Requirements for PS seedling tray sheets
The performance requirements for PS (polystyrene) seedling tray sheet require a comprehensive consideration of material properties, processing technology, and actual application scenarios. The following is a detailed analysis based on industry standards and practical experience:
1. Basic Material Requirements for PS Sheet Extrusion machine
Raw Material Purity and Ratio
Resin Selection: Food-contact-grade PS resin (e.g., meeting GB 4806.6) is preferred. Avoid recycled materials containing heavy metals or plasticizers.
Additives:
Ultraviolet (UV) Antioxidant: Typically added at a level of 0.3%-0.5% (0.3-0.5%) to improve outdoor weathering resistance and slow yellowing and embrittlement.
Antioxidant: Add 0.1%-0.3% of a hindered phenolic antioxidant to inhibit oxidative degradation during processing and use.
Nucleating Agent: Improves crystallinity, increasing sheet rigidity and heat distortion temperature.
Physical Properties
Density: 1.04-1.09 g/cm³, consistent with standard PS density. Thickness: Sheet thickness is typically 0.4-1.0mm, with a tolerance within ±10%. For example, a 28×54×4.8cm plastic seedling tray weighing ≥130g is considered high-density and has a service life exceeding 3 years.
Tensile Strength: ≥15MPa in both longitudinal and transverse directions, with an elongation at break ≥3%, ensuring resistance to breakage during handling and use.
Heat Deflection Temperature: ≥70°C to avoid softening and deformation in high-temperature environments.
II. Suitability of Sheets Produced by PS Sheet Extrusion machine for Seedling Tray Production
Molding Process Requirements
Thermoforming: The sheet must exhibit good thermoplastic properties, be able to be quickly formed when heated to 110-130°C, and be dimensionally stable after cooling (heating dimensional change ≤±15%).
Smoothness: The sheet surface should be free of visible scratches, bubbles, or unevenness, with a roughness Ra ≤1.6μm to facilitate subsequent printing or labeling. Transparency: Seedling trays are typically made of transparent or translucent PS sheets with a light transmittance of ≥85%. However, direct sunlight should be avoided to prevent root damage.
III. PP Sheet Extrusion machine for Seedling Trays: Structural Design and Functionality
Hole Design
Shape: Holes should be square, inverted trapezoidal, or conical (bottom diameter 2-5mm smaller than top diameter). This guides vertical root growth and reduces entanglement.
Depth: For vegetable seedlings, the depth is typically 20-50mm; for flower seedlings, it can be increased to 50-100mm to ensure a balanced water retention and air permeability.
Hole Diameter: Small holes (15-20mm diameter) are generally used for leafy vegetables, while larger holes (25-35mm diameter) are used for fruits and vegetables.
Drainage and Air Permeability
Drainage Holes: Drainage holes with a diameter of 2-4mm should be evenly distributed throughout the tray's bottom, with a permeability ratio of ≥99.5% to prevent water accumulation and root rot. Breathable Structure: Some high-end seedling trays feature ventilation slots between the holes to enhance air circulation and reduce humidity and disease risks.
Enhanced Mechanical Properties
Edge Reinforcement: The sheet edges should be thickened to 1.5-3.0mm, or adopt a corrugated structure to increase load-bearing capacity (compression force ≥ 650N).
Impact Resistance: Passes the drop ball impact test (a 1kg steel ball falls freely from a height of 50cm without breaking).
IV. Environmental Adaptability and Durability of Sheets Produced by PP Sheet Extruders for Seedling Tray Production
Weather Resistance
UV Protection: After adding UV treatment, xenon lamp aging tests (ISO 4892-2) show a yellowing index (ΔE) of ≤5 after 300 hours, and a tensile strength retention of ≥80%.
Temperature Tolerance: No cracking or softening after continuous use for 2 hours in temperatures between -20°C and 45°C. Chemical Stability
Corrosion Resistance: Must be resistant to common pesticides (such as Bordeaux mixture and carbendazim) and fertilizers (such as potassium nitrate), with no swelling or discoloration after immersion for 24 hours.
Disinfection Resistance: Can be disinfected by immersion in quaternary ammonium disinfectants (such as benzalkonium bromide) without material degradation.
V. PS Sheet Extrusion machine: Sheets for Seedling Trays: Environmental Protection and Sustainability
Recycling and Regeneration
Recyclability: Sheets must comply with EU EN 13432 or US ASTM D6400 standards. The recycled content should generally not exceed 50% (up to 90% for black trays), but mechanical properties must meet the standards.
Labeling Requirements: Products must be labeled "Recyclable" and clearly indicate the recycled content (e.g., "50% PCR"). Degradable Options
Biogenic Modification: Using starch or lignin blended with PS (e.g., adding 30% lignin) can achieve a biodegradation rate of up to 90% (within 180 days) and complies with GB/T 20197-2025.
Certification Requirements: Degradable PS seedling trays must pass the China Green Product Certification (CNCA-CGP-11) or the EU OK Compost certification.
VI. Testing and Certification of Sheets Produced byr PS Sheet Extrusion machine for Seedling Trays
Routine Inspection Items
Appearance Inspection: Visually inspect the sample surface for flatness and crack-free conditions, and for complete hole integrity.
Dimensional Measurement: Use calipers to measure sheet thickness, hole diameter, and depth. The tolerance must meet design requirements.
Mechanical Property Testing: Use a tensile testing machine to test tensile strength, and a compression testing machine to test compressive strength.
Weathering Assessment: Compare color difference and mechanical property changes after xenon lamp aging testing. Certification Standards
Domestic Standards: GB 4806.6 (Food Contact Grade PS), NY/T 4203-2022 (Plastic Seedling Trays).
International Standards: ISO 18602 (Plastic Seedling Trays), EN 13432 (Compostable Packaging).
VII. Application Scenarios and Selection Recommendations for Seedling Trays Produced byr PS Sheet Extrusion machine
Vegetables and Flowers: Recommended PS sheets with a thickness of 0.6-1.0mm, 72-200 holes, and available in black (warming in winter) or silver-gray (cooling in summer).
Rice and Tobacco: Use PS sheets with a thickness of 1.0-1.5mm. When using floating seedling technology, ensure the sheet buoyancy is ≥ 0.5N/cm².
Industrial Seedlings
For large-scale production: Choose injection-molded, high-density PS trays (weight ≥ 130g). They can be reused for over 5 years, reducing long-term costs. Precision seedling cultivation: Use PS sheets with a surface corona treatment (surface tension ≥38 dyn/cm) to enhance substrate adhesion and reduce root dangling.
VIII. Typical formulation examples for sheet produced byr PS Sheet Extrusion machine for seedling trays
Ingredients
Ratio (mass percentage)
Function
PS resin 95%-98%
Base material
UV absorber 0.3%-0.5%
Resistant to UV aging
Antioxidant 0.1%-0.3%
Prevents oxidative degradation
Nucleating agent 0.1%-0.2%
Improves crystallization and rigidity
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