Recommendations for the use of water-based defoamers
Recommendations for the use of water-based defoamers
The effect of water-based defoamers is affected by many factors such as the timing of addition, dosage, and process adaptability. The following specific suggestions are given from the five stages of preliminary preparation, addition operation, process control, effect verification, and subsequent management:
1. Preparation before use: Accurately adapt the system
Clear system characteristics
Component analysis: Master the types and concentrations of components such as resins (such as acrylic acid, polyurethane), emulsifiers, and thickeners in the water-based system. For example, a high-content non-ionic emulsifier system is prone to produce stable foam, and mineral oils or polyether-modified silicone defoamers with strong foam breaking ability need to be selected.
Environmental parameters: Record the pH value, temperature, and viscosity range of the system. Strong acid (pH<3) or strong alkali (pH>10) environments may destroy the molecular structure of the defoamer, and acid- and alkali-resistant polyether defoamers need to be selected; high-viscosity systems (>10000mPa·s) should choose self-emulsifying products with good dispersibility.
Determine parameters by small test
Gradient test: Add defoamer in a gradient of 0.05%-0.5%, and observe the defoaming speed (seconds/minutes) and anti-foaming time (hours). For example, a water-based paint system with a 0.2% addition amount completely eliminates foam within 30 seconds and suppresses foam for 6 hours, which can be determined as the optimal dosage.
Compatibility verification: Mix the defoamer with the system in a ratio of 1:10, and observe whether it is stratified or flocculated after standing for 24 hours. If stratification occurs, replace the defoamer with a more matching hydrophilic-lipophilic balance (HLB).
2. Addition operation: scientific control nodes
Choose the best time
Production stage: Add in the early stage of grinding and dispersion to destroy the foam generated by the mixing of raw materials in advance. For example, adding defoamer simultaneously when grinding pigments can reduce the amount of foam generated by mechanical stirring by 70%.
Construction stage: Add 30 minutes before spraying to ensure that the defoamer is evenly dispersed. If foam appears during spraying, it can be immediately treated with local spraying with diluted defoamer (add water at a ratio of 1:5).
Standardized addition method
Dispersing equipment: Use a high-speed disperser (speed 1500-3000rpm) to stir for 5-10 minutes, or circulate through a sand mill 1-2 times to ensure that the defoamer particle size is <5μm. For example, after sand grinding of a certain emulsion system, the defoamer particle size is reduced from 10μm to 3μm, and the defoaming efficiency is increased by 40%.
Addition order: Add the defoamer first, then add other additives to avoid the defoamer being wrapped by the surfactant. For example, in the coating formula, the defoamer should be added first, and then the leveling agent, wetting agent, etc.
3. Process control: Dynamically adjust parameters
Monitor system changes
Viscosity fluctuations: When the system viscosity increases by more than 20%, an additional 0.05%-0.1% defoamer needs to be added. For example, a certain water-based adhesive has an increased viscosity due to excessive thickener, and the amount of foam is reduced by 50% after adding defoamer.
Temperature influence: For every 10℃ increase, the activity of the defoamer increases by 15%-20%, but it may fail when it exceeds 60℃. For high temperature systems (such as above 70℃), high temperature resistant fluorocarbon modified defoamers should be used.
Dealing with sudden problems
Excessive defoaming: If the system has defects such as shrinkage cavities and orange peel, immediately add 0.02%-0.05% thickener to adjust the viscosity, or replace the defoamer with better compatibility.
Foam rebound: In the late stage of foam suppression (such as 4 hours later), the foam volume rebounds by more than 30%, and the defoamer can be added in stages (50% of the first amount).
4. Effect verification: quantitative evaluation indicators
Appearance inspection
Foam height: Use a measuring cylinder to measure the initial foam height of the system (such as 100mm) and the height after defoaming (should be ≤10mm), and calculate the defoaming rate (≥90% is qualified).
Surface defects: Use a magnifying glass (50 times) to check whether the coating has fish eyes and pinholes, and the defect density should be <1/m².
Performance test
Adhesion: According to GB/T 9286 standard test, the cross-cut method rating should reach 0-1 level.
Water resistance: After immersion for 24 hours, the coating has no blistering or shedding.
5. Post-use management: Optimize long-term solutions
Establish use archives
Record the type, dosage, addition time, system parameters and defoaming effect of each defoamer added to form a database. For example, a factory analyzed 3 months of data and found that the amount of defoamer needed to be increased by 20% during high temperatures in summer.
Regular evaluation and improvement
Compare the defoamer performance of different suppliers every quarter and select the product with the best cost performance. For example, a company reduced the cost of defoamers by 15% and increased the defoaming efficiency by 10% through competitive product testing.
Waste treatment
Wastewater containing defoamers needs to be discharged after flocculation and sedimentation (PAC dosage 50-100mg/L) and activated carbon adsorption (residence time 30 minutes) to ensure COD≤100mg/L.