Molded Pulp Package Tray Production Process

The production process of pulp molded package trays is a multi-step coordinated system engineering, covering the core steps of raw material processing, pulp preparation, molding, shaping, post-processing, etc. Its process is highly flexible, and specific parameters and auxiliary processes can be adjusted according to product functional requirements (such as food-grade packaging or industrial cushioning materials). AGICO presents you the details and secrets with in-depth analysis of each step:

Paper Pulp Classification and Grades

Category	Type	Description
By Raw Material	Wood Pulp	Made from softwood or hardwood, used for writing, printing, and packaging papers.
	Non-Wood Pulp	Derived from bamboo, straw, bagasse, cotton — mainly used in specialty papers and eco-friendly packaging.
	Recycled Pulp	Recovered from waste paper, commonly used for newsprint, packaging, and tissue paper.
By Processing Method	Mechanical Pulp	Uses mechanical grinding, retains most lignin, lower brightness and durability, cost-effective for newspapers and catalogs.
	Chemical Pulp	Uses chemicals to remove lignin, offers strong, high-quality fibers — for printing, writing, and packaging papers.
	Semi-Chemical Pulp	Combination of mild chemical treatment and mechanical refining; balances strength and cost, often used for corrugated cardboard.
By Grade	Bleached Pulp	Pulp that has undergone bleaching for brightness and purity — used for high-end printing and writing papers.
	Unbleached Pulp	Natural color pulp, stronger fibers — used in kraft paper, cartons, and industrial packaging.
	Dissolving Pulp	Highly purified pulp for chemical conversion into cellulose derivatives like rayon or cellophane.

Bleached Virgin Pulp:

• Source: Coniferous or hardwood wood or grass is chemically bleached, with high fiber purity and whiteness ≥85%.
• Application: Fast food boxes, food trays, and other scenes that directly involve food must comply with GB 4806.8-2016 Food Contact Material Hygiene Standard.
• Special treatment: Add waterproof agent (rosin emulsion, added amount 0.5%~1.2%), oil-proof agent (fluorocarbon compound, oil-resistant temperature ≥120 ℃ ), and ensure safety through high temperature sterilization (121 ℃ /15min).

Waste paper pulp:

• Source: Recycled cartons, newspapers, etc. After deinking and screening, the fiber length is controlled at 1.2~2.5mm.
• Application: In industrial fields such as electronic product linings and medical device packaging, the cost is reduced by 30% to 50% and it meets the requirements of the circular economy.
• Limitation: The fiber strength is low and the bonding strength needs to be enhanced through pulping process.

Key steps in pulping process:

Pulping:

• Equipment: Hydraulic pulper (power 15~30kW, speed 800~1200r/min), which breaks the pulp into fiber suspension with a concentration controlled at 4%~6%.
• Technical points: Avoid excessive shearing that causes fiber length loss (target fiber length ≥ 1.0 mm).

Screening and purification:

• Equipment: Conical sand remover (removal rate ≥ 95%), pressure screen (aperture 0.15~0.25mm), to remove impurities such as sand and adhesives.
• Test indicators: slurry ash content ≤0.8%, impurity content ≤50mg/kg.

Beating control:

• Equipment: disc refiner or cylindrical refiner separates the fibers into fine fibers through the refiner teeth to increase the bonding area.
• Parameters: Beating degree (°SR) needs to be adjusted according to the product:
• Fast food box: 28~35°SR (considering dehydration speed and molding strength).
• Industrial packaging: 22~28°SR (priority dehydration efficiency).
• Abnormal treatment: When the beating degree is too high, add dilution water to reduce the concentration; when it is too low, extend the refining time or adjust the tooth disc gap.

How to Configure Pulp Making System for production lines:

• Small pulp molding production line: hydraulic pulper + pulp tank (volume 2~5m³), meeting the daily output demand of 1~3 tons.
• Large pulp molding production line: fully automatic pulping system (including pulping, sand removal, pulp grinding and pulp storage integration), with a daily production capacity of more than 20 tons.

How to Improve Paper Tray Functions

Pulp Molding Additive Types According to Function:

Water repellent:

• Rosin saponified emulsion: reacts with the hydroxyl groups on the fiber surface to form a hydrophobic film with a contact angle of ≥110°.
• Cationic starch: Strengthens hydrogen bonds between fibers through charge adsorption and improves wet strength (wet tensile index ≥ 15N·m/g).

Oil repellent:

• Perfluoroalkyl compounds (PFAS): form a low surface energy coating with a grease and oil penetration resistance time of ≥2h (ASTM F119-82 standard).

Functional fillers:

• Nano calcium carbonate: Add 5%~8% to improve product rigidity (elastic modulus increases by 20%~30%).
• Bamboo fiber: replaces part of wood pulp and enhances degradation performance (natural degradation rate ≥90% in 180 days).

Equipment For Vacuum Adsorption Molding:

Slurry concentration and stability control:

• Online monitoring: Use microwave concentration sensor (accuracy ±0.1%) to adjust the pulp pool level and flow in real time.
• Dynamic homogenization: Slurry circulation system (flow rate 10~20m³/h) prevents fiber sedimentation and ensures uniform molding.

Pulp Injection Molding Machine:

• Applicable products: shallow plate tableware (such as lunch boxes, trays).
• Workflow:
  • The grouting head injects the slurry into the mesh surface of the concave mold (mesh aperture 0.3~0.5mm).
  • Vacuum adsorption (vacuum degree -0.06~-0.08MPa) forms a wet blank, and the dehydration time is 3~5s.
  • The punch is pressed down (pressure 0.2~0.5MPa) for secondary dehydration, and the dryness of the wet blank reaches 25%~30%.
• Advantages: fast molding speed (cycle ≤ 10s), suitable for mass production.

Vacuum-type Molding Machine:

• Applicable products: complex structure packaging (such as electronic product lining, multi-cavity cushion tray).
  Workflow:
  • The concave mold is immersed in the pulp pool, and the vacuum adsorption fiber is deposited (the slurry absorption time is 5~15s, adjustable).
  • The male and female dies are closed and pressurized (pressure 0.5~1.0MPa), and the dryness of the wet blank is increased to 30%~35%.
• Advantages: The product thickness uniformity is better (CV value ≤ 5%), but the equipment investment is 20%~30% higher.

How to Control the Thickness and Defect:

Thickness adjustment is realized by controlling pulp absorption time, for every 1s increase in slurry absorption time, the wet molded pulp tray thickness increases by 0.1~0.2mm.

• Edge is too thin: adjust the immersion angle of the die (15°~30° inclination is recommended).
• Uneven fiber distribution: optimize the slurry flow rate (0.5~1.0m/s) or add rheological additives (such as CMC, concentration 0.1%~0.3%).

Hot Pressing and Drying Process

Temperature-pressure coupling control Technology:

• Temperature range: 150~180 ℃ (measured temperature on the mold surface). Temperatures below 135 ℃ will result in incomplete curing of the resin and the product will be easily deformed.
• Pressure range: 1.5~3.0MPa, adjusted according to product density (target density 0.6~1.2g/cm³).
• Time control: fast food boxes (20~30s), industrial thick-walled parts (60~120s).

Pulp Mold Die Design Optimization:

• Meshless hot pressing mold: Made of mirror stainless steel (Ra≤0.8μm), it reduces surface texture and eliminates the need for finishing steps.
• Multi-cavity mold temperature control: zone heating (temperature difference ≤ 5 ℃ ) to avoid local overheating and warping.

Drying method:

• Hot air circulation drying: temperature 80~100 ℃ , time 20~40min, dryness ≥90%.
• Infrared drying: saves 30% energy, but the irradiation distance needs to be controlled (200~300mm) to prevent carbonization.

Moisture migration model:

• Initial stage (moisture content 30%~15%): surface moisture evaporation rate dominates, and high wind speed (2~3m/s) is required.
• Later stage (moisture content 15%~5%): internal diffusion control, the temperature needs to be lowered (60~70 ℃ ) to prevent cracking.

Post-processing and Quality Control

Finishing process:

• Laser trimming machine: accuracy ±0.1mm, remove burrs and emboss LOGO (depth 0.2~0.5mm).
• Roller calendering: Line pressure 50~80N/cm, eliminate reticulation, surface roughness Ra≤3.2μm.

Sterilization technology comparison:

Quality inspection standards:

• Physical properties: compressive strength (≥200N/100mm, GB/T 6544), drop test (no damage at a height of 1.2m).
• Hygiene indicators: coliform bacteria (not to be detected), heavy metal migration (Pb≤1mg/kg).

Pulp Mold Die Structural Design And Engineering

Pulp Mold Die Function-oriented Design:

• Positioning structure: The boss and the slot cooperate (tolerance ±0.2mm) to ensure the assembly accuracy of the product.
• Cushioning performance: Honeycomb hollow design (aperture 5~10mm), energy absorption rate increased by 40%.
• Load-bearing optimization: The thickness of the reinforcement rib is 1.5 times that of the base, and the spacing is ≤20mm (bending strength ≥50MPa).

Details processing:

• The fillet radius is ≥1.5mm to avoid stress concentration and fiber breakage.
• Surface texture: smooth surface (friction coefficient ≤ 0.15) for sliding assembly, rough surface (friction coefficient ≥ 0.3) for non-slip stacking.

Pulp Mold Die Materials And Manufacturing

Adsorption pulp mold die material selection:

• Aluminum alloy (6061-T6): lightweight (density 2.7g/cm³), suitable for fast-moving consumer goods molds (lifespan ≥ 500,000 times).
• Epoxy resin + glass fiber: complex curved surface molding (minimum corner fillet R0.5mm), cost reduction by 40%.

Hot stamping mold core technology:

• Brass mold: thermal conductivity 109W/(m·K), suitable for rapid heating (heating rate ≥5 ℃ /s).
• Stainless steel (316L): Excellent corrosion resistance, suitable for high humidity environments (lifespan ≥ 100,000 times).

Pulp Mold Die maintenance:

• Clean the mesh daily (ultrasonic cleaning, frequency 40kHz) to prevent fiber clogging.
• Check the mold cavity flatness every month (tolerance ±0.05mm), and if it exceeds the tolerance, it needs to be ground and repaired.

Molded Pulp Package Tray Compared with Plastic Packages

Pulp Molded Tray vs (EPS)Plastic Packages:

Pulp Molded Tray Application Cases

• Food industry: After a fast food chain brand adopted paper pulp lunch boxes, it reduced its annual plastic consumption by 1,200 tons and reduced its carbon emissions by 15%.
• Electronics industry: A mobile phone manufacturer uses a honeycomb structure lining, and the transportation damage rate is reduced from 3% to 0.5%.
• Medical field: Sterilized pulp trays replace PVC and meet ISO 13485 medical device packaging standards.

Join AGICO Now for Green Molded Pulp Package Production

The production of molded pulp package products is a deep integration of material science, mechanical engineering and an environmentally friendly process. AGICO supplies complete paper tray production line with refined process control, innovative structural design and efficient pulp mold die manufacturing, molded pulp tray products such as eggtrays, bottle trays, industrial package trays are perfect options to replace traditional plastic packaging. Join AGICO in the pulp molding industry will accelerate your company to upgrade to high-end and intelligent, and become one part of global green packaging.