JP3173740B2 - Saponified ethylene-vinyl acetate copolymer solution and use thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a coating film of a saponified ethylene-vinyl acetate copolymer (hereinafter abbreviated as EVOH) on the surface of various plastics and the like to give a high oxygen barrier property. The present invention relates to an EVOH solution and a coating laminate thereof, which are useful for the following.

[0002]

2. Description of the Related Art A film obtained from EVOH is excellent in transparency, oxygen barrier property, etc., and is useful as a packaging material for foods, medical products, industrial chemicals and the like, or as a composite material laminated with plastic film, paper and metal foil. is there. In the case of forming an EVOH film, any method can be used. However, a relatively thin film can be formed, and the film can be easily formed on a complex base material such as a hollow container. A solution coating method of applying a solution obtained by dissolving EVOH in a solvent to a base material has attracted attention because it can form a film and a coating operation can be performed with a relatively simple apparatus.

In such a method, a flame treatment, an anchor coat treatment, a primer treatment and the like are conventionally performed on the surface of the substrate in order to enhance the adhesion to the substrate. Compounds and polyester / isocyanate compounds are suitably used. However, when the above-mentioned anchor coat treatment is performed, the process becomes longer, or the treatment agent or treatment device is required, which leads to an increase in cost. In order to solve this drawback, Japanese Patent Application Laid-Open No. Hei 4-8745 proposes blending a polyoxazoline compound with EVOH.

[0004]

However, the present inventor studied the above technique in detail and found that the stability of the EVOH solution and the transparency of the coating film after molding were insufficient. That is, it is desired to develop an EVOH solution which is excellent in gas barrier properties, adhesion, transparency of a coating film, storage stability, coating property, and can be sufficiently adhered to a substrate without performing anchor treatment. is there.

[0005]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that the ethylene content and the saponification degree satisfy the following equation: 20 to 60 mol%.
The saponified ethylene-vinyl acetate copolymer is dissolved in a mixed solvent of water and a lower alcohol having 1 to 4 carbon atoms by using the saponified ethylene-vinyl acetate copolymer solution, The present inventors have found that the object of the present invention can be achieved, and completed the present invention.

[0006] 120-1.46 Et + 3.31 (Sv-9
9.6) <Tm <220-1.46Et + 3.31 (Sv
-99.6) where Tm: melting point by differential scanning calorimeter (° C.) Et: ethylene content (mol%) Sv: saponification degree (mol%)

Hereinafter, the method of the present invention will be specifically described. EVOH used in the present invention has an ethylene content of 20.
〜60 mol%, preferably 25-55 mol%, and the degree of saponification of the vinyl acetate component must be 90 mol% or more, preferably 95 mol% or more. If the ethylene content is less than 20 mol%, the gas barrier property at high humidity decreases, while if it exceeds 60 mol%, the film barrier properties such as sufficient gas barrier property and printability deteriorate. On the other hand, when the saponification degree is less than 90 mol%, the gas barrier properties and the moisture resistance are reduced.

Further, the EVOH has a melting point Tm determined from a peak temperature measured by a differential scanning calorimeter (DSC).
The greatest feature is that EVOH in a range satisfying the following expression defined by the ethylene content (Et mol%) and the degree of saponification (Sv mol%) is used. 120-1.46 Et +
3.31 (Sv-99.6) <Tm <220-1.46E
If the value of t + 3.31 (Sv-99.6) Tm is smaller than the above range, the gas barrier properties of oxygen and the like decrease, and if the value of t + 3.31 (Sv-99.6) Tm increases, the stability of the solution deteriorates. The adhesion to the substrate is reduced, and the object of the present invention cannot be achieved.

[0009] EVOH as defined in the present invention is generally not commercially available. That is, in the conventional EVOH, the melting point is higher than the melting point of the present invention regardless of the ethylene content and the saponification degree, and the object of the present invention cannot be achieved with the EVOH having such a high melting point. Further, the saponified copolymer is a small amount of propylene, isobutene,
α such as α-octene, α-dodecene and α-octadecene
-It may contain comonomer such as olefin, unsaturated carboxylic acid or salt thereof, partial alkyl ester, complete alkyl ester, nitrile, amide, anhydride, unsaturated sulfonic acid or salt thereof.

In the present invention, the solvent for the above-mentioned saponified product is 10 to 90% by weight of water and at least one of lower alcohols having 1 to 4 carbon atoms, particularly propyl alcohol or butyl alcohol, methyl alcohol and ethyl alcohol is 90 to 10%. A mixture by weight is used. The amount of water is 10
To 90% by weight, preferably 30 to 70% by weight.
If the content is 0% by weight or less or 90% by weight or more, a problem arises in that a uniform solution is difficult to obtain and the coating film becomes opaque. Examples of the alcohol component propyl alcohol include n-propyl alcohol and iso-propyl alcohol, and examples of butyl alcohol include n-butyl alcohol, iso-butyl alcohol, sec-butyl alcohol, and tert-butyl alcohol. Propyl alcohol is preferably used.

As a method for obtaining EVOH satisfying the above-mentioned Tm value, there is an arbitrary method, and the degree of polymerization may be controlled at the time of polymerization or saponification of EVOH, or the saponification degree distribution may be considered. In practice, it is advantageous to treat EVOH obtained by an ordinary industrial production method with a peroxide or the like. Hereinafter, such a method will be described in detail.

An ethylene content of 20 to 60 mol%, a saponification degree of 90 mol% or more and a melting point of 220 to 1.46 Et of the above formula
Having a melting point higher than the Tm value calculated from +3.31 (Sv-99.6) (for example, when the ethylene content is 38 mol% and the saponification degree is 99.6 mol%, the Tm
Is 164.5 ° C. from the above formula, and a temperature higher than that, for example, having a melting point of 173 ° C.) is dissolved in the above-mentioned mixed solvent of water and a lower alcohol. The EVOH concentration is suitably from 1 to 50% by weight. Hydrogen peroxide (usually a 30 % by weight aqueous solution) is added to the solution so that EVOH / hydrogen peroxide ( 30 % by weight) = 1 / 0.03 to 1/3 (weight ratio) with respect to EVOH. , 40 to 90 ° C. under stirring and treated for 5 to 50 hours. The order of adding water, alcohol, EVOH, and hydrogen peroxide at this time is not limited to the above order. Of course, it is also possible to charge the above-mentioned composition at once. At the end of the treatment, one point is a point at which the viscosity of the solution at the time of starting becomes about 10% or less of the initial viscosity.

The thus obtained EVOH solution can be used as it is as the EVOH solution of the present invention.
Preferably, an enzyme such as catalase is added to decompose and remove residual hydrogen peroxide. The method for removing the residual hydrogen peroxide is not limited to the above method, and any known removal method may be employed as long as the effects of the present invention are not impaired. Further, the solution may be replaced with a solvent and dissolved in a mixed solvent of water and alcohol as defined in the present invention to form an arbitrary solution. When the thus obtained EVOH solution is applied to a substrate, the concentration of the EVOH solution is not particularly limited, but is preferably about 1 to 50% by weight in consideration of coating properties to various substrates and storage stability. desirable.

The substrate on which the EVOH is applied in the present invention is not particularly limited, and may be a stretched or unstretched film, sheet, hollow container, or the like of various plastics such as polyethylene, polypropylene, polyester, polystyrene, polyvinyl chloride, and nylon. Examples include paper, cellophane, cellulose acetate, natural rubber, synthetic rubber, and metal. The thickness of such a substrate is suitably about 10 to 1000 μm.

According to the present invention, the EVOH coating film and the substrate can be firmly adhered to each other without applying an anchor treatment to the substrate as in the prior art at the time of such coating. As a coating method at this time, a roll coating method such as a Meyer bar, gravure and reverse roll method, a spray coating method, a dip coating method and any other known methods can be applied. Then, after applying the EVOH solution to the substrate, drying is performed by a known method. As an example, the drying may be performed at a drying temperature of 30 to 150 ° C., preferably about 70 to 120 ° C. for about 3 seconds to 5 minutes. In this drying, the volatile components in the coating film, that is, water and alcohol are removed, but usually, the drying is carried out until the volatile component becomes 2% by weight or less.

Thus, a transparent coating film of EVOH is formed, and its thickness is practically about 0.5 to 15 μm. If it is less than 0.5, it is difficult to exhibit sufficient gas barrier properties, while if it is more than 15 μm, it will be difficult to control it. If necessary, a moisture-proof layer can be formed on the coating by a vinylidene chloride resin coat or a vinyl chloride-vinyl acetate copolymer coat.

A laminate in which various substrates are coated with an EVOH solution is useful as a packaging material or container for foods, beverages, medicines, medicines and the like. As a layer structure of a packaging material and a container having high practicality, typically, a substrate (polyester, polyethylene, etc.) having a thickness of 10 to 1000 μ / a thickness of 0.5 to 1
5 μm of EVOH (volatile content: 0.5 to 5% by weight) or 0.5 μm to 3 μm on the EVOH layer having the above structure.
A vinylidene chloride resin layer or a vinyl chloride-vinyl acetate copolymer layer is provided. The shape may be any shape such as a film shape, a sheet shape, a hollow bottle, and a tube.

[0018]

The present invention will be specifically described below with reference to examples. In the examples, “parts” and “%” mean on a weight basis unless otherwise specified. Example 1 EVOH (ethylene content 29 mol%, saponification degree 99.6 mol%, melting point 188 ° C. , Nippon Synthetic Chemical Industry) was added to 73 parts of a mixed solvent containing 50% water and 50% iso-propyl alcohol.
"Soarnol D2908" ) 15 parts and 60-
The mixture was stirred at 70 ° C. for about 2 hours to prepare a clear solution. Next, 12 parts of a hydrogen peroxide solution ( 30 % aqueous solution) was added to the solution, and the mixture was reacted at 80 ° C under stirring for about 20 hours.
And further added catalase to a concentration of 3000 ppm to remove residual hydrogen peroxide.
A solution was obtained. The ethylene content of EVOH in the EVOH solution is 29 mol%, the degree of saponification is 99.6 mol%,
The melting point Tm was 158 ° C. as measured by DSC.
This Tm value satisfies 78 ° C. <Tm <178 ° C. specified in the present application. The EVOH solution was left in a constant temperature room at 20 ° C., and the number of days until EVOH started to gel was examined. As a result, no gelation was observed even after 60 days had passed, and the EVOH solution was good.

Next, a stretched polyester film (thickness 25)
The above EVOH solution was applied to the corona-treated surface of μ) by an applicator coating method, and dried at 100 ° C. for 3 minutes to obtain a laminate having an EVOH film thickness of 3 μ. The laminate has an oxygen permeability of 5 cc / m ² · day · atm (20 ° C., 65% R
In (H), the delamination adhesion was 80 g / 15 mm (T peel, 300 mm / min tensile speed). In addition, the above E
When a 3 μm thick EVOH single layer film was prepared from the VOH solution and the transparency of the film was measured, the haze value was 3.8.
%Met.

Examples 2 to 5 Under the respective conditions (addition amount of hydrogen peroxide, reaction temperature and reaction time) according to the EVOH (raw material) and the composition shown in Table 1.
Thus, an EVOH solution was obtained in the same manner as in Example 1. EVOH above
The same evaluation as in Example 1 was performed for the solution. In Example 3, predetermined amounts of water, alcohol, EVOH and hydrogen peroxide were charged at once to obtain an EVOH solution. Real
EVOH (raw material) used in Examples 2 to 5 is as follows:
It is. Example 2: "Soarnol" manufactured by Nippon Synthetic Chemical Industry Co., Ltd.
D2920 ”, Example 3;
Anol D2908 ”, Example 4; Nippon Synthetic Chemical Industry
“Soarnol K3835”, Example 5; Nippon Gosei
"Soarnol EUX" manufactured by Chemical Industry Co., Ltd.

Comparative Example 1 85 parts of a mixed solvent containing 50% of water and 50% of iso-propyl alcohol and a commercially available EVOH (ethylene content 29 mol%, saponification degree 99.5 mol%, melting point 188 ° C., Example 1)
In the same manner as described above, 77 ° C. <Tm <177 ° C., the melting point of which is not specified in the present application) (15 parts) was added, and the mixture was stirred at 60 to 70 ° C. for about 2 hours to prepare a transparent solution to obtain EVOH. In the same manner as in Example 1, the above solution was examined for storage stability, oxygen permeability of the laminate, and transparency of the delamination adhesive film.

Comparative Examples 2 and 3 Using the EVOH shown in Table 1, the EVOH was used in the same manner as in Example 1.
A solution was prepared and evaluated similarly. Comparative Example 4 One part of a polyoxazoline compound having a molecular weight of 200,000 (2-ethyl-2-oxazoline) was added to the commercially available EVOH solution of Comparative Example 1 and stirred at 80 ° C. for about 2 hours to prepare an EVOH solution. Was measured. Table 2 shows the EVOH solution concentrations, Tm values, and evaluation results of the examples and the comparative examples.

[0023]

[Table 1] *: () Shows the mixing weight ratio of water / alcohol. **: In Example 4, ethyl alcohol was used as the alcohol. ***: One part of polyoxazoline compound was added.

[0024]

[Table 2] *: The interlayer adhesion when anchor coating (polyester coating agent) is performed is 65 g / 15 mm

[0025]

According to the present invention, E having a specific melting point is used.
Since VOH is used, the EVOH water-alcohol solution has excellent storage stability, and can be coated on various substrates, and has excellent barrier properties, adhesion, transparency and moldability of a formed film. .

Claims (3)

(57) [Claims] An ethylene content satisfying the following formula: 20 to 6
An ethylene-vinyl acetate copolymer characterized by dissolving a saponified ethylene-vinyl acetate copolymer having 0 mol% and a saponification degree of 90 mol% or more in a mixed solvent of water and a lower alcohol having 1 to 4 carbon atoms. Saponified polymer solution 120-1.46 Et + 3.31 (Sv-99.6) <T
m <220-1.46Et + 3.31 (Sv-99.6) where Tm: melting point (° C.) by differential scanning calorimeter Et: ethylene content (mol%) Sv: saponification degree (mol%) 2. The melting point is calculated according to the formula Tm ≧ 220-1.46 Et.
+3.31 (Sv-99.6), a saponified ethylene-vinyl acetate copolymer having a saponification degree of 90 mol% or more and an ethylene content of 20 to 60 mol% in a mixed solvent of water and alcohol. 2. A saponified ethylene-vinyl acetate copolymer solution according to claim 1, wherein a saponified ethylene-vinyl acetate copolymer treated with hydrogen peroxide is used. 3. A laminate comprising a substrate coated with the saponified solution of the ethylene-vinyl acetate copolymer according to claim 1 or 2.