What are the bottom sealing technologies for food paper buckets

Food paper buckets are an indispensable packaging format for the catering and retail industries. Their quality and safety are directly linked to the product experience and brand reputation. Bottom sealing technology is crucial for ensuring leak-proof, moisture-proof, and load-bearing performance. A sophisticated bottom seal not only ensures the safety of the contents but also enhances end-consumer satisfaction.

1. Heat Sealing

Heat sealing is currently the most mainstream and reliable bottom sealing technology used in food paper bucket production. It utilizes high temperature and high pressure to melt the coatings, such as polyethylene (PE) or polylactic acid (PLA), on the bottom and sides of the bucket. Pressure then fuses them together, creating a seamless seal.

Process Flow:

Preheating: The bottom paper and the barrel body of the bucket are preheated by a heating device before entering the sealing station.

Hot Pressing: The upper and lower molds (usually heated molds) are rapidly closed, applying high temperature and high pressure to the joint between the preheated bottom and barrel body. High temperature melts the coating, while high pressure ensures sufficient molecular penetration and bonding.

Cooling and Forming: After the press-fit process is complete, the mold rapidly cools, or the paper barrel enters a cooling stage, allowing the melted coating to solidify and form a secure seal.

Technical Advantages:

High Sealability: Hot-press sealing creates a continuous, uniform seal, effectively preventing liquid leakage and is particularly suitable for liquid foods such as soup and porridge.

High Load-Bearing Capacity: The cured PE or PLA coating forms a sturdy "bottom" that can withstand heavy weight and is not easily broken by the contents.

Automated Production: This technology is highly compatible with automated production lines, offering high efficiency and excellent consistency, making it suitable for large-scale mass production.

Applications:

Hot Drink Cups: For coffee, milk tea, etc.

Takeout Boxes: For porridge, noodles, and soup.

Ice Cream Buckets: Requires long-term low-temperature maintenance and moisture resistance.

2. Mechanical Crimping/Rolling

Mechanical crimping is a physical bottom-sealing technology, commonly used in early paper barrel production and for some non-fluid food packaging. This technology uses mechanical force to physically curl and nest the bottom edge of the paper barrel with the bottom edge of the barrel body, forming an interlocking structure.

Process Flow:

Pre-cutting and Punching: The paper barrel bottom is pre-punched to a specific shape, and the barrel body bottom is also pre-treated.

Mechanical Crimping: A specialized crimping die applies pressure and rotates the bottom and barrel body of the paper barrel, causing the edges to curl inward or outward, locking them together.

Technical Limitations:

Poor Sealing: Mechanical crimping relies primarily on physical locking rather than molecular fusion, resulting in inferior leak-proofing compared to heat press sealing and making it unsuitable for liquid packaging.

Limited Load-bearing Capacity: The load-bearing capacity is relatively low, and the crimping may loosen under heavy pressure.

Aesthetics: The crimping may be uneven, affecting the product's appearance.

Application Scenarios:

Dry goods packaging: Such as potato chip buckets and popcorn buckets, which do not require high sealing performance.

Some early or low-end paper barrel products.

III. Ultrasonic Sealing

Ultrasonic sealing is an emerging non-contact bottom sealing technology. It uses frictional heat generated by ultrasonic vibrations to instantly melt the joint between the bottom and the barrel, thereby achieving adhesion.

Process Flow:

Ultrasonic Vibration: An ultrasonic transducer generates high-frequency vibrations, which are transmitted to the joint of the paper barrel via a welding head.

Frictional Heating: High-frequency vibrations create intense friction on the contact surface, causing a sharp increase in local temperature and melting the coating.

Molecular Fusion: The melted coating fuses at the microscopic level, forming a strong bond.

Technical Advantages:

Fast and Efficient: The sealing process takes only milliseconds, resulting in extremely high production efficiency.

Energy-Efficient and Environmentally Friendly: No external heating is required, resulting in low energy consumption.

Cleanliness: The sealing process produces no smoke or odor, creating a friendly working environment.

Technical Challenges:

Equipment Cost: Ultrasonic equipment is relatively expensive, requiring a significant initial investment.

Process Parameter Control: Parameters such as amplitude, pressure, and time must be precisely controlled; failure to do so could result in a loose seal or damage to the barrel.

Application Scenarios:

High-end customized barrels.

Production lines with high demands for production speed and environmental friendliness.

IV. Cold Gluing (Adhesive Sealing)

Cold Gluing uses a food-grade adhesive to bond the barrel base to the barrel body. While simple to operate, it places extremely high demands on the adhesive's performance and safety.

Process Flow:

Gluing: Automated equipment precisely applies a layer of food-grade adhesive to the joint between the barrel base and barrel body.

Pressure: The mold applies pressure to the glued joint to ensure the adhesive fully penetrates and cures.

Technical Limitations:

Sealing: Tiny gaps may remain after the glue cures, making it less leak-proof than heat press sealing.

Safety: Environmentally friendly, non-toxic glue that meets food contact standards must be used, which is relatively expensive.

Curing Time: The adhesive requires a certain curing time, which may affect production cycle times.

Application Scenarios:

Some paper drums made of special materials are not suitable for heat press sealing.

Production lines with low production speed requirements.