The materials used to make paper bowls must balance load bearing, leakproofing and safety. The core is composed of a substrate, a functional coating and a small amount of auxiliary materials. Each material has a distinct function, and they work together to meet the special needs of paper bowl. It is classified as follows:
1.Core Substrate: Paper layer (Determines Load-Bearing Strength and hardness)
The paper layer is the basic skeleton of the paper bowl, providing structural support for the bowl and ensuring that the bowl holds food steadily without collapsing. Common types include:
Food-grade white cardboard: the most common basic material, dense in texture and hardness, with a smooth surface that is easy to print (such as brand logos and takeout paper bowls). Usually 250g/m2 to 400g/m2 thick, suitable for serving at room temperature or medium temperature (≤80°C), such as rice, noodles and stir-fried vegetables. It's cheap and easy to process. Kraft paper: Kraft kraft paper be used in paper bowls that prioritise eco-friendliness or great intensity requirements. Its fibres are highly elastic and tear resistant, allowing it to retain some stiffness even when wet, making it ideal for serving soupy foods or as an external support layer for takeaway bowls. Some kraft paper has been bleached to ensure its surface complies with food contact hygiene requirements.
Corrugated paper: Thickened paper bowls, used only in exceptional circumstances (such as large containers of food for families or outdoor picnic bowls) are made from a mix of corrugated core and tissue paper. The corrugated structure provides enhanced cushioning and heat retention, while also increasing overall carrying capacity. However, it is relatively bulky and rarely used in small, everyday paper bowls. ii. Key Functional Layer: Coating (Addressing Leakage Prevention and heat resistance issues)
paper substrate themselves are absorbent, so coating is needed to seal the interfiber gaps prevent fluid and grease from seeping through. Different coatings are suitable for different uses:
Polyethylene (PE) coating: The most commonly used coating material is polyethylene film, which is a lamination process on the inside of a paper layer (some outer layers are also coated with polyethylene to improve water resistance). Polyethylene is chemically stable and has a temperature resistance between -40°C and 110°C. It effectively stops the infiltration of water and oil and is safe to touch food (food grade PE compliant). Widely used in room temperature takeout bowls, cold drinks bowls, instant noodles buckets lining (Instant noodles buckets are generally "a"paper + PE"composite structure). Polypropylene (PP) coating: paper bowls suitable for contact with hot food (e.g. hot soup or freshly cooked food at ≤ 130°C). Polypropylene has better heat resistance and hardness than polyethylene, making the coating less susceptible to softening and deformation due to high temperature. Some microwaveable paper bowls (labeled "microwave") use polypropylene coatings, but they cost slightly more than polyethylene and are more demanding to process.
Plant-based paints (such as PLA paints): New environmentally friendly, biodegradable paints made from renewable sources such as corn and starch, using polylactic acid as a raw material, replace traditional plastic paints. It degrades in the natural environment after use and reduces white pollution. Suitable for eco-conscious restaurants or disposable eco-friendly paper bowls. However, it is slightly weaker (usually ≤90°C), more expensive and therefore not readily available. III. Supplementary Materials (Improving User Experience and Safety)
Adhesive: Used for seams (such as curled edges and connections between the bottom and the bowl body) in the making of paper bowls. Food-grade adhesives (such as water-based acrylic adhesive) must be used to ensure a strong bond and prevent the movement of harmful substances, which can lead to cracking and leakage if the bond fails.
Printing ink: For printing patterns on the outer layer of paper bowls only, food-grade eco-friendly ink (such as water-based ink) must be used. These inks do not contain heavy metals (such as lead and mercury) and volatile hazardous substances. The printed layer and the inner layer in contact with food must be separated by polyethylene or paper layer to prevent ink contamination.
Impermeable Film (Special Purpose): Some paper bowls used for high oil or corrosive foods (such as chili oil and acidic sauces) add an additional ultra-thin impermeable film (such as EVOH film) to the inner surface of the PE/PP coating to further enhance barrier properties and prevent prolonged exposure to oils or acidic substances that cause the coating to age and leakage.
