Composite supercritical fluid coating and preparation method thereof

Abstract

The invention belongs to the technical field of coatings, and particularly relates to a composite supercritical fluid coating and a preparation method thereof. The composite supercritical fluid coating is obtained by dissolving a polymer coating into a composite supercritical fluid, the composite supercritical fluid is obtained by adding substances with specific properties on the basis of supercritical carbon dioxide; the specific substance is specifically selected from perfluoroalkane, perfluoroether, siloxane, aliphatic ether, tertiary amine, alkynol, alkynediol and the like. According to the present invention, the specific structure substance is introduced, such that the dissolving property of the single supercritical carbon dioxide can be significantly changed, and the selectivity of the fluid can be increased, such that the solubility of the polymer coating material with the large polarity in the supercritical fluid can be effectively increased, and the more polar polymers can be effectively dissolved in the supercritical carbon dioxide; and the application range of the supercritical fluid is expanded.

Description

Technical Field

[0001] The invention belongs to the technical field of coatings, and in particular relates to a composite supercritical fluid coating and a preparation method thereof. Background Art

[0002] Conventional solvent-based coatings are mainly composed of film-forming materials and organic solvents. The film-forming materials contain polymers, additives and other ingredients, which are used for bonding and film formation, while the organic solvents are used to dilute the coating to achieve the viscosity required for construction. However, during the construction of this type of coating, the fast-volatile organic solvents will quickly evaporate into the atmosphere, which not only poses a direct threat to human health, but also pollutes the environment. In addition, the remaining slow-volatile organic solvents and co-solvents will continue to evaporate slowly with changes in temperature, and a small amount of residual solvents will dry and form a film on the surface of the object. However, more than two-thirds of these volatile organic compounds (VOCs) will be released into the air.

[0003] Supercritical fluid coating systems are very different from conventional systems. Supercritical CO2 is currently the most widely used and studied supercritical fluid, and it has unique solvent properties. 30% to 70% of organic solvents in traditional coatings can be replaced by CO2. However, since CO2 is a weak Lewis acid, its polarizability is the smallest among all hydrocarbons except methane. It can only show very weak polarity under high pressure. This limits the solubility of supercritical fluids, and can only produce weak interaction forces with polymers with relatively large polarity, and the solubility is very small, so in this regard, the application of supercritical fluid coatings is limited.

[0004] Therefore, it is necessary to study a new type of supercritical fluid system that can effectively replace the organic solvents in traditional coatings, reduce the harm to human body and the environment, and achieve good solubility properties for various polymers. Summary of the invention

[0005] The purpose of the present invention is to provide an environmentally friendly composite supercritical fluid coating with excellent solubility and a preparation method thereof.

[0006] The composite supercritical fluid coating proposed by the present invention is obtained by dissolving a polymer coating in a composite supercritical fluid. The composite supercritical fluid is obtained by adding a specific substance having the following characteristics to supercritical carbon dioxide: ① the structure contains a basic group with low polarity or low electron donation, so it can have an affinity with CO2; ② such substance contains a group that is easy to produce hydrogen bonding or weak hydrogen bonding, which can effectively increase the solubility of the polymer containing the corresponding hydrogen bonding group in the supercritical fluid (hydrogen bonding is a strong intermolecular force, which can produce intermolecular hydrogen bonding forces under supercritical conditions, and greatly affect the dissolution of the supercritical fluid); ③ compared with organic solvents, it has lower reaction activity; ④ after CO2 reaches a supercritical state, such substance can also reach a supercritical state; the specific substance is specifically selected from perfluoroalkanes, perfluoroethers, siloxanes, fatty ethers, tertiary amines, alkynols and acetylenic diols, etc., and mainly contains oxygen and nitrogen atom groups.

[0007] In the present invention, the mass ratio of supercritical carbon dioxide to the specific substance in the composite supercritical fluid is 0.5-5; preferably, the mass ratio of the two is 2 / 3-3 / 2.

[0008] In the present invention, the mass ratio of the polymer coating to the composite supercritical fluid in the composite supercritical fluid coating is 2-50, preferably 3-20.

[0009] In the present invention, the polymer coating is preferably a fluorocarbon polymer coating.

[0010] In the present invention, the specific substance is preferably tetrafluorodichloroethane.

[0011] The present invention also provides a method for preparing a composite supercritical fluid coating, which involves the use conditions of the composite supercritical fluid, and the specific steps are:

[0012] (1) According to the proportion of each component material, the polymer coating is placed in a high-pressure phase equilibrium device with a variable volume and a glass observation window; CO2 and a specific substance are injected using a booster pump;

[0013] (2) using a phase equilibrium device to adjust the system temperature and pressure so that CO2 and the specific substance simultaneously reach a supercritical state to form a composite supercritical fluid; waiting for the polymer coating to be completely dissolved in the composite supercritical fluid to form a homogeneous system;

[0014] (3) Gradually increase the volume of the container to gradually reduce the system pressure. When the pressure drops to a certain level, the sample precipitates and turbidity is observed. The pressure and temperature of the turbidity point are recorded to obtain a composite supercritical fluid coating with new solubility properties.

[0015] In the present invention, the polymer coating can be a fluorocarbon polymer coating. For example, the weight fraction ratio of the fluorocarbon polymer coating and the composite supercritical fluid is controlled at 2:1; the weight fraction ratio of carbon dioxide and the specific substance tetrafluorodichloroethane in the composite supercritical fluid is controlled at 3:2. Two parts of the fluorocarbon polymer coating are placed in a phase equilibrium device, and then one part of a gas containing 60% carbon dioxide and 40% of the specific substance is introduced into the phase equilibrium device. The booster pump is operated to pressurize to 15Mpa, and the heater heats the phase equilibrium device to 45°C. At this time, a composite supercritical fluid is formed and maintained for 2 hours. By changing the volume of the phase equilibrium device, when the pressure drops to 8Mpa and the temperature is 39°C, a composite supercritical fluid coating with new solubility properties is obtained.

[0016] The present invention proposes a novel solution to the problems of low cohesive energy density and weak solvation ability of supercritical carbon dioxide in the prior art. In the existing supercritical carbon dioxide technology, due to its low cohesive energy density and weak solvation ability, only a small part of molecules with weak polarity can be dissolved in carbon dioxide. This limits the application scope of supercritical carbon dioxide.

[0017] In order to solve this problem, the present invention introduces a substance with a specific structure. The addition of this substance can significantly change the solubility of a single supercritical carbon dioxide and increase the selectivity of the fluid. In this way, the present invention successfully improves the solubility of supercritical carbon dioxide, making it better able to dissolve polymers with greater polarity.

[0018] In addition, this specific substance can effectively enhance polarity and increase the solubility of larger polymers in supercritical fluids, and also enable more polar polymers to be effectively dissolved in supercritical carbon dioxide, thereby expanding the application range of supercritical fluids.

[0019] Furthermore, this improvement of the present invention further improves the supercritical fluid coating system. By reducing the proportion of organic solvents, VOC (volatile organic compound) emissions are reduced, greatly reducing environmental pollution. This improvement is not only beneficial to environmental health, but also to human health.

[0020] The method provided by the present invention can significantly improve the solubility and fluid selectivity of supercritical carbon dioxide, while also reducing the proportion of organic solvents and reducing environmental pollution. This method is expected to play an important role in future industrial applications. DETAILED DESCRIPTION

[0021] The present invention is further described below by way of examples.

[0022] Embodiment 1:

[0023] The composite supercritical fluid in a composite supercritical fluid coating A comprises the following components by weight fraction:

[0024] carbon dioxide 60 Tetrafluoroethylene dichloride 40

[0025] The weight fraction ratio of the fluorocarbon polymer coating (containing 10% of a diluent) to the composite supercritical fluid is 2:1, and the mass fraction ratio of carbon dioxide to tetrafluoroethylene dichloroethane in the composite supercritical fluid is 3:2.

[0026] Two parts of fluorocarbon polymer coatings were placed in a phase equilibrium device, and then one part of gas containing 60% carbon dioxide and 40% of a specific substance was introduced into the phase equilibrium device and pressurized to 15 MPa by a booster pump. The temperature of the phase equilibrium device was raised to 45°C by a heater to form a composite supercritical fluid. After maintaining for 2 hours, by changing the volume of the phase equilibrium device, when the pressure dropped to 8 MPa and the temperature was 39°C, a composite supercritical fluid coating A with new solubility properties was obtained.

[0027] Embodiment 2:

[0028] The composite supercritical fluid in a composite supercritical fluid coating B comprises the following components by weight fraction:

[0029] carbon dioxide 50 Tetrafluoroethylene dichloride 50

[0030] The weight fraction ratio of the fluorocarbon polymer coating (containing 10% of a diluent) to the composite supercritical fluid is 3:1, and the weight fraction ratio of the carbon dioxide to the characteristic substance in the composite supercritical fluid is 1:1.

[0031] Three parts of fluorocarbon polymer coatings were placed in a phase equilibrium device, and then one part of a gas containing 50% carbon dioxide and 50% tetrafluorodichloroethane was introduced into the phase equilibrium device and pressurized to 15 MPa by a booster pump. The temperature of the phase equilibrium device was raised to 45°C by a heater to form a composite supercritical fluid. After maintaining for 2 hours, by changing the volume of the phase equilibrium device, when the pressure dropped to 8 MPa and the temperature was 39°C, a composite supercritical fluid coating B with new solubility properties was obtained.

[0032] The fluorocarbon polymer composite supercritical fluid coating and the fluorocarbon polymer coating under the two conditions are sprayed by a spray gun with the same aperture.

[0033] Adhesion is tested using the crosshatch method: 6 parallel cuts are made in the coating and another 6 parallel cuts are made perpendicular to the first cuts, all loose film fragments are removed and the cut areas are visually inspected. Comparing this to the six-level grading scale, the performance of the test depends mainly on the adhesion of the coating to the upper layer or substrate.

[0034] Level 0: The coating breaks on the substrate surface and has no adhesion, so it is usually not used.

[0035] Level 1: Suitable for dry indoor walls with less wear and tear.

[0036] Level 2: Suitable for indoor and outdoor walls and indoor floors that are subject to more wear and tear.

[0037] Level 3: Suitable for floors and steel structures that are subject to severe mechanical and manual wear.

[0038] Level 4: Suitable for building structures in harsh environments such as ocean, chemical, and heavy industries.

[0039] The film thickness was measured using a TT230 coating thickness gauge from Juechang Precision Measuring Instruments (Shanghai) Co., Ltd.

[0040] The paint coverage is calculated by the area that can be sprayed with the same 1 liter of paint.

[0041] The number of pinholes is determined by visually inspecting the paint surface and counting the number of small holes on the paint surface of 0.5m*0.5m.

[0042] name Solvent content Film thickness Paint rate Number of pinholes Adhesion Fluorocarbon polymer coating 35％ 42nm 42％ 10 Level 2 Fluorocarbon polymer composite supercritical fluid coating A 10％ 63nm 65％ 9 Level 2 Fluorocarbon polymer composite supercritical fluid coating B 10％ 60nm 51％ 10 Level 2

[0043] It can be seen from the above table that under the condition of reducing the solvent by 25%, the coating rate of fluorocarbon polymer composite supercritical fluid coating is significantly higher than that of ordinary fluorocarbon polymer spray coating. The increase in film thickness and coating rate indicates that the utilization rate of the coating is also greatly improved, which helps to reduce the generation of paint residue and hazardous waste.

Claims

1. A composite supercritical fluid coating, characterized in that: The composite supercritical fluid is obtained by dissolving a polymer coating in a composite supercritical fluid. The composite supercritical fluid is obtained by adding a specific substance having the following properties to supercritical carbon dioxide: ① the structure contains a basic group with low polarity or low electron donation effect, which can produce affinity with CO2; ② the substance contains a group that is easy to produce hydrogen bonding or weak hydrogen bonding, which can effectively increase the solubility of the polymer containing the corresponding hydrogen bonding group in the supercritical fluid; ③ compared with organic solvents, it has lower reaction activity; ④ after CO2 reaches the supercritical state, it can also reach the supercritical state; the specific substance is selected from perfluoroalkanes, perfluoroethers, siloxanes, fatty ethers, tertiary amines, acetylenic alcohols and acetylenic diols.

2. The composite supercritical fluid according to claim 1, characterized in that: The mass ratio of the supercritical carbon dioxide to the specific substance is 0.5-5; the mass ratio of the polymer coating to the composite supercritical fluid is 2-50.

3. The composite supercritical fluid according to claim 2, characterized in that: The mass ratio of the supercritical carbon dioxide to the specific substance is 2 / 3-3 / 2; the mass ratio of the polymer coating to the composite supercritical fluid is 3-20.

4. The composite supercritical fluid according to claim 1, 2 or 3, characterized in that: The polymer coating is a fluorocarbon polymer coating; and the specific substance is tetrafluoroethylene dichloroethane.

5. The method for preparing the composite supercritical fluid coating according to claim 1, 2, 3 or 4, characterized in that: The specific steps are: (1) According to the proportion of each component material, the polymer coating is placed in a high-pressure phase equilibrium device with a variable volume and a glass observation window; CO2 and a specific substance are injected using a booster pump; (2) Using a phase equilibrium device to adjust the system temperature and pressure, so that CO2 and the specific substance simultaneously reach a supercritical state to form a composite supercritical fluid; the polymer coating is completely dissolved in the composite supercritical fluid to form a homogeneous system; (3) The volume of the container is gradually increased to gradually reduce the system pressure. When the pressure is reduced to a certain level, the sample precipitates and turbidity is observed. The pressure and temperature of the turbidity point are recorded to obtain a composite supercritical fluid coating with new solubility properties.