High-transmittance insulating ink for back contact batteries and its preparation method

Abstract

This invention discloses a high-transmittance insulating ink for back-contact batteries and its preparation method, belonging to the technical field of insulating inks. The insulating ink comprises the following components by mass percentage: 60%~64% base resin, 1%~2% thiol, 2%~4% tackifier, and 25%~30% diluent; wherein the base resin is a hydroxyl-terminated polyester-modified acrylate, the thiol is ethylene dithiol, the tackifier is at least one of terpene resin, C5 petroleum resin, and C9 petroleum resin, and the diluent is at least one of 1,4-butanediol diacrylate, pentaerythritol triacrylate, and dipropylene glycol diacrylate. This invention utilizes the reaction of the dithiol's dithiol group with the hydroxyl groups (-OH) or double bonds in the hydroxyl-terminated polyester-modified acrylate to form thioether bonds (-S-) or thioester bonds, constructing a three-dimensional cross-linked network, thereby significantly improving the hardness and transmittance of the cured resin system. The reasonable combination of tackifier and diluent allows the ink to achieve high adhesion while maintaining hardness.

Description

Technical Field

[0001] This invention belongs to the field of insulating ink technology, specifically relating to a high-transmittance insulating ink for back contact batteries and its preparation method. Background Technology

[0002] In the production process of back-contact solar cells, the quality of the insulating ink directly affects the cell's performance and lifespan. When printing conductive main grids on conductive grids arranged with different polarities, insulating ink is needed to cover the conductive grids of the other polarity to prevent short circuits. However, traditional insulating inks have some significant shortcomings. First, the hardness of traditional insulating inks is often insufficient. During the lamination process of photovoltaic modules, the upper main grid may come into contact with the lower grids, causing a short circuit and leading to a decrease in cell performance. Second, it is often difficult to balance the hardness and adhesion of insulating inks. Increasing the hardness of traditional insulating inks often reduces their adhesion to the solar cells, which can cause the insulating ink to peel off during use, affecting the stability and reliability of the cell. Third, the light transmittance of traditional insulating inks often does not meet the requirements of the cell, which reduces the bifaciality of the cell.

[0003] To address these issues, a novel insulating ink is needed that can maintain high light transmittance while simultaneously ensuring both hardness and adhesion. However, existing technologies often fail to meet these requirements at the same time. Some solutions increase ink hardness at the expense of light transmittance and adhesion; others, while improving both, fail to provide sufficient hardness to prevent short circuits. Therefore, developing a high-transmittance insulating ink for back-contact cells that provides sufficient hardness without sacrificing light transmittance and adhesion has become a significant technological challenge in photovoltaic cell manufacturing.

[0004] It should be noted that this part of the present invention only provides background technology related to the present invention, and does not necessarily constitute prior art or known technology. Summary of the Invention

[0005] This invention provides a high-transmittance insulating ink for back-contact batteries and its preparation method, which solves at least the following problems: 1) The insufficient hardness of traditional insulating inks leads to short circuits between the upper main grid and the lower fine grid during the lamination process of photovoltaic modules, affecting battery performance; 2) Increasing the hardness of insulating inks reduces their adhesion to the battery cells, which may cause the insulating ink to fall off, affecting battery stability and reliability; 3) The transmittance of traditional insulating inks does not meet the requirements of batteries, reducing the bifaciality of batteries.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a high-transmittance insulating ink for back-contact batteries. The insulating ink comprises the following components by weight percentage: 60%~64% matrix resin, 1%~2% thiol, 2%~4% tackifier, and 25%~30% diluent; wherein the matrix resin is a hydroxyl-terminated polyester modified acrylate, the thiol is ethylene dithiol, the tackifier is at least one of terpene resin, C5 petroleum resin, and C9 petroleum resin, and the diluent is at least one of 1,4-butanediol diacrylate, pentaerythritol triacrylate, and dipropylene glycol diacrylate.

[0007] Preferably, the hydroxyl-terminated polyester modified acrylate has a light transmittance >90%, a molecular weight of 150,000 to 200,000, a viscosity of 10,000 to 50,000 cps, and a hydroxyl content of 5.1% to 6.5%.

[0008] Preferably, the diluent includes pentaerythritol triacrylate and dipropylene glycol diacrylate, with a mass ratio of pentaerythritol triacrylate to dipropylene glycol diacrylate of (0.5~1.5):(0.8~4).

[0009] Preferably, the insulating ink further includes the following components by weight percentage: 1% to 5% curing agent, 1% to 5% leveling agent, 0.1% to 1% UV absorber, and 0.1% to 1.5% antioxidant.

[0010] Preferably, the curing agent is at least one of imidazole, ethylenediamine, and 4-methylbenzophenone.

[0011] Preferably, the leveling agent is at least one of polydimethylsiloxane and polymethylalkylsiloxane.

[0012] Preferably, the ultraviolet absorber is at least one of 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, and phenyl salicylate.

[0013] Preferably, the antioxidant is at least one of 2,6-tert-butyl-4-methylphenol, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], phosphite, benzotriazole, ethylenediaminetetramethylenephosphonic acid, and oxalic acid dihydrazide.

[0014] Secondly, the present invention also provides a method for preparing a high-transmittance insulating ink for a back contact battery. The preparation method is used to prepare the above-mentioned high-transmittance insulating ink for a back contact battery, and the preparation method includes:

[0015] S1. Weigh each component according to its mass percentage;

[0016] S2. Add the matrix resin to the reactor and stir at 300-500 rpm for 10-20 minutes at room temperature;

[0017] S3. Add thiol and thickener in sequence, stirring at 500-800 rpm for 15-25 minutes after each component is added;

[0018] S4. Add the diluent, then increase the stirring speed to 800-1000 rpm and stir for 30-40 minutes.

[0019] S5. Filter the mixture obtained by stirring S4 through a filter screen with a mesh size of 20~200 to obtain a high-transmittance insulating ink for back contact batteries.

[0020] Preferably, S3 further includes the addition of a curing agent, a leveling agent, a UV absorber, and an antioxidant.

[0021] Preferably, the specific preparation method of the matrix resin includes:

[0022] S10. Weigh the following components by mass: 50-70 parts acrylate monomer, 1-2 parts initiator, and 30-50 parts first solvent;

[0023] S20. First, dissolve the hydroxyl-terminated polyester in the first solvent. The amount of hydroxyl-terminated polyester added is 30%-50% of the mass of the acrylate monomer. Then, add the acrylate monomer and at least part of the initiator and stir evenly.

[0024] S30. Under nitrogen protection, heat to the preset temperature and react for 4 to 6 hours. The preset temperature range is 60 to 100℃.

[0025] After S40 and S30 have reacted completely, the mixture is cooled and then precipitated in a second solvent. After filtration, washing, and drying, the matrix resin is obtained.

[0026] Preferably, S30 includes directly heating to a preset temperature under nitrogen protection and conducting a constant-temperature reaction for 4 to 6 hours.

[0027] Preferably, S30 includes multi-gradient segmented heating to a preset temperature under nitrogen protection, with each segment undergoing a isothermal reaction, and the total reaction time being 4 to 6 hours.

[0028] Preferably, when the temperature is directly raised to the preset temperature in S30, all the initiator is directly added in S20.

[0029] Preferably, when the temperature is raised to the preset temperature in S30 in a multi-gradient segmented manner, a portion of the initiator is added in S20, and another portion of the initiator is added equally in each temperature segment of S30.

[0030] Preferably, S20 further includes the addition of a hydroxyl-containing acrylate monomer, wherein the amount of the hydroxyl-containing acrylate monomer added is 20% to 30% of the mass of the acrylate monomer, and the hydroxyl-containing acrylate monomer is at least one of hydroxyethyl methacrylate and hydroxypropyl acrylate.

[0031] Preferably, S20 further includes the addition of a chain transfer agent, which is dodecyl mercaptan.

[0032] Preferably, the acrylate monomer is at least one of methyl acrylate, butyl acrylate, and hydroxyethyl methacrylate.

[0033] Preferably, the initiator is at least one of benzoyl peroxide and azobisisobutyronitrile.

[0034] Preferably, the first solvent is at least one of toluene, tetrahydrofuran, and ethyl acetate.

[0035] Preferably, the second solvent is at least one of methanol and n-hexane.

[0036] Preferably, the hydroxyl-terminated polyester is prepared by polycondensation reaction of polyol and polyacid; wherein the molar ratio of polyacid to polyol is 1:(1.2~1.4).

[0037] The beneficial effects of this invention are:

[0038] This invention provides a high-transmittance insulating ink for back-contact solar cells, which can effectively improve the bifaciality of photovoltaic cells and meet the requirements of high-power photovoltaic modules in solar power generation systems. Simultaneously, due to the high hardness and good adhesion of this insulating ink, it can reduce the short-circuit risk of photovoltaic modules during the lamination process, improving the reliability and stability of the modules. This is of great significance for improving the long-term operating efficiency of solar power generation systems and reducing maintenance costs.

[0039] This invention has wide applications in photovoltaic cell manufacturing, solar power generation systems, and related new energy technology fields. With the increasing global demand for renewable energy, the performance improvement of photovoltaic cells, as a key component of solar power generation, is crucial to the development of the entire industry. As new energy technologies develop, the performance requirements for photovoltaic cells are constantly increasing. The application of this technical solution can promote innovation in photovoltaic cell technology and facilitate the development of new energy technologies. Therefore, this technical solution has broad market demand and promising application prospects.

[0040] Specifically:

[0041] 1. This invention adds thiol, whose dithiol group reacts with the hydroxyl (-OH) or double bond in the hydroxyl-terminated polyester modified acrylate to form thioether bond (-S-) or thioester bond, thus constructing a three-dimensional cross-linked network, thereby significantly improving the hardness and light transmittance of the cured resin system and effectively preventing short circuits between the upper main grid and the lower fine grid.

[0042] 2. This invention enhances the adhesion between the insulating ink and the battery cell by adding terpene resin, C5 petroleum resin, and C9 petroleum resin tackifiers as adhesion promoters, preventing detachment during use. Furthermore, many components used in this invention contain hydroxyl groups, which effectively improves compatibility with the battery's ITO layer, thereby enhancing the ink's adhesion.

[0043] 3. The matrix resin of this invention is a hydroxyl-terminated polyester modified acrylate with a light transmittance >90%, meeting the light transmittance requirements of the battery cell. Simultaneously, the tackifier of this invention has high compatibility with both the battery substrate and the matrix resin, effectively wetting the substrate surface and preventing phase separation that could lead to a decrease in light transmittance. Detailed Implementation

[0044] In this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0045] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0046] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. The terms "optional" and "discretionary" mean that they may or may not be included (or may or may not be present).

[0047] This invention provides a high-transmittance insulating ink for back-contact batteries. The insulating ink comprises the following components by weight percentage: 60%~64% base resin, 1%~2% thiol, 2%~4% tackifier, and 25%~30% diluent; wherein the base resin is a hydroxyl-terminated polyester modified acrylate, the thiol is ethylene dithiol, the tackifier is at least one of terpene resin, C5 petroleum resin, and C9 petroleum resin, and the diluent is at least one of 1,4-butanediol diacrylate, pentaerythritol triacrylate, and dipropylene glycol diacrylate.

[0048] Preferably, the content of the matrix resin is 60% to 64%, and can be 60%, 60.5%, 61%, 61.5%, 62%, 62.5%, 63%, 63.5%, 64%, and any value between them.

[0049] Preferably, the content of thiol is 1% to 2%, and can be 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, and any value between them.

[0050] Preferably, the content of the tackifier is 2% to 4%, and can be 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, 3.2%, 3.4%, 3.6%, 3.8%, 4%, and any value between them.

[0051] Preferably, the content of the diluent is 25% to 30%, and can be 25%, 25.5%, 26%, 26.5%, 27%, 27.5%, 28%, 28.5%, 29%, 29.5%, 30%, and any value between them.

[0052] The insulating ink of this invention can maintain good light transmittance while possessing good hardness and excellent adhesion, meeting the requirements of back-contact battery components. It features a high bifaciality, effectively improving battery production yield and lifespan. One possible principle is that the dithiol groups of the thiol in the ink react with the hydroxyl groups (-OH) or double bonds in the hydroxyl-terminated polyester-modified acrylate to form thioether bonds (-S-) or thioester bonds, creating a high-density and highly uniform three-dimensional cross-linked network. This effectively improves the ink's hardness and light transmittance. Simultaneously, the polyester segments provide a flexible skeleton, enhancing the ink's toughness and preventing brittleness due to increased hardness. Furthermore, specific tackifiers are used to achieve better adhesion. This invention uses at least one of 1,4-butanediol diacrylate, pentaerythritol triacrylate, and dipropylene glycol diacrylate in appropriate proportions as an active diluent, introducing more cross-linking points, increasing the density and uniformity of the cross-linked network, further improving hardness and light transmittance. Simultaneously, the introduction of more hydroxyl groups improves compatibility with the ITO layer, thereby enhancing adhesion. This invention uses terpene resin, C5 petroleum resin, or C9 petroleum resin in appropriate proportions as a tackifier. This tackifier exhibits high compatibility with both the battery substrate and the matrix resin, effectively wetting the substrate surface and preventing phase separation that could lead to a decrease in light transmittance. The hydroxyl groups in the ink of this invention help improve compatibility with the battery's ITO layer, thereby enhancing adhesion. Simultaneously, this invention rationally employs a combination of diluent and tackifier, strengthening the adhesion between the insulating ink and the battery cell and preventing detachment during use.

[0053] Preferably, the transmittance of the hydroxyl-terminated polyester modified acrylate is >90%, and can be 91%, 92%, or higher, or any value between them. As the main component of the ink, the transmittance of the matrix resin largely determines the transmittance of the ink itself. The hydroxyl-terminated polyester modified acrylate used as the matrix resin in this invention has a transmittance >90%, thus enabling the ink of this invention to also have high transmittance, meeting the requirements of back-contact cells and improving the bifaciality of photovoltaic modules.

[0054] Preferably, the molecular weight of the hydroxyl-terminated polyester-modified acrylate is 150,000 to 200,000, and can be any value between 150,000, 160,000, 170,000, 180,000, 190,000, and 200,000. The purpose of this invention in rationally controlling the molecular weight of the hydroxyl-terminated polyester-modified acrylate is to increase the crosslinking density, thereby improving the hardness of the ink. It should be noted that the molecular weight of the hydroxyl-terminated polyester-modified acrylate is the weight-average molecular weight (M). w ).

[0055] Preferably, the viscosity of the hydroxyl-terminated polyester-modified acrylate is 10,000~50,000 cps, and can be 10,000 cps, 20,000 cps, 30,000 cps, 40,000 cps, 50,000 cps, or any value between them. The purpose of this invention in rationally controlling the viscosity of the hydroxyl-terminated polyester-modified acrylate is to inhibit penetration and enhance coating uniformity, thereby enhancing the adhesion of the ink.

[0056] Preferably, the hydroxyl content of the hydroxyl-terminated polyester modified acrylate is 5.1% to 6.5%, and can be 5.1%, 5.3%, 5.5%, 5.8%, 6.0%, 6.3%, 6.5%, or any value between them. The purpose of this invention in rationally controlling the hydroxyl content of the hydroxyl-terminated polyester modified acrylate is threefold: First, the hydroxyl groups in the hydroxyl-terminated polyester modified acrylate react with the mercapto groups in the thiol to form thioether bonds (-S-), constructing a three-dimensional cross-linked network, thereby improving the ink's hardness and light transmittance; Second, a suitable hydroxyl content helps improve the compatibility of the ink with the battery ITO layer, thus enhancing adhesion; Third, a suitable hydroxyl content helps improve the ink's light transmittance.

[0057] Furthermore, in existing technologies, the hardness and adhesion of inks are mutually balancing; inks with high hardness tend to have poor adhesion, while inks with good adhesion are often too soft. Therefore, this invention balances the hydroxyl content and molecular weight to obtain an ink that satisfies both the requirements for hardness and adhesion.

[0058] Preferably, the diluent comprises pentaerythritol triacrylate and dipropylene glycol diacrylate, with a mass ratio of pentaerythritol triacrylate to dipropylene glycol diacrylate of (0.5~1.5):(0.8~4). When pentaerythritol triacrylate (trifunctional) and dipropylene glycol diacrylate are compounded, the -O- groups in both the trifunctional acrylate and dipropylene glycol diacrylate are utilized to balance hardness and flexibility, achieving high adhesion while ensuring hardness.

[0059] Preferably, the insulating ink further includes the following components by weight percentage: 1%~5% curing agent, 1%~5% leveling agent, 0.1%~1% UV absorber, and 0.1%~1.5% antioxidant. This invention also adds appropriate proportions of auxiliary components to the insulating ink, which helps to comprehensively improve the various properties of the insulating ink and extend its service life.

[0060] Preferably, the curing agent is at least one selected from imidazole, ethylenediamine, and 4-methylbenzophenone. The curing agent is used to achieve the transformation of the insulating ink from liquid to solid state through chemical cross-linking, and to comprehensively improve mechanical strength, environmental resistance, and electrical insulation performance.

[0061] Preferably, the leveling agent is at least one of polydimethylsiloxane and polymethylalkylsiloxane. These components help improve the leveling properties of the ink.

[0062] Preferably, the ultraviolet absorber is at least one selected from 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, and phenyl salicylate. The above components are used to absorb ultraviolet light and improve the weather resistance of the ink.

[0063] Preferably, the antioxidant is at least one selected from 2,6-tert-butyl-4-methylphenol, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], phosphite, benzotriazole, ethylenediaminetetramethylenephosphonic acid, and oxalohydrazide. The above components are used to prevent oxidation of the ink during use.

[0064] This invention also provides a method for preparing a high-transmittance insulating ink for back contact batteries. The method includes:

[0065] S1. Weigh each component according to its mass percentage;

[0066] S2. Add the matrix resin to the reactor and stir at 300-500 rpm for 10-20 minutes at room temperature;

[0067] S3. Add thiol and thickener in sequence, stirring at 500-800 rpm for 15-25 minutes after each component is added;

[0068] S4. Add the diluent, then increase the stirring speed to 800-1000 rpm and stir for 30-40 minutes.

[0069] S5. Filter the mixture obtained by stirring S4 through a filter screen with a mesh size of 20~200 to obtain a high-transmittance insulating ink for back contact batteries.

[0070] As can be seen from the above process, the preparation method of the high-transmittance insulating ink for back contact batteries in this application is simple and low-cost. The final product can be obtained by rotating and stirring each component and then filtering it, which is suitable for large-scale industrial production.

[0071] Preferably, S3 also includes a curing agent, a leveling agent, a UV absorber, and an antioxidant. Adding appropriate proportions of auxiliary components to the insulating ink helps to comprehensively improve its various properties and extend its service life.

[0072] It should be noted that, without significantly altering the ink's transmittance, hardness, and adhesion properties, other additives can be selectively added according to the actual application scenario. These additives may include, but are not limited to, dispersants, coupling agents, and hydrophobic agents.

[0073] Preferably, the specific preparation method of the matrix resin includes:

[0074] S10. Weigh the following components by mass: 50-70 parts acrylate monomer, 1-2 parts initiator, and 30-50 parts first solvent;

[0075] S20. First, dissolve the hydroxyl-terminated polyester in the first solvent. The amount of hydroxyl-terminated polyester added is 30%-50% of the mass of the acrylate monomer. Then, add the acrylate monomer and at least part of the initiator and stir evenly.

[0076] S30. Under nitrogen protection, heat to the preset temperature and react for 4 to 6 hours. The preset temperature range is 60 to 100℃.

[0077] After S40 and S30 have reacted completely, the mixture is cooled and then precipitated in a second solvent. After filtration, washing, and drying, the matrix resin is obtained.

[0078] Specifically, in S30, the double bond (1630 cm⁻¹) is monitored using a Fourier transform infrared absorption spectrometer (FTIR). -1 The disappearance of the reaction indicates the endpoint.

[0079] Preferably, the ratio between the hydroxyl groups of the terminal hydroxyl polyester and the double bonds of the acrylate monomer affects the grafting rate and crosslinking density. Therefore, the present invention controls the molar ratio of hydroxyl groups to double bonds to be (1:1) to (1:2).

[0080] Preferably, S30 includes directly heating to a preset temperature under nitrogen protection and conducting a constant-temperature reaction for 4 to 6 hours.

[0081] Preferably, when the temperature is directly raised to the preset temperature in S30, all the initiator is directly added in S20.

[0082] More preferably, S30 includes multi-gradient segmented heating to a preset temperature under nitrogen protection, with each segment undergoing a isothermal reaction, and the total reaction time being 4 to 6 hours.

[0083] More preferably, when the temperature in S30 is increased to the preset temperature in a multi-gradient segmented manner, a portion of the initiator is added in S20, and then another portion of the initiator is added equally in each temperature segment of S30. Using gradient heating and staged feeding can reduce the risk of side reactions, avoid local cross-linking, reduce the randomness of chain termination, optimize molecular weight distribution, and precisely control the hydroxyl content.

[0084] Preferably, step S20 further includes the addition of a hydroxyl-containing acrylate monomer, wherein the amount of the hydroxyl-containing acrylate monomer added is 20% to 30% of the mass of the acrylate monomer, and the hydroxyl-containing acrylate monomer is at least one of hydroxyethyl methacrylate and hydroxypropyl acrylate. Introducing a hydroxyl-containing acrylate monomer (HEMA, HPA) to supplement the hydroxyl value helps to precisely control the hydroxyl value.

[0085] Preferably, step S20 further includes the addition of a chain transfer agent, which is dodecyl mercaptan. The chain transfer agent can limit chain growth, ensuring that the molecular weight and viscosity are within a set range.

[0086] Preferably, the acrylate monomer is at least one of methyl acrylate, butyl acrylate, and hydroxyethyl methacrylate.

[0087] Preferably, the initiator is at least one of benzoyl peroxide and azobisisobutyronitrile. Excessive initiator concentration can easily lead to gelation; this invention rationally controls the addition ratio of the initiator to avoid this situation. The reaction temperature in S30 is related to the half-life of the initiator. When benzoyl peroxide (BPO) is used as the initiator, the reaction temperature is controlled at 80~100℃; when azobisisobutyronitrile (AIBN) is used as the initiator, the reaction temperature is controlled at 60~80℃.

[0088] Preferably, the first solvent is at least one of toluene, tetrahydrofuran, and ethyl acetate. More preferably, the first solvent is at least one of toluene and ethyl acetate. Most preferably, the first solvent is toluene. Compared to polar solvents such as DMF, when the first solvent is a non-polar solvent such as toluene or ethyl acetate, it is more conducive to free radical chain growth, reduces the occurrence of side reactions, and at the same time, because homogeneous reactions can reduce phase separation, thereby improving the transmittance of the final product.

[0089] Preferably, the second solvent is at least one of methanol and n-hexane. This invention employs rigorous post-treatment (ultrafiltration, multiple precipitation) to remove small molecule impurities and oligomers (molecular weight cutoff below 100,000), further improving the transmittance of the final product.

[0090] Preferably, the hydroxyl-terminated polyester is prepared by polycondensation reaction of polyol and polyacid; wherein the molar ratio of polyacid to polyol is 1:(1.2~1.4). This invention rationally controls the excess proportion of hydroxyl groups in the hydroxyl polyester, thereby achieving precise control of the hydroxyl value.

[0091] Preferably, the polyol is at least one of ethylene glycol and glycerol.

[0092] Preferably, the polyacid is at least one of adipic acid and phthalic acid.

[0093] Preferably, a catalyst is also added during the polycondensation reaction, and the catalyst is tetrabutyl titanate.

[0094] Preferably, the hydroxyl functionality of the controlled-end hydroxyl polyester of the present invention is 2 to 4, thereby achieving precise control of the hydroxyl value.

[0095] Specifically, the preparation method of hydroxyl-terminated polyester is as follows:

[0096] S100. Add polyol, polyacid, and catalyst to the reactor, and heat to 180~220℃ under nitrogen protection to carry out polycondensation reaction.

[0097] S200, the reaction endpoint is determined by measuring the acid value (titration method) or viscosity change (usually takes 6-8 hours);

[0098] S300, after cooling, yields a hydroxyl-terminated polyester, and the hydroxyl value is confirmed by titration.

[0099] The following are specific examples of the synthesis of the matrix resin of the present invention. They are exemplary and do not constitute any limitation on the present invention.

[0100] The specific testing methods for the matrix resin properties in the synthesis examples are as follows:

[0101] Transmittance: The transmittance of the cured film at a wavelength of 450 nm (film thickness 100 μm) was measured using a UV spectrophotometer.

[0102] Molecular weight: determined by gel permeation chromatography (GPC) using polystyrene as standard and tetrahydrofuran as mobile phase. The output result is the weight-average molecular weight (M). w ) and polymer dispersibility index (PDI);

[0103] Viscosity: Measured at 25℃ using a rotational viscometer, in accordance with GB / T 2794-2013;

[0104] Hydroxyl value: determined by acetylation-titration method according to ASTM D4274.

[0105] Specific synthesis example 1

[0106] Step 1: Synthesis of hydroxyl-terminated polyesters:

[0107] 1.25 mol ethylene glycol (25% excess hydroxyl groups), 1 mol adipic acid, and 0.1 wt% tetrabutyl titanate were added to the reactor, and the mixture was heated to 200°C under nitrogen protection to carry out a polycondensation reaction.

[0108] The reaction was terminated when the acid value was ≤5 mg KOH / g, and the reaction time was 7 hours.

[0109] After cooling, a hydroxyl-terminated polyester was obtained, and the hydroxyl value was confirmed to be 6.0% by titration.

[0110] Step 2: Modified acrylate copolymerization:

[0111] S10. Weigh the following components by mass: 25 parts of hydroxyl-terminated polyester, 55 parts of butyl acrylate (BA), 2 parts of benzoyl peroxide (BPO), 40 parts of toluene, 15 parts of hydroxyethyl methacrylate (HEMA), and 0.5 parts of dodecyl mercaptan.

[0112] S20. Dissolve the hydroxyl-terminated polyester in toluene, add butyl acrylate (BA), hydroxyethyl methacrylate (HEMA), dodecyl mercaptan and all of the benzoyl peroxide (BPO) and stir until homogeneous.

[0113] S30. Under nitrogen protection, the temperature is raised to 85°C and reacted for 5 hours (FTIR monitoring shows the disappearance of double bonds).

[0114] S40, after cooling, precipitates in methanol, is filtered, washed, and vacuum dried (60℃, 24h) to obtain the matrix resin.

[0115] The properties of the obtained matrix resin were tested, and the test results are shown in Table 1.

[0116] Table 1

[0117]

[0118] Specific synthesis example 2

[0119] Step 1: Synthesis of hydroxyl-terminated polyesters:

[0120] 1.3 mol glycerol (30% excess hydroxyl groups), 1 mol adipic acid, and 0.08 wt% tetrabutyl titanate were added to the reactor, and the mixture was heated to 190°C under nitrogen protection to carry out a polycondensation reaction.

[0121] The reaction was terminated when the acid value was ≤4 mg KOH / g, and the reaction time was 8 hours.

[0122] After cooling, a hydroxyl-terminated polyester was obtained, and the hydroxyl value was confirmed to be 6.2% by titration.

[0123] Step 2: Modified acrylate copolymerization:

[0124] S10. Take the following components by mass parts: 20 parts of hydroxyl-terminated polyester, 50 parts of methyl acrylate (MA), 1.5 parts of azobisisobutyronitrile (AIBN), 35 parts of ethyl acetate, and 10 parts of hydroxypropyl acrylate (HPA).

[0125] S20. Dissolve the hydroxyl-terminated polyester in ethyl acetate, add methyl acrylate (MA), hydroxypropyl acrylate (HPA) and half of azobisisobutyronitrile (AIBN) and stir until homogeneous.

[0126] S30. First, heat the mixture to 70°C under nitrogen protection and react for 3 hours. Then, add the remaining half of the azobisisobutyronitrile (AIBN) and heat the mixture to 80°C under nitrogen protection for another 3 hours.

[0127] S40, after cooling, precipitates in n-hexane, is ultrafiltered (molecular weight cutoff below 100,000), washed, and dried to obtain the matrix resin.

[0128] The properties of the obtained matrix resin were tested, and the test results are shown in Table 2.

[0129] Table 2

[0130]

[0131] To better understand the above technical solutions, the following detailed description will be provided in conjunction with specific embodiments. These embodiments are merely preferred implementations of the present invention and are not intended to limit the scope of the invention.

[0132] Table 3

[0133]

[0134] The insulating inks used in Examples 1-10 and Comparative Examples 1-2 were prepared according to the formulations listed in Table 3. The manufacturers and models of some of the component reagents used in the examples and comparative examples of this application are as follows. It should be noted that the following content does not constitute a limitation on the scope of protection of this application, but is merely illustrative:

[0135] Matrix resin (self-prepared, see specific synthesis example 1 and specific synthesis example 2);

[0136] Thiol (ethylenedithiol, manufactured by Shanghai Yuanye Biotechnology Co., Ltd., model number S48113);

[0137] Tackifier (terpene resin, manufactured by Hubei Jusheng Technology Co., Ltd., model JS3658);

[0138] Diluents (1,4-Butanediol diacrylate, manufactured by Shanghai Yuanye Biotechnology Co., Ltd., model S70072), (Pentaerythritol triacrylate, manufactured by Shanghai Yuanye Biotechnology Co., Ltd., model S64762), (Dipropylene glycol diacrylate, manufactured by Shanghai Yuanye Biotechnology Co., Ltd., model Y39402);

[0139] Curing agent (4-methylbenzophenone, manufactured by Shanghai Yuanye Biotechnology Co., Ltd., model S42202);

[0140] Leveling agent (polydimethylsiloxane, manufactured by Shanghai Yuanye Biotechnology Co., Ltd., model S56577);

[0141] Ultraviolet absorber (2-hydroxy-4-methoxybenzophenone, manufactured by Shanghai Yuanye Biotechnology Co., Ltd., model S30840);

[0142] Antioxidant (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], manufactured by Shanghai Yuanye Biotechnology Co., Ltd., model S67391).

[0143] Example 1

[0144] A method for preparing a high-transmittance insulating ink for back-contact batteries, the method comprising:

[0145] S1. Weigh each component according to Table 3;

[0146] S2. Add the matrix resin to the reactor and stir at 400 rpm for 15 minutes at room temperature.

[0147] S3. Add thiol, thickener, curing agent, leveling agent, UV absorber and antioxidant in sequence. Stir at 700 rpm for 20 minutes after each component is added.

[0148] S4. Add the diluent, then increase the stirring speed to 900 rpm and stir for 35 minutes.

[0149] S5. Filter the mixture obtained by stirring S4 through a filter screen with a mesh size of 150 to obtain a high-transmittance insulating ink for back contact batteries.

[0150] The matrix resin is the hydroxyl-terminated polyester modified acrylate prepared in Specific Synthesis Example 2; the thiol is ethylene dithiol; the tackifier is a terpene resin; the diluent includes pentaerythritol triacrylate and dipropylene glycol diacrylate, with a mass ratio of pentaerythritol triacrylate to dipropylene glycol diacrylate of 1:2; the curing agent is 4-methylbenzophenone; the leveling agent is polydimethylsiloxane; the ultraviolet absorber is 2-hydroxy-4-methoxybenzophenone; and the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid].

[0151] Examples 2-7

[0152] Both methods provide a method for preparing a high-transmittance insulating ink for back contact batteries. For the specific preparation method, please refer to Example 1. The difference lies in the different component ratios.

[0153] Example 8

[0154] A method for preparing a high-transmittance insulating ink for back contact batteries is provided. For the specific preparation method, please refer to Example 1. The difference is that in Example 8, the base resin is the hydroxyl-terminated polyester modified acrylate prepared in the specific synthesis example 1.

[0155] Example 9

[0156] A method for preparing a high-transmittance insulating ink for back contact batteries is provided. The specific preparation method is described in Example 1, except that the diluent in Example 9 is 1,4-butanediol diacrylate.

[0157] Example 10

[0158] A method for preparing a high-transmittance insulating ink for back contact batteries is provided. The specific preparation method is described in Example 1. The difference is that in Example 10, only thiol and tackifier were added in S3. This example does not add curing agent, leveling agent, UV absorber and antioxidant.

[0159] Comparative Example 1

[0160] An insulating ink preparation method is provided. For the specific preparation method, please refer to Example 1. The difference is that thiols are not added to the components of Comparative Example 1.

[0161] Comparative Example 2

[0162] An insulating ink preparation method is provided. For the specific preparation method, please refer to Example 1. The difference is that the base resin in Comparative Example 2 is a common unmodified acrylate resin commonly used in the prior art.

[0163] Test case

[0164] To verify the performance of the product of the present invention, relevant performance tests were conducted on the insulating inks prepared in Examples 1-10 and Comparative Examples 1-2, respectively. The specific methods are as follows, and the specific test results are shown in Table 4:

[0165] Pencil hardness: Refer to the test method of GB / T 6739-2006 "Determination of Hardness of Paint Film by Pencil Method".

[0166] Adhesion: Refer to the test method of GB / T 9286-2021 "Paints and Varnishes Cross-cut Test".

[0167] Transmittance test: Refer to the test method of GB / T 2410-2008 "Determination of transmittance and haze of transparent plastics".

[0168] Bifacial ratio: The specific calculation formula is bifacial ratio = conversion efficiency of the back side of the battery / conversion efficiency of the front side of the battery * 100%.

[0169] Table 4

[0170]

[0171] As can be seen from Example 1 and Comparative Examples 1-2, when the synergistic effect of hydroxyl and mercapto groups is lost in the components, the insulating ink can no longer effectively form a three-dimensional cross-linked network with high density and high uniformity, which seriously affects the hardness, adhesion, and light transmittance of the ink, and thus affects the bifaciality of the battery.

[0172] As can be seen from Examples 1 and 2-10, using the preferred components and proportions of the present invention helps to further improve the hardness, adhesion, and light transmittance of the ink, thereby improving the bifaciality of the battery.

[0173] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A high-transmittance insulating ink for back-contact batteries, characterized in that, The insulating ink comprises the following components by weight percentage: 60%~64% base resin, 1%~2% thiol, 2%~4% tackifier, and 25%~30% diluent; The matrix resin is a hydroxyl-terminated polyester modified acrylate, the thiol is ethylene dithiol, the tackifier is at least one of terpene resin, C5 petroleum resin, and C9 petroleum resin, and the diluent is at least one of 1,4-butanediol diacrylate, pentaerythritol triacrylate, and dipropylene glycol diacrylate.

2. The high-transmittance insulating ink for back contact batteries according to claim 1, characterized in that, The hydroxyl-terminated polyester modified acrylate has a light transmittance >90%, a molecular weight of 150,000 to 200,000, a viscosity of 10,000 to 50,000 cps, and a hydroxyl content of 5.1% to 6.5%.

3. The high-transmittance insulating ink for back contact batteries according to claim 1, characterized in that, The diluent includes pentaerythritol triacrylate and dipropylene glycol diacrylate, with a mass ratio of pentaerythritol triacrylate to dipropylene glycol diacrylate of (0.5~1.5):(0.8~4).

4. The high-transmittance insulating ink for back contact batteries according to claim 1, characterized in that, The insulating ink also includes the following components by weight percentage: 1%~5% curing agent, 1%~5% leveling agent, 0.1%~1% UV absorber, and 0.1%~1.5% antioxidant.

5. The high-transmittance insulating ink for back contact batteries according to claim 4, characterized in that, The curing agent is at least one of imidazole, ethylenediamine, and 4-methylbenzophenone; And / or, The leveling agent is at least one of polydimethylsiloxane and polymethylalkylsiloxane; And / or, The ultraviolet absorber is at least one of 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, and phenyl salicylate. And / or, The antioxidant is at least one of 2,6-tert-butyl-4-methylphenol, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], phosphite, benzotriazole, ethylenediaminetetramethylenephosphonic acid, and oxalic acid dihydrazide.

6. A method for preparing a high-transmittance insulating ink for back-contact batteries, characterized in that, The preparation method is used to prepare a high-transmittance insulating ink for back contact batteries as described in any one of claims 1 to 5, and the preparation method includes: S1. Weigh each component according to its mass percentage; S2. Add the matrix resin to the reactor and stir at 300-500 rpm for 10-20 minutes at room temperature; S3. Add the thiol and the thickener in sequence, stirring at 500-800 rpm for 15-25 minutes after each component is added; S4. Add the diluent, then increase the stirring speed to 800-1000 rpm and stir for 30-40 minutes; S5. The mixture obtained by stirring S4 is filtered through a filter screen with a pore size of 20-200 mesh to obtain the high-transmittance insulating ink for back contact batteries.

7. The preparation method according to claim 6, characterized in that, S3 also includes the addition of curing agents, leveling agents, UV absorbers, and antioxidants.

8. The preparation method according to claim 6, characterized in that, The specific preparation method of the matrix resin includes: S10. Weigh the following components by mass: 50-70 parts acrylate monomer, 1-2 parts initiator, and 30-50 parts first solvent; S20. First, dissolve the hydroxyl-terminated polyester in the first solvent. The amount of the hydroxyl-terminated polyester added is 30%-50% of the mass of the acrylate monomer. Then, add the acrylate monomer and at least part of the initiator and stir until uniform. S30. Under nitrogen protection, heat to the preset temperature and react for 4 to 6 hours. The preset temperature range is 60 to 100℃. After S40 and S30 have reacted completely, the mixture is cooled and then precipitated in a second solvent. After filtration, washing, and drying, the matrix resin is obtained.

9. The preparation method according to claim 8, characterized in that, S30 involves directly heating to a preset temperature under nitrogen protection and then conducting a constant-temperature reaction for 4-6 hours. or, S30 involves multi-gradient, segmented heating to a preset temperature under nitrogen protection, with each segment undergoing a isothermal reaction, and the total reaction time is 4-6 hours.

10. The preparation method according to claim 9, characterized in that, When the temperature in S30 is directly raised to the preset temperature, all the initiator is directly added in S20; or, When the temperature in S30 is raised to the preset temperature in a multi-gradient segmented manner, a portion of the initiator is added to S20, and another portion of the initiator is added equally to each temperature segment in S30.

11. The preparation method according to claim 8, characterized in that, S20 also includes the addition of a hydroxyl-containing acrylate monomer, wherein the amount of the hydroxyl-containing acrylate monomer added is 20% to 30% of the mass of the acrylate monomer, and the hydroxyl-containing acrylate monomer is at least one of hydroxyethyl methacrylate and hydroxypropyl acrylate. And / or, S20 also includes the addition of a chain transfer agent, which is dodecyl mercaptan.

12. The preparation method according to claim 8, characterized in that, The acrylate monomer is at least one of methyl acrylate, butyl acrylate, and hydroxyethyl methacrylate; And / or, The initiator is at least one of benzoyl peroxide and azobisisobutyronitrile; And / or, The first solvent is at least one of toluene, tetrahydrofuran, and ethyl acetate; And / or, The second solvent is at least one of methanol and n-hexane.

13. The preparation method according to claim 8, characterized in that, The hydroxyl-terminated polyester is prepared by polycondensation reaction of polyol and polyacid; The molar ratio of polyacids to polyols is 1:(1.2~1.4).

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