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Recently, with the continuous fermentation of OLED display, OLED materials have become popular, and the high barrier film has become the target of the capital world. What is the high barrier film? "High barrier" is undoubtedly a very ideal property, which is one of the features required by many polymer packaging materials. In technical terms, high barrier refers to the very low permeability of low molecular weight chemicals, such as gases and organic compounds.

High barrier packaging materials can effectively maintain the original performance of the product and extend the life of the product.

 

Common high barrier materials

 

At present, the commonly used barrier materials in high polymer materials mainly include the following:

 

1

Polyvinyl Dichloride（PVDC）

 

PVDC has excellent barrier to oxygen and water vapor.

The high crystallinity, high density and the existence of hydrophobic groups of PVDC make the water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) extremely low, which makes PVDC have excellent gas barrier performance. Compared with other materials, PVDC can better extend the shelf life of packaging articles. In addition, it has good printing adaptability and is easy to be heat sealable, so it is widely used in the field of food and drug packaging.

 

2

Ethylene vinyl alcohol copolymer（EVOH）

 

EVOH is a copolymer of Ethylene and Vinyl Alcohol, with very good barrier performance. This is because the molecular chain of EVOH contains OH groups, and hydrogen bonds are easily formed between the OH groups on the molecular chain, so that the intermolecular force is strengthened, the molecular chains are stacked more closely, so that the crystallinity of EVOH is higher, thus having excellent barrier performance.

But the online coating learned that EVOH structure contains a lot of hydrophilic OH groups, which makes EVOH easy to absorb moisture, thus greatly reducing the barrier performance; In addition, the high cohesion and high crystallinity between molecules and within molecules lead to poor heat-sealing performance.

 

3

Poly amide（PA）

 

Generally speaking, nylon has good gas resistance, but it has poor water vapor resistance and strong water absorption. It swells with the increase of water absorption, resulting in a sharp decline in gas resistance and moisture resistance. The strength and packaging size stability will also be affected. 

In addition, nylon has excellent mechanical performances, toughness and wear resistance, good cold and heat resistance, good chemical stability, easy processing, good printing ability, but poor heat-sealing performance.

PA resin has a barrier performance, but its moisture absorption rate is large, which affects its barrier performance, so it can’t be used as an outer layer generally.

 

4

Polyester（PET、PEN）

 

PET is the most common and widely used barrier material in polyester. PET has excellent barrier performance due to its symmetrical chemical structure, good flatness of molecular chains, tight stacking of molecular chains and easy crystallization orientation.

In recent years, PEN has a rapid development in application and with good hydrolysis resistance, chemical resistance and UV resistance. The structure of PEN is similar to that of PET, the difference is that the main chain of PET contains benzene ring, while the main chain of PEN is naphthalene ring.

Because naphthalene ring has greater conjugation effect than benzene ring, its molecular chain is more rigid and its structure is more planar, so PEN has better comprehensive performance than PET.

 

 

Barrier technology of high barrier materials

 

In order to improve the barrier performance of barrier materials, the following technical means are commonly used at present:

 

1

Multi-layer lamination

 

Multi-layer lamination refers to the lamination of two or more films with different barrier performance through a process. In this way, if the permeation molecules want to reach the inside of the packaging, they must pass through several layers of film, which is equivalent to extending the permeation path, thus improving the barrier performance.

The method is a lamination film with excellent comprehensive performance prepared by combining the advantages of various films, and the process is simple.

However, compared with the intrinsic high barrier material, the film prepared by this method is thicker, and it is easy to have problems that will affect the barrier performance, such as bubbles or cracks and folds. Moreover, the equipment requirements are relatively complex and the cost is high.

 

2

Surface Coating

 

Surface coating refers to the deposition of metal oxides or nitrides on the polymer surface by physical meteorological deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), molecular layer deposition (MLD), layer by layer self-assembly (LBL), or magnetron sputtering deposition, so as to form a dense coating with excellent barrier performance on the film surface.

However, these methods have problems such as time-consuming process, expensive equipment and complex process, and the coating may produce pinholes, cracks and other defects in the service process.

 

3

Nano lamination material

 

Nano lamination material is a kind of material made of schistose structure nano-particles which is impermeable and with large length-diameter ratio by Intercalation method, in-situ polymerization or sol-gel method. The addition of schistose structure nano-particles can not only reduce the volume fraction of polymer matrix in the system to reduce the solubility of permeation molecules, but also extend the permeation path of permeation molecules, reduce the diffusion rate of permeation molecules, and improve the barrier performance.

 

4

Surface Modifier

 

The polymer surface is easy to affect the adsorption, barrier and printing of the polymer surface due to its frequent contact with the external environment.

In order to make the polymer better used in daily life, the surface of the polymer is usually treated. It mainly includes surface chemical treatment, surface grafting modifier and plasma surface treatment.

The technical requirements of such methods are easy to meet, the equipment is relatively simple, and the one-time investment cost is low, but the long-term stability cannot be achieved. Once the surface is damaged, the barrier performance will be seriously affected.

 

5

Biaxially Oriented

 

Through biaxially oriented, the polymer film can be oriented in both vertical and horizontal directions, so that the order of molecular chain arrangement is improved, and the stacking is more compact, so that small molecules are more difficult to pass through, thus improving the barrier performance. This method makes the preparation process of the intrinsic high barrier polymer film complex, and the barrier performance is difficult to be significantly improved.

 

Application of High Barrier Materials

 

In fact, high barrier film has already appeared in daily life. At present, high polymer high barrier materials are mainly used in food and drug packaging, electronic element packaging, solar cell packaging, OLED packaging.

 

Packaging of Food and Drug

 

EVOH 7-layer co-extrusion barrier film

Food and drug packaging is currently the most widely used field of high barrier materials. It is mainly to prevent the oxygen and water vapor in the air from entering the packaging to deteriorate the food and drugs and greatly reduce the shelf life.

According to the online coating, the barrier requirements for food and drug packaging are not particularly high, and the water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) of the barrier materials are required to be lower than 10g/m2/day and 100cm3/m2/day respectively.

 

Packaging of Electronic Elements

Electronic Elements Packaging Film

With the rapid development of modern electronic information, people put forward higher requirements for electronic elements, which are developing towards portability and multi-function. This puts forward higher requirements for packaging materials of electronic elements. They should not only have good insulation, but also be able to protect them from the corrosion of external oxygen and water vapor, and also have a certain strength, which requires the use of high polymer barrier materials. 

The barrier performance requirements for packaging materials of general electronic elements are that the water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) should be lower than 10-1g/m2/day and 1cm3/m2/day, respectively.

 

 

Packaging of Solar Cell

Solar cell packaging film

As solar energy is exposed to the air all the year round, oxygen and water vapor in the air are easy to corrode the metallised layer outside the solar cell, which seriously affects the use of solar cells. Therefore, it is necessary to package the solar cell module with high barrier materials, which can not only ensure the service life of the solar cell, but also enhance the impact resistance strength of the battery.

According to the online coating, the requirements for the barrier performance of solar cells to packaging materials are that the water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) should be lower than 10-2g/m2/day and 10-1cm3/m2/day, respectively.

 

Packaging of OLED

OLED packaging film

OLED has been entrusted with the important task of the next generation display since its early development, but its short life has always been a major problem that restricts its commercial application. The main reason that affects the service life of OLED is that electrode materials and luminous material are very sensitive to oxygen, water and impurities, and are easy to be contaminated, leading to the reduction of element performance, thereby reducing the luminous efficiency and shortening the service life.

In order to ensure the luminous efficiency of the product and extend its service life, the element must be isolated from oxygen and water during packaging. In addition, in order to ensure that the service life of flexible OLED displays is longer than 10000h, the water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) of barrier materials must be lower than 10-6g/m2/day and 10-5cm3/m2/day respectively, which are far higher than the standard for barrier performance in the fields of organic photovoltaic, solar cell packaging, food, drug and electronic element packaging technology, Therefore, flexible base materials with excellent barrier performance must be selected to package elements to meet the strict requirements of product life.

This article is from "Injection molding Network".

 

Guangdong Weifu Packaging Material Co., Ltd. has been established for 38 years, with a registered capital of 45.2 million US dollars, a fixed investment of 1 billion RMB and an annual sales volume of 3 billion RMB. Weifu has multiple subsidiaries and production bases to support each other, and is equipped with leading film and woven sacks production equipment from domestic and abroad. The products and customized services are not only imported into the world's top 500 enterprises, but also exported to the USA, Italy, Germany, Southeast Asia, more than 20 countries and regions. With the goal of realizing green and environmental protection in the whole process of products,Weifu integrates diversified industrial resources and builds an international group enterprise with core competitiveness.