Process for producing ethylene-vinyl alcohol copolymer water-containing pellets

Abstract

The present invention provides a method for producing hydrated EVOH pellets, said method comprising: a first step wherein a hydrated EVOH, which is at a temperature of from 80°C to 130°C and has a moisture content W1 of from 10% by mass to 90% by mass, is introduced into an extruder, and is melted and kneaded thereby; and a second step wherein hydrated EVOH pellets are obtained by cutting a hydrated EVOH extruded from the extruder. With respect to this method for producing hydrated EVOH pellets, the extruder has a back slit; water is discharged from the back slit; the temperature of the hydrated EVOH extruded from the extruder is from 80°C to 120°C; the moisture content W2 of the hydrated EVOH extruded from the extruder is from 5% by mass to 50% by mass; and the ratio of the moisture content W2 to the moisture content W1, namely W2 / W1 is 0.2 or more but less than 1. Since the present production method is capable of efficiently reducing water in a hydrated EVOH, while suppressing elution of EVOH, hydrated EVOH pellets are able to be produced with high productivity. In addition, since the drying efficiency of the present production method is high, the obtained dry EVOH pellets are able to be suppressed in thermal deterioration.

Description

Technical Field

[0001] The present invention relates to a method for producing ethylene-vinyl alcohol copolymer water-containing pellets.

Background Art

[0002] Ethylene-vinyl alcohol copolymer (hereinafter sometimes referred to as EVOH) is a polymer material excellent in oxygen barrier property, flavor retention property, oil resistance, non-charging property, mechanical strength, etc., and is widely used after being formed into films, sheets, containers, etc. As a method for producing EVOH, a method is generally used in which an ethylene-vinyl ester copolymer obtained by copolymerizing ethylene and a vinyl ester such as vinyl acetate is saponified in an organic solvent containing alcohol in the presence of a saponification catalyst.

[0003] As one of the post-treatment methods for the alcohol solution of EVOH obtained by saponification, the alcohol solution of EVOH is introduced into a device, brought into contact with water in the device to replace the alcohol in the solution with water, and after reducing the water in the water-containing EVOH derived from the device, it is cut to obtain EVOH water-containing pellets (Patent Document 1) is known.

[0004] Patent Document 1 describes a method for obtaining EVOH water-containing pellets by reducing the water in the water-containing EVOH composition obtained by replacing alcohol with water using a kneader having a liquid discharge port, and then extruding and cutting from a die. Further, Patent Document 2 describes a method for obtaining water-containing EVOH with a reduced water content by kneading the water-containing EVOH obtained by bringing the water / methanol solution of EVOH into contact with water vapor using a twin-screw extruder (front stage) in which a vent is installed downstream (die side) from the inlet.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in these methods, when reducing the water in the water-containing EVOH, EVOH may elute into the discharged water and be discharged together with the water from the liquid discharge port of the kneader or the vent of the twin-screw extruder. Therefore, when continuous operation is performed, EVOH elution marks are left on the liquid discharge port and the vent, and if left unattended for a long time, the liquid discharge port and the vent may become clogged, which may affect the production. Thus, a method for reducing the water in the water-containing EVOH while suppressing the elution of EVOH has been demanded. In addition, EVOH is prone to thermal degradation, has high drying efficiency, and a method for suppressing the degradation of the obtained dried EVOH pellets due to heat has also been demanded.

[0007] The present invention has been made to solve the above problems, and an object thereof is to provide a method for producing EVOH water-containing pellets with high drying efficiency, which can efficiently reduce the water in the water-containing EVOH while suppressing the elution of EVOH.

Means for Solving the Problems

[0008] The above problems are solved by providing a method for producing EVOH water-containing pellets, which includes a first step of introducing water-containing EVOH having a water content W1 of 10 to 90% by mass and a temperature of 80 to 130°C into an extruder and melt-kneading it, and a second step of obtaining EVOH water-containing pellets by cutting the water-containing EVOH discharged from the extruder, wherein the extruder has a back slit from which water is discharged, the temperature of the water-containing EVOH discharged from the extruder is 80 to 120°C, the water content W2 of the water-containing EVOH discharged from the extruder is 5 to 50% by mass, and the ratio (W2 / W1) of the water content W2 to the water content W1 is 0.2 or more and less than 1.

[0009] In this case, the cylinder temperature of the extruder is preferably 70 to 110° C. It is also preferable that the extruder does not have a liquid discharge port downstream of the inlet of the water-containing EVOH. It is also preferable that the screw rotation speed of the extruder is 10 to 2000 rpm.

[0010] It is preferable that the production method further comprises the steps of introducing an EVOH solution containing 50 parts by mass or more of an alcohol having a boiling point of 100°C or less per 100 parts by mass of EVOH into a container, contacting the EVOH with water vapor in the container to extract the alcohol together with the water vapor, and extracting the water-containing EVOH from the container, and introducing the water-containing EVOH extracted from the container into the extruder.

[0011] The EVOH preferably has an ethylene unit content of 20 to 60 mol %. Effect of the Invention

[0012] According to the production method of the present invention, it is possible to efficiently reduce the amount of water in the hydrous EVOH while suppressing the dissolution of EVOH, so that hydrous EVOH pellets can be produced with good productivity, and since the drying efficiency is high, deterioration due to heat of the obtained dried EVOH pellets can be suppressed. [Brief description of the drawings]

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0014] In the present invention, a first step of introducing a water-containing EVOH having a water content W1 of 10 to 90% by mass and a temperature of 80 to 130°C into an extruder and melt-kneading it, and a second step of obtaining EVOH water-containing pellets by cutting the water-containing EVOH discharged from the extruder are provided. The extruder has a back slit from which water is discharged, the temperature of the water-containing EVOH discharged from the extruder is 80 to 120°C, the water content W2 of the water-containing EVOH discharged from the extruder is 5 to 50% by mass, and the ratio (W2 / W1) of the water content W2 to the water content W1 is 0.2 or more and less than 1. It is a method for producing EVOH water-containing pellets. According to this production method, since water in the water-containing EVOH can be efficiently reduced while suppressing the elution of EVOH, EVOH water-containing pellets having a predetermined water content can be produced with high productivity.

[0015] In this specification, the water-containing EVOH introduced into the extruder may be referred to as the water-containing EVOH used in the present invention, and the water-containing EVOH obtained by discharging from the extruder may be referred to as the water-containing EVOH obtained in the present invention.

[0016] The water-containing EVOH used in the present invention is preferably in a paste form containing EVOH and water. The water content W1 of the water-containing EVOH is 10 to 90% by mass, and the temperature is 80 to 130°C. Also, as described later, the water-containing EVOH may contain other components such as alcohol and alkali metal salts.

[0017] The EVOH constituting the water-containing EVOH used in the present invention (hereinafter may be expressed as "the EVOH used in the present invention" or "the above-mentioned EVOH") is usually obtained by saponifying an ethylene-vinyl ester copolymer. The ethylene content in the above-mentioned EVOH is preferably 20 to 60 mol%. When the ethylene content of the EVOH is 20 mol% or more, it becomes easier to prevent the water content of the water-containing EVOH supplied to the extruder from being reduced and the melt viscosity of the water-containing EVOH in the extruder from becoming too low, so the elution of the EVOH is further suppressed. The ethylene content is more preferably 23 mol% or more, still more preferably 25 mol% or more, and particularly preferably 30 mol% or more. On the other hand, when the ethylene content of the above-mentioned EVOH is 60 mol% or less, the gas barrier property is improved. The ethylene content is more preferably 50 mol% or less, still more preferably 45 mol% or less, and particularly preferably 40 mol% or less. It should be noted that the ethylene content and the saponification degree of the EVOH do not substantially change at the end of the saponification process and at the end of the subsequent processes described later, and are usually measured after all the processes are completed.

[0018] The method for producing the above-mentioned EVOH will be specifically described below. As described above, the above-mentioned EVOH is usually obtained by saponifying an ethylene-vinyl ester copolymer. The copolymerization of ethylene and vinyl ester may be any of solution polymerization, suspension polymerization, emulsion polymerization, and bulk polymerization. Also, it may be either continuous or batch. An example of the polymerization conditions in solution polymerization is shown below.

[0019] As the solvent used, alcohols having a boiling point of 100°C or lower are preferred from the viewpoints of the solubility of the ethylene-vinyl ester copolymer and EVOH, handleability, and the ability to efficiently replace alcohol with water. The boiling point is more preferably 80°C or lower, and still more preferably 70°C or lower.

[0020] Examples of alcohols having a boiling point of 100°C or lower include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, t-butyl alcohol, etc., and methanol is particularly preferred.

[0021] As initiators used for polymerization, for example, azonitrile initiators such as 2,2-azobisisobutyronitrile, 2,2-azobis-(2,4-dimethylvaleronitrile), 2,2-azobis-(4-methoxy-2,4-dimethylvaleronitrile), 2,2-azobis-(2-cyclopropylpropionitrile) and organic peroxide initiators such as isobutyryl peroxide, cumyl peroxypivalate, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, t-butyl peroxypivalate, lauroyl peroxide, benzoyl peroxide, t-butyl hydroperoxide can be used.

[0022] Examples of vinyl esters include vinyl fatty acid esters such as vinyl acetate, vinyl propionate, and vinyl pivalate, and vinyl acetate is preferred. Further, EVOH can contain 0.0002 to 0.2 mol% of a vinyl silane compound as a copolymerization component. Here, examples of vinyl silane compounds include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxy-ethoxy)silane, and γ-methacryloxypropylmethoxysilane. Among them, vinyltrimethoxysilane and vinyltriethoxysilane are preferably used.

[0023] The polymerization conditions are preferably as follows. (1) Temperature; preferably 20 to 90 °C, more preferably 40 °C to 70 °C. (2) Time (average residence time in the case of a continuous process); preferably 2 to 15 hours, more preferably 3 to 11 hours. (3) Polymerization rate; preferably 10 to 90% with respect to the charged vinyl ester, more preferably 30 to 80%. (4) Resin content in the solution after polymerization; preferably 5 to 85% by mass, more preferably 20 to 70% by mass.

[0024] In addition to ethylene and vinyl esters, monomers copolymerizable therewith, such as α-olefins such as propylene, butylene, isobutylene, pentene, hexene, α-octene, α-dodecene; 3-acyloxy-1-propene, 3-acyloxy-1-butene, 4-acyloxy-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-methyl-1-butene, 4-acyloxy-2-methyl-1-butene, 4-acyloxy-3-methyl-1-butene, 3,4-diacyloxy-2-methyl-1-butene, 4-acyloxy-1-pentene, 5-acyloxy-1-pentene, 4,5-diacyloxy-1-pentene, 4-acyloxy-1-hexene, 5-acyloxy-1-hexene, 6-acyloxy-1-hexene, 5,6-diacyloxy-1-hexene, 1,3-diacetoxy-2-methylenepropane and other alkenes having an ester group; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, anhydrides, salts, mono- or dialkyl esters thereof; nitriles such as acrylonitrile, methacrylonitrile; amides such as acrylamide, methacrylamide; olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid or salts thereof; alkyl vinyl ethers, vinyl ketones, N-vinyl pyrrolidone, vinyl chloride, vinylidene chloride, etc. can also be polymerized in a small amount. The content of other monomer units other than ethylene, vinyl ester and vinyl alcohol in the EVOH is preferably 20 mol% or less, and may preferably be 10 mol% or less, 5 mol% or less, 3 mol% or less, 1 mol% or less, 0.1 mol% or less. The EVOH may not contain the other monomer units.

[0025] After polymerization for a predetermined time and reaching a predetermined polymerization rate, a polymerization inhibitor is added as necessary, and after unreacted ethylene gas is evaporated and removed, unreacted vinyl ester is expelled. As a method for expelling unreacted vinyl ester, for example, a polymerization solution from which ethylene has been removed is continuously supplied at a constant rate from the upper part of a tower filled with Raschig rings, and a vapor of an organic solvent, preferably an alcohol having a boiling point of 100 °C or lower, most preferably methanol, is blown in from the lower part of the tower. A mixed vapor of the organic solvent and unreacted vinyl ester is distilled out from the top of the tower, and a copolymer solution from which unreacted vinyl ester has been removed is taken out from the bottom of the tower.

[0026] An alkali catalyst is added to the copolymer solution from which unreacted vinyl ester has been removed to saponify the vinyl ester component in the copolymer. Either a continuous method or a batch method can be used for the saponification. As the alkali catalyst, sodium hydroxide, potassium hydroxide, an alkali metal alcoholate, etc. are used. Further, as the solvent used for saponification, methanol is preferable. For example, the saponification conditions are as follows. (1) Concentration of ethylene-vinyl ester copolymer in the solution; 10 to 50% by mass (2) Reaction temperature; 30 to 150 °C (3) Catalyst usage amount; 0.005 to 0.6 equivalent (per vinyl ester component) (4) Time (in the case of continuous method, average residence time); 10 minutes to 6 hours

[0027] Generally, in the case of continuous saponification, methyl acetate generated by saponification can be removed more efficiently, so a resin with a high degree of saponification can be obtained with a smaller amount of catalyst compared to the batch method. Also, in the case of continuous saponification, it is necessary to saponify at a higher temperature to prevent precipitation of EVOH generated by saponification. Therefore, in the continuous method, it is preferable to set the reaction temperature and catalyst amount within the following ranges. Reaction temperature; 70 to 150 °C. Catalyst usage amount; 0.005 to 0.1 equivalent (per vinyl ester component).

[0028] The saponification degree of the resulting EVOH varies depending on the purpose, but is preferably 80 mol% or more of the vinyl ester component, more preferably 95 mol% or more, still more preferably 98 mol% or more, and particularly preferably 99 mol% or more from the viewpoint of further improving the gas barrier properties. The saponification degree can be arbitrarily adjusted depending on the conditions.

[0029] As described above, particularly when producing EVOH pellets with excellent melt stability and good long-run properties, the saponification degree of EVOH is preferably 99.7 mol% or more, more preferably 99.8 mol% or more, still more preferably 99.9 mol% or more, and particularly preferably 99.95 mol% or more. However, in order to obtain such EVOH, it is preferable to further adjust the saponification conditions as follows.

[0030] As a method for obtaining EVOH with a high saponification degree of 99.9 mol% or more, a continuous method is preferable. Examples of methods for obtaining a high saponification degree by a continuous method include a method of adding a catalyst from multiple locations in the saponification reaction tower, a method of increasing the amount of catalyst used, and a method of increasing the amount of methanol blown in from the lower part of the saponification reaction tower. In addition, as a method for obtaining EVOH with a high saponification degree of 99.9 mol% or more by a batch method, examples include a method of adding the catalyst in multiple portions, a method of increasing the amount of catalyst used, and a method of increasing the amount of methanol vapor or nitrogen gas blown into the saponification reaction tank.

[0031] Through the saponification process, a solution or paste containing EVOH is obtained. Since the EVOH after the saponification reaction contains an alkali catalyst, by-products such as sodium acetate and potassium acetate, and other impurities, these may be removed by neutralization and washing as necessary. Here, when washing the EVOH after the saponification reaction with ion-exchanged water or the like that contains almost no metal ions, chloride ions, etc., a part of the catalyst residues such as sodium acetate and potassium acetate may remain in the EVOH.

[0032] As a post-treatment method for the saponified EVOH solution or paste, in a tower vessel, a mixed vapor of a solvent and water is supplied from the lower part of the vessel, and the EVOH solution or paste is supplied from a position above the supply position of the mixed vapor, so that a part of the solvent present in the supplied EVOH solution or paste is replaced with water to obtain a high-concentration EVOH solution. The concentration of EVOH in the EVOH solution supplied to the tower vessel is preferably 15 to 50% by weight, more preferably 25 to 40% by weight. Also, it is preferable that the ratio of the supply amount of the EVOH solution to the supply amount of the mixed vapor (solution supply amount / vapor supply amount) is 100 / 400 to 100 / 8 by weight ratio. Further, it is preferable that the water content in the mixed vapor is 20 to 70% by weight. The solvent used for the mixed vapor is preferably an alcohol having a boiling point of 130°C or lower, and examples of such alcohols include alcohols such as methanol, ethanol, propanol, and butanol. An alcohol having a boiling point of 100°C or lower is more preferable, and among them, methanol is preferable in terms of easy availability, low cost, low boiling point, and easy handling.

[0033] The EVOH solution or paste thus obtained usually contains 50 parts by weight or more of an alcohol having a boiling point of 100°C or lower per 100 parts by weight of EVOH. Also, the alcohol content is preferably 1000 parts by weight or less, more preferably 500 parts by weight or less. By setting the alcohol content within this range, the fluidity of the EVOH solution is ensured and efficient resin production is possible. The alcohol is preferably methanol. In addition, the saponified EVOH solution may be not only an alcohol solution but also a solution of a mixed solvent in which other solvents such as water are added to the extent that EVOH does not precipitate, if necessary.

[0034] A method for obtaining the hydrous EVOH used in the present invention preferably further comprises the steps of introducing the EVOH solution obtained as described above, which contains 50 parts by mass or more of an alcohol having a boiling point of 100° C. or less per 100 parts by mass of EVOH, contacting the EVOH with steam in the vessel to extract the alcohol together with the steam, and extracting the hydrous EVOH from the vessel, and introducing the hydrous EVOH extracted from the vessel into an extruder described below. Such a method not only makes it possible to efficiently replace the alcohol in the EVOH solution with water, but also makes it easy to adjust the water content and temperature of the EVOH.

[0035] The method of contacting the EVOH solution introduced into the vessel with water vapor in the vessel is not particularly limited, and may be either a continuous method or a batch method. The shape of the vessel is also not particularly limited, but a tower-type vessel is preferable for the continuous method, and a tank-type vessel is preferable for the batch method. From the viewpoint of production efficiency, the continuous method is industrially preferable. Examples of the tower-type vessel include a plate tower such as a perforated plate tower or a bubble cap tower, and a packed tower containing ring-type packing.

[0036] In a tower-shaped container, steam is supplied from the lower part of the container, and an EVOH solution or paste is supplied from a position above the steam supply position. By doing so, the solvent (alcohol) present in the supplied EVOH solution or paste is led out together with the steam, and it is preferable to lead out the water-containing EVOH with a water content of 10 to 90% by mass from the container. If the introduction amount of steam is too small, the removal efficiency of the solvent (alcohol) is poor. On the contrary, if it is too large, it is disadvantageous in terms of cost. Therefore, it is preferably 0.3 to 30 times, more preferably 0.5 to 10 times, and even more preferably 0.7 to 5 times in terms of mass ratio with respect to the introduction amount of the EVOH solution or paste. The steam brought into contact with the EVOH solution or paste may contain 10 parts by mass or less of the solvent (alcohol) per 100 parts by mass of the steam. However, in order to efficiently remove the solvent (alcohol), it is preferable that the steam does not contain the solvent (alcohol). The water-containing EVOH may contain 0 to 10 parts by mass of the solvent (alcohol) per 100 parts by mass of the EVOH. Furthermore, the water-containing EVOH may contain saponification catalyst residues and the like.

[0037] The alcohol vapor and steam led out from the upper part of the tower are condensed in a condenser, recovered as an aqueous alcohol solution, and purified and reused as necessary. The EVOH solution or paste is in direct contact with the steam in the container, and the content of the solvent (alcohol) gradually decreases. During this period, the EVOH is in a swollen paste state and can be led out from the container without gelling while maintaining fluidity. EVOH dissolves in a methanol / water mixed solvent at a temperature of about 60 to 70°C under normal pressure. However, when the solvent is only water, it does not dissolve under normal pressure. However, for example, in the presence of pressurized steam at a temperature of 90°C or higher, the EVOH can maintain fluidity even in a state where it contains substantially only water.

[0038] The temperature inside the container is preferably 100 to 150 °C. If the temperature inside the container is less than 100 °C, the fluidity of the water-containing EVOH becomes insufficient, and there is a risk of gelation or blockage inside the container. More preferably, it is 110 °C or higher, and even more preferably, it is 120 °C or higher. On the other hand, if the temperature inside the container exceeds 150 °C, the EVOH may deteriorate. More preferably, it is 140 °C or lower.

[0039] Also, if the pressure inside the container is too low, the removal efficiency of alcohol may deteriorate. The pressure inside the container is preferably 0.1 MPa or higher, more preferably 0.15 MPa or higher, and even more preferably 0.2 MPa or higher. On the other hand, if the pressure inside the container is too high, the water content of the water-containing EVOH derived from the container may become too high, resulting in a risk that the melt viscosity of the water-containing EVOH introduced into the extruder described later becomes too low. Therefore, the pressure inside the container is preferably 0.6 MPa or lower, more preferably 0.5 MPa or lower, and even more preferably 0.4 MPa or lower.

[0040] After contacting the EVOH solution with steam as described above, the water-containing EVOH is derived from the container. The water-containing EVOH is preferably used as the water-containing EVOH supplied to the extruder in the first step described later.

[0041] In the first step, water-containing EVOH with a water content W1 of 10 to 90% by mass and a temperature of 80 to 130 °C is introduced into an extruder and melt-kneaded. The form of the water-containing EVOH introduced into the extruder is not particularly limited, and examples include paste form. As described above, by directly contacting the EVOH solution with steam inside the container, paste-like water-containing EVOH can be obtained. The EVOH is derived from the container without gelling while maintaining its fluidity.

[0042] The water content W1 of the water-containing EVOH introduced into the extruder is 10 to 90% by mass. When the water content W1 is less than 10% by mass, the melt viscosity of the water-containing EVOH becomes too high, making it impossible to discharge the water-containing EVOH from the tip of the extruder or increasing the elution of EVOH. Also, in order to ensure fluidity, the melting temperature of the water-containing EVOH increases, and the hue of the EVOH, which can deteriorate, worsens. The water content W1 is preferably 20% by mass or more, more preferably 30% by mass or more, still more preferably 40% by mass or more, and particularly preferably 45% by mass or more. On the other hand, when the water content W1 exceeds 90% by mass, the melt viscosity of the water-containing EVOH becomes too low, increasing the elution of EVOH. The water content W1 is preferably 80% by mass or less, more preferably 70% by mass or less, still more preferably 60% by mass or less, and particularly preferably 55% by mass or less. The water content W1 of the water-containing EVOH introduced into the extruder is measured by the method described in the examples below. The water content W1 can be adjusted, for example, by the conditions when post-treating the EVOH solution or paste, the conditions when obtaining the water-containing EVOH from the EVOH solution or paste, etc.

[0043] The temperature of the water-containing EVOH supplied to the extruder is 80 to 130°C. When the temperature is less than 80°C, the melt viscosity of the water-containing EVOH becomes too high, making it impossible to discharge the water-containing EVOH from the tip of the extruder or increasing the elution of EVOH. The temperature is preferably 90°C or more, more preferably 95°C or more. On the other hand, when the temperature exceeds 130°C, the melt viscosity of the water-containing EVOH becomes too low, increasing the elution of EVOH. The temperature is preferably 125°C or less, more preferably 115°C or less. The temperature of the water-containing EVOH can be adjusted, for example, by the conditions when obtaining the water-containing EVOH from the EVOH solution or paste, etc.

[0044] From the viewpoints of preserving the working environment and the surrounding environment and making it difficult for the obtained water-containing EVOH pellets to stick to each other, the content of alcohol having a boiling point of 100°C or less in the water-containing EVOH introduced into the extruder is preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 1% by mass or less, and particularly preferably 0.5% by mass or less.

[0045] The water-containing EVOH introduced into the extruder may contain, for example, about 0.1 to 5% by mass in terms of metal of an alkali metal salt corresponding to residues of the catalyst used in the saponification step, etc., and may also contain by-products salts, other impurities, etc. The content of components other than EVOH, water and alcohols having a boiling point of 100°C or lower in the water-containing EVOH supplied to the extruder is preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 3% by mass or less, and particularly preferably 1% by mass or less.

[0046] Figure 1 is a view showing the cylinder configuration (upper side of Figure 1) and the screw configuration (lower side of Figure 1) of the extruder used in Example 1 etc. described later. The first step will be further described with reference to Figure 1.

[0047] The extruder used in the first step may be a single-screw extruder or a multi-screw extruder, but a twin-screw extruder is preferred. Also, the L / D of the extruder is preferably 8 to 30, more preferably 9 to 25, and even more preferably 10 to 20. As the cylinder 1, a block cylinder or the like is used. An inlet 2 for water-containing EVOH is provided in the cylinder 1 of the extruder. After the water-containing EVOH is introduced into the inlet 2, the screw disposed in the cylinder 1 rotates, and along the axis of the cylinder 1, it flows toward the tip side (downstream side 3) of the cylinder 1. At this time, the water in the water-containing EVOH is discharged from the liquid discharge port (back slit 4) provided in the cylinder 1, and the water content rate of the water-containing EVOH is reduced. Thus, a major feature of the present invention is that the extruder used in the first step has a back slit 4, and water in the water-containing EVOH is discharged therefrom. The back slit 4 is a drainage slit (liquid discharge port) provided on the upstream side 7 of the flow 5 of the water-containing EVOH rather than the inlet 2 for the water-containing EVOH. Conventionally, the drainage slit (liquid discharge port 9) of the extruder was provided under the inlet 2 (Fig. 4) or on the downstream side 3 of the flow 5 of the water-containing EVOH rather than the inlet 2 (Fig. 5). However, when continuous operation is performed, EVOH elution marks are formed on the liquid discharge port 9, and if left unattended for a long time, the liquid discharge port 9 may become clogged, which may affect production, so periodic cleaning was necessary. As a result of intensive studies to suppress the generation of EVOH elution marks, the present inventor surprisingly found that by providing the above-described back slit 4 in the cylinder 1 and draining water therefrom, the elution of EVOH into the discharged water is suppressed and the generation of EVOH elution marks is suppressed.

[0048] When the extruder is viewed in a plan view from a direction perpendicular to the axis of the cylinder 1, a back slit 4 is installed on the upstream side 7 of the flow 5 of the water-containing EVOH rather than the inlet 2 of the water-containing EVOH, and the inlet 2 and the back slit 4 do not overlap, that is, the most downstream portion 3 of the back slit 4 is preferably arranged upstream of the most upstream portion 7 of the inlet 2. It is also preferable that the extruder does not have a liquid discharge port 9 downstream of the inlet 2 of the water-containing EVOH, and it is more preferable that it does not have a liquid discharge port 9 other than the back slit 4. When the extruder does not have a liquid discharge port 9 other than the back slit 4, the elution of EVOH tends to be more suppressed. The type of the back slit 4 used in the present invention is not particularly limited, and a general dehydration slit is used. Specifically, a wedge wire type dehydration slit, a screen mesh type dehydration slit, etc. are used.

[0049] The cylinder temperature of the extruder is preferably 70 to 110 °C. When the cylinder temperature is in such a range, the elution of EVOH is further suppressed. The temperature is preferably 105 °C or lower, more preferably 100 °C or lower, and even more preferably 95 °C or lower. Here, the cylinder temperature is the maximum temperature in the portion downstream of the water-containing EVOH inlet 2.

[0050] As the screw of the extruder, a segment type or the like is used. The screw rotation speed is preferably 10 to 2000 rpm. By setting the screw rotation speed within such a range, the elution of EVOH is further suppressed. The screw rotation speed is more preferably 50 rpm or more, even more preferably 120 rpm or more, still more preferably 150 rpm or more, and particularly preferably 200 rpm or more. On the other hand, the screw rotation speed is more preferably 1500 rpm or less, even more preferably 1000 rpm or less, still more preferably 800 rpm or less, and particularly preferably 500 rpm or less.

[0051] The water content W2 of the water-containing EVOH discharged from the extruder needs to be 5 to 50% by mass. When the water content W2 is less than 5% by mass, the melt viscosity of the water-containing EVOH becomes too high, making it impossible to discharge the water-containing EVOH from the tip of the extruder or increasing the eluted EVOH. The water content W2 is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. On the other hand, when the water content W2 exceeds 50% by mass, the melt viscosity of the water-containing EVOH becomes too low, increasing the eluted EVOH. The water content W2 is preferably 45% by mass or less, more preferably 40% by mass or less.

[0052] In the present invention, the ratio (W2 / W1) of the water content W2 of the water-containing EVOH discharged from the extruder to the water content W1 of the water-containing EVOH introduced into the extruder needs to be 0.2 or more and less than 1. When the ratio (W2 / W1) is within such a range, the elution of EVOH is further suppressed. The ratio (W2 / W1) is preferably 0.3 or more, more preferably 0.4 or more, even more preferably 0.5 or more, particularly preferably 0.55 or more, and most preferably 0.6 or more. On the other hand, the ratio (W2 / W1) is preferably 0.9 or less, more preferably 0.85 or less, even more preferably 0.8 or less, particularly preferably 0.75 or less, and most preferably 0.7 or less. The water content W2 can be adjusted, for example, by the water content W1, the cylinder temperature, the screw rotation speed, etc. Also, as described above, by providing a back slit, the water content W2 can be adjusted by draining the water while suppressing the elution of EVOH into the discharged water.

[0053] The temperature of the water-containing EVOH discharged from the extruder needs to be 80 to 120°C. When the temperature is less than 80°C, the melt viscosity of the water-containing EVOH becomes too high, making it impossible to discharge the water-containing EVOH from the tip of the extruder or increasing the eluted EVOH. The temperature is preferably 85°C or higher. On the other hand, when the temperature exceeds 120°C, the melt viscosity of the water-containing EVOH becomes too low, increasing the eluted EVOH. The temperature is preferably 115°C or lower, more preferably 110°C or lower, still more preferably 100°C or lower, and particularly preferably 93°C or lower. The temperature and water content W2 of the water-containing EVOH discharged from the extruder are measured by the method described in the examples.

[0054] From the viewpoint of further suppressing the elution of EVOH, it is preferable that the temperature of the water-containing EVOH introduced into the extruder is higher than the temperature of the water-containing EVOH discharged from the extruder. It is more preferable that the temperature of the water-containing EVOH introduced into the extruder is 1°C or higher than the temperature of the water-containing EVOH discharged from the extruder, still more preferable that it is 5°C or higher, and particularly preferable that it is 10°C or higher.

[0055] In the second step, EVOH water-containing pellets are obtained by cutting the water-containing EVOH discharged from the extruder. The method is not particularly limited, and examples include a method of directly cutting the water-containing EVOH (in a molten state) discharged from the extruder, and a method of extruding the water-containing EVOH discharged from the extruder into a coagulating liquid in a strand shape, coagulating it, and then cutting it. Among them, a method of directly cutting the water-containing EVOH is preferred. As a method of directly cutting the water-containing EVOH discharged from the extruder, a hot cut method or an underwater cut method, etc. are adopted. The cutting method of the EVOH water-containing composition obtained in step 1 described in Patent Document 1 is preferably used as a suitable one. From the viewpoint of ease of handling of the EVOH water-containing pellets, the nozzle diameter is preferably 2 to 5 mmφ (φ represents diameter; the same applies hereinafter). The size of the produced EVOH water-containing pellets can be, for example, when spherical (or substantially spherical), the diameter is 1 mm or more and 10 mm or less, and when cylindrical, the diameter is 1 mm or more and 10 mm or less, and the length is 1 mm or more and 10 mm or less. In addition, when extruded in a strand shape, coagulated, and then cut, cylindrical pellets are obtained, and when directly cut in a molten state, spherical (or substantially spherical) pellets are obtained. Thus, the method of cutting the water-containing EVOH in a molten state does not require considering the take-up speed for stably forming strands compared to the method of extruding into a coagulating liquid, extruding in a strand shape, coagulating, and then cutting, so it is excellent in productivity. For example, even in the case where it is not easy to form strands, such as EVOH with a low ethylene content, it is easy to manufacture EVOH water-containing pellets by cutting in a molten state.

[0056] As a method of extruding in a strand shape, coagulating, and then cutting, a method of extruding the water-containing EVOH into the coagulating liquid in a strand shape can be mentioned. Water is used as the coagulating liquid, but a small amount of alcohol may be contained. The temperature of the coagulating liquid is preferably 0 to 50°C, and the temperature of the water-containing EVOH during extrusion is 80 to 120°C. Due to this temperature difference, the water-containing EVOH can be coagulated in a short time. The temperature of the coagulating liquid is preferably 0 to 30°C. The coagulated strands are cut into pellets with a cutter. A strand cutter is preferably used as the cutter.

[0057] The water-containing EVOH is extruded in a strand shape into the coagulating liquid by a nozzle having an arbitrary shape. The shape of such a nozzle is not particularly limited, but a cylindrical shape is preferable. In this way, the water-containing EVOH is extruded from the nozzle in a strand shape. At this time, the strand does not necessarily have to be single, and it can be extruded in any number between several and several hundreds. Next, the extruded EVOH in a strand shape is cut after sufficient coagulation to obtain water-containing EVOH pellets. Thereafter, if necessary, it may be washed as described later. The size of such pellets can be, for example, in the case of a cylindrical shape, the diameter is 1 mm or more and 10 mm or less, the length is 1 mm or more and 10 mm or less, and in the case of a spherical shape, the diameter is 1 mm or more and 10 mm or less.

[0058] Before drying the obtained water-containing EVOH pellets, washing and addition of additives are carried out as necessary. As the washing method and the method of adding additives, the methods described in Patent Document 1 for the pellets of the water-containing EVOH composition obtained in Step 1 can be adopted. Further, before drying, the water-containing EVOH pellets may be melt-kneaded again by an extruder and then cut and pelletized. As the melt-kneading method, cutting method, and drying method of the obtained pellets at this time, the melt-kneading method of Step 2, the pelletizing method of the EVOH resin obtained in Step 2, the drying method of the obtained pellets, etc. described in Patent Document 1 are adopted.

[0059] The melt flow rate (MFR) (190 °C, load 2160 g) of the EVOH resin composition pellets obtained using the water-containing EVOH pellets is preferably 0.5 to 100 g / 10 min, more preferably 1 to 50 g / 10 min, and even more preferably 1.5 to 20 g / 10 min. When the MFR is 0.5 g / 10 min or more, the moldability tends to be good, and when the MFR is 100 g / 10 min or less, the mechanical properties of the obtained molded product tend to be good. The MFR is measured by the method described in the examples described later.

[0060] The thus obtained EVOH can be formed into various molded articles such as films, sheets, containers, pipes, fibers, etc. by melt molding, and is used in various applications. According to the production method of the present invention, the productivity of such EVOH can be improved.

Examples

[0061] Hereinafter, the present invention will be described more specifically with reference to examples.

[0062] [Evaluation Method] (1) Measurement of water content Using 3 g of the water-containing EVOH and EVOH water-containing pellets obtained in the examples and comparative examples, the water content of the water-containing EVOH and EVOH water-containing pellets was measured with a halogen moisture analyzer "HR73" manufactured by METTLER at a drying temperature of 180 °C and a drying time of 15 minutes.

[0063] (2) Evaluation of EVOH elution According to the methods described in the examples and comparative examples, EVOH water-containing pellets were continuously produced, and it was visually confirmed whether there were white EVOH elution marks at the liquid discharge port provided in the twin-screw extruder, and evaluated according to the following evaluation criteria. It is considered that EVOH eluted in the discharged water causes EVOH elution marks at the liquid discharge port. A: Even after continuous operation for 10 days or more, no EVOH elution marks were observed at the liquid discharge port B: EVOH elution marks were observed at the liquid discharge port during continuous operation for more than 7 days and less than 10 days C: EVOH elution marks were observed at the liquid discharge port during continuous operation for more than 5 days and less than 7 days D: EVOH elution marks were observed at the liquid discharge port during continuous operation for more than 3 days and less than 5 days E: EVOH elution marks were observed at the liquid discharge port during continuous operation for more than 1 day and less than 3 days F: EVOH elution marks were observed at the liquid discharge port during continuous operation for less than 1 day G: Paste-like water-containing EVOH leaked from the liquid discharge port and operation could not be carried out

[0064] (3) Melt Flow Rate (MFR) The EVOH hydrous pellets obtained in the examples and comparative examples were put into ion-exchanged water (bath ratio 20), stirred and washed for 2 hours, and deliquinated. This operation was repeated three times. 10 kg of the deliquinated pellets were subjected to removal of surface water using a centrifuge. The hydrous pellets, which had a moisture content of 33% by mass after centrifugal dehydration, were put into a twin-screw extruder shown below, and melt-kneaded under the following conditions while the resin temperature at the discharge port was set to 100°C and a treatment liquid consisting of an aqueous solution of acetic acid / sodium acetate / phosphoric acid was added from the trace component addition section at the tip of the discharge port side. The amount of EVOH fed per unit time was 10 kg / hour (including the mass of water contained), and the amount of the treatment liquid fed per unit time was 0.67 L / hour. The composition of the treatment liquid was an aqueous solution containing 6.7 g / L of acetic acid, 11.3 g / L of sodium acetate, and 1 g / L of phosphoric acid. (Twin-screw extruder conditions) Equipment: 30mmΦ twin screw extruder Length: 45.5 Screw: Same direction full intermeshing type Screw speed: 300 rpm Cylinder temperature: 100℃ Die temperature: 105℃ Number of die holes: 5 holes (3mmΦ) -Removal speed: 5m / min

[0065] The molten EVOH resin discharged from the twin-screw extruder was then cut with a hot cutter to obtain roughly spherical pellets. The roughly spherical pellets had a moisture content of 20% by mass. The resulting pellets were dried under a nitrogen stream at 90°C for 15 hours and at 105°C for 15 hours to obtain roughly spherical EVOH pellets (moisture content 0.3% by mass) with a short diameter of 2.7 mm and a long diameter of 3.7 mm.

[0066] Regarding the EVOH pellets obtained above, the MFR was measured according to the method described in JIS K 7210:2014. Specifically, the EVOH pellets were filled into a cylinder with an inner diameter of 9.55 mm and a length of 162 mm of a melt indexer L244 (manufactured by Poong Industrial Co., Ltd.), melted at 190 °C, and then a plunger with a mass of 2,160 g and a diameter of 9.48 mm was used to apply an equal load to the melted resin composition. The amount of the resin composition extruded per unit time (g / 10 min) through an orifice with a diameter of 2.1 mm provided at the center of the cylinder was measured.

[0067] (4) Measurement of alcohol content 5 g of the water-containing EVOH used in the examples and comparative examples was cryogenically pulverized in liquid nitrogen, sampled (about 500 mg) into a vial for HSS immediately after pulverization, and methanol was analyzed under the following conditions. Two measurements were carried out for each sample, and the alcohol content was calculated from the average. · Headspace (HSS)-GC / MS Oven temperature: 120 °C (MHE method: [120 °C × 30 min] × 5 times) Loop temperature: 200 °C Transfer temperature: 200 °C, with shaking GC / MS Column: DB-WAXetr (30 m - 0.25 mm - 0.5 μm) Oven: 50 °C (held for 5 minutes) → 10 °C / min → 200 °C (held for 10 minutes) Inlet: 230 °C (split ratio 20:1) Measurement mode: SIM (m / z = 31)

[0068] (Example 1) A solution of EVOH containing 100 parts by mass of EVOH with an ethylene unit content of 32 mol% and a saponification degree of 99.98 mol%, 60 parts by mass of methanol and 40 parts by mass of water was continuously supplied from the topmost stage of a tray column with a column diameter of 0.3 m and 10 stages, and steam was blown in from the bottommost stage to bring the EVOH solution and the steam into countercurrent contact. The temperature inside the column was 130 °C and the pressure inside the column was 0.3 MPa. The water-containing EVOH obtained by countercurrent contact with the steam was withdrawn from the bottom of the column. The temperature of the obtained water-containing EVOH was 120 °C, and the water content (W1) measured according to the above evaluation method was 54.5% by mass. Also, the alcohol content was 0.05% by mass. The results are shown in Table 1.

[0069] The obtained EVOH with a water content (W1) of 54.5% by mass was supplied at 42 kg / hr to a twin-screw extruder having a backlit 4 disposed on the upstream side 7 from the inlet 2 of the water-containing EVOH, with the resin temperature set at 110°C, as shown in Fig. 1, and extruded under the following conditions from a die having 8 holes with a pore diameter of 30 mm attached to the tip of the extruder. The melt was cut with a hot cutter having two blades (Fig. 6) at a distance of 0.05 mm from the die to obtain flat spherical EVOH water-containing pellets. The resin temperature at this time was 110°C, and the water content (W2) measured according to the above evaluation method was 38% by mass. The resin temperature was measured by a temperature sensor in contact with the melt installed near the discharge outlet at the tip of the cylinder. EVOH water-containing pellets were continuously produced under the above conditions, and the elution of EVOH into the water discharged from the twin-screw extruder was evaluated according to the above evaluation method. Also, for a part of the obtained EVOH water-containing pellets, the MFR was measured according to the above evaluation method. These results are shown in Table 1. The flow rate of the cutter circulating water was 300 liters / min, and the rotational speed of the cutter blade was 3000 rpm. Further, the obtained EVOH water-containing pellets were put into ion-exchanged water (bath ratio 20), stirred and washed for 2 hours, and the operation of draining was repeated 3 times. After removing the surface water from the drained pellets using a centrifuge, they were dried at 95°C for 3 hours under a nitrogen stream with an oxygen concentration of 1% by volume or less to obtain dry resin composition pellets with a water content of 0.5% by mass. When the water content was 0.8% by mass or less when dried at 95°C for 3 hours under a nitrogen stream with an oxygen concentration of 1% by volume or less, it was judged that the drying efficiency was good. <Conditions of Twin-Screw Extruder> L / D :14 Diameter :30mm Screw :Full Flight Rotation speed :300rpm Cylinder temperature: 90°C (highest temperature in the part downstream from the water-containing EVOH inlet 2) Die temperature :120°C Number of die holes: 8

[0070] (Examples 2 - 8, Comparative Examples 1 - 6) The conditions were adjusted so that the ethylene unit content, saponification degree, alcohol content, temperature and water content W1 of the resin supplied to the extruder, the arrangement of the liquid discharge port, the cylinder temperature, the screw rotation speed, the temperature of the resin extruded from the extruder, and the water content W2 of the resin extruded from the extruder were as described in Table 1. Except for this, the water-containing EVOH pellets were produced and evaluated in the same manner as in Example 1. The results are shown in Table 1. Figure 2 shows the cylinder configuration of the twin-screw extruder in Example 2, Figure 3 shows Example 3, Figure 4 shows Comparative Example 1, and Figure 5 shows Comparative Example 2 and the cylinder configuration of the twin-screw extruder in 6.

[0071]

Table 1

[0072] From the comparison between Examples 1 to 6 and Comparative Examples 1, 2, and 6, it can be seen that when using an extruder with a back slit, the elution of EVOH into the water discharged from the extruder was suppressed. Also, from the comparison between Example 1 and Examples 2 and 3, it can be seen that by not installing slits (liquid discharge ports) other than the back slit in the extruder, the elution of EVOH can be further suppressed. Furthermore, from the comparison between Example 1, Example 4, and Example 5, it can be seen that by adjusting the resin temperature and cylinder temperature supplied to the extruder, the elution of EVOH can be further suppressed. Also, from Example 6, it can be seen that even in EVOH with a low ethylene unit content, the elution of EVOH is sufficiently suppressed.

[0073] On the other hand, when the water content W2 was high as in Comparative Example 3 and Comparative Example 5, the elution of EVOH tended to occur. Also, when the temperature of the water-containing EVOH supplied to the extruder was high as in Comparative Example 4, the elution of EVOH tended to occur even when a back slit was installed.

Explanation of Symbols

[0074] 1 Cylinder 2 Inlet 3 Downstream side 4 Back slit 5 Flow of water-containing EVOH 6 Temperature sensor 7 Upstream side 8 Full flight screw 9 Liquid discharge port 30 Hot cutter 31 Melt supply port 32 Die 33 Rotary blade 34 Rotating shaft 35 Cutter box 36 Cooling water supply port 37 Cooling water 38 Water film 39 Pellet discharge port 40 Cooling water and pellets

Claims

1. A first step of introducing a water-containing ethylene-vinyl alcohol copolymer having a water content W1 of 10 to 90% by mass and a temperature of 80 to 130° C. into an extruder and melt-kneading the copolymer; and A second step of cutting the hydrous ethylene-vinyl alcohol copolymer discharged from the extruder to obtain hydrous ethylene-vinyl alcohol copolymer pellets, The extruder has a back slit through which water is discharged; The temperature of the water-containing ethylene-vinyl alcohol copolymer discharged from the extruder is 80 to 120° C., The water content W2 of the water-containing ethylene-vinyl alcohol copolymer discharged from the extruder is 5 to 50 mass%; and A method for producing hydrous ethylene-vinyl alcohol copolymer pellets, in which the ratio of the moisture content W2 to the moisture content W1 (W2 / W1) is 0.2 or more and less than 1.

2. The method according to claim 1, wherein the cylinder temperature of the extruder is 70 to 110°C.

3. The method according to claim 1 or 2, wherein the extruder does not have a liquid discharge port downstream of an inlet for the water-containing ethylene-vinyl alcohol copolymer.

4. The method according to any one of claims 1 to 3, wherein the screw rotation speed of the extruder is 10 to 2000 rpm.

5. The method further comprises the steps of: introducing an ethylene-vinyl alcohol copolymer solution containing 50 parts by mass or more of an alcohol having a boiling point of 100° C. or less per 100 parts by mass of the ethylene-vinyl alcohol copolymer into a vessel; contacting the ethylene-vinyl alcohol copolymer with water vapor in the vessel to extract the alcohol together with the water vapor; and extracting a water-containing ethylene-vinyl alcohol copolymer from the vessel; The method according to any one of claims 1 to 4, wherein the water-containing ethylene-vinyl alcohol copolymer discharged from the vessel is introduced into the extruder.

6. The method according to any one of claims 1 to 5, wherein the ethylene-vinyl alcohol copolymer has an ethylene unit content of 20 to 60 mol%.

Images