High water vapor barrier EVA graphene packaging adhesive film and preparation method thereof

Abstract

The invention discloses a high water vapor barrier EVA graphene packaging adhesive film and a preparation method thereof, and belongs to the technical field of functional polymer composite materials. The preparation method comprises the following steps: dropwise adding epichlorohydrin and an alkaline agent into a graphene oxide dispersion liquid, enabling the pH value of a reaction system to be greater than 12, keeping for a period of time to obtain a colloidal product, and then washing and drying to obtain the modified graphene oxide. The preparation method comprises the following steps: feeding 96.5 to 98.7 weight percent of EVA (Ethylene Vinyl Acetate) master batch, 1.2 to 3.2 weight percent of modified graphene oxide and 0.05 to 0.2 weight percent of initiator into an open mill for coarse mixing; and after the open milling is finished, putting the mixture into a double-screw extruder for blending and extruding to obtain a blend. The blend is placed in a mold to be subjected to hot-pressing cross-linking to form a film, and the EVA graphene packaging adhesive film is obtained after pressure relief and demolding. The packaging adhesive film obtained by the preparation method has high water vapor barrier property and excellent weather resistance, the preparation process is simple, the cost is low, and large-scale industrial production is facilitated.

Description

Technical Field

[0001] The present application relates to the field of functional polymer composite materials, and in particular to a high water vapor barrier EVA graphene encapsulation film and a preparation method thereof. Background Art

[0002] Ethylene-vinyl acetate copolymer (EVA) is a general-purpose polymer with good impact resistance, water resistance, high and low temperature resistance, ozone resistance, and environmental stress cracking resistance. It is widely used in foam materials, films, injection molding & blow molding products, wires and cables, hot melt adhesives, solar energy and other fields.

[0003] Especially in the photovoltaic field, nearly 75% of solar panels on the market use EVA as the packaging material for photovoltaic modules. During the use of photovoltaic modules, EVA packaging film, as one of the key raw materials in photovoltaic modules, can effectively prevent water, steam, dust, etc. from corroding crystalline silicon cells, and plays a decisive role in their service life. However, during long-term outdoor use, EVA film is affected by ultraviolet radiation, high temperature and high humidity environment, and will degrade or hydrolyze, resulting in aging phenomena such as discoloration, delamination, blistering, corrosion, etc., which greatly reduces the photoelectric conversion efficiency and service life of photovoltaic modules. Therefore, it is urgent to develop EVA packaging materials with high performance such as high water vapor barrier to meet market demand.

[0004] In order to improve the water vapor barrier performance of EVA encapsulation film, the existing technology often achieves this by coating a layer of nitride water barrier film on the surface of EVA (CN201711457739.5), or by adding an alkaline water barrier agent to eliminate or neutralize the small amount of free acetic acid contained in EVA and the acidic small molecular substances produced during the aging process. However, there are still problems such as poor internal bonding of the material and low comprehensive mechanical properties of the modified EVA, which cannot meet the existing technology and market demand. Summary of the invention

[0005] The purpose of this application is to construct a high water vapor barrier EVA graphene encapsulation film and a preparation method thereof, which has high water vapor barrier and excellent weather resistance, and the preparation process is simple and low cost, which is conducive to large-scale industrial production.

[0006] In a first aspect, the present application provides a method for preparing a high water vapor barrier EVA graphene encapsulation film, comprising:

[0007] (1) epichlorohydrin and an alkaline agent are added dropwise to a graphene oxide dispersion to make the pH value of the reaction system greater than 12 and maintain for a period of time to obtain a colloidal product, and then washed with water and dried to obtain modified graphene oxide;

[0008] (2) feeding 96.5-98.7 wt% of EVA masterbatch, 1.2-3.2 wt% of modified graphene oxide, and 0.05-0.2 wt% of initiator into an open mill for rough mixing; after the open milling is completed, the mixture is placed in a twin-screw extruder for blending and extrusion to obtain a blend;

[0009] (3) placing the blend in a mold for hot pressing and cross-linking to form a film, and releasing the pressure and demolding to obtain the EVA graphene encapsulation film.

[0010] In some embodiments, the step (1) comprises: adding epichlorohydrin and an alkaline agent to a graphene oxide dispersion at a temperature of 40 to 80° C., so that the pH value of the reaction system is greater than 12 and maintained for 2 to 6.5 hours to obtain a colloidal product, washing the colloidal product with water to obtain a pH value of 6.5 to 7, and obtaining modified graphene oxide after freeze-drying.

[0011] In some embodiments, the alkaline agent includes sodium hydroxide and / or potassium hydroxide.

[0012] In some embodiments, the mass ratio of the graphene oxide to the epichlorohydrin is 0.1-0.5:1.

[0013] In some embodiments, the graphene oxide is a sheet structure, and the width of the graphene oxide is 0.5 to 5 μm.

[0014] In some embodiments, the step (2) includes: feeding 96.5-98.7wt% EVA masterbatch, 1.2-3.2wt% modified graphene oxide, and 0.05-0.2wt% initiator into an open mill, and roughly mixing at 70-90°C for 1.3-3h; after the open mill is completed, placing them in a twin-screw extruder at a temperature of 80-100°C for blending and extrusion to obtain a blend.

[0015] In some embodiments, the initiator is an organic peroxide.

[0016] In some embodiments, the organic peroxide includes a mixture of one or more of diisopropylbenzene peroxide, di-tert-butyl peroxide, diisopropylbenzene hydroperoxide, 2,5-dimethyl-2,5-di-tert-butyl peroxyhexane, 4,4-di(tert-amylperoxy)butyl valerate, tert-butyl peroxy-2-ethylhexyl carbonate, and 3,3-di(tert-butylperoxy)hexyl butyrate.

[0017] In some embodiments, the step (3) includes: placing the blend in a mold with a diameter of 0.1 to 0.5 mm, setting the film forming pressure to 5 to 10 MPa, the film forming temperature to 120 to 160° C., and the pressure holding time to 30 to 60 min; after the temperature naturally drops to room temperature, the pressure is released and the mold is demolded to obtain the EVA graphene encapsulation film.

[0018] In some embodiments, the adhesive films are stacked and hot pressed by lamination, and the lamination can be a single-layer film or a multi-layer film.

[0019] In some embodiments, the single-layer film has a thickness of 0.1-0.5 mm.

[0020] In a second aspect, the present application provides a high water vapor barrier EVA graphene encapsulation film prepared by the above preparation method, wherein the thickness of the EVA graphene encapsulation film is 0.1 to 1 mm, and the vinyl acetate group content of the EVA graphene encapsulation film is 15 wt % to 35 wt %.

[0021] Compared with the prior art, the above solution of the present application can at least achieve the following advantages:

[0022] (1) By modifying the epoxy groups of graphene oxide, in-situ grafting of EVA is achieved, and the bonding force between graphene oxide and the EVA matrix is ​​enhanced without affecting the processing properties of EVA itself. In addition, the physical barrier layer of the EVA film is formed by the graphene sheet, thereby effectively reducing the water vapor permeability of the EVA film.

[0023] (2) The high water-resistance graphene-based EVA encapsulation film can be prepared simply and efficiently, and the method is simple and feasible and easy to industrialize. DETAILED DESCRIPTION

[0024] The present application provides a method for preparing a high water vapor barrier EVA graphene encapsulation film, comprising:

[0025] S110 Graphene oxide modification: epichlorohydrin and an alkaline agent are added dropwise to the graphene oxide dispersion to make the pH value of the reaction system greater than 12 and maintain for a period of time to obtain a colloidal product, which is then washed with water and dried to obtain modified graphene oxide.

[0026] Optionally, epichlorohydrin and an alkaline agent are added dropwise to a graphene oxide dispersion at a temperature of 40 to 80° C. to obtain a colloidal product after the pH value of the reaction system is greater than 12 and maintained for 2 to 6.5 hours. The colloidal product is washed with water to obtain a pH value of 6.5 to 7, and the modified graphene oxide is obtained after freeze-drying.

[0027] Furthermore, the alkaline agent includes sodium hydroxide and / or potassium hydroxide. The mass ratio of the graphene oxide to the epichlorohydrin is 0.1 to 0.5:1. The graphene oxide is a sheet structure, and the width of the graphene oxide is 0.5 to 5 μm.

[0028] Preparation of S120 graphene EVA composite material: 96.5-98.7wt% EVA masterbatch, 1.2-3.2wt% modified graphene oxide, and 0.05-0.2wt% initiator are fed into an open mill for rough mixing; after the open mill is completed, they are placed in a twin-screw extruder for blending and extrusion to obtain a blend.

[0029] Optionally, 96.5-98.7wt% EVA masterbatch, 1.2-3.2wt% modified graphene oxide, and 0.05-0.2wt% initiator are fed into an open mixer and roughly mixed at 70-90°C for 1.3-3h; after the open mixer is completed, the mixture is placed in a twin-screw extruder and extruded at a temperature of 80-100°C to obtain a blend.

[0030] Furthermore, the initiator is an organic peroxide, which includes a mixture of one or more of diisopropylbenzene peroxide, di-tert-butyl peroxide, diisopropylbenzene hydroperoxide, 2,5-dimethyl-2,5-di-tert-butyl peroxide hexane, 4,4-di(tert-amyl peroxy) valerate n-butyl ester, tert-butyl peroxy-2-ethylhexyl carbonate, and 3,3-di(tert-butyl peroxy) butyrate.

[0031] S130: placing the blend in a mold for hot pressing and cross-linking to form a film, and releasing the pressure and demoulding to obtain the EVA graphene encapsulation adhesive film.

[0032] Optionally, the step (3) comprises: placing the blend in a mold with a diameter of 0.1 to 0.5 mm, setting the film forming pressure to 5 to 10 MPa, the film forming temperature to 120 to 160° C., and the pressure holding time to 30 to 60 min; after the temperature naturally drops to room temperature, releasing the pressure and demolding to obtain the EVA graphene encapsulation film.

[0033] Furthermore, the adhesive film is stacked and hot pressed by lamination, and the lamination method can be a single-layer film or a multi-layer film. The thickness of the single-layer film is 0.1-0.5 mm.

[0034] In a second aspect, the present application provides a high water vapor barrier EVA graphene encapsulation film prepared by the above preparation method, wherein the thickness of the EVA graphene encapsulation film is 0.1 to 1 mm, and the vinyl acetate group content of the EVA graphene encapsulation film is 15 wt % to 35 wt %.

[0035] The present application can be better understood according to the following embodiments. However, it is easy for those skilled in the art to understand that the contents described in the embodiments are only used to illustrate the present application, and should not and will not limit the present application described in detail in the claims.

[0036] Example

[0037] A method for preparing a high water vapor barrier EVA graphene encapsulation film, comprising:

[0038] (1) 5 g of graphene oxide was dispersed in a deionized water solution and subjected to ultrasonic treatment for 15 min; the temperature was raised to 60° C., and then 1.5 g of epichlorohydrin was slowly added dropwise, and sodium hydroxide was added in batches, and the pH of the reaction system was maintained at 13 for 5 h, and a colloidal product was obtained. The colloidal product was washed with water to a pH value of 6.5, and the modified graphene oxide was obtained after freeze-drying.

[0039] (2) EVA (VA content of 28%) was fed into an open mill for refining at a temperature of 80°C. After the EVA formed a film on the roller, modified graphene oxide and initiator (diisopropylbenzene peroxide) were dripped onto the film and spread on the film with a scraper. After the film was dry, the rubber was cut and turned over continuously. After the rough mixing in the open mill, it was placed in a twin-screw extruder for co-extrusion, and the screw temperature was set to 100°C. The specific addition amounts of EVA masterbatch, modified graphene oxide, and initiator are shown in Table 1.

[0040] (3) The mixed and extruded blend is placed in a 0.4 mm mold, and the film forming pressure is set to 10 MPa, the film forming temperature is set to 100 °C, and the film forming time is set to 40 min; after the temperature naturally drops to room temperature, the pressure is released and the mold is demolded. The multilayer composite film is prepared in the order of EVA film-graphene EVA composite film-EVA film, and after being placed in the mold, it is first pressurized and the temperature is continuously raised while maintaining the pressure.

[0041] The water vapor transmission test was carried out according to the standard "GB 21529 Determination of water vapor transmission rate of plastic film and sheet by electrolytic sensing method", and the results are shown in Table 1.

[0042] Table 1 Preparation process and water vapor permeability of encapsulation film

[0043]

[0044]

[0045] It can be seen from Table 1 that the high water vapor barrier EVA graphene encapsulation film provided in the present application has better water vapor barrier performance. If pure EVA films are respectively bonded to the two surfaces of the composite film, the water vapor barrier performance of the encapsulation film can be further improved when the EVA graphene composite film is thinner.

[0046] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application claimed for protection, but only represents selected embodiments of the present application.

Claims

1. A method for preparing a high water vapor barrier EVA graphene encapsulation film, characterized in that: include: (1) epichlorohydrin and an alkaline agent are added dropwise to a graphene oxide dispersion to make the pH value of the reaction system greater than 12 and maintain for a period of time to obtain a colloidal product, and then washed with water and dried to obtain modified graphene oxide; (2) feeding 96.5-98.7 wt% of EVA masterbatch, 1.2-3.2 wt% of modified graphene oxide, and 0.05-0.2 wt% of initiator into an open mill for rough mixing; after the open milling is completed, the mixture is placed in a twin-screw extruder for blending and extrusion to obtain a blend; (3) placing the blend in a mold for hot pressing and cross-linking to form a film, and releasing the pressure and demolding to obtain the EVA graphene encapsulation film.

2. The preparation method according to claim 1, characterized in that: The step (1) comprises: adding epichlorohydrin and an alkaline agent dropwise to a graphene oxide dispersion at a temperature of 40 to 80° C., making the pH value of the reaction system greater than 12 and maintaining the pH value for 2 to 6.5 hours to obtain a colloidal product, washing the colloidal product with water to make its pH value 6.5 to 7, and obtaining modified graphene oxide after freeze-drying.

3. The preparation method according to claim 2, characterized in that: The alkaline agent includes sodium hydroxide and / or potassium hydroxide.

4. The preparation method according to claim 2, characterized in that: The mass ratio of the graphene oxide to the epichlorohydrin is 0.1 to 0.5:1; Or / and, the graphene oxide is a lamellar structure, and the width of the graphene oxide is 0.5 to 5 μm.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The step (2) comprises: feeding 96.5-98.7wt% of EVA masterbatch, 1.2-3.2wt% of modified graphene oxide, and 0.05-0.2wt% of initiator into an open mill, and roughly mixing them at 70-90°C for 1.3-3h; after the open milling is completed, placing them in a twin-screw extruder at a temperature of 80-100°C for blending and extrusion to obtain a blend.

6. The preparation method according to claim 5, characterized in that: The initiator is an organic peroxide.

7. The preparation method according to claim 6, characterized in that: The organic peroxide includes a mixture of one or more of diisopropylbenzene peroxide, di-tert-butyl peroxide, diisopropylbenzene hydroperoxide, 2,5-dimethyl-2,5-di-tert-butyl peroxyhexane, 4,4-di(tert-amylperoxy)butyl valerate, tert-butyl peroxy-2-ethylhexyl carbonate, and 3,3-di(tert-butylperoxy)hexyl butyrate.

8. The preparation method according to any one of claims 1 to 4, characterized in that: The step (3) comprises: placing the blend in a mold with a diameter of 0.1 to 0.5 mm, setting the film forming pressure to 5 to 10 MPa, the film forming temperature to 120 to 160° C., and the pressure holding time to 30 to 60 min; after the temperature naturally drops to room temperature, releasing the pressure and demolding to obtain the EVA graphene encapsulation film.

9. The preparation method according to claim 8, characterized in that: The adhesive films are stacked and hot pressed by lamination, and the lamination can be a single-layer film or a multi-layer film; The thickness of the single-layer film is 0.1-0.5 mm.

10. A high water vapor barrier EVA graphene encapsulation film, characterized in that: The EVA graphene encapsulation film is prepared by the preparation method according to any one of claims 1 to 9, wherein the thickness of the EVA graphene encapsulation film is 0.1 to 1 mm, and the vinyl acetate group content of the EVA graphene encapsulation film is 15 wt% to 35 wt%.

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