Preparation method of high cross-linking degree POE encapsulation adhesive film and photovoltaic module

Abstract

The application relates to the field of photovoltaic packaging adhesive films, and discloses a preparation method of a high-crosslinking-degree POE packaging adhesive film and a photovoltaic module. The preparation method comprises the following steps: mixing an ethylene-alpha olefin copolymer and an initiator, and reacting at a temperature higher than an initiation temperature of the initiator to obtain a modified polyolefin resin; the initiator is at least one of dicumyl peroxide, methyl ethyl ketone peroxide and di-tert-butyl peroxide; raw materials including the modified polyolefin resin, a crosslinking agent and a crosslinking aid are taken; the crosslinking agent is at least one of tert-amyl peroxy(2-ethylhexyl) carbonate, dicyclohexyl peroxydicarbonate and azobis isobutyronitrile; and all the raw materials are blended and extruded at a temperature higher than an initiation temperature of the crosslinking agent and not higher than 110 DEG C to be shaped. By using the preparation method, the POE packaging adhesive film has high crosslinking degree and crosslinking speed, good PID resistance and long-term stability, and is also endowed with high light transmittance and low haze.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic encapsulation films, and more particularly to a method for preparing a high-crosslinking POE encapsulation film and a photovoltaic module. Background Technology

[0002] In the photovoltaic industry, encapsulating film is one of the key materials to ensure the long-term stable operation of solar cell modules. It not only needs to protect the cells from external environmental damage, such as humidity, oxygen and extreme weather conditions, but also needs to ensure electrical insulation and mechanical strength between cells, while maximizing the transmittance of sunlight to improve the overall photoelectric conversion efficiency.

[0003] Polyolefin elastomers (POEs) have become one of the mainstream materials in photovoltaic encapsulation films due to their excellent weather resistance, high light transmittance, and good adhesion properties. However, with the continuous advancement of photovoltaic technology and increasingly stringent market demands, the performance of traditional POE films has gradually revealed limitations, particularly in terms of lower crosslinking degree than ethylene-vinyl acetate copolymer (EVA) and slower crosslinking speed.

[0004] In recent years, in order to improve the crosslinking speed and degree of crosslinking of POE encapsulation films, the industry has developed some new technical solutions. These solutions, without changing the crosslinking agent and co-crosslinking agent, introduce modified resins containing active groups to enable the film to crosslink more quickly during the lamination process, thereby reducing lamination time and improving module production efficiency (such as patent CN110713798A). However, this method has the problem of poor compatibility between highly active group resins and α-olefin copolymers, which limits the further improvement of crosslinking speed and is not conducive to improving the degree of crosslinking. Summary of the Invention

[0005] To address the aforementioned technical problems, namely the limited effectiveness of existing methods for improving the crosslinking degree and speed of POE encapsulation films, this invention provides a method for preparing a high-crosslinking degree POE encapsulation film and a photovoltaic module. Using the preparation method of this invention, the resulting POE encapsulation film exhibits high crosslinking degree and speed, imparting excellent resistance to potential-induced degradation (PID) and long-term stability, while also achieving high light transmittance and low haze.

[0006] The specific technical solution of this invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a highly crosslinked POE encapsulating film, comprising the following steps:

[0008] S1: Mix ethylene-α-olefin copolymer and initiator, and react at a temperature higher than that of the initiator to obtain modified polyolefin resin; the initiator is at least one of dicumyl peroxide, methyl ethyl ketone peroxide and di-tert-butyl peroxide;

[0009] S2: Take raw materials including modified polyolefin resin, crosslinking agent and co-crosslinking agent; the crosslinking agent is at least one of (2-ethylhexyl) tert-amyl peroxide, dicyclohexyl peroxide, and azobisisobutyronitrile;

[0010] S3: After blending and extruding all the raw materials in step S2 at a temperature higher than the crosslinking agent initiation temperature but not higher than 110°C, the mixture is molded to obtain a highly crosslinked POE encapsulation film.

[0011] Before blending and extruding the ethylene-α-olefin copolymer with a crosslinking agent and a co-crosslinking agent, this invention first reacts the ethylene-α-olefin copolymer under the action of an initiator to form a modified polyolefin resin with a long-chain branched structure. This improves the entanglement and overlap between molecular chains, thus facilitating further crosslinking under the action of the crosslinking agent. The resulting POE encapsulation film has a high degree of crosslinking, achieving better anti-PID performance and long-term stability, and also provides a wider processing window, increasing its crosslinking speed during lamination. Furthermore, modifying the ethylene-α-olefin copolymer with an initiator can disrupt the original crystallinity of the ethylene-α-olefin copolymer, thereby giving the POE encapsulation film higher light transmittance and lower haze.

[0012] In the ethylene-α-olefin copolymer modification stage and the subsequent blending extrusion molding stage, this invention employs specific initiators and crosslinking agents, respectively, achieving the following effects: In the ethylene-α-olefin copolymer modification stage (step S1), the initiator used is at least one of dicumyl peroxide, methyl ethyl ketone peroxide, and di-tert-butyl peroxide. These initiators require relatively high temperatures to rapidly initiate the reaction and have long half-lives, enabling the obtained modified polyolefin resin to have a mildly crosslinked and branched structure. While ensuring a high degree of crosslinking in the POE encapsulation film, this also facilitates thorough mixing at lower temperatures during the subsequent blending extrusion process in step S3, allowing the crosslinking agent and crosslinking aid to interact effectively. The crosslinking agent and other additives contained in the raw materials can better exert their functions. In the subsequent blending extrusion molding stage (step S3), the crosslinking agent used is at least one of (2-ethylhexyl) tert-amyl peroxide, dicyclohexyl peroxide, and azobisisobutyronitrile. These crosslinking agents can initiate the reaction at a lower temperature and have a shorter half-life. Combined with the lower blending extrusion temperature in step S3 (not higher than 110°C), it can not only initiate further crosslinking reactions during the blending extrusion process in step S3, but also avoid the self-polymerization or vaporization and escape of additives due to excessively high extrusion temperature, as well as the resin gelling and curing, which hinders the extrusion process and affects the product appearance. Through the above effects, the POE encapsulation film can achieve high crosslinking degree and crosslinking speed while possessing better anti-PID performance and long-term stability.

[0013] Preferably, step S1 includes the following process: mixing an initiator, an ethylene-α-olefin copolymer and a solvent, and reacting at 120~200°C for 0.5~2 hours to obtain a modified polyolefin resin.

[0014] Furthermore, during the reaction, the stirring speed is 200~500 rpm.

[0015] Furthermore, the solvent includes at least one selected from n-hexane, cyclohexane, n-heptane, n-octane, n-decane, benzene, toluene, xylene, ethylbenzene, and chlorobenzene.

[0016] Preferably, step S1 includes the following process: mixing and extruding the initiator and ethylene-α-olefin copolymer at 150~200°C to obtain the modified polyolefin resin.

[0017] Furthermore, the mixing and extrusion process is carried out using a twin-screw extruder with a screw speed of 20-80 rpm.

[0018] Preferably, in step S1, the mass ratio of the ethylene-α-olefin copolymer to the initiator is 100:0.1~0.3.

[0019] In step S1, the modification of the ethylene-α-olefin copolymer under the action of the initiator can be achieved by reacting in a solvent or by mixing and extruding as described above. During the modification process, as the amount of initiator increases and the reaction temperature rises, the entanglement and overlap between the molecular chains of the modified polyolefin resin can be improved, thereby increasing the degree of crosslinking and the crosslinking speed of the final POE encapsulation film. However, when the amount of initiator is too large or the reaction temperature is too high, the modified polyolefin resin will form a crosslinked network structure with an excessively high degree of crosslinking, which is not conducive to achieving sufficient mixing at a lower temperature during the subsequent blending and extrusion process in step S3. Based on this, the present invention controls the mass ratio of ethylene-α-olefin copolymer to initiator at 100:0.1~0.3, and controls the temperature at 120~200℃ when using a solvent system for reaction, and at 150~200℃ when using a mixing and extrusion method for reaction. This allows the POE encapsulation film to better balance the performance in terms of degree of crosslinking, crosslinking speed, light transmittance, haze, anti-PID performance, and long-term stability.

[0020] Preferably, in step S2, the raw material comprises the following components in parts by weight: 90-100 parts of modified polyolefin resin, 0.6-0.8 parts of crosslinking agent, and 0.5-0.7 parts of co-crosslinking agent.

[0021] Further, in step S2, the raw materials also include the following components in parts by weight: 1-10 parts of functional masterbatch, 0.1-0.4 parts of additives; the additives include silane coupling agents; the functional masterbatch includes POE silane graft masterbatch and / or POE blend light stabilizer masterbatch.

[0022] Further, step S3 includes the following process: after shearing and dispersing the modified polyolefin resin, crosslinking agent, co-crosslinking agent and additives, it is mixed with functional masterbatch, co-extruded at a temperature higher than the crosslinking agent initiation temperature but not higher than 110°C, and then molded to obtain a highly crosslinked POE encapsulation film.

[0023] Preferably, in step S1, the ethylene-α-olefin copolymer includes at least one of ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-hexene copolymer, ethylene-octene copolymer, ethylene-butadiene copolymer, ethylene-isoprene copolymer, ethylene-isobutene copolymer, and ethylene-norbornene copolymer.

[0024] Preferably, in step S3, the temperature of the co-extrusion is 70~110℃.

[0025] Preferably, in step S3, the forming method is casting or calendering.

[0026] Secondly, the present invention provides a photovoltaic module, including a highly cross-linked POE encapsulating film prepared by the aforementioned preparation method.

[0027] Preferably, the photovoltaic module includes glass, a first encapsulating film, a cell array, a second encapsulating film, and glass stacked in sequence; the first encapsulating film and / or the second encapsulating film is the highly cross-linked POE encapsulating film.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] (1) In this invention, an initiator is first used to modify the ethylene-α-olefin copolymer to form a modified polyolefin resin with a long-chain branched structure. This can promote further cross-linking between polyolefin molecular chains under the action of a cross-linking agent when it is blended, extruded and molded with other raw materials. This results in the POE encapsulation film having the characteristics of high cross-linking degree, wide processing window, fast cross-linking speed, good anti-PID performance and long-term stability. It can also give it high light transmittance and low haze.

[0030] (2) In the ethylene-α olefin copolymer modification stage and the subsequent blending extrusion molding stage, the present invention uses specific initiators and crosslinking agents, which enable the POE encapsulation film to achieve high crosslinking degree and crosslinking speed while having better anti-PID performance and long-term stability.

[0031] (3) By controlling the ratio between the ethylene-α olefin copolymer and the initiator, as well as the reaction temperature during the modification process of the ethylene-α olefin copolymer, the present invention can make the POE encapsulation film better take into account the crosslinking degree, crosslinking speed, light transmittance, haze, anti-PID performance and long-term stability. Attached Figure Description

[0032] Figure 1 This is a cole-cole diagram of the modified polyolefin resin and the ethylene-butene copolymer. Detailed Implementation

[0033] The present invention will be further described below with reference to embodiments.

[0034] A method for preparing a highly crosslinked POE encapsulating film includes the following steps:

[0035] S1: Mix ethylene-α-olefin copolymer and initiator, and react at a temperature higher than that of the initiator to obtain modified polyolefin resin; the initiator is at least one of dicumyl peroxide, methyl ethyl ketone peroxide and di-tert-butyl peroxide;

[0036] S2: Take raw materials including modified polyolefin resin, crosslinking agent and co-crosslinking agent; the crosslinking agent is at least one of (2-ethylhexyl) tert-amyl peroxide, dicyclohexyl peroxide, and azobisisobutyronitrile;

[0037] S3: After blending and extruding all the raw materials in step S2 at a temperature higher than the crosslinking agent initiation temperature but not higher than 110°C, the mixture is molded to obtain a highly crosslinked POE encapsulation film.

[0038] In one specific embodiment, in step S1, the ethylene-α-olefin copolymer includes at least one of ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-hexene copolymer, ethylene-octene copolymer, ethylene-butadiene copolymer, ethylene-isoprene copolymer, ethylene-isobutene copolymer, and ethylene-norbornene copolymer.

[0039] In one specific embodiment, step S1 includes the following process: mixing an initiator, an ethylene-α-olefin copolymer, and a solvent, and reacting them at 120-200°C and 200-500 rpm for 0.5-2 hours to obtain a modified polyolefin resin; the solvent includes at least one selected from n-hexane, cyclohexane, n-heptane, n-octane, n-decane, benzene, toluene, xylene, ethylbenzene, and chlorobenzene.

[0040] As another specific embodiment, step S1 includes the following process: adding the initiator and ethylene-α-olefin copolymer into a twin-screw extruder, mixing and extruding at 150~200°C and screw speed of 20~80 rpm to obtain modified polyolefin resin.

[0041] In one specific embodiment, in step S1, the mass ratio of the ethylene-α-olefin copolymer to the initiator is 100:0.1~0.3.

[0042] In one specific embodiment, in step S2, the raw materials include the following components in parts by weight: 90-100 parts of modified polyolefin resin, 0.6-0.8 parts of crosslinking agent, and 0.5-0.7 parts of co-crosslinking agent.

[0043] In one specific embodiment, in step S2, the raw materials further include the following components in parts by weight: 1-10 parts of functional masterbatch and 0.1-0.4 parts of additives; the additives include silane coupling agents; the functional masterbatch includes POE silane graft masterbatch and / or POE blend light stabilizer masterbatch; step S3 includes the following process: after shearing and dispersing the modified polyolefin resin, crosslinking agent, co-crosslinking agent and additives, they are mixed with the functional masterbatch, co-extruded at a temperature higher than the crosslinking agent initiation temperature but not higher than 110°C, and then molded to obtain a highly crosslinked POE encapsulating film.

[0044] In one specific implementation, in step S3, the temperature of the co-extrusion is 70~110℃.

[0045] In one specific implementation, in step S3, the molding method is either casting molding or calendering molding.

[0046] A photovoltaic module includes a highly cross-linked POE encapsulating film prepared by the aforementioned method.

[0047] In one specific embodiment, the photovoltaic module includes glass, a first encapsulating film, a cell array, a second encapsulating film, and glass stacked sequentially; the first encapsulating film and / or the second encapsulating film is the highly cross-linked POE encapsulating film.

[0048] The present invention will now be described through specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Variations and advantages that can be conceived by those skilled in the art without departing from the spirit and scope of the inventive concept are included in the present invention, and the scope of protection of the present invention is defined by the appended claims and any equivalents thereof.

[0049] Example 1

[0050] The POE encapsulation film of this embodiment is prepared according to the following steps:

[0051] (1) Preparation of modified polyolefin resin:

[0052] Weigh out 0.1 parts by weight of dicumyl peroxide (half-life of 10h at 117℃), 50 parts of ethylene-butene copolymer, 50 parts of ethylene-octene copolymer and 1000 parts of xylene, add them to a 500L closed reactor, stir and react at 150℃ and 300rpm for 1h, then evaporate and remove xylene under 60Pa pressure to obtain modified polyolefin resin.

[0053] (2) Material preparation:

[0054] Weigh out 95 parts of modified polyolefin resin, 5 parts of POE silane graft masterbatch, 0.6 parts of tert-amyl peroxide (2-ethylhexyl) carbonate (half-life of 1 h at 116 °C), 0.5 parts of triallyl cyanurate and 0.3 parts of trimethylallyloxysilane according to the weight.

[0055] (3) Preparation of premix:

[0056] Modified polyolefin resin, tert-amyl peroxide (2-ethylhexyl) carbonate, triallyl cyanurate, and trimethylallyloxysilane were added to a high-speed disperser and sheared and dispersed for 20 minutes to obtain a premix.

[0057] (4) Preparation of compound materials:

[0058] The premix and POE silane graft masterbatch were mixed at 300 rpm for 45 min to obtain the compound.

[0059] (5) Extrusion molding:

[0060] The compound material is injected into a single-screw extruder through a feeding system, co-extruded at 90°C, cast into a film, and then drawn into an embossing roller to press and form a pattern. After cooling and shaping, it is slit and wound to obtain the POE encapsulation film of this embodiment with a thickness of 0.5 mm.

[0061] Using the POE encapsulating film prepared in this embodiment, a photovoltaic module with the following structure is assembled: it is composed of glass, a first encapsulating film, a cell array, a second encapsulating film, and glass stacked in sequence. Both the first encapsulating film and the second encapsulating film are POE encapsulating films prepared in this embodiment.

[0062] Example 2

[0063] The POE encapsulation film of this embodiment is prepared according to the following steps:

[0064] (1) Preparation of modified polyolefin resin:

[0065] Weigh 0.1 parts by weight of dicumyl peroxide (with a half-life of 10 h at 117 °C) and 100 parts by weight of ethylene-butene copolymer, add them to a twin-screw extruder, set the screw speed to 50 rpm and the temperature to 165 °C, and perform co-extrusion to obtain modified polyolefin resin.

[0066] (2) Material preparation:

[0067] Weigh out 90 parts by weight of modified polyolefin resin, 10 parts by weight of POE silane graft masterbatch, 0.8 parts by weight of tert-amyl peroxide (2-ethylhexyl) carbonate (half-life of 1 h at 116 °C), 0.7 parts by weight of triallyl cyanurate and 0.1 parts by weight of trimethylallyloxysilane.

[0068] (3) Preparation of premix:

[0069] Modified polyolefin resin, tert-amyl peroxide (2-ethylhexyl) carbonate, triallyl cyanurate, and trimethylallyloxysilane were added to a high-speed disperser and sheared and dispersed for 30 minutes to obtain a premix.

[0070] (4) Preparation of compound materials:

[0071] The premix and POE silane graft masterbatch were mixed at 400 rpm for 50 min to obtain the compound.

[0072] (5) Extrusion molding:

[0073] The compound material is injected into a single-screw extruder through a feeding system, co-extruded at 95°C, cast into a film, then drawn into an embossing roller, pressed to form a pattern, cooled and shaped, then slit and wound to obtain the POE encapsulation film of this embodiment with a thickness of 0.4 mm.

[0074] Using the POE encapsulating film prepared in this embodiment, a photovoltaic module with the following structure is assembled: it is composed of glass, a first encapsulating film, a cell array, a second encapsulating film, and glass stacked in sequence. Both the first encapsulating film and the second encapsulating film are POE encapsulating films prepared in this embodiment.

[0075] Example 3

[0076] The POE encapsulation film of this embodiment is prepared according to the following steps:

[0077] (1) Preparation of modified polyolefin resin:

[0078] Weigh out 0.1 parts by weight of methyl ethyl ketone peroxide (half-life of 10h at 105℃), 50 parts of ethylene-propylene copolymer, 50 parts of ethylene-butadiene copolymer and 500 parts of n-octane, add them to a 500L closed reactor, stir and react at 120℃ and 500rpm for 2h, then evaporate and remove n-octane under 60Pa pressure to obtain modified polyolefin resin.

[0079] (2) Material preparation:

[0080] Weigh out 98 parts by weight of modified polyolefin resin, 2 parts by weight of POE blend light stabilizer masterbatch, 0.7 parts by weight of benzoyl peroxide (half-life of 5 min at 120 °C), 0.6 parts by weight of ethylene glycol dimethacrylate and 0.4 parts by weight of vinyltrimethoxysilane.

[0081] (3) Preparation of premix:

[0082] Modified polyolefin resin, benzoyl peroxide, ethylene glycol dimethacrylate and vinyltrimethoxysilane were added to a high-speed disperser and sheared and dispersed for 40 min to obtain a premix.

[0083] (4) Preparation of compound materials:

[0084] The premix and POE blended light stabilizer masterbatch were mixed at 500 rpm for 45 minutes to obtain the compound.

[0085] (5) Extrusion molding:

[0086] The compound material is injected into a single-screw extruder through a feeding system, co-extruded at 80°C, cast into a film, then drawn into an embossing roller, pressed to form a pattern, cooled and shaped, then slit and wound to obtain the POE encapsulation film of this embodiment with a thickness of 0.6 mm.

[0087] Using the POE encapsulating film prepared in this embodiment, a photovoltaic module with the following structure is assembled: it is composed of glass, a first encapsulating film, a cell array, a second encapsulating film, and glass stacked in sequence. Both the first encapsulating film and the second encapsulating film are POE encapsulating films prepared in this embodiment.

[0088] Example 4

[0089] The POE encapsulation film of this embodiment is prepared according to the following steps:

[0090] (1) Preparation of modified polyolefin resin:

[0091] Weigh 0.1 parts by weight of methyl ethyl ketone peroxide (with a half-life of 10 h at 105 °C) and 100 parts by weight of ethylene-butene copolymer, add them to a twin-screw extruder, set the screw speed to 50 rpm and the temperature to 160 °C, and perform co-extrusion to obtain modified polyolefin resin.

[0092] (2) Material preparation:

[0093] Weigh out 97 parts by weight of modified polyolefin resin, 1 part of POE silane graft masterbatch, 2 parts of POE blend light stabilizer masterbatch, 0.6 parts of dicyclohexyl peroxide (half-life of 1 min at 110℃), 0.6 parts of diethylene glycol dimethacrylate and 0.1 parts of vinyltrimethoxysilane.

[0094] (3) Preparation of premix:

[0095] Modified polyolefin resin, dicyclohexyl peroxide, diethylene glycol dimethacrylate, and vinyltrimethoxysilane were added to a high-speed disperser and sheared and dispersed for 30 minutes to obtain a premix.

[0096] (4) Preparation of compound materials:

[0097] The premix and POE silane graft masterbatch were mixed at 400 rpm for 50 min to obtain the compound.

[0098] (5) Extrusion molding:

[0099] The compound material is injected into a single-screw extruder through a feeding system, co-extruded at 88°C, cast into a film, then drawn into an embossing roller, pressed to form a pattern, cooled and shaped, then slit and wound to obtain the POE encapsulation film of this embodiment with a thickness of 0.4 mm.

[0100] Using the POE encapsulating film prepared in this embodiment, a photovoltaic module with the following structure is assembled: it is composed of glass, a first encapsulating film, a cell array, a second encapsulating film, and glass stacked in sequence. Both the first encapsulating film and the second encapsulating film are POE encapsulating films prepared in this embodiment.

[0101] Example 5

[0102] The POE encapsulation film of this embodiment is prepared according to the following steps:

[0103] (1) Preparation of modified polyolefin resin:

[0104] Weigh out 0.1 parts by weight of methyl ethyl ketone peroxide (half-life of 10h at 105℃), 50 parts of ethylene-hexene copolymer, 50 parts of ethylene-norbornene copolymer, and 600 parts of n-decane, and add them to a 500L closed reactor. Stir the reactor at 200℃ and 200rpm for 1h. Then evaporate the n-decane under 60Pa pressure to obtain the modified polyolefin resin.

[0105] (2) Material preparation:

[0106] Weigh out 100 parts by weight of modified polyolefin resin, 0.6 parts by weight of azobisisobutyronitrile (with a half-life of 10 min at 100 °C), 0.5 parts by weight of triallyl isocyanurate and 0.2 parts by weight of γ-methacryloyloxypropyltrimethoxysilane.

[0107] (3) Preparation of mixture:

[0108] Modified polyolefin resin, azobisisobutyronitrile, triallyl isocyanurate and γ-methacryloyloxypropyltrimethoxysilane were added to a high-speed disperser and sheared and dispersed for 1 hour to obtain a mixture.

[0109] (4) Extrusion molding:

[0110] The mixture is injected into a single-screw extruder through a feeding system, co-extruded at 100°C, cast into a film, then drawn into an embossing roller, pressed to form a pattern, cooled and shaped, then slit and wound to obtain the POE encapsulation film of this embodiment with a thickness of 0.3 mm.

[0111] Using the POE encapsulating film prepared in this embodiment, a photovoltaic module with the following structure is assembled: it is composed of glass, a first encapsulating film, a cell array, a second encapsulating film, and glass stacked in sequence. Both the first encapsulating film and the second encapsulating film are POE encapsulating films prepared in this embodiment.

[0112] Example 6

[0113] The POE encapsulation film of this embodiment is prepared according to the following steps:

[0114] (1) Preparation of modified polyolefin resin:

[0115] Weigh 0.3 parts by weight of di-tert-butyl peroxide (with a half-life of 34 h at 115 °C) and 100 parts by weight of ethylene-butene copolymer, add them to a twin-screw extruder, set the screw speed to 50 rpm and the temperature to 150 °C, and perform co-extrusion to obtain modified polyolefin resin.

[0116] (2) Material preparation:

[0117] Weigh out 97 parts by weight of modified polyolefin resin, 1 part of POE silane graft masterbatch, 2 parts of POE blend light stabilizer masterbatch, 0.6 parts of azobisisobutyronitrile (half-life of 2 min at 120℃), 0.6 parts of diethylene glycol dimethacrylate and 0.1 parts of vinyltrimethoxysilane.

[0118] (3) Preparation of premix:

[0119] Modified polyolefin resin, azobisisobutyronitrile, diethylene glycol dimethacrylate and vinyltrimethoxysilane were added to a high-speed disperser and sheared and dispersed for 30 minutes to obtain a premix.

[0120] (4) Preparation of compound materials:

[0121] The premix, POE silane graft masterbatch, and POE blended light stabilizer masterbatch were mixed at 400 rpm for 50 min to obtain the compound.

[0122] (5) Extrusion molding:

[0123] The compound material is injected into a single-screw extruder through a feeding system, co-extruded at 85°C, cast into a film, then drawn into an embossing roller, pressed to form a pattern, cooled and shaped, then slit and wound to obtain the POE encapsulation film of this embodiment with a thickness of 0.4 mm.

[0124] Using the POE encapsulating film prepared in this embodiment, a photovoltaic module with the following structure is assembled: it is composed of glass, a first encapsulating film, a cell array, a second encapsulating film, and glass stacked in sequence. Both the first encapsulating film and the second encapsulating film are POE encapsulating films prepared in this embodiment.

[0125] Comparative Example 1

[0126] This comparative example is an EVA encapsulating film, differing from Example 2 only in that the modified polyolefin resin is replaced with ethylene-vinyl acetate copolymer; all other raw materials and steps are the same as in Example 2. Specifically, the EVA encapsulating film of this comparative example is prepared according to the following steps:

[0127] (1) Material preparation:

[0128] Weigh out 90 parts by weight of ethylene-vinyl acetate copolymer, 10 parts by weight of EVA silane graft masterbatch, 0.8 parts by weight of tert-amyl peroxide (2-ethylhexyl) carbonate (half-life of 1 h at 116 °C), 0.7 parts by weight of triallyl cyanurate and 0.1 parts by weight of trimethylallyloxysilane.

[0129] (2) Preparation of premix:

[0130] Ethylene-vinyl acetate copolymer, tert-amyl peroxide (2-ethylhexyl) carbonate, triallyl cyanurate, and trimethylallyloxysilane were added to a high-speed disperser and sheared and dispersed for 30 min to obtain a premix.

[0131] (3) Preparation of compound materials:

[0132] The premix and EVA silane graft masterbatch were mixed at 400 rpm for 50 min to obtain the compound.

[0133] (4) Extrusion molding:

[0134] The compound material is injected into a single-screw extruder through a feeding system, co-extruded at 95°C, cast into a film, then drawn into an embossing roller, pressed to form a pattern, cooled and shaped, then slit and wound to obtain the EVA encapsulation film of this comparative example with a thickness of 0.4 mm.

[0135] Comparative Example 2

[0136] The only difference between this comparative example and Example 2 is that the modified polyolefin resin in this comparative example is replaced with an ethylene-butene copolymer; all other raw materials and steps are the same as in Example 2. Specifically, the POE encapsulating film of this comparative example is prepared according to the following steps:

[0137] (1) Material preparation:

[0138] Weigh out 90 parts by weight of ethylene-butene copolymer, 10 parts by weight of POE silane graft masterbatch, 0.8 parts by weight of tert-amyl peroxide (2-ethylhexyl) carbonate (half-life of 1 h at 116 °C), 0.7 parts by weight of triallyl cyanurate and 0.1 parts by weight of trimethylallyloxysilane.

[0139] (2) Preparation of premix:

[0140] Ethylene-butene copolymer, tert-amyl peroxide (2-ethylhexyl) carbonate, triallyl cyanurate, and trimethylallyloxysilane were added to a high-speed disperser and sheared and dispersed for 30 min to obtain a premix.

[0141] (3) Preparation of compound materials:

[0142] The premix and POE silane graft masterbatch were mixed at 400 rpm for 50 min to obtain the compound.

[0143] (4) Extrusion molding:

[0144] The compound material is injected into a single-screw extruder through a feeding system, co-extruded at 95°C, cast into a film, then drawn into an embossing roller, pressed to form a pattern, cooled and shaped, then slit and wound to obtain the POE encapsulation film of this comparative example with a thickness of 0.4 mm.

[0145] Comparative Example 3

[0146] The only difference between this comparative example and Example 1 is that the modified polyolefin resin in this comparative example is replaced with ethylene-butene copolymer and ethylene-octene copolymer; all other raw materials and steps are the same as in Example 1. Specifically, the POE encapsulation film of this comparative example is prepared according to the following steps:

[0147] (1) Material preparation:

[0148] Weigh out 47.5 parts by weight of ethylene-butene copolymer, 47.5 parts by weight of ethylene-octene copolymer, 5 parts by weight of POE silane graft masterbatch, 0.6 parts by weight of tert-amyl peroxide (2-ethylhexyl) carbonate (half-life of 1 h at 116 °C), 0.5 parts by weight of triallyl cyanurate and 0.3 parts by weight of trimethylallyloxysilane.

[0149] (2) Preparation of premix:

[0150] Ethylene-butene copolymer, ethylene-octene copolymer, tert-amyl peroxide (2-ethylhexyl) carbonate, triallyl cyanurate, and trimethylallyloxysilane were added to a high-speed disperser and sheared and dispersed for 20 min to obtain a premix.

[0151] (3) Preparation of compound materials:

[0152] The premix and POE silane graft masterbatch were mixed at 300 rpm for 45 min to obtain the compound.

[0153] (4) Extrusion molding:

[0154] The compound material is injected into a single-screw extruder through a feeding system, co-extruded at 90°C, cast into a film, then drawn into an embossing roller, pressed to form a pattern, cooled and shaped, then slit and wound to obtain the POE encapsulation film of this comparative example with a thickness of 0.5 mm.

[0155] Comparative Example 4

[0156] The only difference between this comparative example and Example 1 is that the modified polyolefin resin in this comparative example is replaced with ethylene-butene copolymer and ethylene-octene copolymer, and the amount of crosslinking agent and co-crosslinking agent is increased. All other raw materials and steps are the same as in Example 1. Specifically, the POE encapsulation film of this comparative example is prepared according to the following steps:

[0157] (1) Material preparation:

[0158] Weigh out 47.5 parts by weight of ethylene-butene copolymer, 47.5 parts by weight of ethylene-octene copolymer, 5 parts by weight of POE silane graft masterbatch, 0.8 parts by weight of tert-amyl peroxide (2-ethylhexyl) carbonate (half-life of 1 h at 116 °C), 0.7 parts by weight of triallyl cyanurate and 0.3 parts by weight of trimethylallyloxysilane.

[0159] (2) Preparation of premix:

[0160] Ethylene-butene copolymer, ethylene-octene copolymer, tert-amyl peroxide (2-ethylhexyl) carbonate, triallyl cyanurate, and trimethylallyloxysilane were added to a high-speed disperser and sheared and dispersed for 20 min to obtain a premix.

[0161] (3) Preparation of compound materials:

[0162] The premix and POE silane graft masterbatch were mixed at 300 rpm for 45 min to obtain the compound.

[0163] (4) Extrusion molding:

[0164] The compound material is injected into a single-screw extruder through a feeding system, co-extruded at 90°C, cast into a film, then drawn into an embossing roller, pressed to form a pattern, cooled and shaped, then slit and wound to obtain the POE encapsulation film of this comparative example with a thickness of 0.5 mm.

[0165] Comparative Example 5

[0166] The only difference between this comparative example and Example 2 is that the initiator dicumyl peroxide is replaced with tert-amyl (2-ethylhexyl) carbonate peroxide in this comparative example; all other raw materials and steps are the same as in Example 2. Specifically, the POE encapsulating film of this comparative example is prepared according to the following steps:

[0167] (1) Preparation of modified polyolefin resin:

[0168] Weigh 0.1 parts by weight of tert-amyl peroxide (2-ethylhexyl) carbonate (half-life of 1 h at 116 °C) and 100 parts by weight of ethylene-butene copolymer, add them to a twin-screw extruder, set the screw speed to 50 rpm and the temperature to 160 °C, and perform co-extrusion to obtain modified polyolefin resin.

[0169] (2) Material preparation:

[0170] Weigh out 90 parts by weight of modified polyolefin resin, 10 parts by weight of POE silane graft masterbatch, 0.8 parts by weight of tert-amyl peroxide (2-ethylhexyl) carbonate (half-life of 1 h at 116 °C), 0.7 parts by weight of triallyl cyanurate and 0.1 parts by weight of trimethylallyloxysilane.

[0171] (3) Preparation of premix:

[0172] Modified polyolefin resin, tert-amyl peroxide (2-ethylhexyl) carbonate, triallyl cyanurate, and trimethylallyloxysilane were added to a high-speed disperser and sheared and dispersed for 30 minutes to obtain a premix.

[0173] (4) Preparation of compound materials:

[0174] The premix and POE silane graft masterbatch were mixed at 400 rpm for 50 min to obtain the compound.

[0175] (5) Extrusion molding:

[0176] The compound material is injected into a single-screw extruder through a feeding system, co-extruded at 95°C, cast into a film, then drawn into an embossing roller, pressed to form a pattern, cooled and shaped, then slit and wound to obtain the POE encapsulation film of this comparative example with a thickness of 0.4 mm.

[0177] Comparative Example 6

[0178] The only difference between this comparative example and Example 5 is that the reaction temperature in step (1) is increased in this comparative example; all other raw materials and steps are the same as in Example 5. Specifically, the POE encapsulating film of this comparative example is prepared according to the following steps:

[0179] (1) Preparation of modified polyolefin resin:

[0180] Weigh out 0.1 parts by weight of methyl ethyl ketone peroxide (with a half-life of 10 h at 105 °C), 50 parts of ethylene-hexene copolymer, 50 parts of ethylene-norbornene copolymer, and 600 parts of n-decane, and add them to a 500 L sealed reactor. Stir the reactor at 200 rpm at 250 °C for 1 h to obtain the modified polyolefin resin.

[0181] (2) Material preparation:

[0182] Weigh out 100 parts by weight of modified polyolefin resin, 0.6 parts by weight of azobisisobutyronitrile (with a half-life of 10 min at 100 °C), 0.5 parts by weight of triallyl isocyanurate and 0.2 parts by weight of γ-methacryloyloxypropyltrimethoxysilane.

[0183] (3) Preparation of mixture:

[0184] Modified polyolefin resin, azobisisobutyronitrile, triallyl isocyanurate and γ-methacryloyloxypropyltrimethoxysilane were added to a high-speed disperser and sheared and dispersed for 1 hour to obtain a mixture.

[0185] (4) Extrusion molding:

[0186] The mixture is fed into a single-screw extruder through a feeding system, co-extruded at 100°C, cast into a film, then drawn into an embossing roller, pressed to form a pattern, cooled and shaped, then slit and wound to obtain the POE encapsulation film of this comparative example with a thickness of 0.3 mm.

[0187] Comparative Example 7

[0188] The only difference between this comparative example and Example 2 is that the reaction temperature in step (1) is increased in this comparative example; all other raw materials and steps are the same as in Example 2. Specifically, the POE encapsulating film of this comparative example is prepared according to the following steps:

[0189] (1) Preparation of modified polyolefin resin:

[0190] Weigh 0.1 parts by weight of dicumyl peroxide (with a half-life of 10 h at 117 °C) and 100 parts by weight of ethylene-butene copolymer, add them to a twin-screw extruder, set the screw speed to 50 rpm and the temperature to 230 °C, and perform co-extrusion to obtain modified polyolefin resin.

[0191] (2) Material preparation:

[0192] Weigh out 90 parts by weight of modified polyolefin resin, 10 parts by weight of POE silane graft masterbatch, 0.8 parts by weight of tert-amyl peroxide (2-ethylhexyl) carbonate (half-life of 1 h at 116 °C), 0.7 parts by weight of triallyl cyanurate and 0.1 parts by weight of trimethylallyloxysilane.

[0193] (3) Preparation of premix:

[0194] Modified polyolefin resin, tert-amyl peroxide (2-ethylhexyl) carbonate, triallyl cyanurate, and trimethylallyloxysilane were added to a high-speed disperser and sheared and dispersed for 30 minutes to obtain a premix.

[0195] (4) Preparation of compound materials:

[0196] The premix and POE silane graft masterbatch were mixed at 400 rpm for 50 min to obtain the compound.

[0197] (5) Extrusion molding:

[0198] The compound material is injected into a single-screw extruder through a feeding system, co-extruded at 95°C, cast into a film, then drawn into an embossing roller, pressed to form a pattern, cooled and shaped, then slit and wound to obtain the POE encapsulation film of this comparative example with a thickness of 0.4 mm.

[0199] Comparative Example 8

[0200] The only difference between this comparative example and Example 6 is that the amount of initiator in step (1) is increased in this comparative example; all other raw materials and steps are the same as in Example 6. Specifically, the POE encapsulation film of this comparative example is prepared according to the following steps:

[0201] (1) Preparation of modified polyolefin resin:

[0202] Weigh 0.6 parts by weight of di-tert-butyl peroxide (with a half-life of 34 h at 115 °C) and 100 parts by weight of ethylene-butene copolymer, add them to a twin-screw extruder, set the screw speed to 50 rpm and the temperature to 150 °C, and perform co-extrusion to obtain modified polyolefin resin.

[0203] (2) Material preparation:

[0204] Weigh out 97 parts by weight of modified polyolefin resin, 1 part of POE silane graft masterbatch, 2 parts of POE blend light stabilizer masterbatch, 0.6 parts of azobisisobutyronitrile (half-life of 2 min at 120℃), 0.6 parts of diethylene glycol dimethacrylate and 0.1 parts of vinyltrimethoxysilane.

[0205] (3) Preparation of premix:

[0206] Modified polyolefin resin, azobisisobutyronitrile, diethylene glycol dimethacrylate and vinyltrimethoxysilane were added to a high-speed disperser and sheared and dispersed for 30 minutes to obtain a premix.

[0207] (4) Preparation of compound materials:

[0208] The premix, POE silane graft masterbatch, and POE blended light stabilizer masterbatch were mixed at 400 rpm for 50 min to obtain the compound.

[0209] (5) Extrusion molding:

[0210] The compound material is injected into a single-screw extruder through a feeding system, co-extruded at 85°C, cast into a film, then drawn into an embossing roller, pressed to form a pattern, cooled and shaped, then slit and wound to obtain the POE encapsulation film of this comparative example with a thickness of 0.4 mm.

[0211] Test Example 1: Rheological Analysis of Modified Polyolefin Resins

[0212] Rheological analysis was performed on the modified polyolefin resins in Examples 1-6 (referred to as modified polyolefin resins 1-6, respectively) and the ethylene-butene copolymer in Comparative Example 2. The method was as follows: a rotational rheometer (HAAKE MARS40, ThermoFisher) was used to perform frequency scanning on each sample at 100°C. The test results are shown in […]. Figure 1 .

[0213] In the Cole-Cole diagram, linear polymers form a semi-circular curve; the further the curve deviates from the semi-circular curve, the higher the proportion of long-branched structures in the polymer. Figure 1 As can be seen from the data, modified polyolefin resins 1 to 6 all contain long branched structures.

[0214] Test Example 2: Performance Test of Encapsulating Film

[0215] The encapsulating films prepared in each embodiment and comparative example were subjected to performance tests, specifically including:

[0216] (1) Melting point and enthalpy of fusion of the encapsulating film:

[0217] The results were obtained using a differential scanning calorimeter (DSC 25, TA Instruments). The test method was as follows: Under a nitrogen atmosphere, the sample was first heated to 100°C and held for 2 min to eliminate thermal history. Then, it was cooled to 0°C at a rate of 10°C / min and held for 2 min. The sample was then reheated to 100°C at a rate of 10°C / min. The DSC curve of the heating process was recorded, and the melting temperature and enthalpy of the polymer and its fractions were obtained based on the curve of the second heating.

[0218] (2) Curing properties of the encapsulating film (TC10, TC90, ML and MH):

[0219] The vulcanization curve was obtained by testing at 145°C for 15 minutes using a vulcanizer (RPA elite, TA Instruments).

[0220] (3) Degree of crosslinking of the encapsulating film:

[0221] According to the national standard GB / T 29848-2013, the xylene extraction method was used for determination.

[0222] (4) Light transmittance of the encapsulating film:

[0223] Measured using a UV-Vis spectrophotometer (Cary 5000, Agilent Technologies).

[0224] (5) Haze of the encapsulating film:

[0225] Measured using a high-precision haze meter (SGH-2, Beijing Aobotai Technology Co., Ltd.).

[0226] (6) Power degradation of photovoltaic modules after PID test:

[0227] Tested in accordance with IEC TS 62804-1:2015.

[0228] The performance test results are shown in Tables 1 and 2.

[0229] Table 1

[0230]

[0231] Table 2

[0232]

[0233] As can be seen from Tables 1 and 2:

[0234] (1) Comparing Comparative Example 1, Comparative Example 2 and Example 2, it can be seen that:

[0235] ① Compared with directly using ethylene-α olefin copolymer and crosslinking agent and other materials to form a film (Comparative Example 2), the method of the present invention, that is, first modifying the ethylene-α olefin copolymer under the action of an initiator, and then blending it with crosslinking agent and other materials to form a film (Example 1), can effectively improve the crosslinking degree of POE encapsulation film, and to a certain extent improve the problem that the crosslinking degree of POE encapsulation film is significantly lower than that of EVA encapsulation film (Comparative Example 1);

[0236] ② The melting point, enthalpy of fusion, TC10 and TC90 of Example 2 are significantly lower than those of Comparative Example 2, indicating that the method of the present invention can make the processing window of POE encapsulation film wider, easier to process, and can accelerate the crosslinking speed, which will help to shorten the lamination time and improve production efficiency.

[0237] ③ Compared with the direct use of polyolefin copolymers and crosslinking agents to form films (Comparative Example 2), the method of the present invention (Example 1) can also effectively reduce the haze of POE encapsulation film, improve its light transmittance and anti-PID performance, and is significantly better than EVA encapsulation film in these properties (especially anti-PID performance).

[0238] (2) Comparing Comparative Examples 3, 4 and 1, it can be seen that when ethylene-α-olefin copolymer is directly blended with crosslinking agents and other materials to form a film, although increasing the amount of crosslinking agent and co-crosslinking agent can improve the crosslinking degree, processing window, crosslinking speed and anti-PID properties of the encapsulating film to a certain extent, the effect is limited. However, the method of the present invention can improve the above properties to a greater extent, and at the same time reduce the haze of the film. The reason for this is that the present invention reacts the ethylene-α-olefin copolymer under the action of an initiator to form a modified polyolefin resin with a long-chain branched structure, which can improve the degree of entanglement and overlap between molecular chains, thereby facilitating further crosslinking under the action of the crosslinking agent, improving the crosslinking degree, crosslinking speed and anti-PID properties of the film, and giving it a wider processing window; in addition, modifying the ethylene-α-olefin copolymer with an initiator can also destroy the original crystallization of the ethylene-α-olefin copolymer, which is beneficial to reducing the haze of the film.

[0239] (3) Comparing Comparative Example 5 and Example 2, it can be seen that in the process of pre-modifying the ethylene-α-olefin copolymer using an initiator, compared with the use of an initiator with a shorter half-life (Comparative Example 5), the present invention uses an initiator with a longer half-life (Example 2), which enables the prepared encapsulating film to have lower haze, as well as better anti-PID performance and long-term stability. The reason for this is that using an initiator with a longer half-life enables the obtained modified polyolefin resin to have a slightly cross-linked and branched structure. While ensuring that the POE encapsulating film achieves a high degree of cross-linking, it also enables the subsequent process of blending and extruding the modified polyolefin resin with other materials to achieve sufficient mixing at a lower temperature, allowing the cross-linking agent, co-cross-linking agent, functional masterbatch and silane coupling agent to play their roles better.

[0240] (4) Comparing Comparative Example 6 with Example 5, Comparative Example 7 with Example 2, and Comparative Example 8 with Example 6, it can be seen that during the pre-modification of ethylene-α-olefin copolymer using an initiator, excessively high reaction temperatures (Comparative Example 6, Comparative Example 7) or excessive initiator dosage (Comparative Example 8) negatively impact the haze and anti-PID properties of the encapsulating film. The reason is that when the reaction temperature is too high or the initiator dosage is too high, the modified polyolefin resin forms a cross-linked network structure with an excessively high degree of cross-linking, which is not conducive to achieving sufficient mixing at a lower temperature during the co-extrusion process of the modified polyolefin resin with other materials.

[0241] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Unless otherwise specified, the raw materials and equipment used in this invention are conventional in the art and can be obtained through conventional commercial means; unless otherwise specified, the methods used in this invention are conventional methods in the art.

[0242] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a highly cross-linked POE encapsulating film, characterized in that, Includes the following steps: S1: An ethylene-α-olefin copolymer and an initiator are mixed in a mass ratio of 100:0.1~0.3, and the reaction is carried out at a temperature higher than that of the initiator. Specifically, the initiator, the ethylene-α-olefin copolymer and the solvent are mixed and reacted at 120~200℃ for 0.5~2h, or the initiator and the ethylene-α-olefin copolymer are mixed at 150~200℃ and extruded to obtain a modified polyolefin resin. The initiator is at least one of dicumyl peroxide, methyl ethyl ketone peroxide and di-tert-butyl peroxide. S2: Take raw materials comprising the following components by weight: 90-100 parts of modified polyolefin resin, 0.6-0.8 parts of crosslinking agent, and 0.5-0.7 parts of co-crosslinking agent; the crosslinking agent is at least one of (2-ethylhexyl) tert-amyl peroxide, dicyclohexyl peroxide, and azobisisobutyronitrile. S3: After blending and extruding all the raw materials in step S2 at a temperature higher than the crosslinking agent initiation temperature but not higher than 110°C, the mixture is molded to obtain a highly crosslinked POE encapsulation film.

2. The preparation method according to claim 1, characterized in that, In step S1, the stirring speed is 200~500 rpm during the reaction.

3. The preparation method according to claim 1, characterized in that, In step S1, the mixing and extrusion process is carried out using a twin-screw extruder.

4. The preparation method according to claim 3, characterized in that, In step S1, during the mixing and extrusion process, the screw speed of the twin-screw extruder is 20~80 rpm.

5. The preparation method according to claim 1, characterized in that, In step S2, the raw materials also include the following components in parts by weight: 1 to 10 parts of functional masterbatch and 0.1 to 0.4 parts of additives.

6. The preparation method according to claim 5, characterized in that, The additives include silane coupling agents.

7. The preparation method according to claim 5, characterized in that, The functional masterbatch includes POE silane graft masterbatch and / or POE blend light stabilizer masterbatch.

8. The preparation method according to claim 1, characterized in that, In step S3, the temperature of the co-extrusion is 70~110℃.

9. A photovoltaic module, characterized in that, This includes highly cross-linked POE encapsulating films prepared by the preparation method described in any one of claims 1 to 8.

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