Novel light conversion EVA (Ethylene Vinyl Acetate) adhesive film and preparation method thereof

Abstract

According to the novel light conversion EVA adhesive film and the preparation method thereof provided by the invention, the light conversion adhesive film prepared by using the method can solve the problems that a light conversion agent in a traditional light conversion film is easy to separate out, the service life of the adhesive film is short and the processing difficulty is high, and meanwhile, key indexes of light transmittance and vulcanization performance are not influenced. The preparation process comprises the following steps: a) under the action of an initiator, grafting EVA resin with an olefin derivative containing an ultraviolet absorption group to obtain modified EVA resin; and b) mixing and curing the modified EVA resin, an initiator, an assistant crosslinker, an antioxidant, an anti-ultraviolet aid and the like, and carrying out casting extrusion to obtain the light conversion adhesive film. Test results show that the vulcanization performance, the mechanical performance and the optical performance of the light conversion adhesive film all meet industrial standards, groups with the light conversion function are connected into the resin in a chemical bonding mode, and the light conversion adhesive film is free of migration, easy to process and long in service life.

Description

Technical Field

[0001] The present invention relates to the technical field of EVA photovoltaic encapsulant films, in particular to the technical field of EVA light conversion encapsulant films, and belongs to the category of photovoltaic encapsulation materials. Background Art

[0002] In recent years, the world's photovoltaic industry has developed rapidly, especially in China, which has ranked first in the world in terms of production since 2008. However, at present, the photoelectric conversion efficiency of industrially produced solar cells has stagnated between 24% and 25%, and it is difficult to continue to improve. How to improve the photoelectric conversion efficiency of photovoltaic cells has become one of the focuses of the world's photovoltaic industry. According to theoretical calculations, the power generation efficiency of solar cells can reach 26.8% - 30%. These losses partly come from the natural limitations of photoelectric conversion. Among the natural limitations, in addition to factors such as p-n junction dark current loss and temperature (the efficiency of the cell decreases linearly with temperature), the most prominent are two interrelated factors: ① is the inherent spectrum of the sun; ② is the inherent bandgap width of the semiconductor material. These two factors jointly determine that for light waves with wavelengths less than the minimum absorption limit, the part of the photon energy greater than the bandgap width is generally released through thermal vibration, that is, heat is generated rather than photoelectric conversion, and light waves with wavelengths greater than the maximum absorption limit are completely ineffective for photovoltaic power generation. Although ultraviolet light with wavelengths in the range of 300 - 400 nm in the current cell can be partially absorbed and converted, the efficiency is not ideal.

[0003] EVA (ethylene-vinyl acetate copolymer) is a thermoplastic polymer material. It has low cost, is easy to mold, has outstanding optical properties, and relatively good mechanical and electrical properties, so it is used as a packaging material for solar cells. The usage situation in the past nearly 30 years shows that the EVA packaging material can basically work stably for 20 years. Since it can not only absorb ultraviolet light but also convert it into visible light, the light-converting EVA encapsulation film has become a research hotspot. However, the existing light-converting agents cannot completely absorb ultraviolet light below 400 nm and the emitted spectrum is not strong enough to significantly improve the conversion efficiency of silicon-based solar cells. At the same time, the current light-converting agents on the market mainly include inorganic metal oxide fluorescent powders, organic dye fluorescent powders, and rare earth complexes. Among them, the inorganic metal oxide fluorescent powders have poor compatibility with the EVA film, are easy to damage the transparency, have weak ultraviolet absorption, and the overall light-converting efficiency is not high; the rare earth coordination compounds have weak ultraviolet absorption, a narrow range of fluorescence emission wavelengths, and the emitted light is difficult to be completely converted by the cell, and the overall light-converting efficiency is also not high. Moreover, in order to improve the compatibility, it must be treated with an organic polymer coating, which is costly; while the organic dye fluorescent powders have good compatibility with the EVA film, the film has excellent transparency, strong ultraviolet absorption, and greatly improves the overall light-converting efficiency. However, they are not resistant to yellowing under ultraviolet light irradiation, which restricts the application of the light-converting EVA film. Therefore, the preparation of a new type of EVA film with good transparency, high power gain for photovoltaic power generation, and resistance to UV yellowing has become one of the research focuses in the photovoltaic industry. Summary of the Invention

[0004] The present invention provides a new type of light-converting EVA film and its preparation method. The light-converting film prepared by this method can solve the problems of easy precipitation of the light-converting agent, short film life, and difficult processing in traditional light-converting films, and at the same time does not affect the key indicators of light transmittance and vulcanization performance.

[0005] Its preparation process includes: a) Under the action of an initiator, the EVA resin is grafted with an olefin derivative containing an ultraviolet absorption group to obtain a modified EVA resin; b) After mixing and curing the modified EVA resin with an initiator, a co-crosslinking agent, an antioxidant, an anti-ultraviolet auxiliary agent, etc., it is cast and extruded to obtain a light-converting EVA film.

[0006] Further, the preparation of the light-converting EVA film includes the following steps: pre-mixing the raw materials, standing and then entering a casting machine, and passing through the processes of extrusion, casting into a film, cooling, slitting, and winding to prepare a light-converting film for photovoltaic modules.

[0007] The test results show that the vulcanization performance, mechanical properties, and optical properties of this light-converting film meet the industry standards. The groups with light-converting functions are incorporated into the resin by chemical bonding, do not migrate, are easy to process, and have a long lifespan.

[0008] A novel light conversion EVA film, wherein the EVA resin is characterized in that it is a random or block polymer obtained by polymerizing ethylene and vinyl acetate, with a molecular weight Mw between 30,000 and 250,000, a PDI of 1.5 - 3, and an MFR measured under the conditions of 190 °C and a load of 2.16 kg being 1 - 50 g / 10 min, preferably 10 - 30 g / 10 min, and a density of 0.85 - 0.95 g / cm 3 ; the vinyl acetate content is 10 - 45 wt%, preferably 20 - 35%; the volume resistivity is 10 13 -10 16 Ω·cm.

[0009] Furthermore, the olefin derivatives containing ultraviolet absorption groups include the following structures:

[0010]

[0011] It should be noted that for those of ordinary skill in the art, without departing from the method of the present invention, making appropriate derivatives of the above structures should also be regarded as the protection scope of the present invention.

[0012] Furthermore, the addition amounts of the respective substances in the grafting reaction are as follows in parts by mass: 100 parts of EVA resin; 1 - 5 parts of olefin derivatives containing ultraviolet absorption groups; 0.1 - 1 part of initiator.

[0013] Furthermore, the crosslinking agent in the light conversion EVA film is a peroxide crosslinking agent, including but not limited to one or more of the following: 1,1 - bis(tert - butylperoxy)-3,3,5 - trimethylcyclohexane, tert - butyl peroxy - 2 - ethylhexyl carbonate, 1,1 - bis(tert - amylperoxy)-3,3,5 - trimethylcyclohexane, 2,5 - dimethyl - 2,5 - (bis - tert - butylperoxy)hexane, 1,1 - bis(tert - amylperoxy)cyclohexane, 1,1 - bis(tert - butylperoxy)cyclohexane, 1,1 - bis(tert - amylperoxy)-3,3,5 - trimethylcyclohexane, 2,2 - bis(tert - butylperoxy)butane, tert - amyl peroxy - 2 - ethylhexyl carbonate, tert - amyl peroxy carbonate, tert - butyl peroxy - 3,3,5 - trimethylhexanoate, tert - butyl peroxy - 2 - ethylhexyl carbonate, tert - butyl peroxy - isopropyl carbonate. The amount of the crosslinking agent is 0.1 - 5 parts by weight. Preferably 0.5 - 2 parts by weight.

[0014] Furthermore, the co-crosslinking agent is one or more of polyfunctional acrylate substances, including but not limited to one or several of the following: trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, tris(2-hydroxyethyl)isocyanurate triacrylate, ethoxylated trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, ethoxylated glycerol triacrylate, propoxylated glycerol triacrylate, pentaerythritol tetraacrylate, ethoxylated pentaerythritol tetraacrylate, trimethylolpropane tetraacrylate, ditrimethylolpropane tetraacrylate, ditrimethylolpropane tetramethacrylate, propoxylated pentaerythritol tetraacrylate, tricyclodecane dimethanol diacrylate, propoxylated neopentyl glycol diacrylate, ethoxylated bisphenol A diacrylate, ethoxylated bisphenol A dimethacrylate, 2-butyl-2-ethyl-1,3-propanediol diacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate. Based on 100 parts by weight of the matrix resin, the dosage of the co-crosslinking agent is 0.1-5 parts by weight, preferably 0.1-2 parts by weight.

[0015] Furthermore, the coupling agent is a silane coupling agent, including but not limited to one or several of the following: γ-chloropropylmethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, γ-glycidoxypropyltrimethoxysilane, 3-(trimethoxysilyl)propyl-2-methyl-2-acrylate, anilinomethyltriethoxysilane, octyltrimethoxysilane. The dosage of the coupling agent is 0.1-3 parts by weight, preferably 0.1-0.6 parts by weight.

[0016] Further, the antioxidant is one or several of hindered phenol antioxidants or phosphate antioxidants, including but not limited to one or several of the following: n-octadecyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, pentaerythritol tetrakis [3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], bis(3,5-di-tert-butyl-4-hydroxypropionyl) hydrazine, 2,2'-oxamido-bis [ethyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)] propionate, N,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxyhydrocinnamide), 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, triethylene glycol bis [3-(3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 4,6-bis(octylthiomethyl) o-cresol, tris(2,4-di-tert-butylphenyl) phosphite, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite, bis(2,6-di-tert-butyl-4-methylphenyl) pentaerythritol diphosphite. Based on 100 parts by weight of the matrix resin, the dosage of the antioxidant is 0.01-1 part by weight, preferably 0.05-0.5 part by weight.

[0017] Compared with the complex preparation process of traditional light conversion film, the light conversion film of the present invention can be successfully prepared by fine-tuning on the basis of the process of ordinary film, and the light conversion agent is introduced into the resin by chemical bonding, without precipitation, and the film has a long service life; the vulcanization performance, mechanical performance and optical performance of the film all meet the industry standards. Detailed implementation mode

[0018] The present invention will be further described below through specific examples. The examples described in the present invention are only for the purpose of illustrating the present invention and do not limit the scope of the present invention.

[0019] The following examples are used to illustrate the present invention, but do not limit the scope of the present invention. In this application, "parts" and "%" are by weight, unless otherwise specified.

[0020] Preparation Example 1

[0021] A preparation method of a novel light conversion EVA film is carried out according to the following steps: mixing EVA resin, olefin derivative A containing ultraviolet absorption groups and an initiator in a mixer for 120 min until uniform; feeding into a twin-screw extruder for grafting reaction and then pelletizing to obtain grafted EVA-1.

[0022] Shearing the compatibilizer, coupling agent, ultraviolet absorber, crosslinking agent and anti-PID additive with a high-speed disperser for 30 min to reduce the viscosity of the mixed additives to 1-300 mPa·s; adding the mixed additives into the grafted EVA-1 and mixing at high speed for 6-12 h until the additives are completely absorbed.

[0023] The mixed ingredients are added into a casting machine through a feeding system, extruded by casting at 80 - 120°C, the film is drawn into an embossing roller for pressing to form patterns, then cut and wound after cooling and shaping, and finally packaged into finished products as required.

[0024] Preparation Example 2

[0025] A preparation method of a novel light conversion EVA film is carried out according to the following steps: EVA resin, olefin derivative B containing ultraviolet absorption groups, and an initiator are mixed in a mixer for 120 min until homogeneous; then put into a twin-screw extruder for grafting reaction and granulated to obtain grafted EVA-2.

[0026] The compatibilizer, coupling agent, ultraviolet absorber, crosslinking agent, and anti-PID auxiliary agent are sheared by a high-speed disperser for 30 min to reduce the viscosity of the mixed auxiliary agents to 1 - 300 mPa·s; the mixed auxiliary agents are added to the grafted EVA-2 and mixed at high speed for 6 - 12 h until the auxiliary agents are completely absorbed.

[0027] The mixed ingredients are added into a casting machine through a feeding system, extruded by casting at 80 - 120°C, the film is drawn into an embossing roller for pressing to form patterns, then cut and wound after cooling and shaping, and finally packaged into finished products as required.

[0028] Preparation Example 3

[0029] A preparation method of a novel light conversion EVA film is carried out according to the following steps: EVA resin, olefin derivative C containing ultraviolet absorption groups, and an initiator are mixed in a mixer for 120 min until homogeneous; then put into a twin-screw extruder for grafting reaction and granulated to obtain grafted EVA-3.

[0030] The compatibilizer, coupling agent, ultraviolet absorber, crosslinking agent, and anti-PID auxiliary agent are sheared by a high-speed disperser for 30 min to reduce the viscosity of the mixed auxiliary agents to 1 - 300 mPa·s; the mixed auxiliary agents are added to the grafted EVA-3 and mixed at high speed for 6 - 12 h until the auxiliary agents are completely absorbed.

[0031] The mixed ingredients are added into a casting machine through a feeding system, extruded by casting at 80 - 120°C, the film is drawn into an embossing roller for pressing to form patterns, then cut and wound after cooling and shaping, and finally packaged into finished products as required.

[0032] Preparation Example 4

[0033] A preparation method of a novel light conversion EVA film is carried out according to the following steps: EVA resin, olefin derivative D containing ultraviolet absorption groups, and an initiator are mixed in a mixer for 120 min until homogeneous; then put into a twin-screw extruder for grafting reaction and granulated to obtain grafted EVA-4.

[0034] Shear the compatibilizer, coupling agent, ultraviolet absorber, crosslinking agent, and anti-PID aid with a high-speed disperser for 30 min to reduce the viscosity of the mixed aid to 1 - 300 mPa·s; add the well-mixed aid to the grafted EVA-4 and mix at high speed for 6 - 12 h until the aid is completely absorbed.

[0035] Add the well-mixed ingredients into the casting machine through the feeding system, extrude by casting at 80 - 120 °C, the film is drawn into the embossing roller for pressing to form patterns, cut and wound after cooling and shaping, and packaged into finished products as required.

[0036] Test results:

[0037]

[0038] It can be found from the characterization data and application data that the processing parameters of the EVA light conversion film prepared by this technology are consistent with those of the conventional film, without obvious modification to the production line, which well solves the problem of the relatively complex current production process of the light conversion film; the mechanical property indexes such as the peel strength and tensile strength of the film are excellent and stable, solving the problem of the decline in mechanical properties caused by adding functional aids in traditional light conversion films; the absorption in the ultraviolet region in each example is significantly reduced, indicating that the film can effectively convert ultraviolet light, thus protecting the components.

Claims

1. A preparation method of a novel light conversion EVA film, characterized in that: It includes the following steps: a) Using EVA resin and an olefin derivative containing an ultraviolet absorption group as raw materials, an EVA graft resin is obtained under the action of an initiator; b) After mixing and curing the EVA graft resin with an initiator, a co-crosslinking agent, an antioxidant, an anti-ultraviolet auxiliary agent, etc., a light conversion film is obtained by casting and extrusion.

2. The preparation method of the novel light conversion EVA film according to claim 1, characterized in that: The EVA resin therein is a random or block polymer obtained by polymerizing ethylene and vinyl acetate, with a molecular weight Mw between 30,000 and 250,000, a PDI of 1.5 - 3, an MFR measured under the conditions of 190 °C and a load of 2.16 kg being 1 - 50 g / 10 min, and a density of 0.85 - 0.95 g / cm 3 , and the vinyl acetate content is 10 - 45 wt%.

3. The preparation method of the novel light conversion EVA film according to claim 1, characterized in that: The olefin derivative containing an ultraviolet absorption group therein includes the following structures:

4. The preparation method of the novel light conversion EVA film according to claim 1, characterized in that: The addition amounts of each substance in step a) are respectively in parts by mass: 100 parts of EVA resin; 1-5 parts of an olefin derivative containing an ultraviolet absorption group; 0.1-1 part of an initiator.

5. The preparation method of the novel light conversion EVA film according to claim 1, characterized in that: b) The antioxidant in step b) is one or more of an ultraviolet absorber and an anti-thermal aging decomposing agent, preferably including one or more of antioxidant 1010, antioxidant 770 and antioxidant 4720; The silane coupling agent is an organosilicon compound containing two different chemically active groups in the molecule, preferably including one or more of vinyltriacetoxysilane and γ-methacryloxypropyltrimethoxysilane; The organic peroxide crosslinking agent includes one or more of dicumyl peroxide, tert-butyl peroxy-2-ethylhexyl carbonate and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane; The co-crosslinking agent includes one or more of triallyl isocyanurate, triallyl cyanurate, trimethylolpropane triacrylate and trimethylolpropane trimethacrylate.

6. The preparation method of the novel light conversion EVA film according to claim 1, characterized in that: b) The addition amounts of each component in step b) are as follows:

7. According to the preparation method of the novel light conversion EVA film according to claim 1, characterized in that: It includes the following steps: Pre-mix the raw materials, let them stand still and then enter the casting machine, and through the processes of extrusion, film casting, cooling and slitting, and winding, a light conversion film for photovoltaic modules is prepared. Compared with the complex preparation process of traditional light conversion films, the light conversion film of the present invention can be successfully prepared by making fine adjustments to the process of ordinary films, and the light conversion agent is introduced into the resin by chemical bonding, without precipitation, and the film has a long service life; the vulcanization performance, mechanical properties and optical properties of the film all meet the industry standards.

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