What should be paid attention to when processing synthetic resin of water-based environmental protection paint?

The question you asked is particularly critical! The core of water-based environmental protection paint synthetic resin processing is to control the influence of moisture, system stability and environmental compliance, with emphasis on raw material adaptation, process parameter control and impurity avoidance, so as to avoid problems such as delamination, gelation and environmental protection failure.

I. Main points of raw material pretreatment and adaptation

Dehydration and impurity removal are the basis: all raw materials (monomers, initiators and additives) need to be dehydrated in advance, and the water content of monomers should be controlled below 0.1% to avoid abnormal polymerization reaction (such as uneven molecular weight distribution) caused by water; Solid raw materials (such as initiator and pigment) need to be screened with 80-100 mesh to remove impurities and caking, so as to prevent the dispersion of resin from being affected.

Compatibility verification of raw materials: give priority to water-based special raw materials, such as water-based initiators (ammonium persulfate and potassium persulfate) and nonionic emulsifiers, to avoid demulsification of the system caused by the use of oily additives; The compatibility of monomer ratio (such as the ratio of acrylate to styrene) is proved by small tests in advance to prevent phase separation during polymerization.

Pre-control of environmental protection indicators: choose low VOC (volatile organic compounds) monomers and formaldehyde-free additives, and give priority to purchasing raw materials that meet GB/T 23993-2020 "Technical Requirements for Environmental Protection Label Products of Waterborne Coatings" to control environmental protection risks from the source.

Second, the core synthesis process control matters

1. Control of polymerization reaction parameters

Precise temperature control: the reaction temperature should be stabilized at the set value of 2℃ (for example, acrylic resin polymerization is often 70-85℃), and the heating rate should not be too fast (≤2℃/min) to avoid local overheating leading to resin gelatinization and discoloration; In the cooling stage, the temperature should be slowly cooled to below 40℃ to prevent the system from delamination caused by excessive temperature difference.

Feeding speed and sequence: monomer is added by dropping, and the dropping acceleration is even (controlled within 2-4 hours according to the reaction scale), so as to avoid the uncontrolled reaction caused by one-time feeding; The initiator needs to be added in batches (30% initially and 2-3 times for the rest) to ensure sufficient polymerization and uniform molecular weight distribution.

Mixing speed adaptation: the mixing speed is controlled at 150-300r/min to ensure the uniform mixing of raw materials, and at the same time avoid excessive bubbles generated by high-speed mixing (bubbles will affect the leveling performance of subsequent coating construction).

2. System stability guarantee

Dynamic adjustment of pH value: The pH value should be monitored in real time during the reaction, and the pH value of the system should be controlled at 7.5-9.0 by neutralizing agents such as ammonia water and dimethyl ethanolamine (the adaptation range of different resin types is slightly different) to avoid resin hydrolysis caused by too low pH value and pigment flocculation caused by too high pH value.

Maintenance of emulsion system: the dosage of emulsifier should be accurate (accounting for 3%-5% of the total monomer), and compound emulsifier (anion+nonionic) should be given priority to improve stability; If there are signs of demulsification (such as delamination and precipitation) during the reaction, a small amount of emulsifier should be added in time and stirred evenly.

III. Precautions for Post-processing and Storage

Post-treatment process optimization: after the reaction, it needs to be cured (heat preservation and stirring for 1-2 hours) to ensure the full reaction of residual monomers (the content of residual monomers should be ≤ 0.1%); Filtering by a 200-300 mesh filter bag, removing gel particles and impurities generated in the reaction process, and improving the transparency and workability of the resin.

Storage conditions should be controlled: the resin products should be stored in a cool and ventilated environment, and the temperature should be controlled at 5-35℃ to avoid direct sunlight and low-temperature freezing (freezing will destroy the emulsion structure); Storage containers should be sealed to prevent moisture volatilization and foreign impurities from mixing. The shelf life is generally 6-12 months, and the stability should be checked regularly.

Safe and environmentally friendly operation: keep the workshop ventilated during processing to avoid the accumulation of VOC and ammonia; The waste water needs to be neutralized (the pH value is adjusted to 6-9) before it is discharged, and the waste residue (such as filtered impurities and discarded raw materials) needs to be recycled by classification, which meets the environmental protection treatment standards.

Fourth, the main points of avoiding common problems

Avoid abnormal viscosity of resin: strictly control the solid content (the solid content of conventional waterborne resin is 40%-60%). When the viscosity is high, it can be diluted with appropriate amount of water, and when it is low, it needs to be supplemented with thickener (such as hydroxyethyl cellulose).

Prevent yellowing of finished products: choose anti-yellowing monomers (such as methyl methacrylate) and avoid using easily oxidized raw materials; Reduce the high temperature residence time during processing and keep away from oxidants during storage.