JP2013209491A - Aqueous coating liquid, gas barrier coating layer and multilayer structure obtained by using the aqueous coating liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aqueous coating liquid by which coating layer excellent in gas barrier performance in high humidity can be obtained.SOLUTION: Zirconium ammonium carbonate is blended as a cross-linking agent into PVA-based resin that contains the structural unit shown by general formula (1) [In the formula, RR, and Reach independently show hydrogen atoms or organic groups, X shows a single bond or a joining chain, and R, Rand Reach independently show hydrogen atoms or organic groups].

Description

  The present invention relates to an aqueous coating solution containing a polyvinyl alcohol-based resin and a crosslinking agent, and more specifically, to obtain a coating layer in which a crosslinked structure of a polyvinyl alcohol-based resin is formed and excellent in gas barrier properties under high humidity. Further, the present invention relates to a water-based coating solution that can be used, a gas barrier coating layer obtained by using the aqueous coating solution, and a multilayer structure.

Polyvinyl alcohol-based resin (hereinafter abbreviated as PVA-based resin) is transparent and has excellent gas barrier properties, so it is widely used as a packaging material for products such as foods, medicines, and cosmetics in which oxygen is a factor of alteration. It has been.
However, PVA-based resins are easy to absorb moisture and gas barrier properties are greatly reduced by moisture absorption. Therefore, they are used as multilayer structures in which the surface of the PVA-based resin layer is protected with a thermoplastic resin layer having excellent water vapor barrier properties. .
The layer containing the PVA-based resin is usually formed by applying an aqueous coating solution containing the PVA-based resin on the substrate and drying it because the PVA-based resin is not suitable for hot melt molding. ing.

  However, even if it is protected with a thermoplastic resin layer, etc., it is not possible to completely eliminate the effects of moisture when used under high humidity, or when the contents contain a lot of moisture, or when boil / retort treatment is required. It is difficult to improve the water resistance and moisture resistance of the PVA resin layer itself.

As a method for imparting water resistance to a PVA-based resin, a method for forming a crosslinked structure with a crosslinking agent is known, and such a technique is also being studied for a multilayer structure including a PVA-based resin layer.
For example, a technique for obtaining a gas barrier film excellent in hot water resistance by applying an aqueous coating solution containing a PVA-based resin, an inorganic layered compound, and a PVA-based resin crosslinking agent to a substrate has been proposed. (For example, refer to Patent Document 1.)

  Further, recently proposed PVA-based resins having a 1,2-diol structure in the side chain have various characteristics not found in general PVA-based resins. Since it is larger than PVA-based resin, water resistance is an essential technique depending on its use. For example, a zirconium compound has been proposed as a suitable crosslinking agent for such PVA-based resin. (For example, see Patent Document 2.)

JP 2003-205582 A JP 2006-299238 A

The excellent gas barrier property of the PVA resin is considered to be due to the high crystallinity due to a simple resin structure and the formation of a strong crystal structure due to hydrogen bonding between hydroxyl groups.
Therefore, it is general that when the PVA-based resin is cross-linked, the crystallinity is lowered, so that the gas barrier property is also lowered.

Actually, in the example of Patent Document 1, the water resistance is improved by cross-linking the PVA resin with a cross-linking agent, but the gas barrier property is not improved.
That is, the common view of those skilled in the art is that it is difficult to achieve both improvement in water resistance due to the formation of a crosslinked structure and gas barrier properties, particularly gas barrier properties under high humidity, in PVA-based resins.

  The present invention has been made in view of the above-described circumstances, and its purpose is an aqueous coating liquid that has a water resistance due to the formation of a crosslinked structure and that provides a coating layer that is excellent in gas barrier properties under high humidity. Is to provide.

  As a result of intensive studies in view of the above circumstances, the present invention uses an ammonium zirconium carbonate as a crosslinking agent for a PVA-based resin containing a structural unit represented by the following general formula (1), and an aqueous solution containing these. The inventors have found that the object of the present invention can be achieved by a coating solution, and have completed the present invention.

  Since the aqueous coating liquid of the present invention has a crosslinked structure of PVA-based resin, and a coating layer having excellent gas barrier properties under high humidity can be obtained, as a gas barrier protective layer for various substrates, or a food, It is suitable as a gas barrier layer in a multilayer structure used as a packaging material for chemicals, agricultural chemicals, cosmetics, electronic parts and the like, particularly as a packaging material requiring boil / retort treatment.

This is because the aqueous coating solution of the present invention is applied to a substrate and the like, and in the heating and drying process, carbonic acid in ammonium ammonium carbonate blended as a crosslinking agent and ammonium are volatilized during heating and drying to become only zirconium. A covalent bond is formed between the zirconium and the side chain 1,2-diol structure of the PVA resin, and the zirconium is arranged between the molecular chains of the PVA resin to inhibit gas permeation. Presumed to be.
Such an effect is a specific phenomenon that cannot be obtained with other zirconium compounds listed in Patent Document 2 but can be obtained only when ammonium zirconium carbonate is used.

The description of the constituent requirements described below is an example (representative example) of an embodiment of the present invention, and is not limited to these contents.
Hereinafter, the present invention will be described in detail.

[PVA resin]
First, the PVA resin used in the present invention will be described.
The PVA-based resin used in the resin composition of the present invention has a 1,2-diol structural unit represented by the following general formula (1), and R ¹ , R ² , and R ³ in the general formula (1). Each independently represents a hydrogen atom or an organic group, X represents a single bond or a bond chain, and R ⁴ , R ⁵ , and R ⁶ each independently represent a hydrogen atom or an organic group.

Particularly, it is most preferable that R ^{1 to} R ³ and R ^{4 to} R ⁶ in the 1,2-diol structural unit represented by the general formula (1) are all hydrogen atoms, and X is a single bond. A PVA resin having a structural unit represented by the general formula (1 ′) is preferably used.

In addition, R ^{1 to} R ³ and R ^{4 to} R ⁶ in the structural unit represented by the general formula (1) may be an organic group as long as the resin characteristics are not significantly impaired. Examples of the organic group include an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, and a tert-butyl group. May have a functional group such as a halogen group, a hydroxyl group, an ester group, a carboxylic acid group, or a sulfonic acid group, if necessary.

Further, X in the 1,2-diol structural unit represented by the general formula (1) is most preferably a single bond in terms of thermal stability and stability under high temperature or acidic conditions. A bonded chain may be used as long as it does not inhibit the effects of the present invention. Examples of such a bonded chain include hydrocarbons such as alkylene, alkenylene, alkynylene, phenylene, and naphthylene (these hydrocarbons include fluorine, chlorine, bromine, and the like). _other, -O of may be substituted by a _{halogen) -, - (CH 2 O} ) m -, - (OCH 2) m -, - (CH 2 O) m CH 2 -, - CO-, _{-COCO -, - CO (CH 2} ) m CO -, - CO (C 6 H 4) CO -, - S -, - CS -, - SO -, - SO 2 -, - NR -, - CONR-, -NRCO-, -CSNR-, -NRCS-, -NRNR-, _{HPO 4 -, - Si (OR} ) 2 -, - OSi (OR) 2 -, - OSi (OR) 2 O -, - Ti (OR) 2 -, - OTi (OR) 2 -, - OTi (OR) ₂ O—, —Al (OR) —, —OAl (OR) —, —OAl (OR) O—, and the like (R is each independently an optional substituent, preferably a hydrogen atom or an alkyl group, M is a natural number). Among them, an alkylene group having 6 or less carbon atoms, particularly a methylene group or —CH ₂ OCH ₂ — is preferable from the viewpoint of stability during production or use.

  Although it does not specifically limit as a manufacturing method of PVA-type resin used by this invention, (i) The method of saponifying the copolymer of a vinyl ester type monomer and the compound shown by following General formula (2), ( ii) a method of saponifying and decarboxylating a copolymer of a vinyl ester monomer and a compound represented by the following general formula (3); or (iii) a vinyl ester monomer and a compound represented by the following general formula (4): The method of saponifying and deketalizing the copolymer with is preferably used.

In the general formulas (2), (3) and (4), R ¹ , R ² , R ³ , X, R ⁴ , R ⁵ and R ⁶ are all the same as in the case of the general formula (1). . R ⁷ and R ⁸ are each independently a hydrogen atom or R ⁹ —CO— (wherein R ⁹ is an alkyl group having 1 to 4 carbon atoms). R ¹⁰ and R ¹¹ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

As the methods (i), (ii), and (iii), for example, the method described in JP-A-2006-95825 can be used.
Of these, it is preferable to use 3,4-diacyloxy-1-butene as the compound represented by the general formula (2) in the method (i) from the viewpoint of excellent copolymerization reactivity and industrial handleability. In particular, 3,4-diacetoxy-1-butene is preferably used.
In addition, the reactive ratio of each monomer when vinyl acetate is used as the vinyl ester monomer and 3,4-diacetoxy-1-butene is copolymerized is r (vinyl acetate) = 0.710, r ( 3,4-diacetoxy-1-butene) = 0.701, which is r in the case of vinyl ethylene carbonate which is an example of the compound represented by the general formula (3) used in the method (ii). Compared with (vinyl acetate) = 0.85 and r (vinyl ethylene carbonate) = 5.4, 3,4-diacetoxy-1-butene is excellent in copolymerization reactivity with vinyl acetate. is there.

  The chain transfer constant of 3,4-diacetoxy-1-butene is Cx (3,4-diacetoxy-1-butene) = 0.003 (65 ° C.), which is Cx (vinyl ethylene) of vinyl ethylene carbonate. Carbonate) = 0.005 (65 ° C.) and 2,2-dimethyl-4-vinyl-1,3-dioxolane which is an example of a compound represented by the general formula (4) used in the method (iii). Compared with Cx (2,2-dimethyl-4-vinyl-1,3-dioxolane) = 0.023 (65 ° C.), the degree of polymerization is less likely to increase and the polymerization rate is not reduced. Is shown.

  In addition, such 3,4-diacetoxy-1-butene is a by-product generated when saponifying the copolymer, and a by-product generated during the saponification from a structural unit derived from vinyl acetate frequently used as a vinyl ester monomer. It is an industrially significant advantage that it is the same as the resulting compound, and it is not necessary to provide any special equipment or process for the subsequent treatment or solvent recovery system, and conventional equipment can be used.

The above 3,4-diacetoxy-1-butene can be synthesized by, for example, a synthesis method via an epoxybutene derivative described in WO 00/24702, USP 5,623,086, USP 6,072,079, -It can manufacture by the reaction which isomerizes 1,4-diacetoxy-1-butene which is an intermediate product of a butanediol manufacturing process using metal catalysts, such as palladium chloride.
At the reagent level, Across products can be obtained from the market.

If the PVA resin obtained by the method (ii) or (iii) is insufficiently decarboxylated or deacetalized, a carbonate ring or an acetal ring remains in the side chain, and such a PVA resin When the resin is melt-molded, the cyclic group may cause the PVA-based resin to be cross-linked to generate a gel-like material.
Therefore, also from this point, the PVA resin obtained by the method (i) is preferably used in the present invention.

Examples of the vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valelate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, versatic. Although vinyl acid acid etc. are mentioned, vinyl acetate is preferably used economically.
In addition to the above-mentioned monomers (vinyl ester monomers, compounds represented by the general formulas (2), (3), (4)), a range that does not significantly affect the physical properties of the resin, specifically 10 mol% If within, α-olefin such as ethylene or propylene as a copolymerization component; hydroxy group-containing α- such as 3-buten-1-ol, 4-penten-1-ol, 5-hexene-1,2-diol Derivatives such as olefins and acylated products thereof; unsaturated acids such as itaconic acid, maleic acid and acrylic acid or salts or mono- or dialkyl esters thereof; nitriles such as acrylonitrile; amides such as methacrylamide and diacetone acrylamide; Olefin sulfonic acid such as ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, AMPS or the like A compound such as a salt thereof may be copolymerized.

  The degree of saponification (measured in accordance with JIS K6726) of the PVA resin used in the present invention is usually 95 to 100 mol%, particularly 98 to 99.9 mol%, and further 99 to 99.8 mol%. Are preferably used. If the degree of saponification is too low, the resulting coating layer may have insufficient gas barrier properties.

Moreover, the average degree of polymerization (measured according to JIS K6726) of the PVA-based resin is usually 300 to 2000, particularly 800 to 1500, and more preferably 1000 to 1300.
If the average degree of polymerization is too large, the viscosity of the aqueous coating solution may increase and the coating workability may decrease. Conversely, if it is too small, the mechanical strength of the coating layer tends to be insufficient. .

  The content of the 1,2-diol structural unit contained in the PVA-based resin is usually 2 to 10 mol%, particularly 3 to 8 mol%, and more preferably 5 to 7 mol%. If the content is too low or too high, the resulting coating layer tends to have insufficient gas barrier properties under high humidity.

The content of the 1,2-diol structural unit in the PVA resin is determined from a ¹ H-NMR spectrum (solvent: DMSO-d6, internal standard: tetramethylsilane) of a completely saponified PVA resin. Specifically, if calculated from the peak area derived from the hydroxyl proton, methine proton, and methylene proton in the 1,2-diol unit, the methylene proton in the main chain, the proton in the hydroxyl group linked to the main chain, etc. Good.

In addition, the PVA resin used in the present invention may be one kind or a mixture of two or more kinds. When a mixture is used, the degree of polymerization, the degree of saponification, and 1,2-diol are used. It is preferable that the average value of the content of the structural unit is in the above range.
In addition, it is possible to use a PVA resin that does not contain a 1,2-diol component in the side chain as the PVA resin, for example, unmodified PVA, but in that case, 1,2- PVA-based resin having a diol component is the main component, specifically 50% by weight or more, particularly preferably 80% by weight or more of the total amount of PVA-based resin.

[Ammonium zirconium carbonate]
Next, the ammonium zirconium carbonate blended as a cross-linking agent for the PVA resin in the aqueous coating solution of the present invention will be described.
Such ammonium zirconium carbonate is generally a compound represented by the chemical formula (NH ₄ ) ₂ ZrO (CO ₃ ) ₂ H ₂ O, and is widely used as a crosslinking agent for resins.

  Zirconium ammonium carbonate can be produced by a known production method, and examples of commercially available products include “Zircosol AC-7” manufactured by Daiichi Rare Element Chemical Industries, “Baycoat 20” manufactured by Nippon Light Metal Co., Ltd. Can do.

[Water-based coating solution]
The aqueous coating liquid of the present invention comprises the above-mentioned PVA resin as a main component and is blended with ammonium zirconium carbonate, and may contain other components as required.

  The concentration in the aqueous coating solution of the present invention is usually from 2.5 to 40% by weight, preferably from 5 to 40% by weight, particularly preferably from 5 to 10% by weight. If the concentration is too high, the viscosity of the coating solution may become too high, resulting in poor coating workability, bubbles in the coating solution may be difficult to escape, and it may be difficult to obtain a uniform coating layer. is there. On the other hand, if the concentration is too low, productivity may be lowered, for example, multiple coatings are required to obtain a coating layer having a desired thickness, and drying takes a long time.

  In addition, the amount of ammonium zirconium carbonate in the aqueous coating solution of the present invention is usually 2 to 20 parts by weight, particularly 3 to 20 parts by weight, especially 3 to 6 parts per 100 parts by weight of the PVA resin. A range of parts by weight is preferably used. If the content is too much or too little, the resulting coating layer tends to have insufficient gas barrier properties under high humidity.

The pH of the aqueous coating solution of the present invention at 20 ° C. is usually 6 to 14, and particularly preferably 8 to 12, particularly 8 to 10. If the pH is too acidic, the coating solution and the resulting coating layer are likely to become cloudy, and if it is too alkaline, the water resistance of the coating layer may be insufficient.
In addition, as a method for adjusting the pH of the aqueous coating solution, a known acidic compound or alkaline compound may be blended so as to have a desired pH, but sodium hydroxide is particularly preferably used.

  As a method for producing the aqueous coating liquid of the present invention, a known method for preparing an aqueous liquid containing a plurality of water-soluble compounds can be employed. For example, (1) an aqueous solution of PVA resin, ammonium zirconium carbonate (2) A method of preparing an aqueous solution of PVA resin and mixing and dissolving ammonium zirconium carbonate, (3) An aqueous solution of PVA resin and ammonium zirconium carbonate are poured into water. And a method of dissolving at the same time. Among them, the method (2) is preferably used because a uniform and good aqueous liquid can be easily obtained.

  In the production of such an aqueous coating solution, a stirring operation is important in both dissolution of the PVA resin and mixing and homogenization with ammonium zirconium carbonate, and a known stirrer can be used. , Medium speed rotating type stirrer, high speed rotating shear type stirrer and the like.

  In addition, if it is in the range which does not inhibit the effect of this invention, it is also possible to mix | blend water-soluble resin other than PVA-type resin specific to this invention with the aqueous coating liquid of this invention. Examples of such water-soluble resins include unmodified PVA, various modified PVA resins, polyvinyl pyrrolidone, and polyacrylic acid. Various aqueous emulsions can also be blended.

Among these, since there is little concern about phase separation in the coating liquid and in the coating layer, PVA resins are preferably used, and various modified PVA resins are used particularly for the purpose of imparting new functions. be able to.
Such a modified PVA resin is a product obtained by saponifying a copolymer of a vinyl ester monomer and various monomers. Examples of such a monomer include ethylene, propylene, isobutylene, α-octene, α-dodecene, α -Olefins such as octadecene, hydroxy group-containing α-olefins such as 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol and derivatives thereof such as acylated products, acrylic acid, Unsaturated acids such as methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, undecylenic acid, its salts, monoesters, dialkyl esters, nitriles such as acrylonitrile, methacrylonitrile, diacetone acrylamide, acrylamide, methacryl Amides such as amides, ethylene Olefin sulfonic acids such as acid, allyl sulfonic acid, methallyl sulfonic acid or salts thereof, alkyl vinyl ethers, dimethylallyl vinyl ketone, N-vinyl pyrrolidone, vinyl compounds such as vinyl chloride, isopropenyl acetate, 1-methoxyvinyl acetate And substituted vinyl acetates such as

  Moreover, you may use together well-known crosslinking agents other than zirconium carbonate ammonium in the range which does not inhibit the effect of this invention as a crosslinking agent of PVA-type resin in the aqueous coating liquid of this invention. Examples of such cross-linking agents include zirconium compounds other than ammonium zirconium carbonate, zirconium compounds such as zirconium oxynitrate, titanium compounds such as titanium lactate, aldehyde compounds such as glyoxal, methylol compounds such as methylolated melamine, and boric acid. And boron compounds such as borax.

  The aqueous coating liquid of the present invention is within the range not impairing the effects of the present invention, such as an antifoaming agent, a surfactant, an ultraviolet absorber, an antioxidant, a colorant, a fluorescent dye, an antiseptic, and an antifungal agent. In addition, a conventionally known additive or a layered inorganic compound for further improving gas barrier properties may be contained. Further, it may contain an organic solvent other than water for the purpose of improving the wettability to the substrate or adjusting the drying speed, and specifically, an alcohol having 1 to 4 carbon atoms that is miscible with water. And ketones.

[Coating layer]
The aqueous coating solution of the present invention thus obtained can be applied to various substrates and dried to form a coating layer.
The base material is not particularly limited, and the material is a thermoplastic resin, a synthetic resin such as a thermosetting resin, a metal material such as glass or aluminum foil, a natural material such as paper or wood, and the shape is a film. , Sheets, nonwoven fabrics, various molded products, and the like.
Of these, a multilayer structure is preferably used by coating a film- or sheet-like substrate to form a coating layer, and further laminating other layers, which is practically important.
Hereinafter, an example using a film-like substrate will be mainly described.

Examples of the thermoplastic resin include low density polyethylene, ultra low density polyethylene, high density polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer. Polyolefin resins such as polymers and ionomer resins; aromatic polyester resins such as polyethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate; aliphatic polyester resins such as polylactic acid, polybutylene succinate and polybutylene succinate adipate; Polyamide resins such as nylon-6, nylon 6,6, metaxylylenediamine-adipic acid condensation polymer; acrylic resins such as polymethacrylate and polymethylmethacrylate; polystyrene, styrene Styrene resins such as acrylonitrile; cellulose triacetate, cellulose resins such as di cellulose acetate;
Halogen-containing resins such as polyvinyl chloride, polyvinylidene chloride, and polyvinylidene fluoride; engineering plastics such as polycarbonate resin, polysulfone resin, polyether sulfone resin, polyether ether ketone resin, polyphenylene oxide resin, and liquid crystal polymer; Can do.

Among these thermoplastic resins, polypropylene, polyethylene terephthalate, nylon and the like are preferably used. In particular, these films, a film formed by biaxial stretching, and a film formed by vapor-depositing silica, alumina or the like on the surface thereof. Etc. are preferably used.
In addition, when using a film base material, about 10-1000 micrometers is suitable for the thickness.

As a method for applying the aqueous coating liquid of the present invention to the above-mentioned substrate, a gravure method such as a direct gravure method or a reverse gravure method; a roll coating method such as a two-roll beat coating method or a bottom feed three-roll method A known coating method such as a doctor knife method, a die coating method, a dip coating method, or a bar coating method can be used.
In addition, depending on the substrate, surface treatment such as plasma treatment, corona treatment, electron beam treatment, primer treatment, anchor treatment, etc. is performed in order to improve the adhesion with the coating layer by the aqueous coating solution of the present invention. It is preferable to use those subjected to.

After the aqueous coating liquid of the present invention is applied to a substrate, moisture and other volatile components are removed by drying. The drying temperature at that time should be appropriately adjusted depending on the thickness of the coating layer, but is usually 10 to 200 ° C., and particularly preferably 20 to 150 ° C., particularly 30 to 120 ° C. . Further, the drying time is appropriately adjusted according to the above-mentioned drying temperature so that the volatile component is a predetermined amount or less, but is usually 0.1 to 120 minutes, and particularly 0.5 to 60. Done in minutes.
In the process of heating and drying, the PVA resin of the present invention is crosslinked with ammonium zirconium carbonate to form a crosslinked structure.

  Thus, a coating layer containing a crosslinked structure of PVA-based resin is formed, and the film thickness is usually 0.05 to 50 μm, particularly 0.1 to 30 μm, particularly 1 to 20 μm. A range is preferably used. If the film thickness is too thin, sufficient gas barrier properties may not be obtained. On the other hand, if the film thickness is too thick, the flexibility of a multilayer structure tends to be impaired.

In this coating layer, usually, another thermoplastic resin is further laminated to form a multilayer structure, but such a thermoplastic resin can be the same as described above. When the PVA-based resin layer is a (a1, a2,...) And the thermoplastic resin layer is b (b1, b2,...), Not only a two-layer structure of a / b but also b / a / b, a / b / a, a1 / a2 / b, a / b1 / b2, b2 / b1 / a / b1 / b2, b1 / b2 / a / b3 / b4, a1 / b1 / a2 / b2, etc. Combinations are possible, and a layer structure of b / a / b or b2 / b1 / a / b1 / b2 is particularly preferable.
In addition, it is also a preferable embodiment to provide an adhesive layer between the PVA resin layer (a) and the thermoplastic resin layer (b).

  Furthermore, it is also a preferred embodiment to provide a vapor deposition layer made of a metal or an inorganic component on the surface of the multilayer structure or the interface between the layers.

The film thickness of such a multilayer structure is usually from 0.1 to 100 μm, in particular from 1 to 50 μm, in particular from 2 to 30 μm. If the film thickness is too thin, sufficient gas barrier properties tend not to be obtained. Conversely, if the film thickness is too thick, flexibility tends to be impaired.
Moreover, the ratio (a / b) of the thicknesses of the PVA resin layer (a) and the thermoplastic resin layer (b) in the multilayer structure is the ratio of the thickest layers when there are a plurality of layers. The ratio is usually 1/99 to 50/50, and particularly preferably in the range of 1/99 to 30/70, particularly 5/95 to 30/70.

Examples of the present invention will be described below, but the present invention is not limited to the description of the examples unless it exceeds the gist.
In the examples, “parts” and “%” mean weight basis unless otherwise specified.

Example 1
<Production of PVA resin>
A reaction vessel equipped with a reflux condenser and a stirrer was charged with 1500 parts of vinyl acetate, 75 parts of methanol, and 180 parts of 3,4-diacetoxy-1-butene, and 0.05 mol% of azobisisobutyronitrile (as opposed to the preparation). (Vinyl acetate) was added and the temperature was raised under a nitrogen stream while stirring to initiate polymerization. When the polymerization rate of vinyl acetate reaches 75%, m-dinitrobenzene is added to complete the polymerization, and then unreacted vinyl acetate monomer is removed from the system by blowing methanol vapor. A combined methanol solution was obtained.
Next, the methanol solution was further diluted with methanol, adjusted to a concentration of 35%, charged into a kneader, and while maintaining the solution temperature at 40 ° C., a 2% methanol solution of sodium hydroxide was used as a vinyl acetate structural unit in the copolymer. Further, saponification was carried out by adding 8 mmol per 1 mol of the total amount of 3,4-diacetoxy-1-butene structural units. As saponification progressed, when saponified substances were precipitated and formed into particles, they were separated by filtration, washed well with methanol and dried in a hot air drier to produce the intended PVA resin.

  The saponification degree of the obtained PVA-based resin was 99.5 mol% when analyzed by the alkali consumption required for hydrolysis of residual vinyl acetate and 3,4-diacetoxy-1-butene. The average degree of polymerization was 1200 when analyzed according to JIS K 6726. The content of the 1,2-diol structural unit represented by the general formula (1) is measured by 1H-NMR (300 MHz proton NMR, d6-DMSO solution, internal standard substance: tetramethylsilane, 50 ° C.). The calculated value was 6 mol%.

<Preparation of aqueous coating solution>
36.1 parts of the obtained PVA-based resin is added to 665 parts of purified water at room temperature with stirring to obtain a dispersion. The dispersion was heated to 80 ° C. with stirring, stirred for 30 minutes, and then cooled to obtain a 5% PVA aqueous solution.
To 100 parts of the obtained PVA aqueous solution, 7.69 parts of ammonium zirconium carbonate (“Zircosol AC-7” manufactured by Daiichi Rare Element Chemical Co., Ltd.) (10% by weight of PVA resin in terms of ZrO ₂ ) was added for 10 minutes. After stirring and mixing, the pH was adjusted to 8.8 using 0.1N sodium hydroxide H aqueous solution to obtain an aqueous coating solution.

<Production of multilayer structure>
The obtained aqueous coating solution was applied to the corona-treated surface of a corona-treated polyester film ("Taiko Polyester Film FE2001" manufactured by Futamura Chemical Co., Ltd.) using a bar coater # 30 so that the coating thickness after drying was 3 μm. . Drying was performed at 150 ° C. for 10 minutes to obtain a multilayer structure.

<Oxygen permeability>
The oxygen permeability of the obtained multilayer structure in an atmosphere of 23 ° C. and 80% RH for 30 minutes was measured using an oxygen permeation tester (“OXTRAN 2/20” manufactured by MOCON). From the obtained measured value, the oxygen permeability of the coating layer (oxygen permeability of the coating layer) was determined according to the following formula, and a converted value of 3 μm thickness was further calculated.
The results are shown in Table 1.
1 / P _total = 1 / P _sample + 1 / P _base
P _total : Oxygen permeability of the multilayer structure P _sample : Oxygen permeability of the coating layer P _base : Oxygen permeability of the _base film

Comparative Example 1
In Example 1, an aqueous coating solution and a multilayer structure were prepared and evaluated in the same manner as in Example 1 except that ammonium zirconium carbonate was not used. The results are shown in Table 1.

Comparative Example 2
Example 1 Example 2 except that 2.27 parts (10% by weight of PVA-based resin in terms of Ti) of titanium lactate (“Orgatics TC-310” manufactured by Matsumoto Trading Co., Ltd.) was used in place of ammonium zirconium carbonate. An aqueous coating solution and a multilayer structure were prepared in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 1.

Comparative Example 3
In Example 1, in place of ammonium zirconium carbonate, zirconium oxynitrate (“ZN” manufactured by Daiichi Rare Element Chemical Industries, Ltd.) was used except that 3.95 parts (10% by weight of PVA resin in terms of ZrO ₂ ) was used. An aqueous coating solution and a multilayer structure were prepared in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 1.

Comparative Example 4
In Example 1, instead of ammonium zirconium carbonate, 4.94 parts of zirconium oxychloride ("ZC-20" manufactured by Daiichi Rare Element Chemical Industry Co., Ltd.) (10% by weight of PVA resin in terms of ZrO ₂ ) was used. Except for the above, an aqueous coating solution and a multilayer structure were prepared in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Table 1.

[Table 1]

From the above results, the multilayer structure having a coating layer of an aqueous coating solution in which ammonium carbonate is blended with a PVA resin having a 1,2-diol structure in the side chain of Example 1 is a gas barrier under high humidity. It was excellent in properties.
On the other hand, a sufficient gas barrier property was not obtained with a metal compound known as a metal-based crosslinking agent for a PVA-based resin having no 1,2-diol structure in the side chain without using a crosslinking agent.

  Since the aqueous coating liquid of the present invention provides a coating layer having excellent gas barrier properties under high humidity, it can be used as a gas barrier protective layer for various substrates, or for foods, chemicals, agricultural chemicals, cosmetics, electronic parts, etc. It is suitable as a gas barrier layer in a multilayer structure used as a packaging material, particularly as a packaging material requiring boil / retort treatment.

Claims (5)

An aqueous coating solution obtained by blending ammonium zirconium carbonate as a crosslinking agent in a PVA resin containing a structural unit represented by the following general formula (1).

[Wherein R ¹ , R ² and R ³ each independently represents a hydrogen atom or an organic group, X represents a single bond or a bond chain, and R ⁴ , R ⁵ and R ⁶ each independently represent hydrogen. Indicates an atom or an organic group. ] The aqueous coating solution according to claim 1, wherein the compounding amount of ammonium zirconium carbonate is 2 to 20 parts by weight with respect to 100 parts by weight of the PVA resin. The aqueous coating solution according to claim 1 or 2, wherein the pH at 20 ° C is 6 to 14. A gas barrier coating layer obtained by coating and drying the aqueous coating solution according to any one of claims 1 to 3 on a support substrate. A multilayer structure having at least one coating layer according to claim 4.