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how much do you know about the barrier material in plastic packaging industry- EVOH
- Aug 08, 2018 -

Introduction

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EVOH has been the most widely used high barrier material. The film type of this material in addition to the non tensile type, there are two-way stretching type, aluminum evaporation, adhesive coating type, and two-way tensile type of heat-resistant type for aseptic packaging products.
  The barrier properties of EVOH depend on the content of ethylene, and generally when the ethylene content increases, the gas barrier decreases, but it is easy to process.
  EVOH is characterized by excellent barrier to gas and excellent processability, in addition to transparency, gloss, mechanical strength, scalability, wear resistance, cold resistance and surface strength are excellent.
Performance
  In today's available polymers, the gas permeability of polyvinyl alcohol (PVOH) is the lowest. However, the Pvoh is water-soluble and difficult to process.
  The EVOH copolymer is made from ethylene and vinyl acetate, and then by hydrolysis of the copolymer to obtain ethylene-vinyl alcohol. Therefore, the high barrier effect is still retained, and there is a noticeable improvement in moistureproof and processability.
  In nature, the Evoh copolymer is highly crystalline, and its properties depend mainly on the relative concentration of the copolymer monomer. Generally speaking, when the ethylene content increases, the gas barrier performance decreases, moistureproof performance improves, and the resin is easier to process.
  The most notable characteristic of Evoh resin is its barrier effect on gas. It is used in the packaging structure to improve the retention of fragrance and quality by preventing the infiltration of oxygen. In the use of inflatable packaging technology, EVOH resin effectively retained to protect the product of carbon dioxide or nitrogen.
  Due to the presence of hydroxyl groups in the molecular structure of EVOH resins, evoh resins have hydrophilic and hygroscopic nature. When the adsorption of moisture, the gas barrier properties will be affected.
  However, the moisture content in the barrier layer can be carefully controlled, using multi-layer technology, such as polyolefin and other strong wet resin to wrap up the Evoh resin layer, you can do this.
  Evoh Resin also has a strong resistance to oil and organic solvent performance. After 1 years of immersion in various solvents and oils, the percentage of weight increase is as follows: The solvent of cyclohexane, xylene, petroleum ether, benzene and acetone is 0%, and the ethylene glycol is 2 68°f. 3%, the methanol is 12. 2%, the salad oil is 0. 1%
  EVOH resin has high mechanical strength, elasticity, surface hardness, wear resistance and weather resistance, and has strong antistatic properties. The Evoh film has high gloss and low haze, so it is highly transparent.
  EVOH resin is the most commercially strong barrier resin, the highest thermal stability of the resin, this property allows the production of waste can be recycled and reused, raw materials containing up to more than 20% of the Evoh.
Processing technology
There are three basic ways to use EVOH to provide compartments in multiple layers of structure: coextrusion. The Evoh resin is formed by the combination of polyolefin or poly-phenolic amine. Evoh films are laminated onto other substrates or coated with other materials. Coating of various substrates or single-layer containers with evoh resin. Without special changes, it is easy to process on traditional manufacturing equipment.
  Using commercial equipment, EVOH resins are suitable for the following processes: Single or multilayer thin film extrusion, sheet and profile extrusion, coextrusion blow molding, coextrusion coating, lamination (or lamination) and injection molding.
  Two processes, such as thermoforming, vacuum forming and printing, which contain EVOH resin frames or evoh films, are easy to carry out. Like other polymers, evoh resins can be modified by overheating.
  Coating techniques, including multilayer or coextrusion coatings, can also be used to produce multilayer structures, and the resulting structure is very similar to the coextrusion structure. can be used Evoh resin spraying, immersion or drum coating methods. The production of containers containing carbonated beverages or to the purpose of blocking solvents, spices or odors. The adhesion of evoh resins to most polymers is poor, and in order to overcome this difficulty, special design bonding resins or "bonding resins" are required. Except for nylon, the EVOH resin can be well adhered to nylon without the use of a bonding resin.
Application
Barrier-layer structures containing EVOH resins are used in all hard and soft packaging and in all types of food processing, including aseptic, hot-injected, and pressurized cooking. Products containing EVOH materials are: condiments (soy sauce), tomato sauce, juice, edible batter, meat products, cheese products and processed fruits.
  Non-food applications include solvents, chemicals and packaging of pharmaceutical-related products.
  Manufacturers of fuel tanks, fuel tubes and air-conditioning equipment for motor vehicles are evaluating the use of EVOH structures to reduce hydrocarbon and/or freon emissions.

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