Development and Production of Multi-Cavity Molds for Plastic Food Containers

1. Introduction

Plastic food containers are among the most widely used consumables in the food delivery and food packaging industries. With the explosive growth of the food delivery industry, market demand for food containers continues to rise, while higher requirements are placed on container quality, hygiene standards, and production costs. Multi-cavity molds, as a core means of improving production efficiency and reducing unit costs, have become the mainstream technical solution for large-scale food container production. This article systematically introduces the development process and production key points of multi-cavity molds for plastic food containers.

2. Product Characteristics of Plastic Food Containers

2.1 Structural Features

Plastic food containers are typically thin-wall shallow-cavity vessels, with the following product characteristics:

• Extremely thin walls: Generally 0.5–1.2 mm, classified as typical thin-wall injection molded parts
• Diverse shapes: Square, round, rectangular, multi-compartment, etc.
• Stacking structure: Stacking steps at the rim for easy multi-layer stacking
• Sealing structure: Snap-fit or sealing grooves at the rim for sealing with lids
• Reinforcing ribs: Ribs on the bottom and side walls to ensure rigidity
• Multi-compartment design: Some containers have internal dividers for holding different foods

2.2 Common Specifications

2.3 Performance Requirements

• Food contact safety: Comply with GB 4806.7 and other food-contact material standards
• Temperature resistance: -20°C to +120°C (microwave safe)
• Sealing performance: No leakage after lid closure
• Stacking performance: No deformation under multi-layer stacking
• Hygiene requirements: No odor, no harmful substance migration

3. Overall Multi-Cavity Mold Scheme Design

3.1 Determining the Number of Cavities

Food containers are mass-produced products, typically using multi-cavity molds:

Cavity Number Selection Principles:

• Injection molding machine clamping force meets requirements
• Mold size matches injection molding machine platen
• Balanced filling of all cavities
• Uniform cooling
• Optimal economic efficiency

3.2 Overall Mold Structure

3.3 Cavity Layout Design

(1) Layout Principles

• Each cavity symmetrically distributed to ensure balanced filling
• Cavity spacing meets cooling channel layout requirements
• Mold center of gravity coincides with injection molding machine center
• Runner length minimized

(2) Typical Layouts

4. Mold Structure Design Key Points

4.1 Gating System Design

(1) Hot Runner System

• Use valve gate hot runners for sequential filling
• Number of hot nozzles matches cavity count, generally 1 per cavity
• Precise hot runner temperature control (±1°C) to prevent material degradation
• Use balanced runner design to ensure uniform filling of all cavities

(2) Gate Design

• Use pin-point gates or tunnel gates for automatic degating
• Gate diameter: φ0.8–φ1.5 mm (thin-wall parts)
• Gate location at container bottom center or corner
• Gate locations avoid food contact surfaces

4.2 Cooling System Design

(1) Cooling Channel Layout

(2) Conformal Cooling Technology

• Use 3D-printed conformal cooling inserts, with cooling channels following the container wall contour
• Cooling efficiency improved by 30%–50%
• Molding cycle shortened by 20%–30%
• Effectively reduces product warpage deformation

(3) Cooling Parameters

• Cooling water temperature: 10–15°C
• Cooling water flow rate: 15–25 L/min
• Cooling time: 3–8 s (thin-wall parts)

4.3 Ejection System Design

(1) Multi-Point Ejection

• Number of ejector pins: Based on container size, generally 8–20
• Ejector pin diameter: φ3–φ6 mm
• Ejector pin distribution: Evenly distributed, denser at corners
• Ejection stroke: 20–50 mm

(2) Air-Assisted Ejection

• For thin-wall containers, use air-assisted ejection to assist demolding
• Compressed air pressure: 0.2–0.4 MPa
• Air-assisted ejection can reduce the number of ejector pins and reduce product deformation

(3) Stripper Plate Ejection

• For deep-cavity containers, use stripper plate ejection
• Stripper plate-to-core clearance ≤0.03 mm
• Stripper plate surfaces require nitriding treatment to improve wear resistance

4.4 Venting System Design

(1) Vent Groove Design

• Vent groove depth: 0.015–0.025 mm
• Vent groove width: 3–8 mm
• Vent groove locations: Parting surface, ejector pin clearances, insert clearances

(2) Vent Inserts

• Install vent inserts in areas prone to air entrapment
• Vent inserts use powder metallurgy materials with good permeability
• Vent inserts require regular cleaning to prevent clogging

4.5 Stacking and Sealing Structure Design

(1) Stacking Structure

• Stacking steps at the rim to ensure stable multi-layer stacking
• Stacking height: 3–5 mm
• Stacking fit clearance: 0.1–0.2 mm

(2) Sealing Structure

• Sealing grooves at the rim for sealing with lids
• Sealing groove depth: 1–2 mm
• Sealing groove width: 1.5–2.5 mm

5. Mold Material Selection

5.1 Mold Steel Selection