A method for surface coating modification of expanded microspheres

Abstract

The application provides a surface coating modification method of expanded microspheres and relates to the technical field of microsphere modification. Through a three-step process of "surface oxidation activation-in-situ coating-curing and drying", a uniform, firm and thin high-density coating layer is formed on the surface of the expanded microspheres, the density of the expanded microspheres is obviously improved, and the problems of floating and poor dispersibility of the expanded microspheres in slurry are solved.

Description

Technical Field

[0001] This invention belongs to the field of microsphere modification technology, and relates to a method for surface coating modification of expanded microspheres. Background Technology

[0002] Expandable microspheres are functional materials with a core-shell structure. Their shells are typically made of thermoplastic resin, while the core encapsulates a foaming agent such as a low-boiling-point alkane. When heated above the shell's softening temperature, the core foaming agent vaporizes and expands, causing the microspheres to expand tens to hundreds of times in volume. The equivalent density (equivalent density = microsphere weight / microsphere volume) is generally less than 0.1 g / cm³. 3 It can even be as low as 0.02~0.03 g / cm³. 3 This results in a lightweight, hollow structure that is widely used in coatings, insulation materials, sealing materials, and lightweight fillers. Expanded microspheres possess excellent properties such as light weight, thermal insulation, and buffering, but this also limits their application. When added to slurry, expanded microspheres exhibit two main drawbacks: low density leading to floating and poor dispersibility causing agglomeration. These drawbacks are particularly pronounced in aqueous systems, especially the density-induced floating defect. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method for surface coating modification of expandable microspheres.

[0004] The technical solution of the present invention is as follows:

[0005] A method for surface coating modification of expandable microspheres includes the following steps: S1. Oxidation activation is performed on the surface of the expanded microspheres to obtain pre-activated microspheres; S2. A coating liquid is formed on the surface of the pre-activated microspheres described in step S1, and then dried to obtain coated expanded microspheres. The coating liquid, by weight, comprises the following raw material components: 5-20% inorganic powder, 3-10% water-based binder, 0.5-2% dispersant, 0.1-0.5% defoamer, with the balance being water.

[0006] Preferably, the expanded microspheres in step S1 are selected from expanded or unexpanded expanded microspheres, with an average particle size of 10-500 μm; The oxidation activation involves oxidizing the surface of the expanded microspheres and chemically grafting a silane coupling agent.

[0007] More preferably, the oxidation activation method is as follows: the expanded microspheres are added to the pretreatment solution, and an oxidizing gas is continuously introduced under stirring for 20-60 minutes. Then, the mixture is filtered, washed, and dried to obtain the preactivated microspheres. The pretreatment solution is composed of deionized water, silane coupling agent and anhydrous ethanol in a volume ratio of 100:1-5:5-20.

[0008] More preferably, the oxidizing gas is selected from one or more of oxygen, air, and ozone; The silane coupling agent is selected from epoxy silane coupling agents or amino silane coupling agents.

[0009] Preferably, the method for forming a coating liquid on the surface of the pre-activated microspheres in step S2 is as follows: the pre-activated microspheres and the coating liquid are mixed evenly at a weight ratio of 1:5-20 and stirred continuously for 60-150 minutes, then filtered and washed with water.

[0010] More preferably, the stirring speed during continuous stirring is 300-500 rpm and the temperature is 30-60℃.

[0011] More preferably, under continuous stirring, the inorganic powder and the aqueous binder are jointly adsorbed and deposited on the surface of the expanded microspheres.

[0012] Preferably, the true density of the inorganic powder in step S2 is not less than 3 g / cm³. 3 The inorganic powder is selected from one or more of the following: nano-silica, nano-tungsten powder, nano-iron powder, nano-iron oxide, nano-iron tetroxide, nano-tungsten oxide, nano-zinc oxide, nano-barium oxide, nano-titanium dioxide, nano-alumina, nano-calcium carbonate, and nano-barium sulfate. The waterborne adhesive mentioned in step S2 is selected from one or more of waterborne polyurethane, waterborne acrylic resin, silica sol and waterborne epoxy resin.

[0013] Preferably, the expanded microspheres are selected from unexpanded expanded microspheres, and the drying temperature in step S2 is lower than the initial expansion temperature of the expanded microspheres.

[0014] Preferably, the coated expandable microspheres in step S2 are composed of the expandable microspheres and a coating layer, wherein the coating layer coats the expandable microspheres; The thickness of the coating layer is 0.5-5 μm.

[0015] The beneficial effects of this invention are: (1) The present invention forms a uniform, firm and thin high-density coating layer on the surface of the expanded microspheres through a three-step process of “surface oxidation activation - in-situ coating - curing and drying”, thereby improving the density of the expanded microspheres. The equivalent density of the expanded microspheres after expansion can be increased by 3 times or more, which solves the problem of the expanded microspheres floating and poor dispersibility in the slurry.

[0016] (2) The present invention uses oxidizing gas to oxidize the surface of the expanded microspheres, and realizes the oxidation and grafting of the expanded microspheres in one step, thereby improving the surface roughness and specific surface area of ​​the expanded microspheres. This is beneficial for the adsorption and deposition of inorganic powder and water-based binder on the surface of the pre-activated microspheres, and ultimately forms a relatively strong coating layer. Attached Figure Description

[0017] Figure 1 The image shows a comparison of FT-IR values ​​of the expanded microspheres in Example 1 before and after treatment. Detailed Implementation

[0018] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0019] This invention provides a method for surface coating modification of expandable microspheres, comprising the following steps: S1. Oxidation activation is performed on the surface of the expanded microspheres to obtain pre-activated microspheres; S2. A coating liquid is formed on the surface of the pre-activated microspheres in step S1, and then dried to obtain coated expanded microspheres. The coating liquid, by weight, comprises the following raw material components: 5-20% inorganic powder, 3-10% water-based binder, 0.5-2% dispersant, 0.1-0.5% defoamer, with the balance being water.

[0020] This invention utilizes a process of "surface oxidation activation - in-situ coating - curing and drying" to form a coating layer composed of inorganic powder and binder on the surface of expanded microspheres, creating coated expanded microspheres. This increases the true density of the expanded microspheres and solves the problem of "floating due to low density" in the application of expanded microspheres, especially since this problem is more pronounced after expansion. Even unexpanded expanded microspheres may exhibit this problem after expansion, as they may float due to their low density when the slurry is not yet cured. Simultaneously, the coating layer has high surface polarity and a significantly lower density than the outer shell of the expanded microspheres, thus improving its wetting and penetration ability with the slurry and facilitating the dispersion of the expanded microspheres in the slurry. Therefore, this invention, by increasing the density, surface polarity, and reducing the density of the expanded microspheres, improves the dispersibility of coated expanded microspheres in slurries and avoids the defects of "floating" and "agglomeration."

[0021] In this invention, the coating solution employs a low binder content method. The organic structure on the surface of the pre-activated microspheres can form physical and / or chemical adsorption with the binder and inorganic powders, inducing the binder and inorganic powders to deposit on the surface of the expanded microspheres, thereby forming a coating layer composed of inorganic powders and binder on the surface of the expanded microspheres. Because the inorganic powder content in the coating solution is higher than that of the binder, the inorganic powder weight ratio in the coating layer is higher, resulting in a higher density of the coating layer. Consequently, the coated expanded microspheres have a significantly higher density than the original expanded microspheres.

[0022] In some embodiments, the expanded microspheres in step S1 are selected from expanded microspheres or unexpanded expanded microspheres, with an average particle size of 10-500 μm; Oxidative activation involves oxidizing the surface of the expanded microspheres and chemically grafting silane coupling agents.

[0023] The modification method of this invention is suitable for both expanded and unexpanded expanded microspheres. The density of expanded microspheres is typically as low as 0.1 g / cm³. 3 Even as low as 0.02~0.03 g / cm³ 3 Using the modification method of this invention, the density of the coated expanded microspheres can be increased by 3 times or more, and the density can even reach 0.5 g / cm³. 3 Or higher.

[0024] In some embodiments, the oxidation activation method is as follows: expanded microspheres are added to a pretreatment solution, an oxidizing gas is continuously introduced under stirring for 20-60 minutes, and then filtered, washed and dried to obtain pre-activated microspheres; The pretreatment solution consists of deionized water, silane coupling agent and anhydrous ethanol in a volume ratio of 100:1-5:5-20.

[0025] The outer shell of expanded microspheres is generally made of a relatively inert and dense polymer material, with a glass transition temperature (Tg) much higher than room temperature. This invention uses an oxidizing gas for oxidation, achieving slight oxidation of the surface of the expanded microspheres without damaging their main structure. This oxidation forms active groups such as hydroxyl, carbonyl, and carboxyl groups, increasing polarity. Simultaneously, these groups can undergo adsorption and dehydration reactions with the silanol groups generated from the hydrolysis of the silane coupling agent, thereby grafting the silane coupling agent onto the surface of the expanded microspheres. The oxidation activation improves the surface roughness of the expanded microspheres. The organic structure in the silane coupling agent has good affinity for inorganic powders and adhesive polymers, facilitating their adsorption and deposition on the surface of the expanded microspheres.

[0026] In this invention, there is no particular limitation on the volume ratio of expanded microspheres to pretreatment solution in the above-mentioned oxidation activation. For example, the volume ratio of expanded microspheres to pretreatment solution can be 1:10-50.

[0027] Furthermore, the oxidizing gas is selected from one or more of oxygen, air, and ozone; The silane coupling agent is selected from epoxy silane coupling agents or amino silane coupling agents.

[0028] Epoxy-silane coupling agents or amino-silane coupling agents can form epoxy or amino groups on the surface of expanded microspheres. The higher polarity of the epoxy or amino groups results in good affinity with the higher polarity of inorganic powders and binder polymers, facilitating their adsorption and deposition on the surface of the expanded microspheres. There are no particular limitations on epoxy-silane coupling agents or amino-silane coupling agents; for example, epoxy-silane coupling agents can be KH-560, and amino-silane coupling agents can be KH-550, KH-554, KH-792, etc.

[0029] In some embodiments, the method for forming a coating solution on the surface of the pre-activated microspheres in step S2 is as follows: the pre-activated microspheres and the coating solution are mixed evenly at a weight ratio of 1:5-20 and stirred continuously for 60-150 min, then filtered and washed with water. In this invention, the pre-activated microspheres are dispersed in the coating solution, and through simple stirring, the inorganic powders and binder polymers in the coating solution can be adsorbed and deposited on the surface of the expanded microspheres.

[0030] For example, the weight ratio of pre-activated microspheres to coating solution can be 1:5, 1:6, 1:8, 1:10, 1:12, 1:14, 1:15, etc. Insufficient stirring time results in inadequate adsorption and deposition, leading to an excessively thin coating layer or even uneven coating of the expanded microspheres. Excessive stirring time may damage the expanded microspheres, or result in an excessively thick coating layer, causing the surface of the coating layer to be too loose or the density of the expanded microspheres in the coating layer to be too high.

[0031] In some embodiments, the stirring speed is 300-500 rpm and the temperature is 30-60℃.

[0032] In some embodiments, under continuous stirring, inorganic powder and aqueous binder are jointly adsorbed and deposited on the surface of the expanded microspheres.

[0033] In some embodiments, the true density of the inorganic powder in step S2 is not less than 3 g / cm³. 3 The inorganic powder is selected from one or more of the following: nano-silica, nano-tungsten powder, nano-iron powder, nano-iron oxide, nano-iron tetroxide, nano-tungsten oxide, nano-zinc oxide, nano-barium oxide, nano-titanium dioxide, nano-alumina, nano-calcium carbonate, and nano-barium sulfate. In step S2, the waterborne binder is selected from one or more of waterborne polyurethane, waterborne acrylic resin, silica sol, and waterborne epoxy resin. The density of inorganic powder is much higher than that of the binder polymer; therefore, the coating layer has a higher density, which can further increase the density of the coated expanded microspheres.

[0034] The true density of inorganic powders is not less than 3 g / cm³. 3 The coating layer has a high density, and even with a thin coating layer, the coated expandable microspheres can have a significantly higher true density compared to the expandable microspheres (before coating).

[0035] In some embodiments, the expanded microspheres are selected from unexpanded expanded microspheres, and the drying temperature in step S2 is lower than the initial expansion temperature of the expanded microspheres. Unexpanded expanded microspheres will expand when heated to a certain temperature; therefore, the drying temperature needs to be lower than the initial expansion temperature of the expanded microspheres. The coated unexpanded expanded microspheres are added to the slurry and then expanded.

[0036] Of course, if it is necessary for the unexpanded expanded microspheres to foam and expand simultaneously during drying, the temperature of the unexpanded expanded microspheres during drying should reach or exceed the expansion temperature, and the resulting microspheres are equivalent to the coating of the expanded microspheres.

[0037] In some embodiments, the coated expandable microspheres in step S2 consist of expandable microspheres and a coating layer, wherein the coating layer coats the expandable microspheres. The coating thickness is 0.5-5 μm. Further, the coating thickness can be 3-5 μm. The greater the coating thickness, the higher the density of the coated expanded microspheres.

[0038] When the expanded microspheres are unexpanded, their particle size is typically 10-50 μm. After expansion, the particle size of the expanded microspheres can typically increase by 3-5 times, or even more, reaching approximately 30-200 μm. Therefore, the coating thickness of this invention is relatively low compared to the size of the expanded microspheres.

[0039] The technical solution of the present invention will be further described and illustrated below with reference to various embodiments. Unless otherwise specified, the parts mentioned in the following embodiments are parts by weight.

[0040] Example 1: Coating of expanded microspheres The pretreatment solution is prepared by combining deionized water, silane coupling agent KH-560, and anhydrous ethanol in a volume ratio of 100:2:10.

[0041] At room temperature, 1 volume fraction of expanded microspheres (average particle size 120 μm, equivalent density 0.05 g / cm³) 3 Add 20 parts by volume of the above pretreatment solution, continuously introduce oxygen while stirring at 300 rpm for 30 min, filter to separate the solid, wash the solid with anhydrous ethanol, and dry at 60°C overnight to obtain pre-activated microspheres.

[0042] Without adding silane coupling agent KH-560 to the pretreatment solution, the FT-IR analysis of the preactivated microspheres obtained by the above oxidation activation method is shown in the attached figure. Figure 1 As shown, comparing the characteristic absorption peaks before and after treatment demonstrates that the above-mentioned oxidation activation method results in a mild, trace oxidation of the organic resin outer shell of the expanded microspheres by oxygen. This oxidation generates polar active groups such as hydroxyl, carbonyl, and carboxyl groups in situ on the outer shell surface. This oxidation occurs only in a very thin region on the microsphere surface and does not damage the overall shell structure. The hydroxyl groups provide active sites for reaction with KH-560.

[0043] The coating liquid, by weight, consists of the following raw material components: 13% nano barium sulfate, 7% waterborne polyurethane slurry (solid content 55%), 1% dispersant BYK190 and 0.3% dimethyl silicone oil defoamer, with the remainder being water.

[0044] The pre-activated microspheres and coating solution were mixed evenly at a weight ratio of 1:5. The mixture was then stirred continuously at 400 rpm for 90 min at 40 °C. The solid was then separated and collected. The solid was washed three times with deionized water, dried at 60 °C for 2 h, and then dried at 120 °C for 2 h to obtain coated expanded microspheres.

[0045] Example 2 The difference between this embodiment and Embodiment 1 is that in Embodiment 1, the weight ratio of pre-activated microspheres to coating solution was adjusted from 1:5 to 1:13. The remaining steps remain unchanged.

[0046] Example 3 The difference between this embodiment and Embodiment 1 is that in Embodiment 1, the weight ratio of pre-activated microspheres to coating solution was adjusted from 1:5 to 1:20. The remaining steps remain unchanged.

[0047] Comparative Example 1 The difference between this comparative example and Example 1 is that in Example 1, when the pre-activated microspheres were coated, the pre-activated microspheres were replaced with an equal weight of the expanded microspheres from Example 1. The remaining steps remained unchanged.

[0048] That is, in this comparative example, the expanded microspheres were directly added to the coating solution for coating.

[0049] Comparative Example 2 The difference between this comparative example and Example 1 is that in Example 1, the pretreatment solution did not contain the silane coupling agent KH-560. The remaining steps remained unchanged.

[0050] Example 4: Coating of expanded microspheres The pretreatment solution is prepared by combining deionized water, silane coupling agent KH-550, and anhydrous ethanol in a volume ratio of 100:3:15.

[0051] At room temperature, 1 volume fraction of expanded microspheres (average particle size 100 μm, equivalent density 0.03 g / cm³) 3 Add 30 parts by volume of the above pretreatment solution, continuously introduce air while stirring at 300 rpm for 60 min, filter to separate the solid, wash the solid with anhydrous ethanol, and dry at 60°C overnight to obtain pre-activated microspheres.

[0052] The coating liquid, by weight, consists of the following raw material components: 5% nano-alumina, 5% waterborne polyurethane slurry (55% solid content), 0.7% dispersant BYK190 and 0.4% dimethyl silicone oil defoamer, with the remainder being water.

[0053] The pre-activated microspheres and coating solution were mixed evenly at a weight ratio of 1:10. The mixture was then stirred continuously at 400 rpm for 110 min at 50 °C. The solid was then separated and collected. The solid was washed three times with deionized water, dried at 60 °C for 2 h, and then heated to 120 °C for 2 h to obtain coated expanded microspheres.

[0054] Example 5 The difference between this embodiment and Embodiment 4 is that in Embodiment 4, the content of nano-alumina in the coating solution was adjusted from 5% to 20%, and the water content was reduced accordingly. The remaining steps remained unchanged.

[0055] Example 6 The difference between this embodiment and Embodiment 4 is that in Embodiment 4, the nano-alumina in the coating solution is replaced with an equal weight content of nano-tungsten oxide. The remaining steps remain unchanged.

[0056] Example 7: Pre-activation of unexpanded expanded microspheres The pretreatment solution is prepared by combining deionized water, silane coupling agent KH-550, and anhydrous ethanol in a volume ratio of 100:3:12.

[0057] At room temperature, 1 volume fraction of unexpanded expanded microspheres (average particle size 30 μm, equivalent density 1.1 g / cm³) 3 Add 30 parts by volume of the above pretreatment solution, continuously introduce oxygen while stirring at 300 rpm for 45 min, filter to separate the solid, wash the solid with anhydrous ethanol, and dry at 60°C overnight to obtain pre-activated microspheres.

[0058] The coating liquid, by weight, consists of the following raw material components: 10% nano-alumina, 10% waterborne polyurethane slurry (55% solid content), 0.8% dispersant BYK190 and 0.4% dimethyl silicone oil defoamer, with the remainder being water.

[0059] The pre-activated microspheres and coating solution were mixed evenly at a weight ratio of 1:12. The mixture was then stirred continuously at 300 rpm for 60 min at 60 °C. The solid was then separated and collected. The solid was washed three times with deionized water, dried at 60 °C for 2 h, and then dried at 120 °C for 2 h to obtain coated expanded microspheres.

[0060] Example 8 The difference between this embodiment and Embodiment 7 is that in Embodiment 7, the temperature was increased to 150°C for 2 hours after drying at 120°C, and then maintained at 150°C for 60 seconds for expansion and foaming. The remaining steps remained unchanged.

[0061] Performance testing The coating layer thickness and equivalent density of the coated expandable microspheres of Examples 1-8 and Comparative Examples 1-2 are shown in Table 1 below.

[0062] Table 1

[0063] The results above show that coating the surface of the expandable microspheres with a coating layer composed of inorganic powder and binder polymer can significantly increase the density of the expandable microspheres. The thicker and denser the coating layer, the higher the density of the coated expandable microspheres. However, as shown in Comparative Example 1, the surface of the expandable microspheres was not oxidized or activated, so a coating layer could not be formed. As shown in Comparative Example 2, the surface of the expandable microspheres was only oxidized without silane grafting, resulting in a very thin coating layer and a low effect on increasing the density of the expandable microspheres.

[0064] The raw material composition, by 100% by weight, is: 10% expanded microspheres or coated expanded microspheres, 40% water-based polyurethane slurry, 1% dispersant BYK190, 0.5% dimethyl silicone defoamer, and the balance being water. All raw material components are stirred and dispersed evenly to form a homogeneous dispersion. The dispersion is left at room temperature for one month, and the presence of floating microspheres on the surface is observed.

[0065] The results are shown in Table 2 below.

[0066] Table 2

[0067] Therefore, the coated expandable microspheres of the present invention can be well dispersed in aqueous slurries even after expansion, and have good stability.

[0068] As described above, the basic principles, main features, and advantages of the present invention have been shown and described. Those skilled in the art should understand that the present invention is not limited to the above embodiments, which are merely preferred embodiments and should not be construed as limiting the scope of the invention. All equivalent changes and modifications made in accordance with the scope of the patent and the description should still fall within the scope of the present invention. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for surface coating modification of expandable microspheres, characterized in that, Includes the following steps: S1. Oxidation activation is performed on the surface of the expanded microspheres to obtain pre-activated microspheres; S2. A coating liquid is formed on the surface of the pre-activated microspheres described in step S1, and then dried to obtain coated expanded microspheres. The coating liquid, by weight, comprises the following raw material components: 5-20% inorganic powder, 3-10% water-based binder, 0.5-2% dispersant, 0.1-0.5% defoamer, with the balance being water.

2. The surface coating modification method for expanded microspheres according to claim 1, characterized in that, The expanded microspheres mentioned in step S1 are selected from expanded or unexpanded expanded microspheres, with an average particle size of 10-500 μm; The oxidation activation involves oxidizing the surface of the expanded microspheres and chemically grafting a silane coupling agent.

3. The surface coating modification method for expanded microspheres according to claim 2, characterized in that, The oxidation activation method is as follows: the expanded microspheres are added to the pretreatment solution, and an oxidizing gas is continuously introduced under stirring for 20-60 minutes. Then, the solution is filtered, washed, and dried to obtain the preactivated microspheres. The pretreatment solution is composed of deionized water, silane coupling agent and anhydrous ethanol in a volume ratio of 100:1-5:5-20.

4. The surface coating modification method for expanded microspheres according to claim 3, characterized in that, The oxidizing gas is selected from one or more of oxygen, air, and ozone; The silane coupling agent is selected from epoxy silane coupling agents or amino silane coupling agents.

5. The surface coating modification method for expanded microspheres according to claim 1, characterized in that, The method for forming a coating liquid on the surface of the pre-activated microspheres in step S2 is as follows: the pre-activated microspheres and the coating liquid are mixed evenly at a weight ratio of 1:5-20 and stirred continuously for 60-150 minutes, then filtered and washed with water.

6. The surface coating modification method for expanded microspheres according to claim 5, characterized in that, The stirring speed for continuous stirring is 300-500 rpm, and the temperature is 30-60℃.

7. The surface coating modification method for expanded microspheres according to claim 5, characterized in that, Under continuous stirring, the inorganic powder and the aqueous binder are adsorbed and deposited on the surface of the expanded microspheres.

8. The surface coating modification method for expanded microspheres according to claim 1, characterized in that, The true density of the inorganic powder in step S2 is not less than 3 g / cm³. 3 The inorganic powder is selected from one or more of the following: nano-silica, nano-tungsten powder, nano-iron powder, nano-iron oxide, nano-iron tetroxide, nano-tungsten oxide, nano-zinc oxide, nano-barium oxide, nano-titanium dioxide, nano-alumina, nano-calcium carbonate, and nano-barium sulfate. The waterborne adhesive mentioned in step S2 is selected from one or more of waterborne polyurethane, waterborne acrylic resin, silica sol and waterborne epoxy resin.

9. The surface coating modification method for expanded microspheres according to claim 1, characterized in that, The expanded microspheres are selected from unexpanded expanded microspheres, and the drying temperature in step S2 is lower than the initial expansion temperature of the expanded microspheres.

10. The surface coating modification method for expanded microspheres according to claim 1, characterized in that, The coated expandable microspheres in step S2 consist of the expandable microspheres and a coating layer, wherein the coating layer coats the expandable microspheres; The thickness of the coating layer is 0.5-5 μm.

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