JP2001270946A - Aqueous dispersion of ethylene/vinyl alcohol copolymer and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous dispersion of an ethylene/vinyl alcohol copolymer excellent in shelf stability by adding to a copolymer solution an easily available chemical or compound as a dispersion stabilizer for the purpose of inhibiting deposition of fine polymer particles and to provide a method for manufacturing the dispersion. SOLUTION: The aqueous dispersion of an ethylene/vinyl alcohol copolymer wherein a surfactant is added as a dispersion stabilizer is manufactured, for example, by a series of following process; dissolving under heat a dispersion copolymer in a aqueous alcoholic solvent; adding thereto a surfactant as a dispersion stabilizer; depositing by cooling fine particles having a uniform particle size; further stirring for dispersing the fine particle and finally removing the alcohol in the aqueous alcoholic solvent under reduced pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an aqueous dispersion obtained by dispersing an ethylene-vinyl alcohol copolymer in an aqueous solvent as a dispersoid, and a method for preparing the same. More specifically, in an aqueous solvent containing water as a main component, ethylene-vinyl obtained by adding a dispersion stabilizer to a dispersoid ethylene-vinyl alcohol copolymer to improve the standing stability of the dispersion. The present invention relates to a method for preparing an aqueous dispersion of an alcohol copolymer.

[0002]

2. Description of the Related Art In the packaging of products such as foods, pharmaceuticals, and electronic components, barrier-coated materials are used for the purpose of suppressing the invasion of oxygen or moisture, which is a problem in maintaining the quality and performance of these products. Many are used. As a barrier coating material, a vinylidene chloride copolymer has a good barrier property against oxygen, water vapor, and other gases, and is used in a large number of fields. However, chlorine-containing polymers such as vinylidene chloride copolymer often cause dioxins and the like during incineration depending on the combustion temperature and conditions. for that reason,
In recent years, there has been an increasing demand for a substitute for a vinylidene chloride copolymer that does not contain halogen and has a barrier property against oxygen and moisture.

[0003] Polyvinyl alcohol is a resin which exhibits excellent gas barrier properties like a vinylidene chloride copolymer and does not contain halogen. This polyvinyl alcohol, when completely dried, has excellent gas barrier properties, oil resistance, and transparency. However, since the temperature difference between its melting point and decomposition point is small, it is difficult to perform hot-melt molding, and because of its high hydrophilicity, it is poor in water resistance, moisture resistance, and boil resistance. There is a major problem in that the application to a barrier coating material is to be reduced, for example, the properties and mechanical performance are reduced.
The problem is that, although gas barrier properties and oil resistance are inferior, the characteristics of low-density polyethylene, which is excellent in hot-melt moldability, are used to make ethylene-vinyl alcohol copolymer resin, and low-density polyethylene and polyvinyl It overcomes the disadvantages of both polymers without compromising the strengths of both polymers.

That is, an ethylene-vinyl alcohol copolymer resin has high gas barrier properties against oxygen and the like, excellent fragrance retention, oil resistance, resistance to organic solvents, weather resistance, transparency, and extrudability and thermoformability. It has been widely applied as a packaging material and a coating material for surfaces of plastic, metal, paper, wood, and the like. In particular, the expectation as an environment-friendly gas barrier resin is further increasing because it does not contain chlorine in the molecule. In particular, it is suitable for use as a gas barrier coating for packaging materials of products that dislike oxygen or moisture, such as foods, pharmaceuticals, and electronic components.

Heretofore, as a method of forming a coating film of an ethylene-vinyl alcohol copolymer, melt extrusion has been carried out by utilizing its extrudability and thermoformability.
Methods such as injection molding and film lamination are widely used. The film obtained by these methods is relatively thick, but in order to further expand the application field,
There is a demand for a method capable of forming a thin film and easily forming a film even with a complicated shape. Specifically, a technique of applying and forming a thin film using a solution or a dispersion of an ethylene-vinyl alcohol copolymer has attracted attention. At this time, it is strongly required to suppress the amount of evaporation of the organic solvent in the drying and forming of the film after the application, from the viewpoint of improving the working environment and considering the surrounding environment. Therefore, there is a particularly strong demand for using an aqueous dispersion in which a poorly water-soluble ethylene-vinyl alcohol copolymer is uniformly dispersed in an aqueous solvent containing water as a main component.

The properties of the ethylene-vinyl alcohol copolymer itself, such as its gas barrier properties, are inseparable from its high crystallinity. However, it is not easy to obtain a uniform aqueous dispersion because of the high crystallinity. Numerous studies have been made on a method for preparing an aqueous dispersion of the ethylene-vinyl alcohol copolymer, and some methods have been proposed. For example, a method of dissolving an ethylene-vinyl alcohol copolymer in a mixed solvent of water and alcohol, blending a surfactant, and removing the alcohol by dialysis (JP-A-54-78748).
), A method of adding a surfactant, dissolving an ethylene-vinyl alcohol copolymer in a mixed solvent of water and alcohol, and removing the alcohol while forcibly and rapidly stirring with a high-speed mixer or the like (Japanese Patent Application Laid-Open No. 54-1979). No. 101844),
After dissolving the ethylene-vinyl alcohol copolymer in which alcohols and surfactants are added and dissolved in the precipitant, the pH of the solution is made acidic, and the aggregated particles are once filtered, then re-dispersed by neutralization. (Japanese Patent Application Laid-Open No. 56-614)
No. 30).

When the practicality of the method for preparing an aqueous dispersion disclosed in the above-mentioned patent publication is examined in detail, the following problems remain. In the method disclosed in JP-A-54-78748, a dialysis method is used to remove the alcohol, so that the solvent removal step is complicated. Workability decreases. In the method disclosed in Japanese Patent Application Laid-Open No. 54-101844, the stability of the obtained dispersion is poor, and the viscosity increases due to the increase in concentration, resulting in reduced workability and coatability. In the method disclosed in JP-A-56-61430, the entire process of preparing a dispersion is complicated, for example, including a process of once aggregating and filtering, and accordingly, various types of solvents are used. There is a practical problem in reuse. Further, similarly, the higher the concentration, the higher the viscosity and the lower the processability and coatability.

Further, in order to reduce the crystallinity of the ethylene-vinyl alcohol copolymer, which is a major obstacle to the preparation of the aqueous dispersion, the modified ethylene-vinyl alcohol copolymer is subjected to hydrogen peroxide treatment. A method of obtaining an aqueous dispersion by synthesizing and using the modified copolymer having a lowered melting point (Japanese Patent Application Laid-Open No. Hei 7-118471) has also been proposed.

The method of using the modified copolymer has low viscosity even at a high concentration and good storage stability, but uses an explosive peroxide in the step of synthesizing the modified product. In addition, operations such as centrifugation for separating the synthetic denatured product are complicated. In addition, using a modified copolymer,
This still involves some problems in practical use, such as not dispersing the ethylene-vinyl alcohol copolymer itself.

As a means for reducing the viscosity at a high concentration, a method for preparing an aqueous dispersion using an ethylene-vinyl alcohol copolymer having a hydrophilic group introduced into a molecule and / or at a terminal as a dispersion stabilizer has been proposed. Several have been reported. For example, a method in which an ethylene-vinyl alcohol copolymer and a component containing an ionic group are combined in a block or graft form as a dispersant for the ethylene-vinyl alcohol copolymer (JP-A-4-225)
No. 032), and a method using a composite polymer in which an ethylene-vinyl alcohol copolymer and a polyether component are bonded in a block or graft form (JP-A-6-16747). In the method of adding a copolymer modified product imparting hydrophilicity to these ethylene-vinyl alcohol copolymers as a dispersion stabilizer, the ethylene-vinyl alcohol copolymer portion contains the content of the dispersion stabilizer inherent therein. Thus, a dispersion having a high solid content and a high storage stability is obtained. However, it is necessary to separately synthesize various modified ethylene-vinyl alcohol copolymers used for the dispersion stabilizer, and the entire preparation operation is complicated. When using an aqueous dispersion also containing these ethylene-vinyl alcohol copolymer modified products, mixed with the ethylene-vinyl alcohol copolymer in the film to be formed, the ethylene-vinyl alcohol copolymer modified product is also used. Inevitably included. Depending on the content ratio, the properties of the formed film have some influence.

As described above, many of the methods for preparing an aqueous dispersion of an ethylene-vinyl alcohol copolymer which have been proposed so far involve the use of an aqueous dispersion of an ethylene-vinyl alcohol copolymer.
An alcohol mixed solution is used as a starting material. However, as a result of examining the practicality in detail, none of the cases seems to be practical.

[0012]

In order that an aqueous dispersion of an ethylene-vinyl alcohol copolymer has excellent storage stability and does not impair high gas barrier properties even in a film obtained from the aqueous dispersion, an aqueous dispersion of the ethylene-vinyl alcohol copolymer must be used. It is desirable that the particle size of the dispersoid fine particles in the liquid is fine and uniform. Ethylene-
When a water-alcohol mixed solution of a vinyl alcohol copolymer is used as a starting material, the particle size of the precipitated fine particles is the most important factor for determining the particle size of the fine particles in the aqueous dispersion as the final product. Therefore, it is desired to develop a method for controlling the particle size of the fine particles precipitated from the mixed solution.

The present invention solves the above-mentioned problems, and
An object of the present invention is to add a readily available drug or compound as a dispersion stabilizer to a water-alcohol mixed solution of an ethylene-vinyl alcohol copolymer, thereby precipitating fine and uniform dispersoid fine particles. Another object of the present invention is to provide a method for easily preparing an aqueous dispersion of an ethylene-vinyl alcohol copolymer at a high yield. Also, the present invention
As an aqueous dispersion obtained by a preparation method using the above-mentioned readily available drug / compound as a dispersion stabilizer, the storage stability is high, and, even when the concentration is increased, the viscosity does not become high, the processability, It is an ultimate object of the present invention to provide an aqueous dispersion of an ethylene-vinyl alcohol copolymer having a new composition while maintaining coatability.

[0014]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventor has studied the characteristics required for a drug or compound suitable for a dispersion stabilizer, and the dispersion stabilizer is uniformly mixed with an aqueous solvent. At the same time, the present inventors have conceived that a component exhibiting a high affinity for an ethylene-vinyl alcohol copolymer and exhibiting an action of lowering its crystallinity is suitable.
In addition to the above conditions, in order to keep the storage stability of the obtained aqueous dispersion at a high level, it was conceived that at the storage temperature, it is desirable to also have a property of maintaining a concentration that does not cause disproportionation. . In accordance with this idea, a search was made for compounds having the above-mentioned various properties from readily available general-purpose compounds. As a result, the ethylene-vinyl alcohol copolymer is heated and dissolved using a water-alcohol mixed solvent, and a surfactant is added in advance as a dispersant, followed by cooling. It has been found that fine and uniform fine particles of an ethylene-vinyl alcohol copolymer can be dispersed by actually blending a surfactant in a water-alcohol solution. Based on such knowledge, the present inventors have further studied, and an aqueous dispersion of an ethylene-vinyl alcohol copolymer prepared using a surfactant as a dispersion stabilizer can be dispersed even after a long time. The present inventors have found that the particles do not agglomerate with each other and have excellent storage stability, and have completed the present invention.

That is, the aqueous dispersion of the ethylene-vinyl alcohol copolymer of the present invention is obtained by heating and dissolving the ethylene-vinyl alcohol copolymer in a water-alcohol mixed solvent, and adding a surfactant as a dispersion stabilizer in the solution. Then, the ethylene-vinyl alcohol copolymer fine particles precipitated by cooling are dispersed in a water-alcohol mixed solvent by stirring, and the alcohol contained in the mixed solvent is removed from the obtained dispersion. can get,
An aqueous dispersion of an ethylene-vinyl alcohol copolymer, which is an aqueous dispersion in which fine particles of an ethylene-vinyl alcohol copolymer are dispersed in an aqueous solvent containing water as a main component.

The aqueous dispersion of the ethylene-vinyl alcohol copolymer of the present invention may be prepared, for example, by adding the surfactant as a dispersion stabilizer to a water-alcohol solution of the ethylene-vinyl alcohol copolymer. In
It is preferable to select the amount of the surfactant to be added in the range of 0.5 to 20 parts by weight per 100 parts by weight of the ethylene-vinyl alcohol copolymer.

In the aqueous dispersion of the ethylene-vinyl alcohol copolymer of the present invention, the surfactant added as a dispersion stabilizer is preferably an anionic surfactant. It is more preferable that the surfactant added as a dispersion stabilizer has a polyethylene oxide structure in the molecule.

In addition, the method for preparing the aqueous ethylene-vinyl alcohol copolymer dispersion of the present invention comprises dispersing ethylene-vinyl alcohol copolymer fine particles in an aqueous solvent whose main component is water, When preparing an aqueous dispersion of an ethylene-vinyl alcohol copolymer dispersed with a surfactant to be added as a dispersant, the ethylene-vinyl alcohol copolymer is dissolved by heating using a water-alcohol mixed solvent. After adding a surfactant, the mixture is cooled to precipitate fine particles of the ethylene-vinyl alcohol copolymer, and then the fine particles are dispersed by stirring.Then, the alcohol contained in the mixed solvent is removed under reduced pressure. Ethylene-vinyl alcohol copolymer aqueous dispersion characterized by using the solvent of the dispersion as an aqueous solvent by distilling off It is the preparation method.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, there is provided an aqueous dispersion in which dispersoid ethylene-vinyl alcohol copolymer fine particles are dispersed in an aqueous solvent, and the fine particles are used as a dispersion stabilizer in a precipitation step. It is characterized by being prepared by adding a surfactant and precipitating as fine particles from a solution using a water-alcohol mixed solvent.

In the present invention, in the fine particle precipitation step, the surfactant added in advance to the water-alcohol solution of the ethylene-vinyl alcohol copolymer as a dispersion stabilizer includes an anionic surfactant and a cationic surfactant ,
Both amphoteric and non-ionic surfactants can be used. For example, alkali soap, metal soap, organic base soap, alkyl sulfate, alkyl sulfonate, alkyl benzene sulfonate, alkyl naphthalene sulfonate, alkyl sulfosuccinate, alkyl diphenyl ether disulfonate, alkyl Anionic surfactants such as phosphates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkyl phenyl ether sulfates, polyoxyethylene alkyl ether sulfonates, polycarboxylic acid type polymer surfactants, and alkylamine salts , Cationic surfactants such as alkylammonium salts and alkylpyridinium salts, amphoteric surfactants such as alkyl pedine and alkyl β-alanine, polyvinyl alcohol, polyoxyethylene alkyl ether, polyoxy Tylene higher alcohol ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, polyhydric alcohol fatty acid ester, polyoxyethylene polyhydric alcohol fatty acid ester, polyoxyethylene fatty acid amide, sorbitan monofatty acid ester, sorbitan difatty acid ester, sorbitan Trifatty acid ester, polyoxyethylene sorbitan monofatty acid ester, polyoxyethylene sorbitan difatty acid ester, polyoxyethylene sorbitan trifatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, sucrose fatty acid ester, polyoxyethylene hydrogenated castor oil, Non-ionic surfactants such as polyoxyethylene alkylamines and polyoxyethylene fatty acid amides Available.

Further, one or more of the above surfactants may be used. That is, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and any one of non-ionic surfactants are selected, and two or more types of the surfactants are classified. Compounds can be used in combination. Alternatively, an anionic surfactant, a cationic surfactant, an amphoteric surfactant,
Also, two or more compounds classified into different surfactant groups from nonionic surfactants can be selected and used in combination.

When the coating film formed by using the aqueous dispersion of the present invention is used for packaging pharmaceuticals and foods, it is preferable to use a surfactant which is acceptable even if it is taken into the body. . For example, food additives such as propylene glycol alginate, glycerin fatty acid ester, sodium chondroitin sulfate, sucrose fatty acid ester, sorbitan fatty acid ester, and propylene glycol fatty acid ester, or higher alcohol sodium sulfate, polyoxyethylene alkyl ether sodium sulfate, polyoxy It is preferable to use surfactants for pharmaceuticals and cosmetics, such as ethylene higher alcohol ethers, polyoxyethylene sorbitan fatty acid esters, glycerol fatty acid esters, and polyethylene glycol fatty acid esters. One or more of these surfactants for food additives, medicines and cosmetics can be used.

Although various surfactants can be used as described above, it is more preferable to use an anionic surfactant in consideration of the viscosity stability of the final dispersion. Further, in addition to the anionic surfactant as a main component, a form in which other cationic surfactants, amphoteric surfactants, and nonionic surfactants are also used as secondary components is more preferable. Become.

In order to enhance the storage stability of the resulting dispersion, it is more preferable to use a surfactant having a polyethylene oxide structure containing an oxy group (ether oxygen) having an affinity for water in the surfactant molecule. preferable. Such surfactants include, for example, anionic surfactants such as polyoxyethylene alkyl ether sulfate, polyoxyethylene alkyl phenyl ether sulfate, polyoxyethylene alkyl ether sulfonate, polyoxyethylene alkyl ether, and polyoxyethylene alkyl ether. Oxyethylene higher alcohol ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyoxyethylene fatty acid ester,
Nonionic surfactants such as polyoxyethylene polyhydric alcohol fatty acid ester, polyoxyethylene hydrogenated castor oil, polyoxyethylene alkylamine, and polyoxyethylene fatty acid amide can be mentioned. In addition, in addition to the surfactant having a polyethylene oxide structure which is mainly added, other surfactants can also be used as a secondary additive, which is still more preferable.

In particular, it is more preferable to use an anionic surfactant having a polyethylene oxide structure.
In addition, a mode in which a nonionic surfactant having a polyethylene oxide structure is used in combination with the anionic surfactant is also more preferable.

The amount of the surfactant used as a dispersant can exert a function of uniformly and stabilizing the dispersion of fine particles, and when mixed into an ethylene-vinyl alcohol copolymer film, its gas barrier property and other properties can be improved. It is preferable that the amount does not lower the mechanical performance. Although it depends on the molecular weight (average molecular weight) of the surfactant, usually, the surfactant is used in an amount of 0.5 to 2 based on 100 parts by weight of the ethylene-vinyl alcohol copolymer.
0 parts by weight, preferably 1 to 10 parts by weight, more preferably 2 to 10 parts by weight may be added.

The above-mentioned aqueous dispersion of ethylene-vinyl alcohol copolymer of the present invention can be prepared by the following method. Specifically, the ethylene-vinyl alcohol copolymer is dissolved by heating using a water-alcohol mixed solvent, and after adding a surfactant as a dispersant, the mixture is cooled to disperse the ethylene-vinyl alcohol copolymer. Precipitate fine particles, disperse the dispersoid fine particles by stirring,
This is a method in which an alcohol contained in the mixed solvent is distilled off under reduced pressure to make the solvent of the dispersion liquid an aqueous solvent.
By using this preparation method, the ethylene-vinyl alcohol of the present invention is obtained by dispersing dispersoid ethylene-vinyl alcohol copolymer fine particles in an aqueous solvent whose main component is water together with a surfactant as a dispersion stabilizer. The aqueous copolymer dispersion can be prepared with good reproducibility.

The aqueous dispersion of the present invention acts on the dispersoid fine particles of the ethylene-vinyl alcohol copolymer in addition to the surfactant added as the above-mentioned dispersion stabilizer to wet the water on the surface. It is more preferable to add a compound having various ether structures to increase the property. The compound having an ether structure is preferably added after the precipitation of the dispersoid fine particles. As long as the action of the surfactant added in the precipitation step of the dispersoid fine particles is not impaired, the compound having an ether structure is subjected to the precipitation step,
It may be added to the mixed solvent in advance.

The aqueous dispersion of the ethylene-vinyl alcohol copolymer of the present invention is used as a dispersion stabilizer in an aqueous solvent when the fine particles of the ethylene-vinyl alcohol copolymer are precipitated from the water-alcohol solution. By taking the composition to which the surfactant is added, the copolymer dissolved in the aqueous solvent precipitates as fine particles without being aggregated with each other by cooling, and becomes a stable dispersion. Further, after uniformly dispersing the fine particles obtained by stirring, by removing the alcohol contained in the water-alcohol solution,
An aqueous dispersion having improved storage stability is obtained. Further, since the aggregation of the dispersoid fine particles is suppressed, even when the concentration of the ethylene-vinyl alcohol copolymer is increased, it is possible to prevent the liquid viscosity from increasing due to the formation of the aggregate. Therefore, the thin coating film formed from the coating film of the finely dispersed dispersoid particles having excellent storage stability, processability, and coatability has a dense structure, and the ethylene-vinyl alcohol copolymer originally has. Various properties such as gas barrier properties can be effectively achieved.

Hereinafter, the aqueous dispersion of the ethylene-vinyl alcohol copolymer of the present invention and the method for preparing the same will be described more specifically.

Since the aqueous dispersion of the ethylene-vinyl alcohol copolymer of the present invention is mainly used for forming a gas barrier coating film, the ethylene-vinyl alcohol copolymer has an ethylene content of 20%. ５０50 mol%, preferably 20-45 mol%. Normal,
This ethylene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl acetate copolymer. Mainly in the application of the gas barrier coating film, in the ethylene-vinyl alcohol copolymer, the ratio of saponified vinyl acetate, which is the vinyl alcohol part, is 90 mol% or more,
Preferably, 95 mol% or more of the copolymer is used.

That is, when the ethylene content is less than 20 mol%, the mechanical stability at high temperature is insufficient, and as a result, the gas barrier property of the coating film is lowered, and
If it exceeds 0 mol%, the gas barrier properties of the coating film derived from the vinyl alcohol portion will decrease. Further, even if the ethylene content is 20 to 45 mol%, if the degree of saponification of vinyl acetate is less than 90%, the ratio of the vinyl alcohol portion is still insufficient, and the gas barrier property of the coating film is reduced.

First, in order to form dispersoid fine particles of an ethylene-vinyl alcohol copolymer, a predetermined amount of the ethylene-vinyl alcohol copolymer is dissolved in a water-alcohol mixed solvent while heating. Ethylene-vinyl alcohol copolymer itself is poorly water-soluble, so it has a dissolving ability, and also increases the solubility of the copolymer by using a mixed solvent containing an alcohol that is uniformly mixed with water. . When a surfactant is added to this solution, and then cooled to lower the liquid temperature, the solubility is naturally lowered to form a supersaturated solution. At this time, if the degree of supersaturation is made sufficiently large, the particles do not grow into large crystals, and fine-particle precipitation occurs spontaneously and uniformly throughout the liquid layer. At this time, a surfactant acts to generate finer particles. Further, not only the concentration and ethylene content of the ethylene-vinyl alcohol copolymer but also the ratio of water to alcohol in the water-alcohol mixed solvent greatly affects the formation of fine particles. The ratio of water to alcohol in the mixed solvent used is generally from 1: 9 to 7: 3, preferably from 2: 8 to 6: 4. If the water content exceeds 70%, the solubility of the ethylene-vinyl alcohol copolymer decreases, and it becomes impossible to achieve a sufficient amount of dissolution. Conversely, the water content is 10%
If less than, the solubility of the copolymer becomes unnecessarily high,
Due to the difference in solubility due to cooling, the solution becomes unsuitable for depositing fine particles of uniform shape and size. In particular, in the final stage, when the alcohol is distilled off, the ratio of the amount of the copolymer to be precipitated increases, which is not preferable because it causes agglomeration.

Using the above-mentioned mixed solvent in a suitable ratio, the concentration of the ethylene-vinyl alcohol copolymer in the initial solution is 5 to 30%, preferably 10 to 2%.
It is good to be 0%.

When the concentration of the copolymer exceeds 30%, it becomes difficult to dissolve the whole amount in the mixed solvent even by heating. Even if dissolved, the stability of the resulting solution will be poor. That is, when cooled, it becomes too supersaturated, which makes it difficult to controlly generate copolymer fine particles having a uniform shape and size in the liquid layer.

On the other hand, if the concentration of the copolymer is less than 5%, a supersaturated state sufficient to cause precipitation of fine particles of a desired size cannot be achieved by cooling. In other words, instead of simultaneous precipitation of fine particles from the supersaturated state, crystallization is performed once formed and using fine particles as nuclei, and the obtained particle size becomes unsuitable for the dispersoid.
Further, in the first place, the total amount of the copolymer is small, and it is difficult to achieve a high concentration of the particulate copolymer contained in the final aqueous dispersion.

At this time, when the dispersion is carried out using a solution having a high concentration of the ethylene-vinyl alcohol copolymer, the water content is preferably high, and when the concentration is low, the water content is preferably low.

As described above, the composition of the ethylene-vinyl alcohol copolymer has an ethylene content of 20%.
５０50 mol%, preferably 20-45 mol%. At this time, in the resin having a low ethylene content of the ethylene-vinyl alcohol copolymer, it is preferable that the content of water in the mixed solvent used for dissolution is large, while in the case of the resin having a high ethylene content, the content of water is preferably small. .

When dissolving the above-mentioned ethylene-vinyl alcohol copolymer under heating, alcohols used as a water-alcohol mixed solvent include, for example, methanol, ethanol, propyl alcohol (1-propanol), isopropyl alcohol (2 -Propanol), butyl alcohol (1-butanol), isobutyl alcohol (2
-Butanol), sec-butyl alcohol, tert
-Butyl alcohol, n-amyl alcohol (1-pentanol), such as a chain alcohol having no more than 6 monovalent carbon atoms, ethylene glycol, propylene glycol,
One or two or more general-purpose alcohols that are uniformly miscible with water, such as a chain-type dihydric alcohol having no more than 6 carbon atoms, such as 1,4-butanediol, can be used. Thereafter, a step of distilling off the alcohols in the mixed solvent under reduced pressure is provided, and therefore, it is preferable to use one having a boiling point lower than that of water and being liquid at normal temperature. Even at ordinary temperature or low temperature, methanol, ethanol, and isopropyl alcohol, which can be easily distilled under reduced pressure and are easily available, are more preferable.

When dissolving the ethylene-vinyl alcohol copolymer, the temperature of the solution is 50 ° C. to 120 ° C., preferably 6 ° C.
The temperature may be selected from the range of 0 ° C. to the reflux temperature of alcohols in the mixed solvent. If the dissolution is performed at a temperature equal to or higher than the reflux temperature of the water-alcohol mixed solvent, it is necessary to apply a pressure against the vaporization of the alcohol from the solvent to the gas phase.

After heating and dissolving, a surfactant is added to the ethylene-vinyl alcohol copolymer solution. The amount of the above-mentioned surfactant added as a dispersion stabilizer is
The selection is made according to the amount of fine particles of the ethylene-vinyl alcohol copolymer in the dispersion, that is, the amount of the ethylene-vinyl alcohol copolymer dissolved in the solution. The selection is made in consideration of the final amount of the aqueous dispersion and the content of the fine particles of the ethylene-vinyl alcohol copolymer. For example, when the content of the ethylene-vinyl alcohol copolymer in the final aqueous dispersion is 10 to 30%,
The total amount of the surfactant added as a dispersion stabilizer is 0.5 to 20 parts by weight, preferably 1 to 10 parts by weight, more preferably 2 to 10 parts by weight, based on 100 parts by weight of the ethylene-vinyl alcohol copolymer. It is advisable to use parts by weight.

The process of precipitating the fine particles of the ethylene-vinyl alcohol copolymer from the solution containing the surfactant is performed by cooling the heated solution and lowering the liquid temperature below the critical solution temperature of the ethylene-vinyl alcohol copolymer. Achieved. In preparing the aqueous dispersion of the present invention, the critical dissolution temperature varies depending on the ethylene content in the copolymer, the concentration of the copolymer dissolved in the solution, and the content of water in the solution, and is accompanied by it. The temperature at which the fine particles are deposited is also selected. The temperature of the liquid may be selected so that the difference in solubility before and after cooling is sufficiently large. It is preferable to select the amount of the copolymer to be heated and dissolved in the solution within the above-described preferable range, and to cool the temperature to about 30 ° C. or lower to precipitate fine particles.

The fine particles of the ethylene-vinyl alcohol copolymer precipitated by cooling are stirred by stirring the liquid.
After uniformly dispersing, a dispersion liquid using a water-alcohol mixed solvent as a dispersion solvent is once obtained.

The step of dispersing the ethylene-vinyl alcohol copolymer fine particles can be carried out, for example, by a reactor equipped with a stirrer. In order to increase the efficiency of stirring and quickly obtain a dispersion having better uniformity, an apparatus such as a homogenizer, a high-speed mixer, a colloid mill, a high-pressure jet emulsifying and dispersing machine, and a wet attritor can be used.

At the time of stirring, the amount of liquid can be increased by further adding a solvent such as water or alcohol to facilitate dispersion. However, the solid content of the final product is lower than the target value. Add a small amount.

Further, in order to further stabilize the dispersion, other dispersion stabilizers, specifically, an ether compound which can be easily mixed and dissolved in the above-mentioned water-alcohol mixed solution can be added as an auxiliary. . For example, dimethyl ether,
Diethyl ether, diisopropyl ether, dibutyl ether, diisoamyl ether (diisopentyl ether), 2,2-dimethoxypropane, 1,1,3,3
-Tetramethoxypropane, cyclohexanone dimethyl acetal, divinyl ether, vinyl ethyl ether, vinyl isopropyl ether, vinyl propyl ether, vinyl isobutyl ether, vinyl 2-ethylhexyl ether, tetrahydrofuran, tetrahydropyran, 1,3-dioxane, 1,4-dioxane Ether, cyclic ethers, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl, which are also used as low boiling point solvents such as methyl tert-butyl ether, anisole and dibenzyl ether Ether, ethylene glycol dibutyl ether, diethylene glycol, diethyl Glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, triethylene glycol, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, triethylene Glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol dibutyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether, propylene glycol monoethyl Ether, propylene glycol monobutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol dibutyl ether, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, dipropylene glycol dimethyl ether, dipropylene glycol Propylene glycol diethyl ether, dipropylene glycol dibutyl ether, tripropylene glycol,
Polypropylene and glycol ethers such as tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monobutyl ether, tripropylene glycol dimethyl ether, tripropylene glycol diethyl ether, tripropylene glycol dibutyl ether, and propylene glycol monomethyl ether acetate;
Ethyl glycidyl ether, methyl glycidyl ether, allyl glycidyl ether, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, 2-methyloctyl glycidyl ether, phenyl glycidyl ether, ethylene glycol diglycidyl ether,
Glycidyl ethers such as neopentyl glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, polyethylene glycol, polypropylene glycol, ethylene glycol-
Polyethers such as propylene glycol copolymer, polytetramethylene ether glycol and polyethylene glycol dimethyl ether are exemplified. In addition, resin compounds in which a polyol such as glycerin, pentaerythritol, trimethylolpropane, bisphenol A, sorbitol, or sucrose is used as a core and ethylene glycol or propylene glycol is bonded to the polyol are also included. The resin compound has a structure in which a chain similar to polyethylene glycol and polypropylene glycol is added to a core polyol, and exhibits properties similar to polyethylene glycol and polypropylene glycol.

Among them, a chain similar to polyethylene glycol or polypropylene glycol is added to polyethylene glycol, polypropylene glycol, ethylene glycol-propylene glycol copolymer, or a core polyol having properties similar to polyethylene glycol or polypropylene glycol. The resin compound thus obtained is a compound more suitable as another dispersion stabilizer to be added auxiliary in the present invention. That is, these polyglycol compounds have the advantage of being uniformly dissolved in water, and of maintaining the desired concentration without evaporation when the alcohol in the mixed solvent is subsequently distilled off under reduced pressure. I have it.

The above-mentioned auxiliary compound, which is an auxiliary compound, is preferably added after cooling the solution to precipitate fine particles of the ethylene-vinyl alcohol copolymer. . In the present invention, as long as the action of the surfactant used as the main dispersion stabilizer is not impaired, it may be added when the ethylene-vinyl alcohol copolymer is dissolved by heating or before cooling the heated solution. it can.

The amount of the ether compound to be added is selected according to the amount of fine particles of the ethylene-vinyl alcohol copolymer in the dispersion. The selection is made in consideration of the final amount of the aqueous dispersion and the content of the fine particles of the ethylene-vinyl alcohol copolymer. For example, when the content of the ethylene-vinyl alcohol copolymer in the final aqueous dispersion is set to 10 to 30%, based on 100 parts by weight of the ethylene-vinyl alcohol copolymer,
The total amount of the ether compound added as an auxiliary dispersion stabilizer may be 0.1 to 20 parts by weight, preferably 1 to 10 parts by weight.

Further, when uniformly dispersing the precipitated dispersoid fine particles by stirring, in addition to the surfactant previously added at the time of heating and dissolving, various surfactants can be additionally added again. In this stirring step, a surfactant to be supplementarily added can be used in combination with the ether compound as the auxiliary dispersion stabilizer component. This supplementary surfactant supplements the action of the surfactant initially added, further increases the wettability of the dispersoid fine particles in water in an aqueous solvent, and further facilitates the dispersion. Having. Therefore, it is more preferable to use one or two or more of the same surfactants as those added to the ethylene-vinyl alcohol copolymer solution at first.

Including this supplementary surfactant,
The total amount of the surfactant used is an amount that does not decrease the gas barrier property or other mechanical performance when mixed into the ethylene-vinyl alcohol copolymer film produced using the aqueous dispersion of the final product. Good to do. Usually, based on 100 parts by weight of the ethylene-vinyl alcohol copolymer, the total amount of the surfactant used is 0.5 to 20 parts by weight, preferably 1 to 10 parts by weight, more preferably 2 to 10 parts by weight. It is better to select a range.

Unlike the above-mentioned surfactants and ether compounds added as auxiliary dispersion stabilizers,
It has no essential role in accelerating the dispersion, but when the aqueous dispersion of the present invention is applied and a film is formed, the following components are also contained in the dispersion as additional components to be used. Can be.

When forming a coating film by coating or the like, a film-forming auxiliary may be added to the aqueous dispersion of the ethylene-vinyl alcohol copolymer of the present invention in order to improve the film forming property. . As a film-forming auxiliary for the ethylene-vinyl alcohol copolymer, a water-soluble auxiliary is used, and for example, glycols such as ethylene glycol, propylene glycol, and glycerin can be used.

The amount of the film-forming aid used is an amount that helps the formation of a film and does not lower the gas barrier properties and other mechanical properties of the obtained film. Usually, 1 to 100 parts by weight, preferably 1 to 10 parts by weight of the above-mentioned film-forming aid can be added to 100 parts by weight of the ethylene-vinyl alcohol copolymer.

In addition, in order to improve the coating properties of the dispersion and the performance of the coating film, for example, inorganic powders for improving the blocking resistance of the coating film, and various powders for improving the coating property. Various additives such as a polymer can be added to such an extent that the gas barrier properties and other mechanical properties of the ethylene-vinyl alcohol copolymer as the main component are not reduced.

The aqueous dispersion liquid of the present invention is cooled after adding a surfactant as a dispersion stabilizer in a water-alcohol mixed solvent, and the precipitated dispersoid fine particles are uniformly dispersed and distributed by stirring. After forming the liquid, the alcohol in the water-alcohol mixed solvent contained in this dispersion is removed by distillation under reduced pressure to obtain a final aqueous dispersion. The alcohol is distilled off under reduced pressure at a reduced pressure of 0.1 to 200 mmHg, preferably 1 to 100 mmHg. During this vacuum distillation,
The temperature of the liquid is selected in the range of 0 to 50C, preferably 5 to 40C. At that time, the liquid temperature at the time of distillation under reduced pressure may be higher than the liquid temperature at the time of fine particle precipitation. If the temperature is lower than 0 ° C. (freezing point), the fluidity of the solution decreases as the alcohol is distilled off, and a uniform aqueous dispersion often cannot be obtained. Conversely, if the temperature exceeds 50 ° C., the amount of the ethylene-vinyl alcohol copolymer dissolved in the water-alcohol mixed solvent becomes too large. As a result, as the alcohol is distilled off, the copolymer gradually precipitates and causes adhesion of the fine particles to each other, or the fine particles are gradually precipitated to increase the particle size, or the dispersion liquid gels. There is a possibility. Therefore, in order to avoid such a problem, it is preferable to select the temperature of the liquid in the above-described range during the distillation under reduced pressure. Although the most desirable aqueous dispersion is obtained by completely removing the alcohol from the water-alcohol mixed solvent, it is theoretically not possible to completely remove the alcohol from the mixed solvent. End the departure. In addition, as long as the remaining amount of the alcohol does not deteriorate the working environment at the time of coating, a small amount of the remaining alcohol may be used from the viewpoint of economy.

The aqueous dispersion of the ethylene-vinyl alcohol copolymer of the present invention can be prepared by employing the above-mentioned preparation method so that the final aqueous dispersion contains the ethylene-vinyl alcohol copolymer in an amount of about 5% by weight to 50%. %, Preferably in the range of 10% to 40% by weight.

[0058]

The present invention will be specifically described below with reference to examples. In addition, although the example shown below as a specific example of this invention is an example of the best embodiment in this invention, this invention is not limited to these specific examples.

Example 1 A mixed solvent having a water-alcohol ratio of 1: 1 was added to 10 parts by weight of an ethylene-vinyl alcohol copolymer having an ethylene content of 29 mol%, a saponification degree of 99.5 mol%, and a polymerization degree of 1,000. 45 parts by weight of water and 45 parts by weight of isopropyl alcohol. Then, the mixture is heated and stirred at 80 ° C. to prepare a water-isopropyl alcohol solution of an ethylene-vinyl alcohol copolymer having a concentration of about 10%. To this heated solution, 5 parts by weight of a 10% water-isopropyl alcohol (1: 1) solution of sodium polyoxyethylene alkyl ether sulfate (0.5 part by weight as sodium polyoxyethylene alkyl ether sulfate) is added. The solution was cooled to 5 ° C and the temperature was reduced to 5 ° C.
, And allowed to stand for 24 hours to precipitate fine particles of the ethylene-vinyl alcohol copolymer to obtain an initial dispersion. After adjusting the obtained initial dispersion to 25 ° C.,
While stirring vigorously, 10 parts by weight of a 5% polyethylene glycol (molecular weight: 1,000) water-isopropyl alcohol (1: 1) solution (0.5 parts by weight as polyethylene glycol) is added to uniformly disperse the fine particles.

Next, the isopropyl alcohol in the solvent was distilled off at 30 ° C. under reduced pressure while stirring the dispersion. No aggregation of the dispersed fine particles was observed in the course of distilling off isopropyl alcohol, and an aqueous dispersion of an ethylene-vinyl alcohol copolymer having an average particle size of 0.9 μm and a solid concentration of 18% was finally obtained.

Further, in this aqueous dispersion, in a standing stability test at 40 ° C. for 7 days, no aggregation of the fine particles was observed. Therefore, it is determined that the standing stability satisfies practical requirements.

A biaxially oriented polypropylene film (thickness 2
0 μm), using the aqueous dispersion prepared by the above-described preparation method, coating to a thickness of 3 μm,
A heat drying treatment was performed at 0 ° C. for 5 minutes. This ethylene
The film coated with the vinyl alcohol copolymer coating shows a good oxygen gas barrier property as shown in Example 7 below.

Example 2 A mixed solvent having a water-alcohol ratio of 1: 2 was added to 10 parts by weight of an ethylene-vinyl alcohol copolymer having an ethylene content of 44 mol%, a saponification degree of 99.5 mol%, and a polymerization degree of 1,000. 30 parts by weight of water and 60 parts by weight of isopropyl alcohol. Then, the mixture is heated and stirred at 80 ° C. to prepare a water-isopropyl alcohol solution of an ethylene-vinyl alcohol copolymer having a concentration of about 10%. To this heated solution, 5 parts by weight of a 10% aqueous solution of a surfactant, sodium polyoxyethylene alkyl phenyl ether sulfate (1: 1) (0.5 parts by weight as sodium polyoxyethylene alkyl phenyl ether sulfate), was added. I do. This solution is cooled to 20 ° C. and left for 24 hours while maintaining the temperature at 20 ° C., thereby precipitating ethylene-vinyl alcohol copolymer fine particles to obtain an initial dispersion. After the initial dispersion liquid was heated to 25 ° C., 10% by weight of a 5% polyethylene glycol (molecular weight: 1,000) water-isopropyl alcohol (1: 1) solution (0.5 part by weight as polyethylene glycol) while stirring vigorously. Add. Furthermore, stirring is performed while 15 parts by weight of water is dropped, and the fine particles are uniformly dispersed.

Next, isopropyl alcohol in the solvent was distilled off at 30 ° C. under reduced pressure while stirring the dispersion. No aggregation of the dispersed fine particles was observed in the process of distilling off isopropyl alcohol, and an aqueous dispersion of an ethylene-vinyl alcohol copolymer having an average particle diameter of 0.6 μm and a solid concentration of 18% was finally obtained.

The aqueous dispersion did not show aggregation of fine particles in a standing stability test at 40 ° C. for 7 days. Therefore, it is determined that the standing stability satisfies practical requirements.

A biaxially oriented polypropylene film (thickness 2
0 μm), using the aqueous dispersion prepared by the above-described preparation method, coating to a thickness of 3 μm,
A heat drying treatment was performed at 0 ° C. for 5 minutes. This ethylene
The film coated with the vinyl alcohol copolymer coating shows a good oxygen gas barrier property as shown in Example 7 below.

Example 3 A mixed solvent having a water-alcohol ratio of 1: 2 was added to 10 parts by weight of an ethylene-vinyl alcohol copolymer having an ethylene content of 44 mol%, a saponification degree of 99.5 mol%, and a polymerization degree of 1,000. 30 parts by weight of water and 60 parts by weight of isopropyl alcohol. Then, the mixture is heated and stirred at 80 ° C. to prepare a water-isopropyl alcohol solution of an ethylene-vinyl alcohol copolymer having a concentration of about 10%. To this heated solution, 5 parts by weight of a 10% water-isopropyl alcohol (1: 1) solution of a surfactant polyoxyethylene lauryl ether (0.5 parts by weight as polyoxyethylene lauryl ether) is added. This solution is cooled to 20 ° C. and left for 24 hours while maintaining the temperature at 20 ° C., thereby precipitating ethylene-vinyl alcohol copolymer fine particles to obtain an initial dispersion. After the initial dispersion was heated to 25 ° C., with vigorous stirring,
15 parts by weight of water is dropped to uniformly disperse the fine particles.

Next, isopropyl alcohol in the solvent was distilled off at 30 ° C. under reduced pressure while stirring the dispersion. No aggregation of the dispersed fine particles was observed in the course of distilling off isopropyl alcohol, and an aqueous dispersion of an ethylene-vinyl alcohol copolymer having an average particle diameter of 1.1 μm and a solid content of 19% was finally obtained.

Further, in this aqueous dispersion, in the standing stability test at 40 ° C. for 7 days, no aggregation of the fine particles was observed. Therefore, it is determined that the standing stability satisfies practical requirements.

A biaxially oriented polypropylene film (thickness 2
0 μm), using the aqueous dispersion prepared by the above-described preparation method, coating to a thickness of 3 μm,
A heat drying treatment was performed at 0 ° C. for 5 minutes. This ethylene
The film coated with the vinyl alcohol copolymer coating shows a good oxygen gas barrier property as shown in Example 7 below.

Example 4 A mixed solvent having a water-alcohol ratio of 1: 2 was added to 10 parts by weight of an ethylene-vinyl alcohol copolymer having an ethylene content of 44 mol%, a saponification degree of 99.5 mol%, and a polymerization degree of 1,000. 30 parts by weight of water and 60 parts by weight of isopropyl alcohol. Then, the mixture is heated and stirred at 80 ° C. to prepare a water-isopropyl alcohol solution of an ethylene-vinyl alcohol copolymer having a concentration of about 10%. To this heated solution, 5 parts by weight of a 10% water-isopropyl alcohol (1: 1) solution of the surfactant sodium dodecylbenzenesulfonate (0.5 parts by weight as sodium dodecylbenzenesulfonate) is added. The solution was cooled to 20 ° C. and kept at 20 ° C. for 2 hours.
By allowing the mixture to stand for 4 hours, fine particles of the ethylene-vinyl alcohol copolymer are precipitated to form an initial dispersion. After the initial dispersion is heated to 25 ° C., 15 parts by weight of water is added dropwise with vigorous stirring to uniformly disperse the fine particles.

Next, the isopropyl alcohol in the solvent was distilled off at 30 ° C. under reduced pressure while stirring the dispersion. No aggregation of the dispersed fine particles was observed in the process of distilling off isopropyl alcohol, and an aqueous dispersion of an ethylene-vinyl alcohol copolymer having an average particle diameter of 0.7 μm and a solid content of 19% was finally obtained.

Further, in this aqueous dispersion, in the standing stability test at 40 ° C. for 7 days, no aggregation of the fine particles was observed. Therefore, it is determined that the standing stability satisfies practical requirements.

A biaxially oriented polypropylene film (thickness 2
0 μm), using the aqueous dispersion prepared by the above-described preparation method, coating to a thickness of 3 μm,
A heat drying treatment was performed at 0 ° C. for 5 minutes. This ethylene
The film coated with the vinyl alcohol copolymer coating shows a good oxygen gas barrier property as shown in Example 7 below.

Example 5 A mixed solvent having a water-alcohol ratio of 6:11 was mixed with 15 parts by weight of an ethylene-vinyl alcohol copolymer having an ethylene content of 44 mol%, a saponification degree of 99.5 mol%, and a polymerization degree of 1,000. 30 parts by weight of water and 55 parts by weight of isopropyl alcohol. Then, the mixture is heated and stirred at 80 ° C. to prepare a water-isopropyl alcohol solution of an ethylene-vinyl alcohol copolymer having a concentration of about 15%. To this heated solution, 5 parts by weight of a 10% water-isopropyl alcohol (1: 1) solution of sodium polyoxyethylene alkyl ether sulfate (0.5 part by weight as sodium polyoxyethylene alkyl ether sulfate) is added. This solution is cooled to 20 ° C. and left for 24 hours while maintaining the temperature at 20 ° C., thereby precipitating fine particles of the ethylene-vinyl alcohol copolymer, thereby obtaining an initial dispersion. After the initial dispersion liquid was heated to 25 ° C., 10% by weight of a 5% polyethylene glycol (molecular weight: 1,000) water-isopropyl alcohol (1: 1) solution (0.5 part by weight as polyethylene glycol) while stirring vigorously. Add. Further, stirring is performed while dropping 12 parts by weight of water to uniformly disperse the fine particles.

Then, the isopropyl alcohol in the solvent was distilled off at 30 ° C. under reduced pressure while stirring the dispersion. No aggregation of the dispersed fine particles was observed in the process of distilling off isopropyl alcohol, and an aqueous dispersion of an ethylene-vinyl alcohol copolymer having an average particle diameter of 0.9 μm and a solid concentration of 25% was finally obtained.

Further, in this aqueous dispersion, in the standing stability test at 40 ° C. for 7 days, no aggregation of the fine particles was observed. Therefore, it is determined that the standing stability satisfies practical requirements.

Biaxially oriented polypropylene film (thickness 2
0 μm), using the aqueous dispersion prepared by the above-described preparation method, coating to a thickness of 3 μm,
A heat drying treatment was performed at 0 ° C. for 5 minutes. This ethylene
The film coated with the vinyl alcohol copolymer coating shows a good oxygen gas barrier property as shown in Example 7 below.

Example 6 A mixed solvent having a water-alcohol ratio of 1: 3 was added to 10 parts by weight of an ethylene-vinyl alcohol copolymer having an ethylene content of 44 mol%, a saponification degree of 99.5 mol%, and a polymerization degree of 1,000. 22.5 parts by weight of water and 67.5 parts by weight of isopropyl alcohol. And 8
The mixture is heated and stirred at 0 ° C. to prepare a water-isopropyl alcohol solution of about 10% ethylene-vinyl alcohol copolymer. To this heated solution, 5 parts by weight of a 10% water-isopropyl alcohol (1: 1) solution of sodium polyoxyethylene alkyl ether sulfate (0.5 part by weight as sodium polyoxyethylene alkyl ether sulfate) is added. This solution is cooled to 20 ° C. and left for 24 hours while maintaining the temperature at 20 ° C., thereby precipitating fine particles of the ethylene-vinyl alcohol copolymer, thereby obtaining an initial dispersion. This initial dispersion is added to 25
C., while stirring vigorously, 20% ethylene-acrylic acid copolymer resin sodium salt (acrylic acid content 20% by weight) as a surfactant component to be supplementarily added
5 parts by weight of an aqueous solution (1 part by weight as ethylene-acrylic acid copolymer resin sodium salt) is added. Furthermore, stirring is performed while 15 parts by weight of water is dropped, and the fine particles are uniformly dispersed.

Next, isopropyl alcohol in the solvent was distilled off at 30 ° C. under reduced pressure while stirring the dispersion. No aggregation of the dispersed fine particles was observed during the process of distilling off isopropyl alcohol, and an aqueous dispersion of an ethylene-vinyl alcohol copolymer having an average particle diameter of 0.6 μm and a solid concentration of 21% was finally obtained.

Further, in this aqueous dispersion, in a standing stability test at 40 ° C. for 7 days, no aggregation of the fine particles was observed. Therefore, it is determined that the standing stability satisfies practical requirements.

A biaxially oriented polypropylene film (thickness 2
0 μm), using the aqueous dispersion prepared by the above-described preparation method, coating to a thickness of 3 μm,
A heat drying treatment was performed at 0 ° C. for 5 minutes. This ethylene
The film coated with the vinyl alcohol copolymer coating shows a good oxygen gas barrier property as shown in Example 7 below.

(Example 7) Using an aqueous dispersion obtained under the preparation conditions described in Examples 1 to 6, a biaxially stretched polypropylene film (20 μm thick) was coated to a thickness of 5 μm. At 120 ° C. for 5 minutes. The oxygen permeability of the film on which the coating film was formed was evaluated in order to verify the oxygen gas barrier property. The oxygen permeability under the conditions of a temperature of 20 ° C. and a humidity of 65 RH is less than 10 cc / m ² · day · atm for all of the aqueous dispersions obtained in Examples 1 to 6. Even after the washing dispersion was left for 7 days, the oxygen permeability of the resulting coating film did not change within the range of the measured values.

Comparative Example 1 A mixed solvent having a water-alcohol ratio of 1: 2 was added to 10 parts by weight of an ethylene-vinyl alcohol copolymer having an ethylene content of 44 mol%, a saponification degree of 99.5 mol%, and a polymerization degree of 1,000. 30 parts by weight of water and 60 parts by weight of isopropyl alcohol. Then, the mixture is heated and stirred at 80 ° C. to prepare a water-isopropyl alcohol solution of an ethylene-vinyl alcohol copolymer having a concentration of about 10%. The heated solution is cooled to 20 ° C. and left for 24 hours while maintaining the temperature at 20 ° C., thereby precipitating fine particles of the ethylene-vinyl alcohol copolymer to obtain an initial dispersion. After the initial dispersion was heated to 25 ° C., 5 parts by weight of a 10% aqueous solution of a surfactant, sodium dodecylbenzenesulfonate (1: 1) (0.1% as sodium dodecylbenzenesulfonate) was added with vigorous stirring. 5 parts by weight). Furthermore, stirring is performed while 15 parts by weight of water is dropped, and the fine particles are uniformly dispersed.

Next, the isopropyl alcohol in the solvent was distilled off at 30 ° C. under reduced pressure while stirring the dispersion. No aggregation of the dispersed fine particles was observed in the process of distilling off isopropyl alcohol, and finally an aqueous dispersion of an ethylene-vinyl alcohol copolymer having an average particle size of 2.2 μm and a solid content of 19% was obtained.

However, in this aqueous dispersion to which the surfactant was added after the precipitation of the fine particles, in the standing stability test at 40 ° C. for 7 days, the fine particles were found to aggregate and settle. That is, it is determined that the storage stability is not as excellent as that of Example 4 using the same surfactant.

A biaxially oriented polypropylene film (thickness 2
0 μm), using the aqueous dispersion prepared by the above-described preparation method, coating to a thickness of 3 μm,
A heat drying treatment was performed at 0 ° C. for 5 minutes. This ethylene
The film coated with the vinyl alcohol copolymer film was inferior in the oxygen gas barrier property as compared with the case where the aqueous dispersion of the above-described example was used.

[0088]

The aqueous dispersion of the ethylene-vinyl alcohol copolymer of the present invention is prepared by adding a surfactant in advance as a dispersion stabilizer, precipitating fine dispersoids, and then dispersing. Therefore, aggregation of the dispersoid fine particles is suppressed, and the aqueous dispersion has high storage stability. Also,
The preparation method involves heating and dissolving the ethylene-vinyl alcohol copolymer in a water-alcohol mixed solvent, adding a surfactant as a dispersion stabilizer, and then cooling to precipitate dispersoid fine particles having a uniform particle diameter. Forming, then stirring and dispersing the dispersoid fine particles, and finally,
Since the step of distilling off the alcohol in the alcohol mixed solvent under reduced pressure is employed, an aqueous dispersion having a desired composition can be efficiently prepared with good reproducibility and without complicated steps.
Further, the surfactant used as the dispersion stabilizer in the present invention is a widely available and easily available compound, and accordingly, the cost of preparing the aqueous dispersion itself is also high.
It also has the advantage of relatively restraining.

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Claims (5)

[Claims] An ethylene-vinyl alcohol copolymer is dissolved by heating in a water-alcohol mixed solvent, a surfactant is added to the solution as a dispersion stabilizer, and then the ethylene-vinyl alcohol copolymer precipitated by cooling is added. The coalesced fine particles are dispersed in a water-alcohol mixed solvent by stirring, and ethylene-vinyl is obtained in an aqueous solvent containing water as a main component, which is obtained by removing the alcohol contained in the mixed solvent from the obtained dispersion. An aqueous dispersion of an ethylene-vinyl alcohol copolymer, which is an aqueous dispersion in which alcohol copolymer fine particles are dispersed. 2. When the surfactant is added as a dispersion stabilizer to a water-alcohol solution of an ethylene-vinyl alcohol copolymer, in the solution, the surfactant per 100 parts by weight of the ethylene-vinyl alcohol copolymer is used. The aqueous dispersion of an ethylene-vinyl alcohol copolymer according to claim 1, wherein the amount of the surfactant added is selected in the range of 0.5 to 20 parts by weight. 3. The aqueous dispersion of an ethylene-vinyl alcohol copolymer according to claim 1, wherein the surfactant added as a dispersion stabilizer is an anionic surfactant. 4. The aqueous dispersion of an ethylene-vinyl alcohol copolymer according to claim 1, wherein the surfactant added as a dispersion stabilizer has a polyethylene oxide structure in a molecule. 5. An ethylene-vinyl alcohol copolymer aqueous solution obtained by dispersing dispersoid ethylene-vinyl alcohol copolymer fine particles in an aqueous solvent whose main component is water together with a surfactant added as a dispersion stabilizer. In the preparation of the dispersion, the ethylene-vinyl alcohol copolymer is dissolved by heating using a water-alcohol mixed solvent, and after adding a surfactant as a dispersant, the mixture is cooled to obtain an ethylene-vinyl alcohol copolymer. After precipitating the dispersoid fine particles,
The dispersoid fine particles are dispersed by stirring, and then the alcohol contained in the mixed solvent is distilled off under reduced pressure, whereby the solvent of the dispersion is an aqueous solvent, and the ethylene-vinyl alcohol copolymer aqueous solution is used. A method for preparing a dispersion.