Resins and Additives for Solvent-Free Polyurethane Coatings
Solvent-Free Polyurethane Coatings are widely used in many fields due to their environmental friendliness (low VOC), high performance and construction safety. The following is a detailed analysis of their typical uses, alternative resin systems and commonly used additives:
1. Industrial Floor
Features: High wear resistance, impact resistance, and chemical resistance (such as acid, alkali, grease).
Scenes: Factory workshops, warehouses, parking lots, etc.
Features: Resistant to salt spray, sea water and chemicals.
Scenes: Oil pipelines, ships, bridges, chemical storage tanks.
3. Electronic Packaging
Features: Insulation, heat and humidity resistance, low shrinkage.
Scenes: Circuit boards and electronic components potting.
4. Cars/Transportation
Features: Flexibility, weather resistance.
Applications: Automobile chassis coating, high-speed rail track shock-absorbing pads.
5. Food/Medical Equipment
Features: Non-toxic, FDA certified, easy to clean.
Scenes: Food processing plant floors and the inner walls of pharmaceutical equipment.
The core of solvent-free PU coating is the reaction of isocyanate (such as MDI/HDI) and polyol , but the following resins can be substituted or blended according to needs:
|
Resin Type |
Features |
Applicable scenes |
|
Epoxy resin |
It has high adhesion and chemical resistance, but is brittle and is often blended with PU to improve toughness. |
Floor primer, anti-corrosion coating. |
|
Acrylic resin |
Good weather resistance, quick drying, and can be cured by UV (requires active diluent). |
Outdoor coatings, UV curing systems. |
|
Polyaspartic acid |
Ultra-fast curing (at low temperature), high weather resistance, and relatively high cost. |
Rapid construction projects (e.g. airport runway repairs). |
|
Silicone modified PU |
High temperature resistant (200℃+), hydrophobic, but expensive. |
High temperature equipment coating, aerospace. |
|
Bio-based polyols |
Renewable raw materials (such as castor oil derivatives) are environmentally friendly but may have slightly inferior performance. |
Green building, sustainable packaging. |
Solvent-free systems require additives to optimize construction and performance:
|
Additive Type |
effect |
|
Reduces surface defects (orange peel, pinholes) and improves gloss. |
|
|
Eliminate bubbles during mixing and construction, and avoid holes after curing. |
|
|
Wetting and dispersing agents |
Improve the dispersibility of fillers (such as silica, calcium carbonate) and prevent sedimentation. |
|
Delays yellowing and degradation (especially for outdoor use). |
|
|
Improve fire resistance (such as phosphorus series, aluminum hydroxide). |
|
|
Plasticizers |
Adjust flexibility (use with caution, may migrate and affect environmental performance). |
|
Curing accelerator |
To accelerate the reaction (such as organotin and amines), the dosage should be controlled to avoid shortening the application period. |
1. NCO/OH ratio : Strictly calculate the equivalent ratio of isocyanate to polyol to avoid incomplete curing or performance degradation.
2. Viscosity control : The solvent-free system has high viscosity, which can be improved by selecting low-viscosity resins or adding reactive diluents (such as glycidyl ethers).
3. Environmental compliance : Ensure that all components comply with regulations such as REACH and FDA (e.g. banning phthalate plasticizers).
4. Construction window : Adjust the catalyst dosage to balance the curing speed and operation time (e.g. slow down the reaction in summer).
1. Water-based PU/solvent-free hybrid system : combining low VOC and easy construction.
2. Self-healing coatings : Add microencapsulated healing agents (such as dicyclopentadiene).
3. Nano filler : Nano SiO₂/Al₂O₃ improves mechanical strength and wear resistance.
Resins and additives can be flexibly combined according to specific needs. It is recommended to verify the feasibility of the formula through small-scale tests.
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