JPH05209059A - Powder of saponified ethylene-vinyl acetate copolymer and its use - Google Patents

Abstract

(57) [Summary] [Objective] An aqueous dispersion of a saponified ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVOH) which has a low viscosity and is excellent in leaving stability even in a high concentration range of the dispersion. Provide EVOH powder to give. [Structure] A step of heating and dissolving EVOH having an ethylene content of 20 to 60 mol% and a saponification degree of 90 mol% or more in a mixed solvent of an alcohol having 1 to 4 carbon atoms and water, cooling the obtained solution to obtain the EVOH. A step of precipitating, a step of obtaining a stable dispersion by adding an aliphatic ketone to a solution containing the precipitated saponified product, a step of drying the resulting dispersion,
EVOH powder manufactured from.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a saponified ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVOH) powder obtained by a special production method and its use.

[0002]

2. Description of the Related Art Generally, it is known that a film produced from EVOH as a raw material has excellent transparency and luster, and also has excellent chemical resistance and gas barrier property. It has excellent properties compared to other resin films and is very useful as a food packaging material.

As a method of using the EVOH, EVOH is used.
Is used to form a molded product such as a bottle or a film, and a method of coating a molded product made of another resin with an EVOH liquid to improve the physical properties of the molded product. Among these, there are advantages and disadvantages in the usage mode depending on the purpose and application, but in the case of the coating method, the EVOH film can be easily formed even on a molded product having a complicated shape, and the film thickness is thin. Since a film can be formed, there are advantages such as being economically advantageous. However, when EVOH is used as a solution, the viscosity of the solution increases remarkably as the concentration of EVOH increases, causing problems in coatability.
Therefore, in reality, it is necessary to use a dilute solution.

As a solution to this problem, attempts have been made to utilize a dispersion liquid of EVOH as a coating liquid. As a method for producing such a dispersion, a water-organic solvent homogeneous solution of EVOH is cooled to precipitate particles, and then the organic solvent in the precipitation dispersion is removed, or EVOH powder is directly dispersed in an aqueous medium. The method of making it known is known. The former method has the merit that a stable dispersion liquid can be obtained, but it is very inconvenient because water must be handled during storage and transportation.

On the other hand, the latter method is very useful in market distribution without the above inconvenience. EVOH originally manufactured industrially is in powder form. However, if this is directly dispersed in water, it lacks stability, so it is necessary to prepare a redispersible powder. Regarding the conventional pulverization of EVOH, a method is known in which EVOH is dissolved in a solvent and resin particles precipitated by mixing EVOH such as acetone with a phasic solvent or by lowering the temperature are dried (JP-A-2-8230). Has been.

[0006]

However, as a result of the detailed study of the technique disclosed in the above-mentioned publication by the present inventors, the following problems were found. The EVOH powder (particles) obtained by the above method is suitable for use in melt molding, powder coating, etc., which is used without passing through water, but is used as an EVOH aqueous dispersion in which the powder is dispersed in water. There are many problems. That is, although the dispersion has a relatively low viscosity at a high concentration, it has a drawback that the standing stability, the transparency of the formed film and the oxygen barrier property are inferior to those of the conventional EVOH solution.

The present invention has been made to solve the above-mentioned drawbacks, and its purpose is to prepare EVOH in a water-dispersed state.
An object of the present invention is to provide a powder of EVOH and an aqueous dispersion thereof, which has a low viscosity even in a high concentration region, is excellent in leaving stability, and can provide a film having excellent transparency and oxygen barrier property.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve such problems, and as a result, during the EVOH powder production process, an EVOH-solvent such as acetone is added to the EVOH solution as a starting material. Instead of EVOH solution, an EVOH dispersion liquid that has low viscosity and excellent leaving stability by adding EVOH solvent in the step after the EVOH particles are once precipitated and is easy to apply and can form a uniform coating film. The inventors have found that the following is obtained and completed the present invention.

That is, the above objects are as follows: (1) Ethylene content 20 to 60 mol%, saponification degree 90
A mol% or more saponified ethylene-vinyl acetate copolymer is heated and dissolved in a mixed solvent of alcohol having 1 to 4 carbon atoms and water to obtain a solution having a saponified product concentration of 1% by weight or more and less than 20% by weight. Step (2) Step of cooling the obtained solution to precipitate the saponified product (3) Step of adding an aliphatic ketone to the precipitated solution containing the saponified product under stirring to obtain a stable dispersion liquid ( 4) It is achieved by being manufactured by the step of drying the above dispersion liquid so that the EVOH content is 50% by weight or more. The present invention will be described in detail below.

The EVOH used in the present invention is a copolymerizable monomer such as propylene, butylene, acrylic acid, methacrylic acid, acrylic acid ester, methacrylic acid ester, maleic anhydride in addition to ethylene and vinyl acetate components. Also, a terpolymer with a third component such as acrylic acid amide can be used, and the amount thereof is preferably 10 mol% or less.

The ethylene content in EVOH is 20-6.
It is essential that the content is 0 mol%, and if the content is less than 20 mol%, the water resistance of the coating film produced from the aqueous dispersion of the present invention is lowered, so that the gas barrier property under high humidity is also lowered. On the other hand, when it exceeds 60 mol%, the oxygen barrier property of the above-mentioned coating is deteriorated. The preferred ethylene content is 25-
55 mol%. 90 degree of saponification of EVOH
It is essential that the content is at least mol%, and if the saponification degree is less than 90 mol%, the oxygen barrier property of the coating film is insufficient, and it is not suitable for the use of the present invention. The preferable saponification degree range is 96.
It is at least mol%. The steps will be sequentially described below.

Step (1) The alcohol used in the present invention has 1 to 4 carbon atoms.
Of methyl alcohol, ethyl alcohol,
n-propyl alcohol, iso-propyl alcohol,
n-butyl alcohol, iso-butyl alcohol, t-
One or more mixed alcohols such as butyl alcohol may be mentioned, but industrially, methyl alcohol and iso-propyl alcohol are preferable from the viewpoint of cost and removability. The mixing ratio of water and alcohol is not particularly limited, but water / alcohol = 9/1 to 1/9 by weight ratio is preferable, and water / alcohol = 7/3 to 3/7 is more preferable.
Is. If the mixing ratio is out of this range, the solubility of EVOH decreases, so that it is difficult to prepare a homogeneous EVOH solution, and a dispersion of good quality cannot be obtained.

The preferable range of the melting temperature is 50 to 120 ° C.
The range is. EVO for water-alcohol mixed solvent
The amount of H can be added up to the solubility at a temperature of 50 to 120 ° C. The EVOH concentration at this time is 1% by weight or more and less than 20% by weight, which is in consideration of the solubility in a water-alcohol mixed solvent and the stability of the solution, and is preferably 1 to 15% by weight. The EVOH solution is produced according to known procedures. That is, EVOH is mixed with the above water-alcohol mixed solvent, and mixed and stirred under conditions of a rotation speed of 200 to 1000 rpm using a stirrer equipped with stirring blades such as a turbine type and a ribbon type under heating at 50 to 120 ° C. To prepare a solution of EVOH.

Step (2) The EVOH solution obtained in Step (1) is cooled to obtain EVOH.
Precipitate fine particles to form a dispersion. That is, step (1)
By lowering the temperature of the EVOH solution (above the critical melting temperature of EVOH) to below the critical melting temperature of EVOH, EVOH fine particles are deposited by utilizing the difference in solubility due to the temperature difference. The cooling temperature of this process is EVOH
Considering the precipitation effect of fine particles, it is usually preferable to set the temperature to 40 ° C. or lower.

Then, if necessary, the solvent in the EVOH dispersion is removed and the EVOH dispersion is concentrated. The concentration method in this case may be a well-known method, such as a centrifugal separation method (aggregation).
Examples of the method include a filtration method, a decompression method, a heating method, and the like, and the centrifugation method is most preferable because it can efficiently concentrate in a short time. The EVOH concentration after the concentration is preferably 20% by weight or more, and if it is less than 20% by weight, it takes time to remove alcohol in the step (4). Furthermore, the preferred range is 20-35.
% By weight.

Step (3) Aliphatic ketone is added to the EVOH dispersion obtained in step (2) to improve the dispersion stability of EVOH fine particles in the dispersion. That is, the aliphatic ketone remains as an anticoagulant,
This prevents water-alcohol swelling of the EVOH fine particles and makes it possible to produce an EVOH dispersion having stable dispersibility. Acetone, methyl ethyl ketone, or the like is preferably used as the aliphatic ketone used in this step. The amount used is 100 to 20 with respect to 100 parts by weight of EVOH.
00 parts by weight is preferable, and more preferably 250 to 150.
0 parts by weight. When the amount of the aliphatic ketone added exceeds the above range, it takes time to remove the solvent in the step (4), and when it is less, the stability of the EVOH dispersion liquid deteriorates. The aliphatic ketone may be added to the EVOH dispersion with stirring, and any stirrer may be used.

Step (4) Solvents such as aliphatic ketone, alcohol and water are removed from the EVOH dispersion liquid described above to adjust the content of EVOH to 50% by weight or more to obtain EVOH powder. That is, while stirring the EVOH dispersion under reduced pressure (30 to 100 mmHg) or / and under heating (40 to 80 ° C.), all or part of the aliphatic ketone, alcohol and water in the dispersion is removed. The above EVOH powder is obtained.

Thus, the EVOH powder of the present invention is obtained. The powder has excellent storage stability and can be stored for a long period of time without causing gelation or blocking. Further, such a powder can be used as it is in a heat-melted state and used for molding or coating, but by dispersing the powder in water, good EVO
An H aqueous dispersion can be obtained. That is, the powder can be uniformly dispersed in water with stirring. This is a so-called redispersion type EVOH powder. More specifically, water and, if necessary, a surfactant, a protective colloid agent, an antiblocking agent for preventing sticking at the time of forming a film, a film-forming aid, etc. are added to the above powder, and a high speed mixer, a homogenizer or the like is forced. By a known method using a high speed stirrer, EVO
H powder is emulsified and dispersed.

Usual anionic and nonionic surfactants are used as the surface active agent, and specific examples of the anionic surface active agent include sodium vinyl sulfonate, sodium dodecylbenzene sulfonate, sodium lauryl sulfonate, and the like. Examples of the nonionic type include polyoxyethylene type polyoxyethylene lauryl ether, polyoxyethylene nonylphenol ether, polyoxyethylene sorbitan monooleate, polyoxypropylene type and polyoxyethylene-polyoxypropylene copolymer type. The amount of the surfactant used is preferably in the range of 0.1 to 10 parts by weight with respect to 100 parts by weight of EVOH as an amount that can be emulsified and dispersed and does not impair the characteristics of the coating film of the EVOH dispersion.

As the protective colloid agent, polyvinyl alcohol, partially saponified polyvinyl alcohol, polyvinyl alcohol derivative, modified polyvinyl alcohol, cellulose derivative such as hydroxyethyl cellulose and hydroxypropyl cellulose, sodium polyacrylate,
Examples thereof include polyacrylic acid amide and polyvinylpyrrolidone. The amount used is preferably in the range of 0.1 to 10 parts by weight based on 100 parts by weight of EVOH for the same reason as for the surfactant. 1-2 for surfactants and protective colloid agents
It is preferably added as a 0% by weight aqueous solution.

Further, examples of the anti-blocking agent include inorganic powders such as silica and talc, and examples of the film forming aid include polyhydric alcohols such as ethylene glycol, propylene glycol and glycerin. The amount used is EV
The inorganic powder is appropriately selected from the range of 0.01 to 10 parts by weight and the film-forming auxiliary is selected from the range of 5 to 100 parts by weight with respect to 100 parts by weight of OH. These surfactants, protective colloid agents, antiblocking agents, etc. are not necessarily used when redispersing the powder in water, but may be optionally added at the stage of the production step (2) or step (3) of the present invention. It is also possible to set it.

Thus, an EVOH aqueous dispersion using the EVOH powder of the present invention is obtained. The dispersion is E
It is commercialized as an aqueous dispersion having a VOH concentration of 10 to 40% by weight. Thus, the obtained aqueous dispersion has a low Brookfield viscosity of 5 to 1000 (cps / 20 ° C.) even when the EVOH concentration is as high as 10 to 40% by weight, and is extremely excellent in coatability. There is. Moreover, even if the dispersion is stored or transported for a long period of time, it is thickened, gelled,
There is no trouble such as coagulation and it is very stable.

Films, sheets, and
Known methods such as gravure, Mayer bar, reverse roll, dip, and spray are used for coating molded articles such as tubes, pipes and bottles. At this time, the coat film thickness is practically about 1 to 10 μm. Films, sheets, tubes, pipes, pots and the like coated with the dispersion liquid of the present invention are useful for packaging foods, electrical parts, machine parts and the like, or for heating pipes, wallpaper and the like.

[0024]

[Operation] According to the present invention, when EVOH powder is produced from a water-alcohol solution of EVOH, a uniform solvent is added to the EVOH solution in the step after precipitation of the particles to form a uniform EVOH particle. In the state of EVOH aqueous dispersion obtained by dispersing the powder in water, it is possible to obtain a powder having a low viscosity and excellent stability even at a high concentration, and to easily coat and form a uniform film.
An aqueous dispersion of VOH can be obtained.

[0025]

EXAMPLES The present invention will be specifically described below with reference to examples. In the examples, "parts" and "%" mean weight basis unless otherwise specified. Example 1 Step (1) 60 parts of iso-propyl alcohol and 30 parts of water were added to 10 parts of EVOH having an ethylene content of 38 mol% and a saponification degree of 99.5 mol%, and the mixture was rotated by a stirrer of a turbine type stirring blade. Mixing and stirring were carried out for about 2 hours under heating at several 500 rpm and 80 ° C. to prepare a 10% EVOH water-alcohol solution.

Step (2) The EVOH solution of step (1) was allowed to stand in a thermostat at 5 ° C. for 24 hours to precipitate EVOH fine particles to obtain a fine particle dispersion liquid. After returning the dispersion liquid to room temperature, it was transferred to a centrifuge and centrifuged for 30 minutes at a rotation speed of 7,000 rpm, and then the supernatant liquid was removed to obtain 40 parts of 25% EVOH concentrated liquid. Step (3) Next, 50 parts of acetone was added to the concentrated liquid, and the mixture was stirred for about 15 minutes with the same stirrer as in the step (1) to obtain a stable EVOH dispersion liquid.

Step (4) The EVOH dispersion liquid obtained in the step (3) was transferred to an evaporator, and while being heated to 60 ° C., the pressure was gradually reduced to 30 mm.
The solvent in the dispersion was dried and removed with Hg for about 2 hours to remove EVO.
The H content was 70%. Volatile content 30%, average particle size 1
μ EVOH powder was obtained. The following test was conducted to evaluate the redispersion liquid of the obtained EVOH powder. Water 69
30 parts of the EVOH powder obtained in the step (4) was gradually dispersed into the above parts with stirring, 1 part of a surfactant (sodium lauryl sulfate) was further added, and the mixture was thoroughly forcibly stirred to obtain 21% EV.
An OH aqueous dispersion was obtained.

Examples 2 to 4 EVOH powders in Table 1 and EVOH aqueous dispersions in Table 2 were obtained by the same steps as in Example 1 using the EVOH water-alcohol solution shown in Table 1. However, in Example 2, methyl ethyl ketone was used as the aliphatic ketone instead of acetone, and in Example 2, an antiblocking agent (talc) was used.
Was added in an amount of 0.2 part, and in Example 4, a film-forming aid (propylene glycol) was added in an amount of 5 parts. Further, in step (2) of Example 3, concentration was carried out under reduced pressure and heating (30 mmHg, 40 ° C.).

Comparative Example 1 In step (4) of Example 1, the EVOH content was 40%.
After obtaining the EVOH powder of, a 25% EVOH aqueous dispersion was prepared. Comparative Example 2 In Example 2, the same operation as in Example 2 was performed except that acetone was added in step (1) but no addition was performed in step (3).

Comparative Example 3 Example 4 is the same as Example 4 except that the step (3) is omitted.
The same operation was performed. Table 2 shows the physical properties of the EVOH dispersions obtained in the above Examples and Comparative Examples and the EVOH coatings (4 to 6 μm thick) obtained from the dispersions by the Mayer bar coating method. The drying condition of the coating was 120 ° C. × 5 minutes.

[0031]

[Table 1]

Note) Et; ethylene, MeOH; methanol, i-PrOH; iso-propyl alcohol, n-P
rOH; n-propyl alcohol

[0033]

[Table 2] Table 2

Note) * 1: Measured with a B-type viscometer * 2; 100 ml of 100 ml of the EVOH aqueous dispersion obtained.
The mixture was transferred to a graduated cylinder of No. 2 and allowed to stand at room temperature for 60 minutes, and the amount of the separated transparent liquid was measured. Separately, EVOH aqueous dispersion (10
(0 g was put in a 200 ml beaker) was allowed to stand at room temperature for 24 hours, and then the redispersibility was examined when the mixture was stirred at 60 rpm for 5 minutes.

Stability was evaluated based on the following criteria.

EVOH of the present invention having the physical properties shown in Table 2
The EVOH aqueous dispersion obtained from the powder has a low viscosity even at a high concentration, has good leaving stability, and is also excellent in transparency and oxygen barrier property after film formation.

[0037]

[Effect] The EVOH powder of the present invention produced by cooling the EVOH water-alcohol mixed solution to precipitate EVOH fine particles, then concentrating and then drying, has a low viscosity and is stable upon standing even at a high concentration. It is possible to provide an EVOH aqueous dispersion having excellent properties, and the dispersion has good coatability on various films and molded products. Further, the aqueous dispersion is also excellent in film-forming properties, the resulting coating is also excellent in oxygen barrier properties, has good transparency, and is odorless and harmless, and therefore, for example, food-related containers, It is also useful for packaging.

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Claims (6)

[Claims] (1) Heating an ethylene-vinyl acetate copolymer saponified product having an ethylene content of 20 to 60 mol% and a saponification degree of 90 mol% or more in a mixed solvent of an alcohol having 1 to 4 carbon atoms and water. Step of dissolving to obtain a solution having the saponified product concentration of 1% by weight or more and less than 20% by weight (2) Step of cooling the obtained solution to precipitate the saponified product (3) The deposited saponified product Step of adding an aliphatic ketone to a solution containing it under stirring to obtain a stable dispersion (4) Drying the above dispersion so that the content of the saponified ethylene-vinyl acetate copolymer is 50% by weight or more. Saponified ethylene-vinyl acetate copolymer powder characterized by being produced by combining processes 2. The saponified powder of ethylene-vinyl acetate copolymer according to claim 1, wherein the cooling temperature in the step (2) is 40 ° C. or lower. 3. The ethylene-vinyl acetate copolymer according to claim 1, wherein the mixing ratio of water and alcohol in the step (1) is water / alcohol = 9/1 to 1/9 (weight ratio). Polymer saponified powder 4. The saponified powder of ethylene-vinyl acetate copolymer according to claim 1, which is dried under reduced pressure and / or heating in step (4). 5. A saponified ethylene-vinyl acetate copolymer dispersion, characterized in that the powder of claim 1 is dispersed in water. 6. The saponified ethylene-vinyl acetate copolymer saponified product according to claim 5, wherein the concentration of the saponified ethylene-vinyl acetate copolymer is 10 to 40% by weight.