Laminating is a very important process in the production of solar modules. The life, performance and aesthetics of the components are all laid out in the laminate. In the process, there are often some fatal problems that often cause the components to be completely scrapped. This will undoubtedly increase our production costs. So it is necessary to make some conclusions. The laminator is the main instrument used in the vacuum laminating process. Its role is to heat and pressurize the EVA under vacuum conditions to achieve curing of the EVA and achieve solar cell sealing. There are several major problems with laminating components: Air bubble, cell shift, back plate fold, bust bend, etc. This summary will explore the reasons for the above-mentioned quality problems from four aspects. In the production process, according to the content of this summary, we will be able to find a solution. First, the process parameters The laminating process is to meet the requirements of EVA cross-linking degree of 75-85%; EVA and glass and TPT bonding tight (peel strength, glass / EVA greater than 30N/cm, TPT/EVA greater than 15N/cm), the battery is not Displacement, components without obvious bubbles. The specific operation is mainly to set several parameters of the laminator. The setting of these several parameters takes into account many factors. The main point of the ideal lamination parameter setting is to pump at a lower temperature and then cure the EVA at a higher temperature. This process can be roughly divided into three steps: • At the beginning, the temperature of the components inside the laminator was low, EVA melted, and there was good fluidity, but the cross-linking speed was slow. The vacuum pump evacuates the lower chamber, so the gas inside the module is quickly and easily pumped away. The upper chamber is kept under vacuum and the components are not stressed. · EVA curing stage. As the module temperature rises to a higher temperature, a rapid cross-linking reaction occurs in EVA. The lower chamber continues to be evacuated and the gas generated during the curing process is promptly discharged. At the same time, the upper chamber is inflated and the pressure difference between the upper chamber and the lower chamber causes the rubber layer in the laminator to exert pressure on the assembly. · The end phase. EVA curing is completed. First, the upper chamber is evacuated and the pressure is removed. Then the lower chamber is inflated and the lid is opened. The two most important parameters of the lamination process are time and temperature 1.1, time The duration of the lamination process includes evacuation time and lamination time, the length of time being critical to the lamination quality. The time is determined based on the characteristics of the EVA. In general, the temperature difference between the bottom glass and the middle EVA reaches 50°C as soon as the module has just entered the laminator table. In the next 2 minutes or so, the EVA gradually warms up to the molten state, and continues thereafter. The temperature reaches the optimal curing temperature. This determines the timing of vacuum and lamination. 1.1.1, vacuum time Corresponds to the pumping time before pressurization. Mainly refers to the next room pumping. After the evacuation phase is completed, the upper chamber is pressurized and pressurized, so the evacuation time corresponds to the timing of the pressurization. The purpose of the pumping: First, the air in the gap between the packaging material and the gas generated during the lamination process are used to eliminate air bubbles in the module. First, a pressure difference is created inside the laminator to generate the pressure required for lamination. The short evacuation time means that the lamination is too early. At this time, the EVA has good fluidity and will flow under pressure, resulting in displacement of the cell sheet, bending of the bus bar, and wrinkling of the back of the module. At the same time, due to the short time, there may be bubbles inside the module. Evacuation time is too long: it means that the time of the components in the laminating machine is prolonged, which makes EVA cross-linking degree high, easy to age yellowing or even degumming. 1.1.2, lamination time Lamination time is divided into inflation time and lamination hold time Inflation time: corresponds to the pressure applied to the assembly during lamination. The longer the inflation time, the greater the pressure. Because the general structure of the polymer formed after cross-linking like EVA is relatively loose, the presence of pressure can make the EVA film more dense after curing and has better mechanical properties. It also enhances the adhesion of EVA to other materials. The inflation time is generally carried out in stages, and each time should not be too long. Inflating time is too long: If the total lamination time is not changed, then the lamination and holding time must be shortened, which will make the EVA density in the assembly smaller and the thickness larger, affecting the mounting frame. If the lamination and holding time is not changed, the total lamination time will be prolonged, which will lead to a series of consequences: air bubbles may occur in the components, the degree of cross-linking of EVA is high, and yellowing may occur during the use of the components, which may affect the service life. The inflation time is shorter: it will not reach the set pressure, affecting the procedure. The effect on the density of the cured EVA is very small, and it does not have any effect on the residual air bubbles. The adhesion between EVA and TPT, EVA and glass is relatively small. This situation is generally less frequent. Lamination retention time: The retention time corresponding to the pressure applied to the assembly is the longest period in the entire process. The sum of the extraction time, the lamination time and the extraction time correspond to the total curing time. Keeping it for a long time: It may cause air bubbles in the components. The degree of cross-linking of EVA is too high, and yellowing may occur during the use of the components, which may affect the service life. The holding time is too short: EVA cross-linking degree will be low, there may be cell shift, back plate folds and other phenomena. 1.2, temperature Temperature is another key parameter in the lamination stage. The temperature setting is set according to the curing temperature recommended by the EVA manufacturer. However, in actual production, there are some situations to consider: Since the laminating stage is performed in a closed environment, the temperature at this time will be higher than the temperature measured when the lid is opened. Therefore, when the temperature measurement is performed, it is generally required to be about 1 to 2 degrees lower than the set temperature. High temperatures: High temperatures can lead to multiple consequences: 1. The high temperature will be caused by the decomposition of some cross-linking agents in EVA to produce oxygen. Since EVA is already cured at this time, the gas is not easily eliminated, resulting in bubbles in the components. 2. The temperature is too high, making EVA cure in advance when vacuuming, and the vacuum is not completely exhausted. There will be residual gas in some parts, such as the leading part of the bus bar, causing air bubbles in the module. 3. The temperature is too high, making EVA cure in advance when vacuuming occurs, leading to the unevenness of the leading part of the bus bar, and the occurrence of back panel folds at this location. 4. The high temperature will make the cross-linking degree of EVA high, making the components easily yellow and aging during use. Low temperature: 1. The temperature is low, so that after the end of vacuuming, the EVA fluidity is still good after the lamination stage begins. At this time, the lamination will occur with the displacement of the cell, the spacing between the strings will become smaller, and even the cell will be fragmented, chipped, etc. Happening. 2. When the temperature is low, the degree of cross-linking of EVA will be low, and the bonding strength between the raw materials will be low, which will affect the service life of the components. 1.3, pressure The size of the pressure corresponds to the length of the inflation time, the longer the inflation time, the greater the pressure, and vice versa. Stress control should pay attention to several aspects: 1.3.1, pressure value too much stress. Too much pressure may cause the cell to be crushed, and in addition, it can easily cause the flow of EVA, causing the solar cell to shift. Of course, a large pressure has a certain effect on removing remaining air bubbles from the module and reducing backplane wrinkles. The pressure is too small. The effect on the density of the cured EVA is very small, which does not have any effect on the residual air bubbles. The adhesion between EVA and TPT, EVA and glass is relatively small. During the operation, the pressure should be increased as much as possible without causing the solar cell to break or shift. 1.3.2, press speed The pressing speed corresponds to the inflation speed and pressure difference. The faster the inflation speed, the faster the press speed; the greater the pressure difference, the faster the press speed. For Bosch laminator, there is only one inflation valve, so its inflation speed is constant. If you want to reduce the speed of pressing, you need to subdivide the restart process so that the pressure difference is as uniform as possible, and the inflation time is as wide as possible. Shenke laminator has two types: fast inflation valve and slow inflation valve. Each section of inflation begins at the same time. When the vacuum reaches the set value quickly, the quick inflation valve is closed and only the slow inflation valve is enabled. Pressing too fast: It may cause the cell to be crushed and it is also easy to displace the cell due to the flow of EVA. Second, contact The so-called contact refers to the component into the laminating machine work surface, directly or indirectly contact with other objects, such as high-temperature cloth, silica gel plate, work surface and the pores on it. Since the laminating process is carried out in a confined space, the items contacted by the components have a certain influence on the lamination quality. When checking the causes of the quality, it is necessary to consider this part of the reason. 2.1, high temperature cloth The high-temperature cloth is a layer of high-temperature resistant material that is laid on the upper and lower parts of the assembly during the laminating stage, which facilitates access to the material, protects the components, and improves the lamination quality. Since high-temperature materials in high-temperature cloths are imported products, the price is high, so they must be used carefully. 2.1.1, Introduction High-temperature cloth, also known as PTFE cloth, washed cloth, is a kind of high-temperature resistant paint cloth, which adopts high-quality imported glass fiber as weaving material, and weave plain weave or special weave into advanced glass fiber cloth substrate. Then use a unique technology to fully immerse, dip, coat imported Teflon (polytetrafluoroethylene) resin, made of high-temperature paint with various thickness. it has: 1. Stable size, high strength, elongation coefficient less than 5‰. 2. For low temperature -196 °C, high temperature 350 °C, with weather resistance, anti-aging. The practical application, such as continuous placement at 250°C for 200 days, will not only reduce the strength but also reduce the weight; at a high temperature of 350°C for 120 hours, the weight will only decrease by about 0.6%; at -180°C Cracking does not occur at extremely low temperatures and maintains the original softness. 3. The watch has a low coefficient of friction and good insulation. 4. Good anti-adhesion, easy to clean various oils, stains or other attachments such as EVA attached to the surface. 5. Good corrosion resistance, resistance to various strong acid and alkali corrosion, no burning, anti-aging. 6. Light transmittance reaches 6-13%. 7. With high insulation performance (small dielectric constant: 2.6, tangent below 0.0025), UV protection, anti-static. 2.1.2 Functions and Effects The function of the high temperature cloth is to lay the upper and lower sides of the assembly in the laminating stage. The bottom is to facilitate the feeding and discharging. The cover is on the top to isolate the silica gel plate from the back plate of the assembly. The effect of high-temperature cloths on laminate components is mainly the number of high-temperature cloths and whether there are attachments on them. Excessive hot cloth: The direct consequence is an increase in the pressure exerted on the assembly. For the impact of the component, see 1.3.1. 2.2, silicone plate Silicone board is one of the important parts of solar module laminating machine. Its quality is related to the quality of the module product. At present, there are three main types of rubber for laminating machine on the market, one is Rubber Sheet, and the main ingredient is Sanyuanyi. Propylene rubber has the advantages of good acid resistance, and its disadvantages are heavy odor and low temperature resistance. The other is a silicone rubber plate, which has high temperature resistance, strong tearing performance, and excellent aging resistance. The third type is compound rubber sheet, which combines the advantages of rubber sheet and silica gel sheet. It is both acid-resistant and high-temperature resistant. The number of times of lamination is far higher than that of rubber sheet and silica gel sheet. It is an ideal accessory product for solar module laminating machine. 2.2.1, contractility Silicone plates are as shrinkable as other rubber materials. The silica gel plate is fixed under the cover of the laminator, and then pressed to seal the work surface. Under the lamination, the pressure is applied, and the components are laminated by contacting the back of the module with a high-temperature cloth. Due to the shrinkage of the silica gel plate, it has a certain influence on the lamination quality of the components. Silicone plate shrinkage will cause backplane folds, cause EVA to move, and drive the cell to move. Therefore, the quality problems associated with the shrinkage of the silicone plate are: the displacement of the cell and the wrinkling of the back plate. Sometimes this strange phenomenon occurs: When laminating, the orientation of the components will have different effects. This is related to the shrinkage direction of the silicone plate. If EVA, the shrinkage direction of the back plate and the shrinkage direction of the silica gel plate are all the same, the impact on the quality of the component is small, and vice versa. 2.2.2, tightness The shrinkage of the silicone plate can be controlled. The specific method is to change the tightness of the silicone plate. Of course, some silicone laminators are not adjustable, which requires that when you change the silica gel plate, you must pay attention to moderate elasticity. Silicone plates are too tight: Silicone plates are too tight and the pressure on the components will not be uniform, causing the cells to shift. Silica gel plates are relatively loose: due to the shrinkage of the silica gel plates, the back plates of the modules may wrinkle and the cell plates may shift. 2.3, stomata During the lamination process, the vacuum or aeration process passes through the air holes in the working platform of the laminator. Therefore, the distribution of the air holes and the direction of the gas movement in the module during the vacuum application have a certain influence on the lamination quality of the components. In addition, the components The placement direction is different, and the lamination quality is also different, which has a great relationship with the above two reasons. Third, the material The materials that affect the lamination quality of the components are nothing more than EVA, backplanes, and solder ribbons. Other problems such as the color difference of the cell sheet and glass defects are not related to the lamination stage. Therefore, it is important to summarize the three materials related to lamination. 3.1, EVA There are problems with the components in the laminator section, which is related to EVA. The component problems caused by EVA mainly include: displacement of the cell, air bubbles, folds of the back plate, and bending of the bus bar. There are many reasons for these quality problems, and the degree of cross-linking and shrinkage associated with EVA itself. 3.1.1, degree of crosslinking The degree of cross-linking is the most important parameter that reflects the performance of EVA. The so-called degree of cross-linking, popular speaking, refers to the degree of cross-linking of EVA, and the appearance of the reflection is the stickiness of EVA or the bond strength with other materials. In terms of composition, the degree of cross-linking is the extent to which the cross-linking agent reacts. Linear or lightly branched polymers are converted into a three-dimensional network by the action of a cross-linking agent. It can significantly increase the cohesive strength, thermal stability, etc. of the polymer. The low degree of cross-linking: will make the EVA fluidity is still better after the lamination stage begins. At this time, the lamination will occur with the shift of the cell, the spacing between the strings becomes smaller, and even cause the cells to be fragmented and chipped. In addition, in the long term, the degree of cross-linking is relatively low, and the bond strength between the EVA and the glass and the back sheet is insufficient, which may affect the service life of the module. The factors causing the low degree of cross-linking are: low lamination temperature and short lamination hold time. The degree of cross-linking is too high: it will cause yellowing of the components during the subsequent use, and will affect the service life. Factors that cause high cross-linking are: high lamination temperature and long lamination time. 3.1.2, shrinkage The shrinkage of EVA refers to the dimensional change ratio before and after the EVA is melted at a certain temperature. Shrinkage has a large impact on the components. The shrinkage is divided into longitudinal and transverse directions. Generally, the longitudinal (MD) is less than 4% and the transverse (TD) is less than 2%. However, the smaller the actual use, the better. The shrinkage rate is too large: after the EVA is laminated, it is easy to cause the cell sheet to shift, and even cause the cell sheet to crack. 3.1.3. Others The quality problems caused by EVA, in addition to the above reasons, there are other reasons, such as: EVA storage environment is unreasonable, so that moisture absorption, causing component bubbles; vacuum cleaning caused by degumming. 3.2 Backplane The quality of laminates associated with backsheets is mainly backsheet folds and backsheet depressions. The original meaning of causing wrinkles is divided into its own reasons and other reasons. The reason for itself is related to its shrinkage rate and its own properties; other reasons include EVA, high-temperature cloth, etc. 3.2.1, shrinkage The flexibility of the backplane mainly affects the lamination process in the production process of the module. The backplane with a large elasticity will cause the EVA to contract during the lamination process, causing the cell to shift or even cause the battery cell to fragment. In general, due to the relatively low probability of backplane shrinkage causing component lamination quality, backplane problems are generally due to other reasons. 3.2.2. Others There are: 1. EVA is stuck on the high temperature cloth or silicone plate, causing the back plate to sag after lamination. 2. The back sheet of TPE structure, especially the back sheet of BBF material, is soft due to its soft material, and its inner layer EVA and the EVA used in production are not well melted, resulting in a low degree of cross-linking of EVA and causing a number of consequences. 3.3, ribbon The problem caused by the ribbon is mainly the bending of the ribbon. The reason that the busbar bends on the one hand is that during use, the busbar itself is not even, resulting in bending after lamination, which affects the appearance of the module; on the other hand, the abnormal flow of the EVA causes bending of the busbar. There are many reasons for the flow of EVA. Please refer to the EVA section. Fourth, the environment The impact of the environment on laminating quality is mainly reflected in the impact on raw materials, while the material with stricter environmental requirements is only EVA. The adsorption capacity of EVA film is strong. During use and storage, it is necessary to pay attention to moisture-proof and dustproof and avoid contact with colored objects. • If moisture is absorbed, the bond strength between EVA and the glass and the backboard will be affected, and the water content in the EVA will vaporize as the temperature increases, creating bubbles. • If dust is collected, the light transmittance of the module will be affected, and the adhesion of EVA to the glass and the back sheet will be reduced, and even air bubbles will be generated. • Contaminated if it comes in contact with a colored, dirty object. V. Conclusion The lamination stage is the one with the most problems. Once there are quality problems, it is necessary to investigate the causes in a timely manner, correct irrational places, and make the production of high-quality and high-efficiency. Therefore, it is necessary to systematically summarize the various problems in the lamination process and their causes.
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