Recently, with the continuous fermentation of OLED display, OLED materials topic are very hot, and the high resistance diaphragm has become the target of capital industry.
What is the high resistance diaphragm? This article is for you to decipher the high resistance diaphragm on the tuyere.
"High barrier" is undoubtedly a very ideal property, which is one of the characteristics required by many polymer packaging materials. In technical terms, high barrier refers to the very low permeability to low molecular weight chemicals, such as gases and organic compounds.
High barrier packaging materials can effectively maintain the original performance of products and extend the service life of products.
|Common high barrier materials
At present, the barrier materials commonly used in polymer materials are as follows:
1. Polyvinylidene chloride (PVDC)
PVDC has excellent barrier to oxygen and water vapor.
PVDC's high crystallinity, high density and hydrophobic group make its oxygen permeability and gas permeability very low, which makes PVDC have excellent gas barrier, which can better extend the shelf life of packaging products compared with other materials. In addition, it has good printing adaptability and easy heat sealing, 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, which has very good barrier performance. This is because the molecular chain of EVOH contains hydroxyl groups, and the hydroxyl groups on the molecular chain are easy to form hydrogen bonds, so that the intermolecular force is strengthened and the molecular chain is more tightly stacked, which makes EVOH have higher crystallinity and excellent barrier performance.
However, EVOH structure contains a large number of hydrophilic hydroxyl groups, which makes EVOH easy to absorb moisture, thus greatly reducing the barrier performance; In addition, the large cohesive force and high crystallinity between molecules lead to poor heat sealing performance.
3. Polyamide (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 and moisture resistance. The stability of its strength and package size will also be affected.
In addition, nylon has excellent mechanical properties, strong toughness and wear resistance, good cold and heat resistance, good chemical stability, easy processing, good printability, but poor heat sealing property.
PA resin has a certain barrier property, but its moisture absorption rate is high, which affects its barrier property, so it can not be used as outer layer.
4. Polyester (PET, pen)
Pet is the most common and widely used barrier material in polyester. Pet has excellent barrier properties due to its symmetrical chemical structure, good planarity of molecular chain, close stacking of molecular chain and easy crystal orientation.
In recent years, the application of pen is developing rapidly, which has good resistance to hydrolysis, chemicals and UV. The structure of pen is similar to that of pet, but the main chain of pet contains benzene ring, while the main chain of pen contains naphthalene ring.
Because of the greater conjugation effect of naphthalene ring than benzene ring, higher molecular chain rigidity and more planar structure, pen has better comprehensive properties than pet.
Barrier technology of high barrier materials
In order to improve the barrier performance of barrier materials, the commonly used technical means are as follows:
1. Multilayer composite
Multilayer composite refers to the combination of two or several films with different barrier properties by a certain process. In this way, the permeation molecules have to pass through several layers of membranes in order to reach the interior of the package, which is equivalent to extending the permeation path and improving the barrier performance.
This method is a kind of composite film with excellent comprehensive properties, which combines the advantages of various films.
However, compared with the intrinsic high barrier material, the film prepared by this method is thicker, and it is easy to have problems such as bubbles or cracking folds, which affect the barrier performance. Moreover, the equipment requirements are relatively complex and the cost is high.
2. Surface coating
Surface coating is the deposition of metal oxide or nitride on polymer surface by physical vapor 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 and excellent barrier coating on the film surface.
However, these methods are time-consuming, expensive equipment and complex process, and the coating may have pinholes, cracks and other defects in service.
3. Nanocomposites
Nanocomposites are nanocomposites made by intercalation, in situ polymerization or sol-gel method, using inpermeable and large size ratio of flake nanoparticles. The addition of flake nanoparticles can not only reduce the volume fraction of polymer matrix in the system to reduce the solubility of permeating molecules, but also extend the permeation path of permeating molecules, reduce the diffusion rate of permeating molecules, and improve the barrier performance.
4. Surface modification
Due to the frequent contact with the external environment, the surface adsorption, barrier and printing of polymer are easily affected.
In order to make the polymer better used in daily life, the surface of polymer is usually treated. It mainly includes: surface chemical treatment, surface grafting modification and plasma surface treatment.
This kind of method is easy to meet the technical requirements, simple equipment, low one-time investment cost, but can not achieve long-term stable effect, once the surface is damaged, the barrier performance will be seriously affected.
5. Biaxial tension
By biaxial stretching, the polymer film can be oriented in both vertical and horizontal directions, the order of molecular chain arrangement is improved, and the stacking is more compact, so that small molecules are more difficult to pass through, and the barrier performance is improved. This method complicates the preparation process of intrinsic high barrier polymer film, and the barrier performance is also difficult to be significantly improved.
|Application of high barrier materials
In fact, high barrier materials have already appeared in daily life. At present, high barrier materials are mainly used in food and drug packaging, electronic device packaging, solar cell packaging, OLED packaging.
1. Food and drug packaging
EVOH seven layer coextrusion high resistance diaphragm
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 from entering the packaging, so as to make the food and drugs deteriorate and greatly reduce the shelf life.
For food and drug packaging, the barrier requirements are not particularly high. The WVTR and OTR of barrier materials are lower than 10g / m2 / day and 100cm3 / m2 / day respectively.
2. Electronic device packaging
Packaging film for electronic devices
With the rapid development of modern electronic information, people put forward higher requirements for electronic components, which are portable and multifunctional. This puts forward higher requirements for electronic device packaging materials, which not only have good insulation, but also can protect them from the corrosion of oxygen and water vapor, but also have a certain strength, which requires the use of polymer barrier materials.
The barrier requirements of packaging materials for general electronic devices are that the water vapor permeability (WVTR) and oxygen permeability (OTR) should be lower than 10-1g / m2 / day and 1cm3 / m2 / day respectively.
3. Solar cell packaging
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 metallized 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 guarantee the service life of the solar cell, but also enhance the resistance strength of the battery.
The barrier property of solar cell packaging materials is that the water vapor transmittance (WVTR) and oxygen transmittance (OTR) should be lower than 10-2g / m2 / day and 10-1cm3 / m2 / day respectively.
4. OLED packaging
OLED packaging film
OLED has been entrusted to the next generation of displays since its early development, but its short service life has always been a major problem restricting its commercial application. The main reason affecting the service life of OLED is that the electrode materials and light-emitting materials are very sensitive to oxygen, water and impurities, which are easy to be contaminated, resulting in the decline of device performance, thus reducing the luminous efficiency and shortening the service life.
In order to ensure the luminous efficiency of the product and prolong its service life, the device must be isolated from oxygen and water during packaging.
In addition, in order to ensure the service life of flexible OLED display is more than 10000 h, the water vapor transmittance (WVTR) and oxygen transmittance (OTR) of barrier materials must be lower than 10-6 g / m2 / day and 10-5 cm3 / m2 / day respectively, which is far higher than the barrier performance requirements in organic photovoltaic, solar cell packaging, food, drug and electronic device packaging technology, Therefore, flexible substrate materials with excellent barrier performance must be selected to package the devices to meet the strict requirements of product life.
|
|