JP2010077352A - Method for producing saponified ethylene-vinyl acetate copolymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for obtaining a saponified ethylene-vinyl acetate copolymer with suppressed coloring and excellent appearance.
(Step 1) After adding an alkali catalyst to an alcohol solution of an ethylene-vinyl acetate copolymer in an amount of 0.0001 to 0.03 mol / l and mixing with the solution;
(Step 2) contacting an alcohol solution of the ethylene-vinyl acetate copolymer with an acetalization catalyst;
(Step 3) Saponifying the alcohol solution of the ethylene-vinyl acetate copolymer after the contact with the acetalization catalyst in Step 2 above using an alkali catalyst;
A process for producing a saponified ethylene-vinyl acetate copolymer.
[Selection figure] None

Description

  The present invention relates to a method for producing a saponified ethylene-vinyl acetate copolymer.

  Saponified ethylene-vinyl acetate copolymer (hereinafter sometimes abbreviated as EVOH) is a useful polymer material excellent in oxygen shielding properties, oil resistance, non-charging properties, mechanical strength, etc. It is widely used as various packaging materials. In the EVOH field, appearance problems that occur during molding, such as coloring and fish eyes, are one of the important issues to be overcome. In particular, in the use of a transparent packaging material in which the contents can be visually confirmed, coloring of EVOH is associated with discoloration of the contents, so that high-quality EVOH with less coloring has recently been demanded.

  EVOH can be produced by hydrolysis or alcoholysis treatment (hereinafter sometimes referred to as saponification) of an ethylene-vinyl acetate copolymer (hereinafter sometimes abbreviated as EVAc) with an alkali catalyst or the like. In order to improve the quality of such EVOH, and in particular to suppress coloring of EVOH, a method for improving the saponification process has been proposed.

  In Patent Document 1, EVAAc having an ethylene content of 15 to 60 mol% in a methanol solvent is saponified with an alkali catalyst until the saponification degree of the vinyl acetate component becomes 70 to 98 mol% using a tower reactor. The resulting ethylene-vinyl acetate copolymer partially saponified solution is added with water or water / methanol at the boiling point to form a mixed solution, re-saponified in the presence of an alkali catalyst, and acetic acid. By obtaining a highly saponified EVOH solution having a saponification degree of a vinyl component of 99.4 mol% or more, and sequentially extruding the high saponification EVOH solution in a coagulation bath and subjecting it to an acid treatment, It is said that EVOH pellets having a uniform shape and excellent melt moldability can be obtained.

  Patent Document 2 discloses a method for producing EVOH in which EVAc is saponified using a methanol solution containing an alkali catalyst, and the copolymer obtained by saponification under a predetermined pressure in a first reactor. A solution containing a partially saponified product is supplied from the first reactor to the second reactor, and the saponified product is further saponified under a pressure higher than the pressure in the first reactor, The production of EVOH of saponification degree is described. In Patent Document 2, the alkali catalyst used for the saponification of EVAc causes deterioration and coloring of a polymer called caustic burn, and the acetic acid compound as a by-product remains in the product. It is described that it is preferable to use a smaller amount of alkali catalyst because the thermal stability is lowered and this may cause coloring or gelled generation. In the invention of Patent Document 2, it is said that EVOH having a high degree of saponification can be efficiently produced by reducing the amount of alkali catalyst used at the time of saponification, and EVOH having a poor appearance such as coloring can be obtained. ing.

  Patent Document 3 discloses an EVOH production method in which EVAc is saponified in an alcohol solvent in the presence of an alkali catalyst, and 100 ppm or more and 15000 ppm based on the ethylene-vinyl acetate copolymer in the alcohol solvent. A method for producing EVOH characterized by supplying the following water is described. According to this invention, coloring of EVOH is suppressed, and EVOH with improved appearance characteristics is obtained.

Japanese Patent No. 4046245 International Publication No. 2002/050137 Pamphlet JP 2002-69123 A

  Thus, in order to improve the quality of EVOH, several improved saponification methods of EVAc have been proposed. However, in the above-described method, EVOH quality that has been increasing in recent years, in particular, it is still difficult to say that the effect is sufficient in terms of suppressing coloring of EVOH, and EVOH with less coloring is required. ing.

  The present inventors have studied in detail why the above-described production method does not provide a sufficient EVOH coloring suppression effect. As a result, the vinyl acetate used as a raw material in the process of polymerizing ethylene and vinyl acetate to obtain EVAc is used. The conclusion was reached that the amount of acetaldehyde that cannot be ignored and the presence of acetaldehyde generated as a by-product in the reaction system are not considered.

  Generally, EVAc is produced by copolymerizing vinyl acetate and ethylene in the presence of a solvent such as alcohol, and then removing unreacted ethylene or vinyl acetate. However, the EVAc solution after such removal still remains a raw material. It contains vinyl acetate or a vinyl acetate derivative generated by a polymerization reaction (hereinafter, both are collectively referred to as vinyl acetate esters) as impurities, which cannot be ignored. Vinyl acetates readily undergo hydrolysis or alcoholysis under alkaline conditions and decompose into acetic acid and acetaldehyde. The generated acetaldehyde is highly reactive, and thus causes various reactions under saponification reaction conditions using an alkali catalyst. For example, acetaldehyde causes a condensation reaction to form an aldehyde such as crotonaldehyde or sorbaldehyde. The presence of such acetaldehyde-derived by-products causes coloring of the manufactured EVOH and other poor quality. Therefore, it is desirable that unreacted vinyl acetate is completely removed at the stage of producing EVAc. However, since it requires a large amount of energy, complete removal is very difficult from the viewpoint of industrial production. It was difficult.

  Therefore, the object of the present invention is to solve the above-mentioned problems, and inactivate vinyl acetates which are impurities in the EVAc solution and acetaldehyde generated by hydrolysis or alcoholysis thereof in advance. It is an object of the present invention to provide a method for producing EVOH, which is subjected to a saponification reaction and is excellent in appearance with suppressed coloring.

As a result of diligent investigations aimed at achieving the above-mentioned problems, the inventors of the present invention changed the alcohol solution of EVAc to a dilute alkaline solution, thereby converting the vinyl acetate remaining in the EVAc solution into acetic acid and acetaldehyde in advance. After conversion, it was found that EVOH having excellent quality without coloring can be produced by inactivating acetaldehyde using an acetalization catalyst and then saponifying with an alkali catalyst.
That is, the present invention
(Step 1) After adding and mixing an alkali catalyst in an alcohol solution of ethylene-vinyl acetate copolymer in the range of 0.0001 to 0.03 mol / l to the solution;
(Step 2) contacting an alcohol solution of the ethylene-vinyl acetate copolymer with an acetalization catalyst;
(Step 3) Saponifying the alcohol solution of the ethylene-vinyl acetate copolymer after the contact with the acetalization catalyst in Step 2 above using an alkali catalyst;
Is a method for producing a saponified ethylene-vinyl acetate copolymer.

Preferably, the content of vinyl acetate in the alcohol solution of the ethylene-vinyl acetate copolymer used in Step 1 is 0.015 mol / l or less.
Also preferably, the alcohol is methanol.
Further preferably, the acetalization catalyst is at least one selected from the group consisting of inorganic acids, organic sulfonic acids, carboxylic acids, Lewis acids or acidic cation exchange resins.
Preferably, the saponification degree of the ethylene-vinyl acetate copolymer after being subjected to step 2 is 5 mol% or less.
Preferably, in the step 3 in the production method of the present invention, the alcohol solution of the ethylene-vinyl acetate copolymer after the contact with the acetalization catalyst in the step 2 is supplied to the upper part of the tower reactor. The alcohol solvent is supplied as vapor from the bottom of the tower, and the alcohol solvent and acetate are discharged as vapor from the top of the tower, and an alkali catalyst is supplied into the tower to saponify the ethylene-vinyl acetate copolymer.

  According to the present invention, acetaldehyde, which is a by-product by hydrolysis of vinyl acetates that are impurities in an ethylene-vinyl acetate copolymer, is inactivated by an acetalization reaction and then subjected to a saponification reaction. Coloring of the saponified ethylene-vinyl acetate copolymer obtained can be suppressed.

  In the method for producing a saponified ethylene-vinyl acetate copolymer of the present invention, (step 1) an alkali catalyst is added to the alcohol solution of EVAc in the range of 0.0001 to 0.03 mol / l to the solution. (Step 2) The alcohol solution of EVAAc is brought into contact with the acetalization catalyst. (Step 3) The alcohol solution of EVAAc after the contact with the acetalization catalyst in Step 2 is used with an alkali catalyst. Saponification is essential. Details of each step are described below.

Step 1 is a step of hydrolyzing or alcoholically decomposing an acetic acid vinyl ester remaining in EVAc into acetic acid and acetaldehyde by making the alcohol solution of EVAAc a dilute alkaline solution.
It is important to adjust the concentration of the alkali catalyst so that the side reaction of acetaldehyde does not proceed while converting the vinyl acetate remaining in the EVAc solution into acetic acid and acetaldehyde. In general, hydrolysis or alcoholysis of vinyl acetates is more reactive than saponification of the acetate group of EVAc, and the reaction proceeds in a dilute alkaline solution. The present invention pays attention to this point. By converting the alcohol solution of EVAc into a dilute alkaline solution, hydrolysis or addition of vinyl acetates is performed before saponification of the acetate group of EVAc. It is characterized by performing only alcohol decomposition.

The concentration of the alkali catalyst in step 1 needs to be 0.0001 to 0.03 mol / l. When the concentration of the alkali catalyst in Step 1 is lower than 0.0001 mol / l, hydrolysis or alcoholysis of vinyl acetates does not proceed sufficiently, and the remaining vinyl acetates are described later in Step 3 In addition to causing hydrolysis or alcoholysis, the produced acetaldehyde condenses as described later, which may cause coloring of EVOH. On the other hand, if the concentration of the alkali catalyst in step 1 is too higher than 0.03 mol / l, acetaldehyde is not only generated, but acetaldehyde condenses to produce crotonaldehyde or sorbaldehyde. These acetaldehyde condensates are acetalized in Step 2 described later, but have a higher boiling point and poor water solubility compared to acetaldehyde acetalized products. For this reason, even if impurities are removed by washing or drying the produced EVOH, it becomes difficult to remove the acetal of the acetaldehyde condensate, which adversely affects the quality such as coloring of the EVOH. Moreover, since the saponification reaction of EVAc will advance when the density | concentration of an alkali catalyst is too high, the alcohol solution of EVAAc will become high viscosity and there exists a possibility that process permeability may worsen.
A more preferable range of the concentration of the alkali catalyst in Step 1 is 0.0002 to 0.02 mol / l, and more preferably 0.0004 to 0.01 mol / l.

  Although EVAAc uses what copolymerized ethylene and vinyl acetate, the monomer composition in particular is not restrict | limited. In order to obtain EVOH having good resin performance such as processing characteristics and oxygen barrier property during molding, it is preferable to use EVAc having an ethylene content in the range of 15 to 60 mol%. In addition, monomers other than ethylene and vinyl acetate, for example, aliphatic vinyl esters such as vinyl propionate and vinyl pivalate; vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri (β-methoxy-ethoxy) silane, γ- Vinyl silanes such as methacryloxypropylmethoxysilane; aliphatic vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, isopropyl vinyl ether, n-propyl vinyl ether, isobutyl vinyl ether and n-butyl vinyl ether; allyl compounds such as allyl acetate and allyl chloride; propylene, isobutylene, Α-olefins such as 1-octene and 1-dodecene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, and itaconic acid, or anhydrides, salts thereof, Dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid or salts thereof; vinyl ketone, N-vinyl pyrrolidone, vinyl chloride, A small amount (usually 5 mol% or less) of vinylidene chloride or the like may be copolymerized.

  Step 1 is not limited to vinyl acetate, and any compound having a vinyl ester structure can produce the carboxylic acid and acetaldehyde corresponding to the chemical structure by hydrolysis or alcoholysis, so that the effects of the present invention can be achieved. For example, when an EVAc alcoholic solution copolymerized with vinyl propionate and containing vinyl propionate as an impurity is treated by the method of the present invention, the vinyl propionate is propionic acid by hydrolysis or alcoholysis. And converted to acetaldehyde. The same applies to the case where the EVAAc polymer chain has a vinyl ester structure.

  In the method of the present invention, alcohol is used as a solvent for the EVAc solution. As will be described later, alcohol is essential for inactivating acetaldehyde in Step 2. Examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, n-butyl alcohol, and the like, and methanol is most preferable.

  In addition, the concentration of EVAc in the alcohol solution of EVAc is not particularly limited, but in order to improve the process passability and the mixing property with the catalyst used in each step, the concentration of EVAc is 5 to 80% by mass. It is preferable to be in the range, and more preferably in the range of 20 to 60% by mass.

  The alkali catalyst used in Step 1 is not particularly limited, and examples thereof include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide and lithium hydroxide; alkali metal alkoxides such as sodium methoxide, sodium ethoxide and potassium t-butoxide; Alkali metal carbonates such as sodium carbonate, sodium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate; alkali metal carboxylates such as sodium acetate, potassium acetate, sodium propionate; diazabicycloundecene, diazabicyclononene, triethylamine, Amines such as diethylamine, triethanolamine, diethanolamine, monoethanolamine, ethylenediamine and aniline; ammonia and the like. Among these, sodium hydroxide, potassium hydroxide, sodium methoxide, and sodium ethoxide are preferable. These alkali catalysts may be used individually by 1 type, and may use 2 or more types together.

  The reaction temperature in step 1 is preferably in the range of 30 ° C. to the boiling point of the alcohol used as the solvent. For example, when methanol is used as a solvent, the temperature range of a suitable solution is 30 ° C to 65 ° C, and more preferably 50 to 60 ° C.

  The reaction time in step 1 depends on the type of solvent used, the type and amount of the alkali catalyst, the reaction temperature, and the like. For example, methanol as the solvent and sodium methoxide as the alkali catalyst at 0.01 mol / l. When the reaction temperature is 60 ° C., the reaction time is preferably in the range of 0.5 to 15 minutes. In general, the reaction time in Step 1 is preferably 0.1 minutes or more, and more preferably 0.2 minutes or more. However, an unnecessarily long reaction time should be avoided in Step 1 of the method of the present invention from the viewpoints of the suppression of side reactions of acetaldehyde and the suppression of the saponification reaction of the acetate group of EVAc, usually 30 minutes. Or less, more preferably 20 minutes or less.

  The content of vinyl acetate in the EVAc alcohol solution used in Step 1 is preferably 0.015 mol / l or less. When the content of vinyl acetate exceeds 0.015 mol / l, hydrolysis or alcoholysis of vinyl acetates does not proceed sufficiently in Step 1, and the remaining vinyl acetate is hydrolyzed in Step 3 described later. While causing decomposition or alcoholysis, acetaldehyde condenses and may cause EVOH coloring. As a method for chasing vinyl acetate from the EVAc alcohol solution, for example, the EVAc alcohol solution is continuously supplied from the upper part of the plate tower at a constant rate in the range of 30 ° C. to the boiling point of the alcohol used as the solvent. From the bottom, the same kind of alcohol used in the supplied EVAAc alcohol solution is used as steam, and 0.1 to 10 parts by mass is blown into 1 part by mass of EVAc. The alcohol and unreacted vinyl acetate are injected from the top of the tower. And the like, and a method of taking out an alcohol solution of EVAc from which unreacted vinyl acetate has been removed from the bottom of the column can be employed.

  Step 2 in the method of the present invention is a step of inactivating acetaldehyde by immediately contacting an alcohol solution of EVAc containing acetaldehyde generated in Step 1 with an acetalization catalyst. Acetaldehyde reacts with alcohol present as a solvent in the presence of an acetal catalyst to be converted into an acetal compound. Compared to acetaldehyde, the acetal compound is stable even under alkaline conditions, and even if the alcohol solution of EVAc containing the acetal compound is subsequently saponified in the presence of an alkali catalyst in step 3, coloring of the obtained EVOH is difficult to proceed. Become.

  The acetalization catalyst used in Step 2 is not particularly limited. For example, inorganic acids such as sulfuric acid, hydrochloric acid, and phosphoric acid; organic acids such as benzenesulfonic acid, p-toluenesulfonic acid, naphthalenesulfonic acid, methanesulfonic acid, and trifluoromethanesulfonic acid. Examples thereof include sulfonic acids; carboxylic acids such as trifluoroacetic acid; Lewis acids such as boron trifluoride, boron trifluoride diethyl ether complex, aluminum chloride, iron (III) chloride, and titanium tetrachloride. It is also possible to use an acidic cation exchange resin. The functional group exhibiting the catalytic activity of the acidic cation exchange resin is preferably sulfonic acid, and examples thereof include Amberlyst 15, Amberlyst 16, Amberlyst 31 (trade names, manufactured by Rohm and Haas); Ion PK, Diaion RCP (trade name, manufactured by Mitsubishi Chemical Co., Ltd.), Dowex G26, Dowex MONOSSPHERE M31 (trade name, manufactured by Dow Chemical Co., Ltd.), and the like. These acetalization catalysts may be used alone or in combination of two or more. Among these, sulfuric acid, organic sulfonic acid, and acidic cation exchange resin are preferable.

  In step 2, the amount of the acetalization catalyst used is not particularly limited. However, in order to sufficiently inactivate the acetaldehyde generated in step 1 (acetalize), 1 mol of the acetalization catalyst added in step 1 is used. It is preferable that it is equal to or more than the equivalent. If an unnecessarily excessive amount of the acetalization catalyst is used, the acetalization catalyst remains in the EVOH after production, and a gel or a color tends to be generated during melt molding. The upper limit of the amount of the acetalization catalyst used is preferably 10 molar equivalents or less of the alkali catalyst added in Step 1, and more preferably 5 molar equivalents or less. However, this is not the case when an acidic cation exchange resin is used and the process can easily remove the catalyst.

  What is necessary is just to set reaction temperature of the process 2 equivalent to the process 1, and it is suitable to set it as the range of the boiling point of alcohol used as a solvent from 30 degreeC.

  In addition, the reaction time in Step 2 depends on the type and amount of the acetalization catalyst, the type of solvent, and the reaction temperature, but in order to sufficiently advance the acetalization, the time for contacting with the acetalization catalyst is 1 minute. The above is preferable. A more preferred reaction time is 5 minutes or more, and even more preferred is 10 minutes or more. However, if the reaction time is increased unnecessarily, in step 2 of the method of the present invention, the acetalization catalyst also acts as a saponification catalyst for the acetate group of EVAc to increase the degree of saponification, and the alcohol solution of EVAc Therefore, it is preferable to be 300 minutes or less, more preferably 150 minutes or less.

  In the step 1 or the step 2, there is no particular limitation on the method of contacting the alkali catalyst or the acetalization catalyst with the alcohol solution of EVAc. As a general method, there is a method of mixing an alcohol solution of EVAc with an alkali catalyst or an acetalization catalyst using a general stirring tank equipped with propeller blades, paddle blades, and the like. If the alkali catalyst or acetalization catalyst is sufficiently dispersed or dissolved in the EVAc alcohol solution, various inline continuous mixers such as a static mixer can be used to efficiently produce the alcohol solution of the EVAc and the alkali catalyst or acetalization. The catalyst can be mixed and reacted continuously. In addition, when an acidic cation exchange resin is used as the acetalization catalyst in Step 2, a method of allowing an EVAc alcohol solution to pass through a container filled with the acidic cation exchange resin can also be suitably used. In the method of the present invention, step 1 and step 2 may be performed in independent reactors and mixers, or step 1 and step 2 may be performed sequentially using one reactor. One reactor and a mixer may be divided into two or more sections, and Step 1 and Step 2 may be performed continuously.

  Moreover, it is preferable that the saponification degree of EVAc in the alcohol solution of EVAc after the process 2 is 5 mol% or less. As described so far, when the amount and reaction time of the alkali catalyst in Step 1 are not appropriate or when the reaction time in Step 2 is not appropriate, saponification of the acetate group of EVAc tends to proceed. . When the saponification degree is 5 mol% or more, the alcohol solution of EVAc becomes highly viscous and the fluidity is deteriorated, so that it becomes difficult to efficiently saponify in Step 3.

  The alcohol solution of EVAc that has undergone the above-described Step 1 and Step 2 is saponified in Step 3.

  The alkali catalyst used at the process 3 is not specifically limited, The thing similar to the alkali catalyst which can be used at the process 1 can be used. However, in order to obtain EVOH having a high saponification degree, it is preferable to use a strong alkaline catalyst, for example, alkali metal hydroxide such as sodium hydroxide, potassium hydroxide, lithium hydroxide; sodium methoxide, Examples include alkali metal alkoxides such as sodium ethoxide and potassium t-butoxide. Of these, sodium hydroxide, potassium hydroxide, sodium methoxide, and sodium ethoxide are particularly preferably used.

  The method of the saponification reaction in step 3 is not particularly limited. A method in which an alcohol solution of EVAc after step 2 is charged into a reactor and an alkali catalyst is added while stirring to saponify; an alcohol of EVAc after step 2 is added to a tower reactor such as a plate column Examples include a method of introducing a solution and mixing with an alkali catalyst. In order to efficiently perform the saponification reaction, it is preferable to saponify the acetic acid ester generated by the transesterification reaction between the alcohol serving as the solvent and the acetic acid ester group contained in EVAc, out of the reaction system. Preferably, the EVAc alcohol solution after step 2 is supplied to the upper part of the tower reactor, and the same kind of alcohol used for the supplied EVAc alcohol solution is supplied as vapor from the lower part of the tower reactor. Then, a method of discharging the mixed vapor of alcohol and generated acetate from the top of the column and supplying an alkali catalyst into the column to saponify the ethylene-vinyl acetate copolymer can be employed. For example, the amount of alcohol vapor blown is preferably about 0.1 to 10 parts by mass with respect to 1 part by mass of EVAc.

  In general, as the saponification reaction proceeds, the solubility of EVOH produced in alcohol decreases, and therefore, it is preferable to carry out the reaction in Step 3 by applying pressure and heating. The preferred pressure range is 0.1 MPa to 1.0 MPa, and the preferred reaction temperature range is 60 ° C to 180 ° C. In addition, for the purpose of controlling the solubility and degree of saponification of EVOH, water; aliphatic polyhydric alcohols such as glycerin and ethylene glycol; formic acid, acetic acid, acetoacetic acid, etc. Carboxylic acid or the like may be added.

  The usage-amount of the alkali catalyst in the process 3 can be adjusted according to the ethylene content rate of EVAAc, the target saponification degree, etc. Generally, when obtaining a saponification degree of 90 mol% or more, 0.1 to 100 mol% is preferable with respect to the amount of acetate groups contained in EVAc. As described above, when the process is used to drive out the acetic acid ester generated by using alcohol as the solvent, even if the amount of the alkali catalyst used is as small as 0.1 to 10 mol%, the saponification degree is high efficiently. EVOH can be produced.

  Although the range of the saponification degree of EVOH produced by the method of the present invention is not particularly limited, EVOH having a high saponification degree of 99.0 to 100 mol% is preferable in order to bring out the resin performance of EVOH. . Depending on the application, EVOH having a saponification degree lower than 99.0 mol% can be produced.

  As a post-treatment method of an EVOH alcohol solution obtained by saponification, for example, an EVOH alcohol / water mixed solution is prepared by adding water in such an amount that EVOH does not precipitate. For example, a method of extruding into an alcohol / water mixed solution having a low alcohol concentration and precipitating it in a strand form and then cutting it may be employed. The pellets thus obtained are porous, and the saponification catalyst residue can be easily removed by washing with water, and can be easily handled in the subsequent washing and drying process.

  The porous pellets thus obtained are washed and drained, and trace components such as boron compounds, alkali metal salts and alkaline earth metal salts are appropriately added. As a method of obtaining EVOH pellets to which these trace components are added, (1) a method in which an aqueous solution of trace components is sprayed on EVOH pellets, mixed with a Henschel mixer and then dried, (2) powdered trace components are added to EVOH pellets. A method of mixing and dry blending with a super mixer, (3) A method of immersing EVOH pellets in an aqueous solution containing a trace component, drying and then drying, (4) Melting and kneading EVOH pellets with trace components in a water-containing state A method of drying after discharging from the extruder can be employed.

  The melt index (MI) of EVOH obtained as described above is preferably 0.1 to 200 g / 10 minutes. In this specification, the measured value under a load of 190 ° C. and 2160 g is adopted as MI. However, for those having a melting point near 190 ° C. or exceeding 190 ° C., a semilogarithm with a plurality of measured values at the temperature equal to or higher than the melting point under the above load, with the reciprocal absolute temperature as the horizontal axis and MI as the vertical axis (logarithmic scale) A value plotted as a graph and extrapolated to 190 ° C. is used.

  The EVOH obtained by the method of the present invention can be blended with EVOH having a different degree of polymerization, ethylene content and degree of saponification and melt-molded. In addition, other plasticizers, antioxidants, colorants, UV absorbers, fluorescent brighteners, slip agents, antistatic agents, cross-linking agents such as boric acid, inorganic fillers, inorganic desiccants, various fibers, etc. It is also possible to add an appropriate amount of materials.

  The EVOH obtained in the present invention can be formed into various molded products such as films, sheets, containers, pipes, fibers and the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to this Example. Hereinafter, “%” and “part” are based on mass unless otherwise specified. Unless otherwise specified, use methanol with a purity of 99% or more and a moisture content of 0.1% or less, and use all ion-exchanged water (conductivity: 1.0 to 2.0 μS / cm). did. The water conductivity was measured with CM-30ET manufactured by Toa Denpa Kogyo.

(1) Preparation of alkaline catalyst solution Sodium hydroxide (NaOH: purity of 97% or more) or sodium methoxide (NaOMe: purity of 95% or more) is dissolved in methanol at room temperature, and a predetermined concentration used in each example and comparative example A methanol solution was prepared.

(2) Preparation of acetalization catalyst solution Methanol containing sulfuric acid (purity 95% or more), trifluoroacetic acid (TFA: purity 98% or more) or p-toluenesulfonic acid monohydrate (TsOH: purity 99% or more) at room temperature And a methanol solution having a predetermined concentration to be used in each example and comparative example was prepared.

(3) Quantification of vinyl acetate in EVAc solution 5 ml of the EVAc solution to be analyzed was put into 100 ml of hexane, and EVAAc was precipitated, filtered, and the recovered solution was subjected to Shimadzu gas chromatograph GC-14B (column : J & W Scientific DB-1710 (30 m), inlet temperature: 150 ° C., analysis temperature: 100 ° C. (8 min hold) → temperature rise at 20 ° C./min→250° C. (5 min hold), carrier gas: helium) The vinyl acetate content was quantified. In quantification, a calibration curve was prepared in advance under the above analysis conditions using a hexane solution of vinyl acetate having a different concentration as a standard solution.

(4) Determination of aldehydes in EVOH 1,1,1,3,3,3-hexafluoro-2 containing 1,000 mg / l 2,4-dinitrophenylhydrazine (DNPH) in 0.5 g of dried EVOH 10 ml of a propanol / acetic acid mixed solution (1,1,1,3,3,3-hexafluoro-2-propanol / acetic acid = 9: 1 (mass ratio)) was added and stirred at 50 ° C. for 1 hour. The solution was put into 50 ml of acetonitrile to precipitate EVOH, and then filtered through a filter having a pore size of 0.45 μm. Subsequently, the solution was concentrated on a rotary evaporator and then diluted with acetonitrile to a total volume of 10 ml. The solution was subjected to Shimadzu high performance liquid chromatograph (column: Shiseido CAPCELL PAK C18 MG type, column temperature 45 ° C., solvent: acetonitrile / water (acetonitrile / water = 70/30 (mass ratio)), flow rate 1 ml / min, UV The total content (unit: ppm) was quantified using acetaldehyde, crotonaldehyde, and sorbaldehyde as DNPH compounds. For the determination, a calibration curve prepared with a commercially available aldehyde-DNPH compound was used.

(5) Measurement of degree of saponification of EVAc The EVAc solution after completion of Step 2 in each Example and Comparative Example was concentrated with a rotary evaporator, and then dried with a vacuum dryer at 40 ° C for 10 hours to obtain dry EVAAc. After dissolving 20 mg of the EVAc in 0.6 ml of deuterated chloroform, ¹ H-NMR measurement was performed under the following measurement conditions, and methine hydrogen of vinyl alcohol units observed at 3.1 to 4.1 ppm (saponified site) The degree of saponification was determined from the ratio of the integrated value of methine hydrogen (unsaponified site) of vinyl acetate units observed at 4.5 to 5.2 ppm.
Measurement conditions Device name: JEOL superconducting nuclear magnetic resonance apparatus Lambda 500, observation frequency: 500 MHz, measurement temperature: 25 ° C., integration number: 1024 times

(6) Measurement of saponification degree of EVOH The pellets of dry EVOH obtained in each Example and Comparative Example were pulverized, and 20 mg of the powder was mixed with heavy dimethyl sulfoxide / heavy trifluoroacetic acid (mass ratio: heavy dimethyl sulfoxide). / Heavy trifluoroacetic acid = 95/5) After being dissolved in 0.6 ml, ¹ H-NMR measurement was performed under the following measurement conditions, and methine hydrogen of vinyl alcohol units observed at 3.1 to 4.1 ppm. The degree of saponification was determined from the ratio between the integrated value (saponified site) and the integrated value of methyl group hydrogen (unsaponified site) of vinyl acetate units observed at 1.9 to 2.0 ppm.
Measurement conditions Device name: JEOL superconducting nuclear magnetic resonance apparatus Lambda 500, observation frequency: 500 MHz, measurement temperature: 80 ° C., integration count: 128 times

Example 1
[Step 1]
A reaction vessel having a capacity of 10 l provided with a stirring blade is charged with 8.5 l of a methanol solution having an ethylene content of 35 mol% and an EVAc content of 48 mass% and an unreacted residual vinyl acetate concentration of 0.014 mol / l. The liquid temperature was adjusted to 60 ° C. Next, a methanol solution of 1.3 mol / l sodium hydroxide was added all at once to make the sodium hydroxide concentration in the reaction vessel 0.023 mol / l, and stirring was continued for 10 minutes. After the reaction, the vinyl acetate concentration in the EVAc solution was measured and found to be 0 mol / l without being detected.
[Step 2]
Subsequently, a 2.0 mol / l sulfuric acid methanol solution was gradually added to adjust the sulfuric acid concentration in the reaction vessel to 1.5 molar equivalents of sodium hydroxide added in Step 1. While maintaining the liquid temperature at 60 ° C., the mixture was stirred for 30 minutes. The degree of saponification of EVAc after the reaction was 2.4 mol%.
[Step 3]
Subsequently, the EVAc solution having finished Step 2 was charged into a reactor having a capacity of 15 liters equipped with a stirring blade, a gas inlet, and a cooling condenser, and methanol was added and mixed to make the EVAc content 20%. The liquid condensed by the cooling condenser was set to be able to be removed and collected outside the reaction system. The liquid temperature was adjusted to 60 ° C. while nitrogen was blown into the reactor at a rate of 5 l / min. A methanol solution containing 2 mol / l sodium methoxide was added thereto in an amount of 0.4 molar equivalent (calculated from the ethylene content and the degree of saponification after step 2) based on the remaining acetic acid ester groups of EVAc. During the saponification reaction, nitrogen acetate is blown into the reactor in order to drive out methyl acetate generated as a by-product in the reaction system together with methanol in the reaction system. Continued. This was condensed and recovered using a cooling condenser. Six hours after the start of the reaction, sodium methoxide and an equimolar amount of acetic acid were added for neutralization to stop the saponification reaction.

[Production of EVOH pellets]
50 parts by mass of water was added per 100 parts by mass of the neutralized reaction solution obtained above to solidify EVOH in the solution into a cake. Then, the liquid removal operation from the cake-like EVOH was performed using a centrifuge. Next, while supplying water at 60 l / min from above the centrifuge, the liquid was removed for 10 minutes, and the EVOH was washed with water.
The bulk EVOH thus obtained was dried at 60 ° C. for 10 hours using a vacuum dryer. Subsequently, the mixture was dissolved in a mixed solvent of water / methanol (water / methanol = 35/65 (mass ratio)) at 80 ° C. for 5 hours with stirring to obtain a 35 mass% EVOH solution. Next, the stirring was stopped and the temperature was lowered to 65 ° C. and left for 5 hours to degas the EVOH solution. This EVOH solution is extruded from a metal plate having a circular opening having a diameter of 3.5 mm into a mixed solution of water / methanol = 9/1 (mass ratio) at 5 ° C., deposited into a strand, and cut. A cylindrical pellet was obtained. The moisture content of the obtained EVOH pellets was 70% by mass (based on wet mass).
The operation of adding 20 liters of water to 1.5 kg of the water-containing EVOH pellets thus obtained, washing the mixture with stirring at 25 ° C. for 2 hours, and then removing the liquid was repeated twice. Next, washing with 1.0 g / l aqueous acetic acid solution while stirring at 25 ° C. for 2 hours was repeated twice, followed by washing with 20 L of water while stirring at 25 ° C. for 2 hours. Then, the operation of draining was repeated 6 times. Next, the EVOH pellets were put into 15 l of an aqueous solution containing 5.4 mmol / l sodium acetate and 12 mmol / l acetic acid, and immersed and stirred at 25 ° C. for 5 hours. After the treated EVOH pellets were drained, the EVOH pellets were dried at 80 ° C. for 3 hours and then at 120 ° C. for 30 hours with a dryer in a nitrogen atmosphere to obtain dried EVOH pellets. The degree of saponification of the obtained EVOH pellets was 99.5 mol%, and MI was 2.0 g / 10 min (190 ° C., 2160 g under load). The aldehyde content was 15 ppm.

[Evaluation of colorability after single-layer film formation]
The obtained EVOH pellets were formed into a single layer by using a 20 mm extruder D2020 (D (mm) = 20, L / D = 20, compression ratio = 2.0, screw: full flight) manufactured by Toyo Seiki Seisakusho Co., Ltd. Was performed under the following conditions to obtain a monolayer film.
Extrusion temperature: C1 / C2 / C3 / Die = 180/200/220/220 ° C.
Screw rotation speed: 80rpm
Discharge rate: 2.5 kg / hr
Take-up roll temperature: 80 ° C
Take-up roll speed: 6.1 m / min.
Film thickness: 20 μm
The single-layer film produced by the above method was wound around a paper tube, and the degree of coloration of the film end face was determined with the naked eye as follows.
Criterion A: No coloring
B: Slightly yellow
C: Yellowing

Example 2
In Example 1, the acetalization catalyst added in Step 2 was a 2.0 mol / l trifluoroacetic acid methanol solution, and the addition amount was 1.5 molar equivalents of sodium hydroxide added in Step 1. EVOH pellets were obtained in the same manner as in Example 1. Vinyl acetate was not detected in the EVAc solution when step 1 was completed (0 mol / l), and the degree of saponification of EVAc when step 2 was completed was 2.3 mol%. The EVOH pellets obtained had a saponification degree of 99.5 mol% and an MI of 1.9 g / 10 min (190 ° C., under 2160 g load). Further, the content of aldehydes was 12 ppm, and the determination result of the coloration resistance evaluation after the single layer film formation was A determination.

Example 3
[Step 1]
A reaction vessel having a capacity of 10 l provided with a stirring blade is charged with 8.5 l of a methanol solution having an ethylene content of 35 mol% and an EVAc content of 48 mass% and an unreacted residual vinyl acetate concentration of 0.014 mol / l. The liquid temperature was adjusted to 60 ° C. Next, a methanol solution of 1.3 mol / l sodium hydroxide was added all at once to make the sodium hydroxide concentration in the reaction vessel 0.023 mol / l, and stirring was continued for 10 minutes. No vinyl acetate was detected in the EVAc solution at the end of the reaction (0 mol / l).
[Step 2]
Subsequently, 100 g (dry weight basis) of an acidic cation exchange resin (IER; Dowex MONOSSPHERE M31) activated in advance in an acidic form was swollen in 1 l of methanol, and then in step 1 It added to the obtained EVAc solution and stirred for 30 minutes. The EVAc solution after the reaction was filtered through a screen mesh having a pore size of 100 μm to remove the acidic cation exchange resin. The degree of saponification of EVAc after the reaction was 2.0 mol%.
The operation after step 3 was carried out in the same manner as in Example 1 to obtain EVOH pellets. The degree of saponification of the EVOH pellets was 99.6 mol%, and the MI was 2.1 g / 10 min (190 ° C., under a load of 2160 g). In addition, the content of aldehydes was 10 ppm, and the determination result of the coloration resistance evaluation after the single-layer film formation was A determination.

Example 4
In Step 1 of Example 1, EVOH pellets were obtained in the same manner as in Example 1 except that the sodium hydroxide concentration in the reaction vessel was 0.019 mol / l and the reaction time was 2 minutes. Vinyl acetate was not detected in the EVAc solution when Step 1 was completed (0 mol / l), and the degree of saponification of EVAc when Step 2 was completed was 1.2 mol%. The EVOH pellets obtained had a saponification degree of 99.6 mol% and an MI of 2.1 g / 10 min (190 ° C., under 2160 g load). In addition, the content of aldehydes was 10 ppm, and the determination result of the coloration resistance evaluation after the single-layer film formation was A determination.

Example 5
[Step 1]
Into a reaction vessel having a capacity of 10 l provided with a stirring blade, 8.2 l of a methanol solution having an ethylene content of 35 mol% and an EVAc content of 50% by mass and an unreacted residual vinyl acetate concentration of 0.002 mol / l is charged. The liquid temperature was adjusted to 60 ° C. Next, a 1.3 mol / l sodium hydroxide methanol solution was added all at once to adjust the sodium hydroxide concentration in the reaction vessel to 0.008 mol / l, and stirring was continued for 2 minutes. No vinyl acetate was detected in the EVAc solution at the end of the reaction (0 mol / l).
[Step 2]
Subsequently, a 2.0 mol / l sulfuric acid methanol solution was gradually added to adjust the sulfuric acid concentration in the reaction vessel to 1.5 molar equivalents of sodium hydroxide added in Step 1. While maintaining the liquid temperature at 60 ° C., the mixture was stirred for 30 minutes. The degree of saponification of EVAc after the reaction was 0.4 mol%.
The operation after step 3 was carried out in the same manner as in Example 1 to obtain EVOH pellets. The degree of saponification of the EVOH pellets was 99.5 mol%, and the MI was 2.1 g / 10 min (190 ° C., under 2160 g load). Further, the content of aldehydes was 5 ppm, and the determination result of the coloration resistance evaluation after the single layer film formation was A determination.

Example 6
[Step 1]
Two pipe reactors with built-in static mixers connected by piping, methanol solution with an ethylene content of 29 mol% and an EVAc content of 47% by mass and an unreacted residual vinyl acetate concentration of 0.002 mol / l (Liquid temperature 60 ° C.) was fed to the first tubular reactor at a rate of 1.0 kg / hour. At the same time, a methanol solution of 2.0 mol / l sodium methoxide was supplied to the first tubular reactor, so that the concentration of sodium methoxide in the reactor was 0.008 mol / l. The reaction time from the mixing of sodium methoxide and EVAc to the step 2 was 0.5 minutes.
[Step 2]
Subsequently, in a second tubular reactor, it is mixed with a 2.0 mol / l p-toluenesulfonic acid methanol solution so that the p-toluenesulfonic acid concentration is 1.5 molar equivalents of sodium methoxide. Adjusted. In this way, the mixed liquid was discharged into a 10 l container and stirred at a liquid temperature of 60 ° C. for 30 minutes. The degree of saponification of EVAc after the reaction was 0.4 mol%. When the reaction was completed, vinyl acetate in the EVAc solution was not detected (0 mol / l).
[Step 3]
Subsequently, the above-mentioned EVAc solution was introduced at a rate of 0.9 kg / hour into the 9th-stage shelf plate of the plate tower (saponification tower, total number of stages: 10), and 2 mol / l sodium hydroxide The methanol solution was supplied from the 8th stage to make 0.05 equivalent (calculated from the ethylene content and the degree of saponification after Step 2) with respect to the residual acetate group of the EVAc. On the other hand, methanol vapor was supplied from the second stage at a rate of 4.0 kg / hour, and methanol vapor containing methyl acetate generated by the saponification reaction was expelled from the top. The tower internal temperature was 112 ° C., and the tower pressure was 0.51 MPa. Neutralization was performed by sequentially adding sodium hydroxide and an equimolar amount of acetic acid supplied to the EVOH solution (EVOH concentration: 36%) obtained from the bottom of the column.
Subsequent steps were performed in the same manner as in Example 1 to obtain EVOH pellets. The degree of saponification of the EVOH pellets was 99.8 mol%, and the MI was 2.0 g / 10 min (190 ° C., 2160 g under load). Further, the content of aldehydes was 0.7 ppm, and the determination result of the coloration resistance evaluation after the single layer film formation was A determination.

Comparative Example 1
EVOH pellets were obtained in the same manner as in Example 1 except that Step 2 was omitted in Example 1. The degree of saponification of EVAc when Step 1 was completed was 2.1 mol%, and vinyl acetate was not detected in the EVAc solution (0 mol / l). The degree of saponification of the EVOH pellets was 99.6 mol%, and the MI was 2.0 g / 10 min (190 ° C., under a load of 2160 g). Further, the content of aldehydes was 52 ppm, and the determination result of the coloration resistance evaluation after single-layer film formation was B determination.

Comparative Example 2
In Example 1, EVOH pellets were obtained in the same manner as in Example 1 except that the sodium hydroxide concentration in Step 1 was 0.1 mol / l. When the step 2 was completed, the saponification degree of EVAc was 10.2 mol%, and vinyl acetate was not detected in the EVAc solution (0 mol / l). The degree of saponification of the EVOH pellets was 99.6 mol%, and the MI was 2.1 g / 10 min (190 ° C., under a load of 2160 g). Further, the content of aldehydes was 65 ppm, and the determination result of the coloration resistance evaluation after the single-layer film formation was C determination.

Comparative Example 3
EVOH pellets were obtained in the same manner as in Example 5 except that Step 2 was omitted in Example 5. The degree of saponification of EVAc when step 1 was completed was 0.5 mol%, and vinyl acetate was not detected in the EVAc solution (0 mol / l). The degree of saponification of the EVOH pellets was 99.9 mol%, and the MI was 2.0 g / 10 min (190 ° C., under a load of 2160 g). Further, the content of aldehydes was 40 ppm, and the determination result of the coloration resistance evaluation after single-layer film formation was B determination.

Comparative Example 4
EVOH pellets were obtained in the same manner as in Example 6 except that Step 1 and Step 2 were omitted in Example 6. The degree of saponification of the EVOH pellets was 99.9 mol%, and the MI was 2.0 g / 10 min (190 ° C., under a load of 2160 g). Further, the content of aldehydes was 42 ppm, and the determination result of the coloration resistance evaluation after the single-layer film formation was B determination.

  The conditions and evaluation results of Examples 1 to 6 and Comparative Examples 1 to 4 are summarized in Table 1. In the Examples, it can be seen that EVOH with suppressed coloring is obtained.

Claims (6)

(Step 1) After adding and mixing an alkali catalyst in an alcohol solution of ethylene-vinyl acetate copolymer in the range of 0.0001 to 0.03 mol / l to the solution;
(Step 2) contacting an alcohol solution of the ethylene-vinyl acetate copolymer with an acetalization catalyst;
(Step 3) Saponifying the alcohol solution of the ethylene-vinyl acetate copolymer after the contact with the acetalization catalyst in Step 2 above using an alkali catalyst;
A process for producing a saponified ethylene-vinyl acetate copolymer. The method for producing a saponified ethylene-vinyl acetate copolymer according to claim 1, wherein the content of vinyl acetate in the alcohol solution of the ethylene-vinyl acetate copolymer used in Step 1 is 0.015 mol / l or less. . The method for producing a saponified ethylene-vinyl acetate copolymer according to claim 1 or 2, wherein the alcohol is methanol. 4. The ethylene- according to claim 1, wherein the acetalization catalyst is at least one selected from the group consisting of inorganic acids, organic sulfonic acids, carboxylic acids, Lewis acids, or acidic cation exchange resins. A method for producing a saponified vinyl acetate copolymer. The method for producing an ethylene-vinyl acetate copolymer saponified product according to any one of claims 1 to 4, wherein the saponification degree of the ethylene-vinyl acetate copolymer after Step 2 is 5 mol% or less. In the step 3, the alcohol solution of the ethylene-vinyl acetate copolymer after the contact with the acetalization catalyst in the step 2 is supplied to the upper part of the tower reactor, and the alcohol solvent is supplied as a vapor from the lower part of the tower. The alcohol solvent and acetate ester are discharged as vapor from the top of the column, and an alkali catalyst is supplied into the column to saponify the ethylene-vinyl acetate copolymer. The manufacturing method of the ethylene-vinyl acetate copolymer saponified product in any one.