JPH1087860A - Method for coating with ethylene-vinyl alcohol copolymer solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method for coating with an ethylene-vinyl alcohol copoly mer soln. with does not give a thick coating layer and is suitable for production of a small lot size by using a soln. of an ethylene-vinyl alcohol copolymer in a specific solvent which heating the soln. SOLUTION: A soln. prepd. by dissolving an ethylene-vinyl alcohol copolymer having an ethylene content of 20-50mol% in a water-alcohol mixed solvent is applied to a substrate while keeping the soln. at 50-80 deg.C. The alcohol used is a lower alcohol such as methyl alcohol, ethyl alcohol, or propyl alcohol and its concn. in the mixed solvent is 10-90%. The concn. of the resin is usually 5-30%. The coating is pref. done by gravure roll coating. In this case, the coated surface is pref. subjected to a smoothening treatment just after the coating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating an ethylene-vinyl alcohol copolymer solution capable of obtaining a packaging material having excellent oxygen barrier properties by coating the surface of various sheets and films.

[0002]

2. Description of the Related Art As a food packaging material, a film obtained by coating polyvinylidene chloride on a polypropylene film or the like is widely used because of its high oxygen gas barrier property. However, this film generates chlorine gas at the time of waste incineration. There were problems such as damaging the incinerator and adversely affecting the environment.

In recent years, as a food packaging material which does not cause such problems, ethylene-vinyl alcohol copolymer (hereinafter referred to as EVOH) has been laminated on other films or sheets due to its high oxygen gas barrier property. Things are being used.

[0004] As such a laminating method, an EVOH film formed by a melt extrusion method (T-die or inflation) is laminated with another film such as a polyester film or a polypropylene film, or an EVOH film is laminated.
And a method of obtaining a multilayer film by co-extruding a multilayer film and polypropylene.

[0005]

However, according to these methods, the thickness of the EVOH layer increases,
Costs are also high. Also, the equipment for performing this is large-scale, so it is suitable for continuous production and not suitable for small-lot production.

[0006]

SUMMARY OF THE INVENTION The present invention provides a method for coating an ethylene-vinyl alcohol copolymer solution suitable for small-lot production without increasing the thickness of an EVOH layer in a packaging material. An object of the present invention is to provide a packaging material having excellent oxygen barrier properties by applying a coating to the surface of various sheets and films.

That is, the invention according to claim 1 is based on a solution obtained by dissolving an ethylene-vinyl alcohol copolymer having an ethylene content of 20 to 50 mol% in a mixed solvent of water and alcohol while heating the solution to 50 to 80 ° C. According to a second aspect of the present invention, after the substrate is coated with a gravure roll, the coated surface is immediately subjected to a smoothing treatment. .

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below.

The present invention provides an ethylene content of 20 to 50 mol%.
Coating a solution obtained by dissolving the ethylene-vinyl alcohol copolymer in a mixed solvent of water-alcohols at 50 to 80 ° C. while heating the substrate to a temperature of 50 to 80 ° C. Has solved the above-mentioned problem, and the numerical basis is as follows.

That is, the ethylene content of EVOH is 20
If it is less than mol%, the water resistance deteriorates, and the gas barrier property at high temperatures decreases.

On the other hand, if it exceeds 50 mol%, sufficient gas barrier properties cannot be obtained. EVOH is obtained by saponifying an ethylene-vinyl acetate copolymer, and the degree of saponification is preferably 90 mol% or more from the viewpoint of gas barrier properties.

As a solvent for dissolving EVOH, a mixed solvent of water and alcohol is used. As the alcohols, lower alcohols such as methyl alcohol, ethyl alcohol and propyl alcohol are used, and the alcohol concentration in the mixed solvent is adjusted to the ethylene content of EVOH,
Depends on saponification degree and type of alcohol, but 10% to 9
It is selected from the range of 0%.

The resin concentration of the EVOH solution is usually 5 to
It is appropriately determined within the range of 30% depending on the coating film thickness and the like.

Next, as a coating method, a coating method such as a gravure roll method, a reverse roll method, and a knife coater method can be applied, but a gravure roll method is preferable in terms of uniformity of a coating film.

It is necessary to heat the EVOH solution to 50 to 80 ° C. during coating. That is, below 50 ° C., the viscosity of the solution is high and a uniform coating cannot be obtained, and above 80 ° C., the solution evaporates violently,
The coating thickness is not constant because the resin concentration is not stable.

In the case of the gravure roll method, a coating having a uniform film thickness without streaks can be obtained by immediately smoothing the coated surface after coating with the gravure roll.

For such a smoothing treatment, a method of pressing a roll having a plain surface against the coating surface is employed.

Various substrates such as a polypropylene film, a polyethylene film, a nylon film, a polyester film, paper, and a nonwoven fabric are used as the substrate on which the EVOH is coated.

It is desirable to use a film that has been subjected to corona discharge treatment or anchor coating treatment in order to improve the adhesion to the EVOH coating layer.

The EV coated on the substrate as described above
The film thickness of OH is suitably about 0.5 to 5 μm, and if it is 0.5 μm or less, the gas barrier property is insufficient.

Next, an embodiment (experiments and results thereof) will be described. EVOH: ethylene content 20 mol%, saponification degree 9
9.5 mol% Solvent: 50% isopropyl alcohol and 50% water
EVOH was dissolved in the above solvent to obtain a solution having a resin concentration of 15%.

Substrate: Biaxially stretched polypropylene film This solution is applied to the above substrate with a gravure roll while heating the solution to a temperature of 60 ° C., and the application surface is gently applied with a plain roll near the gravure roll. The surface was smoothed. The coated substrate was dried in a drying oven at 100 ° C. for 30 seconds. The resulting EVOH film was a uniform EVOH film having a thickness of 2 μm, an oxygen permeability of ^{2 to 4} cc / m ² , and a film having a high barrier property at 24 hours.

[0023]

As described above, according to the method of the present invention, a thin EVOH film can be obtained, and a large-scale production equipment is not required. It becomes possible to coat the material.

Claims (2)

[Claims] The present invention is characterized in that a solution obtained by dissolving an ethylene-vinyl alcohol copolymer having an ethylene content of 20 to 50 mol% in a mixed solvent of water and alcohol is coated on a substrate while heating to 50 to 80 ° C. Coating method of ethylene-vinyl alcohol copolymer solution. 2. The method for coating an ethylene-vinyl alcohol copolymer solution according to claim 1, wherein said substrate is coated with a gravure roll, and then a coating surface is smoothed immediately.