The inevitable choice of plastic packaging for the

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The inevitable choice of plastic packaging for high barrier materials

packaging, especially plastic packaging, can be seen everywhere in modern society. The rapid development of the packaging industry is due to its ability to protect and stabilize products for a long time, and to avoid product damage, pollution and moisture. To achieve the best protection effect, high barrier materials are the inevitable choice

in a broad sense, barrier packaging has been used for many years. Barrier packaging is designed to protect the product and its contents from the infiltration of pollutants, flavors, pigments and odors. Sometimes, it is also used to prevent the leakage of the contents

in other cases, multi-layer structure (lamination or coextrusion) is required to improve strength and barrier performance. Even for seemingly simple products such as fast food, the packaging can be very complex. These multilayer structures often contain 7 or more different plastic layers, and each layer has different structural barrier or bonding effects

synthetic special barrier resin, namely polyvinylidene chloride (PVDC), came out in the 1950s. After the development in the 1960s, plastic barrier packaging has experienced great development since then. Soon, ethylene/vinyl alcohol (EVOH) was put into commercial application in the 1970s

barrier packaging industry has been changing since then. Because different applications have different requirements, ideal polymer barrier materials do not exist now and may never appear. For example, in some cases, such as PVC film with poor oxygen barrier properties, it is often used in supermarkets as meat packaging display, mainly because PVC film can keep meat red and attract customers during display time. However, if meat needs long-term transportation or storage, it must have good oxygen barrier performance to prevent meat deterioration

(I) at present, barrier packaging plastics can indeed be damaged to meet the needs. However, problems still exist, which restrict the application and development of barrier packaging plastics in many applications. These problems mainly include:

(1) high cost, generally higher than simple single-layer plastic packaging, such as LDPE and LLDPE

(2) it is particularly easy to pollute and degrade when exposed to water. EVOH is the most suitable material to solve this problem, but hydroxyl not only gives excellent barrier properties, but also makes the material easy to hydrolyze. Therefore, EVOH can only be used as the inner layer of multilayer structure

(3) treatment and reuse. Most multi-layer packaging contains a variety of plastics (such as HDPE and PET), so it is not easy to mix and reuse

(4) challenges from alternative materials. Traditional materials such as glass and new materials such as silica glass veneer can provide excellent barrier properties

(II) according to its oxygen and water permeability and air permeability, the barrier is 2 Price reference: the resin shall have the following permeability characteristics:

1. oxygen: the resin whose oxygen permeability (OTR) is less than 2ml/mil thickness/100 square inches under atmospheric pressure for 24 consecutive hours. Most oxygen permeability measurements are carried out at a temperature of 73 ℃ and a relative humidity determined according to specific conditions. Many conventional resins have an oxygen permeability of 5, while most new resins are equal to or lower than 1. For example, the oxygen permeability of standard metallized PET film does not exceed 0.3; Materials with oxygen permeability lower than 0.1 are classified as high barrier materials, including PVDC and EVOH. Other materials are classified as medium barrier materials

2. water vapor (moisture): resin with moisture permeability (WVTR) lower than 0.1. We define and classify the structure of moisture barrier polymers according to the classification of pharmaceutical blister packaging industry. In other words, films with moisture permeability higher than 0.1 are classified as ultra-low barrier films, films from 0.06 to 0.1 are classified as low barrier films, films from 0.03 to 0.06 are classified as medium barrier films, and films equal to or lower than 0.03 are classified as high barrier films

a variety of resin films with moisture permeability of 1 have been put on the market for many years. Ptcfe is the latest and best moisture proof film at present, and its moisture permeability is lower than 0.3. It is considered to be the only high moisture proof film resin at present. The moisture permeability is generally measured at 100 ℃ and 90% relative humidity

(III) various barrier materials

1, Polyoxymethylene (POM)

polyoxymethylene is a multifunctional engineering resin. Its chemical structure, regular molecular structure and high crystallinity make it have excellent resistance to water, gasoline, research and development of graphene composites for dissolved wires and cables, structural design and process design of graphene cables, preparation and filing of product standards, achievement transformation and industrialization promotion agents, and a variety of other neutral chemicals

pom can be processed by injection molding and extrusion. Its specific uses include: air spray container, gasoline tank cover, chemical spray, soap dispenser, paint mixer, water pipe fittings, gears, creep resistant shell, wear-resistant surface, etc

the barrier test shows that the film thickness exceeds the maximum stress before the first drop of the force; When the lower yield point is mils without initial transient effect, the permeability of unfilled Ticona Celcon polyoxymethylene and glass reinforced polyoxymethylene is roughly the same. DuPont Delrin products have excellent permeability resistance and strength characteristics for a variety of substances, making them suitable for use as containers, especially air spray containers

ticona Celcon POM can withstand high humidity and high temperature water for a long time. Therefore, this material is widely used in water pipe related applications

2. Acrylonitrile resin (AMA)

this is a transparent rubber modified acrylonitrile material, which has excellent chemical resistance, gas resistance and high modulus or stiffness. It is mainly used for packaging. The permeability of AMA depends on the presence of additives and the chemical composition of acrylonitrile and comonomer categories. Hot forming, film extrusion, sheet extrusion, extrusion blow molding, tape casting, injection molding, injection blow molding and injection drawing blow molding can be used

it is mainly used for packaging, including food packaging: processing meat, fish, cheese, condiments, sauces, juices and concentrated fruit juices; Drug packaging: pharmaceutical and skin patches; Personal care: cosmetic packaging, mouthwash, perfume, etc

The barex of

bp is a kind of acrylonitrile/methyl methacrylate copolymer grafted on acrylonitrile rubber. Barex 210 and 218 resins are high barrier and impact resistant modified copolymer resins. Compared with all kinds of plastics used in single-layer packaging, barex resin has the lowest oxygen permeability. Its performance often exceeds that of multi-layer structure containing EVOH and pvdg, and its cost is low. Encapsulated in nitrogen, carbon dioxide and other beneficial gases, it can prolong the storage life and prevent oxygen from entering the package

under various relative humidity, barex resin has extremely high barrier to oxygen. However, the increase of temperature will affect the barrier performance. In terms of water vapor barrier properties, barex resin is comparable to other plastic packaging materials other than polyolefins. In applications where waterproof requirements are critical, the water vapor barrier performance of barex resin can be enhanced by polyolefin orientation or lamination. (to be continued)

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