A supercritical carbon dioxide spraying method controlled by viscosity

Abstract

This invention discloses a viscosity-controlled supercritical carbon dioxide spraying method, belonging to the field of industrial resin spraying. The core technology of this method is to control the spraying quality by adjusting the viscosity of the supercritical carbon dioxide and coating mixture—the sole factor. Specifically, a target viscosity value for the mixture is set, and the viscosity calculation model in the viscosity control module calculates the specific target values ​​for the temperature, pressure, and component ratios of both the supercritical carbon dioxide and the coating at that set target viscosity value. The system is then controlled in real-time according to the target values. After the target viscosity value is reached, a spraying test is conducted, and the target viscosity value of the mixture is readjusted based on the spraying quality until the spraying quality is satisfactory. This invention achieves high-quality, low-cost, low-consumption, continuous, and high-efficiency supercritical carbon dioxide spraying by controlling the outlet viscosity of the mixed coating.

Description

Technical Field

[0001] This invention belongs to the field of industrial resin spraying and is a supercritical carbon dioxide spraying method with viscosity control. Background Technology

[0002] Paints and coatings sprayed onto workpiece surfaces can provide functions such as corrosion protection, water resistance, decoration, and insulation. The coating industry uses a large amount of volatile organic compounds (VOCs). These not only produce photochemical smog and damage the ozone layer, but also have a distinctive odor that can affect human mucous membranes and skin. Prolonged exposure can lower the body's immunity, damage the hematopoietic system, and even cause cancer.

[0003] Supercritical CO2 spraying technology was first researched by Union Carbide in the United States. Among them, patent application number: US133068, first proposed that supercritical carbon dioxide can replace organic solvents in the field of spraying; patent number: US5027742, put supercritical carbon dioxide into practice in spraying equipment; patent number: US5057342, proposed that supercritical carbon dioxide can be used as a diluent to spray high-level sprays. However, there are still many problems to be solved for supercritical carbon dioxide spraying.

[0004] Subsequently, domestic patents related to process spraying were all based on spraying processes and equipment for specific occasions. In order to reduce the emission of organic solvents, environmentally friendly coatings such as water-based coatings and water-based coatings were proposed, but due to their great limitations in use, they failed to be promoted. Based on supercritical carbon dioxide spraying technology, China has only recently begun to develop several patents. Patent application number CN201721789936.2 proposes using liquid carbon dioxide as a diluent for coatings, replacing existing organic solvents. Patent application number CN201811465806.2 applies supercritical carbon dioxide spraying to specific production processes, improving spraying equipment. Patent application number CN201810877540.6 proposes using ionic liquids as co-solvents to enhance the solubility of carbon dioxide in coatings. Patent application number CN202020267125.1 automatically mixes coatings by controlling the opening of regulating valves, meeting the industrialization needs of spraying technology. Patent application number CN202022036535.8 proposes a supercritical carbon dioxide spraying system suitable for high-solids-content coatings and capable of continuous high-pressure spraying. Patent application number CN202120192571.5 proposes using a control box to operate the system, reducing workload. The aforementioned patents continuously improve the supercritical carbon dioxide spraying process and equipment, but they do not address the quality of supercritical carbon dioxide spraying. The question of how to achieve the required spraying quality remains unresolved, and no one has proposed controlling viscosity to ensure spraying quality. Typically, under individual spraying conditions, the temperature, pressure, and component ratio of the mixed coating outlet are adjusted through numerous experiments to ensure the required spraying quality. However, research indicates that the aforementioned supercritical carbon dioxide spraying patents still suffer from substandard spraying quality, high coating consumption, and high costs. Furthermore, each spraying condition requires extensive experimental adjustments, resulting in a large workload and significant expenditure of manpower and resources. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a viscosity-controlled supercritical carbon dioxide spraying method. This method establishes viscosity as the sole factor controlling spraying quality. A viscosity control module is used to control the entire supercritical carbon dioxide spraying system. Controllable viscosity at the outlet of the mixed coating indicates that the required spraying quality is achieved, thus realizing high-quality, continuous, low-cost, and low-consumption continuous supercritical carbon dioxide spraying. Furthermore, this invention is applicable to various spraying conditions, greatly enhancing the applicability of supercritical carbon dioxide spraying.

[0006] The technical solution of the present invention is as follows:

[0007] A viscosity-controlled supercritical carbon dioxide spraying method is characterized by controlling the spraying quality by adjusting the viscosity of the supercritical carbon dioxide and coating mixture as the sole factor. The viscosity of the supercritical carbon dioxide and coating mixture determines the fluid flowability, droplet size, and dispersion performance, and the fluid flowability and dispersion are key factors in determining the surface spraying quality.

[0008] Specifically, this means: setting a target viscosity value for the mixture, and under a supercritical carbon dioxide atmosphere, using the viscosity calculation model in the viscosity control module to calculate the specific target values ​​for various indicators of the supercritical carbon dioxide and coating at this set target viscosity value. These indicators include the temperature, pressure, and component ratio of the supercritical carbon dioxide and coating, respectively. Then, the system is controlled in real time based on the specific target values ​​of each indicator. After the specific target values ​​are reached, a spraying test is conducted, and the target viscosity value of the mixture is readjusted based on the quality of the spraying until the spraying quality is qualified.

[0009] Furthermore, the viscosity calculation model is based on an empirical formula derived from precise experiments on the viscosity of multi-component mixed coatings under complex working conditions. Since the viscosity of the mixed coating is directly related to temperature, pressure, carbon dioxide, and the ratio of the coating components, this empirical formula is easily derived. Therefore, the empirical formula for the viscosity of carbon dioxide mixed with the coating is as follows:

[0010] lnμ mix =Alnμ co2 +Blnμ resin +Cx co2 +Dx resin

[0011] Where μ mix The viscosity of a mixture, μ co2 and μ resin x represents the viscosity of CO2 and the coating, respectively. co2 and x resin , representing the mass fractions of CO2 and coating in the mixture, respectively, while A, B, C, and D represent the coefficients obtained by fitting the experimental data;

[0012] The viscosity of carbon dioxide is related to temperature and pressure. Using a material property platform, the viscosity values ​​of carbon dioxide as a function of pressure and temperature can be found. A bivariate polynomial can be used, and data processing software can be employed to fit the data, yielding the viscosity-temperature-pressure relationship of carbon dioxide.

[0013] μ co2 =E + F × P + G × T + H × P 2 +I×P×T+J×T 2 +K×P 3 +L×P 2 ×T+M×P×T2 +N×T 3

[0014] In the formula, μ co2 P refers to the viscosity of CO2, T refers to the pressure of carbon dioxide, and E, F, G, H, I, J, K, L, M, and N are all coefficients obtained from the fitting.

[0015] Most coatings are incompressible fluids, and their viscosity is a single function of temperature, as illustrated by the Andrade equation:

[0016] μ resin =Xe YT +Z

[0017] In the formula, μ resin The viscosity of the coating is indicated by T, which refers to the temperature. The coefficients X, Y, and Z are obtained by fitting the viscosity values ​​measured in experiments. The pressure and temperature of the coating need to be adjusted to match the pressure and temperature of carbon dioxide.

[0018] Furthermore, the supercritical carbon dioxide spraying method can be implemented through a control system, which includes a viscosity control module and a mixing spraying module. The viscosity control module includes a supercritical carbon dioxide supply module, a coating supply module, and a viscosity calculation model. The supercritical carbon dioxide supply module and the coating supply module each include a pressurizing device, a heating device, and a flow regulating device. The viscosity calculation model is used to calculate the specific mass fraction of CO2 and coating in the mixture, the required temperature and pressure of carbon dioxide, and the required temperature and pressure of coating based on the set target viscosity value of the mixture, ensuring that the pressure and temperature values ​​of the coating are consistent with those of the carbon dioxide. The supercritical carbon dioxide supply module and the coating supply module are used to adjust the calculated required flow rate, temperature, and pressure of CO2 and coating to the specific target values, respectively. The mixing spraying module is used to mix carbon dioxide and coating and to conduct spraying tests.

[0019] The advantages of this invention are as follows: Compared to traditional supercritical carbon dioxide spraying, the addition of a viscosity control module allows for strict control of the outlet viscosity of the mixed coating, thereby ensuring spraying quality. Using outlet viscosity as the sole factor in spraying quality significantly saves time and reduces coating consumption. Furthermore, this method is applicable to various spraying conditions; as long as the outlet viscosity of the mixed coating meets the requirements, spraying can proceed, greatly improving the applicability of supercritical carbon dioxide spraying. Attached Figure Description

[0020] Figure 1 This is a technical solution diagram of the present invention. Detailed Implementation

[0021] The working process of this patent is described below with reference to the accompanying drawings and specific embodiments:

[0022] In this example, epoxy high-curing paint is used as the coating. By measuring the viscosity of the epoxy high-curing paint at various temperatures, a series of data with temperature as the dependent variable and viscosity as the independent variable are obtained. Then, the relationship between the viscosity of the epoxy high-curing paint and temperature is fitted, and the following is obtained:

[0023] μ resin =10576×e -0.045×T -1144.75

[0024] The AP1700 material property platform provides information on the viscosity of carbon dioxide as a function of pressure and temperature. Using data processing software to fit the data, the viscosity-temperature-pressure relationship for carbon dioxide can be obtained:

[0025] Z=78.37-3.12×T+7.5×P-0.01×T 2 +0.24×T×P-0.568×P 2 +

[0026] 0.000097×T 3 +0.00015×T 2 ×P-0.0065×T×P 2 +0.01472×P 3

[0027] By changing the temperature, pressure, and component ratio of carbon dioxide and coating, the viscosity value of the mixed coating is obtained. For example, when the temperature is 35℃, the pressure is 12MPa, and the mixing ratio of supercritical carbon dioxide and coating is 3:7, the viscosity value of the mixed coating is 20cp. Changing these four variables again yields a series of mixed coating viscosity values. Through the above two formulas, the viscosity values ​​of carbon dioxide and coating at different temperatures and pressures can be obtained. Therefore, a series of data is obtained with carbon dioxide viscosity, coating viscosity, carbon dioxide mass flow rate ratio, and coating mass flow rate ratio as dependent variables, and mixed coating viscosity as the independent variable. Using data processing software, an empirical formula for the viscosity mixing of carbon dioxide and coating is obtained.

[0028] lnμ mix =0.646lnμ co2 +0.428lnμ resin +1.842x co2 +1.217x resin

[0029] In this example, the viscosity μ of the mixed coating at the outlet of the spraying industry is first given. mix=20cp. According to the viscosity calculation model of the mixed coating, when the temperature is 35℃, the pressure is 12MPa, and the ratio of supercritical carbon dioxide to coating components is 3:7, the viscosity of the outlet mixed coating can reach 20cp. The control information is transmitted to the supercritical CO2 supply module and the coating supply module.

[0030] The supercritical CO2 supply module mainly includes a carbon dioxide cylinder, a carbon dioxide pressurization device, a carbon dioxide heating device, a carbon dioxide pneumatic flow regulating valve, and pressure and temperature sensors. The carbon dioxide is pressurized to a pressure of 12MPa, heated to a temperature of 35℃, and finally enters the supercritical carbon dioxide-coating mixing and spraying module after passing through the flow regulating valve to ensure that the mass flow rate of carbon dioxide accounts for 30% of the total flow rate.

[0031] The coating supply module mainly includes a coating tank, a coating pressurization device, a coating heating device, a coating pneumatic flow regulating valve, and pressure and temperature sensors. The coating is pressurized to a pressure of 12MPa, heated to a temperature of 35℃, and finally enters the supercritical carbon dioxide-coating mixing and spraying module after passing through the flow regulating valve to ensure that the mass flow rate of the coating accounts for 70% of the total flow rate.

[0032] The supercritical carbon dioxide-coating mixing and spraying module mainly includes a mixing vessel and a spray gun. Supercritical carbon dioxide at a pressure of 12MPa and a temperature of 35℃ is mixed with the coating. After the mixing is completed, the outlet valve of the mixing vessel is opened to control the coating spray gun to start the spraying operation.

[0033] After the first spraying operation, observe the sprayed surface. If the sprayed surface is uniform and meets all spraying quality standards, then continue spraying with a mixed paint viscosity of 20 cp. If the sprayed surface is uneven and the coating surface is rough, producing an orange peel effect, it indicates that the outlet viscosity is too high. In this case, adjust the given outlet viscosity μ. mix Reduce the viscosity to 18 cp and repeat the above steps. If the coating shows signs of sagging and poor hiding power, it indicates that the outlet viscosity is too low. Adjust the given outlet viscosity μ. mix Increase the pressure to 22 cp and repeat the above steps until the sprayed surface is uniform and meets all spraying quality standards.

Claims

1. A viscosity-controlled supercritical carbon dioxide spraying method, characterized in that, The spraying quality is controlled by adjusting the viscosity of the supercritical carbon dioxide and paint mixture, which is the only factor. A target viscosity value for the mixture is set. Under a supercritical carbon dioxide atmosphere, the viscosity calculation model in the viscosity control module calculates the specific target values ​​for various indicators of the supercritical carbon dioxide and coating at this set target viscosity value. These indicators include the temperature, pressure, and component ratio of the supercritical carbon dioxide and coating. Then, the system is controlled in real time according to the specific target values ​​of each indicator. After the specific target values ​​are reached, a spraying test is conducted, and the target viscosity value of the mixture is readjusted according to the spraying quality until the spraying quality is qualified. The viscosity calculation model is based on an empirical formula for mixing carbon dioxide and coating viscosity: ； in Indicates the viscosity of the mixture. and These represent the viscosity of CO2 and the viscosity of the coating, respectively. and , representing the mass fractions of CO2 and coating in the mixture, respectively, while A, B, C, and D represent the coefficients obtained by fitting the experimental data; The viscosity of carbon dioxide is related to temperature and pressure. The viscosity-temperature-pressure relationship of carbon dioxide is as follows: ； In the formula, P refers to the viscosity of CO2, T refers to the pressure of carbon dioxide, and E, F, G, H, I, J, K, L, M, and N are all coefficients obtained from the fitting. Most coatings are incompressible fluids, and their viscosity is a single function of temperature, as illustrated by the Andrade equation: ； In the formula, The viscosity of the coating is indicated by T, which refers to the temperature. The coefficients X, Y, and Z are obtained by fitting the viscosity values ​​measured in experiments. The pressure and temperature of the coating need to be adjusted to match the pressure and temperature of carbon dioxide.

2. The supercritical carbon dioxide spraying method controlled by viscosity according to claim 1, characterized in that, The supercritical carbon dioxide spraying method described above can be implemented through a control system, which is mainly composed of a viscosity control module. This viscosity control module includes a supercritical carbon dioxide supply module, a coating supply module, a viscosity calculation model, and a mixing and spraying module. The supercritical carbon dioxide supply module and the coating supply module each include a pressurizing device, a heating device, and a flow regulating device. The viscosity calculation model is used to calculate the specific mass fraction of CO2 and coating in the mixture based on the set target viscosity value of the mixture, as well as the required temperature and pressure for both carbon dioxide and coating, ensuring that the pressure and temperature values ​​of the coating are consistent with those of the carbon dioxide. The supercritical carbon dioxide supply module and the coating supply module are used to adjust the calculated required flow rate, temperature, and pressure of CO2 and coating to the specific target values, respectively. The mixing and spraying module is used to conduct spraying tests.

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