JP2011111473A - Method for producing ethylene-vinyl alcohol copolymer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an ethylene-vinyl alcohol copolymer efficiently producing a high-quality and homogeneous product by highly removing impurities, such as residues of saponification catalysts and by-products produced in saponification and solvents. <P>SOLUTION: On a flow passage of paste between a dealcoholization process and a pelletization process, a pipe mixer and a water feed pipe which adds washing water having a predetermined weight ratio to the paste are provided. The paste comprising a mixture of EVOH and water/alcohol derived from the dealcoholization process is introduced along with the washing water into the pipe mixer and stirred and mixed so that the surface and the inside of the paste are repeatedly shifted. After deriving the paste, a part of or all of the alcohol contained in the paste is replaced with water, thereby obtaining a water-containing composition of ethylene-vinyl alcohol copolymer with a low alcohol content. Also, the part of or all of the alcohol, impurities, etc., are removed with high efficiency from the paste. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing an ethylene-vinyl alcohol copolymer, and more specifically, ethylene and vinyl ester as raw materials for an ethylene-vinyl alcohol copolymer (hereinafter also referred to as “EVOH”) are alcoholized. Related to a method for producing an ethylene-vinyl alcohol copolymer capable of highly removing impurities such as by-products generated during polymerization and saponification, catalyst residues used during saponification, and alcohol solvent It is.

  Ethylene-vinyl alcohol copolymer (EVOH) is excellent in transparency, gas barrier properties against oxygen, solvent resistance, oil resistance, mechanical strength, etc., molded into films, sheets, bottles, etc. It is widely used as various packaging materials such as pharmaceutical packaging materials, industrial chemical packaging materials, and agricultural chemical packaging materials.

  This EVOH is usually produced by saponifying an ethylene-vinyl ester copolymer obtained by copolymerization of a fatty acid vinyl ester such as vinyl acetate with ethylene in an alcohol solvent in the presence of a catalyst under high temperature and high pressure conditions. Is done. The alcohol solution of EVOH in the high-temperature and high-pressure state obtained in the saponification step is brought into a water / alcohol mixed solution of EVOH that is stable at normal pressure by contacting with water or water vapor in a container. The viscosity is adjusted by adjusting the ratio and pressure, and after being melted and kneaded using an extruder, it is extruded into a strand in a low-temperature coagulation bath mainly composed of water and cut (pelletized). After being washed and dried, the film is used for forming a film, a sheet, a bottle, etc.

  However, in the above conventional EVOH production method, when the EVOH water / alcohol solution is extruded into a coagulation bath to form a strand of EVOH and the alcohol is washed (removed), the alcohol washed out in the coagulation bath is in the air. It has the problem of volatilizing and causing the working environment to deteriorate.

  Therefore, as a method for solving the above-mentioned problems, the EVOH water / alcohol mixed solution (EVOH and water) which is stable at normal pressure is used before pelletization using an extruder (pelletization for obtaining a final product). / Paste made of a mixture of alcohol) with a kneader or the like to reduce the moisture content, and then pelletize (intermediate pelletization). After washing and drying the intermediate pellet, the above-mentioned extruder is used. A method for obtaining final EVOH product pellets has been proposed (see Patent Documents 2 and 3).

  However, in the production methods disclosed in Patent Documents 2 and 3, an apparatus for producing an EVOH hydrous composition pellet (intermediate pellet) as an intermediate product and an apparatus for drying the intermediate pellet are required. This is disadvantageous in terms of manufacturing costs. In addition, it takes time and energy to dehydrate and dry the above intermediate pellets, and the EVOH intermediate pellets that have stayed in the dryer for a long period of time are subject to thermal degradation. There is a difficulty that it is likely to cause.

  Furthermore, the EVOH water-containing composition as an intermediate product usually contains impurities such as catalyst residues used during saponification, by-products generated during saponification, alcohol as a solvent, and the like. If included, EVOH pellets obtained as a final product and molded articles (films, sheets, bottles, etc.) using the pellets may have problems such as coloring. However, in the EVOH manufacturing method (Patent Documents 2 and 3) in which the cleaning is performed after the intermediate pellet is generated, since the cleaning is performed in a solid (pellet shape) state, impurities are completely removed to the inside of the pellet. There was a problem that was difficult.

  Accordingly, the inventors of the present invention manufactured a EVOH composition in the process of producing EVOH and water / alcohol mixture (high viscosity paste) by pelletizing using an extruder (pellet for obtaining a final product). The composition of this paste contains less than 10 parts by weight of alcohol and 20 to 100 parts by weight of water with respect to 100 parts by weight of EVOH. An ethylene-vinyl alcohol copolymer composition capable of obtaining an EVOH composition having a low water content without performing washing or heat drying after pelletization, and a method for producing the pellets (Refer to Patent Document 4).

Japanese Patent Laid-Open No. 11-77684 JP 2002-284811 A International Publication No. 2004/009313 International Publication No. 2009/084509

  However, the method for producing ethylene-vinyl alcohol copolymer pellets by the present inventors (Patent Document 4) is improved in the removal rate of the impurities as compared with the conventional EVOH production method described above. As a result of further investigation, in this production method, the viscosity of the paste made of a mixture of EVOH and water / alcohol to be cleaned is high. Since the inside of the paste is not easily exposed to water, the impurities may not be sufficiently removed, and an improvement is desired.

  The present invention has been made in view of such circumstances, and impurities such as saponification catalyst residues, by-products and solvents generated during saponification are highly removed, and a high-quality and homogeneous product can be efficiently produced. The object is to provide a method for producing an ethylene-vinyl alcohol copolymer that can be produced.

  In order to achieve the above object, the production method of the present invention introduces an alcohol solution of an ethylene-vinyl alcohol copolymer or a water / alcohol mixed solvent solution into a washing container, and contacts with water or water vapor in the washing container. A part of the alcohol is discharged out of the container together with water or water vapor to obtain a paste comprising a water-containing composition of the ethylene-vinyl alcohol copolymer, and the ethylene-vinyl alcohol copolymer. A water-containing composition is supplied to an extruder, melted and kneaded, and then discharged and cut to obtain a pellet of an ethylene-vinyl alcohol copolymer, thereby producing an ethylene-vinyl alcohol copolymer. A paste mixer between the dealcoholization step and the pelletizing step, a pipe mixer and the above A water supply pipe for adding a predetermined weight ratio of cleaning water to the waste, and the paste drawn from the cleaning container is introduced into a pipe mixer together with the cleaning water, and the surface and the inside of the paste Are mixed after being stirred and mixed so that they are repeatedly replaced, and a part or all of the alcohol contained in the paste is replaced with water, whereby the water-containing ethylene-vinyl alcohol copolymer composition having a low alcohol content is obtained by the extrusion. Take the method of supplying to the machine.

  That is, the present inventors have further conducted intensive studies in order to solve the above problems. As a result, the high-viscosity paste made of a mixture of EVOH and water / alcohol is not simply brought into contact with water on the paste flow path before being supplied to the pelletizing process extruder (after the dealcoholization process), Each part of the paste (surface and inside, laminar outer and inner layers of the paste, or high-viscosity region and low-viscosity region, etc.) is repeatedly replaced while the surface is renewed with a large amount of washing water supplied into the paste flow path. In this way, it is possible to remove the impurities in the paste almost completely by interposing a device (mechanism) that contacts the washing water many times without leaving the entire paste. The headline, the present invention has been reached.

  The method for producing an ethylene-vinyl alcohol copolymer of the present invention is based on the above knowledge, and before being put into the pelletizing process extruder, EVOH and water together with a large amount of washing water. / A paste composed of a mixture of alcohol is passed through a pipe mixer having kneading and stirring / mixing functions, and kneaded in a liquid phase so that the surface and the inside of the paste (the outer layer and the inner layer in a laminar flow) are repeatedly switched. ing. For this reason, not only the surface of the paste but also the inside thereof is in contact with the washing water, whereby part or all of the alcohol together with the washing water and impurities such as residual catalyst and by-products during polymerization and saponification Are removed with high efficiency. Therefore, according to the method for producing an ethylene-vinyl alcohol copolymer of the present invention, impurities in the obtained EVOH water-containing composition are reduced, and the final product EVOH and the quality of the molded product using this EVOH are reduced. Can be improved.

  Further, in the production method of the present invention, when the pipe mixer is a static mixer, the paste made of the EVOH hydrous composition becomes a laminar flow when passing through the static mixer. Each laminar flow repeats splitting, diversion, inversion and merging. Therefore, according to the method for producing an ethylene-vinyl alcohol copolymer of the present invention, the paste can be efficiently stirred and mixed without using power for kneading.

  Furthermore, while the paste introduced into the static mixer is kneaded (kneaded in the liquid phase), it naturally moves from the paste introduction (upstream) side to the outlet (downstream) side by the pressure (pumping) in the paste flow path. And discharged from the pipe mixer. Therefore, the method for producing an ethylene-vinyl alcohol copolymer of the present invention can smoothly pass through this static mixer (pipe mixer) even if it is a high-viscosity paste.

  In the production method of the present invention, in particular, the ethylene-vinyl alcohol copolymer water-containing composition having a low alcohol content derived from the outlet of the pipe mixer is upstream of the inlet of the pipe mixer. A circulation flow path for circulating in the paste flow path is provided so that a part of the low alcohol content ethylene-vinyl alcohol copolymer-containing composition joins the paste before introduction of the pipe mixer. In this case, the alcohol-water substitution rate and the removal rate of impurities such as residual catalyst and by-products during polymerization and saponification can be improved, and the paste that flows continuously Homogenization (homogenization) can be achieved.

  Conventionally, in order to improve physical properties such as heat resistance of an ethylene-vinyl alcohol copolymer, additives (auxiliaries) such as carboxylic acid compounds, boron compounds and phosphoric acid compounds are added to this EVOH. was there. However, in the conventional EVOH production method, after EVOH is pelletized (or after intermediate pelletization), the pellets are immersed in an aqueous solution containing the additive, and then dehydrated and dried. The above-mentioned additive tends to be unevenly distributed on the surface of the pellet, and has a problem that it is difficult to uniformly disperse in the pellet.

  On the other hand, in the production method of the present invention, the washing water added to the paste derived from the step of obtaining the paste (dealcoholization step) is a carboxylic acid compound (carboxylic acid, carboxylate), boron. In the case of containing at least one additive selected from a compound and a phosphoric acid compound, the additive can be uniformly dispersed into the paste as the paste is kneaded (surface renewal). In addition, there is no need to provide a process and equipment for adding the above-mentioned additive, and there is an advantage that the number of man-hours involved in the production can be reduced and the equipment can be simplified.

  Furthermore, in the production method of the present invention, the water content of the ethylene-vinyl alcohol-based copolymer water-containing composition after passing through the pipe mixer (before being charged into the pelletizing step) is 100 wt% of the ethylene-vinyl alcohol-based copolymer. When the EVOH water-containing composition is melt-kneaded and pelletized with an extruder, the L / D value (effective screw length / screw diameter) is large. There is no need to use a special extruder such as, which is advantageous.

  In addition, when the water content of the ethylene-vinyl alcohol-based copolymer water-containing composition after passing through the pipe mixer is too low, the viscosity of the ethylene-vinyl alcohol-based copolymer water-containing composition is increased, and the resin is transferred. Efficiency tends to decrease, and conversely, when it is too high, production efficiency tends to decrease when the resin is dehydrated and dried.

  The water content of the ethylene-vinyl alcohol copolymer pellets obtained from the pelletizing step is preferably less than 10 parts by weight with respect to 100 parts by weight of the ethylene-vinyl alcohol copolymer.

It is a flowchart which shows the outline of 1st Embodiment of the manufacturing method of the ethylene-vinyl alcohol-type copolymer of this invention. It is a flowchart which shows the outline of 2nd Embodiment of the manufacturing method of the ethylene-vinyl alcohol-type copolymer of this invention.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to this embodiment.

FIG. 1 is a flowchart showing an outline of a first embodiment of a method for producing an ethylene-vinyl alcohol copolymer of the present invention.
This EVOH production process involves saponification of an alcohol solution of an ethylene-vinyl ester copolymer (ethylene-vinyl acetate in this example) to obtain an EVOH alcohol solution (not shown). An alcohol solution of EVOH is brought into contact with water vapor in a tower-type cleaning vessel to obtain a paste comprising a mixture of EVOH and water / alcohol; A pelletizing step for pelletizing using a cutter or the like, and a pipe mixer on the paste flow path (pipe) between the dealcoholizing step and the pelletizing step. A water supply pipe for adding washing water in a weight ratio is provided.

First, the ethylene-vinyl ester copolymer used in the present invention and the EVOH obtained in the present invention will be described in advance.
EVOH obtained in the present invention is a water-insoluble thermoplastic resin. The EVOH is usually obtained by saponifying an ethylene-vinyl ester copolymer obtained by copolymerizing a fatty acid vinyl ester and ethylene, and mainly comprises an ethylene structural unit and a vinyl alcohol structural unit. It contains a certain amount of vinyl ester structural units generated by the conversion.

  The fatty acid vinyl ester compound is typically vinyl acetate, but other examples include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, Vinyl laurate, vinyl stearate, vinyl benzoate, vinyl versatate and the like can be used alone or in combination.

  In the present invention, in addition to ethylene and fatty acid vinyl ester, an ethylenically unsaturated monomer that can be copolymerized within a range that does not inhibit the properties required for EVOH may be copolymerized. The following can be mentioned. For example, olefins such as propylene, 1-butene, isobutene, 2-propen-1-ol, 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 3,4 3,4-Diacyloxy-1-butene, especially 3,4-diacetoxy, which are hydroxy group-containing α-olefins such as dihydroxy-1-butene and 5-hexene-1,2-diol, and esterified products thereof -1-butene and the like. In addition, unsaturated acids or salts thereof such as acrylic acid, methacrylic acid, crotonic acid, (anhydrous) phthalic acid, (anhydrous) maleic acid, (anhydrous) itaconic acid, and mono- or dialkyl esters having 1 to 18 carbon atoms Is given. Further, acrylamide such as acrylamide, C1-C18 N-alkylacrylamide, N, N-dimethylacrylamide, 2-acrylamidepropanesulfonic acid or a salt thereof, and acrylamidepropyldimethylamine or an acid salt thereof or a quaternary salt thereof. Methacrylamide, N-alkylmethacrylamide having 1 to 18 carbon atoms, N, N-dimethylmethacrylamide, 2-methacrylamideamidopropanesulfonic acid or its salt, methacrylamidepropyldimethylamine or its acid salt and its quaternary And methacrylamides such as salts. Also, N-vinylamides such as N-vinylpyrrolidone, N-vinylformamide, N-vinylacetamide, vinyl cyanides such as acrylonitrile and methacrylonitrile, alkyl vinyl ethers having 1 to 18 carbon atoms, hydroxyalkyl vinyl ethers, alkoxy Vinyl ethers such as alkyl vinyl ethers, vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, vinyl halides such as vinyl bromide, vinyl silanes such as trimethoxyvinyl silane, and allyl acetate, allyl chloride, trimethyl- ( 3-acrylamido-3-dimethylpropyl) -ammonium chloride, acrylamido-2-methylpropanesulfonic acid, vinyl ethylene carbonate, glycerin monoallyl ether and the like.

  Further, the ethylene content of EVOH is determined at the time of polymerization of ethylene and fatty acid vinyl ester, and does not change before and after saponification. The ethylene content is a value measured based on ISO14663 as the ethylene content in EVOH, and is usually 20 to 60 mol%, preferably 20 to 55 mol%, more preferably 25 to 50 mol%. If the ethylene content is too small, the moldability at the time of melt molding tends to be reduced. Conversely, if it is too much, the gas barrier property when used in a molded product tends to be lowered.

  The average saponification degree of the vinyl ester component in the EVOH is a value measured based on JIS K6726 (however, the EVOH resin is a solution uniformly dissolved in water / methanol solvent), and usually 90 to 100 mol%, Preferably it is 95-100 mol%, More preferably, it is 99-100 mol%. When the saponification degree is too low, gas barrier properties, moisture resistance and the like tend to be lowered.

  The melt flow rate (MFR) (210 ° C., load 2160 g) in EVOH is usually 0.1 to 100 g / 10 minutes, preferably 0.5 to 50 g / 10 minutes, more preferably 1 to 30 g / 10 minutes. It is. If this melt flow rate is too small, the molding process tends to be difficult due to a high torque state during melt molding, and if it is too large, the appearance and gas barrier properties of the molded product will be reduced. Tend to.

  For copolymerization (reaction) of ethylene and a fatty acid vinyl ester, a polymerization method such as solution polymerization, suspension polymerization, emulsion polymerization, bulk polymerization or the like is used, and among these, solution polymerization is preferably used. In addition, as a solvent used for solution polymerization, it is necessary to dissolve ethylene and a fatty acid vinyl ester and an ethylene-vinyl ester copolymer that is a polymerization product thereof, and alcohol is usually used. It is done. Preferred are alcohols having 1 to 4 carbon atoms, and specific examples include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, t-butyl alcohol and the like. In consideration of the saponification treatment described later, if the solvent used in the saponification treatment is the same as the solvent used in the polymerization, it is not necessary to replace the solvent and the treatment such as recovery and reuse can be efficiently performed. Therefore, methanol (MeOH) is particularly preferably used as the polymerization solvent.

  Saponification of an ethylene-vinyl ester copolymer obtained by solution polymerization or the like is performed using a saponification catalyst in a state in which the copolymer is dissolved in alcohol or a water / alcohol mixed solvent. In the case of a water / alcohol mixed solvent, the mixing ratio is usually (10/90) to (90/10), preferably (20/80) to (80/20) in terms of the weight ratio of (water / alcohol), Preferably they are (40/60)-(60/40). The concentration of the ethylene-vinyl ester copolymer resin in the alcohol or water / alcohol solution of the ethylene-vinyl ester copolymer is usually 20 to 70% by weight, preferably 30 to 60% by weight, More preferably, it is 35 to 50% by weight.

  Examples of the saponification catalyst include an alkali catalyst and an acid catalyst. For example, specific examples of the alkali catalyst include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkali metal alkoxides such as sodium methylate, sodium ethylate, potassium methylate and lithium methylate. Examples of the acid catalyst include inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, organic acids such as metasulfonic acid, zeolite, and cation exchange resin. From the viewpoint of handleability and industrial productivity, an alkali catalyst is preferable, and an alkali metal hydroxide is particularly preferable. About the usage-amount of the said catalyst, it selects suitably by the target saponification degree etc. For example, when an alkali catalyst is used, it is usually 0.001 to 100 mmol equivalent, preferably 3 to 30 mmol equivalent, relative to the amount of fatty acid vinyl ester.

  Regarding the saponification method, any one of a batch method, a continuous method (belt method), and a column method can be adopted depending on the target saponification degree. For reasons such as reduction of the amount of catalyst during saponification and the saponification reaction proceeding with high efficiency, it is preferable to use a tower type apparatus (not shown).

  Usually, the saponification reaction is carried out under heat and pressure, but the pressure may be adjusted according to the desired ethylene content. For example, specifically, the pressure is usually selected from the range of 0 to 10 MPaG, preferably 0.1 to 5 MPaG, and the temperature is usually 50 to 180 ° C, preferably 80 to 160 ° C. The saponification reaction time is usually 0.1 to 6 hours. The “MPaG” unit is a unit in the gauge value and indicates a difference between absolute pressure and atmospheric pressure (the same applies to “MPaG” below).

  Then, the EVOH after the saponification reaction is derived from the reaction system as an alcohol solution or water / alcohol solution in a high temperature and high pressure state, and is stored directly or directly in a tank or the like as necessary. Supplied to the washing container. For example, specifically, S in FIG.

  In the saponification reaction, the vinyl ester portion of the ethylene-vinyl ester copolymer is converted to a hydroxyl group, and the leaving group is by-produced as a carboxylic acid ester. For example, when vinyl acetate is used as the vinyl ester, methyl acetate (MeAc) is by-produced as a by-product during saponification.

  In addition, when the saponification catalyst is an alkali catalyst, the metal contained in the catalyst becomes a carboxylic acid metal salt as a by-product. For example, when vinyl acetate is used as the vinyl ester and sodium hydroxide is used as a catalyst, sodium acetate is by-produced. Moreover, a corresponding aldehyde is by-produced by reduction of carboxylic acid or oxidation of alcohol. For example, acetaldehyde is by-produced during the saponification of the ethylene-vinyl acetate copolymer.

  Next, the process until the EVOH alcohol obtained in the saponification treatment step or the alcohol in the water / alcohol solution is replaced with water to obtain an EVOH water-containing composition having a low alcohol content will be described.

  The method for producing an ethylene-vinyl alcohol copolymer in the present invention includes the replacement of alcohol (methanol) in the alcohol solution of EVOH with water, a by-product generated during saponification, and a catalyst used during saponification. The removal of the residue and the like (dissolution in water) is performed in multiple steps. More specifically, the alcohol remaining in the paste (hereinafter referred to as residual alcohol) and impurities such as residual catalyst and by-products during polymerization and saponification are highly efficient on the paste flow path after the conventional dealcoholization process. The process of completely removing the paste (apparatus for kneading the paste in the pipe in the liquid phase) is added. At this time, depending on the case, the dealcoholizing step and the step of removing the impurities and the like may be performed a plurality of times.

<Description of the dealcoholization process>
First, the washing apparatus in the dealcoholization step is provided with a tower type container such as a plate tower such as a perforated plate tower or a bubble bell tower, or a packed tower. In the above-mentioned tray column type, the number of theoretical plates is usually 2 to 20 plates, preferably 5 to 15 plates. Also, in the packed tower type, the amount of packing is set in accordance therewith. An EVOH alcohol solution or a water / alcohol solution and water vapor (water) are introduced into such a tower-type container, and a part of the alcohol in the EVOH solution is replaced with water by contacting both of them. / Alcohol solution and a mixture of water and alcohol are withdrawn from the tower vessel.

  The EVOH alcohol solution or water / alcohol solution, the introduction position of water vapor (water), and the EVOH water / alcohol mixed solution (paste) and the extraction position of the water / alcohol mixture are arbitrary. The EVOH alcohol solution and water can be contacted by either counter-current or co-current. However, from the viewpoint of substitution efficiency, it is preferable to make contact with counter-current. Specifically, an alcohol solution of EVOH or a water / alcohol solution is introduced from the top of the tower, steam is introduced from the bottom of the tower and brought into countercurrent contact with the solution, alcohol vapor is led out together with the steam from the top of the tower, It is preferable to adopt a form in which the water / alcohol solution (paste) is led out from the bottom of the tower.

  In addition, the supply position of the EVOH alcohol solution when using a plate column is usually 2 to 8 stages below the top of the tower, and preferably 2 to 4 stages below. Forming an aqueous layer on the shelf by supplying water or adjusting the amount of water vapor derived to the stage above the supply position is a water and alcohol solution derived from the top of the tower. This is preferable because it prevents entrainment of EVOH and the like in the mixed steam and prevents contamination of the steam transfer pipe and the condenser.

  Moreover, although the supply position of water vapor | steam is a tower bottom normally from the point of substitution efficiency, depending on the case, you may be 1-5 steps | paragraphs higher than it. Note that the mixed vapor of alcohol and water derived from the tower can be liquefied using a condenser, separated and purified, and reused.

  For example, specifically, as shown in FIG. 1, an EVOH alcohol (methanol) or water / alcohol solution obtained in the saponification process is obtained using a tower-shaped cleaning container 1 having a number of shelves 1d. Introducing into the cleaning container 1 from the paste inlet 1a at the top of the tower, and contacting with the steam introduced into the cleaning container 1 from the steam inlet 1s at the bottom of the tower, the alcohol in the EVOH or the water / alcohol solution A part of the alcohol is replaced, and a paste composed of a mixture of EVOH and water / alcohol is led out from the paste outlet 1b at the bottom of the tower, and a part of the substituted alcohol is discharged together with water vapor at the outlet 1c at the top of the tower. From the container.

  At this time, in addition to the alcohol substituted with water (and / or water vapor), by-products during saponification are discharged together with the water from the exhaust port 1c, and problems such as coloring of the EVOH and its molded product are caused. Impurities to be generated can be reduced.

  The content of the alcohol in the water / alcohol solution (paste) of EVOH derived from the tower-type container and the amount of water is the amount of water (and / or water vapor) introduced into the alcohol solution of EVOH introduced into the container, the tower It can be controlled by the temperature and pressure inside. The above water control method cannot be said unconditionally depending on the specifications of the tower type container to be used, for example, the number of shelves, the ratio of the cross-sectional area and the tower length, the number of shelves, the hole diameter and number of the perforated plate, etc. The conditions shown below are preferably used.

  The EVOH concentration of the EVOH alcohol solution or water / alcohol solution to be introduced is usually 20 to 50% by weight, preferably 30 to 45% by weight, more preferably 35 to 40% by weight. When the solvent is water / alcohol, the mixing ratio is usually (10/90) to (90/10), preferably (20/80) to (80 / 20), more preferably (40/60) to (60/40).

  If the amount of water vapor (or water) introduced into the tower-type container is too small, the substitution efficiency with alcohol is insufficient, and conversely if too large, it is disadvantageous in terms of cost. The amount of the water vapor is usually 0.01 to 30 times (weight ratio), preferably 0.1 to 10 times, more preferably 0.5 to 5 times the amount of EVOH solution introduced. .

  The temperature of the introduced water (water vapor) is usually 30 to 200 ° C, preferably 80 to 180 ° C, and more preferably 100 to 150 ° C. From the viewpoint of substitution efficiency, it is particularly preferable to introduce it into the vessel as water vapor. The water (steam) may be a reused product obtained by purifying a mixed steam of alcohol and water derived from the above-mentioned container, or may be a mixed steam containing a slight amount of alcohol. In the case of a mixed steam containing a small amount of alcohol, the alcohol content is usually 10 parts by weight or less with respect to 100 parts by weight of water vapor, and from the viewpoint of water-alcohol substitution efficiency, the alcohol content is more Less, ideally not containing at all.

  The temperature in the tower container is usually 80 to 200 ° C, preferably 100 to 180 ° C, and more preferably 110 to 150 ° C. If the temperature is too low, the viscosity of the EVOH solution in the container may increase and the replacement efficiency may decrease. Conversely, if the temperature is too high, the resin itself tends to deteriorate.

  The pressure in the tower container is usually 0 to 10 MPaG, preferably 0 to 5 MPaG, and more preferably 0.1 to 3 MPaG. If the pressure is too low, the replacement efficiency tends to decrease. If the pressure is too high, the temperature in the container rises and EVOH tends to thermally deteriorate.

  The mixture of EVOH and water / alcohol derived from the tower vessel through the above dealcoholization step (hereinafter referred to as “paste” to be cleaned by the present invention) is usually 10 to 200% of alcohol with respect to 100 parts by weight of EVOH. It is a liquid containing part by weight. The amount of alcohol is preferably 20 to 150 parts by weight, more preferably 30 to 100 parts by weight. The paste usually contains 20 to 200 parts by weight of water with respect to 100 parts by weight of EVOH, preferably 30 to 150 parts by weight, and more preferably 40 to 100 parts by weight of water.

  In this case, the water / alcohol ratio is usually (10/90) to (90/10), preferably (20/80) to (80/20), more preferably (water / alcohol). Is (30/70) to (70/30). When the content of the alcohol and water is too large, a load tends to be applied to the stirring and mixing performed by the pipe mixer. Moreover, when there is too little content of alcohol or water, a viscosity will become high, and there exists a tendency for the substitution efficiency of the latter half of a tower-type container to fall, or derivation | leading-out from a tower-type container becomes difficult.

  Furthermore, the residual saponification catalyst contained in the paste becomes acetic acid salt of the cation when the saponification catalyst is an alkali catalyst, and becomes acetic acid when the saponification catalyst is an acid catalyst. The content of the residual saponification catalyst is usually 1000 to 4000 ppm with respect to EVOH, preferably 1500 to 3000 ppm, and more preferably 1700 to 2700 ppm. In the case of an alkali catalyst, the content is obtained by extracting an alkali (metal) with a 1% by weight acetic acid solution and measuring the content by ion chromatography.

  If necessary, water (and / or water vapor) is introduced into EVOH between the dealcoholization step and the pelletization step described later, a water / methanol adjustment step, a step of adding an additive described later, or EVOH. There is no problem even if a process is performed. For example, before the EVOH paste obtained in the dealcoholization step is subjected to the pelletizing step, the paste preferably contains a heat stabilizer, and particularly preferably contains acetic acid and boric acid. In the case of acetic acid, the content is usually 1500 to 4000 ppm with respect to EVOH, and in the case of boric acid, the content is usually 100 to 1000 ppm with respect to EVOH.

<Description of the process of removing impurities, etc.>
Next, a process of removing impurities, residual alcohol and the like in the paste using a pipe mixer, which is a characteristic process of the present invention, will be described.
The paste derived from the washing container in the dealcoholization step is transported using a paste flow path (pipe) provided between the dealcoholization step and a pelletizing step (described later) as the next step, for example, It passes through a pipe mixer interposed in the middle (intermediate part) of the paste flow path by pumping using a pump or the like. Thereby, it becomes possible to remove impurities and the like in the paste in-line.

  The above-mentioned pipe mixer is of a type that forcibly rotates an impeller, a screw, etc. arranged in the pipe using a power source provided inside or outside the pipe (pipe-type stirrer, etc.), as well as a movable part. Flow mixers (motionless mixers) that do not have an in-line type, such as orifice mixers, ramond mixers, static mixers (Kenix type, SMX type, Venturi type, dispersion plate type, twist plate type, jet type) A mixer or a combination of these forced type and static type is used. Among them, a static mixer is preferably employed that has a small pressure loss, is maintenance-free, and can efficiently stir and mix a highly viscous fluid (paste) by a laminar flow generated inside.

  In addition, a water supply pipe for adding a predetermined weight ratio of washing water to the paste (water-containing composition of EVOH) is disposed in the paste flow path upstream from the paste introduction port of the pipe mixer. The washed water is introduced into the pipe mixer together with the paste.

  The greatest feature of the present invention is that the pipe mixer has a built-in device for stirring and mixing the paste, and consists of a mixture of EVOH and water / alcohol in a large amount of washing water added to the paste. The paste is kneaded (kneaded in the liquid phase) while the surface is renewed so that the surface and the inside (outer layer and inner layer) are switched repeatedly, and this paste-like EVOH resin contacts the washing water evenly to the inside. It is the point which is comprised so that it can do. Also, by stirring and mixing in the pipe mixer, the washing water replaces and dissolves the remaining alcohol in the paste to obtain a high alcohol concentration, and the impurities and the like in the paste are sufficiently absorbed and dissolved. Become. The washing water having the high alcohol concentration is discharged from the outlet of the pipe mixer together with the EVOH water-containing composition having a low alcohol content and high purity.

  For example, specifically, as shown in FIG. 1, the paste (EVOH water-containing composition) derived from the paste outlet 1b of the tower-type cleaning container 1 in the dealcoholization step is used with a pump (paste pump) P. Introduced into a pipe mixer (static mixer 2), each of the static mixer 2 is arranged in the static mixer 2 together with the washing water introduced from the washing water pipe W connected to the upstream side of the paste introduction port 2a of the static mixer 2. Each laminar flow generated in the paste is divided, converted, inverted and merged by the mixing elements (right element 2c, left element 2d). Further, by repeating these steps, a part or all of the remaining alcohol in the paste is replaced with water, and this is discharged from the paste outlet 2b of the static mixer 2 together with the washing water.

  In addition, the bath ratio (amount of cleaning water supplied) in the pipe mixer can be expressed as a weight ratio of introduced cleaning water / introduced paste, and is usually 0.5 to 10, preferably 0.6 to 5, Preferably it is 0.8-3. The bath ratio affects the alcohol replacement efficiency. If the bath ratio is too high, the economy tends to decrease. If the bath ratio is too low, the replacement / cleaning efficiency tends to decrease.

  Furthermore, although the residence time of the paste in the said pipe mixer changes with the characteristics of the target EVOH, it is usually 0.5 to 10 hours, preferably 1 to 8 hours, more preferably 1 to 5 hours. It is.

  The amount of paste made of a mixture of EVOH and water / alcohol to the pipe mixer varies depending on the bath ratio, but is usually 10 to 90% by volume / hour, preferably 10 to 10% of the internal volume of the pipe mixer. 50% by volume / hour, more preferably 10-25% by volume / hour. If the amount is too small, the substitution efficiency with alcohol tends to be reduced. Conversely, if the amount is too large, the derivation speed from the pipe mixer cannot catch up and tends to be uneconomical.

  In addition, the temperature of the paste which consists of a mixture of EVOH and water / alcohol to be introduce | transduced is 40-110 degreeC normally, Preferably it is 50-100 degreeC.

  Further, it is preferable to keep the temperature of the pipe mixer constant. The temperature in the said pipe mixer is 50-150 degreeC normally, Preferably it is 60-120 degreeC, More preferably, it is 70-110 degreeC. When the said temperature is too high, a paste viscosity will become low, and when too low, a viscosity may rise and it may become difficult to handle. In particular, the temperature is preferably adjusted with washing water. This is to maintain the fluidity of the introduced paste. Therefore, the temperature of the washing water is usually 70 to 160 ° C., preferably 90 to 130 ° C., more preferably 100 to 120 ° C. in consideration of natural heat dissipation.

  Furthermore, although the passage of the paste in the present invention through a pipe mixer can be performed under normal pressure conditions, it can be performed by changing the pressure as necessary. The pressure is usually 0 to 1 MPaG, preferably 0 to 0.6 MPaG, more preferably 0 to 0.3 MPaG. If the pressure is too high, the temperature in the container rises and EVOH tends to be thermally deteriorated.

  Moreover, it is preferable to add at least one heat stabilizer selected from carboxylic acid compounds (carboxylic acids, carboxylate salts, boron compounds and phosphoric acid compounds) to the washing water introduced into the pipe mixer. With the kneading of the paste in water (kneading in the liquid phase), the thermal stabilizer can be uniformly dispersed in the paste simultaneously with the washing.

  As the carboxylic acid compound, a carboxylic acid having 2 to 4 carbon atoms is preferable, and a monovalent or divalent compound is preferably used. Specifically, oxalic acid, succinic acid, benzoic acid, citric acid, acetic acid, propionic acid, lactic acid and the like are exemplified, and among these, acetic acid is preferably used from the viewpoint of cost and availability.

  When the carboxylic acid is added, the carboxylic acid content in the EVOH paste obtained after passing through the pipe mixer is a value measured by a titration method, and is usually 10 to 10,000 ppm, preferably 50 to 3000 ppm, more preferably EVOH. Preferably it is 100-2000 ppm. If the content of carboxylic acid is too small, the effect of containing carboxylic acid tends to be insufficient, and conversely if too large, it tends to be difficult to obtain a uniform film. In addition, the density | concentration of carboxylic acid in wash water is 10-3000 ppm normally, Preferably it is 20-1000 ppm, More preferably, it is 30-500 ppm.

  Moreover, a carboxylate may be added intentionally from the viewpoint of the equilibrium effect of the heat stabilizer, and the carboxylate is usually a carboxylate having 2 to 4 carbon atoms. Monovalent or divalent ones are preferably used. Specifically, salts such as alkali metal salts (sodium, potassium, etc.) and alkaline earth metal salts (calcium, magnesium, etc.) such as oxalic acid, succinic acid, benzoic acid, citric acid, acetic acid, propionic acid, lactic acid, etc. Of these, acetate is preferable from the viewpoint of cost and availability, and sodium acetate is particularly used.

  When the carboxylate is added, the carboxylate content in the EVOH paste obtained after passing through the pipe mixer is usually 10 to 5000 ppm with respect to the EVOH paste in terms of metal in atomic absorption analysis. Is 30 to 1000 ppm, more preferably 50 to 700 ppm. If the amount is too small, coloring may occur during melt molding, and if the amount is too large, the melt viscosity may increase. In addition, the density | concentration of the carboxylate salt in washing water is 10-3000 ppm normally, Preferably it is 20-1000 ppm, More preferably, it is 30-500 ppm.

  Examples of the boron compound include boric acids such as boric acid, boric acid esters and borates, and borohydrides, but are not limited to these, but boric acid or borates are particularly preferably used. . Specifically, examples of boric acids include orthoboric acid, metaboric acid, and tetraboric acid. Examples of boric acid esters include triethyl borate and trimethyl borate. Examples include alkali metal salts of acids, alkaline earth metal salts, and borax. Of these compounds, boric acid is preferred.

  When the boron compound is added, the content of the boron compound in the EVOH paste obtained after passing through the pipe mixer is usually 10 to the EVOH paste in terms of boron (after ashing and analyzed by ICP emission spectrometry). It is 10,000 ppm, preferably 100 to 8000 ppm, and more preferably 100 to 7000 ppm. If the content of the boron compound is too small, the effect of improving the thermal stability is small, and if it is too large, gelation may occur or moldability tends to be poor. In addition, the density | concentration of the boron compound in wash water is 10-3000 ppm normally, Preferably it is 20-1000 ppm, More preferably, it is 30-500 ppm.

  Examples of the phosphoric acid compound include various acids such as phosphoric acid and phosphorous acid, and salts thereof. The phosphate may be contained in any form of primary phosphate, secondary phosphate, and tertiary phosphate, and the cation species is not particularly limited, but alkali metal Salts and alkaline earth metal salts are preferred. Among these, it is preferable to add the phosphate compound in the form of sodium dihydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate.

  When the above phosphate compound is added, the content of the phosphate compound in the EVOH paste obtained after passing through the pipe mixer is usually converted to phosphate radicals (analyzed by ion chromatography) with respect to the EVOH paste. 1 to 1000 ppm. By adding so as to be in the above range, coloring of the molded product and generation of gels and fish eyes can be suppressed, and if the content is too small, a tendency to color during melt molding is seen, conversely If the amount is too large, gels and fish eyes of the molded product may be easily generated. In addition, the density | concentration of the phosphoric acid compound in washing water is 1-3000 ppm normally, Preferably it is 10-1000 ppm, More preferably, it is 20-500 ppm.

Next, the structure of the static mixer 2 used in the process of removing the residual alcohol and impurities will be described in detail.
The static mixer 2 used in this embodiment has a plurality of mixing elements (the right element 2c and the left element 2d) that divide the paste into a laminar flow and convert, invert and merge these laminar flows. A set is arranged. In FIG. 1, in order to emphasize the internal structure, the diameter is drawn larger than that of the surrounding pipe, but the pipe diameter is not particularly limited. The attached equipment is preferably equipped with a temperature control means such as a jacket or a coil.

  In addition to the spiral type shown in Fig. 1, the mixing element (mixing blade) installed in the static mixer 2 is of various types such as a stator type and a combination of a spiral and a stator for each block. Can be used.

  Furthermore, in this embodiment, although the example which installs the static mixer 2 horizontally was shown, this static mixer 2 may be inclined and arranged with respect to the horizontal. In addition, this inclination angle is 0-45 degrees normally, Preferably it is 10-30 degrees. Moreover, as for the inclination of the static mixer 2, it is desirable to arrange the paste introduction side (2a) on the upper side and arrange the paste outlet side (2b) on the lower side. By adjusting the installation position (tilt) in this way, a highly viscous paste can be passed efficiently.

  And in the said embodiment, although the example which arrange | positioned the water supply piping W which adds washing water to a paste in the upstream from the paste inlet 2a of the static mixer 2 was shown, this water supply piping W is shown in the paste outlet 2b. The washing water discharge port may be provided on the upstream side of the paste introduction port 2a. In this configuration, the paste (water-containing composition of EVOH) and the washing water come in countercurrent contact. In that case, the washing water is placed on the static mixer 2 in the direction of the paste flow. A space (clearance) that allows the flow in the opposite direction is required. Therefore, in this case, the amount of paste introduced into the static mixer 2 may be limited, and the flow rate may be controlled to such an extent that a margin (space) is created in the upper part.

  According to the method for producing EVOH in the present embodiment, the paste-like EVOH-containing composition that has passed through the pipe mixer comprises a part or all of alcohol (methanol) together with the washing water, and a catalyst used during saponification. Impurities such as residues and by-products are removed with high efficiency. Further, since at least one additive selected from a carboxylic acid, a carboxylate, a boron compound, and a phosphoric acid compound is added to the washing water as a heat stabilizer, The additive can be uniformly dispersed and mixed in the paste.

  And the water content of the EVOH water-containing composition obtained through the pipe mixer is usually 30 to 400 parts by weight, preferably 40 to 240 parts by weight, more preferably 50 to 150 parts by weight with respect to 100 parts by weight of EVOH. is there. Moreover, although the alcohol which could not be removed may be contained, the content thereof is usually less than 10 parts by weight, preferably less than 5 parts by weight with respect to 100 parts by weight of EVOH. Usually, it is preferable to monitor the content of alcohol in the EVOH water-containing composition in the pipe mixer, and to set the end point when the alcohol content is less than 10 parts by weight with respect to 100 parts by weight of EVOH.

  Furthermore, content of the residual saponification catalyst which the obtained EVOH hydrous composition has is 0-3000 ppm normally with respect to EVOH, Preferably it is 0-2000 ppm, More preferably, it is 0-1000 ppm. In addition, the said content is calculated | required as an acetate salt in the case of an alkali catalyst.

  In the present embodiment, the alcohol removal step using the tower-type washing container does not completely remove the alcohol and keeps the fluidity, thereby preventing the processing efficiency from being lowered. In the process of removing residual alcohol, impurities, etc. using a pipe mixer, even if the paste becomes high concentration and high viscosity by contacting it with washing water while stirring and mixing under in-line conditions, the alcohol can be efficiently used As a result, EVOH, which was in a swollen state containing alcohol, contracted with a decrease in the alcohol content, and the catalyst residue and by-products used during saponification with water and alcohol from the paste were reduced. It is discharged and a high purity / high quality EVOH water-containing composition (water content: 30 to 400 parts by weight with respect to 100 parts by weight of EVOH) is obtained. It is.

  Therefore, the EVOH water-containing composition having a low alcohol content as obtained in the present embodiment can be obtained only in the tower-type cleaning container 1 in the dealcoholization process because the viscosity of the EVOH paste is high in the latter half of the cleaning container 1. This is difficult because the fluidity is lowered and the substitution efficiency of alcohol-water is lowered, and the liquid cannot be derived from the cleaning container 1. In addition, if only the pipe mixer is used to replace most of the alcohol in the EVOH alcohol solution with water, the initial solution viscosity introduced into the pipe mixer is low, and the introduced washing water cannot remain in the EVOH paste for a long time. Therefore, the substitution efficiency is low, the process takes time, and a large amount of water is required, which is not practical.

  Next, a process of drying and pelletizing (product pellet) the paste-form EVOH-containing composition having a low alcohol content obtained through the pipe mixer (a process for removing impurities and the like) will be described.

  The pelletizing step includes (A) a method of forming a paste-like EVOH water-containing composition with a low alcohol content into a pellet shape with the water content, and then reducing the water content, and (B) the alcohol content. A method of forming into a pellet shape after reducing the water content of a small paste-like EVOH hydrous composition can be mentioned.

  As the method of the above (A), for example, a paste-form EVOH-containing composition having a low alcohol content is extruded through a hole and cut in a fluid state to obtain round pellets (for example, hot cut or underwater And a method of extruding and solidifying a strand in a refrigerant bath having a temperature lower than that of the water-containing resin and cutting the strand to obtain a cylindrical pellet. And the obtained pellet is dried with various drying methods.

  In the method (B), for example, the water content in the paste-form EVOH-containing composition with a low alcohol content is usually 1 to 50 weights with respect to 100 parts by weight of EVOH in advance using a centrifuge or an extruder. Part, preferably 1 to 40 parts by weight, more preferably 1 to 30 parts by weight, after reducing the amount of water, pelletize using an extruder or the like. For the above pelletization, EVOH resin is extruded into a strand shape by an extruder and cut to obtain a cylindrical pellet, or the molten resin immediately after being extruded from the extruder is cut to obtain a round pellet. And a method (hot cut) to obtain. In particular, in consideration of the thermal efficiency of the drying process and the thermal history of the resin, when an extruder is used, it is possible to perform a series of operations for reducing the moisture of the EVOH water-containing composition and pelletizing it (B It is preferable to adopt the method of

Examples of the extruder used in the pelletizing step include a single screw extruder and a twin screw extruder.
The diameter (mmφ) of the extruder is usually 40 to 180, preferably 60 to 140, and more preferably 70 to 110. Moreover, L / D of the said extruder is 10-80 normally, Preferably it is 15-70, More preferably, what is 15-60 is used. If the L / D is too small, the dehydration effect tends to be insufficient or the ejection tends to be unstable, and conversely if too large, there is a tendency to cause excessive shearing heat generation. Among these, a twin screw extruder having the same screw rotation direction is more preferable in that sufficient kneading can be obtained by appropriate shearing.

  At this time, the temperature of the resin in the extruder is usually 80 to 250 ° C, preferably 90 to 240 ° C, and more preferably 100 to 230 ° C. When the said temperature is too high, there exists a tendency for resin to carry out deterioration coloring, and when too low, there exists a tendency for a moisture reduction efficiency to fall. The method for adjusting the resin temperature is not particularly limited, but usually, a method of appropriately setting the temperature of the cylinder in the extruder is used.

  The screw rotation speed of the extruder is usually 10 to 1000 rpm depending on the size of the shaft, preferably 30 to 800 rpm, more preferably 50 to 400 rpm. If the rotational speed is too small, the ejection tends to be unstable, and if it is too large, the resin may be deteriorated due to undesirable heat generation.

  For example, specifically, as shown in FIG. 1, the paste-like EVOH-containing water is composed of a first extruder 3 and a second extruder 4, a strand cutter (pelletizer: not shown), etc., and has passed through the static mixer 2. The composition (EVOH-Paste) is sequentially charged into the first extruder 3 and the second extruder 4 and melt-kneaded to gradually reduce the moisture in the EVOH water-containing composition, and the second extruder 4 After cooling the strand-like or ribbon-like EVOH composition discharged from the tube, the EVOH composition is cut (pelletized) into a predetermined size using a strand cutter or the like to obtain EVOH pellets having a low alcohol content and a low water content. .

  As the 1st extruder 3 and the 2nd extruder 4 used for the said pelletization process, a common single screw extruder, a twin screw extruder, etc. can be used. A twin screw extruder is more preferable in that sufficient kneading can be obtained by appropriate shearing.

  The resin temperature in the extruder is usually set to 80 to 250 ° C., and the water content of the EVOH composition after discharging the first extruder 3 is usually 30 to 35 parts by weight with respect to 100 parts by weight of EVOH. 2 The water content of the EVOH composition after discharging from the extruder 4 is adjusted to be usually less than 10 parts by weight, preferably 0 to 8 parts by weight with respect to 100 parts by weight of EVOH. In the pelletizing step, when it is desired to reduce the water content of the EVOH composition as much as possible, the resin temperature in the extruder is usually set in the range of 120 to 250 ° C, preferably 150 to 230 ° C. Is done. Conversely, in order to suppress the thermal degradation of the EVOH composition as much as possible, when the water content is to be maintained, the resin temperature in the extruder is usually 80 to 105 ° C, preferably 85 to 100 ° C, More preferably, it is carried out by setting in the range of 90 to 100 ° C.

  Furthermore, in the extrusion using the extruder, it is preferable to discharge water or water vapor from at least one location of the extruder in order to melt and knead the EVOH composition in a water-containing state. The water discharging means for that purpose is not particularly limited, and a method of discharging from a dewatering hole, a vent port or a dewatering slit provided in a cylinder (barrel) of the extruder can be adopted. Especially, since a dehydration slit can discharge | emit both water and water vapor | steam and there are few adhesion and leakage of resin, it is used preferably. In addition, you may use two or more said water | moisture-content discharging means, In that case, even if it is the same kind, you may use it combining a different thing.

  In addition, the method of pelletizing the EVOH composition discharged from the second extruder 4 is not particularly limited, but the EVOH composition is extruded in a strand form from a die (die) of the extruder, and after cooling, an appropriate method is obtained. A method of cutting to a suitable length is preferably used. As a method for cooling the discharged strand, a method of contacting a liquid held at a temperature lower than the temperature of the extruded resin, a method of blowing cool air, or the like is used.

  The shape of the cut pellet is usually cylindrical, and the size of the die is 2 to 6 mmφ from the viewpoint of convenience when used as a molding material later, and the cut length of the strand is About 1-6 mm is used suitably. In addition, the method of cutting in air | atmosphere or water while the EVOH composition discharged from the extruder is still a molten state is also used suitably.

  In the pelletization step, two or more types of EVOH compositions having different degrees of polymerization, ethylene content, degree of saponification and the like obtained through a process different from the EVOH water-containing composition (EVOH-Paste) are used. It is also possible to blend and melt mold. In addition, other plasticizers, lubricants, stabilizers, surfactants, colorants, UV absorbers, antistatic agents, desiccants, crosslinkers, metal salts, fillers, and various fiber reinforcing agents are added in appropriate amounts. Thus, melt kneading can also be performed.

  Next, a pellet drying process (not shown) for reducing the moisture content of the EVOH pellets obtained in the pelletizing process as necessary will be described.

  The EVOH pellets obtained from the pelletizing step can be used as they are if the moisture is sufficiently removed in the extruder and the amount of moisture is less than 0.3 parts by weight with respect to 100 parts by weight of EVOH. Moreover, when the moisture removal is inadequate, excess moisture is removed by using for a pellet drying process.

As a method for drying the EVOH pellets, various drying methods can be employed. Specific examples include a stationary drying method and a fluidized drying method. It is also possible to employ a multi-stage drying method using different drying methods. In particular, the method of drying by the fluidized drying method in the first stage and the stationary drying method in the second stage is preferable in that the color tone of the pellet and the molded product using the pellet is good. In drying, it is also preferable to circulate an inert gas such as nitrogen gas (N ₂ Gas) from the viewpoint that the color tone of the molded product becomes good.

For example, specifically, by supplying an inert gas such as nitrogen gas (N ₂ Gas) to the drying container and circulating it as necessary, the moisture content of the EVOH pellets obtained in the above pelletization step is determined as the product. The level is reduced to less than 0.3 parts by weight based on 100 parts by weight of EVOH.

  According to the method for producing an ethylene-vinyl alcohol copolymer in the present invention, since the residence time required for the drying step is short, the resulting EVOH (pellet) does not undergo thermal deterioration, and EVOH and the EVOH Improves the quality of molded products using

Next, a second embodiment of the method for producing an ethylene-vinyl alcohol copolymer of the present invention will be described.
FIG. 2 is a flowchart showing an outline of a second embodiment of the method for producing an ethylene-vinyl alcohol copolymer of the present invention. In addition, the code | symbol R in a figure shows the circulating flow path which circulates a paste.

  As in the first embodiment, the EVOH production process is also performed by using a saponification treatment process (not shown) of an ethylene-vinyl ester copolymer (ethylene-vinyl acetate in this example) and the tower-type washing container 1. , A dealcoholization step for obtaining a paste comprising a mixture of EVOH and water / alcohol, and a pelletizing step for pelletizing the washed EVOH hydrous composition using an extruder 3, 4 and a strand cutter, etc. And a pipe mixer (static mixer 2) on the paste flow path (pipe) between the dealcoholization step and the pelletizing step, and a water supply pipe for adding washing water of a predetermined weight ratio to the paste W is disposed.

  The second embodiment is different from the first embodiment in that the low alcohol content EVOH hydrous composition derived from the outlet of the pipe mixer (static mixer 2) is disposed upstream of the inlet of the pipe mixer. A circulation flow path R is provided to circulate in the paste flow path so that a part of the EVOH hydrous composition having a low alcohol content after passing through the pipe mixer joins the paste before the pipe mixer is introduced. This is the point.

  With the above configuration, in the method for producing an ethylene-vinyl alcohol copolymer in the second embodiment, since the paste circulates, the residence time of this paste in the pipe mixer can be extended. Therefore, this EVOH manufacturing method makes it possible to shorten the overall length of the pipe mixer (total length in the longitudinal direction of the flow path) and to reduce and save the amount of cleaning water supplied from the water supply pipe W. Can do.

  Moreover, the circulation of the paste can further improve the substitution rate of alcohol-water and the removal rate of impurities such as residual catalyst and by-products during the polymerization and saponification, and the homogenization of the flowing paste. There is also an advantage that (uniformization) can be achieved.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. In the examples, “parts” and “%” mean weight basis unless otherwise specified.

[Example 1]
[Methanol solution of EVOH]
A polymerization can with a cooling coil was charged with 330 parts by weight of vinyl acetate, 60 parts by weight of methanol, and 500 ppm of acetyl peroxide (vs. vinyl acetate). The system was temporarily replaced with nitrogen gas, and then replaced with ethylene. The ethylene was injected until the pressure became 3.6 MPa. Then, it heated up to 68 degreeC, stirring, and superposed | polymerized for 6 hours until the polymerization rate of vinyl acetate became 50 weight%. Thereafter, the polymerization reaction was stopped to obtain a methanol solution of ethylene-vinyl acetate copolymer having an ethylene content of 29 mol% (resin content was 48% by weight).

<Saponification process>
A methanol solution of the above-mentioned ethylene-vinyl acetate copolymer, from which the residual vinyl acetate in the reaction solution had been removed, was fed at a rate of 30 parts by weight / hour from the top of the plate tower, and at the same time, the acetic acid in this copolymer A sodium hydroxide methanol solution of 0.54 parts by weight / hour was fed from the top of the column with respect to the number of moles of the group. On the other hand, methanol was supplied from the lower part of the tower at 60 parts by weight / hour. The tower internal temperature was 120 to 140 ° C., and the tower pressure was 0.36 MPaG. A methanol solution of EVOH was obtained 0.5 hours after the start of charging. The EVOH has an ethylene content of 29 mol% and a saponification degree of 99.5 mol%, and the paste contains sodium acetate corresponding to the sodium content of sodium hydroxide as a saponification catalyst. The “MPaG” unit is a unit in the gauge value and indicates a difference between the absolute pressure and the atmospheric pressure.

<Dealcoholization process>
Next, the methanol solution of EVOH was supplied to a tower-type washing container (10-stage tray tower). The sampled methanol solution of EVOH was continuously supplied at 80 parts by weight / hour from the top of the tower-type washing container to the second shelf. On the other hand, steam at 130 ° C. was continuously supplied from the bottom shelf at 60 parts by weight / hour, and the methanol solution of EVOH and the steam were brought into contact with each other countercurrently in the tray tower. The temperature in the tower-type cleaning container was 120 ° C., and the pressure in the container was 0.2 MPaG.

  Then, from the paste outlet at the bottom of the tower type cleaning container, 75 parts by weight of methanol and 75 parts by weight of water are contained per 100 parts by weight of EVOH (water / methanol (weight ratio) = 50/50). EVOH and water / A paste made of a mixture with alcohol (hereinafter referred to as “paste”) was obtained. In addition, 4700 ppm sodium acetate was contained in the obtained paste.

  For 100 parts by weight of EVOH, 75 parts by weight of methanol and 75 parts by weight of water (water / methanol (weight ratio) = 50/50), and for paste containing 4700 ppm sodium acetate with respect to EVOH, An aqueous solution containing acid and acetic acid was added to adjust the moisture content of the paste at the same time.

<Process to remove impurities>
A paste (141 parts by weight of methanol and 247 parts by weight of water (water / methanol (weight ratio) = 64/36) with respect to 100 parts by weight of EVOH, the resin content is 21% by weight, and acetic acid is 2100 ppm with respect to EVOH. , Containing 7900 ppm sodium acetate and 4300 ppm boric acid) was pumped with a pump P, passed through the pipe mixer (static mixer 2) described in the first embodiment, and washed under the following conditions.

A) Washing (stirring / mixing) conditions • Static mixer Diameter: 158mm Total length: 46m
・ Number of mixing elements: 24 ・ Insulation jacket temperature: 79 ℃
B) EVOH paste conditions-Supply amount: 17 parts by weight / hour-Supply paste temperature: 80 ° C
・ Paste residence time: 3 hours ・ Discharge amount: 6.4 parts by weight / hour C) Wash water conditions Wash water composition (relative to water)
: Acetic acid 160ppm
Sodium acetate 200ppm
Boric acid 110ppm
Sodium dihydrogen phosphate 80ppm
Calcium phosphate 150ppm
-Supply amount: 16 parts by weight / hour-Temperature: 85 ° C
The bath ratio (washing water weight / paste weight ratio) was adjusted to 0.94.

  Then, from the paste outlet 2b of the static mixer 2, EVOH water / methanol paste that became a mochi-like cloudy high-viscosity paste: 54% by weight of EVOH resin, 45% by weight of water, 1% of methanol (based on 100 parts by weight of EVOH 83 parts by weight of water and 2 parts by weight of methanol) 1360 ppm of acetic acid, 530 ppm of sodium acetate, 4550 ppm of boric acid, 80 ppm of sodium dihydrogen phosphate, and 150 ppm of calcium phosphate were obtained.

  From the above results, together with the washing water, some or all of the residual methanol and EVOH and impurities that may cause problems such as coloring in the molded product using the EVOH (residual catalyst and by-products during saponification, etc.) ) Are removed with high efficiency.

  According to the method for producing an ethylene-vinyl alcohol copolymer of the present invention, impurities in the obtained EVOH product are reduced, and the quality of a molded product using the EVOH and EVOH is improved. Moreover, the obtained EVOH pellets are formed into molded articles such as films, sheets, cups, bottles, etc. by melt molding such as extrusion molding and injection molding. Widely used for packaging applications such as agricultural chemicals.

1 Washing vessel 2 Static mixer 3 Extruder 4 Extruder

Claims (6)

  An alcohol solution of an ethylene-vinyl alcohol copolymer or a water / alcohol mixed solvent solution is introduced into a washing container, and brought into contact with water or water vapor in the washing container, so that a part of the alcohol together with water or water vapor is outside the container. And a dealcoholization step for obtaining a paste comprising a water-containing composition of an ethylene-vinyl alcohol copolymer, supplying the ethylene-vinyl alcohol-based copolymer water-containing composition to an extruder, and melt-kneading, A pelletizing step of discharging and cutting to obtain ethylene-vinyl alcohol copolymer pellets, the method of producing an ethylene-vinyl alcohol copolymer, comprising the dealcoholizing step and the pelletizing step A pipe mixer and a predetermined weight ratio of washing water are added to the paste on the paste flow path. The water pipe is disposed, the paste led out from the washing container is introduced into the pipe mixer together with the washing water, and after being stirred and mixed so that the surface and the inside of the paste are repeatedly switched, the paste is led out, Ethylene-vinyl alcohol characterized in that a part or all of the alcohol contained in the paste is replaced with water and an ethylene-vinyl alcohol copolymer water-containing composition having a low alcohol content is supplied to the extruder. A method for producing a copolymer.   The pipe mixer is a static mixer, and when the paste passes through the static mixer, the paste is repeatedly divided, converted, inverted, and joined, whereby the paste is stirred and mixed. The manufacturing method of the ethylene-vinyl alcohol-type copolymer of Claim 1.   A circulation passage is provided for circulating the water-containing ethylene-vinyl alcohol copolymer composition having a low alcohol content derived from the outlet of the pipe mixer to the paste passage upstream of the inlet of the pipe mixer. 3. The ethylene- of claim 1 or 2, wherein a part of the low-alcohol-containing ethylene-vinyl alcohol copolymer water-containing composition joins the paste before introduction of the pipe mixer. A method for producing a vinyl alcohol copolymer.   The ethylene-vinyl alcohol copolymer according to any one of claims 1 to 3, wherein the washing water contains at least one additive selected from a carboxylic acid, a carboxylate salt, a boron compound, and a phosphoric acid compound. Manufacturing method.   The water content of the ethylene-vinyl alcohol copolymer water-containing composition after passing through the pipe mixer is 30 to 400 parts by weight with respect to 100 parts by weight of the ethylene-vinyl alcohol copolymer. A method for producing an ethylene-vinyl alcohol copolymer according to claim 1.   The water content of the ethylene-vinyl alcohol copolymer pellet obtained from the pelletizing step is less than 10 parts by weight with respect to 100 parts by weight of the ethylene-vinyl alcohol copolymer. The method for producing an ethylene-vinyl alcohol copolymer according to one item.

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