JPS6055540B2 - Method for producing saponified ethylene↓-vinyl acetate copolymer powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing saponified ethylene-vinyl acetate copolymer powder, the purpose of which is to avoid contamination of the polymer with harmful components such as surfactants, which requires operations such as reprecipitation. The object of the present invention is to obtain a saponified powder having perfectly spherical particles without any process.

Conventionally, the following three methods are known as methods for producing ethylene-vinyl acetate copolymer powder: a mechanical pulverization method, a chemical dissolution method, and a dispersion method.

The first method, that is, the mechanical pulverization method, is to cool the saponified ethylene-vinyl acetate copolymer in the form of granules or pellets to a low temperature using liquid nitrogen or the like, and then pass it through a pulverizer with high shearing force. This method obtains irregularly shaped particles with an average particle size of 500 p, but this method requires specially designed equipment and requires a refrigerant such as liquid nitrogen.
In addition, it is necessary to process the saponified powdered copolymer into pellets or the like in advance.

In addition, it is generally difficult to obtain powder with a particle size smaller than 75p using this method. The second method, which is a chemical method, involves dissolving the saponified copolymer in a good polymer solvent such as xylene or toluene, and then adding a large amount of a non-solvent such as methanol to precipitate the powdered polymer. However, in this method, the operations of dissolving the polymer and reprecipitating the polymer with a non-solvent are complicated, and the solvent used cannot be reused as it is after being separated from the saponified powder. It is uneconomical because it must be separated into a good solvent and a non-solvent. The third method, that is, the dispersion method, involves dispersing the saponified copolymer in a solvent using a dispersant at a temperature above the softening point of the copolymer under stirring conditions with a high degree of shearing.
Thereafter, the saponified copolymer is cooled to below its softening point to obtain a saponified powder.

Water is generally used as the solvent for economical reasons.
Further, a surfactant is used as a dispersant. This method has the advantage of being easy to operate, making the process continuous, and being able to obtain powder with spherical particles. However, on the other hand, the surfactant used as a dispersant remains in the powder, which causes the copolymer to Unfavorable changes in the properties of the saponified material occur, such as an increase in water sensitivity and a decrease in electrical insulation values. To eliminate this drawback, a method is generally used in which the saponified powder separated from the dispersion is washed with a large amount of water to reduce the surfactant concentration in the powder to a level that does not cause any unfavorable changes in the properties of the saponified product. (Tokuko Sho 51-25371
(Japanese Patent Application Laid-Open No. 51-122194), this method not only complicates the operation but also requires wastewater treatment of water containing a surfactant, so it cannot be said to be an economical method. The inventors of the present invention have taken note of the above problems and have conducted intensive research into a new method for producing saponified powder. As a result, in a mixture of alcohol with a certain carbon number range and water in a specific ratio, ethylene-vinyl acetate The saponified copolymer does not dissolve but swells at temperatures above its softening point, so it becomes fine particles and disperses in the liquid by stirring, and this dispersion is heated at a temperature below the softening point of the saponified copolymer. The present invention was achieved by discovering that a spherical saponified powder can be obtained by cooling the powder to a temperature of 100%.

That is, the present invention provides a saponified product of an ethylene-vinyl acetate copolymer obtained by partially or completely saponifying an ethylene-vinyl acetate copolymer containing 10 to 5 volume% of vinyl acetate, The main components are alcohol having 2 to 4 carbon atoms and water, and the mixing ratio of water to alcohol is
In a mixed solution containing 40 to 200 parts by weight of water per 100 parts by volume of alcohol, the saponified copolymer is stirred vigorously at a temperature higher than the softening point of the saponified copolymer. Dispersing and then cooling the dispersion. The present invention relates to a method for producing saponified ethylene-vinyl acetate copolymer powder, characterized by the following.

In the present invention, the liquid in which the ethylene-vinyl acetate copolymer is dispersed contains alcohol and water as essential main components.
The alcohol used as a component of the dispersion in the present invention has 2 to 4 carbon atoms, and specifically, ethanol,
n-propanol, isopropanol, n-butanol, Sec-butanol, tert-butanol,
Among these, isopropanol is the most preferred alcohol.

Alcohols with carbon numbers of 2 or less, that is, methanol, have a small swelling ability for polymers, so the saponified copolymer does not disperse in the liquid, and alcohols with carbon numbers of 5 or more dissolve the saponified copolymer in the alcohol, causing the saponified copolymer to dissolve in the liquid. The viscosity increases and the compatibility between alcohol and water decreases, making it difficult for the saponified copolymer to be dispersed in the liquid, making it impossible to obtain spherical saponified powder, which is undesirable. Furthermore, the mixing ratio of alcohol and water in the mixed liquid in which the saponified substance used in the present invention is dispersed is 10 parts by volume of alcohol to 40 to 20,008 parts by volume of water, particularly preferably 10 parts by volume (alcohol) at 20C. 100 to 60 parts of water.

If the amount of water is less than 4 parts by volume per 10 parts by volume of alcohol, the saponified material will swell too much with the alcohol and will not form spherical particles, but will become irregularly shaped coarse particles. If the amount is more than 1 part, the dispersibility of the saponified product becomes poor and the particles become filamentous, both of which are undesirable. In addition, the ratio of the saponified product to the mixed liquid in which it is to be dispersed is such that if the ratio of the liquid to the saponified copolymer is too small, the dispersion will be poor, and if it is too large, it will be uneconomical. Mixed liquid 100% for heel volume
~50 parts by weight, especially 200 to 35 parts by weight is preferred.

Also, the melt index is approximately 201). When powdering the saponified ethylene-vinyl acetate copolymer or the modified product obtained by grafting an unsaturated carboxylic acid to the saponified ethylene-vinyl acetate copolymer shown below, a mixture containing only water and alcohol components cannot be used. In some cases, it may not become a spherical powder, in which case, in addition to alcohol and water, toluene,
It is effective to add a good solvent for polymers such as xylene as a third component at a ratio of 15 to 10 parts by weight, preferably 20 to 10 parts by weight, per 10 parts by weight of alcohol.

In the method of the present invention, in order to disperse the saponified ethylene-vinyl acetate copolymer into the above-mentioned mixture, the temperature is higher than the softening point of the saponified material (VICAT softening point ASTM D-1525), usually 9(1)C or higher. Stir to disperse the saponified material in the liquid.

At temperatures below the softening point of the saponified material, the saponified material cannot be pulverized because it will not be split by stirring. The preferred temperature of the mixed liquid during stirring (dispersion temperature) is specifically 90 to 220C1
Especially 95-13 (generations). Although there is no problem in dispersing at a temperature of 2200C or higher, it is uneconomical because the heat load of heating and cooling increases.

Further, the necessary stirring speed when stirring the saponified material in the mixed solution is 60 m/min or more at the tip of the stirring blade, preferably 10 to 400 n1/min. The type of stirring blade is preferably a turbine type, a propeller type, or an inclined paddle type, but any type of device may be used as long as it provides at least an appropriate amount of shearing action. Further, the time required for dispersion, that is, stirring time, may be at least 1 minute at a temperature higher than the softening point of the saponified material, and is usually 1 minute to 1 powder. Further, the pressure during dispersion may be any pressure that maintains the dispersion liquid in a liquid phase, that is, a pressure higher than the vapor pressure of the dispersion mixture at the operating temperature, and the dispersion is usually carried out under vapor pressure. The vapor pressure of the dispersion mixture varies depending on the type of alcohol and the mixing ratio of alcohol and water, but at a temperature of 95 to 130°C, it is approximately 1.5 to 5k9/C7l! (gauge pressure). The saponified ethylene-vinyl acetate copolymer used in the method of the present invention may be a saponified product synthesized by any method, including saponification in an alcohol medium, saponification in water, and saponification in a mixed medium of alcohol and water. Since the medium used in these saponification methods is partially the same as the components of the dispersion used in the method of the present invention, the saponified product obtained in the saponification process can be processed without drying. This is preferred because the wet cake after solid-liquid separation can be used as it is in the present invention. In addition, the saponified ethylene-vinyl acetate copolymer used in the method of the present invention has a concentration of alkali metal salt of acetic acid contained as an impurity in the saponified product.
．． If it exceeds 5% by weight, this salt may cause the saponified particles to aggregate, so it is necessary to reduce the concentration of the alkali metal salt of acetic acid in the saponified product to 2.5% by weight or less. This alkali metal salt of acetic acid is produced as a reaction by-product when saponifying ethylene-vinyl acetate copolymer using an alkali metal catalyst such as alkali hydroxide or sodium alcoholate. Since the content varies depending on the amount of alkali used, the degree of saponification, etc., the salt content in the saponified material used in the present invention is 2.
If it is 5% by weight or more, it is necessary to wash the saponified product with water or the like in advance to reduce the salt concentration. The present invention has the advantage that the saponified product containing the washed solution can be used as it is without drying. The dispersion containing saponified powder obtained by the method of the present invention may be used as it is as a saponified dispersion after dispersion is completed, but in order to obtain saponified powder as a product, it is necessary to add the saponified powder to the liquid. After dispersion is complete, the dispersion is cooled with stirring to a temperature below the softening point of the saponified material, preferably below 8C, more preferably below 70C, and the liquid is separated by filtration or centrifugation. After removal, dry.

The powder obtained by the present invention has an average particle size of 20 to 500.
Since it is in the range of p and is almost perfectly spherical,
The powder has good flowability, which is advantageous because it makes handling of the saponified powder extremely easy in various applications.

The method of the invention has many advantages over conventional methods.

The advantages are, firstly, that the powdering operation is simpler than conventional chemical dissolution methods because it only involves heating and cooling the dispersion liquid composition and there is no reprecipitation operation, and secondly, there is no reprecipitation process, so dispersion is easier. After solid-liquid separation, the liquid can be recycled and used as is without purification, and thirdly, the dispersion temperature can be lower than that of the dispersion method, and it does not have a negative effect on the quality of the powder of saponified substances such as surfactants. Since the powder is not washed, it is not necessary to wash the obtained powder, and a highly pure powder can be obtained by simply drying it.Fourthly, the amount of liquid for the saponified material to be powdered used in the present invention is smaller than that of conventional chemicals. This method is smaller than the dissolution method, so the equipment can be made smaller.

In addition, in the conventional dispersion method for powdering saponified materials, for example, the method described in JP-A-51-1221, the concentration of salt contained in the saponified material is set to 0.1 as cations during powdering.
It was necessary to reduce the concentration of acetate to less than 2.5% by weight (less than 0.36% by weight in terms of acetate), but in the present invention, the concentration of acetate in the saponified product may be 2.5% by weight or less, The permissible concentration of acetate in the saponified material used for powdering is significantly higher than in conventional methods.

Therefore, compared to the prior art, the present invention can be used even with a saponified product having a high acetate concentration, and cleaning to reduce acetate in the saponified product can be greatly simplified. This point is also one of the advantages of the present invention. The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples.

Examples 1 to 3 90% saponified product of ethylene-vinyl acetate copolymer with vinyl acetate content of 1% by weight (melt index 21F3s)
Manufactured by Mitsui Polychemical Co., Ltd. Product name: Dumilan D-2
A mixture of the pellets from 19), isopropanol, and water in the proportions shown in Table 1 was placed in an autoclave with a capacity of z and equipped with a stirrer equipped with three six-blade turbine blades, and the mixture was heated from room temperature to 100°C in three powders. The mixture was heated and then stirred for 1 minute at 10°C.

Then, the autoclave was cooled to 50C with stirring after about 1 hour, and when the autoclave was opened, the saponified particles were found dispersed in the liquid. The saponified powder was separated from the liquid by filtering the dispersion and then dried to obtain a spherical saponified powder. Table 1 shows the analysis results of the particle size of the obtained powder. Comparative Examples 1 to 2 In Example 1, the dispersion composition was changed as shown in Table 2, and the stirring speed was changed to 1000 Rpm (stirring blade tip speed 17
The same operation was performed using the same apparatus as in Example 1, except that the temperature was 2n1/min).

When the autoclave was opened after cooling, the saponified material formed into a large lump and adhered around the stirring blade of the autoclave, and was not dispersed in the liquid, so that no powder was obtained. Examples 4 to 5 Ethylene-vinyl acetate copolymer pellets with a vinyl acetate content of 2% (trade name: EVAFLEX, Mitsui Polychemical Co., Ltd.) listed in Table 3 were added to the same device as used in Examples 1 to 3. ), 400 ml of isopropyl alcohol, 800 ml of water, 52 g of sodium hydroxide
was charged, and a saponification reaction was carried out at 150C for 1 hour while stirring at 800 RPM (7).

After the reaction, the mixture was cooled to 50° C. with stirring and the lid of the autoclave was opened to obtain a coarse saponified material having a size of about 100p to 5Tm. After solid-liquid separation by filtration, the wet cake of saponified coarse particles was placed in 1200ml of water at 50°C.
The mixture was washed with gentle stirring for three times to remove sodium acetate, a side reaction product. The sodium acetate concentration in the saponified coarse particles after washing was 1 to 2% by weight. After washing the saponified coarse particles, solid-liquid separation is performed again to separate the liquid, the wet cake containing about 350 g of saponified material is placed in the autoclave again, and a mixed solution of isopropanol and water in the proportions shown in Table 3 is added to the wet cake. I put in 1200m1. The autoclave was heated with stirring to 100°C in about 3 batches and then cooled to 503°C with stirring in about 1 batch. When the autoclave was opened, saponified powder in the form of spherical particles was dispersed in the liquid. The results are shown in Table 3. Example 6 Vinyl acetate content (wt%, ethylene-vinyl acetate copolymer with melt index 33 (trade name: Evaflex-15)
0) 400g and 800ml of isopropanol, 400ml of water
ml, 61.4 g of sodium hydroxide was reacted with 3 powders at 150°C in the same equipment as in Examples 4 and 5, and the degree of saponification was 98.2.
Saponified coarse particles with a melt index of 17.8 were obtained.

This was washed with 1200ml of warm water and the sodium acetate content in the saponified product was reduced to 6. . % by weight to 1.6% by weight. This saponified coarse particle and isopropanol 3
20 ml, toluene 80 ml, and water 800 ml were placed in an autoclave, and 1,200
Powdering operation was performed at a stirring speed of RPM, and spherical powder particles with an average particle diameter of about 100 μm were obtained. Comparative Example 3 In an autoclave with an internal capacity of 250 mt, 90% saponified pellets of ethylene-vinyl acetate copolymer [Melt Index 21 & Product name: Dumilan D-219s manufactured by Mitsui Polychemical Co., Ltd.] Kitamosui 190 m1 and a surfactant ( 1.2 g of sodium laurylbenzenesulfonate) was added, and the rotation speed was 2000 RPM (stirring blade tip speed 30
The mixture was heated to 100C with about 1 powder while stirring at 0 n1/min), and then cooled to 50C with about 1 powder.

When I opened the autoclave, there were 2 to 5 saponified substances. The particles were flat and no spherical powder was obtained.
Examples 7 to 8, Comparative Example 4 50 g of 90% saponified ethylene-vinyl acetate copolymer [Melt Index 21 & trade name: Dumilan D-219s manufactured by Mitsui Polychemical Co., Ltd.] and 100 mL of water were placed in an autoclave with a capacity of 250 ml. 50 ml of the alcohol shown in Table 4 was added thereto, heated to 100° C. for about 15 minutes under stirring at a rotational speed of 2000 RPM (stirring blade tip speed 300 n1/min), and then cooled to 50° C. for about 1 min.

Claims (1)

[Claims] 1 Ethylene containing 10 to 50% by weight of vinyl acetate
The saponified product of vinyl acetate copolymer is mainly composed of an alcohol having 2 to 4 carbon atoms and water, and the mixing ratio of water to alcohol is 40 to 200 parts by volume of alcohol to 100 parts by volume of alcohol.
Dispersing the saponified copolymer in the mixed liquid in the range of 0 parts by volume by vigorously stirring at a temperature higher than the softening point of the saponified copolymer, and then cooling the dispersion. A method for producing a saponified ethylene-vinyl acetate copolymer powder, characterized by: