Ethylene-vinyl alcohol copolymer resin composition as well as preparation method and application thereof

Abstract

The invention discloses an ethylene-vinyl alcohol copolymer resin composition as well as a preparation method and application thereof, the composition comprises an ethylene-vinyl alcohol copolymer structure and a structural unit as shown in the following formula (1): # imgabs0 #, in the formula, R1, R2, R3 and R4 are respectively and independently selected from H and alkyl with 1-4 carbon atoms. The composition is excellent in high-temperature yellowing resistance, gas barrier property and strength, and a film prepared from the composition is excellent in tear resistance.

Description

Technical Field

[0001] The present invention relates to an ethylene-vinyl alcohol copolymer resin composition and a molded product thereof, and more particularly to a preparation method of the ethylene-vinyl alcohol copolymer resin composition and a molded product thereof. Background Art

[0002] Generally, ethylene-vinyl alcohol copolymer (hereinafter referred to as EVOH) has transparency, gas barrier properties, aroma retention, and oil resistance, and is often used in various packaging materials such as food packaging materials, pharmaceutical packaging materials, and industrial chemical packaging materials. In addition to being processed into films, EVOH is also processed into containers of various shapes, and has high requirements for its mechanical strength and processability. In addition, when multi-layer sheets containing EVOH are formed into containers, due to the diversity and design of container shapes, the pursuit of the appearance, barrier properties, and strength of the molded containers makes users put forward higher requirements for the performance of EVOH resin. Compared with materials such as polypropylene, polyester, and nylon, EVOH has poor processability and poor thermal stability.

[0003] In order to solve this problem, CN106459548B discloses a method of mixing EVOH with polyamide resin and fatty acid magnesium salt, and CN104350102B discloses a method of mixing EVOH with polyamide resin, carboxylic acid metal salt and unsaturated aldehyde; CN111944262B and CN113024936B disclose a method of mixing two or more EVOHs with different ethylene contents; CN1231501C discloses a method of grafting epoxy compounds on EVOH through melt reaction to improve the performance and stretchability of thermoformed containers; CN104603163B and CN1965003B disclose adding special monomers during the EVOH polymerization process to obtain EVOH resin or composition particles with better performance, excellent thermal stability when manufacturing films or sheets, and excellent appearance after heat treatment.

[0004] However, as in the method disclosed in the above patent, blending other resins will reduce the gas barrier properties of the material; mixing EVOH with different compositions and structures will reduce performance because the different materials cannot be completely uniform, which will lead to an increase in the defective rate when continuously stretching to form films, cups, plates or bottles; the method of grafting epoxy compound modification is not only cumbersome but also leads to a decrease in the moisture resistance of the material. The modification of polyhydroxy comonomers during polymerization will improve the high temperature yellowing resistance and long-term processing of EVOH, but it will not improve the barrier properties of the resin, the tensile processing performance, and the strength of the product.

[0005] CN109996843B and CN110036060B introduce lactone ring structure into the terminal structure of EVOH and control the ratio of carboxylic acid group to lactone ring group to solve the problem of thermal degradation of resin at high temperature. However, the change of the form of the terminal group cannot change the main structure of the resin, and the strength of the resin and the performance of the product are not improved. CN1120184C introduces carboxyl group and lactone ring into ethylene-vinyl alcohol copolymer with ethylene unit content of 2-19 mol%, and the thermal stability, water resistance, gas barrier performance and water vapor barrier performance are improved. However, the introduction of carboxylic acid or carboxylic acid ester monomers easily causes intermolecular crosslinking, which leads to the deterioration of the high temperature and long-term processing performance of the resin.

[0006] Therefore, it is necessary to develop an EVOH resin material with excellent comprehensive properties such as high-temperature anti-yellowing, gas barrier, strength and mechanics in the field. Summary of the invention

[0007] In view of this, one of the objects of the present invention is to provide an ethylene-vinyl alcohol copolymer resin composition and a preparation method, which not only has excellent high-temperature anti-yellowing performance, gas barrier properties and strength performance, but also the film prepared therefrom has excellent tear resistance.

[0008] A second object of the present invention is to provide a molded article prepared from the ethylene-vinyl alcohol copolymer resin composition.

[0009] The first aspect of the present invention provides an ethylene-vinyl alcohol copolymer resin composition, which comprises an ethylene-vinyl alcohol copolymer structure and a structural unit represented by the following formula (1):

[0010]

[0011] In the formula, R1, R2, R3, and R4 are independently selected from H, an alkyl group having 1 to 4 carbon atoms, preferably H or methyl;

[0012] The content of the structural unit represented by formula (1) is 0.01 to 10 mol %, preferably 0.02 to 5 mol %, more preferably 0.05 to 2 mol %, based on the total molar amount of the monomer units of the ethylene-vinyl alcohol copolymer and the structural unit represented by formula (1).

[0013] In one embodiment, in the structural unit represented by formula (1), R1, R2, R3, and R4 may be the same as or different from each other.

[0014] In one embodiment, based on the total molar amount of the monomer units of the ethylene-vinyl alcohol copolymer and the structural unit represented by formula (1), the content of the ethylene monomer unit in the ethylene-vinyl alcohol copolymer is 10 to 60 mol%, preferably 20 to 50 mol%, and more preferably 25 to 48 mol%.

[0015] In one embodiment, the ethylene-vinyl alcohol copolymer resin composition is prepared by copolymerization of ethylene monomer, vinyl ester monomer and α-methylene lactone monomer; wherein the α-methylene lactone monomer is a compound having a structure shown in the following formula (2):

[0016]

[0017] In the formula, R1, R2, R3, R4 are the same as R1, R2, R3, R4 in formula (1), that is, R1, R2, R3, R4 are independently selected from H, an alkyl group having 1-4 carbon atoms, preferably H or methyl.

[0018] In a preferred embodiment, the α-methylene lactone monomer is selected from one or more of α-methylene-γ-valerolactone (MVL) and α-methylene-γ-butyrolactone (MBL).

[0019] In a preferred embodiment, the vinyl ester monomer is selected from one or more of vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl versatate, etc., preferably vinyl acetate.

[0020] In one embodiment, the ethylene-vinyl alcohol copolymer resin composition comprises the following monomer mole percentage compositions:

[0021] Ethylene monomer 10-60%;

[0022] Vinyl ester monomer 50-89%;

[0023] α-Methylene lactone monomer 0.01~10%.

[0024] In a specific embodiment, the ethylene-vinyl alcohol copolymer resin composition is obtained by preparing a copolymer through copolymerization of ethylene monomer, vinyl ester monomer and α-methylene lactone monomer, followed by saponification.

[0025] The second aspect of the present invention provides a method for preparing the ethylene-vinyl alcohol copolymer resin composition, comprising:

[0026] The process of preparing a copolymer by copolymerizing ethylene monomer, vinyl ester monomer and α-methylene lactone monomer,

[0027] and a step of saponifying the copolymer.

[0028] In one embodiment, the copolymerization reaction pressure is 2-7 MPa.

[0029] In one embodiment, the copolymerization reaction temperature is 40 to 80° C. and the reaction time is 0.5 to 6 hours.

[0030] In one embodiment, the saponification reaction temperature is 55 to 120° C. and the reaction time is 0.2 to 5 h.

[0031] The third aspect of the present invention provides application of the ethylene-vinyl alcohol copolymer resin composition.

[0032] Specifically, a molded article is provided, which is made of the ethylene-vinyl alcohol copolymer resin composition described above, or the ethylene-vinyl alcohol copolymer resin composition prepared by the above method.

[0033] In a specific embodiment, the shaped object is obtained by melt molding.

[0034] In one specific embodiment, the shaped article is a film.

[0035] In one specific embodiment, the shaped object is a container.

[0036] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0037] The present invention introduces a γ-lactone ring comonomer into the ethylene-vinyl alcohol copolymer raw material, so that the main chain of the polymer is distributed with a γ-lactone ring structure, which reduces the oxidation and dehydration reaction tendency of the main chain hydroxyl group at high temperature, and has excellent high-temperature anti-yellowing performance, gas barrier properties, product strength and film tear resistance. DETAILED DESCRIPTION

[0038] In order to facilitate the understanding of the present invention, the present invention will be further described below in conjunction with examples. It should be understood that the following examples are only for a better understanding of the present invention and do not mean that the present invention is limited to the following examples.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the invention belongs. The term "and / or" as may be used herein includes any and all combinations of one or more of the associated listed items.

[0040] The ethylene-vinyl alcohol copolymer resin composition of the present invention comprises an ethylene-vinyl alcohol copolymer structure and a structural unit represented by the following formula (1):

[0041]

[0042] In the formula, R1, R2, R3, and R4 are independently selected from H and an alkyl group having 1 to 4 carbon atoms; R1, R2, R3, and R4 may be the same or different from each other;

[0043] Based on the total molar amount of the monomer units of the ethylene-vinyl alcohol copolymer and the structural units represented by formula (1), the content of the structural units represented by formula (1) is 0.01 to 10 mol%, for example, 0.01 mol%, 0.1 mol%, 0.5 mol%, 1 mol%, 2 mol%, 3 mol%, 4 mol%, 5 mol%, 6 mol%, 7 mol%, 8 mol%, 9 mol%, 10 mol%, etc.

[0044] The EVOH of the present invention contains the structural unit of the above formula (1), that is, the structural unit having γ-lactone. The substituents R1, R2, R3, and R4 are not particularly limited and may be hydrogen atoms or alkyl groups with less than 4 carbon atoms, preferably methyl groups or hydrogen atoms.

[0045] The amount of the lactone structural unit represented by the above formula (1) introduced into the EVOH resin composition of the present invention is 0.01 to 10 mol%, preferably 0.02 to 5 mol%, and more preferably 0.05 to 2 mol%. If the amount introduced is less than 0.01 mol%, the effect of the present invention cannot be fully exhibited. On the contrary, if it exceeds 10 mol%, there is a tendency that the processing performance is reduced or the gel point is increased.

[0046] In one embodiment, the content of the ethylene monomer unit in the ethylene-vinyl alcohol copolymer is 10 to 60 mol%, preferably 20 to 50 mol%, and more preferably 25 to 48 mol%, based on the total molar amount of the monomer units of the ethylene-vinyl alcohol copolymer and the structural unit represented by formula (1). When the ethylene monomer content is less than 10 mol%, the gas barrier properties at high humidity are reduced and the appearance is deteriorated. On the contrary, when it exceeds 50 mol%, there is a tendency for the gas barrier properties to be reduced.

[0047] In one embodiment, the ethylene-vinyl alcohol copolymer resin composition is prepared by copolymerization of ethylene monomer, vinyl ester monomer and α-methylene lactone monomer; wherein the α-methylene lactone monomer is a compound having a structure shown in the following formula (2):

[0048]

[0049] In the formula, R1, R2, R3, R4 are the same as R1, R2, R3, R4 in formula (1), that is, R1, R2, R3, R4 are independently selected from H, an alkyl group having 1-4 carbon atoms, preferably H or methyl.

[0050] The ethylene-vinyl alcohol copolymer resin composition provided by the present invention introduces a comonomer having a γ-lactone ring, so that the main chain of the polymer is distributed with a γ-lactone ring structure, which reduces the oxidation and dehydration reaction tendency of the main chain hydroxyl group at high temperature, improves the long-term processability and high-temperature yellowing resistance of the EVOH product at high temperature, and exhibits excellent gas barrier performance. The unique γ-lactone structure has high stability, and while improving the mechanical properties of the polymer, it can also avoid adverse side reactions such as cross-linking, thereby improving its strength and the excellent tear resistance of the prepared film.

[0051] Regarding the preparation method of EVOH of the present invention, copolymerization of ethylene monomer and vinyl ester monomer is an existing technology, and the present invention has no special limitation. The conventional preparation process of EVOH in the field can be adopted. For example, a method of saponifying a copolymer obtained by copolymerizing ethylene monomer, vinyl ester monomer and α-methylene lactone monomer can be adopted.

[0052] Among them, the α-methylene lactone monomer is preferably one or more of α-methylene-γ-valerolactone (MVL) and α-methylene-γ-butyrolactone (MBL);

[0053] α-Methylene-γ-valerolactone and α-Methylene-γ-butyrolactone are compounds represented by the following formula (3) and the following formula (4), respectively.

[0054]

[0055] Among them, the vinyl ester monomers include one or more of vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl versatate, etc., and vinyl acetate is preferably used.

[0056] In addition, in the present invention, when the above copolymerization is carried out, copolymerizable ethylenically unsaturated monomers can be further copolymerized within the scope that does not hinder the effect of the present invention. The copolymerization ratio is not particularly limited and can be determined according to the actual demand for the target product. As the ethylenically unsaturated monomer, one or more of the following raw materials can be used: olefins such as propylene, 1-butene, and isobutylene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid (anhydride), and itaconic acid (anhydride), their salts or mono- or di-alkyl esters with 1 to 18 carbon atoms; acrylamide, N-alkyl acrylamide with 1 to 18 carbon atoms, N, N-dimethyl acrylamide, and other acrylamides; methacrylamide, N-alkyl methacrylamide with 1 to 18 carbon atoms, N, N-dimethyl methacrylamide Methacrylamides such as N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, etc. N-vinyl amides; vinyl cyanides such as acrylonitrile and methacrylonitrile; vinyl ethers such as alkyl vinyl ethers having 1 to 18 carbon atoms, hydroxyalkyl vinyl ethers, alkoxyalkyl vinyl ethers, etc.; halogenated vinyls such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, vinyl bromide, etc.; vinyl silanes; allyl acetate; allyl chloride; allyl alcohol; dimethylallyl alcohol; acrylamide-2-methylpropane sulfonic acid; vinyl carbonate.

[0057] The copolymerization ratio of the α-methylene lactones, vinyl ester monomers, ethylene monomers, etc. is not particularly limited, and can be determined according to the amount of the structural unit represented by the formula (1) introduced into EVOH.

[0058] For example, the ethylene-vinyl alcohol copolymer resin composition is prepared by using monomers having the following molar percentage compositions:

[0059] Ethylene monomer 10-60%, for example 10%, 20%, 30%, 40%, 50%, 60%, etc., preferably 20-50%, more preferably 25-48%;

[0060] Vinyl ester monomer 50-89%, for example 50%, 60%, 70%, 80%, 89%, etc.;

[0061] α-Methylene lactone monomer 0.01-10%, for example 0.01%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., preferably 0.02-5%, more preferably 0.05-2%.

[0062] Specifically, the preparation method of the ethylene-vinyl alcohol copolymer resin composition may include the following steps:

[0063] The process of preparing a copolymer by copolymerizing ethylene monomer, vinyl ester monomer and α-methylene lactone monomer,

[0064] and a step of saponifying the copolymer.

[0065] Among them, the process of preparing the copolymer by copolymerizing ethylene monomer, vinyl ester monomer and α-methylene lactone monomer can be carried out by the following method, but is not limited thereto:

[0066] There are no particular restrictions on copolymerizing α-methylene lactone monomers, vinyl ester monomers and ethylene monomers. A known copolymerization method in the field of bulk polymerization, solution polymerization, suspension polymerization, dispersion polymerization or emulsion polymerization may be used, and solution polymerization is usually performed.

[0067] The present invention adopts a monomer copolymerization method known in the art. The relevant operation and process conditions, and the devices used therein, can be selected and carried out by the corresponding conventional selections in the art. There is no particular limitation to this. The technicians can optimize the known processes in the prior art according to actual needs. Specifically, for example, the conditions listed below in the present invention can be adopted:

[0068] During the copolymerization reaction, the system pressure is maintained constant, which can be 2-7MPa for the copolymerization reaction;

[0069] For the copolymerization reaction, the temperature may be 40 to 80° C., and the reaction time may be 0.5 to 6 hours, until the polymerization rate reaches 20 to 60%.

[0070] After the copolymerization reaction is completed, a terminator can be added to stop the reaction, and a stripping tower can be used to remove residual unreacted vinyl acetate, etc., wherein the terminator can include copper acetate, N, N-dialkylhydroxylamine, styrene derivatives, hydroquinone derivatives, quinone derivatives, piperidine derivatives, conjugated polyenes, etc., and there is no particular restriction on the amount thereof, as long as the purpose of terminating the reaction can be achieved. There is no particular restriction on the feeding method of the monomer components during the copolymerization, and any method such as batch feeding, batch feeding, and continuous feeding can be adopted.

[0071] A solvent is used during the copolymerization. As the solvent, any conventional solvent in the field can be used. Common examples include lower alcohols such as methanol, ethanol, propanol, and butanol, and ketones such as acetone and methyl ethyl ketone. Industrially, methanol is preferably used.

[0072] A polymerization initiator is used during the copolymerization. The polymerization initiator may be a conventional option in the art, for example, one or more of the following raw materials: azobisisobutyronitrile, acetyl peroxide, benzoyl peroxide, lauroyl peroxide and other known free radical polymerization initiators, tert-butyl peroxyneodecanoate, tert-butyl peroxypivalate, α,α'-bis(peroxyneodecanoyl)diisopropylbenzene, cumyl peroxyneodecanoate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, 1-cyclohexyl-1-methylethyl peroxyneodecanoate, tert-hexyl peroxyneodecanoate, tert-hexyl peroxypivalate Peroxy esters such as di-n-propyl dicarbonate, diisopropyl dicarbonate, di-sec-butyl dicarbonate, di(4-tert-butylcyclohexyl) dicarbonate, di-2-ethoxyethyl dicarbonate, di(2-ethylhexyl) dicarbonate, dimethoxybutyl dicarbonate, and di(3-methyl-3-methoxybutyl) dicarbonate; low-temperature active free radical polymerization initiators such as diacyl peroxides such as di(3,3,5-trimethylhexanoyl) peroxide, diisobutyryl peroxide, and dilauroyl peroxide.

[0073] There is no particular limitation on the addition ratio of the above-mentioned solvent and polymerization initiator. In actual use, technicians can determine the dosage based on experience based on existing technology. Usually, the amount of solvent is 10 to 80 wt% of the total mass of the polymerization monomers, and the amount of polymerization initiator is 0.05 to 1 wt% of the total mass of the polymerization monomers.

[0074] Among them, the process of saponifying the obtained copolymer can be carried out by methods known in the art. The specific operating steps and process conditions, and the equipment used can all be carried out by corresponding conventional selections in the art. There is no particular limitation on this. Technicians can optimize it according to actual needs based on the known processes in the prior art.

[0075] Specifically, during the saponification, the copolymer obtained as described above is dissolved in alcohol or an alcohol-water composition and saponified using an alkali catalyst or an acid catalyst.

[0076] As the alcohol used in saponification, one or more of methanol, ethanol, propanol, tert-butyl alcohol, etc. can be cited, and methanol is particularly preferred. The concentration of the copolymer dissolved in the alcohol is not particularly limited and can be appropriately selected according to the viscosity of the system, usually 10 to 60 wt%.

[0077] As the catalyst used in the saponification, one or more of the following raw materials can be used: a base catalyst of an alkali metal hydroxide or alkoxide such as sodium hydroxide, potassium hydroxide, sodium methoxide, sodium ethoxide, potassium methoxide, lithium methoxide, etc., and an acid catalyst such as sulfuric acid, hydrochloric acid, nitric acid, methanesulfonic acid, zeolite, cation exchange resin, etc. There is no particular limitation on the amount of the catalyst used, and it can be appropriately selected according to the saponification method, the target saponification degree, etc. When a base catalyst is used, it is usually 0.001 to 0.5 molar equivalents, preferably 0.005 to 0.2 molar equivalents, relative to the total amount of the vinyl ester monomer.

[0078] For the saponification method, the reaction temperature can be 55 to 120°C and the reaction time can be 0.2 to 5 hours;

[0079] After the saponification reaction is completed, an appropriate acid solution may be added for neutralization to terminate the reaction. The saponification method may be any of batch saponification, continuous saponification on a conveyor belt, and tower continuous saponification, depending on the target saponification degree. From the viewpoint of reducing the amount of the alkali catalyst during saponification and the viewpoint of facilitating the saponification reaction to proceed efficiently, tower saponification under a certain pressure is preferably used.

[0080] After the above operations are completed, the product obtained by saponification is subsequently subjected to conventional post-treatments such as neutralization, washing, drying, and granulation to obtain the desired ethylene-vinyl alcohol copolymer resin composition product.

[0081] The saponification degree of the ethylene-vinyl alcohol copolymer resin composition of the present invention is not particularly limited.

[0082] Specifically, the saponification degree may be 90 mol% or more, preferably 95 mol% or more, and more preferably 99 mol% or more. When the saponification degree is less than 90 mol%, gas barrier properties and moisture resistance tend to decrease.

[0083] In specific implementation, the ethylene-vinyl alcohol copolymer resin composition of the present invention can be prepared by the following method, the steps are:

[0084] In a polymerization kettle, appropriate amounts of vinyl ester monomer, solvent, polymerization initiator, and α-methylene lactone monomer are added as required, and replaced with nitrogen and ethylene in sequence, and then ethylene monomer is introduced until the copolymerization reaction pressure is reached, and the temperature is raised to the polymerization reaction temperature under stirring, and the system pressure is maintained constant, and the polymerization reaction is carried out for a certain time to reach a preset polymerization rate; then a terminator is added to stop the polymerization reaction, and a stripping tower is used to remove the residual unreacted vinyl ester monomer to obtain a reaction liquid containing ethylene-vinyl alcohol copolymer resin;

[0085] An appropriate amount of alcohol is added to the reaction solution containing the ethylene-vinyl alcohol copolymer resin to dissolve the copolymer resin, and then a certain amount of alkali catalyst or acid catalyst is added to carry out a saponification reaction at a certain temperature for a certain time; then an acid solution is added to the reaction solution for neutralization to terminate the reaction, water is added to the neutralized reaction solution to precipitate solids, which are filtered, washed with water (until the conductivity of the washing solution after washing is less than 10 μS / cm), and granulated to obtain an ethylene-vinyl alcohol copolymer resin composition.

[0086] The ethylene-vinyl alcohol copolymer resin composition particles are preferably further washed with water or acid until the conductivity of the washing liquid reaches 3 μS / cm.

[0087] In addition, in the present invention, the EVOH resin composition containing the lactone structural unit represented by the above formula (1) can be mixed with other EVOH or modified EVOH to obtain a composition. The EVOH composition of the present invention can be a composition in which all EVOH in the composition has the structural unit represented by the formula (1), and in addition, only a part of the EVOH can have the structural unit represented by the formula (1).

[0088] There are no particular limitations on the method for mixing two or more EVOHs, and examples include a method in which each EVOH is dissolved in a solvent such as water-alcohol or dimethyl sulfoxide and mixed in a solution state, a method in which an ethylene-vinyl acetate copolymer of each EVOH before saponification is dissolved in an alcohol solvent such as methanol and mixed and saponified, or a method in which each EVOH is melt-mixed, etc. A melt mixing method is usually used.

[0089] Examples of the melt mixing method include a mixing method using a known kneading device such as a kneader, an extruder, a mixing roll, a Banbury mixer, a plasto mill, and the like. In general, a single-screw or twin-screw extruder is preferably used industrially.

[0090] The EVOH resin composition of the present invention can be directly used for melt molding as it is, or can be mixed with other components to obtain a composition based on the EVOH resin composition of the present invention within the scope that does not hinder the purpose of the present invention, and then used for melt molding, for example, saturated aliphatic amides (such as stearic acid amide, etc.), unsaturated fatty acid amides (such as oleic acid amide, etc.), bis fatty acid amides (such as bis fatty acid ethylene glycol amide, etc.), fatty acid metal salts (such as calcium stearate, magnesium stearate, etc.), low molecular weight polyolefins (such as low molecular weight polyethylene or low molecular weight polypropylene with a molecular weight of about 500 to 10,000), inorganic salts (such as hydrotalcite, etc.), plasticizers (such as aliphatic polyols such as ethylene glycol, glycerol, hexylene glycol, etc.), oxygen absorbents (for example, as inorganic oxygen absorbents, reduced iron powders, materials to which water-absorbing substances or electrolytes are added, aluminum powder, potassium sulfite, light Catalyst titanium oxide, etc.; as an organic compound oxygen absorbent, it can be ascorbic acid and its fatty acid esters or metal salts, etc., hydroquinone, gallic acid, polyphenols such as phenolic resins containing hydroxyl groups, disalicylic aldehyde-imine cobalt, tetramethylene pentamine cobalt, cobalt-Schiff base complexes, porphyrins, macrocyclic polyamine complexes, polyethyleneimine-cobalt complexes and other nitrogen-containing compounds and transition metal coordination combinations, terpene compounds, amino acids and hydroxyl-containing reducing substances, trityl compounds, etc.; as a polymer oxygen absorbent, it can be a nitrogen-containing resin and a transition metal coordination combination (for example: a combination of MXD nylon and cobalt), a mixture of a tertiary hydrogen-containing resin and a transition metal (for example, a combination of polypropylene and cobalt), a mixture of a carbon-carbon unsaturated bond resin and a transition metal (for example, a combination of polybutadiene and cobalt), a photo-oxidative destructive resin (for example, polyketone), anthracene polymers (for example, polyvinyl anthracene) and the like);

[0091] In addition, photoinitiators (benzophenone, etc.), peroxide supplements (commercially available antioxidants, etc.), deodorants (activated carbon, etc.), heat stabilizers, light stabilizers, antioxidants, ultraviolet absorbers, colorants, antistatic agents, surfactants, antibacterial agents, anti-caking agents, slip agents, fillers (such as inorganic fillers, etc.), other resins (such as polyolefins, polyamides, etc.), etc. may be further added to the above-mentioned mixtures.

[0092] In addition, from the viewpoint of improving the thermal stability of the resin, in the EVOH resin composition of the present invention, it is preferred to add acids such as acetic acid and phosphoric acid, or metal salts of alkali metals, alkaline earth metals, transition metals, etc., or boric acid or its metal salt as a boron compound, within the scope that does not hinder the purpose of the present invention.

[0093] The amount of acetic acid added is preferably 0.001 to 1 part by weight, more preferably 0.005 to 0.2 part by weight, and particularly preferably 0.010 to 0.1 part by weight relative to 100 parts by weight of the EVOH resin composition. If the amount added is less than 0.001 part by weight, the effect is not significant. On the contrary, if the amount added exceeds 1 part by weight, the appearance of the obtained molded product tends to deteriorate, which is not preferred.

[0094] In addition, as the metal salt, there can be mentioned metal salts of organic acids such as acetic acid, propionic acid, butyric acid, lauric acid, stearic acid, oleic acid, behenic acid, or inorganic acids such as sulfuric acid, sulfurous acid, carbonic acid, and phosphoric acid, such as sodium, potassium, calcium, and magnesium, preferably acetates, phosphates, and hydrogen phosphates. In addition, as the addition amount of the metal salt, it is preferably 0.0005 to 0.01 parts by weight, more preferably 0.001 to 0.05 parts by weight, and particularly preferably 0.002 to 0.03 parts by weight relative to 100 parts by weight of the EVOH resin composition, in terms of metal conversion. When the addition amount is less than 0.0005 parts by weight, the effect is not obvious. On the contrary, if it exceeds 0.01 parts by weight, there is a tendency for the appearance of the obtained molded product to deteriorate, which is not preferred. In addition, when two or more salts of alkali metals and / or alkaline earth metals are added to EVO H, the total amount thereof is preferably within the range of the above addition amount.

[0095] As the borate metal salt, in addition to calcium borate, cobalt borate, zinc borate (zinc tetraborate, zinc metaborate, etc.), aluminum potassium borate, ammonium borate (ammonium metaborate, ammonium tetraborate, ammonium pentaborate, ammonium octaborate, etc.), cadmium borate (cadmium orthoborate, cadmium tetraborate, etc.), potassium borate (potassium metaborate, potassium tetraborate, potassium pentaborate, potassium hexaborate, potassium octaborate, etc.), silver borate (silver metaborate, silver tetraborate, etc.), copper borate (copper borate, copper metaborate, copper tetraborate, etc.), sodium borate (sodium metaborate, sodium diborate, sodium tetraborate, sodium pentaborate, sodium hexaborate, sodium octaborate, etc.), lead borate (lead metaborate, lead hexaborate, etc.), nickel borate (original borate, etc.), In addition to the borate minerals such as nickel borate, nickel diborate, nickel tetraborate, nickel octaborate, etc.), barium borate (barium orthoborate, barium metaborate, barium diborate, barium tetraborate, etc.), bismuth borate, magnesium borate (magnesium orthoborate, magnesium diborate, magnesium metaborate, trimagnesium tetraborate, pentamagnesium tetraborate, etc.), manganese borate (manganous borate, manganese metaborate, manganese tetraborate, etc.), lithium borate (lithium metaborate, lithium tetraborate, lithium pentaborate, etc.), etc., it can also be borax, colemanite, borate, magnesia borate, suianite, boraxite and other borate minerals, preferably borax, boric acid, sodium borate (sodium metaborate, sodium diborate, sodium tetraborate, sodium pentaborate, sodium hexaborate, sodium octaborate, etc.). In addition, the amount of the boron compound added is preferably 0.001 to 1 part by weight, more preferably 0.002 to 0.2 part by weight, and particularly preferably 0.005 to 0.1 part by weight relative to 100 parts by weight of the EVOH resin composition, in terms of boron conversion. If the amount added is less than 0.001 part by weight, the effect is not significant. On the contrary, if it exceeds 1 part by weight, the appearance of the obtained molded product tends to deteriorate, which is not preferred.

[0096] Specifically, the method of adding an acid or a metal salt thereof to the EVOH resin composition to obtain a composition based on the EVOH resin composition of the present invention is not particularly limited, and can be listed as follows:

[0097] 1) A method of contacting an EVOH resin composition having a moisture content of 20 to 80 wt % with an aqueous solution of an acid or a metal salt thereof to make it contain the acid or the metal salt, and then drying the mixture;

[0098] 2) A method in which an acid or a metal salt thereof is contained in a uniform solution (water / alcohol solution, etc.) of an EVOH resin composition, extruded into a rope in a coagulation liquid, and then the rope obtained is cut into small pellets, and then dried;

[0099] 3) A method in which an EVOH resin composition is mixed with an acid or a metal salt and then melt-kneaded using an extruder or the like;

[0100] 4) When manufacturing an EVOH resin composition, the alkali (sodium hydroxide, potassium hydroxide, etc.) used in the saponification step is neutralized with an acid such as acetic acid, and the amount of the remaining acid such as acetic acid or the by-produced alkali metal salt such as sodium acetate and potassium acetate is adjusted by washing with water.

[0101] In order to more significantly obtain the effects of the present invention, the method of 1), 2) or 4) in which the dispersibility of the acid or its metal salt is excellent is preferred.

[0102] Then the composition based on the EVOH resin composition of the present invention obtained in the above-mentioned method 1), 2) or 4) is dried. As a drying method, any drying method in the field can be used. For example, mechanical stirring and dispersion or stirring and dispersion with hot air, while fluid drying; or static drying without applying dynamic effects such as stirring and dispersion. As dryers for fluid drying, cylindrical / trough type stirring dryers, round tube dryers, rotary dryers, fluidized bed dryers, vibrating fluidized bed dryers, cone rotary dryers, etc. can be listed. In addition, as dryers for static drying, as material static types, intermittent box dryers can be listed, as material transfer types, belt dryers, tunnel dryers, vertical dryers, etc. can be listed, but they are not limited to these dryers; fluid drying and static drying can also be combined.

[0103] As the heating gas used in the drying process, air or an inert gas (nitrogen, helium, argon, etc.) can be used, and the temperature of the heating gas is preferably 40 to 150° C. from the viewpoint of productivity and prevention of thermal degradation of EVOH. The time of the drying process varies depending on the water content of the composition based on the EVOH resin composition and the amount of treatment, and is generally preferably about 15 minutes to 72 hours from the viewpoint of productivity and prevention of thermal degradation of EVOH.

[0104] The composition based on the EVOH resin composition is dried under the above conditions, and the moisture content after the drying treatment is preferably 0.001 to 5wt%, more preferably 0.01 to 2wt%, and particularly preferably 0.1 to 1wt%. When the moisture content is less than 0.001wt%, there is a tendency for the moldability to decrease during long-term use. On the contrary, if it exceeds 5wt%, foaming may occur during extrusion molding, which is not preferred.

[0105] In specific implementation, one preparation method of the composition based on the EVOH resin composition of the present invention is to mix the aqueous solution of optional carboxylic acid, alkali metal salt, phosphoric acid compound, boron compound with the EVOH resin composition particles of the present invention, stir, impregnate, and then dry.

[0106] The ethylene-vinyl alcohol copolymer resin composition of the present invention or a composition based on the ethylene-vinyl alcohol copolymer resin composition of the present invention can be prepared into a molded article such as a film, various types of containers, and the like.

[0107] The molded object is prepared by a melt molding method, which is a well-known molding method in the art. The relevant operation and process conditions, and the devices used therein, can be carried out by the corresponding conventional selections in the art, and there is no particular limitation on this.

[0108] The method of the present invention is specifically described below by listing examples.

[0109] Unless otherwise specified, the reagents, materials and instruments used in the following examples are conventional reagents, conventional materials and conventional instruments in the art and can be obtained commercially.

[0110] In each embodiment and comparative example of the present invention, the main raw materials used are from the following sources:

[0111] Vinyl acetate (99.9%, Celanese (Nanjing) Chemical Co., Ltd.);

[0112] Ethylene (99.9%, Air Liquide);

[0113] Methanol (99.5%, Shanxi Coking);

[0114] α-Methylene-γ-valerolactone (MVL) (97%, Aladdin);

[0115] α-Methylene-γ-butyrolactone (MBL) (95%, Aladdin);

[0116] Methyl methacrylate (99.9%, Jilin Petrochemical Company of PetroChina Co., Ltd.);

[0117] Sodium hydroxide (99%, Beijing Inokai Technology Co., Ltd.);

[0118] Acetic acid (99.5%, Beijing Inokai Technology Co., Ltd.);

[0119] Phosphoric acid (85%, Beijing Inokai Technology Co., Ltd.);

[0120] Boric acid (99.5%, Beijing Inokai Technology Co., Ltd.);

[0121] Sodium acetate (99%, Beijing Inokai Technology Co., Ltd.).

[0122] The main test methods used in the embodiments of the present invention and the comparative examples are as follows:

[0123] The ethylene-vinyl alcohol copolymer resin composition pellets were blown into 20±2 μm films at 220° C. The appearance, oxygen barrier properties, tensile modulus, tear resistance, and melt index were evaluated according to the following methods:

[0124] 1. Chroma (high temperature anti-yellowing performance): The yellowness index of the film was measured on an X-Rite Ci600-7800 desktop spectrophotometer.

[0125] 2. Appearance: Visually observe the above film and evaluate it according to the following standards;

[0126] ○...No streaks or haziness were observed on the film, and it was stretched evenly;

[0127] △...A hazy feeling is observed on the film, and the stretching is uneven;

[0128] ×... Streaks were observed on the film, and cracks were generated in the EVOH layer.

[0129] 3. Gas barrier properties: tested using the method specified in GB / T 19789-2021.

[0130] 4. Tensile modulus: tested using the method specified in GB / T 1040.3-2006.

[0131] 5. Tear resistance: Tested using the method specified in GB / T 16578.1-2008.

[0132] 6. Melt index: tested using the method specified in GB / T 3682.2-2018 (test conditions 210°C, 2.16Kg).

[0133] Example 1

[0134] Polymerization reaction: In a 10L polymerization kettle with a cooling coil, add 5kg (58.14mol) of vinyl acetate, 1kg of methanol, 10g (0.061mol) of azobisisobutyronitrile, and 50g (0.51mol) of α-methylene-γ-butyrolactone. After replacing the system with nitrogen, replace it with ethylene and pressurize ethylene until the ethylene pressure reaches 3.6MPa. Raise the temperature to 60°C while stirring, maintain the system pressure constant, and polymerize for 4 hours until the polymerization rate is 50% and the amount of ethylene monomer participating in the polymerization reaction is 12.50mol. Then, add 15g of sorbic acid terminator to stop the polymerization reaction, and use a stripping tower to remove the residual unreacted vinyl acetate to obtain a reaction solution containing ethylene-vinyl acetate copolymer.

[0135] Saponification reaction: Methanol was added to the reaction solution containing ethylene-vinyl acetate copolymer obtained above to dissolve it, so that the concentration of ethylene-vinyl acetate copolymer in the solution was 15 wt%. 2.5 kg of the solution was taken, and 0.6 kg of 10 wt% NaOH methanol solution (the molar equivalent relative to the vinyl acetate unit in the ethylene-vinyl acetate copolymer was 0.4) was added thereto. The saponification reaction of EVAc was started at 60°C with stirring. After 5 hours of reaction, 100 g of acetic acid and 600 g of water were added to neutralize the reaction solution to terminate the reaction.

[0136] Post-saponification treatment: the neutralized reaction solution is poured into water to precipitate EVOH resin, the obtained EVOH resin is collected by filtration, and washed with water until the conductivity of the washing liquid is less than 10 μS / cm, dried at 60°C for 48 hours to obtain flocculent EVOH, dissolved in a water / methanol mixed solution (water / methanol mass ratio of 4 / 6) at 80°C with stirring, the temperature of the dissolution tank is lowered to 65°C and left for 5 hours, and after degassing, it is extruded into a 5°C water / methanol mixed solution (water / methanol mass ratio of 9 / 1), and precipitated in the form of wire, and cut to obtain EVOH resin particles (diameter of about 4 mm, length of about 5 mm), and then washed with water and 1 g / L acetic acid aqueous solution repeatedly until the conductivity of the washing liquid is 3 μS / cm to obtain ethylene-vinyl alcohol copolymer resin composition particles.

[0137] In the above-mentioned ethylene-vinyl alcohol copolymer resin composition particles, the ethylene monomer content is 30 mol%, the structural unit of formula (1) is 1 mol%; and the saponification degree is 99.8 mol%.

[0138] The EVOH resin composition is blended with other components: 0.80 g / L of acetic acid as a carboxylic acid, 0.50 g / L of sodium acetate as an alkali metal salt, 0.015 g / L of phosphoric acid as a phosphate compound, and 0.2 g / L of boric acid as a boron compound are mixed in water at respective concentrations to prepare 3 L of an aqueous solution of the blended composition, into which 0.3 kg of the above-mentioned ethylene-vinyl alcohol copolymer resin composition particles are added, and the mixture is immersed at 25°C for 5 hours under stirring, and then dried at 80°C for 3 hours and further dried at 120°C for 24 hours to obtain composition particles based on the ethylene-vinyl alcohol copolymer resin composition, which are used to prepare molded products, and their performance is tested. The results are shown in Table 1 below.

[0139] Example 2

[0140] Polymerization reaction: In a 10L polymerization kettle with a cooling coil, 3kg (34.88mol) of vinyl acetate, 2.4kg of solvent methanol, 50g (0.126mol) of di(4-tert-butylcyclohexyl) peroxydicarbonate initiator, 150g (1.53mol) of α-methylene-γ-butyrolactone, and 200g (1.78mol) of α-methylene-γ-valerolactone were added, and the system was replaced with nitrogen, and then replaced with ethylene, and ethylene was pressed until the ethylene pressure reached 2MPa. The temperature was raised to 40°C while stirring, and the system pressure was maintained constant. The polymerization was carried out for 6 hours until the polymerization rate was 20%, and the ethylene monomer participating in the polymerization reaction was 4.28mol. Then, 15g of anhydrous cupric acetate was added to stop the polymerization reaction, and the residual unreacted vinyl acetate was removed using a stripping tower to obtain a reaction solution containing ethylene-vinyl acetate copolymer.

[0141] Saponification reaction: Methanol was added to the reaction solution containing ethylene-vinyl acetate copolymer obtained above to dissolve it, so that the concentration of ethylene-vinyl acetate copolymer in the solution was 15wt%. 2.5kg of the solution was taken, and 0.07kg of 10wt% NaOH methanol solution (the molar equivalent relative to the vinyl acetate unit in the ethylene-vinyl acetate copolymer was 0.05) was added thereto. The saponification reaction of EVAc was carried out by stirring at 110°C. After reacting for 1 hour, 12g of acetic acid and 600g of water were added to neutralize the reaction solution to terminate the reaction.

[0142] Saponification post-treatment: The same post-treatment method as in Example 1 was used to obtain EVOH resin particles (with a diameter of about 4 mm and a length of about 5 mm).

[0143] In the above-mentioned ethylene-vinyl alcohol copolymer resin composition particles, the ethylene monomer content is 38 mol%, the structural unit of formula (1) is 10 mol%; and the saponification degree is 99.9 mol%.

[0144] The same treatment method as in Example 1 was used to prepare composition particles based on the ethylene-vinyl alcohol copolymer resin composition, and the particles were used to prepare molded products, and their properties were tested. The results are shown in Table 1 below.

[0145] Example 3

[0146] Polymerization reaction: In a 10L polymerization kettle with a cooling coil, add 6kg (69.77mol) of vinyl acetate, 0.6kg of solvent methanol, 150g (0.62mol) of initiator benzoyl peroxide, and 1g (0.0089mol) of α-methylene-γ-valerolactone. After replacing the system with nitrogen, replace it with ethylene and pressurize ethylene until the ethylene pressure reaches 6.8MPa. Raise the temperature to 80°C while stirring, maintain the system pressure constant, and polymerize for 0.5 hours until the polymerization rate is 60%, and the amount of ethylene monomer participating in the polymerization reaction is 13.95mol. Then, add 100g of terminator sorbic acid to stop the polymerization reaction, and use a stripping tower to remove the residual unreacted vinyl acetate to obtain a reaction solution containing ethylene-vinyl acetate copolymer.

[0147] Saponification reaction: Methanol was added to the obtained reaction solution containing ethylene-vinyl acetate copolymer to dissolve it, so that the concentration of ethylene-vinyl acetate copolymer in the solution was 15wt%. 2.5kg of the solution was taken, and 0.31kg of 10wt% NaOH methanol solution (the molar equivalent relative to vinyl acetate monomer was 0.2) was added thereto. The saponification reaction of EVAc was started by stirring at 70°C. After reacting for 4 hours, 50g of acetic acid and 600g of water were added to neutralize the above reaction solution to terminate the reaction.

[0148] Saponification post-treatment: The same post-treatment method as in Example 1 was used to obtain EVOH resin particles (with a diameter of about 4 mm and a length of about 5 mm).

[0149] In the above-mentioned ethylene-vinyl alcohol copolymer resin composition particles, the content of ethylene monomer is 25 mol%, the content of the structural unit of formula (1) is 0.01 mol%; and the degree of saponification is 99.85 mol%.

[0150] The same treatment method as in Example 1 was used to prepare composition particles based on the ethylene-vinyl alcohol copolymer resin composition, and the particles were used to prepare molded products, and their properties were tested. The results are shown in Table 1 below.

[0151] Example 4

[0152] Polymerization reaction: In a 10L polymerization kettle with a cooling coil, add 5kg (58.14mol) of vinyl acetate, 3kg of solvent tert-butyl alcohol, 10g (0.061mol) of initiator azobisisobutyronitrile, and 100g (0.89mol) of α-methylene-γ-valerolactone. After replacing the system with nitrogen, replace it with ethylene and pressurize ethylene until the ethylene pressure reaches 5MPa. Raise the temperature to 60°C while stirring, maintain the system pressure constant, and polymerize for 3 hours until the polymerization rate is 40% and the amount of ethylene monomer participating in the polymerization reaction is 19.03mol. Then, add 15g of terminator sorbic acid to stop the polymerization reaction, and use a stripping tower to remove the residual unreacted vinyl acetate to obtain a reaction solution containing ethylene-vinyl acetate copolymer.

[0153] Saponification reaction: Methanol was added to the obtained reaction solution containing ethylene-vinyl acetate copolymer to dissolve it, so that the concentration of ethylene-vinyl acetate copolymer in the solution was 15wt%, 2.5kg of the solution was taken, and 0.136kg of 10wt% NaOH methanol solution (the molar equivalent relative to the vinyl acetate unit in the ethylene-vinyl acetate copolymer was 0.1) was added thereto, and after stirring evenly, it was introduced into the top of the packed tower, and methanol vapor was introduced into the bottom of the tower to maintain the tower temperature at 110°C, and the saponification reaction of EVAc was started. The resin stayed in the tower for 0.2 hours. After saponification, the resin was discharged from the bottom of the tower, 22g of acetic acid and 600g of water were added, and the above reaction solution was neutralized to terminate the reaction.

[0154] Saponification post-treatment: The same post-treatment method as in Example 1 was used to obtain EVOH resin particles (with a diameter of about 4 mm and a length of about 5 mm).

[0155] In the above-mentioned ethylene-vinyl alcohol copolymer resin composition particles, the ethylene monomer content is 45 mol%, the structural unit of formula (1) is 0.12 mol%; and the saponification degree is 99.92 mol%.

[0156] The same treatment method as in Example 1 was used to prepare composition particles based on the ethylene-vinyl alcohol copolymer resin composition, and the particles were used to prepare molded products, and their properties were tested. The results are shown in Table 1 below.

[0157] Comparative Example 1

[0158] The method of Example 1 was followed, except that 50 g of α-methylene-γ-butyrolactone was replaced with 50 g of vinyl acetate, and other operations and conditions remained unchanged. The performance was tested and the results are shown in Table 1 below.

[0159] Comparative Example 2

[0160] The method of Example 1 was followed, except that 50 g of α-methylene-γ-butyrolactone was replaced with 50 g of methyl methacrylate. Other operations and conditions remained unchanged, and the performance was tested. The results are shown in Table 1 below.

[0161] Table 1 Performance evaluation results of Examples 1 to 4 and Comparative Examples 1 to 2

[0162]

[0163] Since the EVOH of the present invention contains a specific structural unit having γ-lactone, a film having excellent appearance, gas barrier properties and strength can be obtained.

[0164] It is easy to understand that the above embodiments are only examples for clear explanation and do not mean that the present invention is limited thereto. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the present invention.

Claims

1. An ethylene-vinyl alcohol copolymer resin composition, characterized in that It comprises an ethylene-vinyl alcohol copolymer structure and a structural unit represented by the following formula (1): In the formula, R1, R2, R3, and R4 are independently selected from H, an alkyl group having 1 to 4 carbon atoms, preferably H or methyl; The content of the structural unit represented by formula (1) is 0.01 to 10 mol %, preferably 0.02 to 5 mol %, more preferably 0.05 to 2 mol %, based on the total molar amount of the monomer units of the ethylene-vinyl alcohol copolymer and the structural unit represented by formula (1).

2. The ethylene-vinyl alcohol copolymer resin composition according to claim 1, characterized in that The content of the ethylene monomer unit in the ethylene-vinyl alcohol copolymer is 10 to 60 mol %, preferably 20 to 50 mol %, and more preferably 25 to 48 mol %, based on the total molar amount of the monomer unit of the ethylene-vinyl alcohol copolymer and the structural unit represented by formula (1).

3. The ethylene-vinyl alcohol copolymer resin composition according to claim 1, characterized in that The ethylene-vinyl alcohol copolymer resin composition is prepared by copolymerization of ethylene monomer, vinyl ester monomer and α-methylene lactone monomer; wherein the α-methylene lactone monomer is a compound having a structure shown in the following formula (2): In the formula, R1, R2, R3, and R4 are the same as R1, R2, R3, and R4 in formula (1).

4. The ethylene-vinyl alcohol copolymer resin composition according to claim 3, characterized in that The α-methylene lactone monomer is selected from one or more of α-methylene-γ-valerolactone (MVL) and α-methylene-γ-butyrolactone (MBL).

5. The ethylene-vinyl alcohol copolymer resin composition according to claim 3, characterized in that The vinyl ester monomer is selected from one or more of vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl versatate, etc., preferably vinyl acetate.

6. The ethylene-vinyl alcohol copolymer resin composition according to claim 3, characterized in that: The ethylene-vinyl alcohol copolymer resin composition comprises the following monomer molar percentage compositions: Ethylene monomer 10-60%; Vinyl ester monomer 50-89%; α-Methylene lactone monomer 0.01~10%.

7. The ethylene-vinyl alcohol copolymer resin composition according to any one of claims 1 to 6, characterized in that: The ethylene-vinyl alcohol copolymer resin composition is prepared by copolymerizing ethylene monomer, vinyl ester monomer and α-methylene lactone monomer to obtain a copolymer, which is then saponified.

8. A method for preparing the ethylene-vinyl alcohol copolymer resin composition according to any one of claims 1 to 7, characterized in that: include: The process of preparing a copolymer by copolymerizing ethylene monomer, vinyl ester monomer and α-methylene lactone monomer, and a step of saponifying the copolymer.

9. The preparation method according to claim 8, characterized in that: The copolymerization reaction pressure is 2-7 MPa; and / or The copolymerization reaction temperature is 40 to 80° C. and the reaction time is 0.5 to 6 h; and / or The saponification reaction temperature is 55-120° C. and the reaction time is 0.2-5 h.

10. A molded article, characterized in that: Made from the ethylene-vinyl alcohol copolymer resin composition according to any one of claims 1 to 7, or the ethylene-vinyl alcohol copolymer resin composition prepared by the method according to claim 8 or 9; Preferably, the molded object is obtained by melt molding; Preferably, the shaped article is a film; Preferably, the shaped object is a container.

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