Coating formulation: development of FEVE coated photovoltaic back film coating

There are two main types of back membrane of solar cell: fluorine-containing and non fluorine-containing The back membrane of solar cell includes two kinds of double-sided fluorine-containing and single-sided fluorine-containing It can be divided into compound type (compound type) and coating type The back films (TPT, kpk, etc.) of composite solar cells are mostly made of PVF or PVDF and other fluorine films developed by some fluorine chemical enterprises in Europe and America, which are bonded with pet substrate by adhesives Due to the existence of adhesives on both sides of pet substrate, the quality of adhesives is different, and the composite process is uneven, Shenyang steel structure fireproof coating construction expert punde Building Fire Engineering Co., Ltd Recommended introduction: since its establishment, Shenyang punde Construction Fire Engineering Co., Ltd has cultivated a group of professional construction teams with excellent equipment, rich experience and serious responsibility with advanced and scientific management methods and strict engineering quality assurance and after-sales service system It has undertaken a number of fire system installation projects, which has been praised by customers Every idea and special requirement of you will be fully considered by us and fully realized in the construction technology, which will become the cornerstone of our successful long-term development We are looking forward to your invitation, to provide you with quality services and high-quality technical support! All construction coatings have passed ISO9001 Coatings home news: 0 Introduction solar cell back film from the category is divided into two main categories of fluorine-containing and fluorine-free, fluorine-containing back film is divided into two kinds of double-sided fluorine-containing and single-sided fluorine-containing It can be divided into compound type (compound type) and coating type The back films (TPT, kpk, etc.) of composite solar cells are mostly made of PVF or PVDF and other fluorine films developed by some fluorine chemical enterprises in Europe and America, which are bonded with pet substrate by adhesives Due to the existence of adhesives on both sides of pet substrate, the quality of adhesives is different In addition, the composite process is uneven In the long-term outdoor use of battery components, the composite backing film is affected by the double factors of humidity and temperature, which is prone to damage such as the hydration of the adhesive layer, and eventually leads to the peeling between the fluorine film (PVF or PVDF, etc.) and pet substrate, which is difficult to meet Long term reliability requirements for battery components In recent years, the domestic compound type back film manufacturing enterprises do not have the cost and quality advantages in the main raw materials and core technologies, resulting in the lower overall core competitiveness and profit space of the products Some domestic enterprises use coating method to produce the back film of photovoltaic cells, and some achievements have been achieved The coating type back film adopts ether FEVE fluorocarbon coating, which is coated on pet substrate to form a fluorocarbon coating layer Due to the excellent performance of FEVE fluorocarbon coating, the coated solar cell back film also has good anti-aging effect Domestic companies such as Suzhou Zhonglai, Hangzhou fandu, hafuolong, Lianhe new material and foster all adopt coating method to prepare solar photovoltaic back film, which has great advantages in cost and technology of back film Development of 1 FEVE coated photovoltaic back film coating Limited by the use environment and conditions of photovoltaic back film, the related detection of photovoltaic back film is very strict, and almost all performance indicators are related to the coating In addition to the conventional basic performance detection, including pure film and laminated parts, the performance inspection under UV, high temperature and high humidity, and "hot and cold cycle + wet freezing" should also be conducted, focusing on the matching between the paint film and the substrate, EVA, silica gel, etc This requires that all factors should be taken into account in the formulation design of the coating, as well as the coating process and drying conditions The key points of formulation design test include film-forming resin, cross-linking agent, pigment and filler, auxiliary agent and solvent In the development of photovoltaic back film coating, the selection of film-forming resin is the most important In view of the harsh use environment and long-term stable use requirements of the backplane, FEVE ether fluororesin is currently the preferred resin for coating photovoltaic back film It has excellent outdoor weather resistance, acid and alkali resistance, salt fog resistance, high temperature and humidity resistance and excellent mechanical properties The srf350 produced by Dalian Yongrui Fluorine Material Co., Ltd belongs to solvent type ether fluorine resin During the test, we used srf350 fluorine resin to develop photovoltaic back film coating, which has excellent weather resistance, moisture and heat aging resistance and high EVA bonding strength 1.1 see Table 1 for main technical indexes of srf350 resin 1.2 see Table 2 for the formulation of photovoltaic back film coating and the main performance of fluororesin back film coating fpc-20 See Table 3 for the test results of main performance indexes of fluororesin back film coating fpc-20 Note: corona treatment of pet base material; curing conditions are 150 ℃× 3min, 50 ℃× 48h 2 The influence of nano functional filler and adhesion promoting resin on the coating performance It was found that the addition of nano functional filler and adhesion promoting resin in the formulation can greatly improve the coating performance, especially on the substrate adhesion, PCT aging and EVA adhesion performance The test results are shown in Table 4 From the test results in Table 4, it can be seen that: 1) the surface properties of 1 ා and 2 ා coatings on different PET substrates are quite different, and the adhesion on the surface of white pet substrates is significantly better than that on translucent and transparent PET substrates Under the influence of adhesion, the PCT aging and EVA bonding strength of translucent and transparent films are also poor 2) 2 The adhesion of the coating on the translucent and transparent PET substrate was improved obviously after adding 3% - 5% nano functional filler and 2% - 5% adhesion promoting resin The influence of coating film on the adhesion of pet substrate the surface of pet substrate needs to be modified before application, such as corona method, photochemical method, low temperature plasma method and primer method The manufacturers of coating type back film mostly adopt corona method and bottom coating method, but no matter which method is adopted, it will increase cost, increase process and reduce production efficiency How to improve the adhesion of coating film to pet substrate in the coating formulation is a difficult problem for coating technicians At present, there are many kinds of pet substrate used in photovoltaic back film, most of which are 250 μ m thick, with three kinds of appearance: white, translucent (milky white) and transparent The adhesion between the coating film and pet substrate is mainly tested by the grid method The adhesion of FEVE fluorocarbon coating on most PET substrates except white is poor, especially on the translucent and transparent films The poor adhesion between the film and pet directly results in the peeling off of the film and pet substrate when EVA is bonded, and also directly affects the wet heat aging performance and EVA bonding performance, resulting in the unsatisfactory bonding strength of EVA, which is one of the main factors restricting the application of FEVE coated photovoltaic back film coating The adhesion will also affect the MEK wiping performance Poor adhesion will cause the film to fall off and expose the pet substrate during the MEK wiping process It is difficult to pass the MEK wiping for 100 times The best way to improve the adhesion between the coating and pet substrate is to add adhesion enhancer and adhesion promoting resin Adhesion enhancers are mainly various coupling agents, and there are many kinds of adhesion enhancers We focused on aldehyde ketone resin, Chloroether resin, chloroacetate resin, polyester resin and special acrylic resin with good adhesion to pet substrate After investigating a large number of adhesion promoters and promoting resins, it is found that most of them have poor miscibility with fluoro resin, and those with good miscibility are mostly limited by the amount of additives, which have little effect on the improvement of adhesion and film performance, especially on the wet heat aging 4 The effect of coating on PCT aging properties pet substrate is easy to degrade into acids and alcohols in hot and humid environment, and the resulting acids will further accelerate the decomposition rate The moisture permeability of PET film is higher than that of PVDF film of the same thickness by 4-5 times Water vapor permeability is one of the important indexes to evaluate the performance of back membrane If the performance of back membrane to block water vapor penetration is poor, the moisture in the air will enter into the inner side through the back membrane, and the water vapor penetration will affect the adhesion performance of EVA, leading to the separation of back membrane and EVA, and then the moisture will directly contact the battery sheet, making the battery sheet oxidized The water vapor permeability of the back film mainly depends on the pet substrate The back film needs certain mechanical strength, good electrical insulation, low water permeability, good adhesion with silica gel and EVA, good weather resistance, etc Hygrothermal aging (double 85 test) is the most severe test in environmental test With the extension of hygrothermal aging time, the mechanical properties of the back film slowly decline After reaching a certain time point, the performance drops sharply and the back film fails The results show that the crystallization of PET layer is the main factor, the pet layer becomes brittle, the impact strength is reduced, and finally the back film fails The sensitivity of pet crystallinity to temperature is greater than that to humidity In order to shorten the development time, PCT is generally used in the formulation development to accelerate the wet heat aging inspection, which speeds up the test process PCT test is generally called pressure cooking pot test or saturated steam test It can be used as the accelerated inspection of double 85 test with short inspection period Generally, the test conditions are: temperature 121 ℃; relative humidity 100%; pressure 0.2MPa Inspection time: 24-96h The method is to press the back film on the ground glass with the encapsulated EVA, and the pressing condition depends on the package technology and the type of EVA After pressing, put it into the PCT test box, and check the sample after the specified time Under the PCT aging test, the coating is generally manifested as: 1) multilayer structure stratification (composite type), which is mainly caused by poor hydrolysis resistance of adhesive and hydrolysis of ester group and amide group; 2) blistering or peeling of coating, which is mainly caused by poor water resistance or adhesion of coating; 3) mechanical strength reduction (embrittlement), which is mainly affected by PET substrate; 4) yellowing, which is mainly caused by EVA aging And coating effect Through a lot of experiments, it is found that the aging of PCT is not only affected by the properties of fluororesin itself, but also by pigments, fillers, auxiliaries and curing agents In addition to the selection of high-quality pigments, fillers can be added to improve the water resistance, adhesion and flexibility of the coating For example, adding nano functional filler can improve the aging performance of PCT obviously If some coupling agents, adhesion promoters and curing promoters are added, the film will blister or even fall off in PCT test, such promoters should be selected carefully The curing agent also has an effect on PCT aging properties After investigating different curing agents, HDI Trimer is the best choice The effect of coating on the bonding strength of EVA is that EVA is used to bond and fix toughened glass and main body of power generation (such as battery) The quality of transparent EVA material directly affects the service life of components EVA exposed to air is easy to age and turn yellow, which affects the light transmittance of components and the power generation quality of components In addition to the quality of EVA itself, the lamination process of component manufacturers also has a great impact For example, the crosslinking degree of EVA is not up to standard, and the bonding strength of EVA with toughened glass and back film is not enough, which will cause the early aging of EVA and affect the service life of components The adhesion of pet fluorocarbon coating is required firstly, which solves the adhesion problem of the coating to pet, so the adhesion strength of the coating to EVA can be considered The test method is 180 ° tensile test The standard requires that the tensile force is greater than 40n / mm When the tensile force is greater than the peel force, it is expected to peel from the EVA bonding surface, which is considered for the rework of defective parts The surface tension of the film must be relatively balanced to the adhesion of EVA and pet A large number of experiments show that the additives with strong surface tension reduction, such as some silicon containing additives, can reduce the bonding strength of EVA