Sheet is a design decision

Most packaging briefs start with a shape. The more interesting ones start with the sheet: a black core with white skins so the container looks premium without printing, a coloured inner layer for brand coding, or a recycled core hidden between two virgin skins. All of these are co-extrusion decisions, made on the extruder long before anyone opens a mold drawing. Shantou Longsheng Industry Co., Ltd. builds the DSI-PP multi-layer co-extrusion line for this class of work.

What multi-layer buys you

• A hidden function layer — a recycled or mineral-filled core cuts cost and carbon while the food-contact surface stays virgin
• Colour without ink — a pigmented core under transparent skins gives depth printing cannot match
• Barrier adjustment — an EVOH or tie layer where oxygen and moisture control matters
• Shrinkage tuning — a core with different filler loading balances warp in thin-wall parts

Design limits worth respecting

Co-extrusion does not remove physics. Total thickness still sets stiffness, so a three-layer sheet with a 40 percent recycled core is less rigid than solid virgin sheet of the same gauge; the design has to add ribs or gauge where it matters. Layer adhesion is the other limit: incompatible resins need a tie layer, which costs money and thickness. Discuss both with the machine supplier before the mold is cut.

Processing consequences downstream

Co-extruded sheet behaves slightly differently in thermoforming. Skins and core soften at different rates, so the heating profile has to be re-tuned; our service team runs a heating trial on the customer's own mold during commissioning. Trimming matters too, because a brittle core can chip at the cut line if the sheet is too cold.

Matching line to product

• DSI-PP multi-layer co-extrusion for PP food containers, cups and trays in two or three layers
• LSI series PET/PLA single-screw extruder with drying and crystallising system for APET and PLA sheet where moisture control is decisive
• SI-PE for PE-based and industrial sheet

About Shantou Longsheng

Shantou Longsheng Industry Co., Ltd., founded 1998 in Shantou, Guangdong Province, operates a 30,000 m² plant, holds the "Longsheng" trademark, 25 granted patents (1 invention, 24 utility models) and high-tech enterprise status. We supply sheet extruders, multi-station thermoformers, vacuum forming machines, cup making machines and precision molds.

Visit https://www.stlongsheng.com