The global photovoltaic industry has started a new round of prosperity cycle. The rapid warming of the photovoltaic markets in China, Japan and the United States promotes this business cycle. The continuous progress of photovoltaic technology promotes the continuous increase in the degree of segmentation of the photovoltaic market. In addition to the application types of traditional photovoltaic power generation, the combined application of photovoltaic technology and civilian products has begun to show vitality. This article compares and analyzes the characteristics of two raw materials, EVA and PVB, for photovoltaic modules, and analyzes their process characteristics.
EVA adhesive film shows its advantages in the field of solar cell encapsulation
The encapsulation bonding material used in the crystalline silicon solar cell industry is an adhesive. Before the 1980s, liquid silicone resin and polyvinyl butyral resin sheet (PVB) were tried at home and abroad, but they were eliminated due to high price, harsh construction conditions and poor physical properties. Since the 1980s, EVA film has been developed abroad. It is a hot-melt adhesive film. It is non-sticky and anti-blocking at room temperature. It has obtained quite satisfactory results in solar cell packaging and outdoor use.
EVA (Ethylene Vinyl Acetate: ethylene-vinyl acetate copolymer).
EVA is a kind of hot melt adhesive, that is, at room temperature, EVA is solid, no viscosity, poor light transmittance When the EVA is heated to a certain temperature, the EVA will melt and bond to the objects in contact with it. EVA used for solar cell encapsulation is a specially designed thermosetting hot melt adhesive, that is, a cross-linking reaction occurs while heating and melting. When the temperature is low, the speed of the cross-linking reaction is very slow, and the time required to complete the curing is relatively long, otherwise the time required is relatively short. Therefore, it is necessary to choose an appropriate lamination temperature so that the EVA can obtain fluidity in the melt, and at the same time a curing reaction occurs. As the reaction progresses, the degree of cross-linking increases, and the EVA loses its fluidity and acts as an encapsulation.
The performance at different temperatures is: melting temperature (70-80℃). At this time, the EVA is heated and melted, and the fluidity is good, which is the best time for vacuuming. At the curing temperature, the cross-linking agent contained in EVA generates free radicals, and cross-linking occurs between EVA molecules, resulting in a three-dimensional network structure, poor fluidity, and high viscosity. This temperature is suitable for laminating components to make their structure tighter and higher bond to glass and backplane. When the temperature is higher than the curing temperature, the cross-linking agent decomposes gas, which is easy to cause bubbles in the component, and at the same time, the cross-linking degree of EVA decreases, and it is easy to vulcanize and turn yellow, resulting in shrinkage.
PVB (Poly vinyl butyral: polyethylene butyral).
In 1935, American scientists invented a polymer material that can be sandwiched between two layers of ordinary glass - polyvinyl butyral, the English name is POLYVINLBUTARAL, abbreviated as PVB. It is a polymer formed by the condensation reaction of high molecular polyvinyl alcohol and butyraldehyde, and has nearly 23% by weight of vinyl alcohol groups in the final polymer. This polyvinyl butyral is plasticized with a special plasticizer (usually triethylene glycol esters), and a continuous 0.38 is formed by an extruder system and precise thickness control. ~1. 52mm thick film.
The difference between PVB film and EVA film
1. Application field
EVA is mainly used for the encapsulation of crystalline silicon cells, and a small number of thin films are also used, mainly playing a role in protecting the battery and closely fitting the cell to the cover glass. At present, the products used in the market are most well-known in Dupont's Telaar, but there are also many other international manufacturers in the production of various products, such as 3M, etc., and there are several domestic manufacturers that can be used for solar energy, such as Foster, Swick, Hayworth, etc.; Jinwei EVA low temperature solar encapsulating film production line is in a monopoly position in the photovoltaic film industry.
PVB is currently mainly used in thin film batteries, double glass modules, building integration (BIPV) and other fields, production enterprises and product models are few, currently Dupont, Kuraray and so on, there are also individual enterprises in China that are trying to produce, such as Xinfu Pharmaceutical.
2. Lamination process
The temperature requirements of PVB and EVA are different. EVA has good thermoplasticity and no higher equipment requirements than PVB. PVB has higher temperature requirements (about 155 °C) and higher requirements for laminators.
3. Others
PVB is a building material, which has very good gas barrier properties, and the adhesion performance is very good, and the weather resistance is much better. The disadvantage is that the barrier performance to water vapor is too poor, which is unacceptable for solar cells. And too soft is not easy to operate. The price is also more than 3 times that of EVA.
