A method for preparing modified ethylene-vinyl acetate copolymer, the modified ethylene-vinyl acetate copolymer and its applications

Abstract

This invention relates to the field of polymer materials, and discloses a method for preparing modified ethylene-vinyl acetate copolymer, the modified ethylene-vinyl acetate copolymer, and its applications. The method includes: melt extruding ethylene-vinyl acetate copolymer, low-density polyethylene, a silane coupling agent, and an antioxidant in a twin-screw extruder to obtain the modified ethylene-vinyl acetate copolymer. When the modified ethylene-vinyl acetate copolymer prepared using the method provided by this invention is used as an adhesive coating for a pre-coated film, no primer is required, which simplifies the pre-coated film preparation process, reduces the amount of adhesive applied, and improves the production efficiency of the pre-coated film.

Description

Technical Field

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

[0002] Pre-coated films typically consist of a substrate layer, a base layer, and a hot melt adhesive layer. They are widely used for sealing and protecting card materials such as ID cards, historical documents, photos, and credit cards; for protecting the outer packaging of items such as books, cartons, and medicine boxes; and for food packaging.

[0003] The substrate layer is usually a biaxially oriented polyester (BOPET) film or a biaxially oriented polypropylene (BOPP) film, with a thickness of 12-20 μm. BOPP film has the characteristics of high transparency, good gloss, non-toxicity, odorless, water resistance, heat resistance, low price, and soft texture, making it an ideal material for the lamination process. The bottom coating layer is usually a high molecular weight polyethyleneimine aqueous solution (AC agent). The hot melt adhesive layer is usually ethylene-vinyl acetate (EVA) resin, with a thickness of 5-15 μm.

[0004] Because existing EVA coatings on BOPP films exhibit poor adhesion, an AC agent is often applied to the BOPP film before EVA coating. However, AC agents typically contain large amounts of organic solvents such as methanol and ethanol. After coating, the AC agent solvent needs to be dried to form a base coating on the BOPP film surface. This not only poses a risk of flammability and explosion but also results in significant energy waste due to the long drying tunnels and high heat required for drying the AC agent solvent. Summary of the Invention

[0005] The purpose of this invention is to reduce the amount of primer used while ensuring high bonding strength between ethylene-vinyl acetate resin as a hot melt adhesive bonding coating in a pre-coated film and the substrate layer.

[0006] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a modified ethylene-vinyl acetate copolymer, the method comprising:

[0007] Ethylene-vinyl acetate copolymer, low-density polyethylene, silane coupling agent and antioxidant are melt-extruded in a twin-screw extruder;

[0008] The weight ratio of the ethylene-vinyl acetate copolymer, the low-density polyethylene, and the silane coupling agent is 100:10-50:1-20.

[0009] Based on a total usage of 100 parts by weight of the ethylene-vinyl acetate copolymer, the low-density polyethylene, and the silane coupling agent, the amount of the antioxidant is 0.01-0.2 parts by weight.

[0010] The low-density polyethylene has a melt flow rate of 5-20 g / 10 min at 190℃ and under a load of 2.16 kg, a weight-average molecular weight greater than 500,000, and a molecular weight distribution coefficient greater than 20.

[0011] The conditions for melt extrusion molding must at least satisfy the following: the twin-screw extruder comprises five sections along the material conveying direction, the temperatures of the five sections are sequentially 150-160℃, 150-170℃, 160-200℃, 160-200℃ and 150-170℃, the vacuum degree of each of the five sections is independently 0.02MPa-0.09MPa, and the rotational speed of the twin-screw extruder is 200-400rpm.

[0012] A second aspect of the present invention provides a modified 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 modified ethylene-vinyl acetate copolymer described in the second aspect above in the preparation of a pre-coated film.

[0014] A fourth aspect of the present invention provides a pre-coated film in which the adhesive coating is obtained by coating extrusion molding of the modified ethylene-vinyl acetate copolymer described in the second aspect above in a single screw extruder.

[0015] The modified ethylene-vinyl acetate copolymer prepared by the method provided by this invention can be used as an adhesive coating for a pre-coated film without the need for a primer, which simplifies the preparation process of the pre-coated film, reduces the amount of adhesive applied, and improves the production efficiency of the pre-coated film. Detailed Implementation

[0016] 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.

[0017] It should be noted that the vinyl acetate content in this invention is also the content of vinyl acetate structural units.

[0018] It should be noted that the formula for calculating the molecular weight distribution coefficient in this invention is: Molecular weight distribution coefficient = weight-average molecular weight / number-average molecular weight.

[0019] As previously stated, a first aspect of the present invention provides a method for preparing a modified ethylene-vinyl acetate copolymer, the method comprising:

[0020] Ethylene-vinyl acetate copolymer, low-density polyethylene, silane coupling agent and antioxidant are melt-extruded in a twin-screw extruder;

[0021] The weight ratio of the ethylene-vinyl acetate copolymer, the low-density polyethylene, and the silane coupling agent is 100:10-50:1-20.

[0022] Based on a total usage of 100 parts by weight of the ethylene-vinyl acetate copolymer, the low-density polyethylene, and the silane coupling agent, the amount of the antioxidant is 0.05-0.2 parts by weight.

[0023] The low-density polyethylene has a melt flow rate of 5-20 g / 10 min at 190℃ and under a load of 2.16 kg, a weight-average molecular weight greater than 500,000, and a molecular weight distribution coefficient greater than 20.

[0024] The conditions for melt extrusion molding must at least satisfy the following: the twin-screw extruder comprises five sections along the material conveying direction, the temperatures of the five sections are sequentially 150-160℃, 150-170℃, 160-200℃, 160-200℃ and 150-170℃, the vacuum degree of each of the five sections is independently 0.02MPa-0.09MPa, and the rotational speed of the twin-screw extruder is 200-400rpm.

[0025] Preferably, the weight ratio of the ethylene-vinyl acetate copolymer, the low-density polyethylene, and the silane coupling agent is 100:10-35:1-15.

[0026] In a preferred embodiment, the amount of antioxidant is 0.1-0.2 parts by weight, based on a total amount of 100 parts by weight of the ethylene-vinyl acetate copolymer, the low-density polyethylene, and the silane coupling agent.

[0027] Preferably, the length-to-diameter ratio of the twin-screw extruder is 30-53:1.

[0028] The inventors of this invention have discovered that when the vinyl acetate content in the ethylene-vinyl acetate copolymer is too low, the modified ethylene-vinyl acetate copolymer prepared has poor adhesion; while when the vinyl acetate content in the ethylene-vinyl acetate copolymer is too high, the modified ethylene-vinyl acetate copolymer prepared has a large shrinkage defect during processing.

[0029] The inventors of this invention have also discovered that when the melt flow rate of the ethylene-vinyl acetate copolymer is too low, the flowability of the modified ethylene-vinyl acetate copolymer prepared using it is poor, and the adhesion between the prepared modified ethylene-vinyl acetate copolymer and the substrate is reduced; while when the melt flow rate of the ethylene-vinyl acetate copolymer is too high, the strength of the prepared modified ethylene-vinyl acetate copolymer is reduced, which in turn increases its shrinkage during processing.

[0030] Preferably, the ethylene-vinyl acetate copolymer has a melt flow rate of 10-30 g / 10 min at 190°C and a load of 2.16 kg, and the vinyl acetate content is 15-25 wt%.

[0031] More preferably, the ethylene-vinyl acetate copolymer has a melt flow rate of 15-25 g / 10 min at 190°C and a load of 2.16 kg, and a vinyl acetate content of 15-20 wt%.

[0032] In a preferred embodiment, the silane coupling agent is selected from at least one of γ-(methacryloyloxy)propyltrimethoxysilane (KH570), γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH560), and γ-aminopropyltriethoxysilane (KH550).

[0033] Preferably, the antioxidant is selected from at least one of phenolic antioxidants and phosphite antioxidants.

[0034] In a preferred embodiment, the phenolic antioxidant is selected from at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010), octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1076), 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanuric acid (antioxidant 3114), and 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene (antioxidant 330);

[0035] The phosphite antioxidant is selected from at least one of tris(2,4-di-tert-butylphenyl) phosphite (antioxidant 168), bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite (antioxidant 626), and bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite (antioxidant PEP-36).

[0036] According to a preferred embodiment, the antioxidant is a combination of antioxidant 1010 and antioxidant 168, and the weight ratio of antioxidant 1010 to antioxidant 168 is 1:1-2.

[0037] As previously stated, a second aspect of the present invention provides a modified ethylene-vinyl acetate copolymer prepared by the method described in the first aspect.

[0038] Preferably, the modified ethylene-vinyl acetate copolymer has an average particle size of 0.5-3 mm.

[0039] As previously stated, a third aspect of the present invention provides the application of the modified ethylene-vinyl acetate copolymer described in the second aspect above in the preparation of a pre-coated film.

[0040] As previously stated, a fourth aspect of the present invention provides a pre-coated film in which the adhesive coating is obtained by coating extrusion molding of the modified ethylene-vinyl acetate copolymer described in the second aspect in a single-screw extruder.

[0041] Preferably, the conditions for coating extrusion molding are at least: the extrusion temperature of the single-screw extruder is 190-240℃, the rotation speed of the single-screw extruder is 100-400rpm, and the length-to-diameter ratio of the single-screw extruder is 30-53:1.

[0042] Preferably, the thickness of the adhesive coating in the pre-coated film is 5-15 μm.

[0043] The present invention will be described in detail below through examples.

[0044] In the following examples, unless otherwise specified, all raw materials used were commercially purchased.

[0045] In the following examples, unless otherwise specified, each part by weight represents 1 kg.

[0046] In the following examples, the length-to-diameter ratio of both the twin-screw extruder and the single-screw extruder is 45:1.

[0047] Ethylene-vinyl acetate copolymer: purchased from Yanshan Petrochemical, grade EVA19F16, VA content 18wt%, melt mass flow rate 16g / 10min.

[0048] Low-density polyethylene I: purchased from Yanshan Petrochemical, grade 1C7A, melt flow rate 7g / 10min, weight-average molecular weight 600,000, molecular weight distribution coefficient 30.

[0049] Low-density polyethylene II: purchased from Yanshan Petrochemical, grade 1C7A-GD, melt flow rate 7.5 g / 10 min, weight-average molecular weight 300,000, molecular weight distribution coefficient 12.

[0050] Low-density polyethylene III: purchased from Yanshan Petrochemical, grade 1I2A, melt flow rate 2g / 10min, weight-average molecular weight 650,000, molecular weight distribution coefficient 35.

[0051] Silane coupling agent: KH550, purchased from Qufu Chenguang Chemical Co., Ltd.

[0052] Antioxidant 1010: Purchased from Shijiazhuang Jiatuo Chemical Technology Co., Ltd.

[0053] Antioxidant 168: Purchased from Shijiazhuang Jiatuo Chemical Technology Co., Ltd.

[0054] Example 1

[0055] 85 parts by weight of ethylene-vinyl acetate copolymer, 10 parts by weight of low-density polyethylene I, 5 parts by weight of silane coupling agent, 0.05 parts by weight of antioxidant 1010 and 0.1 parts by weight of antioxidant 168 were added to a twin-screw extruder. Along the material conveying direction, the temperatures of the five sections of the twin-screw extruder were set to 155℃, 160℃, 170℃, 170℃ and 160℃, and the vacuum degrees of the five sections were 0.03MPa, 0.03MPa, 0.03MPa and 0.03MPa, respectively. The extruder speed was set to 300 rpm for melt extrusion molding to obtain modified ethylene-vinyl acetate copolymer G1 with an average particle size of 3 mm.

[0056] Example 2

[0057] 75 parts by weight of ethylene-vinyl acetate copolymer, 17 parts by weight of low-density polyethylene I, 8 parts by weight of silane coupling agent, 0.05 parts by weight of antioxidant 1010 and 0.1 parts by weight of antioxidant 168 were added to a twin-screw extruder. Along the material conveying direction, the temperatures of the five sections of the twin-screw extruder were set to 160℃, 165℃, 175℃, 175℃ and 165℃, and the vacuum degrees of the five sections were 0.04MPa, 0.04MPa, 0.04MPa and 0.04MPa, respectively. The extruder speed was set to 350 rpm for melt extrusion molding to obtain modified ethylene-vinyl acetate copolymer G2 with an average particle size of 3 mm.

[0058] Comparative Example 1

[0059] This comparative example was conducted using a method similar to that of Example 1, except that the amounts of raw materials were different. Specifically, 65 parts by weight of ethylene-vinyl acetate copolymer, 10 parts by weight of low-density polyethylene I, 25 parts by weight of silane coupling agent, 0.05 parts by weight of antioxidant 1010 and 0.1 parts by weight of antioxidant 168 were used, and the remaining conditions were the same as in Example 1, resulting in modified ethylene-vinyl acetate copolymer DG1.

[0060] Comparative Example 2

[0061] This comparative example was conducted using a method similar to that of Example 1, except that the amounts of raw materials were different. Specifically, 90 parts by weight of ethylene-vinyl acetate copolymer, 10 parts by weight of low-density polyethylene I, 0.05 parts by weight of antioxidant 1010 and 0.1 parts by weight of antioxidant 168 were used, and silane coupling agents were not used. All other conditions were the same as in Example 1, resulting in modified ethylene-vinyl acetate copolymer DG2.

[0062] Comparative Example 3

[0063] This comparative example was conducted using a method similar to that of Example 1, except that the amounts of raw materials were different. Specifically, 85 parts by weight of ethylene-vinyl acetate copolymer, 5 parts by weight of low-density polyethylene I, and 10 parts by weight of silane coupling agent were used. No antioxidant was used, and all other conditions were the same as in Example 1, resulting in modified ethylene-vinyl acetate copolymer DG3.

[0064] Comparative Example 4

[0065] This comparative example was conducted using a method similar to that of Example 1, except that the amounts of raw materials were different. Specifically, 90 parts by weight of ethylene-vinyl acetate copolymer, 10 parts by weight of silane coupling agent, 0.05 parts by weight of antioxidant 1010 and 0.1 parts by weight of antioxidant 168 were used, and the remaining conditions were the same as in Example 1, resulting in modified ethylene-vinyl acetate copolymer DG4.

[0066] Comparative Example 5

[0067] This comparative example was conducted using a method similar to that of Example 1, except that low-density polyethylene I was replaced by low-density polyethylene II in equal weight, while all other conditions remained the same as in Example 1, resulting in modified ethylene-vinyl acetate copolymer DG5.

[0068] Comparative Example 6

[0069] This comparative example was conducted using a method similar to that of Example 1, except that low-density polyethylene I was replaced by low-density polyethylene III in equal weight, while all other conditions remained the same as in Example 1, resulting in modified ethylene-vinyl acetate copolymer DG6.

[0070] Comparative Example 7

[0071] This comparative example was conducted using a method similar to that of Example 1, except that a single-screw extruder was used for melt extrusion molding, and all other conditions were the same as in Example 1, resulting in modified ethylene-vinyl acetate copolymer DG7.

[0072] Comparative Example 8

[0073] This comparative example was conducted using a method similar to that of Example 1, except that the temperatures of the five sections along the material conveying direction were 155°C, 160°C, 240°C, 180°C, and 160°C respectively, while the other conditions were the same as in Example 1, resulting in modified ethylene-vinyl acetate copolymer DG8.

[0074] Test case

[0075] The modified ethylene-vinyl acetate copolymers prepared in the examples and comparative examples were extruded and coated onto BOPET substrates using a single-screw extruder to a thickness of 10 μm, resulting in a pre-coated film. The pre-coated film was then subjected to the following tests, and the results are shown in Table 1. The conditions for the single-screw extruder were: extrusion temperature of 235°C and extrusion speed of 400 rpm.

[0076] (1) Peel strength: The peel strength between the adhesive coating and the BOPET substrate in the pre-coated film was tested according to the test method in GB / T 2790-1995.

[0077] (2) Width reduction: Under the condition of an extrusion speed of 200m / min, calculate the difference between the width of the extruder die and the width of the modified EVA film on the substrate.

[0078] (3) Maximum processing speed: The highest processing speed that can be achieved when the shrinkage is controlled within 3cm.

[0079] (4) Oxidation induction period: The oxidation induction period of the modified EVA film was tested according to the test method in GB19466.4-2009 at a temperature of 190℃.

[0080] Table 1

[0081] Example 1 4.9 2.5 200 32.6 Example 2 4.6 2.0 200 33.1 Comparative Example 1 5.5 3.5 170 32.5 Comparative Example 2 1.2 2.0 200 31.8 Comparative Example 3 4.4 3.5 150 0.3 Comparative Example 4 5.2 5.5 150 32.3 Comparative Example 5 4.8 4.5 160 31.9 Comparative Example 6 4.2 2.8 130 31.6 Comparative Example 7 3.8 3.3 150 23.2 Comparative Example 8 4.8 3.2 160 16.5

[0082] As can be seen from the results in Table 1, the modified ethylene-vinyl acetate copolymer prepared by the method provided in this invention has good adhesion properties (peel strength and oxidation induction time) and processing properties (shrinkage and maximum processing speed) to the substrate when used as an adhesive coating for a pre-coated film.

[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 method for preparing modified ethylene-vinyl acetate copolymer, characterized in that, The method includes: Ethylene-vinyl acetate copolymer, low-density polyethylene, silane coupling agent and antioxidant are melt-extruded in a twin-screw extruder; The weight ratio of the ethylene-vinyl acetate copolymer, the low-density polyethylene, and the silane coupling agent is 100:10-50:1-20. Based on a total usage of 100 parts by weight of the ethylene-vinyl acetate copolymer, the low-density polyethylene, and the silane coupling agent, the amount of the antioxidant is 0.05-0.2 parts by weight. The low-density polyethylene has a melt flow rate of 5-20 g / 10 min at 190℃ and under a load of 2.16 kg, a weight-average molecular weight greater than 500,000, and a molecular weight distribution coefficient greater than 20. The ethylene-vinyl acetate copolymer has a melt flow rate of 10-30 g / 10 min at 190°C and a load of 2.16 kg, and a vinyl acetate content of 15-25 wt%. The conditions for melt extrusion molding must at least satisfy the following: the twin-screw extruder comprises five sections along the material conveying direction, the temperatures of the five sections are sequentially 150-160℃, 150-170℃, 160-200℃, 160-200℃ and 150-170℃, the vacuum degree of each of the five sections is independently 0.02MPa-0.09MPa, and the rotational speed of the twin-screw extruder is 200-400rpm.

2. The method according to claim 1, wherein, The weight ratio of the ethylene-vinyl acetate copolymer, the low-density polyethylene, and the silane coupling agent is 100:10-35:1-15; and / or, Based on a total weight of 100 parts by weight of the ethylene-vinyl acetate copolymer, the low-density polyethylene, and the silane coupling agent, the amount of the antioxidant is 0.1-0.2 parts by weight; and / or, The length-to-diameter ratio of the twin-screw extruder is 30-53:

1.

3. The method according to claim 1 or 2, wherein, The silane coupling agent is selected from at least one of γ-(methacryloyloxy)propyltrimethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, and γ-aminopropyltriethoxysilane.

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

5. The method according to claim 4, wherein, The phenolic antioxidant is selected from at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanuric acid, and 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene; The phosphite antioxidant is selected from at least one of tris(2,4-di-tert-butylphenyl) phosphite, bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite, and bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite.

6. The modified ethylene-vinyl acetate copolymer prepared by the method according to any one of claims 1-5.

7. The application of the modified ethylene-vinyl acetate copolymer according to claim 6 in the preparation of a pre-coated film.

8. A pre-coated film, characterized in that, The adhesive coating in the pre-coated film is obtained by coating extrusion molding of the modified ethylene-vinyl acetate copolymer as described in claim 6 in a single-screw extruder.

9. The pre-coated film according to claim 8, wherein, The conditions for coating extrusion molding must at least meet the following: the extrusion temperature of the single screw extruder is 190-240℃, the rotation speed of the single screw extruder is 100-300rpm, and the length-to-diameter ratio of the single screw extruder is 30-53:1.