JP7610514B2 - Multilayer structure, vacuum packaging bag and vacuum insulator - Google Patents

Description

The present invention relates to a multilayer structure, a vacuum packaging bag and a vacuum insulator.

Traditionally, polyurethane foam has been widely used as an insulator in refrigerators, residential insulating walls, storage tanks, etc. In recent years, vacuum insulators have been used as an alternative insulator. Vacuum insulators make it possible to achieve insulating properties equivalent to those of insulators made of polyurethane foam, but in a thinner and lighter form. Vacuum insulators are expanding their uses and demand as insulators used to insulate heat transfer equipment such as heat pump application equipment, heat storage equipment, living spaces, vehicle interior spaces, etc.

For example, a vacuum insulator may have a structure that includes a vacuum packaging bag and a core material disposed inside the vacuum packaging bag. One of the characteristics required for a vacuum packaging bag is barrier properties. For this reason, vacuum packaging bags with improved barrier properties and barrier films for use therein have been proposed.

For example, Patent Document 1 describes a gas barrier film having a vapor deposition film on one side of an ethylene-vinyl alcohol copolymer film and a coating layer of polyvinyl alcohol containing an inorganic substance adjacent to the vapor deposition film, as a film used for vacuum packaging bags with enhanced gas barrier properties.

JP 2008-114520 A

However, the barrier properties of the conventional gas barrier films described above may deteriorate when subjected to physical stresses such as stretching or bending during the manufacturing process of vacuum insulators, for example.

The object of the present invention is to provide a multilayer structure, a vacuum packaging bag and a vacuum insulator that can maintain high barrier properties even when subjected to physical stress such as bending.

That is, the present invention relates to a multilayer structure comprising: [1] a substrate (X), an inorganic vapor deposition layer (Y), and an overcoat layer (Z) in this order, wherein the substrate (X) is made of a biaxially stretched polyvinyl alcohol-based resin film, the overcoat layer (Z) contains a modified polyvinyl alcohol (A) having a vinyl alcohol unit (a) and a monomer unit (b) having a polar group other than the vinyl alcohol unit (a), and the thickness of the overcoat layer (Z) is 0.003 μm or more and 5 μm or less;
[2] The multilayer structure according to [1], in which the proportion of the monomer units (b) having a polar group in all monomer units constituting the modified polyvinyl alcohol (A) is 0.05 mol % or more and 30 mol % or less;
[3] The multilayer structure according to [1] or [2], wherein the polar group is at least one selected from the group consisting of a carboxy group, an ester group, and a silanol group;
[4] The multilayer structure according to any one of [1] to [3], which has a maximum strength ratio (I(B)/I(C) _MAX ) of 1.20 or more, which is determined by the following steps (1) to (3);
(1) At five arbitrarily selected points on the surface of the overcoat layer (Z), a depth direction analysis is performed by TOF-SIMS.
(2) For each detected fragment, the average value of the maximum fragment intensity at each measurement point (I(B)) and the average value of the intensity at the measurement point midway between the measurement start point and the measurement point of maximum intensity at each measurement point (I(C)) are calculated, and the ratio of these values is defined as the intensity ratio (I(B)/I(C)).
(3) The maximum of the intensity ratios (I(B)/I(C)) found for each fragment is determined as the maximum intensity ratio (I(B)/I(C) _MAX ).
[5] The multilayer structure according to any one of [1] to [4], further comprising a layer (J) other than the substrate (X), the inorganic vapor deposition layer (Y), and the overcoat layer (Z);
[6] The multilayer structure according to [5], which comprises at least two other layers (J), and comprises a substrate (X), an inorganic vapor deposition layer (Y), and an overcoat layer (Z) between the at least two other layers (J);
[7] The multilayer structure according to any one of [1] to [6], wherein the biaxially stretched polyvinyl alcohol-based resin film is a biaxially stretched film containing as a main component an ethylene-vinyl alcohol copolymer having an ethylene unit content of 10 mol% or more and 65 mol% or less and a saponification degree of 90 mol% or more;
[8] The multilayer structure according to any one of [1] to [7], which has an oxygen permeability of 2.0 ml/( ^m2 ·day·atm) or less, measured in accordance with JIS K7126 under conditions of 40°C, 0% RH (carrier gas side) and 90% RH (oxygen supply side), after three repeated reciprocating movements in a Gelbo-Fleck test in accordance with ASTM F 392;
[9] A vacuum packaging bag comprising the multilayer structure according to any one of [1] to [8];
[10] A vacuum insulator comprising the vacuum packaging bag of [9] and a core material disposed inside the vacuum packaging bag, the inside of which is reduced in pressure;
This is achieved by providing

The present invention provides a multilayer structure, a vacuum packaging bag, and a vacuum insulator that can maintain high barrier properties even when subjected to physical stress such as bending.

1 is a graph showing one of the measurement results of SiO ₂ in a depth direction analysis using a TOF-SIMS in Example 4.

In this specification, unless otherwise specified, "gas barrier properties" refers to the ability to barrier gases other than water vapor. In addition, in this specification, when simply stated as "barrier properties", it means both gas barrier properties and water vapor barrier properties. In addition, the property of "being able to maintain high barrier properties even when subjected to physical stress such as bending" is sometimes expressed as "flex resistance".

(Multilayer structure)
The multilayer structure of the present invention comprises a substrate (X), an inorganic vapor deposition layer (Y) and an overcoat layer (Z) in this order, the substrate (X) being a biaxially stretched polyvinyl alcohol-based resin film (hereinafter sometimes abbreviated as "biaxially stretched PVA-based resin film"), the overcoat layer (Z) containing a modified polyvinyl alcohol (A) (hereinafter sometimes abbreviated as "modified PVA (A)") having a vinyl alcohol unit (a) and a monomer unit (b) having a polar group other than the vinyl alcohol unit (a), and the thickness of the overcoat layer (Z) is 0.003 μm or more and 5 μm or less. The multilayer structure of the present invention tends to exhibit good bending resistance by comprising an inorganic vapor deposition layer (Y) on the substrate (X) and a specific thickness of the overcoat layer (Z) containing the modified PVA (A). In the multilayer structure, the substrate (X) and the inorganic vapor deposition layer (Y) may be in direct contact with each other, or another layer may be interposed. Similarly, the inorganic vapor deposition layer (Y) and the overcoat layer (Z) may be in direct contact with each other or may have another layer interposed therebetween, but it is preferable that the inorganic vapor deposition layer (Y) and the overcoat layer (Z) are in direct contact with each other. In the multilayer structure, the inorganic vapor deposition layer (Y) and the overcoat layer (Z) may be provided on both sides of the substrate (X), respectively.

(Substrate (X))
The multilayer structure of the present invention exhibits excellent gas barrier properties by having the biaxially stretched PVA-based resin film as the substrate (X). In addition, the substrate (X) is made of a biaxially stretched PVA-based resin film, and thus has high affinity with the inorganic vapor deposition layer (Y) described below, and thus has improved flex resistance.

The biaxially stretched PVA-based resin film is a biaxially stretched film whose main component is a PVA-based resin. The main component refers to the component with the largest content by mass. The content of the PVA-based resin in the substrate (X), i.e., the biaxially stretched PVA-based resin film, is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 99% by mass or more.

The PVA-based resin may be any resin having vinyl alcohol units formed by saponifying vinyl ester units, such as polyvinyl alcohol (hereinafter sometimes abbreviated as "PVA") resin and ethylene-vinyl alcohol copolymer (hereinafter sometimes abbreviated as "EVOH") resin. Of these, EVOH resin is preferred as the PVA-based resin from the viewpoint of obtaining a multilayer structure with excellent flex resistance. In other words, the substrate (X) is preferably made of a biaxially stretched EVOH resin film.

Examples of PVA resins include PVA resins obtained by homopolymerizing vinyl esters such as vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl pivalate, and vinyl versatate, followed by saponification. The PVA resin in the present invention may be a modified PVA resin that has been copolymerized or post-modified. Homopolymerization of vinyl esters and saponification of vinyl ester homopolymers can be carried out by known methods. Copolymerized modified PVA resins are produced by copolymerizing, for example, the vinyl esters described above with unsaturated monomers copolymerizable with vinyl esters, followed by saponification, and the amount of modification is usually less than 10 mol%.

Examples of unsaturated monomers copolymerizable with vinyl esters include olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, and α-octadecene; hydroxyl-containing α-olefins such as 3-buten-1-ol, 4-penten-1-ol, and 5-hexen-1-ol, as well as derivatives thereof such as acylated products; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, and undecylenic acid, as well as their salts, monoesters, and dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; diacetone acrylamide, acrylic amides such as amide and methacrylamide; olefin sulfonic acids or salts thereof such as ethylene sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid; vinyl compounds such as alkyl vinyl ethers, dimethylallyl vinyl ketone, N-vinyl pyrrolidone, vinyl chloride, vinyl ethylene carbonate, 2,2-dialkyl-4-vinyl-1,3-dioxolane, glycerin monoallyl ether, and 3,4-diacetoxy-1-butene; substituted vinyl acetates such as isopropenyl acetate and 1-methoxyvinyl acetate; vinylidene chloride, 1,4-diacetoxy-2-butene, and vinylene carbonate.

Post-modified PVA resins are obtained by post-modifying PVA using methods such as acetoacetate esterification, acetalization, urethanization, etherification, grafting, phosphate esterification, and oxyalkylenation.

In the present invention, the viscosity average degree of polymerization of the PVA resin is preferably 1100 or more, more preferably 1200 or more. The viscosity average degree of polymerization of the PVA resin is preferably 4000 or less, more preferably 2600 or less. If the viscosity average degree of polymerization of the PVA resin is 1100 or more, the mechanical strength of the resulting vacuum packaging bag is good, which is preferable. On the other hand, if the viscosity average degree of polymerization is 4000 or less, the processability during film formation and stretching is good, which is preferable. The saponification degree of the PVA resin is preferably 90 mol% or more, more preferably 95 mol% or more, and even more preferably 99 mol% or more. The saponification degree of the PVA resin may be 100 mol% or less or 99.9 mol% or less. If the saponification degree is within the above range, the water resistance is improved and the gas barrier property against humidity is good, which is preferable. The viscosity average degree of polymerization and the saponification degree of the PVA resin can be measured according to the method described in JIS K 6726 (1994).

EVOH resin is usually obtained by saponifying a copolymer of ethylene and a vinyl ester such as vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl pivalate, and vinyl versatate. The production and saponification of the copolymer of ethylene and a vinyl ester can be performed by a known method. The saponification degree of the vinyl ester component of the EVOH resin is preferably 90 mol% or more, more preferably 95 mol% or more, and even more preferably 99 mol% or more. By setting the saponification degree to 90 mol% or more, the gas barrier property can be improved. The saponification degree of the EVOH resin may be 100 mol% or less, or 99.99 mol% or less. The saponification degree of the EVOH resin is determined by performing nuclear magnetic resonance ( ¹ H-NMR) measurement and measuring the peak area of the hydrogen atoms contained in the vinyl ester structure and the peak area of the hydrogen atoms contained in the vinyl alcohol structure.

The ethylene unit content of the EVOH resin is preferably 10 mol% or more, more preferably 15 mol% or more, even more preferably 20 mol% or more, and even more preferably 25 mol% or more. The ethylene unit content of the EVOH resin is preferably 65 mol% or less, more preferably 55 mol% or less, and even more preferably 50 mol% or less. When the ethylene unit content is 10 mol% or more, the gas barrier properties and flex resistance tend to be maintained well under high humidity. On the other hand, when the ethylene unit content is 65 mol% or less, the gas barrier properties can be improved. The ethylene unit content of the EVOH resin can be determined by the NMR method.

In addition, the EVOH resin may have units derived from other monomers other than ethylene, vinyl esters, and saponified products thereof, to the extent that the object of the present invention is not hindered. When the EVOH resin has the other monomer units, the content of the other monomer units relative to the total monomer units of the EVOH resin is preferably 30 mol% or less, more preferably 20 mol% or less, even more preferably 10 mol% or less, and particularly preferably 5 mol% or less. When the EVOH resin has units derived from the other monomers, the lower limit may be 0.05 mol% or 0.10 mol%. Examples of the other monomers include alkenes such as propylene, butylene, pentene, and hexene; 3-acyloxy-1-propene, 3-acyloxy-1-butene, 4-acyloxy-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-methyl-1-butene, 4-acyloxy-2-methyl-1-butene, 4-acyloxy-3-methyl 1-butene, 3,4-diacyloxy-2-methyl-1-butene, 4-acyloxy-1-pentene, 5-acyloxy-1-pentene, 4,5-diacyloxy-1-pentene, 4-acyloxy-1-hexene, 5-acyloxy-1-hexene, 6-acyloxy-1-hexene, 5,6-diacyloxy-1-hexene, 1,3-diacetoxy-2-methyl alkene having an ester group such as dimethylpropane or a saponification product thereof; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid or anhydrides, salts, or mono- or dialkyl esters thereof; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as vinyl sulfonic acid, allyl sulfonic acid, methallylsulfonic acid or salts thereof; vinyl silane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxy-ethoxy)silane, γ-methacryloxypropylmethoxysilane; alkyl vinyl ethers, vinyl ketones, N-vinylpyrrolidone, vinyl chloride, vinylidene chloride, and the like.

In addition, when the EVOH resin is a blend of two or more different types of EVOH resins, the average ethylene unit content or saponification degree of the entire EVOH resin shall be regarded as the ethylene unit content or saponification degree of the EVOH resin.

The biaxially stretched PVA-based resin film may contain other components, such as carboxylic acid compounds, phosphate compounds, boron compounds, metal salts, stabilizers, antioxidants, UV absorbers, antistatic agents, lubricants, colorants, fillers, desiccants, reinforcing agents such as various fibers, etc., as long as the effects of the present invention are not impaired.

As the substrate (X), a film formed using a PVA-based resin is used. Such a film can be formed by a known method, such as a casting method in which a solution of a PVA-based resin is cast onto a metal surface such as a drum or an endless belt to form a film, or a melt molding method in which the resin is melt-extruded using an extruder.

Such PVA-based resin films are used after being biaxially stretched according to known methods such as simultaneous biaxial stretching and sequential biaxial stretching. From the viewpoints of thickness uniformity, barrier properties, mechanical properties, and film-forming properties, the stretching ratio is preferably in the range of 2.5 to 4.5 times in the longitudinal direction (MD direction), 2.5 to 4.5 times in the transverse direction (TD direction), and 7 to 15 times in the areal stretching ratio, and more preferably in the range of 2.5 to 3.5 times in the longitudinal direction, 2.5 to 3.5 times in the transverse direction, and 8 to 12 times in the areal stretching ratio. If the PVA-based resin film is not biaxially stretched, bending resistance and gas barrier properties may be reduced.

The thickness of the substrate (X) is not particularly limited, but from the viewpoint of industrial productivity, it is preferably 5 μm or more, more preferably 8 μm or more, and even more preferably 10 μm or more. The thickness of the substrate (X) is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, and particularly preferably 30 μm or less. The thickness is the average value of the values measured at any five points. The same applies to other thicknesses below.

(Inorganic vapor deposited layer (Y))
The inorganic vapor deposition layer (Y) is usually a layer having a barrier property against oxygen and water vapor, and can be formed by vapor deposition of an inorganic material. Examples of the inorganic material include metals (e.g., aluminum), metal oxides (e.g., silicon oxide), and the like. , aluminum oxide), metal nitrides (e.g., silicon nitride), metal nitride oxides (e.g., silicon oxynitride), and metal carbonitrides (e.g., silicon carbonitride). Among these, aluminum, aluminum oxide, From the viewpoint of excellent barrier properties after bending, silicon oxide, magnesium oxide, and silicon nitride are preferred, and aluminum is more preferred.

The method for forming the inorganic vapor deposition layer (Y) is not particularly limited, and examples thereof include physical vapor deposition methods such as vacuum deposition (e.g., resistance heating deposition, electron beam deposition, molecular beam epitaxy, etc.), sputtering, and ion plating; chemical vapor deposition methods such as thermal chemical vapor deposition (e.g., catalytic chemical vapor deposition), photochemical vapor deposition, plasma chemical vapor deposition (e.g., capacitively coupled plasma, inductively coupled plasma, surface wave plasma, electron cyclotron resonance, dual magnetron, atomic layer deposition, etc.), and metalorganic vapor deposition.

The thickness of the inorganic vapor deposition layer (Y) varies depending on the type of components constituting the inorganic vapor deposition layer (Y), but is preferably 0.002 μm or more and 0.5 μm or less, more preferably 0.005 μm or more and 0.2 μm or less, and even more preferably 0.01 μm or more and 0.1 μm or less. When the thickness of the inorganic vapor deposition layer (Y) is 0.002 μm or more, the barrier properties against oxygen and water vapor tend to be better. Also, when the thickness of the inorganic vapor deposition layer (Y) is 0.5 μm or less, the barrier properties after bending tend to be better maintained.

(Overcoat Layer (Z))
The overcoat layer (Z) contains a modified PVA (A). When the overcoat layer (Z) contains the modified PVA (A), the flex resistance tends to be improved. The modified PVA (A) has a vinyl alcohol unit (a) and a monomer unit (b) having a polar group. The monomer unit (b) does not contain a vinyl alcohol unit (a). The modified PVA (A) is not particularly limited as long as it has a vinyl alcohol unit (a) and a monomer unit (b), but it is preferable that it is not alkylene-modified.

The vinyl alcohol unit (a) is a unit represented by _-CH2CH (OH)-. The proportion of the vinyl alcohol unit (a) in all monomer units constituting the modified PVA (A) is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 75 mol% or more, and in some cases even more preferably 80 mol%, 85 mol%, 90 mol% or 95 mol% or more.

The monomer unit (b) is a monomer unit other than the vinyl alcohol unit (a) and has a polar group. The polar group may be a monovalent group or a divalent or higher group. The polar group is not particularly limited, but from the viewpoint of further improving the bending resistance, it is preferable that it is at least one selected from the group consisting of a carboxy group, an ester group (-COO-) and a silanol group. The polar group may be a group represented by -COOR (R is a hydrocarbon group) as a group containing an ester group. As the hydrocarbon group represented by the above R, an alkyl group is preferable, and an alkyl group having 1 to 3 carbon atoms is more preferable. The silanol group refers to a group (Si-OH) in which a hydroxyl group (-OH) is bonded to a silicon atom.

The modified PVA (A) can be produced by methods such as copolymerization modification or post-modification, similar to the modified PVA that can be used for the substrate (X) described above.

For example, the monomer unit (b) having a carboxy group can be introduced into the modified PVA (A) by using an unsaturated acid such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, or undecylenic acid as an unsaturated monomer. The monomer unit (b) having an ester group can be introduced into the modified PVA (A) by using an ester of an unsaturated acid as an unsaturated monomer or by adjusting the degree of saponification. The monomer unit (c) having a silanol group can be introduced into the modified PVA (A) by using a compound having an unsaturated double bond and a trialkoxysilyl group such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(β-methoxy-ethoxy)silane, or γ-methacryloxypropylmethoxysilane as an unsaturated monomer. At least a part of the trialkoxysilyl group becomes a silanol group upon saponification.

The proportion of the polar group-containing monomer unit (b) in the total monomer units constituting the modified PVA (A) is preferably 0.05 mol% or more, more preferably 0.10 mol% or more. The proportion of the polar group-containing monomer unit (b) is preferably 30 mol% or less, more preferably 25 mol% or less.

When the modified PVA (A) has a monomer unit (b) containing a carboxy group as a polar group, the proportion of the monomer unit (b) containing a carboxy group in the total monomer units constituting the modified PVA (A) is preferably 0.05 mol% or more, more preferably 0.50 mol% or more. The proportion of the monomer unit (b) containing a carboxy group is preferably 10 mol% or less, more preferably 5 mol% or less. When the proportion of the monomer unit (b) containing a carboxy group is in the above range, the bending resistance tends to be better.

When the modified PVA (A) has a monomer unit (b) containing an ester group as a polar group, the proportion of the monomer unit (b) containing an ester group in the total monomer units constituting the modified PVA (A) is preferably 5 mol% or more, more preferably 10 mol% or more. The proportion of the monomer unit (b) containing an ester group is preferably 30 mol% or less, more preferably 25 mol% or less. When the proportion of the monomer unit (b) containing an ester group is in the above range, the bending resistance tends to be better.

When the modified PVA (A) has a monomer unit (b) containing a silanol group as a polar group, the proportion of the monomer unit (b) containing a silanol group in the total monomer units constituting the modified PVA (A) is preferably 0.05 mol% or more, more preferably 0.1 mol% or more. The proportion of the monomer unit (b) containing a silanol group is preferably 5 mol% or less, more preferably 2 mol% or less. When the proportion of the monomer unit (b) containing a silanol group is in the above range, the bending resistance tends to be better.

The modified PVA (A) has a monomer unit (b) containing a carboxy group or a silanol group, and may further have a monomer unit (b) containing an ester group. In this case, the preferred ratio of the monomer unit (b) containing a carboxy group or a silanol group in the total monomer units constituting the modified PVA (A) is the same as the preferred ratio of the monomer unit (b) containing a carboxy group or a silanol group described above. On the other hand, in this case, the ratio of the monomer unit (b) containing an ester group in the total monomer units constituting the modified PVA (A) is preferably 0.1 mol% or more and 10 mol% or less, more preferably 0.3 mol% or more and 5 mol% or less, and even more preferably 1 mol% or more and 3 mol% or less. When the ratio of each monomer unit is within the above range, the bending resistance tends to be better.

The total content of vinyl alcohol units (a) and monomer units (b) having a polar group in all monomer units constituting the modified PVA (A) is preferably 95 mol % or more, more preferably 99 mol % or more, and in some cases may be even more preferably 99.9 mol % or more.

The viscosity average degree of polymerization of the modified PVA (A) is preferably 1000 or more and 4000 or less, and more preferably 1200 or more and 2600 or less. When the viscosity average degree of polymerization of the modified PVA (A) is 1000 or more, the mechanical strength of the resulting vacuum packaging bag is improved, which is preferable. On the other hand, when the viscosity average degree of polymerization is 4000 or less, the film-forming properties, etc. are improved, which is preferable.

From the viewpoint of improving bending resistance, the content of modified PVA (A) in the overcoat layer (Z) is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, and may be 95% by mass or more. The overcoat layer (Z) may be substantially composed of modified PVA (A) alone, or may be composed of modified PVA (A) alone.

The overcoat layer (Z) may contain other components other than the modified PVA (A) to the extent that the effect of the present invention is not impaired. Examples of other components that may be contained in the overcoat layer (Z) include inorganic acid metal salts such as carbonates, hydrochlorides, nitrates, hydrogen carbonates, sulfates, hydrogen sulfates, and borates, organic acid metal salts such as oxalates, acetates, tartrates, and stearates, metal complexes such as cyclopentadienyl metal complexes (e.g., titanocene) and cyano metal complexes (e.g., Prussian blue), layered clay compounds, crosslinking agents, polymer compounds other than the modified PVA (A), plasticizers, antioxidants, ultraviolet absorbers, and flame retardants. The content of the other components in the overcoat layer (Z) is preferably less than 50% by mass, more preferably less than 20% by mass, even more preferably less than 10% by mass, particularly preferably less than 5% by mass, and may be 0% by mass (not including other components).

The thickness of the overcoat layer (Z) is 0.003 μm or more, preferably 0.02 μm or more, and more preferably 0.06 μm or more. The thickness of the overcoat layer (Z) is 5 μm or less, preferably 1 μm or less, more preferably 0.5 μm or less, even more preferably 0.2 μm or less, and particularly preferably 0.15 μm or less. If the thickness of the overcoat layer (Z) is outside the above range, the barrier properties after bending tend to decrease.

It is preferable that the overcoat layer (Z) has a maximum intensity ratio (I(B)/I(C) _MAX ) of 1.20 or more, which is determined by the following steps (1) to (3).
(1) At five arbitrarily selected points on the surface of the overcoat layer (Z), analysis is performed in the depth direction (inorganic vapor deposition layer (Y) direction) by TOF-SIMS (time-of-flight secondary ion mass spectrometry).
(2) For each detected fragment, the average value of the maximum fragment intensity at each measurement point (I(B)) and the average value of the intensity at the measurement point midway between the measurement start point (surface) and the measurement point of maximum intensity at each measurement point (I(C)) are calculated, and the ratio of these values is defined as the intensity ratio (I(B)/I(C)).
(3) The maximum of the intensity ratios (I(B)/I(C)) found for each fragment is determined as the maximum intensity ratio (I(B)/I(C) _MAX ).

TOF-SIMS is an analysis method in which an ion beam (primary ions) is irradiated onto a sample, and the emitted secondary ions (fragments) are acquired by a TOF (Time Of Flight) method and subjected to mass analysis. In the analysis of the depth direction, sputtered ions are used, and it is possible to perform the analysis of the depth direction while sputtering the multilayer structure. Therefore, in the analysis of the depth direction using TOF-SIMS, measurement points are obtained intermittently. "Five arbitrarily selected points" means five arbitrarily selected points on the surface of the overcoat layer (Z) of the multilayer structure, and the range analyzed at each measurement point is a range of 250 μm × 250 μm. Since the maximum intensity is measured at each of the five arbitrarily selected measurement points, the average value is taken as I (B), and the average value of the intermediate measurement points between the measurement start point and the maximum intensity measurement point measured at each measurement point is taken as I (C). For example, if the maximum intensity is obtained at the 11th measurement point, the 6th measurement point is the intermediate measurement point, and if the maximum intensity is obtained at the 10th measurement point, the 5th and 6th measurement points are the intermediate measurement points. In addition, I(B) and I(C) are calculated for each fragment, and the intensity ratio (I(B)/I(C)) is also calculated for each fragment. The maximum intensity ratio (I(B)/I(C)) among the intensity ratios (I(B)/I(C)) for each fragment is defined as the maximum intensity ratio (I(B)/I(C) _MAX ).

The maximum intensity ratio (I(B)/I(C) _MAX ) can be used as an index showing the degree of uneven distribution of the fragments, and when the maximum intensity ratio (I(B)/I(C) _MAX ) is around 1, it can be determined that there is a tendency for the fragments to be distributed uniformly, and when (I(B)/I(C) _MAX ) is large, it can be determined that there is a tendency for the fragments to be unevenly distributed. In the present invention, the maximum intensity ratio (I(B)/I(C) MAX ) is used as an index for confirming that polar groups are unevenly distributed at the interface between the overcoat layer (Z) and the inorganic vapor deposition layer (Y), and when (I(B)/I(C) _MAX ) is 1.20 or more, the vicinity of the measurement point showing the maximum intensity I(B) is considered to be the interface _between the overcoat layer (Z) and the inorganic vapor deposition layer (Y).

The maximum intensity ratio (I(B)/I(C) _MAX ) of the overcoat layer (Z) is preferably 1.20 or more, more preferably 1.40 or more, even more preferably 1.70 or more, and particularly preferably 2.00 or more. When the maximum intensity ratio (I(B)/I(C) _MAX ) of the overcoat layer (Z) is equal to or more than the lower limit, the polar groups in the overcoat layer (Z) tend to be unevenly distributed at the interface with the inorganic vapor deposition layer (Y), and as a result, the flex resistance tends to be improved. On the other hand, the maximum intensity ratio (I(B)/I(C) _MAX ) may be 5.00 or less, 4.00 or less, or 3.00 or less.

The fragments of the overcoat layer (Z) observed by TOF-SIMS are not particularly limited, and examples thereof include silicon-based fragments such as SiO ₂ , and alcohol-based fragments such as C ₂ H ₃ O and C ₃ H ₅ O. Specifically, the surface analysis of the overcoat layer (Z) in the depth direction using TOF-SIMS can be measured by the method described in the Examples.

(Method for producing a multi-layer structure)
The method for producing the multilayer structure of the present invention is not particularly limited, and examples thereof include a production method including: a step (i) of applying a coating liquid (S) containing a modified PVA (A) and a solvent onto an inorganic vapor deposition layer (Y) of a laminate having an inorganic vapor deposition layer (Y) on one surface of a substrate (X); and a step (ii) of removing the solvent from the coating liquid (S) after application to form an overcoat layer (Z).

The laminate having an inorganic vapor deposition layer (Y) on one side of the substrate (X) used in step (i) can be prepared by a method similar to the method for forming the inorganic vapor deposition layer (Y) described above. A commercially available product can also be used as the laminate having an inorganic vapor deposition layer (Y) on one side of the substrate (X).

In step (ii), a coating liquid (S) containing modified PVA (A) and a solvent is applied onto the inorganic vapor deposition layer (Y).

The solvent used in the coating liquid (S) is not particularly limited, but is preferably water as the main component, and may be water alone. Other solvents used when water is the main component are preferably alcohols such as methanol, ethanol, and isopropanol.

The solids concentration of the coating liquid (S) is preferably 0.01 to 15% by mass, more preferably 0.05 to 10% by mass, and even more preferably 0.1 to 5% by mass, from the viewpoints of the storage stability of the coating liquid (S), the coatability to the inorganic vapor deposition layer (Y), and the degree of uneven distribution of polar groups in the resulting overcoat layer (Z). The solids concentration can be calculated, for example, by dividing the mass of the solids remaining after distilling off the solvent from the coating liquid (S) by the mass of the coating liquid (S) used in the treatment.

The method for applying the coating liquid (S) is not particularly limited, and known methods such as casting, dipping, roll coating, gravure coating, screen printing, reverse coating, spray coating, kiss coating, die coating, metalling bar coating, chamber doctor combined coating, curtain coating, and bar coating can be used.

The thickness of the layer (Z) formed after coating the coating liquid (S) on the inorganic vapor deposition layer (Y) can be controlled by the solids concentration of the coating liquid (S) or the coating method. For example, in the case of the gravure coating method, the cell volume of the gravure roll can be changed.

In step (ii), the solvent in the coating liquid (S) applied onto the inorganic vapor deposition layer (Y) is removed to form an overcoat layer (Z) on the inorganic vapor deposition layer (Y). There is no particular limitation on the method for removing the solvent from the coating liquid (S) after application, and for example, a known drying method can be applied. Examples of drying methods include hot air drying, hot roll contact, infrared heating, and microwave heating. The drying temperature may be, for example, 80°C or higher and 180°C or lower, or 90°C or higher and 150°C or lower.

It is preferable to coat the coating liquid (S) on the inorganic vapor deposition layer (Y), leave it to stand, and then dry it. The time to stand after coating until drying is, for example, 1 second or more, and preferably 2 seconds or more. The time to stand may be, for example, 1 minute or less. By leaving it to stand in this way, the polar groups in the overcoat layer (Z) formed tend to be unevenly distributed near the interface with the inorganic vapor deposition layer (Y). In order to promote the uneven distribution, it is also preferable to set the solid content concentration of the coating liquid (S) in a relatively low range. In this way, the fluid state of the coating liquid (S) on the inorganic vapor deposition layer (Y) is maintained for a long time, which tends to promote the uneven distribution.

(Other Layer (J))
The multilayer structure of the present invention may include a layer (J) other than the substrate (X), the inorganic vapor deposition layer (Y), and the overcoat layer (Z) in order to improve various properties (e.g., heat sealability, barrier properties, mechanical properties, etc.). Such a multilayer structure of the present invention can be produced, for example, by adhering or forming another layer (J) directly or via an adhesive layer to a laminate including the substrate (X), the inorganic vapor deposition layer (Y), and the overcoat layer (Z). Examples of the other layer (J) include, but are not limited to, an ink layer, a polyolefin layer, a polyester layer, a polyamide layer, and a thermoplastic resin layer such as an ethylene-vinyl alcohol copolymer resin layer. An adhesive layer is also an example of the other layer (J). The multilayer structure of the present invention preferably includes at least two other layers (J), and more preferably includes the substrate (X), the inorganic vapor deposition layer (Y), and the overcoat layer (Z) between the at least two other layers (J).

The multilayer structure of the present invention may include an ink layer for printing a product name or a pattern. Examples of the ink layer include a film obtained by drying a liquid in which a polyurethane resin containing a pigment (e.g., titanium dioxide) is dispersed in a solvent, but a film obtained by drying an ink containing a polyurethane resin not containing a pigment or other resin as a main component, or a resist for forming electronic circuit wiring may also be used. Examples of the coating method for the ink layer include gravure printing, as well as various coating methods such as a wire bar, a spin coater, and a die coater. The thickness of the ink layer is preferably 0.5 μm or more and 10.0 μm or less, and more preferably 1.0 μm or more and 4.0 μm or less.

By forming the outermost layer of the multilayer structure of the present invention as a polyolefin layer, it is possible to impart heat sealability to the multilayer structure and improve the mechanical properties of the multilayer structure. From the viewpoint of improving heat sealability and mechanical properties, the polyolefin is preferably polypropylene or polyethylene. In addition, in order to improve the mechanical properties of the multilayer structure, it is preferable to laminate at least one film selected from the group consisting of a film made of polyester, a film made of polyamide, and a film made of a hydroxyl group-containing polymer. From the viewpoint of improving the mechanical properties, polyethylene terephthalate (PET) is preferable as the polyester, nylon-6 is preferable as the polyamide, and an ethylene-vinyl alcohol copolymer is preferable as the hydroxyl group-containing polymer.

The other layer (J) may be a layer formed by extrusion coating lamination. There is no particular limitation on the extrusion coating lamination method that can be used in the present invention, and any known method may be used. In a typical extrusion coating lamination method, a laminate film is produced by feeding a molten thermoplastic resin to a T-die and cooling the thermoplastic resin taken out from a flat slit of the T-die.

Other extrusion coat lamination methods besides the single lamination method include the sandwich lamination method and the tandem lamination method. The sandwich lamination method is a method in which molten thermoplastic resin is extruded onto a first substrate, and a second substrate is supplied from a separate unwinder (unwinding machine) and bonded together to produce a laminate. The tandem lamination method is a method in which two single lamination machines are connected together to produce a five-layer laminate at once.

(Adhesive Layer (H))
In the multilayer structure of the present invention, the inorganic vapor deposition layer (Y) may be laminated so as to be in direct contact with the substrate (X), or the inorganic vapor deposition layer (Y) may be laminated on the substrate (X) via an adhesive layer (H) disposed between the substrate (X) and the inorganic vapor deposition layer (Y). By interposing the adhesive layer (H), the adhesive strength between the substrate (X) and the inorganic vapor deposition layer (Y) may be increased. In addition, when laminating a layer (J) other than the adhesive layer (H), the adhesive strength between the layers may be increased by laminating the layers via the adhesive layer (H). As the adhesive constituting the adhesive layer (H), a two-liquid reactive polyurethane adhesive in which a polyisocyanate component and a polyol component are mixed and reacted is preferable. In addition, the adhesiveness may be further improved by adding a small amount of additives such as a known silane coupling agent. Suitable examples of the silane coupling agent include silane coupling agents having reactive groups such as an isocyanate group, an epoxy group, an amino group, a ureido group, and a mercapto group. By strongly bonding the substrate (X) and the inorganic vapor deposition layer (Y) via the adhesive layer (H), the bending resistance of the multilayer structure of the present invention can be further improved.

When an adhesive layer (H) is disposed between the substrate (X) and the inorganic vapor deposition layer (Y), the thickness of the adhesive layer (H) is preferably in the range of 0.03 μm to 0.18 μm. By setting the thickness of the adhesive layer (H) in this range, deterioration of the barrier properties and appearance can be more effectively suppressed during the manufacture or processing of the vacuum packaging bag used in the vacuum insulator of the present invention, and further, the impact resistance of the vacuum insulator of the present invention can be improved. The thickness of the adhesive layer (H) is more preferably in the range of 0.04 μm to 0.14 μm, and even more preferably in the range of 0.05 μm to 0.10 μm.

For the multilayer structure of the present invention, in a Gelbow Freck test in accordance with ASTM F 392, after repeated reciprocation three times, the oxygen permeability measured in accordance with JIS K7126 under conditions of 40°C, 0% RH (carrier gas side) and 90% RH (oxygen supply side) is preferably 2.0 ml/( ^m2 day atm) or less, more preferably 1.0 ml/( ^m2 day atm) or less, even more preferably 0.5 ml/( ^m2 day atm) or less, and particularly preferably 0.40 ml/( ^m2 day atm) or less. Here, "40°C, 0% RH (carrier gas side), 90% RH (oxygen supply side)" means that at 40°C, the relative humidity on the carrier gas side is 90% RH and the relative humidity on the oxygen supply side is 0%, and "2.0 ml/( ^m2 ·day·atm)" means that 2.0 ml of oxygen permeates per day through 1 ^m2 of film with a pressure difference of 1 atmosphere of oxygen gas.

(Vacuum packaging bag)
The multilayer structure of the present invention has excellent gas barrier properties after bending, and is therefore effective in suppressing deterioration of gas barrier properties in the production of vacuum packaging bags and the like. The vacuum packaging bag of the present invention comprises the multilayer structure of the present invention. The vacuum packaging bag is a packaging bag that is usually used with the inside reduced pressure, and comprises a film material containing the multilayer structure described above as a partition wall separating the inside from the outside. The vacuum packaging bag may comprise a plurality of the multilayer structures.

It is preferable that the surface layer of the vacuum packaging bag of the present invention is a polyolefin layer (hereinafter sometimes abbreviated as PO layer) from the viewpoint of imparting heat sealability or improving mechanical properties. The polyolefin constituting such a polyolefin layer is preferably polypropylene or polyethylene. In addition, when emphasis is placed on further improving the mechanical properties of the vacuum packaging bag, it is preferable to laminate at least one film selected from the group consisting of a biaxially oriented polypropylene film, a polyester film, a polyamide film, and a PVA-based resin film as the other layer (J). From the viewpoint of improving mechanical properties, polyethylene terephthalate (PET) is preferable as the polyester, nylon-6 is preferable as the polyamide, and ethylene-vinyl alcohol copolymer resin is preferable as the PVA-based resin.

The vacuum packaging bag of the present invention may have the following configuration, for example, from the outer layer to the inner layer of the vacuum insulator, where "/" means that the layers are laminated directly or via an adhesive layer, and "//" means that the layers are laminated via an adhesive layer.
(1) Overcoat layer (Z)/inorganic vapor deposition layer (Y)/substrate (X)/PO layer (2) Polyester layer//overcoat layer (Z)/inorganic vapor deposition layer (Y)/substrate (X)/PO layer (3) Polyester layer//substrate (X)/inorganic vapor deposition layer (Y)/overcoat layer (Z)/PO layer (4) Polyamide layer//overcoat layer (Z)/inorganic vapor deposition layer (Y)/substrate (X)/PO layer (5) Polyamide layer//substrate (X)/inorganic Vapor deposition layer (Y)/overcoat layer (Z)/PO layer (6) PO layer//overcoat layer (Z)/inorganic vapor deposition layer (Y)/substrate (X)//PO layer (7) overcoat layer (Z)/inorganic vapor deposition layer (Y)/substrate (X)/inorganic vapor deposition layer (Y)/overcoat layer (Z)/PO layer (8) polyester layer//overcoat layer (Z)/inorganic vapor deposition layer (Y)/substrate (X)/inorganic vapor deposition layer (Y)/overcoat layer (Z)/PO layer ( 9) Polyamide layer//overcoat layer (Z)/inorganic vapor deposition layer (Y)/substrate (X)/inorganic vapor deposition layer (Y)/overcoat layer (Z)//PO layer (10) PO layer//overcoat layer (Z)/inorganic vapor deposition layer (Y)/substrate (X)/inorganic vapor deposition layer (Y)/overcoat layer (Z)//PO layer (11) Polyester layer/inorganic vapor deposition layer//overcoat layer (Z)/inorganic vapor deposition layer (Y)/substrate (X)//PO layer (12) Polyamide layer/overcoat layer (Z)/inorganic vapor deposition layer (Y)/substrate (X)//PO layer (13) Polyamide layer/inorganic vapor deposition layer//overcoat layer (Z)/inorganic vapor deposition layer (Y)/substrate (X)//PO layer (13) PO layer/inorganic vapor deposition layer//overcoat layer (Z)/inorganic vapor deposition layer (Y)/substrate (X)//PO layer (14) Polyamide layer/inorganic vapor deposition layer//overcoat layer (Z)/inorganic vapor deposition layer (Y)/substrate (X)/inorganic vapor deposition layer (Y)/overcoat layer (Z)/PO layer (15) PO layer/inorganic vapor deposition layer//overcoat layer (Z ) / inorganic vapor deposition layer (Y) / substrate (X) / inorganic vapor deposition layer (Y) / overcoat layer (Z) // PO layer (16) Polyamide layer // polyester layer / inorganic vapor deposition layer // overcoat layer (Z) / inorganic vapor deposition layer (Y) / substrate (X) // PO layer (17) PO layer // polyester layer / inorganic vapor deposition layer // overcoat layer (Z) / inorganic vapor deposition layer (Y) / substrate (X) // PO layer (18) Polyamide layer // polyester layer / aluminum oxide Aluminum oxide vapor deposition layer // overcoat layer (Z) / inorganic vapor deposition layer (Y) / substrate (X) // PO layer (19) PO layer // polyester layer / aluminum oxide vapor deposition layer // overcoat layer (Z) / inorganic vapor deposition layer (Y) / substrate (X) // PO layer (20) Polyamide layer // substrate (X) / inorganic vapor deposition layer (Y) // overcoat layer (Z) // overcoat layer (Z) / inorganic vapor deposition layer (Y) / substrate (X) // PO layer (21) PO layer // substrate ( X) / inorganic vapor deposition layer (Y) / overcoat layer (Z) // overcoat layer (Z) / inorganic vapor deposition layer (Y) / substrate (X) // PO layer (22) Nylon layer / inorganic vapor deposition layer / polyester layer // inorganic vapor deposition layer / polyester layer // overcoat layer (Z) / inorganic vapor deposition layer (Y) / substrate (X) // PO layer (23) Polyester layer // Nylon layer // overcoat layer (Z) / inorganic vapor deposition layer (Y) / substrate (X) // PO layer (24) Nylon layer // polyester layer // overcoat layer (Z) / inorganic vapor deposition layer (Y) / substrate (X) // PO layer (25) Polyester layer / polyester layer / inorganic vapor deposition layer // overcoat layer (Z) / inorganic vapor deposition layer (Y) / substrate (X) // PO layer (26) Polyester layer / aluminum oxide vapor deposition layer // polyester layer / aluminum oxide vapor deposition layer // overcoat layer (Z) / inorganic vapor deposition layer (Y) / substrate (X) // PO layer

(Vacuum insulation)
The vacuum insulator of the present invention comprises the vacuum packaging bag of the present invention and a core material disposed inside the vacuum packaging bag, and the inside is decompressed. Usually, in the vacuum insulator of the present invention, the space inside the vacuum packaging bag is in a vacuum state. The vacuum state here does not necessarily mean an absolute vacuum state, but indicates that the pressure of the space inside the vacuum packaging bag is sufficiently lower than atmospheric pressure. The pressure of the space inside the vacuum packaging bag is determined based on the required performance and ease of manufacture, and is usually 2 kPa (about 15 Torr) or less, preferably 200 Pa or less, more preferably 20 Pa or less, and even more preferably 2 Pa or less, from the viewpoint of exhibiting low thermal conductivity performance. The pressure of the space inside the vacuum packaging bag may be 0.001 Pa or more.

There are no particular limitations on the core material used in the vacuum insulator of the present invention, so long as it has low thermal conductivity. For example, examples of the core material include perlite powder, silica powder, precipitated silica powder, diatomaceous earth, calcium silicate, glass wool, rock wool, and resin foam (e.g., styrene foam, urethane foam). In addition, hollow containers made of resin or inorganic materials; honeycomb structures, etc. may also be used as the core material. In addition, the core material may contain an adsorbent that adsorbs water vapor or gas, etc., if necessary.

The thermal conductivity of the vacuum insulator of the present invention immediately after manufacture is preferably 7.0 mW/(m·K) or less, more preferably 6.5 mW/(m·K) or less. On the other hand, the thermal conductivity immediately after manufacture may be 1.0 mW/(m·K) or more. If the thermal conductivity is 7.0 mW/(m·K) or less, the low thermal conductivity performance of the vacuum insulator tends to be good. If the thermal conductivity is 1.0 mW/(m·K) or more, a vacuum insulator having good low thermal conductivity performance can be obtained at a relatively low cost. Here, "thermal conductivity" is a value measured in accordance with JIS A 1412-1 (1999).

The vacuum insulator of the present invention has excellent bending resistance, so that the thermal conductivity after bending at 90° tends to be good. The thermal conductivity after bending at 90° is preferably 7.5 mW/(m·K) or less, more preferably 7.0 mW/(m·K) or less, and even more preferably 6.5 mW/(m·K) or less.

There is no particular limitation on the method for producing the vacuum insulator of the present invention, and any commonly used method can be used. For example, the following methods 1 to 3 can be used to produce a vacuum insulator of any shape and size depending on the intended use.
(Method 1) First, two sheets of multilayer structures having a rectangular shape in plan view, with a heat-sealable layer (e.g., a polyolefin layer) arranged on at least one surface, are prepared. The two multilayer structures are stacked so that the heat-sealable layers are on the inside, and any three sides are heat-sealed to produce a packaging bag. Next, a core material is filled inside the packaging bag. Next, the space inside the packaging bag is evacuated, and the last side is heat-sealed in this state to obtain a vacuum insulator.
(Method 2) First, a sheet of a multilayer structure having a rectangular shape in plan view is folded so that the layer having heat sealability is on the inside, and any two sides are heat-sealed to produce a packaging bag. Next, a core material is filled inside the packaging bag. Next, the space inside the packaging bag is evacuated, and the last side is heat-sealed in this state to obtain a vacuum insulator.
(Method 3) First, a core material is sandwiched between two multilayer structures, or the multilayer structure is folded to sandwich the core material. Next, the peripheral portion where the multilayer structures overlap is heat-sealed, leaving a vacuum exhaust port, to produce a packaging bag with the core material disposed inside. Next, the space inside the packaging bag is evacuated, and the vacuum exhaust port is heat-sealed in this state to obtain a vacuum insulator.

As described above, the vacuum insulator of the present invention is preferably obtained by heat-sealing the multilayer structure of the present invention. Since the multilayer structure of the present invention has an inorganic vapor deposition layer (Y), heat bridging (a phenomenon in which the aluminum foil transfers heat and the insulation performance is reduced) seen in vacuum insulators obtained from films having metal foil such as aluminum foil is unlikely to occur, and the vacuum insulator of the present invention tends to exhibit excellent insulation performance. From the viewpoint of suppressing this heat bridging, the vacuum insulator of the present invention may be a vacuum insulator obtained by heat-sealing the multilayer structure of the present invention and a film having metal foil. Examples of films having metal foil include films having layer structures such as polyamide layer/polyester layer/metal foil/PO layer, polyamide layer/metal foil/PO layer, and polyester layer/metal foil/PO layer.

The vacuum insulator of the present invention can be used for various applications requiring cold or warm insulation. In particular, the vacuum insulator is extremely unlikely to deteriorate in its low thermal conductivity over time even when used under high temperature or high humidity conditions, and has a sufficient service life as an insulating material, making it useful for all thermal insulation applications requiring low thermal conductivity, such as tanks for water heaters, tanks for hot water toilets, tanks for vending machines, tanks for fuel cells, tanks for automobiles, thermal insulation bags for food, etc., for keeping PET bottles or cans warm, for keeping washing machine drums warm, servers for coffee and tea, etc., and jar pots.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. In the examples, "/" indicates that the two layers sandwiching "/" are directly laminated, and "//" indicates that the two layers sandwiching "//" are laminated via an adhesive.
(Materials used in the Examples and Comparative Examples)
VM-XL: "EVAL (registered trademark) VM-XL" manufactured by Kuraray Co., Ltd., aluminum-deposited biaxially stretched EVOH film (EVOH ethylene unit content 32 mol%, EVOH saponification degree 99.9 mol%, thickness 12 μm)
VM-PET: Toray Industries, Inc.'s "VM-PET1510", aluminum-deposited PET film (thickness 12 μm)
PET12: Toray Industries, Inc.'s "Lumirror (registered trademark) P60", PET film (thickness 12 μm)
PE50: Idemitsu Unitech Co., Ltd. "Unilux (registered trademark) LS760C", LLDPE film (thickness 50 μm)
Modified PVA (1): Polyvinyl alcohol with a viscosity average degree of polymerization of 1700, a degree of saponification of 98 mol%, and a silanol modification amount (proportion of monomer units containing silanol groups (vinyl silane triol or units in which a part of the hydroxyl group of vinyl silane triol is an alkoxy group)) of 0.2 mol% Modified PVA (2): Polyvinyl alcohol with a viscosity average degree of polymerization of 1700 and a degree of saponification of 78 mol% (proportion of monomer units containing ester groups (vinyl acetate units) of about 22 mol%) Modified PVA (3): Polyvinyl alcohol with a viscosity average degree of polymerization of 1800, a degree of saponification of 98 mol%, and a degree of itaconic acid modification amount (proportion of monomer units containing carboxy groups (vinyl itaconate units)) of 1.0 mol% PVA (1): Polyvinyl alcohol with a viscosity average degree of polymerization of 1700 and a degree of saponification of 100 mol% "Takelac (registered trademark) A520" (manufactured by Mitsui Chemicals, Inc., two-liquid polyurethane adhesive polyol component)
"Takenate (registered trademark) A50" (manufactured by Mitsui Chemicals, Inc., two-component polyurethane adhesive isocyanate component)

(Evaluation Method)
(1) Thickness of the overcoat layer (Z) The multilayer structures obtained in the examples and comparative examples were cut with a microtome to prepare slices (thickness 0.3 μm) for cross-sectional observation. The prepared slices were fixed to a sample base with carbon tape and subjected to platinum ion sputtering at an acceleration voltage of 30 kV for 30 seconds. The cross section of the multilayer structure was observed with a field emission transmission electron microscope [apparatus: SU8000 manufactured by Hitachi High-Technologies Corporation], and the thickness of the overcoat layer (Z) was calculated. The measurement conditions were an acceleration voltage of 1 kV and a magnification of 20,000 times.

(2) Oxygen permeability after bending The multilayer structures obtained in the Examples and Comparative Examples were cut into pieces of 20 cm x 25 cm, and a Gelbo Flex test (bending test) was carried out in accordance with ASTM F 392 using a Gelbo Flex Tester (BE-1005) manufactured by Tester Sangyo Co., Ltd. Specifically, the cut multilayer structures were conditioned at 23°C and 50% RH, and the conditioned multilayer structures were formed into cylindrical shapes with a diameter of 3.5 inches under the same atmosphere, and both ends were fixed to the Gelbo Flex Tester, and a reciprocating motion was performed three times with an initial interval of 7 inches, an interval at maximum bending of 1 inch, a twist of 440 degrees in the first 3.5 inches of the stroke, and a linear horizontal motion for the subsequent 2.5 inches.

The oxygen permeability (unit: ml/( ^m2 ·day·atm)) of the multilayer structure after bending was measured using a MOCON OX-TRAN2/20 in accordance with JIS K7126. The multilayer structure was set so that the deposition layer side faced the oxygen supply side and the substrate side faced the carrier gas side, and the measurement was performed under conditions of 40°C, 90% RH, and 1 atm for the oxygen supply side and 40°C, 0% RH, and 1 atm for the carrier gas side. Nitrogen gas containing 2% by volume of hydrogen gas was used as the carrier gas. The oxygen permeability after bending was evaluated based on the following evaluation criteria.
A: greater than 0.2 and equal to or less than 0.3 B: greater than 0.3 and equal to or less than 0.4 C: greater than 0.4 and equal to or less than 0.5 D: greater than 0.5 and equal to or less than 0.6 E: greater than 0.6 and equal to or less than 0.8 F: greater than 0.8 The units of the above numerical values are "ml/( ^m2 ·day·atm)".

(3) Thermal Conductivity of Vacuum Insulator Using each of the multilayer structures (4-2) and the multilayer structures (C1-2) and (C2-2) obtained in Example 4 and Comparative Examples 1 and 2, a vacuum insulator was produced. Specifically, the multilayer structures were cut to 20 cm x 25 cm, and two sheets of each covering material were obtained. The two resulting covering materials were overlapped with the PE layers facing each other, and the three sides were heat-sealed with a width of 10 mm to produce a three-sided packaging bag. A small bag containing calcium oxide as a low thermal conductive core material and an adsorbent was filled from the opening of the resulting packaging bag, and the packaging bag was sealed at a temperature of 20°C and an internal pressure of 1.0 Pa using a vacuum insulation panel manufacturing device (manufactured by NPC Co., Ltd., KT-500RD type) to produce a vacuum insulator. For the low thermal conductive core material, glass fiber dried for 4 hours under an atmosphere of 160°C was used. The obtained vacuum insulator was stored at 23° C. and 50% RH for a certain period of time, and then the thermal conductivity (mW/(m·k)) of the vacuum insulator was measured using a thermal conductivity measuring device (FOX314 model, manufactured by Eiko Seiki Co., Ltd.) with one side of the vacuum insulator at 38° C. and the other side at 12° C. The measurement was performed on the vacuum insulator before folding and on the vacuum insulator after folding once vertically (90°).

(4) Measurement of maximum intensity ratio (I(B)/I(C) _MAX ) For the multilayer structures obtained in the Examples and Comparative Examples, a depth direction analysis of the overcoat layer surface was performed by TOF-SIMS under the following conditions using a "TOF-SIMS5" manufactured by ION-TOF. Five measurement points were arbitrarily selected, and the average of the maximum intensity in each fragment was taken as I(B), and the average of the intensities at the measurement points midway between the measurement start point and the measurement point of the maximum intensity in each measurement point was taken as I(C), and the intensity ratio (I(B)/I(C)) in each fragment was calculated. From the intensity ratio (I(B)/I(C)) in each fragment, the maximum intensity ratio (I(B)/I(C) _MAX ) and its fragment were identified.
<Measurement conditions>
Primary ion source: _Bi3 ⁺⁺ Bu mode, 0.2pA at 25 keV (10kHz)
Charge correction: Electron Flooding, No Oxygen Flooding
Sputter ion source: Ar ₁₃₀₀₊ , 2nA at 5KeV (100μsec)
Measurement range: 500 x 500 μm (Sputtering)
250 x 250 μm (128 x 128 pix) Analysis, 128 scans
Sequence: 2 frames analysis / 3 frames sputtering in 1 scan
Analysis software: Surface Lab 6 (ION-TOF)

(Production Example 1)
2.5 g of modified PVA (1) and 47.5 g of distilled water were mixed, stirred at 90° C. for 1 hour, and then cooled to room temperature to obtain a 5% by mass aqueous PVA solution. Next, 24.0 g of the resulting aqueous PVA solution, 8.24 g of distilled water, and 7.76 g of methanol were mixed and stirred at room temperature for 30 minutes to prepare a coating solution (S-1).

(Production Examples 2 to 4)
Coating solutions (S-2) to (S-4) were prepared in the same manner as in Production Example 1, except that modified PVA (2) (Production Example 2), modified PVA (3) (Production Example 3), or PVA (1) (Production Example 4) was used instead of modified PVA (1).

(Production Example 5)
3.42 parts by mass of tetramethoxysilane (TMOS) was dissolved in 4.1 parts by mass of methanol, followed by dissolving 0.68 parts by mass of γ-glycidoxypropyltrimethoxysilane, followed by adding 0.26 parts by mass of distilled water and 0.64 parts by mass of 0.1N (0.1 normal) hydrochloric acid to prepare a sol, which was stirred at 10° C. for 1 hour to carry out hydrolysis and condensation reactions. The resulting sol was diluted with 9.25 parts by mass of distilled water and then quickly added to 31.7 parts by mass of a 10% by mass aqueous solution of PVA (1) to prepare a coating liquid (S-5).

(Production Example 6)
2.5 g of modified PVA (1) and 47.5 g of distilled water were mixed, stirred at 90° C. for 1 hour, and then cooled to room temperature to obtain a 5% by mass aqueous PVA solution. Next, 8.0 g of the resulting aqueous PVA solution, 24.08 g of distilled water, and 7.92 g of methanol were mixed and stirred at room temperature for 30 minutes to prepare a coating solution (S-6).

(Production Example 7)
6.0 g of modified PVA (1) and 44.0 g of distilled water were mixed, stirred at 90° C. for 1 hour, and then cooled to room temperature to obtain a PVA aqueous solution with a concentration of 12% by mass. Next, 30.0 g of the obtained PVA aqueous solution, 2.72 g of distilled water, and 7.28 g of methanol were mixed and stirred at room temperature for 30 minutes to prepare a coating liquid (S-7).

Example 1
The coating liquid (S-1) was applied to the aluminum vapor deposition surface of "VM-XL" using a bar coater so that the thickness after drying would be 30 nm, and then the coating was left to stand for 3 seconds. The coating was then dried at 100°C for 3 minutes to produce a multilayer structure (1-1) in which the overcoat layer (Z)/aluminum vapor deposition layer/biaxially stretched EVOH layer were laminated in this order. The maximum strength ratio (I(B)/I(C) _MAX ) of the overcoat layer (Z) of the resulting three-layer multilayer structure (1-1) was measured according to the method described in the evaluation method (4) above. The results are shown in Table 1.

A two-component adhesive (Takelac A-520 and Takenate A-50) was applied to one side of each of "PET12" and "PE50", and the layers were laminated to form a structure of PET12/adhesive layer/overcoat layer (Z)/aluminum vapor deposition layer/biaxially oriented EVOH layer/adhesive layer/PE50 to produce a multilayer structure (1-2). The thickness of the overcoat layer (Z) and the oxygen permeability after bending of the resulting seven-layer multilayer structure (1-2) were measured according to the methods (1) and (2) above. The results are shown in Table 1.

(Examples 2 to 11, Comparative Examples 1 to 8)
Except for changing the layer structure (deposition film), the type of coating solution, the standing time after coating, and the thickness of the overcoat layer (Z) as shown in Table 1, the multilayer structures (2-1) to (11-1) of the three-layer structure and the multilayer structures (2-2) to (11-2) of the seven-layer structure of the three-layer structure and the multilayer structures (C1-1) to (C8-1) of the seven-layer structure and the multilayer structures (C1-2) to (C8-2) of the seven-layer structure of the three-layer structure and the seven-layer structure of the seven-layer structure were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1. Also, one of the measurement results of the depth profile analysis (fragment SiO ₂ ) obtained by the TOF-SIMS measurement in Example 4 is shown in FIG. 1. Also, for Example 4 and Comparative Examples 1 and 2, the thermal conductivity of the vacuum insulator was measured according to the method described in (3) above. The results are shown in Table 2.

(Examples 12 to 15)
Three-layer multilayer structures (12-1) to (15-1) and seven-layer multilayer structures (12-2) to (15-2) of Examples 12 to 15 were produced in the same manner as in Example 1, except that the type of coating liquid, the standing time after coating, and the thickness of the overcoat layer (Z) were changed as shown in Table 3. For the resulting multilayer structures (12-2) to (15-2), the thickness of the overcoat layer (Z) and the oxygen permeability after bending were measured according to the methods (1) and (2) above. The results are shown in Table 3.

From Examples 1 to 6, it can be seen that when modified PVA (A) is used, good bending resistance is shown, and among them, Example 3, in which the thickness of the overcoat layer is 0.09 μm, is remarkably excellent in bending resistance. Also, from Examples 4 to 6, 12 to 15, it can be seen that when modified PVA having a silanol group, an ester group, or a carboxy group is used, good bending resistance is shown. When the overcoat layer (Z) is not provided as in Comparative Example 1, bending resistance is poor, and when non-modified PVA is used as in Comparative Examples 2 to 4, bending resistance is also poor. Furthermore, when a PET film is used as the substrate instead of a PVA-based resin film as in Comparative Examples 5 and 6, the gas barrier property is significantly reduced, and even when a coating liquid in which PVA and a silane compound are mixed is used as in Comparative Examples 7 and 8, bending resistance is insufficient.

A comparison of Examples 4, 7, and 8 reveals that when the solids concentration of the coating liquid for forming the overcoat layer (Z) is different, the maximum intensity ratio (I(B)/I(C) _MAX ) of TOF-SIMS is different, and thus there is a difference in flex resistance. From these results, it is considered that when the solids concentration is appropriate as in Example 4, specific polar groups (groups from which _SiO2 fragments are derived in Example 4) tend to be unevenly distributed at the interface of the inorganic vapor deposition layer (Y), resulting in improved flex resistance.

Comparison of Examples 4 and 9 to 11 shows that the maximum strength ratio (I(B)/I(C) _MAX ) and flex resistance differ depending on the standing time after coating with the coating liquid. As in Example 4, coating with the coating liquid (S-1) using a bar coater, waiting for 3 seconds before drying, resulted in good flex resistance.

FIG. 1 is a graph showing one of the measurement results of the depth direction analysis using TOF-SIMS in Example 4, in which the fragment is SiO ₂ and shows the maximum intensity ratio (I(B)/I(C) _MAX ). In the graph of FIG. 1, the X-axis (horizontal axis) is Dose density (a parameter in the depth direction, the larger the value, the deeper the measurement point), and the Y-axis (vertical axis) is Intensity (the intensity of the SiO ₂ fragment, the larger the value, the greater the amount present). From this graph, it can be seen that the intensity of SiO ₂ is increased in the interface region between the overcoat layer (Z) and the inorganic vapor deposition layer (Y), and it can be said that a result was obtained that suggests that silanol groups are unevenly distributed at the interface. Although it is not certain, it is believed that in Example 4 and the like, the interaction between the silanol groups and aluminum, which is a component of the inorganic vapor deposition layer (Y), causes the silanol groups to be unevenly distributed at the interface, and the overcoat layer (Z) and the inorganic vapor deposition layer (Y) to adhere firmly to each other, thereby suppressing the occurrence of defects in the inorganic vapor deposition film due to bending, and as a result, suppressing the deterioration of the barrier property due to bending.

Claims (9)

A substrate (X), an inorganic vapor deposition layer (Y), and an overcoat layer (Z) are provided in this order;
The substrate (X) is made of a biaxially stretched polyvinyl alcohol-based resin film,
the overcoat layer (Z) contains a modified polyvinyl alcohol (A) having a vinyl alcohol unit (a) and a monomer unit (b) having a polar group other than the vinyl alcohol unit (a);
The thickness of the overcoat layer (Z) is 0.003 μm or more and 1 μm or less,
the proportion of the monomer units (b) having a polar group in all monomer units constituting the modified polyvinyl alcohol (A) is 0.05 mol % or more and 30 mol % or less;
A multilayer structure, wherein the content of the modified polyvinyl alcohol (A) in the overcoat layer (Z) is 70% by mass or more. The multilayer structure according to claim 1, wherein the polar group is at least one selected from the group consisting of a carboxy group, an ester group, and a silanol group. 3. The multilayer structure according to claim 1, wherein the maximum intensity ratio (I(B)/I(C) _MAX ) determined by the following steps (1) to (3) is 1.20 or more.
(1) At five arbitrarily selected points on the surface of the overcoat layer (Z), a depth direction analysis is performed by TOF-SIMS.
(2) For each detected fragment, the average value of the maximum fragment intensity at each measurement point (I(B)) and the average value of the intensity at the measurement point midway between the measurement start point and the measurement point of maximum intensity at each measurement point (I(C)) are calculated, and the ratio of these values is defined as the intensity ratio (I(B)/I(C)).
(3) The maximum of the intensity ratios (I(B)/I(C)) found for each fragment is determined as the maximum intensity ratio (I(B)/I(C) _MAX ). The multilayer structure according to any one of claims 1 to 3, further comprising a layer (J) other than the substrate (X), the inorganic vapor deposition layer (Y), and the overcoat layer (Z). The multilayer structure according to claim 4, comprising at least two of the other layers (J), and comprising a substrate (X), an inorganic vapor deposition layer (Y) and an overcoat layer (Z) between the at least two other layers (J). The multilayer structure according to any one of claims 1 to 5, wherein the biaxially stretched polyvinyl alcohol-based resin film is a biaxially stretched film mainly composed of an ethylene-vinyl alcohol copolymer having an ethylene unit content of 10 mol% or more and 65 mol% or less and a saponification degree of 90 mol% or more. The multilayer structure according to any one of claims 1 to 6, wherein the oxygen permeability measured in accordance with JIS K7126 under conditions of 40°C, 0% RH (carrier gas side) and 90% RH (oxygen supply side) after three repeated reciprocating movements in a Gelbow Freck test in accordance with ASTM F 392 is 2.0 ml/( ^m2 day atm) or less. A vacuum packaging bag comprising the multilayer structure according to any one of claims 1 to 7. A vacuum insulator comprising the vacuum packaging bag according to claim 8 and a core material disposed inside the vacuum packaging bag, the inside of which is decompressed.

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