Ethylene-vinyl alcohol copolymer as well as preparation method, application and film thereof

Abstract

The invention relates to the field of resin, and discloses an ethylene-vinyl alcohol copolymer, a preparation method and application thereof, and a film. The melt index of the copolymer at 190 DEG C under the load of 21.6 kg is MFR21.6, the melt index of the copolymer at 190 DEG C under the load of 5 kg is MFR5, the melt index of the copolymer at 190 DEG C under the load of 2.16 kg is MFR2.16, and MFR21.6, MFR5 and MFR2.16 meet the following relation: 10 < = MFR21.6 / MFR2.16-MFR5 / MFR2.16 < = 25. The ethylene-vinyl alcohol copolymer provided by the invention has relatively good processing stability, so that the processing operation period is long, and the ethylene-vinyl alcohol copolymer also has relatively few surface defects and relatively small crystal point defects.

Description

Technical Field

[0001] The present invention relates to the field of resins, and particularly to ethylene-vinyl alcohol copolymers, their preparation methods, applications, and films. Background Art

[0002] Ethylene-vinyl alcohol copolymers (EVOH), especially those with an ethylene content of 20-50 mol%, have excellent gas barrier properties, approximately 10,000 times that of ordinary polyethylene. Coupled with their transparency, processability, solvent resistance, and antistatic properties, they are widely used in packaging materials, automotive fuel tanks, oxygen barrier floor heating pipes, textile materials, and medical materials. Ethylene-vinyl alcohol copolymers are usually processed by melt processing during use. As a polymer containing polyhydroxy structures in its molecular structure, EVOH is prone to intermolecular and intramolecular dehydration under high-temperature conditions, resulting in a decrease in processing stability, especially defects such as crystal points during the film-forming process. Summary of the Invention

[0003] The purpose of the present invention is to overcome the problems of unstable processing of ethylene-vinyl alcohol copolymers and defects generated during the film-forming process in the prior art, and to provide ethylene-vinyl alcohol copolymers, their preparation methods, applications, and films.

[0004] To achieve the above purpose, the first aspect of the present invention provides an ethylene-vinyl alcohol copolymer. The melt index of the copolymer at 190 °C and a load of 21.6 kg is MFR 21.6 , the melt index of the copolymer at 190 °C and a load of 5 kg is MFR 5 , the melt index of the copolymer at 190 °C and a load of 2.16 kg is MFR 2.16 ,

[0005] The MFR 21.6 , MFR 5 and MFR 2.16 satisfy the following relationship:

[0006] 10 ≤ MFR 216 / MFR 216 - MFR 5 / MFR 216 ≤ 25.

[0007] The second aspect of the present invention provides a method for preparing an ethylene-vinyl alcohol copolymer. The method includes:

[0008] (1) Polymerize vinyl acetate and ethylene in the presence of a first solvent and an initiator;

[0009] (2) Sequentially mix a second solvent and a terminator in the product of step (1) to obtain an ethylene-vinyl acetate copolymer solution;

[0010] (3) Contact the ethylene-vinyl acetate copolymer solution with a base to obtain an ethylene-vinyl alcohol copolymer.

[0011] The third aspect of the present invention provides an ethylene-vinyl alcohol copolymer prepared by the above method.

[0012] The fourth aspect of the present invention provides the application of the above ethylene-vinyl alcohol copolymer in at least one of packaging materials, automobile fuel tanks, oxygen-barrier floor heating pipes, textile materials, and medical materials.

[0013] The fifth aspect of the present invention provides an ethylene-vinyl alcohol copolymer film, and the film is prepared from the above copolymer.

[0014] Through the above technical solutions, the ethylene-vinyl alcohol copolymer provided by the present invention has good processing stability, resulting in a long processing operation cycle. More preferably, when it is used to prepare an ethylene-vinyl alcohol film, the obtained film has fewer surface defects and smaller crystal point defects. Detailed Embodiments

[0015] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values and individual point values of each range, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0016] The first aspect of the present invention provides an ethylene-vinyl alcohol copolymer, and the melt index of the copolymer at 190 °C and a load of 21.6 kg is MFR 21.6 , the melt index of the copolymer at 190 °C and a load of 5 kg is MFR 5 , the melt index of the copolymer at 190 °C and a load of 2.16 kg is MFR 2.16 ,

[0017] The MFR 21.6 , MFR 5 and MFR 2.16 satisfy the following relationship:

[0018] 10 ≤ MFR 21.6 / MFR 2.16 -MFR 5 / MFR 2.16 ≤ 25, and can be 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25 or the range formed by any two of the above values and the values within the range.

[0019] In the present invention, when the ethylene-vinyl alcohol copolymer satisfies the above relationship, it has good processing stability, resulting in a long processing operation cycle. When it is used to prepare an ethylene-vinyl alcohol film, the obtained film has fewer surface defects and smaller crystal point defects.

[0020] More preferably, 12 ≤ MFR 21.6 / MFR 2.16 -MFR 5 / MFR 2.16 ≤ 22.

[0021] According to the present invention, in order to obtain better processing stability, fewer surface defects and smaller crystal point defects, the change in the screw current of the copolymer when using a blown film machine is less than or equal to 1 A.

[0022] In the present invention, when the change in the screw current of the copolymer when using a blown film machine is less than or equal to 1 A, it has good processing stability.

[0023] According to the present invention, the content of the structural unit derived from ethylene in the copolymer is 20 - 50 mol%, which can be 20 mol%, 22 mol%, 25 mol%, 30 mol%, 35 mol%, 40 mol%, 45 mol%, 48 mol%, 50 mol% or any range formed by any two of the above values and the values within the range, preferably 22 - 48 mol%. The above content of the structural unit derived from ethylene is based on the total molar content of the copolymer.

[0024] In the present invention, when the content of the structural unit derived from ethylene in the copolymer is within the above range, it has good balance between barrier properties and melt processability, and has good use effects when processed into materials such as films and sheets.

[0025] According to the present invention, at 190 °C and under a load of 2.16 kg, the melt index of the copolymer is 1 - 10 g / 10 min, which can be 0.1 g / min, 0.2 g / min, 0.3 g / min, 0.4 g / min, 0.5 g / min, 0.6 g / min, 0.7 g / min, 0.8 g / min, 0.9 g / min, 1 g / min, 2 g / min, 4 g / min, 6 g / min, 8 g / min, 10 g / min or any range formed by any two of the above values and the values within the range.

[0026] In the present invention, when the melt index is within the above range, it has good processing fluidity and can be widely applied.

[0027] According to the present invention, the weight-average molecular weight of the copolymer is 20,000 - 200,000 g / mol, and it can be 20,000 g / mol, 40,000 g / mol, 60,000 g / mol, 80,000 g / mol, 100,000 g / mol, 120,000 g / mol, 140,000 g / mol, 160,000 g / mol, 180,000 g / mol, 200,000 g / mol or any value within the range formed by any two of the above values; the molecular weight distribution of the copolymer is 1 - 3, and it can be 1, 1.5, 2, 2.5, 3 or any value within the range formed by any two of the above values.

[0028] In the present invention, when the weight-average molecular weight and the molecular weight distribution of the copolymer are within the above ranges, the copolymer has both good mechanical properties and melt processability, and a better application effect is obtained.

[0029] According to the present invention, at 25 °C, the intrinsic viscosity of the copolymer is 0.1 - 1 dl / g, and it can be 0.1 dl / g, 0.2 dl / g, 0.3 dl / g, 0.4 dl / g, 0.5 dl / g, 0.6 dl / g, 0.7 dl / g, 0.8 dl / g, 0.9 dl / g, 1 dl / g or any value within the range formed by any two of the above values.

[0030] In the present invention, when the intrinsic viscosity of the copolymer is within the above range, the copolymer has both good mechanical properties and melt processability, and a better application effect is obtained.

[0031] According to the present invention, the degree of alcoholysis of the copolymer is 99 - 99.9%, and it can be 99%, 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9% or any value within the range formed by any two of the above values.

[0032] In the present invention, when the degree of alcoholysis of the copolymer is within the above range, the polymer has excellent barrier properties and finds wide application effects in the field of barrier packaging.

[0033] The second aspect of the present invention provides a method for preparing ethylene-vinyl alcohol copolymer, and the method includes:

[0034] (1) Polymerize vinyl acetate and ethylene in the presence of a first solvent and an initiator;

[0035] (2) Sequentially mix a second solvent and a terminator in the product of step (1) to obtain an ethylene-vinyl acetate copolymer solution;

[0036] (3) Contact the ethylene-vinyl acetate copolymer solution with a base to obtain an ethylene-vinyl alcohol copolymer.

[0037] In the present invention, through the above method, an ethylene-vinyl alcohol copolymer with good processing stability is obtained, enabling a long processing operation cycle. When it is used to prepare an ethylene-vinyl alcohol film, the resulting film can have a smaller number of surface defects and smaller crystal point defects.

[0038] In the present invention, the second solvent is mixed first and then the terminator is mixed. On the one hand, the second solvent can be used to preliminarily terminate the self-polymerization of vinyl acetate. On the other hand, the product after mixing the second solvent and the terminator can be better mixed, enabling the terminator to play a better role.

[0039] In the present invention, the molar ratio of hydroxide ions in the base to the vinyl acetate structural unit in the ethylene-vinyl acetate copolymer is 0.005 - 0.045:1, and it can be 0.005:1, 0.01:1, 0.015:1, 0.02:1, 0.025:1, 0.03:1, 0.035:1, 0.04:1, 0.045:1 or any range formed by any two of the above values and the values within the range.

[0040] In the present invention, by controlling the molar ratio of hydroxide ions in the base to the vinyl acetate unit in the ethylene-vinyl acetate copolymer within the above range, a higher reaction efficiency and a lower generation of reaction by-products can be obtained, and an ethylene-vinyl alcohol copolymer with a high degree of alcoholysis and a low by-product content can be obtained.

[0041] Preferably, the molar ratio of hydroxide ions in the base to the vinyl acetate unit in the ethylene-vinyl acetate copolymer is 0.01 - 0.03:1.

[0042] Preferably, the content of the ethylene-vinyl acetate copolymer in the ethylene-vinyl acetate copolymer solution is 40 wt% - 60 wt%, and it can be 40 wt%, 45 wt%, 50 wt%, 60 wt% or any range formed by any two of the above values and the values within the range.

[0043] In the present invention, by controlling the content of the ethylene-vinyl acetate copolymer in the ethylene-vinyl acetate copolymer solution within the above range, the reaction rate is increased, thereby improving the reaction efficiency.

[0044] Preferably, the conditions of the contact include: the temperature is 50 - 65°C, and it can be 50°C, 55°C, 60°C, 65°C or any range formed by any two of the above values and the values within the range, and the time is 4 - 6 h, and it can be 4 h, 4.5 h, 5 h, 5.5 h, 6 h or any range formed by any two of the above values and the values within the range. Preferably, the pressure of the contact is normal pressure.

[0045] In the present invention, when the conditions for controlling the contact are within the above ranges and the reaction is carried out under normal pressure conditions, it is easy to implement and operate, and the ethylene-vinyl alcohol copolymer prepared also has good processing stability, resulting in a long processing operation cycle.

[0046] In the present invention, in actual operation, in order to better mix the base, the base is an alkali solution.

[0047] In the present invention, the solvent in the alkali solution is not limited as long as it can dissolve the base and does not affect the alcoholysis of ethylene-vinyl acetate. Preferably, the solvent of the alkali solution is an alcohol solvent, preferably an alcohol solvent with 1-4 carbon atoms, more preferably at least one of methanol, ethanol, propanol, ethylene glycol, n-butanol and tert-butanol, and more preferably methanol; the solvent of the alkali solution and the first solvent can be the same or different.

[0048] Preferably, the concentration of the base in the alkali solution is 20 wt%-40 wt%, and it can be 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt% or any range formed by any two of the above values and the values within the range.

[0049] In the present invention, by controlling the base to be an alkali solution and the concentration of the alkali solution within the above ranges, the concentration of the reactants is relatively high and they can be mixed evenly, taking into account the reaction efficiency and ensuring a relatively high degree of alcoholysis of the ethylene-vinyl alcohol copolymer.

[0050] In the present invention, the type of the base in the alkali solution is not limited, and a conventional type of base in the art can be used as long as it can provide an alkaline environment. For example, the base is sodium hydroxide and / or potassium hydroxide.

[0051] Preferably, based on the weight of the vinyl acetate, the dosage of the initiator is 0.001 wt%-0.5 wt%, and it can be 0.001 wt%, 0.005 wt%, 0.01 wt%, 0.015 wt%, 0.02 wt%, 0.025 wt%, 0.03 wt%, 0.035 wt%, 0.04 wt%, 0.045 wt%, 0.05 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt% or any range formed by any two of the above values and the values within the range.

[0052] In the present invention, controlling the dosage of the initiator within the above ranges can control the molecular weight of the copolymer and improve the reaction efficiency.

[0053] In the present invention, the type of the initiator is not limited as long as it can make vinyl acetate and ethylene polymerize better. The initiator is an azo initiator and / or a peroxide initiator. Preferably, the azo initiator is at least one of azodiisobutyronitrile, azodiisovaleronitrile, azoisobutyronitrile formamide, azodicyclohexylcarbonitrile, and dimethyl azodisobutyrate; preferably, the peroxide initiator is an organic peroxide and / or an inorganic peroxide; more preferably, the organic peroxide is at least one of benzoyl peroxide, tert-butyl peroxybenzoate, methyl ethyl ketone peroxide, diisobutyryl peroxide, tert-amyl peroxyneodecanoate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, tert-amyl peroxy pivalate, tert-butyl peroxyacetate, and dibutyl peroxydicarbonate; further preferably, the inorganic peroxide is at least one of hydrogen peroxide, ammonium persulfate, and potassium persulfate.

[0054] In the present invention, the dosage of the first solvent is not limited as long as it does not affect the polymerization of vinyl acetate and ethylene. Preferably, based on the weight of the vinyl acetate, the dosage of the first solvent is 5 wt%-50 wt%, and it can be 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt% or any range and values within the range formed by any two of the above values.

[0055] In the present invention, controlling the dosage of the first solvent within the above range can ensure that the copolymer has an appropriate weight-average molecular weight and control the monomer conversion rate.

[0056] Preferably, the dosage of the ethylene is such that the pressure of the polymerization system is 2-6 MPaG, and it can be 2 MPaG, 3 MPaG, 4 MPaG, 5 MPaG, 6 MPaG or any range and values within the range formed by any two of the above values.

[0057] In the present invention, when controlling the dosage of the ethylene such that the polymerization pressure is within the above range, it is possible to control the content of the structural units derived from ethylene in the ethylene-vinyl acetate copolymer, so that the copolymer has an appropriate content of ethylene structural units.

[0058] Preferably, the polymerization conditions include: the temperature is 40-70 °C, and it can be 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C or any range and values within the range formed by any two of the above values, and the time is 2-9 h, and it can be 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h or any range and values within the range formed by any two of the above values.

[0059] In the present invention, when the conditions for controlling the polymerization are within the above ranges, it can ensure that the copolymer has an appropriate weight-average molecular weight and is easy to control the monomer conversion rate. At the same time, considering the reaction rate, it has the prospect of industrial production.

[0060] Preferably, the first solvent, the second solvent and the fourth solvent are each independently an alcohol solvent. In the present invention, the first solvent, the second solvent and the fourth solvent may be the same or different.

[0061] In the present invention, there is no limitation on the alcohol solvent. The first solvent can enable the smooth polymerization of ethylene and vinyl acetate, and the second solvent can inhibit the self-polymerization of vinyl acetate to form polyvinyl acetate. The fourth solvent can cooperate with the ethylene-vinyl acetate copolymer to form ethylene-vinyl alcohol. The first solvent, the second solvent and the fourth solvent are each independently preferably an alcohol solvent having 1 to 4 carbon atoms, more preferably at least one of methanol, ethanol, propanol, ethylene glycol, n-butanol and tert-butanol. The first solvent is more preferably methanol, the second solvent is more preferably ethanol, and the fourth solvent is more preferably methanol.

[0062] Preferably, based on the weight of the vinyl acetate, the amount of the second solvent is 1% to 30% by weight, and it can be 1%, 10%, 15%, 20%, 25%, 30% by weight or any range formed by any two of the above values and the values within the range.

[0063] In the present invention, controlling the amount of the second solvent within the above range can reduce the reaction rate and inhibit the self-polymerization of vinyl acetate to form polyvinyl acetate, so that the viscosity of the obtained ethylene-vinyl acetate copolymer solution remains stable.

[0064] Preferably, the amount of the terminator is 100 - 5000 ppm of the amount of vinyl acetate used in step (1), and it can be 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1700 ppm, 2000 ppm, 2200 ppm, 2500 ppm, 2800 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm or any range formed by any two of the above values and the values within the range, and more preferably 300 - 3000 ppm.

[0065] In the present invention, controlling the amount of the terminator within the above range can effectively reduce the content of polyvinyl acetate in the ethylene-vinyl acetate copolymer, thereby obtaining better processing stability of the ethylene-vinyl alcohol copolymer.

[0066] In the present invention, the terminator is not limited as long as it can prevent vinyl acetate from self-polymerizing, and is preferably selected from at least one of 2,4-diphenyl-4-methyl-1-pentene, 2,2-diphenyl-1-trinitrophenylhydrazine, 1,1-diphenyl-2-trinitrophenylhydrazine, 2,4-diphenyl-4-methyl-1-pentene, copper acetate, cuprous chloride, and ferric chloride.

[0067] Preferably, the method further comprises: removing ethylene from the product of step (1) in step (2).

[0068] Preferably, the ethylene removal is carried out after mixing with the second solvent.

[0069] In the present invention, carrying out the step of removing ethylene after mixing with the second solvent can reduce the reaction activity, and at the same time reduce the concentration and viscosity of the ethylene-vinyl acetate copolymer solution, which is beneficial to the flash evaporation and removal of dissolved ethylene in the solution.

[0070] Preferably, the way of removing ethylene is vacuum flash evaporation.

[0071] More preferably, the pressure when the product of step (1) is mixed with the second solvent is 2-6 MPaG, which can be 2 MPaG, 3 MPaG, 4 MPaG, 5 MPaG, 6 MPaG, or any range formed by any two of the above values and the values within the range, and the pressure when mixing the terminator is atmospheric pressure.

[0072] In the present invention, controlling the pressure when mixing the terminator within the above range can be mixed at atmospheric pressure without a high-pressure feeding pump, and the operation is convenient.

[0073] In the present invention, the ethylene removal can be carried out before mixing the terminator, at which time the pressure when mixing the terminator is atmospheric pressure, or after mixing the terminator, at which time the pressure when mixing the terminator is 2-6 MPaG.

[0074] In the present invention, when the pressure of mixing the product of step (1) with the terminator is atmospheric pressure, better viscosity stability can be obtained, and a high-pressure feeding pump is not required, and the operation is convenient.

[0075] Preferably, the conditions for mixing the product of step (1) with the second solvent include: the temperature is 40-70 °C, which can be 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, or any range formed by any two of the above values and the values within the range, and the time is 1-5 h, which can be 1 h, 2 h, 3 h, 4 h, 5 h, or any range formed by any two of the above values and the values within the range.

[0076] In the present invention, controlling the conditions for mixing the second solvent within the above range is consistent with the polymerization reaction conditions, without the need to adjust the process parameters, and the operation is convenient and the mixing is uniform.

[0077] Preferably, the conditions for mixing the product of step (1) with the terminator include: the temperature is 10 - 40°C, which can be 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C or any range and values within the range formed by any two of the above values, and the time is 0.1 - 2 h, which can be 0.1 h, 0.2 h, 0.4 h, 0.6 h, 0.8 h, 1 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h, 2 h or any range and values within the range formed by any two of the above values.

[0078] In the present invention, controlling the conditions for adding the terminator within the above range is easy to operate and can make the terminator mix uniformly with the ethylene - vinyl acetate copolymer solution.

[0079] In the present invention, in order to remove vinyl acetate, the method further includes: introducing a third solvent vapor after mixing the terminator.

[0080] In the present invention, during the actual operation process, the third solvent vapor can be introduced in a counter - current contact manner. For example, if the removal of vinyl acetate is carried out in a distillation column, the ethylene - vinyl acetate solution after adding the terminator is introduced into the top of the distillation column, and the third solvent vapor is introduced into the bottom of the distillation column to distill off the unreacted vinyl acetate monomer from the top of the column.

[0081] Preferably, the conditions for introducing the third solvent vapor include: the temperature is 65 - 80°C, which can be 65°C, 68°C, 70°C, 75°C, 74°C, 76°C, 78°C, 80°C or any range and values within the range formed by any two of the above values, the pressure is 100 - 180 kPa, which can be 100 kPa, 110 kPa, 120 kPa, 130 kPa, 140 kPa, 150 kPa, 160 kPa, 170 kPa, 180 kPa or any range and values within the range formed by any two of the above values, and the time is 0.5 - 3 h, which can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h or any range and values within the range formed by any two of the above values.

[0082] In the present invention, controlling the conditions for introducing the third solvent vapor within the above range can make the gas - liquid exchange between the solvent vapor and the ethylene - vinyl acetate copolymer solution sufficient, thereby removing vinyl acetate.

[0083] In the present invention, there is no limitation on the third solvent as long as it can carry away vinyl acetate. Preferably, the third solvent is an alcohol solvent, more preferably an alcohol solvent with 1 - 4 carbon atoms, still more preferably at least one of methanol, ethanol, propanol, ethylene glycol, n - butanol and tert - butanol, and even more preferably methanol.

[0084] In the present invention, the third solvent may be the same as or different from the first solvent, the second solvent, and the first solvent.

[0085] In the present invention, in order to remove the excess third solvent, first solvent, and second solvent, the method further includes: performing vacuum distillation after introducing the third steam.

[0086] In the present invention, the method further includes: mixing the ethylene-vinyl alcohol copolymer solution after alcoholysis with an acid in contact with a base, and the amount of the acid is 1-2000 ppm of the ethylene-vinyl alcohol copolymer; in actual use, an acid solution can be used, and the concentration of the acid solution is 0.05-5% by weight.

[0087] In the present invention, by mixing the ethylene-vinyl alcohol copolymer with an acid and within the above range, the base added for alcoholysis can be neutralized to obtain a better product quality.

[0088] In the present invention, the acid is not limited, as long as it can provide cationic hydrogen, and preferably at least one of acetic acid, propionic acid, boric acid, and sodium dihydrogen phosphate.

[0089] In the present invention, in order to obtain the final product, the method further includes: extruding, cooling, and washing the product obtained by mixing the ethylene-vinyl alcohol copolymer with an acid. The temperature of the cooling is 0-10°C.

[0090] In the third aspect of the present invention, there is provided an ethylene-vinyl alcohol copolymer prepared by the above method.

[0091] According to the present invention, the parameters of the ethylene-vinyl alcohol copolymer have been described above and will not be elaborated here.

[0092] In the fourth aspect of the present invention, there is provided an application of the above ethylene-vinyl alcohol copolymer in at least one of packaging materials, automobile fuel tanks, oxygen barrier floor heating pipes, textile materials, and medical materials.

[0093] In the fifth aspect of the present invention, there is provided an ethylene-vinyl alcohol copolymer film, and the film is prepared from the above copolymer.

[0094] According to the present invention, the number of surface defects of the film ≤ 300 pieces / m 2 。

[0095] According to the present invention, the proportion of crystal points larger than 300 μm in the film is not higher than 5%.

[0096] In the present invention, the method for preparing the ethylene-vinyl copolymer into a film is not limited, and conventional testing methods in the art can be used. For example, a blown film machine or a cast film machine can be used.

[0097] In the present invention, during actual operation, if the number of surface defects of the film is to be measured, a single-screw extruder in a blown film machine can be used to melt and extrude and then blow the film at 200 - 250 °C, and the blow-up ratio is 2 - 4.

[0098] In the present invention, during actual operation, if the number of crystal points is to be measured, a cast film machine can be used to obtain a film at 200 - 250 °C and a stretching speed of 2.5 - 3.5 m / min, and then the number of crystal points is counted. The counting method is not limited, and conventional methods can be used.

[0099] A more preferred embodiment of the present invention is as follows:

[0100] (1) In the presence of 5 - 50 parts by weight of a first solvent and 0.001 - 0.5 parts by weight of an initiator, 100 parts by weight of vinyl acetate and ethylene are polymerized (temperature is 40 - 70 °C, time is 2 - 9 h), and the amount of ethylene used is such that the pressure of the polymerization system is 2 - 6 MPaG;

[0101] (2) Keeping the pressure unchanged, 1 - 30 parts by weight of a second solvent is mixed in the product of step (1) (temperature is 40 - 70 °C, time is 1 - 5 h), ethylene is removed by vacuum flashing to make the pressure atmospheric pressure, and then 100 - 5000 ppm relative to the amount of vinyl acetate used in step (1) is mixed in the product (temperature is 10 - 40 °C, time is 0.1 - 2 h);

[0102] (3) Third solvent vapor is introduced into the product of step (2) (temperature is 65 - 80 °C, pressure is 100 - 180 kPa, time is 0.5 - 3 h), and then methanol and ethanol are removed by vacuum distillation;

[0103] (4) The product of step (3) is contacted with an alkali solution with a concentration of 20 wt% - 40 wt% (temperature is 50 - 65 °C, time is 4 - 6 h), wherein the molar ratio of hydroxide ions in the alkali to vinyl acetate units in the ethylene-vinyl acetate copolymer is 0.005 - 0.045:1;

[0104] (5) The product in step (4) is contacted with an acid of 1 - 2000 ppm;

[0105] (6) The product of step (5) is extruded, cooled at 0 - 10 °C and washed.

[0106] The present invention will be described in detail below through examples.

[0107] Example 1

[0108] (1) Add 100 parts by weight of vinyl acetate, 12 parts by weight of methanol, and 0.1 part of azobisisobutyronitrile into a pressure polymerization kettle equipped with a jacket, a stirrer, a raw material inlet, a temperature and pressure detector, and a reaction product discharge port. Raise the temperature to 60 °C, introduce ethylene, maintain the pressure at 3.8 MPaG, and react under stirring for 4 hours;

[0109] (2) Add 20 parts by weight of ethanol (while keeping the temperature and pressure unchanged for 3 h), stir evenly, then relieve the pressure and flash distill to remove ethylene. The pressure is normal pressure, and 500 ppm of 2,4-diphenyl-4-methyl-1-pentene relative to vinyl acetate is mixed in the product (for 0.5 h at a temperature of 25 °C);

[0110] (3) Introduce methanol vapor (for 2 h at a temperature of 70 °C and a pressure of 140 kPa), distill to remove unreacted vinyl acetate, and remove methanol and ethanol by vacuum distillation to obtain ethylene-vinyl acetate copolymer;

[0111] (4) Prepare a methanol solution of ethylene-vinyl acetate copolymer, a solution with a mass fraction of ethylene-vinyl acetate copolymer of 50% by weight, and then add an alkali solution for alcoholysis at 65 °C (for 5 h at normal pressure). The alkali solution is a methanol solution of NaOH with a concentration of 30% by weight, and control the molar ratio of hydroxide ions to vinyl acetate in the ethylene-vinyl acetate copolymer to be 0.02:1. After alcoholysis, an EVOH methanol solution can be obtained;

[0112] (5) Add acetic acid solution to the obtained EVOH methanol solution and stir evenly; among them, the dosage of acetic acid is 1000 ppm relative to the weight parts of EVOH solid matter, and the concentration of the acetic acid solution is 2% by weight;

[0113] (6) Pass the ethylene-vinyl alcohol copolymer solution obtained by alcoholysis through an extrusion device with an orifice plate, extrude it into an aqueous solution at 5 °C, form strips after precipitation, and then use a general cutting method to cut it into particles. Add water to clean the ethylene-vinyl alcohol copolymer particles through a kettle-type container with a stirring device, wash for 2 hours each time, and wash repeatedly 2 times. After washing 2 times, add a mixed solution of water and alcohol to the kettle-type container with a stirring device, wash at 75 °C for 2 hours, then wash with water 1 time. During the water washing process, add 0.01 part of acetic acid relative to 100 parts of EVOH for pickling, and then centrifuge and dehydrate, and dry to obtain EVOH particles.

[0114] The parameters of the obtained EVOH are shown in Tables 1 and 2.

[0115] Example 2

[0116] (1) Add 100 parts by weight of vinyl acetate, 5 parts by weight of methanol, and 0.1 part of azobisisobutyronitrile into a pressure polymerization kettle equipped with a jacket, a stirrer, a raw material inlet, a temperature and pressure detector, and a reaction product discharge port. Raise the temperature to 70 °C, introduce ethylene, and maintain the pressure at 5 MPaG. React for 2 hours under stirring;

[0117] (2) Add 5 parts by weight of ethanol (while keeping the temperature and pressure unchanged for 5 h). After stirring evenly, relieve the pressure and flash to remove ethylene. The pressure is normal pressure. Add 100 ppm of 2,4-diphenyl-4-methyl-1-pentene relative to vinyl acetate in the product (for 0.1 h at a temperature of 40 °C);

[0118] (3) Introduce methanol vapor (for 3 h at a temperature of 65 °C and a pressure of 100 kPa), distill to remove unreacted vinyl acetate, and remove methanol and ethanol by vacuum distillation to obtain ethylene-vinyl acetate copolymer;

[0119] (4) Prepare a methanol solution of ethylene-vinyl acetate copolymer, a solution with a mass fraction of ethylene-vinyl acetate copolymer of 40% by weight. Then add an alkali solution at 60 °C for alcoholysis (for 4 h at normal pressure). The alkali solution is a methanol solution of NaOH with a concentration of 20% by weight, and control the molar ratio of hydroxide ions to vinyl acetate in ethylene-vinyl acetate copolymer to be 0.005:1. After alcoholysis, an EVOH methanol solution can be obtained;

[0120] (5) Add acetic acid solution to the obtained EVOH methanol solution and stir evenly. Among them, the dosage of acetic acid is 1000 ppm relative to the weight parts of EVOH solid matter, and the concentration of acetic acid solution is 2% by weight;

[0121] (6) Pass the ethylene-vinyl alcohol copolymer solution obtained by alcoholysis through an extrusion device with an orifice plate and extrude it into an aqueous solution at 5 °C. After it precipitates into strips, use a general cutting method to cut it into particles. Add water to wash the ethylene-vinyl alcohol copolymer particles through a kettle-shaped container with a stirring device, wash for 2 hours each time, and wash repeatedly 2 times. After washing 2 times, add a mixed solution of water and alcohol to the kettle-shaped container with a stirring device, wash at 75 °C for 2 hours, and then wash with water once. During the water washing process, add 0.01 part of acetic acid relative to 100 parts of EVOH for pickling, and then centrifuge and dehydrate, and dry to obtain EVOH particles.

[0122] The parameters of the obtained EVOH are shown in Tables 1 and 2.

[0123] Example 3

[0124] (1) Add 100 parts by weight of vinyl acetate, 50 parts by weight of methanol, and 0.1 part of azobisisobutyronitrile into a pressure polymerization kettle equipped with a jacket, a stirrer, a raw material inlet, a temperature and pressure detector, and a reaction product discharge port. Raise the temperature to 40 °C, introduce ethylene, and maintain the pressure at 2 MPaG. React under stirring for 2 hours;

[0125] (2) Add 30 parts by weight of ethanol (while keeping the temperature and pressure unchanged for 1 h), stir evenly, then relieve the pressure and flash to remove ethylene. The pressure is normal pressure. Add 1000 ppm of 2,2-diphenyl-1-picrylhydrazyl relative to vinyl acetate in the product (for 1 h at a temperature of 10 °C);

[0126] (3) Introduce methanol vapor (for 0.5 h at a temperature of 80 °C and a pressure of 180 kPa), distill to remove unreacted vinyl acetate, and remove methanol and ethanol by vacuum distillation to obtain ethylene-vinyl acetate copolymer;

[0127] (4) Prepare a methanol solution of ethylene-vinyl acetate copolymer, a solution with a mass fraction of ethylene-vinyl acetate copolymer of 60% by weight. Then add an alkali solution at 55 °C for alcoholysis (for 6 h at normal pressure). The alkali solution is a methanol solution of NaOH with a concentration of 30% by weight, and control the molar ratio of hydroxide ions to vinyl acetate in ethylene-vinyl acetate copolymer to be 0.045:1. After alcoholysis, an EVOH methanol solution can be obtained;

[0128] (5) Add acetic acid solution to the obtained EVOH methanol solution and stir evenly. Among them, the amount of acetic acid is 1000 ppm relative to the weight of EVOH solids, and the concentration of the acetic acid solution is 1.5% by weight;

[0129] (6) Pass the ethylene-vinyl alcohol copolymer solution obtained by alcoholysis through an extrusion device with an orifice plate and extrude it into an aqueous solution at 5 °C. After it precipitates into strips, use a common cutting method to cut it into particles. Add water to clean the ethylene-vinyl alcohol copolymer particles through a kettle-type container with a stirring device, wash for 2 hours each time, and wash repeatedly 2 times. After washing 2 times, add a mixed solution of water and alcohol to the kettle-type container with a stirring device, wash at 75 °C for 2 hours, then wash with water 1 time. During the water washing process, add 0.01 part of acetic acid relative to 100 parts of EVOH for pickling, and then centrifuge and dehydrate, and dry to obtain EVOH particles.

[0130] The parameters of the obtained EVOH are shown in Tables 1 and 2.

[0131] Example 4

[0132] According to the method of Example 1, the difference is that in step (2), the terminator is changed to copper acetate.

[0133] The parameters of the obtained EVOH are shown in Tables 1 and 2.

[0134] Example 5

[0135] According to the method of Example 1, the difference is that in step (2), ethanol is changed to methanol.

[0136] The parameters of the obtained EVOH are shown in Tables 1 and 2.

[0137] Example 6

[0138] According to the method of Example 1, the difference is that in step (2), ethanol is changed to tert-butanol.

[0139] The parameters of the obtained EVOH are shown in Tables 1 and 2.

[0140] Example 7

[0141] According to the method of Example 1, the difference is that in step (2), ethylene is first removed by vacuum flashing, and after the pressure is normal pressure, ethanol and 2,4-diphenyl-4-methyl-1-pentene are added.

[0142] The parameters of the obtained EVOH are shown in Tables 1 and 2.

[0143] Example 8

[0144] According to the method of Example 1, the difference is that in step (2), ethanol and 2,4-diphenyl-4-methyl-1-pentene are first added, and then ethylene is removed by vacuum flashing to make the pressure normal pressure.

[0145] The parameters of the obtained EVOH are shown in Tables 1 and 2.

[0146] Example 9

[0147] According to the method of Example 1, the difference is that the molar ratio of the base to the vinyl acetate unit in the ethylene-vinyl acetate copolymer is 0.1:1.

[0148] The parameters of the obtained EVOH are shown in Tables 1 and 2.

[0149] Comparative Example 1

[0150] According to the method of Example 1, the difference is that in step (2), neither ethanol nor terminator is added.

[0151] The parameters of the obtained EVOH are shown in Tables 1 and 2.

[0152] Comparative Example 2

[0153] According to the method of Example 1, the difference is that in step (2), ethanol is not added.

[0154] The parameters of the obtained EVOH are shown in Tables 1 and 2.

[0155] Comparative Example 3

[0156] According to the method of Example 1, except that in step (2), the terminator is not added.

[0157] The parameters of the obtained EVOH are shown in Tables 1 and 2.

[0158] Comparative Example 4

[0159] According to the method of Example 1, except that in step (1), 12 parts of methanol and 20 parts of ethanol are added together, and in step (2), ethanol is not added.

[0160] The parameters of the obtained EVOH are shown in Tables 1 and 2.

[0161] Comparative Example 5

[0162] According to the method of Example 1, except that in step (2), the addition order of ethanol and the terminator is exchanged.

[0163] The parameters of the obtained EVOH are shown in Tables 1 and 2.

[0164] Test Example:

[0165] Test method for melt index: GB / T3682.1;

[0166] Method for determining the content of ethylene structural units in ethylene-vinyl alcohol: GBT 41877.2-2022;

[0167] Test method for weight-average molecular weight and molecular weight distribution: Measured by GPC method;

[0168] Test and calculation method for intrinsic viscosity:

[0169] Accurately weigh about 1 g (accurate to 0.2 mg) of the dried EVOH sample, put it into a 250 mL ground glass Erlenmeyer flask, add 50 mL of dimethyl sulfoxide, reflux and dissolve it in a water bath at 80 °C. After complete dissolution, transfer it to a 100 mL volumetric flask and make up the volume. The concentration of the sample solution is denoted as C. Filter the sample solution and put it into an Ubbelohde viscometer, and keep it at a constant temperature in a constant temperature water bath at 30 ± 0.1 °C for 15 min. Viscosity measurement: After calibrating the viscometer to be vertical, conduct the test according to the usage method of the Ubbelohde viscometer, let the sample solution fall naturally in the viscometer tube, accurately record the time when the sample liquid level flows through two measurement lines with a stopwatch. After measuring several times repeatedly, take the average value, denoted as t1. Blank test: Put the filtered dimethyl sulfoxide into the viscometer, accurately measure the time when the dimethyl sulfoxide flows through two measurement lines after keeping it at a constant temperature under the condition of 30 ± 0.1 °C. After measuring several times repeatedly, take the average value, denoted as t0.

[0170] Result calculation and representation: The intrinsic viscosity [η] (dL / g) of EVOH is calculated by the following formula:

[0171] Relative viscosity: η r = t / t0;

[0172] Specific viscosity: η sp = (t - t0) / t0 = η r - 1;

[0173] Intrinsic viscosity:

[0174] Measurement of degree of alcoholysis: Crush the dry EVOH to 100 mesh, extract and purify it with deionized water in turn, and dry it at 120 °C. The obtained ethylene-vinyl alcohol copolymer is subjected to NMR measurement under the following conditions, and the degree of alcoholysis is obtained by the following analysis method:

[0175] Analysis method: Obtain the integral value (I1) of the peak with a chemical shift of 3.7 - 4 ppm and the integral value (I2) of the peak with a chemical shift of 0.6 - 1.8 ppm from the spectrum measured at 40 °C. Obtain the integral value (I3) of the peak with a chemical shift of 3.1 - 3.7 ppm, the integral value (I4) of the peak with a chemical shift of 0.6 - 1.8 ppm and the integral value (I5) of the peak with a chemical shift of 1.9 - 2.1 ppm from the spectrum measured at 95 °C. Here, the peak with a chemical shift of 0.6 - 1.8 ppm is mainly from methylene protons, and the peak with a chemical shift of 1.9 - 2.1 ppm is from the protons of the methyl in the unhydrolyzed vinyl acetate unit. The degree of alcoholysis (mol%) is calculated by the following formula from these integral values:

[0176]

[0177] Test method for the number of defects and the change value of the screw current: Use dried EVOH particles and a SG-45 film blowing machine. The temperature of the extruder part in the film blowing machine is 220°C / 230°C / 230°C. Blow the film in an upward blowing manner with a blow-up ratio of 3. After continuous operation for 10 hours, prepare a film sample of 30 cm * 24 cm. Then use a surface defect detector MVT-SIS to analyze the surface defects in the film and count the number of defects above 0.5 mm * 0.5 mm in the sample; examine the change in the screw current of the film blowing machine. The change in the screw current reflects the thermal stability. If the thermal stability is poor, the screw current will increase, and if the stability is good, the current remains unchanged. During the production process, the change amount of the screw current should be ≤ 1 A.

[0178] Test method for crystal points: Use a cast film machine and a gel detection system for detection, with the model: ME20-MFA-FSA100V2. Among them, the screw is a single screw with L / D ≥ 25, the screw temperature is 230°C / 230°C / 230°C, the screw speed is 15 rpm, the stretching speed is 3.1 m / min, the width of the cast film is controlled at 15 mm, and the film thickness is controlled at 20 - 40 μm. Use a linear array camera and an LED light source to test the crystal point defects of the cast film.

[0179] Table 1

[0180]

[0181]

[0182] Table 2

[0183]

[0184]

[0185] From the above results, it can be seen that the resin composition of the present invention has good thermal stability and has fewer surface defect numbers and crystal points when made into a film.

[0186] 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 technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. An ethylene-vinyl alcohol copolymer, characterized in that, The melt flow rate of the copolymer at 190 °C and a load of 21.6 kg is MFR 21.6 , the melt flow rate of the copolymer at 190 °C and a load of 5 kg is MFR 5 , the melt flow rate of the copolymer at 190 °C and a load of 2.16 kg is MFR 2.16 , The MFR 21.6 , MFR 5 and MFR 2.16 satisfy the following relationship: 10 ≤ MFR 21.6 / MFR 2.16 -MFR 5 / MFR 2.16 ≤ 25 2. The copolymer according to claim 1, wherein, 12 ≤ MFR 21.6 / MFR 2.16 -MFR 5 / MFR 2.16 ≤ 22; and / or, the change in the screw current of the copolymer when using a blown film machine is less than or equal to 1 A; and / or, the content of structural units derived from ethylene in the copolymer is 20-50 mol%, preferably 22-48 mol%; and / or, the copolymer has a melt index of 1-10 g / 10 min at 190 °C under a load of 2.16 kg; and / or, the copolymer has a weight average molecular weight of 20,000-200,000 g / mol; the molecular weight distribution of the copolymer is 1-3; and / or, at 25 °C, the intrinsic viscosity of the copolymer is 0.1-1 dL / g; and / or, the degree of alcoholysis of the copolymer is 99-99.9%.

3. A method for preparing an ethylene-vinyl alcohol copolymer, characterized in that, the method comprises: (1) Polymerizing vinyl acetate and ethylene in the presence of a first solvent and an initiator; (2) Sequentially mixing a second solvent and a terminator in the product of step (1) to obtain an ethylene-vinyl acetate copolymer solution; (3) Contacting the ethylene-vinyl acetate copolymer solution with a base to obtain an ethylene-vinyl alcohol copolymer.

4. The method according to claim 3, wherein, the molar ratio of hydroxide ions in the base to the vinyl acetate structural units in the ethylene-vinyl acetate copolymer is 0.005-0.045:1, preferably 0.01-0.03:

1.

5. The method according to claim 3 or 4, wherein, the content of the ethylene-vinyl acetate copolymer in the ethylene-vinyl acetate copolymer solution is 40 wt%-60 wt%; and / or, the conditions of the contact include: temperature is 50-65 °C, time is 4-6 h; and / or, the pressure of the contact is atmospheric pressure; and / or, the base is sodium hydroxide and / or potassium hydroxide.

6. The method according to any one of claims 3-5, wherein, based on the weight of the vinyl acetate, the amount of the second solvent used is 1 wt%-30 wt%; and / or, the amount of the terminator used is 100-5000 ppm, preferably 300-3000 ppm, of the amount of vinyl acetate used in step (1); and / or, the terminator is selected from at least one of 2,4-diphenyl-4-methyl-1-pentene, 2,2-diphenyl-1-trinitrophenylhydrazine, 1,1-diphenyl-2-trinitrophenylhydrazine, 2,4-diphenyl-4-methyl-1-pentene, copper acetate, cuprous chloride, and ferric chloride; and / or, the method further comprises: removing ethylene in the product of step (1) in step (2); preferably, the method for removing ethylene is vacuum flashing; preferably, the ethylene is removed after mixing the second solvent.

7. The method according to any one of claims 3-6, wherein, the conditions for mixing the product of step (1) with the second solvent include: temperature is 40-70 °C, time is 1-5 h; And / or, the conditions for mixing the product of step (1) with the terminator include: temperature is 10 - 40°C, time is 0.1 - 2 h; And / or, the pressure for mixing the product of step (1) with the second solvent is 2 - 6 MPaG; And / or, the pressure for mixing the product of step (1) with the terminator is atmospheric pressure.

8. An ethylene-vinyl alcohol copolymer prepared by the method according to any one of claims 3 - 7; Preferably, the melt index of the copolymer at 190 °C and a load of 21.6 kg is MFR 21.6 , the melt index of the copolymer at 190 °C and a load of 5 kg is MFR 5 , the melt index of the copolymer at 190 °C and a load of 2.16 kg is MFR 2.16 , The MFR 21.6 , MFR 5 and MFR 2.16 satisfy the following relationship: 10 ≤ MFR 21.6 / MFR 2.16 -MFR 5 / MFR 2.16 ≤ 25; More preferably, 12 ≤ MFR 21.6 / MFR 2.16 -MFR 5 / MFR 2.16 ≤ 22; Preferably, when the copolymer is extruded using a single-screw extruder, the change in the screw current is less than or equal to 1 A; Preferably, the content of structural units derived from ethylene in the copolymer is 20 - 50 mol%, preferably 22 - 48 mol%; Preferably, the copolymer has a melt index of 1 - 10 g / 10 min at 190°C under a load of 2.16 kg; Preferably, the copolymer has a weight-average molecular weight of 20,000 - 200,000 g / mol; the molecular weight distribution of the copolymer is 1 - 3; Preferably, at 25°C, the intrinsic viscosity of the copolymer is 0.1 - 1 dL / g; Preferably, the degree of alcoholysis of the copolymer is 99 - 99.9%; 9. Use of the ethylene-vinyl alcohol copolymer according to claim 1, 2 or 8 in at least one of packaging materials, automobile fuel tanks, oxygen-barrier floor heating pipes, textile materials and medical materials.

10. An ethylene-vinyl alcohol film, characterized in that, the film is prepared from the copolymer according to claim 1, 2 or 8; Preferably, the number of surface defects of the film ≤ 300 per m 2 ; Preferably, the proportion of crystal points larger than 300 μm in the film is not higher than 5%.

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