JP2006307075A - Method for manufacturing water-based dispersion of ethylene/vinyl alcohol copolymer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ethylene/vinyl alcohol copolymer water-based dispersion which forms the film excellent in the gas barrier property and transparency. <P>SOLUTION: The method for manufacturing an ethylene/vinyl alcohol copolymer water-based dispersion is characterized by using an oxidized polyolefin or an acid-modified polyolefin as a dispersion stabilizer for an ethylene/vinyl alcohol copolymer. The dried film of the said water-based dispersion is excellent in the gas barrier property and transparency and is usable preferably as a coating material for films, metals, rust-proof steel plates and coated papers. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an aqueous dispersion of an ethylene-vinyl alcohol copolymer using an oxidized polyolefin or an acid-modified polyolefin as a dispersion stabilizer and a method for producing the same. In particular, the present invention relates to a method for producing an aqueous dispersion of an ethylene-vinyl alcohol copolymer having a dry coating film having a high gas barrier property.

The ethylene-vinyl alcohol copolymer has features such as high gas barrier properties, oil resistance, and transparency, and is widely used in various applications including food packaging applications. Generally, it is used in the form of a composite film by melt molding or laminating, but there is a problem that it is difficult to cope with a thin film thickness or a complicated shape. Therefore, efforts have been made to overcome the problem by coating the base film as an ethylene-vinyl alcohol copolymer solution or aqueous dispersion.

An organic solvent such as dimethyl sulfoxide was used as a solvent used in the method of coating an ethylene-vinyl alcohol copolymer as a solution on a base film, but in the film formation process after coating, the organic solvent was evaporated. As a result, the work environment will be adversely affected.

On the other hand, in Patent Document 1, an ethylene-vinyl alcohol copolymer is treated with hydrogen peroxide in a mixed solution of water and isopropanol to obtain a modified product, and an inorganic layered compound is added to obtain a film having high gas barrier properties. A method has been proposed. However, it is necessary to use a peroxide in the manufacturing process, which is a problem in terms of safety.

Further, the ethylene-vinyl alcohol copolymer has a high gas barrier property due to a high crystallinity, but has a low dispersibility due to the high crystallinity. For this reason, it is difficult to prepare an aqueous dispersion, and various methods have been studied for its production method.

For example, Patent Document 2 proposes a method for obtaining an aqueous dispersion excellent in stability by enhancing dispersibility using an ethylene-vinyl alcohol copolymer modified product in which ionic groups are randomly introduced. . However, the ethylene-vinyl alcohol copolymer must be modified in advance, and the gas barrier property of the film obtained by applying the aqueous dispersion decreases as the crystallinity decreases due to modification. As a result, the high gas barrier property, which is the original purpose, is sacrificed.

In Patent Document 3, two types of thermoplastic polymers having different molecular weights (ethylene / α, β-unsaturated carboxylic acid copolymer) and a surfactant are used in combination and emulsified using a biaxial kneader. Thus, an emulsion having an average particle diameter of 7 μm and 1.8 μm is obtained. However, this emulsification method cannot obtain a particle size of 1 μm or less, and is not suitable for use in coating with a thin film. On the other hand, in Patent Document 4, an ethylene / α, β-unsaturated carboxylic acid copolymer is used as a dispersion stabilizer and neutralized. However, it is difficult to emulsify only with the ethylene / α, β-unsaturated carboxylic acid copolymer used, and water vapor permeability is obtained by using the copolymer, but the target gas barrier property is sufficient. It cannot be said.
JP 2003-276124 A JP-A-5-86240 JP-A-11-193340 WO2003 / 25058

An object of the present invention is to provide an aqueous dispersion that is excellent in dispersion stability and excellent in gas barrier properties and transparency of the obtained coating film without modifying the ethylene-vinyl alcohol copolymer.

In order to solve the above-mentioned problems, the present inventor has proceeded with a study on dispersion of an ethylene-vinyl alcohol copolymer, and in addition to having good solubility with the ethylene-vinyl alcohol copolymer as a characteristic of the dispersant used, It has been found that an oxidized polyolefin or an acid-modified polyolefin that dissolves or emulsifies together with an ethylene-vinyl alcohol copolymer in a mixed solvent of water and alcohol, which is a dissolution condition.

That is, the present invention relates to a method for producing an ethylene-vinyl alcohol copolymer aqueous dispersion characterized by using an oxidized polyolefin or an acid-modified polyolefin as a dispersion stabilizer for an ethylene-vinyl alcohol copolymer.

The dried coating film of the aqueous dispersion obtained in the present invention is characterized by good transparency and high gas barrier properties.
Although the mechanism by which the aqueous dispersion according to the present invention exhibits an excellent effect has not been clarified, since the particle size of the aqueous dispersion obtained by using an oxidized polyolefin or an acid-modified polyolefin is small, a dry coating film In this case, it is considered that the gas barrier property is improved as a result of increasing the filling property.

Hereinafter, the present invention will be specifically described.
What was synthesize | combined by the well-known method can be used for the ethylene-vinyl alcohol copolymer used by this invention. Generally, it is produced by saponifying a copolymer of ethylene and vinyl acetate, and this can also be used in the present invention. The ethylene content of the ethylene-vinyl alcohol copolymer used in the present invention is preferably in the range of 20 to 50 mol% in terms of the stability of the dispersion and gas barrier properties under high humidity. Further, the saponification degree of the ethylene-vinyl alcohol copolymer is preferably 80 mol% or more, more preferably 95 mol% or more in terms of obtaining high gas barrier properties.

As the oxidized polyolefin or acid-modified polyolefin used as a dispersion stabilizer in the present invention, polyolefin oxidized by a known method and waxes or acid-modified polyolefin can be used. Examples of the oxidized polyolefin include oxidized wax having a carboxyl group such as polyethylene oxide, polypropylene oxide, polybutylene oxide and the like, as well as montan wax, microcrystalline wax, candelilla wax and carnauba wax. Examples of the acid-modified polyolefin include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, and maleic anhydride-modified polybutylene.
The oxidized polyolefin is preferably neutralized with an alkali metal hydroxide or an amine compound from the viewpoint of dispersion stabilization. The neutralization degree is preferably 50 to 100 mol%. However, the present invention is not limited thereby.

In the present invention, a surfactant can be used as a dispersion stabilization aid. For example, examples of the anionic surfactant include a carboxylic acid type surfactant, a sulfate ester type surfactant, a sulfonic acid type surfactant, a phosphate ester type surfactant, and a borate ester type surfactant.
Cationic surfactants include fatty acid amine salt surfactants, quaternary ammonium salt surfactants, and amphoteric surfactants.
Nonionic surfactants include polyoxyethylene alkyl ether types, ether types represented by polyoxyethylene polyoxypropylene ether types, ester types such as polyoxyethylene alkyl ester types, amino ether types, ether ester types, alkanols. Examples of the amide type are polyoxyethylene alkyl esters. Furthermore, there are polymer surfactants and reactive surfactants, and these can be used alone or in combination of two or more.

The aqueous dispersion in the present invention is preferably prepared in a mixed solvent of water and alcohol from the viewpoint of the solubility of the ethylene-vinyl alcohol copolymer and the effect on the average particle size of the aqueous dispersion. Examples of the alcohol include methyl alcohol, ethyl alcohol, isopropyl alcohol and the like, but are not limited thereto.

Depending on the dispersion method, the type of oxidized polyolefin, the solvent and amount used, the type of surfactant and the amount used, the properties of the emulsion and the particle size differ. As other resin components, various aqueous resins and copolymers of ethylene and ethylenically unsaturated carboxylic acid and / or ester thereof can be used in combination as long as the effects of the present invention are not impaired. Examples of the ethylenically unsaturated carboxylic acid include (meth) acrylic acid, maleic acid, fumaric acid, tetrahydrophthalic acid, itaconic acid, citraconic acid, and crotonic acid, and examples of the ethylenically unsaturated carboxylic acid include acrylic acid. Methyl acid, ethyl acrylate, butyl acrylate, hexyl acrylate, octyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, hexyl methacrylate, octyl methacrylate, monomethyl maleate, dimethyl maleate, methyl crotonic acid , Methyl fumarate, methyl itaconate and the like. Among the copolymers of ethylene and ethylenically unsaturated carboxylic acid, an ethylene-acrylic acid copolymer is preferable from the viewpoint of dispersion stability.

Furthermore, plasticizers, film-forming aids, inorganic layered compounds, leveling agents, antiseptics, antibacterial agents, antifoaming agents, colorants, fragrances, dispersion stabilizers, viscosity modifiers, crosslinking agents, and the like can be used as necessary.

The means for aqueous dispersion is not particularly limited, but the temperature can be increased above the melting point of the resin, equipment that can be used even under pressure if necessary, equipment that can obtain high shear force, Further, it is preferable to use a method using a combination with mechanical dispersion such as a high-pressure homogenizer, and equipment capable of controlling heating and cooling.
These are selected and used depending on the physical properties of the raw materials used, the amount of functional groups, the amount of surfactant used, the properties of the aqueous dispersion, and the like, but are not limited thereto.

The coating method of the obtained aqueous dispersion is a method usually performed, for example, a doctor blade method, a roll coater method, an air knife method, a gravure method, and depending on the situation, a spray method, a dipping method, etc. may be mentioned. There is no limit. Although the thickness of the ethylene-vinyl alcohol copolymer layer applied by the above method varies depending on the purpose, it is usually preferably 10 μm or less. Furthermore, before performing a coating process, the film etc. which become a base material can be surface-treated by well-known methods, such as a corona treatment and an anchor coat process.

  The dried coating film obtained by coating the aqueous dispersion of the present invention is excellent in gas barrier properties, transparency, solvent resistance, etc., and is preferably used as a coating material for films, metals, rust-proof steel plates and processed paper. be able to.

The following examples illustrate the invention. However, the present invention is not limited at all by these Examples and Comparative Examples. The test method is as follows.

<Average particle size>
The measurement was performed using NICOM 380 (trademark) manufactured by PARTICS SIZING SYSTEMS.

<Oxygen permeability>
1. A biaxially stretched polypropylene film (thickness 20 μm) is coated with an aqueous dispersion at a film thickness of 3 μm, and heat-dried at 105 ° C. for 2 minutes to obtain a laminated film.
2. Measurement and evaluation were performed under the conditions of a temperature of 23 ° C., a humidity of 50% RH, a measurement area of 50 cm ² , and an oxygen concentration of 100% by an isobaric method using MOCON OX-TRAN.

<Transparency>
1. A PET film (film thickness: 100 μm, commercially available) is coated with an aqueous dispersion using a bar coater, dried at a drying temperature of 105 ° C. and a drying time of 2 minutes, and a laminate having an EVOH layer thickness of 1.2 μm. Get.
2. Based on JIS K-7105, the haze of the film produced with the haze measuring machine (HAZE METER MODEL TC-H3DPK manufactured by TOKYO DENSHOKU CO., LTD.) Is measured.

Example 1
In an emulsification facility with an internal capacity of 1.0 L equipped with a stirrer, thermometer and temperature controller, an ethylene-vinyl alcohol copolymer (Kuraray Eval F104B; ethylene content 32 mol%, saponification degree 99.5 mol%, polymerization 15), polyethylene oxide (PED136 manufactured by Clariant; acid value 60.5) 1.5 g, 32.5% aqueous sodium hydroxide solution 0.2 g, nonionic surfactant (Emernon 3299V manufactured by Kao; polyoxyethylene distea) Rate) 0.8 g, 341 g of water and 341 g of isopropanol are added and dissolved by heating at 120 ° C. for 1 hour. The obtained solution is cooled at 5 ° C. for 2 hours to precipitate glassy fine particles to obtain an initial dispersion. The dispersion was heated to 30 ° C., and isopropanol was distilled off under reduced pressure to obtain an aqueous dispersion having an average particle size of 0.20 μm and a solid content concentration of 6.6%.

Example 2
In the same emulsification equipment as used in Example 1, 20 g of ethylene-vinyl alcohol copolymer (Eval F104B), 2.0 g of polyethylene oxide (PED136), 0.3 g of 32.5% aqueous sodium hydroxide, 209 g of water 209 g of isopropanol is added and dissolved by heating at 120 ° C. for 1 hour. The obtained solution is cooled at 5 ° C. for 2 hours to precipitate glassy fine particles to obtain an initial dispersion. The dispersion was heated to 30 ° C., and isopropanol was distilled off under reduced pressure, to obtain an aqueous dispersion having an average particle size of 0.43 μm.

Comparative dispersion example 1
In the same emulsification equipment as used in Example 1, 35 g of ethylene-vinyl alcohol copolymer (Eval F104B), ethylene-acrylic acid copolymer (Honeywell AC5120; acid value 120) 3.5 g, 32.5 A 1.0% aqueous solution of sodium hydroxide, 386 g of water and 386 g of isopropanol are added and dissolved by heating at 110 ° C. for 1 hour. The obtained solution is cooled at 5 ° C. for 2 hours to precipitate glassy fine particles to obtain an initial dispersion. The dispersion was heated to 30 ° C., and isopropanol was distilled off under reduced pressure, and an aqueous dispersion having an average particle size of 0.79 μm was obtained.

Comparative dispersion example 2
In the same emulsification equipment as used in Example 1, 20 g of ethylene-vinyl alcohol copolymer (Eval F104B), ethylene-acrylic acid copolymer (Primacol 5990 manufactured by Dow Chemical; acid value 155) 2.0 g Add 32.5% sodium hydroxide aqueous solution 0.7g, nonionic surfactant (Emernon 3299V) 1.1g, water 219g, isopropanol 219g and heat dissolve at 110 ° C for 1 hour. The obtained solution is cooled at 5 ° C. for 2 hours to precipitate glassy fine particles to obtain an initial dispersion. The dispersion was heated to 30 ° C., and isopropanol was distilled off under reduced pressure, to obtain an aqueous dispersion having an average particle size of 0.58 μm.

Since the aqueous dispersion of the present invention can be obtained without using an ethylene-vinyl alcohol copolymer modified product, it can be supplied efficiently. The aqueous dispersion is excellent in stability, the average particle size is small, and the resulting coating film has good transparency and high gas barrier properties, and is therefore effective as a gas barrier coating agent. .

Claims (3)

A process for producing an ethylene-vinyl alcohol copolymer aqueous dispersion, characterized by using an oxidized polyolefin or an acid-modified polyolefin as a dispersion stabilizer for an ethylene-vinyl alcohol copolymer.   Furthermore, the manufacturing method of the ethylene-vinyl alcohol copolymer aqueous dispersion of Claim 1 using surfactant. A film, a metal, a rust-proof steel plate and a processed paper coated with an aqueous dispersion produced by the method according to claim 1.