Core-shell structure reflective microbead for road marking coating and preparation method of core-shell structure reflective microbead

Abstract

The invention provides a core-shell structure reflective microbead for a road marking coating and a preparation method thereof, and belongs to the technical field of road marking reflective materials, and the preparation method comprises the following steps: carrying out amination modification on the surface of a core layer of a fluorinated glass microbead through a silane coupling agent, and grafting a temperature-sensitive polymer outside a shell layer to obtain a temperature-sensitive core-shell reflective microbead. The invention provides a core-shell structure reflective microsphere for a road marking coating and a preparation method of the core-shell structure reflective microsphere. The visibility of the reflective microsphere in a complex climate is improved.

Description

Technical Field

[0001] This invention relates to the field of road marking reflective materials technology, specifically to a core-shell structured reflective microsphere for road marking paint and its preparation method. Background Technology

[0002] Road markings are an important component of traffic safety facilities. Reflective glass beads used in road markings can improve road visibility at night or in low-visibility conditions, thereby reducing traffic accidents. Therefore, it is necessary to increase the refractive index of reflective glass microspheres.

[0003] Chinese Patent Publication No. CN119528445A, entitled "A Method for Preparing High-Refractive-Index Large-Diameter Glass Microspheres for Road Markings and its Spheroidization Molding," discloses a method for preparing high-refractive-index large-diameter glass microspheres for road markings and its spheroidization molding. The microspheres, by weight, comprise: 30-40 parts titanium dioxide, 30-40 parts silicon dioxide, 10-15 parts barium nitrate, 10-15 parts zirconium nitrate, 5-7 parts zinc oxide, 3-5 parts boric acid, 3-5 parts calcium fluoride, 5-110 parts Nb₂O₅, and 5-15 parts La₂O₃-ZrO₂ composite. This technical solution not only improves the refractive index of the glass microspheres but also maintains a high yield.

[0004] However, like the above-mentioned technical solutions, the reflective microspheres currently used in road reflective markings are in a random and static distribution state in the coating matrix, and their reflection angle is relatively fixed. When the incident angle of light changes due to weather (such as rain, fog) or vehicle headlight angle and road surface temperature, the static microsphere structure cannot achieve adaptive optimization, resulting in insufficient visibility guarantee under complex climatic conditions. Summary of the Invention

[0005] In view of this, the present invention provides a core-shell structured reflective microsphere for road marking paint and a method for preparing the same, thereby increasing the visibility of the reflective microsphere under complex weather conditions.

[0006] To achieve the above objectives, the present invention provides a method for preparing core-shell structured reflective microspheres for road marking paint, comprising the following steps: S1. Fluorinated glass microspheres are dispersed in ethanol and subjected to ultrasonic treatment. Then, a silane coupling agent is added and stirred to form a stable suspension. The stable suspension is heated to carry out the reaction. The surface of the fluorinated glass microspheres is functionalized by bonding the amino group of the silane with the hydroxyl group on the surface of the fluorinated glass microspheres, thus obtaining activated core-shell fluorinated glass microspheres. S2. Dissolve the thermosensitive polymer in a solvent, add a crosslinking agent and a carbodiimide condensing agent in sequence, stir and activate in the dark to activate the carboxyl group at the end of the thermosensitive polymer to N-hydroxysuccinimide ester, and obtain the activated thermosensitive polymer solution. S3. The activated core-shell fluorinated glass microspheres are ultrasonically dispersed in another solvent to obtain a microsphere suspension. The microsphere suspension is added dropwise to the activated thermosensitive polymer solution, and then an organic base is added. The mixture is heated and stirred to carry out the reaction. After the reaction is completed, the microspheres are separated, washed, and dried to obtain thermosensitive core-shell reflective microspheres.

[0007] Optionally, the silane coupling agent is γ-aminopropyltriethoxysilane, and the concentration of the silane coupling agent dissolved in ethanol after adding the silane coupling agent is 4.5~5.5 wt%.

[0008] Optionally, in step S1, the ultrasonic treatment time is 15-25 min; the refractive index of the fluorinated glass microspheres is ≥1.95; the stirring time is 25-35 min; and the heating reaction of the stable suspension is carried out by reflux at 58-62℃ for 3.5-4.5 h.

[0009] Optionally, the thermosensitive polymer is poly(N-isopropylacrylamide) or a copolymer thereof; the solvent is one of anhydrous N,N-dimethylformamide, dimethyl sulfoxide, and acetonitrile; the crosslinking agent is N-hydroxysuccinimide or N-hydroxysulfosuccinimide; the carbodiimide condensing agent is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride or dicyclohexylcarbodiimide; and the light-protected stirring conditions are a temperature of 22~25℃ and a time of 1.5~2.5h.

[0010] Optionally, the organic base is triethylamine or N,N-diisopropylethylamine; the ultrasonic dispersion time in step S3 is 8-10 min; the conditions for stirring after heating are that the temperature rises to 38-42℃ and magnetic stirring is carried out for 22-26 h under nitrogen protection.

[0011] Optionally, the separation of microbeads is carried out by centrifugation, wherein the centrifugation conditions are a rotation speed of 7000~9000 rpm and a time of 8~12 min.

[0012] Optionally, the cleaning process involves alternating between anhydrous N,N-dimethylformamide and acetone for 2-3 cycles.

[0013] Optionally, the drying is performed in a vacuum drying oven at 48-52°C for 5-7 hours.

[0014] To achieve the above objectives, the present invention also includes a method for preparing core-shell structured reflective microspheres for road marking paint, wherein the reflective microspheres have a low critical phase transition temperature of 30~40℃. The above-described technical solution of the present invention has at least the following beneficial effects: The reflective microspheres obtained by the technical solution provided by this invention exhibit a hydrated state when the ambient temperature is below the critical phase transition temperature (LCST). This hydration occurs due to the hydrophilic nature of the thermosensitive polymer molecular chains, creating a steric hindrance effect between the microspheres and maintaining a relatively large spacing between them. When the ambient temperature rises above the LCST, the thermosensitive polymer molecular chains undergo a drastic phase transition, dehydrating and shrinking, transforming from an extended chain shape into a hydrophobic spherical conformation. This results in a reduction in steric hindrance and a smaller spacing between the microspheres. This reversible change in the spacing between the microspheres directly alters the propagation path of light in the microsphere array, thereby adaptively optimizing the reflection efficiency of light at different incident angles. This achieves adaptive optimization of the reflective microspheres under varying temperatures and light angles, increasing the visibility of the reflective microspheres in complex climates. Attached Figure Description

[0015] Figure 1 Infrared spectra of the microbeads of Example 1 and Comparative Examples 1-3 of the present invention; Figure 2 The low critical phase transition temperature spectra of the microspheres in Example 1 and Comparative Examples 1-3 of this invention; Figure 3 This is a scanning electron microscope image of the activated core-shell fluorinated glass microspheres obtained in step S1 of Example 1 of the present invention; Figure 4 This is a scanning electron microscope image of the temperature-sensitive core-shell reflective microspheres obtained in Example 1 of the present invention.

[0016] In the figure: Fluorinated glass beads + KH-550 + PNIPAM represent Example 1, fluorinated glass beads + KH-550 represent Comparative Example 1, fluorinated glass beads represent Comparative Example 2, and ordinary glass beads represent Comparative Example 3. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will be described in conjunction with the accompanying drawings of the embodiments of the present invention. Figures 1-4 The technical solutions of the embodiments of the present invention will be clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0018] Example 1 This invention provides a method for preparing core-shell structured reflective microspheres for road marking paint, comprising the following steps: S1. Fluorinated glass microspheres with a refractive index of 1.95 were dispersed in ethanol and sonicated for 20 min. A silane coupling agent solution obtained by mixing γ-aminopropyltriethoxysilane with ethanol was added. The mass concentration of γ-aminopropyltriethoxysilane in the silane coupling agent solution was 5 wt%. After adding the silane coupling agent solution, the mixture was stirred for 30 min to form a stable suspension. The stable suspension was refluxed at 60 °C for 4 h. The surface of the fluorinated glass microspheres was functionalized by bonding between the amino group of silane and the hydroxyl group on the surface of the fluorinated glass microspheres, thus obtaining activated core-shell fluorinated glass microspheres.

[0019] S2. Dissolve poly(N-isopropylacrylamide) (PNIPAM) in 30 mL of anhydrous N,N-dimethylformamide (DMF), and then add N-hydroxysuccinimide (NHS) and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC·HCl) in sequence. Stir and activate at 25°C in the dark for 2 hours. At this time, the carboxyl groups at the end of PNIPAM are activated into active NHS esters, and the activated thermosensitive polymer solution is obtained.

[0020] S3. Disperse the activated core-shell fluorinated glass microspheres in 10 mL of DMF and sonicate for 10 min to obtain a microsphere suspension. Add the microsphere suspension dropwise to the activated thermosensitive polymer solution and add triethylamine. Heat the reaction system to 40 °C and magnetically stir under nitrogen protection for 24 h. After the reaction, separate the microspheres by centrifugation at 8000 rpm for 10 min. Wash the centrifuged microspheres three times with DMF and acetone alternately to remove physically adsorbed PNIPAM. Then dry them in a vacuum drying oven at 50 °C for 6 h to obtain thermosensitive core-shell reflective microspheres.

[0021] Example 2 This invention provides a method for preparing core-shell structured reflective microspheres for road marking paint, comprising the following steps: S1. Fluorinated glass microspheres with a refractive index of 1.97 were dispersed in ethanol and sonicated for 15 min. A silane coupling agent solution obtained by mixing γ-aminopropyltriethoxysilane with ethanol was added. The mass concentration of γ-aminopropyltriethoxysilane in the silane coupling agent solution was 4.5 wt%. After adding the silane coupling agent solution, the mixture was stirred for 25 min to form a stable suspension. The stable suspension was refluxed at 62 °C for 3.5 h. The surface of the fluorinated glass microspheres was functionalized by bonding between the amino group of silane and the hydroxyl group on the surface of the fluorinated glass microspheres, thus obtaining activated core-shell fluorinated glass microspheres.

[0022] S2. Dissolve poly(N-isopropylacrylamide) (PNIPAM) in 30 mL of anhydrous N,N-dimethylformamide (DMF), then add N-hydroxysuccinimide (NHS) and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC·HCl) sequentially. Stir and activate at 22°C in the dark for 2.5 hours. At this time, the carboxyl groups at the end of PNIPAM are activated into active NHS esters, resulting in an activated thermosensitive polymer solution.

[0023] S3. The activated core-shell fluorinated glass microspheres were dispersed in 10 mL of DMF and sonicated for 8 min to obtain a microsphere suspension. The microsphere suspension was added dropwise to the activated thermosensitive polymer solution, and triethylamine was added. The reaction system was heated to 38 °C and magnetically stirred for 26 h under nitrogen protection. After the reaction was completed, the microspheres were separated by centrifugation at 7000 rpm for 12 min. The microspheres obtained by centrifugation were washed twice with DMF and acetone alternately to remove the physically adsorbed PNIPAM. Then, they were dried in a vacuum drying oven at 52 °C for 5 h to obtain thermosensitive core-shell reflective microspheres.

[0024] Example 3 This invention provides a method for preparing core-shell structured reflective microspheres for road marking paint, comprising the following steps: S1. Fluorinated glass microspheres with a refractive index of 1.98 were dispersed in ethanol and sonicated for 25 min. A silane coupling agent solution obtained by mixing γ-aminopropyltriethoxysilane with ethanol was added. The mass concentration of γ-aminopropyltriethoxysilane in the silane coupling agent solution was 5.5 wt%. After adding the silane coupling agent solution, the mixture was stirred for 25 min to form a stable suspension. The stable suspension was refluxed at 58 °C for 4.5 h. The surface of the fluorinated glass microspheres was functionalized by bonding between the amino group of silane and the hydroxyl group on the surface of the fluorinated glass microspheres, thus obtaining activated core-shell fluorinated glass microspheres.

[0025] S2. Dissolve poly(N-isopropylacrylamide) (PNIPAM) in 30 mL of anhydrous N,N-dimethylformamide (DMF), then add N-hydroxysuccinimide (NHS) and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC·HCl) sequentially. Stir and activate at 24°C in the dark for 1.5 hours. At this time, the carboxyl groups at the end of PNIPAM are activated into active NHS esters, resulting in an activated thermosensitive polymer solution.

[0026] S3. The activated core-shell fluorinated glass microspheres were dispersed in 10 mL of DMF and sonicated for 9 min to obtain a microsphere suspension. The microsphere suspension was added dropwise to the activated thermosensitive polymer solution, and triethylamine was added. The reaction system was heated to 42 °C and magnetically stirred for 22 h under nitrogen protection. After the reaction was completed, the microspheres were separated by centrifugation at 9000 rpm for 8 min. The microspheres obtained by centrifugation were washed twice with DMF and acetone alternately to remove the physically adsorbed PNIPAM. Then, they were dried in a vacuum drying oven at 48 °C for 7 h to obtain thermosensitive core-shell reflective microspheres.

[0027] Comparative Example 1 Compared to Example 1, the only difference is the omission of steps S2 and S3. Fluorinated glass microspheres with a refractive index of 1.95 were dispersed in ethanol and sonicated for 20 min. A silane coupling agent solution obtained by mixing γ-aminopropyltriethoxysilane with ethanol was added. The mass concentration of γ-aminopropyltriethoxysilane in the silane coupling agent solution was 5 wt%. After adding the silane coupling agent solution, the mixture was stirred for 30 min to form a stable suspension. The stable suspension was refluxed at 60°C for 4 h. The surface of the fluorinated glass microspheres was functionalized through bonding between the amino groups of the silane and the hydroxyl groups on the surface of the fluorinated glass microspheres, resulting in activated core-shell fluorinated glass microspheres.

[0028] Comparative Example 2 Fluorinated glass microspheres with a refractive index of 1.95.

[0029] Comparative Example 3 Ordinary glass microspheres with a refractive index of 1.5.

[0030] The microbeads of Example 1 and Comparative Examples 1-3 were subjected to relevant detection, and the infrared spectra were obtained as follows: Figure 1 In the figure, fluorinated glass beads + KH-550 + PNIPAM represents Example 1, fluorinated glass beads + KH-550 represents Comparative Example 1, fluorinated glass beads represent Comparative Example 2, and ordinary glass beads represent Comparative Example 3.

[0031] Depend on Figure 1 As can be seen, the fluorinated glass beads in the examples achieved silane coupling agent modification and successfully grafted the thermosensitive polymer PNIPAM. Analysis is as follows: Infrared spectrum of ordinary glass beads: ~3450 cm⁻¹ -1 The broad and intense peak is due to the OH stretching vibration, originating from water molecules (H₂O) physically adsorbed on the glass surface or from silanol groups (Si-OH) within the glass network structure. This broad and strong peak is evidence of the glass's hygroscopic nature. ~1630 cm⁻¹ -1 The sharp, weak peak is due to the HOH bending vibration, with a peak at 3450 cm⁻¹. -1The peaks at ~1050 cm⁻¹ correspond to the bending vibration mode of adsorbed water molecules. These two peaks together confirm the presence of water. -1 The extremely strong and broad absorption band (the most prominent spectral feature) is due to the asymmetric stretching vibration of Si-O-Si, a characteristic vibration of the interconnected network of silicon-oxygen tetrahedra [SiO4]. Its broadening is a direct manifestation of the long-range disordered amorphous structure of glass. ~780cm -1 The intermediate absorption band is a symmetric stretching vibration of Si-O-Si, which is also one of the vibrational modes of the silicon-oxygen network framework. ~460cm -1 The broad absorption band is due to the bending vibration of O-Si-O or the rocking vibration of Si-O bonds, which reflects the deformation vibration of the silicon-oxygen tetrahedron itself and is another key characteristic of silicate materials.

[0032] Infrared spectrum of fluorinated glass beads: Compared to ordinary glass beads, fluorination results in the presence of Si-F bonds. Si-F characteristic peak: ~930 cm⁻¹ -1 At this point, the "fluorinated silicate glass" curve shows a distinct shoulder or bulge, while the "ordinary silicate glass" curve declines smoothly, which is the most direct evidence of the presence of fluorine. Main peak shift: The strongest absorption peak of "ordinary silicate glass" (Si-O-Si asymmetric stretching vibration) is located at ~1050 cm⁻¹. -1 The corresponding main peak of "fluorinated silicate glass" generally shifts to higher wavenumbers (blue shift), with the peak value moving to ~1100 cm⁻¹. -1 Nearby, and the intensity has decreased.

[0033] Infrared spectrum of fluorinated glass beads + silane coupling agent: Compared to fluorinated glass beads, surface modification with silane coupling agent (KH-550) results in the presence of characteristic absorption peaks of KH-550 molecules. The core principle is that the ethoxy group (-OCH2CH3) of KH-550 hydrolyzes to a silanol group (-Si-OH), which then undergoes a condensation reaction with the silanol groups (Si-OH) on the glass bead surface, forming a strong Si-O-Si covalent bond. This allows the organic functional groups of KH-550 (especially the amino group -NH2) to be firmly grafted onto the glass bead surface. After introducing KH-550, a peak appears at ~2930 cm⁻¹. -1 and ~2970 cm -1 The nearby absorption peaks are due to the asymmetric and symmetric stretching vibrations of the CH bonds. These originate from the -CH2- on the propyl chain and the terminal -CH3 in the KH-550 molecule. This is one of the most direct pieces of evidence for the successful grafting of the organic layer, as the inorganic fluorinated glass itself does not contain CH bonds. ~3300-3500 cm⁻¹ -1The broad peak variation in this region is attributed to the superposition of NH stretching vibrations and OH stretching vibrations. The superposition of the -NH2 group at the end of KH-550 (which produces a doublet, but is often broadened by hydrogen bonding) and the silanol groups on the glass surface results in a significantly enhanced peak in this region with a changed shape. ~1640 cm⁻¹ -1 The newly added or enhanced absorption peaks in the vicinity are attributed to the NH bending vibration. These are characteristic absorption peaks of primary amines (-NH2), indicating the presence of KH-550. ~800 cm⁻¹ -1 The nearby possible shoulder peak is attributed to the stretching vibration of the Si-C bond. Origin: Si-C bonds connecting organic functional groups and the inorganic silicon-oxygen framework in the KH-550 molecule. Confirmation of this peak provides strong evidence for chemical bonding (not just physical adsorption).

[0034] Infrared spectrum of fluorinated glass beads + silane coupling agent + thermosensitive polymer (PNIPAM): at ~1650 cm⁻¹ -1 A very sharp and strong absorption peak appears at ~1550 cm⁻¹, which is the C=O stretching vibration of the amide-I band. This covers the weak peak of the NH bending vibration in the original KH-550 band. -1 A novel absorption peak appears at ~2970 cm⁻¹, which is the amide-II band. The simultaneous appearance of these two "amide doublets" is strong evidence of successful PNIPAM grafting. -1 The CH stretching vibration peak at ~1385 cm⁻¹ is sharply enhanced due to the large number of isopropyl groups (-CH(CH₃)₂) on the PNIPAM side chain, each containing two methyl groups. At ~1385 cm⁻¹... -1 and ~1365 cm -1 A distinct "double peak" or shoulder peak will appear nearby, which is caused by the symmetrical bending vibration coupling split of the two methyl groups in the isopropyl group. This is a very characteristic "fingerprint" absorption of PNIPAM.

[0035] The low critical phase transition temperature (LCST) of the microbeads in Example 1 and Comparative Examples 1-3 was detected, and the results were obtained. Figure 2 .Depend on Figure 2 It is known that only the microspheres prepared in Example 1 exhibit temperature sensitivity, with a low critical phase transition temperature range of 30~40℃. If the temperature corresponding to 50% transmittance is taken as the LCST, its LCST is 33℃. That is, the reflective microspheres prepared in the embodiments of the present invention are temperature sensitive and can adapt to different temperatures and angles of light reflection efficiency in complex climates, thereby increasing the visibility of the reflective microspheres in complex climates.

[0036] The activated core-shell fluorinated glass microspheres obtained in step S1 of Example 1 and the temperature-sensitive core-shell reflective microspheres obtained in step S3 were respectively subjected to electron microscopy to obtain... Figure 3 and Figure 4 .

[0037] Figure 3 The surface of the fluorinated glass beads was successfully modified with KH-550. Figure 4 The modification of KH-550 fluorinated glass beads grafted with thermosensitive polymers was successful, with cross-linked network polymers on the surface.

[0038] The above are preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing core-shell structured reflective microbeads for road marking paint, characterized by, The method comprises the following steps: S1, dispersing fluorinated glass microbeads in ethanol and performing ultrasonic treatment, then adding a silane coupling agent solution, stirring to form a stable suspension, heating the stable suspension to react, bonding the amino group of the silane and the hydroxyl group on the surface of the fluorinated glass microbeads to realize surface functionalization of the fluorinated glass microbeads, and obtaining activated core-shell fluorinated glass microbeads; S2, dissolving a temperature-sensitive polymer in a solvent, sequentially adding a crosslinking agent and a carbodiimide condensing agent, stirring to activate in the dark, activating the carboxyl group at the end of the temperature-sensitive polymer into N-hydroxysuccinimide ester, and obtaining an activated temperature-sensitive polymer solution; S3, ultrasonic dispersion of the activated core-shell fluorinated glass microbeads in another solvent to obtain a microbead suspension, dropwise adding the microbead suspension to the activated temperature-sensitive polymer solution, adding an organic base, stirring after heating to react, separating the microbeads after the reaction is completed, washing, drying, and obtaining temperature-sensitive core-shell reflective microbeads.

2. The method for preparing core-shell structured reflective microbeads for road marking paint according to claim 1, characterized by, The silane coupling agent solution is obtained by dissolving γ-aminopropyl triethoxysilane in ethanol, and the mass concentration of γ-aminopropyl triethoxysilane in the silane coupling agent solution is 4.5-5.5 wt%.

3. The method for preparing core-shell structured reflective microspheres for road marking paint according to claim 1, characterized in that, The ultrasonic treatment time in the S1 step is 15-25 min; the refractive index of the fluorinated glass microbeads is greater than or equal to 1.95; the stirring time is 25-35 min; and the heating reaction of the stable suspension is refluxing at 58-62℃ for 3.5-4.5 h.

4. The method for preparing core-shell structured reflective microbeads for road marking paint according to claim 1, characterized in that, The temperature-sensitive polymer is poly(N-isopropyl acrylamide) or a copolymer thereof; the solvent is one of anhydrous N,N-dimethylformamide, dimethyl sulfoxide, and acetonitrile; the crosslinking agent is N-hydroxysuccinimide or N-hydroxysulfosuccinimide; the carbodiimide condensing agent is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride or dicyclohexyl carbodiimide; and the light-protected stirring condition is a temperature of 22-25℃ and a time of 1.5-2.5 h.

5. The method of producing core-shell structured reflective microbeads for road marking paint according to claim 1, characterized by, The organic base is triethylamine or N,N-diisopropylethylamine; the ultrasonic dispersion time in the S3 step is 8-10 min; and the stirring reaction condition after heating is a temperature of 38-42℃, magnetic stirring under nitrogen protection for 22-26 h.

6. The method of producing core-shell structured reflective microbeads for road marking paint according to claim 1, wherein The separation of the microbeads is achieved by centrifugation, and the centrifugation condition is a rotation speed of 7000-9000 rpm and a time of 8-12 min.

7. The method of producing core-shell structured reflective microbeads for road marking paint according to claim 1, wherein The washing is achieved by alternatingly using anhydrous N,N-dimethylformamide and acetone for 2-3 times.

8. The method of producing core-shell structured reflective microbeads for pavement marking paint according to claim 1, wherein The drying is achieved by using a vacuum drying oven, and the drying condition is a temperature of 48-52℃ and a time of 5-7 h.

9. The retroreflective microbeads for road marking paint prepared by the process according to any one of claims 1 to 8, characterized in that The low critical phase transition temperature of the reflective microbeads is 30-40℃.

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