An ethylene-vinyl alcohol copolymer resin composition

Abstract

The present application discloses an ethylene-vinyl alcohol copolymer (EVOH) resin composition, which is prepared by polymerization and alcoholysis reaction, and the content of EVOH with ethylene content less than 15 mol% is less than 3 wt%. The present application also discloses a preparation method of the EVOH resin composition. The EVOH resin composition prepared by the present application has the content of EVOH with ethylene content less than 15 mol% less than 3 wt%, and the processing performance is significantly improved, the yellowing at high temperature is obviously reduced, and the defect number after melt blowing is reduced; thus the multilayer sheet, film and container prepared by the present application do not have crystal point, stripe and other defects.

Description

Technical Field

[0001] This invention relates to the field of ethylene-vinyl alcohol copolymers, specifically to ethylene-vinyl alcohol copolymer resin compositions and their preparation methods. Background Technology

[0002] Ethylene-vinyl alcohol copolymer (EVOH), especially EVOH with an ethylene content of 20-50 mol%, has excellent gas barrier properties, approximately 10,000 times that of ordinary polyethylene. Combined with its transparency, processability, solvent resistance, and antistatic properties, it is widely used in packaging materials, automotive fuel tanks, oxygen-barrier underfloor heating pipes, textile materials, and medical materials.

[0003] Chinese patent document CN 114426753 A discloses an ethylene-vinyl alcohol copolymer composition and its preparation method: the composition includes an ethylene-vinyl alcohol copolymer, a carboxyl-containing substance, a potassium salt, and a sodium salt, wherein the carboxyl-containing substance includes acetic acid and a carboxylic acid containing a carbon-carbon double bond; the preparation method of the composition includes the following steps: the ethylene-vinyl acetate copolymer obtained by polymerization is alcoholyzed with sodium hydroxide, then granulated, and then washed, during which acetic acid and a carboxylic acid containing a carbon-carbon double bond are added for washing, and then potassium salt is added.

[0004] The prior art has the following drawbacks: the multilayer sheets, films and containers made from the EVOH resin composition are prone to defects such as crystal points and streaks. Summary of the Invention

[0005] On the one hand, the present invention provides an EVOH resin composition that does not produce defects such as crystal points or streaks in multilayer sheets, films and containers made therefrom, including those obtained by polymerization and alcoholysis reactions; the content of EVOH with ethylene content <15mol% is less than 3wt%.

[0006] Furthermore, its preparation also includes adding the EVOH alcohol solution after alcoholysis to the additive, cooling and precipitating it, and washing it multiple times; including washing with a mixed solution of water and alcohol; this can further improve the multilayer sheets, films and containers made from the EVOH resin composition from being less prone to defects such as crystal points and streaks.

[0007] Furthermore, the additive is a heat stabilizer and / or an antioxidant; this further ensures that multilayer sheets, films, and containers made from the obtained EVOH resin composition will not produce defects such as crystal points and streaks.

[0008] Furthermore, the additive is one or more of carboxylic acids, alkali metal salts, alkaline earth metal salts, boric acid and its salts, and phosphoric acid and its salts; this further ensures that the multilayer sheets, films, and containers made from the obtained EVOH resin composition will not have defects such as crystal points and streaks.

[0009] Furthermore, the weight ratio of the alcohol to water is 1-50:50-99; this further ensures that the multilayer sheets, films, and containers made from the obtained EVOH resin composition will not have defects such as crystal points and streaks.

[0010] Furthermore, the alcohol is an alcohol with ≤4 carbon atoms; this further ensures that the multilayer sheets, films, and containers made from the obtained EVOH resin composition will not have defects such as crystal points and streaks.

[0011] Furthermore, the alcohol with ≤4 carbon atoms is one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, and tert-butanol; this further ensures that the multilayer sheets, films, and containers made from the obtained EVOH resin composition will not have defects such as crystal points and streaks.

[0012] Furthermore, the washing process also includes water washing and carboxylic acid compound washing; this further ensures that multilayer sheets, films, and containers made from the obtained EVOH resin composition will not have defects such as crystal points and streaks.

[0013] Secondly, the present invention provides a method for preparing the EVOH resin composition of the present invention, comprising a polymerization reaction and an alcoholysis reaction; after adding 0.01-1 parts by weight of additives to the alcoholysis-derived EVOH methanol solution, the mixture is introduced into an aqueous solution at 0-10°C, cut into particles, washed with water first, then washed with a mixed solution of water and alcohol, and finally washed with acetic acid, centrifuged to dehydrate, and dried to obtain the final product.

[0014] Thirdly, the present invention provides the application of the EVOH resin composition described herein in membranes, multilayer sheets and containers.

[0015] The present invention has the following beneficial effects:

[0016] The EVOH resin composition prepared by this invention has an ethylene content of <15mol% and an EVOH content of less than 3wt%, which significantly improves its processing performance, can significantly reduce yellowing at high temperatures, and reduce the number of defects after melt blown film production; thus, the multilayer sheets, films and containers produced will not have defects such as crystal points and streaks. Detailed Implementation

[0017] 1. Definition

[0018] (1) Polymerization reaction: The process of converting low molecular weight monomers into high molecular weight polymers.

[0019] (2) Alcohololysis: the reaction in which acyl halides, acid anhydrides, esters, etc. are decomposed by alcohols to generate esters and other compounds.

[0020] (3) Washing: To clean.

[0021] (4) Cooling: refers to the process of lowering the temperature of a hot object without causing a phase change.

[0022] (5) Precipitation: The solute separates from the solution.

[0023] 2. Various preferred solutions involving the scope

[0024] (1) The weight ratio of alcohol to water is 1-20:55-90.

[0025] (2) The weight ratio of alcohol to water is 5-40:85-90.

[0026] (3) Methanol is preferred.

[0027] (4) The carboxylic acid compound is preferably acetic acid or propionic acid.

[0028] (5) The additives are preferably one or more of acetic acid, propionic acid, boric acid and sodium dihydrogen phosphate.

[0029] (6) Add 0.01-1 parts of additive solution relative to the weight of EVOH solids to the obtained EVOH methanol solution and stir until homogeneous. Extrude the EVOH methanol solution obtained from alcoholysis into an aqueous solution at 0-10℃ through an extrusion device with a perforated plate. After precipitating into strips, cut them into granules using a common cutting method. Add water to a kettle with a stirring device to wash the EVOH granules, washing for 2 hours each time, repeating the washing twice. After washing twice, add a mixed solution of water and alcohol to a kettle with a stirring device, wash at 60-90℃ for 2 hours, then wash with water again. During the water washing process, add 0.005-0.1 parts of acetic acid relative to the weight of EVOH solids for acid washing, centrifuge to dehydrate, and dry to obtain EVOH granules.

[0030] 3. Detection Method

[0031] Test method for EVOH content of ethylene content <15mol% in granules: Accurately weigh 1g of sample and place it in an Erlenmeyer flask. Add 100g of a mixed solvent of water and ethanol (10g ethanol + 90g water), reflux in a water bath at 100℃ for 4 hours, filter, save the filtrate, add another 100g of water and reflux for 4 hours, filter again, evaporate the filtrates from both filtrations, and weigh the amount of residue. The ratio of the amount of residue to the amount of sample is the EVOH content of ethylene content <15mol% in the granules.

[0032] Method for determining the number of surface defects in membrane products: A 30cm*24cm membrane sample was prepared using an SG-45 blown film machine, and the surface defects in the membrane were analyzed using a surface defect analyzer MVT-SIS. The number of defects larger than 0.5mm*0.5mm in the sample was counted.

[0033] Example 1

[0034] The polymerization and alcoholysis processes are carried out according to existing technology to obtain EVOH methanol solution.

[0035] Add 0.3 parts by weight of the additive solution relative to the EVOH solid to the obtained EVOH methanol solution and stir until homogeneous; wherein the additive and its content are 300 ppm of propionic acid, 200 ppm of boric acid and 400 ppm of sodium dihydrogen phosphate relative to the weight of the EVOH solid.

[0036] The EVOH methanol solution obtained from alcoholysis was extruded into an aqueous solution at 5°C using an extruder equipped with a perforated plate. After precipitating into strips, the strips were cut into granules using a standard cutting method. The EVOH granules were then washed with water in a stirred tank, with each wash lasting 2 hours, repeated twice. After two washes, a mixture of water and alcohol was added to the stirred tank, and the mixture was washed at 65°C for 2 hours, followed by a second water wash. During this water wash, 0.01 parts (by weight) of propionic acid relative to the EVOH solids were added for acid washing. The mixture was then centrifuged, dehydrated, and dried to obtain the EVOH granules.

[0037] The EVOH particles obtained after drying were tested and found to contain 2.1 wt% EVOH with an ethylene content of <15 mol%. After heat treatment at 150℃ for 5 hours, the yellowness index increased by ΔYI = 10.

[0038] The dried EVOH particles were extruded and blown into a film using a single screw. After 10 hours of continuous operation, the number of surface defects in the EVOH film was found to be 12, and the change in screw current ΔA = 1A.

[0039] Example 2

[0040] The polymerization and alcoholysis processes are carried out according to existing technology to obtain EVOH methanol solution.

[0041] Add 0.6 parts by weight of additive solution relative to the EVOH solid to the obtained EVOH methanol solution and stir until homogeneous; wherein the additive and its content are 200 ppm acetic acid, 300 ppm boric acid and 500 ppm sodium dihydrogen phosphate relative to the weight of EVOH solid.

[0042] The EVOH methanol solution obtained from alcoholysis was extruded into an aqueous solution at 5°C using an extruder equipped with a perforated plate. After precipitating into strips, the strips were cut into granules using a standard cutting method. The EVOH granules were then washed with water in a stirred tank for 2 hours each time, repeated twice. After two washes, a mixture of water and alcohol was added to the stirred tank, and the mixture was washed at 68°C for 2 hours, followed by a second water wash. During this water wash, 0.05 parts by weight of acetic acid relative to the EVOH solids were added for acid washing. The mixture was then centrifuged, dehydrated, and dried to obtain the EVOH granules.

[0043] The EVOH particles obtained after drying were tested and found to contain 1.9 wt% EVOH with an ethylene content of <15 mol%. After heat treatment at 150℃ for 5 hours, the yellowness index increased by ΔYI = 8.

[0044] The dried EVOH particles were extruded and blown into a film using a single screw. After 10 hours of continuous operation, the number of surface defects in the EVOH film was found to be 14, and the change in screw current ΔA = 1A.

[0045] Example 3

[0046] The polymerization and alcoholysis processes are carried out according to existing technology to obtain EVOH methanol solution.

[0047] Add 0.8 parts by weight of additive solution relative to the EVOH solid to the obtained EVOH methanol solution and stir until homogeneous; wherein the additive and its content are 300 ppm acetic acid, 300 ppm boric acid and 600 ppm potassium dihydrogen phosphate relative to the weight of EVOH solid.

[0048] The EVOH methanol solution obtained from alcoholysis was extruded into an 8°C aqueous solution through an extrusion device equipped with a perforated plate. After precipitating into strips, the strips were cut into granules using a standard cutting method. The EVOH granules were then washed with water in a stirred tank, with each wash lasting 2 hours, repeated twice. After two washes, a mixture of water and alcohol was added to the stirred tank, and the mixture was washed at 70°C for 2 hours, followed by a second water wash. During this water wash, 0.05 parts by weight of acetic acid relative to the EVOH solids were added for acid washing. The mixture was then centrifuged, dehydrated, and dried to obtain the EVOH granules.

[0049] The EVOH particles obtained after drying were tested and found to contain 1.8 wt% EVOH with an ethylene content of <15 mol%. After heat treatment at 150℃ for 5 hours, the yellowness index increased by ΔYI = 7.

[0050] The dried EVOH particles were extruded and blown into a film using a single screw. After 10 hours of continuous operation, the number of surface defects in the EVOH film was found to be 17, and the change in screw current ΔA = 1A.

[0051] Comparative Example 1

[0052] The polymerization and alcoholysis processes are carried out according to existing technology to obtain EVOH methanol solution.

[0053] Add 0.6 parts by weight of additive solution relative to the EVOH solid to the obtained EVOH methanol solution and stir until homogeneous; wherein the additive and its content are 200 ppm acetic acid, 300 ppm boric acid or 500 ppm sodium dihydrogen phosphate relative to the weight of EVOH solid.

[0054] The EVOH methanol solution obtained from alcoholysis was extruded into an aqueous solution at 5°C using an extrusion device with a perforated plate. After precipitating into strips, the strips were cut into granules using a common cutting method. The EVOH granules were then washed with water in a stirred tank, with each wash lasting 2 hours. This washing was repeated twice, followed by a final water wash. During the water wash, 0.05 parts of acetic acid (based on the weight of the EVOH solids) were added for acid washing. After centrifugation and dehydration, the EVOH granules were obtained.

[0055] The EVOH particles obtained after drying were tested and found to contain 4.8 wt% EVOH with an ethylene content of <15 mol%. After heat treatment at 150℃ for 5 hours, the yellowness index increased by ΔYI = 19.

[0056] The dried EVOH particles were extruded and blown into a film using a single screw. After 10 hours of continuous operation, the number of surface defects in the EVOH film was found to be 27, and the change in screw current ΔA = 2A.

[0057] The examples provided are for illustrative purposes only and are not intended to limit the scope of the invention. Therefore, non-essential modifications and adjustments made to the embodiments by those skilled in the art based on the above description are still within the scope of this invention. Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This descriptive method is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An ethylene-vinyl alcohol copolymer resin (EVOH) composition, comprising a product obtained by polymerization and alcoholysis; characterized in that: The content of EVOH with ethylene content <15mol% is less than 3wt%.

2. The EVOH resin composition according to claim 1, characterized in that: Its preparation also includes adding the EVOH alcohol solution after alcoholysis to the additive, cooling and precipitating it, and washing it multiple times; including washing with a mixed solution of water and alcohol.

3. The EVOH resin composition according to claim 2, characterized in that: The additives are heat stabilizers and / or antioxidants.

4. The EVOH resin composition according to claim 3, characterized in that: The additive is one or more of the following: carboxylic acid, alkali metal salt, alkaline earth metal salt, boric acid and its salt, and phosphoric acid and its salt.

5. The EVOH resin composition according to any one of claims 2-4, characterized in that: The weight ratio of the alcohol to water is 1-50:50-99.

6. The EVOH resin composition according to any one of claims 2-5, characterized in that: The alcohol is an alcohol with ≤4 carbon atoms.

7. The EVOH resin composition according to claim 6, characterized in that: The alcohols with ≤4 carbon atoms are one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, and tert-butanol.

8. The EVOH resin composition according to any one of claims 2-7, characterized in that: The washing process also includes water washing and carboxylic acid compound washing.

9. A method for preparing the EVOH resin composition according to any one of claims 1-8, comprising a polymerization reaction and an alcoholysis reaction; characterized in that: Add 0.01-1 parts by weight of EVOH solids to the methanol solution of EVOH after alcoholysis, then introduce it into an aqueous solution at 0-10℃, cut it into particles, wash it with water first, then wash it with a mixed solution of water and alcohol, finally add acetic acid for washing, centrifuge to dehydrate, and dry it to obtain the final product.

10. Use of the EVOH resin composition according to any one of claims 1-8 in films, multilayer sheets and containers.