A hyperbranched high molecular weight poly(propylene carbonate) for photovoltaic module encapsulation and its preparation method

Abstract

The present invention discloses a hyperbranched high molecular weight poly(propylene carbonate) for photovoltaic module encapsulation and its preparation method. The poly(propylene carbonate) is prepared by chain extension of a carbon dioxide-based polycarbonate diol containing long branched chains with triisocyanate and a small molecule diol. The poly(propylene carbonate) has the advantages of good mechanical properties, high light transmittance, excellent water and oxygen barrier properties, anti-yellowing, resistance to ultraviolet aging, hydrolysis resistance, and high bonding strength. At the same time, the hyperbranched structure can reduce the fluidity of the PPC-T film at high temperatures, ensuring the integrity of the photovoltaic module at high temperatures. When the poly(propylene carbonate) replaces the EVA film for photovoltaic module encapsulation, no additional heat cross-linking is required, which can simplify the production steps of photovoltaic cells and effectively improve production efficiency. In addition, the PPC-T film can avoid the generation of acidic molecules, reduce the damage to photovoltaic cell modules, and thus extend the service life.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer material synthesis, and more specifically, relates to a hyperbranched high molecular weight poly(propylene carbonate) for photovoltaic module encapsulation and a preparation method thereof. Background Art

[0002] At present, the global demand for the installed capacity of photovoltaic cells continues to grow. In order to prevent the direct exposure of silicon wafers to air, which may cause the attenuation of photovoltaic performance and extend the service life of the cells, EVA films are usually used to seal the silicon wafers, and the upper protective glass and the lower protective material, polyvinyl fluoride composite film (TPT), are bonded together to encapsulate the solar cell module. EVA is a type of ethylene-vinyl acetate copolymer, which has the advantages of low price, good encapsulation performance, and resistance to ultraviolet aging. However, EVA films need to be heat-crosslinked to achieve the above effects, which makes the production process of solar cells relatively complex. In addition, EVA cannot achieve 100% insulation. During long-term use, moisture in the atmosphere will gradually penetrate into the module through the silicone and the backsheet, accelerating the decomposition of EVA and generating freely moving acetic acid. These acidic molecules react with the alkali precipitated on the glass surface to produce sodium ions, which will cause a sharp drop in the power of the cell module and greatly shorten the service life of the solar cell. Moreover, the EVA-glass encapsulation system is relatively bulky, resulting in increased transportation costs and poor flexibility in installation and use. Therefore, the thin-filmization of the battery and the encapsulation material will become a new development trend, and lighter solar cells will gradually replace those using EVA as the encapsulation material. Summary of the Invention

[0003] The object of the present invention is to overcome the defects that traditional EVA films need heat-crosslinking and generate acidic molecules, which cause inevitable damage to photovoltaic modules, and to provide a novel carbon dioxide-based polycarbonate diol (PCDL) with long branched chains, whose properties can be regulated by the polymerization unit number of the alkyl glycidyl ether monomer with long branched chains, and to provide a hyperbranched high molecular weight poly(propylene carbonate) (PPC-T) using this PCDL as a raw material for photovoltaic module encapsulation.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A carbon dioxide-based polycarbonate diol (PCDL), whose structural characteristics are shown in formula (1), where (a + b) / (c + d) > 9; (a + c) / (b + d) = 0 - 10; n = 6 - 14; a, b, c, d, and n are all integers.

[0006]

[0007] The preparation method of the above carbon dioxide-based polycarbonate diol includes the following steps:

[0008] Add alkyl glycidyl ether, propylene oxide, chain transfer agent, tetrahydrofuran and catalyst into a high-pressure reactor, charge carbon dioxide, heat for copolymerization. After the reaction is completed, pour the product into deionized water, stir for purification, and finally separate the liquid and dry to obtain carbon dioxide-based polycarbonate diol.

[0009] Preferably, in the above preparation method, the branched-chain length of the alkyl glycidyl ether is C8-C16; the chain transfer agent is 1,4-butanediol (BDO), 1,6-hexanediol (HDO) or 1,3-propanediol (PDO).

[0010] Preferably, in the above preparation method, the catalyst is a two-component catalyst composed of borane and organic amine; the borane is triethylborane (TEB), triphenylborane (TPB) or tributylborane (TBB); the organic amine is triethylamine (TEA), N,N-diisopropylethylamine (DIPEA) or N,N-dimethylcyclohexylamine (DMCHA).

[0011] Preferably, in the above preparation method, the molar feed ratio of propylene oxide to catalyst is 200-800:1; the molar feed ratio of propylene oxide to chain transfer agent is 20-80:1; the internal pressure range in the reaction kettle after carbon dioxide is introduced is 0.5-2.0 MPa, the reaction temperature is 40-70 °C, and the reaction time is 8-16 h.

[0012] A hyperbranched high molecular weight polycarbonate propylene carbonate for photovoltaic module encapsulation is formed by one-step polymerization with the above carbon dioxide-based polycarbonate diol as the soft segment and the hard segment composed of triisocyanate and small molecule diol chain extender; the preparation method specifically includes the following steps:

[0013] Add carbon dioxide-based polycarbonate diol and small molecule diol into a dried three-necked round-bottom flask, evacuate and dehydrate at 110-120 °C for 2-3 h, then cool to 60-70 °C under the protection of a nitrogen atmosphere. Subsequently, add triisocyanate and catalyst, inject into a mold after mechanical stirring, close the mold, place it on a flat vulcanizing machine for molding, remove the mold, and open the mold after cooling to obtain a colorless transparent and elastic hyperbranched high molecular weight polycarbonate propylene carbonate film for photovoltaic module encapsulation.

[0014] Preferably, in the above preparation method, the triisocyanate is triphenylmethane triisocyanate (TTI) or L-lysine triisocyanate (LTI); the small molecule diol chain extender is 1,4-butanediol (BDO), 1,6-hexanediol (HDO) or 1,3-propanediol (PDO); the catalyst is tin octoate, dibutyltin dilaurate or stannous octoate; the molar ratio of the -OH group in the small molecule diol to the -NCO group in the triisocyanate is 1:1.0-1.1; the dosage of the catalyst is 0.001%-0.01% of the total mass of the small molecule diol and the triisocyanate.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) The carbon dioxide-based PCDL of the present invention is obtained by one-pot one-step polymerization of alkyl glycidyl ether, propylene oxide, carbon dioxide and a chain transfer agent under a non-metallic catalyst. The preparation method is simple and safe, and can avoid the residue of metal catalysts in the product. The obtained carbon dioxide-based PCDL is an amorphous structure and has a high density. The hyperbranched high molecular weight poly(propylene carbonate) (PPC-T) film obtained by chain extension with triisocyanate and small molecule alcohol as raw materials has high transparency and excellent water and oxygen barrier properties. Applying it to the encapsulation adhesive film of photovoltaic modules can extend the service life of solar cells.

[0017] (2) The carbon dioxide-based PCDL of the present invention has a large number of polar groups inside, such as carbonate groups (-COO-) and urethane groups (-NHCOO-). In addition to providing good UV resistance, hydrolysis resistance and antioxidant properties for the PPC-T film, the carbonate groups can also form strong intramolecular hydrogen bonds between polar groups, so it has good tensile strength and tear strength.

[0018] (3) An alkyl side chain is introduced into the carbon dioxide-based PCDL of the present invention. The glass transition temperature and chain segment flexibility of PCDL can be regulated by the side chain length and polymerization unit number of the alkyl glycidyl ether monomer. By changing the number of polymer units containing side chains, the flexibility of the PPC-T film can be regulated, so as to play a buffering role to better ensure the integrity of photovoltaic modules. The hyperbranched structure extended by triisocyanate can reduce the fluidity of PPC-T and prevent the photovoltaic cell from being damaged at high temperatures.

[0019] (4) The hyperbranched high molecular weight polypropylene carbonate (PPC-T) of the present invention has the advantages of high light transmittance, yellowing resistance, UV aging resistance, hydrolysis resistance, high barrier properties and high bonding strength. It can be used to replace the traditional EVA film for the encapsulation of photovoltaic cells, which can avoid the cumbersome steps of heating and cross-linking during encapsulation and improve production efficiency; at the same time, it can avoid the generation of acidic molecules to increase the life of photovoltaic cells, and provide a new practical film material for the field of photovoltaic module encapsulation to realize lightweight solar cells.

[0020] In summary, the PPC-T of the present invention has the characteristics of EVA film, can meet the use requirements in photovoltaic module packaging, and can be applied to solar cell packaging to not only save the heating cross-linking step, making the production of solar cells more convenient and quick, but also avoid the generation of acidic molecules to extend the life of photovoltaic cells. More importantly, the introduction of alkyl side chains can adjust the flexibility of the PPC-T film and buffer the stress changes of the photovoltaic module due to environmental changes. Secondly, the hyperbranched structure can prevent the film from flowing away at high temperatures, thereby better ensuring the integrity of the photovoltaic module.

[0021] The present invention can be further explained and illustrated in conjunction with the following specific examples, but the specific examples do not limit the present invention in any form. DETAILED DESCRIPTION

[0022] Embodiment 1:

[0023] In anhydrous and oxygen-free environment, 200 g C8-C10 alkyl glycidyl ether, 12 g propylene oxide, 38 μL triethylamine, 1.9 mL 1,4-butanediol, 33 mL tetrahydrofuran, and 1.0 mL triethyl boron solution were added to a 500 mL high-pressure reactor in sequence, filled with 1 MPa carbon dioxide, and reacted in a 55 ° C oil bath for 8 h. After the reaction, the reactor was cooled to room temperature with cold water and the carbon dioxide pressure was released. The reaction was quenched with a dilute hydrochloric acid solution, and then poured into deionized water and stirred to remove the residual catalyst. The polymer solution was separated and vacuum dried to obtain PCDL 1, which was subjected to molecular weight test, nuclear magnetic resonance analysis, hydroxyl value titration and thermal performance analysis. The specific data are listed in Table 1.

[0024] Embodiment 2:

[0025] In an anhydrous and anaerobic environment, 200 g of C8-10 alkyl glycidyl ether, 48 g of propylene oxide, 38 μL of triethylamine, 1.2 mL of 1,4-butanediol, 33 mL of tetrahydrofuran, and 1.5 mL of tributylboron were successively added to a 500 mL high-pressure reactor. 1 MPa of carbon dioxide was charged, and the reaction was carried out in an oil bath at 55 °C for 8 h. After the reaction, the reactor was cooled to room temperature with cold water and the carbon dioxide pressure was released. The reaction was quenched with a dilute hydrochloric acid solution, and then poured into deionized water and stirred to remove the residual catalyst. The polymer solution was obtained by liquid separation, and PCDL 2 was obtained after vacuum drying to remove the solvent. Its molecular weight test, NMR analysis, hydroxyl value titration, and thermal property analysis were carried out, and the specific data are listed in Table 1.

[0026] Example 3:

[0027] In an anhydrous and anaerobic environment, 100 g of C10-12 alkyl glycidyl ether, 96 g of propylene oxide, 23 μL of N,N-diisopropylethylamine, 610 μL of 1,4-butanediol, 33 mL of tetrahydrofuran, and 13.3 mg of triphenylboron were successively added to a 500 mL high-pressure reactor. 1 MPa of carbon dioxide was charged, and the reaction was carried out in an oil bath at 55 °C for 8 h. After the reaction, the reactor was cooled to room temperature with cold water and the carbon dioxide pressure was released. The reaction was quenched with a dilute hydrochloric acid solution, and then poured into deionized water and stirred to remove the residual catalyst. The polymer solution was obtained by liquid separation, and PCDL 3 was obtained after vacuum drying to remove the solvent. Its molecular weight test, NMR analysis, hydroxyl value titration, and thermal property analysis were carried out, and the specific data are listed in Table 1.

[0028] Example 4:

[0029] In an anhydrous and anaerobic environment, 100 g of C12-14 alkyl glycidyl ether, 96 g of propylene oxide, 21 μL of N,N-dimethylcyclohexylamine, 243 μL of 1,4-butanediol, 33 mL of tetrahydrofuran, and 412 μL of tributylboron solution were successively added to a 500 mL high-pressure reactor. 1 MPa of carbon dioxide was charged, and the reaction was carried out in an oil bath at 55 °C for 8 h. After the reaction, the reactor was cooled to room temperature with cold water and the carbon dioxide pressure was released. The reaction was quenched with a dilute hydrochloric acid solution, and then poured into deionized water and stirred to remove the residual catalyst. The polymer solution was obtained by liquid separation, and PCDL 4 was obtained after vacuum drying to remove the solvent. Its molecular weight test, NMR analysis, hydroxyl value titration, and thermal property analysis were carried out, and the specific data are listed in Table 1.

[0030] Table 1. Molecular weight, composition, and glass transition temperature of polycarbonate diol.

[0031]

[0032] In Table 1, PPC% is the molar percentage of polycarbonate units obtained by copolymerization of propylene oxide and carbon dioxide, i.e., the proportion of a in the following structural formula; PDGE% is the molar percentage of polycarbonate units obtained by polymerization of alkyl glycidyl ether and carbon dioxide, i.e., the proportion of b in the following structural formula; PPO% is the molar percentage of polyether units obtained by homopolymerization of epoxy monomers, i.e., the proportion of c + d.

[0033]

[0034] The binary-component catalytic system composed of borane and organic amine can effectively catalyze the polymerization of epoxy monomers and carbon dioxide in the presence of a chain transfer agent to generate polycarbonate diol with long branched chains. Among them, it can be seen from the data in Table 1 that the molecular weight of PCDL can be regulated by changing the molar ratio of epoxy monomers and chain transfer agents; the glass transition temperature of PCDL decreases with the increase of the branched chain length and the number of polymerization units of alkyl glycidyl ether, because long branched chains can increase the flexibility of the chain. In addition, the glass transition temperature of PCDL also increases with the increase of molecular weight.

[0035] Example 5:

[0036] Add 30 g of the polycarbonate diol PCDL 1 and 2.0 g of BDO to a 250 mL three-necked round-bottom flask, evacuate and dehydrate at 115 °C for 3 h. After completion, cool the reaction substrate to 70 °C under the protection of a nitrogen atmosphere, slowly add 10.86 g of TTI and 10 mg of stannous octoate catalyst, mechanically stir for 5 min, then pour into a mold, close the mold, place it on a flat vulcanizing machine at 160 °C for 30 min, remove the mold, and after cooling, open the mold to obtain colorless transparent and elastic PPC-T 1, with a hard segment content of 30%, a molecular weight of 45.3 kDa, and a PDI of 1.67.

[0037] Example 6:

[0038] Add 30 g of the polycarbonate diol PCDL 1 and 0.52 g of BDO to a 250 mL three-necked round-bottom flask, evacuate and dehydrate at 115 °C for 3 h. After completion, cool the reaction substrate to 70 °C under the protection of a nitrogen atmosphere, slowly add 7.0 g of TTI and 10 mg of stannous octoate catalyst, mechanically stir for 5 min, then pour into a mold, close the mold, place it on a flat vulcanizing machine at 160 °C for 30 min, remove the mold, and after cooling, open the mold to obtain colorless transparent and elastic PPC-T 2, with a hard segment content of 20%, a molecular weight of 42.9 kDa, and a PDI of 1.69.

[0039] Example 7:

[0040] 30 g of the polycarbonate diol PCDL 2 and 2.2 g of BDO were added to a 250 mL three-necked round-bottom flask and vacuum dehydrated at 115 °C for 3 h. After completion, the reaction substrate was cooled to 70 °C under a nitrogen atmosphere, 10.66 g of LTI and 10 mg of stannous octoate catalyst were slowly added. After mechanical stirring for 5 min, it was poured into a mold. The mold was closed and placed on a flat vulcanizing machine at 160 °C for molding for 30 min, then the mold was removed. After cooling, the mold was opened to obtain colorless transparent and elastic PPC-T 3, with a hard segment content of 30%, a molecular weight of 48.2 kDa, and a PDI of 1.72.

[0041] Example 8:

[0042] 30 g of the polycarbonate diol PCDL 3 and 2.2 g of BDO were added to a 250 mL three-necked round-bottom flask and vacuum dehydrated at 115 °C for 3 h. After completion, the reaction substrate was cooled to 70 °C under a nitrogen atmosphere, 10.66 g of LTI and 10 mg of stannous octoate catalyst were slowly added. After mechanical stirring for 5 min, it was poured into a mold. The mold was closed and placed on a flat vulcanizing machine at 160 °C for molding for 30 min, then the mold was removed. After cooling, the mold was opened to obtain colorless transparent and elastic PPC-T 4, with a hard segment content of 30%, a molecular weight of 49.2 kDa, and a PDI of 1.77.

[0043] Example 9:

[0044] 30 g of the polycarbonate diol PCDL 4 and 2.95 g of BDO were added to a 250 mL three-necked round-bottom flask and vacuum dehydrated at 115 °C for 3 h. After completion, the reaction substrate was cooled to 70 °C under a nitrogen atmosphere, 9.91 g of LTI and 10 mg of stannous octoate catalyst were slowly added. After mechanical stirring for 5 min, it was poured into a mold. The mold was closed and placed on a flat vulcanizing machine at 160 °C for molding for 30 min, then the mold was removed. After cooling, the mold was opened to obtain colorless transparent and elastic polycarbonate-based PPC-T 5, with a hard segment content of 30%, a molecular weight of 46.9 kDa, and a PDI of 1.65.

[0045] Example 10:

[0046] The obtained PPC-T 1-5 were respectively tested for light transmittance according to GB / T 2410-2008, mechanical properties according to GB / T1040.1-2006, peel strength according to GB / T 2790-1995, resistance to ultraviolet aging according to IEC612152-2:2016, and barrier properties according to ASTM D3985-05. The obtained data are listed in Table 2.

[0047] Comparative Example 1:

[0048] The commercial EVA films were subjected to all the tests in Example 10 and compared with PPC-T of the present invention. The obtained data are listed in Table 2.

[0049] Table 2. Comparison of the related properties of PPC-T and commercial EVA films

[0050]

[0051] A series of hyperbranched poly(propylene carbonate) PPC-T was prepared by using the carbon dioxide-based PCDL prepared in the present invention as the soft segment and different triisocyanates as the chain extender. Since the carbon dioxide-based PCDL is an amorphous structure with a high density, the PPC-T films all exhibit high transparency and excellent light transmittance, which are superior to commercial EVA films. The mechanical properties of PPC-T can be regulated by the molecular weight of PCDL, the length and number of polymerization units of alkyl glycidyl ether in PCDL, the content and type of hard segments in the present invention. From the data in Table 2, it can be seen that the more the number of polymerization units of alkyl glycidyl ether in PCDL and the longer the side chain, the higher the elongation at break of the obtained PPC-T, showing high elasticity. Since there are a large number of carbonate groups in the carbon dioxide-based PCDL of the present invention, the PPC-T film exhibits excellent UV resistance, and almost no yellowing occurs under standard test conditions, while the EVA film turns yellow under these test conditions. In addition, the barrier property of the PPC-T film decreases slightly with the increase in the number of polymerization units of alkyl glycidyl ether, but is superior to commercial EVA films.

[0052] Therefore, the PPC-T prepared in the present invention exhibits excellent mechanical properties, UV aging resistance, high peel strength, high light transmittance and high barrier property, and can replace traditional EVA films in photovoltaic modules to improve the production efficiency of photovoltaic modules and overcome the generation of acidic molecules to extend the service life of photovoltaic cells. The hyperbranched structure can reduce the fluidity of the film at high temperatures. By regulating the molecular weight of the carbon dioxide-based PCDL and the number of polymerization units of alkyl glycidyl ether, the related properties of PPC-T can be regulated to meet the actual use requirements. In addition, the polycarbonate diol prepared in the present invention has controllable chain segment flexibility, glass transition temperature and molecular weight, which can be adjusted according to the actual needs of use, and has considerable application prospects.

Claims

1. A hyperbranched high molecular weight poly(propylene carbonate) for photovoltaic module encapsulation, characterized in that it is formed by one-step polymerization with a carbon dioxide-based polycarbonate diol as the soft segment and a hard segment composed of a triisocyanate and a small molecule diol chain extender; The structural characteristics of the carbon dioxide-based polycarbonate diol are shown in formula (1), where (a + b) / (c + d) > 9; (a + c) / (b + d) = 0 - 10; n = 6 - 14; a, b, c, d, and n are all integers, 2. The hyperbranched high molecular weight poly(propylene carbonate) for photovoltaic module encapsulation according to claim 1, wherein The preparation method of the carbon dioxide-based polycarbonate diol includes the following steps: Add an alkyl glycidyl ether, propylene oxide, a chain transfer agent, tetrahydrofuran, and a catalyst into a high-pressure reaction kettle, fill it with carbon dioxide, heat it for copolymerization, pour the product into deionized water after the reaction is completed, stir and purify it, and finally separate the liquid and dry it to obtain the carbon dioxide-based polycarbonate diol.

3. The hyperbranched high molecular weight poly(propylene carbonate) for photovoltaic module encapsulation according to claim 2, wherein, The branched chain length of the alkyl glycidyl ether is C8 - C16; the chain transfer agent is 1,4-butanediol, 1,6-hexanediol, or 1,3-propanediol.

4. The hyperbranched high molecular weight poly(propylene carbonate) for photovoltaic module encapsulation according to claim 2, wherein The catalyst is a two-component catalyst composed of borane and an organic amine; the borane is triethyl borane, triphenyl borane, or tributyl borane; the organic amine is triethylamine, N,N-diisopropylethylamine, or N,N-dimethylcyclohexylamine.

5. The hyperbranched high molecular weight poly(propylene carbonate) for photovoltaic module encapsulation according to claim 2, characterized in that, The molar feed ratio of propylene oxide to the catalyst is 200 - 800:1; the molar feed ratio of propylene oxide to the chain transfer agent is 20 - 80:1; the internal pressure range in the reaction kettle after carbon dioxide is introduced is 0.5 - 2.0 MPa, the reaction temperature is 40 - 70 °C, and the reaction time is 8 - 16 h.

6. The preparation method of the hyperbranched high molecular weight poly(propylene carbonate) for photovoltaic module encapsulation according to claim 1, characterized in that Including the following steps: Add the carbon dioxide-based polycarbonate diol and the small molecule diol into a dried three-necked round-bottom flask, vacuum dehydrate at 110 - 120 °C for 2 - 3 h, then cool to 60 - 70 °C under the protection of a nitrogen atmosphere, subsequently add the triisocyanate and the catalyst, inject it into a mold after mechanical stirring, close the mold, place it on a flat vulcanizer for molding, remove the mold, and open the mold after cooling to obtain a colorless transparent and elastic hyperbranched high molecular weight poly(propylene carbonate) film for photovoltaic module encapsulation.

7. The preparation method according to claim 6, wherein The triisocyanate is triphenylmethane triisocyanate or L-lysine triisocyanate; the small molecule diol chain extender is 1,4-butanediol, 1,6-hexanediol, or 1,3-propanediol; the catalyst is stannous octoate, dibutyltin dilaurate, or stannous octoate; the molar ratio of the -OH group in the small molecule diol to the -NCO group in the triisocyanate is 1:1.0 - 1.1; the dosage of the catalyst is 0.001% - 0.01% of the total mass of the small molecule diol and the triisocyanate.

Images