Photochromic emulsion coating materials and methods for their preparation

Abstract

The application belongs to the technical field of coating materials, and discloses a photochromic emulsion coating material and a preparation method thereof, wherein the preparation method comprises the following steps: preparing a photochromic Pickering emulsion of modified nanocellulose-spiropyran; and polymerizing the photochromic Pickering emulsion, and then obtaining the photochromic emulsion coating material with the modified nanocellulose-spiropyran as a shell layer and a cavity inside after the oil phase is volatilized. The design of the hollow structure in the application can solve the problem that the color changing rate and fatigue resistance of the spiropyran cannot be simultaneously achieved, and the prepared photochromic emulsion coating material can form a film, and can overcome the influence of the compatibility with additives, thermal stability, acid-base stability and the like of the photochromic material in the actual application process, so that the substrate coating is endowed with better air permeability and moisture permeability while the light fatigue resistance, stability and light response rate of the spiropyran are ensured, and the use of other additives is further reduced.

Description

Technical Field

[0001] This invention belongs to the field of coating materials technology, specifically relating to a photochromic emulsion coating material and its preparation method. Background Technology

[0002] Photochromic emulsion coating materials are a type of functional coating that can undergo reversible color changes under light (especially ultraviolet light). They are usually in the form of water-based emulsions, which are easy to apply to textiles, paper, plastics or metal surfaces, and are widely used in smart textiles, anti-counterfeiting labels, decorative materials and responsive interface design.

[0003] The key function of photochromic emulsion coating materials comes from photochromic molecules, the most common of which is spiropyran. Spiropyran undergoes molecular structural isomerization under ultraviolet light irradiation, changing from a colorless closed-ring state to a colored open-ring state; when the light source is removed or exposed to visible light, it can reversibly return to its original state.

[0004] In the existing technology, the introduction of spiropyran is usually done through physical blending, that is, spiropyran is directly dispersed in the emulsion. The process is simple, but the durability is limited. Summary of the Invention

[0005] The purpose of this invention is to provide a photochromic emulsion coating material and its preparation method, so as to solve the technical problem of limited durability of existing photochromic emulsion coating materials.

[0006] The first aspect of the present invention provides a method for preparing a photochromic emulsion coating material, comprising: Step 1: Prepare a modified nanocellulose-spiropyran photochromic Pickering emulsion; Step 2: Polymerize the photochromic Pickering emulsion. After polymerization, allow the oil phase to evaporate to obtain a photochromic emulsion coating material with a modified nanocellulose-spiropyran shell and an internal cavity.

[0007] Preferably, step 1 specifically includes: Step 1.1: Dissolve 2 to 6 parts of modified nanocellulose in 40 to 50 parts of deionized water and disperse by ultrasonication to obtain an aqueous solution of modified nanocellulose; Step 1.2: Add 30 to 40 parts of silanized spiropyran dichloromethane solution with a mass concentration of 0.2 g / mL to 0.4 g / mL dropwise to the modified nanocellulose aqueous solution for emulsification to obtain modified nanocellulose-spiropyran photochromic Pickering emulsion.

[0008] Preferably, the modified nanocellulose is modified nanocellulose containing vinyl functional groups.

[0009] Preferably, the duration of ultrasonic dispersion is 2 min to 10 min; During emulsification, the speed of the emulsifier is 8000 rpm / min to 14000 rpm / min, and the emulsification time is 5 min to 18 min.

[0010] Preferably, step 2 specifically includes: The photochromic Pickering emulsion was added to a three-necked flask containing 4-10 parts of deionized water, heated to 75°C-80°C, and 1.0-2.0 parts of crosslinking agent and 3.0-4.0 parts of initiator were added dropwise. The mixture was kept warm and stirred for a preset time. After the dichloromethane evaporated, a photochromic emulsion coating material with a modified nanocellulose-spiropyran shell and an internal cavity was obtained.

[0011] Preferably, the crosslinking agent is ethylene glycol dimethacrylate, and the mass concentration of the crosslinking agent is 0.5% to 1.5%.

[0012] Preferably, the initiator is ammonium persulfate, and the mass concentration of the initiator is 3% to 7%.

[0013] Preferably, the preset duration is 60 min to 120 min.

[0014] A second aspect of the present invention provides a photochromic emulsion coating material, which is prepared using the above-described method for preparing photochromic emulsion coating materials.

[0015] The photochromic emulsion coating material and its preparation method of the present invention have the following advantages compared with the prior art: This invention uses modified nanocellulose-spiropyran as a Pickering stabilizer to prepare a photochromic emulsion coating material with a modified nanocellulose-spiropyran shell, spiropyran on the inner wall, and a hollow interior. On the one hand, this invention utilizes the high light transmittance and corrosion resistance of modified nanocellulose to block the influence of the external environment and protect the spiropyran; on the other hand, the hollow structure provides sufficient open and closed ring space for the spiropyran, reducing steric hindrance and maintaining the original advanced photoresponse characteristics of the spiropyran. The hollow structure design of this invention solves the problem of simultaneously achieving the color-changing rate and fatigue resistance of spiropyran. Furthermore, the prepared photochromic emulsion coating material can form a film, overcoming the influence of compatibility with additives, thermal stability, and acid-base stability on photochromic materials in practical applications. While ensuring the photofatigue resistance, stability, and photoresponse rate of spiropyran, it also imparts better air and moisture permeability to the substrate coating, further reducing the use of other additives. It shows good application prospects in leather, textiles, paper, coatings, and other fields, and can significantly increase the added value of products. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating the preparation method of the photochromic emulsion coating material according to an embodiment of the present invention.

[0017] Figure 2 This is a schematic diagram of the structure of the photochromic emulsion coating material according to an embodiment of the present invention.

[0018] Figure 3 (a) is a graph showing the absorbance change of silanized spiropyran under UV-Vis irradiation at different pH conditions in Example 1 of the present invention; (b) is a graph showing the absorbance change of photochromic emulsion coating material under UV-Vis irradiation at different pH conditions in Example 1 of the present invention.

[0019] Figure 4 This is a schematic diagram illustrating the stable cycling performance of the photochromic emulsion coating material as a fabric coating in Embodiment 2 of the present invention.

[0020] Figure 5 In the diagram, (a) represents a blank fabric F0 and a cotton fabric F0 coated with the photochromic emulsion coating material of Example 3 of this invention. CPHs (a) shows the results of the air permeability test; (b) shows the difference between the blank fabric F0 and the cotton fabric F0 coated with the photochromic emulsion coating material of Example 3 of this invention. CPHs The results of the moisture permeability test are shown in the figure. Detailed Implementation

[0021] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0022] The first aspect of this invention provides a method for preparing a photochromic emulsion coating material, such as... Figure 1 As shown, it includes: Step 1: Prepare the modified nanocellulose-spiropyran photochromic Pickering emulsion, specifically as follows: Step 1.1: Dissolve 2 to 6 parts of modified nanocellulose in 40 to 50 parts of deionized water and disperse by ultrasonication to obtain an aqueous solution of modified nanocellulose. For example, the amount of modified nanocellulose can be 2, 3, 4, 5, or 6 parts; the amount of deionized water can be 40, 45, or 50 parts, etc.

[0023] In this embodiment of the invention, ultrasonic dispersion specifically involves ultrasonic dispersion for 2 to 10 minutes under the action of a cell disruptor.

[0024] The modified nanocellulose mentioned above is modified nanocellulose containing vinyl functional groups.

[0025] Step 1.2: Slowly add 30 to 40 parts of a silanized spiropyran dichloromethane solution with a mass concentration of 0.2 g / mL to 0.4 g / mL to the modified nanocellulose aqueous solution for emulsification, thereby achieving grafting of modified nanocellulose and silanized spiropyran to obtain a photochromic Pickering emulsion of modified nanocellulose-spiropyran. Exemplarily, the mass concentration of the silanized spiropyran dichloromethane solution can be 0.2 g / mL, 0.3 g / mL, 0.4 g / mL, etc., preferably 0.3 g / mL; the amount of the silanized spiropyran dichloromethane solution can be 30 parts, 35 parts, 40 parts, etc.

[0026] After grafting modified nanocellulose with silanized spiropyran, the hydrophobicity of the modified nanocellulose is greatly improved due to the hydrophobicity of spiropyran. The amphiphilic properties and Pickering stability of the modified nanocellulose-spiropyran are also greatly enhanced.

[0027] The structural formula of silanized spiropyran is as follows:

[0028] In step 1.2 above, emulsification is specifically performed using an emulsifier with a rotation speed of 8000 rpm / min to 14000 rpm / min for a duration of 5 min to 18 min.

[0029] Step 2: Polymerize the photochromic Pickering emulsion obtained in Step 1. After polymerization, allow the oil phase to evaporate to obtain the following: Figure 2 The modified nanocellulose-spiropyran shown is a photochromic emulsion coating material with a shell and an internal cavity, specifically: The photochromic Pickering emulsion obtained in step 1 is added to a 250 mL three-necked flask containing 4 to 10 parts of deionized water. The temperature is raised to 75°C to 80°C, preferably 75°C. Then, 1.0 to 2.0 parts of crosslinking agent and 3.0 to 4.0 parts of initiator are added dropwise to the three-necked flask. The mixture is kept at this temperature and stirred for a preset time. After the dichloromethane evaporates, a photochromic emulsion coating material with a modified nanocellulose-spiropyran shell and an internal cavity is obtained. For example, the amount of deionized water used in this step can be 4, 5, 6, 7, 8, 9, or 10 parts; the amount of crosslinking agent can be 1 or 2 parts; and the amount of initiator can be 3 or 4 parts.

[0030] To ensure the polymerization efficiency of the photochromic Pickering emulsion, the photoresponsiveness of spiropyran, and the stability of the resulting emulsion, the crosslinking agent in this embodiment of the invention is preferably ethylene glycol dimethacrylate, and the mass concentration of the crosslinking agent is 0.5% to 1.5%. For example, the mass concentration of the crosslinking agent can be 0.5%, 1%, 1.5%, etc. Crosslinking agents within the above dosage range can avoid the problems of sparse network and easy spiropyran leakage due to insufficient dosage, and the problem of segment rigidity due to excessive dosage. Further, the initiator used in this embodiment of the invention is ammonium persulfate, and the mass concentration of the initiator is 3% to 7%. For example, the mass concentration of the initiator can be 3%, 4%, 5%, 6%, 7%. Initiators within this dosage range can avoid the problems of incomplete polymerization, wide emulsion particle size distribution, and poor stability caused by insufficient initiator dosage, and the problems of explosive polymerization and emulsion demulsification caused by excessive initiator dosage.

[0031] In step 2 of this embodiment, the preset time for heat preservation and stirring is 60 min to 120 min to ensure that the monomer conversion rate is >95%.

[0032] A second aspect of the present invention provides a photochromic emulsion coating material, which is prepared using the above-described method for preparing photochromic emulsion coating materials.

[0033] The performance of the photochromic emulsion coating material of the present invention will be described in detail below with more specific embodiments.

[0034] Example 1 Two parts of modified nanocellulose containing vinyl functional groups were dissolved in 50 parts of deionized water and ultrasonically dispersed for 4 min using a cell disruptor to obtain an aqueous solution of modified nanocellulose.

[0035] 40 parts of a 0.2 g / mL silanized spiropyran dichloromethane solution were added dropwise to the modified nanocellulose aqueous solution, and then emulsified using an emulsifier at 12000 rpm / min for 5 min to obtain a modified nanocellulose-spiropyran photochromic Pickering emulsion.

[0036] The photochromic Pickering emulsion was added to a 250 mL three-necked flask containing 4 parts of deionized water, and the temperature was raised to 75°C. Then, 1.0 part of 0.5% ethylene glycol dimethacrylate and 3.0 parts of 3% ammonium persulfate were added dropwise to the three-necked flask. The mixture was kept warm and stirred for 60 min. After the dichloromethane evaporated, a photochromic emulsion coating material with a modified nanocellulose-spiropyran shell and an internal cavity was obtained.

[0037] To verify the performance of the photochromic emulsion coating material prepared in the embodiments of the present invention, its absorbance under UV-Vis irradiation at different pH conditions was compared with that of silanized spiropyran. The results are as follows. Figure 3 As shown. Figure 3 As shown in (a), silanized spiropyran exhibits good photochromic properties at pH=6. However, under acidic and alkaline conditions, the color and absorbance do not change significantly after UV-vis irradiation. In contrast, the photochromic emulsion coating material prepared in this embodiment of the invention, when placed in three environments (pH=1, 6, and 13) and subjected to different light irradiations, shows significant changes in both color and absorbance, such as... Figure 3 As shown in (b), the photochromic emulsion coating material prepared in this embodiment of the invention can effectively isolate the influence of the external environment on the grafted silanized spiropyran, while the light transmittance of the shell material allows the silanized spiropyran to maintain good photoresponsiveness.

[0038] Example 2 Four parts of modified nanocellulose containing vinyl functional groups were dissolved in 45 parts of deionized water and ultrasonically dispersed for 6 min under the action of a cell disruptor to obtain an aqueous solution of modified nanocellulose.

[0039] 40 parts of a 0.3 g / mL silanized spiropyran dichloromethane solution were added dropwise to a modified nanocellulose aqueous solution, and then emulsified using an emulsifier at 12000 rpm / min for 5 min to obtain a modified nanocellulose-spiropyran photochromic Pickering emulsion.

[0040] The photochromic Pickering emulsion was added to a 250 mL three-necked flask containing 7 parts of deionized water, and the temperature was raised to 75°C. Then, 1.0 part of 0.5% ethylene glycol dimethacrylate and 3.0 parts of 3% ammonium persulfate were added dropwise to the three-necked flask. The mixture was kept warm and stirred for 60 min. After the dichloromethane evaporated, a photochromic emulsion coating material with a modified nanocellulose-spiropyran shell and an internal cavity was obtained.

[0041] The prepared photochromic emulsion coating material was used as a fabric coating, and a reversible color-changing cycle test was conducted under ultraviolet and visible light. The fabric sample was irradiated under ultraviolet (UV) light for a period of time until the color no longer changed, at which point its K / S value was measured. Then, it was irradiated under visible light (Vis) for a certain period of time, and its K / S value was measured again when the color no longer changed; this constituted one cycle of reversible color change. The above operation was repeated, and the K / S values ​​of multiple cycles were recorded. The results are shown below. Figure 4 As shown, according to Figure 4It can be confirmed that the photochromic emulsion coating material has excellent reversible photochromic properties; after 50 reversible color-changing cycles, K / S only decreases by 6%.

[0042] Example 3 Six parts of modified nanocellulose containing vinyl functional groups were dissolved in 50 parts of deionized water and ultrasonically dispersed for 8 min under the action of a cell disruptor to obtain an aqueous solution of modified nanocellulose.

[0043] 35 parts of a 0.4 g / mL silanized spiropyran dichloromethane solution were added dropwise to the modified nanocellulose aqueous solution, and then emulsified using an emulsifier at 12000 rpm / min for 5 min to obtain a modified nanocellulose-spiropyran photochromic Pickering emulsion.

[0044] The photochromic Pickering emulsion was added to a 250 mL three-necked flask containing 3 parts of deionized water, and the temperature was raised to 75°C. Then, 2.0 parts of 0.5% ethylene glycol dimethacrylate and 4.0 parts of 3% ammonium persulfate were added dropwise to the three-necked flask. The mixture was kept warm and stirred for 60 min. After the dichloromethane evaporated, a photochromic emulsion coating material with a modified nanocellulose-spiropyran shell and an internal cavity was obtained.

[0045] The embodiments of the present invention respectively tested blank fabric F0 and cotton fabric F0 coated with photochromic emulsion coating material. CPHs The air permeability and moisture permeability were tested, and the results are as follows: Figure 5 As shown, according to Figure 5 (a) indicates that the air permeability of the photochromic cotton fabric is slightly lower than that of the uncoated blank fabric. The photochromic emulsion coating material prepared in this embodiment of the invention forms a coating with uniform channels on the fabric surface, which promotes the air permeability of the fabric. Figure 5 (b) indicates that the photochromic cotton fabric still maintains good moisture permeability. Since the shell material of the photochromic emulsion coating is nanocellulose, and the surface of the cotton fabric is also composed of cellulose macromolecules, it has a strong adsorption capacity for water vapor. Therefore, the moisture permeability of the photochromic cotton fabric can still be maintained at 3000 g / d*m. 2 The above is not significantly different from blank fabric.

[0046] In this embodiment of the invention, a modified nanocellulose aqueous solution is used as the aqueous phase and a dichloromethane solution is used as the oil phase. During the emulsification process, a silanized spiropyran solution is added dropwise. The silanized groups are hydrolyzed to form silanol groups, which then condense with the hydroxyl groups on the modified nanocellulose to prepare a modified nanocellulose-spiropyran-stabilized photochromic Pickering emulsion. The photochromic Pickering emulsion is then polymerized, and the dichloromethane is volatilized to obtain a nanocellulose-based photochromic emulsion coating material with a hollow structure.

[0047] This invention uses modified nanocellulose-spiropyran as a Pickering stabilizer to prepare a photochromic emulsion coating material with a modified nanocellulose-spiropyran shell, spiropyran on the inner wall, and a hollow interior. On the one hand, this invention utilizes the high light transmittance and corrosion resistance of modified nanocellulose to block the influence of the external environment and protect the spiropyran; on the other hand, the hollow structure provides sufficient open and closed ring space for the spiropyran, reducing steric hindrance and maintaining the original advanced photoresponse characteristics of the spiropyran. The hollow structure design of this invention solves the problem of simultaneously achieving the color-changing rate and fatigue resistance of spiropyran. Furthermore, the prepared photochromic emulsion coating material can form a film, overcoming the influence of compatibility with additives, thermal stability, and acid-base stability on photochromic materials in practical applications. While ensuring the photofatigue resistance, stability, and photoresponse rate of spiropyran, it also imparts better air and moisture permeability to the substrate coating, further reducing the use of other additives. It shows good application prospects in leather, textiles, paper, coatings, and other fields, and can significantly increase the added value of products.

[0048] The above descriptions are merely a few embodiments of the present invention and are not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any modifications or alterations made by those skilled in the art without departing from the scope of the technical solution of the present invention using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a photochromic emulsion coating material, characterized in that, include: Step 1: Prepare a modified nanocellulose-spiropyran photochromic Pickering emulsion; Step 2: Polymerize the photochromic Pickering emulsion. After polymerization, allow the oil phase to evaporate to obtain a photochromic emulsion coating material with a modified nanocellulose-spiropyran shell and an internal cavity.

2. The method for preparing the photochromic emulsion coating material according to claim 1, characterized in that, Step 1 is as follows: Step 1.1: Dissolve 2 to 6 parts of modified nanocellulose in 40 to 50 parts of deionized water and disperse by ultrasonication to obtain an aqueous solution of modified nanocellulose; Step 1.2: Add 30 to 40 parts of silanized spiropyran dichloromethane solution with a mass concentration of 0.2 g / mL to 0.4 g / mL dropwise to the modified nanocellulose aqueous solution for emulsification to obtain modified nanocellulose-spiropyran photochromic Pickering emulsion.

3. The method for preparing the photochromic emulsion coating material according to claim 2, characterized in that, The modified nanocellulose is a modified nanocellulose containing vinyl functional groups.

4. The method for preparing the photochromic emulsion coating material according to claim 2, characterized in that, The duration of ultrasonic dispersion is 2 min to 10 min; During emulsification, the speed of the emulsifier is 8000 rpm / min to 14000 rpm / min, and the emulsification time is 5 min to 18 min.

5. The method for preparing the photochromic emulsion coating material according to claim 2, characterized in that, Step 2 is as follows: The photochromic Pickering emulsion was added to a three-necked flask containing 4-10 parts of deionized water, heated to 75°C-80°C, and 1.0-2.0 parts of crosslinking agent and 3.0-4.0 parts of initiator were added dropwise. The mixture was kept warm and stirred for a preset time. After the dichloromethane evaporated, a photochromic emulsion coating material with a modified nanocellulose-spiropyran shell and an internal cavity was obtained.

6. The method for preparing the photochromic emulsion coating material according to claim 5, characterized in that, The crosslinking agent is ethylene glycol dimethacrylate, and the mass concentration of the crosslinking agent is 0.5% to 1.5%.

7. The method for preparing the photochromic emulsion coating material according to claim 5, characterized in that, The initiator is ammonium persulfate, and the mass concentration of the initiator is 3% to 7%.

8. The method for preparing the photochromic emulsion coating material according to claim 5, characterized in that, The preset duration is 60 min to 120 min.

9. A photochromic emulsion coating material, characterized in that, It was prepared using the preparation method of the photochromic emulsion coating material according to any one of claims 1-8.

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