JPS60124661A - Method for forming coating film of saponified ethylene/ vinyl acetate copolymer - Google Patents

Abstract

PURPOSE:To obtain a coating film having remarkably improved transparency and gas barrier properties, by dissolving a saponified ethylene/vinyl acetate copolymer in a mixture consisting of water, a specified alcohol and formic acid as a solvent and applying the soln. to a substrate to form a coating film of said saponified copolymer. CONSTITUTION:A saponified ethylene/vinyl acetate copolymer having an ethylene content of 25-55mol% and a degree of saponification of vinyl acetate component of 90mol% or below is dissolved in a mixture consistig of 10-60wt% water, 5-70wt% at least one member selected from among propyl alcohol, butyl alcohol and benzyl alcohol and 2-85wt% formic acid as a solvent. A substrate is coated with the resulting soln. and drived to form a coating film of said saponified copolymer. The soln. contains said saponified copolymer at a concn. of pref. 0.5-15wt%.

Description

DETAILED DESCRIPTION OF THE INVENTION Obtained from a saponified ethylene-vinyl acetate copolymer having an ethylene content of 25 to 55 mol% and a degree of saponification of the vinyl acetate component of 90 mol% or more. The resulting film has excellent transparency and oxygen barrier properties, and is useful as a variety of packaging materials for foods, medical products, industrial chemicals, etc., or as a composite material laminated with plastic film, paper, metal foil, etc.

When forming a film of the saponified product, any method can be used, but it ends up forming a relatively thin film, and it is not suitable for substrates with complex shapes such as hollow containers. A solution coating method, in which a solution of the saponified product dissolved in a solvent is applied to a substrate, is attracting attention because a film can be easily formed and the coating operation can be performed using relatively simple equipment.

In this method, many solvents have been proposed for the saponified product, for example, Japanese Patent Publication No. 46-23
Water-containing propyl alcohol and water-containing butyl alcohol described in Japanese Patent Publication No. 911 and Japanese Patent Publication No. 47-48489 are considered to be promising in that they produce transparent films.

However, the present inventors have investigated and found that when forming a coating film using such a hydroalcoholic system, a coating film with good transparency cannot be obtained unless the coating solution is maintained at a high temperature of 50°C and the coating operation is performed. Disadvantages: The storage stability and storage stability of the coating liquid are poor, and there are disadvantages such as the need to re-dissolve at high temperature when using it. ! I made it clear. Maintaining such a high temperature not only requires extra thermal energy, but also causes changes in the concentration of the coating solution due to evaporation of the solvent, which can be solved in terms of process control, such as having to perform the coating operation in a closed system. This is a problem that should be addressed. Furthermore, it is difficult to form a microscopically homogeneous coating film in terms of coating film properties such as transparency and gas barrier properties, so it cannot be said that it is necessarily sufficient to meet the recent strict quality requirements. There is a need to further improve the physical properties of the coating film.

However, the present inventors have attempted to solve this problem (as a result of extensive research, we have developed a solution of a saponified ethylene-vinyl acetate copolymer with an ethylene content of 125 to 55 mol% and a degree of saponification of the vinyl acetate component of 90 mol% or more). (A) as a solvent when coating on a base material and drying to form a coating film of the saponified product.
Water 10-60% by weight (B) Small amount of propyl alcohol, butyl alcohol or benzyl alcohol ft< )-tr 1135-7
The present invention was completed based on the finding that the object can be achieved when a mixture consisting of 0% by weight ('C) formic acid and 2 to 85% by weight is used.

In the present invention, when such a specific mixed solvent is used, a stable coating film with improved transparency and gas barrier properties is always obtained even when the coating operation is performed at room temperature, so no special management is required during the coating operation. Its industrial usefulness is extremely great in that it is necessary and the drawbacks of the conventional method can be overcome.

The saponified ethylene-vinyl acetate copolymer used in the present invention has an ethylene content of 25 to 55 mol%, preferably 28 to 4 mol%.
The degree of saponification of the vinyl acetate component should be 90 mol% or more, preferably 95 mol% or more. If the ethylene content is less than 25 mol %, the gas barrier property at high temperatures will decrease, while if it is above 55 mol %, the physical properties of the coating film, such as sufficient gas barrier property and printability, will deteriorate. Further, when the degree of saponification is 90 mol% or less, gas barrier properties and moisture resistance decrease.

The saponified copolymer further contains a small amount of α-olefin such as propylene, isobutyne, a-octene, a-dodecene, and a-octadecene, an unsaturated carboxylic acid or a salt thereof,
Partial alkyl esters and complete alkyl esters may contain co-7mers such as nitriles, amides, anhydrides, unsaturated sulfonic acids, or salts thereof.

In the present invention, as the solvent for the saponified product, (A) water 10 to 60fii1%, (B) 7' lobil alcohol,
It uses a mixture consisting of 5 to 70% by weight of at least one of butyl alcohol or bennor alcohol and 2 to 85% by weight of CC')m acid.
The above-mentioned drawbacks of propyl alcohol or water/butyl alcohol solvents are solved by incorporating a specific amount of formic acid.

Formic acid or hydrated formic acid is also known as a solvent for saponified ethylene-vinyl acetate copolymer, but the present inventors' studies have shown that it is possible to use formic acid simply in combination with a solution of saponified ethylene-vinyl acetate copolymer. Formic acid is considered to have unique performance among various solvents, and the effect of the present application is that (A) the water content in the publicly known mixed solvent must be 10 to 60% by weight, preferably 30 to 50% by weight. Must be.

If it is less than 10% by weight, it is difficult to obtain a uniform solution, and if it is more than 60% by weight, the problem arises that the solubility of the saponified product is severely reduced. In addition, the content of propyl alcohol, butyl alcohol, and benol alcohol in (B) must be 5 to 70% by weight, preferably 40 to 60% by weight.
If it is less than 5% by weight, the solubility will decrease unless a large amount of formic acid is used, and if it is more than 70% by weight, it will be difficult to obtain a homogeneous solution and it will be impractical, and (C)Il
The content of acid must be 2 to 85% by weight, preferably 5 to 40% by weight, particularly preferably 10 to 30% by weight. If it is less than 2% by weight, the effect of the present invention will be poor and the effect of its addition will not be recognized. However, the use of formic acid of 85% by weight or more is not preferable in terms of corrosion of the equipment.As the propyl alcohol of component (B), n-propyl alcohol, 1so-
Propyl alcohol is also n as butyl alcohol.
-butyl alcohol, 1so-butyl alcohol, 5e
Examples include C-butyl alcohol, tert-butyl alcohol, and 1so-propyl alcohol is preferably used. Even if formic acid is added to alcohols other than (B), a coating film with good transparency cannot be obtained.

Further, in (C), formic acid may be any alkyl ester such as methyl ester, ethyl ester, propyl ester, etc., and the same effect of the present invention can be obtained.

The concentration of the saponified ethylene-vinyl acetate copolymer solution is not particularly limited and can be coated within any range, but it is usually 0.
．． The amount is preferably about 5 to +5, m%. One of the features of the present invention is that even if the concentration is low and the coating liquid is used, the coating film will not become cloudy. A relatively highly concentrated solution is used, and as a result, the adjustment of the coating film thickness is unavoidably troublesome. Considering this, the present invention has great advantages in this respect as well.

The effects of the present invention are particularly pronounced when a coating liquid with a low a1 degree, that is, about 3 to 10% by weight, is used. Moreover, since the coating liquid mentioned above has excellent stability, there is no need to worry about precipitation of saponified substances even without special operations such as heating. Since it has excellent properties, coating film formation can be carried out at any temperature around room temperature.

In the present invention, the substrate to which the saponified ethylene-vinyl acetate copolymer is applied is not particularly limited, and includes films, sheets, hollow containers, and paper made of various plastics such as polyethylene, polypropylene, polyester, polystyrene, and polyvinyl chloride. , cellophane, cellulose acetate, natural rubber, synthetic rubber, metal, etc.

The film thickness of such a material is suitably about 10 to 1000 microns. In the present invention, the laminate obtained by applying a saponified ethylene-vinyl acetate copolymer to such a base material is usually put to practical use as a packaging material as it is, but if necessary, such a base material can be used. The saponified ethylene-vinyl acetate copolymer can also be used as a single-layer film, sheet, etc. by peeling off the coating.

As a coating method, any known method such as a roller coating method, a spray coating method, a dip coating method or the like can be applied.

Further, depending on the type of the base material, surface oxidation treatment, flame treatment, anchor coating treatment, primer treatment, etc. can be carried out as appropriate in order to improve the adhesive force with the saponified ethylene-vinyl acetate copolymer layer.

As the anchor treatment agent, polyurethane compounds and polyester isocyanate compounds can be suitably used. The practical thickness of the anchor foot layer is about 0.05 to 3 μm.

After applying a solution of saponified ethylene-vinyl acetate copolymer to a substrate, drying is performed. Drying temperature is 30-15
Heating at a temperature of 0°C, preferably 50 to 120°C, for about 3 seconds to 5 minutes is enough. Despite the fact that C1 water and @acids have fairly high boiling points,
It is thought that the coexisting alcohols promote the evaporation of formic acid and water, and the above-mentioned drying temperature is sufficient. The drying of the paint film can be done until most of the volatile matter is removed (although it is possible to dry the paint film until the volatile matter is almost completely removed), it is necessary to prevent the occurrence of 2-inking in the paint film and to maintain the transparency and interlayer adhesion of the paint film for a long period of time. It is advantageous to leave 0.5 to 10% by weight of volatile matter in the coating film so that water can be retained at 0.3% by weight.
~9% by weight, 0-0.5% by weight of alcohol, 0% of formic acid
It is desirable to set the composition of the tub, coating liquid, and drying conditions so that the ratio is 1.5% by weight.

In this way, a transparent coating film of the saponified ethylene-vinyl acetate copolymer is formed, and the film thickness is 0.5~
A thickness of about 10μ is practical. If it is less than 0.5μ, it will be difficult to exhibit sufficient gas barrier properties (on the other hand, if the film thickness is more than 10μ, it will be difficult to control it.If necessary, the coating film may be further coated with vinylidene chloride resin, vinylidene chloride resin, etc.). Of course, it is also possible to form a moisture-proof layer with vinyl acetate copolymer Ni-F, etc. The resulting coating film can be a single-layer film or sheet of saponified ethylene-vinyl acetate copolymer, or it can be laminated onto polyester, polyolefin, etc. As a composite material, it is useful as a packaging material or container for foods, beverages, drugs, pharmaceuticals, etc.The layer structure of highly practical packaging materials and containers is typically a base material with a film thickness of 10 to 1000μ (polyester, polyethylene etc.)/IR thickness 0.05
~3μ anchor knee) Jl/film thickness 0.5~10μ saponified ethylene-vinyl acetate copolymer (volatile fraction fi0
．． 5 to 5% by weight) or on top of the saponified ethylene-vinyl acetate copolymer layer with the above structure, an additional twig thickness of 0.5 to 5% by weight)
There is a vinylidene chloride 0j fat layer of about 3μ (1 is the one provided with a vinyl chloride-vinyl acetate copolymer layer).

Its shape may be arbitrary, such as a film, a sheet, a hollow bottle, or a tube.

Hereinafter, the method of the present invention will be explained in more detail with reference to examples. Unless otherwise specified, 5%, parts, and li are based on weight.

Example 1 Water 30%, 1so-propyl alcohol 50%, formic acid 2
95 parts of a mixed solvent containing
9.5 mol %) 59 was added and stirred at 40 to 50°C for about 1 hour to prepare a transparent solution. On the other hand, on a polyethylene terephthalate film with a film thickness of 50 μm, 100 parts of a polyurethane adhesive base agent, 6.5 parts of a hardening agent, and 900 parts of ethyl acetate were added.
Membrane lv3 using a polyurethane compound solution consisting of
μ anchor foot treatment was applied.

The film treated in this way was immersed in the coating solution at a temperature of 25°C, and immediately dried at 70°C for 2 minutes to reduce the water content to 1.
．． 3%, fio containing 1so-propyl alcohol, 1%
, formic acid fjlo, and a 2% saponified ethylene-vinyl acetate copolymer copolymer (I11 thickness 5 μm) coating film was formed.

The transparency of the #t171iI product is ^STM 01003-
52, the haze value was 13%, indicating very good transparency.

(The haze value of the base material is 14%) Also, when the oxygen barrier property was measured according to ^STN 01434-58, the oxygen permeability was 7 cc (NTP)/-
2.241+r.at-, showing good gas-blocking properties.

Furthermore, when the interlayer adhesion strength was measured, all interlayer adhesion strengths were 300 g/25 am or more, which was extremely good.

Further, even when the above laminate was left in an atmosphere of 65% R11,20'C for 10 days, no cracking or decrease in transparency was observed, and the appearance and interlayer adhesion remained almost unchanged.

Illusion Example 1 When the same experiment as Example 1 was conducted except that the use of formic acid was omitted, the haze value was 85% and the oxygen permeability was 45cc (formerly 'P) 7m2・241+r・al
Both values decreased to m. When the liquid temperature during coating was raised to 60°C, the haze value was 55% and the oxygen permeability was 4.
0cc(NTP)/+s2・24hr-atm Control Examples 2 and 3 Ethylenediamine was used instead of formic acid (Control Example 2),
An experiment was conducted according to the same procedure except that ethyl alcohol was used instead of 1so-propyl alcohol (Control Example 3). The haze value is 80% for control example 2 and 31 for control example 3.
5%, and the oxygen permeability of control example 2 was 41cc (NTP
) 7m2・24br-at+s, control example 3 was 43cc (
NTP)/+s' ・24hr-ata+.

Examples 2 to 81 Comparative Examples 4 to 9 Coating films were formed according to Example 1 under the conditions shown in Tables 1 and 2. The results are shown in Tables 1 and 2.

However, in Example 7.8, a layer of vinylidene chloride with a thickness of 2μ was added on the saponified ethylene-vinyl acetate copolymer layer.
A fat layer and a vinyl chloride-vinyl acetate copolymer layer are respectively provided.

In addition, the oxygen permeability of each base material (cc (NTP)/m' ・2
41+r-atm) is as follows.

Claims (1)

[Scope of Claims] 1. A solution of a saponified ethylene-vinyl acetate copolymer having an ethylene content of 25 to 55 mol% and a degree of saponification of vinyl acetate component of 90 mol% or more is applied to a base material and dried. In forming a coating film of the compound, as a solvent (A) water 10-60% by weight (B) a small amount of propyl alcohol, butyl alcohol or benzyl alcohol (5-70% by weight of each type) (C) @acid 2 =85% by weight of ethylene-
Method for forming a coating film of saponified vinyl acetate copolymer. 2. The method according to claim 1, characterized in that a substrate anchor-coated with a polyurethane compound is used. 3. Base material with film thickness 10-1000μ/film thickness 0.05-3μ
A laminate consisting of an anchor coat layer with a film thickness of 0.5 to 10
2. The method according to item 2, characterized in that a coating film of a cyanide of ethylene-vinyl acetate copolymer of μ is formed. 4. The method according to claim 3, characterized in that the volatile content in the coating film of the saponified ethylene-vinyl acetate copolymer is 0.5 to 1031% by weight. 5. The method according to claims 1 to 4, characterized in that a solution having a resin concentration of 0.5 to 15% by weight is used as the solution of the saponified ethylene-vinyl acetate copolymer. 6. Claims 1 to 6, characterized in that after applying a solution of saponified ethylene-vinyl acetate copolymer to a substrate, drying is performed at 30 to 150°C for 3 seconds to 5 minutes.
The method described in Section 4.