China's high-grade wood coatings mainly consist of polyurethane (PU) and polyester (PE) paints. These two types are classified differently in national standards, with significant differences in composition, performance, application, and curing mechanisms.
1. Base Components: Polyester paint (PE) is made from unsaturated polyester and cross-linking monomers, while polyurethane paint (PU) includes polyester, acrylic resin, polyether, and epoxy resins containing hydroxyl groups (component B). PU also contains a prepolymer or adduct of polyisocyanate with NCO groups (component A).
2. Number of Components: PE typically has 3-4 components, including styrene solution, initiator, accelerator, and paraffin solution. PU usually comes in 1-3 components, such as one-component, two-component, or with a thinner added during application. The standard ratio for two-component PU is usually 1:0.5–1:0.5–1.5.
3. Classification: PE can be gas-dissolved or anaerobic, and further categorized into wax and non-wax types. PU is divided into single-component and two-component, with the latter being more common in the market. Two-component PU uses hydroxyl-curing agents.
4. Solvents: PE uses solvents like styrene, while PU relies on anhydrous xylene, cyclohexanone, or butyl acetate.
5. Solid Content: PE has nearly 100% solid content, whereas PU ranges from 40% to 70%.
6. Working Time: PE has a short working time of 15–20 minutes, while PU lasts 4–8 hours.
7. Curing Conditions: PE requires oxygen for anaerobic curing or air drying, while PU cures at room temperature or low heat through an addition polymerization reaction between NCO and OH groups.
8. Health and Safety: PE is solvent-free and less harmful, while PU is solvent-based, containing up to 60% volatile organic compounds. It requires proper ventilation due to its toxicity, flammability, and potential for environmental pollution.
9. Drying Time: PE takes longer to dry fully—surface dry in 30–40 minutes, full dry over 24 hours. PU dries faster, with surface dry in 15–20 minutes and full dry under 24 hours.
10. Recoating Interval: Both PE and PU allow "wet-on-wet" application, but the timing varies depending on the type.
11. Performance: PE offers excellent physical and chemical properties and is solvent-free. PU also provides strong performance and durability.
Interestingly, many products labeled as "polyester paint" on the market today are actually polyurethane paints. These are often two-component systems, requiring mixing with a hardener and thinner before use. They are easy to apply, making them popular for home decoration. To tell the difference, check the number of components: PE usually has more than four, while PU is available in single or two-component forms.
1. Diluent: A mix of cyclohexanone, butyl acetate, and anhydrous xylene is commonly used. 2. Dilution Ratio: Xylene is often used as a diluent, sometimes mixed with acetone in a 1:1.5 ratio. Some products suggest 1:2 or even 1:4, depending on the manufacturer’s instructions.
Fastening Screws, also known as positioning screws, fastening also known as machine rice screws, headless screws, stop screws
1. Application scope: Hexagonal set screws with concave end are used for machine parts with high hardness requirements or frequently adjusted, and are a kind of screws designed for fixing the relative positions of machine parts.
2. Commonly used fastening type: flat end fastening, tip fastening, concave end fastening, column end fastening
3. Reference standards.
Flat end fastening: GB77, DIN913, ISO7026
Tip tightening: GB78, DIN914, ISO4027
Concave end tightening: GB80, DIN916, ISO4029
Column end tightening:GB79.DIN915.ISO4028
Socket Set Screw ,Hex Set Screw,Set Screw Types,Cup Point Set Screw
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