Ethylene-vinyl alcohol copolymer resin and method for producing the same, ethylene-vinyl alcohol copolymer film

Abstract

This invention relates to the field of ethylene copolymers, specifically disclosing an ethylene-vinyl alcohol copolymer resin. The MFR (Mean Free Rate) of the ethylene-vinyl alcohol copolymer resin is A g / 10min at 190°C and a load of 2.16 kg, B g / 10min at 210°C and a load of 2.16 kg, and C g / 10min at 230°C and a load of 2.16 kg. The absolute value X of C-B and the absolute value Y of B-A satisfy Y / X = 0.6-0.9. This ethylene-vinyl alcohol copolymer resin exhibits better processing stability and more stable product dimensions. Furthermore, it can reduce the number of crystal points in the film and improve the fluctuation of the number of crystal points in the film.

Description

Technical Field

[0001] This invention relates to the field of ethylene copolymers, specifically to an ethylene-vinyl alcohol copolymer resin and its preparation method, and an ethylene-vinyl alcohol copolymer film. Background Technology

[0002] Ethylene-vinyl alcohol copolymers (EVOH), especially those with an ethylene content of 20-50 mol%, possess excellent gas barrier properties, approximately 10,000 times that of ordinary polyethylene. Based on their transparency, processability, solvent resistance, and antistatic properties, they are widely used in packaging materials, automotive fuel tanks, oxygen-barrier underfloor heating pipes, textiles, and medical materials. In downstream processing, EVOH is typically produced into multilayer films, sheets, and pipes through screw extrusion followed by blown film production, casting, and injection molding. The processing temperature during screw extrusion is usually 190-250℃, more preferably 210-230℃. Within this temperature range, the melt flowability of EVOH has a crucial impact on the stable control of the processing. Common issues encountered during EVOH processing include numerous crystal points on the film surface, unstable film barrel dimensions, high processing torque, and severe edge shrinkage in cast films.

[0003] Therefore, there is an urgent need to develop an EVOH resin that reduces the processing torque of screw extruders and the degree of edge shrinkage in cast films, so as to ensure smooth processing and stable product dimensions. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems existing in the prior art and to provide an ethylene-vinyl alcohol copolymer resin and its preparation method, as well as an ethylene-vinyl alcohol copolymer film, wherein the ethylene-vinyl alcohol copolymer resin has excellent processing stability.

[0005] To achieve the above objectives, the first aspect of the present invention provides an ethylene-vinyl alcohol copolymer resin, wherein the MFR of the ethylene-vinyl alcohol copolymer resin at 190°C and a load of 2.16 kg is A g / 10 min, the MFR at 210°C and a load of 2.16 kg is B g / 10 min, and the MFR at 230°C and a load of 2.16 kg is C g / 10 min, wherein the absolute value X of CB and the absolute value Y of BA satisfy: Y / X = 0.6-0.9.

[0006] A second aspect of the present invention provides a method for preparing an ethylene-vinyl alcohol copolymer resin, wherein a first ethylene-vinyl alcohol copolymer and a second ethylene-vinyl alcohol copolymer are mixed to obtain the ethylene-vinyl alcohol copolymer resin; Wherein, the degree of alcoholysis of the first ethylene-vinyl alcohol copolymer is ≥99%; the degree of alcoholysis of the second ethylene-vinyl alcohol copolymer is 50-80%; The mass ratio of the first ethylene-vinyl alcohol copolymer to the second ethylene-vinyl alcohol copolymer is 1:0.002-0.1.

[0007] A third aspect of the present invention provides an ethylene-vinyl alcohol copolymer resin prepared by the preparation method described above.

[0008] A fourth aspect of the present invention provides an ethylene-vinyl alcohol copolymer film, wherein the substrate of the ethylene-vinyl alcohol copolymer film is the ethylene-vinyl alcohol copolymer resin as described above.

[0009] Through the above technical solution, the present invention can achieve at least the following beneficial effects: The ethylene-vinyl alcohol copolymer resin provided by this invention exhibits a significant decrease in viscosity at 210-230℃, and its melt index satisfies Y / X=0.6-0.9. This results in better stability of the ethylene-vinyl alcohol copolymer resin during film formation processing. For example, the processing torque is more stable during screw extrusion, the film barrel dimensional stability is better during extrusion blown film process, and the edge shrinkage is lower during casting process. This leads to smoother processing, higher dimensional stability of the film product, and further reduces the number of crystal points in the film, improving the fluctuation of the number of crystal points in the film. Detailed Implementation

[0010] 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.

[0011] The first aspect of the present invention provides an ethylene-vinyl alcohol copolymer resin, wherein the MFR of the ethylene-vinyl alcohol copolymer resin at 190°C and a load of 2.16 kg is A g / 10 min, the MFR at 210°C and a load of 2.16 kg is B g / 10 min, and the MFR at 230°C and a load of 2.16 kg is C g / 10 min, wherein the absolute value X of CB and the absolute value Y of BA satisfy: Y / X = 0.6-0.9.

[0012] The ethylene-vinyl alcohol copolymer resin provided by this invention exhibits a significant decrease in viscosity at 210-230℃. The inventors of this invention ingeniously discovered that its melt index satisfies Y / X=0.6-0.9, resulting in better stability of the ethylene-vinyl alcohol copolymer resin during film formation. For example, the processing torque is more stable during screw extrusion, the film barrel dimensional stability is better during extrusion blown film process, and the edge shrinkage is lower during casting process, thereby making the processing smoother and the dimensional stability of the film product higher. Furthermore, it can also reduce the number of crystal points in the film and improve the fluctuation of the number of crystal points in the film.

[0013] In this invention, the melt flow index is tested in accordance with GB / T 3682.1-2018.

[0014] In this invention, Y / X = 0.6-0.9, for example, it can be 0.6, 0.62, 0.64, 0.66, 0.68, 0.7, 0.72, 0.74, 0.76, 0.78, 0.8, 0.82, 0.84, 0.86, 0.88, or 0.9, or it can be a range formed by any two of the above values, or any intermediate value within that range. More preferably, Y / X = 0.65-0.85.

[0015] According to the present invention, the degree of alcoholysis of the ethylene-vinyl alcohol copolymer resin is 98-99.9%.

[0016] In this invention, the degree of alcoholysis is measured using mid-infrared spectroscopy. Specifically, the degree of alcoholysis is measured using the mid-infrared spectroscopy technique, specifically by measuring the methyl and methylene groups in the ethylene-vinyl alcohol copolymer at 1430 cm⁻¹. -1 Using the combined frequency vibration peak heights of the left and right sides as a benchmark, a standard sample was used to establish a 1375cm peak height. -1 With 1430cm -1 The linear relationship between the ratio of the highest absorbance values ​​of the obliquely cut baseline within the region and the degree of alcoholysis is given by: Degree of alcoholysis% of the sample to be tested = -19.437X + 100.77, where X is 1375 cm⁻¹. -1 With 1430cm -1 The peak height ratio.

[0017] In this invention, the degree of hydrolysis of the ethylene-vinyl alcohol copolymer resin meets the above-mentioned range, which is more conducive to the copolymer resin having both excellent gas barrier properties and good processability.

[0018] More preferably, the degree of alcoholysis of the ethylene-vinyl alcohol copolymer resin is 98.5-99.9%.

[0019] According to the present invention, preferably, the ethylene-vinyl alcohol copolymer resin has a weight-average molecular weight of 50,000-120,000 g / mol and a molecular weight distribution index of 1-3.

[0020] More preferably, the weight-average molecular weight of the ethylene-vinyl alcohol copolymer resin is 60,000-85,000 g / mol.

[0021] In this invention, at least one of the weight-average molecular weight or molecular weight distribution of the ethylene-vinyl alcohol copolymer resin satisfies the above-mentioned range, which is more conducive to controlling the melt index of the ethylene-vinyl alcohol copolymer resin to meet the above-mentioned range, improving the processing stability of the ethylene-vinyl alcohol copolymer resin, and further enabling the ethylene-vinyl alcohol copolymer resin to have better mechanical properties.

[0022] In this invention, the weight-average molecular weight and molecular weight distribution index are tested by gel permeation chromatography.

[0023] According to the present invention, preferably, the content of structural units from ethylene in the ethylene-vinyl alcohol copolymer resin is 20-50 mol.

[0024] In this invention, the content of structural units derived from ethylene was tested in accordance with GB / T 41877.2-2022.

[0025] In this invention, the content of structural units derived from ethylene in the ethylene-vinyl alcohol copolymer resin meets the above-mentioned range, which is more conducive to improving the melt processability and gas barrier properties of the copolymer resin.

[0026] More preferably, the content of structural units from ethylene in the ethylene-vinyl alcohol copolymer resin is 25-48 mol.

[0027] More preferably, the content of structural units from ethylene in the ethylene-vinyl alcohol copolymer resin is 30-40 mol.

[0028] According to the present invention, preferably, A is 0.5-5.

[0029] According to the present invention, preferably, B is 1-12.

[0030] According to the present invention, preferably, C is 1.5-25.

[0031] In this invention, at least one of A, B and C satisfies the above-mentioned range, which can further improve the processing stability of the ethylene-vinyl alcohol copolymer resin.

[0032] More preferably, A is 1-3.

[0033] More preferably, B is 2-9.

[0034] More preferably, C is 3.5-12.

[0035] According to the present invention, preferably, the coefficient of variation of B is ≤10%.

[0036] According to the present invention, preferably, the coefficient of variation of C is ≤10%.

[0037] In this invention, the coefficient of variation = (SD / MN) × 100%, where MN is the mean and SD is the standard deviation. The formula for calculating the standard deviation SD is:

[0038] Where N is the total number of test samples, N≥5; x i Let be the test value of the i-th sample.

[0039] In this invention, the coefficients of variation of B and C reflect the degree of fluctuation of the melt index between different samples of ethylene-vinyl alcohol resin at 210℃ and 230℃, and directly reflect the stability of the melt index of ethylene-vinyl alcohol resin. When at least one of the coefficients of variation of B and C meets the above range, it is more conducive to improving the processing stability and product dimensional stability of the ethylene-vinyl alcohol resin, and further reducing the number of crystal points and quality stability in the film.

[0040] More preferably, the coefficient of variation of B is ≤6%.

[0041] More preferably, the coefficient of variation of C is ≤6%.

[0042] A second aspect of the present invention provides a method for preparing an ethylene-vinyl alcohol copolymer resin, wherein a first ethylene-vinyl alcohol copolymer and a second ethylene-vinyl alcohol copolymer are mixed to obtain the ethylene-vinyl alcohol copolymer resin; Wherein, the degree of alcoholysis of the first ethylene-vinyl alcohol copolymer is ≥99%; the degree of alcoholysis of the second ethylene-vinyl alcohol copolymer is 50-80%; The mass ratio of the first ethylene-vinyl alcohol copolymer to the second ethylene-vinyl alcohol copolymer is 1:0.002-0.1.

[0043] In this invention, in order to further improve the processing stability of the obtained ethylene-vinyl alcohol copolymer resin, the mass ratio of the first ethylene-vinyl alcohol copolymer to the second ethylene-vinyl alcohol copolymer is 1:0.005-0.05.

[0044] More preferably, the degree of alcoholysis of the first ethylene-vinyl alcohol copolymer is 99-99.9%.

[0045] More preferably, the degree of alcoholysis of the first ethylene-vinyl alcohol copolymer is 99.3-99.9%.

[0046] More preferably, the degree of alcoholysis of the second ethylene-vinyl alcohol copolymer is 60-78%.

[0047] In some specific embodiments of the present invention, the degree of alcoholysis of the second ethylene-vinyl alcohol copolymer is 68-78%.

[0048] In this invention, the content of structural units from ethylene in the first ethylene-vinyl alcohol copolymer is 20-50 mol%, preferably 25-48 mol%, and more preferably 30-40 mol%.

[0049] In this invention, the weight-average molecular weight of the first ethylene-vinyl alcohol copolymer is 50,000-120,000 g / mol, and the molecular weight distribution index is 1-3.

[0050] More preferably, the weight-average molecular weight of the first ethylene-vinyl alcohol copolymer is 50,000-85,000 g / mol.

[0051] In this invention, the content of structural units from ethylene in the second ethylene-vinyl alcohol copolymer is 20-50 mol%, preferably 25-48 mol%, and more preferably 30-40 mol%.

[0052] In this invention, the weight-average molecular weight of the second ethylene-vinyl alcohol copolymer is 50,000-120,000 g / mol, and the molecular weight distribution index is 1-3.

[0053] More preferably, the weight-average molecular weight of the second ethylene-vinyl alcohol copolymer is 60,000-100,000 g / mol.

[0054] In some specific embodiments of the present invention, the content of structural units derived from ethylene in the first ethylene-vinyl alcohol copolymer and the second ethylene-vinyl alcohol copolymer is the same.

[0055] According to the present invention, preferably, in order to further improve the processing stability of the obtained ethylene-vinyl alcohol copolymer resin, the preparation method includes: A first solution containing a first ethylene-vinyl alcohol copolymer is mixed with a second solution containing a second ethylene-vinyl alcohol copolymer. The mixed solution is then molded, washed, and dried to obtain the ethylene-vinyl alcohol copolymer resin.

[0056] According to the present invention, preferably, the content of the first ethylene-vinyl alcohol copolymer in the first solution is 40-60 wt%.

[0057] According to the present invention, preferably, the content of the second ethylene-vinyl alcohol copolymer in the second solution is 40-60 wt%.

[0058] According to the present invention, preferably, the solvent of the first solution and the solvent of the second solution are each independently selected from at least one of methanol, ethanol, propanol, ethylene glycol, n-butanol and tert-butanol.

[0059] In this invention, the method for preparing the first solution containing the first ethylene-vinyl alcohol copolymer can be a conventional choice in the art. For example, the first solution containing the first ethylene-vinyl alcohol copolymer is obtained by the following method: An alkali is added to a solution containing ethylene-vinyl acetate copolymer to initiate an alcoholysis reaction. Acetic acid is then added to adjust the pH to neutral, terminating the reaction and yielding a first solution. The amount of alkali used and the alcoholysis conditions are such that the degree of alcoholysis of the first ethylene-vinyl alcohol copolymer is ≥99%.

[0060] In some specific embodiments of the present invention, the molar ratio of the alkali to the vinyl acetate structural units in the ethylene-vinyl acetate copolymer is 0.01-0.3:1; the conditions for alcoholysis include a temperature of 50-70°C and a time of 5-8 hours.

[0061] In this invention, the method for preparing the second solution containing the second ethylene-vinyl alcohol copolymer can be a conventional choice in the art. For example, the second solution containing the second ethylene-vinyl alcohol copolymer can be obtained by the following method: An alkali is added to a solution containing ethylene-vinyl acetate copolymer to initiate an alcoholysis reaction. Acetic acid is then added to adjust the pH to neutral, terminating the reaction and yielding a second solution. The amount of alkali used and the alcoholysis conditions are such that the degree of alcoholysis of the second ethylene-vinyl alcohol copolymer is 50-80%.

[0062] In some specific embodiments of the present invention, the molar ratio of the alkali to the vinyl acetate structural units in the ethylene-vinyl acetate copolymer is 0.002-0.1:1; the conditions for alcoholysis include: a temperature of 50-70°C and a time of 0.5-4h.

[0063] In this invention, the washing conditions can be conventional choices in the art, and this invention does not impose any particular limitations on them.

[0064] Preferably, in order to further improve the washing effect, an additive may be added in at least one of the processes of mixing the first ethylene-vinyl alcohol copolymer and the second ethylene-vinyl alcohol copolymer, the molding process, and the washing process.

[0065] In some specific embodiments of the present invention, the additive is acetic acid and / or propionic acid.

[0066] In some specific embodiments of the present invention, the amount of the additive is 100-5000 ppm of the total mass of the first ethylene-vinyl alcohol copolymer and the second ethylene-vinyl alcohol copolymer.

[0067] A third aspect of the present invention provides an ethylene-vinyl alcohol copolymer resin prepared by the preparation method described above.

[0068] A fourth aspect of the present invention provides an ethylene-vinyl alcohol copolymer film, wherein the substrate of the ethylene-vinyl alcohol copolymer film is the ethylene-vinyl alcohol copolymer resin as described above.

[0069] In this invention, the processing and molding process of the ethylene-vinyl alcohol copolymer film can be a conventional choice in the art, such as casting.

[0070] In some specific embodiments of the present invention, the casting conditions include: the maximum screw speed of the casting machine is 200-300 rpm, the maximum stress is 120-200 Nm, the screw temperature is set in three zones, namely 190±15℃, 220±15℃ and 220±15℃, the screw speed is 60-80 rpm, and the film traction speed is 1-5 m / s.

[0071] According to the present invention, preferably, the thickness of the ethylene-vinyl alcohol copolymer film is 20-40 μm.

[0072] According to the present invention, preferably, the average number of crystal points in the ethylene-vinyl alcohol copolymer film is ≤5000 per square meter.

[0073] In this invention, the number of crystal points is tested using a linear array camera. The testing method involves detecting the crystal points in the thin film using a linear array camera during the casting process, with one square meter of thin film used as a test sample. The coefficient of variation is calculated as described previously. The casting conditions can be as described previously.

[0074] More preferably, based on 1 square meter of ethylene-vinyl alcohol copolymer film, the average number of crystal points in the ethylene-vinyl alcohol copolymer film is 2000-5000.

[0075] More preferably, based on 1 square meter of ethylene-vinyl alcohol copolymer film, the average number of crystal points in the ethylene-vinyl alcohol copolymer film is 2000-4000.

[0076] According to the present invention, preferably, the coefficient of variation of the number of crystal points in the ethylene-vinyl alcohol copolymer film is ≤15% based on 1 square meter of ethylene-vinyl alcohol copolymer film.

[0077] In this invention, the coefficient of variation of the number of crystal points in the ethylene-vinyl alcohol copolymer film reflects the degree of fluctuation of the crystal points and directly reflects the quality stability of the ethylene-vinyl alcohol copolymer film. When the number of crystal points in the ethylene-vinyl alcohol copolymer film meets the above-mentioned range, it indicates that the ethylene-vinyl alcohol copolymer resin described in the first aspect of this application has good processing stability, and the film made from it has better quality stability. The calculation method of the coefficient of variation can be as shown above.

[0078] In some preferred embodiments of the present invention, the coefficient of variation of the number of crystal points in the ethylene-vinyl alcohol copolymer film is ≤10%, based on 1 square meter of ethylene-vinyl alcohol copolymer film.

[0079] The present invention will be described in detail below through embodiments. It should be understood that the following embodiments are only used to further explain and illustrate the content of the present invention, and are not intended to limit the present invention.

[0080] Unless otherwise specified, all reagents and materials used in the following examples were purchased from reputable chemical reagent suppliers and were of analytical purity.

[0081] In the following examples, the ethylene-vinyl acetate copolymer solution was prepared by the following method: Ethylene-vinyl acetate copolymer solution 1: 100 parts by weight of vinyl acetate, 19 parts by weight of methanol and 0.1 parts by weight of azobisisobutyronitrile were added to a pressure polymerization reactor. The reaction was carried out at 60°C and 3.7 MPa of ethylene for 5.5 h under stirring. Then, 20 parts by weight of methanol and 500 ppm of copper acetate relative to the weight of vinyl acetate were added to obtain a methanol solution containing 42 wt% ethylene-vinyl acetate copolymer (32 wt% of structural units from ethylene, weight average molecular weight of 89073 g / mol, and molecular weight distribution index of 1.9).

[0082] Ethylene-vinyl acetate copolymer solution 2: 100 parts by weight of vinyl acetate, 11 parts by weight of methanol and 0.07 parts by weight of azobisisobutyronitrile were added to a pressure polymerization reactor. The reaction was carried out at 60°C and ethylene pressure of 3.8 MPa for 5 h under stirring. Then, 20 parts by weight of methanol and 500 ppm of copper acetate relative to the weight of vinyl acetate were added to obtain a methanol solution containing 40 wt% ethylene-vinyl acetate copolymer (32 wt% of structural units from ethylene, weight average molecular weight of 138116 g / mol, and molecular weight distribution index of 2.8).

[0083] Example 1 S1. Add NaOH methanol solution to ethylene-vinyl acetate copolymer solution 1, so that the molar ratio of NaOH to the structural unit from vinyl acetate in the ethylene-vinyl acetate copolymer is 0.1:1. After reacting at 65℃ for 6 hours, add acetic acid to adjust the pH value to neutral and terminate the reaction to obtain a first solution containing the first ethylene-vinyl alcohol copolymer, the degree of alcoholysis of the first ethylene-vinyl alcohol copolymer is 99.5%.

[0084] S2. Add NaOH methanol solution to ethylene-vinyl acetate copolymer solution 1, so that the molar ratio of NaOH to the structural unit from vinyl acetate in the ethylene-vinyl acetate copolymer is 0.04:1. After reacting at 65℃ for 3 hours, add acetic acid to adjust the pH to neutral and terminate the reaction to obtain a second solution containing a second ethylene-vinyl alcohol copolymer. The degree of alcoholysis of the second ethylene-vinyl alcohol copolymer is 75.6%.

[0085] S3. Mix the first solution and the second solution at a mass ratio of 1:0.02 for the first ethylene-vinyl alcohol copolymer and the second ethylene-vinyl alcohol copolymer, and then add acetic acid, an additive with a total mass of 600 ppm of the first ethylene-vinyl alcohol copolymer and the second ethylene-vinyl alcohol copolymer.

[0086] S4. The above mixed solution is molded, washed, and dried to obtain ethylene-vinyl alcohol copolymer resin P1. The degree of alcoholysis of P1 is 99.3%.

[0087] The weight-average molecular weight and molecular weight distribution index of the first ethylene-vinyl alcohol copolymer, the second ethylene-vinyl alcohol copolymer, and ethylene-vinyl alcohol copolymer resin P1 are shown in Table 1.

[0088] The values ​​of A, B, and C, as well as the Y / X ratio, of ethylene-vinyl alcohol copolymer resin P1 are shown in Table 2.

[0089] Example 2 Ethylene-vinyl alcohol copolymer resin P2 was prepared according to the method in Example 1, except that... S1. The molar ratio of NaOH to the structural units derived from vinyl acetate in the ethylene-vinyl acetate copolymer is 0.2:1. After reacting at 65℃ for 4 hours, acetic acid is added to adjust the pH to neutral, and the reaction is terminated to obtain a first solution containing the first ethylene-vinyl alcohol copolymer. The degree of alcoholysis of the first ethylene-vinyl alcohol copolymer is 99.6%. S2. The molar ratio of NaOH to the structural units derived from vinyl acetate in the ethylene-vinyl acetate copolymer is 0.02:1. After reacting at 65°C for 2 hours, acetic acid is added to adjust the pH to neutral, and the reaction is terminated to obtain a second solution containing a second ethylene-vinyl alcohol copolymer. The degree of alcoholysis of the second ethylene-vinyl alcohol copolymer is 65.9%. S3. Mix the first solution and the second solution at a mass ratio of 1:0.006 for the first ethylene-vinyl alcohol copolymer and the second ethylene-vinyl alcohol copolymer.

[0090] The degree of alcoholysis of P2 is 99.4%.

[0091] Example 3 Ethylene-vinyl alcohol copolymer resin P3 was prepared according to the method in Example 1, except that... S1. The molar ratio of NaOH to the structural units derived from vinyl acetate in the ethylene-vinyl acetate copolymer is 0.06:1. After reacting at 65℃ for 5.5 h, acetic acid is added to adjust the pH to neutral, and the reaction is terminated to obtain a first solution containing the first ethylene-vinyl alcohol copolymer. The degree of alcoholysis of the first ethylene-vinyl alcohol copolymer is 99.1%. The degree of alcoholysis of P3 is 98.6%.

[0092] Example 4 Ethylene-vinyl alcohol copolymer resin P4 was prepared according to the method in Example 1, except that... S1. The molar ratio of NaOH to the structural units derived from vinyl acetate in the ethylene-vinyl acetate copolymer is 0.2:1. After reacting at 65℃ for 7.5h, acetic acid is added to adjust the pH to neutral, and the reaction is terminated to obtain a first solution containing the first ethylene-vinyl alcohol copolymer. The degree of alcoholysis of the first ethylene-vinyl alcohol copolymer is 99.9%. The degree of alcoholysis of P4 is 99.22%.

[0093] Example 5 Ethylene-vinyl alcohol copolymer resin P5 was prepared according to the method in Example 1, except that... S2. The molar ratio of NaOH to the structural units derived from vinyl acetate in the ethylene-vinyl acetate copolymer is 0.008:1. After reacting at 65℃ for 2 hours, acetic acid is added to adjust the pH to neutral, and the reaction is terminated to obtain a second solution containing a second ethylene-vinyl alcohol copolymer. The degree of alcoholysis of the second ethylene-vinyl alcohol copolymer is 55.7%. The degree of alcoholysis of P5 is 98.6%.

[0094] Example 6 Ethylene-vinyl alcohol copolymer resin P6 was prepared according to the method in Example 1, except that... S2. The molar ratio of NaOH to the structural units derived from vinyl acetate in the ethylene-vinyl acetate copolymer is 0.07:1. After reacting at 65℃ for 3 hours, acetic acid is added to adjust the pH to neutral, and the reaction is terminated to obtain a second solution containing a second ethylene-vinyl alcohol copolymer. The degree of alcoholysis of the second ethylene-vinyl alcohol copolymer is 79.5%. The degree of alcoholysis of P6 is 99.1%.

[0095] Example 7 Ethylene-vinyl alcohol copolymer resin P7 was prepared according to the method in Example 1, except that... S3. Mix the first solution and the second solution at a mass ratio of 1:0.002 for the first ethylene-vinyl alcohol copolymer and the second ethylene-vinyl alcohol copolymer.

[0096] The degree of alcoholysis of P7 is 99.5%.

[0097] Example 8 Ethylene-vinyl alcohol copolymer resin P8 was prepared according to the method in Example 1, except that... S3. Mix the first solution and the second solution at a mass ratio of 1:0.06 between the first ethylene-vinyl alcohol copolymer and the second ethylene-vinyl alcohol copolymer.

[0098] The degree of alcoholysis of P8 is 98.1%.

[0099] Example 9 Ethylene-vinyl alcohol copolymer resin P9 was prepared according to the method in Example 1, except that... S1. Replace ethylene-vinyl acetate copolymer solution 1 with ethylene-vinyl acetate copolymer solution 2, and the degree of alcoholysis of the first ethylene-vinyl alcohol copolymer is 99.5%; S2. Add NaOH methanol solution to ethylene-vinyl acetate copolymer solution 1, so that the molar ratio of NaOH to the structural unit from vinyl acetate in the ethylene-vinyl acetate copolymer is 0.04:1. After reacting at 65℃ for 2.5h, add acetic acid to adjust the pH to neutral and terminate the reaction to obtain a second solution containing a second ethylene-vinyl alcohol copolymer. The degree of alcoholysis of the second ethylene-vinyl alcohol copolymer is 74.1%.

[0100] The degree of alcoholysis of P9 is 99.2%.

[0101] Comparative Example 1 The ethylene-vinyl alcohol copolymer resin DP1 was prepared according to the method in Example 1, except that... S3. Mix the first solution and the second solution at a mass ratio of 1:0.0005 for the first ethylene-vinyl alcohol copolymer and the second ethylene-vinyl alcohol copolymer.

[0102] The degree of alcoholysis of DP1 is 99.5%.

[0103] Comparative Example 2 The ethylene-vinyl alcohol copolymer resin DP2 was prepared according to the method of Example 1, except that... S2. The molar ratio of NaOH to the structural units derived from vinyl acetate in the ethylene-vinyl acetate copolymer is 0.15:1. After reacting at 65℃ for 5 hours, acetic acid is added to adjust the pH to neutral, and the reaction is terminated to obtain a second solution containing a second ethylene-vinyl alcohol copolymer. The degree of alcoholysis of the second ethylene-vinyl alcohol copolymer is 90.9%. The degree of alcoholysis of DP2 is 99.4%.

[0104] Comparative Example 3 The ethylene-vinyl alcohol copolymer resin DP3 was prepared according to the method in Example 1, except that... S1. The molar ratio of NaOH to the structural units derived from vinyl acetate in the ethylene-vinyl acetate copolymer in the system is 0.06:1. After reacting at 65℃ for 3 hours, acetic acid is added to adjust the pH to neutral, and the reaction is terminated to obtain a first solution containing the first ethylene-vinyl alcohol copolymer. The degree of alcoholysis of the first ethylene-vinyl alcohol copolymer is 98.5%. The degree of alcoholysis of DP3 is 98.3%.

[0105] Comparative Example 4 Similar to Example 1, except that in S3 the second solution is replaced with pentaerythritol in an amount equal to that of the second ethylene-vinyl alcohol copolymer.

[0106] The degree of alcoholysis of DP4 is 99.5%.

[0107] Comparative Example 5 The ethylene-vinyl alcohol copolymer resin DP5 was prepared according to the method in Example 1, except that... S3. Mix the first solution with the ethylene-vinyl acetate copolymer solution 1 at a mass ratio of 1:0.01 for the first ethylene-vinyl alcohol copolymer and the ethylene-vinyl acetate copolymer, and then add acetic acid, an additive with a total mass of 600 ppm of the first ethylene-vinyl alcohol copolymer and the ethylene-vinyl acetate copolymer.

[0108] The degree of alcoholysis of DP5 is 98.5%.

[0109] Comparative Example 6 NaOH methanol solution was added to ethylene-vinyl acetate copolymer solution 1, so that the molar ratio of NaOH to the structural units derived from vinyl acetate in the ethylene-vinyl acetate copolymer was 0.1:1. After reacting at 65℃ for 5.2 h, acetic acid was added to adjust the pH to neutral, and the reaction was terminated. Acetic acid additive at a total mass of 600 ppm of the ethylene-vinyl acetate copolymer was added. The solution was then molded, dried, and washed to obtain an ethylene-vinyl alcohol copolymer with a degree of alcoholysis of 99.3%.

[0110] Table 1

[0111] Table 2

[0112] Application examples The ethylene-vinyl alcohol copolymer resins prepared in the above examples and comparative examples were cast into films using a ME20-MFA-FSA100V2 casting film machine to obtain ethylene-vinyl alcohol copolymer films M1-M9 and DM1-DM6 with a film thickness of 30±10μm. The specific casting conditions were as follows: The screw model is Pheomix 19 / 25 OS Screw 3:1 L / D 25, with a maximum speed of 250 rpm and a maximum stress of 160 Nm. The screw temperature setting is divided into three zones: 190℃ / 220℃ / 220℃. The screw speed is 70 rpm, and the film traction speed is 2.5 ± 0.5 m / s.

[0113] The number of crystal points and the coefficient of variation of the number of crystal points for ethylene-vinyl alcohol copolymer films M1-M9 and DM1-DM6 are shown in Table 3.

[0114] The standard deviations of the dimensions of ethylene-vinyl alcohol copolymer films M1-M9 and DM1-DM6 in the width and thickness directions were tested. Width (cm) and thickness (μm) values ​​of 20 films were randomly measured along the casting direction, and the standard deviation (SD) was calculated using the following formula:

[0115] Where MN is the average value; N is the total number of test samples; x i This represents the test value for the i-th sample. The width MN is 27 cm, and the thickness MN is 20 μm.

[0116] Table 3

[0117] Table 4

[0118] 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. An ethylene-vinyl alcohol copolymer resin, characterized in that it comprises: The MFR of the ethylene-vinyl alcohol copolymer resin at 190°C and 2.16 kg load is A g / 10 min, the MFR at 210°C and 2.16 kg load is B g / 10 min, and the MFR at 230°C and 2.16 kg load is C g / 10 min, wherein the absolute value X of CB and the absolute value Y of BA satisfy: Y / X = 0.6-0.

9.

2. The ethylene-vinyl alcohol copolymer resin according to claim 1, wherein, The degree of alcoholysis of the ethylene-vinyl alcohol copolymer resin is 98-99.9%; And / or, the weight-average molecular weight of the ethylene-vinyl alcohol copolymer resin is 50,000-120,000 g / mol; And / or, the molecular weight distribution index of the ethylene-vinyl alcohol copolymer resin is 1-3.

3. The ethylene-vinyl alcohol copolymer resin according to claim 1 or 2, wherein, The content of structural units derived from ethylene in the ethylene-vinyl alcohol copolymer resin is 20-50 mol.

4. The ethylene-vinyl alcohol copolymer resin according to claim 1 or 2, wherein, A is 0.5-5; And / or, B is 1-12; And / or, the coefficient of variation of B is ≤10%; And / or, C is 1.5-20; And / or, the coefficient of variation of C is ≤10%.

5. The ethylene-vinyl alcohol copolymer resin according to claim 1 or 2, wherein, Y / X = 0.65 - 0.

85.

6. A method for preparing an ethylene-vinyl alcohol copolymer resin, characterized in that, The preparation method includes: The first ethylene-vinyl alcohol copolymer and the second ethylene-vinyl alcohol copolymer are mixed to obtain the ethylene-vinyl alcohol copolymer resin; Wherein, the degree of alcoholysis of the first ethylene-vinyl alcohol copolymer is ≥99%; and the degree of alcoholysis of the second ethylene-vinyl alcohol copolymer is 50-80%. The mass ratio of the first ethylene-vinyl alcohol copolymer to the second ethylene-vinyl alcohol copolymer is 1:0.002-0.

1.

7. The preparation method according to claim 6, wherein, The preparation method includes: A first solution containing a first ethylene-vinyl alcohol copolymer is mixed with a second solution containing a second ethylene-vinyl alcohol copolymer. The mixed solution is then molded, washed, and dried to obtain the ethylene-vinyl alcohol copolymer resin.

8. The preparation method according to claim 7, wherein, The first solution contains 40-60 wt% of the first ethylene-vinyl alcohol copolymer. And / or, the content of the second ethylene-vinyl alcohol copolymer in the second solution is 40-60 wt%; And / or, the solvent of the first solution and the solvent of the second solution are each independently selected from at least one of methanol, ethanol, propanol, ethylene glycol, n-butanol and tert-butanol.

9. The preparation method according to claim 6 or 7, wherein, In the first ethylene-vinyl alcohol copolymer, the content of structural units derived from ethylene is 20-50 mol%; And / or, the weight-average molecular weight of the first ethylene-vinyl alcohol copolymer is 50,000-120,000 g / mol, and the molecular weight distribution index is 1-3; And / or, in the second ethylene-vinyl alcohol copolymer, the content of structural units derived from ethylene is 20-50 mol%; And / or, the weight-average molecular weight of the second ethylene-vinyl alcohol copolymer is 50,000-120,000 g / mol, and the molecular weight distribution index is 1-3.

10. An ethylene-vinyl alcohol copolymer resin prepared by any one of claims 6-9.

11. An ethylene-vinyl alcohol copolymer film, characterized in that, The substrate of the ethylene-vinyl alcohol copolymer film is the ethylene-vinyl alcohol copolymer resin according to any one of claims 1-5 and 10.

12. The ethylene-vinyl alcohol copolymer film according to claim 11, wherein, The thickness of the ethylene-vinyl alcohol copolymer film is 20-40 μm.

13. The ethylene-vinyl alcohol copolymer film according to claim 11, wherein, Based on 1 square meter of ethylene-vinyl alcohol copolymer film, the average number of crystal points in the ethylene-vinyl alcohol copolymer film is ≤5000; And / or, based on 1 square meter of ethylene-vinyl alcohol copolymer film, the coefficient of variation of the number of crystal points in the ethylene-vinyl alcohol copolymer film is ≤15%.

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