Process for the preparation of ethylene-vinyl acetate copolymers, ethylene-vinyl acetate copolymers and their use

Abstract

The application relates to the field of high polymer materials, and discloses a method for preparing ethylene-vinyl acetate copolymer, the ethylene-vinyl acetate copolymer and application thereof. The method comprises the following steps: (1) in the presence of organic peroxide, ethylene and vinyl acetate are subjected to polymerization reaction in a loop reactor to obtain a melt I; (2) the melt I is subjected to melt blending granulation in a double-screw extruder together with an antioxidant to obtain the ethylene-vinyl acetate copolymer. The ethylene-vinyl acetate copolymer prepared by the method has high transmittance, high volume resistivity, few crystal points, low yellow index and excellent mechanical properties, and can meet the performance requirements of photovoltaic adhesive films.

Description

Technical Field

[0001] This invention relates to the field of polymer materials, and more specifically, to a method for preparing ethylene-vinyl acetate copolymer, the ethylene-vinyl acetate copolymer, and its applications. Background Technology

[0002] In recent years, the global photovoltaic power generation industry has shown a good development trend, with the output and installation volume of photovoltaic modules continuously increasing. my country has become a major consumer of EVA resin for solar cell encapsulation films.

[0003] Currently, the vinyl acetate (VA) content of EVA resin used in photovoltaic films on the market is generally above 25 wt%, typically around 28 wt%. However, the higher the VA content, the more severe the corrosion to high-voltage equipment, and the higher the requirements for the equipment. Prolonged production of products with high VA content will reduce the service life of the equipment. Summary of the Invention

[0004] The purpose of this invention is to overcome the aforementioned defects in the prior art and, while ensuring high light transmittance, provide an ethylene-vinyl acetate copolymer with low VA content, high volume resistivity, and low yellow index.

[0005] To achieve the above objectives, a first aspect of the present invention provides a method for preparing an ethylene-vinyl acetate copolymer, the method comprising:

[0006] (1) In the presence of organic peroxides, ethylene and vinyl acetate are polymerized in a loop reactor to obtain melt I;

[0007] (2) Melt I and antioxidant are melt-blended and granulated in a twin-screw extruder to obtain the ethylene-vinyl acetate copolymer;

[0008] The antioxidant is added to the twin-screw extruder at a feed rate of 3-20 kg / h.

[0009] The ethylene feed rate is 20-22 t / h, and the vinyl acetate pumping speed is 300-400 rpm.

[0010] In step (1), the conditions for the polymerization reaction must at least satisfy: temperature of 190-310℃ and pressure of 260-320MPa;

[0011] In step (2), the conditions for melt blending granulation must at least meet the following requirements: temperature of 150-220℃ and extrusion speed of 200-400rpm.

[0012] A second aspect of the present invention provides an ethylene-vinyl acetate copolymer prepared by the method described in the first aspect above.

[0013] A third aspect of the present invention provides the application of the ethylene-vinyl acetate copolymer described in the second aspect above in the preparation of photovoltaic films.

[0014] The ethylene-vinyl acetate copolymer prepared by the method provided in this invention has high transmittance, high volume resistivity, fewer crystal points, low yellow index, and excellent mechanical properties, which can meet the performance requirements of photovoltaic films. Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] As previously described, a first aspect of the present invention provides a method for preparing an ethylene-vinyl acetate copolymer, the method comprising:

[0017] (1) In the presence of organic peroxides, ethylene and vinyl acetate are polymerized in a loop reactor to obtain melt I;

[0018] (2) Melt I and antioxidant are melt-blended and granulated in a twin-screw extruder to obtain the ethylene-vinyl acetate copolymer;

[0019] The antioxidant is added to the twin-screw extruder at a feed rate of 3-20 kg / h.

[0020] The ethylene feed rate is 20-22 t / h, and the vinyl acetate pumping speed is 300-400 rpm.

[0021] In step (1), the conditions for the polymerization reaction must at least satisfy: temperature of 190-310℃ and pressure of 260-320MPa;

[0022] In step (2), the conditions for melt blending granulation must at least meet the following requirements: temperature of 150-220℃ and extrusion speed of 200-400rpm.

[0023] Preferably, the feed rate of the antioxidant is 5-10 kg / h. The inventors of this invention have discovered that products prepared from ethylene-vinyl acetate copolymers obtained under this preferred condition exhibit better resistance to yellowing.

[0024] Preferably, the organic peroxide is selected from at least one of tert-butyl peroxide 3,5,5-trimethylhexanoate, (bis)-3,5,5-trimethylhexanoyl peroxide, tert-butyl peroxide benzoate, tert-butyl peracetate, tert-butyl peroxypentanoate, tert-butyl peroxypentanoate, and tert-butyl peroxyneodecanate.

[0025] In a preferred embodiment, the antioxidant is selected from at least one of hindered phenolic antioxidants, hindered amine antioxidants, and phosphite antioxidants.

[0026] Preferably, the hindered phenolic antioxidant is selected from at least one of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester (antioxidant 1076), pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010), and 2,6-di-tert-butyl-p-cresol (antioxidant BHT); the hindered amine antioxidant is selected from poly(4-hydroxyethyl-2,2,6,6-tetramethyl-1-piperidineethanol) ester (light stabilizer 6). 22) At least one of bis-2,2,6,6-tetramethylpiperidinol sebacate (light stabilizer 770) and [(3,5-di-tert-butyl-4-hydroxyphenyl)methyl]butylmalonate di(1,2,2,6,6-pentamethyl-4-piperidinol) ester (light stabilizer 144); the phosphite antioxidant is selected from at least one of bis(octadecyl pentaerythritol diphosphite) (antioxidant 619) and tris(2,4-di-tert-butylphenyl) phosphite (antioxidant 168).

[0027] More preferably, the antioxidant is a combination of antioxidant 619 and antioxidant 1076.

[0028] As previously stated, a second aspect of the present invention provides an ethylene-vinyl acetate copolymer prepared by the method described in the first aspect.

[0029] Preferably, the melt flow rate of the ethylene-vinyl acetate copolymer is 15-25 g / 10 min, and the vinyl acetate content is 15-22 wt%.

[0030] More preferably, the melt flow rate of the ethylene-vinyl acetate copolymer is 18-22 g / 10 min, and the vinyl acetate content is 18-20 wt%.

[0031] Preferably, the yellow index of the ethylene-vinyl acetate copolymer is <1.

[0032] As previously stated, a third aspect of the present invention provides the application of the ethylene-vinyl acetate copolymer described in the second aspect above in the preparation of photovoltaic films.

[0033] The present invention will be described in detail below through examples.

[0034] In the following examples, unless otherwise specified, all raw materials used were commercially purchased.

[0035] Ethylene: Produced by Yanshan Petrochemical Company.

[0036] Vinyl acetate: Produced by Yanshan Petrochemical Company.

[0037] Organic peroxide: tert-butyl peroxide 3,5,5-trimethylhexanoate, purchased from AKZO.

[0038] Antioxidant I: Phosphite antioxidant, Antioxidant 619, brand name JYANOX-619, purchased from Beijing Jiyi Holdings Group Co., Ltd.

[0039] Antioxidant II: Hindered phenolic antioxidant, antioxidant 1076, brand name Irganox1076, purchased from BASF.

[0040] Example 1

[0041] (1) Ethylene and organic peroxide were added to a loop reactor at a rate of 20t / h. The temperature of the reactor was controlled at 250℃ and the pressure at 300MPa. Vinyl acetate was pumped in at a speed of 330rpm to carry out the polymerization reaction and obtain melt I.

[0042] (2) Add the melt I to a twin-screw extruder, control the temperature of the extruder to 190°C and the rotation speed to 350 rpm, add antioxidant 1076 and antioxidant 619 (the weight ratio of the two is 1:1) to the twin-screw extruder at a feed rate of 7 kg / h for melt blending and granulation to obtain EVA-1.

[0043] The specific parameters and processes of this embodiment are listed in Table 1.

[0044] Example 2

[0045] This embodiment uses a similar method to Example 1, except that the pump speed for vinyl acetate is 360 rpm, and all other conditions are the same as in Example 1, resulting in EVA-2, as detailed in Table 1.

[0046] Example 3

[0047] This embodiment uses a similar method to Example 1, except that the pump speed for vinyl acetate is 400 rpm, and all other conditions are the same as in Example 1, resulting in EVA-3, as detailed in Table 1.

[0048] Example 4

[0049] This embodiment uses a similar method to Example 1, except that the reactor temperature is controlled at 310°C, while all other conditions are the same as in Example 1, resulting in EVA-4, as detailed in Table 1.

[0050] Example 5

[0051] This embodiment uses a similar method to Example 1, except that antioxidant 1076 and antioxidant 619 (in a weight ratio of 1:1) are added to a twin-screw extruder at a feed rate of 4 kg / h for melt blending and granulation. All other conditions are the same as in Example 1, and EVA-5 is obtained. See Table 1 for details.

[0052] Comparative Example 1

[0053] This comparative example was conducted using a method similar to that of Example 1, except that the pump speed for vinyl acetate was 470 rpm, and all other conditions were the same as in Example 1, resulting in EVA-D1, as detailed in Table 1.

[0054] Comparative Example 2

[0055] This comparative example was conducted using a method similar to that of Example 1, except that no antioxidant was added and all other conditions were the same as in Example 1, resulting in EVA-D2, as detailed in Table 1.

[0056] Comparative Example 3

[0057] This comparative example was carried out using a method similar to that of Example 1, except that the polymerization pressure was 350 MPa, and all other conditions were the same as in Example 1, resulting in EVA-D3, as detailed in Table 1.

[0058] Comparative Example 4

[0059] This comparative example was carried out using a method similar to that of Example 1, except that the polymerization temperature was 180°C, and all other conditions were the same as in Example 1, resulting in EVA-D4, as detailed in Table 1.

[0060] Comparative Example 5

[0061] This comparative example was conducted using a method similar to that of Example 1, except that the extruder temperature was 240°C, and all other conditions were the same as in Example 1, resulting in EVA-D5, as detailed in Table 1.

[0062] Test case

[0063] The EVA granules prepared in the examples and comparative examples were mixed with 0.8 wt% crosslinking initiator (TBEC), 0.1 wt% UV absorber (UV-326), 0.3 wt% silane coupling agent (KH-570), and 0.2 wt% co-crosslinking agent (TMPTMA) based on the total weight of the EVA granules. The mixture was then processed into a 400 μm thick film using a casting film machine (model ME-30 / 5200, manufacturer: OCS, Germany). The specific processing parameters were: processing temperature 100℃, extrusion speed 7 rpm, and traction speed 2 m / min. The performance test results are shown in Table 2. The specific test methods are as follows:

[0064] (1) Melt mass flow rate: The test was conducted according to the method specified in GB / T 3682.1-2018. Specifically, the test temperature was 190℃ and the load was 2.16 kg.

[0065] (2) Tensile properties: The EVA granules were tested according to the method specified in GB / T 1040.2-2006, specifically at a test speed of 100 mm / min; the films were tested according to the method specified in GB / T 1040.3-2006, specifically at a test speed of 500 mm / min.

[0066] (3) Vinyl acetate content: determined according to the method specified in GB / T 30925-2014.

[0067] (4) Light transmittance: The transmittance shall be determined in accordance with the method specified in GB / T 2410-2008.

[0068] (5) Crystal point: The crystal point was determined according to the method specified in Q / SZSY.07.10-2008.

[0069] (6) Surface resistance and volume resistance: measured according to the methods specified in GB / T 1410-2006.

[0070] (7) Yellow index: The yellow index shall be determined according to the method specified in HG / T 3862-2006.

[0071] (8) Degree of crosslinking: determined by xylene extraction method.

[0072] Table 1

[0073] Polymerization reaction Ethylene consumption (t / h) 20 20 20 20 20 Vinyl acetate pump speed (rpm) 330 360 400 330 330 Temperature (°C) 250 250 250 310 250 Pressure (MPa) 300 300 300 300 300 Melt blending granulation Temperature (°C) 190 190 190 190 190 Rotational speed (rpm) 350 350 350 350 350 Antioxidant feed rate (kg / h) 7 7 7 7 4 name EVA-1 EVA-2 EVA-3 EVA-4 EVA-5

[0074] Continued from Table 1

[0075]

[0076]

[0077] Table 2

[0078]

[0079] Continued from Table 2

[0080]

[0081] As can be seen from the results in Table 2, the EVA granules prepared by the method provided by the present invention have high volume resistivity and good mechanical properties after being processed into films, and the light transmittance is above 90%. The yellowing degree of both the granules and the films after aging is low.

[0082] Furthermore, the results in Table 2 also show that the EVA granules in Comparative Example 1 had a higher VA content, resulting in a lower volume resistivity and decreased mechanical properties. Comparative Example 2 did not contain any antioxidants, and the excessively high extrusion processing temperature in Comparative Example 5 caused severe yellowing of the product, resulting in a high yellow index, which did not meet the standards for photovoltaic film products. Additionally, the excessively high processing temperature in Comparative Example 5 made pelletizing difficult. The melt flow rates in Comparative Examples 3 and 4 were too low, requiring higher processing temperatures, leading to high energy consumption. Low-temperature processing resulted in uneven mixing of various additives during film preparation, leading to uneven film performance and low crosslinking degree.

[0083] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A process for the production of ethylene-vinyl acetate copolymer, characterized in that, The method includes: (1) In the presence of organic peroxides, ethylene and vinyl acetate are polymerized in a loop reactor to obtain melt I; (2) The melt I and the antioxidant are melt-blended and granulated in a twin-screw extruder to obtain the ethylene-vinyl acetate copolymer; The antioxidant is added to the twin-screw extruder at a feed rate of 3-20 kg / h. The ethylene feed rate is 20-22 t / h, and the vinyl acetate pumping speed is 300-400 rpm. In step (1), the conditions for the polymerization reaction must at least satisfy: temperature of 190-310℃ and pressure of 260-320MPa; In step (2), the conditions for melt blending granulation must at least meet the following requirements: temperature of 150-220℃ and extrusion speed of 200-400 rpm; The melt flow rate of the ethylene-vinyl acetate copolymer is 15-25 g / 10 min, and the vinyl acetate content is 15-22 wt%.

2. The method of claim 1, wherein, The feed rate of the antioxidant is 5-10 kg / h.

3. The method of claim 1 or 2, wherein, The organic peroxide is selected from at least one of the following: tert-butyl peroxide 3,5,5-trimethylhexanoate, (bis)-3,5,5-trimethylhexanoyl peroxide, tert-butyl peroxide benzoate, tert-butyl peracetate, tert-butyl peroxypentanoate, tert-butyl peroxyneoplastate, and tert-butyl peroxyneodecanate.

4. The method of claim 1 or 2, wherein, The antioxidant is selected from at least one of hindered phenolic antioxidants, hindered amine antioxidants, and phosphite antioxidants.

5. The method of claim 4, wherein, The hindered phenolic antioxidant is selected from at least one of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 2,6-di-tert-butyl-p-cresol; the hindered amine antioxidant is selected from at least one of poly(4-hydroxyethyl-2,2,6,6-tetramethyl-1-piperidinol) succinate, bis-2,2,6,6-tetramethylpiperidinol sebacate, and di(1,2,2,6,6-pentamethyl-4-piperidinyl) butylmalonate; the phosphite antioxidant is selected from at least one of dioctadecyl pentaerythritol diphosphite and tris(2,4-di-tert-butylphenyl) phosphite.

6. An ethylene-vinyl acetate copolymer prepared by the method according to any one of claims 1-5, wherein the melt mass flow rate of the ethylene-vinyl acetate copolymer is 15-25 g / 10 min and the vinyl acetate content is 15-22 wt%.

7. The ethylene-vinyl acetate copolymer according to claim 6, wherein, The melt flow rate of the ethylene-vinyl acetate copolymer is 18-22 g / 10 min, and the vinyl acetate content is 18-20 wt%.

8. The ethylene-vinyl acetate copolymer according to claim 6 or 7, wherein The yellow index of the ethylene-vinyl acetate copolymer is <1.

9. The use of the ethylene-vinyl acetate copolymer according to any one of claims 6-8 in the preparation of photovoltaic films.

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