The difference and characteristics between co extruded film and composite film

  In the processing of thin films, one raw material is extruded onto another already made thin film or onto different types of already made thin films, which are then bonded together using an adhesive to form a multi-layer film. This product is called a composite film. Co extruded film has most of the characteristics of composite film, but there is one difference, that is, all layers of co extruded film are extruded at the same time, and the layers are bonded by hot melt without adhesive.

    Multi layer co extruded barrier film refers to a functional composite film produced by using multiple extruders to separately extrude a melt of resin with high barrier properties and other resins through a shared die. Multi layer co extrusion composite is a green composite production process, especially for the current food packaging industry. The raw materials used are generally certified by the US food and health safety agency.

    The raw materials are centrally supplied to each layer through specialized feeding pipelines, and there is no exposure of raw materials or environmental pollution during the processing. The bonding layer is made of modified LLDPE as raw material, which is non-toxic to the environment, food, and human body, and does not exhibit traditional dry composite, i.e. solvent residue phenomenon, and has no waste gas pollution; Unlike dry composite, solvent-free composite, and general single-layer extrusion composite processes, which require a drying oven for processing, energy consumption is also lower. In addition, the multi-layer co extrusion composite process also has the following advantages.

(1) The low cost multi-layer co extrusion composite process uses a variety of resins with different functions, and only one blow molding process can be used to produce multifunctional composite film products, which can reduce production costs. Moreover, the resin raw materials with the required performance can be reduced to the minimum thickness while meeting the customer's usage requirements. The thinnest single layer can reach 2-3 μ m, greatly reducing the amount of expensive resin used and thus lowering material costs.

(2) The flexible multi-layer co extrusion technology can combine multiple raw materials in different combinations, fully utilizing materials with different properties. It can be molded in one go without being limited by market related product specifications, effectively meeting the needs of different packaging occasions. The more layers there are, the more flexible the structural design, and the lower the cost.

(3) The co extrusion composite process with high composite performance combines the melted adhesive and base resin together. The peel strength of this composite is very high, usually up to 3N/15mm or more, and even cannot be peeled off, which is suitable for general packaging materials. For products with high requirements for peel strength, thermal adhesive resin can be added for composite, and the peel strength can reach 14N/15mm or even higher.

(4) Widely used and widely applicable, multi-layer co extruded composite products can cover almost all packaging fields: food, daily chemical products, beverages, pharmaceuticals, protective films, and even aerospace products. Currently, many dry composite products in China have adopted co extrusion composite technology abroad. Toothpaste tubes that cannot be produced by dry composite technology. Paper plastic aluminum composite products. Aerospace and other products are also produced using co extrusion composite technology. With the in-depth research and continuous innovation in co extrusion composite resin, process, and equipment, multi-layer co extrusion composite will expand to a wider range.

Firstly, multi-layer co extruded barrier film is a type of plastic film. In the field of plastic products, we usually refer to flat plastic products with a thickness of less than 0.2 mm as plastic films, those with a thickness between 0.2 and 0.7 mm as plastic sheets, and those with a thickness greater than 0.7 mm as sheets.

Multi layer co extruded barrier film should have certain gas barrier properties. The impermeability here refers to the shielding ability of plastic products (containers, films) against small molecule gases and odors. We usually measure the opacity of plastic products by gas permeability.

General plastics such as PE and PP have higher gas permeability values, indicating poorer gas barrier properties, while resin materials such as PA, PVDC, EVOH have much lower gas permeability values than general plastics, indicating better gas barrier properties. Therefore, we usually refer to multi-layer co extruded films containing at least one resin material from PA, PVDC, or EVOH as multi-layer co extruded barrier films.

Multi layer co extruded products of resins such as PE, PA, TIE, EVOH, etc. can be used for vacuum packaging of dairy products, jams, meat products, etc.

Multi layer co extruded films often adopt a symmetrical structure of ABCBA5 layers, with PA or EVOH as the barrier layer and polyethylene as the heat sealing layer. Adhesive resin is used to separate non connected barrier layers and heat sealing layers. PA or EVOH is a resin that is extremely sensitive to humidity and is protected by a polyethylene layer, fully utilizing its excellent oxygen barrier properties.

In general, the structure of multi-layer co extruded film depends on the functional requirements of the film. On the premise of meeting the process requirements, different polymer combinations are used to meet the functional requirements of packaging materials, such as barrier, heat sealing, body strength, thermal puncture, environmental adaptability, secondary processing characteristics, extended storage and shelf life. From the analysis of functional requirements, a combination of five polymers is sufficient.

But co extruded composite films with seven, nine, eleven, or even more layers have begun to be applied in the market, making it a trend and rapidly developing. The structural design of co extruded films is gradually required to systematically achieve the ideal state of integrating functionality, technology, cost, environmental protection, safety, and secondary processing.