Recently, with the continuous fermentation of OLED display, OLED materials are hot, and the high barrier film has become the object of the pursuit of the capital.
So what is a high barrier film? This article decrypts the high barrier film on the tuyere for you.
"High barrier" is undoubtedly a very desirable property, which is one of the required characteristics of 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 material can effectively maintain the original performance of the product and extend the product life.
| common high separation materials
At present, polymer materials commonly used barrier materials are mainly the following kinds:
1. Polyvinylidene chloride (PVDC)
PVDC has excellent resistance to oxygen and water vapor.
PVDC's high crystallization, high density and the existence of hydrophobic base make its oxygen permeability and permeable gas rate is very low, so that PVDC has excellent gas barrier, compared with other materials can better extend the shelf life of packaging items, plus its printing adaptability, easy to heat seal, so it is widely used in the field of food and medicine packaging.
2. Ethylene-vinyl alcohol Copolymer (EVOH)
EVOH is a copolymer of ethylene and vinyl alcohol, which has very good barrier properties. This is because the molecular chain of EVOH contains the hydroxyl group, and the hydroxyl group on the molecular chain is easy to form hydrogen bonds, so that the intermolecular force is strengthened, the molecular chain accumulation is closer, so that the crystallinity of EVOH is higher, so that it has excellent barrier performance.
However, the structure of EVOH contains a large number of hydrophilic hydroxyl groups, which makes EVOH easy to absorb moisture, so that the barrier performance is greatly reduced. In addition, the high intramolecular and intermolecular cohesiveness and high crystallinity result in poor heat sealing performance.
3. Polyamide (PA)
Generally speaking, nylon gas resistance is good, but the water vapor barrier is poor, strong water absorption, and with the increase of water absorption and swelling, so that the gas resistance, moisture resistance performance sharply decreased, its strength and stability of package size will also be affected.
In addition, nylon has excellent mechanical properties, strong wear resistance, good cold resistance and heat resistance, good chemical stability, easy processing, good printability, but poor heat sealing.
PA resin has certain barrier characteristics, but the hygroscopic rate is large, which affects its barrier, so it can not be used as the outer layer.
4. Polyester (PET, PEN)
The most common and widely used barrier material in polyester is PET. PET has excellent barrier properties due to its symmetrical chemical structure, good molecular chain plane, tight molecular chain stack and easy crystallization orientation.
In recent years, PEN has been applied rapidly, which has good hydrolysis resistance, chemical resistance and UV resistance. The structure of PEN is similar to that of PET, except that PET has a benzene ring in its main chain, while PEN has a naphthalene ring in its main chain.
Because naphthalene has greater conjugated effect than benzene ring, the molecular chain is more rigid, and the structure is more planar, so PEN has better comprehensive performance than PET.
| high separation barrier technology of materials
In order to improve the barrier performance of the barrier material, the technical means commonly used at present are mainly as follows:
1. Multilayer composite
Multilayer composite refers to the composite of two or several films with different barrier properties through a certain process. In this way, osmotic molecules to reach the packaging interior has to pass through several layers of film, equivalent to extending the osmotic path, so that the barrier performance is improved.
The method synthesizes the advantages of various membranes to prepare a composite film with excellent comprehensive properties, and its process is simple.
However, compared with the intrinsic high barrier material, the thin film prepared by this method is thicker, and it is easy to appear bubbles or cracks and folds, which affect the barrier properties. Moreover, the equipment requirements are relatively complex and the cost is high.
2. Surface coating
Surface coating is the use of physical meteorological deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), molecular layer deposition (MLD), layer self-assembly (LBL) or magnetron sputtering deposition and other technologies on the polymer surface deposition of metal oxides or nitrides and other materials, so as to form a dense and excellent barrier coating on the surface of the film.
However, these methods have some problems, such as time-consuming process, expensive equipment and complicated technology, and the coating may produce pinhole, crack and other defects during service.
3. Nanocomposites
Nanocomposites are prepared by intercalation, in situ polymerization or sol-gel method using impenetrable sheet nanoparticles with large aspect ratio. The addition of flake nanoparticles can not only reduce the volume fraction of polymer matrix in the system to reduce the solubility of permeable molecules, but also prolong the permeable path of permeable molecules, reduce the diffusion rate of permeable molecules, so that the barrier performance is improved.
4. Surface modification
Polymer surface often contact with the external environment, easy to polymer surface adsorption, barrier, printing have an impact.
In order to make the polymer more suitable for everyday use, the surface of the polymer is usually treated. It mainly includes: surface chemical treatment, surface graft modification and plasma surface treatment.
This kind of method is easy to meet the technical requirements, the equipment is simple, the one-time investment cost is low, but can not achieve the long-term stability of the effect, once the surface is damaged, the barrier performance will be seriously affected.
5. Stretch both ways
By bidirectional stretching, the polymer film can be oriented in both vertical and horizontal directions, improve the order of molecular chain arrangement and pile more tightly, so that small molecules are more difficult to pass through, and then improve the barrier performance. This method complicates the preparation process of intrinsic high barrier polymer films, and the barrier performance is difficult to be significantly improved.
The application of | high barrier materials
High barrier film has already appeared in daily life, the current polymer high barrier material is mainly used in food and medicine packaging, electronic device packaging, solar cell packaging, OLED packaging.
1. Food and drug packaging
Food and drug packaging is the most widely used field of high barrier materials. The main purpose is to prevent the oxygen and water vapor in the air into the packaging and spoil food and medicine, and greatly reduce their shelf life.
For food and drug packaging, the barrier requirements are not particularly high, and the water vapor transmittance (WVTR) and oxygen transmittance (OTR) of the material should be lower than 10g/m2/day and 100cm3/m2 /day respectively.
2. Electronic device packaging
With the rapid development of modern electronic information, people have put forward higher requirements for electronic components, which are developing towards portability and multi-function. This puts forward higher requirements for electronic device packaging materials, which should not only have good insulation, but also be able to protect it from the corrosion of external oxygen and water vapor, but also have a certain strength, which requires the use of polymer barrier materials.
General electronic devices for packaging material barrier requirements for water vapor transmittance (WVTR) and oxygen transmittance (OTR) to be lower than 10-1g/m2/day and 1cm3/m2 /day.
3. Solar cell packaging
Because the solar energy is exposed to the air all year round, the oxygen and water vapor in the air are easy to corrode the metallized layer outside the solar cell, which seriously affects the use of the solar cell. Therefore, it is necessary to use high barrier materials for packaging of solar cell modules, which can not only ensure the service life of solar cells, but also enhance the resistance strength of the battery.
Solar cells for packaging material barrier requirements for water vapor transmittance (WVTR) and oxygen transmittance (OTR) to be lower than 10-2g/m2/day and 10-1cm3/m2/day.
4. OLED packaging
OLED has been placed in the next generation of display since the early stage of development, but its short life has been a major problem restricting its commercial application. The main reason affecting the service life of OLED is that electrode materials and luminous materials are very sensitive to oxygen, water and impurities, and are easy to be polluted, which leads to the deterioration of device performance, reducing luminous efficiency and shortening service life.
In order to ensure the luminous efficiency of the product and extend its service life, the device must be isolated from oxygen and water during packaging.
And in order to ensure the service life of flexible OLED display is more than 10000h, the water vapor transmittance (WVTR) and oxygen transmittance (OTR) of the blocking material must be lower than 10-6g/m2/day and 10-5cm3/m2/day, respectively. Its standard is much higher than the barrier performance requirements in the organic photovoltaic, solar cell packaging and packaging technology of food, medicine and electronic devices and other fields, so we must choose the flexible substrate material with excellent barrier performance to package the device, in order to meet the strict requirements of product life.
