A welding sizing method for 0BB battery and application thereof

Abstract

The application discloses a welding glue applying method for 0BB batteries and application thereof, and belongs to the technical field of solar photovoltaic batteries, and specifically comprises the following steps: S1, temporarily fixing UV glue on a glass fixture by silk printing, and fixing the solder strip by ultraviolet curing after the solder strip is laid; S2, after curing, aligning the solder strip with the battery piece on which soldering paste or conductive glue is printed; S3, laser or hot-press welding the solder strip and the battery piece; and S4, after welding, low-temperature heating is conducted to make the glue layer automatically expand or shrink to separate from the adherend, so that the temporarily fixed UV glue is removed. According to the glue applying method, after welding, low-temperature heating is conducted to make the glue layer automatically expand or shrink to separate from the adherend, the adverse effects caused by glue aging and residue are eliminated, and the long-term reliability and stability of the 0BB battery are improved. The problem that the power generation efficiency of the battery is reduced after the glue ages due to the fact that the glue is permanently left on the battery piece after the glue is applied in the prior art is solved, and the application has the potential to be applied to the preparation of photovoltaic batteries.

Description

Technical Field

[0001] This invention relates to the field of solar photovoltaic cell technology, specifically to a welding adhesive application method for OBB cells and its application. Background Technology

[0002] Zero-Busbar (OBB) technology for photovoltaic cells is an innovative cell structure design that eliminates the main grid lines on the front of traditional solar cells. Instead, it uses a more refined interconnection method to collect and transmit current, aiming to reduce shading loss, increase the effective light-emitting area, and reduce silver paste consumption, thereby improving cell efficiency and reducing costs.

[0003] However, the traditional OBB battery adhesive application method involves directly printing adhesive onto the battery cell, fixing the solder ribbon after the adhesive cures, and then laser welding the wires. This leaves the adhesive permanently on the battery cell, and its aging can negatively impact power generation. Existing thermally expandable UV debonding adhesives generally use a system of general-purpose acrylic monomers combined with low-microsphere additives, which suffers from significant technical bottlenecks such as a single debonding mechanism, inability to eliminate interface residues, uncontrollable crosslinking degree, poor material compatibility, and restrictions on compliant additives. Currently, the industry cannot simultaneously solve the four major contradictions of low-temperature debonding, zero residue, bonding stability, and sulfur-free and pollution-free operation by simply relying on simple raw material compounding.

[0004] Therefore, there is an urgent need for a coating method for 0BB batteries that can effectively remove residual adhesive from the welding process to improve the long-term reliability and power generation stability of 0BB batteries, while taking into account process compatibility and mass production feasibility. Summary of the Invention

[0005] Therefore, the present invention provides a welding adhesive application method for OBB batteries and its application, in order to solve the problem in the prior art that the power generation efficiency of the battery is reduced due to the permanent presence of adhesive on the battery cell after adhesive application and the resulting aging of the adhesive.

[0006] To achieve the above objectives, the present invention provides the following technical solution: According to a first aspect of the present invention, a welding adhesive application method for OBB batteries is provided, specifically including the following steps: S1. Screen print temporary fixing UV adhesive on the glass fixture, lay the solder ribbon, and then cure with UV light to fix the solder ribbon. S2. After curing, align the solder ribbon with the battery cell printed with solder paste or conductive adhesive. S3. Laser or hot-press welding of the welding strip to the battery cell; S4. After welding, low-temperature heating causes the adhesive layer to expand or contract automatically and detach from the bonded object, thereby removing the temporary fixing UV adhesive.

[0007] Further, the temporary UV-fixing adhesive described in step S1 comprises the following components by weight: 35-45 parts of acrylate prepolymer, 20-35 parts of acrylate monomer, 18-22 parts of thermally expandable microspheres, 3-8 parts of thermal phase change microspheres, 1-5 parts of thermal migration aid, 0.1-1 parts of sulfur-free non-thiol free radical chain transfer agent, 2-5 parts of photoinitiator, and 0.01-0.1 parts of polymerization inhibitor.

[0008] Further, the acrylate prepolymer is an acrylate copolymer; the acrylate monomer is cyclotrimethylolpropane methyl acetal acrylate; the photoinitiator is diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide; and the polymerization inhibitor is 2,6-di-tert-butyl-4-methylphenol.

[0009] Furthermore, the initial expansion temperature of the thermally expandable microspheres is 85℃, the maximum operating temperature is 130℃, the particle size is 20-30μm, the outer shell is an acrylate polymer, and the core is a hydrocarbon; the outer shell of the thermal phase change microspheres is a thermoplastic acrylate polymer, and the core is an alkane with a melting point of 55-80℃ and a boiling point above 200℃; the thermal migration aid is a fluorosilicone modified acrylate copolymer with a viscosity of 3500-5500cps, a fluorine mass fraction of 0.5%-2%, a silicon mass fraction of 1%-3%, and no small molecule silicon or small molecule fluorine additives; the sulfur-free non-thiol free radical chain transfer agent is α-methylstyrene dimer.

[0010] Furthermore, the outer shell of the thermal phase change microspheres is polymethyl methacrylate, and the core is n-octacosane.

[0011] Furthermore, the preparation method of the thermal phase change microspheres specifically includes the following steps: S1. Prepare an oil phase by melting n-octacosane at 50-70℃ and mixing it with polymethyl methacrylate and benzoyl peroxide at a mass ratio of 1:1:0.05; S2. Dissolve polyvinyl alcohol in deionized water to a final concentration of 20-30 mg / mL to obtain the aqueous phase; S3. Mix the oil phase and the aqueous phase at a mass ratio of 1:10 and prepare an emulsion using a high-speed homogenizer. After the emulsion is prepared, react at 80-100℃ for 1-5 hours, wash with ethanol and dry to obtain phase-separated microspheres.

[0012] Furthermore, the preparation of the temporary UV-fixing adhesive specifically includes the following steps: S1. Under normal temperature and light-protected conditions, add acrylate prepolymer, acrylate monomer, heat migration aid and polymerization inhibitor into a stirred tank, stir at 300-500 r / min for 25-40 min until completely transparent and homogeneous; S2. Keep the system temperature below 25℃, slowly add sulfur-free non-thiol free radical chain transfer agent, and continue stirring for 10-15 minutes to make it uniformly dissolved and dispersed. S3. Add thermal expansion microspheres and thermal phase change microspheres under low-speed stirring, and strictly control the speed at 200-300 rpm to avoid damage to the microsphere shell and ensure the integrity of the microspheres. S4. Finally, add the photoinitiator, stir in the dark for 15-20 minutes, filter through a 100-mesh filter, and store in a sealed container in the dark to obtain a temporary UV fixative.

[0013] Furthermore, the thickness of the temporary UV adhesive screen printing is 10-50 μm; the UV curing conditions are a wavelength of 400-450 nm and a light intensity of 600-1000 mW / cm². 2 The curing time is 3-10 seconds; the material of the solder strip is tin or silver.

[0014] Furthermore, the temperature of the laser or hot-press welding in step S3 is 160-200℃, and the time is 1-10s.

[0015] Furthermore, the low-temperature heating conditions described in step S4 are heating at 100-140℃ for 0.5-5 minutes.

[0016] According to a second aspect of the present invention, a welding and sizing method for OBB cells is provided for application in the preparation of photovoltaic cells.

[0017] The present invention has the following advantages: 1. This invention differs from traditional photovoltaic cell adhesive application methods, which involve directly applying adhesive to the cell, fixing the solder ribbon after the adhesive cures, and then laser or hot-pressing the wires. The adhesive remains permanently on the cell, and its aging negatively impacts power generation. The adhesive application method provided by this invention uses screen printing to temporarily fix UV adhesive onto a glass fixture, completing the stretching and UV curing of the solder ribbon. The cell, printed with solder paste or conductive adhesive, is then precisely aligned with the fixture and subjected to short-time high-temperature welding. After welding, a low-temperature heating process utilizes the adhesive's thermal expansion or contraction properties to automatically detach it from the solder ribbon interface, thus achieving a reliable connection between the solder ribbon and the cell, with no adhesive residue remaining on the cell surface.

[0018] 2. The temporary fixing UV adhesive used in the adhesive application method provided by the present invention includes thermally expandable microspheres and thermally phase-change microspheres. At 100-120°C, the core of the thermally expandable microspheres vaporizes, causing the microspheres to expand, while the long-chain alkane core of the thermally phase-change microspheres melts and remains liquid, seeping out from the cracks in the outer shell and rapidly spreading to the interface between the adhesive layer and the solder ribbon to form a physical isolation, and plasticizing the surrounding acrylate polymer, reducing the cohesive strength of the adhesive layer. The combination of the two can effectively remove residual adhesive.

[0019] 3. In this invention, a fluorosilicone-modified acrylate copolymer is added as a heat migration aid to the temporary UV fixation adhesive. Due to the low surface energy of the fluorosilicone-modified acrylate copolymer, the adhesion of the adhesive layer after heating is reduced, so as to facilitate the removal of residual adhesive.

[0020] 4. The adhesive application method provided by this invention avoids the problems of optical obstruction, uneven thermal stress and aging degradation caused by long-term adhesion of adhesive layer in traditional methods, improves the long-term reliability and photoelectric conversion efficiency of battery modules, and the entire process does not require the volatilization of adhesive layer, but only relies on physical separation mechanism to complete non-invasive separation, providing a new process path for the efficient and non-destructive packaging of OBB batteries.

[0021] 5. The adhesive application method provided by this invention has significant cost and efficiency advantages. Traditional photovoltaic cell adhesive application methods are difficult to apply adhesive to ultra-fine solder ribbons smaller than 0.2mm. The adhesive application method provided by this invention pre-applies adhesive to the glass fixture, thus it can be applied to solder ribbons with a wider range of diameters, greatly reducing the amount of solder ribbon and corresponding silver used, and saving raw material costs. At the same time, this invention can accurately fix multiple sets of solder ribbons on a large-area fixture at the same time, which is suitable for the large-scale production of OBB batteries, greatly improving battery production efficiency and reducing equipment and labor costs.

[0022] 6. This invention addresses the technical shortcomings of existing technologies, such as high debonding temperature, severe residue, poor adhesion stability, sulfur contamination, and a single mechanism. It provides a temporary UV fixation adhesive that uses room-temperature liquid weakly functional acrylic copolymer resin combined with cyclic monomers to construct a composite debonding system of highly filled microspheres with critical expansion, controllable weak crosslinking, and low surface energy modification at the interface. This system achieves rapid debonding at temperatures below 120°C while avoiding sulfur contamination, ensuring homogeneous and low crosslinking of the cured film, and preventing small molecule migration contamination. It is suitable for high-end photovoltaic cell manufacturing processes such as OBB. Attached Figure Description

[0023] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0024] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0025] Figure 1 This invention provides photographs of a temporary UV-cured adhesive before and after curing, as an example of its preparation; wherein, Figure 1 Photo A shows the temporary fixative UV adhesive before curing. Figure 1 B is a photo of the temporary fixative UV adhesive after curing; Figure 2 A photograph of the temporary UV adhesive-bonded glass fixture and welding strip provided in Embodiment 1 of the present invention; Figure 3 This is a photograph of the temporary UV adhesive after it has been debonded by low-temperature heating, as provided in Embodiment 1 of the present invention. Figure 4 Shear strength diagrams of temporary UV-fixing adhesives prepared in the preparation examples and comparative examples 1-7 provided by the present invention in the glass-glass substrate; Figure 5 Shear strength diagrams of temporary UV-fixing adhesives prepared for the preparation examples and comparative examples 1-7 provided by the present invention in the glass-stainless steel substrate; Figure 6 This is a graph showing the initial expansion time and full expansion time of the adhesive layer obtained by applying adhesive using the methods in Examples 1-4 of this invention. Figure 7 These are photographs of the adhesive layer obtained by applying the adhesive using the method in Example 1 of this invention, before and after heating at 120°C; wherein, Figure 7 Photo A shows the adhesive layer before heating. Figure 7 B is a photograph of the adhesive layer after heating; Figure 8 These are photographs of the adhesive layer obtained by applying the adhesive using the method in Example 2 of this invention, before and after heating at 120°C; wherein, Figure 8 Photo A shows the adhesive layer before heating. Figure 8 B is a photograph of the adhesive layer after heating; Figure 9 These are photographs of the adhesive layer obtained by applying the adhesive using the method in Example 3 of this invention, before and after heating at 120°C; wherein, Figure 9 Photo A shows the adhesive layer before heating. Figure 9 B is a photograph of the adhesive layer after heating; Figure 10 These are photographs of the adhesive layer obtained by applying the adhesive using the method in Example 4 of this invention, before and after heating at 120°C; wherein, Figure 10 Photo A shows the adhesive layer before heating. Figure 10 B is a photograph of the adhesive layer after heating. Detailed Implementation

[0026] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] According to a first aspect of the present invention, a welding adhesive application method for OBB batteries is provided, specifically including the following steps: S1. Screen print temporary fixing UV adhesive on the glass fixture, lay the solder ribbon, and then cure with UV light to fix the solder ribbon. S2. After curing, align the solder ribbon with the battery cell printed with solder paste or conductive adhesive. S3. Laser or hot-press welding of the welding strip to the battery cell; S4. After welding, low-temperature heating causes the adhesive layer to expand or contract automatically and detach from the bonded object, thereby removing the temporary fixing UV adhesive.

[0028] The temporary UV-fixing adhesive in step S1 comprises the following components by weight: 35-45 parts acrylate prepolymer, 20-35 parts acrylate monomer, 18-22 parts thermally expandable microspheres, 3-8 parts thermal phase change microspheres, 1-5 parts thermal migration aid, 0.1-1 parts sulfur-free non-thiol free radical chain transfer agent, 2-5 parts photoinitiator, and 0.01-0.1 parts polymerization inhibitor.

[0029] The acrylate prepolymer is an acrylate copolymer; the acrylate monomer is cyclotrimethylolpropane methyl acetal acrylate; the photoinitiator is diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide; and the polymerization inhibitor is 2,6-di-tert-butyl-4-methylphenol.

[0030] Among them, the thermal expansion microspheres have an initial expansion temperature of 85℃, a maximum working temperature of 130℃, a particle size of 20-30μm, an outer shell of acrylate polymer, and a core of hydrocarbon; the thermal phase change microspheres have an outer shell of thermoplastic acrylate polymer and a core of alkane with a melting point of 55-80℃ and a boiling point above 200℃; the thermal migration aid is a fluorosilicone modified acrylate copolymer with a viscosity of 3500-5500cps, a fluorine mass fraction of 0.5%-2%, a silicon mass fraction of 1%-3%, and no small molecule silicon or small molecule fluorine additives; the sulfur-free non-thiol free radical chain transfer agent is α-methylstyrene dimer.

[0031] The outer shell of the thermal phase change microspheres is polymethyl methacrylate, and the core is n-octacosane.

[0032] The preparation method of thermal phase change microspheres specifically includes the following steps: S1. Prepare an oil phase by melting n-octacosane at 50-70℃ and mixing it with polymethyl methacrylate and benzoyl peroxide at a mass ratio of 1:1:0.05; S2. Dissolve polyvinyl alcohol in deionized water to a final concentration of 20-30 mg / mL to obtain the aqueous phase; S3. Mix the oil phase and the aqueous phase at a mass ratio of 1:10 and prepare an emulsion using a high-speed homogenizer. After the emulsion is prepared, react at 80-100℃ for 1-5 hours, wash with ethanol and dry to obtain phase-separated microspheres.

[0033] The preparation of the temporary UV fixation adhesive specifically includes the following steps: S1. Under normal temperature and light-protected conditions, add acrylate prepolymer, acrylate monomer, heat migration aid and polymerization inhibitor into a stirred tank, stir at 300-500 r / min for 25-40 min until completely transparent and homogeneous; S2. Keep the system temperature below 25℃, slowly add sulfur-free non-thiol free radical chain transfer agent, and continue stirring for 10-15 minutes to make it uniformly dissolved and dispersed. S3. Add thermal expansion microspheres and thermal phase change microspheres under low-speed stirring, and strictly control the speed at 200-300 rpm to avoid damage to the microsphere shell and ensure the integrity of the microspheres. S4. Finally, add the photoinitiator, stir in the dark for 15-20 minutes, filter through a 100-mesh filter, and store in a sealed container in the dark to obtain a temporary UV fixative.

[0034] The thickness of the temporary UV adhesive screen printing is 10-50μm; the UV curing conditions are a wavelength of 400-450nm and a light intensity of 600-1000mW / cm². 2 The curing time is 3-10 seconds; the solder ribbon material is tin or silver.

[0035] In step S3, the temperature for laser or hot-press welding is 160-200℃, and the time is 1-10s.

[0036] In step S4, the low-temperature heating conditions are 100-140℃ for 0.5-5 minutes.

[0037] According to a second aspect of the present invention, a welding and sizing method for OBB cells is provided for application in the preparation of photovoltaic cells.

[0038] To better illustrate the technical path of the present invention, the following preparation examples, comparative examples, and embodiments are provided.

[0039] Preparation Example Preparation of temporary UV fixative: S1. Preparation of thermal phase change microspheres: a. Prepare an oil phase by melting n-octacosane at 60°C and mixing it with polymethyl methacrylate and benzoyl peroxide at a mass ratio of 1:1:0.05; b. Dissolve polyvinyl alcohol in deionized water to a final concentration of 25 mg / mL to obtain the aqueous phase; c. Mix the oil phase and the aqueous phase at a mass ratio of 1:10, and prepare an emulsion using a high-speed homogenizer. After the emulsion is prepared, react at 90°C for 3 hours, wash with ethanol and dry to obtain phase-separated microspheres. S2. Preparation of temporary UV fixative: a. Under normal temperature and light-protected conditions, 41.9g of acrylate copolymer (purchased from Hubei Shuaiyan Ligao Biomedical Co., Ltd.), 25g of cyclotrimethylolpropane methyl acetal acrylate (purchased from Hubei Jiufenglong Chemical Co., Ltd., CAS: 66492-51-1, CTFA), 4g of fluorosilicone modified acrylate copolymer (purchased from Hubei Dongguan Jingshang New Material Development Co., Ltd., model: UV-9843-9), and 0.1g of 2,6-di-tert-butyl-4-methylphenol (purchased from Wuhan Huaxiang Kejie Biotechnology Co., Ltd., CAS: 128-37-0, BHT) were added to a stirred tank. The stirring speed was 400r / min, and the mixture was stirred for 30min until it was completely transparent and homogeneous. The entire process was carried out in the dark without ultraviolet light to prevent premature polymerization of the raw materials. b. The system temperature is controlled below 25℃. 0.5g of α-methylstyrene dimer (purchased from Wuxi Zhiyuan Chemical Co., Ltd., CAS: 6362-80-7, AMSD) is slowly added and stirred for 15min to ensure uniform dissolution and dispersion. The chain transfer agent is chemically stable under ambient temperature and light-protected conditions and does not undergo polymerization. It only achieves homogeneous mixing of the system and avoids excessively high local concentrations. c. Add 20g of thermal expansion microspheres (purchased from PolyChem Corporation, USA, model: 120DU25) and 5g of thermal phase change microspheres under low-speed stirring. The stirring speed is strictly controlled at 250rpm to avoid damage to the microsphere shell and ensure the integrity of the microspheres. d. Finally, add 3.5g of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (purchased from Angxing New Carbon Materials Changzhou Co., Ltd., CAS: 162881-26-7, TPO), stir in the dark for 20 minutes, filter through a 100-mesh filter, and store in a sealed container in the dark to obtain a temporary UV fixative. Figure 1 A); it can be seen that the prepared temporary UV fixation adhesive is a pale yellow viscous liquid.

[0040] Comparative Example 1 This comparative example is based on the preparation example, except that thermal phase change microspheres are not added to the temporary fixation UV adhesive, while the other specific parameters are the same as those in the preparation example.

[0041] Comparative Example 2 This comparative example is based on the preparation example, except that expanded microspheres are not added to the temporary fixation UV adhesive, while the other specific parameters are the same as those in the preparation example.

[0042] Comparative Example 3 This comparative example is based on the preparation example, except that no fluorosilicone-modified acrylate copolymer is added to the temporary fixation UV adhesive, while the other specific parameters are the same as those in the preparation example.

[0043] Comparative Example 4 This comparative example is based on the preparation example, except that α-methylstyrene dimer is not added to the temporary fixation UV adhesive, while the other specific parameters are the same as those in the preparation example.

[0044] Comparative Example 5 This comparative example is based on the preparation example, except that an equal amount of trimethylolpropane triacrylate (TMTPA) was used to replace cyclotrimethylolpropane methyl acetal acrylate in the temporary fixation UV adhesive, while the other specific parameters are the same as in the preparation example.

[0045] Comparative Example 6 This comparative example is based on the preparation example, except that the α-methylstyrene dimer was replaced with an equal amount of dodecyl mercaptan in the temporary fixation UV adhesive, while the other specific parameters are the same as those in the preparation example.

[0046] Comparative Example 7 This comparative example is based on the preparation example, the difference being that the mass of each component in the temporary fixation UV adhesive is: The temporary UV-fixing adhesive in step S1 comprises the following components by weight: 46.9g acrylate copolymer, 30g cyclotrimethylolpropane methyl acetal acrylate, 10g thermally expandable microspheres, 5g thermal phase change microspheres, 4g fluorosilicone-modified acrylate copolymer, 0.5g α-methylstyrene dimer, 3.5g diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, and 0.1g 2,6-di-tert-butyl-4-methylphenol. That is, the amount of thermally expandable microspheres added is 10 parts, and the other specific parameters are the same as in the preparation example.

[0047] Example 1 S1. A temporary fixing UV adhesive prepared by screen printing was prepared on a glass fixture. The screen printing thickness was 30 μm. After the solder ribbon was laid out, it was cured with ultraviolet light to fix the solder ribbon. The ultraviolet curing conditions were a wavelength of 405 nm and a light intensity of 800 mW / cm². 2 Curing time: 3 seconds. The photo after curing is shown below. Figure 2 As shown; S2. After curing, align the solder ribbon with the battery cell printed with solder paste or conductive adhesive. S3. Laser weld the welding strip to the battery cell at 180°C for 5 seconds; S4. After welding, heat at 120℃ for 1 minute to allow the adhesive layer to automatically expand or contract and detach from the bonded object, thereby removing the temporary fixing UV adhesive. Figure 3 ).

[0048] It can be seen that after temporary fixation with UV adhesive ( Figure 1 B) The light yellow viscous liquid turned into a light yellow solid, and the surface was not noticeably sticky to the touch. The curing and surface drying of the temporary UV adhesive on the surface were good.

[0049] Example 2 This embodiment is based on embodiment 1, except that the thickness of the temporary fixed UV adhesive screen printing is 20μm, while the other specific parameters are the same as in embodiment 1.

[0050] Example 3 This embodiment is based on embodiment 1, except that the thickness of the temporary fixed UV adhesive screen printing is 40μm, while the other specific parameters are the same as in embodiment 1.

[0051] Example 4 This embodiment is based on embodiment 1, except that the thickness of the temporary fixed UV adhesive screen printing is 50μm, while the other specific parameters are the same as in embodiment 1.

[0052] Test Example 1 To verify the performance of the temporary UV fixation adhesives prepared in each preparation example of the present invention, the torque, viscosity and thixotropy of the temporary UV fixation adhesives at high speed (10 rpm) and low speed (1 rpm) were measured by a rotational rheometer. The rotor was set to No. 29 and the test temperature was 25°C. The results are recorded in Table 1.

[0053] Table 1. Torque, viscosity, and thixotropic index of temporary fixing UV adhesive at high and low speeds.

[0054] As can be seen, the torque, viscosity, and thixotropy of the temporarily fixed UV adhesive significantly decreased after removing the thermal phase change microspheres and thermal expansion microspheres (Comparative Examples 1 and 2) and in Comparative Example 7 with reduced thermal expansion microsphere content. This is because the shell materials of both the thermal phase change microspheres and thermal expansion microspheres are acrylate polymers, which have good compatibility with acrylate prepolymers and monomers. Removing or reducing these two components reduces the viscosity and torque of the adhesive under shear. Furthermore, as solid fillers, the removal of these two microspheres weakens the skeletal strength of the adhesive, making it more prone to thinning under shear and resulting in a decrease in the thixotropic index. In Comparative Example 3 without added thermal migration aids, the fluorosilicone-modified acrylate copolymer, as a low surface energy material, acts as a lubricant under shear, effectively reducing the viscosity of the adhesive. After removal, the adhesive becomes more viscous, exhibiting higher torque, viscosity, and thixotropic index. The rheological properties of Comparative Example 4, without the addition of α-methylstyrene dimer, were similar to those of the prepared example. However, replacing the sulfur-free non-thiol radical chain transfer agent with a thiol chain transfer agent (dodecyl mercaptan) resulted in a slight decrease in the rheological properties of the UV adhesive. This indicates that the chain transfer agent only acts as a sulfur-free non-thiol radical chain transfer agent during the adhesive curing process and has no significant effect on the torque, viscosity, and thixotropic index of the uncured adhesive. Replacing CTFA with TMTPA significantly increased the viscosity, torque, and thixotropic index of the adhesive, indicating a higher crosslinking density of linear acrylate monomers in the adhesive.

[0055] Test Example 2 Following the method in GB / T 7124-2008, the test conditions were set to an adhesive layer thickness of 30 μm. The shear strength of the temporary fixing UV adhesives prepared in the preparation examples and Comparative Examples 1-7 was measured between glass-glass substrates and glass-stainless steel substrates. The results are as follows: Figure 4 and Figure 5 As shown.

[0056] The results showed that the temporary fixing UV adhesives prepared in the preparation examples and Comparative Examples 1-7 exhibited shear strengths of 1.44 MPa, 1.30 MPa, 0.93 MPa, 2.00 MPa, 1.39 MPa, 1.60 MPa, 1.41 MPa, and 1.37 MPa between glass and glass substrates, respectively. However, their shear strengths between glass and stainless steel substrates were 2.58 MPa, 2.32 MPa, 1.70 MPa, 3.24 MPa, 2.21 MPa, 2.72 MPa, 2.53 MPa, and 2.40 MPa, respectively. This indicates that the temporary fixing UV adhesive demonstrated stronger adhesion between glass and stainless steel substrates. This is because the adhesive has better wettability on the stainless steel surface, making it easier for the adhesive to spread. Furthermore, the presence of scratches or depressions on the stainless steel surface, compared to smooth glass, facilitates the physical anchoring of the adhesive layer. Compared to the preparation examples, the temporary fixed UV adhesives prepared in Comparative Examples 1, 2, and 7 showed reduced shear strength between glass-glass substrates by 9.72%, 35.42%, and 4.86%, respectively, and reduced shear strength between glass-stainless steel substrates by 10.08%, 34.11%, and 6.98%, respectively. This is because thermal phase change microspheres and thermal expansion microspheres, as rigid fillers, can form physical crosslinking points and stress transfer skeletons for the adhesive layer after curing, enhancing the mechanical interlocking ability between the adhesive layer and the substrate, thereby improving shear strength. Furthermore, the amount of thermal expansion microspheres added is much higher than that of thermal phase change microspheres, so removing or reducing them has a greater impact on the shear strength of the adhesive layer. Comparative Example 3 showed a 38.89% increase in shear strength between glass-glass substrates compared to the preparation examples, and a 25.58% increase in shear strength between glass-stainless steel substrates. The fluorosilicone-modified acrylate copolymer, as a thermal migration aid, has low surface energy and can migrate to the interface surface during curing, forming a weak boundary layer and reducing the adhesion between the adhesive layer and the substrate. Therefore, the shear strength of the adhesive layer was significantly improved after removing the thermal migration aid. α-Methylstyrene dimer, a sulfur-free non-thiol radical chain transfer agent used to regulate the molecular weight and distribution during adhesive curing, resulted in a larger molecular weight and wider molecular weight distribution in the adhesive layer after its removal, leading to increased disorder in the crosslinking network and decreased cohesive strength. Replacing the sulfur-free non-thiol radical chain transfer agent with a thiol chain transfer agent did not significantly decrease the shear strength of the UV adhesive on glass-glass and glass-stainless steel substrates. This is further confirmed by the fact that the shear strength of Comparative Examples 4 and 6 decreased by 3.47% and 2.08% between glass-glass substrates, respectively, and by 14.34% and 1.94% between glass-stainless steel substrates, respectively, compared to the prepared examples. Replacing CTFA with TMTPA slightly increased the shear strength of the adhesive.

[0057] Test Example 3 To verify the debonding performance of the adhesive application method of the present invention, the debonding time of the coated adhesive layer was measured by heating and baking. Specifically, the following steps were performed: Temporary UV-fixing adhesive was applied to a glass fixture according to step S1 of Examples 1-4, and heated in an oven at a low temperature of 120°C. The initial expansion time and complete expansion time of the adhesive layer were recorded and photographed. Due to time and cost considerations, only the adhesive application methods of Examples 1-4 were used for the determination in Test Example 3. The results are as follows: Figures 4-8 As shown.

[0058] Depend on Figure 6 It can be seen that the initial expansion times of the adhesive layers prepared in Examples 1-4 were 12.1s, 10.3s, 13.9s, and 16.4s, respectively, and the complete expansion times were 33.0s, 30.1s, 36.3s, and 39.8s, respectively. This indicates that the initial expansion time and complete expansion time of the adhesive layer are positively correlated with the thickness of the adhesive layer. Figures 7-10 It can be seen that when the adhesive coating thickness is less than 30 μm (Example 2), the bubbles do not significantly lift the adhesive layer; when it is greater than 50 μm, the bubbles cannot lift the adhesive layer. Therefore, the adhesive coating thickness should be 30-50 μm when applying the adhesive.

[0059] Test Example 4 The adhesive prepared in Preparation Example 8 was coated onto a glass fixture with a coating thickness of 30 μm. It was then cured under ultraviolet light according to the parameters in Example 1. The fixture was placed on a temperature-controlled heating stage and heated starting at 50°C with a heating frequency of 5°C. Each heating was held for 30 seconds. The adhesive layer was observed, and the time for the adhesive layer to fully expand was recorded as the debonding temperature. The debonding state, residual adhesive, battery EL state, and room temperature bonding stability were also recorded. The structure is recorded in Table 2.

[0060] Table 2 Debonding temperature, debonding state, residual adhesive condition, and room temperature bonding stability of temporary fixing UV adhesive

[0061] It can be seen that the debonding temperature of the temporary fixed UV adhesive with added thermally expanded microspheres decreased significantly, and the decrease was positively correlated with the amount of thermally expanded microspheres added. The adhesive layer without added thermally expanded microspheres could not automatically debond under heating conditions and had a large amount of residual adhesive. The EL state of the 0BB battery showed obvious dark spots, but the adhesion was strong at room temperature. This indicates that the thermally expanded microspheres are the main component for debonding the temporary fixed UV adhesive and do not affect the adhesive layer's bonding performance. The debonding temperatures of Comparative Examples 2 and 3, without added thermal phase change microspheres and thermal migration aids, were slightly higher than the prepared example, but no significant difference was observed. Although the adhesive layers in these two groups could automatically curl up at low-temperature heating, there were sticky residues and oily residual films. The 0BB battery showed obvious dark spots, and the adhesive layer's adhesion performance was normal. This indicates that thermal phase change microspheres and thermal migration aids can reduce the adhesive layer's adhesion under heating conditions by reducing the interfacial interaction between the adhesive layer and the substrate. In Comparative Example 5, where CTFA was replaced by TMTPA, the debonding temperature was significantly higher than in the preparation example. After heating, the adhesive became brittle and fractured, leaving significant fragments after peeling. Localized mottling appeared on the cell surface, and the adhesive layer easily peeled off at room temperature. This indicates that the cyclic CTFA monomer provided appropriate crosslinking and flexibility to the adhesive layer. Replacing it with a trifunctional monomer resulted in excessively high crosslinking density, leading to brittleness. Comparative Example 6, which replaced the sulfur-free non-thiol free radical chain transfer agent with a thiol-based chain transfer agent, achieved effective debonding, but the sulfur element corroded the cell during heating, causing slight grid line corrosion, making it unsuitable for photovoltaic cell bonding.

[0062] The above results demonstrate that the temporary UV-fixing adhesive prepared in the present invention can effectively peel off the adhesive layer at 102°C while maintaining good adhesion at room temperature, leaving no adhesive residue after peeling, and without significantly affecting the battery state. Furthermore, its low-temperature heating peeling relies on the synergistic effect of thermally expanding microspheres, thermal phase change microspheres, and thermal migration aids.

[0063] Test Example 5 Referring to GB / T 2790-1995 "Test Method for 180° Peel Strength of Adhesives", corresponding test pieces were prepared to test the peel strength of the temporary fixing UV adhesives prepared in the preparation examples and comparative examples 1-7 against glass, tin and silver substrates at room temperature, 120°C for 2 min and 180°C for 5 s. The results are recorded in Table 3.

[0064] Table 3. Peel strength of temporary fixing UV adhesive to glass, tin, and silver substrates at room temperature, 120°C, and 180°C.

[0065] As can be seen, the temporary UV adhesive prepared in the preparation examples exhibits good adhesion properties on glass, tin, and silver substrates at room temperature, with peel strengths of 4.25 N / mm, 2.32 N / mm, and 2.30 N / mm, respectively. After removing the thermal phase change microspheres and thermal expansion microspheres, the cohesive strength of the adhesive layer decreases due to the lack of rigid fillers, resulting in a slight decrease in peel strength. The three comparative examples lacking the thermal migration aid all showed higher peel strength on all three substrates. This is because the removal of the low surface energy component enhances the bonding ability between the adhesive layer and the substrate, leading to an increase in peel strength. At 120℃ and 180℃, the prepared examples exhibited the lowest peel strength, with the peel strength approaching 0 after heating at 120℃ for 2 min. Comparative Examples 4 and 6 were similar to the prepared examples but slightly higher. Comparative Examples 1-3 and 7 showed significantly higher peel strength under heating conditions than the prepared examples, indicating that the UV adhesive prepared in the prepared examples can achieve rapid peeling at 120℃. Furthermore, the thermal phase change microspheres, thermal expansion microspheres, and thermal migration aids in the adhesive solution act as auxiliary peeling components, significantly weakening the adhesion between the adhesive layer and the substrate under heating conditions. The chain transfer agent only plays an auxiliary role by limiting the molecular weight and distribution of the adhesive solution during curing. Comparative Example 5, by replacing the cyclic monomer with a linear acrylate monomer, significantly improved the adhesion strength of the adhesive layer to glass, tin, and silver substrates, indicating that the use of cyclic monomers helps reduce the crosslinking density of the adhesive layer, thus aiding in peeling.

[0066] Test Example 6 To further quantify the adhesive properties, residual characteristics, migration safety, and photovoltaic process compatibility of the adhesive of the present invention, the surface energy, extractable organic matter, halide ion content, and heavy metal / sulfur ion content of the UV adhesives prepared in the preparation examples and comparative examples were tested. The test results are shown in Table 4.

[0067] Table 4. Results of surface energy, extractable organic matter, halide ion content, and heavy metal / sulfide ion content of temporary UV-fixing adhesives.

[0068] It can be seen that the temporary UV fixation adhesive prepared in the preparation examples of this invention has low surface energy, low content of extractable organic matter and halide ions, and no heavy metal and sulfur ion residues were detected. It can meet the requirements of high bonding cleanliness and easy peeling for temporary fixation adhesives in 0BB photovoltaic cells. The surface energy of the adhesive layer increased by 27.4% after the absence of the thermal migration aid; while the surface energy of the adhesive layer increased by 12.8% after the absence of the thermal phase change microspheres, significantly affecting the debonding performance. Compared with the preparation examples, the surface energies of Comparative Examples 1 and 7 increased by 60.2% and 39.4%, respectively, indicating that although the main function of the thermal expansion microspheres is to cause the adhesive layer to expand in volume after heating, their absence also significantly affects the surface energy of the adhesive layer, and is positively correlated with the amount added. The surface energy of the adhesive layers in Comparative Examples 4 and 6, which did not contain α-methylstyrene dimer and replaced α-methylstyrene dimer with dodecyl mercaptan, did not significantly increase compared with the preparation examples, but the halide ion content of Comparative Example 6 increased, and trace amounts of sulfur ion residues were detected in the adhesive solution, which indirectly confirms the conclusion of Test Example 4. In the five comparative groups where linear monomers were replaced with cyclic monomers, the surface energy of the adhesive increased due to the increased crosslinking density, and higher levels of halogen ions and extractable organic matter were detected in the adhesive.

[0069] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A welding adhesive application method for OBB batteries, characterized in that, Specifically, the following steps are included: S1. Screen print temporary fixing UV adhesive on the glass fixture, lay the solder ribbon, and then cure with UV light to fix the solder ribbon. S2. After curing, align the solder ribbon with the battery cell printed with solder paste or conductive adhesive. S3. Laser or hot-press welding of the welding strip to the battery cell; S4. After welding, low-temperature heating causes the adhesive layer to expand or contract automatically and detach from the bonded object, thereby removing the temporary fixing UV adhesive.

2. The welding and adhesive application method for OBB batteries as described in claim 1, characterized in that, The temporary UV-fixing adhesive described in step S1 comprises the following components by weight: 35-45 parts of acrylate prepolymer, 20-35 parts of acrylate monomer, 18-22 parts of thermally expandable microspheres, 3-8 parts of thermal phase change microspheres, 1-5 parts of thermal migration aid, 0.1-1 parts of sulfur-free non-thiol free radical chain transfer agent, 2-5 parts of photoinitiator, and 0.01-0.1 parts of polymerization inhibitor.

3. The welding and adhesive application method for OBB batteries as described in claim 2, characterized in that, The acrylate prepolymer is an acrylate copolymer; the acrylate monomer is cyclotrimethylolpropane methyl acetal acrylate; the photoinitiator is diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide; and the polymerization inhibitor is 2,6-di-tert-butyl-4-methylphenol.

4. The welding and adhesive application method for OBB batteries as described in claim 2, characterized in that, The thermally expandable microspheres have an initial expansion temperature of 85℃, a maximum operating temperature of 130℃, and a particle size of 20-30μm. The outer shell is an acrylate polymer, and the core is a hydrocarbon. The thermal phase change microspheres have an outer shell of thermoplastic acrylate polymer and a core of alkane with a melting point of 55-80℃ and a boiling point above 200℃. The thermal migration aid is a fluorosilicone modified acrylate copolymer with a viscosity of 3500-5500cps, a fluorine mass fraction of 0.5%-2%, a silicon mass fraction of 1%-3%, and is free of small molecule silicon and small molecule fluorine additives. The sulfur-free non-thiol free radical chain transfer agent is α-methylstyrene dimer.

5. The welding and adhesive application method for OBB batteries as described in claim 2, characterized in that, The outer shell of the thermal phase change microspheres is polymethyl methacrylate, and the core is n-octacosan. The preparation method specifically includes the following steps: S1. Prepare an oil phase by melting n-octacosane at 50-70℃ and mixing it with polymethyl methacrylate and benzoyl peroxide at a mass ratio of 1:1:0.05; S2. Dissolve polyvinyl alcohol in deionized water to a final concentration of 20-30 mg / mL to obtain the aqueous phase; S3. Mix the oil phase and the aqueous phase at a mass ratio of 1:10 and prepare an emulsion using a high-speed homogenizer. After the emulsion is prepared, react at 80-100℃ for 1-5 hours, wash with ethanol and dry to obtain phase-separated microspheres.

6. The welding and adhesive application method for OBB batteries as described in claim 1, characterized in that, The preparation of the temporary UV fixation adhesive specifically includes the following steps: S1. Under normal temperature and light-protected conditions, add acrylate prepolymer, acrylate monomer, heat migration aid and polymerization inhibitor into a stirred tank, stir at 300-500 r / min for 25-40 min until completely transparent and homogeneous; S2. Keep the system temperature below 25℃, slowly add sulfur-free non-thiol free radical chain transfer agent, and continue stirring for 10-15 minutes to make it uniformly dissolved and dispersed. S3. Add thermal expansion microspheres and thermal phase change microspheres under low-speed stirring, and strictly control the speed at 200-300 rpm to avoid damage to the microsphere shell and ensure the integrity of the microspheres. S4. Finally, add the photoinitiator, stir in the dark for 15-20 minutes, filter through a 100-mesh filter, and store in a sealed container in the dark to obtain a temporary UV fixative.

7. The welding and adhesive application method for OBB batteries as described in claim 1, characterized in that, The thickness of the temporary UV adhesive screen printing is 10-50μm; the UV curing conditions are a wavelength of 400-450nm and a light intensity of 600-1000mW / cm². 2 The curing time is 3-10 seconds; the material of the solder strip is tin or silver.

8. The welding and adhesive application method for OBB batteries as described in claim 1, characterized in that, The temperature of the laser or hot-press welding in step S3 is 160-200℃, and the time is 1-10s.

9. The welding and adhesive application method for OBB batteries as described in claim 1, characterized in that, The low-temperature heating conditions described in step S4 are heating at 100-140℃ for 0.5-5 minutes.

10. Application of a welding and sizing method for OBB cells in the preparation of photovoltaic cells.

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