Ethylene-vinyl alcohol copolymers, methods of making, uses, and films

Abstract

The present application relates to the field of resins, discloses an ethylene-vinyl alcohol copolymer and a preparation method, application and film thereof. The copolymer has a melt index of MFR 21.6 at 190 DEG C and a load of 21.6 kg, a melt index of MFR5 of the copolymer at 190 DEG C and a load of 5 kg, a melt index of MFR 2.16 of the copolymer at 190 DEG C and a load of 2.16 kg, and the MFR 21.6 , MFR5 and MFR 2.16 satisfy the following relationship: 10 ≤ MFR 21.6 / MFR 2.16 -MFR5 / MFR 2.16 ≤ 25. The ethylene-vinyl alcohol copolymer provided by the present application has good processing stability, long processing operation cycle, less surface defect number and small crystal point defect.

Description

Technical Field

[0001] This invention relates to the field of resins, and more specifically to ethylene-vinyl alcohol copolymers, their preparation methods, applications, and films. Background Technology

[0002] Ethylene-vinyl alcohol copolymer (EVOH), especially EVOH copolymers with an ethylene content of 20-50 mol%, possesses excellent gas barrier properties, approximately 10,000 times that of ordinary polyethylene. Combined with its transparency, processability, solvent resistance, and antistatic properties, it is widely used in packaging materials, automotive fuel tanks, oxygen-barrier underfloor heating pipes, textile materials, and medical materials. EVOH copolymers are typically processed using melt processing. As a polymer containing multiple hydroxyl groups in its molecular structure, EVOH is prone to intermolecular and intramolecular dehydration under high-temperature conditions, leading to decreased processing stability, particularly resulting in defects such as crystal points during film formation. Summary of the Invention

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

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

[0005] The MFR 21.6 MFR5 and MFR 2.16 The following relationship must be satisfied:

[0006] 10≤MFR 216 / MFR 216 -MFR5 / MFR 216 ≤25.

[0007] A second aspect of the present invention provides a method for preparing an ethylene-vinyl alcohol copolymer, the method comprising:

[0008] (1) In the presence of a first solvent and an initiator, vinyl acetate is polymerized with ethylene;

[0009] (2) The second solvent and the terminator are mixed sequentially in the product of step (1) to obtain an ethylene-vinyl acetate copolymer solution;

[0010] (3) The ethylene-vinyl acetate copolymer solution was contacted with an alkali to obtain an ethylene-vinyl alcohol copolymer.

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

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

[0013] A fifth aspect of the present invention provides an ethylene-vinyl alcohol copolymer film, said film being prepared from the above-described copolymer.

[0014] Through the above technical solution, the ethylene-vinyl alcohol copolymer provided by the present invention has good processing stability, resulting in a long processing cycle. More preferably, when used to prepare ethylene-vinyl alcohol films, the resulting films have fewer surface defects and smaller crystal point defects. Detailed Implementation

[0015] 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.

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

[0017] The MFR 21.6 MFR5 and MFR 2.16 The following relationship must be satisfied:

[0018] 10≤MFR 21.6 / MFR 2.16 -MFR5 / MFR 2.16 ≤25 can be a range of values ​​formed by any two of the following values: 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, or more.

[0019] In this invention, the ethylene-vinyl alcohol copolymer satisfies the above relationship and has good processing stability, resulting in a long processing cycle. When used to prepare ethylene-vinyl alcohol films, the resulting films have fewer surface defects and smaller crystal point defects.

[0020] Even better, 12≤MFR 21.6 / MFR 2.16 -MFR5 / MFR 2.16 ≤22.

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

[0022] In this invention, the change in screw current when the copolymer is used with a blown film machine is less than or equal to 1A, which has good processing stability.

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

[0024] In this invention, the content of structural units derived from ethylene in the copolymer is within the above range, which has a good balance of barrier properties and melt processability, and has good performance when processed into materials such as films and sheets.

[0025] According to the present invention, the copolymer has a melt index of 1-10 g / 10 min at 190°C and a load of 2.16 kg, 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 two of the above values, or values ​​within the range.

[0026] In this invention, the melt flow index is within the above range, which indicates good processing fluidity and wide applicability.

[0027] According to the present invention, the weight-average molecular weight of the copolymer is 20,000-200,000 g / mol, which can be any two of the following values: 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 values ​​within the range thereof; the molecular weight distribution of the copolymer is 1-3, which can be any two of the following values: 1, 1.5, 2, 2.5, 3, or values ​​within the range thereof.

[0028] In this invention, the weight-average molecular weight and molecular weight distribution of the copolymer are within the above range, which gives the copolymer both good mechanical properties and melt processability, resulting in better application effects.

[0029] According to the present invention, at 25°C, the intrinsic viscosity of the copolymer is 0.1-1 dl / g, which 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 two of the above values ​​within a range or within a range.

[0030] In this invention, the intrinsic viscosity of the copolymer is within the above range, which enables the copolymer to have both good mechanical properties and melt processability, thus achieving better application results.

[0031] According to the present invention, the degree of alcoholysis of the copolymer is 99-99.9%, which can be any two values ​​of 99%, 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9% or above, or values ​​within such ranges.

[0032] In this invention, the degree of alcoholysis of the copolymer is within the above range, which gives the polymer excellent barrier properties and achieves wide application in the field of barrier packaging.

[0033] A second aspect of the present invention provides a method for preparing an ethylene-vinyl alcohol copolymer, the method comprising:

[0034] (1) In the presence of a first solvent and an initiator, vinyl acetate is polymerized with ethylene;

[0035] (2) The second solvent and the terminator are mixed sequentially in the product of step (1) to obtain an ethylene-vinyl acetate copolymer solution;

[0036] (3) The ethylene-vinyl acetate copolymer solution was contacted with an alkali to obtain an ethylene-vinyl alcohol copolymer.

[0037] In this invention, the ethylene-vinyl alcohol copolymer obtained by the above method has good processing stability, resulting in a long processing cycle. When used to prepare ethylene-vinyl alcohol films, the resulting films have fewer surface defects and smaller crystal point defects.

[0038] In this invention, the second solvent is mixed first, followed by the terminating agent. On the one hand, the second solvent can be used to initially terminate the self-polymerization of vinyl acetate. On the other hand, the product after mixing with the second solvent is better mixed with the terminating agent, allowing the terminating agent to function more effectively.

[0039] In this invention, the molar ratio of hydroxide ions in the alkali to vinyl acetate structural units in the ethylene-vinyl acetate copolymer is 0.005-0.045:1, which 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 two of the above values ​​within a range.

[0040] In this invention, by controlling the molar ratio of hydroxide ions in the alkali to vinyl acetate units in the ethylene-vinyl acetate copolymer within the above range, a higher reaction efficiency and a lower generation of reaction byproducts are achieved, resulting in an ethylene-vinyl alcohol copolymer with high degree of alcoholysis and low byproduct content.

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

[0042] Preferably, the content of ethylene-vinyl acetate copolymer in the ethylene-vinyl acetate copolymer solution is 40-60% by weight, which can be any two values ​​of 40%, 45%, 50%, 60% or more, or values ​​within that range.

[0043] In this invention, the content of ethylene-vinyl acetate copolymer in the ethylene-vinyl acetate copolymer solution is controlled within the above range to increase the reaction rate and thus improve the reaction efficiency.

[0044] Preferably, the contact conditions include: a temperature of 50-65°C, which can be any two of 50°C, 55°C, 60°C, 65°C, or higher, and a time of 4-6 hours, which can be any two of 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, or higher. Preferably, the contact pressure is atmospheric pressure.

[0045] In this invention, the contact conditions are controlled within the above range, and the reaction is carried out under normal pressure, which is easy to achieve and convenient to operate. The prepared ethylene-vinyl alcohol copolymer also has good processing stability, resulting in a long processing cycle.

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

[0047] In this invention, the solvent in the alkaline solution is not limited, as long as it can dissolve the alkali and does not affect the alcoholysis of ethylene-vinyl acetate. Preferably, the solvent of the alkaline 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 alkaline solution can be the same as or different from the first solvent.

[0048] Preferably, the concentration of alkali in the alkaline solution is 20-40% by weight, which can be any two values ​​of 20%, 25%, 30%, 35%, 40% or more, or a value within that range.

[0049] In this invention, the alkali is controlled to be an alkaline solution and the concentration of the alkaline solution is kept within the above range, so that the reactant concentration is high and the mixture is uniform, thus taking into account both reaction efficiency and ensuring a high degree of alcoholysis of the ethylene-vinyl alcohol copolymer.

[0050] In this invention, there is no limitation on the type of alkali in the alkaline solution. Any conventional type of alkali in the art can be used as long as it can provide an alkaline environment. For example, the alkali is sodium hydroxide and / or potassium hydroxide.

[0051] Preferably, based on the weight of the vinyl acetate, the amount of the initiator is 0.001 wt% to 0.5 wt%, which 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 two of the above values ​​within a range.

[0052] In this invention, controlling the amount of initiator within the above range can control the molecular weight of the copolymer and improve the reaction efficiency.

[0053] In this invention, the type of initiator is not limited, as long as it can facilitate better polymerization of vinyl acetate and ethylene. The initiator is an azo initiator and / or a peroxide initiator. Preferably, the azo initiator is at least one selected from azobisisobutyronitrile, azobisisovalerate, azoisobutylcyanoformamide, azobiscyclohexylformitrile, and dimethyl azobisisobutyrate. Preferably, the peroxide initiator is an organic peroxide and / or an inorganic peroxide. More preferably, the organic peroxide is at least one selected from benzoyl peroxide, benzoyl tert-butyl peroxide, methyl ethyl ketone peroxide, diisobutyryl peroxide, tert-pentyl peroxyneodecanate, bis(4-tert-butylcyclohexyl peroxide), tert-pentyl peroxypentate, tert-butyl peroxyacetate, and dibutyl peroxydicarbonate. Further preferably, the inorganic peroxide is at least one selected from hydrogen peroxide, ammonium persulfate, and potassium persulfate.

[0054] In this invention, there is no limitation on the amount of the first solvent, as long as it does not affect the polymerization of vinyl acetate and ethylene. Preferably, based on the weight of the vinyl acetate, the amount of the first solvent is 5-50% by weight, which can be any two of the following values: 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any value within the range formed by any two of the above values.

[0055] In this invention, controlling the amount of the first solvent within the above range ensures that the copolymer has a suitable weight-average molecular weight and controls the monomer conversion rate.

[0056] Preferably, the amount of ethylene used results in a polymerization system pressure of 2-6 MPaG, which can be any two of the following values: 2 MPaG, 3 MPaG, 4 MPaG, 5 MPaG, 6 MPaG, or a value within that range.

[0057] In this invention, by controlling the amount of ethylene used so that the polymerization pressure is within the above range, it is possible to control the content of structural units from ethylene in the ethylene-vinyl acetate copolymer, so that the copolymer has a suitable content of ethylene structural units.

[0058] Preferably, the polymerization conditions include: a temperature of 40-70°C, which can be any two values ​​of 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C or higher, and a time of 2-9 hours, which can be any two values ​​of 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours or higher, and a time ... hours, 3.5 hours, 4 hours, 4 hours, 4.5 hours, 5 hours, 5 hours, 5 hours, 5 hours, 5 hours, 5 hours, 6 hours, 6.5 hours, 7 hours, 7 hours, 7 hours, 7 hours, 8 hours, 8.5 hours, 9 hours or higher, and a time of 9 hours, 2 hours, 9 hours, 9 hours or higher, and a time of 2 hours, 2 hours, 9 hours, 2 hours, 9 hours, 9 hours or higher, and a time of 2 hours, 2 hours, 9 hours, 2 hours, 9 hours, 9 hours or

[0059] In this invention, controlling the polymerization conditions within the above range ensures that the copolymer has a suitable weight-average molecular weight and easy-to-control monomer conversion rate, while also taking into account the reaction rate, thus showing promise for industrial production.

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

[0061] In this invention, the alcohol solvent is not limited. The first solvent is sufficient to facilitate the polymerization of ethylene and vinyl acetate, and the second solvent is sufficient to inhibit the self-polymerization of vinyl acetate into polyvinyl acetate. The fourth solvent is sufficient to react with the ethylene-vinyl acetate copolymer to form ethylene-vinyl alcohol. The first, second, and fourth solvents are each preferably alcohol solvents with 1-4 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 wt% to 30 wt%, which can be any two values ​​forming a range or value within the range of 1 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, or more.

[0063] In this 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 into polyvinyl acetate, thereby keeping the viscosity of the obtained ethylene-vinyl acetate copolymer solution stable.

[0064] Preferably, the amount of the terminating agent is 100-5000 ppm of the amount of vinyl acetate used in step (1), and can be any two of the following values: 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 more, or a value within the range of any two of the above values, more preferably 300-3000 ppm.

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

[0066] In this invention, the terminator is not limited and can be used to prevent vinyl acetate from self-polymerizing. It 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 includes removing ethylene from the product of step (1) in step (2).

[0068] Preferably, the ethylene removal occurs after mixing with the second solvent.

[0069] In this invention, placing the ethylene removal step after mixing the second solvent can reduce the reactivity and simultaneously reduce the concentration and viscosity of the ethylene-vinyl acetate copolymer solution, which facilitates the flash removal of ethylene dissolved in the solution.

[0070] Preferably, the method for removing ethylene is vacuum flash evaporation.

[0071] More preferably, the pressure at which the product of step (1) is mixed with the second solvent is 2-6 MPaG, which can be any two of the following values: 2 MPaG, 3 MPaG, 4 MPaG, 5 MPaG, 6 MPaG, or a value within the range of these values. The pressure at which the terminating agent is mixed is atmospheric pressure.

[0072] In this invention, controlling the pressure during mixing of the terminator within the above range allows for mixing at atmospheric pressure without the need for a high-pressure feed pump, making operation convenient.

[0073] In this invention, the removal of ethylene can be performed before mixing the terminating agent, at which point the pressure during mixing of the terminating agent is atmospheric pressure, or after mixing the terminating agent, at which point the pressure during mixing of the terminating agent is 2-6 MPaG.

[0074] In this invention, the pressure at which the product of step (1) is mixed with the terminator is atmospheric pressure to obtain better viscosity stability, and no high-pressure feeding pump is required, making the operation convenient.

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

[0076] In this invention, the conditions for mixing the second solvent are consistent with the polymerization reaction conditions within the above range, eliminating the need to adjust process parameters. This makes the operation convenient and ensures uniform mixing.

[0077] Preferably, the conditions for mixing the product and the terminator in step (1) include: a temperature of 10-40°C, which can be any two values ​​of 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C or above, and a time of 0.1-2h, which can be any two values ​​of 0.1h, 0.2h, 0.4h, 0.6h, 0.8h, 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h or above, and a time ...0.8h, 0.9h, 0.2h, 0.4h, 0.6h, 0.8h, 0.9h, 0.2h, 0.9h, 0.9h, 0.9h, 0.9h, 0.9h, 0.9h, 0.9h, 0.9h

[0078] In this invention, controlling the conditions for adding the terminator within the above range is simple to operate and allows the terminator to be mixed evenly with the ethylene-vinyl acetate copolymer solution.

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

[0080] In this invention, during actual operation, a third solvent vapor can be introduced through countercurrent contact. For example, if the removal of vinyl acetate is carried out in a distillation column, the ethylene-vinyl acetate solution after the addition of 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 remove the unreacted vinyl acetate monomer from the top of the column by distillation.

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

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

[0083] In this invention, the third solvent is not limited, as long as it can carry away vinyl acetate. Preferably, the third solvent 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 even more preferably methanol.

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

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

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

[0087] In this invention, mixing the ethylene-vinyl alcohol copolymer with an acid within the above range can neutralize the alkali added for alcoholysis, thereby obtaining better product quality.

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

[0089] In this invention, to obtain the final product, the method further includes: extruding, cooling, and washing the product of the ethylene-vinyl alcohol copolymer mixed with acid. The cooling temperature is 0-10°C.

[0090] A third aspect of the present invention provides an ethylene-vinyl alcohol copolymer prepared by the method described above.

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

[0092] The fourth aspect of the present invention provides the application of the above-mentioned ethylene-vinyl alcohol copolymer in at least one of packaging materials, automotive fuel tanks, oxygen-barrier floor heating pipes, textile materials and medical materials.

[0093] A fifth aspect of the present invention provides an ethylene-vinyl alcohol copolymer film, said film being prepared from the above-described copolymer.

[0094] According to the present invention, the number of surface defects of the thin film is ≤300 / m 2 .

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

[0096] In this invention, there are no limitations on the method for preparing ethylene-ethylene copolymer into a film. 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 this invention, in actual operation, if the number of defects on the film surface is to be measured, a single-screw extruder in a blown film machine can be used to melt-extrude and blow film at 200-250℃, with a blow-up ratio of 2-4.

[0098] In this invention, in actual operation, if the number of crystal points is to be measured, a film can be obtained using a casting film machine at 200-250℃ and a stretching speed of 2.5-3.5m / min, and then the number of crystal points can be counted. There are no restrictions on the counting method; any conventional method 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 are polymerized with ethylene (at a temperature of 40-70°C for 2-9 hours), wherein the amount of ethylene used is such that the pressure of the polymerization system is 2-6 MPaG.

[0101] (2) Keep the pressure constant, mix 1-30 parts by weight of the second solvent into the product of step (1) (temperature 40-70℃, time 1-5h), remove ethylene by flash evaporation under reduced pressure, so that the pressure is normal pressure, and then mix 100-5000 ppm of vinyl acetate relative to the amount used in step (1) (temperature 10-40℃, time 0.1-2h) into the product.

[0102] (3) In the product of step (2), a third solvent vapor (temperature 65-80℃, pressure 100-180kPa, time 0.5-3h) is introduced, and methanol and ethanol are removed by vacuum distillation.

[0103] (4) Contact the product of step (3) with an alkaline solution of 20-40% by weight (temperature 50-65℃, time 4-6h), 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) Contact the product from step (4) with an acid of 1-2000 ppm;

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

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

[0107] Example 1

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

[0109] (2) Add 20 parts by weight of ethanol (keep the temperature and pressure constant for 3 hours), stir evenly, and then remove ethylene by flash evaporation after depressurization. The pressure is normal. Mix 2,4-diphenyl-4-methyl-1-pentene relative to vinyl acetate at 500 ppm (time 0.5 hours, temperature 25°C).

[0110] (3) Methanol vapor was introduced (time was 2 hours, temperature was 70°C, pressure was 140 kPa), unreacted vinyl acetate was removed by distillation, and methanol and ethanol were removed by vacuum distillation to obtain ethylene-vinyl acetate copolymer.

[0111] (4) Prepare a methanol solution of ethylene-vinyl acetate copolymer with a mass fraction of 50% by weight. Then, add an alkaline solution at 65°C for alcoholysis (time is 5h, pressure is normal pressure). The alkaline solution is a methanol solution of NaOH with a concentration of 30% by weight. The molar ratio of hydroxide ions to vinyl acetate in the ethylene-vinyl acetate copolymer is controlled 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 until homogeneous; wherein, the amount of acetic acid used is 1000 ppm relative to the weight of EVOH solids, and the concentration of acetic acid solution is 2% by weight.

[0113] (6) The ethylene-vinyl alcohol copolymer solution obtained from alcoholysis was extruded into an aqueous solution at 5°C through an extrusion device with a perforated plate. After precipitating into strips, the strips were cut into granules using a common cutting method. The ethylene-vinyl alcohol copolymer granules were washed with water in a stirred tank for 2 hours each time, and the washing was repeated twice. After the two washings, a mixed solution of water and alcohol was added to the stirred tank, and the mixture was washed at 75°C for 2 hours. Then, it was washed with water once more. During the water washing process, 0.01 parts of acetic acid were added relative to 100 parts of EVOH. After acid washing, the mixture was centrifuged to remove water and dried to obtain EVOH granules.

[0114] The obtained EVOH parameters 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 parts by weight of azobisisobutyronitrile to a pressure polymerization reactor equipped with a jacket, stirrer, raw material inlet, temperature and pressure gauge, and reaction product outlet. Raise the temperature to 70°C, maintain the ethylene pressure at 5 MPaG, and react for 2 hours under stirring.

[0117] (2) Add 5 parts by weight of ethanol (keep the temperature and pressure constant for 5 hours), stir evenly, and then remove ethylene by flash evaporation after depressurization. The pressure is normal. The product is mixed with 100 ppm of 2,4-diphenyl-4-methyl-1-pentene relative to vinyl acetate (time is 0.1 hours and temperature is 40°C).

[0118] (3) Methanol vapor was introduced (time was 3h, temperature was 65℃, pressure was 100kPa), unreacted vinyl acetate was removed by distillation, and methanol and ethanol were removed by vacuum distillation to obtain ethylene-vinyl acetate copolymer.

[0119] (4) Prepare a methanol solution of ethylene-vinyl acetate copolymer with a mass fraction of 40% by weight. Then, add an alkaline solution at 60°C for alcoholysis (time is 4, pressure is normal). The alkaline solution is a methanol solution of NaOH with a concentration of 20% by weight. The molar ratio of hydroxide ions to vinyl acetate in the ethylene-vinyl acetate copolymer is controlled 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 until homogeneous; wherein, the amount of acetic acid used is 1000 ppm relative to the weight of EVOH solids, and the concentration of acetic acid solution is 2% by weight.

[0121] (6) The ethylene-vinyl alcohol copolymer solution obtained from alcoholysis was extruded into an aqueous solution at 5°C through an extrusion device with a perforated plate. After precipitating into strips, the strips were cut into granules using a common cutting method. The ethylene-vinyl alcohol copolymer granules were washed with water in a stirred tank for 2 hours each time, and the washing was repeated twice. After the two washings, a mixed solution of water and alcohol was added to the stirred tank, and the mixture was washed at 75°C for 2 hours. Then, it was washed with water once more. During the water washing process, 0.01 parts of acetic acid relative to 100 parts of EVOH were added for acid washing. After centrifugation and dehydration, the EVOH granules were obtained after drying.

[0122] The obtained EVOH parameters 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 parts by weight of azobisisobutyronitrile to a pressure polymerization reactor equipped with a jacket, stirrer, raw material inlet, temperature and pressure gauge, and reaction product outlet. Raise the temperature to 40°C, maintain the ethylene pressure at 2 MPaG, and react for 2 hours under stirring.

[0125] (2) Add 30 parts by weight of ethanol (keep the temperature and pressure constant for 1 hour), stir evenly, then release the pressure and flash evaporate to remove ethylene at atmospheric pressure. Mix 1000 ppm of 2,2-diphenyl-1-trinitrophenylhydrazine relative to vinyl acetate (time 1 hour, temperature 10°C) into the product.

[0126] (3) Methanol vapor was introduced (time was 0.5 h, temperature was 80 °C, pressure was 180 kPa), unreacted vinyl acetate was removed by distillation, and methanol and ethanol were removed by vacuum distillation to obtain ethylene-vinyl acetate copolymer.

[0127] (4) Prepare a methanol solution of ethylene-vinyl acetate copolymer with a mass fraction of 60% by weight. Then, add an alkaline solution at 55°C for alcoholysis (time is 6h, pressure is normal). The alkaline solution is a methanol solution of NaOH with a concentration of 30% by weight. The molar ratio of hydroxide ions to vinyl acetate in the ethylene-vinyl acetate copolymer is controlled 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 until homogeneous; wherein, the amount of acetic acid used is 1000 ppm relative to the weight of EVOH solids, and the concentration of acetic acid solution is 1.5% by weight.

[0129] (6) The ethylene-vinyl alcohol copolymer solution obtained from alcoholysis was extruded into an aqueous solution at 5°C through an extrusion device with a perforated plate. After precipitating into strips, the strips were cut into granules using a common cutting method. The ethylene-vinyl alcohol copolymer granules were washed with water in a stirred tank for 2 hours each time, and the washing was repeated twice. After the two washings, a mixed solution of water and alcohol was added to the stirred tank, and the mixture was washed at 75°C for 2 hours. Then, it was washed with water once more. During the water washing process, 0.01 parts of acetic acid relative to 100 parts of EVOH were added for acid washing. After centrifugation and dehydration, the EVOH granules were obtained after drying.

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

[0131] Example 4

[0132] The method is the same as in Example 1, except that in step (2), the terminating agent is changed to copper acetate.

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

[0134] Example 5

[0135] The method is the same as in Example 1, except that in step (2), ethanol is replaced with methanol.

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

[0137] Example 6

[0138] The method is the same as in Example 1, except that in step (2), ethanol is replaced with tert-butanol.

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

[0140] Example 7

[0141] The method is the same as in Example 1, except that in step (2), ethylene is first removed by flash evaporation under reduced pressure, and after the pressure is normal, ethanol and 2,4-diphenyl-4-methyl-1-pentene are added.

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

[0143] Example 8

[0144] The method is the same as in Example 1, except that in step (2), ethanol and 2,4-diphenyl-4-methyl-1-pentene are added first, and then ethylene is removed by flash evaporation under reduced pressure, so that the pressure is atmospheric pressure.

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

[0146] Example 9

[0147] The method is the same as in Example 1, except that the molar ratio of the alkali to the vinyl acetate units in the ethylene-vinyl acetate copolymer is 0.1:1.

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

[0149] Comparative Example 1

[0150] The method is the same as in Example 1, except that in step (2), ethanol and a terminator are not added.

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

[0152] Comparative Example 2

[0153] The method is the same as in Example 1, except that ethanol is not added in step (2).

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

[0155] Comparative Example 3

[0156] The method is the same as in Example 1, except that no terminator is added in step (2).

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

[0158] Comparative Example 4

[0159] The method is the same as in Example 1, except that in step (1), 12 parts of methanol and 20 parts of ethanol are added together, while in step (2), no ethanol is added.

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

[0161] Comparative Example 5

[0162] The method is the same as in Example 1, except that in step (2), the order in which ethanol and the terminating agent are added is reversed.

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

[0164] Test example:

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

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

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

[0168] Methods for testing and calculating intrinsic viscosity:

[0169] Accurately weigh approximately 1 g (accurate to 0.2 mg) of dried EVOH sample and place it in a 250 mL Erlenmeyer flask with a ground glass stopper. Add 50 mL of dimethyl sulfoxide (DMSO) and reflux in an 80 °C water bath to dissolve. After complete dissolution, transfer the solution to a 100 mL volumetric flask and dilute to a final concentration. Record the concentration of the sample solution as C. Filter the sample solution and place it in an Ubbelohde viscometer tube. Incubate the solution in a constant temperature water bath at 30 ± 0.1 °C for 15 min. Viscosity Measurement: After calibrating the viscometer vertically, perform the test according to the Ubbelohde viscometer operating instructions. Allow the sample solution to fall naturally in the viscometer tube and accurately record the time it takes for the sample liquid surface to flow across the two measurement lines using a stopwatch. Repeat the measurement several times and take the average value, recorded as t1. Blank Test: Place the filtered DMSO in the viscometer and incubate at 30 ± 0.1 °C. Accurately measure the time it takes for the DMSO to flow across the two measurement lines. Repeat the measurement several times and take the average value, recorded as t0.

[0170] Results Calculation and Expression: The intrinsic viscosity [η] (dL / g) of EVOH is calculated using 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] Degree of alcoholysis test: Dry EVOH was pulverized to 100 mesh, purified by extraction with deionized water, and dried at 120℃. The obtained ethylene-vinyl alcohol copolymer was subjected to NMR analysis under the following conditions, and the degree of alcoholysis was determined using the following analytical method:

[0175] Analysis Method: From the spectrum measured at 40℃, calculate the integral values ​​(I1) of the peak with a chemical shift of 3.7-4 ppm and (I2) of the peak with a chemical shift of 0.6-1.8 ppm. From the spectrum measured at 95℃, calculate the integral values ​​(I3) of the peak with a chemical shift of 3.1-3.7 ppm, (I4) of the peak with a chemical shift of 0.6-1.8 ppm, and (I5) of the peak with a chemical shift of 1.9-2.1 ppm. Here, the peak with a chemical shift of 0.6-1.8 ppm mainly originates from methylene protons, and the peak with a chemical shift of 1.9-2.1 ppm originates from methyl protons in the un-hydrolyzed vinyl acetate unit. The degree of hydrolysis (mol%) is calculated from these integral values ​​using the following formula:

[0176]

[0177] Test method for defect count and screw current variation: Using dried EVOH granules, an SG-45 blown film extruder was used. The extruder temperature was 220℃ / 230℃ / 230℃. Top-blowing was employed with a blow-up ratio of 3. After 10 hours of continuous operation, film samples of 30cm*24cm were prepared. Surface defects in the film were analyzed using a surface defect analyzer (MVT-SIS). The number of defects larger than 0.5mm*0.5mm in the samples was counted. The variation in screw current was examined. The variation in screw current reflects thermal stability. Poor thermal stability leads to an increase in screw current, while good stability results in a constant current. During production, the variation in screw current should be ≤1A.

[0178] Crystal point testing method: The casting film machine and gel detection system (model: ME20-MFA-FSA100V2) were used for testing. The screw was a single screw with L / D≥25, the screw temperature was 230℃ / 230℃ / 230℃, the screw speed was 15rpm, and the stretching speed was 3.1m / min. The width of the cast film was controlled at 15mm, and the film thickness was controlled at 20-40μm. A line scan camera and LED light source were used to test for crystal point defects in the cast film.

[0179] Table 1

[0180]

[0181]

[0182] Table 2

[0183]

[0184]

[0185] The results above show that the resin composition of the present invention has good thermal stability and has fewer surface defects and crystal points when preparing 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 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, characterized in that, The melt index of the copolymer at 190°C and 21.6 kg load is MFR. 21.6 The copolymer has a melt index (MFR) of 5 at 190°C and 5 kg load, and a melt index (MFR) of 2.16 kg load. 2.16 , The MFR 21.6 MFR5 and MFR 2.16 The following relationship must be satisfied: 14≤MFR 21.6 / MFR 2.16 - MFR5 / MFR 2.16 ≤22。 2. The copolymer according to claim 1, wherein, The change in screw current when the copolymer is used with a blown film machine is less than or equal to 1A; And / or, the content of structural units derived from ethylene in the copolymer is 20-50 mol%; And / or, the copolymer has a melt index of 1-10 g / 10 min at 190°C and a load of 2.16 kg; And / or, the weight-average molecular weight of the copolymer is 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. The copolymer according to claim 2, wherein, The copolymer contains 22-48 mol of structural units derived from ethylene.

4. A method for preparing the ethylene-vinyl alcohol copolymer according to any one of claims 1-3, characterized in that, The method includes: (1) In the presence of a first solvent and an initiator, vinyl acetate is polymerized with ethylene; (2) The second solvent and the terminator are mixed sequentially in the product of step (1) to obtain an ethylene-vinyl acetate copolymer solution; (3) The ethylene-vinyl acetate copolymer solution was contacted with an alkali to obtain an ethylene-vinyl alcohol copolymer; The conditions for mixing the product with the second solvent in step (1) include: a temperature of 40-70°C and a time of 1-5 hours.

5. The method according to claim 4, wherein, The molar ratio of hydroxide ions in the alkali to vinyl acetate structural units in the ethylene-vinyl acetate copolymer is 0.005-0.045:

1.

6. The method according to claim 5, wherein, The molar ratio of hydroxide ions in the alkali to vinyl acetate structural units in the ethylene-vinyl acetate copolymer is 0.01-0.03:

1.

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

8. The method according to claim 4 or 5, wherein, Based on the weight of the vinyl acetate, the amount of the second solvent is 1% to 30% by weight. And / or, the amount of the terminating agent is 100-5000 ppm of the amount of vinyl acetate used in step (1); And / or, the terminating agent is selected from at least one of 2,4-diphenyl-4-methyl-1-pentene, 1,1-diphenyl-2-trinitrophenylhydrazine, copper acetate, cuprous chloride and ferric chloride; And / or, the method further includes: removing ethylene from the product of step (1) in step (2).

9. The method according to claim 8, wherein, The amount of the terminator is 300-3000 ppm of the amount of vinyl acetate used in step (1).

10. The method according to claim 8, wherein, The method for removing ethylene is vacuum flash evaporation; And / or, the removal of ethylene occurs after mixing with a second solvent.

11. The method according to claim 4 or 5, wherein, The conditions for mixing the product of step (1) with the terminator include: a temperature of 10-40°C and a time of 0.1-2 h; And / or, the pressure at which the product of step (1) is mixed with the second solvent is 2-6 MPaG; And / or, the pressure at which the product of step (1) is mixed with the terminator is atmospheric pressure.

12. The use of the ethylene-vinyl alcohol copolymer according to any one of claims 1-3 in at least one of packaging materials, automotive fuel tanks, oxygen-barrier underfloor heating pipes, textile materials, and medical materials.

13. An ethylene-vinyl alcohol film, characterized in that, The film is made from the copolymer described in any one of claims 1-3.

14. The ethylene-vinyl alcohol film according to claim 13, wherein, The number of surface defects on the thin film is ≤300 per m. 2 ; And / or, the proportion of crystal points larger than 300 μm in the film is not higher than 5%.

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