JP2002047364A - Aqueous gas barrier coating agent, film coating with the same and method of preparing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoplastic resin film which has a high gas barrier property even in high humidity and is industrially prepared at low cost. SOLUTION: The aqueous gas barrier coating agent has a pH of 6-9 is composed of a polyvinyl alcohol and an isobutylene-maleic acid anhydride copolymer with the mass ratio of 97/3-20/80 and an alkaline compound. The thermoplastic resin film is coated with the coating agent. In the method of preparing the gas barrier film, the gas barrier film is heat-treated at a temperature of >=150 deg.C after the coating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a thermoplastic resin film having excellent gas barrier properties and a gas barrier coating agent.

[0002]

2. Description of the Related Art Thermoplastic resin films such as polyamides and polyesters are widely used as packaging materials because of their excellent strength, transparency, moldability and gas barrier properties. However, when used for applications requiring long-term storage properties, such as retort-treated foods, higher gas barrier properties are required.

In order to improve gas barrier properties, polyvinylidene chloride (P) is coated on the surface of these thermoplastic resin films.
VDC) has been widely used for food packaging and the like, but PVDC generates organic substances such as acidic gas at the time of incineration. Therefore, in recent years, interest in the environment has increased, and a shift to other materials has been strongly desired. ing.

[0004] On the other hand, polyvinyl alcohol (PVA) is an alternative material to PVDC. This material does not generate toxic gas and has a high gas barrier property in a low humidity atmosphere, but the gas barrier property rapidly decreases as the humidity increases, and it may not be possible to use it for packaging foods containing moisture. Many.

A film made of a copolymer of vinyl alcohol and ethylene (EVOH) is known as a film in which the gas barrier property of PVA under a high humidity is reduced, but the gas barrier property under a high humidity is practically used. In order to maintain the level, it is necessary to increase the ethylene content to some extent. When EVOH is used as a coating material, it is necessary to dissolve it using an organic solvent or a mixed solvent of water and an organic solvent, which is not desirable from the viewpoint of environmental problems and also requires a step of recovering the organic solvent. Therefore, there is a problem that the cost increases.

[0006] As a method of coating a film with a liquid composition comprising a water-soluble polymer and exhibiting high gas barrier properties even under high humidity, an aqueous solution comprising PVA and a partially neutralized product of polyacrylic acid or polymethacrylic acid is used. A method has been proposed in which both polymers are crosslinked by an ester bond by coating the film and heat-treating it (Japanese Patent Laid-Open No.
10-237180). This method requires long-time heating at a high temperature in order to sufficiently advance the esterification reaction, and there is a problem in productivity.

On the other hand, it has been widely known that a polymer containing a maleic acid unit has been made water-resistant by reacting with a hydroxyl group such as PVA or polysaccharide. For example, JP-A-8-
No. 66991 discloses that a layer composed of a 25-50% partially neutralized product of isobutylene-maleic acid copolymer and PVA has excellent water resistance. In addition, JP
Japanese Patent No. -1649 proposes a method for making a PVA film water-resistant by mixing an alkyl vinyl ether-maleic acid copolymer with PVA.

[0008]

In order to solve the above-mentioned problems, the present inventors have developed a thermoplastic resin film capable of maintaining a high gas barrier property even under high humidity and an industrially inexpensive film. It aims to provide a method that can be manufactured.

[0009]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that by blending an alkaline compound with a coating solution composed of PVA and isobutylene-maleic anhydride and adjusting the pH of the solution to a specific range. A sufficient crosslink is formed between PVA and isobutylene-maleic anhydride, and this is coated on the surface of a thermoplastic resin film and dried to obtain a film having excellent gas barrier properties under high humidity. Heading, the present invention has been reached. That is, the gist of the present invention is as follows. (1) A water-based gas barrier coating agent comprising a mixture of polyvinyl alcohol and isobutylene-maleic anhydride copolymer having a mass ratio of 97/3 to 20/80, and an alkali compound, and having a pH of 6 to 9. (2) The water-based gas barrier coating agent according to claim 1, wherein an alkali compound having a boiling point of 200 ° C or lower is used as the alkali compound. (3) The aqueous gas barrier coating agent according to claim 1, wherein a mixture of an alkaline compound having a boiling point of 200 ° C or lower and an alkaline earth metal hydroxide is used as the alkaline compound. (4) A gas barrier film obtained by forming a coating comprising the water-based gas barrier coating agent according to any one of (1) to (3) on at least one surface of the thermoplastic resin film. (5) A method for producing a gas barrier film, comprising applying the water-based gas barrier coating agent according to (1) to (3) to a thermoplastic resin film and then heat-treating the film at a temperature of 150 ° C. or higher.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

In the present invention, the thermoplastic resin film to which the coating agent is applied includes nylon 6, nylon 6
6, a film made of polyamide resin such as nylon 46, polyester resin such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polybutylene naphthalate, polyolefin resin such as polypropylene, polyethylene or a mixture thereof, or a laminate of these films Among them, polyethylene terephthalate and nylon 6 are particularly preferred. These may be unstretched films or stretched films.

As a method for producing a film, a thermoplastic resin is heated and melted by an extruder and extruded from a T-die.
An unstretched film is obtained by cooling and solidifying with a cooling roll or the like, or extruded from a circular die and solidified by water cooling or air cooling to obtain an unstretched film. In the case of producing a stretched film, a method in which the unstretched film is wound once or continuously stretched by a simultaneous biaxial stretching method or a sequential biaxial stretching method is preferable. In view of performance such as mechanical properties and thickness uniformity of the film, a method of combining a flat film forming method using a T-die and a tenter stretching method is preferable.

In the present invention, the mass ratio of PVA to isobutylene-maleic anhydride copolymer is 97/3 to 20/8.
0, preferably in the range of 90/10 to 40/60. When the mass ratio of PVA exceeds 97,
If it is less than 20, the gas barrier properties of the film particularly under a high humidity atmosphere are deteriorated.

The PVA used in the present invention can be obtained by a known method such as complete or partial saponification of a vinyl ester polymer. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, vinyl versatate and the like, with vinyl acetate being most preferred industrially.

As long as the effects of the present invention are not impaired, another vinyl compound may be copolymerized with the vinyl ester. Other vinyl monomers include unsaturated monocarboxylic acids such as crotonic acid, acrylic acid and methacrylic acid, and esters, salts, anhydrides, amides and nitriles thereof, and unsaturated acids such as maleic acid, itaconic acid and fumaric acid. Examples thereof include dicarboxylic acids and salts thereof, α-olefins having 2 to 30 carbon atoms, alkyl vinyl ethers, and vinylpyrrolidones.

In the present invention, in order to impart gas barrier properties to the film surface, it is preferable that the vinyl alcohol unit in PVA is at least 40 mol%. If the vinyl alcohol unit is less than 40 mol%, isobutylene-
The rate of ester bond reaction with the maleic anhydride copolymer decreases, and the gas barrier property is impaired. Further, when a large amount of a hydrophobic copolymer component is contained, the water solubility of the resin is impaired.

As the saponification method, a known alkali saponification method or acid saponification method can be used, and among these, a method of alcoholysis using methanol in an alkali hydroxide is preferable. The saponification degree is preferably 80% or more, more preferably 97% or more, and particularly preferably 99% or more. If the saponification degree is too low, the barrier performance decreases, and at the same time, the water solubility of the polymer is impaired.

Next, the isobutylene-maleic anhydride copolymer used in the present invention is obtained by polymerizing maleic anhydride and isobutylene by a known method such as solution radical polymerization.

In addition, a small amount of another vinyl compound can be copolymerized with the isobutylene-maleic anhydride copolymer as long as the effects of the present invention are not impaired. As other vinyl compounds, for example, acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, vinyl formate, vinyl esters such as vinyl acetate, styrene, p-styrene sulfonic acid, 2-3 carbon atoms such as ethylene, propylene and isobutylene
And a compound having a reactive group that reacts with a hydroxyl group of PVA or the like.

The maleic acid unit in the isobutylene-maleic anhydride copolymer in the present invention preferably contains at least 10 mol%. When the amount of the maleic acid unit is less than 10 mol%, the formation of a crosslinked structure by the reaction with the vinyl alcohol unit in the PVA is insufficient, and the gas barrier property is reduced.

The isobutylene used in the present invention
The maleic acid units in the maleic anhydride copolymer tend to have a maleic anhydride structure in which the adjacent carboxyl groups are dehydrated and cyclized in a dry state, and open to a maleic acid structure when wet or in an aqueous solution.

The water-based gas barrier coating agent (hereinafter referred to as "coating agent") in the present invention is used for the aqueous solution of PVA and isobutylene-maleic anhydride copolymer, and for the carboxyl group in isobutylene-maleic anhydride copolymer. An appropriate ratio of an alkali compound is added to the mixture, and the pH of the solution is adjusted to 6 to 9
It is necessary to adjust to the range. In general, when an isobutylene-maleic anhydride copolymer is dissolved in water to form an aqueous solution, it is known that the dissolution time can be shortened by adding an appropriate amount of an alkali compound. For example, when added to an equimolar amount with the carboxyl group in the isobutylene-maleic anhydride copolymer, the solution can be easily adjusted, but a problem arises in that the transparency of the coating film decreases when the film is applied and dried, Further, the gas barrier properties of the obtained film are low. On the other hand, when the blending amount of the alkali compound is too small, not only is it necessary to dissolve the isobutylene-maleic anhydride copolymer for a long time, but also the stability of the liquid is lowered and during coating, precipitation or turbidity occurs. Not preferred. This may be because the compatibility between PVA and the isobutylene-maleic anhydride copolymer and the stability of the aqueous solution are changed depending on the amount of the alkali compound added. According to the study of the present inventors, the pH of the solution was 6 to 6.
The most favorable result is obtained when adjusted to the range of 9,
A film obtained by applying the coating agent thus adjusted to the film and subjecting it to a heat treatment for drying has high transparency of the coating film and excellent gas barrier properties under high humidity.
As the alkali compound, any compound capable of neutralizing the carboxyl group in the isobutylene-maleic anhydride copolymer may be used, and a hydroxide of an alkali metal or an alkaline earth metal,
Examples include ammonium hydroxide and organic ammonium hydroxide compounds.

Among them, preferred are alkali compounds having a boiling point of 200 ° C. or lower, such as ammonium hydroxide, primary amines such as methylamine, ethylamine, propylamine and butylamine, and dimethylamine, diethylamine and methylethylamine. Secondary amines,
Tertiary amines such as trimethylamine and triethylamine are exemplified.

Most of such a coating agent containing a low-boiling alkali compound volatilizes during the process of drying and heat treatment after coating on a film, so that the activity of the carboxyl group of the isobutylene-maleic anhydride copolymer increases. It is considered that the crosslinking reaction is promoted, and as a result, excellent gas barrier properties are obtained.

Further, it has been found that a more excellent gas barrier property can be obtained by mixing and blending an alkaline earth metal which becomes a divalent metal ion as an alkali compound. This is because the carboxyl group of the isobutylene-maleic anhydride copolymer is cross-linked by alkaline earth metal ions, and in addition to the formation of a cross-link between PVA and the isobutylene-maleic anhydride copolymer, a synergistic effect is exhibited. Conceivable.

The coating agent may be prepared by a known method using a dissolving pot equipped with a stirrer. For example, a method is preferred in which PVA and an isobutylene-maleic anhydride copolymer are separately prepared as aqueous solutions and mixed before use. At this time, it is preferable to mix the alkali compound with an aqueous solution of isobutylene-maleic anhydride copolymer. When a compound having a low boiling point is used as the alkali compound, it is preferable to perform the reaction in a closed system so that the alkali compound does not evaporate and change its composition when dissolved by heating and mixing. What is important in the present invention is to adjust the pH of the finally mixed coating agent to a range of 6 to 9, which depends on the type of alkali compound, PVA and isobutylene-.
Since the ratio varies depending on the mixing ratio of the maleic anhydride copolymer, the blending amount must be appropriately selected.

In the present invention, the gas barrier properties of the resulting film can be further improved by adding a small amount of a water-swellable layered inorganic compound such as vermiculite, montmorillonite or hectorite to the coating agent.

For the film of the present invention, a mixed solution of PVA, isobutylene-maleic anhydride copolymer and an alkali compound is prepared, coated on the surface of the film, dried by heating, and further heated at a temperature of 150 ° C. or more. Obtained by heat treatment. A small amount of an organic solvent such as alcohol can be added to the coating agent for the purpose of increasing the solubility, shortening the drying step, and improving the stability of the solution. Further, in order to enhance the gas barrier properties of the film of the present invention, it is necessary that a cross-linking reaction by an ester bond occurs between PVA and isobutylene-maleic anhydride copolymer. It is also possible to add a catalyst such as In this case, when ammonium hydroxide or the like is used as the alkali compound, most of the alkali compound is evaporated by drying and heating after coating, and the catalyst is activated.

In the present invention, the thickness of the layer comprising PVA and the isobutylene-maleic anhydride copolymer is preferably at least 0.1 μm in order to sufficiently enhance the gas barrier properties of the film. The polymer concentration of the coating agent is
Although it is appropriately changed depending on the viscosity and reactivity of the liquid and the specifications of the apparatus to be used, it is preferable that the concentration be in the range of 5 to 50% by mass of the whole solution. With a dilute solution, it is difficult to coat a layer having a sufficient thickness to exhibit gas barrier properties, and a problem that a long time is required in a subsequent drying step is likely to occur. On the other hand, if the concentration of the solution is too high, problems may occur in the mixing operation, storage stability, and the like.

The method for coating the film with the coating agent of the present invention is not particularly limited, but ordinary methods such as gravure roll coating, reverse roll coating, wire bar coating, and die coating can be used. The coating may be performed before stretching the film, or may be performed on the stretched film. To perform coating prior to stretching, first coat the unstretched film, dry it, and then supply it to a tenter-type stretching machine to simultaneously stretch the film in the running direction and width direction (simultaneous biaxial stretching) or heat-treat it. Alternatively, the film may be stretched in the running direction of the film using a multi-stage heat roll or the like, coated, dried, and then stretched in the width direction (sequential biaxial stretching) by a tenter-type stretching machine. Also,
It is also possible to combine stretching in the running direction with simultaneous biaxial stretching in a tenter. Further, a method of coating before stretching and then performing stretching and heat treatment is a preferable method because a high temperature during stretching and heat treatment can be used for a crosslinking reaction.

In the present invention, a temperature of 150 ° C. is used to effect a crosslinking reaction between PVA and isobutylene-maleic anhydride copolymer formed on one or both sides of the film.
As described above, it is necessary to perform heat treatment in an atmosphere of preferably 180 ° C. or higher. By setting the heat treatment temperature to 150 ° C. or higher, the crosslinking reaction can proceed sufficiently, and a film having sufficient gas barrier properties can be obtained.

The heat treatment may be carried out in a hot air oven or by a known method such as a method in which a film is brought into contact with the surface of a hot roller or the like.

[0033]

Although the action of the alkali compound in the coating agent is not clear, it is partially neutralized with a suitable amount of alkali to improve the solubility of isobutylene-maleic anhydride. This is considered to be due to the fact that the two polymers were mixed more uniformly, and the tightness of both polymers was maintained even after drying. If the amount of the alkali compound is too large, not only does the compatibility between PVA and isobutylene-maleic anhydride decrease, but it also reacts with hydroxyl groups in the cross-linking reaction between the two polymers, and as a catalyst for the reaction. It is considered that the activity of the acting carboxyl group is reduced and the crosslinking reaction is less likely to occur.

[0034]

Next, the present invention will be described in detail with reference to examples.

The gas barrier property was determined by measuring the oxygen permeability in an atmosphere at 20 ° C. and a relative humidity of 85% using an oxygen barrier measuring device manufactured by Mocon Corporation.

Example 1 As PVA, polyvinyl alcohol UF040G manufactured by Unitika Chemical Co., Ltd. (degree of saponification: 99.6%, average degree of polymerization: 5)
00) was dissolved in pure water to obtain a 10% by mass aqueous solution. Isobutylene-isovan 04 (manufactured by Kuraray Co., Ltd.) was dissolved as an isobutylene-maleic anhydride in an aqueous solution containing 60% by mole of ammonium hydroxide based on the carboxyl group to obtain a 10% by mass solution.
Next, both aqueous solutions were mixed so that the mass ratio of PVA and isobutylene-maleic anhydride would be 70/30, and stirred at room temperature to prepare a coating agent. The pH of the coating agent was 7.4. This coating agent was coated on a biaxially stretched PET film (Emblem PET12 manufactured by Unitika Ltd., thickness 12 μm) with a Mayer bar so that the coating film thickness after drying was about 2 μm. After drying for minutes, it was heat-treated in a hot air oven at 200 ° C. for 10 seconds.
The resulting film has an oxygen permeability of 101 ml / m ² · d
ay ・ MPa

Comparative Example 1 The same operation as in Example 1 was performed using only the PVA aqueous solution as the coating agent. The resulting film had an oxygen permeability of 450 ml / m ² · day · MPa, and was insufficient in gas barrier properties to be used as a food packaging film.

Examples 2 to 6, Comparative Example 2 A gas barrier was prepared in the same manner as in Example 1 except that the mixing ratio of PVA and isobutylene-maleic anhydride, and the types and amounts of alkali compounds were changed as shown in Table 1. A functional PET film was obtained. Table 1 shows the oxygen permeability of the obtained film.

Example 7 Using a biaxially stretched nylon 6 film having a thickness of 15 μm, a gas barrier nylon film was obtained in the same manner as in Example 6. Table 1 shows the oxygen permeability of the obtained film.

Example 8 As PVA, polyvinyl alcohol UF040G manufactured by Unitika Chemical Co., Ltd. (degree of saponification: 99.6%, average degree of polymerization: 5)
00) was dissolved in pure water to obtain a 20% by mass aqueous solution. Isobutylene-isovan 04 (manufactured by Kuraray Co., Ltd.) as an isobutylene-maleic anhydride was dissolved in an aqueous solution containing 60 mol% of ammonium hydroxide and 3% of calcium hydroxide with respect to the carboxyl group to obtain a 20 mass% solution. Next, both aqueous solutions were mixed so that the mass ratio of PVA and isobutylene-maleic anhydride would be 70/30, and stirred at room temperature to prepare a coating solution.
Next, an extruder (75 mm
Extruded into a sheet at a cylinder temperature of 260 ° C. and a T-die temperature of 280 ° C. using a gentle compression type single screw having a diameter and an L / D of 45, and closely adhered to a cooling roll adjusted to a surface temperature of 10 ° C. It was quenched to obtain an unstretched film having a thickness of 120 μm. Subsequently, the unstretched film was guided to a gravure roll type coater, coated so that the coat thickness after drying was 20 μm, and dried in a hot air dryer at 80 ° C. for 30 seconds. Next, the film was supplied to a tenter-type simultaneous biaxial stretching machine, preheated at a temperature of 100 ° C. for 2 seconds, and then stretched at 95 ° C. at a magnification of 3 times in a vertical direction and 3.5 times in a horizontal direction. In addition, at a transverse relaxation rate of 5%,
After a heat treatment for 5 seconds and cooling to room temperature, the stretched film was wound up. Table 1 shows the oxygen permeability of the obtained film.

Example 9 An extruder (75 mm diameter,
Using a gentle compression type single screw with an L / D of 45), extrude it into a sheet at a cylinder temperature of 260 ° C and a T-die temperature of 270 ° C, and closely quench it on a cooling roll adjusted to a surface temperature of 10 ° C. And an unstretched film having a thickness of 150 μm. Subsequently, the unstretched film was guided to a gravure roll coater, and the same coating solution as prepared in Example 8 was coated so that the coating thickness after drying became 20 μm, and dried in a hot air dryer at 80 ° C. for 30 seconds. did. Next, the film was supplied to a tenter-type simultaneous biaxial stretching machine, preheated at a temperature of 100 ° C. for 2 seconds, and then stretched at 170 ° C. at a magnification of 3 times in a vertical direction and 3.5 times in a horizontal direction. Next, a heat treatment was performed at 200 ° C. for 15 seconds at a transverse relaxation rate of 5%, and after cooling to room temperature, the stretched film was wound. Table 1 shows the oxygen permeability of the obtained film.

[0042]

[Table 1]

[0043]

According to the present invention, there is provided a thermoplastic resin film which has high gas barrier properties even under high humidity and can be manufactured industrially at low cost.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B32B 27/30 102 B32B 27/30 102 C08J 7/04 CFD C08J 7/04 CFDP C09D 5/00 C09D 5 / 00Z 123/22 123/22 129/04 129/04 // C08L 101: 00 C08L 101: 00 (72) Inventor Kiyotaka Nakanishi 31-3 Uji Hinojiri, Uji City, Kyoto Unitika Uji Plastics Factory ( 72) Inventor Toyoki Uyama 31-3 Uji Hinojiri, Uji-city, Kyoto, Japan Unitika Uji Plastic Factory Co., Ltd. (72) Inventor Kento 23 Uji Kozakura, Uji-city, Kyoto 23 Unitika Central Research Laboratory F term (reference) 4D075 BB21Z CA42 DA04 DB31 DC36 EB56 4F006 AA12 AA35 AA38 AB13 AB20 AB24 AB72 AB73 BA05 CA07 4F073 AA17 BA06 BA23 BA29 BB01 EA01 E A11 EA41 EA65 GA01 4F100 AA01A AA18A AK01B AK08A AK08J AK21A AK21J AK24A AK24J AK42B AK80A AL01A BA02 BA03 BA06 EH462 EJ38B EJ412 GB15 GB23 JB16B JD02A 4J008 CB131 CB131 CB131 CB131

Claims (5)

[Claims] 1. Polyvinyl alcohol and isobutylene-
The mass ratio of the maleic anhydride copolymer is 97/3 to 20/8
0 and an alkaline compound having a pH of 6
Water-based gas-barrier coating agent which is -9. 2. The water-based gas barrier coating agent according to claim 1, wherein an alkali compound having a boiling point of 200 ° C. or lower is used as the alkali compound. 3. The aqueous gas barrier coating agent according to claim 1, wherein a mixture of an alkaline compound having a boiling point of 200 ° C. or lower and an alkaline earth metal hydroxide is used as the alkaline compound. 4. A gas barrier film comprising a thermoplastic resin film on at least one side of which a coating comprising the water-based gas barrier coating agent according to claim 1 is formed. 5. A method for producing a gas barrier film, comprising applying the water-based gas barrier coating agent according to claim 1 to a thermoplastic resin film and then heat-treating the film at a temperature of 150 ° C. or higher.