The production method of epoxy resin for food-grade silicone products

Precise Material Preparation for Food-Grade Silicone Drop Casting

The foundation of high-quality food-grade silicone drop casting lies in meticulous material preparation. This process involves three core components: base silicone polymer, platinum-based curing agent, and food-safe pigments. The base silicone must comply with FDA 21 CFR 177.2600 and EU 10/2011 standards, ensuring it contains no phthalates, bisphenol A, or heavy metals.

Component Ratios:

• For medical-grade applications, the platinum curing agent should constitute 1.5-2% of the total mixture by weight.
• When incorporating pigments, maintain a 0.5-3% concentration to preserve mechanical properties while achieving vibrant colors.
• Additives like antimicrobial agents (0.1-0.5%) require special handling to prevent catalyst inhibition.

Mixing Protocols:

• Use a dual-speed planetary mixer operating at 150-200 RPM for initial blending, followed by 500 RPM for final homogenization.
• Scrape container walls every 3 minutes during mixing to prevent unincorporated material.
• The mixture must reach a viscosity of 15,000-25,000 cPs (measured with a Brookfield DV-E viscometer) before proceeding.

Quality Control:

• Perform a gelation test by placing 1g of mixture on a glass plate at 25°C. The material should reach a tack-free state in 18-22 minutes.
• Conduct a flow test by measuring the spread diameter of 10g mixture on a flat surface (should maintain 8-10cm diameter).

Equipment Setup and Environmental Control

Creating optimal conditions for drop casting requires precise environmental management and specialized equipment calibration.

Temperature and Humidity:

• Maintain workspace at 23±1°C with relative humidity below 65% (use dehumidifiers in tropical climates).
• For temperature-sensitive pigments, implement a climate-controlled room with ±0.5°C accuracy.

Drop Casting Machinery:

• Positive displacement pumps with ceramic nozzles (0.1-5mm diameter) ensure consistent droplet sizes.
• Multi-axis robotic arms with laser positioning achieve ±0.05mm placement accuracy.
• Real-time viscosity sensors adjust pump pressure automatically during operation.

Mold Preparation:

• Clean molds with isopropyl alcohol and dry at 60°C for 30 minutes before use.
• Apply silicone-based mold release agents in a 3μm thick layer using an airbrush system.
• Preheat molds to 40°C for thermal shock prevention during material deposition.

Drop Casting Execution and Layering Techniques

The core of the process involves precise material deposition and multi-layer construction for complex geometries.

Single-Layer Casting:

• For flat products like silicone coasters, deposit material at 0.5mm/s travel speed using a 2mm nozzle.
• Maintain 2mm spacing between droplets to prevent merging during initial gelation.
• After deposition, vibrate the mold at 50Hz for 2 minutes to eliminate air bubbles.

Multi-Layer Construction:

• When building 3D structures, apply each 0.3mm layer with a 15-minute interval between deposits.
• Use a temperature-controlled platform (45°C) to accelerate surface curing between layers.
• For transparent products, implement a UV curing station (365nm wavelength) between layers to enhance adhesion.

Color Gradation Techniques:

• Create ombre effects by varying pigment concentration during deposition (0.5% to 3% gradient).
• Use a dual-cartridge system to switch colors mid-process with <1 second transition time.
• For marbled patterns, oscillate the nozzle at 2Hz frequency while depositing different colored materials.

Post-Casting Curing and Quality Assurance

The final phase ensures complete polymerization and compliance with food safety standards.

Curing Protocols:

• Room temperature curing (25°C) requires 24 hours for full polymerization.
• Accelerated curing at 60°C reduces this to 4 hours but requires strict humidity control (<40% RH).
• For medical applications, implement a two-stage curing process: 40°C for 2 hours followed by 80°C for 1 hour.

Mechanical Property Verification:

• Conduct tensile tests (ASTM D412) to ensure minimum 8MPa strength for food contact items.
• Measure elongation at break (minimum 300%) using a 50kN load cell.
• Perform compression set tests (ASTM D395) with 25% deformation for 24 hours at 70°C.

Surface Quality Inspection:

• Use optical profilometry to verify surface roughness (Ra <0.2μm for medical products).
• Conduct dye penetration tests to detect subsurface voids.
• Inspect for pinholes using a 50W LED backlight system.

Regulatory Compliance Checks:

• Extractable testing per ISO 10993-18 for total metal content (<1ppm for lead, cadmium).
• Volatile organic compound analysis to ensure compliance with REACH Annex XVII.
• Microbiological testing for total plate count (<100 CFU/g) and specific pathogens.

By implementing these precise methodologies, manufacturers can produce food-grade silicone products with consistent quality, meeting stringent international standards while enabling complex designs and functional properties.