres, comprising the following steps:

[0006] S1. Mixing: SiO2, TiO2, BaO, CaO, BaSO4 and ZrO2 raw materials are mixed in proportion to obtain a batch;

[0007] S2. Sieving: The batch materials are sieved to ensure uniform mixing;

[0008] S3. Electrothermal melting: The sieved batch material is placed in an electric furnace for melting and clarification to form a homogenized glass melt;

[0009] S4. Centrifugal Bead Spinning: The homogenized glass liquid is passed through a centrifugal bead spinning device to form glass microbead prototypes and collected;

[0010] S5. Annealing: The collected glass microsphere prototypes are annealed to eliminate internal stress;

[0011] S6. Flame polishing: The annealed glass microspheres are subjected to flame exposure treatment using a set of flame guns to obtain high-refractive-index glass microspheres with smooth surfaces.

[0012] In one feasible embodiment, in step S1, the composition of the batch material, by weight percentage, comprises:

[0013] SiO2: 10%-15%,

[0014] TiO2: 30%-40%,

[0015] BaO: 45%-50%,

[0016] CaO: 1%-2%,

[0017] BaSO4: 1%-3%,

[0018] ZrO2: 1%-3%.

[0019] In one feasible embodiment, in step S2, the sieving is performed using a 200-mesh sieve.

[0020] In one feasible embodiment, in step S3, the melting temperature is 1400~1500℃, and the clarification and homogenization temperature is 1550~1600℃.

[0021] In one feasible scheme, in step S3, the temperature is increased to the melting temperature at a heating rate of 10℃ / min. After the batch material is completely melted, the temperature is increased to the clarification and homogenization temperature at a heating rate of 5℃ / min. The clarification and homogenization time is 1~1.5 hours.

[0022] In one feasible embodiment, in step S4, the feeding rate of the centrifugal bead-spinning process is 3~5 kg / min, and the centrifugal speed is 5000~12000 rpm.

[0023] In one feasible approach, in step S5, the annealing process involves heating the glass microsphere prototype to 650-700°C and holding it at that temperature for 10-30 minutes, followed by furnace cooling.

[0024] In one feasible embodiment, in step S6, the flame polishing employs an oxygen-natural gas flame, wherein the volume ratio of natural gas to oxygen in the flame gun is between 1:1.4 and 1:1.6.

[0025] In one feasible embodiment, during step S6, the exposure time of the glass microspheres in the flame during the flame polishing process is controlled to be 0.05~0.2s.

[0026] Secondly, the present invention provides a high refractive index glass microsphere, which is prepared by any of the above methods.

[0027] Compared with the prior art, the present invention has at least the following beneficial effects:

[0028] BaSO4 is preferred as a clarifying agent. Under the premise of effectively avoiding the environmental pollution, coloring and impurity introduction problems that may be caused by other clarifying agents, the SO3 gas generated by decomposition can effectively promote the clarification and homogenization of high viscosity glass melt. The BaO remaining after decomposition is still the main component of high refractive index glass.

[0029] The synergistic addition of high-refractive-index component ZrO2 as a crystallization inhibitor improves the stability of the glass network without affecting the refractive index of the glass microspheres, making the system more inclined to maintain a disordered glassy state. In synergy with BaSO4, it suppresses crystallization within the glass microspheres during the melting and refining homogenization stages.

[0030] Flame polishing is used to post-process glass microspheres, which transforms the microcrystals precipitated on the surface of the glass microspheres back into an amorphous glass state. At the same time, it repairs defects such as micro-scratches, pits and contaminants on the surface of the glass microspheres, thus solving the problem of crystallization on the surface of glass microspheres. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 A photograph of the glass microspheres prepared in Example 1 of the present invention is shown;

[0033] Figure 2 SEM images of the glass microspheres prepared in Example 1 of the present invention are shown. Detailed Implementation

[0034] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0035] All raw materials used in this invention are common in the field, and those skilled in the art can directly purchase them from the market or prepare the same / similar raw materials themselves.

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] This invention relates to two strategies for suppressing internal and external crystallization in glass microspheres. Internal crystallization in glass microspheres is often closely related to the melting, clarification, and homogenization processes of glass. This invention uses BaSO4 as a clarifier, a sophisticated design that is highly synergistic with the BaO-SiO2-TiO2 glass system, offering unique advantages compared to conventional clarifiers such as As2O3, Sb2O3, CaF2, and Na2SO4. First, As2O3 is heavily criticized for its high toxicity. Second, Sb2O3 is easily reduced to metallic Sb in reducing (Ti glass) systems, causing coloring problems. CaF2 contains F⁻ ions that readily corrode equipment, pollute the environment after volatilization, and also reduce the stability and refractive index of the glass. Although Na2SO4 has a low decomposition temperature, the Na2O produced during decomposition can disrupt the glass network and induce crystallization, thereby reducing the glass's refractive index, chemical stability, and high-temperature viscosity, which is detrimental to the preparation of high-refractive-index glasses. BaSO4 completely avoids the above problems. Furthermore, the BaO produced by its decomposition at high temperatures is a major component of high-refractive-index glass, introducing no impurities. The generated SO3 gas bubbles are large and have strong upward force, effectively merging and carrying smaller bubbles upwards, promoting the clarification and homogenization of high-viscosity glass melt. Simultaneously, to further suppress internal crystallization in the glass, this invention also adds a small amount of ZrO2 as a crystallization inhibitor in the formulation design. 4+ The binding force between ZrO2 ions and oxygen ions is extremely strong. When ZrO2 enters a glass network mainly composed of [SiO4] and [TiO4] / [TiO6], it forms very robust and stable [ZrO6] or [ZrO4] structural units, thereby improving the stability of the glass network and making the system more inclined to maintain a disordered glassy state. At the same time, ZrO2 itself is a high refractive index component and has good wear resistance properties; adding a small amount will not affect the refractive index of the glass microspheres.

[0038] The driving forces behind surface crystallization and internal crystallization in glass differ fundamentally. Surface atoms possess higher free energy, lower nucleation barriers, and higher mobility, resulting in a stronger crystallization driving force. Therefore, surface crystallization is difficult to address through glass formulation design or the addition of crystallization inhibitors. This invention addresses surface crystallization by employing a flame polishing method. This method utilizes a reducing high-temperature flame (to prevent surface oxidation from affecting the refractive index) to subject microspheres to extremely rapid, shallow, and brief heating and cooling cycles, forcing the surface-precipitated microcrystals to transform into a non-static glass structure. Flame polishing not only effectively eliminates the crystallized layer on the surface of glass microspheres but also repairs minor surface scratches, pits, and contaminants generated during the production process. The process is simple and suitable for mass production.

[0039] Example 1: A method for preparing high refractive index glass microspheres, the steps of which are as follows:

[0040] S1. Mixing: SiO2, TiO2, BaO, CaO, BaSO4 and ZrO2 raw materials are mixed at mass fractions of 10%, 35%, 50%, 1.5%, 2.0% and 1.5% respectively to obtain the batch material;

[0041] S2. Sieving: The batch material is sieved through a 200-mesh sieve to ensure uniform mixing;

[0042] S3. Electrothermal melting: The sieved batch material is placed in an electric furnace and heated to 1450°C at a heating rate of 10°C / min. After the batch material is completely melted, the temperature is continued to rise to 1550°C at a heating rate of 5°C / min. The mixture is then clarified and homogenized for 1.5 hours to obtain a homogenized glass melt.

[0043] S4. Centrifugal Beading: The homogenized glass melt is fed into a centrifugal beading device with a centrifugal speed of 6000 rpm at a feed rate of 4 kg / min to form glass microbeads and collect them.

[0044] S5. Annealing: Place the collected glass microsphere prototypes into an annealing furnace, heat to 650℃ and hold for 30 minutes, then cool with the furnace.

[0045] S6. Flame Polishing: A set of flame guns is used to expose the annealed glass microspheres to flame. The volume ratio of natural gas to oxygen in the flame gun is controlled at 1:1.5, and the exposure time of the glass microspheres in the flame is controlled at 0.2s. Finally, high refractive index glass microspheres are obtained.

[0046] Example 2: A method for preparing high refractive index glass microspheres, the process of which is basically the same as that of Example 1, except that step S1 is changed to: mixing SiO2, TiO2, BaO, CaO, BaSO4 and ZrO2 raw materials at mass fractions of 10%, 40%, 45%, 1.0%, 2.0% and 2.0% respectively to obtain a batch material; step S3 is changed to: placing the sieved batch material in an electric furnace and heating it to 1500°C at a heating rate of 10°C / min, and after the batch material is completely melted, continuing to heat it to 1600°C at a heating rate of 5°C / min, clarifying and homogenizing for 1 hour to obtain a homogenized glass melt.

[0047] Example 3: A method for preparing high-refractive-index glass microspheres, the process of which is basically the same as that of Example 1, except that the centrifugal speed in step S4 is changed to 12000 rpm; the annealing process in step S5 is changed to heating to 700℃ and holding for 10 min; and the exposure time of the glass microspheres in the flame in step S6 is changed to 0.05 s.

[0048] Comparative Example 1: A method for preparing high refractive index glass microspheres. The difference between this method and Example 1 is that BaSO4 is not added during the mixing process in step S1. Instead, step S1 is changed to mixing SiO2, TiO2, BaO, CaO, BaSO4 and ZrO2 raw materials at mass fractions of 10%, 40%, 47%, 1.5% and 1.5% respectively to obtain a batch.

[0049] Comparative Example 2: A method for preparing high refractive index glass microspheres. The process differs from that of Example 1 in that step S1 is changed to: mixing SiO2, TiO2, BaO, CaO, BaSO4 and ZrO2 raw materials at mass fractions of 10%, 35%, 48%, 1.5%, 4.0% and 1.5% respectively to obtain a compound.

[0050] Comparative Example 3: A method for preparing high refractive index glass microspheres. The difference between this method and Example 1 is that ZrO2 is not added during the mixing process in step S1. Instead, step S1 is changed to mixing SiO2, TiO2, BaO, CaO, BaSO4 and ZrO2 raw materials at mass fractions of 11.5%, 35%, 50%, 1.5% and 2.0% respectively to obtain a batch.

[0051] Comparative Example 4: A method for preparing high refractive index glass microspheres. The process differs from that of Example 1 in that step S1 is changed to: mixing SiO2, TiO2, BaO, CaO, BaSO4 and ZrO2 raw materials at mass fractions of 10%, 35%, 47.5%, 1.5%, 2.0% and 4.0% respectively to obtain a compound.

[0052] Comparative Example 5: A method for preparing high refractive index glass microspheres, the process of which differs from that of Example 1 in that BaSO4 in step S1 is replaced with an equal mass fraction of Na2SO4.

[0053] Comparative Example 6: A method for preparing high refractive index glass microspheres. The difference between Comparative Example 6 and Example 1 is that Comparative Example 6 does not include the flame polishing process in step S6.

[0054] Comparative Example 7: A method for preparing high refractive index glass microspheres, the process of which differs from that of Example 1 in that the volume ratio of natural gas to oxygen in the spray gun in step S6 is changed to 1:1.7.

[0055] This invention measures the particle size of glass microspheres prepared in all examples and comparative examples according to standard GB / T21782.1-2008, the crystallization rate of glass microspheres prepared in all examples and comparative examples according to JC / T2511-2019, the refractive index of glass microspheres prepared in all examples and comparative examples according to GB / T7962.1-2010, and the retroreflection coefficient of glass microspheres prepared in all examples and comparative examples according to GB / T18833-2012. All measurement results are shown in Table 1.

[0056] Table 1 Test results of glass microspheres

[0057] .

[0058] As can be seen from the test results in Table 1, the glass microspheres prepared in Examples 1-3 of this invention have lower crystallization rates, higher refractive indices, and higher retroreflection coefficients. Examples 1 and 2 have the same particle size and can be used for road markings, while Example 3, due to its higher centrifugal speed, has a smaller particle size and can be used for reflective fabric. Compared to Example 1, Comparative Examples 1 and 2 changed the amount of clarifying agent BaSO4. Comparative Example 1 removed BaSO4, resulting in ineffective clarification and homogenization of the glass, intensified internal crystallization of the glass microspheres, and a non-uniform structure, ultimately leading to a decrease in its refractive index and retroreflection coefficient. Comparative Example 2 increased the amount of BaSO4; excessive use of BaSO4 caused secondary bubbles and a small amount of sulfate precipitation, ultimately resulting in a significant decrease in the retroreflection coefficient of the glass microspheres. Compared to Example 1, Comparative Examples 3 and 4 changed the amount of the crystallization inhibitor ZrO2. Comparative Example 3 removed the use of ZrO2, resulting in a significant increase in the crystallization rate of the glass microspheres, ultimately leading to a decrease in their refractive index and retroreflection coefficient. Comparative Example 4, on the other hand, added an excessive amount of ZrO2, causing problems such as ZrO2 crystallization itself and excessive glass melt viscosity introducing bubbles, which in turn caused a slight decrease in refractive index and retroreflection coefficient. In Comparative Example 5, compared to Example 1, the clarifying agent was replaced with Na2SO4. Na2SO4 can also have a clarifying effect, but it decomposes into Na2O instead of BaO. Na2O has a lower refractive index and can damage the glass network, inducing crystallization, resulting in an increase in the crystallization rate of the glass microspheres and a decrease in their refractive index and retroreflection coefficient. In Comparative Example 6, compared to Example 1, the flame polishing process was removed. The glass microspheres that were not flame polished had severe surface crystallization, thus exhibiting a higher crystallization rate and a lower retroreflection coefficient. Compared to Example 1, Comparative Example 7 changed the ratio of natural gas and oxygen in the flame gun. This change caused the natural gas to burn completely, forming an oxidizing flame rather than a reducing flame. The oxidizing flame caused excessive oxidation of the glass microsphere surface, resulting in high haze. The high haze surface caused the retroreflection coefficient of the glass microsphere to drop sharply.

[0059] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high refractive index glass microspheres, characterized in that, Includes the following steps: S1. Mixing: SiO2, TiO2, BaO, CaO, BaSO4 and ZrO2 raw materials are mixed in proportion to obtain a batch; S2. Sieving: The batch materials are sieved to ensure uniform mixing; S3. Electrothermal melting: The sieved batch material is placed in an electric furnace for melting and clarification to form a homogenized glass melt; S4. Centrifugal Bead Spinning: The homogenized glass liquid is passed through a centrifugal bead spinning device to form glass microbead prototypes and collected; S5. Annealing: The collected glass microsphere prototypes are annealed to eliminate internal stress; S6. Flame polishing: The annealed glass microspheres are subjected to flame exposure treatment using a set of flame guns to obtain high-refractive-index glass microspheres with smooth surfaces. In step S1, the composition of the batch material, by weight percentage, includes: SiO2: 10%-15%, TiO2: 30%-40%, BaO: 45%-50%, CaO: 1%-2%, BaSO4: 1%-3%, ZrO2: 1%-3%, In step S6, the flame polishing uses an oxygen-natural gas flame, and the volume ratio of natural gas to oxygen in the flame gun is between 1:1.4 and 1:1.

6. In step S6, during the flame polishing process, the exposure time of the glass microspheres in the flame is controlled to be 0.05~0.2s; In step S4, the feeding speed of the centrifugal bead-spinning process is 3~5 kg / min, and the centrifugal speed is 5000~12000 rpm.

2. The preparation method according to claim 1, characterized in that, In step S2, the sieving is performed using a 200-mesh sieve.

3. The preparation method according to claim 1, characterized in that, In step S3, the melting temperature is 1400~1500℃, and the clarification and homogenization temperature is 1550~1600℃.

4. The preparation method according to claim 3, characterized in that, In step S3, the temperature is increased to the melting temperature at a heating rate of 10℃ / min. After the batch material is completely melted, the temperature is increased to the clarification and homogenization temperature at a heating rate of 5℃ / min. The clarification and homogenization time is 1~1.5 hours.

5. The preparation method according to claim 1, characterized in that, In step S5, the annealing process is as follows: the glass microsphere prototype is heated to 650~700℃ and held for 10~30 minutes, and then cooled in the furnace.

6. A high refractive index glass microsphere, characterized in that, It is prepared by the method described in any one of claims 1 to 5.

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