Characteristics of co-extruded and laminated films

The majority of laminate films are made from plastic, but can also be made from paper, metal foil (usually aluminium) or fabric. In co-extruded films, all layers are extruded together at the same time, so there are no other non-plastic materials such as aluminium foil or paper.

Coextruded films can be layered under certain conditions, but co-extruded films do not, so they will behave differently under tensile tension; in addition, because the materials in co-extruded films are bonded together by hot melt, they produce spherical bubbles when pinched hard, whereas composite films do not produce spherical bubbles when pinched hard because they are bonded by binder.

Multi-layer co-extruded barrier film is a functional laminate film made by using multiple extruders to extrude a melt of a resin with high barrier properties and other resins, respectively, through a common die. Multi-layer co-extrusion is a green composite production process, especially for the current food packaging industry, using raw materials generally certified by the U.S. food and health safety agencies, raw materials by a special material pipeline centralised for each layer of the unified material supply, processing without raw material exposure, no environmental pollution and other phenomena. The concluding layer is modified LLDPE as raw material, which is non-toxic to the environment, food and human body, not to mention the traditional dry lamination, the so-called solvent residue phenomenon, no waste gas pollution; also different from the dry lamination, solvent-free lamination and general single-layer extrusion lamination process, which requires a dry box for processing, therefore, energy consumption is also less. In addition, the multi-layer co-extrusion lamination process also has the following advantages. Nanjing Sumino Seiko specialises in co-extruded film and laminated film production lines

(1) Low cost

The multi-layer co-extrusion process uses a variety of different functional resins to produce multi-functional laminated film products using only one blow moulding process, which reduces production costs. In addition, it is possible to reduce the thickness of the resin material to the minimum required to meet the customer's requirements, with the thinnest single layer being 2~3μm, which greatly reduces the amount of expensive resin used, thus reducing material costs.

(2) Structural flexibility

Multi-layer co-extrusion technology can be used to match a variety of raw materials in different combinations, making full use of the different properties of raw materials and forming them in one go, without being restricted by the relevant product specifications of the market, and can effectively meet the needs of different packaging occasions.

(3) High composite performance

Co-extrusion lamination process will be molten adhesive and base resin composite together, this process composite peel strength is very high, usually up to 3N/15mm or more, even can not be peeled, adapt to the general packaging materials. For products with high peel strength requirements, hot adhesive resin can be added to the composite, peel strength up to 14N/15mm, or even higher.

(4) Wide range of applications, wide range of use environments

Multi-layer co-extruded composite products can cover almost all packaging fields: food, daily chemical products, beverages, pharmaceuticals, protective films and even aerospace products, etc. Many domestic dry composite products have been used abroad with co-extrusion compounding process. Toothpaste tubes that cannot be produced by the dry lamination process. Paper-plastic aluminium composite products. Aerospace and other products are also used co-extrusion composite process to achieve. With co-extruded composite resin, process and equipment in all aspects of in-depth research and continuous innovation, multi-layer co-extrusion composite will expand to a broader range.

Firstly, multilayer co-extruded barrier films are a type of plastic film. In the field of plastic products, we usually call the thickness of 0.2 mm below the flat plastic products called plastic film, the thickness of 0.2 ~ 0.7 mm called plastic sheet, and the thickness of more than 0.7 mm called sheet.

Multilayer co-extruded barrier films should have certain gas barrier properties. Here the permeability refers to the ability of plastic products (containers, films) to shield small molecules of gas and odours. We usually use gas permeability to measure the size of the barrier performance of plastic products.

PE, PP and other general-purpose plastics gas permeability value is large, that is, the gas barrier performance is poor, while PA, PVDC, EVOH and other resin materials, gas permeability value is much lower than the general-purpose plastics, barrier performance is better. Therefore, we will usually contain at least PA, PVDC, EVOH in a resin material of the multilayer co-extruded film as a multilayer co-extruded barrier film. Nanjing Sumino Seiko specialises in co-extruded film and laminate production lines

Multi-layer co-extruded films containing PE, PA, TIE, EVOH and other resins are used for vacuum packaging of dairy products, jams, meat products, etc.

The multilayer co-extruded films are mostly made in a symmetrical 5-layer ABCBA structure, with PA or EVOH as the barrier layer and polyethylene as the heat sealing layer. PA or EVOH, which are extremely moisture-sensitive resins, are protected by the polyethylene layer and their excellent oxygen barrier properties are fully exploited.

In a general sense, the structure of a multilayer co-extruded film depends on the functional requirements of the film. The combination of different polymers is used to meet the functional requirements of the packaging material in terms of barrier, heat seal, body strength, thermal puncture, environmental suitability, secondary processing characteristics, extended storage and shelf life, etc., provided that the process requirements are met. In terms of functional requirements, a combination of five polymers is sufficient.

However, coextruded laminated films with seven, nine, eleven or even more layers are already being used in the market, making this a trend that is growing rapidly. The structural design of co-extruded films is gradually requiring a systematic approach to achieve the ideal combination of function, technology, cost, environmental protection, safety and secondary processing.

So what are the advantages of the structural features of multi-layer co-extruded films that combine the barrier and heat seal layers into a more multi-layer functional split? Here is an example of a 7-layer co-extruded film compared to a 5-layer co-extruded film:

1. Cost comparison

The substitution of a cheaper polymer for a more expensive polymer on the surface layer reduces the cost of the product and provides the heat sealing properties of an ionic chain polymer and high moisture barrier properties. A 7-layer co-extruded blown film is more economical than a 5-layer material with the same barrier and heat sealability.

2. Barrier properties

By replacing a single polymer with two different polymers on the barrier layer, the barrier properties can be greatly improved. For example, combining an EVOH layer with a typical nylon material maintains the impermeability of PA, but because the EVOH layer is sandwiched between two layers of PA amine, it increases the strength of the EVOH and improves the crack resistance of the EVOH, making it a film with high barrier properties that are not possible with a 5-layer co-extruded filmze. The increased cost of adding EVOH can be added to the total consumption of the structure. 20% PA structured 5-layer co-extruded films have an oxygen transmission rate of 3.5 units, but attaching EVOH to a 7-layer film under the same conditions results in a transmission rate of 0.13 units. Nanjing Sumino Seiko specialises in co-extruded film and laminated film production lines

3. Anti-cracking properties

The performance of PA co-extruded films with up to five layers can be improved by using co-extruded films with more layers. For example, the use of additional adhesive layers can improve the film's barrier properties by increasing the film's water vapour barrier effect. Another advantage gained is that the film can be made softer, have a better feel and have good crack resistance.

As polymer synthesis technology continues to advance, new polymers with unique physical and mechanical properties can be used to meet a wide range of packaging needs. The functionality and structure of multi-layer co-extruded composite base films will have greater flexibility and economy. The application and refinement of forming equipment and processes, together with the unique and effective design of the composite structure, will revolutionise the pursuit and mindset of film manufacturers with regard to the diversification of packaging functions, the rationalisation of packaging structures and the maximisation of packaging benefits.

Co-extruded and laminated films are both common packaging materials used in the plastic flexible packaging industry, and those who know something about them often have trouble distinguishing between them. Here is a brief explanation of the obvious differences between them.

1. Process differences
In the processing of film, a raw material is extruded onto another film already made or different types of film already made, using adhesives to bond to each other and become a multi-layer film, a product called composite film. Co-extruded films have most of the characteristics of composite films, but there is one difference, namely that all layers of co-extruded films are extruded together at the same time, and the layers are bonded to each other by hot melt without adhesives.

2. The difference in raw materials
Most laminates are made from plastic, but can also be made from paper, metal foil (usually aluminium) or fabric. In co-extruded films, all layers are extruded together at the same time, so there will be no other non-plastic materials such as aluminium foil or paper. Co-extruded films do not use aluminium foil.

3. Differences in identification techniques
Coextruded film can be layered under certain conditions, but co-extruded film will not, so there will be different forms of expression between the two under tensile tension; in addition, because the materials of co-extruded film are bonded together by hot melt, so when pinched, it will produce bubbles like spheres, while composite film is bonded by binder, so when pinched, it will not produce spherical bubbles.