JP3194614B2 - Aqueous dispersion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous dispersion of an ethylene-vinyl alcohol copolymer.

[0002]

2. Description of the Related Art An ethylene-vinyl ester copolymer, particularly an ethylene-vinyl alcohol copolymer obtained by saponifying an ethylene-vinyl acetate copolymer (abbreviated as EVOH).
Because of its excellent gas barrier properties against oxygen and the like and resistance to oils and chemicals, it has been attracting attention as a material for protective coatings for packaging materials, plastic molded products, metal surfaces, paper, wood, and the like.

[0003] In particular, high gas barrier properties are required for films, sheets, laminates, hollow containers, and the like for food packaging, which require prevention of oxidation of contents or retention of aroma. Further, a coating material for preventing bleeding of a plasticizer is required for a PVC wallpaper, a PVC leather, a sheet and the like made of soft vinyl chloride. Therefore, it is widely practiced to provide EVOH having excellent gas barrier properties, fragrance retention properties, and oil / chemical resistance in the inner layer, the outer layer, or the intermediate layer to satisfy these required performances to a high degree.

In general, as a method for forming an EVOH layer, a method by melt extrusion or injection molding, a method of laminating an EVOH film, and the like are widely practiced.
On the other hand, a method has been proposed in which an EVOH solution or an aqueous dispersion is applied and dried. This method is attracting attention because a relatively thin film can be formed and a film having a complicated shape such as a hollow container can be easily formed.

However, in the method of applying an EVOH solution, it is basically difficult to use a solution having a high concentration because of viscosity, and the solvent is an organic solvent such as dimethyl sulfoxide or a mixed solvent of a large amount of alcohol and water. During the formation process, there is a problem that the working environment is deteriorated due to the volatilization of the organic solvent, and a device for recovering the organic solvent is required, which is economically disadvantageous. On the other hand, the method of applying the EVOH aqueous dispersion is a solvent based on water, and is considered to be advantageous from the viewpoint of the working environment and economy, and is expected.

[0006] The aqueous emulsified dispersion of EVOH is obtained by emulsifying and dispersing ordinary EVOH in the presence of an ordinary surfactant or an ordinary polymer protective colloid, for example, polyethylene oxide, carboxymethylcellulose, hydroxyethylcellulose, polyvinyl alcohol and the like. It is known in JP-A-54-101844 and JP-A-56-61430. However, according to studies by the present inventors, the aqueous emulsion dispersion of EVOH obtained by these known methods has insufficient dispersion stability and is difficult to be practically used for coating.

JP-A-54-101844 discloses a so-called randomly copolymerized random copolymer obtained by terpolymerizing a vinyl monomer such as acrylic acid or acrylamide with ethylene-vinyl acetate and saponifying it. Combined EVO
H itself is shown to be dispersed using a conventional surfactant as a dispersion stabilizer.

However, according to the study of the present inventors, no improvement in emulsion dispersion stability was observed with a simple ternary random copolymerized EVOH, and a practical emulsion dispersion was not obtained. In the case where acrylic acid having an ionic group is copolymerized, the emulsion dispersion stability is improved by the ionic group, but because the weak ionic group is randomly contained, unless the content is increased Dispersion stability cannot be sufficiently achieved, and the structure of the EVOH is greatly disturbed, and the barrier properties of the formed film are lowered, which is not practical.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide an aqueous dispersion of an EVOH-based aqueous dispersion, particularly an aqueous emulsified dispersion, which has remarkably improved stability during storage or use and has excellent dispersion stability.

[0010]

The above objects can be attained by self-emulsifying and dispersing using a specific ion-modified EVOH copolymer into which a sulfonate anionic group is randomly introduced as EVOH.

The most important feature of the present invention is that the EVOH aqueous emulsion dispersion is remarkably improved in storage or use stability and excellent in dispersion stability. It has excellent dispersion stability, and there is almost no significant increase in particle size due to aggregation of particles during storage or use.Thus, it is possible to apply a thinner uniform film with good film forming properties, and the dried film has excellent barrier properties. is there.

The ion-modified EVOH used in the present invention has a sulfonate anionic group of 0.05 to 10 mol%, and has an ethylene content of 15 to 65 mol% which is randomly modified.
A saponified ethylene-vinyl ester copolymer having a degree of saponification of 90 mol% or more, including those that are insoluble in water at ordinary temperature (hereinafter abbreviated as ion-modified EVOH). Absent. The term "insoluble in water at normal temperature" refers to a substance having a concentration of 1% and an insoluble content of 50% or more when dissolved in water at 30 ° C for 1 day. The insoluble content is preferably higher, more preferably 80% or more, more preferably 90% or more.

The sulfonic acid anionic group includes groups which exhibit sulfonic acid anionicity in water, such as sulfonic acid, sulfonic acid salt, sulfate ester and sulfate ester base, and these acids and bases are simultaneously contained. Is also good.
Sulfonic acid or the base is preferable because the dispersion stabilizing effect is excellent.

The content of the ionic group must be 0.05 to 10 mol% with respect to the EVOH component unit in the ion-modified EVOH from the viewpoint of the dispersion stabilizing effect, and must be in a range insoluble in water at ordinary temperature. More preferably, the content is 0.3 to 7 mol%, particularly 0.5 to 5 mol%. 0.05 mol%
If it is less than 10, the dispersion stability is low, and if it exceeds 10 mol%, the water resistance of the film obtained by applying and drying the aqueous emulsion dispersion is poor and cannot be used. The ion-modified EVOH may contain another unit containing no ionic group as long as the dispersion stabilizing effect is not significantly impaired.

The composition of the EVOH component in the ion-modified EVOH must have an ethylene content of 15 to 65 mol% and a saponification degree of 90 mol% (the saponification degree in the present invention indicates the saponification degree of the vinyl ester unit). . If the ethylene content is less than 15 mol%, the stability of the aqueous emulsified dispersion will be poor, and if it exceeds 65 mol%, the gas barrier properties will be poor and unsuitable. The ethylene content is preferably from 20 to 55 mol% from the viewpoint of the stability and gas barrier properties of the aqueous emulsion dispersion.

If the degree of saponification is less than 90 mol%, the gas barrier property of the polymer becomes insufficient, so that 90 mol%
You need to use the above. The higher the degree of saponification, the higher the barrier property, and desirably 95 mol% or more, and more preferably 97 mol% or more.

The degree of polymerization of the EVOH is selected according to the application, but an extremely low one is usually 400 or more, preferably 700 or more, because the strength of the formed film is low and is not preferred. The higher the degree of polymerization, the more advantageous it is to apply and use as an aqueous emulsified dispersion, and usually up to about 5,000. The degree of polymerization is measured by a viscosity method in the same manner as for ordinary EVOH, except that the effect of ion repulsion is prevented by adding a salt. If necessary, a copolymerizable monomer other than the ethylene unit, vinyl ester unit and sulfonic acid anionic group unit may be copolymerized in an amount of 5 mol% or less. Where ion modified EV
The polymerization degree of OH is determined from the intrinsic viscosity measured at 30 ° C. in a water / phenol-based mixed solvent (weight ratio 15/85) containing 1 mol / l ammonium thiocyanate.

The vinyl ester can be copolymerized with ethylene such as vinyl formate, vinyl acetate, vinyl propionate, vinyl benzoate, vinyl trifluoroacetate, vinyl pivalate, and the like. Convertible monomers can be used, but vinyl acetate is particularly preferred.

The structure of the ion-modified EVOH is not particularly limited as long as it has a so-called randomly introduced sulfonate anionic group, and those produced by various methods can be used.

For example, a method in which a monomer containing a sulfonic acid anionic group is radically copolymerized with ethylene and a vinyl ester, and then the vinyl ester unit in the obtained copolymer is saponified to be converted into a vinyl alcohol unit. A method in which a sulfonic acid anionic group-containing component is added to a polymer by an addition reaction, or ethylene-
After the addition reaction of the sulfonic acid anionic group-containing component to the vinyl ester copolymer, a method of saponifying a vinyl ester unit in the copolymer to convert the vinyl ester unit into a vinyl alcohol unit may, for example, be mentioned. Methods such as polymerization, saponification and addition reaction can be carried out by known methods.

As the sulfonic acid anionic group-containing monomer copolymerized with ethylene and vinyl ester, a monomer capable of radical homopolymerization or radical copolymerization having a sulfonic acid anionic group or a group convertible to a sulfonic acid anionic group is used. it can. An example is shown below.

O Sulfonate anionic group-containing monomer For example, acrylamide type sulfonate monomer such as sodium 2-acrylamido-2-methylpropane sulfonate, styrene type sulfonate monomer such as potassium styrene sulfonate, sodium allyl sulfonate Allyl sulfonate monomers such as the above, vinyl sulfonates such as sodium vinyl sulfonate, ammonium salts thereof, and acid monomers thereof. Esters of these sulfonic acids can also be used by converting the esters into their salts or acids after polymerization.

These monomers can be used alone or in combination. Copolymerization with other monomers is also possible as long as the dispersion stabilizing effect is not impaired.

Examples of the addition reaction to EVOH include a Michael addition reaction of a vinyl monomer containing a sulfonic acid anionic group to its hydroxyl group, or an acetalization or ketalization with an aldehyde or ketone containing a sulfonic acid anionic group, or a sulfonate anion. Addition of a group-containing epoxy compound, esterification with sulfuric acid and the like can be mentioned.

The method of emulsifying and dispersing the ion-modified EVOH is not limited, and a known method can be used.

For example, a solution of ion-modified EVOH is
The EVOH particles are brought into contact with water, which is a non-solvent for OH, with stirring to reduce the EVOH particles to 3 μm or less, preferably 2 μm or less, and optimally 1 μm or less.
An aqueous emulsified dispersion can be obtained by precipitating as fine particles of m or less and then removing the solvent. Here, the diameter of the fine particles is a number average particle diameter.

The solid concentration of the aqueous emulsified dispersion is appropriately determined depending on the intended use and the like, but it is a feature of the present invention that a highly concentrated and stable dispersion can be obtained. The solid concentration is preferably at least 10% by weight, more preferably at least 15% by weight, and most preferably at least 20% by weight. The upper limit of the solid content concentration is not particularly limited. However, if the concentration is too high, the storage stability of the aqueous dispersion becomes slightly poor. Therefore, it is usually preferably 60% by weight or less, more preferably 50% by weight or less. Optimally, it is at most 40% by weight.

As the solvent, for example, methyl alcohol,
Monohydric alcohols such as ethyl alcohol, propyl alcohol and butyl alcohol, dihydric alcohols such as ethylene glycol and propylene glycol, and trihydric alcohols such as glycerin
Polyhydric alcohols, phenols, phenols such as cresol, ethylenediamine, amines such as trimethylenediamine, dimethylsulfoxide, dimethylacetamide,
N-methylpyrrolidone or the like, or a hydrate thereof may be used alone or in combination of two or more. Particularly preferred solvents are alcohol-water mixed solvents such as water-methyl alcohol, water-normal propyl alcohol, water-isopropyl alcohol and the like.

The organic solvent in the solvent can be removed by an appropriate method such as an evaporation method, an extraction method or a dialysis method. It is desirable that the degree of removal be high, but it is possible to leave a small proportion of the organic solvent in view of economy.

As another method, a method of heating and dissolving ion-modified EVOH in a solvent which dissolves at a high temperature but becomes insoluble at a low temperature, and then cools the solution to precipitate and disperse it as fine particles can be adopted. Thereafter, by replacing the solvent with water, an aqueous emulsified dispersion can be obtained.

As the solvent that dissolves at a high temperature and precipitates at a low temperature, the above-mentioned solvents alone or a mixed solvent with water can be used.

As still another method, ion-modified EVO
A method of contacting a solution of H with a non-solvent or cooling and filtering the particles precipitated and dispersed and dispersing the particles in water is also possible.

In some cases, the ion-modified EVOH can be directly dispersed in water. For example, ion modified E
It is also possible to emulsify the dispersion by mixing VOH with water and stirring with a stirrer or a ball mill. However, there is a problem that a long time is required for dispersion.

In the present invention, a suitable aqueous dispersion is prepared by using an ion-modified EVOH as a solvent and stirring at a temperature of 5 ° C.
Dissolve at 0-75 ° C to form a solution, then cool (temperature -1
0-30 ° C.) to precipitate and disperse (emulsify) the EVOH particles, then remove the alcohol under reduced pressure (temperature 10-30 ° C., pressure 10-150 mmHg), and further remove a desired amount of water. As a result, there is a method of obtaining an aqueous dispersion having a desired solid content concentration.

The aqueous dispersion of the present invention contains an alkali metal compound such as sodium hydroxide, sodium chloride, sodium acetate, sodium sulfate, sodium nitrate, calcium hydroxide, calcium chloride, calcium acetate, calcium sulfate for the purpose of decreasing the viscosity. , Calcium nitrate, alkaline earth metal compounds such as
0.5% by weight (based on the polymer) may be added. The formulation is
It may be before or after the EVOH is made into fine particles.

The aqueous emulsified dispersion obtained by the method of the present invention is useful as a coating material for forming a film having excellent gas barrier properties. For example, it can be used in a wide range of applications such as fine powder by spray drying and binders and vehicles of paints and adhesives.

If necessary, ordinary surfactants and protective colloids can be added to the aqueous emulsion dispersion of the present invention as long as the object of the present invention is not hindered. Further, an aqueous dispersion of another resin, a stabilizer against light or heat, a pigment, a lubricant, a fungicide, a film-forming aid, and the like can be added.

As described above, according to the present invention, an aqueous dispersion having a high solid content and excellent in stability during storage or use can be obtained, and since it is aqueous, there is no problem such as environmental pollution. It has an advantage, and can be applied to various substrate surfaces as a useful coating agent capable of forming a thin film having excellent gas barrier properties, fragrance retention properties, and oil and chemical resistance by coating and drying. Here, the base material is, in particular, a thermoplastic resin ｛polyolefin (polyethylene, polypropylene, etc.), polyester, polyamide, polyvinyl chloride, polyvinylidene chloride, polycarbonate, polystyrene, polyvinyl alcohol, vinyl acetate resin (ethylene-vinyl acetate copolymer, etc.) ), Etc. (films, sheets, cups, bottles, etc.) are suitable, and fiber aggregates (paper, nonwoven fabric, woven fabric, fibrous casing, etc.), inorganic substances (cement, etc.), Metal, polyvinyl chloride resin wallpaper, photographic paper and the like are also included.

The method of applying the aqueous dispersion of the present invention to the surface of a substrate includes discharging from a casting head,
Any means such as roll coating, doctor roll coating, doctor knife coating, curtain flow coating, spraying, dipping, and brushing are exemplified. Examples of a method of drying and heat treating the substrate coated in this manner include a dry heat treatment method, for example, an infrared irradiation method and a hot air drying method. These infrared irradiation, hot air drying and the like may be used alone or in combination. Also dry
The temperature of the heat treatment is preferably 30 to 180 ° C,
The lower limit is preferably 50 ° C. or higher, and optimally 80 ° C.
° C or higher. The drying and heat treatment time is preferably from 5 seconds to 10 minutes, more preferably from 1 to 5 minutes. During drying and heat treatment, conditions such as increasing and decreasing the temperature, for example, treating at a low temperature at first and then gradually increasing the temperature are free. By performing such drying and heat treatment, a film having excellent gas barrier properties is formed on the substrate surface. Further, the thickness of the film after coating, drying and heat treatment of the aqueous dispersion of the present invention is preferably 0.5 to 15 μm, more preferably 1 to 10 μm, and most preferably 2 to 6 μm.
m.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the examples. Parts in Examples are parts by weight unless otherwise specified. The solvent composition is also shown by weight ratio.

[0041]

【Example】

Example 1 Sodium 2-acrylamido-2-methylpropanesulfonate unit was randomly copolymerized with 0.5 mol% of an EVOH component, ethylene content was 34 mol%, and saponification degree was 9
50 parts of a sulfonic acid anion-modified EVOH having a polymerization degree of 1100 and a polymerization degree of 1100 (97% of a water-insoluble component) were added to and mixed with 600 parts of a mixed solvent of water / methyl alcohol = 30/70, and dissolved by heating at 65 ° C.

When this solution was cooled to 10 ° C. with stirring, particles were precipitated and stably dispersed to obtain a uniform dispersion. The average particle size was 0.6 μm. Then, the dispersion was evaporated under reduced pressure at 20 ° C. with stirring to remove methyl alcohol. In the process of distilling off methyl alcohol, particles are hardly aggregated and stable, with an average particle diameter of 0.6 μm,
An aqueous emulsified dispersion having a solid content of 27% was obtained. The storage stability was also good, and almost no aggregation was observed in a storage test at 40 ° C. for 10 days.

Then, this aqueous emulsified dispersion was applied to the primer-treated surface of a biaxially stretched polyethylene terephthalate film (film thickness: 20 μm) and dried at 110 ° C. for 5 minutes.
When the oxygen barrier property of the film (EVOH thickness 3 μm) was measured at 20 ° C. and 0% RH, the oxygen permeation was 3.8 cc / m ² · day · atm, indicating good performance as a food packaging material. Was. (Hereinafter, the measurement conditions and units for the amount of oxygen permeation are the same.)

On the other hand, for comparison, when dispersion was carried out using unmodified ordinary EVOH having the same ethylene content, saponification degree and polymerization degree in place of the sulfonic acid anion-modified EVOH (Comparative Example 1), Saponification as a nonionic surfactant nonylphenyl ether ethylene oxide adduct known as a dispersant in EVOH (Comparative Example 2), sodium dodecylbenzenesulfonate as anionic surfactant (Comparative Example 3), or polymer protective colloid Example 1 was a partially saponified polyvinyl alcohol having a degree of polymerization of 80 mol% and a degree of polymerization of 600 (Comparative Example 4).
Dispersion was attempted under the same conditions as described above, but in each case, the heated and dissolved solution was cooled with stirring and aggregated at the stage where particles were precipitated, and no dispersion was obtained.

Further, acrylic acid, ethylene and vinyl acetate are randomly terpolymerized, and the copolymer is saponified to obtain
EVO with acrylic acid content 2.5 mol%, ethylene content 33 mol%, saponification degree 99.6 mol%, polymerization degree 800
H was obtained. Sodium dodecylbenzenesulfonate was used at 1% by weight based on the EVOH;
Self-dispersed under the same conditions as described above, and the methyl alcohol was removed by evaporation to obtain an aqueous emulsified dispersion having an average particle diameter of 1.0 μm and a solid content of 20%. After standing at 40 ° C. for 10 days, aggregation was slightly observed. This aqueous emulsified dispersion was applied and dried in the same manner as in Example 1 to obtain a film (EVOH layer thickness 3).
The measured amount of oxygen permeation (μm) was 14.
(Comparative Example 5)

Thus, it can be seen that the introduction of the sulfonic acid anionic group of the present invention significantly improves the emulsion dispersion stability of EVOH in water, enables self-dispersion, and provides a stable aqueous emulsion dispersion.

EXAMPLE 2 1.2 mol% of potassium 2-acrylamido-2-methylpropanesulfonate was randomly copolymerized with respect to the EVOH component. The ethylene content was 48 mol%, and the saponification degree was 99.2.
50 parts by mol of ion-modified EVOH (water-insoluble content: 91%) having a degree of polymerization of 800 and water / isopropyl alcohol = 30
The mixture was mixed with 600 parts of a / 70 mixed solvent and heated at 70 ° C. with stirring.

Next, the solution was cooled to 5 ° C. with stirring to obtain a stable dispersion having a particle diameter of 0.7 μm. This dispersion was evaporated at 25 ° C. under reduced pressure to remove isopropyl alcohol, thereby obtaining a stable aqueous emulsion dispersion having a solid content of 23% and an average particle diameter of 0.7 μm.

Example 3 The sodium allyl sulfonate was added to the EVOH component at a concentration of 0.1%.
6 mole% ethylene content randomly copolymerized 28
Mol%, a saponification degree of 99.7 mol%, and a polymerization degree of 600, 50 parts of anion-modified EVOH (water-insoluble content: 93%) were mixed with water /
Isopropyl alcohol = 40/60 mixed solvent 500
And heated and melted at 75 ° C. This solution was added dropwise to 200 parts of a mixed solvent of water / = isopropyl alcohol 20/80 maintained at 20 ° C. while stirring with a high-speed stirrer. As a result, particles were precipitated and dispersed to obtain a stable dispersion. The average particle size was 0.9 μm.

Next, this dispersion was evaporated at 20 ° C. under reduced pressure to remove isopropyl alcohol, thereby obtaining an aqueous dispersion having a solid content of 20%. The average particle size of this aqueous dispersion is 0.9.
At μm, there is almost no particle enlargement in the vacuum evaporation process,
A stable aqueous emulsion dispersion was obtained. A film obtained by coating and drying in the same manner as in Example 1 (EVOH layer thickness 3
μm) was 6.5, which was good.

Example 4 Sodium 2-methacrylamido-2-memethylpropanesulfonate was introduced at 1 mol% with respect to the EVOH component by a Michael addition reaction of EVOH to a hydroxyl group. The ethylene content was 34 mol%, and the saponification degree was 99.5. Mol%, degree of polymerization 10
100 parts of EVOH (water insoluble content: 95%) were mixed with 800 parts of a mixed solvent of ethyl alcohol / water = 50/50, and dissolved by heating at 70 ° C.

By dispersing and distilling off ethyl alcohol in the same manner as in Example 1, a stable aqueous emulsion dispersion having a solid content of 22% and a particle diameter of 0.8 μm was obtained.

Example 5 A hydroxyl group of EVOH was subjected to an acetalization reaction with sodium benzaldehyde-p-sulfonate to introduce 0.8 mol% of the sulfonic acid anionic group with respect to the EVOH component. The ethylene content was 38 mol%, and the saponification was carried out. The dispersion was carried out under the same conditions as in Example 1 except that an anion-modified EVOH having a degree of polymerization of 99.5 mol% and a polymerization degree of 1100 (water insoluble content: 94%) was used, and methyl alcohol was distilled off. Thus, an aqueous emulsion dispersion having an average particle diameter of 0.9 μm was obtained. Although some aggregation of particles was recognized in the dispersion, the oxygen permeation amount of the film (EVOH layer thickness 5 μm) applied and dried under the same conditions as in Example 1 was 5.1, which was good.

[0054]

As described above, the aqueous emulsified dispersion self-emulsified and dispersed using the ion-modified EVOH of the present invention is an aqueous dispersion having a high solid content and excellent stability during storage or use. Also, since it is water-based, it has the advantage of not causing problems such as environmental pollution, and can be used as a useful coating agent capable of forming a thin film showing excellent gas barrier properties, fragrance retention properties, and oil and chemical resistance by coating and drying. Is of high industrial value.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Li, Hiroto 1621 Sazu, Kurashiki-shi, Okayama Pref. Kuraray Co., Ltd. Examiner, Shoko Mitani Field (Int.Cl. ⁷ , DB name) C08L 23/26 C08L 29/04 C09D 123/26 C09D 129/04 C08F 8/36

Claims (2)

(57) [Claims] An aqueous solution of an ethylene-vinyl alcohol copolymer having an ethylene content of 15 to 65 mol%, wherein 0.05 to 10 mol% of a sulfonic acid anionic group is randomly introduced and modified at room temperature and which is insoluble in water at ordinary temperature. Dispersion. 2. An aqueous dispersion according to claim 1 applied to a substrate.
A coating material made of