In paint formulations, hydroxyethyl cellulose (HEC) is a common thickener and rheology modifier that can improve the storage stability, leveling and construction properties of paints. In order to add hydroxyethyl cellulose to paints and ensure that it works effectively, certain steps and precautions need to be followed. The specific process is as follows:
1. Properties of hydroxyethyl cellulose
Hydroxyethyl cellulose is a non-ionic water-soluble polymer with excellent thickening, film-forming, water-retaining, suspension and emulsifying properties. It is commonly used in water-based paints, adhesives, ceramics, inks and other products. It is obtained by replacing part of the hydroxyl groups on the cellulose molecular chain with hydroxyethyl groups, so it has good water solubility.
The main functions of HEC in paints are:
Thickening effect: Increase the viscosity of the paint, prevent the paint from sagging, and make it have excellent construction properties.
Suspension effect: It can evenly disperse and stabilize solid particles such as pigments and fillers to prevent them from settling.
Water retention effect: Enhance the water retention of the coating film, extend the open time, and improve the wetting effect of the paint.
Rheology control: adjust the fluidity and leveling of the coating, and improve the brush mark problem during construction.
2. Addition steps of hydroxyethyl cellulose
Pre-dissolution step In actual operation, hydroxyethyl cellulose needs to be evenly dispersed and dissolved through a pre-dissolution process. In order to ensure that cellulose can fully play its role, it is usually recommended to dissolve it in water first, rather than adding it directly to the coating. The specific steps are as follows:
Choose a suitable solvent: usually deionized water is used as the solvent. If there are other organic solvents in the coating system, the dissolution conditions need to be adjusted according to the properties of the solvent.
Slowly sprinkle hydroxyethyl cellulose: Slowly and evenly sprinkle hydroxyethyl cellulose powder while stirring the water to prevent agglomeration. The stirring speed should be slow to avoid slowing down the dissolution rate of cellulose or forming “colloids” due to excessive shear force.
Standing dissolution: After sprinkling hydroxyethyl cellulose, it needs to be left to stand for a period of time (usually 30 minutes to several hours) to ensure that the cellulose is completely swollen and dissolved in water. The dissolution time depends on the type of cellulose, solvent temperature and stirring conditions.
Adjust the dissolution temperature: Increasing the temperature helps to accelerate the dissolution process of hydroxyethyl cellulose. It is usually recommended to control the solution temperature between 20℃-40℃. Too high a temperature may cause cellulose degradation or solution deterioration.
Adjusting the pH value of the solution The solubility of hydroxyethyl cellulose is closely related to the pH value of the solution. It usually dissolves better under neutral or slightly alkaline conditions, with a pH value between 6-8. During the dissolution process, the pH value can be adjusted by adding ammonia or other alkaline substances as needed.
Adding hydroxyethyl cellulose solution to the coating system After dissolution, add the solution to the coating. During the addition process, it should be added slowly and stirred continuously to ensure sufficient mixing with the coating matrix. During the mixing process, it is necessary to select a suitable stirring speed according to the different systems to prevent the system from foaming or cellulose degradation due to excessive shear force.
Adjusting viscosity After adding hydroxyethyl cellulose, the viscosity of the coating can be controlled by adjusting the amount added. Generally, the amount of hydroxyethyl cellulose used is between 0.3%-1.0% (relative to the total weight of the coating), and the specific amount added needs to be adjusted experimentally according to the formulation requirements of the coating. Too high an amount of addition may cause the coating to have too high viscosity and poor fluidity, affecting construction performance; while insufficient addition may not be able to play the role of thickening and suspension.
Conduct leveling and storage stability tests After adding hydroxyethyl cellulose and adjusting the coating formula, the coating construction performance needs to be tested, including leveling, sag, brush mark control, etc. At the same time, the coating storage stability test is also required to observe the sedimentation of the coating after standing for a period of time, the viscosity change, etc., to evaluate the stability of hydroxyethyl cellulose.
3. Precautions
Prevent agglomeration: During the dissolution process, hydroxyethyl cellulose is very easy to absorb water and swell, so it needs to be sprinkled into the water slowly and ensure sufficient stirring to prevent the formation of lumps. This is a key link in the operation, otherwise it may affect the dissolution rate and uniformity.
Avoid high shear force: When adding cellulose, the stirring speed should not be too high to avoid damaging the cellulose molecular chain due to excessive shear force, resulting in a decrease in its thickening performance. In addition, in the subsequent coating production, the use of high shear equipment should also be avoided as much as possible.
Control the dissolution temperature: When dissolving hydroxyethyl cellulose, the water temperature should not be too high. It is generally recommended to control it at 20℃-40℃. Under high temperature conditions, cellulose may degrade, resulting in a decrease in its thickening effect and viscosity.
Solution storage: Hydroxyethyl cellulose solutions generally need to be prepared and used immediately. Long-term storage will affect its viscosity and stability. It is usually recommended to prepare the required solution on the day of paint production to maintain its optimal performance.
The addition of hydroxyethyl cellulose to the paint is not only a simple physical mixing process, but also needs to be combined with actual process requirements and operating specifications to ensure that its thickening, suspension and water retention properties are fully utilized. During the addition process, pay attention to the pre-dissolution step, the control of the dissolution temperature and pH value, and the full mixing after addition. These details will directly affect the quality and performance stability of the paint.
Post time: Sep-19-2024