Polyvinyl acetal film for photovoltaic use, preparation method and photovoltaic module thereof

Abstract

The invention discloses a polyvinyl acetal film for photovoltaic use, a preparation method and a photovoltaic module thereof, and belongs to the technical field of polymer materials. The preparation method of the film comprises the following steps: plasticizing a first-layer film mixture, an intermediate film mixture and a third-layer film mixture, and then forming them through a three-layer co-extrusion die head; the first-layer film mixture and the third-layer film mixture both comprise the following raw materials in parts by weight: 70 to 80 parts of polyvinyl acetal resin and 20 to 30 parts of plasticizer; the intermediate film mixture comprises the following raw materials in parts by weight: 80 to 90 parts of polyvinyl acetal resin and 10 to 20 parts of plasticizer; the invention combines an outer layer structure with different functions with an inner layer structure, so as to finally obtain a polyvinyl acetal film for photovoltaic use having good adhesion, flexibility, fluidity and insulation.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and in particular relates to a polyvinyl acetal film for photovoltaics, a preparation method and a photovoltaic module thereof. Background Art

[0002] With the continuous consumption of fossil fuel resources and the continuous enhancement of human environmental awareness, more economical, environmentally friendly and sustainable new energy sources are gradually replacing traditional fossil energy. Among them, the photovoltaic industry has begun to receive the focus of human attention. Photovoltaic modules mainly include glass substrates, photovoltaic films and battery chips. The structure is as follows: Figure 1 As shown. Affected by the use environment of photovoltaic modules, the electrodes are susceptible to oxidation and corrosion by moisture and corrosive gases in the air. The photovoltaic protective film needs to have good volume resistivity, adhesion, flexibility, etc., so as to protect the battery cells.

[0003] In the field of photovoltaic films, although EVA films are widely used, their weather resistance and water vapor resistance are poor. They are prone to aging and yellowing under ultraviolet radiation, which affects the transparency of the film. Although POE / EPE films have better water vapor barrier and anti-aging capabilities than traditional EVA films, their adhesion to glass is relatively poor. Polyvinyl acetal films have begun to become an important choice for photovoltaic films due to their good adhesion, excellent weather resistance, water vapor resistance and impact resistance.

[0004] However, as a protective film for photovoltaic materials, high requirements are placed on the synergistic effects of the insulation, adhesion, flexibility and fluidity of polyvinyl acetal films. If the insulation of polyvinyl acetal films is poor, the photovoltaic module is prone to leakage, resulting in excessive power attenuation of the module. If the adhesion of polyvinyl acetal films is poor, it cannot be firmly bonded to the glass, which can easily affect the safety of photovoltaic modules. If the fluidity of polyvinyl acetal films is poor, it will be difficult to achieve the bonding of the film and the glass; if the fluidity of polyvinyl acetal films is high, the film and the glass will bond faster, and bubbles or streaks will easily occur in uneven places or defects; therefore, polyvinyl acetal films need to have more suitable fluidity. If the flexibility of polyvinyl acetal films is poor, when the photovoltaic module is impacted by foreign objects, it will not be able to absorb part of the impact energy and play a certain buffering role, making it difficult to provide safety protection for the photovoltaic module. Therefore, it is of great significance to achieve the synergy of the performance of polyvinyl acetal films for photovoltaics. Summary of the invention

[0005] The purpose of the present invention is to provide a photovoltaic polyvinyl acetal film, a preparation method and a photovoltaic module thereof, aiming to solve the problem in the prior art that it is difficult to simultaneously achieve the insulation, adhesion, flexibility and fluidity of the photovoltaic film.

[0006] The invention discloses a photovoltaic polyvinyl acetal film, comprising a three-layer structure, which sequentially comprises a first film layer, an intermediate film layer and a third film layer, wherein the thickness ratio of the first film layer to the third film layer is 1:1; the thickness ratio of the intermediate film layer to the first film layer is 1-3:1, and the thickness of the photovoltaic polyvinyl acetal film is 0.18-3.4 mm.

[0007] The present invention also discloses a method for preparing the above photovoltaic polyvinyl acetal film, which comprises the following steps:

[0008] The first film mixture, the middle film mixture and the third film mixture are plasticized by two or more extruders and then formed by a three-layer co-extrusion die to obtain the photovoltaic polyvinyl acetal film.

[0009] The first layer film mixture and the third layer film mixture both include the following raw materials in parts by weight: 70-80 parts of polyvinyl acetal resin and 20-30 parts of plasticizer.

[0010] The intermediate film mixture comprises the following raw materials in parts by weight: 80 to 90 parts of polyvinyl acetal resin and 10 to 20 parts of plasticizer.

[0011] Preferably, the plasticizing temperature of the first layer film mixture and the third layer film mixture is 110-200°C.

[0012] Preferably, the plasticizing temperature of the intermediate layer film mixture is 170-280°C.

[0013] Preferably, the temperature of the three-layer co-extrusion die is 130-200°C.

[0014] Preferably, during the plasticization process of the intermediate layer film mixture, 10 to 45% of the total mass of the plasticizer and 100% of the total mass of the polyvinyl alcohol acetal resin in the intermediate layer film mixture are first mixed at 10 to 25° C. for 20 to 45 minutes to obtain a first mixture, and then the first mixture and the remaining raw materials are added to the extruder for plasticization together.

[0015] Preferably, the glass transition temperature of the first film layer and the third film layer is 18-28° C., and the melt index at 150° C. is 12.0-18.0 g / 10 min.

[0016] Preferably, the glass transition temperature of the intermediate layer film is 30-45° C., and the melt index at 150° C. is 1.5-6.5 g / 10 min.

[0017] Preferably, when used to prepare the first and third layers of the polyvinyl acetal film for photovoltaics, the raw material polyvinyl acetal resin has a hydroxyl value of 16.5 to 21.0%, and / or an acetoxy content of 0.5 to 2.0%.

[0018] Preferably, when used to prepare an intermediate film of a photovoltaic polyvinyl acetal film, the raw material polyvinyl acetal resin has a hydroxyl value of ≤16.0%, and / or an acetoxy content of 8.0 to 15.0%.

[0019] Preferably, when used to prepare an intermediate film of a photovoltaic polyvinyl acetal film, the raw material polyvinyl acetal resin has a hydroxyl value of 9 to 16.0%, and / or an acetoxy content of 8.0 to 15.0%.

[0020] Preferably, the plasticizer includes at least one of triethylene glycol diisooctanoate, dioctyl phthalate, dioctyl sebacate, tetraethylene glycol di-n-heptanoate, dimethyl phthalate, dioctyl adipate and dibutyl sebacate.

[0021] Preferably, the first film layer mixture, the middle film layer mixture and the third film layer mixture also contain a primary antioxidant, a secondary antioxidant and an ultraviolet absorber.

[0022] Preferably, when used to prepare the first and third layers of polyvinyl acetal film for photovoltaics, the amount of the main antioxidant added to the raw material is 1 to 3‰ of the mass of the plasticizer added in the corresponding film, the amount of the auxiliary antioxidant added is 2 to 4‰ of the mass of the plasticizer added in the corresponding film, and the amount of the ultraviolet absorber added is 1 to 3‰ of the mass of the plasticizer added in the corresponding film.

[0023] Preferably, when used to prepare an intermediate layer film of polyvinyl acetal film for photovoltaics, the amount of the main antioxidant added to the raw material is 1-6‰ of the mass of the plasticizer added, the amount of the auxiliary antioxidant added is 2-8‰ of the mass of the plasticizer added, and the amount of the ultraviolet absorber added is 1-9‰ of the mass of the plasticizer added.

[0024] Preferably, the main antioxidant is antioxidant 1010 or antioxidant 1098.

[0025] Preferably, the secondary antioxidant is one of antioxidant 168, antioxidant 626 and antioxidant PEP-36.

[0026] Preferably, the ultraviolet absorber is UV-326 or UV-329.

[0027] The present invention also discloses a photovoltaic module, comprising a glass substrate, a first photovoltaic film, a battery chip, a second photovoltaic film, and a glass substrate stacked in sequence, wherein the first photovoltaic film and / or the second photovoltaic film is a photovoltaic polyvinyl acetal film as described in the above invention.

[0028] Beneficial effects of the present invention:

[0029] 1. The present invention provides a photovoltaic polyvinyl acetal film, which uses a film with a high hydroxyl value and a high plasticizer content as an outer layer structure to achieve good adhesion, flexibility and fluidity of the photovoltaic polyvinyl acetal film; and uses a film with a low hydroxyl value and a low plasticizer content as an intermediate layer to achieve good insulation and water barrier properties of the photovoltaic polyvinyl acetal film; and finally obtains a photovoltaic polyvinyl acetal film with good adhesion, flexibility, fluidity and insulation by combining an outer layer structure with different functions with an inner layer structure, so that the final photovoltaic film product has a melt index of 5.0 to 15.0 g / 10 min at 150° C., a knock value of 8 to 9, and a volume resistivity of more than 1.0×10 15 Ω·cm, showing good flexibility.

[0030] 2. The present invention adds plasticizers in stages during the preparation of the intermediate film. The reason is that the acetoxy content of the polyvinyl alcohol acetal resin in the intermediate film mixture is relatively high and the non-polar acetal content is relatively low, resulting in poor compatibility between the resin and the plasticizer. If they are added simultaneously at one time, it is very easy to cause uneven plasticization of the resin and the plasticizer, thereby affecting the melt index and volume resistivity and other properties of the film. However, by adding the plasticizer in stages, the incompatibility between the resin and the plasticizer can be effectively reduced and the mixing effect of the resin and the plasticizer can be improved.

[0031] 3. The present invention provides a preparation process for polyvinyl acetal film for photovoltaic use. The process is not only simple in process, but also requires widely available raw materials. The core materials only include PVB resins with specific hydroxyl and acetoxy contents, plasticizers and standardized industrial additives, which greatly improves the convenience and cost-effectiveness of raw material acquisition. By innovatively adopting multi-layer film combination technology and precisely controlling the structural formula and performance parameters of each film layer, not only the high quality of the photovoltaic film is ensured, but also a significant reduction in production costs is achieved, bringing unprecedented economic benefits and competitiveness improvement to the photovoltaic industry.

[0032] 4. The polyvinyl acetal film for photovoltaics provided by the present invention has widely available raw materials, simple process, and is easy to industrialize and produce, thus reducing unnecessary procurement and processing processes. Through simple technical means, it achieves improvements in key indicators such as adhesion, insulation, flexibility, and bonding strength of photovoltaic films, thus providing a solid guarantee for the long-term and stable operation of photovoltaic modules. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention will be further described below in conjunction with the accompanying drawings.

[0034] Figure 1is a schematic diagram of the structure of a photovoltaic module in the background technology;

[0035] Figure 2 It is a schematic structural diagram of the polyvinyl acetal film of the present invention;

[0036] In the figure: 1, first film layer, 2, middle film layer, 3, third film layer. DETAILED DESCRIPTION

[0037] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] A method for preparing a polyvinyl acetal film for photovoltaic use comprises the following steps:

[0039] Add the first layer of film mixture into the extruder and plasticize at a temperature of 110-200°C;

[0040] 10 to 45% of the total weight of the plasticizer in the intermediate film mixture and 100% of the total weight of the polyvinyl acetal resin are mixed at 10 to 25° C. for 20 to 45 minutes to obtain a first mixture, and then the first mixture and the remaining raw materials are added to an extruder and plasticized at a temperature of 170 to 280° C.;

[0041] Add the third layer film mixture into the extruder and plasticize at a temperature of 110-200°C;

[0042] The plasticized melt is formed into a three-layer structure through the flow channel of the distributor and extruded through a die head at a temperature of 130-200°C. The thickness ratio of the first film 1 and the third film 3 is controlled to be 1:1; the thickness ratio of the intermediate film 2 to the first film 1 is 1-3:1, and the thickness of the photovoltaic polyvinyl acetal film is 0.18-3.4 mm, so as to obtain the photovoltaic polyvinyl acetal film.

[0043] The first layer film mixture and the third layer film mixture include the following raw materials in parts by weight: 70-80 parts of polyvinyl acetal resin, 20-30 parts of plasticizer, 0.02-0.09 parts of primary antioxidant, 0.04-0.12 parts of auxiliary antioxidant, and 0.02-0.09 parts of ultraviolet absorber.

[0044] The first film mixture and the polyvinyl alcohol acetal resin in the first film mixture have a hydroxyl value of 16.5 to 21.0%, and or, an acetoxy content of 0.5 to 2.0%.

[0045] The intermediate film mixture comprises the following raw materials in parts by weight: 80-90 parts of polyvinyl acetal resin, 10-20 parts of plasticizer, 0.01-0.12 parts of primary antioxidant, 0.04-0.16 parts of auxiliary antioxidant and 0.01-0.18 parts of ultraviolet absorber.

[0046] The hydroxyl value of the polyvinyl acetal resin in the intermediate film mixture is ≤16.0%, and or, the acetoxy content is 8.0-15.0%.

[0047] The hydroxyl value of the polyvinyl acetal resin in the intermediate film mixture is 9-16%, and the acetoxy content is 8.0-15.0%.

[0048] The plasticizer includes at least one of triethylene glycol diisooctanoate, dioctyl phthalate, dioctyl sebacate, tetraethylene glycol di-n-heptanoate, dimethyl phthalate, dioctyl adipate and dibutyl sebacate.

[0049] The main antioxidant is antioxidant 1010 or antioxidant 1098.

[0050] The auxiliary antioxidant is one of antioxidant 168, antioxidant 626 and antioxidant PEP-36.

[0051] The ultraviolet absorber is UV-326 or UV-329.

[0052] Example 1

[0053] A method for preparing a polyvinyl acetal film for photovoltaic use comprises the following steps:

[0054] Add the first layer of film mixture into the extruder and plasticize at 140°C;

[0055] 35.7% of the total weight of dioctyl sebacate in the middle layer film mixture and 100% of the total weight of polyvinyl acetal resin in the middle layer film mixture are mixed at 15° C. for 35 minutes to obtain a first mixture, and then the first mixture and the remaining raw materials are added to an extruder and plasticized at a temperature of 180° C.;

[0056] Add the third layer film mixture into the extruder and plasticize at 140°C;

[0057] The plasticized melt is formed into a three-layer structure through the flow channel of the distributor and extruded through a die at a temperature of 150°C. The thickness ratio of the first film 1 and the third film 3 is controlled to be 1:1; the thickness ratio of the intermediate film 2 to the first film 1 is 1:1, and the thickness of the photovoltaic polyvinyl acetal film is 1.52 mm, thus obtaining the photovoltaic polyvinyl acetal film.

[0058] The first layer film mixture and the third layer film mixture include the following raw materials in parts by weight: 80 parts of polyvinyl acetal resin, 20 parts of triethylene glycol diisooctanoate, 0.0315 parts of antioxidant 1010, 0.063 parts of antioxidant 168, and 0.042 parts of UV-329.

[0059] The hydroxyl value of the polyvinyl acetal resin in the first layer film mixture and the third layer film mixture was 19.0%, and the acetoxy content was 1.5%.

[0060] The intermediate layer film mixture includes the following raw materials in parts by weight: 86 parts of polyvinyl acetal resin, 14 parts of dioctyl sebacate, 0.042 parts of antioxidant 1098, 0.084 parts of antioxidant PEP-36, and 0.084 parts of UV-326.

[0061] The hydroxyl value of the polyvinyl acetal resin in the intermediate film mixture is 13.0%, and the acetoxy content is 9.0%.

[0062] Example 2

[0063] A method for preparing a polyvinyl acetal film for photovoltaic use, compared with Example 1, the difference lies in the different raw material ratio and plasticizing process of the intermediate layer film mixture, specifically:

[0064] The intermediate layer film mixture includes the following raw materials in parts by weight: 90 parts of polyvinyl acetal resin, 10 parts of dioctyl sebacate, 0.03 parts of antioxidant 1098, 0.06 parts of antioxidant PEP-36, and 0.06 parts of UV-326;

[0065] The plasticizing process of the intermediate film mixture is as follows: 20% of the total mass of dioctyl sebacate in the intermediate film mixture and 100% of the total mass of polyvinyl acetal resin in the intermediate film mixture are mixed at 15° C. for 35 minutes to obtain a first mixture, and then the first mixture and the remaining raw materials are added to an extruder and plasticized at a temperature of 180° C.;

[0066] The remaining raw materials, parameters and preparation process are the same as those in Example 1.

[0067] Example 3

[0068] A method for preparing a polyvinyl acetal film for photovoltaic use, compared with Example 1, the difference is that the raw material ratio of the intermediate layer film mixture is different, specifically:

[0069] The intermediate film mixture includes the following raw materials in parts by weight: 80 parts of polyvinyl acetal resin, 20 parts of dioctyl sebacate, 0.06 parts of antioxidant 1098, 0.12 parts of antioxidant PEP-36, and 0.12 parts of UV-326;

[0070] The remaining raw materials, parameters and preparation process are the same as those in Example 1.

[0071] Example 4

[0072] A method for preparing a polyvinyl acetal film for photovoltaics, compared with Example 1, the difference is that the hydroxyl value of the polyvinyl acetal resin in the intermediate layer film mixture is 9.0%, the acetoxy content is 9.0%, and the other raw materials, parameters and preparation process are the same as Example 1.

[0073] Example 5

[0074] A method for preparing a polyvinyl acetal film for photovoltaics, compared with Example 1, the difference is that the hydroxyl value of the polyvinyl acetal resin in the intermediate layer film mixture is 16.0%, the acetoxy content is 9.0%, and the other raw materials, parameters and preparation process are the same as Example 1.

[0075] Example 6

[0076] A method for preparing a polyvinyl acetal film for photovoltaics, compared with Example 1, the difference is that the first layer film mixture and the first layer film mixture include the following raw materials in parts by weight: 70 parts of polyvinyl acetal resin, 30 parts of triethylene glycol diethylhexanoate, 0.045 parts of antioxidant 1010, 0.09 parts of antioxidant 168, and 0.06 parts of UV-329, and the remaining raw materials, parameters and preparation process are the same as Example 1.

[0077] Example 7

[0078] A method for preparing a polyvinyl acetal film for photovoltaics, compared with Example 1, the difference is that the hydroxyl value of the polyvinyl acetal resin in the intermediate layer film mixture is 13.0%, the acetoxy content is 8.0%, and the other raw materials, parameters and preparation process are the same as Example 1.

[0079] Example 8

[0080] A method for preparing a polyvinyl acetal film for photovoltaics, compared with Example 1, the difference is that the hydroxyl value of the polyvinyl acetal resin in the intermediate layer film mixture is 13.0%, the acetoxy content is 15.0%, and the other raw materials, parameters and preparation process are the same as Example 1.

[0081] Example 9

[0082] A method for preparing a polyvinyl acetal film for photovoltaics, compared with Example 1, the difference is that the "dioctyl sebacate" in Example 1 is replaced by "a mixture of dioctyl sebacate and dioctyl phthalate in a mass ratio of 1:1", and the remaining raw materials, parameters and preparation process are the same as Example 1.

[0083] Example 10

[0084] A method for preparing a polyvinyl acetal film for photovoltaics, compared with Example 1, the difference is that the "dioctyl sebacate" in Example 1 is replaced by "dioctyl phthalate", and the remaining raw materials, parameters and preparation process are the same as Example 1.

[0085] Embodiment 11

[0086] A method for preparing a polyvinyl acetal film for photovoltaic use, compared with Example 1, the difference is that the thickness ratio of the intermediate film 2 to the first film 1 is 3:1, and the other raw materials, parameters and preparation process are the same as Example 1.

[0087] Example 12

[0088] A method for preparing a polyvinyl acetal film for photovoltaics, compared with Example 1, the difference is that the hydroxyl value of the polyvinyl acetal resin in the first layer film mixture and the third layer film mixture is 16.5%, and the other raw materials, parameters and preparation process are the same as Example 1.

[0089] Example 13

[0090] A method for preparing a polyvinyl acetal film for photovoltaics, compared with Example 1, the difference is that the hydroxyl value of the polyvinyl acetal resin in the first layer film mixture and the third layer film mixture is 21%, and the other raw materials, parameters and preparation process are the same as Example 1.

[0091] Comparative Example 1

[0092] A method for preparing a polyvinyl acetal film for photovoltaic use comprises the following steps:

[0093] 35.7% of the total mass of dioctyl sebacate and 100% of the total mass of polyvinyl acetal resin in the intermediate layer film mixture are mixed at 15°C for 35 minutes to obtain a first mixture, and then the first mixture and the remaining raw materials are added to an extruder, plasticized at 180°C, and then extruded through a die at 150°C to obtain a photovoltaic polyvinyl acetal film with the same thickness as in Example 1. The composition ratio of the intermediate layer film mixture is the same as in Example 1.

[0094] Comparative Example 2

[0095] A method for preparing a polyvinyl acetal film for photovoltaic use comprises the following steps:

[0096] The first layer of film mixture is added into the extruder, plasticized at 140°C and extruded through a die at 150°C to obtain a photovoltaic polyvinyl acetal film having the same thickness as that in Example 1. The composition ratio of the first layer of film mixture is the same as that in Example 1.

[0097] Comparative Example 3

[0098] A method for preparing a polyvinyl acetal film for photovoltaic use comprises the following steps:

[0099] Add the first layer of film mixture into the extruder and plasticize at 140°C;

[0100] Add the third layer film mixture into the extruder and plasticize at 140°C;

[0101] The plasticized melt is formed into a two-layer structure through the flow channel of the distributor and extruded through a die at a temperature of 150° C. The thickness ratio of the first film 1 and the third film 3 is controlled to be 1:1; a photovoltaic polyvinyl acetal film having the same thickness as that of Example 1 is obtained.

[0102] The first film mixture and the first film mixture composition ratio are the same as those in Example 1.

[0103] Comparative Example 4

[0104] A method for preparing a polyvinyl acetal film for photovoltaic use, compared with Example 1, the difference is that a first layer of film mixture is added to an extruder and plasticized at a temperature of 140°C; the plasticized melt is formed into a three-layer structure through a flow channel of a distributor, and extruded through a die head at a temperature of 150°C, and the thickness ratio of the three-layer film is controlled to be 1:1:1; a polyvinyl acetal film for photovoltaic use having the same thickness as Example 1 is obtained, and the composition ratio of the first layer of film mixture is the same as Example 1.

[0105] Comparative Example 5

[0106] A method for preparing a polyvinyl acetal film for photovoltaics, compared with Example 3, the difference is that the intermediate layer film mixture includes the following raw materials in parts by weight: 79 parts of polyvinyl acetal resin, 21 parts of dioctyl sebacate, 0.063 parts of antioxidant 1098, 0.126 parts of antioxidant PEP-36, and 0.126 parts of UV-326, and the remaining raw materials, parameters and preparation process are the same as Example 3.

[0107] Comparative Example 6

[0108] A method for preparing a polyvinyl acetal film for photovoltaics, compared with Example 2, the difference is that the intermediate layer film mixture includes the following raw materials in parts by weight: 91 parts of polyvinyl acetal resin, 9 parts of dioctyl sebacate, 0.027 parts of antioxidant 1098, 0.054 parts of antioxidant PEP-36, and 0.054 parts of UV-326, and the remaining raw materials, parameters and preparation process are the same as Example 2.

[0109] Comparative Example 7

[0110] A method for preparing a polyvinyl acetal film for photovoltaics, compared with Example 1, the difference is that the first layer film mixture and the third layer film mixture include the following raw materials in parts by weight: 81 parts of polyvinyl acetal resin, 19 parts of triethylene glycol diethylhexanoate, 0.0285 parts of antioxidant 1010, 0.057 parts of antioxidant 168, and 0.038 parts of UV-329, and the remaining raw materials, parameters and preparation process are the same as Example 1.

[0111] Comparative Example 8

[0112] A method for preparing a polyvinyl acetal film for photovoltaics, compared with Example 6, the difference is that the first layer film mixture and the third layer film mixture include the following raw materials in parts by weight: 69 parts of polyvinyl acetal resin, 31 parts of triethylene glycol diethylhexanoate, 0.0465 parts of antioxidant 1010, 0.093 parts of antioxidant 168, and 0.062 parts of UV-329, and the remaining raw materials, parameters and preparation process are the same as Example 6.

[0113] Comparative Example 9

[0114] A method for preparing polyvinyl acetal film for photovoltaics, compared with Example 12, the difference is that the hydroxyl value of the polyvinyl acetal resin in the first layer film mixture and the third layer film mixture is 16.0%, and the other raw materials, parameters and preparation process are the same as Example 12.

[0115] Comparative Example 10

[0116] A method for preparing polyvinyl acetal film for photovoltaics, compared with Example 13, the difference is that the hydroxyl value of the polyvinyl acetal resin in the first layer film mixture and the third layer film mixture is 21.5%, and the other raw materials, parameters and preparation process are the same as Example 13.

[0117] Comparative Example 11

[0118] A method for preparing polyvinyl acetal film for photovoltaics, compared with Example 1, the difference is that the raw material plasticization process of the intermediate layer film mixture is different, specifically: all the intermediate layer film mixture is added into the extruder and plasticized at 180°C, and the remaining raw materials, parameters and preparation process are the same as Example 1.

[0119] Comparative Example 12

[0120] A method for preparing a polyvinyl acetal film for photovoltaics, compared with Example 5, the difference is that the hydroxyl value of the polyvinyl acetal resin in the intermediate layer film mixture is 17.0%, and the other raw materials, parameters and preparation process are the same as Example 5.

[0121] The moisture content, knock value, melt index, volume resistivity, and glass transition temperature of the photovoltaic polyvinyl acetal films prepared in Examples 1 to 13 and Comparative Examples 1 to 12 were measured. The measurement method is as follows:

[0122] 1) Moisture content: Evenly distribute 1g of the film to be tested in a weighing bottle with constant weight, place it in a blast drying oven at 105℃ and dry it for 2h. The moisture content can be calculated based on the ratio of the reduced mass of the sample to the original mass of the sample (control standard 0.2~0.5);

[0123] 2) Melt index at 150°C: Cut the prepared polyvinyl acetal film into pieces and pass it through a melt index meter at 150°C and a load of 21.6 kg. The outflow mass after 10 minutes is recorded as its melt index.

[0124] 3) Volume resistivity: The prepared polyvinyl acetal film was sandwiched between two electrodes and measured at a voltage of 100 V;

[0125] 4) Impact value: according to the test requirements of national standard GB / T 32020-2015 (polyvinyl butyral interlayer for laminated glass);

[0126] 5) Glass transition temperature (Tg): Use a DSC-250 differential scanning calorimeter to first keep the sample at 0°C for 5 min, then increase the temperature from 0°C to 180°C at a heating rate of 10°C / min, and keep it at 180°C for 5 min; then cool from 180°C to 0°C, keep it at this temperature for 5 min, and then increase the temperature from 0°C to 180°C at a heating rate of 10°C / min to finally obtain the DSC curve and glass transition temperature of the sample to be tested.

[0127] The test results are shown in Table 1.

[0128] Table 1 Performance test of polyvinyl acetal films in Examples 1 to 13 and Comparative Examples 1 to 12

[0129]

[0130] Note:

[0131] The knock value is an important indicator for evaluating the bonding strength between film and glass. After the polyvinyl acetal film is fully bonded to the glass, it is knocked by a steel hammer. The surface area S of the film exposed after the knock can effectively reflect the bonding strength between the film and the glass. Among them, 95≤S<100, the knock value is 0; 90≤S<95, the knock value is 1; 85≤S<90, the knock value is 2; 60≤S<85, the knock value is 3; 40≤S<60, the knock value is 4; 20≤S<40, the knock value is 5; 10≤S<20, the knock value is 6; 5≤S<10, the knock value is 7; 2≤S<5, the knock value is 8; S<2, the knock value is 9; S=0, the knock value is 10. Therefore, the larger the knock value, the better the bonding performance between the film and the glass. The hydroxyl content in the film is one of the key conditions for achieving effective bonding between the film and the glass.

[0132] The melt index at 150℃ indicates the flow of polyvinyl acetal film at high temperature. If the melt index is too low, the fluidity of the film is poor, and it will be difficult to achieve the bonding of the film and glass; if the melt index is too high, the fluidity of the film is good, the film and glass are bonded quickly, and bubbles or streaks are easily generated at uneven places or defects.

[0133] Volume resistivity indicates the resistance of a material to electric current per unit volume and is used to characterize the electrical properties of a material. The higher the volume resistivity, the more effective the material is as an electrical insulating component;

[0134] Glass transition temperature (Tg) refers to the temperature corresponding to the transition from glass state to highly elastic state. The glass transition temperature is the lowest temperature at which the molecular chain segments can move. Its level is directly related to the flexibility of the molecular chain. The greater the flexibility of the molecular chain, the lower the glass transition temperature; the greater the rigidity of the molecular chain, the higher the glass transition temperature. The flexibility of polyvinyl acetal film is closely related to the glass transition temperature of the first layer, the middle layer, and the third layer in the film.

[0135] It can be seen from the data recorded in Table 1 that Examples 1 to 13 use a combination of film layers and effectively control the structure and formula of each film layer to ensure that the final photovoltaic film product maintains good performance: the film has a melt index of 5.5 to 13.2 g / 10 min at 150 ° C, a knock value of 8 to 9, and a volume resistivity of ≥2.1×10 15 Ω·cm, showing good flexibility;

[0136] The film of Comparative Example 1 is not a three-layer structure, but only consists of the middle film. The film of Comparative Example 2 is also not a three-layer structure, but only consists of the first film. The film of Comparative Example 3 has a two-layer structure, which consists of the first film and the third film. The film of Comparative Example 4 has a three-layer structure, which consists entirely of the first film. It can be seen from the test results in Table 1 that compared with Example 1, the volume resistivity of the film obtained in Comparative Example 1 is not only reduced, but also the knock value and the melting index at 150°C are significantly lower, resulting in poor fluidity of the film, making it difficult to achieve the bonding of the film to the glass, and poor bonding performance with the glass; the volume resistivity of the films obtained in Comparative Examples 2 and 3 is significantly lower; the melting index of Comparative Example 4 at 150°C is significantly higher, the fluidity of the film is higher, the film is bonded to the glass faster, and bubbles or streaks are easily generated at uneven places or defects, so the film obtained in Example 1 has better insulation performance;

[0137] It can be seen from the test results of Example 3 and Comparative Example 5 that the increase of the plasticizer content in the intermediate film mixture will lead to a significant decrease in the volume resistivity of the film. It can be seen from the test results of Example 2 and Comparative Example 6 that the decrease of the plasticizer content in the intermediate film mixture has improved the volume resistivity of the film to a certain extent, but the lower plasticizer content makes it difficult to plasticize the intermediate layer resin and cannot be processed normally. Therefore, it is most appropriate to control the mass ratio of the plasticizer to the polyvinyl alcohol acetal resin in the intermediate film mixture to be 10-20:80-90;

[0138] It can be seen from the test results of Comparative Example 7 and Example 1 that the volume resistivity of the film is greatly improved by reducing the content of plasticizer in the first layer of film mixture and the third layer of film mixture, but the flexibility of the film is poor. It can be seen from the test results of Comparative Example 8 and Example 6 that the content of plasticizer in the first layer and the third layer is increased, and the melt index of Comparative Example 8 at 150°C is significantly higher, which exceeds the normal use requirements. The fluidity of the film is relatively large, and the film is attached to the glass quickly, and bubbles or streaks are easily generated at uneven places or defects.

[0139] It can be seen from the test results of Comparative Example 9 and Example 12 that the hydroxyl value of the polyvinyl alcohol acetal resin in the first layer film mixture and the third layer film mixture is reduced. Although the volume resistivity of the film is slightly improved, the bonding performance of the film is reduced, and it is more difficult to bond with the glass. It can be seen from the test results of Comparative Example 10 and Example 13 that when the hydroxyl value of the polyvinyl alcohol acetal resin in the first layer film mixture and the third layer film mixture exceeds a certain limit, it is easy to absorb moisture due to the presence of a large number of hydroxyl groups, resulting in a low volume resistivity of the film, which is not conducive to the long-term use of photovoltaic modules.

[0140] It can be seen from the test results in Comparative Example 11 and Example 1 that during the plasticization process of the intermediate layer film mixture, pre-mixing of part of the plasticizer with the polyvinyl acetal resin helps to improve the mixing uniformity of the polyvinyl acetal resin and the plasticizer, improve the plasticization effect, and thereby improve the melt index fluidity, volume resistivity and flexibility of the film.

[0141] It can be seen from the test results in Comparative Example 12 and Example 5 that when the hydroxyl value of the polyvinyl alcohol acetal resin in the intermediate layer film mixture reaches a certain limit, the water absorption of the film is enhanced, resulting in a certain degree of sudden drop in the volume resistivity of the film.

[0142] From the above analysis, it can be seen that the melt index of the film obtained in Examples 1-13 at 150°C is relatively moderate, and the film has a relatively suitable fluidity. While achieving effective bonding between the film and the glass, it can prevent the generation of bubbles, streaks, etc., and exhibits higher volume resistivity and better flexibility. Therefore, the present invention can simultaneously achieve improvements in the insulation, adhesion, flexibility and fluidity of photovoltaic films.

[0143] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0144] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A polyvinyl acetal film for photovoltaic use, It is characterized in that The invention comprises a three-layer structure, which comprises a first film layer, an intermediate film layer and a third film layer in sequence, wherein the first film layer, the intermediate film layer and the third film layer are respectively obtained by plasticizing and co-extruding a first film mixture, an intermediate film mixture and a third film mixture; The first layer film mixture and the third layer film mixture both include the following raw materials in parts by weight: 70-80 parts of polyvinyl acetal resin and 20-30 parts of plasticizer; The intermediate film mixture comprises the following raw materials by weight: 80-90 parts of polyvinyl acetal resin and 10-20 parts of plasticizer; The hydroxyl value of the polyvinyl acetal resin in the first layer film mixture and the third layer film mixture is 16.5 to 21.0%; The hydroxyl value of the polyvinyl acetal resin in the intermediate film mixture is ≤16.0%; During the plasticization of the intermediate film mixture, 10 to 45% of the total weight of the plasticizer in the intermediate film mixture and 100% of the total weight of the polyvinyl alcohol acetal resin in the intermediate film mixture are first mixed at 10 to 25° C. for 20 to 45 minutes to obtain a first mixture, and then the first mixture and the remaining raw materials are added to the extruder for plasticization; The plasticizer includes at least one of triethylene glycol diisooctanoate, dioctyl phthalate, dioctyl sebacate, tetraethylene glycol di-n-heptanoate, dimethyl phthalate, dioctyl adipate and dibutyl sebacate.

2. The photovoltaic polyvinyl acetal film according to claim 1, It is characterized in that The acetoxy content of the polyvinyl acetal resin in the first layer film mixture and the third layer film mixture is 0.5-2.0%.

3. The photovoltaic polyvinyl acetal film according to claim 1, It is characterized in that The acetoxy content of the polyvinyl acetal resin in the intermediate layer film mixture is 8.0-15.0%.

4. The photovoltaic polyvinyl acetal film according to claim 1, It is characterized in that The thickness ratio of the first film layer to the third film layer is 1:1; the thickness ratio of the intermediate film layer to the first film layer is 1-3:

1.

5. The photovoltaic polyvinyl acetal film according to claim 1, It is characterized in that The photovoltaic polyvinyl acetal film has a thickness of 0.18 to 3.4 mm, a melt index of 5.0 to 15.0 g / 10 min at 150° C., a knock value of 8 to 9, and a volume resistivity of more than 1.0×10 15 Ω·cm.

6. A photovoltaic polyvinyl acetal film according to any one of claims 1 to 5, It is characterized in that The hydroxyl value of the polyvinyl acetal resin in the intermediate layer film mixture is 9.0 to 16.0%.

7. A method for preparing a photovoltaic polyvinyl acetal film according to any one of claims 1 to 6, It is characterized in that The following steps are involved: The first film mixture, the middle film mixture and the third film mixture are plasticized by an extruder and then formed by a three-layer co-extrusion die to obtain a photovoltaic polyvinyl acetal film.

8. The method for preparing a photovoltaic polyvinyl acetal film according to claim 7, It is characterized in that The plasticizing temperatures of the first layer film mixture and the third layer film mixture are 110-200°C, the plasticizing temperature of the middle layer film mixture is 170-280°C, and the temperature of the three-layer co-extrusion die is 130-200°C.

9. A photovoltaic module, comprising a glass substrate, a first photovoltaic film, a battery chip, a second photovoltaic film, and a glass substrate stacked in sequence. It is characterized in that The first photovoltaic film and / or the second photovoltaic film is the photovoltaic polyvinyl acetal film according to any one of claims 1-6.

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