An overview of the classification and working principle of vacuum laminators

An overview of the classification and working principle of vacuum laminators

Component packaging mainly relies on vacuum lamination equipment, that is, vacuum lamination machine. Through the pressure action of the vacuum laminator under certain conditions of vacuum, temperature and time, the EVA film, the bonding material in the module stack, can bond the backplane, solar cells and glass together to become a laminate. Realize the protection of the battery.

  1. Introduction and classification of laminators

The laminator integrates vacuum technology, pneumatic transmission technology and PID temperature control technology. It has various shapes and structures. Figure 1 shows an early semi-automatic laminator, which can laminate 1 conventional component at a time; Figure 2 shows a transmission laminator, which can laminate 3 to 4 conventional components at a time. The working principles of the two laminators are basically the same. The lamination temperature, air extraction time, lamination time, and inflation time can be set on the console. There are two control methods: automatic and manual.

Figure 1 - Office automatic laminator
Figure 1 – Office automatic laminator
Figure 2 - Transmission Laminator
Figure 2 – Transmission Laminator

The whole set of laminating machine includes feeding table, control cabinet, computer display screen, heating station, laminating cavity (host) and discharging table. The main process of lamination is completed in the lamination cavity, and other mechanisms play an auxiliary role. The internal structure of the laminator cavity mainly includes an upper chamber, a lower chamber and a hot plate. There is a rubber airbag inside the upper cover of the laminator, and the upper chamber refers to the cavity between the airbag and the upper cover plate. The distance between the upper cover and the hot plate is generally 15~30mm, and there is a sealing ring around it. After the upper cover is lowered, a sealed cavity is formed, which is called the lower chamber. The bottom plate is a heating plate, and the heating plate is a conveyor belt made of high temperature resistant polytetrafluoroethylene high temperature cloth.

The heating method and vacuuming ability of the laminator are the key factors that affect the lamination effect. The heating methods of laminators generally include oil heating, electric heating and oil-electric hybrid heating. In the oil heating method, the heating plate is generally made of a whole steel plate, and a circulation hole is punched in the middle of the steel plate, so that the hot oil circulates inside the hot plate to realize the heating function; electric heating generally adopts the method of block heating, for example, a size of about 3000mm × The 40000mm hot plate is usually divided into 16~32 heating areas to be controlled separately, so as to realize the whole plate heating. The oil heating cost is low, and it is easier to achieve uniform temperature. The general accuracy is ±2 °C, but the oil pump needs to be used all the time, and the oil is continuously heated. At the same time, the oil circuit needs to be maintained and the heating oil is replaced regularly; the electric heating cost is high, but the temperature rises Fast, temperature uniformity is better, and the accuracy can usually reach ± ​​1.5 ℃. Now the advanced electric heating method can also achieve local temperature compensation. For example, after the laminate enters the cavity, the glass will warp during the entire vacuuming process, so that the EVA cross-linking rate at the four corners of the module is low, so it can be Increase the set temperature of the heating modules in these four corners by 1~3°C to ensure the uniformity of EVA crosslinking. Electric heating reduces lamination time and increases productivity.

In the early days, there was an imported thimble-type laminator. The thimble structure was installed on the electric heating plate. At the beginning of heating, the laminate could be ejected without contacting the hot plate, and the air heat transfer was used to realize the stacking of components. The uniform heating and temperature rise of the layered parts is conducive to the uniform melting of EVA, reducing the initial deformation of the laminated parts and improving the process yield. However, this heating method is complicated and expensive, so this kind of laminator has not been developed. . With the rapid development of double-glass modules, a laminator that can be heated up and down has appeared again. The heating plate in the lower chamber of this laminator remains unchanged, while the upper cover plate uses infrared heating to heat the module stack. Heating on the back side can effectively shorten the lamination time and increase productivity.

Most of the domestic laminators used oil heating at first, and now they mostly use electric heating. The vacuum degree of the laminator is mainly controlled by the vacuum pump. There are many ways of vacuuming, such as the combination of the rotary vane pump and the Rhodes pump, and the more advanced one is the combination of the rotary rod pump and the Rhodes pump to achieve vacuum.

According to the operation mode, the laminator can be divided into manual laminator, semi-automatic laminator and full-automatic laminator; according to the size of the hot plate of the cavity, it can be divided into one pressing and one pressing (made up of 60 conventional batteries connected in series). Based on the 270W module, one module is laminated at a time), one press three, one press four; according to the number of working chambers, it can be divided into single-chamber laminator and double-chamber laminator. The single-chamber laminator has only one heating chamber, and the lamination is completed at one time; the double-chamber laminator has two heating chambers in the front and rear, which can realize two-step lamination, which not only saves space, but also increases production capacity, and can be used for one-stage lamination. Low temperature, in order to better vacuum and avoid the generation of air bubbles, high temperature is used for two-stage lamination to achieve the effect of rapid cross-linking. In addition, the laminator can also be divided into a single-layer laminator and a multi-layer laminator according to the number of layers to be laminated. Figure 3 shows the structure of the multi-layer laminator.

Figure 3 - Multilayer Laminator
Figure 3 – Multilayer Laminator

There are many manufacturers of laminators. Chinese manufacturers mainly include Qinhuangdao Orit, Shanghai Shenke, Qinhuangdao Boshuo Optoelectronics, Qinhuangdao Regin, and foreign manufacturers mainly include Meiya, 3S, Nisshinbo, etc.

  1. The working process of the laminator

During lamination, the temperature of the hot plate needs to be set according to the characteristics of EVA. The general temperature range is 135~150℃. The vacuuming and lamination time also need to be adjusted according to the characteristics of different EVA. Bubble, battery rupture and other phenomena, the crosslinking rate is qualified, and the peel strength between EVA and the back sheet is qualified.

The working process of the laminator is mainly divided into the following four steps:
(1) The stacked parts of the feeding component are fed into the heating plate area of ​​the laminator through the conveyor belt of the feeding table;
(2) The vacuum heating laminator quickly closes the lid, and the upper and lower chambers are evacuated at the same time. The purpose of vacuuming the upper chamber is to adsorb the silicone blanket to the upper cover and prevent the silicone blanket from pressing on the laminate. Usually, the pumping time of the lower chamber is required to be 4 to 6 minutes. Generally, the vacuum degree of the lower chamber will reach more than 20Pa within 20 seconds, which is almost in a complete vacuum state, otherwise small bubbles will be generated inside the module. During this process, the laminate begins to gradually heat up and the EVA begins to melt;

(3) The upper chamber of the pressure-holding heating and cross-linking curing laminator starts to inflate, the lower chamber continues to be evacuated, a pressure difference is formed between the upper and lower chambers, and the silicone blanket begins to exert pressure on the laminated parts. The bonding strength of EVA to the backplane and glass can also discharge the gas generated during the cross-linking and curing process of EVA. The pressure-holding heating time is generally 10 to 20 minutes. The lower chamber is kept in a vacuum and the upper chamber is kept inflated during the whole process.

(4) After the discharge is cooled and the pressure-holding curing time reaches the set value, the lower chamber is inflated, the upper chamber is evacuated, the lower chamber air pressure rises to the atmospheric pressure, and then the cover is opened, and the cured laminate is transferred to the discharge table for natural cool down.

  1. Precautions

In the process of using the laminator, the following matters need to be paid attention to
(1) When the laminator is closed, the pressure is huge, so remember that there should be no other objects on the edge of the chamber to prevent accidental injury or equipment damage;
(2) Before opening the cover, it is necessary to check whether the inflation of the lower chamber is completed, otherwise the cover cannot be opened to avoid damage to the equipment;
(3) There is an emergency button on the console, which can be pressed in an emergency to power off the whole machine. After troubleshooting, reset the emergency button;
(4) If the laminator has not been used for a long time, it should run empty for several cycles after starting up, so as to exhaust the residual gas and water vapor adsorbed in the cavity, so as to ensure the lamination quality.

  1. Automatic production line

In the early stage of the development of the photovoltaic industry, each process on the Chinese module production line is basically independent, and the semi-finished parts of each process need to be manually handled and circulated, so the product quality is affected by many human factors. Although there are automatic assembly lines in foreign countries, the price is very expensive, so few companies buy and use them. With the rapid development of the photovoltaic industry in recent years, China’s automated and semi-automated assembly lines have developed rapidly, and have been favored and used by the majority of module companies with high cost performance, greatly improving module production efficiency and product quality.

Compared with the traditional manual line, the layout of the automatic production line is obviously different except for the battery string matrix laying unit, and most of the other production equipment are the same. The automatic production line mainly increases the circulation track between each station to realize the assembly In the automatic flow of the whole production process, the automatic feeding and unloading of each equipment is realized by robots or manipulators.

The automatic typesetting workstation of the fully automatic battery string matrix laying unit is shown in Figure 4. It is mainly composed of a glass correcting and conveying unit, a front EVA feeding and laying mechanism, a battery string adsorption and placement correcting mechanism, a bus bar placement mechanism, and a bus bar It is composed of automatic welding mechanism of interconnecting strip, rear EVA and back plate feeding mechanism and detection mechanism. Groups, I/O modules, motor reducers, etc. The main mechanical parts are frame structure, drive shaft, conveyor belt, suction cup group, traverse module, lifting module, guide rail, manipulator, etc. Generally, laser sensor edge positioning or CCD image calculation and positioning are used to quickly and accurately place the battery strings in place according to the production process requirements.

Figure 4 - Automatic Typesetting Workstation
Figure 4 – Automatic Typesetting Workstation

In practical applications, a semi-automatic assembly line is generally used for typesetting and lamination, and the entire lamination process is decomposed into different stations. Some stations use automatic operation, and some stations use manual operation. A very simple action, which greatly improves work efficiency. When semi-automatic flow is used, the EVA and the backplane are usually cut with equipment offline, the glass is automatically loaded online, then the first EVA is laid, the battery strings are automatically adsorbed and laid, then the bus bars are placed and welded, and finally Laying EVA and backplane, that is, the various actions of the whole process are decomposed into different processes on the assembly line, so as to achieve an efficient and reasonable operation rhythm.

The automated assembly line has the following advantages:
(1) The equipment adopts a fully automatic management operation mode, automatic typesetting, automatic component circulation and online cleaning and detection, automatic glue application, automatic testing, and no need for manual labor;
(2) It adopts a process-based production and just-in-time circulation scheme, and the rhythm can be controlled (generally less than 50 seconds/piece).
Each workstation of the pipeline realizes data integration, calculation, analysis, monitoring, quality controllable and quantifiable;
(3) PLC master-slave communication is used for control, which can control each process independently; in any process, as long as there is accumulation, the system can automatically judge, and change the direction of distribution and circulation of accumulated products to ensure the smooth production line;
(4) It can realize intelligent and big data management, and monitor the production capacity and yield of each section in real time.

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