In paint formulations, polymers, also known as binders, play a foundational role. They help form the paint film and determine most of the core characteristics of the product, such as durability, adhesion, and chemical resistance. So, what are the properties of plastic materials in the coatings industry? Let’s explore with Vichem in the following article.
RELATIONSHIP BETWEEN CHEMICAL STRUCTURE AND PHYSICAL PROPERTIES
The final properties of the paint film are determined by the molecular structure of the polymer itself. This relationship is demonstrated through three main factors:
Molecular Weight and Toughness
The molecular weight of a polymer is an indicator representing the average length of the molecular chains. The longer the chains, the more contact points and intermolecular interactions the polymer has. This enhances the toughness, tensile strength, and abrasion resistance of the paint film.
In solvent-borne paints, controlling molecular weight is crucial. This process helps balance ease of application with the mechanical strength of the film.
Glass Transition Temperature (Tg)
Tg is one of the most important indicators of polymers. It represents the temperature at which the material transitions from a hard, brittle state (like glass) to a soft, flexible state.
- High Tg: The paint film will be hard, with good abrasion resistance, but less flexible and prone to cracking under deformation. Epoxy floor paints often have a high Tg.
- Low Tg: The paint film will be soft, tough, and have good adhesion, but is easily scratched and attracts dirt. This is particularly important in waterborne paints, where the minimum film formation temperature (MFFT) must be lower than the ambient application temperature to ensure perfect film formation.
Cross-Linking
This is the chemical mechanism that allows polymers to form a three-dimensional (3D) spatial network. Instead of just individual long chains, cross-linking creates strong chemical bridges between them.
- Mechanism: Reactive functional groups on the polymer chains, such as hydroxyl (-OH), isocyanate (-NCO), or epoxy (epoxy ring), react with a curing agent.
- Result: The cross-linked network enhances hardness, chemical resistance, heat resistance, and especially exceptional solvent resistance, making the paint film insoluble once formed.
CURING MECHANISMS OF CERTAIN TYPES OF RESINS IN INDUSTRIAL PAINTS
Epoxy Paint
Epoxy paint cures through a two-component reaction via ring-opening addition between the epoxy groups of the resin and the amine groups of the polyamine curing agent.
Reaction: R1-NH2 + Epoxy Ring → R1-NH-C-C-OH
This reaction produces no by-products. However, it generates new hydroxyl (-OH) linkages, which provide excellent adhesion to various surfaces.
Polyurethane (PU) Paint and Polyurea Paint
Both types of paints are based on the reaction of isocyanate groups (-NCO), but with different reactive compounds.
PU Paint: Reaction between isocyanate and polyol (compounds with -OH groups).
R1-NCO + R2-OH → R1-NH-COO-R2
Polyurea Paint: Reaction between isocyanate and polyamine (compounds with -NH or -NH2 groups).
R1-NCO + R2-NH2 → R1-NH-CO-NH-R2
The difference in reactive groups makes polyurea cure significantly faster than PU. Amine groups have much higher affinity and reaction speed with isocyanate compared to hydroxyl groups.
Wetting and Dispersing Additives
Polymers in paints serve as the primary dispersants. The long polymer chains adsorb onto the surface of pigment particles, creating a protective layer. This layer operates through two mechanisms:
- Electrostatic Repulsion: In waterborne paint systems, functional groups on the polymer ionize, generating like charges that cause pigment particles to repel each other.
- Steric Hindrance: Long polymer chains extend from the pigment surface, creating a physical barrier that prevents agglomeration.
Fillers
Fillers such as CaCO3, Talc, or Mica are not just for cost reduction. They improve the mechanical properties of the paint film:
- CaCO3: Increases hardness and opacity.
- Talc and Mica: Enhances adhesion and water resistance.
COMPARISON AND PRACTICAL APPLICATIONS OF PLASTIC MATERIALS
| Comparison Criteria | Epoxy Paint | Polyurethane Paint |
| Hardness | Very high, excellent | High, more flexible |
| Elasticity | Low, brittle | High, good crack resistance |
| Chemical Resistance | Excellent (acids, alkalis) | Very good (solvents, gasoline) |
| Abrasion Resistance | Outstanding | Very good, impact resistant |
| Applications | Factory floor coatings, chemical corrosion protection, storage tanks. | Wood coatings, metal coatings, exterior coatings, waterproofing coatings. |
| Environment | Ideal for static environments with chemical exposure. | Ideal for dynamic environments with temperature changes and impacts. |
Selecting the appropriate polymer in coating formulations is not solely based on cost but on a deep understanding of their chemical structure and mechanical properties. This forms the foundation for creating sustainable and efficient products.
VICHEM – AUTHORIZED DISTRIBUTOR OF CHEMICAL ADDITIVES IN VIETNAM
Vichem is an authorized distributor of chemical additives with full legal compliance information in Vietnam. We not only provide high-quality products but also deliver international-standard after-sales services. Our services include:
- Technical Consulting: Assisting customers in selecting product samples suitable for their intended use.
- Color Matching Testing: Vichem’s expert team conducts color matching tests to ensure results meet design standards.
- Practical Application Support: Accompanying customers in integrating into production lines to ensure optimal performance.
For more information about our products, please contact us through the following channels:
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